mls1
Electrical
- Aug 15, 2002
- 133
We have an installation in which an the switchgear and PTs were replaced for an older hydro generator but the regulator was not. It was not discovered until after the system was installed that the regulators (Westinghouse BJ-30) specifically calls for an open delta PT circuit. The regulating PTs were replaced with three phase wye PTs. There are two simple options we are considering and would appreciate some advice on:
1. Connected the wye PTs directly to the BJ-30. The BJ-30 rectifies the three connections and the line-to-line voltage is the same as the old open delta system. This would leave the BJ-30 sensing circuit floating. Looking at the schematic there doesn't appear to be anything preventing this except the field forcing cross current compensator. Any suggestion if this would be a concern?
2. Move the ground point on the PT secondary from the neutral to Phase B. This would ground the PTs similar to a corner grounded delta. The regulator is the only thing these PTs are used for and the A and C phase voltages would be 120V to ground matching identically the electrical characteristics of the open delta (same voltage and phase relationship). We can't see any issues with doing this but I can honestly say I've never seen it done. Any concerns?
Thank you!
1. Connected the wye PTs directly to the BJ-30. The BJ-30 rectifies the three connections and the line-to-line voltage is the same as the old open delta system. This would leave the BJ-30 sensing circuit floating. Looking at the schematic there doesn't appear to be anything preventing this except the field forcing cross current compensator. Any suggestion if this would be a concern?
2. Move the ground point on the PT secondary from the neutral to Phase B. This would ground the PTs similar to a corner grounded delta. The regulator is the only thing these PTs are used for and the A and C phase voltages would be 120V to ground matching identically the electrical characteristics of the open delta (same voltage and phase relationship). We can't see any issues with doing this but I can honestly say I've never seen it done. Any concerns?
Thank you!