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ETAP PowerStation 4.0

User Guide

Copyright 2001 Operation Technology, Inc.

All Rights Reserved This manual has copyrights by Operation Technology, Inc. All rights reserved. Under the copyright laws, this manual may not be copied, in whole or in part, without the written consent of Operation Technology, Inc. The Licensee may copy portions of this documentation only for the exclusive use of Licensee. Any reproduction shall include the copyright notice. This exception does not allow copies to be made for other persons or entities, whether or not sold. Under this law, copying includes translating into another language. Certain names and/or logos used in this document may constitute trademarks, service marks, or trade names of Operation Technology, Inc. or other entities. • Access, Excel, ODBC, SQL Server, Windows NT, Windows 2000, Windows Me, Windows

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Chapter 13

Short-Circuit Analysis

The PowerStation Short-Circuit Analysis program analyzes the effect of three-phase, line-to-ground, line-to-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 Short-Circuit 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.

Operation Technology, Inc. 13-1 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 Short-Circuit Study Case Editor.

Alert View

Short-Circuit Display Options

Save Fault kA for PowerPlot

LG, LL, LLG & 3-Phase Faults – 30 cycle

LG, LL, LLG & 3-Phase Faults – 1.5-4 Cycle

LG, LL, LLG & 3-Phase Faults – ½ cycle

3-Phase Faults – 30 Cycle Network

3-Phase Faults – Device Duty

Get Archived Data

Get Online Data

Halt Current Calculation

Short-Circuit Report Manager

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 short-circuit 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.



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 three-phase 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 three-phase 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.



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.



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 on-line 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.


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 Short-Circuit Study Case Editor.

3-Phase Faults – Device Duty (IEC 909)

3-Phase Faults – Transient Study (IEC 363)

LG, LL, LLG & 3-Phase Faults (IEC 909)

Short-Circuit Display Options

Save Fault kA for PowerPlot

View Alert

Short-Circuit Report Manager

Get Archived Data

Get Online Data

Halt Current Calculation

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 short-circuit 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.



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.



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 on-line 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.


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



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.



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.



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 short-circuit 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.



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



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.



The following example shows Ra calculations when X/R ratio is fixed:

½ Cycle Network 1.5-4 Cycle Network

Input: Xsc 15 25

Input: X/R = 10

Calculated: Ra 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

Input: Xsc 15 25

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 C Factor = 1.0 Other < 1001 V C Factor = 1.05 1001 to 35000 V C Factor = 1.1 > 35000 V C Factor = 1.1



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.



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



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.


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.



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.


ID Select the check boxes under this heading to display the ID of the selected AC elements on the one-line diagram.



Rating Select the check boxes under this heading to display the ratings of the selected AC elements on the one-line diagram.

Device Type Rating Gen. (Generator) kW / MW Power Grid (Utility) MVAsc Motor HP / kW Load kVA / MVA Panel Connection Type (# of Phases - # of Wires) Transformer kVA / MVA Branch, Impedance Base MVA Branch, Reactor Continuous Amps Cable / Line # of Cables - # of Conductor / Cable - Size Bus kA Bracing Node Bus Bracing (kA) CB Rated Interrupting (kA) Fuse Interrupting (ka) Relay 50/51 for Overcurrent Relays PT & CT 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 button. Click on this button to display the cable/line conductor type on the one-line diagram.

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 button. Click on this button to display the cable/line length on the one-line diagram. 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 Impedance Generator Subtransient reactance Xd” Power Grid (Utility) Positive Sequence Impedance in % of 100 MVA (R + j X) Motor % LRC Transformer Positive Sequence Impedance (R + j X per unit length) Branch, Impedance Impedance in ohms or % Branch, Reactor Impedance in ohms Cable / Line Positive Sequence Impedance (R + j X in ohms or per unit length)



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.


ID Select the check boxes under this heading to display the IDs of the selected AC-DC elements on the one-line 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 Rating Charger AC kVA & DC kW (or MVA / MW) Inverter DC kW & AC kVA (or MW / MVA) UPS kVA VFD 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 Amp Charger AC FLA & DC FLA Inverter DC FLA & AC FLA UPS Input, output, & DC FLA



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.


13.4.4 DC Page


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 one-line diagram.

Device Type Rating Battery Ampere Hour Motor HP / kW Load kW / MW Elementary Diagram kW / MW Converter kW / MW Cable # 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 button. Click on this button to display the conductor type on the one-line diagram.

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 button. Click on this button to display the cable length (one way) on the one-line diagram.

Z Select the check boxes under this heading to display the impedance values of the cables and impedance branches on the one-line diagram.



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.



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 Pub. Year Title IEEE C37.04 IEEE C37.04f IEEE C37.04g IEEE C37.04h IEEE C37.04i

1979 (1988) 1990 1986 1990 1991

Standard Rating Structure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis and Supplements

IEEE C37.010 IEEE C37.010b IEEE C37.010e

1979 (1988) 1985 1985

Standard Application Guide for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis and Supplements

IEEE C37.013 1997 Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis

IEEE C37.20.1 1993 Standard for Metal Enclosed Low-Voltage Power Circuit Breaker Switchgear

IEEE Std 399 1990 Power System Analysis -- the Brown Book IEEE Std 141 1986 Electric Power Distribution for Industrial Plants -- the Red Book IEEE Std 242 1986 IEEE Recommended Practice for Protection and Coordination of

Industrial and Commercial Power Systems – the Buff Book UL 489_9 1996 Standard for Safety for Molded-Case Circuit Breakers, Molded-

Case 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.



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 short-circuit 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 Xsc Utility X” Turbo generator Xd” Hydro-generator with amortisseur winding Xd” Hydro-generator without amortisseur winding 0.75 Xd’ Condenser Xd” Synchronous motor Xd” Induction Machine

> 1000 hp @ 1800 rpm or less Xd” > 250 hp @ 3600 rpm Xd” All other > 50 hp 1.2 Xd” < 50 hp 1.67 Xd”

½ Cycle Network Impedance (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 1.5-4 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



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 30-cycle fault calculation.

Type of Machine Xsc Utility X” Turbo generator Xd’ Hydro-generator with amortisseur winding Xd’ Hydro-generator without amortisseur winding Xd’ Condenser Infinity Synchronous motor Infinity Induction machine Infinity

30-Cycle Network Impedance



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

IIremote

total=

• 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 short-circuit 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:

IV

Zmom rms symmpre fault

eq, , = −

3 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 MF Imom rms asymm m mom rms symm, , , ,=

where MFm is the momentary multiplying factor, calculated from

MF emX R= +

−1 2

2π/



3) Calculate the peak value of momentary short-circuit current using the following formula:

I MF Imom peak p mom rms symm, , ,=

where MFp is the peak multiplying factor, calculated from

MF epX R= +

−2 1

π/

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:

IV

Zrms symmpre fault

eqint, , = −

3 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

MF erX R

t= +

−1 2

4π/

where t is the circuit breaker contact parting time in cycles, as given in the following table:

Circuit Breaker Rating in Cycles

Contact Parting Time in Cycles

8 4 5 3 3 2 2 1.5



The following table shows the Multiplying Factors for Remote Contributions (MFr).

X/R Ratio

8 Cycle CB (4 cy CPT)



2 Cycle CB (1.5 cy CPT)

100 1.487 1.540 1.599 1.63 90 1.464 1.522 1.585 1.619 80 1.438 1.499 1.569 1.606 70 1.405 1.472 1.548 1.59 60 1.366 1.438 1.522 1.569

50 1.316 1.393 1.487 1.54 45 1.286 1.366 1.464 1.255 40 1.253 1.334 1.438 1.499 35 1.215 1.297 1.405 1.472 30 1.172 1.253 1.366 1.438

25 1.126 1.201 1.316 1.393 20 1.078 1.142 1.253 1.334 18 1.059 1.116 1.223 1.305 16 1.042 1.091 1.190 1.271 14 1.027 1.066 1.154 1.233

12 1.015 1.042 1.116 1.190 10 1.007 1.023 1.078 1.142 9 1.004 1.015 1.059 1.116 8 1.002 1.009 1.042 1.091 7 1.001 1.005 1.027 1.066

6 1.000 1.002 1.015 1.042 5 1.000 1.00. 1.007 1.023 4 1.000 1.000 1.002 1.009 3 1.000 1.000 1.000 1.002 2 1.000 1.000 1.000 1.000 1 1.000 1.000 1.000 1.000

MFr Remote Contributions Multiplying Factors; Total Current Basis CBs



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.

X/R Ratio




2 Cycle CB (1.5 cy CPT)

100 1.252 1.351 1.443 1.512 90 1.239 1.340 1.441 1.511 80 1.222 1.324 1.435 1.508 70 1.201 1.304 1.422 1.504 60 1.175 1.276 1.403 1.496

50 1.141 1.241 1.376 1.482 45 1.121 1.220 1.358 1.473 40 1.098 1.196 1.337 1.461 35 1.072 1.169 1.313 1.446 30 1.044 1.136 1.283 1.427

25 1.013 1.099 1.247 1.403 20 1.000 1.057 1.201 1.371 18 1.000 1.039 1.180 1.356 16 1.000 1.021 1.155 1.339 14 1.000 1.003 1.129 1.320

12 1.000 1.000 1.099 1.299 10 1.000 1.000 1.067 1.276 9 1.000 1.000 1.051 1.263 8 1.000 1.000 1.035 1.250 7 1.000 1.000 1.019 1.236

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.

Iint,rms,adj = AMFi Iint,rms,symm where

AMFi = MFl + NACD (MFr – MFl)



6) For symmetrically rated breakers, the adjusted rms value of interrupting short-circuit current is

calculated using the following formula.

SIint,rms,adj

iAMF=

Iint,rms,symm

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.

IV

Zrms symmpre fault

eqint, , = −

3 where Zeq is the equivalent impedance at the faulted bus from the ½ cycle network.



2) Calculate the adjusted asymmetrical rms value of the interrupting short-circuit current duty using the

following formula:

I MF Irms adj rms,symmint, , int,= where MF is the multiplying factor, considering the system X/R ratio and the low voltage circuit breaker testing power factors, calculated from

MF e

e

X R

X R test

= +

+

−

−

2 1

2 1

( )

(

/

( / )

π

π

) for unfused power breakers or

MF e

e

X R

X R test

= +

+

−

−

1 2

1 2

2

2

π

π

/

( / ) 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.



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 Asymm. KA rms Asymm. KA rms Asymm. KA Crest Asymm. KA Crest LV Bus Bracing Symm. KA rms Symm. KA rms Asymm. KA rms Asymm. KA rms HV CB C&L Capability kA rms Asymm. KA rms C&L Capability kA Crest Asymm. KA Crest Momentary Duty HV CB Interrupting kA*** Adjusted kA 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.


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 Pub. Year Title IEC 56 1978 High voltage alternating-current circuit-breakers IEC 282-1 1985 Fuses for voltages exceeding 1000 V ac IEC 61363 1998 Electrical Installations of Ships and Mobile and Fixed Offshore

Units IEC 781 1989 Application guide for calculation of short-circuit currents in low

voltage radial systems IEC 909-1 1991 Short-circuit calculation in three-phase ac systems IEC 909-2 1988 Electrical equipment - data for short-circuit current calculations in

accordance with IEC 909 IEC 947-1 1988 Low voltage switchgear and controlgear, Part 1: General rules IEC 947-2 1989 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. Near-to-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.



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.

KG =

ZK = KG(R+ Xd”) kVn cmax kVr 1+x”

d sinφr



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 Nominal Voltage Un

For Maximum Short-Circuit Current Calculation

cmax

For Minimum Short-Circuit Current Calculation

cmin Low voltage: 100 V to 1000 V

230 V / 400 V 1.00 0.95 Other voltages 1.05 1.00

Medium voltage: > 1 kV to 35 kV 1.10 1.00 High voltage: > 35 kV to 230 kV 1.10 1.00

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 cUZ

kn

k

" =3

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 kp k= 2 "I where k is a function of the system R/X ratio at the fault location.



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.

I Ib 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:

=machines usasynchronofor

machines ssynchronoufor "

"

k

kb

qIII

µµ

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:

−=

RXftII kdc /

2exp2 min" π

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.



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 II I

k r

k r

G

G

max max

min min

==

λλ

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 Device Capability SC Current Duty MV CB Making ip AC Breaking Ib,symm Ib,asymm * Ib, asymm Idc * LV CB Making Ip Breaking Ib,symm Ib,asymm * 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.



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,

−∗+=

RXftII symmbasymmb /

4exp21 min,,

π

−=

RXftII symmbdc /

2exp2 min,

π

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:

−∗+=


4exp21 min,,

π

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:

−∗+=


4exp21 min,,

π

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 %.


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 70E-2000. 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.


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.


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



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



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)



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)


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 Short-Circuit 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.



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.



13.10.4 Result Page This page allows you to select formats to view the short-circuit result portion of the output report.



13.10.5 Summary Page This page allows you to select formats to view summary reports of the output report.



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.



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.



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) Voltage Generation Motor Load ======================================================== ============= ============== ============== ID Type Nom.kV BasekV Description % Mag. Ang. MW Mvar MW Mvar ------------ ---- ------ ------ -------------------- ------ ----- ------ ------ ------ ------ Bus3 Load 13.800 14.154 100.0 0.0 3.368 1.355 LVBus Load 0.480 0.480 100.0 0.0 0.121 -0.059 Main Bus SWNG 34.500 34.500 100.0 0.0 0.000 0.000 MCC1 Load 0.480 0.480 LV Motor Control Cen 100.0 0.0 0.421 0.190 Sub 2A Load 13.800 14.154 100.0 0.0 0.000 0.000 Sub 2B Gen. 13.800 13.800 100.0 0.0 6.300 0.000 0.996 -0.616 Sub 3 Load 4.160 4.160 100.0 0.0 0.000 0.000 Sub3 Swgr Load 4.160 4.160 100.0 0.0 0.400 0.170 T1 Load 34.500 34.500 3W-XFMR center bus 100.0 0.0 0.000 0.000 -------------------------------------------------------- ------ ------ ------ 9 Buses Total 6.300 5.306 1.040 CKT / Branch Line / Cable (ohms/1000 ft per phase) Impedance ============ ================================================================= ===================================== ID Library Size L (ft) #/í T (øC) R X Y MVAb % R % X % Y ------------ -------- ---- ------ --- ------ -------- -------- -------- ------- ------- ------- ---------- Cable11 15MCUS1 2 1350. 1 75 0.20200 0.06850 0.000000 100.0 13.61 4.62 0.0000000 Cable2 5MCUS3 350 250. 1 75 0.03860 0.04270 0.000000 100.0 5.58 6.17 0.0000000 CKT / Branch Transformer %Tap Setting Reactor Imped. ============ ======================================= ============= ================= ====== ID MVA kV kV % Z X/R From To X (ohm) X/R % Tol. ------------ ------- ------ ------ ------- ----- ------ ------ -------- ------- ------ T3 1.000 4.160 0.480 6.500 18.0 0.000 0.000 0.00 XFMR 3 1.000 4.160 0.480 7.200 28.0 0.000 0.000 0.00 T2 10.000 34.500 13.800 6.900 23.0 -2.500 0.000 0.00 T1 15.000( base MVA for 3-Winding ) 15.000 34.500 Zps = 7.100 39.0 0.000 0.00 10.000 13.800 Zpt = 7.200 40.0 0.000 0.00 5.000 4.160 Zst = 14.100 38.0 0.000 0.00 CKT / Branch Connected Bus Info. %Impedance (100 MVA Base) ========================= ========================== ========================== ID Type From Bus ID To Bus ID R X Z ------------ ----------- ------------ ------------ ------- ------- -------- Cable11 Line/Cable Sub 2A Bus3 13.6 4.6 14.4 Cable2 Line/Cable Sub 3 Sub3 Swgr 5.6 6.2 8.3 T3 2W XFMR Sub3 Swgr LVBus 36.1 649.0 650.0 XFMR 3 2W XFMR Sub3 Swgr MCC1 25.7 719.5 720.0 T2 2W XFMR Main Bus Sub 2A 2.8 65.5 65.6 T1 3W XFMR Main Bus T1 0.0 0.7 0.7 Sub 2B T1 1.2 46.7 46.7 Sub 3 T1 1.2 47.3 47.3



Conned Bus Machine Info. Rating X/R Ratio % Impedance(Machine Base) % Impedance(100 MVA Base) ============ ================== ====================== ============== ========================= ========================= Bus ID Machine ID Type MVA kV RPM X"/R X'/R R X" X' R X" X' ------------ ------------ ---- ------- ------ ----- ------ ------ ------- ------- ------- ------- ------- ------- Sub 2B Gen1 Gen. 8.824 13.80 1800.0 24.00 24.00 1.000 24.00 37.00 11.3 272.0 419.3 Main Bus Utility Uty. 1500.000 34.50 1800.0 45.00 45.00 2.222 99.98 99.98 0.1 6.7 6.7 Bus3 Mtr2 IndM 0.649 13.20 1800.0 6.34 6.34 3.830 24.28 60.70 513.4 3254.4 8136.0 Sub3 Swgr Pump 1 IndM 0.434 4.00 1800.0 6.27 6.27 3.830 24.01 60.04 815.2 5111.7 12779.3 Bus3 Syn4 SynM 2.982 13.20 1800.0 46.07 46.07 0.334 15.38 23.08 9.7 448.7 673.1 Sub 2B Syn1 SynM 1.170 13.20 1800.0 27.53 27.53 0.559 15.38 23.08 43.7 1202.6 1804.0 MCC1 EqvLVInd-1 IndM 0.461 0.48 1800.0 6.93 6.93 2.652 18.37 45.92 574.7 3980.1 9950.2 LVBus Syn2 SynM 0.134 0.46 1800.0 9.54 9.54 2.097 20.00 30.00 1434.7 13685.0 20527.5 -------------------------------------------------------- Total Connected Generators ( = 1 ): 8.824 MVA Total Connected Motors ( = 6 ): 5.831 MVA 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: Main Bus , Nominal kV = 34.50 Prefault Voltage = 105.00 % of nominal bus kV Base kV = 34.50 = 105.00 % of base kV Contribution 1/2 Cycle 1.5 to 4 Cycle ========================= =============================================== =============================================== From Bus To Bus % V kA kA Imag. kA Symm. % V kA kA Imag. kA Symm. ID ID From Bus Real Imaginary /Real Magnitude From Bus Real Imaginary /Real Magnitude ------------ ------------ -------- -------- --------- ----- --------- -------- -------- --------- ----- --------- Main Bus Total 0.00 0.647 -27.459 42.5 27.466 0.00 0.628 -27.260 43.4 27.267 Sub 2A Main Bus 15.15 0.025 -0.376 14.8 0.377 10.18 0.013 -0.253 19.1 0.253 #T1 Main Bus 0.29 0.036 -0.732 20.5 0.733 0.26 0.029 -0.656 22.7 0.656 Utility Main Bus 105.00 0.586 -26.351 45.0 26.357 105.00 0.586 -26.351 45.0 26.357 Bus3 Sub 2A 16.64 0.062 -0.916 14.8 0.918 11.19 0.032 -0.617 19.1 0.618 #Sub 2B T1 18.48 0.025 -0.652 26.3 0.652 17.52 0.024 -0.618 26.1 0.619 #Sub 3 T1 2.58 0.011 -0.080 7.3 0.081 1.33 0.005 -0.037 7.3 0.038 Mtr2 Bus3 105.00 0.020 -0.108 5.3 0.110 105.00 0.008 -0.046 5.6 0.047 Syn4 Bus3 105.00 0.041 -0.808 19.5 0.809 105.00 0.024 -0.571 23.7 0.571 Gen1 Sub 2B 105.00 0.052 -1.329 25.7 1.330 105.00 0.053 -1.343 25.6 1.344 Syn1 Sub 2B 105.00 0.010 -0.301 29.7 0.301 105.00 0.007 -0.203 29.6 0.203 Sub3 Swgr Sub 3 2.90 0.091 -0.665 7.3 0.671 1.47 0.042 -0.309 7.3 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.



Three-Phase Fault Currents: ( Prefault Voltage = 105 % of the Bus Nominal Voltages ) Bus Information Device Information Momentary Duty Device Capability ==================== ========================= ========================================== ============================ Symm. X/R Asymm. Asymm. Symm. Asymm. Asymm. ID kV ID Type kA rms Ratio M.F. kA rms kA Crest kA rms kA rms kA Crest ------------ ------ ------------ ----------- -------- ----- ----- -------- -------- -------- -------- --------- Bus3 13.80 Bus3 MCC 6.368 10.6 1.451 9.238 15.698 Main Bus 34.50 Main Bus Switchgear 27.466 44.1 1.654 45.417 75.014 40.000 67.500 * CB2 3 cy Sym CB 27.466 44.1 1.654 45.417 75.014 64.000 108.000 CB1 3 cy Sym CB 27.466 44.1 1.654 45.417 75.014 56.000 94.500 CB10 8 cy Tot CB 27.466 44.1 1.654 45.417 75.014 61.000 102.900 Sub 2A 13.80 Sub 2A MCC 6.835 23.0 1.588 10.855 18.099 CB12 8 cy Tot CB 6.835 23.0 1.588 10.855 18.099 60.000 59.400 CB11 8 cy Tot CB 6.835 23.0 1.588 10.855 18.099 80.000 72.900 Sub 2B 13.80 Sub 2B MCC 10.131 36.7 1.639 16.601 27.479 CB5 3 cy Sym CB 10.131 36.7 1.639 16.601 27.479 60.000 67.500 CB4 3 cy Sym CB 10.131 36.7 1.639 16.601 27.479 60.000 67.500 Sub 3 4.16 Sub 3 MCC 27.480 39.6 1.645 45.207 74.758 CB8 5 cy Sym CB 27.480 39.6 1.645 45.207 74.758 39.000 65.000 * CB9 3 cy Sym CB 27.480 39.6 1.645 45.207 74.758 58.000 97.000 Sub3 Swgr 4.16 Sub3 Swgr Bus 24.607 8.7 1.404 34.556 59.061 CB14 5 cy Sym CB 24.607 8.7 1.404 34.556 59.061 78.400 132.300 CB13 5 cy Sym CB 24.607 8.7 1.404 34.556 59.061 78.400 132.300 CB3 5 cy Sym CB 24.607 8.7 1.404 34.556 59.061 78.400 132.300

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 Interrupting Duty Device Capability ==================== ========================= ================================ ================================= Symm. X/R Adj Sym. Test Rated Adjusted ID kV ID Type kA rms Ratio M.F. kA rms kV PF Int. Int. ------------ ------ ------------ ----------- -------- ----- ----- -------- ------ ----- -------- -------- Bus3 13.80 5.985 8.8 Main Bus 34.50 CB2 3 cy Sym CB 27.267 44.3 1.216 33.147 38.000 40.000 40.000 Main Bus 34.50 Fuse1 Fuse 27.466 44.1 1.243 34.128 38.000 15.00 48.000 48.000 Main Bus 34.50 CB1 3 cy Sym CB 27.267 44.3 1.216 33.147 38.000 31.500 34.696 # Main Bus 34.50 CB10 8 cy Tot CB 27.267 44.3 1.279 34.864 38.000 22.800 25.113 * Sub 2A 13.80 CB12 8 cy Tot CB 6.457 23.9 1.115 7.201 15.000 10.000 10.870 Sub 2A 13.80 CB11 8 cy Tot CB 6.457 23.9 1.115 7.201 15.000 20.000 21.739 Sub 2B 13.80 CB5 3 cy Sym CB 10.003 36.8 1.168 11.687 15.000 19.300 20.978 Sub 2B 13.80 CB4 3 cy Sym CB 10.003 36.8 1.168 11.687 15.000 19.300 20.978 Sub 3 4.16 CB8 5 cy Sym CB 27.091 40.0 1.213 32.858 4.760 29.000 31.000 * Sub 3 4.16 CB9 3 cy Sym CB 27.091 40.0 1.198 32.462 4.760 42.400 48.515 Sub3 Swgr 4.16 CB14 5 cy Sym CB 24.218 8.7 1.000 24.218 4.760 41.000 46.913 Sub3 Swgr 4.16 CB13 5 cy Sym CB 24.218 8.7 1.000 24.218 4.760 41.000 46.913 Sub3 Swgr 4.16 CB3 5 cy Sym CB 24.218 8.7 1.000 24.218 4.760 41.000 46.913 Notes: * Indicates buses with short-circuit values exceeding the device ratings. # Indicates buses with short-circuit values exceeding the device marginal ratings (Device Margin: 90%). Method: IEEE - X/R is calculated from separate R & X networks.


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.

13-56 ETAP PowerStation 4.0

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.


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 Short-circuit 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 Monitored Parameter Condition Reported

Momentary Asymmetrical. rms kA Bracing Asymmetrical HV Bus (> 1000 Volts)

Momentary Asymmetrical. crest kA Bracing Crest Momentary Symmetrical. rms kA Bracing Symmetrical

LV Bus (<1000Volts) Momentary Asymmetrical. rms kA Bracing Asymmetrical



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 ANSI Monitored Parameters IEC Monitored Parameters

LVCB Interrupting Adjusted Symmetrical. rms kA Breaking Momentary C&L Making

Momentary C&L Crest kA N/A HV CB Interrupting Adjusted Symmetrical. rms kA Breaking

FUSE Interrupting Adjusted Symmetrical. rms kA Breaking SPDT Momentary Asymmetrical. rms kA Making

SPST Switches Momentary Asymmetrical. rms kA 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 ANSI Reported Condition IEC Reported Condition

LVCB Interrupting Breaking Interrupting Breaking

C&L Making

HV CB

C&L Crest N/A Fuse Interrupting Breaking

SPDT C&L Making SPST Switches C&L Making


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