The best things in life are free. This is what I felt when I am doing this exercise, comparing results from InterPSS with ETAP.

To verify on how an open source software match up to an expensive commercial software like ETAP, I tried comparing the results side by side. I used ETAP 5.5.6 and InterPSS 1.4.04 in my comparison.

The electrical parameters I used are:

Voltage: 132KV
Fault Capacity: 2000 MVA (3 phase), 2000 MVA (1 phase)
X/R: 7 (3 phase), 7 (1 phase)


Transmission Line:
       Positive: 0.243 + j0.143 ohms per km
      Zero 0.39 + j0.36 ohms per km
Length: 15km


Capacity: 30 MVA
Voltage: 132/33KV
Z: 12.5%
X/R: 23.7

I did an ANSI 1/2 cycle fault calculation. The results are as follows:


ETAP 5.5.6

InterPSS 1.4.04

 3L Fault 

3.643 kA

3,642.5 A

 L-G Fault

3.812 kA

3,812.1 A

 L-L Fault

3.155 kA

3,154.5 A

 L-L-G Fault

3.791 kA

3,246.2 A

If you analyze the results, the InterPSS has the same results as ETAP on the ANSI 1/2 cycle fault, except for a slight difference on the L-L-G fault.

These results proves that InterPSS can be used for fault calculation without worrying about erroneous results. Please note however, that in any automated calculation, the results is as good as the inputs. Try to be careful on the parameter values you input into your fault calculation softwares.