cymgrddemo

USER'S GUIDE AND REFERENCE MANUAL

September 2000

CYMGRD for Windows

CYMGRD for Windows

1995-2000 CYME INTERNATIONAL INC.

All Rights Reserved

This publication, or parts thereof, may not be reproduced in any form, by any method, forany purpose.

CYME INTERNATIONAL INC. makes no warranty, either expressed or implied, includingbut not limited to any implied warranties of merchantability or fitness for a particularpurpose, regarding these materials and makes such materials available solely on an "as-is" basis.

In no event shall CYME INTERNATIONAL INC. be liable to anyone for special, collateral,incidental, or consequential damages in connection with or arising out of purchase oruse of these materials. The sole and exclusive liability to CYME INTERNATIONAL,regardless of the form of action, shall not exceed the purchase price of the materialsdescribed herein.

CYME INTERNATIONAL INC. reserves the right to revise and improve its products as itsees fit. This publication describes the state of this product at the time of its publication,and may not reflect the product at all times in the future.

The software described in this document is furnished under a license agreement.

CYME INTERNATIONAL INC.3 Burlington Woods, 4th FloorBurlington, MA 01803-02691-800-361-3627 (781) 229-0269Fax: (781) 229-2336

International and Canada:1485 Roberval, Suite 104St. Bruno QC J3V 3P8Canada(450) 461-3655Fax: (450) 461-0966

Internet : http://www.cyme.com

E-mail : [email protected]

IBM and PC-DOS are registered trademarks of International Business Machines Corporation. MS-DOS and Windows areregistered trademark of Microsoft Corporation. Windows 95 and Windows NT are trademark of Microsoft. Autocad is atrademark of Autodesk Inc.

CYMGRD for Windows

TABLE OF CONTENTS

CHAPTER 1 ....................................................................................................................1

GETTING STARTED ..............................................................................................................................11.1 General introduction .......................................................................................................................11.2 Software and hardware requirements .............................................................................................11.3 Installing CYMGRD for Windows....................................................................................................21.4 CYMGRD analysis modules ...........................................................................................................31.5 Interactive data entry......................................................................................................................31.6 First-time user ................................................................................................................................41.7 Dividing the grid in elements ..........................................................................................................41.8 How to use CYMGRD.....................................................................................................................41.9 Creating Projects and Studies ........................................................................................................5

1.9.1 The "Project" menu ..................................................................................................................61.10 The menu bar of CYMGRD .........................................................................................................81.11 The ribbons ..................................................................................................................................81.12 The Windows menu....................................................................................................................12

CHAPTER 2 ..................................................................................................................15

SOIL RESISTIVITY AND SAFETY ASSESSMENT.............................................................................152.1 Soil resistivity measurements and soil models..............................................................................152.2 Soil resistivity. Methodology and algorithm...................................................................................162.3 The "SOIL" menu .........................................................................................................................17

2.3.1 The “Soil >> Input data” command.........................................................................................182.3.2 The "Soil >> Import from" command ......................................................................................192.3.3 The "Soil >> Calculate" command..........................................................................................192.3.4 The "Soil >> Visualize" command ..........................................................................................20

2.4 The "SAFETY ASSESSMENT" analysis.......................................................................................212.5 The "Graphic Parameters" option .................................................................................................22

CHAPTER 3 ..................................................................................................................23

THE GRID MODULE.............................................................................................................................233.1 General introduction .....................................................................................................................233.2 Electrode types and terminology...................................................................................................233.3 Grounding system structure and location......................................................................................243.4 The "Grid" menu...........................................................................................................................24

3.4.1 The “Grid >> Input data >> Installation” command .................................................................243.4.2 The “Grid >> Input data >> Electrodes” command .................................................................263.4.3 Geometrical station layout.....................................................................................................303.4.4 The Grid >> Input data >> Merge with... command ................................................................303.4.5 The Grid >> Input data >> Import from... command ...............................................................313.4.6 The Grid >> Calculate command ...........................................................................................323.4.7 The Grid >> Visualize command............................................................................................323.4.8 The Grid >> Graphic parameters dialog box ..........................................................................33

3.5 Examining the tabular results file..................................................................................................34

CYMGRD for Windows

CHAPTER 4 ..................................................................................................................37

THE PLOT MODULE ............................................................................................................................374.1 General introduction .....................................................................................................................374.2 The Contours menu......................................................................................................................37

4.2.1 The "Contours >> Calculate" command .................................................................................374.2.2 The "Contours >> Calculate" mouse command ......................................................................394.2.3 The "Contours >> Visualize" command ..................................................................................414.2.4 The "Contours >> View report" command ..............................................................................414.2.5 The "Contours >> Rename" command...................................................................................414.2.6 The "Contours >> Delete" command ......................................................................................414.2.7 The "Contours >> Parameters" command ..............................................................................424.2.8 Inspecting contour plots .........................................................................................................44

4.3 The Profile menu..........................................................................................................................454.3.1 The "Profile >> Calculate" command .....................................................................................454.3.2 The "Profile >> Calculate" mouse command ..........................................................................474.3.3 The "Profile >> Visualize" command ......................................................................................484.3.4 The "Profile >> View report" command ..................................................................................484.3.5 The "Profile >> Rename" command.......................................................................................484.3.6 The "Profile >> Delete" command..........................................................................................484.3.7 The "Profile >> Parameters" command ..................................................................................494.3.8 Inspecting potential profile plots .............................................................................................50

APPENDIX I.....................................................................................................................1

EXAMPLE STUDIES...............................................................................................................................1Most commonly used functions ............................................................................................................1

Keyboard arrows...............................................................................................................................1Using the mouse in 3-D display.........................................................................................................1Double-click......................................................................................................................................1Tile/Auto-tile .....................................................................................................................................1Print/Print all .....................................................................................................................................1Save.................................................................................................................................................1

Example 1: Primary electrode only.....................................................................................................181.1 Resistivity analysis of the substation soil .....................................................................................21.2 Safety assessment analysis ........................................................................................................41.3 Grounding installation data entry.................................................................................................61.4 Surface potential analysis with the PLOT module......................................................................111.5 Potential profile analysis along an axis with the PLOT module ..................................................15

Example 2: Primary, return and distinct electrode ..............................................................................182.1 Grounding installation overview ................................................................................................18

CYMGRD for Windows

APPENDIX II....................................................................................................................1

Comparison with the IEEE80 Guide .....................................................................................................1

APPENDIX III...................................................................................................................1

CADGRD - The CYMGRD - AutoCAD Interface module .......................................................................11.00 Program Summary ......................................................................................................................12.00 Drawing a station ground grid with AutoCAD ................................................................................2

2.1 General.......................................................................................................................................22.2 Drawing the GRID Layout using AutoCAD:..................................................................................32.3 Illustrative example...................................................................................................................10

3.00 Validation & Update of the AutoCAD drawing ............................................................................203.1 Validating the AutoCAD drawing. ..............................................................................................203.2 Updating the AutoCAD drawing.................................................................................................24

4.00 IMPORTING from AutoCAD to CYMGRD...................................................................................265.00 EXPORTING from CYMGRD to AutoCAD..................................................................................296.00 Working with CADGRD ..............................................................................................................31

CYMGRD for Windows

Chapter 1 - Getting Started 1

Chapter 1

GETTING STARTED

1.1 General introduction

CYMGRD for Windows assists engineers who design grounding facilities for substations andbuildings. Firstly, it determines the resistivity of the soil from measured values. The engineermay instruct CYMGRD to interpret the data as though the soil were of uniform resistivity or asthough it consisted of two horizontal layers of different resistivity.

Secondly, it computes the tolerable Step and Touch Voltages per IEEE Standard 80. Theuser defines the fault current magnitude and duration, the thickness and resistivity of a layer ofmaterial (such as crushed rock) applied to the soil surface, and the body weight.

Thirdly, it displays the layout of the grounding grid continuously as the engineer positionsconductors and rods. It is also possible to define other buried conductors not directly connectedto the grid.

Finally, it calculates voltages resulting from a ground fault and displays them in differentcolors in two or three dimensions, making it easy to evaluate the safety of personnel andequipment in and around the grounding grid.

The results of alternative grid designs may be displayed simultaneously for comparison.

1.2 Software and hardware requirements

CYMGRD can be used with Windows 3.1, WorkGroups for Windows 3.11, Windows NT, orWindows 95. Platforms using 100% Windows 3.1 emulation, such as OS/2 version 3.0 (Warp),are equally supported.

The minimum hardware requirements are:

• Pentium computer;

• 32 MB RAM;

• 20 MB free memory on the hard disk;

• A Microsoft mouse or equivalent;

• A color monitor with Super VGA and a graphic card supporting 256 colors or more

• Any printer or plotter supported by Windows

CYMGRD for Windows

2 Chapter 1 - Getting Started

1.3 Installing CYMGRD for Windows

The CYMGRD package includes the installation CD and one protection key which plugsinto the parallel port on your computer. You cannot operate the program without the keyin place. You can, however, install it.

1. Start Microsoft Windows.

2. Insert the CYME CD into the CD-ROM reader.

3. The installation program should start automatically after a few seconds.

If it does not start by itself, use Windows Explorer to inspect the main directory ofthe CYME CD. Locate the icon “Setup32” and double-click on it.

4. Click on the option to “Install Products or Demos”.

5. Choose English and then your version of Windows.

6. Choose CYMGRD from the list of software names.

7. Follow the prompts and screen instructions.

8. Insert the hardware key into the line printer port (e.g., LPT1). Please refer to thedocument sent along with the CYME CD package for "Setting Up the ProtectionKey". Users of Windows NT must also install the proper driver.

CYMGRD for Windows


1.4 CYMGRD analysis modules

The functions described in the General Introduction (section 1.1) are divided among threeanalysis modules which may be accessed from the menu bar or the ribbon (see section 1.12):

The SOIL module interprets the soil resistivity measurements using either a two-layer oruniform soil model. To permit easy verification of the quality of the soil model, CYMGRD plotsthe measured and calculated resistivity on the same graph. The maximum allowable step andtouch voltages are calculated according to IEEE Standard 80. All results are communicated tothe GRID and PLOT modules (see below).

The GRID module calculates the current diffused by every piece (“element”) of conductor inthe grounding grid. The potential at the surface of the soil is determined from these results. Youmay define the grid one conductor at a time and also by using groups of conductors arranged inrectangular sub-grids. Similarly, you may add grounding rods one at a time or in groups. Thestation layout can be displayed in 2 or 3 dimensions. Other buried conductors such as waterpipes or neighboring grounding structures may also be defined, so as to include their effects onthe passage of fault current and the resulting surface voltages. At your option, you may includeor exclude these other structures from the calculations, for comparison purposes. The sameapplies to the grounding rods.

1. The PLOT module displays the results of the soil resistivity and surface potential analysis onthe screen. Color-coded contour plots of surface potentials may be presented in 2 or 3dimensions. Another option is to calculate the Step and Touch Voltages along a straight linein any direction and plot the variation on the same graph with the maximum allowed values.Both options allow easy identification of hazardous areas where the tolerable voltages areexceeded. These graphics can be routed to a printer or a plotter.

1.5 Interactive data entry

CYMGRD features the standard Windows interface and conventional mouse-clickingoperations. The Menu will change depending on the active Module.

Note: Users of the DOS version of CYMGRD may directly import their data files for soilresistivity analysis and grid layout and installation. See section 2.3.2.

CYMGRD for Windows


1.6 First-time user

If you have not used CYMGRD before, we suggest you read this manual before performing agrounding study, to familiarize yourself with the capabilities of the program. Illustrated step-by-step examples have been included in Appendix I, to help you learn how to use CYMGRD.

Note: The README.TXT file may include important information as well. Please read thecontents of this file before operating the program.

1.7 Dividing the grid in elements

The surface potential analysis module (GRID) models the grid by dividing its conductors androds into smaller segments, called "elements". These elements are the basic units that diffusethe injected fault current into the ground. Using a higher number of smaller elements may givegreater calculation precision. However, the total number of elements in any grounding studycannot exceed 2500, including the main (“primary”) grid and any other (“return” or “distinct”)electrodes.

1.8 How to use CYMGRD

CYMGRD is designed to facilitate grounding studies that assess the safety levels of existinggrids or support the design of new ones.

Verifying existing grids

1. For existing grids, soil measurements may be available from the original design. If the soilmodel has already been determined and remains valid, it may not be necessary to enter themeasurements in the SOIL module. The thickness and resistivity of the soil layers may beentered directly. (Note that conducting paths provided by existing grid conductors may biasany new resistivity measurements.)

2. Using the available soil model, take into account the presence of high resistivity surfacematerial (e.g. crushed rock) and determine the maximum permissible touch and step voltagesusing the SAFETY ASSESSMENT command in the SOIL module.

3. Enter the station grid and electrode data and find the ground potential rise (GPR) and stationresistance using the GRID analysis module.

4. Use the PLOT module to find touch and step potentials in specific area(s) of interest.

5. Judge the adequacy of the existing grounding system.

6. If the grid is not adequate, return to step 3 and make the necessary changes to the grid layoutby adding or removing conductors and rods.

CYMGRD for Windows


Designing a new grid

1. Obtain the resistivity measurements using the Wenner technique. Note that the SOILresistivity analysis module supports only Wenner measurements.

2. Activate the SOIL analysis module. Determine the soil model to be used by entering theresistivity measurements and performing the calculations.

3. Using the newly obtained soil model, take into account the presence of high resistivity surfacematerial, and calculate the maximum permissible touch and step voltages using the SAFETYASSESSMENT command of the SOIL module.

4. Follow steps 3, 4, 5 and 6 under Verifying Existing Grids, above.

1.9 Creating Projects and Studies

As soon as CYMGRD is activated for the first time, by double clicking its icon on the desktop,the program displays blank soil resistivity and station layout templates, menu, ribbon and statusbars, as shown below.

CYMGRD for Windows


The various analysis modules are not yet visible on the menu bar because a "Project" and a"Study" need to be defined first. This can also be seen in the status bar of the program (last twolines at the bottom of the screen) which is completely blank, where Prj stands for PRoJect name,

Sty for STudY name, GPR for Ground Potential Rise, Etch for maximum permissible TouCHvoltage, and Estp for maximum permissible STeP voltage.

Note: You can modify the window display by using the command Window >> Displaymode.

1.9.1 The "Project" menu

The "Project" activity allows you to define a “Project”, a “Study”, and a working “directory”. A"Project" contains one or more studies, each of which might be an alternative design for thesame grid. The "Project" and its associated studies may be kept in the default directory(\CYMGRD.WIN), or in an alternate sub-directory.

Open a study by using commands in the Project menu. The steps to open a study are:

1. Define your working directory;

2. Choose a system of units (Imperial or Metric);

3. Create a project (or Open an existing one);

4. Create a study.

Note: You cannot save a Project if there are no studies related to it.

The "Directory" command.

The "Directory" command defines the working directory. Initially, it is \CYMGRD.WIN, butwhen you start the program, CYMGRD will always point to the last directory used in the previoussession. Click on the directory command to specify a new working directory.

CYMGRD for Windows


The "Units" command.

The "Units" command allows you to select the Metric or the Imperial system. For instanceyou can enter the station geometry using either meters or feet. In the current study, you canswitch the “Units” settings at any time without affecting the input data or the results.

Note: Some previous versions of the program used only the metric measurement system.Therefore, the program will have to recalculate the station gradient and the soil model ofany older study created when switching to the imperial system. However, once this stepis completed, switching between the two measurement systems will not require anyfurther recalculations.

The "Project" commands.

Once the working directory and units of measurement have been specified, you can “Create”a new project, "Open" an existing project, "Duplicate" the current project (copy it to anotherproject), or "Delete" the current project. When a project is deleted or duplicated, all studiesassociated with that project are deleted or duplicated. If any of the commands are dimmed, theyare not currently accessible. For example, you cannot "Open" a project if no projects exist in theactive working directory. You can “Import” data directly from other projects to the current project,or you can “Export” data to another project.

The "Study Management" commands.

Once a "Project" has been created or opened, the "Study" option then gives you access to the"Study management” commands, which are similar to the "Project Management" commands.You can “Create" a new study, “Open” a study that already exists, "Save" the contents of thecurrent study, use the "Save as" command to save the contents of the current study underanother name, or "Delete” the current study. A dimmed command is not currently accessible.For example, you cannot “Open” a study if no study exists yet within the active project. Bydefault, when a project is opened, its last active study is also opened.

CYMGRD for Windows


1.10 The menu bar of CYMGRD

Once a project and study have been defined, the Menu bar and Ribbon will feature thecommands of the active Module. The GRID module is active by default. To select a differentmodule, click on the GRID module command and then click on the desired module in the list.

1.11 The ribbons

The most important commands have icons that can be found in the ribbons. Most icons arecommon to all three ribbons, except the six icons in the center of the ribbon.

The icons for the three modules are located at the right side of the ribbon. When you launchCYMGRD, the GRID module is opened by default. To change module, simply click on theappropriate icon.

Icons common to all ribbons:

PROJECT menu

Equivalent to Project >> Directory. Click on this icon to select the working directory tosave your project and the related study.

Equivalent to Project >> Create. Click on this icon to create a new project.

Equivalent to Project >> Open. Click on this icon to open a project that has been savedalready. If you can’t find a project that you saved already, it might be in another workingdirectory.

Equivalent to Project >> Duplicate. Click on this icon to copy the contents of thisproject to another project.

CYMGRD for Windows


Study sub-menu

Equivalent to Project >> Study >> Create. Click on this icon to create a study that willbe part of the current project.

Equivalent to Project >> Study >> Open. Click on this icon to open a study that hasalready been saved in the current project.

Equivalent to Project >> Study >> Save. Click on this icon to save this study in itsrelated project.

SOIL menu

Equivalent to Soil >> Input data. Click on this icon to enter the Wenner measurementsneeded to model a uniform or two-layer soil..

Equivalent to Soil >> Calculate!. Click on this icon to analyze the soil model.

Equivalent to Soil >> Visualize >> Soil model. Click on this icon to display the soilmodel.

Equivalent to Soil >> Visualize >> Soil Analysis Report. Click on this icon to see thesoil analysis report. This icon is not accessible if the soil model hasn’t been calculatedfirst.

Equivalent to Soil >> Calculate! >> Safety Assessment. Click on this icon to calculatethe appropriate touch and step voltages.

Equivalent to Soil >> Safety Assessment Report. Click on this icon to see the safetyassessment report.

CYMGRD for Windows


GRID menu

Equivalent to Grid >> Input data >> Installation.... Click on this icon to see theinstallation data dialog box.

Equivalent to Grid >> Input data >> Electrodes >> Conductors.... Click on this iconto see the conductor data dialog box.

Equivalent to Grid >> Input data >> Electrodes >> Rods.... Click on this icon to seethe rod data dialog box.

Equivalent to Grid >> Calculate! Click on this icon to calculate the surface potentialgradient.

Equivalent to Grid >> Visualize >> Show station layout. Click on this icon to see thestation layout on the screen. This icon is very useful if the station layout has beenclosed by mistake.

Equivalent to Grid >> Visualize >> Show grid analysis report. Click on this icon tosee the grid analysis report.

CYMGRD for Windows


PLOT menu

Equivalent to Profile >> View report or F2. Click on this icon to see the potential profilereport. If there is more than one profile, select one from the list.

WINDOWS MENU:

HELP menu

Click on this icon to activate the Help function.

Equivalent to Contours >> Calculate!. Click on this icon to calculate the surfacepotential and see the grid contours.

Equivalent to Contours >> Visualize. Click on this command to see the contourwindow, if it was closed by mistake. If there are more than one contour, select a contourfrom the list.

Equivalent to Contours >> View report or F2. Click on this icon to see that surfacepotential report. If there are more than one contour, select a report from the list.

Equivalent to Profile >> Calculate!. Click on this icon to calculate the potential profiles.You can calculate many profiles subsequently, by modifying the distance between twosteps or the surface of the area.

Equivalent to Profile >> Visualize.... Click on this icon to see the potential profiles. Ifthere is more than one profile, select a profile from the list.

Equivalent to Windows >> Copy to clipboard or the + key. Click on this command tocopy graphics or text (reports) to the clipboard.

Equivalent to Windows >> Print or Shift-P. Click on this icon to print the active window

Equivalent to Windows >> Print all windows or Ctrl-P. Click on this icon to print allwindows, including windows that have been minimized into icons.

CYMGRD for Windows


1.12 The Windows menu

The "Show ribbon" command

This command allows you to hide the tool bar icons, so as gain more space for the studywindows.

The "Show status bar" command

This toggle allows you to display (or hide) the two lines at the bottom of the screen whichidentify the project and study, as well as the values calculated for the ground potential rise (GPR)and tolerable touch and step voltages.

The "Cascade" command

This command causes multiple windows to overlap such that the title bar of each is visible.

Display Mode must be set to “manual” to enable the Cascade command

The "Tile" command

This command displays multiple windows such that they do not overlap at all and each has anequal area. If you close a window, the others will be tiled again automatically to fill the window.

Display Mode must be set to “manual” to enable the Tile command

The "Close all" command"

This command closes all the windows that are displayed, whether iconized or not.

The "Display mode" command

This command offers three options: a) Manual permits you to adjust the size of individualwindows and use the Cascade and Tile commands (see above); b) maximize forces the activewindow to occupy the entire screen; c) auto tile forces all open windows to share the screenequally.

CYMGRD for Windows


The "Copy to Clipboard" command

This command allows you to copy the contents of the active window (graphic or text) to theWindows Clipboard. You may then insert the image into another application such as Write,Paint, AutoCAD for Windows, etc. This feature is very useful for inserting CYMGRD results inpresentation texts and technical reports. If more than one window is open, click on theappropriate window before selecting the “Copy to Clipboard” command.

Note: If you want to insert a graphic (soil model, grid, etc.) into a word processordocument, transfer it first into a graphics application (e.g. Paint) in order to retain itsformat.

The "Print" command

This command prints the contents of the active window , whether graphics or text.

The "Print all" command

This command allows you to print the contents of all windows at once, whether iconized ornot. For example, if you have just completed the surface potential analysis, the station layoutwindow and the report window will be printed as well.

The "Page setup" command

This command allows you to specify the page layout for printing. You can adjust the top,bottom, left, and right margins, in metric or imperial systems.

The "Printer setup" command

This command allows you to select and, if necessary, configure the printer for CYMGRDgraphs and report outputs.

The Window List

At the bottom of the Window menu appears a list of open windows (Soil Model, Grid Layout,etc.) Clicking on one of these is one way to make it the active window. (The usual way is toclick inside the desired window.)

CYMGRD for Windows

Chapter 2 - SOIL RESISTIVITY AND SAFETY ASSESSMENT 15

Chapter 2

SOIL RESISTIVITY AND SAFETY ASSESSMENT

2.1 Soil resistivity measurements and soil models

CYMGRD uses statistical techniques to interpret soil resistivity measurements in order todefine the soil model for use in the subsequent analysis.

Note: All electrodes in a given study are assumed to be buried in the same soil.

Soil may have a uniform resistivity to a significant depth, but it is common to find that the soilconsists of (at least) two horizontal layers of different resistivities. Thus, CYMGRD offers achoice between “uniform” and “two-layer” soil models. A two-layer model has an upper layer of adefinite depth and a lower layer of an infinite depth but with a different resistivity. CYMGRDdoes not yet offer “multiple layer” soil models.

Of the various soil measurement techniques, CYMGRD supports only the Wenner technique,in which the distance (a) between each pair of probes is equal.

A current I is injected and the resulting voltage V is measured by the voltmeter. The apparent(measured) resistivity is given by

where b is the length of the probe.

Note: CYMGRD interprets only resistivity measurements. Resistance values are notallowed.

( )ρπ

=

++

−+

4

12

42 2 2 2

a V I

a a

a b a b

or ( )ρ π= 2 a V I if a b>>

CYMGRD for Windows

16 Chapter 2 - SOIL RESISTIVITY AND SAFETY ASSESSMENT

2.2 Soil resistivity. Methodology and algorithm

Let ρa be the apparent earth resistivity as computed by a two-layer model, ρ1 and ρ2 theresistivity of the upper and lower soil layers, and h the thickness of the upper soil layer(CYMGRD assumes that the thickness of the lower layer is infinite). The module will find ρ1, ρ2,and h according to the mathematical equations described below. The results will beautomatically communicated to the GRID module which calculates the surface potentials.

K = reflection coefficient = (ρ2 - ρ1) / (ρ2 + ρ1)

n = integer varying from 1 to ∝h = upper layer thickness

a = electrode spacing

ρ1, ρ2 = upper & lower soil layer resistivity

By finding ρ1, ρ2, and h, CYMGRD minimizes the following function:

where the sum spans all the available measurements.

ρmi = measured earth resistivity at probe distance Di

ρ(i) = computed earth resistivity at probe distance Di

Note: CYMGRD uses reduced gradient techniques to calculate the optimal model.

Hint: CYMGRD will identify measurements that do not fit the computed resistivity functionvery well. In order to try to improve the accuracy of the soil model, you may remove oneor more such measurements from the input data and run the analysis again.

CYMGRD for Windows


2.3 The "SOIL" menu

To analyze soil resistivity and/or safety assessment, activate the SOIL module.

Click on Module in the main menu and select Soil from the list, or click on the SOIL icon .

Use the commands of the Soil menu, in order, from top to bottom.

Click on Input data to enter the Wenner-method soil measurements or click on Import fromto import the data files directly.

Hint: The Import function reads data from ASCII format text files. These files may havebeen created by the DOS version of CYMGRD or may be created using any text editor.

Click on Calculate! > soil model to interpret the soil model and generate a report file.

Click on Calculate! > safety assessment to compute the tolerable Touch and Step voltages.

CYMGRD for Windows


2.3.1 The “Soil >> Input data” command

The dialog box shown below allows you to enter the probe distance and the correspondingmeasured resistivity for each measurement made using the Wenner method.

First define whether the soil is uniform or two-layered. If the soil is uniform, CYMGRD willfind the average of the measurements. If you select a two-layer model, CYMGRD will analyzethe model as explained in section 2.2 above. In the example above, a two-layer soil model hasbeen selected.

1. Click on the Insert button

2. Enter the probe distance in the box marked Probe Distance, and its associated resistivityvalue in the Resistivity box.

3. This set of values will then be registered in the table.

(To delete a set of values, position the highlight bar on it and click on the Delete button.)

4. Once all the sets of measurements are entered, click on the "OK" button.

5. Calculate the soil model, using the Calculate! > Soil Model command (section 2.3.3).

Note: You must enter at least one measurement for uniform soil. You must enter at leastthree measurements for two-layer soil. CYMGRD can accept 100 measurementsmaximum.

Note: for former users of CYMGRD for DOS: CYMGRD for Windows can read your oldresistivity data files. See the Import from command (section 2.3.2). You do not need toenter old data again using the Input data command.

CYMGRD for Windows


2.3.2 The "Soil >> Import from" command

Use this command to import the soil measurements from data files created with DOSversions of CYMGRD. Once imported, the measurement values will be saved as part of theactive study.

2.3.3 The "Soil >> Calculate" command

This command calculates the resistivity of the upper and lower layers of soil as well as thethickness of the upper layer. (The lower layer is assumed infinitely thick). In the case of auniform soil, it calculates the average of the resisitivity measurements.

A tabular report of results will appear. At the bottom, it identifies the error between themeasured and calculated resistivities at each of the probe distances given. The RMS error iscomputed to indicate the degree of correspondence between the calculated soil model and themeasured values. It is calculated from:

Once the resistivity measurements have been interpreted, the resulting soil model is madeavailable to the SAFETY ASSESSMENT analysis (Section 2.4) and to the surface potentialanalysis (GRID module, Section 3.4.3).

Note: If the analysis has already been performed, this command will not be accessible.

RMS error =∑ 2error i

Ni

N( )

CYMGRD for Windows


2.3.4 The "Soil >> Visualize" command

This command displays the calculated resistivity curve along with the resistivitymeasurements, for comparison. You should consult this resistivity curve window before youaccept the soil model. See the example below.

The program will automatically indicate measurements that feature RMS errors exceeding theaverage RMS error of the statistical fit. These are so-called “doubtful points”.

The calculated points are represented by a blue curve. Measured points are marked withred circles, while doubtful points are marked with red X’s (see legend, bottom left of thescreen). The resulting soil model is also shown on the rightmost part of the graph legend.

You can track the curve with the mouse. Select any point on the curve with the cursor tosee the probe distance and the calculated apparent resistivity values under the graph.

CYMGRD for Windows


2.4 The "SAFETY ASSESSMENT" analysis

Use this command to calculate the maximum permissible touch and step voltages.

The “Safety assessment” calculations comply with standard North American practice asdescribed in the "IEEE Guide for Safety in AC Substation Grounding", 1986 edition. They takeinto account:

• Body weight of the shock victim (by default equal to 50 kg).

• The thickness and resistivity of material (e.g., crushed rock) placed on the surface of the soil.

• Soil resistivity of Upper and Lower layers, and thickness of Upper layer.

• Shock duration (0.1 seconds by default).

CYMGRD uses the following equations, taken from IEEE 80 (1986), to calculate themaximum permissible touch and step voltages.

For a 50 Kg body weight:

E touch = (1000+1.5Cs(h,k)Ps)0.116/ t

E step = (1000+6Cs(h,k)Ps)0.116/ t


E touch = (1000+1.5Cs(h,k)Ps)0.157/ t

E step = (1000+6Cs(h,k)Ps)0.157/ t

where:

⇒ t is shock duration in sec.

⇒ Cs(h,k) is the derating factor when high resistivity surface material is present. Thereduction factor Cs is a function of the reflection factor k and the thickness of theupper layer h.

⇒ ρs is the resistivity of the surface material in ohm-m.

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Once the calculations are completed, the safety results window appears.

These factors can either be calculated or obtained from graphs according to the IEEE 80Guide. CYMGRD obtains these factors by calculating the infinite summation up to a givenaccuracy.

Transferring the safety analysis results to other modules

CYMGRD automatically transfers the maximum permissible touch and step voltagescalculated by the SAFETY ASSESSMENT to the graphical analysis module (PLOT). In theabove sample dialog box, you can see that this option is active by default.

2.5 The "Graphic Parameters" option

Use these options to remove or display the legend, the reference lines or the markers.Removing the legend allows more space for the resistivity curve.

CYMGRD for Windows

Chapter 3 - THE GRID MODULE 23

Chapter 3

THE GRID MODULE


The GRID module is used to calculate the grounding system’s resistance and ground potentialrise (GPR) and also the potential gradients at the soil surface. You may use these results tooptimize the grid design and also to evaluate the safety of personnel.

3.2 Electrode types and terminology

CYMGRD supports three types of grounding systems. The first is the grid, called the primaryelectrode. The second type, called a return electrode, is a nearby electrode through whichsome of the current dissipated in the soil through the primary electrode returns to the network.Finally, the third type, the distinct electrode, is not connected to the primary or return electrodebut may be subjected to the influence of their electric fields. Although return and distinctelectrodes are not often found as components of a grounding system, it is sometimes necessaryto represent them.

The Primary electrode

This is the grounding grid being analyzed. You may build it up out of conductors and rods.Symmetrical arrangements are easier to input. Asymmetrical arrangements (one conductor orrod at a time) may also be entered.

The Return electrode

If two grounding grids are in the vicinity of each other, and current injected to ground at thefirst grid returns to the system via the second, then the second grid is a Return Electrode. Thepresence of a Return Electrode will alter the surface potential distribution.

You can model the Return electrode in the same way that you model the primary electrode.Even a single rod can serve as a Return electrode. In addition, you must enter the currentabsorbed by the return electrode, in Amperes. This value must be negative. You may easilycompare results with and without the Return electrode.

CYMGRD for Windows

24 Chapter 3 - THE GRID MODULE

The Distinct electrode

Conductive structures like pipelines, cable sheaths, or building foundations which are near agrounding installation, but not connected to the electric network are Distinct electrodes.

Hint: If the substation fence is not bonded to the grounding grid, model the fence postsas distinct electrodes. Otherwise, model them as part of the Primary electrode.

You model the Distinct electrode in the same way that you model the primary electrode.Even a single rod or buried conductor can act as a Distinct electrode.

You must define whether or not all elements of the distinct electrode have the same potential.They have the same potential if they are connected together. If the Distinct electrode is made ofinsulated sections, they do not have the same potentials.

3.3 Grounding system structure and location

CYMGRD is capable of analyzing grounding systems of either symmetrical or asymmetricalconfiguration. A grounding system is made of conductors, which the program divides into“elements” for the purpose of the calculations. If a two-layer soil model is used, then gridconductors must be located in one or the other layer. Rods may be located partly in both layers.

3.4 The "Grid" menu

In the GRID module, you can describe the geometrical arrangement of all grid conductors androds for all three types of electrode, if desired. Visualize the grid layout on screen, and calculatethe ground potential rise and the total grid resistance, using the soil model and specified faultcurrent.

Activate the GRID module by clicking on the GRID icon at the extreme right of theRibbon, or by clicking on Module in the menu and selecting GRID from the list.

3.4.1 The “Grid >> Input data >> Installation” command

This command allows you to define the grounding system components. First enter a namefor the station (optional) in the header field. Then, enter the injected ground (fault) current. Ifnecessary, you may change the values for upper layer thickness, upper layer resistivity, andlower layer resistivity.

Hint: The ground current is the fault current flowing into the ground. All or part of itflows in the grounding grid. Part of it may flow in the ground wires and counterpoises ofall the transmission lines converging on the site. See Parallel Z, below.

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The upper layer thickness, upper layer resistivity and lower layer resistivity values aretransferred by default from the SOIL module, if a soil analysis has been made prior to thesurface potential analysis. If not, you can enter any appropriate soil model directly.

Note: If you select a uniform soil model, enter the same resistivity for both soil layers withan arbitrary upper layer thickness (100m is the limit).

If a return electrode is present, enter the return electrode current. If not, set the current to 0.

The equivalent resistance in parallel with the grounding grid, Parallel Z, is the total equivalentresistance (in ohms) of the sky wires and counterpoises of all the lines connected to thesubstation. The ground current is divided between these two resistances. To direct all the groundfault current into the grid, set Parallel Z to 9999 Ω . The Enable option forPrimary/Return/Distinct rods & conductors are used to select these for the Grid analysis.

Finally, click on the distinct electrode check box if all the elements of the distinct electrodehave the same potential (assuming a distinct electrode is present). If the distinct electrode ismade of isolated elements, make sure this box is clear.

Note: If you change any of the Enable rods/conductors settings above, you will have torecalculate the ground potential rise and grid resistance (Section 3.4.6).

CYMGRD for Windows


3.4.2 The “Grid >> Input data >> Electrodes” command

Use this command to define the geometrical arrangement of the grounding installation, usingthe grid conductors and rods dialog boxes. Although you can enter them in any order, it is moreconvenient to enter conductor data first and then the ground rods data.

Build up the complete grid using arrays of conductors and rods. There are 4 kinds of array:

a) symmetrically arranged grid conductors,

b) asymmetrically arranged grid conductors,

c) symmetrically arranged ground rods, and

d) asymmetrically arranged ground rods.

All types are explained in the following sections.

Symmetrically arranged grid conductors

This type of array is usually rectangular, with a number of conductors laid out along the longand short axes, so as to create a grid. CYMGRD assumes that symmetrically arranged gridconductors are buried horizontally and oriented along two perpendicular axes (the X and Y axesin the graphic window). The spacing between conductors is assumed to be equal along eachaxis, but the spacing along the Y axis can be different from the spacing along the X axis.

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A symmetrical grid dialog box is shown above. Note that the check box “Symmetric” hasbeen checked (þ). The following set of data defines a symmetrically spaced grid:

It is part of the Primary, Return or Distinct electrode. Choose one by clicking.

• The number of grid conductors parallel to the X axis (horizontal on the display)

• The number of grid conductors parallel to the Y axis (vertical on the display).

• The number of elements per conductor, for conductors parallel to the X and Y axis.

• Burial depth (the distance between the soil surface and the center of the conductor).

Note: A positive value of Z denotes a position below the surface of the soil.

• Conductor diameter.

• The coordinates (X1,Y1) and (X2,Y2) of two opposite corners of the array.

Asymmetrically arranged grid conductors

An asymmetrically arranged conductor is a single straight conductor stretched between twopoints defined by coordinates (X1,Y1,Z1) and (X2,Y2,Z2). Each conductor may have a differentdiameter.

An asymmetrical grid dialog box is shown above. Note that the check box “Symmetric” hasNOT been checked. The following set of data defines an asymmetrical grid:

• It is part of the Primary, Return or Distinct electrode. Choose one by clicking.

• The coordinates (X1,Y1,Z1) and (X2,Y2,Z2) of the two ends of each conductor. Conductorsmay be inclined with respect to the soil surface, which CYMGRD assumes to be horizontal.


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• The number of elements for each conductor.

• The conductor diameter.

Note: Both ends of a grid conductor must be in the same layer of soil.

Symmetrically arranged ground rods

A symmetric array of ground rods covers a rectangular area in which rods are located in rowsparallel to the X axis and all rods in a row are equally spaced. All rods defined in the same arrayhave the same burial depth, length and diameter.

A symmetric rods dialog box is shown above. Note that the check box “Symmetric” has beenchecked (þ). The following set of data defines symmetrically arranged ground rods:


• Coordinates (X1,Y1) and (X2,Y2) of two opposite corners of the area where the rods areplaced.

• Number of rows of rods. (“Parallel to the X axis” means “horizontal” on the display.)

• Number of ground rods per row (along the X axis).

• Ground rod length.

• Burial depth (the distance between the soil surface and the top of the rods)

Note A positive value of Z denotes a position below the surface of the soil.

• Ground rod diameter.

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Asymmetrically arranged ground rods

An asymmetric array of ground rods is a single row of equally spaced rods. The position ofthe head of the first rod is given by the coordinates (X1,Y1,Z1) and the position of the last rod inthe row, by the coordinates (X2,Y2,Z2). The head of each rod in between lies on the straight linebetween these two points. All rods defined in the same array have the same length anddiameter. If a single rod is specified (Number of Rods along axis = 1), then enter only the startingpoint coordinates (X1,Y1, Z1).


A dialog box for asymmetrically arranged ground rods is shown above. Note that the checkbox “Symmetric” has NOT been checked. The following set of data defines a row of rods:


• Coordinates (X1,Y1,Z1) and (X2, Y2, Z2) of the two ends of the row of rods.

• The number of rods in the row.

• The number of elements in the upper soil layer (per rod).

• The number of elements in the lower soil layer (per rod).

• The rod length.

• The rod diameter.

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3.4.3 Geometrical station layout

Using different layouts

Build up the grounding grid layout by using combinations of the four types of arrangementsdescribed above. Do the same for the Return and Distinct electrodes if necessary. For moreexplanations on the use the various layouts, refer to Appendix I.

Note: Electrodes are color-coded in the graphic window. Primary electrodes are red,Return electrodes are blue and Distinct electrodes are pink.

Adding and removing entries

Click on the Insert button and enter the data for the first entry of a given type of array.

To delete an entry, click on it in the list to highlight it and click on the Delete button.

Editing data from the list

Scroll through the list of entries by clicking on the scrollbar, or click on the itemto be edited so that it is highlighted. Then click in the data boxes and type in the new data.

Reviewing and verifying the data

When you select a conductor (or a ground rod) in the list with the cursor, it is highlighted inyellow on the grid layout, so that you may see which electrode you have selected. This isparticularly useful when erroneous coordinates have been entered and you wish to correct them.

If you click on the Disable button, the selected electrode is hidden from view in the gridlayout window (and will be ignored in subsequent calculations). To see it again, click on theEnable button.

3.4.4 The Grid >> Input data >> Merge with... command

Use this command to merge the active study with another one, in order to display more thanone grid in the same window (or to combine two sections of the same grid). Click on theDirectory, Project and Study buttons to select the appropriate study. Make sure that theconductors and rods coordinates are not the same (i.e., no overlapping conductors), otherwisewhen you try to calculate, an error message will appear and a report will identify the elementsthat are superimposed.

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3.4.5 The Grid >> Input data >> Import from... command

This command allows you to import a file containing the required data for a groundinganalysis. Data files from DOS versions of CYMGRD can thus be used in the windows version.Since the DOS version produces an ASCII data file with all the required information, you do nothave to enter the data interactively.

Note: CYMGRD for Windows does not save its data in a separate file but as an integralpart of a study; to retrieve it, you need to open the study. See section 1.10.1.

When you import a DOS file to CYMGRD you may want to check for Conductor/Rod overlaps.Note that during calculations CYMGRD will also check for possible Conductor/Rod overlaps.

To check for Conductor overlaps:

Click on Grid >> Input Data >> Electrodes >> Conductors.

Scroll through the list of entries starting from the first conductor, by clicking on the scrollbar. For example, if the current conductor overlaps with conductor # 2, you will obtain thefollowing message:

You can click on the Delete button to remove the element or the Disable button to hide fromview in the grid layout window (and will be ignored in subsequent calculations).

You can repeat the same procedure to check for Rod overlaps.

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3.4.6 The Grid >> Calculate command

This command calculates the grid resistance, ground potential rise, and the current diffusedinto ground by the various elements of the grounding installation.

Once the calculations are complete, a dialog box appears showing the ground potential rise,primary electrode resistance, and total impedance of the installation. (This last item includes theeffect of the Parallel Z.)

CYMGRD automatically calculates the threshold levels for the surface potential contoursbased on the GPR. (See the PLOT module). Click on the “OK” button.

3.4.7 The Grid >> Visualize command

This command allows you to see the station layout in 2D or 3D view, depending on theparameters setting for the station grid. It is active when you are entering data for the grid layout,so that CYMGRD continually updates the grid layout as you enter the data.

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3.4.8 The Grid >> Graphic parameters dialog box

In this dialog box, you can select the display settings for the grounding installation.

Show primary electrode displays the Primary electrode (the grounding grid). To remove thePrimary electrode from view temporarily, click on the check box to remove the check mark.

Show return electrode displays the Return electrode. To remove the Return electrode fromview temporarily, click on the check box to remove the check mark.

Show distinct electrode displays the Distinct electrode. To remove the Distinct electrodefrom view temporarily, click on the check box to remove the check mark.

Hide all rods removes the grounding rods from the display. To remove the rods from viewtemporarily, click on the check box to place a check mark.

Reference lines will extend the axis tick marks across the entire length and height of the gridlayout display if active (þ). These lines may aid you in detecting data entry errors. By default,CYMGRD does not display the lines.

Axes to scale is active (þ) by default. Deactivate it only to aid visibility if the grid is verylong and narrow.

2D / 3D View allows you to view the grid layout in 2 or 3 dimensions. By default, CYMGRDdisplays the layout in 2D view, as shown above. If you select 3D instead, the 3D parameters willbecome accessible. You can define an elevation angle from x-y to indicate the inclination ofthe layout in relation to the X-Y plane (default = 25), an azimuthal angle about z to indicate theclockwise rotation angle around the Z axis, and a camera distance to indicate the depth of theperspective (default = 5).

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Note: To display the graphic parameters dialog box, you can also double-click the leftmouse button inside the grid layout window.

When finished, click on "OK" to activate all the selected options or "Cancel" to remove anychanges you made. Clicking on "Defaults" resets all the values to their original settings.

3.5 Examining the tabular results file

This file contains important and useful information. The file begins by showing thecoordinates for each of elements of the grid conductors, their length and diameter along with thecurrent diffused.

Next, the total length and radius of conductor elements is indicated.

A list of ground rod elements follows, along with the total length of the rods.

The report will indicate that the calculation was "successful" if no errors were found.Otherwise, CYMGRD identifies the erroneous data to correct.

CYMGRD for Windows


Finally, at the very end of the results, CYMGRD indicates the ground potential rise, groundingresistance of the primary electrode, and total impedance of the installation. The total impedanceof the installation is the parallel combination of the calculated grid resistance and the parallelresistance entered in the installation data dialog box.

Important note: Normally, all elements of the grounding installation diffuse a positivecurrent into the ground.

However, the calculations might indicate that the current diffused into the ground by oneor more elements is zero. This means that CYMGRD found that each such elementdiffused a (small) negative current. This situation is due to numerical instability. Toavoid this problem, change the number of elements in the affected conductors (or rods)so that these elements are about as long as other elements in other conductors in thegrid.

If this happens, CYMGRD will indicate in the grid calculation window the number of theelement which diffused the largest negative current into the ground, along with itscoordinates. Furthermore, the program will calculate the sum of all the negative currentsand compare it with the total injected fault current. This is the meaning of the error thatis shown along with the element. If the error exceeds a few percent, the number ofelements should be changed as explained above.

Experience has shown that the negative current is a very small fraction of the injectedfault current and that the error introduced in calculating the station resistance and GPR isnegligible. Simulations performed after changing the number of elements in conductorsindicate no change in the overall results, apart from correcting the negative currents.

CYMGRD for Windows

Chapter 4 - THE PLOT MODULE 37

Chapter 4

THE PLOT MODULE


Use the PLOT module to calculate and view the results of the surface potential analysis. Thegraphic outputs allow you to examine the performance of grid areas by inspecting them on thescreen. Graphic displays include equipotential contour lines and potential profiles (gradients).

Hint: Before running the PLOT module, make sure to compute the tolerable Step andTouch voltages as well as the GPR (Grid Potential Rise). These values are necessary toany analysis of safety. See Sections 2.3.1 and 3.4.6.

4.2 The Contours menu

Use this menu to generate equipotential contour plots in 2D or 3D view. You cannot use the"Calculate" command unless the station GPR and total resistance to ground have beencalculated first in the GRID module (see Section 3.4.6).

4.2.1 The "Contours >> Calculate" command

Click on the Calculate command to see the dialog box below. By default an area largeenough to encompass all electrodes will be analyzed. If you wish, you may restrict the analysisto a smaller (rectangular) area. To do so, enter the coordinates (X1, Y1) and (X2, Y2) of thelower left and upper right corners of the desired area.

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38 Chapter 4 - THE PLOT MODULE

Hints:

1) In this way, you may examine potentials outside the grid area.

2) See Section 4.2.2 for a way to select the area using the mouse.

The number of intervals along each axis indicates the number of subdivisions of theselected area, for calculation purposes. If you need more accurate calculations, increase thenumber of intervals (60 maximum). The calculation time will increase accordingly.

Once you have entered the coordinates and the intervals, click on “OK” to begin thecalculations. When finished, CYMGRD displays a new window to show the resultingequipotential lines.

CYMGRD for Windows


4.2.2 The "Contours >> Calculate" mouse command

An alternative to using the menu command “Calculate” (Section 4.2.1) is to use the mouse:

1. In the grid layout window, position the mouse at one corner of the area of interest.

2. Click the left button, hold it down, and drag the cursor over the area to be analyzed.

Notes:

1) The display must be in 2D. If the display is in 3D, double-click in the station layoutwindow. The parameters dialog box will appear. Select 2D view.

2) If you click and hold the left button of the mouse, you can use the arrow keys on thekeyboard to move the cursor very accurately.

CYMGRD for Windows


Release the left mouse button. A dialog box will appear. Select 2D equipotential plot.

1. If you select an equipotential plot, the coordinates dialog box will appear

2. Enter a title to replace the default title (optional).

3. Click on OK. The program will begin the calculations and will display the resultingequipotential plot.

Note: To display a contour in 3D view, double-click in the contour window. When theparameter dialog box is displayed, select 3D.

CYMGRD for Windows


4.2.3 The "Contours >> Visualize" command

Use the "visualize" command to view contour plots which have already been generated. Thelist box contains the names of all the graphs within the current study. Meaningful names areeasier to locate subsequently. If you choose a title that already exists, it WILL NOT overwritethe first plot (ex: the list can contain two “surface potential plot #1”).

Notes:

1) The gray “X” displayed along with the equipotential contours indicates the location(s)with the lowest surface voltage (highest touch voltage). More than one point mayshare the lowest voltage if the grid is symmetrical.

2) Dark red denotes a more dangerous voltage level than bright red.

4.2.4 The "Contours >> View report" command

The “View report” command replaces the entire contents of the active contour graph windowwith a tabular report. To return to the graphic plot, you must select this command a second time.

A check mark appears to the left of the menu item when the contour graph window is in the“View report” mode.

4.2.5 The "Contours >> Rename" command

Use this command to rename contour graphs which have already been generated. A box willappear, listing the names of the contour plot windows. Click on the appropriate contour nameand then click on “Rename." Enter the new name in the space provided and click on “OK."Once you have renamed the desired contour plots, click on “Done” to exit this list box.

4.2.6 The "Contours >> Delete" command

Use the "Delete" command to delete contour graphs which have already been generated. Abox will appear, listing the names of the contour plot windows. Click on the appropriate nameand click on “delete”. Once you have deleted the desired contour plots, click on “Done” to exitthis list box.

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4.2.7 The "Contours >> Parameters" command

Use this command to define the parameters for the contour plots.

You can specify these parameters either globally or within the active window. Globally, theselected parameters will become the default parameters for all contour plots displayed by theprogram. If you wish to modify the parameters for a single plot window, click in that window tomake it the active one, and then select the active window option. The changes made to theparameters will apply only to the active plot window. The contour parameters dialog box isfurther explained below.

Note: The active window option is disabled if the active window does not contain acontour plot.

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Number of contour levels allows you to select the number of equipotential contour levelswhich will be displayed. Click on the up and down arrow symbols to increase or decrease thesetting.

Touch or Surface potentials tells CYMGRD to display touch or surface potential contourplots. Touch potential is the difference between the ground potential rise (GPR) and the surfacepotential. Click on the appropriate check box. By default, CYMGRD generates touch potentialcontour plots.

Solid filled fills the space between the contour lines with the appropriate colors. It might beuseful when the safety threshold is between two adjacent equipotential contours. Click on theoption to activate it. By default, CYMGRD does not display solid filled graphs.

Show wire mesh fits a flexible grid to the shape of the contours for added clarity. This optionis available only with the solid filled graphs option. By default, CYMGRD does not display a wiremesh.

Show labels adds labels to the equipotential lines on screen, to identify the voltage. Bydefault, CYMGRD displays labels for the equipotential lines.

Reference lines extends reference lines from the axes to cover the grid area. By default,CYMGRD does not display reference lines.

Show substation superimposes the grid conductors and rods on the equipotential contours.It is a very useful feature to identify danger points on the grid. By default, CYMGRD displays thesubstation layout.

Axes to scale preserves the X and Y axes ratio when displaying the plot. Click on the optionto disable it. By default, CYMGRD draws the axes to scale.

Elevation angle to x-y plane rotates the 3D view of the grid about the edge with the highesty-axis coordinate. Click on the up and down arrows to increase and decrease the angle. Bydefault, CYMGRD sets this angle at 25 degrees.

Azimuthal angle about Z rotates the 3D view of the grid about the Z-axis. Click on the leftand right arrows to increase and decrease the angle. By default, CYMGRD sets this angle at215 degrees.

Camera distance adjusts the perspective in 3D view. The closest view is “1” and the farthestis “10”. By default, CYMGRD sets this distance at 5.

Note: For more details on 3D commands, see Appendix 1.

CYMGRD for Windows


2D view and 3D view allow you to select the view by clicking on them. In 2D view, the 3-dimensional display options will be disabled. By default, CYMGRD displays graphs in 2D view.

Thresholds allows you to set the voltage at which the contour colors change.

Touch potential grading thresholds are calculated from the maximum allowable touchvoltage calculated in the SOIL module. The thresholds are listed in ascending order. Belowlevel #1, the touch potential contour lines will be green. Between level #1 and level #2, blue.Between level #2 and level #3, purple. Above level #3 (normally equal to the maximumallowable touch voltage), the contour lines appear in shades of red. (The most dangerous valueswould be dark red and NOT bright red.)

Hint: You may of course change the thresholds.

Surface potential grading thresholds are calculated from the maximum allowable touchvoltage calculated using the SOIL module and the grid GPR calculated using the GRID module.The thresholds are listed in descending order. Above level #1, the surface potential contour lineswill be green. Between level #1 and level #2, blue. Between level #2 and level #3, purple.Below level #3 (normally equal to the difference between the GPR and the maximum allowabletouch voltage), the contour lines will appear in shades of red. (The most dangerous value wouldbe dark red and NOT bright red).

Hint: You may of course change the thresholds.

Equally spaced levels simply divides the interval given by the maximum and minimumpotentials in four equal sub-intervals and color codes them accordingly.

When finished, click on "OK" to put all the selected options in effect or "Cancel" to removeany changes you made. Clicking on "Defaults" retrieves the original threshold values calculatedby the SOIL and GRID modules.

Note: If only a small section of the station is analyzed (see sections 4.2.1 and 4.2.2), thethreshold span should be narrow to get a better display of voltage differences.

4.2.8 Inspecting contour plots

You can track the contours with the mouse by clicking on them. Slide the mouse along thecontours to see the coordinates and voltage of a specific point (values appear at the bottom ofthe screen). The cursor position is displayed simultaneously in the grid layout window, foridentification purposes.

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4.3 The Profile menu

Use the Profile menu to generate touch, step or surface potential profiles along a straight linein any direction. Most of the commands are the same as in the Contour menu.

4.3.1 The "Profile >> Calculate" command

When selected, the “Calculate” command first displays a dialog box to define thecoordinates of the starting point (X1, Y1) and ending point (X2, Y2) of the straight line. Since it isa surface potential analysis, you do not have to enter a Z coordinate.

The step interval defines the distance between the two feet of the shock victim, for thepurpose of displaying the step voltage between two points along the profile. This value shouldbe realistic (e.g., 1m). Click on “OK“ to begin the calculations. CYMGRD will display the resultingpotential profile plot.

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The potential profile displays three pairs of curves, as a function of distance along theselected direction:

The ground potential rise (GPR) and Surface Potential, in RED.

The maximum allowable Touch potential and the actual Touch potential, in BLUE.

The maximum allowable Step potential and the actual Step potential, in GREEN.

CYMGRD reports the numerical values of GPR and the tolerable touch and step voltages inthe bottom right-hand corner. Recall that these values come from the SOIL module results.

Hazardous locations may be identified as those places where the actual touch or step voltage(curved line) exceeds the calculated tolerable maximum (flat line).

Notes:

1) If you do not specify a "maximum touch potential", or if it has not been previouslycalculated, its flat line will not appear on the graph.

2) You may slide the cursor along the curves to see the values at different distances.

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4.3.2 The "Profile >> Calculate" mouse command

Instead of specifying the starting and ending points of the profile via the Calculate menucommand, you may simply draw the straight line using the mouse, as follows:

Notes:

1) The display must be in 2D. If the display is in 3D, double-click in the station layoutwindow. In the parameters dialog box, select 2D view.

2) If you click and hold the left button of the mouse, you can use the arrows on thekeyboard to move the cursor very accurately.

In the station layout window, position the mouse at the starting point of interest. Click the leftbutton, hold it down, and drag the cursor to draw the straight line. In the example below, theending point is (34.51, 39.21).

1. Release the left mouse button. A dialog box will appear. Select Potential profile plot.

CYMGRD for Windows


4.3.3 The "Profile >> Visualize" command

Use the "Visualize" command to display potential profile plots already generated. The list boxcontains the titles of all the current study plots. Meaningful titles are easier to locatesubsequently. If you choose a title that already exists, it WILL NOT overwrite the first plot (i.e.,the list can contain two surface potential plot #1).

4.3.4 The "Profile >> View report" command

The “View report” is a toggle command that replaces the entire contents of the active profilegraph window with a tabular report. To return to the graphic, you must select this command asecond time. A check mark appears to the left of the menu item when the profile graph windowis in the “View report” mode. This command is disabled if no profile has been calculated.

4.3.5 The "Profile >> Rename" command

Use this command to rename profile graphs already generated. A list of profiles will bedisplayed. Click on the appropriate profile name and then on “Rename”. Enter the new name inthe space provided and click on “OK”. Once you have renamed the desired profiles, click on“Done” to exit this list box.

4.3.6 The "Profile >> Delete" command

Use the "Delete" command to delete profile graphs already generated. In the list box, selectthe appropriate profile and click on “Delete”. Once you have deleted the desired profiles, clickon “Done” to exit this list box.

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4.3.7 The "Profile >> Parameters" command

Use this command to define the parameters for the profile plots.

You can specify these parameters either globally or within the active window. Globally, theselected parameters will become the default parameters for all future profile plots generated bythe program. If you wish to modify the parameters for a single plot window, first click inside thatwindow to make it the active one, and then select the active window option. The changes madeto the parameters will apply only to the active plot window. The profile parameters dialog box isfurther explained below.

Note: The active window option is disabled when the selected window is not a profileplot.

Show markers will identify the curves using symbols (squares and triangles). By default,CYMGRD displays markers. To hide them, click to remove the check mark.

Show legend displays the legend at the bottom of the graphic. Click on the check box todisable it. By default, CYMGRD displays the legend. However, CYMGRD will not display thelegend if the "Show markers" option is disabled.

Reference lines will extend lines from the tick marks on the axes of the graph. Click on theoption to activate it. By default, CYMGRD does not display the reference lines.

Surface potentials includes the surface potential and GPR curves in the graphic when active(þ). Click on its check box to disable it. By default, CYMGRD will display the surface potentialcurve.

CYMGRD for Windows


Touch potentials includes the maximum and actual touch potential curves in the graphicwhen active (þ). Click on its check box to disable it. By default, CYMGRD will display the touchpotential curve.

Step potentials includes the maximum and actual step potential curves in the graphic whenactive (þ). Click on its check box to disable it. By default, CYMGRD will display the steppotential curve.

When finished, click on "OK" to put all the selected options in effect or "Cancel" to removeany changes you made. Click on "Defaults" if you want to reset all the values to their defaultsettings.

4.3.8 Inspecting potential profile plots

Before generating potential profile plots along a given axis, it is advisable to run the SOILmodule to determine the maximum permissible touch and step potentials for the soil conditions(see Chapter 3, section 3.4.3).

Up to six curves can be generated for each potential profile plot, depending on the potentialprofile parameters' settings.

You can track the curves with the mouse by clicking on them. Slide the mouse along thecurve to see the distance and the voltage between a specific point and the starting point (valuesappear at the bottom of the screen).

You can also have the absolute coordinates of a specific point along the axis. In order to dothis, track the curve with the mouse while holding down the left mouse button. The label"Location (X, Y)" will appear above the narrow cursor, and the coordinates will replace thedistance and voltage values. In this way, you can link the potential of a point with its coordinates.The same applies for the step potential curve. However, since the step potential is the differencebetween the surface potentials of two consecutive points, the coordinates displayed define thesecond point.

CYMGRD for Windows

Appendix I - EXAMPLE STUDIES 1

Appendix I

EXAMPLE STUDIES

In this appendix, you will find 3 step-by-step sample studies. We have also described the mostcommonly used functions in order to make your work easier.

Most commonly used functions

Keyboard arrows

In 2-D display, you can use the arrow keys to move the cursor slowly in the display windows. Putthe cursor in the appropriate window first.

Using the mouse in 3-D display

In 3-D display (in the PLOT module), you can use the mouse to rotate and elevate the plot. Clickon the LEFT button and hold it down while moving the mouse. You might need some practice tobecome accustomed to it. If you want to move the mouse more slowly, click on the LEFT button,hold it down and use the keyboard arrow keys. To change the camera distance, click on the leftbutton and hold it down. Then, click on the RIGHT button and hold it down too while moving themouse up and down.

Double-click

If you double-click the left mouse button, the parameter dialog box of the active window willappear.

Tile/Auto-tile

You will find this command in the “Window” menu. It divides the screen in equal segments inorder to allocate the same viewing area to all windows. Use the auto-tile setting under “Displaymode” to tile the desktop contents automatically whenever a window is opened or closed.

Print/Print all

You will find the “Print” commands in the “Window” menu. You can print the active window(“Print” command) or the contents of all visible windows (“Print all” command).

Save

When you activate CYMGRD, it automatically opens the last project that was loaded. If youwant to create a new project based on the last one, use the “Duplicate” command and give aspecific title to the new project. If you wish to create a completely new project, use the “Create”command and then give a specific title to the new project. Use the “Study >> Save” commandto save a study. If you try to exit CYMGRD without saving your study, a dialog box will appear,offering to save the current study.

CYMGRD for Windows

2 Appendix I - EXAMPLE STUDIES

Example 1: Primary electrode only

Step-by-step instructions for data entry, analysis and graphic display follow. The first example isa grounding grid (primary electrode) with grounding rods.

1.1 Resistivity analysis of the substation soil

Among the various techniques used for soil resistivity measurement, CYMGRD supports theWenner technique. Suppose that the following measurements were obtained in the area wherethe grounding system will be installed.

Note: CYMGRD interprets only resistivity measurements. It does not accept resistancevalues.

DISTANCE (m) RESISTIVITY (Ω -m)2.00 2764.00 2887.00 26310.00 15713.00 14016.00 12919.00 11722.00 10225.00 99

The soil is not uniform; therefore, we must perform a resistivity analysis to obtain the parametersof the two-layer soil model necessary for further analysis.

Follow the steps below:

1. Activate the CYMGRD program.

2. Use the Project >> Create command and enter a project name (e.g., Project1).

3. Click OK.

4. Use the Project >> Study >> Create command to create a study. Enter a name (e.g.,Study1). The menu bar will be a different one.

5. The default module is GRID. Click on Module >> Soil.

6. Click on Soil >> Input data.

7. In the Soil data dialog box, you may enter a name for the analysis (e.g., Resis1).

8. Click on the diamond marked Two-layer to select it. (It is active by default anyway.)

9. Click on the Insert button and enter each measurement (probe distance and resistivity)Repeat for each set of data (see section 2.3.1).

CYMGRD for Windows


10. Upon verifying the data entered, click “OK”. In the Soil model window, the program willdisplay the registered points.

11. Click on SOIL >> Calculate! >> Soil model. The resistivity curve, the thickness andresistivity of the upper layer and the resistivity of the lower layer are displayed in the soilmodel window.

12. CYMGRD also presents a tabular report in a separate window. Close that window.

CYMGRD for Windows


Note: “Doubtful points” are those measurements which are far enough away from thecomputed resistivity curve that the error between them and the curve exceeds theaverage RMS error between all the measured points and the curve. Normally, youmight consider removing one or more “doubtful” measurements and performingthe resistivity analysis again. For this example, however, continue using thecurrent results.

By default, both the Safety Assessment and the Surface Potential analyses make use of this soilmodel. However, you can modify the soil model parameters (H, upper ρ, lower ρ) if desired.

1.2 Safety assessment analysis

Once you have the soil model, the next step is to define safety criteria for the substation.

To run the safety assessment analysis, follow these steps:

1. Click on Soil >> Calculate! >> Safety assessment.

2. In the Safety parameters dialog box, the program enters the soil model data by default. Letus use the default values for the other data (50 kg body, 200mm of 1000Ω -m crushed rockon the surface, 100 msec shock duration).

Note: The lower layer thickness is not needed as it is considered to be infinite.

3. Verify the data and click on “OK” to calculate the reduction factor Cs(h,k), the maximumallowable touch and step voltages.

CYMGRD for Windows


CYMGRD uses the following equations, taken from IEEE 80 (1986), to calculate the maximumpermissible touch and step voltages.


E touch = (1000+1.5Cs(h,k)Ps)0.116/ t

E step = (1000+6Cs(h,k)Ps)0.116/ t


E touch = (1000+1.5Cs(h,k)Ps)0.157/ t

E step = (1000+6Cs(h,k)Ps)0.157/ t

where:

• t is shock duration, in seconds.

• Cs(h,k) is the derating factor when high resistivity material is present at the soil surface. It isa function of the reflection factor k and the thickness of the surface material layer h.

• s is the resistivity of the surface material, in ohm-m.

Once completed, the results of the safety analysis appear. In our particular example thecomputed values are as follows:

The program communicates the maximum permissible touch and step voltages, calculated in thesafety assessment analysis, to the graphic module (PLOT). The option is active by default, asshown in the above sample dialog box.

4. Click OK. The Safety Assessment Report will appear in a separate window. You could printit via Window >> Print. Otherwise, close the window.

CYMGRD for Windows


1.3 Grounding installation data entry

In our example, the grounding grid is rectangular and symmetrical (meshes of equal area). It is150 m long and 80 m wide. All conductors are buried at a depth of 0.5 m. Seven (7) conductorslie parallel to the X-axis and five (5) parallel to the Y-axis. For analysis purposes, the conductorsparallel to the X-axis are subdivided in 4 segments and those parallel to the Y-axis, in 2

elements.

The diameter of all the conductors is 0.0134m. The grounding installation is in parallel with aresistance of 25 ohms from overhead sky wire and counterpoise resistance. The fault current is2500 A. Finally, twelve (12) grounding rods are connected to the grounding grid at theperimeter. The rods are 6.00 meters long, with diameter 1.9 cm (0.75 in.).

1. Click on Module >> GRID.

2. Click on Grid >> Input data >> Installation...

3. In the Installation dialog box, enter data according to the figure below:

Note: Since there is no return electrode, the return current is 0.

CYMGRD for Windows


4. Verify the data entered and click on “OK”.

5. Click on Grid >> Input Data >> Electrodes >> Conductors.

You can enter the grid and the rods in any order, but it is better to enter the grid layout first andthen the ground rods. CYMGRD supports symmetrical or asymmetrical arrangements ofconductors and rods. Electrodes (primary, return or distinct) consist of combinations of thesearrangements.

6. Click on “Grid >> Input data >> Electrodes >> Conductors” & click on the Insert button.Enter the primary conductor data as shown in the dialog box below. (Do not forget to clickon the Symmetric check box and on the diamond left of Primary to select it):

CYMGRD for Windows


7. Click on the bar, in the lower left corner of the conductors dialogbox.

8. Click on the Insert button. Enter rod data as shown in the dialog box below (do not forget toclick on the Symmetric check box and on the diamond left of Primary to select it):

Note: The Rod depth is the distance from the surface of the earth to the top of the rods.

9. Click on the Insert button again, to add another set of rods (one at (0;40) and one at(150;40))

CYMGRD for Windows


10. Click to remove the check mark next to Symmetric, and enter the following data:

11. Click on OK to finish.

CYMGRD for Windows


12. Optional. To display the grid layout in 3 dimensions, double-click the left mouse buttonanywhere inside the Grid Layout window. The Graphic Parameters dialog box will appear.Click on the 3D View radio button, and click OK.

13. Click on the “Grid >> Calculate!” command to compute the ground potential rise (GPR) andground resistance (Rg) values.

Note: During the calculations, a timer gives you an indication of the speed of processing.

14. Click on OK. A tabular report will appear, listing the positions of the various pieces ofconductor, the current diffused by each, and the GPR and resistance values. You may printthe report via Window >> Print. Otherwise, close the window.

CYMGRD for Windows


1.4 Surface potential analysis with the PLOT module

Use the PLOT module to see the results of the analysis in graphical form. These graphic outputsmake it very easy to study specific areas of interest in the installation. You may see the surfacepotential contours or the surface potential profile in any desired direction.

1. Click on “Module >> PLOT”.

2. Click on “Contours >> Calculate!” to define the lower left and upper right corners of therectangular area over which the contours are to be plotted.

Note: If you have not yet calculated the installation's GPR and total resistance toground, CYMGRD will offer to do that first.

Adjust the area as shown above, so as to view the potentials in the surrounding area outsidethe grid as well. You may change the title, too.

3. Click on “OK” to begin the calculations. When the calculations are complete, the potentialcontours will be superimposed on the grid layout in a new window. (See next page.)

4. Optional. Repeat steps 2 and 3 with #intervals = 21 for more precision.

CYMGRD for Windows


5. Double-click the left mouse button anywhere inside the Contour Plot. The GraphicParameters dialog box will appear. Click to activate the options shown, including 3D view.

6. Click on the “Thresholds“ button.

CYMGRD for Windows


With this option, you can set the thresholds for color coding of the equipotential lines. Usecolor-coding to identify danger areas within and around the substation layout. Shades of redindicate the highest touch potentials.

Touch Potential Grading

The program calculates these three thresholds from the maximum allowable touch voltagecalculated in the soil resistivity analysis module (SOIL). The thresholds are listed in ascendingorder. Threshold #3 is the highest and is equal by default to the maximum allowable touchvoltage. Touch potential contours valued at or above this level appear in shades of red. Blue orgreen sections are less dangerous.

Surface Potential Grading

The program calculates these three thresholds from the maximum allowable touch voltagecalculated in the SOIL module and the station GPR calculated in the GRID module. Thethresholds are listed in descending order. Threshold #3 is the lowest and is equal to theminimum absolute surface potential. Surface Potential contours valued at or below this levelappear in shades of red. Blue or green sections are less dangerous.

Hint: The sum of the surface potential thresholds and the touch potential thresholds shouldalways equal the station GPR.

CYMGRD for Windows


7. Click “OK” to return to the Graphic Parameters dialog box. Click “OK” there to return to thedisplay, which will now be in 3 dimensions.

It is now easy to see how the Touch Voltage rises rapidly at the edges of the grid

8. Inside the Surface Potential Plot window, click and hold down the left mouse button. Movethe mouse to rotate the drawing. Release the button. Repeat to get a different view.

9. Optional. View the absolute Surface Potential instead of the Touch Voltage. Repeat step 5and choose “Surface Potential”.

CYMGRD for Windows


1.5 Potential profile analysis along an axis with the PLOT module

Use the potential profile module to generate touch, step or surface potential profiles alongdifferent axes. An axis is defined by its starting and ending coordinates.

1. Click on “Profile >> Calculate!”. The following dialog will appear.

2. Modify the data as shown above, in order to extend the profile beyond the borders of thegrid.

Hint: You can also define the desired axis with the mouse (see Sections 4.3.2 and 4.3.3).

You must also define a step size. The program uses this step size to calculate the steppotential profile along the axis of interest. If the spacing is equal to the normal spanbetween the two feet of someone walking along the axis, then the difference of the surfacepotential between two adjacent points is the Step Voltage. There is a limit of 200 points, sotry to make sure the length of the axis does not exceed 200 times the step interval.

CYMGRD for Windows


3. Click on OK to calculate the potential profile along the specified axis and to view theresulting curves.

There is a maximum of six potential profile curves (3 pairs). By default, CYMGRD shows theTouch Potential and Maximum Allowed Touch Voltage (in blue) and the Step Potential andMaximum Allowed Step Voltage (in green). You may request the Absolute Surface Potential andthe GPR as well (in red).

4. Double-click the left mouse button anywhere inside the Potential Profile plot. The ProfileGraphics Parameters dialog box will appear. Click on Surface Potentials, to place a checkmark there, and click OK.

CYMGRD for Windows


5. Arrange the windows so that the Grid Layout and Potential Profile windows are visible. (UseWindow >> Tile.)

6. Now slide the mouse cursor sideways inside the Potential Profile window. You should seethe cursor position indicated simultaneously on the Grid Layout, as shown above. Thisfeature can help you identify hazardous areas more easily.

CYMGRD for Windows


Example 2: Primary, return and distinct electrode

The second example is a substation grid without rods. A ground fault occurs within thesubstation, and another electrode at a certain distance from the grid absorbs the current injectedto the grid. This electrode becomes a return electrode. We will analyze the potential profile alonga selected axis with and without the return electrode. We will also analyze the effect of a distinctelectrode without a return electrode.

2.1 Grounding installation overview

The following data applies to this installation:

• The soil is known to be uniform with a resistivity of 100 Ω -m.

• The grounding grid is square (10m x 10m), with its origin at (X1=0.0m, Y1=0.0m)

• The grid conductors are buried at 0.5 meters, with 4 parallel conductors along the X axispartitioned in 4 elements each and 5 parallel conductors along the Y axis partitioned in 3elements each. The diameter of the (#4/0 AWG) grid conductors is 1.34 cm (0.528 in.)

• There is no surface treatment (crushed rock, for instance).

• All the current contributes to the station potential rise. (Parallel impedance of 9999 Ω .)

• The return electrode is a rod with a diameter of 0.2 meters and a length of 1 meter,positioned 45 meters away from the grid. We will assume the top of the rod is at the surfaceof the earth (Z1 = 0.0).

• The current injected to the grid is 100 amps and since the return electrode absorbs it all, thereturn electrode current is -100.0 amps.

• The distinct electrode is an old water pipe, 30cm in diameter and 20m in length.

The steps to enter data are similar to those in Example 1 of this Appendix.

1. To create a new study, click on “Project >> Create”. Enter a name. Click on “OK”.

2. Click on “Project >> Study >> Create”; enter a study name and click on “OK”.

Since the soil model is already known, we do not need to calculate it. We do need to computethe Tolerable Touch and Step voltages, however.

3. Click on “Module >> SOIL” and select “Soil >> Calculate >> Safety Assessment”.

CYMGRD for Windows


Since the soil is uniform, the “upper and lower layers” have the same resistivity and thethickness of the upper layer is arbitrary. There is no surface layer, so put its thickness tozero. To be conservative, use 50 kg body weight. See the dialog box below.

Click on “OK” to calculate the Touch and Step voltages, for use in the GRID and PLOTmodules.

Click on “OK” to acknowledge the results, and close the report window.

Minimize the Soil Model window, since we do not need it.

CYMGRD for Windows


4. Click on “Module >> GRID”.

5. Click on “Grid >> Input data >> Installation...”. The installation data dialog box willappear.

Enter data as shown below. You may use the TAB key to move from one field to the next, but donot click on “OK” until all the data are entered.

CYMGRD for Windows


6. Build the primary grounding electrode.

Click on “Grid >> Input data >> Electrodes >> Conductors”:

Click on the Insert button & enter the data shown in the dialog box above. The counter willindicate 1/1. Proceed to step 7 without clicking on “OK”.

7. Build the return electrode.

Click on “Ground Rods >>” (bottom left): the “Ground Rods” dialog box will appear.

Disable the Symmetric option by clicking on it once, if necessary.

Click on the diamond left of “Return”.

Click on the Insert button & enter data as shown in the dialog box below.

CYMGRD for Windows


Click on “OK”. (We will add the distinct electrode later.)

CYMGRD for Windows


8. Calculate the GPR and resistance.

Click on “Grid >> Calculate!”. Once finished, the GPR and resistance appear.

Click on “OK” to acknowledge the results. Close the grid calculation results window.

9. Calculate the potential profile. Choose “Module >> PLOT”.

Click on “Contours >> Calculate!”.

Enter data as shown in the dialog box below. You may change the title. Here, we extend theboundaries of the area over which the contours will be computed, so as to include some ofthe area beyond the grounding grid. We also increase the precision of the calculation byincreasing the number of intervals.

Click on “OK”. The calculations proceed, and CYMGRD draws a two-dimensional plot.

CYMGRD for Windows


10. Change to 3D view.

Once you see the curves, double-click inside the plot window to display the Graphic Parametersdialog box. Activate the following options:

• Surface Potential instead of Touch Potential.

• Solid Filled

• Show Wire Mesh

• 3D View

Click on “OK”. Maximize the window if necessary. The plot will look like this:

The surface potential is relatively uniform over the surface of the grounding grid, drops offrapidly between the grid and the return electrode, and attains a very large negative value in thevicinity of the latter, due to its high resistance.

CYMGRD for Windows


11. Exclude the return electrode. Choose “Module >> GRID”.

Click on “Grid >> Input data >> Installation”. The installation data dialog box will appear.

Click to remove the check mark (þ) next to “Enable return conductors” & “Enable returnrods”. The program will no longer consider the return electrode in the calculations.

Click on “OK”. Now, because of the change to the grid, CYMGRD notifies you that thepotential plot no longer corresponds to the electrodes.

Click on the ‘Save changes in a new study’ button. The study with the Return electrodewill be saved and a new study without it will be opened.

Give a name for the new study, for example:

Click on “OK”.

CYMGRD for Windows


12. Click on “Grid >> Calculate!”. The GPR and the resistance values are now slightly higher.

Click on “OK” to acknowledge, and close the report window.

13. In the PLOT module, click on “Contours >> Calculate”. Adjust the area as before.

Click on “OK”.

14. Double-click inside the plot window and activate the same options as before, namely:

• Surface Potential instead of Touch Potential.

• Solid Filled

• Show Wire Mesh

• 3D View

Click on “OK”.

CYMGRD for Windows


The surface potential plot is much different now because the high-resistance return electrode isabsent. The surface potential remains relatively uniform over the grid, and then falls offexponentially to zero outside the grid.

Optional. Minimize the Soil Model and Grid Layout windows. Close any open report windows.Use the “Window >> Tile” command to display the two cases simultaneously. In the exampleshown below, 2D View has been selected for both.

CYMGRD for Windows


15. Add a distinct electrode.

The distinct electrode is a 30 cm pipe, 20 meters long, buried at a depth of 3 m.

In the GRID module, click on “Grid >> Input data >> Electrodes >> Conductors”.

Click on Insert button. The counter will indicate (2/2).

Edit this copy as shown below. Make sure to click on “Distinct”.

Click on “OK”. We now have a primary electrode and a distinct electrode.

Again, as in Step 11, CYMGRD notifies you that the potential plot no longer corresponds tothe electrodes because of the change to the grid.

Click on the ‘Save changes in a new study’ button. The study without the Distinctelectrode will be saved and a new study with it will be opened.

Give a name for the new study, for example: “Primary and Distinct”.

Click on “OK”.

Hint: If the distinct electrode disappears at this point, double-click inside the Grid Layoutwindow and click on the Show distinct option in the Graphic Parameters dialog box.

16. Click on “Grid >> Calculate!”. The GPR is almost unchanged.

Click on “OK” and close the grid calculation window.

CYMGRD for Windows


17. In the PLOT module, click on “Contours >> Calculate”. Replace the default title, and enterthe same coordinates as before:

Click on “OK”.

You can see how the Distinct electrode distorts the equipotential lines. (Compare the graphics inthe top left and bottom right corners below.)

You have now completed the tutorial. To exit, click on “Project >> Exit”.

CYMGRD for Windows

Appendix II -COMPARISON WITH THE IEEE80 GUIDE 1

Appendix II

Comparison with the IEEE80 Guide

Appendix II is intended to provide the user with a comparison of the results obtained byCYMGRD and the IEEE80 GUIDE, 1986 edition.

The following three examples will be documented:

♦ Example 1: Preliminary design stage

IEEE80 GUIDE, 1986 Edition, Page 182.

Square grid 70m x 70m, 100 meshes with no ground rods.

♦ Example 2: Improved design


Square grid 70m x 70m, 100 meshes with ground rods placed along the perimeter.

♦ Example 3: Finalized design


Rectangular grid 63m x 84m, 108 meshes with ground rods placed along the perimeter andat selected places in the gird in an effort to further minimize surface touch potentials.

CYMGRD utilizes a finite element analysis algorithm which is more accurate than theapproximate formulas provided in the IEEE80 GUIDE. The finite element analysis algorithmenables CYMGRD to analyze grounding systems of either symmetrical or asymmetricalconfiguration of ground conductors and rods.

CASE NAME : Example 1: Preliminary design stage.

REFERENCE : IEEE80 GUIDE, 1986 Edition, Page 182.

SOIL MODEL : Uniform, soil resistivity = 400 ohm-meters.

SAFETY CALCULATIONS:

Input data:Body weight 70 KgCrushed rock surface layer resistivity 2500 Ω -mCrushed rock surface layer thickness 0.102 mClearing time 0.50 secUniform soil resistivity 400 Ω -m

CYMGRD for Windows

2 Appendix II - COMPARISON WITH THE IEEE80 GUIDE

Results:

REFERENCE MAX.ALLOWABLETOUCH

MAX. ALLOWABLESTEP

REDUCTIONFACTOR CS

CYMGRD 750.03 Volts 2,334.01 Volts 0.634IEEE Guide 80 746.00 Volts 2,320.00 Volts 0.630

GRID DESIGN ASPECTS:

Square grid 70m x 70m, 100 meshes with no ground rods as shown in the IEEE 80EXAMPLE 1 STATION LAYOUT figure shown below.

Input data:Square grid 70m x 70m, 100 meshesGrid conductor diameter 0.01 mBurial depth 0.5 mInjected ground current 1,908 AmpsUniform soil resistivity 400 Ω -m

Results:

In the table that follows Rg and GPR signify the station resistance and ground potential rise.

REFERENCE RG GPRCYMGRD 2.652 Ohms 5,059.92 VoltsIEEE Guide 80 2.680 Ohms 5,152.00 Volts

CASE NAME : Example 2: Improved design.




CYMGRD for Windows


Input data:Body weight 70 KgCrushed rock surface layer resistivity 2500 Ω -mCrushed rock surface layer thickness 0.102 mClearing time 0.50 secUniform Soil Resistivity 400 Ω -m

Results:

REFERENCE MAX. ALLOWABLETOUCH

MAX. ALLOWABLESTEP

REDUCTION FACTORCS



Square grid 70m x 70m, 100 meshes with ground rods placed along the perimeter as shownin the IEEE 80 EXAMPLE 2 STATION LAYOUT figure shown below.

Input data:Square Grid 70m x 70m, 100 meshesGrid conductor diameter 0.01 mLength of Ground rods 7.50 mGround rod diameter 0.01 mBurial Depth 0.5 mInjected ground current 1,908 AmpsUniform soil resistivity 400 Ω -m

Results:

CYMGRD for Windows

4 Appendix II - COMPARISON WITH THE IEEE80 GUIDE


REFERENCE RG GPRCYMGRD 2.510 4,790.00 VoltsIEEE Guide 80 2.750 5,247.00 Volts

CASE NAME : Example 3: Finalized design.




Input data:Body weight 70 KgCrushed rock surface layer resistivity 2500 Ω -mCrushed rock surface layer thickness 0.102 mClearing time 0.50 secUniform Soil Resistivity 400 Ω -m

Results:

REFERENCE MAX. ALLOWABLETOUCH

MAX. ALLOWABLESTEP

REDUCTION FACTORCS


CYMGRD for Windows



Rectangular grid 63m x 84m, 108 meshes with ground rods placed along the perimeter andat selected places in the gird in an effort to further minimize surface touch potentials, as shownin the IEEE 80 EXAMPLE 3 STATION LAYOUT figure shown below.

Input data:Rectangular Grid 70m x 70m, 100 meshesGrid conductor diameter 0.01 mLength of Ground rods 10.0 mGround rod diameter 0.01 mBurial Depth 0.5 mInjected ground current 1,908 AmpsUniform soil resistivity 400 Ω -m

Results:


REFERENCE RG GPRCYMGRD 2.288 Ohms 4,366.51 VoltsIEEE Guide 80 2.620 Ohms 5,000.00 Volts

CYMGRD for Windows

Appendix III - CADGRD - The CYMGRD - AutoCAD Interface module 1

Appendix III

CADGRD - The CYMGRD - AutoCAD Interface module

1.00 Program Summary

CADGRD is a utility program conceived to allow the user to alternate between the AutoCAD andCYMGRD environments. More specifically, CADGRD was conceived as a utility program tosupplement CYMGRD, the module that is dedicated to design grounding facilities fortransmission and distribution substations. For that reason CADGRD needs to be installed in thesame partition as CYMGRD, since it is called by CYMGRD itself.

CADGRD is not a substitute for AutoCAD. In fact, AutoCAD remains a firm software requirementfor CADGRD, because it is AutoCAD that will produce the necessary *.DXF and /or *.DWG filesthat contain the pictorial description of the substation grid layout. Note however that all relevantdata for the engineering analysis of the substation grounding grid, besides the actual grid layout,can also be entered via CADGRD following the same philosophy and input data patterns of theCYMGRD data input interface. This is done by properly assigning attributes to the AutoCAD-drawn entities using special data blocks supported by CADGRD.

The functionality of CADGRD can then be seen as:

CYMGRD invoking, at run time, CADGRD and importing the station data from *.DXF/*.DWG filesinto the CYMGRD environment.

CYMGRD invoking, at run time, CADGRD and exporting the station data (already entered,designed/optimized within CYMGRD), by producing the relevant *.DXF and/or *.DWG filesnecessary for describing the grounding assemblies in the AutoCAD environment.

The advantages of this bilateral communication link between CYMGRD and CADGRD can besummarized as follows:

• CYMGRD has now access to the powerful drawing facilities of the AutoCAD environmentwith full support of its GUI data structures. CADGRD is simply the required vehicle ofinformation transfer.

• Grounding grid layouts can be entered independently and communicated to CYMGRD sothat an engineering analysis can proceed for verification, correction or further designoptimization.

CYMGRD for Windows

2 Appendix III - CADGRD - The CYMGRD - AutoCAD Interface module

• The engineering analysis results for designing a new or reinforcing/optimizing the design ofexisting ground grids can now be efficiently exported in the AutoCAD environment withoutany loss of information.

• Exchange of information between the AutoCAD and CYMGRD environment is renderedtransparent and seamless, even when different persons service either end of the link.

• All the above advantages can be harvested by drawing packages other than AutoCAD, underthe condition that the same *.DXF or *.DWG files are supported.

In what follows a description of the CADGRD utility is given for the AutoCAD environment. Acertain degree of familiarity with AutoCAD is assumed for the reader in order to present theinformation in a concise manner and avoid duplicating AutoCAD user manual details.

This user’s guide should not therefore be used as an aid to comprehend the hereby implicatedAutoCAD functions but, instead, as a means to efficiently use CADGRD within the AutoCADenvironment.

2.00 Drawing a station ground grid with AutoCAD

2.1 General

To draw a GRID layout always start from the “CYMDEF.dwg” file, by activating AutoCAD.No matter how many times the CADGRD program is activated it is this template it needs to useto start a new drawing. This file is the default template used by CADGRD to start theAutoCAD drawing and should never be overwritten. Furthermore, this file should reside inthe same directory as the CYMGRD program and should never be deleted. When thestation drawing is finalized within CADGRD make sure it is saved under another name.

The “CYMDEF.dwg” file contains seven layers, which are used to draw the GRID layout anddefine the data for the CYMGRD analysis. These layers are also reserved in name andfunction for CADGRD and should not be modified in any fashion. In fact, the veryfunctionality of CADGRD depends on them.

CYMGRD for Windows


These seven layers are defined as:

DISTINCT DATA: Layer used to store data for the DISTINCT electrode Conductors/Rods

DISTINCT: Layer used for drawing the layout of the DISTINCT electrode

PRIMARY DATA: Layer used to store data for the PRIMARY electrode Conductors/Rods

PRIMARY: Layer used for drawing the layout of the PRIMARY electrode

RETURN DATA: Layer used to store the data of the RETURN electrode Conductors/Rods

RETURN: Layer used to draw the layout of the RETURN electrode

GENERAL: Layer used to define the general data NAME, SOIL Resistivity etc.

NOTE 1: The Grounding layout/Data should be drawn/defined in the appropriate layer, if theyare represented in a different layer, they might be ignored

NOTE 2: Please refer to CYMGRD utilization guide for definitions of the above used terms.

2.2 Drawing the GRID Layout using AutoCAD:

The GRID layout should be drawn in AutoCAD without any scaling factor. One unit in AutoCADdrawing represents either 1 m or 1 ft in CYMGRD, depending upon the system unit (Metric orImperial) you define in the General Data Block. The coordinates (0,0,0) in AutoCAD correspondto the coordinates (0,0,0) in CYMGRD grid layout.

NOTE: CYMGRD also recognizes both systems of units. Thus a grid entered via CADGRD say,in metric units, is imported into CYMGRD as such respecting the system of units selected withinCADGRD. The same data could however be converted to Imperial units within CYMGRD. Uponexporting the same grid layout to AutoCAD via CADGRD, the data will now be shown in Imperialunits.

CYMGRD for Windows


The entity for grid Conductors:

The Conductors are represented as Lines in AutoCAD via their end points coordinates (X1, Y1,Z1) & (X2, Y2, Z2). The burial depth of the conductor ends (Z1 and/or Z2) is represented by anegative Z coordinate.

NOTE: In CYMGRD the burial depth is always entered as a positive value. This apparentinconsistency however, is automatically taken into account when data is transferred back andforth from CYMGRD.

The diameter of the Conductor is defined in the Conductor Data Block, which is discussed later.

The entity for grounding rods:

A ground rod is represented as a “Circle” in AutoCAD with center coordinates (X, Y, Z). The Rodlength is defined by the “Thickness” of the Circle. A negative value of the “Thickness” representsthe Rod pointing downwards from the center (X, Y, Z).

The diameter of the Circle in AutoCAD drawing is only used for display purposes. The actualdiameter of the Rod used by CYMGRD is defined in the Rod Data Block, which is discussedlater.

NOTE: In CYMGRD the rod length is always entered as a positive value and is implicitlyassumed that the rod points downwards. This apparent inconsistency however, is automaticallytaken into account when data is transferred back and forth from CYMGRD.

CYMGRD for Windows


Data Blocks for the entities

Data blocks are used to define the data for the Conductors, Rods and Substation Groundinganalysis. The AutoCAD “INSERT” command can be invoked to bring up the Data insertion dialogbox as shown below:

CYMGRD for Windows


There are three insertion blocks supported by CADGRD :

Data Block #1: General Data Block (CY_GEN)

The General Data Block is used to define the following CYMGRD analysis parameters:

Then click on “NEXT” to view the remaining attributes:

CYMGRD for Windows


The above mentioned data is only used by CYMGRD and has no bearing at all to the intendedfunction of CADGRD. They can be left with their default values and when the grid layout isimported to CYMGRD, they can be modified within CYMGRD in a relevant context. Thisdata is reserved to the proper layer (GENERAL) which should remain locked and should notnormally be modified within CADGRD. If one, however, decides to do so, the layer must beunlocked and whatever data is entered within AutoCAD will then be transferred to CYMGRD.The interested reader can review the CYMGRD reference guide for the exact definition of theseparameters.

Block #2: Conductor Data Block: (CY_GRID)

The Conductor Data Block is used to assign the following data:

# of elements : Number of elements in the conductor

Conductor diameter : Diameter of the conductor used for CYMGRD analysis

Conductor group no. : 0 - for “asymmetrical” conductor

: 1-9999 for “Symmetrical” conductors

Entity Handle : Unique AutoCAD ID to associate the conductor with its data block

CYMGRD for Windows


Conductor Group Number:

Each conductor is assigned a group number based on whether the conductor is part of asymmetrical conductor assembly or not. This notion is borrowed from CYMGRD since CYMGRDpermits to enter many conductors exhibiting a certain pattern of symmetry as a data short cut.Normally, a ground grid will feature symmetrically spaced as well as stand-alone conductors notnecessarily belonging to any symmetrical pattern. It is the latter that will feature a group numberof 0 and are hereby referred to as “Asymmetrical” conductors. A set of conductors with the samegroup number (any number between 1-9999) are treated as a group of Symmetric conductors.

NOTE1: CADGRD will retain the symmetry of conductor assemblies as entered in CYMGRD solong as this symmetrical pattern is not disturbed in any way within AutoCAD. If, for instance, asymmetrical assembly of 3 conductors parallel to the X-axis with a certain spacing between themhas been defined in CYMGRD, this assembly will be retained within AutoCAD and transferredback to CYMGRD if left as is. If however, any spacing of the original coordinates or even thenumber of elements for any one of the 3 conductors is disturbed, the symmetrical assembly willbe broken down to its components and communicated back to CYMGRD as a new set ofasymmetrical conductors.

NOTE2: The number of elements per conductor is, again, a quantity used for electrical analysiswithin CYMGRD. It bears no relevance to the intended functionality of CADGRD but it could becrucial for actual CYMGRD simulations. A value of 1 is permissible when data for the grid isentered for the first time via AutoCAD, and it remains up to the CYMGRD analyst to really setthis parameter. If, however, data are communicated to AutoCAD via CADGRD from CYMGRD,this parameter should not be modified because the modified value will be passed again toCYMGRD. A Symmetric group of conductors should feature at least a minimum order of 2x2 (4conductors).

Block #3: Rod Data Block: (CY_ROD)

The Rod Data Block is used to assign the following data:

# of upper layer elements : Number of elements/Rod in the upper soil layer

# of lower layer elements : Number of elements/Rod in the lower soil layer

Rod diameter : Diameter of the Rod used for CYMGRD analysis

Enter group no. : 0 - “Asymmetrical” rods

:1-9999 - “Symmetrical” rods

Entity Handle : Unique AutoCAD ID to associate the Rod with its data block

CYMGRD for Windows


Rod Group Number:

Each Rod is assigned a group number based on whether the rod forms part of a symmetricalassembly or not. This notion is borrowed, as for the conductors, from CYMGRD since CYMGRDpermits to enter many rods exhibiting a certain pattern of symmetry as a data short cut.Normally, a ground grid will feature symmetrically spaced rods as well as stand-alone rods notnecessarily belonging to any symmetrical pattern. It is the latter that will feature a group numberof 0 and are hereby referred to as “Asymmetrical” rods. A set of rods with the same groupnumber (any number between 1-9999 but unique for a given group) are treated as a group ofSymmetric Rods. A Symmetric group of Rods should feature a minimum order of 2x2 (4 Rods).

Rods along the same line equidistantly spaced can still be entered with the same groupnumber in AutoCAD as if they were part of a “symmetrical” assembly. CADGRD will properlysupport this data structure.

AutoCAD Entity Handle:

The entity handle is a unique ID used to couple the drawing element (Conductors/Rods) withits associated Data Block. This coupling is important because vital data for the entity arecontained in the Data block. That is why an entity handle must be present for every data block. Infact, every data block demands a distinct and unique handle.

CYMGRD for Windows


When the user places the data block for an entity anywhere in the drawing area, the handlemust be explicitly defined by the user. This can be laborious particularly if the drawing contains alarge number of entities, a situation very likely for sizeable transmission ground grids. In orderto circumvent this difficulty and render data entry easier, CADGRD can automaticallyassign the entity handle assuming the Data blocks are inserted at their “proper insertionpoints” in the AutoCAD drawing. A ‘proper insertion” point for the data block is considered forthe purposes of automated entity handle assignment to be any point of the entity itself. In orderfor CADGRD to automatically assign the entity handles the “Update” activity needs to be invokedfor the drawing at hand before exporting it to CYMGRD.

If the grid data is imported from CYMGRD, it is CADGRD which will take care of bothassigning the entity handles and positioning the data blocks automatically.

NOTE: If, for any reason, the entity handle is not assigned, and the data block is present atthe proper insertion point, the entity handle will be assigned automatically.

2.3 Illustrative example

This following example illustrates the basic procedure using AutoCAD to draw the stationgrounding grid layout.

The following hypothetical data apply to this installation:

• The soil is known to be uniform with a resistivity of 100 Ω -m.

• The grounding grid is square (10m x 10m), with its origin at (X1=0.0m, Y1=0.0m)

• The grid conductors are buried at 0.5 meters, with 4 parallel conductors along the X axispartitioned in 3 elements each and 5 parallel conductors along the Y axis partitioned in 4elements each. The diameter of the #4/0 AWG grid conductor wire is 1.34 cm (0.528 in.)

• There is no surface treatment (crushed rock, for instance).

• The injected current is absorbed entirely by the primary electrode. (Parallel Z= 9999 Ω .)

• There is a return electrode composed of a single grounding rod, with a diameter of 0.02meters and a length of 1 meter, positioned 45 meters away from the grid. We will assumethe top of the rod is at the surface of the earth (Z1 = 0.0).

• The current injected to the primary electrode is 100 amps and the return electrode absorbs itall, the return electrode current is -100.0 amps.

CYMGRD for Windows


To draw the above-depicted Grounding system start with the template file “CYMDEF.dwg” file.This file, as pointed out earlier, is a reserved file and should only be used to begin a drawing, itshould always be resident in the directory of CYMGRD program and should never be overwrittenor moved.

Open the “CYMDEF.dwg” file using AutoCAD and rename the file as “PROJ2.dwg”. We begin bydrawing the primary electrode first. Thus,…

1. Set the Layer to “Primary”

2. Draw one Primary conductor parallel to X-axis and one parallel to the Y-axis:

Command: line

Specify first point: 0,0,-0.5

Specify next point or [Undo]: 0,10,-0.5

Specify next point or [Undo]: <ENTER>, for the X-axis

Command: line

Specify first point: 0,0,-0.5

Specify next point or [Undo]: 10,0,-0.5

Specify next point or [Undo]: <ENTER>, for the Y-axis

CYMGRD for Windows


REMINDER NOTE: When drawing the lines one may also want to use the standard commandsZoom with a convenient associated option like “All” or “Extend” to have a clear view of the drawnentities so far. This may be necessary when elements are first drawn far away from thecoordinates (0.0,0.0), because the CYMDEF.DWG file is configured to make the point(0.0,0.0) visible right from the beginning.

At this point we need to specify the data blocks for the already entered 2 entities becausethey will both be used later by the array command to create copies of themselves. Byspecifying their data blocks, we will also properly duplicate the attributes of the entities.

3. Set the Layer to “Primary data”

4. Insert the conductor data block on the conductor parallel to the Y-axis.

Command: insert

Select CY_GRID on the Insert window

Specify insertion point or [Scale/X/Y/Z/Rotate/PScale/PX/PY/PZ/PRotate]:

CYMGRD for Windows


The insertion point can be any point along the conductor, but it must be on the conductor(see NOTE below). As you move the cursor close to the conductor, the cursor will be highlightedwith a yellow square to indicate the insertion point. The reason the insertion point must be onthe conductor is that, if this is the case, the entity handle will automatically be assignedby CADGRD for all entities in the group thus avoiding specifying the handle for a greatnumber of entities. Do not insert the data block at the END points of the line.

NOTE: It will help for this particular requirement of CADGRD to properly configure AutoCAD, atleast for the current session, to conveniently display the insertion point along the conductor. Todo that, exercise the command OSNAP and make certain that the following boxes ENDPOINT,CENTER, NEAREST are checked ON.

Enter attribute values

# of elements <1>: 4

Conductor diameter <.01>: 0.0134

Enter group no (0 = none) <0>: 1

Enter Entity handle:<ENTER>

5. Insert the conductor data block on the conductor parallel to X-axis.

Command: insert

Select CY_GRID on the Insert window



# of elements <1>: 3

CYMGRD for Windows


Conductor diameter <.01>: 0.0134



6. Complete the Primary Grid layout by making arrays of the Primary conductors & Data blocks

It is well known that by exploiting this AutoCAD option, we enter more efficiently symmetricalstructures as the one we try to emulate in this example.

Command: array

Select the conductor parallel to Y-axis along with its Data block

Select objects: 1 found

Select objects: 1 found, 2 total

Select objects::<ENTER> (to denote end of selected objects)

Enter the type of array [Rectangular/Polar] <R>:<ENTER>

Enter the number of rows (---) <1>:<ENTER>

Enter the number of columns (|||) <1> 5

Specify the distance between columns (|||): 2.5

CYMGRD for Windows


Command: array

Select the conductor parallel to X-axis along with its Data block

Select objects: 1 found

Select objects: 1 found, 2 total

Select objects: <ENTER> to denote end of selected objects

Enter the type of array [Rectangular/Polar] <R>: <ENTER>

Enter the number of rows (---) <1>: 4

Enter the number of columns (|||) <1>:<ENTER>

Enter the distance between rows or specify unit cell (---): 3.33333

CYMGRD for Windows


At this point all relevant data for the primary electrode have been entered. The next stepis to proceed by entering the data for the return electrode.

7. Set the layer to “Return”

8. Draw the return rod at a distance 45 m away from the Grid

Command: circle

Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 55,5,0

Specify radius of circle or [Diameter] <0.1000>: 0.5

9. Set the layer to “Return Data”

10. Insert the Rod Data block

CYMGRD for Windows


Command: insert

Select CY_ROD on the Insert window


The insertion point must be at the center of the circle. Move the cursor close to the centerto the Rod; the cursor will be highlighted with a yellow square to indicate the insertionpoint.


# of upper layer elements <1>: 1

# of lower layer elements <1>: 1

Rod diameter <.01>: 0.02



11. Change the Thickness of the Circle (Return Rod) to –1.0 (Rod Length)

The Thickness is the way to specify the depth of the rod without resorting to full 3_ddescription

Command: ddmodify

CYMGRD for Windows


Click on the Circle (Rod) and change the thickness to -1.0.

This completes the Return Electrode data entry.

The next entry will be for the General Data Block. This block must be inserted in the drawingdespite the fact that only the Title and the Metric/Imperial units are of real value for thedrawing itself. The rest of the data can assume any value and be modified in CYMGRD. The

CYMGRD for Windows


data contained in this data block pertain to the engineering analysis performed by CYMGRD andhave no direct relevance to the drawing itself.

12. Set the Layer to “General”

13. Insert the General Data Block

Command:insert

Select CY_GEN on the Insert window



Title: Example2

System units (M=Metric or I=Imperial ) <M>: M

Distinct electrode flag (0 or 1) <0>: 0

Return electrode current (A) <0>: -100

Upper layer depth (m) <1.0>: 100

Upper layer resistivity (Ohm-m) <100.00>: 100

Lower layer resistivity (Ohm-m) <100.00>: 100

Primary electrode current (A) <1.0>: 100

Parallel impedance (Ohm) <9999.0>: 9999.0

The completed Grid layout/ Data blocks is shown here:

CYMGRD for Windows


3.00 Validation & Update of the AutoCAD drawing

Once the AutoCAD drawing is completed, the Grid drawing must be first validated and thenUpdated using the appropriate CADGRD validation module. This module can be accessed fromthe CYMGRD folder from the Start menu (Windows) by selecting "CAD Interface Module(CADGRD)". These activities are important since they supplement the drawing and render theAutoCAD drawing ready to be imported to CYMGRD for analysis. Neither one should be omitted.

The AutoCAD/CYMGRD conversion module is shown below:

3.1 Validating the AutoCAD drawing.

The Validation option is used to verify the AutoCAD drawing. This will only highlight the errorscaused by the Grid layout, Data insertion points etc. More specifically the validation will addressthe following salient aspects:

• Make certain that all entities have an associated data block.

CYMGRD for Windows


NOTE1: If a data block is not defined for a stand-alone entity, i.e. an entity that has not beendefined via the command “array”, CADGRD will assign a data block to that entity, identicalto the last valid data block of a similar stand-alone entity. In other words, if a data block ismissing for an individual rod, the data block for the last valid individual rod will be in effect. Thispractice assures that once data for an individual rod/conductor is entered there is no need toenter them again for a good number of like entities. Following this practice can be very efficientbut it could also lead to inadvertently assuming wrong data for a good number of entities. Unlesstherefore one is certain, it is preferable to assign a data block to every entity.

NOTE 2: In the case a data block has not been assigned to a stand-alone entity and there is nosimilar entity entered previously (so that CADGRD can draw a template data block as specifiedin NOTE1), the internal default values of CADGRD for data blocks shall be used.

These defaults are as follows:

Stand-alone Conductor

# of elements in conductor = 1Conductor diameter = 0.01

Stand alone Rod

# of rod elements in upper soil layer = 1

# of rod elements in lower soil layer = 1Rod diameter = 0.01

NOTE3: If entities have been generated using the “array” command and no data block has beenassigned to the “seed entity” i.e. the entity that was used as a template to generate the entities-copies, CADGRD will not retain the structure as symmetrical. The symmetrical structure ofentities will be broken down to individual entities while their geometry is retained and theinternal default values, per NOTE 2, will be assigned to every one of them. Thedisadvantage of this is that when the .DWG file is imported into CYMGRD the symmetricalstructure for this particular set of entities will be lost and they will be shown within CYMGRD asindividual entities. This, in turn, may have a considerable bearing on the flexibility of modifyingdata for all of them very conveniently within CYMGRD. It is therefore preferable before using thearray command to make certain that a data block is assigned to the “seed-entity” so that thesymmetrical structure is retained for all future data exchanges with CYMGRD.

• Make certain that all entities and associated data blocks are within acceptablecoordinate limits. The boundary limits are set to be 10,000.00 m in all directions for metricunits and 32,820 ft for Imperial. This check is carried out once the units of the drawing aredefined in the “General” data block. That is why a “general” data block needs to beinserted in the drawing.

CYMGRD for Windows


NOTE1: If no general data block has been entered, a warning is generated that the General”data block is missing, when the drawing is being validated. When the .DWG file is simplysaved from session to session without being validated no general data block is put in it.

NOTE 2: If the .DWG file is not validated and is sent without any validation to CYMGRD, thedefault General data block contents will be assumed, which are the following:

Default General Data block entities

Flag for distinct electrode potential = 0

Primary electrode current = 100.00

Return electrode current = 0.00

Upper soil layer depth =100.00

Upper soil layer resistivity = 100.00Lower layer soil resistivity = 100.00

Parallel Impedance = 999.99

Units flag = M (metric)

It can therefore be seen that CYMGRD will accept the units in Metric if no General datablock is inserted in the XXX.DWG file representing the station grid.

• All entities are assigned to any of the seven reserved CADGRD layers.

NOTE: Ideally, all entities belonging to a given layer should have all their corresponding datablocks in the corresponding data Layer. For instance primary electrode entities should find theircorrespondent data blocks in the primary data layer. If it so happens that data blocks of onelayer are accidentally entered in another layer they will be ignored by CADGRD. Thereserved color codes for every layer and its correspondent data blocks should help in avoidingsuch a situation.

• Verify that length of rods is not positive. If positive values were accidentally entered, theywill be converted to negative for the sake of consistency.

NOTE: CYMGRD functions by assuming a positive rod length, since it implies that the rodalways points downwards. Consistent with this convention, the interface of CYMGRD shows allrod lengths as positive in its dialog boxes. It is CYMGRD that will convert all negative Z’scoming from the XXX.DWG drawing to positive for interface and calculations withinCYMGRD. Similarly it is also CYMGRD that will convert all Z’s to negative whengenerating the equivalent XXX.DWG file

CYMGRD for Windows


• Verify that the Z coordinates are entered as negative. Positive Z’s coordinates will beconverted to negative Z’s to assure information consistency.

NOTE: CYMGRD functions by assuming that a positive Z coordinate points downwards. That iswhy when calculations are performed within CYMGRD the Z’s are considered positive.Consistent with this convention, the interface of CYMGRD shows all Z’s as positive in its dialogboxes. It is CYMGRD that will convert all negative Z’s coming from the XXX.DWG drawingto positive for interface and calculations within CYMGRD. Similarly it is also CYMGRDthat will convert all Z’s to negative when generating the equivalent XXX.DWGF file

To validate the drawing click on FILE menu > Validate drawing

Then select the drawing (Proj2.dwg) file and click open

CYMGRD for Windows


The validation window lists the errors/warnings as a shown below

The above-illustrated procedure is to be followed whenever validation is to be undertaken as astand-alone procedure using CADGRD by itself. This is a good precaution and will, essentially,ensure that no inadvertent warnings/errors are generated from the current status of the AutoCADfile.

When, however, the CADGRD program is called from within CYMGRD to import anAutoCAD drawing (in the form of XXX.DWG file) the validation process is automaticallytriggered and immediately followed by the Updating procedure which is described below.

3.2 Updating the AutoCAD drawing.

The Updating option is used to assign the proper Entity Handle (Conductor/Rod data blocks)and associate the symmetrical groups of Conductors/Rods in the drawing. This option re-buildsthe AutoCAD drawing file (*.DWG, *.DXF) and updates the drawing with default data forundefined parameters. Before using this option, the AutoCAD drawing must be closed.This option also keeps a backup of the original drawing as “*.BK2” before it updates the drawing.

CYMGRD for Windows


To update the drawing click on FILE menu > Update drawing

Select the drawing (Proj2.dwg) file and click open

The Update window lists the errors/warnings as a shown below

CYMGRD for Windows


4.00 IMPORTING from AutoCAD to CYMGRD

To import a drawing from AutoCAD (*.DWG, *.DXF) file, one must be positioned withinCYMGRD. The following steps illustrate the procedure:

Open a new Project and an associated Study using CYMGRD (see CYMGRD user’s guide)

Select the GRID module in CYMGRD (see CYMGRD user’s guide)

Click on the GRID menu and select the activity: > Import from DOS/ACAD. This activity willbe only available to CYMGRD versions that support the AutoCAD interface.

This will open the file selection dialog box.

Select the AutoCAD file name (Proj2.dwg) and click Open. It is at this point that CADGRDshall be invoked, the AutoCAD drawing will be validated and updated by CADGRD and the newDWG file will be created

CYMGRD for Windows


Click Yes on the Warning Dialog box

The GRID layout will appear in CYMGRD after conversion as shown below

CYMGRD for Windows


To verify the Grid Installation Data Click on Click on Grid >> Input data >> Installation...

CYMGRD for Windows


5.00 EXPORTING from CYMGRD to AutoCAD

To Export a GRID layout from CYMGRD, one must be positioned within the CYMGRD package.The following steps illustrate the procedure:

Open the Project, Study using CYMGRD (see CYMGRD user’s guide):

Select GRID module. Select “GRID >> Export to DOS/ACAD”

This will open the file selection dialog box.

Specify a file name (Project2) and select the file type (*.DWG for AutoCAD) which you wantto save as:

CYMGRD for Windows


The exported AutoCAD file with the GRID layout is shown below.

CYMGRD for Windows


6.00 Working with CADGRD

When entering data for a station grid using AutoCAD it is often necessary to maximize theefficiency of data entry particularly when large grids are an issue and when the data attributes fora large number of components needs to be entered.

Tip #1

Make full use of the symmetrical structure of groups of elements by utilizing the “array”command of AutoCAD, particularly for symmetrical arrays of conductor assemblies and rodstructures. When, however, the “array” command is used the data block for the “seed”entry, be it conductor or rod must be entered so that for the rest of the conductors/rodswithin the symmetrical structure of the data block attributes are properly duplicated.

Tip #2

Whenever data are exported from CYMGRD and the station layout comprises symmetricalstructures, make certain that no coordinate displacement or change in any of theassociated data blocks is changed within AutoCAD. If this is the case, CADGRD willdecompose the symmetrical structure into elementary non-symmetrical structures, and datamodification within CYMGRD will be far more laborious. For example if an array of 6x6conductors is exported as a symmetrical structure to AutoCAD and the coordinates or data blockof any of the 36 conductors is modified the whole assembly will be broken down to 36 individualconductors upon importing the same grid back to CYMGRD.

Tip #3

Whenever a large number of asymmetrical (stand-alone) conductors and rods is to beentered, entering the data block for one of them only may be sufficient because CADGRDwill assign the missing data blocks to the values of the last like data block entered. Make certain,however, that the last valid data block does reflect the desired data attributes.

Tip #4

For simplicity of data entry, the Title for the general data block and the system unit(Metric/Imperial) can be entered when a station grid is entered in AutoCAD. The rest of theparameters can be left at the discretion of the CYMGRD package user for fine tuning and finaldecision making. It is important to realize however, that when data are exported fromCYMGRD and these parameters have already been entered, they should not be modifiedwithin AutoCAD because if this is the case, they will be exported back as such to CYMGRD andimportant data may be lost. If no system unit is specified it will be defaulted to Metric.

CYMGRD for Windows


Tip #5

For simplicity of data entry, the number of elements for conductors can be set to 1 when astation grid is entered in AutoCAD. It will be up to the analyst working with CYMGRD toassess whether an increased number of elements per conductor is needed for the finite elementssimulation conducted within CYMGRD. It is important to realize however that if the numberof elements per conductor have already been entered within CYMGRD, they should not bemodified within AutoCAD. If this is the case, they will be exported back as such to CYMGRDand important data having a detrimental effect on simulation integrity may be lost. By virtue ofthe same arguments, the same logic applies to the number of elements in the upper andlower soil layer entered for the grounding rods.

CYMGRD for Windows


cymgrddemo

Documents

reduction

data short

ground potential

correspondent

design grounding

touch allowable

sample dialog

maximum permissible