Transformer Nameplate Rating

B

bwat

EE
Location
NC
Occupation
EE
Am I correct that the amount of (apparent) power you can push through a transformer is actually less than the transformer's nameplate rating because you have to consider the losses of the transformer?



That's something I hadn't really considered before. I always mentally assumed you could put 10MVA through a 10MVA transformer. And so if you wanted 10MVA on the secondary side, maybe you'd be up >10MVA on the source side, but you'd still be under the damage curve by design. But thinking through this, I'm wondering what is true. Are you actually limited to strict nameplate size on the source side such that max MVA delivery is actually nameplate minus transformer losses (including var consumption)?
 
In reality, no. The KVA rating can be exceeded since the short term heat can be cooled at night or with fans. The only time I have seen heat show up that was slightly less than the VA rating was a large amount of harmonics. The business ran 24/7. That did degrade the transformer at a faster rate than expected.

I also wouldn't worry too much about the possible ideal vs non-ideal transformer with relation to the rated VA. It is more of a consideration for protection studies and money calcs when you want to consider the load and no load losses.

It is not going to effect the load you can put on a transformer.
 
How about this for a fun answer: it depends upon where you live (or where you buy your transformers).

Per IEC standards, a transformer kVA rating (and the 'base' for % impedance, % losses, etc) is the _input_ value.

Per ANSI/IEEE standards, the transformer kVA rating is the _output_ value.

The relevant standards are behind paywalls, so looking them up is an exercise left to the student. Here is a LinkedIn description of the topic with relevant standards numbers:
www.linkedin.com

Rated Power of Transformers

During the initial years of transformer development, transformer power rating was specified as output, in kW (sometimes in HP) as the case with other electrical machines like motors and alternators. Typical transformer ratings in 1893 were 1.
www.linkedin.com www.linkedin.com
 
winnie said:
How about this for a fun answer: it depends upon where you live (or where you buy your transformers).

Per IEC standards, a transformer kVA rating (and the 'base' for % impedance, % losses, etc) is the _input_ value.

Per ANSI/IEEE standards, the transformer kVA rating is the _output_ value.

The relevant standards are behind paywalls, so looking them up is an exercise left to the student. Here is a LinkedIn description of the topic with relevant standards numbers:
www.linkedin.com

Rated Power of Transformers

During the initial years of transformer development, transformer power rating was specified as output, in kW (sometimes in HP) as the case with other electrical machines like motors and alternators. Typical transformer ratings in 1893 were 1.
www.linkedin.com www.linkedin.com
Click to expand...

That's fantastic, thank you!

So since I'm typically working with ANSI/IEEE C57 transformers, I was (accidentally) correct in assuming these were the output ratings.
 
bwat said:
Am I correct that the amount of (apparent) power you can push through a transformer is actually less than the transformer's nameplate rating because you have to consider the losses of the transformer?



That's something I hadn't really considered before. I always mentally assumed you could put 10MVA through a 10MVA transformer. And so if you wanted 10MVA on the secondary side, maybe you'd be up >10MVA on the source side, but you'd still be under the damage curve by design. But thinking through this, I'm wondering what is true. Are you actually limited to strict nameplate size on the source side such that max MVA delivery is actually nameplate minus transformer losses (including var consumption)?
Click to expand...
Just for the record, apparent power is KVA. True power it KW
 
winnie said:
How about this for a fun answer: it depends upon where you live (or where you buy your transformers).

Per IEC standards, a transformer kVA rating (and the 'base' for % impedance, % losses, etc) is the _input_ value.

Per ANSI/IEEE standards, the transformer kVA rating is the _output_ value.

The relevant standards are behind paywalls, so looking them up is an exercise left to the student. Here is a LinkedIn description of the topic with relevant standards numbers:
www.linkedin.com

Rated Power of Transformers

During the initial years of transformer development, transformer power rating was specified as output, in kW (sometimes in HP) as the case with other electrical machines like motors and alternators. Typical transformer ratings in 1893 were 1.
www.linkedin.com www.linkedin.com
Click to expand...
Learned something new today...
 
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