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SKM Power*Tools for Windows
Power*Tools
for Windows
IEC 60909_FAULT Reference
Manual
Electrical Engineering Analysis Software
for Windows
Copyright 2006, SKM Systems Analysis, Inc
All Rights Reserved
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12/4/2006
Information in this document is subject to change without notice. No part of this document may be reproduced or
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Contents
1 IEC_FAULT STUDY 1-1
1.1 What is the IEC_FAULT Study?....................................................................1-2
1.2 Engineering Methodology................................................................................1-31.2.1 IEC Standard 909 .......................................................................................1-31.2.2 Comparing the ANSI and IEC Short Circuit Standards .............................1-3
1.2.3 Initial Symmetrical Short Circuit Current ..................................................1-4dc Current...............................................................................................................1-5Peak Current...........................................................................................................1-5
Breaking Current ....................................................................................................1-5
Steady State Current...............................................................................................1-5
1.2.4 IEC Standard 909 Terms ............................................................................1-61.2.5 Conventional Methodology........................................................................1-61.2.6 Requirements for Computer Solutions .......................................................1-71.2.7 Equations....................................................................................................1-71.2.8 IEC Standard 909 Unbalanced Short Circuit Calculations.........................1-9
1.3 PTW Applied Methodology...........................................................................1-111.3.1 Before Running the IEC_FAULT Study..................................................1-111.3.2 Running the IEC_FAULT Study..............................................................1-111.3.3 IEC_FAULT Study Options.....................................................................1-11
Report and Study Options ....................................................................................1-12
Report Type......................................................................................................1-12
Short Circuit Type............................................................................................1-12
All or Selected..................................................................................................1-12
Faulted Bus.......................................................................................................1-12
System Modeling..................................................................................................1-12
Use Sequence Network or Three-Phase Factors ..............................................1-13
Pre-Fault Voltage .............................................................................................1-13
Calculate max. or min. Short Circuit................................................................1-13
System Frequency ............................................................................................1-13
Tmin(.02 to 99 Sec.) for Iband Idc ...................................................................1-13
Model Primary Transformer Tap (Ignore Secondary)......................................1-13
Time Varying Report............................................................................................1-13Voltage Factors ....................................................................................................1-13
1.3.4 Assumptions of the IEC_FAULT Study ..................................................1-141.3.5 Component Modeling...............................................................................1-14
Contribution Data.................................................................................................1-14
Network Feeders ..............................................................................................1-14
Synchronous Generators and Motors ...............................................................1-15
Asynchronous Induction Motors......................................................................1-16
Cables and Transformers......................................................................................1-17
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1.3.6 Error Messages ........................................................................................ 1-181.3.7 Reports..................................................................................................... 1-19
1.4 Application Examples.................................................................................... 1-191.4.1 Generator and Network Feeders .............................................................. 1-191.4.2 Meshed Network Considerations............................................................. 1-221.4.3 Far Versus Near Considerations .............................................................. 1-24
1.4.4 Example from Plant ................................................................................. 1-25
Index IEC_FAULT i
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1 IEC 6 9 9_FAULT Study
This chapter examines the short-circuit current calculation procedures used in the
IEC_FAULT Short Circuit Study. The chapter includes a systematic methodology and
applies the methodology to numerous practical examples. You can also run a
Comprehensive Short Circuit Study (in PTW-DAPPER) or an ANSI Short Circuit Study
(in A_FAULT). The A_FAULT Short Circuit Study and Comprehensive Short Circuit
Study chapters discuss the Short Circuit Methodology applied by each Study, and the
standards followed by each; the A_FAULT Study is based on the American National
Standards Institute (ANSI), while the Comprehensive Short Circuit Study is based onThevenin equivalent circuit representation and Ohms Law.
The IEC_FAULT Study follows the specifications of theInternational Electrotechnical
Commission (IEC) International Standard 909: Short-circuit current calculation in three-
phase a.c. systems.
This chapter discusses:
Engineering Methodology.
PTW Applied Methodology.
Examples.
IN
T
H
IS
C
H
A
P
T
E
R
What is the IEC_FAULT Study?........................................................ IEC_FAULT 1-2
Engineering Methodology .................................................................. IEC_FAULT 1-3
PTW Applied Methodology ............................................................. IEC_FAULT 1-11
Application Examples....................................................................... IEC_FAULT 1-19
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1.1 What is the IEC_FAULT Study?
The IEC_FAULT Short Circuit Study (referred to hereafter as IEC_FAULT) models the
current that flows in the power system under abnormal conditions and determines the
prospective fault currents in an electrical power system. These currents must becalculated in order to adequately specify electrical apparatus withstand and interrupting
ratings. The Study results are also used to selectively coordinate time current
characteristics of electrical protective devices.
Electrical equipment manufactured in Europe is predominately tested and rated against the
IEC equipment standards; therefore, IEC Standard 909 is the preferred method for
calculating fault duties when specifying European equipment. Equipment must withstand
the thermal and mechanical stresses of short circuit currents as described in the Standard.
Both rms and peak short circuit withstand and interrupting duties (referred to as making
and breaking short circuit current duties, respectively) must be calculated and then
compared to the protective device and electrical apparatus ratings. Both maximum and
minimum short circuit currents are available for specifying equipment in accordance with
IEC Standard 909.
Define System Data
Define system topology and connections
Define feeder and transformer sizes
Define fault contribution data
Run IEC_FAULT Study
Saved in DatabaseThree-phase fault currents
Unbalanced fault currents
Calculated IEC fault currents
Reports
Study Setup
Cable Library
Transformer Library
Study Setup
Used by Time Current
Coordination (CAPTOR)
Datablocks
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1.2 Engineering Methodology
IEC Standard 909 describes a detailed method for calculating three-phase and unbalanced
short circuit duties to compare to electrical apparatus ratings. The Standard contains 14
chapters and an appendix. Individual paragraphs are referred to as articles or clauses, and
sub-paragraphs are referred to as sub-clauses. The Standard is divided into two majorsections: far-from-generator short circuits and near-to-generator short circuits.
1.2.1 IEC Standard 909Section One of the Standard, Systems with Short Circuit Currents Having No A.C.
Component Decay (Far-From-Generator Short Circuits), defines the short circuit currents
that are expected at a fault location, assuming that active sources (machines and network
feeders) have no ac decrement. The Standard calls these machines far-from-the-fault-
location. The Standard defines no ac decrement as a symmetrical short circuit current that
has no time-varying change from peak to peak during the fault. The terms near and far are
defined in Section 1.3.4, Assumptions of the IEC_FAULT Study.
Section Two of the Standard, Systems With Short Circuit Currents Having Decaying
A.C. Components (Near-To-Generator Short Circuits), examines machines that are
considered near the fault; they exhibit an ac decrement throughout the duration of the fault
condition. Different source types (network feeders, synchronous motors and generators,
and asynchronous motors) are defined differently based on how their ac decrement is
modeled.
Both Sections One and Two discuss the implications of how the short circuit current
arrives at the fault location, and the impact of the dc decay on the short circuit current.
The Standard defines a contribution as coming from a meshed topology if a contribution
current flow splits into two or more currents between the source of supply and the fault
location. The concept of a meshed network is more complex than merely defining the
system as having loops or parallel connections; special procedures are required when
modeling meshed contributions. In addition, careful attention must be paid when
calculating their dc decay currents, regardless of whether the source of the short circuit
contribution is near or far from the fault location.
IEC Standard 909 is a derivative of the German VDE Short Circuit Standard. As such,
both standards were developed to assist engineers with hand calculations. Some of the
simplifying assumptions necessary for practical hand calculations are not necessarily well-
suited for computerized methods. The computer allows for removal of many of the
limiting assumptions in the hand calculation methods. Whenever PTW identifies a
simplifying assumption in the IEC Standard 909, or if the Standard uses the term may be
considered, the IEC_FAULT Study evaluates the assumption and takes the most
conservative implementation approachthat is, the Study calculates a larger short circuit
current.
1.2.2 Comparing the ANSI and IEC Short Circuit StandardsThere are three significant differences between the IEC methodology and ANSI
methodology.
The first major difference involves calculating the dc decay component. ANSI requires
calculation of a Thevenin equivalent fault point X/R ratio, based on separately derived R
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and X values at the fault point. From that X/R ratio, a single equivalent dc decay can be
determined for multiple sources at the fault location. The IEC Standard uses a unique R/X
ratio, calculated from the complex form of the R and X values at the fault location for
each contribution, and uses this unique ratio for calculating the asymmetrical fault currents
from each machine to the fault point. It could be argued that the IEC Standard is current
based, while the ANSI Standard is impedancebased.
The second major difference involves the dc offset current. Both standards recognize that
calculating the dc offset (the transient solution to the short circuit current calculation) must
be uniquely accomplished when parallel or meshed paths are involved. Both standards
consider the nature of meshed or parallel paths when concerned with the dc offset;
however, the two standards use completely different procedures for calculating this dc
offset current when meshed or parallel paths are involved.
The third major difference involves the ac decrement. The ANSI method globally adjusts
the machine sub-transient impedances when considering different moments of time during
the fault. The IEC method modifies the prospective short circuit currents available from
each machine based on the transfer impedance between the active source and the specific
fault location in question. Clearly, the IEC methodology is more computationally
intensive than the ANSI methodology.
Both short circuit methodologies can be considered as quasi-steady-state solutions to the
fault current problem, and both standards acknowledge that a more dynamic solution
method might yield more accurate results. They do, however, claim sufficient accuracy
for specifying electrical equipment.
The results from IEC and ANSI calculations cannot be directly compared. While both
calculate a withstand duty, the IEC and ANSI methodologies are fundamentally different.
In sample projects, the ANSI closing and latching duty can, at times, be larger than the
IEC peak current duty. However, in other sections of the same project, the opposite is
true. A similar disparity can be found between the IECs breaking current and the ANSIs
symmetrical current interrupting duty. Thus, it can be concluded that when equipment is
rated in accordance with the IEC Standard, then the IEC methodology must be used tocalculate the fault duties; and when equipment is rated in accordance with the ANSI
Standard, then the ANSI methodology must be used to calculate the fault duties.
1.2.3 Initial Symmetrical Short Circuit CurrentIEC Standard 909 calls for calculating the initial symmetrical rms short circuit current
duty at the fault location ( Ik ). It is important to understand that referring to a short circuit
duty means that you must include the necessary multipliers as dictated by the Standard
when calculating short circuit currents. This differs from associated published electrical
apparatus short circuit currents which define these currents as equipment ratings.
Remember that the short circuit duties calculated by the Study must be compared to the
equipment ratings published by the manufacturer. Also, when no special multipliers areused in the short circuit calculations (such as in PTWs Comprehensive Short Circuit
Study), then these values are known as short circuit currents.
The initial symmetrical short circuit current duty is the ratio of the driving point line-to-
neutral voltage to the system impedance at the fault point. Special consideration is given
to defining driving point voltages. A voltage factor (c) is introduced in the Standard,
which is intended to take into account the uncertainties associated with transformer
voltage taps, line capacitance, and so on. Additionally, the network feeder or the source
generator impedances, or both, are specially modified.
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dc Current
An aperiodic dc current duty (Idc ) is not necessarily required in the calculation in order to
specify electrical equipment, but knowledge of the dc decay is critical to determining the
other short circuit current duties specified in the Standard. As stated above, the dc current
is influenced by the R/X ratio seen between each contribution and the fault location.
Conceivably, each contribution can have a unique R/X ratio and hence its own unique dc
decay component. The Standard allows superposition in order to form the Thevenin
equivalent impedance at the fault location, but the dc current contributions are
individually calculated for each source of fault current and those dc fault currents are then
added together at the fault location. This means that any computerized modeling must
calculate and retain the fault point R/X ratio for each source to each fault location.
Peak Current
Given knowledge of the initial symmetrical and Idc duties, a peak or crest one-half cycle
short circuit duty can be defined. The theoretical maximum peak current of a fully offset
waveform is 2 2 Ik (X/R ratio approaching infinity).
When calculating the peak current duty ( Ip ) in meshed networks, the Standard providesthree methods: Method A, Method B, and Method C. While Method A is simple, it is
also the least accurate procedure; it uses the R/X of the smallest meshed branch. Method
B uses the R/X ratio from a meshed network formulated by using the complex (vector)
impedances, and adds a 15% safety factor to allow for inaccuracies. Method C uses
equivalent frequencies to calculate the special multiplying factor used. The IEC_FAULT
Study uses Method B.
The peak current also takes into account any dc decay that exists at one-half cycle into the
onset of the fault condition.
Breaking Current
The IEC Standard 909 breaking current duty ( Ib ) depends on the time for contact partingof the protective device. This is roughly equivalent to the interrupting duties in the ANSI
Standard. If far contributions are considered, the breaking duty equals the initial
symmetrical duty. If near contributions are considered, special multipliers are required to
define the ac decrement component of the short circuit duty. Ib does not include dc offset
or decay. Ib asym includes both ac and dc decay.
Steady State Current
Finally, the IEC Standard 909 calls for calculating a steady state current duty ( Ik ). It
assumes that asynchronous motors have ceased to contribute short circuit current, and that
generation (with static exciters) does not contribute to the steady state current. For far
network feeders, the steady state duty equals the initial symmetrical duty. Both minimum
and maximum steady state currents are calculated. When a minimum steady state duty is
calculated, a minimum driving point voltage is used.
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1.2.4 IEC Standard 909 TermsPTWs Reports conform to IEC Standard 909 notation, including:
c Voltage factor;
cUn
Equivalent voltage source (rms);
f Frequency (Hz);
Ib Symmetrical short circuit breaking current (rms) voltage;
Ib asym Asymmetrical short circuit breaking current;
Ik Steady-state short circuit current (rms);
Ik Initial symmetrical short circuit current (rms);
IkG Initial symmetrical short circuit current at synchronous machine;
IkM Initial symmetrical short circuit current at asynchronous motor;
IG rated Rated current of synchronous machine;
IM rated Rated current of asynchronous motor;
ILR Locked-rotor current of an asynchronous motor;
Idc Decaying aperiodic component of short circuit current;
Ip Peak short circuit current;
KG Correction factor for synchronous machines;
Factor of the calculation of breaking currents;
q Factor for the calculation of breaking currents of asynchronous motors;
Sk Steady state symmetrical short circuit power (apparent power);
Sk Initial symmetrical short circuit power (apparent power);
tmin Minimum time delay;
Un Nominal system voltage, line-to-line (rms);
U rG Rated machine voltage;
Xd Direct axis sub-transient reactance (saturated) of synchronous machine;Xq Quadrature axis sub-transient reactance (saturated) of synchronous machine;
Xd sat Reciprocal of the short circuit ratio;
Factor for the calculation of the steady-state short circuit current;
rG Rated machine power factor angle in degrees.
1.2.5 Conventional MethodologyThe Conventional or Comprehensive short circuit analysis procedure involves reducing
the network at the short circuit location to a single Thevenin equivalent impedance,
determining the associated fault point R/X ratio calculated using complex vector algebra,
and defining a driving point voltage (assuming the effect of transformer taps on bus
voltage). The initial symmetrical short circuit current can be calculated and, given thefault location R/X ratios, the asymmetrical short circuit current at various times during the
onset of the fault can be calculated.
Conventional short circuit analysis techniques do not satisfy IEC Standard 909
methodology. First, IEC Standard 909 disallows complete network reduction techniques
(that is, calculating a single Thevenin equivalent impedance) for determining the peak
short circuit current because the meshed/non-meshed information between each
contributing source and each fault location must be retained. Second, the methodology is
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aimed at adjusting contribution currents at the fault point location, and not simply
adjusting the contribution impedances at the machine buses. IEC Standard 909 is further
complicated by the requirement to model transformers whose turns ratios may not be the
same as the system base voltages, as illustrated in examples A1, A2, and A3 in the IEC
Standard 909 Appendix.
1.2.6 Requirements for Computer SolutionsIn order to attain the necessary data for calculating various short circuit current duties
using computer solutions and in accordance with the IEC Standard 909, it is necessary to
solve multiple networks associated with each specific short circuit location. For example,
at each short circuit location it is necessary to determine:
1. The ac decrement characteristic (far or near) for each machine;
2. Whether each machine or network feeder contributes through a non-meshed or
meshed topology;
3. The R/X ratio each machine or network feeder sees at each fault location;
4. The initial symmetrical short-circuit current which flows through each network feederand machine.
1.2.7 EquationsA summary of the important equations and associated graphs applied in IEC_FAULT
follows. Note that all of the numbered equations used in this section refer to the equations
as numbered in the IEC Standard 909, 1988 edition.
For each short circuit location, IEC_FAULT calculates the Thevenin equivalent and total
initial symmetrical short circuit duty ( Ik). Also, each individual machines IkG
contribution to the fault location is calculated.
For network feeders, the defining equation is:
ZcU
SQ
nQ2
kQ
=
Eq. 5a
Asynchronous machines are represented by:
Z1
M II
LR
M rated
= Eq. 34
Motor impedance and synchronous generators are represented by:
Z K R XGk G G d = + jb g Eq. 35where
KU
U
c
XG
n
rG
MAX
d rG
= + 1 sin
Eq. 36
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The Standard calculates each machines contribution ( Ik , Idc , Ip , Ib , Ik ) using the
following standard equations:
Ik calculated as in Section 1, Article 9, taking into account the voltage factor and the
synchronous machine KG factor:
=
+
IcU
3 R Xk
n
k2
k2
Eq. 14
=IcU
3Zk
n
k
Idc is calculated as:
I 2 I edc k2 f tmin
RX=
Eq. 1
where R/X is calculated knowing the complex (vector) form of the Thevenin equivalent
impedance.
Ip is calculated for non-meshed networks as:
I I 1.02 0.98ep k3RX= +
2 e j Eq. 16
For meshed contributions, Idc and Ip are corrected using Method B:
I 2 I edc MESH k 2 f tmin
RX=
115.
e j Eq. 21
I I 1.02 0.98ep MESH k3RX= +
115 2. e j
For contributions considered far from the fault location:
I = I = Ik b k Eq. 15
For near contributions of synchronous machines:
I = Ib k Eq. 46
where:
= e0.26IkG IrG0 84 0 26. .+
for t .02smin= 0 Eq. 47
= 0.51e 0.30IkG
IrG0 71. +
for t = 0.05smin
= +
0.62 0.72e0.32IkG IrG for t .10smin= 0
= +
0 56 0 94. . e0.38IkG IrG for t .25smin= 0
If the tmin is not as explicitly defined above, interpolation is used between equations.
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For near contributions of asynchronous machines:
I = q Ib k Eq. 71
where is defined as above, and q is calculated as:
q = 1.03 + 0.12 n MWPole Pairl d i for t = 0.02smin Eq. 67
q = 0.79 + 0.12 n MWPole Pair
l d i for t = 0.05smin
q = 0.57 + 0.12 n MWPole Pair
l d i for t = 0.10smin
q = 0.26 + 0.12 n MWPole Pair
l d i for t = 0.25smin
The asymmetrical breaking current is calculated as:
2
dc
2
bbasym III += Eq. A2.4
Calculation of short circuit current duties of asynchronous motors in the case of a short
circuit at the terminals is defined in Sub-Clause 13.2.1, Table II.
Calculations of short circuit current breaking duties of near synchronous and
asynchronous machines contributing through meshed networks are based on Equations 60,
61, and 62 in Sub-Clause 12.2.4.3.
Asynchronous machines do not contribute to the steady state duty (I )k .
The steady state contribution for synchronous machines assumes that the fault current
contribution is considered (as entered in the synchronous generator or motor data boxes of
the Component Editors IEC Contribution subview). Calculation is as follows:
I = Ik max G rated max Eq. 48
I = Ik min G rated min Eq. 49
where:
Imax and Imin are taken from Figures 17 and 18 of Sub-Clause 12.2.1.4, and depend on
whether the machines are turbine generators (round rotor) or salient pole generators.
1.2.8 IEC Standard 909 Unbalanced Short Circuit CalculationsGenerally, the current-based IEC Standard 909 procedure for calculating three-phase
balanced short circuits does not lend itself directly to calculating unbalanced short
circuitsthe process is impedance-based, involving network reduction. It should be noted
that reduced sequence networks do not retain information regarding individual
contributions, which are necessary when contributions through meshed networks must be
analyzed. Therefore, the technique allowed by the IEC Standard 909 uses factors
calculated in the balanced procedure for application in the unbalanced short circuit
calculations. Further, it is important to note that there is no recognition of near-to-
generator/motor-type calculations for unbalanced short circuits; the assumption
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I = I = Ik b k appears to be valid. IEC_FAULT automatically calculates line-to-earth, line-
to-line and line-to-line-to-earth short circuit duties.
Positive- and zero-sequence impedances can be entered for all branch elements.
Transformer neutral impedances also can be entered. It is important to correctly identify
the transformer winding connections for proper modeling of the zero-sequence network.
Except for synchronous motors and generators, the negative-sequence impedance is
always assumed to be equal to the positive-sequence impedance.
In the case of synchronous motors and generators, the negative-sequence reactance is
equal to:
= +
XX X
22
d q
If Xq data is missing or zero, then = X Xd q is assumed and Z 2 = ZG Gb g b g1 . Refer toIEC Standard 909, Section 11.5.3.6.
The negative- and zero-sequence impedance of synchronous motors and generators, like
the positive-sequence impedance, is multiplied by the correction factor KG . Refer to
Equations 37 and 38 in Section 11.5.3.6.
Thus, the positive-, negative-, and zero-sequence machine impedances are:
Z 1 = K R + jXG G G d b g b g
Z 2 = K R X X
2G G G
d qb g + + F
HG I
KJj
Z 0 = K (R + jX )G G 0 0b g For asynchronous motors, Z 1 = Z 2M Mb g b g , as defined in Section 11.5.3.5, and Z 0M b g isassumed to be infinite, and not user-definable. Finally, unbalanced short circuits near-to-
generator are treated as far ( = =I I Ik b k), as defined in Sections 11.3 and 12.3.
Line capacitances and parallel admittances of non-rotating loads are neglected.
The zero-sequence impedance is considered for network feeders. It is calculated
internally from user-defined line-to-earth current, kVA or MVA network contribution
data.
Two options are provided for calculating the unbalanced short circuit components: Idc and
Ip .
The first option uses equivalent three-phase factors. The equivalent is derived by
dividing the sum of individual contribution components by the absolute value of the
total initial symmetrical short circuit current Ikb g . Refer to Sections 9.2.1.2 and9.2.3.2.
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The second option uses factors developed from short circuit-type dependent
combinations of reduced sequence networks to establish a short circuit equivalent
R/X. If any three-phase contribution contributes through a meshed network, the
Method B 15% safety factor is applied to the total short circuit current.
Depending on the option selected, the minimum or maximum voltage factor (c) is applied
to the single equivalent positive-sequence voltage used in determining unbalanced shortcircuit currents.
1.3 PTW Applied Methodology
PTW applies the methodology described in Section 1.2. Section 1.3 describes how to run
the IEC_FAULT Study, including explanations of the various options associated with the
Study.
1.3.1 Before Running the IEC_FAULT StudyBefore running the IEC_FAULT Study, you must:
Define the system topology and connections.
Define feeder and transformer sizes.
Define fault contribution data.
1.3.2 Running the IEC_FAULT StudyYou can run the Study from any screen in PTW, and it always runs on the active project.
To run the IEC_FAULT Study
1. From the Run menu, choose Analysis.
2. Select the check box next to Short Circuit and choose the IEC_FAULT option button.
3. To change the Study options, choose the Setup button.
4. Choose the OK button to return to the Study dialog box, and choose the Run button.
The Short Circuit Study runs, writes the results to the database, and creates a report.
1.3.3 IEC_FAULT Study OptionsThe IEC_FAULT Study dialog box lets you select options for running the Study.
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Following is a list of the available Study options.
Report and Study Options
These boxes allow you to customize the breadth of the Study and its Report.
Report Type
There are three report types. Both the Standard Report With Calculation Details and the
Time Varying Report options produce extensive reports. If the Time Varying Report
option is selected, then you need to define the specific times at which you want to studythe Idc and Ib duties. Typically, you will want to see the duty at specific times, such as
1/2 cycle, and at specific breaker opening times, such as 5 cycles. Time varying entries
are in cycles. The Standard Report, No Calculation Details option, which is the default, is
more concise.
Short Circuit Type
The default is to report both the Balanced & Unbalanced Isc, but you can choose to report
the three-phase Balanced Isc only or the three-phase Unbalanced Isc only.
All or Selected
You can study a fault at a single bus or all buses. If a fault is to be studied at a single bus,
then the faulted bus must be specified. The default is to study the fault currents at allbuses.
Faulted Bus
If Selected Bus is selected in the previous box, use this box to specify the faulted bus.
System Modeling
These options further customize the Study.
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Use Sequence Network or Three-Phase Factors
Two options are provided for calculating the unbalanced short circuit Idc and Ipeak
values. The default option, Use Sequence Network to Calc Ip & Idc Factors, uses factors
developed based on the equivalent positive-, negative-, and zero-sequence network
combination for the type of unbalanced fault studied. If a meshed network is detected, the
Method B safety factor is applied to the unbalanced short circuit current.
The second option uses equivalent three-phase factors. The equivalent is derived by
dividing the sum of the individual positive-, negative-, and zero-sequence contribution
components by the absolute value of the total initial symmetrical current, in accordance
with Sub-Clause 9.2.
Pre-Fault Voltage
The driving point voltage established by the network feeder connection will be modified
by the voltage factors established in the Study setup. The default is to use the c factor.
Otherwise, you may select the driving point voltage calculated as the load flow voltage.
The driving point impedance is not affected by the utility (swing bus) voltage if thevoltage factors are selected.
Calculate max. or min. Short Circuit
You can model the minimum (lk min) or maximum (lk max) steady state short circuit
current duty. PTW automatically ignores asynchronous motor contributions to the steady
state current. Synchronous motors are modeled or not modeled based on their excitation
and whether the Included in Steady State check box in the IEC Contribution subview for
synchronous motors is selected or cleared. Cable resistance changes, due to fault
temperature increases, are not modeled in IEC_FAULT.
System Frequency
The system frequency must be defined, along with tmin , in order to calculate the breaking
current. The system frequency must be specified because the tmin is expressed in the
Standard in seconds. The IEC fault frequency default is 50 hz.
Tmin(.02 to 99 Sec.) for Iband Idc
Tmin is the user-defined time in seconds for reporting Idc , Ib , and Ib (asym) values. The
default is 0.02 seconds.
Model Primary Transformer Tap (Ignore Secondary)
You may model the primary transformer taps by selecting this check box. Secondary taps,
if modeled, are ignored in the IEC_FAULT calculation.
Time Varying ReportThe time varying report boxes allow Idc , Ib , and Ib (asym) values to be reported at four
user-specified times on a single report.
Voltage Factors
Voltage factors are used to define system pre-fault voltages used for fault current
calculations. The voltages can be entered as a range and for specific voltages. Specific
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voltage values override voltage range values. The voltage factors are used only if the pre-
fault voltage was selected as Use Voltage Factor (c).
1.3.4 Assumptions of the IEC_FAULT StudyThe IEC_FAULT Study implements IEC Standard 909 with the following assumptions.
When determining the near/far status of each machine, IEC_FAULT determines the
following:
1. Network feeders are always modeled as far from the short circuit location, as
suggested by Section 1, Clause 7. Network feeders are always defined by the utility
component in PTW. In general, if the network feeders transformer reactance
referenced on its low side X tlvb g is less than twice the equivalent reactance of thenetwork feeder Xqd i , then the network feeder is considered near the fault; thus itrequires that more of the network feeder system be modeled.
2. Any machine directly connected to a fault location is considered a near contribution.
3. A synchronous machine whose IkG contribution at the fault location is greater than
twice its rated current is considered a near contribution.
4. If the sum of all motors (synchronous and asynchronous) Ik contribution at the fault
location is greater than 5% of the total Ik combination at the fault location excluding
all motors, then all motor contribution (as a group) at the fault location is considered
near.
5. Any machine which has not been determined to be near the above is then considered
far, and thus no ac decrement is considered.
1.3.5 Component ModelingIt is best to set the engineering standard to IEC before beginning a new project. See
Setting Application Options in Chapter 3, Getting Started of the Users Guideto
change the engineering standard from ANSI to IEC. The IEC_FAULT Study assumes that
you have entered machine fault characteristics with PTW set to the IEC engineering
standard. However, if data is entered with PTW set to the ANSI engineering standard,
PTW will automatically convert ANSI fault contribution data to equivalent IEC fault data.
The following sections describe the minimum data required for the IEC_FAULT Study to
run.
Contribution Data
Contribution data must be defined for network feeders, synchronous generators,
synchronous motors, and asynchronous motors.
Network Feeders
Network feeders are modeled as Utility components. The driving point voltage and
voltage angle may be specified, but are not used in the IEC_FAULT calculation. The
short circuit contribution data must be specified for this component. It is important to note
that the utility driving point voltage and the equivalent generator source driving point
voltage, if the generator is modeled as a swing bus generator, are not used in the
IEC_FAULT Study. The driving point voltage is controlled only by the c factor identified
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IEC 60909_FAULT Study IEC_FAULT 1-15
SKM Power*Tools for Windows
in the IEC_FAULT Study setup for the voltage range of the bus which is faulted. Refer to
Table 1 of the Standard for recommended voltage ranges. The short circuit contribution
can be entered in amperes, or apparent power in units of kVA or MVA. Three-phase and
single-line-to-earth short circuit contribution values may be entered. A zero single-line-
to-earth short circuit contribution is acceptable, as PTW will assume an infinite zero
sequence impedance if the single-line-to-earth fault current is zero. The default values are
zero for the short circuit contribution magnitude, and 0.067 for the X/R ratio (X/R of 15).
You can also model the driving point voltages as calculated from the Load Flow Study.
When so modeled, no c factors are used.
Synchronous Generators and Motors
Synchronous generator and motor short circuit current contributions are defined in the
Component Editor as shown in the following figure:
Enter the Xd and Xq values; PTW assumes the machine is a salient pole machine if the
two values are not equal. Unique machine stator resistance for the positive- and negative-
sequence, and the zero-sequence component must be entered. You must define these
resistance values; they are notestablished as a percentage of the machine Xd values. The
default values for Xd , Xq and X0 are 0.15 pu on the machine base, and both rg and r0
have a default of 0.01 pu on the same machine base. Thus, synchronous machines are bydefault star-earthed.
PTW calculates the machine kVA and voltage base using the data you enter in the first
subview of the Component Editor. The motor rated size is in mechanical units of work
(output) when entered as horsepower, but in equivalent electrical units of work (input)
when entered as electrical quantities of kVA, MVA or kW. Motor efficiency is used to
convert horsepower to electrical units of work, and power factor is used to convert kW to
kVA. If the rated kVA base in the IEC Contribution subview is zero, then PTW calculates
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the equivalent kVA base from the machine rated size shown in the first subview of the
Component Editor. If the rated kVA base is not zero, PTW will not change it, even if you
enter a revised rated size in the motors first subview. Also, if the rated voltage is not zero,
PTW will not change it. Therefore, you may want to modify the rated machine kVA and
kVA base together; if you do modify them together, the kVA base will remain unchanged,
even if you change the rated size on the first subview of the Component Editor.
IEC_FAULT assumes the machine is salient pole if the Xq does not equal the Xd . Also,
the machine is defined as having a Series One or Series Two excitation characteristic as
follows:
Exciter Type Excitation Limit
Turbine Generator Salient Pole Generator
Series One 1.3 1.6
Series Two 1.6 2.0
The preceding table of Excitation Limits and machine types (turbine generator or salient
pole generator) is used along with Figures 17 and 18 in the Standard for calculating thesteady state contribution from synchronous machines. Fault current calculations for
unbalanced fault conditions follow the same procedures as for three-phase fault currents.
All three sequence impedance models (positive-sequence or Z1 , negative-sequence or
Z2 ,and zero-sequence or Z0 ) are modeled.
The synchronous machine or motor can be grounded through an earthing impedance, and
this value is entered in ohms. PTW automatically multiplies the impedance value by three
when calculating the zero-sequence currents. Do not enter the earthing impedance as
three-times the actual impedance selected, since PTW will perform that calculation. The
default is no earthing impedance.
The positive-, negative-, and zero-sequence impedances of synchronous machines are
modified by the KG factor, as defined in Sub-Clause 11.5.3.6, Equation 36.
When calculating the steady-state short circuit current, you should identify whether or not
the machine should be considered a fault current contribution; by default, PTW does
consider the machine in the Ik calculation. Also, the steady-state current is based on the
saturated reactance (Xd-sat) and the ratio of the Ik to the machine rated current. The
default transient reactance is 1.6 pu on the machine base. Finally, the steady-state current
contribution of the machine is dependent on the type of excitation and the type of
machine, either turbine generator (round rotor) or salient pole generator; the default
assumes a Series One machine with a turbine generator. Thus, the excitation limit of 1.3
times the rated field voltage is used.
In order to fully model a synchronous machine, the rated size of the machine must be
defined, along with the power factor. Motors can be defined in the Component Editor as
either a single motor (the default) or as multiple motors. PTW will calculate the power for
multiple motors modeled at the bus.
Asynchronous Induction Motors
Asynchronous motor short circuit currents must also be modeled in PTW. The
Component Editor IEC contribution data boxes are shown in the following figure:
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IEC 60909_FAULT Study IEC_FAULT 1-17
SKM Power*Tools for Windows
The rated current to lock rotor current ratio must be defined; the default is 0.17 pu on the
machine base. This is an impedance (vice reactance) value. The associated motor R/X
ratio must be defined; the default is 0.067.
The motor rated size is in mechanical units of work (output) when entered as horsepower,
but is in equivalent electrical units of work (input) when entered as electrical quantities of
kVA, MVA or kW. Motor efficiency is used to convert horsepower to electrical units of
work, and power factor is used to convert kW to kVA. If the rated kVA base is zero, then
PTW calculates the equivalent kVA base using the machine rated size as defined in thefirst subview of the Component Editor. The number of pole pairs, combined with the rated
kW of asynchronous machines, is used to calculate the breaking current duty. If multiple
motors are modeled in a single motor object, PTW will model the MW/pp of each of the
individual motors which comprise the group. Asynchronous motors are modeled as delta-
connected.
IEC_FAULT calculates the Thevenin equivalent positive-, negative- and zero-sequence
impedance components independently, and lists these values in the input Report for the
associated contribution. The values may be modified by special factors as specified in the
Standard.
Cables and Transformers
Cables are modeled with a series resistance and reactance in both the positive- and zero-
sequence components. PTW assumes that the negative-sequence impedance is equal to
the positive-sequence value. No zero-sequence shunt capacitance is modeled in
IEC_FAULT.
Transformers also are modeled with a positive- and zero-sequence impedance value. The
zero-sequence impedance path is dependent on the transformer connection. Only shell-
wound three-phase and single-phase transformers modeled in three-phase banks are
modeled in PTW.
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The transformer may be earthed through an earthing impedance, and this value must be
entered in ohms. PTW automatically multiplies the impedance value by three when
calculating the zero-sequence currents. Do not enter the earthing impedance as three-
times the actual impedance selected, since PTW performs that calculation. The default is
no earthing impedance.The earthing impedance is modeled only on the star-connection.
A warning message is shown on the status bar if an earthing impedance is entered for a
non-star (delta connection). If the transformer is connected star-star, an earthingimpedance may be modeled on either or both sides of the transformer, unless the load flow
voltages are used instead of the Voltage Factors.
Transformer primary taps may be modeled. A negative primary tap raises the secondary
voltage. Secondary transformer taps are not modeled in IEC_FAULT. Taps will only be
considered if the IEC_FAULT Study Setup dialog box is set to model them. The driving
point voltages are defined by the Voltage Factors and are not modified by the transformer
tap settings.
Transformer off-nominal voltage ratios, as compared to the primary and secondary bus
system nominal voltages, are modeled when the Model Transformer Taps check box is
selected in the Study setup dialog box. Essentially, PTW will create a fictitious primary
and/or secondary tap to ensure that the voltage ratios are properly matched.
1.3.6 Error MessagesPTW examines the entered data for the IEC_FAULT Study. If PTW finds missing or
incomplete information, it sends an error message to the Study Message dialog box. The
Study Messages dialog box will report both fatal and warning messages. The Study will
attempt to run to completion even if fatal errors are detected, in order to identify any other
errors.
A somewhat common error is:
The cal cul at ed zer o sequence i mpedance i s negat i ve.
It involves the entry of single-line-to-easrth short circuit contribution data. PTW uses the
three-phase fault data and the single-line-to-earth fault data to calculate the positive-,
negative- and zero-sequence impedances from the following per-unit equations:
Z Z
Z1.0
I
I3 1.0
Z Z Z
Z3
I
Z Z
1 2
1f
f1 2 0
0f
1 2
3
sle
sle
=
=
=
+ +
=
b gb g
Utilities often report available single-line-to-earth fault duties on an equivalent three-
phase rating apparent power basis, using the equation:
kVA 3 I kV3 f LLsle=
However, the actual apparent power of a single-line-to-ground fault is:
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IEC 60909_FAULT Study IEC_FAULT 1-19
SKM Power*Tools for Windows
kVA = IkV
31 fsle
where
kV line-to-line voltage.
You cannot use the three-phase equivalent rating of a single-line-to-ground short circuitcontribution. If you do, PTW may attempt to calculate the zero-sequence impedance as a
negative value. The actual apparent power to be entered into PTW is the utility equivalent
single-line-to-earth duty divided by three. Enter the single-line-to-ground fault current
X/R ratio, not the zero sequence impedance X/R ratio.
1.3.7 ReportsFor each fault location, IEC_FAULT reports:
Ik ;
IkG of each machine;
Near/far status of each machine;
Transfer impedance and R/X ratio for each contributing machine.
1.4 Application Examples
The examples that follow illustrate how the IEC_FAULT Study runs on various system
topologies. Unless otherwise specified, all pu values are expressed on a 100 MVA base at
the bus system nominal voltage.
1.4.1 Generator and Network FeedersIn this first example, a network feeder and two generators are modeled in order to
understand how IEC_FAULT models these contributions. The equivalent short circuit
capacity is the same for all the three contributions. The one-line diagram for the system is
as shown:
NETWORK BUS
Ik" 20.86 kAIp 58.13 kAIb 20.86 kAIk 14.86 kA
NETWORK FDRGEN 1 GEN 2
95% PF 75% PF
A portion of the output report is shown:
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T H R E E P H A S E I E C 9 0 9 F A U L T R E P O R TMODEL TRANSFORMER TAPS: NOFREQUENCY ( HZ): 50.CALC. MAX. FAULT CURRENTS
============================================================================== NETWORK BUS 11. 000 kV Vol t age ( PU) : 1. 1000 Tmi n: 0. 02 Sec.
Sk": 397354. kVA Sk: 283064. kVA I b asym. : 28. 610 kAI k"(kA) i dc(kA) i p(kA) I b(kA) I k(kA)
COMPLEX TOTALS 20. 856 27. 698 58. 134 20. 856 14. 857BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
GEN 1 6. 887 9. 147 19. 198 6. 887 6. 464NETWORK FEEDER 5. 249 6. 971 14. 630 5. 249 5. 249GEN 2 8. 720 11. 581 24. 306 8. 720 7. 383
CONTRI BUTI ONS AT SOURCES- - - - - - - r efer r ed t o 11000. vol t age-- - - - - - - -NETWORK FEEDER 5. 249 6. 971 14. 630 5. 249 5. 249GEN 1 6. 887 9. 147 19. 198 6. 887 6. 464GEN 2 8. 720 11. 581 24. 306 8. 720 7. 383
DETAI LED SOURCE I NFORMATI ON- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -NETWORK FEEDER NETWORK FEEDER STATUS: FAR, NON-MESHED
R/ X: 0. 010GEN 1 GENERATOR STATUS: NEAR, NON-MESHED
R/ X: 0. 010I "kG/ I G rat ed: 1. 31u: 1. 000LAMBDA: 1. 32
GEN 2 GENERATOR STATUS: NEAR, NON-MESHEDR/ X: 0. 010I "kG/ I G rat ed: 1. 66u: 1. 000LAMBDA: 1. 46
Examine the short circuit current contribution from the network feeder. The short circuit
contribution is 100 MVA with an R/X ratio of 0.01. The network is serviced from
11 kVtherefore the voltage factor is 1.1., based on Table 1 of the Standard. Using the
impedance of the network feeder from Equation 5a of the Standard:
ZcU
S
=1.111 kV
100 MVA
=1.331
QnQ2
kQ
=
b g2
The initial symmetrical short circuit current available from the network feeder is from Eq.14, and is:
I =cU
3Z
1.1 11 kV
3 1.331
= 5.2486 kA
k
q
q
=
b g
The network feeder is defined as far from the network bus, thus Ik , Ib and Ik are the
same value since there is no ac decrement.
Incidentally, if you run the Comprehensive Short Circuit Study on this example, assuming
a driving point voltage at the source of 1.0 pu voltage, the network feeder produces the
same short circuit current as calculated by the IEC_FAULT Study.
However, note that the magnitude of fault current generated by the two generators is
different than the fault current produced by the network feeder; each of the two generators
produces a different Ik . Following are the reasons this occurs.
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IEC 60909_FAULT Study IEC_FAULT 1-21
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First, examine generator GEN 1. Note that the rated power factor of the machine is 95%
lagging. Using Equation 36, the generator KG factor is calculated as:
K =U
U
c
1+ X sin
1111
1.11+ 1.0 sin cos 0.95
= 0.83825
Gn
rG
max
d rg
-1
=
b ge j
Thus, the short circuit current contribution from this machine is:
I =cU
K X
1.11.0
0.83825 1.0
= 1.3122 pu A
KN
G d
=
b g
But you know the base current is:
I =100,000 kVA
311 kV
= 5248.63 A
base
Thus, the generator produces an initial symmetrical short circuit of:
I = 5248.63 1.3122 pu
= 6887.53 A
k
The generator is directly assigned to the network feeder bus; thus, the generator is
considered near the fault location and the ac decrement must be considered. Note that for
this generator, Ib is smaller than
Ik and Ik is smaller than either Ib or
Ik .
Because generator GEN 2 has a different power factor than generator GEN 1, the KG for
generator GEN 2 is different than that of generator GEN 1. This is why generator GEN 2
has a different (and larger) short-current current contribution to the network bus.The rated
current of generators GEN 1 and GEN 2 is:
I =100,000 kVA
3 11 kV
= 5248.63 A
r G
Thus the ratio of Ik to Irfor generator GEN 1 is:
=
II
6887.53 A
5248.63 A
=1.3122
k
r
This matches the calculated value in the preceding Report.
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IEC 60909_FAULT 1-22 Reference Manual
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This value is used to determine the breaking current, using Figure 16 of the Standard. The
factor is 1.0, since the ratio is less than 2. Therefore the breaking current is equal to
the Ik .
I = I
=1.0 6887.53 A
= 6887.53 A
b k
The scalar sum of the three initial symmetrical short circuit currents is:
=I 6.887 + 5.249 + 8.720 kA
= 20.865 kA
k Bus
This matches the reported complex value because the three contributions are nearly in
phase with one another.
The prospective initial power is:
= S 3 20,865 A 11 kV= 397.6 MVA
k b g
Again, this matches the value in the Report.
1.4.2 Meshed Network ConsiderationsThe second example analyzes meshed versus non-meshed characteristics. It demonstrates
how in Method B a 15% safety factor is used when meshed networks are modeled.
Consider the following one-line diagram:
NETWORK BUS
NETWORK FDR
TX1
TX 1 SEC BUS
TX2
TX2 SEC BUS
CBL-0001
A portion of the Report is shown for a fault at transformer TX1 SEC BUS:
TX 1 SEC BUS 0. 400 kV Vol t age ( PU) : 1. 0000 Tmi n: 0. 02 Sec.Sk": 58062. kVA Sk: 58062. kVA I b asym. : 85. 105 kA
I k"(kA) i dc(kA) i p(kA) I b(kA) I k(kA)COMPLEX TOTALS 83. 806 20. 951 193. 648 83. 806 83. 806BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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IEC 60909_FAULT 1-24 Reference Manual
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1.4.3 Far Versus Near ConsiderationsIn this example the network feeder is replaced with a single generator. The near/far status
of the generator will be examined. The one-line is:
NETWORK BU
TX1
TX 1 SEC BUS
TX2
TX2 SEC BUS
CBL-0001
GEN 1
The generator sub-transient reactance is set at 0.5 pu on its own base of 100 MVA. The
impedances of the branch impedance components are 0.5 pu on a 100 MVA base. The
Report for this case is:
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IEC 60909_FAULT Study IEC_FAULT 1-25
SKM Power*Tools for Windows
TX 1 SEC BUS 0. 400 kV Vol t age ( PU) : 1. 0000 Tmi n: 0. 02 Sec.Sk": 183472. kVA Sk: 183472. kVA I b asym. : 380. 269 kA
I k"(kA) i dc(kA) i p(kA) I b(kA) I k(kA)COMPLEX TOTALS 264. 820 385. 941 749. 023 264. 820 264. 820BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
NETWORK BUS 183. 337 267. 190 518. 554 183. 337 183. 337TX2 SEC BUS 81. 483 118. 751 230. 469 81. 483 81. 483
CONTRI BUTI ONS AT SOURCES- - - - - - - r efer r ed t o 400. vol t age-- - - - - - - -GEN 1 264. 820 385. 941 749. 023 264. 820 264. 820
DETAI LED SOURCE I NFORMATI ON- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
GEN 1 GENERATOR STATUS: FAR, MESHEDR/ X: 0. 017I "kG/ I G rat ed: 1. 83u: 1. 000LAMBDA: 1. 46
The I"I
kG
G
ratio is less than 2; therefore, the generator is considered electrically far from
the fault location. The breaking current and steady state current equal the initial
symmetrical current.
The machines Xd is reduced to 0.3 pu, thereby increasing its short circuit capacity. A
portion of the Report is shown:
TX 1 SEC BUS 0. 400 kV Vol t age ( PU) : 1. 0000 Tmi n: 0. 02 Sec.
Sk": 269468. kVA Sk: 163173. kVA I b asym. : 534. 882 kAI k"(kA) i dc(kA) i p(kA) I b(kA) I k(kA)COMPLEX TOTALS 388. 943 533. 477 1100. 097 379. 210 235. 520BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
NETWORK BUS 269. 268 369. 330 761. 606 262. 530 163. 052TX2 SEC BUS 119. 675 164. 147 338. 491 116. 680 72. 468
CONTRI BUTI ONS AT SOURCES- - - - - - - r efer r ed t o 400. vol t age-- - - - - - - -GEN 1 388. 943 533. 477 1100. 097 379. 210 235. 520
DETAI LED SOURCE I NFORMATI ON- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -GEN 1 GENERATOR STATUS: NEAR, MESHED
R/ X: 0. 027I "kG/ I G rat ed: 2. 69u: 0. 969LAMBDA: 1. 63
Now the I"I
kG
G
ratio is greater than 2 and the machine is considered electrically near the
fault location. The breaking and steady-state current are less than the initial symmetrical
current.
1.4.4 Example from PlantThe following figure is a one-line diagram for the Plant project. The Plant project is
included on the PTW diskettes.
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002-TXAPRI
TXA
C1
C2
C3
M8
M10
RI
005-TXDPRI
006-TX3PRI
007-TXEPRI
024-MVSWG
C10
C19
026-TXGPRI
025-MTR25
029-TXDSEC
TXG
027-DSB3
C13A
L3
028-MTR28
M28#1&2
011-TX3SEC
012-TX3TER
C7
013-DSSWG2
C8
020-DSSWG3
C9
M3
G2
0
21-TXFPRI
TX6
022-DSB2
C12
0
23-MTR23
M7
L1
M4
TX4
TXC
G1
C5
C6G
1
RI
010-MTR10
TX3
M5
C14
C16
C17
016-H2A
017-H1A
Subfeed#1
Subfeed#2A
L10
G3
T
XL1
PANELS1
MCC15A
PANELS3
TX3WND
POWER*TOOLSFORWINDOWS
SWBD1
CB3
R3
FTXC
F5
FTX3
PD-0011
LVP1
CB6R
6
RG2
CBG2
RG3
CBG3
RG1
CBG1 M
CP5
F2
LVP2
LVP3
CB5
R5
CB1
CB2
R2
CBM8
RM8
CBM10
RM10
SW1
CAP#1
F4
C13B
LVP5
028-MTR28B
LVP4
M28#3M
CPM28#3
MC
M28#4
MCPM28#1&2
The following figure shows a portion of the Plant project, including IEC_FAULT results.
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IEC 60909_FAULT Study IEC_FAULT 1-27
SKM Power*Tools for Windows
BLDG 115 SERV
Ik" 8.14 kA
I peak 19.81 kA
Ib (asym) 8.61 kA10 C11
26-TX G PRI
Ik" 7.78 kA
I peak 18.26 kA
Ib (asym) 7.98 kA
025-MTR 25
Ik" 7.80 kA
I peak 18.16 kA
Ib (asym) 8.12 kA
SW M25
F M25
MCP M25
M25
4
X G
027-DSB 3
IEC SHORT CIRCUIT STUDY
FAULT ALL BUSES
BUILDING 115 SERVICE
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IEC 60909_FAULT 1-28 Reference Manual
12/4/2006
A segment of the IEC_FAULT Report follows. The Standard Report, No Calculation
Details option is first presented. For a fault at Bus 28, the Report is:
T H R E E P H A S E I E C 9 0 9 F A U L T R E P O R TMODEL TRANSFORMER TAPS: NOFREQUENCY ( HZ): 50.CALC. MAX. FAULT CURRENTS
==============================================================================027-DSB 3 0. 400 kV Vol t age ( PU) : 1. 0000 Tmi n: 0. 02 Sec.
Sk": 20786. kVA Sk: 6819. kVA I b asym. : 29. 218 kAI k"(kA) i DC(kA) i p(kA) I b(kA) I k(kA)
COMPLEX TOTALS 30. 002 15. 197 69. 606 27. 171 9. 842BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
026- TX G PRI 21. 704 10. 356 50. 126 21. 663 9. 842028- MTR 28 A 4. 154 2. 016 9. 446 2. 686 0. 000028- MTR 28 B 4. 154 2. 827 10. 051 2. 828 0. 000
The total bus initial symmetrical short circuit current is 21.867 kA, with the majority of
the current flowing from the network feeder. The motors connected in MCC 28 contribute
5.229 kA in short circuit current.
More details are provided if the Standard Report with Calculation Details Report format is
selected, as shown below:
T H R E E P H A S E I E C 9 0 9 F A U L T R E P O R TMODEL TRANSFORMER TAPS: NOFREQUENCY ( HZ): 50.CALC. MAX. FAULT CURRENTS
==============================================================================027-DSB 3 0. 400 kV Vol t age ( PU) : 1. 0000 Tmi n: 0. 02 Sec.
Sk": 20786. kVA Sk: 6819. kVA I b asym. : 29. 218 kA
I k"(kA) i DC(kA) i p(kA) I b(kA) I k(kA)COMPLEX TOTALS 30. 002 15. 197 69. 606 27. 171 9. 842BRANCH CONTRI BUTI ONS- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
026- TX G PRI 21. 704 10. 356 50. 126 21. 663 9. 842028- MTR 28 A 4. 154 2. 016 9. 446 2. 686 0. 000028- MTR 28 B 4. 154 2. 827 10. 051 2. 828 0. 000
CONTRI BUTI ONS AT SOURCES- - - - - - - r efer r ed t o 400. vol t age-- - - - - - - -U1 9. 842 3. 085 20. 841 9. 842 9. 842M8 1. 461 0. 815 3. 407 1. 461 0. 000G1 0. 386 0. 232 0. 913 0. 386 0. 000
M25 4. 595 2. 831 10. 911 4. 595 0. 000M 28 # 1&2 4. 154 2. 016 9. 446 2. 686 0. 000M28 #4 2. 077 1. 413 5. 026 1. 414 0. 000M28 #3 2. 077 1. 413 5. 026 1. 414 0. 000
DETAI LED SOURCE I NFORMATI ON- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -U1 NETWORK FEEDER STATUS: FAR, NON-MESHED
R/ X: 0. 240M8 SYNC. MOTOR STATUS: NEAR, NON-MESHED
R/ X: 0. 148I "kG/ I G rat ed: 0. 26u: 1. 000LAMBDA: 0. 24
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IEC 60909_FAULT Study IEC_FAULT 1-29
SKM Power*Tools for Windows
G1 GENERATOR STATUS: FAR, NON-MESHEDR/ X: 0. 137I "kG/ I G rat ed: 0. 36u: 1. 000LAMBDA: 0. 34
M25 ASYNC. MTR. STATUS: NEAR, NON-MESHEDR/ X: 0. 132I "kM/ I M rated: 1. 59MW/ ( pol e pai r ) : 0. 802
uq: 1. 000
M 28 # 1&2 ASYNC. MTR. STATUS: NEAR, NON- MESHEDR/ X: 0. 170I "kM/ I M rated: 11. 51MW/ ( pol e pai r ) : 0. 104uq: 0. 647
M28 #4 ASYNC. MTR. STATUS: NEAR, NON-MESHEDR/ X: 0. 116I "kM/ I M rated: 5. 76MW/ ( pol e pai r ) : 0. 104uq: 0. 681
M28 #3 ASYNC. MTR. STATUS: NEAR, NON-MESHEDR/ X: 0. 116I "kM/ I M rated: 5. 76MW/ ( pol e pai r ) : 0. 104uq: 0. 681
The third Report format, Time Varying Balanced Report, depicts the time varying nature
of the fault current at the bus, and the contributions in each branch. For a fault at Bus 27the report is:
T H R E E P H A S E I E C 9 0 9 F A U L T R E P O R TMODEL TRANSFORMER TAPS: NOFREQUENCY ( HZ): 50.CALC. MAX. FAULT CURRENTS
==============================================================================( A) TOTAL SHORT- CI RCUI T CURRENT
FAULT BUS NOMI NAL R/ X OF V I k" ( SYM. RMS) i p( PEAK) I k( RMS)027-DSB 3 V. ( kV) EQUI V. Z ( PU) ( kA) ( kA) ( kA)
0. 400 0. 213 1. 0000 30. 002 69. 606 9. 842
TI ME ( CYCLES) 0. 5 2. 0 5. 0 12. 5
I b( ASYM. RMS) ( KA) 33. 701 25. 200 21. 134 18. 119I b( SYM. RMS) ( KA) 28. 524 24. 870 21. 132 18. 119
i ( DC) ( KA) 25. 384 5. 752 0. 413 0. 001I b(ASYM) / I b(SYM) 1. 182 1. 013 1. 000 1. 000
( B) BRANCH CURRENT
BRANCH NAME R/X OF I k" ( SYM. RMS) i p( PEAK) I k( RMS)EQUI V. Z ( kA) ( kA) ( kA)
026- TX G PRI 0. 230 21. 704 50. 126 9. 842
TI ME ( CYCLES) 0. 5 2. 0 5. 0 12. 5
I b( ASYM. RMS) ( KA) 25. 098 21. 060 19. 437 17. 947I b( SYM. RMS) ( KA) 21. 684 20. 896 19. 437 17. 947i ( DC) ( KA) 17. 873 3. 701 0. 233 0. 000I b(ASYM) / I b(SYM) 1. 157 1. 008 1. 000 1. 000
BRANCH NAME R/X OF I k" ( SYM. RMS) i p( PEAK) I k( RMS)EQUI V. Z ( kA) ( kA) ( kA)
028- MTR 28 A 0. 170 4. 154 9. 446 0. 000
TI ME ( CYCLES) 0. 5 2. 0 5. 0 12. 5
I b(ASYM. RMS) ( KA) 4. 167 1. 971 0. 790 0. 079I b(SYM. RMS) ( KA) 3. 383 1. 909 0. 790 0. 079i ( DC) ( KA) 3. 441 0. 692 0. 028 0. 000I b(ASYM) / I b(SYM) 1. 232 1. 032 1. 000 1. 000
( B) BRANCH CURRENT
BRANCH NAME R/X OF I k" ( SYM. RMS) i p( PEAK) I k( RMS)EQUI V. Z ( kA) ( kA) ( kA)
028- MTR 28 B 0. 170 4. 154 10. 051 0. 000
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IEC 60909_FAULT 1-30 Reference Manual
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TI ME ( CYCLES) 0. 5 2. 0 5. 0 12. 5
I b(ASYM. RMS) ( KA) 4. 507 2. 283 0. 915 0. 092I b(SYM. RMS) ( KA) 3. 466 2. 070 0. 909 0. 092i ( DC) ( KA) 4. 075 1. 360 0. 152 0. 001I b(ASYM) / I b(SYM) 1. 300 1. 103 1. 007 1. 000
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SKM Power*Tools for Windows
Index
A
ac Decrement, 1-3, 1-4
required in computer solutions, 1-7
ANSI Methodology
compared to IEC methodology, 1-3
Aperiodic dc Current Duty. SeeDecaying Aperiodic Component
of Short Circuit Current
Assumptions of the IEC_FAULT Study, 1-14
Asymmetrical Short Circuit Breaking Current, 1-9
IEC Standard 909 notation of, 1-6
B
Breaking Current, 1-5
C
Computer Requirements
when solving short circuit current duties, 1-7
Contribution Data, 1-14
Conventional Short Circuit Methodology, 1-6
Correction Factor for Synchronous Machines
IEC Standard 909 notation of, 1-6
D
dc Current, 1-5
dc Decay, 1-3, 1-4
dc Offset Current, 1-4
Decaying Aperiodic Component of Short Circuit Current, 1-5
IEC Standard 909 notation of, 1-6
Direct Axis Sub-Transient Reactance (Saturated) of Synchronous
Machine
IEC Standard 909 notation of, 1-6
E
Equations
for aynchronous machines, 1-7
for motor impedance, 1-7
for network feeders, 1-7
for synchronous generators, 1-7
used by IEC_FAULT, 1-7
Equivalent Voltage Source (rms)
IEC Standard 909 notation of, 1-6
Error Messages
IEC_FAULT Study, 1-18
Exciter Type
for machines, 1-16
F
Factor for the Calculation of Breaking Currents of Asynchronous
Motors
IEC Standard 909 notation of, 1-6
Factor for the Calculation of the Steady-State Short Circuit
Current
IEC Standard 909 notation of, 1-6
Factor of the Calculation of Breaking Currents
IEC Standard 909 notation of, 1-6Far Status of Machines
in IEC_FAULT Study, 1-14
Frequency (Hz)
IEC Standard 909 notation of, 1-6
I
IEC Methodology
compared to ANSI methodology, 1-3
IEC Standard 909, 1-1, 1-2, 1-3, 1-4, 1-7
calculating unbalanced short circuits using, 1-9
methods A, B, & C in, 1-5
terms, 1-6
IEC_FAULT Study
assumptions of, 1-14
contribution data, 1-14
definition of, 1-2
equations used by, 1-7
error messages, 1-18
examples, 1-19
far versus near considerations, 1-24
generator and network feeders, 1-19
meshed network considerations, 1-22
Plant project, 1-25
far status of machines, 1-14
line-to-earth, line-to-line, and line-to-line-to-earth calculations,
1-10
methodology, 1-3
near status of machines, 1-14network feeder modeling, 1-14
running the Study, 1-11
Study options, 1-11
Initial Symmetrical Short Circuit Current (rms), 1-4
IEC Standard 909 notation of, 1-6
required in computer solutions, 1-7
Initial Symmetrical Short Circuit Current at Asynchronous Motor
IEC Standard 909 notation of, 1-6
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IEC_FAULT ii Reference Manual
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Initial Symmetrical Short Circuit Current at Synchronous
Machine
IEC Standard 909 notation of, 1-6
Initial symmetrical Short Circuit Duty, 1-7
Initial Symmetrical Short Circuit Power (Apparent Power)
IEC Standard 909 notation of, 1-6
Interrupting Fault Duty, 1-2
L
Locked-Rotor current of an Asynchronous Motor
IEC Standard 909 notation of, 1-6
M
Machine
exciter type, 1-16
Meshed Network. SeeMeshed Topology
Meshed Topology, 1-3
required in computer solutions, 1-7
Methodology
IEC_FAULT Study, 1-3Methods A, B, & C. SeeIEC Standard 909
Minimum Time Delay
IEC Standard 909 notation of, 1-6
N
Near Status of Machines
in IEC_FAULT Study, 1-14
Negative-Sequence Impedance. SeeSymmetrical Component
Impedance Network
Network Feeders
modeling in IEC_FAULT Study, 1-14
Nominal System Voltage, Line-to-Line (rms)
IEC Standard 909 notation of, 1-6
Non-Meshed Network. SeeNon-Meshed Topology
Non-Meshed Topology, 1-8
required in computer solutions, 1-7
P
Peak Short Circuit Current, 1-5
IEC Standard 909 notation of, 1-6
Positive-Sequence Impedance. SeeSymmetrical Component
Impedance Network
Q
Quadrature Axis Sub-Transient Reactance (Saturated) of
Synchronous MachineIEC Standard 909 notation of, 1-6
R
R/X Ratio, 1-5, 1-19
required in computer solutions, 1-7
Rated Current of Asynchronous Motor
IEC Standard 909 notation of, 1-6
Rated Current of Synchronous Machine
IEC Standard 909 notation of, 1-6
Rated Machine Power Factor Angle in Degrees
IEC Standard 909 notation of, 1-6
Rated Machine Voltage
IEC Standard 909 notation of, 1-6
Reciprocal of the Short Circuit Ratio
IEC Standard 909 notation of, 1-6
S
Salient Pole Generators, 1-9
in IEC_FAULT Study, 1-16
Short Circuit Current Breaking Duties, 1-9
Short Circuit Current Duty
computer requirements in solving, 1-7
of asynchronous motors, 1-9
Standard Terms. SeeIEC Standard 909
Steady State Contribution
for synchronous motors, 1-9
Steady State Current, 1-5
Steady State Short Circuit Current
calculating properly, 1-16Steady State Symmetrical Short Circuit Power (Apparent Power)
IEC Standard 909 notation of, 1-6
Steady-State Short Circuit Current (rms)
IEC Standard 909 notation of, 1-6
Symmetrical Component Impedance Networks
positive-, negative-, and zero-sequence, 1-10
Symmetrical Short Circuit Breaking Current (rms) Voltage
IEC Standard 909 notation of, 1-6
T
Terms. SeeIEC Standard 909
Thevenin equivalent, 1-7
Thevenin Equivalent Fault Point X/R Ratio, 1-4
Thevenin Equivalent Impedance, 1-8Transformer
turns ratios, 1-7
Turbine Generators (Round Rotor), 1-9
Turns Ratios, 1-7
U
Unbalanced Short Circuits Calculation
using IEC Standard 909, 1-9
V
Variables. SeeIEC Standard 909: terms
Voltage FactorIEC Standard 909 notation of, 1-6
minimum and maximum, 1-11
W
Withstand Fault Duty, 1-2
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Z Zero-Sequence Impedance. SeeSymmetrical ComponentImpedance Network