Grounding a Wye Wye Transformer

[stickelec]

The installation I was asked to look at was experiencing voltages of about 1000V (2X nominal 480) as their HRG system was being commissioned (primarily as the resistor was removed from the circuit and when the pulsing circuit was tested). As we started to conduct a full investigation and analysis (focusing on zero sequence currents), it was discovered there were 'standard' internal H0-X0 connections at the two POCO service transformers. At this point the analysis was stopped, and the internal bond was removed. The result was the over voltage situation disappeared and the facility has operating correctly for the past 4 years.

Thanks for the explanation. In the situation you mentioned I would be curious if the "pulsing control" was bypassing too much of the resistor-bank. Even in pulse-mode the fault-current should not exceed 10 amps. In the situation I mentioned, the HRG was not under test (no one was in the building when the POCO closed the first cutout), plus - it would have taken thousands of volts & amps to flash-over the CB and blow the 600v cable, etc.

I really appreciate the time you've spent helping me understand all this (thanks to Hv&Lv also). Now, before we quit could you briefly explain the good/bad of grounding the POCO primary to the Plant Ground?

 

[stickelec]

Thank you