3 Phase Protection Relay for a 3 phase open delta circuit

[easpe]

Hi
Does anybody know of a 120v 3 phase protection relay for a 120V 3P open delta with a grounded b phase. The relay operates a automatic transfer backup power system sensing ciruit. There is a Time Mark 263 phase protection relay in the cutler hammer gear now but I am being told it does not provide protection of B phase. I might just install a phase loss relay on 480v line side in series. Anybody run into problems with the Cutler Hammer/Eaton design like this.
Thanks, ed

 

[davidbeach]

Another example of why the open delta 2-VT connection should be avoided if at all possible. If you want to detect phase loss in that situation you will need something that looks at all three phase currents. Probably less expensive to add the third VT and do it right.

 

[rbulsara]

I have not thought this thru, but my first incling is that the relay should work with 2-PT in open delta and B ph grounded. Was just looking at its PDF on web, very limited data there.

If B phase is lost, the AB and BC voltage will change from say 120 to 104, and if you set your UV setting just above it, it should pick up. Also I beleive these relay have phase angle or rotation checkin circuitary which also should pick up.

Also this being a LV application, why not just test it.

 

[rbulsara]

I am tired, may be 60V not 104. Two PTs will be in series across 120V.