Three phase model of single phase system in SKM 1

[deltawhy]

Hi there,
I have a single phase system in which I require an arc flash analysis for. However, I do not have the single phase / unbalanced load package for SKM. I will thus attempt to model this as a three phase system to attain the single phase fault currents. I have looked through any threads in relation to this and have drawn the following conclusion. I would just appreciate it if the industry experts were to chime in to with anything wrong in my assumptions:
Info:
-Single phase 25kVA transformer 1.5%Z, connected L-N on a 25kV three phase line - therefore 14.4kV:120/240V
-Utility information gives Z1 and Z0 for the three phase line

Assumptions:
To acquire the proper single phase bolted fault currents at the transformer secondary, I have done the following.
-model a 75kVA YNyn three phase transformer, 1.5%Z, 25kV:415Y/208V (same full load currents as 1P transformer)
-use the same utility data as given

-calculate the L-G fault current at the secondary of the 75kVA transformer to acquire the accurate single phase fault current.
From here, use this current to calculate the clearing times of the single phase protective devices.


Thanks.

 

[magoo2]

I'd be interested in seeing your sequence networks for the 120 V fault case.

 

[deltawhy]

Well actually a LG fault from an equivalent three phase transformer.