Power Monitoring System1 (1)

POWER MONITORING SYSTEM

1

INTRODUCTION


2

1. INTRODUCTION

With the electric industry undergoing changes, increased attention is being focused on power

supply reliability and power quality. Power providers and users alike are concerned about

reliable power, whether the focus is on interruptions and disturbances or extended outages.

One of the most critical elements in ensuring reliability is monitoring power system

performance. Monitoring can provide information about power flow and demand and help

identity the cause of power system disturbances. It can even help identity problem conditions

on a power system before they cause interruptions or disturbances.

Effective monitoring programs are important for power reliability assurance for both utilities

and customers. While power quality problems can do occur on utility power systems, many

surveys have shown that most customer power quality problems originate within the

customer facility. With this in mind, it is clear that monitoring is essential for both power

suppliers and users to ensure optimal power system performance and effective energy

management.

Key to the success of an effective monitoring program is flexibility, powerful data

processing, understandable reports and easy access to information. The emergence of the

Internet and intracompany intranets has made this possible, allowing quick viewing of data

that assures effective decision-making and fast responses time. Event notification and

program scalability are also critical for addressing the ever-changing environment of the

energy business.

Through this project we try to give an effective and cost power monitoring system.


3

PROJECT

SELECTION


4

2. PROJECT SELECTION

To build a power monitoring system requires that the input voltage and current be measured

and then multiplied with each other to give the active power. The power factor also needs to

be considered for complex loads. The most reliable method to do this is using digital

techniques. A popular solution to this end is developed by Analog Devices.

This device is the ADE 7756 for single phase and ADE7754 (The three phase counterpart).

This IC samples the input voltage and current waves to obtain a high resolution digital

number .It perform instant multiplication and give the output as the active power.

It further proceeds to integrate the power to obtain a 40-bit energy value. It thus combines the

functions of a power meter and an energy meter in a single monolithic IC.

The IC however was not available in the local market and the interfacing with the micro-

controller is difficult. The documentation available about this IC was also limited to the

datasheets and application notes supplied by the manufacturer.

A much more economical option is the AVR ATMEGA 16 Micro-controller [1].

Features of AT MEGA16 are:

1. It is an 8-bit AVR micro-controller with 16k Bytes In-System programmable flash.

2. It also has 8-channel, 10-bit ADC.

3. 8 single-ended channels.

4. 7 Differential Channels in TQFP Package only.

5. 2 Differential Channels with Programmable Gain at 1x, 10x, or 100x.

6. Programmable using serial UART.

7. On chip Analog Comparator. AVR Micro-controller with 16k Bytes In-System

programmable flash.


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This AVR AT MEGA 16 micro-controller is faster than the ATMEL 89C51, which works on

1MHz frequency where as AVR works on 12MHz speed. That means 12 times more number

of instructions per sample.

AVR on a general purpose board has been used for project implementation. Many extra

features have been incorporated for future use and improvements.

The kit has buzzer on board and motor driving IC, which is useful to indicate when the

voltage or power exceeds the certain threshold value. And motor IC can be used to cut of the

supply by activating a relay.


6

WORKING

PRINCIPLE


7

3. WORKING PRINCIPLE

The aim is to electronically measure the power consumed by a load.

P=V x I x cos phi.

R = V x I x sin phi

Where

P= active power (Watts)

R=Reactive power (Watts)

V=RMS value of voltage (Volts)

I=RMS value of current (Amperes)

Phi=phase angle between voltage and current (deg or radian)

Instead of the RMS values, some dc equivalent values have been obtained corresponding to

the amplitudes of the voltage and current sinusoidal. The equivalent values bearing a linear

relationship with the RMS values. A DC equivalent voltage for phi is also obtained. These dc

equivalent voltages are given as input to different channels of an Analog to digital converter,

which comes up with 8-bit of digital data.

This data is then read by the microcontroller and stored in the internal registers. The

microcontroller proceeds to multiply the voltages and current values to obtain V x I.

Cos (phi) is obtained by a look-up table and then multiplied to get a final result.

The power is integrated by the process of accumulation to obtain the energy.

E=Integration of PDF

The integration time is adjusted to be exactly 1 second, including he programs delays by

adding a separate delay subroutine, so as to get the energy in mW-sec.

The results are displayed on an illuminated LCD screen for direct reading as also transmitted

on the serial interface. The microcontroller being programmable can be used to link up most

of the parallel interface.


8

DESIGN

IMPLEMENTATION


9

4. DESIGN IMPLEMENTATION

The power monitoring system developed consists of electronic hardware as well as software

embedded inside it. The software makes the system upgradable and more flexible. More

features can be easily added and unnecessary ones removed. Various digital communication

interface can be programmable to link together many devices and to a central computer as

well.

4.1 BLOCK DIAGRAM

The main block diagram of the project is shown below. It consists of the test circuit which is

used to replace the actual power generator. Then AC-DC converters are used to make the

output of the test circuit compatible with the microcontroller. An AVR microcontroller is

used to perform various computational works on the signals by first converting it into the

digital signal. The outputs are shown on the LCD display and on the computer.

FIGURE 4.1 BLOCK DIAGRM OF THE PROJECT


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4.2 ANALOG CIRCUITS

The analog circuit is responsible for feeding the inputs of the ADC with the dc equivalent

values from the load circuit.

The load circuit has high values voltage and current values that are initially stepped down

using CTs and PTs (current and potential transformers) to low voltage sine waves.

These sine waves are rectified using precision rectifiers to get full-wave rectified signal. This

signal can then be low-pass filtered to obtain the dc value of the rectified wave. The precision

rectifier uses 1N4148 diodes along with the low-offset op-amp to perform rectification.

The phase detection circuit comprises of two zero crossing detectors that convert the stepped

down sine wave to square waves, the square waves are ANDed to obtain the region of

overlap. The duty cycle of this wave thus depends on the phase difference.

There are overall three analog circuits used viz., test circuit, ac-dc converter and phase

differentiator. [2] [3]

Detailed analysis and discussions will be made ahead.


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4.2.1 TEST CIRCUIT

For the test circuit, a voltage source is given to an op-amp based amplifier. The o/p is then

passed through a RC filter to introduce a phase shift and this current is given to a current

amplifier with variable gain. The phase difference between the output signals can be

adjustable from 0 to 90 degree, by using the circuit adjustment provided on the board.

Thus adjustable values of ac current and ac voltage are obtained to determine system

performance.

FIGURE 4.2.1 TEST CIRCUIT

The above circuit has been designed to get output identical to that obtained using the actual

power generator machine.


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4.2.2 AC TO DC CONVERTOR

For converting ac currents and voltages to their respective dc values precision full wave

rectifiers are followed by PI-filters to convert the rectified waves into stable ripple free DC

values.

FIGURE 4.2.2 FULLWAVE RECTIFIERS

This full wave rectifier has a ripple factor of 0.482


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4.2.3 PHASE DIFFERENCE MEASUREMENT CIRCUIT

The phase detection circuit comprises of two zero crossing detectors that convert the sine

waves to square waves. The square waves are ANDed to obtain the region of overlap. The

duty cycle of this wave thus depends on the phase difference. That is then inverted using

inverter and filtered out using the capacitors. This dc value is proportional to the phase

difference between the two input signals. The use of logic gates make the output voltage in

the range of 0 to 5 volt, which satisfies the limited range of the analog to digital converter

input range.

FIGURE 4.2.3 PHASE DIFFERENTIATOR


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The working of the phase differential is explained as below.

The two OP-AMPs are used to convert the sine wave signal to square wave signal. Two such

square wave signals is shown here. One represents the voltage signal and other represents the

current signal.

FIGURE 4.2.3.a VOLTAGE SIGNAL

FIGURE 4.2.3.b CURRENT SIGNAL

These two signals are not in the same phase. When this two signals are given to an AND gate

as an input. The output is also a square wave. The wave is high only when both the signals

are high. That is, at the overlap period only. The wave which we get is as shown below.

FIGURE 4.2.3.c PHASE SIGNAL

This square wave is then passed to filter using a capacitor. The output is then a dc voltage.

When there is no phase difference in the voltage and current signal the output wave is a

perfect square wave and the equivalent output dc voltage is at some fixed high level. And

when there is 90 degree phase shift between voltage and current the output at the AND gate is

zero, with zero dc voltage. Thus at the end we have used an inverter to give output in such a

way that when there is no phase difference output is zero dc voltage and when there is 90

degree phase difference output is high dc voltage.


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4.3 THE MICROCONTROLLER

The AVR has been selected mainly for its low cost along with the built in ADC. It is fast in

operation as it performs 12 instructions per cycle. It has build in ADC which performs analog

to digital converter.

A general purpose board has been used. There are some extra components on the board which

can be used for further advancements in project.

Port A is used as ADC which is a build in the microcontroller.

Port B is used for LED interface.

Port C is used for LCD interface.

Port D is used for speaker output.

FIGURE 4.3 PIN DIAGRAM


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4.4 THE LIQUID CRYSTAL DISPLAY

A standardized 16 by 2 implies 2 lines with 16 characters each display the power and energy.

The LCD is equipped with its own RAM and has control words for a fully flexible display

scheme. Backlighting is available and is used for a power read out even during dim-light

conditions. The backlight can be switched off to reduce power consumption.

The LCD has a contrast adjustment facility which requires a 10k ohm pot to vary the

character contrast. 3 control lines and 8 data lines contribute the remainder.

Control lines:

RS (Register Select) 1 - Command register

0 – Data register

R/W 1 – Read

0 – Write

EN 1 – Enables Bus

0 – Disable Bus

Data Lines:

DB7 – DB0 To carry command and data to the LCD

FIGURE 4.4 LCD DISPLAY

16 x 2 LCD DISPLAY

CONNECTING PINS


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4.5 MAX-232

The MAX 232 is required for the RS-232 interface. The microcontroller transmits data to the

PC on the serial port (COM 5).

The RS-232 standard dictates the voltage levels as -3 to -15 volts for logic 1 and +3 to +15 V

for logic 0. It provides 2-channel RS232C port and requires external 10uF capacitors. The

MAX 232 converts the circuit voltage of 0-5 volt to the RS-232 levels.

The communication parameters are as follows:

1) 8 DATA

2) 1 stop bit

3) No parity

4) Asynchronous

The serial connector can be directly connected to serial port of the computer. Since now a day

USB is widely used, here we have used the Serial to USB converter. Using the serial to USB

convertor kit, it can be directly connected to computer through USB connector.

The microcontroller is set to transmit the data at a baud rate of 56000. At 56000 baud rate the

allowed baud rate error is 0.8%.


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4.6 CIRCUIT BOARD

Test circuit is constructed on a general purpose board. A Zero- insertion socket (ZIF) socket

is used to mount the microcontroller. It facilitates easy removal and replacement of the IC

during multiple instances of the downloading programs.

FIGURE 4.6 CIRCUIT BOARD

Power on the board is obtained by regulating a 9 V dc input from a low voltage variable DC

power supply by IC LM 7805 to obtain precisely +5 V DC .

The voltage input from external circuits is converted to the required range of 0 to 5 volts

using an onboard potential divider meter.

The AC-DC convertor circuit requires a dual 12 to 0 to -12 V supply for the OP-AMPs. A 5V

dc is also obtained for the TTL gates.

Low resistance multistoried wires are used as the links.


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ICs are mounted in their corresponding sockets so as to make them replaceable.

A power ON pilot LED indicates the power on the board.

The 16 lines of the LCD are taken out as flat ribbon cable (FRC) and connected

independently to the LCD display.

The hardware sets up the base for the system. Rest of the work is done by the software inside

the microcontroller.


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4.7 THE MICROCONTROLLER PROGRAM

After getting the digitized current and current voltages values the micro controller has to

perform the following functions.

Initialize the LCD

Initialize the serial port

Voltage, current and phi values are multiplied and displayed on the LCD and sent to the

PC on the serial port.

The algorithm stated below is followed to develop the program-code.

1. Assign suitable variables for different parameters.

2. At the start, a function named “ read_adc ” has been declared. This function is used for

converting the analog voltage given to the microcontroller ADC pins to convert it into the

equivalent digital value.

3. Port A of the microcontroller is actually an ADC port. When the microcontroller is used

as ADC the analog voltages are given to this port. ADC conversion can be set to 8-bit or 10-

bit conversion. With 8-bit conversion maximum measurement of 0.053V is obtained which is

enough for project & 8-bit conversion is used. The input voltage range for ADC port is 0-5

Volts. The method used here is a SAR i.e. successive approximation method. The reference

voltage for the conversion is set to variable so that measurement of voltages more than the 5

V is possible by adjusting the potentiometer.

4. Port B is assigned as output port for running the LEDs. Port there are 8 LEDs

connected to the port B which are used for displaying the current status of the

microcontroller. Whenever the specific conversion is done it is displayed by its LED

indication if something exceeds its threshold value. Its respective LED set on for the

notification. When the system is halt due to some problem then it is indicated by the red LED

which blinks.

5. Port C is initialized for the LCD interface and port D is initialized for buzzer.


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6. Initialize LCD. The LCD static information includes setting of function data length to

8-bits, number of lines to be used to 2, and font of 5x7, display control word bits set

accordingly to blink cursor on/off, clearing display screen for refreshing of data (power and

energy).

7. Serial port initialization includes setting the USART parameters. It is set as receiver in

asynchronous mode. With baud rate of 56000. And communication parameters as 8-bits,

1 – stop bit and No parity.

8. The voltage, current and phase are given to pins 0 to 2 of port A respectively. Read the

voltage value includes.

a. The function named “read_adc” is used and the digital output voltage is

taken into some variable. Then accordingly it is multiplied 5000/255 ratio

to convert it into the equivalent Volts.

b. The voltage value is check against the threshold value. If it is greater than

the threshold then alarm is set to ON. If it is below the threshold value then

it continues.

9. For measuring the current and phase the same procedure as that of voltage is done.

10. In one cycle the microcontroller takes value of each parameter and then calculates the

power. This cycle continues ten times and at the end of each cycle new power is calculated.

Such ten values of the power are then added together to calculate the energy of this ten

cycles. The time period of one energy cycle is of one second i.e. after one second new value

is calculated. Whenever new energy value is calculated it is displayed on the LCD and at the

same time it is send over the serial cable to the computer.

11. In this way the microcontroller takes various parameters value and then calculates some

new parameters for the monitoring purpose.

12. The threshold limit for any parameter can be change by reprogramming the

microcontroller using the parallel port. It can also be changed by adjusting the potentiometer.


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SCREEN MONITORING


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5. SCREEN MONITORING

MATLAB 7.4 is used for developing the on screen monitoring system. The screen window is

as shown in the figure.

FIGURE 5.1 MAIN WINDOW

The above figure is the normal window of the project. All the parameters are shown

viz,voltage, current, phase, active power, reactive power, energy. On the right hand side of

the figure the instantaneous values of the parameters are displayed. These values are real time

values. And units are displayed to the right hand side of the values. There are over all 14

buttons on the window.

Each time new values are received from the microcontroller to the computer these values are

shown and at the same time stored in their respective file. All the voltage values that are

received are shown and saved in the file dataforgraph.m. Here this file is a mat lab file.

Similarly dataforcurrentgraph.m, dataforphasegraph.m, dataforactpowergraph.m,

dataforrepowergraph.m, dataforenergygraph.m, these files are used to store the all the values

of remaining parameters.


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5.1 SOFT ALARM SYSTEM

In the power monitoring system the important aim is to maintain the parameter value within

the allowed range. Here the soft alarms are shown as a color code. There is a predefined limit

of each of the parameter, known as lower limit and upper limit. When value of the parameter

is below the lower limit the value is shown in yellow color. When value of the parameter is

above the upper limit the value is shown in red color. And when the value of the parameter is

within the allowed range it is shown in green color.

FIGURE 5.1.1 MAIN WINDOW DISPLAYING THE SOFT-ALAMS

In the above window voltage value is greater than the upper allowed limit for the voltage,

thus it is shown in red color. Current value is within the allowed range for the current thus it

is shown in green color. The phase value is below the lower limit allowed for the phase range

hence it is shown in the yellow color.

These alarms are called as soft alarm because it just gives the warning that the parameter

value is out of the allowed ranges so that necessary action can be taken on it.


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5.2 SOFT ALARM SETTING

All the limits that set the soft alarm can be changed at the run time.

The button marked as „=‟ in front of every parameter is used for setting the limit for that

parameter.

When the „=‟ button is pressed the command window is opened. It is as shown below.

FIGURE 5.2.1 SOFT-ALARMS SETTING

When the command window popup, values can be entered.

It can be entered as [upper limit lower limit]. First the upper limit and then the lower limit of

that parameter is entered in a square bracket. And then pressing the return key will set the

new range for that parameter.

In the above example voltage limit is to be set. So enter the new limit. The new limits are

4000 and 1000. So when voltage exceeds upper limit it will be shown in red color and when

voltage is below the lower limit it will be shown in yellow and when it is in allowable range

it will be shown in green.


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5.3 ALARM

These alarms are set in the microcontroller at the time of programming only. The threshold

limits for a particular parameter are described in the program. When the parameter value

exceeds that threshold value the microcontroller stop the connection. It gives the beep at the

same time and it will continue till the value is not returned in its allowed range. Also it gives

the command on the computer screen to stop the display and shows the warning window.

This warning window is as shown below.

FIGURE 5.3.1 WARNING WINDOW

Similarly it sends a “SYSTEM AT HALT” message on the LCD.

FIGURE 5.3.2 LCD WARNING WINDOW


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The microcontroller then switches on the relay which turns off the power supply.

The system stays in that condition until the parameter value comes in the allowed range.

When the value comes in the range the system restart itself and displays the same on the

screen and also on the LCD.

FIGURE 5.3.3 SYSTEM RESTARTING WINDOW

The speaker also stops beeping the warning signal.


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5.4 GRAPH DISPLAY

The six buttons on the main screen are used for displaying the graph of the parameters. These

buttons plot the graph of the parameters values that are stored in their respective file.

For example the voltage button plots the graph of voltage values that are stored in the file

named „dataforgraph.m‟ when the voltage button is pressed all this values are plot against the

no. of samples. Voltage graph is displayed in the figure below.

FIGURE 5.4.1 VOLTAGE GRAPH


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Also when the current button is pressed current graph is shown as below.

FIGURE 5.4.2 CURRENT GRAPH

From the above graph all the necessary readings that are required can be directly seen from

the graph. Graph analysis has an importance in system performance. Graph can show many

values at the same time and give us important information.


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5.5 DISCONNECTION

Connections between the microcontroller and computer are made by the serial connection.

Use the software MATLAB for monitoring the parameter value. So this connection cannot be

terminated abruptly at any time. So there is a disconnect button provided. This button is for

proper disconnection. When the disconnect button is pressed the values of the parameters are

stored in the computer so that when were new connection is established there is no loss of the

data. Then it closes the serial object which is used for serially receiving the data. The

confirmation window popup for the disconnection before disconnecting.

This window is shown below

FIGURE 5.5.1 DISCONNECTING WINDOW


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5.6 CLEARING THE DATA

All the data that are stored in the computer can be cleared or delete using this „Clear All‟

button. When Clear All button is pressed the all the data that contains the all parameter values

stored in computer are deleted. This data is useful in plotting the graphs. So for plotting new

graphs this button is used.


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INDUSTRIAL

IMPLEMENTATION


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6. INDUSTRIAL IMPLEMENTATION

Our out house project entailed a study tour at the „ESSAR POWER PLANT‟ in HAZIRA. At

the plant, we were given insights to the power industry and its workings and machineries. [4]

Formal industry training was imparted by experts in the field viz Mr. Jose Numpelli,

Mr. Kulkarni, Mr.Mehta, Mr.Shailesh.

At HAZIRA we were privileged to view an “Energy Management System” which comprised

of 3 gas turbines (GT1, GT2, and GT3) and 1 steam turbine (STG).

Each gas turbine generates 110MW power. And the steam turbine generates 285MW power.

This power plant generates a total power of about 515 MW. This is then distributed over a

common grid of 220KV power line to the various other plants.

FIGURE 6.1 POWER PLANT

The system was a state-of-the-art system which was highly energy efficient. The description

of the gas turbine and steam turbine is given below.


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6.1 GAS TURBINES (GT1, GT2, GT3):

FIGURE 6.1.1 GAS TURBINES

A mixture of air and fuel (gas mixture) was burned to operate a turbine engine whose drive

shaft was connected to a generator which produced power up to 110 MW. The turbine rotates

on the torque generated by the force generated by the explosive mixture of air and fuel.

As shown in the diagram, air and fuel are mixed in the turbine producing a torque to rotate

the drive shaft and hence the generator.

The 3 turbines generated a total of 110*3=330 MW.

The other output of the turbine in the form of the compressed hot gas is generally wasted. But

this system makes use of the potential in the hot, pressurized steam. The steam is given to the

“Heat Recovery Steam Generator”. The generator makes use of the pressurized steam to

produce extra power.


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6.2 STEAM GENERATOR (STG):

FIGURE 6.2.1 STEAM TURBINES

The steam turbine is a very efficient machine. It takes highly pressurized gas (HP1, HP2, and

HP3) from the 3 gas turbines as inputs to the High Pressure steam turbine (HP).

The low pressure component of steam is given separately to a Low Pressure turbine (LP). The

shafts of the HP and LP are interconnected. The shaft is also connected to a generator. This

particular heat recovery steam generator has a potential to produce up to 185 MW of power.

Hence, the whole energy management system produces a total of 515 MW of power.

185MW

CONDENSOR

LP1

HP2

HP3

HP1

HP

STEAM

TURBINE

GENERATOR

LP TURBINE


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6.3 MEASUREMENT AND MONITORING

The Gas turbines and steam turbine are managed by MKV Control System supplied by GE.

The boilers are managed by a control system designed by Siemens called DCS.

The voltage is measure from the potential transformer and current is measure from the current

transformer. These transformers are the step down transformers. They step down the MEGA

watt power into the levels which are suitable for the measurement.

PML meters are the meters which measure the power, voltage line-to-line, voltage

line-to-neutral, voltage unbalance, current, phase and various parameters. These meters are

provided by power measurement limited. The connection between different PML meters is

shown below.

FIGURE 6.3.1 PMML METER

These meters have high input range for parameters. There are many parameters that can be

measure using these parameters. Whereas these meters are much more costly, their price is in

the range of crores. Also these meters are more bulky. And occupy much more space.


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FIGURE 6.3.2 MEASUREMENT AND MONITORING

These meters are connected using three types of systems they are RS-232, RS-485 and LANs.

RS - 232:

It is used when PML meter is to be connected to a single computer over a short distance. The

data is send over serial communication.

RS – 485:

It is used when many PML meters are to be connected to each other and to the computer over

a long distance using a multiplexer. This is particularly used for long distance communication

because of its low transmission loss which is very small as compare to RS-232.

LAN:

LAN is a Local Area Network connection. It is used when monitoring of multi-PML meters

reading is required on computers within an area. Many computers are connected to each other

which individually monitor different PML meters.

PMLs

RS-232

RS-485

ETHERNET PORT

PML

SINGLE PC

PC1

FIX-D MACS

PC2

ION

PC3

HUB

PML

PML

RS-485

PML

RS-485


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TOOLS

AND

EQUIPMENT


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7. TOOLS AND EQUIPMENT

7.1 HARDWARE

The analog circuits were first tested on a breadboard and when found satisfactory soldered on

a General Purpose Board (GPB). Thin multistrand fibers were used for linking.

Soldering had to be done taking care that there were no dry solders and solid reliable joints

are formed. Continuity was tested for each link using the Digital Multimeter (DMM).

Troubleshooting had to be done after soldering to find faulty contacts as well as

malfunctioning components.

The oscilloscope was also an important tool for monitoring waveforms. The digital storage

oscilloscope proved to be of paramount importance as the low frequency waves (50 Hz) were

difficult to look on to the standard Cathode ray Oscilloscope.

The Digital Storage Oscilloscope is an excellent tool for the simplest to the most intricate

circuit designs. Its „Auto Setup‟ mode helps in detecting any type of waveform almost

instantaneously and manual tuning is seldom required.

For working on the microcontroller we have developed a board. This board is kept specific

only for this purpose. Many extra pins are provided for easy debugging. All ports are made

visible by providing connection at each pin for measuring the voltages at that pin. Some extra

components are also added for allowing the user to measure other parameters.

LCD is connected on the board. For communication with the computer, a serial to USB

connector USB is in widespread usage.

The whole hardware is fitted in the wooden box for protection.


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7.2 SOFTWARE

The programmed is developed using the CodeVisionAVR software. It provides many options

and facility for easy programming. Most of the initialization is done by the software once the

uses of the each port are entered. It has great support for debugging the program. Once the

program is compiled with no error and no warnings it is then used to generate the HEX file.

This will then be used to program the microcontroller. [5]

The software also provides the facility to show the output data that is serially transmitted by

the microcontroller to the computer.

Pony-Prog software for programming the microcontroller has been used. The HEX file which

was generated by CodeVisionAVR software is then opened. Pony Pro software allows to

program the microcontroller either using serial port or parallel port. It initially erases the

memory or data that is already present in the microcontroller and then loads the new program.

[6]

For GUI MATLAB version 7 has been used. MATLAB has great support for serial

connection. Windows of various sizes can be shown. On each window useful buttons are

provided for user interfacing. Graphs and warning signs are shown to make it more user

friendly. [7]


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TESTS

AND

RESULTS


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8. TESTS AND RESULTS

The theory behind the test circuit is as follows. A single-phase ac induction motor or a

synchronous motor will have in general the voltage and current phasors shifted as shown.

FIGURE 8.1 PHASOR DIAGRAM

Simulation of this behavior using a single stage R-C circuit is shown in the diagram.

The 10k-ohm Potentiometer used for the R can change the phase angle from 0 to nearly 90

degrees leading. The amplifiers have high input impedance and amplify the sine waves. The

gain of the amplifiers can be set individually by the pots in the feedback paths. Thus a circuit

which produces two sine waves, phase shifted (with adjustable phase shift), and variable

amplitudes is shown.

This circuit takes an input of a single sine wave from the standard laboratory function

generator. This makes the entire setup clean and controllable. A digital CRO was used for

observing the waveforms and testing the circuits. The sine waves are adjusted to a peak of 0.5

V at a frequency equal to 50.00 Hz.

The outputs from the simulation circuit were observed on the digital oscilloscope using both

its channels. Varying the phase pot showed the sine waves shifting from zero phase shifts to

ninety-degree phase shift at extreme position of the pot.

The amplitudes of these sine waves were continuously variable from 0 to 6 V peak by

varying the pot in the feedback path of the inverting amplifiers thus varying the gain of the

op-amps.

The op-amps chosen showed that near ideal behavior under the particular conditions viz.

operation in the linear region and low frequencies. The sine waves were supplied to the

analog circuit where they were rectified using op-amp precision rectifiers and then filtered so


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as to obtain the dc content of the full wave rectified wave.

The digital oscilloscope is very useful in observing that there is no diode drop and that the

inclusion of the op-amps although increases the complexity of the circuit, proves useful so as

to improve the accuracy and reliability of the system.

The dc values at the output circuit are carefully monitored so as to observe the peak value of

the ripple. The oscilloscope is kept in AC mode and the ripple content observed, to be 5mV

peak. The ADC has a resolution of 5V/255=20mV.

Thus it was concluded that the filter circuit was good enough to an accuracy of 1 Bit. Further

it has a noise margin of about 15mV. It was thus concluded that shielding is an absolute

necessity in the industrial environment for accurate operation.

The dc values are also observed to vary smoothly as the amplitudes of the sine waves are

varied as also the phase angles changed.


44

APPLICATIONS


45

9. APPLICATIONS

Power monitoring is a crucial element in ensuring cost optimization for energy

suppliers and users alike.

It also assumes an important role in system stability analysis.

A power monitoring system can be incorporated into a power control system.

They are used to manage inrush conditions during system startup as well as to provide

critical information about voltage irregularities.


46

FUTURE SCOPE

AND

LIMITATIONS


47

10.1 FUTURE SCOPE

This system can be used in a plant to monitor the power consumption of electric

machines.

It indicates whether the instantaneous power consumed is greater or lesser than the

rated value.

The Energy Meter can also be used for billing and verification.

The Alarms for Voltage-sag and high Currents also help in protection and increasing

the life of the machines.

The PC interface as of now is a very crude one, but can be improved upon to include

features like generating logs for analysis and optimization. Computer programs can be

written for automatic billing, graphical analysis and feedback control.

Several other features can be added like, frequency measurement, sag-cycles

detection, voltmeter, ammeter, and power factor measurement.


48

10.2 LIMITATIONS

The power monitoring system has to be calibrated from time to time so as to ensure

accuracy.

The system cannot be used for fractional kW motors, as the current resolution is 1k

Watt.

The accuracy and regulation of the current transformers and potential transformers is

the deciding factor for the performance of the system.

The system as of now does not have any indicator, which indicates whether the power

factor is leading or lagging.

It cannot be used at very high frequencies.


49

APPENDIX


50

11.1 ATMEGA 16 AVR DATASHEET

Features

• High-performance, Low-power AVR®8-bit Microcontroller

• Nonvolatile Program and Data Memories

– 16K Bytes of In-System Self-Programmable Flash

Endurance: 10,000 Write/Erase Cycles

– Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program

True Read-While-Write Operation

– 512 Bytes EEPROM 16-bit

Endurance: 100,000 Write/Erase Cycles Microcontroller

– 1K Byte Internal SRAM with 16K Bytes

– Programming Lock for Software Security In-System

• JTAG (IEEE std. 1149.1 Compliant) Interface Programmable

– Boundary-scan Capabilities According to the JTAG Standard Flash

– Extensive On-chip Debug Support

– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface

• Peripheral Features

– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes

– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture

Mode

– Real Time Counter with Separate Oscillator

– Four PWM Channels

– 8-channel, 10-bit ADC

8 Single-ended Channels

7 Differential Channels in TQFP Package Only

2 Differential Channels with Programmable Gain at 1x, 10x, or 200x

– Byte-oriented Two-wire Serial Interface

– Programmable Serial USART

– Master/Slave SPI Serial Interface

– Programmable Watchdog Timer with Separate On-chip Oscillator

– On-chip Analog Comparator

• Special Microcontroller Features

– Power-on Reset and Programmable Brown-out Detection

– Internal Calibrated RC Oscillator

– External and Internal Interrupt Sources

– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby

and Extended Standby

• I/O and Packages

– 32 Programmable I/O Lines

– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF

• Operating Voltages

– 2.7 - 5.5V for ATmega16L

– 4.5 - 5.5V for ATmega16

• Speed Grades

– 0 - 8 MHz for ATmega16L

– 0 - 16 MHz for ATmega16

• Power Consumption @ 1 MHz, 3V, and 25°C for ATmega16L

– Active: 1.1 mA

– Idle Mode: 0.35 mA

– Power-down Mode: < 1 µA


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12. REFERENCES

[1] http://www.atmel.com/products/avr/default.asp

[2] http://www.analog.com

[3] J.S.Katre,” Wave Shaping Techniques”, chapter 6, pp 70-80.

[4] http://www.essar.com/power.htm

[5] http://www.hpinfotech.ro/html/cvavr.htm

[6] http://www.lancos.com/ppwin95.html

[7] http://www.mathworks.com

Power Monitoring System1 (1)

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