unbalanced primary voltage

[dbelect]

I have encountered a problem with equipment burning up for no appearent reason.
This is a large site and the problem that I have is with temperary power. There are several pad mount tranformers 4160/600v as you can tell I'm in canada and generally use delta wye.
Earler this week we had a disconnect blow up. There was no load on this disconnect and the cable on the load side megered good and the welding machine bank was off.
When it blew it did not take all of the fuses but it did melt two of the line side lugs completly off and burnt the third off in the splitter trough. This causing the disconnect to be blown off the skid hanging with the door open.
The secondary voltage has two lines at 600v and the third 630v.
Could this type of imbalance cause a surge?

 

[itsmoked]

If there was NO load something besides voltage imbalance is the issue.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dbelect]

Yes I agree I'm looking for possible senero's that could cause something like this. The hydro company has done the conections in the transformer.

 

[dpc]

Sounds like it arced over ahead of the fuses, or the incoming cable went to ground.

Voltage imbalance would not cause this. A remote ground fault on the 4160V system could cause 4160 V to appear phase-to-ground and this can sometimes cause insulation failures if it persists.

 

[waross]

It sounds as if you got hit with a serious voltage surge. Did you have an electrical storm in the area? Did you have any other voltage related problems?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Let me say your original description is very typically caused by NOT having extremely tight connections. That causes this with great regularity! Except you stated NO load.

Are you sure of your facts?

It's sort of like. "This body has a bullet hole in it but they say he wasn't shot..."

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dbelect]

I don't think that anywhere on the site had any problems or atleast none where reported. I'm not sure if you caught the detail "blew up" I mean the door was blown open and the disconnect was hanging by the tec cable with 2 of the lugs burnt completely off.
Can you tell me more about this "A remote ground fault on the 4160V system could cause 4160 V to appear phase-to-ground and this can sometimes cause insulation failures if it persists" This sounds more like what happened.

 

[dpc]

It's probably unlikely since the insulation system should be able to withstand line-to-line voltage for a long time. It's a possibility if there was a problem with the insulation at some point. More likely a voltage surge as waross suggested or arc initiated by tracking, rodent, etc.

Also, if the 4160 V system is solidly grounded, the ground fault shouldn't persist long enough to cause problems.

 

[waross]

Hi dpc.
I considered rodents as a first response but if rodents were the cause I would expect the damage to be concentrated in one area. One connection damaged in the splitter trough and two connections damaged on the feed lugs of the switch seems more like a surge. Another possibility may be a three phase short downstream and some less than perfect connections let go under fault current. I favor a voltage surge as the most probable but not the only possibility.

Bill
--------------------
"Why not the best?"
Jimmy Carter