EasyPower^® Tutorial - IEC Short Circuit Analysis

In this tutorial, you will be shown how to use several of EasyPower’s IEC short circuit analysis features.

IEC Option

To run IEC short circuit analysis, you must set the IEC option.

1. Open the Simple.dez file in your Samples directory. Click Maximize to fill your screen with the one-line.
2. Click Tools in the ribbon, click Options, and then select the System tab. Select the following:
   • Frequency: 50 or 60 Hertz.
   • SC Calculation Method: Set this to IEC.
   • Units: You can change this to Metric (optional).
   • Symbols: You can set this to IEC (optional).

   Click OK to save your changes.

3. Click the Home ribbon and click Short Circuit. The ribbon now contains buttons that you can use in your short circuit calculations.

Calculating Fault Currents

Double-click on BUS-3. The bus color changes to light blue and displays fault currents in symmetrical kilo-amps. As shown in the figure below, the motor contributes 1.139 kA and the cable, 4.734 kA to the fault. The total bus fault current, shown at a forty-five degree angle, is 5.873 kA.

Figure 1: Momentary Short Circuit Fault

There are several different methods to fault buses while in the Short Circuit focus:

• Double-click on a bus.
• Select a bus or multiple buses (so they turn green) and click Fault Bus(es).

  Note: To select a single bus, click it with the left mouse button. To select extra buses, click them while holding down the SHIFT key.

• Click Fault Bus(es) without selecting any bus. This runs a batch fault on all the buses in your system.

Changing the IEC Standard Time Interval

The following currents can be calculated in EasyPower:

• Initial (Momentary) current: This is the first cycle current. To display results for this current click Momentary in the Short Circuit ribbon.
• Breaking currents for 0.02 seconds, 0.05 seconds, 0.1 seconds and >0.25 seconds: To display these values, select the corresponding buttons from the ribbon.

You can view up to 3 types of fault current values by time interval. You can also view fault currents in various forms, such as by phase current values (A, B, C) or their symmetrical component values (positive sequence, negative sequence or 3 times the zero sequence). In the figure below, notice the motor current contribution decays with the time interval.

Figure 2: Initial, 0.05s and >0.25s Currents Display

Unsymmetrical Faults

The currents calculated to this point have been 3-phase fault currents. EasyPower also calculates unsymmetrical faults. According to convention, single line-to-ground fault calculations assume the A-phase is faulted. For double line-to-ground and line-to-line faults, the convention is to fault phases B and C.

Single Line-to-Ground Faults

1. Click Line to Ground. The green dot represents ground fault. When this button is selected, all subsequent faults will be single line-to-ground faults.
2. Click Momentary
3. Fault BUS-3 again. The currents will show zero (see figure below). This is because the transformer (delta-delta connection type) and motor are not grounded. By default, EasyPower displays A-phase currents.

   
   

   Figure 3: Single Line-to-Ground Fault

Double Line-to-Ground Faults

1. Click Double Line to Ground. The green dots represents ground fault.
2. A message will appear. Answer Yes to fault the B-phase line rather than the A-phase. All faults will now be double line-to-ground faults.
3. Double-click on BUS-3 again. The B-phase double line-to-ground fault currents are displayed (see figure below).

   
   

   Figure 4: Double Line-to-Ground Fault

Line-to-Line Faults

1. Click Line to Line. Yellow dots represent phase faults. Faults are now line-to-line faults.
2. Fault BUS-3 again to display the B-phase line-to-line fault currents (see figure below).

   
   

   Figure 5: Line-to-Line Fault

Text Reports

1. Select Short Circuit Text Reports from the ribbon.
2. In the Short Circuit Options/Text Output dialog, ensure the Create Short Circuit Report check box is selected, and then click OK.
3. Click 3-Phase. This returns you to 3-phase fault calculations.
4. Click Fault Bus(es). A text report window is created. You can view this report either by selecting IEC Short Circuit Report for (drive):\..\simple.dez (Base case) from the Window button or by double-clicking on the window icon created in the lower left corner. Your text report will look similar to that in the figure below.

   
   

   Figure 6: Short Circuit Text Report

5. You can return to the one-line by selecting Simple from the Window button.

Other Options

Select SC Options from the ribbon and click the One-line Output tab.

In this dialog box (shown below) you can also specify Asymmetrical fault currents or Symmetrical and Peak currents to be displayed on the one-line. You can also show fault currents in Per-Unit or MVA units, and display the units.

Figure 7: Short Circuit One-line Output Dialog Box.

Conclusion

This has been a brief overview of EasyPower’s short circuit program. The EasyPower User Manual and Help system cover these and other short circuit features in greater depth.