Can we use on HRG/ Ungrounded systems?

[Kiribanda]

Gentlemen,

It is a common practice to specify and install circuit breakers rated & tested per ANSI C37.06/ C37.09/ IEC 62271-100 on High Resistance Grounded (HRG) or DELTA-DELTA ungrounded networks, specially in industrial applications on 5-38 kV range. But the application of these HV/ MV circuit breakers on HRG or ungrounded networks had not been discussed in any of these standards and also there is no any special test requirement for this type of application.(It is true that special test requirement and labeling is needed in HRG/ ungrounded applications for LV MCCBs/ PCBs etc)

We all that know during a ground fault on a HRG/ ungrounded network, all the electrical equipments are subjected to over voltages (line to ground voltage now equals to full line to line)with respect to ground till the fault is cleared. As such, we specify VTs with higher overvoltage factors, cables with 133% insulation etc etc. What about MV circuit breakers?.

Therefore,

How can we justify the application of these normal circuit breakers on HRG/ ungrounded systems?

Kiri

 

[dpc]

The breakers are tested to a specific BIL and continuous operating voltage. As long as you are within those parameters and have adequate surge protection, I don't see an issue.

This has been done for the past 100 years or so, so if there was a problem, I think it would be evident by now. The weak links in an ungrounded system are the rotating equipment and transformers, not circuit breakers. With HRG, the overvoltage issues associated with ungrounded systems such as repetitive re-strick, etc. are largely eliminated anyway.