Substation thru fault test

[amps21]

Gents,

I am new to this forum.

I am commissioning a substation where I need to perform thru fault test to confirm relay current stability (For Differential and other relays and measure expected vectors etc.)

Question is what amount of current will flow in the autotransformer neutral and its phase angle, for a SLG fault on the HV side with my source on the LV. The transformer has a stabilizing tertiary winding and it is designed to be loaded.
I know that this magnitude is dependent on System source impedence, transformer LV and Tertiary equivalent impedence etc. Also under certian circumstances the current flow direction in the newtral can flip (in or out) but i am not able to figure out what would be the case here.

The transformer is 300MVA (base)(345/115/24.9 kV Ynaod1) HV-LV 7.3% Tertiary is rated 50MVA. I dont know the tertiary impedence to HV right now but i shall furnish that tomorrow.

For the fault, I have the source on LV side- 3 ph. generator (120V) and i figured 36 Amps in LV for HV SLGF. I believe the neutral shall be 24 Amps. I want to know the phase angle that the neutral current shall have and the magnitude of the tertiary circulating current. (Phase angle in tertiary is relative to neutral current direction. I think the neutral current shall flow out in this case.

Kindly help

Thanks in advance

 

[jghrist]

The amount of current and the phase angle can be determined by calculation using the appropriate sequence networks or by modelling with fault analysis software.