waross - thank you for your suggestions. I prefer a solidly grounded system as I think this might be best for limiting transient overvoltages; but I am not able to go solidly grounded as there is no breaker to trip on transformer primary side-only a fuse.
There is another scheme in which the...
Live2learn - was the instruction to remove the screw for an ungrounded delta system stated in the O&M manual for the VFD? Who is the VFD manufacturer? I am looking for a reference that I can present to the plant VFD technical person.
As David pointed out best option is to replace the existing transformer with a delta-wye solidly grounded. However, this is a costly solution with considerable downtime required.
Can you please provide some details on a suitable grounding transformer so we can at least consider this option? Some...
Transformer is rated 3500kVA 25kV/480Volts Delta-Delta.
Ungrounded delta secondary is causing variable speed drive problems.
Please recommend best means to ground this transformer.
waross - in one of your posts on this thread, you state that 60amps of neutral current on a transformer that size(3750kVA 12.47kV primary) indicates a very good balance on the primary.
The FLC of this transformer is 174Amps, so 60amps seems relatively high to me. Can you show me how to...
cranky108 - thanks for your reply.
For system unbalance - do you mean to look at the 12.47kV voltmeters and make sure they are balanced?
Do you believe that the problem is not on the downstream side of the CT's, that is, on the transformer side but that the problem lies upstream on the utility...
Transformer: 3750kVA
Primary: 12.47kV Wye solidly grounded(connected to the utility line).
Secondary: 2400V Delta
Experiencing occasional 51N trips, that is, primary neutral current. 51N relay picks up at 2.0A.
51N current all the time about 1.0A; with 300:5A CTs equates to 60A primary.
One time...
