Run a Short Circuit Analysis

Open the Short Circuit Focus and Fault a Bus

Open the short circuit focus by clicking Short Circuit on the Home tab.

Fault the lower right-hand bus by double-clicking on it. You should see the following results:

Figure 1: Running Short Circuit Analysis

Notice that we need to make a minor change to the one-line to see the results.

Adjusting the One-line for Results Readability

Drag each motor down enough that the numbers fit between it and the bus.

Figure 2: Readable Text After Adjusting One Line

After adjusting the one-line, you can save the updated arrangement with the Save command even though you are still in the short circuit focus.

Interpreting the Results

Note that the faulted bus is highlighted in blue. The default result units are symmetrical kilo-amps. (You can change this by clicking Tools > Short Circuit Options > One-line Output.)  The faulted bus current is 19.695 kA, which is shown on the right-hand side of the bus at a forty-five degree angle. The contribution from the transformer is 17.272 kA, and the motor contribution is 1.250 kA.

If your results do not match these numbers, recheck the database dialog boxes for each item, comparing them to the dialog boxes shown in this tutorial. To do this, you must first get back to the Database Edit focus by clicking Database Edit.

Looking at a Remote Voltage and Current

EasyPower gives you the ability to view remote voltages and currents (on multiple buses other than the one experiencing the fault).

While the lower right-hand bus is still faulted (highlighted in blue), select the lower left-hand bus by clicking it once (it will turn green). Click Remote V/I on the Short Circuit tab to see the remote voltage and current for that bus. To view the voltage and currents for all remote buses, click Remote V/I without selecting any buses.

Figure 3: Looking at Remote Voltage and Current

As you can see, 0.860 kA from each of the motors flow to the fault on the right-hand bus. For remote buses, the voltage is shown at a forty-five degree angle. In this case, the value is 0.358 per unit, or about 36 percent of nominal. The voltage can be displayed in kV if desired by clicking SC Options > One-line Output.

Looking at Interrupting Results

Click Interrupting on the Short Circuit tab to see the interrupting results. In addition to the half-cycle results, the interrupting (5-cycle) results also appear. To see only the interrupting results, click Momentary and turn the display off for momentary currents.

Figure 4: Viewing Interrupting Results

Notice that the motor contributions decay as the bus voltage is depressed and the time constants of the motors increase. This provides a clear indication of the currents necessary for setting relays.

Figure 5: Motor Contribution to Short Circuit Current

     

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Help was last updated on 5/22/2018