Blown fuses while energizing dry XFRM...

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Teslagt

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One of our customers is having a problem while they want to energize a dry type transformer 2/2.8MVA 13,2kV Delta - 480/277V Wye. It is for a commercial building and the fuses blow at the moment they want to energize. Some people says it could be the inrush current and sugest to increase the ampacity of the fuses. Any comment or idea? Why not with oil filled pad mounted units?

Thanks!!
 
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xformer

Senior Member
Location
Dallas, Tx
Occupation
Master Electrician
Teslagt said:
One of our customers is having a problem while they want to energize a dry type transformer 2/2.8MVA 13,2kV Delta - 480/277V Wye. It is for a commercial building and the fuses blow at the moment they want to energize. Some people says it could be the inrush current and sugest to increase the ampacity of the fuses. Any comment or idea? Why not with oil filled pad mounted units?

Thanks!!
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IMHO, i would agree with the inrush suggestion. You could also look at article 450 for the needed OCPD size. You could also run a insulation test on the transformer primary just to make sure things are good there.
 
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zog

zog

Senior Member
Location
Charlotte, NC
The old "Fuse blew so put in a bigger one" advice. What is the correct size fuse? What is the inrush current?

Have the transformer tested. Your DAR/PI results should clue you into the cause.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
As noted above.

1. Test the transformer first and foremost.
2. Determine the correct size OCP based on transformer sizing.

Randomly changing fuses to over come an issue, when you do not know 100% what the issue is, IS NOT RECOMMENDED.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
zog said:
The old "Fuse blew so put in a bigger one" advice. What is the correct size fuse? What is the inrush current?

Have the transformer tested. Your DAR/PI results should clue you into the cause.
Click to expand...

I spent Christmas Eve and the whole next week rebuilding a paralleling gear when they kept changing the settings on circuit breakers to over come inrush. Seems they were paralleling utility with the generator. They had connected the gen to the load bus and factory had blessed the system.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
ptonsparky said:
You are blowing primary side fusing and you want to increase the size? Jeesh, where is the engineering dept and where do they have their heads?
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It does not take an engineer to figure this out. The job I posted about the engineers were on site and recommended to the EC to adjust the instantaneous and short time up, to account for what they thought was inrush. KABOOM!
 
robbietan

robbietan

Senior Member
Location
Antipolo City
one of our customers did that - energized a dry time transformer without thoroughly checking it. seems that moisture has seeped inside the core and kept blowing up fuses
 
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knoppdude

Senior Member
Location
Sacramento,ca
Teslagt said:
One of our customers is having a problem while they want to energize a dry type transformer 2/2.8MVA 13,2kV Delta - 480/277V Wye. It is for a commercial building and the fuses blow at the moment they want to energize. Some people says it could be the inrush current and sugest to increase the ampacity of the fuses. Any comment or idea? Why not with oil filled pad mounted units?

Thanks!!
Click to expand...

Hi Teslagt, this may seem a dumb question, but is the secondary disconnected from its loads while the transformer is being energized? Also, could the windings be shorted in the transformer? Let us know what you find.
 
Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I had an issue like that over ten years ago. The problem was the inrush current. The darn thing kept blowing the main. Before the reset I checked the connections meggered the wires all was good. Had to wait several days for the engineer and he said increase the trip settings. The system has been in place for about 10 years now with no further issues.
 
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