Single pole recloser- Transformer diff operation

[Prot123]

I'm analysing the following condition and wanted to know your views.

For a radial line feeding into a transformer(Ynd-275/11kV) what will happen to the TF diff relays during the single pole reclose dead time for the line.
Say for a C phase- Gnd fault, during dead time, TF HV will have A phase and B phase current with no C phase current. TF LV in the meantime should have current on all three phase.
Similarly, during the dead time TF HV will have significant negative sequence current and as the LV feeds into motors how will that impact on the performance of the motor. How will this negative sequence transfer from HV to LV. Is there a chance it might trip the motor? Thank you.

 

[stevenal]

Grounded Wye-delta? Transformer will continue to serve the load as an open wye-delta. These connections are widely used at services with no ill effect on motors. Primary neutral impedance can unbalance the low voltage phasors, though.

 

[Prot123]

Thanks for the reply. Do you have any paper or reference on this? Cheers

 

[jghrist]

The phase current balance on the differential will be maintained by the CT connection correction factors. Or if electromechanical differential relays are used, by the use of delta connected CTs on the high side and wye connected CTs on the low side.

 

[stevenal]

Sorry, no references handy. Try searching on "open-wye open delta". Yes, compensation will handle the open periods if set correctly. I think I would worry most about inrush when the open phase closes back in. Some extra care may be needed in the harmonic restraint/blocking settings.