Reference IEC Fault

8/9/2019 Reference IEC Fault

1/37

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


2/37

12/4/2006

Information in this document is subject to change without notice. No part of this document may be reproduced or

transmitted in any form or by any means, electronic or mechanical, without the express written consent of SKM

Systems Analysis, Inc. No patent liability is assumed with respect to the use of the information contained herein.

Although every precaution has been taken in the preparation of this manual, the publisher and author assume no

responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of

information contained herein. For information, address SKM Systems Analysis, Inc., PO Box 3376, Manhattan

Beach, CA 90266-1376, USA.

2006 SKM Systems Analysis, Inc. All rights reserved.

Power*Tools, CAPTOR and DAPPER are registered trademarks and HI_WAVE and I*SIM are trademarks of

SKM Systems Analysis, Inc.

Microsoft is a registered trademark and Windows is a trademark of Microsoft Corporation.

Intel is a registered trademark and Pentium is a trademark of Intel Corporation.

ACAD and AutoCAD are registered trademarks of AUTODESK, Inc.

WordPerfect is a registered trademark of Novell, Inc.

Lotus and 1-2-3 are registered trademarks of Lotus Development Corporation.

Arial is a registered trademark of The Monotype Corporation, PLC.

PIXymbols is a trademark of Page Studio Graphics

ImageStream Graphics Filters is a registered trademark and ImageStream is a trademark of ImageMark Software

Labs, Inc.

PIXymbols Extended Character Set. Copyright 1995. Page Studio Graphics. All rights reserved.For information, address Page Studio Graphics, 3175 North Price Road, Suite 150, Chandler, AZ 85224.

Phone/Fax: (602) 839-2763.

ImageStream Graphics & Presentation Filters. Copyright 1991-1995. ImageMark Software Labs, Inc. All

rights reserved.

Various definitions reprinted from IEEE Std 100-1992, IEEE Standard Dictionary of Electrical and Electronics

Terms, copyright 1992 by the Institute of Electrical and Electronics Engineers, Inc. The IEEE takes no

responsibility or will assume no liability for the reader's misinterpretation of said information resulting from its

placement and context in this publication. Information is reproduced with the permission of the IEEE.

MathType math equation editing fonts are licensed from Design Science, Inc.

1987-1996 by Design Science, Inc. All rights reserved.


3/37


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


4/37

IEC_FAULT ii Reference Manual

12/4/2006

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


5/37


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


6/37

IEC 60909_FAULT 1-2 Reference Manual

12/4/2006

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


7/37

IEC 60909_FAULT Study IEC_FAULT 1-3


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


8/37


12/4/2006

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.


9/37



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.


10/37


12/4/2006

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


11/37



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


12/37


12/4/2006

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.


13/37



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





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


14/37


12/4/2006

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.


15/37



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.


16/37


12/4/2006

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.


17/37



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


18/37


12/4/2006

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


19/37



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


20/37


12/4/2006

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:


21/37



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.


22/37


12/4/2006

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:


23/37



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:


24/37


12/4/2006

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.


25/37



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.


26/37


12/4/2006

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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


27/37


28/37


12/4/2006

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:


29/37



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


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.


30/37


12/4/2006

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.


31/37



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


32/37


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:


==============================================================================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:


==============================================================================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



33/37



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:


==============================================================================( 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


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


028- MTR 28 B 0. 170 4. 154 10. 051 0. 000


34/37


12/4/2006

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


35/37


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


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


Direct Axis Sub-Transient Reactance (Saturated) of Synchronous

Machine


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)


Error Messages

IEC_FAULT Study, 1-18

Exciter Type

for machines, 1-16

F

Factor for the Calculation of Breaking Currents of Asynchronous

Motors


Factor for the Calculation of the Steady-State Short Circuit

Current


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)


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



Initial Symmetrical Short Circuit Current at Asynchronous Motor



36/37

IEC_FAULT ii Reference Manual

12/4/2006

Initial Symmetrical Short Circuit Current at Synchronous

Machine


Initial symmetrical Short Circuit Duty, 1-7

Initial Symmetrical Short Circuit Power (Apparent Power)


Interrupting Fault Duty, 1-2

L

Locked-Rotor current of an Asynchronous Motor


M

Machine

exciter type, 1-16

Meshed Network. SeeMeshed Topology

Meshed Topology, 1-3


Methodology

IEC_FAULT Study, 1-3Methods A, B, & C. SeeIEC Standard 909

Minimum Time Delay


N

Near Status of Machines


Negative-Sequence Impedance. SeeSymmetrical Component

Impedance Network

Network Feeders

modeling in IEC_FAULT Study, 1-14

Nominal System Voltage, Line-to-Line (rms)


Non-Meshed Network. SeeNon-Meshed Topology

Non-Meshed Topology, 1-8


P

Peak Short Circuit Current, 1-5


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


Rated Current of Asynchronous Motor


Rated Current of Synchronous Machine


Rated Machine Power Factor Angle in Degrees


Rated Machine Voltage


Reciprocal of the Short Circuit Ratio


S

Salient Pole Generators, 1-9


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)


Steady-State Short Circuit Current (rms)


Symmetrical Component Impedance Networks

positive-, negative-, and zero-sequence, 1-10

Symmetrical Short Circuit Breaking Current (rms) Voltage


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


37/37

Z Zero-Sequence Impedance. SeeSymmetrical ComponentImpedance Network

Reference IEC Fault

Documents

Transcript of Reference IEC Fault