tripping of main feeder breaker 150A trip when the UPS is pre-commissioned.

[Askarel27]

The main feeder 150AF/150AT is installed in a outdoor switchrack has a 150a ground fault detection feature (EATON ELJBN3150W). It is supplying a UPS (10kVA, 480V) inside a building from a 100AF/30AT circuit breaker. The ground fault unit setting at the switchrack is t(s) = "1.0" and the Ig (A) = "0.03". However when the UPS is turned ON, the main breaker 150A trip. The UPS vendor recommend to increase the level of detection Ig from "0.3" to "1.0". However, the client wanted as per engineering point of view. Is it the EMC filters effect in UPS? Please help.

 

[ScottyUK]

Yes, very likely the filters are allowing current to pass to earth as part of their normal function.