grounded line
grounded line
(OP)
we have a 480/220 delta to delta connected transformer in our workplace.This supplies lighting and airconditioning units (window-type),occasionally we experience line being grounded(shorted ballast,strip wire insulation). How can this prevent this as we have measured line to line voltages reaching 400 v.
Incidentally we have a couple of newly installed equipment equipped with RCCD breakers which ussually trips.
Incidentally we have a couple of newly installed equipment equipped with RCCD breakers which ussually trips.





RE: grounded line
I would expect you might measure high voltages to ground which might be destructive to the insulation. I would not expect that you would measure high phase-to-phase voltages as you reported.
If you search for ungrounded system in the electric power forum, I think you'll find more info.
RE: grounded line
RE: grounded line
1. Use ground fault detector and remove ground faults. However, this would not prevent overvoltages, e.g. the mentioned 400V. This would need a suitable overvoltage suppressors.
2. Replace the trasnformer for 480V/240V with the star winding on its secondary, which may use a suitable grounding scheme, e.g. solidly grounded neutral, or high-resistance grounded neutral system.
3. Explore, whether the corner of the secondary delta winding grounding would be suitable. It is inexpensive solution with the following disadvantages:
3a. The necessity for positive identification of the grounded phase throughout the entire system.
3b. Instruments, meters, and overload relays should not be connected in the grounded phase.
4. Add a zig-zag dry type grounding transformer to establish a neutral.