ground transformer on 3 phase 4 wire 480/277 volt system

[mvsubstation]

Would there be an issue with installing a new zig zag grounding transformer at an existing building 480/277 3 phase, 4 wire service? In order to obtain effectively grounded solar inverter to meet utility requirement, they are requiring a grounding transformer. It seems that having a connection to ground at two different locations (the existing building ground, and the new ground connection for the zig zag), could cause unbalanced neutral current to flow between the two points and cause some ground fault devices not to operate properly among other issues.

 

[davidbeach]

My guess is that the utility wants the ground source on the other side of the transformer, not the 480/277 wye side.

 

[PHovnanian]

Possibly for harmonic mitigation?

A diagram of what the utility is requesting relative to their service and system would be helpful. Simply adding a zig-zag grounding autotransformer can indeed cause problems. For one thing, you can create a path into your system for harmonics generated by nearby (other customers) loads if done incorrectly. On the other hand, it is an effective method for handling your inverters' harmonics if there is no zero sequence path back to the utility.