Marine Isolation

[SDSAUTO]

Hello to all, we recently installed a new 17k isolation transformer in a 58 foot Hatteras. Upon completion, the main breaker upstream of the 220/120 transformer trips when the shore supply switch is turned to that station. This yacht has both service one and service 2, meaning that the port and starboard sides of the boat can supply the mains individually, or together. The problem transformer is the service 1 side. When I apply power to the service 2 side, everything is fine. (separate breaker and transformer, but shared loads)
My logic is that the problem is not in the loads since service 2 handles everything ok. The transformer is a direct replacement and installed exactly the same as service 2. I have 65v and 85v on the lot legs at the breaker. with the neutral unhooked the breaker and gfi remain on. I have tried swapping the voltage sensors (torroids) and the GFCI's, but the problem remains.
What should I be looking for? I admit, the HV systems are not my specialty on yachts. I was called in due to a short in the 32v dc system and discovered the transformer hot legs cooked off of the transformer.
Any help would be appreciated. Thanks!

 

[GoldDigger]

Hello to all, we recently installed a new 17k isolation transformer in a 58 foot Hatteras. Upon completion, the main breaker upstream of the 220/120 transformer trips when the shore supply switch is turned to that station. This yacht has both service one and service 2, meaning that the port and starboard sides of the boat can supply the mains individually, or together. The problem transformer is the service 1 side. When I apply power to the service 2 side, everything is fine. (separate breaker and transformer, but shared loads)
My logic is that the problem is not in the loads since service 2 handles everything ok. The transformer is a direct replacement and installed exactly the same as service 2. I have 65v and 85v on the lot legs at the breaker. with the neutral unhooked the breaker and gfi remain on. I have tried swapping the voltage sensors (torroids) and the GFCI's, but the problem remains.
What should I be looking for? I admit, the HV systems are not my specialty on yachts. I was called in due to a short in the 32v dc system and discovered the transformer hot legs cooked off of the transformer.
Any help would be appreciated. Thanks!

If there is an imbalance in the service voltage between L1-N and L2-N or the transformer primary tap points (if any) are not set identically, connecting the primary side neutral of the transformer will cause very high circulating currents.

If there is a GFCI on the primary side of the transformer, it is likely that there is leakage between the winding and ground or in the wiring outside the transformer. That would cause the GFCI to trip on that service side only.