aelectricalman
Senior Member
- Location
- KY
I've worked with a lot of power quality issues at a lot of different facilities, but I have never seen this before. I'm hoping someone has had this problem before and can shed some ideas on how to approach finding the culprit, so that I don't waste an incredulous amount of time.
Back-story: Facility frequently burns drives, trips breakers, burns transformers up and they have even melted the wiring on all of their CT's and PT on the power logic's in their gear, causing fires and shutdowns. There are two 1000hp DC motors and three 300hp AC motors among the two 2500KVA pad mount transformers (side by side). The facility is an ungrounded 3 wire delta. The power company after the last transformer burn up put back in two dual transformers capable of being delta or wye. The system is still delta however. The neutral paddle is not being used just FYI.
Measuring the PQ in the 2- 2500 KVA transformers (Reliable Power Meter) and independently in the main gear in the mezz (with a Dranitz and a Fluke 43), we confirmed that there is the following;
Transformer 1 = Phase A - 472 V - L to G
Phase B - 473 V - L to G
Phase C - 2.81 V - L to G
Wait......wait.........
Transformer 2 = Phase A - 2.114V - L to G
Phase B - 481.8V - L to G
Phase C - 481.8 V - L to G
Both XFMR's have a L to L voltage of 474V and 482V respectively.
Notes : There is no paralleling of the XFMR's and there is no connection of the two XFMR's past the metering points (That I know of). Any ideas as to what would show its head like this? I'm open to brainstorming and suggestions! I'm going back in the AM. We are going to look at Z of the equipment and inspect for ground loops.
Back-story: Facility frequently burns drives, trips breakers, burns transformers up and they have even melted the wiring on all of their CT's and PT on the power logic's in their gear, causing fires and shutdowns. There are two 1000hp DC motors and three 300hp AC motors among the two 2500KVA pad mount transformers (side by side). The facility is an ungrounded 3 wire delta. The power company after the last transformer burn up put back in two dual transformers capable of being delta or wye. The system is still delta however. The neutral paddle is not being used just FYI.
Measuring the PQ in the 2- 2500 KVA transformers (Reliable Power Meter) and independently in the main gear in the mezz (with a Dranitz and a Fluke 43), we confirmed that there is the following;
Transformer 1 = Phase A - 472 V - L to G
Phase B - 473 V - L to G
Phase C - 2.81 V - L to G
Wait......wait.........
Transformer 2 = Phase A - 2.114V - L to G
Phase B - 481.8V - L to G
Phase C - 481.8 V - L to G
Both XFMR's have a L to L voltage of 474V and 482V respectively.
Notes : There is no paralleling of the XFMR's and there is no connection of the two XFMR's past the metering points (That I know of). Any ideas as to what would show its head like this? I'm open to brainstorming and suggestions! I'm going back in the AM. We are going to look at Z of the equipment and inspect for ground loops.