90o - 30o directional overcurrent for transformer feeder

[Cerkit]

Hi,

Does anyone know why a 90 - 30 relay mal operates for a phase-phase fault when a transformer is on the feeder?

I have read that a 90-45 relay will operate correctly for all faults.

Thanks

 

[Cerkit]

Please see the attached diagram. The relays at B have their vectors resolved for a 2:1:1 fault current distribution, with a 90 - 45 connection the relays all operate for this scenario. If these were 90 - 30 relays my understanding is that for phase R for example, the polarising voltage would be Vyb and this would be shifted 30 degrees then input in to the R phase relay (as opposed to shifted 45 degrees as with the 90 -45 connection), but when I draw out the vectors for the 90 - 30 relay they all appear to have their fault current and polarising voltage within the Operate zone, so I don't see why it is said that with a 90 - 30 connection the phase which the fault current is in antiphase would not operate (maloperate).

Any thoughts on this would be very helpful thanks.

 

[jghrist]

Your diagram didn't get attached. I'm not familiar with 90-30 or 90-45 relays. Do you have any references?