# Homework Help: Calculate 3ph short circuit symmetrical fault, per unit method.

1. Feb 21, 2013

### bluff_boy

1. The problem statement, all variables and given/known data

Calculate the three-phase short-circuit fault currents flowing into all five busbars.

2. Relevant equations

MVA base = 150MVA
All base voltages were set to the local busbar voltages.

Formulas I have used can be seen in the attached photos.

3. The attempt at a solution

I have attached two photos, the first shows me calculating the short-circuit fault current to busbar 5. I have made a per unit diagram and ignored the j terms as there is not resistance for less hassle. I have simulated this using software and it confirms my answer.

The next photo is the problem I'm stuck on, calculating the short-circuit fault current to busbar 2 (BB2). I get stuck because I can't simplify the circuit anymore to get the X fault per unit value. I have tried to use current and voltage dividers, but can't get anywhere near the answer. I have also simulated this problem and get the answer to be 15.954kA

thanks

File size:
23.8 KB
Views:
232
File size:
19.5 KB
Views:
204