The plant is at 50% power. Bus 1A is being transferred from S/P Xfmr 1-1 to S/U Xfmr 1-1. The following indications are present:
S/U breaker: GREEN and WHITE lights lit
S/P breaker: Red and WHITE lights lit
The following then occurs:
1] Incoming breaker from S/P opens when incoming breaker from S/U is closed.
2] RED light on S/U incoming breaker is lit and WHITE light is off.
3] GREEN and WHITE lights are lit on S/P incoming breaker.
[Per SOP-30 if the white light for the incoming breaker (from S/U) is not lit power is to be transferred back to the original source (in this case the S/P transformer)].
d] After power is transferred back to the S/P transformer the station power transformer differential relay actuates
Describe the plant’s response.
With the S/U incoming breaker OPEN (with transferring back, S/U breaker would be open with no WHITE light) and the white light out the closing springs are not charged and the S/U breaker will not reclose until the springs are manually recharged. This breaker will not close on fast transfer. The station power transformer differential relay will cause a fast transfer that will initiate a turbine and reactor trip. Bus 1A will be de-energized and P-50A/C will trip. With the white light out, the breaker can be tripped (locally), but not reclosed.