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Loading of a Transformer

01/28/2012 11:24 AM

We are having 1.5MVA transformer with rating of primary voltage as 11KV & amperage as 76.78amps also with secondary voltage as 420 volts & amperage as 2000 amps.my question is up to till how much i can loaded this transformer(in terms of KW/Current)also weather this is advisable that transformer can loaded 100% for long time?

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Guru
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#1

Re: LOADING OF A TRANSFORMER

01/28/2012 11:59 AM

1.5MVA/(420V x √3) ≈ 2062A.

If the transformer is rated at 2000A continuous, it should be to operate indefinitely at 2000A. However, be aware of any ambient temperature corrections that may apply.

The KW capacity equals the KVA capacity times the power fasctor of the loads, which may vary. For example, if PF = 0.8, then KW capacity 1200 = 1.2MVA.

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#2

Re: Loading of a Transformer

01/29/2012 3:25 AM

Hi

Loading is certainly a very important aspect but at what pf?Certainly 100% loading is also possible but then efficiency again is very important.A transformer is the only electrical equipment giving you a very high efficiency as high as 99.78% but yes then at specific load.You cannot load a Transformer (In this case upto 2000 amps) 100 % and expect an efficiency of 99%.The ideal would be to load it at about 70% to get the best performance.

radhakrishnan k a

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#3

Re: Loading of a Transformer

01/29/2012 3:32 AM

Well it depends on the type of load you have. Generally give a margin of a few hundreds while loading a transformer of this size to be on safer side, You know keeping the service factor and power factor variations, in mind. You need to communicate with your transformer manufacturer to know exactly how much margin you should give while loading.

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#4

Re: Loading of a Transformer

01/29/2012 6:40 AM

Since you have mentioned transformer is rated for secondary voltage of 420Volts and 2000Amps, it means the transformer winding (Cu Sizing) is designed for 2000Amps. Dimension of transformer is fixed accordingly to take care of Core, windings and heatings. If the ambient temperature is within the specified design ambient we can load the transformer 100% continuously. As per 1.5MVA transformer rating, secondary current works out to be 2062A which is more than 2000A.

Transformer can be designed to take periodic over loads also.

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#5
In reply to #1

Re: LOADING OF A TRANSFORMER

01/29/2012 10:35 AM

Hi Tornado.

A minor error which is not worth mentioning; 1,600 instead of 1,200.

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Guru
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#6
In reply to #5

Re: LOADING OF A TRANSFORMER

01/29/2012 10:37 AM

Wrong. 1.5MVA x 0.8 = 1.2MW.

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#7
In reply to #6

Re: LOADING OF A TRANSFORMER

01/29/2012 10:46 AM

Sorry Tornado,

A mixup from my part; I took 2,000 Amps instead of 1.5 MVA.

Thanks for the correction

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#8
In reply to #7

Re: LOADING OF A TRANSFORMER

01/29/2012 10:51 AM

No problem; that happens to me, too. After I posted, I wondered if the 1600 figure came from starting with 2000 instead of 1500.

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#9

Re: Loading of a Transformer

01/29/2012 1:13 PM

Interestingly in Saudi Arabia we were advised by ABB that with fans under the cooling fins we could uprate by 40%, we went ahead, no problem.

Keep in mind it isn't black and white, you don't arrive safely at 2000 amps and then blow up at 2010 amps, it just generates more heat, and so it depends how you get rid of he heat.

At Alcan in Scotland 132/33kV transformers rated 60/75/90 MVA, how? A separate cooler as big as a block of flats had a pump and fans, 60MVA all natural circulation, 75MVA ONAF fans only, and 90 MVA fans and oil pump.

In Scotland we have ambient 10C, in Kuwait we had ambient 45C, so the same transformer has a different rating. Don't be frightened of overloading I've had them so hot you could fry an egg on top, no sun shade, depends who made the transformer and what happens to the materials inside when it gets really hot.

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