Detailed Short Circuit Calculation Using ETAP
Short circuit calculation using ETAP can be done through the ‘Short Circuit Analysis’ module. This module allows the calculation of fault duties according to the C37 Series of the ANSI/IEEE Standards and can be accessed from the mode toolbar as shown in figure 1.
As with other study modes within ETAP, the short-circuit analysis mode options or preferences can be accessed through the Study Case Toolbar while various studies under short-circuit analysis mode can be accessed through the Study Mode Toolbar.
The Study Case Toolbar
The short-circuit analysis mode preferences can be accessed through the Study Case Toolbar. To begin with the short-circuit analysis, a Study Case should be identified. The ‘New Study Case’ button initializes the creation of a new study case. ETAP does this by creating a duplicate copy of the existing study case. If done the first time, clicking the ‘New Study Case’ button will create a copy of the default study case. Once done, the new study case will be available on the drop-down menu.
You can also find from the Study Case toolbar a List of Output Reports where results from previous studies can be viewed. A Report Manager allows you to save the Output Reports in specific formats.
The Study Case Editor can be accessed by clicking the ‘Edit Study Case’ button. The Short-Circuit Study Case Editor contains preferences and parameters in which you can specify the solution control variables, faulted bus selection, applicable standards, and other options for output reports. Under the ‘Standard’ tab, select ANSI to set your short-circuit study based on the C37 series of the ANSI/IEEE standards.
For newer ETAP versions, creating a new study case is accessible in the ‘Edit Study Case’ pop-out menu as shown in the next figure.
The Study Mode Toolbar
By selecting ANSI in the standard tab of the Study Case toolbar, the Study Mode toolbar is set to ANSI/IEEE. The ANSI/IEEE short-circuit toolbar allows you to do the following:
- Run 3-phase device duty calculations based on ANSI c37 series
- Run 1-phase system device duty calculations (Not available on basic software license)
- Calculate ½ cycle RMS symmetrical short circuit currents
- Calculate 1.5-4 cycle RMS symmetrical short-circuit currents
- Calculate 30 cycle RMS symmetrical short-circuit currents
- Specify what you want to display on the one-line diagram
- Open an alert view of the device duty calculation
- Open Report Manager
- Open ANSI Short Circuit Analyzer (Only available to ETAP 14 and above versions)
Application Example
This guide provides a step-by-step approach using the minimum input required in order to run a short-circuit study on ETAP software.
Consider this very simple system composed of one utility source and one generator source. The utility source represents a remote source short-circuit current while the generator represents the local source of short-circuit current.
Model Parameters
Power Grid
There are only a few things to set-up the Power Grid model. The ID, Operation Mode, Rated kV, and the Short-Circuit parameters. Double click on the Power Grid to start filling-in the parameters.
In the ‘Info’ tab, you will find the ‘ID’ field. Type-in the name of the Power Grid.
Navigate to the ‘Operation Mode’ and verify if ‘Swing’ is ticked. Take note that ETAP requires at least one swing source for all available study modes.
The ‘Rating’ tab allows you to input the Power Grid ‘Rated kV’ and ‘Generation Category’. There’s not much to do here than inputting rated kV of the Power Grid.
Next up is the ‘Short-Circuit’ tab. You can either
specify the 3-phase and 1-phase short-circuit kA and X/R while ETAP calculates the rest
OR
specify the percent positive- and zero-sequence resistance and reactance on a 100MVAbase while ETAP calculates the rest.
It depends on what data is readily available to you.
And your done setting-up the Power Grid model. Click the ‘OK’ button to save the settings.
Synchronous Generator
Setting up the generator model can be quite complicated but again we are only up to the minimum input required to run the short-circuit study. Double click on the synchronous generator to start setting-up.
Don’t be overwhelmed with the number of setting tabs available. We’ll only set-up a few.
As with the utility model, fill in the ‘ID’ field with the name of the generator. In the ‘Operation Mode’, you can leave at as ‘Voltage Control’. As mentioned, ETAP only requires at least one swing source to be able to run any of the study modes.
Next tab. ‘Rating’.
In the ‘Rating’ tab, you can specify the generator rated capacity, kV, power factor, efficiency and more. For this example, fill in the parameters as shown in the figure. These parameters were determined for convenience’s sake and do not reflect real-world synchronous generators. After inputting these parameters, move on to the next tab.
The last tab that we are concerned about is the ‘Imp/Model’ with so much field to fill-up but we don’t have to do much here. Just click on the ‘Typical Data’ and verify the values on the figure. Click the ‘OK’ button to save the settings.
Next, we move on to modeling our transmission line.
Transmission Line
There are lesser tabs here compared to the synchronous generator but setting-up the minimum input requirement for the transmission line model takes a bit more than the utility and synchronous generator model.
Again first things first, the ‘Info’ tab.
Fill in the name and the length of the transmission line on the ‘ID’ and the ‘Length’ field, respectively. Don’t forget to set the unit of measurement for the specified length!
The ‘Parameter’ tab allows you to specify the phase and neutral conductors. To that, you can input the conductor parameters that you have or you can refer to the ETAP library and select the conductors from the list.
Click on the ‘Conductor Lib…’ under the ‘Phase Conductor’ to access ETAP Library Quick Pick for Transmission Lines. For this example, navigate to ‘EPRI/M.LAYER’ and select ‘Linnet’.
For the Ground Wire, you can either choose from the available Ground Wire Library or the Conductor Library. For this example, we will choose the ground wire from the Conductor Library. Click on the ‘Conductor Lib…’ and navigate to ‘EPRI/S.LAYER’. Select ‘Penguin’ from the available list.
The last tab to set-up is the ‘Configuration’ tab. In this tab, we specify the transmission line configuration including the spacing and the height. Enter the values as shown in the figure. Click the ‘OK’ button to save the settings.
Study Case
To access the short-circuit module in ETAP, click on the ‘Short-Circuit’ button as shown in the figure.
Navigate to the Study-Case toolbar and click the ‘Edit Study Case’ button. A new window will pop-up where you can specify the study preferences and parameters such as solution control variables, faulted bus selection, applicable standards, and other options for output reports.
On the ‘Info’ tab, select the bus/busses to be faulted from the list of available busses and click the ‘<< Fault’ button. The choice of the bus depends on where the circuit breaker/s are planned to be connected. After the bus selection, the faulted busses are moved from the ‘Don’t Fault’ to the ‘Fault’ field of the ‘Bus Selection’.
You can also verify the faulted busses from the ‘One-Line Diagram’ since they are highlighted red.
Next, navigate to the ‘Standard’ tab of the Short-Circuit Study Case. For this example, select ‘ANSI’ from the ‘Standard’ field and ‘C37.010 – 1979 and Older’ for the ‘Device Duty’ field. Selecting ‘C37.010 – 1979 and Older’ allows the selection of S-factor based on circuit breaker contact parting time as shown in the table below.
Leave other parameters to their default values.
Lastly, navigate to the ‘Adjustment’ tab and uncheck all checkboxes. This is to verify the results later using manual calculations for learning purposes. Click the ‘OK’ button to save the settings.
On actual projects, it is recommended to check all tolerances in order to have conservative results.
ANSI Short-Circuit Mode
After setting up the model and study case parameters, you are now ready to conduct ANSI short-circuit study.
Click on the ‘ANSI 3-Phase Device Duty (ANSI37)’ to start the analysis.
A new window will pop-out requiring you to specify the report name. Enter the output file name of the report and click ‘OK’.
After clicking ‘OK’, the One-Line Diagram should look as shown in figure.
You may choose to modify what is displayed on the One-Line Diagram by clicking the ‘Display Options’ in the ANSI Short-Circuit toolbar.
Click on the ‘Report Manager’ in order to open/view the study output report.
Navigate through the different tabs in the ‘Report Manager’ to select the information you want to view.
For this example, click on the ‘Summary’ tab and select ‘Summary’. Click ‘OK’.
A new window will pop-out containing the report summary as selected on the ‘Report Manager’.
Verify the results using manual calculations. Click here to access the step-by-step guide to sizing circuit breakers using manual calculations.
You can also compare the results using our circuit breaker sizing calculator available in the tools section.
You may also choose to print the results by clicking the ‘Print Report’ button.
There you have it.
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Reference
ETAP Enterprise Solution for Electrical Power Systems Online Help
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