Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
(OP)
One of our customers is served from a 2500 kVA PMT, 5-legged, 35 kV Gnd Wye - 480V Gnd Wye. The 35 kV feed is from a fused Overhead lateral line to a fused terminal pole. The cable from the TP to the transformer is about 100' 1/0 AL EPR cable. The customer has a transfer switch that senses loss of utility voltage and transfers to his generators.
Recently B-phase on the lateral pole blew. The customer load transferred to his generator. However, once load was removed from the transformer the transfer switch sensed good utility voltage and retransferred. Once load was added to the transformer the transfer switch transferred back to the generator. It did this until the customer opened his main breaker.
We duplicated this by opening B-phase on the TP with the customer's main breaker open. Voltages were:
Before Opening Fuse
LG = 284, 284, 283
LL = 491, 491, 490
After Opening Fuse
LG =284. 284, 267
LL = 491, 480, 496
Could someone explain this occurrence and maybe offer a solution to this problem.
Thanks
Recently B-phase on the lateral pole blew. The customer load transferred to his generator. However, once load was removed from the transformer the transfer switch sensed good utility voltage and retransferred. Once load was added to the transformer the transfer switch transferred back to the generator. It did this until the customer opened his main breaker.
We duplicated this by opening B-phase on the TP with the customer's main breaker open. Voltages were:
Before Opening Fuse
LG = 284, 284, 283
LL = 491, 491, 490
After Opening Fuse
LG =284. 284, 267
LL = 491, 480, 496
Could someone explain this occurrence and maybe offer a solution to this problem.
Thanks






RE: Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
Basler has a very good article on the subject.
http://
I guess you could add some type of load between the transformer and ATS to pull the voltage down or change the transformer to a different type. If you could find a way to sense the voltage at the primary, that may work also.
RE: Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
The most practical solution at this location is to add a "small" load to the transformer. Any guidance in estimating the "small" load?
Thanks.
RE: Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
RE: Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
Am I wrong about this?
RE: Gnd wye Gnd wye PMT with one primary phase off - Good voltage on s
The line fuse holder can also be very slightly conductive with the fuse blown hence the need to ground out disconnected wires.