Transformer commissioning and testing

[FreddyNurk]

We have a startup processing plant that is in the process of being constructed, and has not yet reached commissioning phase. As part of the plant, a number of second hand transformers were purchased, with varying condition.

I believe that it is appropriate to arrange for these to be tested before being put into service, or even installed, but being new to this, I'm not sure exactly what tests would be required. I'd imagine that the usual insulation tests with new oil would be appropriate, as would an oil analysis test.

The transformers range in size from 25kVA up to 5MVA. Transformers are privately owned and don't require separate utility testing. All transformers are oil cooled, some ONAN cooling, and at least two are OASIC.

I'd appreciate hearing your suggestions.

 

[davidbeach]

25kVA, oil cooled? Not impossible, but also not very probable.

At a minimum I'd think you'd want an as found oil test, particularly looking for water in the oil. Then probably new oil and enough vacuum to thoroughly dry them out followed by all the standard electrical tests. Once the electrical tests are completed check the oil again.

 

[FreddyNurk]

DavidBeach, I can link a photo of the 25kVA transformer if required. Indeed, normally very unlikely, but its here. Rather silly to be using an oil filled, considering its size, indeed.

I appreciate your suggestions.

 

[ScottyUK]

What does the abbreviation 'OASIC' mean? It's not one I've seen on this side of the pond, and Google didn't return anything meaningful that I could see.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[FreddyNurk]

Scotty, not entirely sure. Its listed on the nameplate next to the temp rise figures, transformer is one of two that is used in a 'rectiformer' plant, produces high DC current for extracting copper through electroplating.

Transformers are American in manufacture, site location is Australia.

I believe that the transformers are not a common item, and thus testing is vitally important in case they need to be repaired / replaced.

 

[sslobodan]

First you should ask for their maintenance data to look what problems they had. In general you should look how they react at over current/over voltage, and that transformers should withstand 120 % load for few hours, 160 load for 15 minutes. You use thermal vision for determining are the windings overheated. If they show some irregularity you should expect that they insulation has been damaged and they will fail in time. Check the protection, with old transformers you most probably purchased their old protection relays and you should check if they are working. Look at the nameplate for their withstandable overcurrent, I would not check it unless they signed up in contract that it will withstand it. It is usually used for new transformers. And on the end check the oil and see if it needs to be replaced, and moisture in side.
Basically you can have the idea what all can be tested by looking what

http://www.transformerservices.com/

have in offer from testing.

 

[davidbeach]

What is the frequency in Australia? If it is 50Hz you need to be aware of the issues of 60Hz equipment being used at 50Hz. You will have to derate the voltages to 5/6 of the nameplate voltages.

 

[FreddyNurk]

We have no maintenance data for the transformers, some were second hand from a reseller, some were 'brand new' and sat in storage for a few years.

With regards to the American equipment, the gear was manufactured in the US specifically for use in Australia, and was purchased second hand by us. So we don't have the 50Hz issue, thankfully. The American equipment was picked up as a complete package.

 

[HVDragon]

Tests:
0. ratio
1. no load
2. resistance
3. isolation
4. I didn't see what are voltage ratings, but tandelta/powera factor test is nessessery
5. short circuit impedance
6. any bushings? - tandelta tests
7. oil probe test


Something terrible is stalking between the high voltage potentials

 

[sslobodan]

I would disagree with short circuit test on a second hand transformer for more than 0.35s unless you have a chance to get it back to the supplier if it fails on the test. I remember one story from my lectures. My professor was hired to test some transformers built for the 600MW power station block. There were 2 identical transformers (i cant remember who was the official producer maybe Siemens or Schneider) one built on contract by Skoda and another by Minel (Minel the company from my country was the part of the deal) So when they were tested Minel passed all the tests but Skoda transformer failed on short circuit test and they had to do that transformer again. Short circuit test is always shortening the life of transformer, Sometimes you can get 3 sometimes 7 before the winding insulation burns up and short circuit one by one winding of a phase(s). Transformers are usually the safest parts of electro system and they can work for many years without a problem to occur. If relaying turns out faulty system before the transformer protection trips they can work even for 50 years without having any major problem.

 

[ScottyUK]

Hi Slava,

The short circuit test is usually performed with a controllable low voltage supply being used to circulate current in one winding of the transformer with the other winding shorted. Test current is limited to rated current. It's a different test to the fault withstand test with I think is what you're describing.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[slavag]

Hi Scotty.
Now, you are have big mistake!!!!!!.
I'm Slava, sslobadan is Slobodan.;-).
BTW, I don't have any problem with SC impedance test, but I
think it's usually tested only in mnf.
Regards.
Slava

 

[whycliffrussell]

I wouldn't rule out PCB testing either (old second hand transformers...). You can purchase a kit called clor-n-oil 50 from Dexsil (many utility companies throughout NA use this stuff all the time) to test for the presence of PCBs.

 

[ScottyUK]

Slava and Slobodan,

My apologies to you both. I obviously can't read what is in front of my eyes. I will pay more attention in future!!


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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[slavag]

Hello Skotty.
I'm only joke .
Slobodan, we are have problem, both of us start from Sl.
Best Regards.
Slava