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Discussion Starter · #1 ·
I have an existing 150 kva, 3 phase, 480\ 110-208 volt transformer. I have an in coming 486 volts on the high side. (DELTA / WYE)
On the low side (x) I have 115 volts to neutral (xo). The transformer is already taped at the maximum 105 percent. My voltage reading from all the x-1, x-2, and x-3 readings are no more that 202 volts. The load on the transformer is (no load).
My question is; is this transformer secondary voltage bad? Shouldent I be reading a secondary voltage of at least 212 volts (phase to phase). Because it is taped at 105%.
I have a megger , How do I test the transformer. ?
Any information greatly appreaciated................
Thanks,
Kris:)
 

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I dont want to be silly in here but what name brand this transformer and which way you ran the tap ??

i know some 150KVA transformer have 4 tap 2 are above rated voltage and 2 at below the voltage.

you should able read the nameplate on the transformer.

and the chart to change the % tap in + or - format.

and those tap useally be on primary side AFAIK.

did this transformer got overloaded before ?? or any unuseal sign of overheated or short ??

some case will have a turn shorted out but for all three legs do that i doubt it.

let us know with more info first

then we can go from there

Merci, Marc
 

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Discussion Starter · #3 ·
Frenchelectrican Thanks for your reply.
The transformer is made by "International Transformer Corp."
If I remember correctly, there are six taps on the transformer. Right now the taps are on the 4 and 6 terminals whitch bring the percentage to 105
%. By re taping, I think that I can bring the voltage down to 90%.
I was just told by the owner that there was a flood a fiew years ago. This transformer did get wet on the bottom coils.
I am soooooo ready to yank this thing out and install a new one. But I thought I would get input from other electricans first.
Kris.
 

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My SOP answer to any electrical equipment that has been in a flood: replace it.

It may work today, and seem to be fine, but who knows what contaminates and chemicals were in the water that penetrated it. This is a disaster waiting to happen.

Again, my SOP answer to any electrical equipment that has been submerged: replace it.
 

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The 105% tap may very well be for a primary voltage that's 105% of 480. Using this tap at 486 would result in about 115/200 on the secondary. This figure is a guess, I didn't calculate it exactly.

Try tapping it at 100%, I suspect the secondary will come out at about 122/211.

I agree with 480sparky completely. Any electrical equipment that has been submerged should be replaced. Are there signs of flooding? if so, point this out to the owner. Then the ball is in his court, not yours.

Several years ago, we had a flood in Reno, most of the industrial buildings in the flooded area had 1 to 4 feet of water in them. The submerged electrical equipment that was not replaced immediately failed within the first year or so. Usually at the most inopportune time. I worked alot of nights then.
 

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While manufactures DO NOT RECOMMEND it transformers can be dried out and meggered, the real issue is any residue blocking any coils, cooling and megger results. I have dried a few transformers (this was an extreme circumstance where replacement was near impossible due to building design) and if they megger out, they should be fine, BUT, with a transformer as the manufacturer recommended you should replace it.

As for the no load voltage I bet as noted you have your taps wrong, experiment, change the taps.
 

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Discussion Starter · #7 ·
Micromind, Thanks for your input.. I will tap it at 100% and see what I come up with. I will also let them know that replacement of the transformer would be in their best interest.

Thanks everyone for your help.
Kris.
 

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my SOP is pretty much clear on this one any electricial equment is flooded is get replaced.

[ this is recomened by most manufacters requrements ]

but for the taps you can change to diffrent postion but follow the nameplate cover if readable and read the numbers very carefull.

but really i really encorge ya to replace this transformer because it can shorted out at wrong time and can cost the comustor a heckva extra headahce.

Merci, Marc
 

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On flooding we get involved in many floods die to water rising and/or fire departments quenching the flames.

On switch gear bolted pressure switches, Fused Safety Switches and and Circuit breakers need to be replaced, The main gear, structural supports and bus should be fine if properly cleaned, the real issues is with the insulating material, normally the fish paper MUST be replaced, but the stand off insulators (commonly called Cherry Insulators) can be cleaned and remain in service, all steel hardware (bolts nuts washers) need to be replaced.

I have been able to restore to service numerous flooded switchboards after water intrusion, with megger reading as good or better that new, performed maintenance on the same equipment in 3 years and the equipment is no worse from the past water.

BUT it takes expierence and perseverance to make sure all water issues (low readings) are resolved, often taking the gear down to component level.
 

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We were working in a school that sat in a low lying area. Found out the hard way after the sparks had settled, the whole gear has been submerged several years earlier. All we did try to open a 400 amp large frame (about a K) breaker. It shorted internaly phase to phase. I saw the dragon roar that day. 2' to 3' dia. by 6' fire ball. Just like a P Oed dragon. The roar was something else. Balls of molten copper imbedded in concete 6' away. Very scary. One of the guys quit the buisness shortly after, he was literaly in the fetal position under some pipes when it all settled. No one got hurt. Who knows what our lungs look like with all the atomized copper in the air.
 

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Copper, carbon, steel, plastic and depending upon the age of the equipment asbestos. BUT with proper maintenance by a qualified firm and technicians this need not happen.
 

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Brian you seem like you might know the reason why. When my boss pushed on the handle of that 400 amp breaker from my story above it just started exploding. We never took it anywere to have it analyzed so we never found out why it shorted phase to phase. It was part of a lineup that went 5kv switch /transformer /breakers, all attached by buss like one big piece of equipment. I threw the hight volt switch and the exploding stopped. It had blown one fuse the other 2 where still intact that's why it was still shorting. I had been doing electric work maybe 8 years at the time. I thought maybe carbon had built up on inside of the breaker and slamming of springs inside loosened it up and thats what ultimately caused the short. Do you have a thought on what might have caused it. It apparently had been under water at least once maybe more.
 
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