SKM powertools - fault contribution

[bspace123]

Hello all

I have a model setup in SKM with a bus which has a single incomer and supplies a bunch of DOL motors. Attached to the bus are also some generators.

When I simulate a fault at the bus and open all the feeders, the fault leave at the bus is 3kA which is showing as being supplied purely from the incomer.

When I simulate the fault at the bus and close all the feeders the fault level at the bus rises to 4.5kA, which is expected as this is the contribution from the motors and generators. However, the branch fault current reading for the incomer also rises.

I thought motors/gens will only increase the fault level at the location of the fault (in this case the bus). Why am I seeing fault levels increase for the same bus fault on the incomer? Shouldn’t this remain at 3kA during both scenarios?

 

[dpc]

What type of fault? For unbalanced faults, the results can be non-intuitive.

 

[bspace123]

Balanced 3 phase fault

 

[dpc]

Then it doesn't seem correct. Make sure the voltages are the same. Some programs calculate the pre-fault voltages based on a prior power flow calculation. Higher voltage will mean higher fault currents.

 

[7anoter4]

After the loss of power of the stator side of the induction motor, the rotor side current can be obtained according to the magnetic flux conservation principle.And the residual voltage of induction motor is deduced.
That means the magnetic flux supported by rotor current which is decreasing, will produce a residual stator voltage and in turn a current up to the fault point.
See[ for instance]:

https://iopscience.iop.org/article/10.1088/1757-899X/199/1/012124