ETAP
PowerStation 4.0


User Guide
Copyright  2001
Operation Technology, Inc.
All Rights Reserved
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Chapter 13
Short-Circuit Analysis
The PowerStation Short-Circuit Analysis program analyzes the effect of three-phase, line-to-ground, lineto-line, and line-to-line-to-ground faults on the electrical distribution systems. The program calculates the
total short-circuit currents as well as the contributions of individual motors, generators, and utility ties in
the system. Fault duties are in compliance with the latest editions of the ANSI/IEEE standards (C37
series) and IEC standards (IEC 909 and others).
This chapter describes definitions and usage of different tools you will need to run short-circuit studies.
In order to give you a better understanding of the standards applied to short-circuit studies and to interpret
output results more easily, some theoretical background and standard information are also included.
The ANSI/IEEE Short-Circuit Toolbar and IEC Short-Circuit Toolbar sections explain how you can
launch a short-circuit calculation, open and view an output report, or select display options. The ShortCircuit Study Case Editor section explains how you can create a new study case, what parameters are
required to specify a study case, and how to set them. The Display Options section explains what options
are available for displaying some key system parameters and the output results on the one-line diagram,
and how to set them.
The ANSI/IEEE Calculation Methods section lists standard compliance information and both general and
detailed descriptions of calculation methods used by the program. In particular, definitions and
discussion of ½, 1.5-4, and 30 cycle networks, calculation of ANSI multiplying factors, and high voltage
and low voltage circuit breaker momentary and interrupting duties are provided. The Required Data
section describes what data are necessary to perform short-circuit calculations and where to enter them. If
you perform short-circuit studies using IEC Standards, the IEC Calculation Methods section provides
useful information on standard compliance, definitions on most commonly used IEC technical terms, and
general and detailed descriptions of calculation methods for all important results, including initial
symmetrical short-circuit current, peak short-circuit current, symmetrical short-circuit breaking current,
and steady-state short-circuit current. Finally, the Short-Circuit Study Output Report section illustrates
and explains output reports and their format.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI Short-Circuit Toolbar
13.1 ANSI Short-Circuit Toolbar
This toolbar is active when you are in Short-Circuit mode and the standard is set to ANSI in the ShortCircuit Study Case Editor.
3-Phase Faults – Device Duty
3-Phase Faults – 30 Cycle Network
LG, LL, LLG & 3-Phase Faults – ½ cycle
LG, LL, LLG & 3-Phase Faults – 1.5-4 Cycle
LG, LL, LLG & 3-Phase Faults – 30 cycle
Save Fault kA for PowerPlot
Short-Circuit Display Options
Alert View
Short-Circuit Report Manager
Halt Current Calculation
Get Online Data
Get Archived Data
3-Phase Faults - Device Duty
Click on this button to perform a three-phase fault study per ANSI C37 Standard. This study calculates
momentary symmetrical and asymmetrical rms, momentary asymmetrical crest, interrupting symmetrical
rms, and interrupting adjusted symmetrical rms short-circuit currents at faulted buses. The program
checks the protective device rated close and latching, and adjusted interrupting capacities against the fault
currents, and flags inadequate devices.
Generators and motors are modeled by their positive sequence subtransient reactances.
3-Phase Faults - 30 Cycle Network
Click on this button to perform a three-phase fault study per ANSI standards. This study calculates shortcircuit currents in their rms values after 30 cycles at faulted buses.
Generators are modeled by their positive sequence transient reactances, and short-circuit current
contributions from motors are ignored.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI Short-Circuit Toolbar
LG, LL, LLG, & 3-Phase Faults - ½ Cycle
Click on this button to perform line-to-ground, line-to-line, line-to-line-to-ground, and three-phase fault
studies per ANSI standards. This study calculates short-circuit currents in their rms values at ½ cycle at
faulted buses.
Generators and motors are modeled by their positive, negative, and zero sequence subtransient reactances.
In all the unbalanced fault calculations (½ cycle, 1.5-4 cycle and 30 cycle), it is assumed that the negative
sequence impedance of a machine is equal to its positive sequence impedance. Generator, motor, and
transformer grounding types and winding connections are taken into consideration when constructing
system positive, negative, and zero sequence networks.
LG, LL, LLG, & 3-Phase Faults - 1.5 to 4 Cycle
Click on this button to perform three-phase, line-to-ground, line-to-line, line-to-line-to-ground, and threephase fault studies per ANSI standards. This study calculates short-circuit currents in their rms values
between 1.5 to 4 cycles at faulted buses.
Generators are modeled by their positive, negative, and zero sequence subtransient reactances, and motors
are modeled by their positive, negative and zero sequence transient reactances. Generator, motor and
transformer grounding types and winding connections are taken into considerations when constructing
system positive, negative, and zero sequential networks.
LG, LL, LLG, & 3-Phase Faults - 30 Cycle
Click on this button to perform three-phase, line-to-ground, line-to-line, line-to-line-to-ground, and threephase fault studies per ANSI standards. This study calculates short-circuit currents in their rms values at
30-cycles at faulted buses.
Generators are modeled by their positive, negative, and zero sequence reactances, and short-circuit
current contributions from motors are ignored. Generator, motor, and transformer grounding types and
winding connections are taken into consideration when constructing system positive, negative, and zero
sequence networks.
Save Fault kA for PowerPlot
Click on this button to save momentary symmetrical short-circuit currents (rms value) for protective
device coordination studies using PowerPlot.
Short-Circuit Display Options
See the Display Options section to customize the short-circuit annotation display options on the one-line
diagram. This dialog box contains options for ANSI short-circuit study results and associated device
parameters.
Alert
After performing a short-circuit study, you can click on this button to open the Alert View, which lists all
devices with critical and marginal violations based on the settings in the study case.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI Short-Circuit Toolbar
Short-Circuit Report Manager
Short-circuit output reports are provided in two forms: ASCII text files and Crystal Reports. The Report
Manager provides four pages (Complete, Input, Result, and Summary) for viewing the different parts of
the output report for both text and Crystal Reports. Available formats for Crystal Reports are displayed in
each page of the Report Manager for ANSI short-circuit studies.
If any other formats other than TextRept are chosen in the Report Manager, the Crystal Reports will be
activated. You can open the whole short-circuit output report or only a part of it, depending on the format
selection.
You can also view output reports by clicking on the View Output Report button on the Study Case
Toolbar. A list of all output files in the selected project directory is provided for short-circuit
calculations. To view any of the listed output reports, click on the output report name, and then click on
the View Output Report button.
Short circuit text output reports (with an .shr extension) can be viewed by any word processor such as
Notepad, WordPad, and Microsoft Word. Currently, by default, the output reports are viewed by
Notepad. You can change the default viewer in the ETAPS.INI file to the viewer of your preference
(refer to Chapter 1).
The text output reports are 132 characters wide with 66 lines per page. For the correct formatting and
pagination of output reports, you MUST modify the default settings of your word processor application.
For Notepad, WordPad, and Microsoft Word applications we have recommend settings that are explained
in the Printing & Plotting section.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI Short-Circuit Toolbar
Halt Current Calculation
The Stop Sign button is normally disabled. When a short-circuit calculation has been initiated, this button
becomes enabled and shows a red stop sign. Clicking on this button will terminate the calculation.
Get Online Data
When PowerStation Management System is set-up, and the Sys Monitor presentation is on-line, you can
bring real-time data into your off-line presentation and run a Load Flow by pressing on this button. You
will notice that the Operating Loads, Bus Voltages, and Study Case Editor will be updated with the online data.
Get Archived Data
When ETAPS Playback is set-up, and any presentation is on Playback mode, you can bring this data into
your presentation and run a Load Flow by pressing on this button. You will notice that the Operating
Loads, Bus Voltages, and Study Case Editor will be updated with the playback data.
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Short-Circuit Toolbar
13.2 IEC Short-Circuit Toolbar
This toolbar is active when you are in Short-Circuit mode and the standard is set to IEC in the ShortCircuit Study Case Editor.
3-Phase Faults – Device Duty (IEC 909)
LG, LL, LLG & 3-Phase Faults (IEC 909)
3-Phase Faults – Transient Study (IEC 363)
Save Fault kA for PowerPlot
Short-Circuit Display Options
View Alert
Short-Circuit Report Manager
Halt Current Calculation
Get Online Data
Get Archived Data
3-Phase Faults - Device Duty (IEC 909)
Click on this button to perform a three-phase fault study per IEC 909 Standard. This study calculates
initial symmetrical rms, peak, symmetrical and asymmetrical breaking rms and steady-state rms shortcircuit currents and their dc offset at faulted buses. The program checks the protective device rated
making and breaking capacities against the fault currents and flags inadequate devices.
Generators are modeled by their positive sequence subtransient reactances, and motors are modeled by
their locked-rotor impedance.
LG, LL, LLG, & 3-Phase Faults (IEC 909)
Click on this button to perform line-to-ground, line-to-line, line-to-line-to-ground, and three-phase fault
studies per IEC 909 Standard. This study calculates initial symmetrical rms, peak and symmetrical
breaking rms, and steady-state rms short-circuit currents at faulted buses.
Generators are modeled by their positive, negative, and zero sequence reactances, and motors are
modeled by their locked-rotor impedance. It is assumed that the negative sequence impedance of a
machine is equal to its positive sequence impedance. Generator, motor, and transformer grounding types,
and winding connections are taken into consideration when constructing system positive, negative, and
zero sequence networks.
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Short-Circuit Toolbar
3-Phase Faults - Transient Study (IEC 363)
Click on this button to perform a three-phase fault study per IEC 61363 Standard. This study calculates
instantaneous values of actual short-circuit current, dc offset, short-circuit current envelope, ac
component, and dc offset in percent for total short-circuit current at faulted buses. The results are
tabulated as a function of time.
Generators are modeled by their positive sequence subtransient reactances, and motors are modeled by
their locked-rotor impedance. Their subtransient and transient time constants and dc time constants are
also considered in the calculation.
Save Fault kA for PowerPlot
Click on this button to save initial symmetrical short-circuit currents (rms value) for protective device
coordination studies using PowerPlot.
Short-Circuit Display Options
See the Display Options section to customize the short-circuit annotation display options on the one-line
diagram. This dialog box contains options for IEC short-circuit study results and associated device
parameters.
Alert View
After performing a short-circuit study, you can click on this button to open the Alert View, which lists all
devices with critical and marginal violations based on the settings in the study case.
Short-Circuit Report Manager
Short-circuit output reports are provided in two forms: ASCII text files and Crystal Reports. The Report
Manager provides four pages (Complete, Input, Result, and Summary) for viewing the different parts of
the output report for both text and Crystal Reports. Available formats for Crystal Reports are displayed in
each page of the Report Manager.
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Short-Circuit Toolbar
You can also view output reports by clicking on the View Output Report button on the Study Case
Toolbar. A list of all output files in the selected project directory is provided for short-circuit
calculations. To view any of the listed output reports, click on the output report name, and then click on
the View Output Report button.
PowerStation text output reports (with an .shr extension) can be viewed by any word processor such as
Notepad, WordPad, and Microsoft Word. Currently, by default, the output reports are viewed by
Notepad. You can change the default viewer in the ETAPS.INI file to the viewer of your preference
(refer to Chapter 1).
The text output reports are 132 characters wide with 66 lines per page. For the correct formatting and
pagination of output reports, you MUST modify the default settings of your word processor application.
For Notepad, WordPad, and Microsoft Word applications we have recommend settings that are explained
in the Printing & Plotting section.
Halt Current Calculation
The Stop Sign button is normally disabled. When a short-circuit calculation has been initiated, this button
becomes enabled and shows a red stop sign. Clicking on this button will terminate the calculation.
Get Online Data
When PowerStation Management System is set-up, and the Sys Monitor presentation is on-line, you can
bring real-time data into your off-line presentation and run a Load Flow by pressing on this button. You
will notice that the Operating Loads, Bus Voltages, and Study Case Editor will be updated with the online data.
Get Archived Data
When ETAPS Playback is set-up, and any presentation is on Playback mode, you can bring this data into
your presentation and run a Load Flow by pressing on this button. You will notice that the Operating
Loads, Bus Voltages, and Study Case Editor will be updated with the playback data.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
13.3 Study Case Editor
The Short-Circuit Study Case Editor contains solution control variables, faulted bus selection, and a
variety of options for output reports. PowerStation allows you to create and save an unlimited number of
study cases. Short-circuit calculations are conducted and reported in accordance with the settings of the
study case selected in the toolbar. You can easily switch between study cases without the trouble of
resetting the study case options each time. This feature is designed to organize your study efforts and
save you time.
With respect to the multi-dimensional database concept of PowerStation, study cases can be used for any
combination of the three major system components, i.e. for any configuration status, one-line diagram
presentation, and Base/Revision data.
The Short-Circuit Study Case Editor can be accessed by clicking on the Study Case button from the Study
Case Toolbar. You can also access this editor from the Project View by clicking on the Short-Circuit
Study Case folder.
Short-Circuit Study Case Toolbar
To create a new study case, go to Project View, right-click on the Short-Circuit Study Case folder, and
select Create New. The program will then create a new study case, which is a copy of the default study
case, and add it to the Short-Circuit Study Case folder.
Project View
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
13.3.1 Info Page
Study Case ID
Study case ID is shown in this entry field. You can rename a study case by simply deleting the old ID
and entering a new ID. The study case ID can be up to 12 alphanumeric characters. Use the Navigator
button at the bottom of the editor to go from one study case to the next existing study case.
XFMR Tap
Two methods are provided for modeling transformer off-nominal tap settings:
Adjust Base kV
Base voltages of the buses are calculated using transformer turn ratios, which include the transformer
rated kVs as well as the off-nominal, tap settings.
Use Nominal Tap
Transformer rated kVs are used as the transformer turn ratios for calculating base voltages of the buses,
i.e., all off-nominal tap settings are ignored and transformer impedances are not adjusted.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
In case a system contains transformers with incompatible voltage ratios (including taps) in a loop, it can
lead to two different base voltage values at a bus, which prevents the short-circuit calculation from
continuing. If this situation occurs, ETAP will post a message to inform you of this condition and give
you the option to continue the calculation with the Use Nominal Tap alternative. If you answer Yes, it
will carry out the calculation with the Use Nominal Tap option.
Cable/OL Heater
Select the appropriate check boxes in this option group to include the impedance of equipment cable and
overload heaters of medium and/or low voltage motors in short-circuit studies.
Report
You can select the following options for short-circuit output reports.
Contribution Level
Choose how far away you want to see the short-circuit current contributions from individual buses to each
faulted bus by specifying the number of bus levels away in this section. Note that for large systems,
choosing a high bus level results in very large output reports (the report grows exponentially with the
number of levels being chosen).
When selecting contribution levels of n buses away, depending on the number of faulted buses, the
calculated results are displayed on the one-line diagram and printed in the output report as follows:
•
Fault 1 (one) bus
Displayed results: whole system
Reported output: n bus levels away
•
Fault more than one bus
Displayed results: 1 bus level away (from the adjacent buses)
Reported output: n bus levels away
Motor Contribution Based on
You can select the following options for considering motor contribution in short-circuit studies.
Motor Status
When this option is selected, motors whose status is either Continuous or Intermittent will make
contributions in short-circuit. Motors with Spare status will not be considered in the short-circuit
analysis.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
Loading Category
When this option is selected, you can select a loading category from the selection box to the right. In the
short-circuit calculation, motors that have non-zero loading in the selected loading category will have a
contribution in short-circuit. Motors with zero loading in the selected loading category will not be
included in the short-circuit analysis.
Both
When this option is selected, a motor will make contribution in short-circuit if it meets either the Motor
Status condition or the Loading Category condition. That is, for a motor to be excluded in the shortcircuit analysis, it has to be in the Spare status and have zero loading in the selected loading category.
Bus Selection
PowerStation is capable of faulting one or more buses in the same run; however, in the latter case buses
are faulted individually, not simultaneously. Depending on the specified fault type, the program will
place a three-phase, line-to-ground, line-to-line, and line-to-line-to-ground fault at each bus which is
faulted for short-circuit studies.
When you open the Short-Circuit Study Case Editor for the first time, all buses are listed in the “Don’t
Fault” list box. This means that none of the buses are faulted. Using the following procedures, you can
decide which bus(es) you want to fault for this study case.
•
•
•
•
To fault a bus, highlight the bus ID in the “Don’t Fault” list box and click on the Fault button. The
highlighted bus will be transferred to the Fault list box.
To remove a bus from the Fault list box, highlight the bus ID and click on the Fault button. The
highlighted bus will be transferred to the “Don’t Fault” list box.
If you wish to fault all buses, or medium voltage buses, or low voltage buses, select that option and
click on the Fault button. The specified buses will be transferred from the “Don’t Fault” list box to
the Fault list box.
To remove all buses, or medium voltage buses, or low voltage buses from the Fault list box, select
that option and click on the Fault button. The specified buses will be transferred from the Fault list
box to the “Don’t Fault” list box.
Remarks 2nd Line
You can enter up to 120 alphanumeric characters in this field. Information entered here will be printed on
the second line of every output report page header line. These remarks can provide specific information
regarding each study case. Note that the first line of the header information is global for all study cases
and is entered in the Project Menu.
13.3.2 Standard Page
Standard
Both ANSI and IEC standards are available for short-circuit studies. Select the short-circuit study
standard by clicking on the standard notation. Note that different sets of solution control variables
(prefault voltage, calculation methods, etc.) are available for each standard.
When you create a new study case the short-circuit standard is set equal to the project standard you have
specified in the Project Standards Editor, which is accessible from the Project Menu. Note that the study
case standard can be changed independently of the project standard.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
When the ANSI standard is selected, this page will appear as shown below.
Study Page – ANSI Standard
When the IEC standard is selected, the study options will change and you will see the page shown below.
Study Case – IEC Standard
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Study Case Editor
Prefault Voltage - ANSI Standard
You can select either fixed or variable prefault voltages for all buses.
Fixed Prefault Voltage
This option allows the user to specify a fixed prefault voltage for all the faulted buses. This fixed value
can be in percent of bus nominal kV or base kV. Bus nominal kV is the value entered in the Bus Editor
by the user to represent the normal operating voltage. The bus base kV is calculated by the program and
is only reported in the results section of the Short-Circuit report for each faulted bus.
The process of computing base kV starts from one of the swing machines, such as a utility or a generator,
by taking its design voltage as the base kV for its terminal bus. It then propagates throughout the entire
system. When it encounters a transformer from one side, the transformer rated voltage ratio will be used
to calculate the base KV for the buses on other sides. If the “Adjust Base kV” option is selected on the
Info Page of the Short-Circuit Study Case editor, the transformer tap values will also be used in the base
kV calculation along with transformer rated voltage ratio. It can be seen from this calculation procedure
that the base kV is close to the operating voltage, provided that the swing machine is operating at its
design setting.
Variable Prefault Voltage
If you select the Vmag x Nominal kV (in the Bus Editor) prefault voltage option, PowerStation uses the
bus voltages entered in the Bus editors as the prefault voltage for faulted buses. Using this option, you
can perform short-circuit studies with each faulted bus having a different prefault voltage. For instance,
you can perform short-circuit studies using the bus voltages calculated from a specific load flow study
and therefore, calculate fault currents for an actual operating condition. To do so, select Update Initial
Bus Voltages from the Load Flow Study Case Editor and run a load flow analysis.
As the short-circuit current is proportional to the prefault voltage, different options will most likely give
different results. However, with any one of the above options, the calculated fault current is the same as
long as the prefault voltage in kV is the same. Then, which option should be used for a study? The
answer is dependent on the user’s engineering judgment and objective of the study. If you want to
calculate the fault current to size protective switching devices, you may want to apply the maximum
possible prefault voltages in the calculation. This can be done by using the option of “Fixed Base kV”. If
the bus normal operating voltage is entered in the Bus Editor as the bus nominal voltage, you may also
use the “Fixed Nominal kV” option.
Machine X/R - ANSI Standard
Fixed and variable machine X/R options are available for short-circuit calculations. Note that selection of
fixed or variable machine X/R impacts only the interrupting (1.5-4 cycle) duty calculations of high
voltage circuit breakers.
Fixed X/R
PowerStation uses the specified machine X/R ratio (=Xd”/Ra) for both ½ cycle and 1.5-4 cycle networks.
The intention of this option is to account for the fact that ANSI standard does not consider variable
machine X/R ratio.
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Short-Circuit Analysis
Study Case Editor
The following example shows Ra calculations when X/R ratio is fixed:
½ Cycle Network
Input:
Xsc
Input:
X/R = 10
Calculated:
Ra
1.5-4 Cycle Network
15
25
1.5
2.5
Variable X/R
PowerStation uses the specified machine X/R ratio and subtransient reactance (Xd”) to calculate the
armature resistance (Ra). This resistance is then used for both ½ cycle and 1.5-4 cycle networks. Note
that the motor reactance for 1.5-4 cycle network is larger than the motor reactance for ½ cycle networks.
Therefore, this option results in a higher machine X/R ratio and a higher short-circuit contribution for the
interrupting fault calculation of a high voltage circuit breaker than the fixed X/R option.
The following example shows Ra and X/R calculations when variable X/R is considered:
½ Cycle Network
1.5-4 Cycle Network
15
25
Input:
Xsc
Input:
X/R = 10
Calculated:
Ra
1.5
1.5
Final:
X/R
10
16.7
HV CB Interrupting Capability
According to ANSI standards, the rated interrupting capability entered in the High Voltage Circuit
Breaker Editor corresponds to the maximum kV of the circuit breaker. When the circuit breaker is
utilized under a voltage below this maximum kV, its capability is actually higher than the rated
interrupting kA. In this section, you specify the operating voltage to be used to adjust breaker rating.
Nominal kV
When this option is selected, the nominal kV of the bus, connected to the circuit breaker, is assumed to be
the operating voltage, and breaker, interrupting rating is adjusted to this voltage value.
Nominal kV & Vf
When this option is selected, the operating voltage of the breaker is calculated as the multiplication of the
prefault voltage and the nominal kV of the bus the circuit breaker is connected to. The circuit breaker
interrupting rating is adjusted to this voltage value.
Prefault Voltage - IEC Standard
Enter voltage C factors for the indicated bus voltage levels. The equivalent voltage source used in the
IEC short-circuit calculations will be adjusted according to this voltage factor as entered in the study case.
The defaults of the voltage C factors are from Table I of IEC 909 Standard.
230 V & 400 V
Other < 1001 V
1001 to 35000 V
> 35000 V
Operation Technology, Inc.
C Factor = 1.0
C Factor = 1.05
C Factor = 1.1
C Factor = 1.1
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
In calculations of the minimum steady-state short-circuit current, the factor Cmin is used as specified in
IEC 909 Standard.
Calculation Method - IEC Standard
X/R for Peak Current
•
•
•
Method A – Using the uniform ratio X/R in calculating the peak current
Method B – Using the X/R ratio at the short-circuit location in calculating the peak current
Method C – Using equivalent frequency in calculating the peak current
Breaking kA
The breaking duty of circuit breakers and fuses are calculated based on the following two methods:
•
•
No Mtr Decay - AC asynchronous (induction) motor decay is not included in the calculation.
With Mtr Decay - AC asynchronous (induction) motor decay is included in the calculation.
Steady-State kA
Steady-state short-circuit current is an rms value which remains after the decay of transient phenomena
•
•
Max Value - Factors are used for steady-state short-circuit current that reflect maximum modeling
inaccuracies. This value is used to determine minimum device ratings.
Min Value - Factors are used for steady-state short-circuit that reflect minimum modeling
inaccuracies. This value is used for relay coordination purposes in preventing the occurrence of
nuisance trips and loading deviations.
Fault Impedance for Line-to-Ground Fault
You may consider fault impedance in the line-to-ground fault calculation. In this section, you specify the
fault impedance to be applied to all the faulted buses.
Include Fault Impedance Zf
Check this box to include fault impedance in the calculation. You can enter fault impedance in the editor
box below.
Fault Impedance Unit
You can enter the fault impedance in either ohms or percent. If the Ohm option is selected, the values in
the R and X editor boxes are in ohms. If you select the Percent option, the values in the R and X editor
boxes are in percent based on 100 MVA and the nominal kV of the faulted bus.
R and X
In these two editor boxes, you enter the fault impedance in either ohms or percent, depending on the fault
impedance unit selected. Note that these values apply to all the faulted buses.
Arc Flash Analysis
You can perform arc flash analysis in 3-phase device duty calculation. In this section, you specify
whether you want to perform the analysis for all faulted buses.
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Short-Circuit Analysis
Study Case Editor
NFPA 70E
Check this box to include an arc flash analysis of NFPA 70E-2000 when you perform 3-phase device duty
calculation.
Protective Device Duty – ANSI Standard
You can select to use either the bus total fault current or the maximum current through a protective device
to compare against protective device duty.
Based on Total Bus Fault Current
Check this box to use the total bus fault current to compare against protective device rating.
Based on Maximum Through Fault Current
Check this box to use the maximum through fault current to compare against protective device rating.
The maximum through fault current is determined as the larger value between the fault current
contribution through a protective device and the total bus fault current minus the contribution through the
device.
Report Breaking Duty vs. CB Time Delay – IEC Standard
When this box is checked, in the IEC Device Duty calculation, the program will report a list of breaking
currents for a number of different delay times in the individual fault calculation result page of the crystal
report.
13.3.3 Alert
The Alert page allows the user to setup alerts on short-circuit calculation results. The objective is to alert
the user of certain conditions of interest in short-circuit studies. The alerts are determined based on
predetermined device ratings and system topology after performing a Short-circuit calculation
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Study Case Editor
Alert
There are two categories of alerts generated by the short-circuit calculations: Critical and Marginal. The
difference between the two is their use of different condition percent values for the same monitored
parameter. If a condition for a Critical Alert is met, then an alert will be generated in the alert view
window and the overloaded element will turn red in the one-line diagram. The same is true for Marginal
Alerts, with the exception that the overloaded component will be displayed in the color magenta. Also,
the Marginal Alerts check box must be selected if the user desires to display the Marginal Alerts. If a
device alert qualifies it for both Critical and Marginal alerts, then only Critical Alerts are displayed.
Bus Alert
Short-circuit simulation Alerts for buses are designed to monitor crest, symmetrical and asymmetrical
bracing conditions. These conditions are determined from bus rating values and Short-circuit analysis
results. The percent of monitored parameter value in the Short-circuit study case alert setup page is fixed
at 100% for Critical Short-circuit Alerts. The Marginal alert percent value is user defined.
Protective Device Alert
The setup of protective device simulation Alerts is similar to that of bus Alerts. The user may enter into
the Short-circuit study case editor alert setup page the monitored parameter percent values for Marginal
Alerts; however, this value is fixed to 100% for Critical level alerts.
Marginal Device Limit
PowerStation flags all protective devices whose momentary and interrupting duties exceed their
capabilities by displaying the element in red on the one-line diagram and flagging it in the output report.
To flag devices with marginal capabilities, select the Marginal Device Limit option and specify the
marginal limit in percent of the device capability.
For example, consider a circuit breaker with an interrupting rating of 42 kA and a calculated short-circuit
duty of 41 kA. The capability of this circuit breaker is not exceeded; however, if the marginal device
limit is set to 95%, the circuit breaker will be flagged in the output report and will be displayed in purple
in the one-line diagram as a device with marginal capability.
Auto Display
The auto display feature of the Short-circuit Study Case Editor Alert Setup page allows the user to decide
if the Alert View Window should be automatically displayed as soon as the Short-circuit calculation is
completed.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
13.4 Display Options
The Short-Circuit Analysis Display Options consist of a Results page and three pages for AC, AC-DC,
and DC info annotations. Note that the colors and displayed annotations selected for each study are
specific to that study.
13.4.1 Result Page
The Result Page of the Display Options is where you select different result annotations to be displayed in
the one-line diagram. Depending on the short-circuit study type, ANSI or IEC, this page gives you
different options for three-phase fault results. If the study type is ANSI short-circuit analysis, you will
see the Result Page as shown below.
If the study type is IEC short-circuit analysis, the options in the 3-Phase Faults section are Peak or Initial
Symmetrical rms current. The rest of the sections are the same as that for the ANSI short-circuit analysis.
Color
Select the color for information annotations to be displayed on the one-line diagram.
Units
Select the Units check box to show kA next to all displayed fault currents on the one-line diagram.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
3-Phase Fault Currents
•
•
For the ANSI short-circuit method (three-phase faults), select momentary or interrupting
symmetrical kA to be displayed on the one-line diagram.
For the IEC short-circuit method (three-phase faults), select peak or initial symmetrical rms kA to
be displayed on the one-line diagram.
LG Fault Currents
Select 3Io to display three times of zero sequence current in kA, or select Ia to display phase A of the
fault current in kA, for line-to-ground fault.
Bus Voltage
Select bus voltage display units in kV or in percent. Bus voltages are only displayed when you fault one
bus in the system. For a line-to-ground fault, PowerStation displays the voltage of phase B of every bus
in the system.
Motor Contributions
Display Medium Voltage Motor Contributions
Select this option to display short-circuit current contributions from medium voltage motors (more than
1kV) on the one-line diagram.
Display Large Low Voltage Motor Contributions
Select this option to display short-circuit current contributions from large low voltage motors (motor sizes
equal to or larger than 100 hp or kW) on the one-line diagram.
Display Small Low Voltage Motor Contributions
Select this option to display short-circuit current contributions from small low voltage motors (motor
sizes smaller than 100 hp or kW) on the one-line diagram.
13.4.2 AC Page
This page includes options for displaying info annotations for AC elements.
Color
Select the color for information annotations to be displayed on the one-line diagram.
ID
Select the check boxes under this heading to display the ID of the selected AC elements on the one-line
diagram.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
Rating
Select the check boxes under this heading to display the ratings of the selected AC elements on the oneline diagram.
Device Type
Gen. (Generator)
Power Grid (Utility)
Motor
Load
Panel
Transformer
Branch, Impedance
Branch, Reactor
Cable / Line
Bus
Node
CB
Fuse
Relay
PT & CT
Rating
kW / MW
MVAsc
HP / kW
kVA / MVA
Connection Type (# of Phases - # of Wires)
kVA / MVA
Base MVA
Continuous Amps
# of Cables - # of Conductor / Cable - Size
kA Bracing
Bus Bracing (kA)
Rated Interrupting (kA)
Interrupting (ka)
50/51 for Overcurrent Relays
Transformer Rated Turn Ratio
kV
Select the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.
For cables/lines, the kV check box is replaced by the
cable/line conductor type on the one-line diagram.
button. Click on this button to display the
A
Select the check boxes under this heading to display the ampere ratings (continuous or full-load ampere)
of the selected elements on the one-line diagram.
For cables/lines, the Amp check box is replaced by the
cable/line length on the one-line diagram.
button. Click on this button to display the
Z
Select the check boxes under this heading to display the rated impedance of the selected AC elements on
the one-line diagram.
Device Type
Generator
Power Grid (Utility)
Motor
Transformer
Branch, Impedance
Branch, Reactor
Cable / Line
Operation Technology, Inc.
Impedance
Subtransient reactance Xd”
Positive Sequence Impedance in % of 100 MVA (R + j X)
% LRC
Positive Sequence Impedance (R + j X per unit length)
Impedance in ohms or %
Impedance in ohms
Positive Sequence Impedance (R + j X in ohms or per unit length)
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
D-Y
Select the check boxes under this heading to display the connection types of the selected elements on the
one-line diagram.
For transformers, the operating tap settings for primary, secondary, and tertiary windings are also
displayed. The operating tap setting consists of the fixed taps plus the tap position of the LTC.
Composite Motor
Click on this check box to display the AC composite motor IDs on the one-line diagram, then select the
color in which the IDs will be displayed.
Use Default Options
Click on this check box to use PowerStation’s default display options.
13.4.3 AC-DC Page
This page includes options for displaying info annotations for AC-DC elements and composite networks.
Color
Select the color for information annotations to be displayed on the one-line diagram.
ID
Select the check boxes under this heading to display the IDs of the selected AC-DC elements on the oneline diagram.
Rating
Select the check boxes under this heading to display the ratings of the selected AC-DC elements on the
one-line diagram.
Device Type
Charger
Inverter
UPS
VFD
Rating
AC kVA & DC kW (or MVA / MW)
DC kW & AC kVA (or MW / MVA)
kVA
HP / kW
kV
Click on the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.
A
Click on the check boxes under this heading to display the ampere ratings of the selected elements on the
one-line diagram.
Device Type
Charger
Inverter
UPS
Operation Technology, Inc.
Amp
AC FLA & DC FLA
DC FLA & AC FLA
Input, output, & DC FLA
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
Composite Network
Click on this check box to display the composite network IDs on the one-line diagram, then select the
color in which the IDs will be displayed.
Use Default Options
Click on this check box to use PowerStation’s default display options.
13.4.4 DC Page
Color
Select the color for information annotations to be displayed on the one-line diagram.
ID
Select the check boxes under this heading to display the IDs of the selected DC elements on the one-line
diagram.
Rating
Select the check boxes under this heading to display the ratings of the selected DC elements on the oneline diagram.
Device Type
Battery
Motor
Load
Elementary Diagram
Converter
Cable
Rating
Ampere Hour
HP / kW
kW / MW
kW / MW
kW / MW
# of Cables - # of Conductor / Cable - Size
kV
Select the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.
For cables, the kV check box is replaced by the
type on the one-line diagram.
button. Click on this button to display the conductor
A
Select the check boxes under this heading to display the ampere ratings of the selected elements on the
one-line diagram.
For cables, the Amp check box is replaced by the
length (one way) on the one-line diagram.
button. Click on this button to display the cable
Z
Select the check boxes under this heading to display the impedance values of the cables and impedance
branches on the one-line diagram.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Display Options
Composite Motor
Click on this check box to display the DC composite motor IDs on the one-line diagram, then select the
color in which the IDs will be displayed.
Use Default Options
Click on this check box to use PowerStation’s default display options.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
13.5 ANSI/IEEE Calculation Methods
PowerStation provides two short-circuit calculation methods based on ANSI/IEEE and IEC standards.
You can select the calculation method from the Short-Circuit Study Case Editor. This section describes
the ANSI/IEEE standard method of calculation.
Standard Compliance
PowerStation short-circuit calculation per ANSI/IEEE standards fully complies with the latest
ANSI/IEEE and UL standards, as listed below:
Standard
IEEE C37.04
IEEE C37.04f
IEEE C37.04g
IEEE C37.04h
IEEE C37.04i
IEEE C37.010
IEEE C37.010b
IEEE C37.010e
IEEE C37.013
Pub. Year
1979 (1988)
1990
1986
1990
1991
1979 (1988)
1985
1985
1997
IEEE C37.20.1
1993
IEEE Std 399
IEEE Std 141
IEEE Std 242
1990
1986
1986
UL 489_9
1996
Title
Standard Rating Structure for AC High-Voltage Circuit Breakers
Rated on a Symmetrical Current Basis and Supplements
Standard Application Guide for AC High-Voltage Circuit
Breakers Rated on a Symmetrical Current Basis and Supplements
Standard for AC High-Voltage Generator Circuit Breakers Rated
on a Symmetrical Current Basis
Standard for Metal Enclosed Low-Voltage Power Circuit Breaker
Switchgear
Power System Analysis -- the Brown Book
Electric Power Distribution for Industrial Plants -- the Red Book
IEEE Recommended Practice for Protection and Coordination of
Industrial and Commercial Power Systems – the Buff Book
Standard for Safety for Molded-Case Circuit Breakers, MoldedCase Switches, and Circuit-Breaker Enclosures
General Description of Calculation Methodology
In ANSI/IEEE short-circuit calculations, an equivalent voltage source at the fault location, which equals
the prefault voltage at the location, replaces all external voltage sources and machine internal voltage
sources.
All machines are represented by their internal impedances. Line capacitances and static loads are
neglected. Transformer taps can be set at either the nominal position or at the tapped position, and
different schemes are available to correct transformer impedance and system voltages if off-nominal tap
setting exists. It is assumed the fault is bolted, therefore, arc resistances are not considered. System
impedances are assumed to be balanced three-phase, and the method of symmetrical components is used
for unbalanced fault calculations.
Three different impedance networks are formed to calculate momentary, interrupting, and steady-state
short-circuit currents, and corresponding duties for various protective devices. These networks are: ½
cycle network (subtransient network), 1.5-4 cycle network (transient network), and 30-cycle network
(steady-state network).
ANSI/IEEE Standards recommend the use of separate R and X networks to calculate X/R values. An X/R
ratio is obtained for each individual faulted bus and short-circuit current. This X/R ratio is then used to
determine the multiplying factor to account for the system DC offset.
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
Using the ½ cycle and 1.5-4 cycle networks, the symmetrical rms value of the momentary and
interrupting short-circuit currents are solved first. These values are then multiplied by appropriate
multiplying factors to finally obtain the asymmetrical value of the momentary and interrupting shortcircuit currents.
Definition of Terms
The following terms are helpful in understanding short-circuit calculations using ANSI/IEEE standards.
½ Cycle Network
This is the network used to calculate momentary short-circuit current and protective device duties at the ½
cycle after the fault. The following table shows the type of device and its associated duties using the ½
cycle network.
Type of Device
Duty
High voltage circuit breaker
Closing and latching capability
Low voltage circuit breaker
Interrupting capability
Fuse
Interrupting capability
Switchgear and MCC
Bus bracing
Relay
Instantaneous settings
½ Cycle Network Duty
The ½ cycle network is also referred to as the subtransient network, primarily because all rotating
machines are represented by their subtransient reactances, as shown in the following table:
Type of Machine
Utility
Turbo generator
Hydro-generator with amortisseur winding
Hydro-generator without amortisseur winding
Condenser
Synchronous motor
Induction Machine
> 1000 hp @ 1800 rpm or less
> 250 hp @ 3600 rpm
All other > 50 hp
< 50 hp
½ Cycle Network Impedance
Xsc
X”
Xd”
Xd”
0.75 Xd’
Xd”
Xd ”
Xd ”
Xd ”
1.2 Xd”
1.67 Xd”
(Xd” = 1/LRC for induction motors)
1.5-4 Cycle Network
This network is used to calculate the interrupting short-circuit current and protective device duties 1.5-4
cycles after the fault. The following table shows the type of device and its associated duties using the 1.54 cycle network.
Type of Device
Duty
High voltage circuit breaker
Interrupting capability
Low voltage circuit breaker
N/A
Fuse
N/A
Switchgear and MCC
N/A
Relay
N/A
1.5-4 Cycle Network Duty
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
The 1.5-4 cycle network is also referred to as the transient network. The type of rotating machine and its
representation is shown in the following table:
Type of Machine
Xsc
Utility
X”
Turbo generator
Xd”
Hydro-generator with amortisseur winding
Xd”
Hydro-generator without amortisseur winding
0.75 Xd’
Condenser
Xd”
Synchronous motor
1.5 Xd”
Induction machine
> 1000 hp @ 1800 rpm or less
1.5 Xd”
> 250 hp @ 3600 rpm
1.5 Xd”
All other > 50 hp
3.0 Xd”
< 50 hp
Infinity
1.5-4 Cycle Network Impedances
(Xd” = 1/LRC for induction motors)
30-Cycle Network
This is the network used to calculate the steady-state short-circuit current and duties for some of the
protective devices 30 cycles after the fault. The following table shows the type of device and its
associated duties using the 1.5-4 cycle network:
Type of Device
Duty
High voltage circuit breaker
N/A
Low voltage circuit breaker
N/A
Fuse
N/A
Switchgear and MCC
N/A
Relay
Overcurrent settings
30-Cycle Network Duty
The type of rotating machine and its representation in the 30-cycle network is shown in the following
table. Note that induction machines, synchronous motors, and condensers are not considered in the 30cycle fault calculation.
Type of Machine
Utility
Turbo generator
Hydro-generator with amortisseur winding
Hydro-generator without amortisseur winding
Condenser
Synchronous motor
Induction machine
30-Cycle Network Impedance
Operation Technology, Inc.
13-27
Xsc
X”
Xd’
Xd’
Xd’
Infinity
Infinity
Infinity
ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
13.5.1 ANSI Multiplying Factor (MF)
The ANSI multiplying factor is determined by the equivalent system X/R ratio at a particular fault
location. The X/R ratio is calculated by the separate R and X networks.
Local and Remote Contributions
A local contribution to a short-circuit current is the portion of the short-circuit current fed predominately
from generators through no more than one transformation, or with external reactance in a series which is
less than 1.5 times the generator subtransient reactance. Otherwise the contribution is defined as remote.
No AC Decay (NACD) Ratio
The NACD ratio is defined as the remote contributions to the total contributions for the short-circuit
current at a given location.
NACD =
•
•
•
I remote
Itotal
Total short-circuit current Itotal = Iremote + Ilocal
NACD = 0 if all contributions are local.
NACD = 1 if all contributions are remote.
13.5.2 Calculation Methods
Momentary (1/2 Cycle) Short-Circuit Current Calc. (Buses & HV CB)
The momentary short-circuit current at the ½ cycle represents the highest or maximum value of the shortcircuit current (before its ac and dc components decay toward the steady-state value). Although, in
reality, the highest or maximum short-circuit current actually occurs slightly before the ½ cycle, the ½
cycle network is used for this calculation.
The following procedure is used to calculate momentary short-circuit current:
1) Calculate the symmetrical rms value of momentary short-circuit current using the following formula:
V
I mom,rms,symm = pre− fault
3Zeq
where Zeq is the equivalent impedance at the faulted bus from the ½ cycle network.
2) Calculate the asymmetrical rms value of momentary short-circuit current using the following formula:
I mom,rms ,asymm = MFm I mom,rms ,symm
where MFm is the momentary multiplying factor, calculated from
MFm = 1 + 2e
Operation Technology, Inc.
−
2π
X /R
13-28
ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
3) Calculate the peak value of momentary short-circuit current using the following formula:
I mom, peak = MFp I mom,rms ,symm
where MFp is the peak multiplying factor, calculated from
π


−
MFp = 2  1 + e X / R 


This value is the calculated Asymmetrical kA Crest printed in the Momentary Duty column of the
Momentary Duty page in the output report.
In both equations for MFm and MFp calculation, X/R is the ratio of X to R at the fault location obtained
from separate X and R networks at ½ cycle. The value of the fault current calculated by this method can
be used for the following purposes:
•
•
•
•
Check closing and latching capabilities of high voltage circuit breakers
Check bus bracing capabilities
Adjust relay instantaneous settings
Check interrupting capabilities of fuses and low voltage circuit breakers
High Voltage Circuit Breaker Interrupting Duty Calculation
The interrupting fault currents for high voltage circuit breakers correspond to the 1.5-4 cycle short-circuit
currents, i.e., the 1.5-4 cycle network is used for this calculation.
The following procedure is used to calculate the interrupting short-circuit current for high voltage circuit
breakers:
1) Calculate the symmetrical rms value of the interrupting short-circuit current using the following
formula:
V −
I int,rms,symm = pre fault
3Zeq
where Zeq is the equivalent impedance at the faulted bus from the 1.5-4 cycle network.
2) Calculate the short-circuit current contributions to the fault location from the surrounding buses.
3) If the contribution is from a Remote bus, the symmetrical value is corrected by the factor of MFr,
calculated from
MFr = 1 + 2e
−
4π
t
X /R
where t is the circuit breaker contact parting time in cycles, as given in the following table:
Circuit Breaker
Rating in Cycles
8
5
3
2
Operation Technology, Inc.
Contact Parting
Time in Cycles
4
3
2
1.5
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
The following table shows the Multiplying Factors for Remote Contributions (MFr).
8 Cycle CB
(4 cy CPT)
1.487
1.464
1.438
1.405
1.366
5 Cycle CB
(3 cy CPT)
1.540
1.522
1.499
1.472
1.438
3 Cycle CB
(2 cy CPT)
1.599
1.585
1.569
1.548
1.522
2 Cycle CB
(1.5 cy CPT)
1.63
1.619
1.606
1.59
1.569
50
45
40
35
30
1.316
1.286
1.253
1.215
1.172
1.393
1.366
1.334
1.297
1.253
1.487
1.464
1.438
1.405
1.366
1.54
1.255
1.499
1.472
1.438
25
20
18
16
14
1.126
1.078
1.059
1.042
1.027
1.201
1.142
1.116
1.091
1.066
1.316
1.253
1.223
1.190
1.154
1.393
1.334
1.305
1.271
1.233
12
10
9
8
7
1.015
1.007
1.004
1.002
1.001
1.042
1.023
1.015
1.009
1.005
1.116
1.078
1.059
1.042
1.027
1.190
1.142
1.116
1.091
1.066
6
5
4
3
2
1
1.000
1.000
1.000
1.000
1.000
1.000
1.002
1.00.
1.000
1.000
1.000
1.000
1.015
1.007
1.002
1.000
1.000
1.000
1.042
1.023
1.009
1.002
1.000
1.000
X/R Ratio
100
90
80
70
60
MFr Remote Contributions Multiplying Factors; Total Current Basis CBs
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
If the contribution is from a Local generator, the symmetrical value is corrected by the factor of MFl,
which is obtained from: ANSI/IEEE C37.010, Application Guide for AC High-Voltage.
8 Cycle CB
(4 cy CPT)
1.252
1.239
1.222
1.201
1.175
5 Cycle CB
(3 cy CPT)
1.351
1.340
1.324
1.304
1.276
3 Cycle CB
(2 cy CPT)
1.443
1.441
1.435
1.422
1.403
2 Cycle CB
(1.5 cy CPT)
1.512
1.511
1.508
1.504
1.496
50
45
40
35
30
1.141
1.121
1.098
1.072
1.044
1.241
1.220
1.196
1.169
1.136
1.376
1.358
1.337
1.313
1.283
1.482
1.473
1.461
1.446
1.427
25
20
18
16
14
1.013
1.000
1.000
1.000
1.000
1.099
1.057
1.039
1.021
1.003
1.247
1.201
1.180
1.155
1.129
1.403
1.371
1.356
1.339
1.320
12
10
9
8
7
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.099
1.067
1.051
1.035
1.019
1.299
1.276
1.263
1.250
1.236
X/R Ratio
100
90
80
70
60
6
1.000
1.000
1.005
1.221
5
1.000
1.000
1.000
1.205
4
1.000
1.000
1.000
1.188
3
1.000
1.000
1.000
1.170
2
1.000
1.000
1.000
1.152
1
1.000
1.000
1.000
1.132
MFl Local Contributions Multiplying Factors; Total Current Basis CBs
4) Calculate the total remote contributions and total local contribution, and thus the NACD ratio.
5) Determine the actual multiplying factor (AMFi) from the NACD ratio and calculate the adjusted rms
value of interrupting short-circuit current using the following formula.
where
Iint,rms,adj = AMFi Iint,rms,symm
AMFi = MFl + NACD (MFr – MFl)
Operation Technology, Inc.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
6) For symmetrically rated breakers, the adjusted rms value of interrupting short-circuit current is
calculated using the following formula.
AMF i Iint,rms,symm
Iint,rms,adj =
S
where the correction factor S reflects an inherent capability of ac high voltage circuit breakers,
which are rated on a symmetrical current basis, and its values are found in the following table.
Circuit Breaker
Contact Parting Time S Factor
4
1.0
3
1.1
2
1.2
1.5
1.3
S Factor for AC High Voltage Circuit Breaker
Rated on a Symmetrical Current Basis
The value of this current is applied to check high voltage circuit breaker interrupting capabilities.
The correction factor S is equal to 1.0 for ac high voltage circuit breakers rated on a total current
basis.
Low Voltage Circuit Breaker Interrupting Duty Calculation
Due to the instantaneous action of low voltage circuit breakers at maximum short-circuit values, the ½
cycle network is used for calculating the interrupting short-circuit current.
The following procedure is used to calculate the interrupting short-circuit current for low voltage circuit
breakers:
1) Calculate the symmetrical rms value of the interrupting short-circuit current from the following
formula.
V −
I int,rms,symm = pre fault
3Zeq
where Zeq is the equivalent impedance at the faulted bus from the ½ cycle network.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
2) Calculate the adjusted asymmetrical rms value of the interrupting short-circuit current duty using the
following formula:
I int,rms,adj = MF I int,rms,symm
where MF is the multiplying factor, considering the system X/R ratio and the low voltage circuit
breaker testing power factors, calculated from
MF =
2 (1 + e
2 (1 + e
−
−
π
X /R )
π
( X / R ) test
)
for unfused power breakers
or
MF =
1 + 2e
1 + 2e
−
−
2π
X /R
2π
( X / R )test
for fused power breakers and molded cases
where (X/R)test is calculated based on the test power factor entered from the Low Voltage Circuit
Breaker Editor. The manufacturer maximum testing power factors given in the following table are
used as the default values:
Max Design (Tested)
Circuit Breaker Type
% PF
(X/R)test
Power Breaker (Unfused)
15
6.59
Power Breaker (Fused)
20
4.90
Molded Case (Rated Over 20,000 A)
20
4.90
Molded Case (Rated 10,001-20,000 A)
30
3.18
Molded Case (Rated 10,000 A)
50
1.73
Maximum Test PF for Low Voltage Circuit Breaker
The calculated duty value Iint,rms,adj can be applied to low voltage breaker interrupting capabilities.
Note that if the calculated multiplication factor is less than 1, it is set to 1 so that the symmetrical fault
current is compared against the symmetrical rating of the device. If the symmetrical fault current is less
than the symmetrical rating of the device, the checking on asymmetrical current will certainly pass.
Fuse Interrupting Short-Circuit Current Calculation
The procedures for calculating the fuse interrupting short-circuit current is the same as those for the
Circuit Breaker Interrupting Duty calculation.
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ETAP PowerStation 4.0
Short-Circuit Analysis
ANSI/IEEE Calculation Methods
Comparison of Device Rating and Short-Circuit Duty
ETAP PowerStation compares the rating of protective devices and busbars with the fault duties of the bus.
The comparison results are listed in the summary page of the output report. The device rating and fault
duty used in the comparison are shown below.
Device Type
Device Capability
Calculated
Short-Circuit Duty
Momentary Duty
HV Bus Bracing
LV Bus Bracing
HV CB
Asymm. KA rms
Asymm. KA rms
Asymm. KA Crest
Asymm. KA Crest
Symm. KA rms
Symm. KA rms
Asymm. KA rms
Asymm. KA rms
C&L Capability kA rms
Asymm. KA rms
C&L Capability kA Crest
Asymm. KA Crest
Interrupting kA***
Adjusted kA
Momentary Duty
HV CB
LV CB
Rated Interrupting kA
Adjusted kA
Comparison of Device Rating and Short-Circuit Current Duty
***The interrupting capability of a high voltage circuit breaker is calculated based on the nominal kV of
the connected bus and the prefault voltage (Vf ) if the flag is set in the Short-Circuit Study Case, as shown
below.
Interrupting kA = (Rated Int. kA) * (Rated Max. kV) / (Bus Nominal kV)
or
Interrupting kA = (Rated Int. kA) * (Rated Max. kV) / (Bus Nominal kV * Vf )
The calculated interrupting kA (as shown above) is then limited to the maximum interrupting kA of the
circuit breaker.
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Calculation Methods
13.6 IEC Calculation Methods
PowerStation provides two short-circuit calculation methods based on ANSI/IEEE and IEC standards.
You can select the calculation method from the Short-Circuit Study Case Editor. This section describes
the IEC standard method of calculation.
Standard Compliance
PowerStation short-circuit calculation per IEC standards fully complies with the latest IEC documentation
as listed below:
Standard
IEC 56
IEC 282-1
IEC 61363
Pub. Year
1978
1985
1998
IEC 781
1989
IEC 909-1
IEC 909-2
1991
1988
IEC 947-1
IEC 947-2
1988
1989
Title
High voltage alternating-current circuit-breakers
Fuses for voltages exceeding 1000 V ac
Electrical Installations of Ships and Mobile and Fixed Offshore
Units
Application guide for calculation of short-circuit currents in low
voltage radial systems
Short-circuit calculation in three-phase ac systems
Electrical equipment - data for short-circuit current calculations in
accordance with IEC 909
Low voltage switchgear and controlgear, Part 1: General rules
Low voltage switchgear and controlgear, Part 2: Circuit-breakers
These standards are for short-circuit calculation and equipment rating in ac systems with nominal voltages
up to 240 kV and operating at 50 Hz or 60 Hz. They cover three-phase, line-to-ground, line-to-line, and
line-to-line-to-ground faults.
IEC 909 and the associated standards classify short-circuit currents according to their magnitudes
(maximum and minimum) and fault distances from the generator (far and near). Maximum short-circuit
currents determine equipment ratings, while minimum currents dictate protective device settings. Nearto-generator and far-from-generator classifications determine whether or not to model the ac component
decay in the calculation, respectively.
IEC 61363 Standard calculates the short-circuit current as a function of time and displays its
instantaneous values using the machine’s subtransient reactance and time constants. This provides an
accurate evaluation of the short-circuit current for sizing protective devices and coordinating relays for
isolated systems such as ships and off-shore platforms.
General Description of Calculation Methodology
In IEC short-circuit calculations, an equivalent voltage source at the fault location replaces all voltage
sources. A voltage factor c is applied to adjust the value of the equivalent voltage source for minimum
and maximum current calculations.
All machines are represented by their internal impedances. Line capacitances and static loads are
neglected, except for those of the zero-sequence system. Regulator and transformer taps are assumed to
be in the main position, and arc resistances are not considered. System impedances are assumed to be
balanced three-phase, and the method of symmetrical components is used for unbalanced fault
calculations. Calculations consider electrical distance from the fault location to synchronous generators.
For a far-from-generator fault, calculations assume that the steady-state value of the short-circuit current
is equal to the initial symmetrical short-circuit current.
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Short-Circuit Analysis
IEC Calculation Methods
Only the dc component decays to zero, whereas for a near-to-generator fault, calculations count for both
decaying ac and dc components. The equivalent R/X ratios determine the rates of decay of both
components, and different values are recommended for generators and motors near the fault.
Calculations also differ for meshed and unmeshed networks. The factor k, which is used to multiply the
initial short-circuit current to get the peak short-circuit current ip, is defined differently for different
system configurations and the methods selected to calculate the R/X ratios.
Definition of Terms
IEC standards use the following definitions, which are relevant in the calculations and outputs of
PowerStation.
Initial Symmetrical Short-Circuit Current (I”k)
This is the rms value of the ac symmetrical component of an available short-circuit current applicable at
the instant of short-circuit if the impedance remains at zero time value.
Peak Short-Circuit Current (ip)
This is the maximum possible instantaneous value of the available short-circuit current.
Symmetrical Short-Circuit Breaking Current (Ib)
This is the rms value of an integral cycle of the symmetrical ac component of the available short-circuit
current at the instant of contact separation of the first pole of a switching device.
Steady-State Short-Circuit Current (Ik)
This is the rms value of the short-circuit current which remains after the decay of the transient
phenomena.
Subtransient Voltage (E”) of a Synchronous Machine
This is the rms value of the symmetrical internal voltage of a synchronous machine which is active behind
the subtransient reactance Xd” at the moment of short-circuit.
Far-From-Generator Short-Circuit
This is a short-circuit condition during which the magnitude of the symmetrical ac component of
available short-circuit current remains essentially constant.
Near-To-Generator Short-Circuit
This is a short-circuit condition to which at least one synchronous machine contributes a prospective
initial short-circuit current which is more than twice the generator’s rated current, or a short-circuit
condition to which synchronous and asynchronous motors contribute more than 5% of the initial
symmetrical short-circuit current (I”k) without motors.
Subtransient Reactance (Xd”) of a Synchronous Machine
This is the effective reactance at the moment of short-circuit. For the calculation of short-circuit currents,
the saturated value of (Xd”) is taken.
According to IEC Standard 909, the synchronous motor impedance used in IEC short-circuit calculations
is calculated in the same way as the synchronous generator.
ZK = KG(R+ Xd”)
kVn
cmax
KG =
kVr 1+x”d sinφr
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Calculation Methods
Where kVn and kVr are the nominal voltage of the terminal bus and the motor rated voltage respectively,
cmax is determined based on machine rated voltage, xd” is machine subtransient reactance (per unit in
motor base), and qr is the machine rated power factor angle.
Minimum Time Delay (Tmin) of a Circuit Breaker
This is the shortest time between the beginning of the short-circuit current and the first contact separation
of one pole of the switching device.
Note that the time delay (Tmin) is the sum of the shortest possible operating time of an instantaneous relay
and the shortest opening time of a circuit breaker. Minimum time delay does not include the adjustable
time delays of tripping devices.
Voltage Factor c
This is the factor used to adjust the value of the equivalent voltage source for minimum and maximum
current calculations according to the following table:
Voltage Factor c
For Maximum Short-Circuit
Current Calculation
For Minimum Short-Circuit
Current Calculation
cmax
cmin
1.00
1.05
1.10
1.10
0.95
1.00
1.00
1.00
Nominal Voltage Un
Low voltage: 100 V to 1000 V
230 V / 400 V
Other voltages
Medium voltage: > 1 kV to 35 kV
High voltage: > 35 kV to 230 kV
The cmax values given in the above table are used as default values in calculations and the user can set
these values from the Short-Circuit Study Case.
Calculation Methods
Initial Symmetrical Short-Circuit Current Calculation
Initial symmetrical short-circuit current (I”k) is calculated using the following formula:
I"k =
cU n
3Z k
where Zk is the equivalent impedance at the fault location.
Peak Short-Circuit Current Calculation
Peak short-circuit current (ip) is calculated using the following formula:
i p = 2 kI " k
where k is a function of the system R/X ratio at the fault location.
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Short-Circuit Analysis
IEC Calculation Methods
IEC standards provide three methods for calculating the k factor:
•
Method A - Uniform ratio R/X. The value of the k factor is determined from taking the smallest ratio
of R/X of all the branches of the network. Only branches that contain a total of 80 percent of the
current at the nominal voltage corresponding to the short-circuit location are included. Branches may
be a series combination of several elements.
•
Method B - R/X ratio at the short-circuit location. The value of the k factor is determined by
multiplying the k factor by a safety factor of 1.15, which covers inaccuracies caused after obtaining
the R/X ratio from a network reduction with complex impedances.
•
Method C - Equivalent frequency. The value of the k factor is calculated using a frequency-altered
R/X. R/X is calculated at a lower frequency and then multiplied by a frequency-dependent
multiplying factor.
Symmetrical Short-Circuit Breaking Current Calculation
For a far-from-generator fault, the symmetrical short-circuit breaking current (Ib) is equal to the initial
symmetrical short-circuit current.
Ib = I "k
For a near-to-generator fault, Ib is obtained by combining contributions from each individual machine. Ib
for different types of machines is calculated using the following formula:
 µI " k
Ib = 
µqI " k
for synchronous machines
for asynchronous machines
where µ and q are factors that account for ac decay. They are functions of the ratio of the minimum time
delay and the ratio of the machine’s initial short-circuit current to its rated current, as well as real power
per pair of poles of asynchronous machines.
IEC standards allow you to include or exclude ac decay effect from asynchronous machines in the
calculation.
DC Component of Short-Circuit Current Calculation
The dc component of the short-circuit current for the minimum delay time of a protective device is
calculated based on initial symmetrical short-circuit current and system X/R ratio:
"
 2πft min 
I dc = I k 2exp −

 X /R 
where f is the system frequency, tmin is the minimum delay time of the protective device under concern,
and X/R is the system value at the faulted bus.
Asymmetrical Short-Circuit Breaking Current Calculation
The asymmetrical short-circuit breaking current for comparison with circuit breaker rating is calculated as
the rms value of symmetrical and dc components of the short circuit current. For fuses, it is the sum of
asymmetrical currents from all first level contribution branches.
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Short-Circuit Analysis
IEC Calculation Methods
Steady-State Short-Circuit Current Calculation
Steady-state short-circuit current Ik is a combination of contributions from synchronous generators. Ik for
each synchronous generator is calculated using the following formula:
I k max = λmax I rG
I k min = λ min I rG
where λ is a function of a generator’s excitation voltage, ratio between its initial symmetrical short-circuit
current and rated current, and other generator parameters, and IrG is the generator’s rated current.
The maximum steady-state current reflects maximum modeling inaccuracies. This value is used to
determine minimum device ratings. The minimum steady-state current reflects minimum modeling
inaccuracies. This value is used for relay coordination purposes in preventing the occurrence of nuisance
trips and loading deviations.
Comparison of Device Rating and Short-Circuit Duty
In the Three-Phase Device Duty calculation, PowerStation compares the protective device rating against
bus short-current duty for the devices that are checked as complying with IEC standard and also have
device rating entered. In case the short-circuit duty is greater than the device duty, PowerStation will flag
the device as underrated in both one-line diagram and output reports. The following table lists the device
ratings and short-circuit duties used for the comparison for MV CB, LV CB, and fuses:
Device Type
MV CB
LV CB
Device Capability
Making
AC Breaking
Ib,asymm *
Idc *
Making
Breaking
Ib,asymm *
SC Current Duty
ip
Ib,symm
Ib, asymm
Ip
Ib,symm
Ib,asymm
Fuse
Breaking
Ib,asymm
Ib,asymm *
Ib,symm
Comparison of Device Rating and Short-Current Duty
*Device capability calculated by PowerStation.
Transient Short-Circuit Calculation
In additional to device duty calculations, PowerStation also provides transient short-circuit calculation per
IEC standard 61363-1. The transient short-circuit calculation presents fault current waveforms as a
function of time, considering a number of factors that affect short-circuit current variations at different
time after the fault. These factors include synchronous machine subtransient reactance, transient
reactance, reactance, subtransient time constant, transient time constant, and dc time constant. It also
considers decay of short-circuit contributions from induction motors. This detailed modeling provides an
accurate evaluation of the short-circuit current for sizing protective devices and coordinating relays for
isolated systems such as ships and off-shore platforms. The calculation can be conducted on both radial
and looped system with one or multiply sources.
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ETAP PowerStation 4.0
Short-Circuit Analysis
IEC Calculation Methods
As calculation results, PowerStation provides short-circuit current as function of time up to 0.1 second at
0.001 second time increment. It also presents short-circuit current as function of cycles up to 1 cycle at
0.1 cycle increment. Along with the instantaneous current values, PowerStation also furnish calculated
AC component, DC component, as well as top envelope of the current waveform. In the summary page,
it also provides the subtransient, transient, and steady state fault current for each bus.
Calculation of IEC Device Capability
As shown in the above table, some of the device capability values are calculated by PowerStation based
on capability provided by users and default parameters given in IEC standards.
•
MV CB – The asymmetrical breaking and dc current ratings for MV CB are calculated as follows,
 4πft min 
I b,asymm = I b,symm 1 + 2 ∗ exp −

 X /R 
 2πft min 
I dc = I b,symm 2exp −

 X /R 
Where f is the system frequency, tmin is the minimum delay time, and Ib,symm is the AC breaking current
provided by the user. Following IEC Standard 56, Figure 9, X/R is calculated based on a testing PF
of 7% at 50Hz.
•
LV CB – The asymmetrical breaking current rating for LV CB is calculated as follows:
 4πft min 
I b,asymm = I b,symm 1 + 2 ∗ exp −

 X /R 
Where f is the system frequency, tmin is the minimum delay time, and Ib,symm is the breaking current
provided by the user. X/R is calculated based on a testing PF given in IEC Standard 947-2, Table XI.
•
Fuse – The asymmetrical breaking current rating for fuse is calculated as follows:
 4πft min 
I b,asymm = I b,symm 1 + 2 ∗ exp −

 X /R 
Where f is the system frequency, tmin is assumed to be a half cycle, and Ib,symm is the breaking current
provided by the user. X/R is calculated based on the default testing PFof 15 %.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Arc Flash Analysis Method
13.7 Arc Flash Analysis Method
The ETAP Arc Flash analysis estimates the arc flash incident energy under a three-phase short-circuit
fault and determines the flash protective boundary to live parts for shock protection based on NFPA 70E2000. The flash protection boundary is the distance a worker not wearing flame-resistant personal
protective equipment (PPE) must stay away from a job site involving a possible hazardous arc flash. The
Arc Flash analysis is conducted in the ANSI/IEEE or IEC Device Duty calculations. You can select to
conduct the Arc Flash analysis from the Short-Circuit Study Case Editor.
The ETAP Arc Flash analysis has the following program features:
•
•
•
•
•
•
•
Report a table of arc flash analysis for every faulted bus.
Compute bolted short circuit current for every faulted bus.
Determine a flash protection boundary as a function of arc duration.
Determine incident energy exposure (Calorie/cm2) as a function of distance for a given duration.
Determine incident energy exposure (Calorie /cm2) as a function of arc duration for a given distance.
Compute incident energy exposure (Calorie /cm2) in open air.
Compute incident energy exposure (Calorie /cm2) in a cubic box.
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ETAP PowerStation 4.0
Short-Circuit Analysis
AC-DC Converter Models
13.8 AC-DC Converter Models
Charger & UPS
In the current version of ETAP PowerStation, when performing AC analyses, chargers and UPSs are
considered as loads to their input AC buses. The rectifiers in these elements block the current from
flowing back into the AC system. Therefore, chargers and UPSs are not included in an AC short-circuit
analysis.
Inverter
An inverter is a voltage source to the AC system. Under fault conditions, it will provide fault
contribution to the AC system. When its terminal bus is faulted, the contribution from an inverter is equal
to the multiplication of its AC full load amp by a constant K, which is entered form the Rating page of the
Inverter Editor. This is the maximum possible contribution from the inverter. As the fault location
moves away from its terminal bus, the contribution from the inverter decreases.
Variable Frequency Drive (VFD)
A VFD can only be inserted between a motor and its terminal bus. In the Rating page of the VFD Editor,
there is a check box for bypass switch. If this box is not checked, there will be no contribution from the
motor connected to the VFD, due to the fact that the rectifiers in VFD block the current from flowing
back into the system. If this box is checked, it is assumed that the switch is closed as soon as a fault
occurs in the system; hence the motor will make contributions to the fault as if the VFD is not present.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Required Data
13.9 Required Data
Bus Data
Required data for short-circuit calculation for buses includes:
•
•
•
Nominal kV (when the prefault voltage option is set to use nominal kV)
%V (when the prefault voltage option is set to use bus voltage)
Type, such as MCC, switchgear, etc., and continuous and bracing ratings
Branch Data
Branch data is entered into the Branch editors, i.e., 3-Winding Transformer Editor, 2-Winding
Transformer Editor, Transmission Line Editor, Cable Editor, Reactor Editor, and Impedance Editor.
Required data for short-circuit calculations for branches includes:
•
•
•
•
Branch Z, R, X, or X/R values and units, tolerance, and temperatures, if applicable
Cable and transmission line length and unit
Transformer rated kV and MVA
Base kV and MVA of impedance branches
For unbalanced short-circuit calculations you will also need:
•
•
Zero
sequence impedances
Transformer winding connections, grounding types, and grounding parameters
Power Grid Data
Required data for short-circuit calculations for utilities includes:
•
•
•
Nominal kV
%V and Angle
3-Phase MVAsc and X/R
For unbalanced short-circuit calculations, you will also need:
•
•
Grounding types and parameters
Single-Phase MVAsc and X/R
Synchronous Generator Data
Required data for short-circuit calculations for synchronous generators includes:
•
•
•
•
Rated MW, kV, and power factor
Xd”, Xd’, and X/R
Generator type
IEC exciter type
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ETAP PowerStation 4.0
Short-Circuit Analysis
Required Data
For unbalanced short-circuit calculations, you will also need:
•
•
Grounding types and parameters
X0
Inverter Data
Required data for short-circuit calculations for inverters includes:
•
•
Rated MW, kV, and power factor
K factor in the Rating page
Synchronous Motor Data
Required data for short-circuit calculations for synchronous motor includes:
•
•
•
Rated kW/hp and kV, and the number of poles
Xd” and X/R
% LRC, Xd, and Tdo’ for IEC short-circuit calculation
For unbalanced short-circuit calculations, you will also need:
•
•
Grounding types and parameters
X0
Induction Motor Data
Required data for short-circuit calculations for induction motors includes:
•
•
Rated kW/hp and kV
X/R plus one of the following:
Xsc at ½ cycle and 1.5-4 cycle if ANSI Short-Circuit Z option is set to Xsc, or
%LRC if ANSI Short-Circuit Z option is set to Std MF
% LRC, Xd, and Td’ for IEC short-circuit calculations
For unbalanced short-circuit calculations, you will also need:
•
•
Grounding types and parameters
X0
Lumped Load Data
Required data for short-circuit calculations for lumped load includes:
•
•
•
•
Rated MVA and kV
% motor load
% LRC, X/R, and Xsc for ½ cycle and 1.5-4 cycle
X’, X, and Td’ for IEC short-circuit calculation
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ETAP PowerStation 4.0
Short-Circuit Analysis
Required Data
Additional data for unbalanced short-circuit calculations includes:
•
Grounding types and parameters
High Voltage Circuit Breaker Data
Required data for short-circuit calculations for high voltage circuit breakers includes:
ANSI Standard Circuit Breaker:
•
•
•
•
•
•
•
Max kV
Rated Int. (rated interrupting capability)
Max Int. (maximum interrupting capability)
C & L rms (rms value of closing and latching capability)
C & L Crest (crest value of closing and latching capability)
Standard
Cycle
IEC Standard Circuit Breaker:
•
•
•
•
Rated kV
Min. Delay (minimum delay time in second)
Making (peak current)
AC Breaking (rms ac breaking capability)
PowerStation calculates the interrupting capabilities of the circuit breaker from the rated and maximum
interrupting capabilities. This value is calculated at the nominal kV of the bus that the circuit breaker is
connected to.
Low Voltage Circuit Breaker Data
Required data for short-circuit calculations for low voltage circuit breakers includes:
ANSI Standard Circuit Breaker:
•
•
•
•
Type (power, molded case, or insulated case)
Rated kV
Interrupting (interrupting capability)
Test PF
IEC Standard Circuit Breaker:
•
•
•
•
•
Type (power, molded case, or insulated case)
Rated kV
Min. Delay (minimum delay time in second)
Making (peak current)
Breaking (rms ac breaking capability)
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ETAP PowerStation 4.0
Short-Circuit Analysis
Required Data
Fuse Data
Required data for short-circuit calculations for fuses includes:
•
Fuse ID
ANSI Standard Fuse:
•
•
Interrupting (interrupting capability)
Test PF
IEC Standard Fuse:
•
•
Breaking (rms ac breaking capability)
Test PF
Other Data
There are some study case related data, which must also be provided, and you can enter this data into the
Short-Circuit Study Case Editor. The data includes:
•
•
•
•
•
•
•
Standard (ANSI/IEC)
XFMR tap option (transformer tap modeling method)
Prefault voltage
Report (report format)
Machine X/R (machine X/R modeling method)
Faulted buses
Cable/OL heater (select this option to include cable and overload heater elements)
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ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10 Output Reports
PowerStation provides short-circuit study output reports with different levels of detail, depending on your
requirements. The following are just some examples that show this flexibility.
13.10.1 View Output Reports From Study Case Toolbar
This is a shortcut for the Report Manger. When you click on the View Output Report button,
PowerStation automatically opens the output report that is listed in the Study Case Toolbar with the
selected format. In the picture shown below, the output report name is Untitled and the selected format is
Complete.
13.10.2 Short-Circuit Report Manager
To open the Short-Circuit Report Manager, simply click on the Report Manager button on the ShortCircuit Study Toolbar. The editor includes four pages (Complete, Input, Result, and Summary)
representing different sections of the output report. The Report Manager allows you to select formats
available for different portions of the report and view it via Crystal Reports as well as a text report. There
are several fields and buttons common to every page, as described below.
Output Report Name
This field displays the name of the output report you want to view.
Project File Name
This field displays the name of the project file based on which report was generated, along with the
directory where the project file is located.
Help
Click on this button to access Help.
OK / Cancel
Click on the OK button to dismiss the editor and bring up the Crystal Reports view to show the selected
portion of the output report. If no selection is made, it will simply dismiss the editor. Click on the Cancel
button to dismiss the editor without viewing the report.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10.3 Input Data Page
This page allows you to select different formats for viewing input data, grouped according to type. They
include: Bus, Cable, Cover, Generator, Loads, Reactor, Transformer, UPS, and Utility.
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Short-Circuit Analysis
Output Reports
13.10.4 Result Page
This page allows you to select formats to view the short-circuit result portion of the output report.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10.5 Summary Page
This page allows you to select formats to view summary reports of the output report.
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ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10.6 Complete Page
In this page you can select the Complete report in Crystal Reports format, which brings up the complete
report for the short-circuit study, or in the text report format, which is described in greater detail in the
Text Report section. The complete report includes input data, results, and summary reports.
Operation Technology, Inc.
13-51
ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10.7 SC Arc Flash Page
This page shows up only when 3-phase device duty calculation is conducted. It allows you to view arc
flash analysis reports.
Operation Technology, Inc.
13-52
ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
13.10.8 Text Report
Sample 1: Input Data
This section lists system information and program parameters; bus input data; transmission line and cable
data; transformer, reactor, and impedance data; branch connections; and machine data, in that order.
Bus Information (Nominal & Base kV)
========================================================
ID
Type Nom.kV BasekV
Description
------------ ---- ------ ------ -------------------Bus3
Load 13.800 14.154
LVBus
Load
0.480
0.480
Main Bus
SWNG 34.500 34.500
MCC1
Load
0.480
0.480 LV Motor Control Cen
Sub 2A
Load 13.800 14.154
Sub 2B
Gen. 13.800 13.800
Sub 3
Load
4.160
4.160
Sub3 Swgr
Load
4.160
4.160
T1
Load 34.500 34.500 3W-XFMR center bus
-------------------------------------------------------9 Buses Total
Voltage
=============
% Mag.
Ang.
------ ----100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
100.0
0.0
Generation
==============
MW
Mvar
------ ------
6.300
-----6.300
CKT / Branch
============
ID
-----------Cable11
Cable2
Line / Cable (ohms/1000 ft per phase)
=================================================================
Library
Size L (ft) #/í T (øC)
R
X
Y
-------- ---- ------ --- ------ -------- -------- -------15MCUS1 2
1350.
1
75
0.20200
0.06850 0.000000
5MCUS3 350
250.
1
75
0.03860
0.04270 0.000000
CKT / Branch
============
ID
-----------T3
XFMR 3
T2
T1
Transformer
=======================================
MVA
kV
kV
% Z
X/R
------- ------ ------ ------- ----1.000
4.160
0.480
6.500
18.0
1.000
4.160
0.480
7.200
28.0
10.000 34.500 13.800
6.900
23.0
15.000( base MVA for 3-Winding )
15.000 34.500
Zps =
7.100
39.0
10.000 13.800
Zpt =
7.200
40.0
5.000
4.160
Zst =
14.100
38.0
CKT / Branch
=========================
ID
Type
------------ ----------Cable11
Line/Cable
Cable2
Line/Cable
T3
2W XFMR
XFMR 3
2W XFMR
T2
2W XFMR
T1
3W XFMR
Operation Technology, Inc.
0.000
%Tap Setting
=============
From
To
------ -----0.000 0.000
0.000 0.000
-2.500 0.000
Impedance
=====================================
MVAb
% R
% X
% Y
------- ------- ------- ---------100.0
13.61
4.62
0.0000000
100.0
5.58
6.17
0.0000000
Reactor
=================
X (ohm)
X/R
-------- -------
Imped.
======
% Tol.
-----0.00
0.00
0.00
0.000
0.000
0.000
Connected Bus Info.
==========================
From Bus ID
To Bus ID
------------ -----------Sub 2A
Bus3
Sub 3
Sub3 Swgr
Sub3 Swgr
LVBus
Sub3 Swgr
MCC1
Main Bus
Sub 2A
Main Bus
T1
Sub 2B
T1
Sub 3
T1
13-53
Motor Load
==============
MW
Mvar
------ -----3.368
1.355
0.121 -0.059
0.000
0.000
0.421
0.190
0.000
0.000
0.996 -0.616
0.000
0.000
0.400
0.170
0.000
0.000
------ -----5.306
1.040
0.00
0.00
0.00
%Impedance (100 MVA Base)
==========================
R
X
Z
------- ------- -------13.6
4.6
14.4
5.6
6.2
8.3
36.1
649.0
650.0
25.7
719.5
720.0
2.8
65.5
65.6
0.0
0.7
0.7
1.2
46.7
46.7
1.2
47.3
47.3
ETAP PowerStation 4.0
Short-Circuit Analysis
Output Reports
Conned Bus
Machine Info.
Rating
Impedance(100 MVA Base)
============ ================== ======================
Bus ID
Machine ID
Type
MVA
kV
RPM
------------ ------------ ---- ------- ------ ----Sub 2B
Gen1
Gen.
8.824
13.80 1800.0
Main Bus
Utility
Uty. 1500.000
34.50 1800.0
Bus3
Mtr2
IndM
0.649
13.20 1800.0
Sub3 Swgr
Pump 1
IndM
0.434
4.00 1800.0
Bus3
Syn4
SynM
2.982
13.20 1800.0
Sub 2B
Syn1
SynM
1.170
13.20 1800.0
MCC1
EqvLVInd-1
IndM
0.461
0.48 1800.0
LVBus
Syn2
SynM
0.134
0.46 1800.0
-------------------------------------------------------Total Connected Generators ( = 1 ):
8.824 MVA
Total Connected Motors
( = 6 ):
5.831 MVA
X/R Ratio
% Impedance(Machine Base)
%
==============
X"/R
X'/R
------ -----24.00
24.00
45.00
45.00
6.34
6.34
6.27
6.27
46.07
46.07
27.53
27.53
6.93
6.93
9.54
9.54
=========================
R
X"
X'
------- ------- ------1.000
24.00
37.00
2.222
99.98
99.98
3.830
24.28
60.70
3.830
24.01
60.04
0.334
15.38
23.08
0.559
15.38
23.08
2.652
18.37
45.92
2.097
20.00
30.00
=========================
R
X"
X'
------- ------- ------11.3
272.0
419.3
0.1
6.7
6.7
513.4
3254.4
8136.0
815.2
5111.7 12779.3
9.7
448.7
673.1
43.7
1202.6
1804.0
574.7
3980.1
9950.2
1434.7 13685.0 20527.5
Note: For motors, X" and X' are reactances used in 1/2 and 1.5--4 cycle system networks respectively.
Sample 2: Detailed Short-Circuit Report for MV Bus
This section tabulates detailed short-circuit results, organized in each faulted bus. This report gives
prefault voltage in percentage of both bus nominal kV and bus base kV, bus ID, bus voltages for the
faulted bus and the surrounding buses in percent, real part and imaginary part of the total short-circuit
current and the contribution ratios of the two, as well as the symmetrical current magnitudes.
Three-phase fault at bus:
Contribution
=========================
From Bus
To Bus
ID
ID
------------ -----------Main Bus
Total
Sub 2A
#T1
Utility
Main Bus
Main Bus
Main Bus
Bus3
#Sub 2B
#Sub 3
Mtr2
Syn4
Gen1
Syn1
Sub3 Swgr
Main Bus
,
Nominal kV =
Base kV
=
34.50
34.50
Prefault Voltage =
=
1/2 Cycle
===============================================
% V
kA
kA
Imag.
kA Symm.
From Bus
Real
Imaginary /Real Magnitude
-------- -------- --------- ----- --------0.00
0.647
-27.459
42.5
27.466
105.00 % of nominal bus kV
105.00 % of base kV
1.5 to 4 Cycle
===============================================
% V
kA
kA
Imag.
kA Symm.
From Bus
Real
Imaginary /Real Magnitude
-------- -------- --------- ----- --------0.00
0.628
-27.260
43.4
27.267
15.15
0.29
105.00
0.025
0.036
0.586
-0.376
-0.732
-26.351
14.8
20.5
45.0
0.377
0.733
26.357
10.18
0.26
105.00
0.013
0.029
0.586
-0.253
-0.656
-26.351
19.1
22.7
45.0
0.253
0.656
26.357
Sub 2A
T1
T1
16.64
18.48
2.58
0.062
0.025
0.011
-0.916
-0.652
-0.080
14.8
26.3
7.3
0.918
0.652
0.081
11.19
17.52
1.33
0.032
0.024
0.005
-0.617
-0.618
-0.037
19.1
26.1
7.3
0.618
0.619
0.038
Bus3
Bus3
Sub 2B
Sub 2B
Sub 3
105.00
105.00
105.00
105.00
2.90
0.020
0.041
0.052
0.010
0.091
-0.108
-0.808
-1.329
-0.301
-0.665
5.3
19.5
25.7
29.7
7.3
0.110
0.809
1.330
0.301
0.671
105.00
105.00
105.00
105.00
1.47
0.008
0.024
0.053
0.007
0.042
-0.046
-0.571
-1.343
-0.203
-0.309
5.6
23.7
25.6
29.6
7.3
0.047
0.571
1.344
0.203
0.312
NACD Ratio = 0.98
Sample 3: Momentary Duty Summary
This section tabulates momentary duties for all protective devices in the system, organized by the buses to
which they are connected. It gives bus ID, nominal kV, device ID and type, calculated device momentary
duties including rms values of symmetrical, asymmetrical, and crest short-circuit current in kA rms,
equivalent X/R ratio at the fault location, and the multiplying factor (MF), as well as device momentary
capacities in terms of rms values of symmetrical, asymmetrical, and crest kA. Over-stressed devices are
flagged.
Operation Technology, Inc.
13-54
ETAP PowerStation 4.0
Short-Circuit Analysis
Three-Phase Fault Currents:
Output Reports
( Prefault Voltage =
Bus Information
====================
Device Information
=========================
ID
-----------Bus3
Main Bus
ID
-----------Bus3
Main Bus
CB2
CB1
CB10
Sub 2A
CB12
CB11
Sub 2B
CB5
CB4
Sub 3
CB8
CB9
Sub3 Swgr
CB14
CB13
CB3
kV
-----13.80
34.50
Sub 2A
13.80
Sub 2B
13.80
Sub 3
4.16
Sub3 Swgr
4.16
105 % of the Bus Nominal Voltages )
Momentary Duty
==========================================
Symm.
X/R
Asymm.
Asymm.
kA rms
Ratio
M.F.
kA rms
kA Crest
-------- ----- ----- -------- -------6.368
10.6 1.451
9.238
15.698
27.466
44.1 1.654
45.417
75.014
27.466
44.1 1.654
45.417
75.014
27.466
44.1 1.654
45.417
75.014
27.466
44.1 1.654
45.417
75.014
6.835
23.0 1.588
10.855
18.099
6.835
23.0 1.588
10.855
18.099
6.835
23.0 1.588
10.855
18.099
10.131
36.7 1.639
16.601
27.479
10.131
36.7 1.639
16.601
27.479
10.131
36.7 1.639
16.601
27.479
27.480
39.6 1.645
45.207
74.758
27.480
39.6 1.645
45.207
74.758
27.480
39.6 1.645
45.207
74.758
24.607
8.7 1.404
34.556
59.061
24.607
8.7 1.404
34.556
59.061
24.607
8.7 1.404
34.556
59.061
24.607
8.7 1.404
34.556
59.061
Type
----------MCC
Switchgear
3 cy Sym CB
3 cy Sym CB
8 cy Tot CB
MCC
8 cy Tot CB
8 cy Tot CB
MCC
3 cy Sym CB
3 cy Sym CB
MCC
5 cy Sym CB
3 cy Sym CB
Bus
5 cy Sym CB
5 cy Sym CB
5 cy Sym CB
Device Capability
============================
Symm.
Asymm.
Asymm.
kA rms
kA rms
kA Crest
-------- -------- --------40.000
64.000
56.000
61.000
67.500 *
108.000
94.500
102.900
60.000
80.000
59.400
72.900
60.000
60.000
67.500
67.500
39.000
58.000
65.000 *
97.000
78.400
78.400
78.400
132.300
132.300
132.300
Sample 4: Interrupting Duty Summary
This section tabulates interrupting duties for all protective devices in the system, organized by the buses
to which they are connected. It gives bus ID, nominal kV, device ID and type, calculated device
interrupting duties including rms values of symmetrical and adjusted symmetrical short-circuit current in
kA rms, equivalent X/R ratio at the fault location, and the multiplying factor (MF), as well as device
interrupting capacities in terms of rated kV, test power factor, rms values of rated interrupting current and
the adjusted interrupting current. Overstressed devices are flagged.
Bus Information
====================
Device Information
=========================
ID
-----------Bus3
Main Bus
Main Bus
Main Bus
Main Bus
Sub 2A
Sub 2A
Sub 2B
Sub 2B
Sub 3
Sub 3
Sub3 Swgr
Sub3 Swgr
Sub3 Swgr
ID
------------
Type
-----------
CB2
Fuse1
CB1
CB10
CB12
CB11
CB5
CB4
CB8
CB9
CB14
CB13
CB3
3 cy
Fuse
3 cy
8 cy
8 cy
8 cy
3 cy
3 cy
5 cy
3 cy
5 cy
5 cy
5 cy
Notes:
Method:
kV
-----13.80
34.50
34.50
34.50
34.50
13.80
13.80
13.80
13.80
4.16
4.16
4.16
4.16
4.16
Sym CB
Sym
Tot
Tot
Tot
Sym
Sym
Sym
Sym
Sym
Sym
Sym
CB
CB
CB
CB
CB
CB
CB
CB
CB
CB
CB
Interrupting Duty
================================
Symm.
X/R
Adj Sym.
kA rms
Ratio
M.F.
kA rms
-------- ----- ----- -------5.985
8.8
27.267
44.3 1.216
33.147
27.466
44.1 1.243
34.128
27.267
44.3 1.216
33.147
27.267
44.3 1.279
34.864
6.457
23.9 1.115
7.201
6.457
23.9 1.115
7.201
10.003
36.8 1.168
11.687
10.003
36.8 1.168
11.687
27.091
40.0 1.213
32.858
27.091
40.0 1.198
32.462
24.218
8.7 1.000
24.218
24.218
8.7 1.000
24.218
24.218
8.7 1.000
24.218
Device Capability
=================================
Test
Rated
Adjusted
kV
PF
Int.
Int.
------ ----- -------- -------38.000
38.000
38.000
38.000
15.000
15.000
15.000
15.000
4.760
4.760
4.760
4.760
4.760
15.00
40.000
48.000
31.500
22.800
10.000
20.000
19.300
19.300
29.000
42.400
41.000
41.000
41.000
* Indicates buses with short-circuit values exceeding the device ratings.
# Indicates buses with short-circuit values exceeding the device marginal ratings (Device Margin:
IEEE - X/R is calculated from separate R & X networks.
Operation Technology, Inc.
13-55
40.000
48.000
34.696 #
25.113 *
10.870
21.739
20.978
20.978
31.000 *
48.515
46.913
46.913
46.913
90%).
ETAP PowerStation 4.0
Short-Circuit Analysis
Alert View
13.11 Alert View
To facilitate the user to check the device ratings after a device duty calculation, ETAP PowerStation
provides a short-Circuit Analysis Alert View which lists all devices that have a critical or marginal rating
violation. This view can be open by clicking on the Alert View button. If the Auto Display box is
checked in the study case, the Alert View will be automatically open once the device duty short-circuit
calculation is completed.
13.11.1 Alert View Entries
Device ID
The Device Identification section of the alert view window lists the names of the components that
qualified as alerts after the Short-circuit calculation.
Type
The type section of the alert view window displays information about the type of the device having the
displayed alert.
Rating
The rating section of the Alert View Window provides the rating information being used to determine
whether an alert should be reported and of what kind of alert was found.
Operation Technology, Inc.
13-56
ETAP PowerStation 4.0
Short-Circuit Analysis
Alert View
Calculated
The calculated section of the alert view window displays the results (duty) from the Short-circuit
calculation. The results listed here are used in combination with those displayed in the ratings section to
determine the operating percent values. These values are then compared to those entered in the Shortcircuit study case editor alarm page.
%Value
This section displays the percent operating values calculated based on the Short-circuit results and the
different device ratings. The values displayed here are directly compared to the percent of monitored
parameters entered directly into the study case editor alarm page. Based on the element type, system
topology and given conditions, the program uses these percent values to determine if and what kind of
alert should be displayed.
Condition
The conditions section of the Alert View Window provides a brief comment about the type of alert being
reported. In the case of Short-circuit alarms, the different conditions reported are the same as those listed
in the bus and protective device monitored parameters tables.
13.11.2 Parameters Monitored and Conditions Reported
Bus Alert
Short-circuit simulation Alerts for buses are designed to monitor crest, symmetrical and asymmetrical
bracing conditions. These conditions are determined from bus rating values and Short-circuit analysis
results. The conditions reported for buses are the same for ANSI and IEC project standards. The
following table contains a list of monitored parameters and the conditions that their corresponding alerts
report.
Bus Alerts Monitored parameters and Condition Reported
Type of Device
HV Bus (> 1000 Volts)
LV Bus (<1000Volts)
Operation Technology, Inc.
Monitored Parameter
Momentary Asymmetrical. rms kA
Condition Reported
Bracing Asymmetrical
Momentary Asymmetrical. crest kA
Bracing Crest
Momentary Symmetrical. rms kA
Bracing Symmetrical
Momentary Asymmetrical. rms kA
Bracing Asymmetrical
13-57
ETAP PowerStation 4.0
Short-Circuit Analysis
Alert View
Protective Device Alert
Short-circuit Alerts monitor certain conditions of interest for both ANSI and IEC project standards. The
conditions reported by the alerts depend on whether the user runs ANSI or IEC Short-circuit analysis.
ANSI and IEC standards have different sets of monitored parameters. The following table contains a list
of monitored parameters used for both standards.
Protective Alerts Monitored parameters
Device Type
LVCB
HV CB
FUSE
SPDT
SPST Switches
ANSI Monitored Parameters
Interrupting Adjusted Symmetrical. rms kA
Momentary C&L
Momentary C&L Crest kA
Interrupting Adjusted Symmetrical. rms kA
Interrupting Adjusted Symmetrical. rms kA
Momentary Asymmetrical. rms kA
Momentary Asymmetrical. rms kA
IEC Monitored Parameters
Breaking
Making
N/A
Breaking
Breaking
Making
Making
Short-Circuit Alerts for protective devices report different conditions depending on the monitored
parameters. The following table contains a list of the corresponding conditions reported in the Alert View
Window.
Protective Device Reported Condition
Device Type
LVCB
HV CB
Fuse
SPDT
SPST Switches
Operation Technology, Inc.
ANSI Reported Condition
Interrupting
Interrupting
C&L
C&L Crest
Interrupting
C&L
C&L
13-58
IEC Reported Condition
Breaking
Breaking
Making
N/A
Breaking
Making
Making
ETAP PowerStation 4.0