crthompson
Electrical
- Aug 8, 2011
- 75
Hello, I just received an email from a customer having issues with a piece of mining switchgear. This unit has a 2750 KVA XFMR with a delta 13.8 KV primary, a delta 2.3 KV secondary @ 2000 KVA, and a wye 480 V secondary @ 750 KVA. The secondaries both feed busses. The 2.3 KV bus supplies power to a continuous miner. The 480 V bus supplies power to various smaller loads. The 480 V feeder bus is protected by a main breaker and each branch has its own breaker. The customer claims that the miner was running along with various unknown 480 V loads when the 480 V main breaker tripped (the 15KV main breaker on the primary of the XFMR DID NOT TRIP). The customer then removed the lids from the unit and saw that there was "some smoke coming from the XFMR". They said that they used a 5KV megger on the secondaries and everything checked out ok. They removed the main breaker's cover and found no physical damage. I will be going to this customer's site in the near future to inspect the equipment. Other than an issue with the XFMR that caused a voltage drop that dipped below the breaker's UV coil threshold on a control XFMR, I can't think of any issue with the main XFMR that would cause the downstream 480 V main breaker to trip (I don't even know that this breaker has a UV coil... Just a possibility). Just off the top of my head, I would think that there is an issue between the 480V main and the 480V feeders to cause the trip but this doesn't explain the "XFMR smoke". It is very possible that there is more than one problem with this switchgear. Has anyone ran into any similar issues out in the field that may shed some light on these problems? Thanks in advance!
I am an engineer, so the glass is twice as big as it needs to be.
I am an engineer, so the glass is twice as big as it needs to be.