Transformer no load losses 3

[vtpwringeniero]

Recently, my company purchased a 3 phase, 3 legged core transformer. High side volts: 4,160 delta, low side volts: 600Y/346 x 480Y/277, nominal capacity: 3650 KVA. The unit is silicon filled.

The test report showed the following:
Exciting Current no load losses
Phase A: 2.25 amps 1,160 watts

Phase B: 1.65 amps 1,440 watts

Phase C: 2.00 amps 4,080 watts

Total no load losses: 6,680 watts.

Is it unusual to have such a distribution of no load losses in a transformer of this type?

 

[electricpete]

I don't know the answer.

I was surprised to see the highest watts didn't come on the phase with highest current.

It could be that the instrumentation used is not particularly accurate in this range. i.e. trying to accurately measure current magnitudes of 1.65Amp on the same instrument that measures displays full load of 500 amps. Just a s.w.a.g. (silly wild as_ guess).

Another question had come up recently on the forum I think it was titled star-delta Trafo) where someone asked about expected no-load currents on transformers.

 

[230842]

The values of the currents seem to be usual, since central core leg normally needs smaller magnetization and loss currents. Such an unbalance in power per phase is not usual, in my opinion.
Nevertheless, there can be a possible reasson tied to the power meassuring methode: The common point of the three voltage imputs of meter equipment could take a voltage displacement due to the load unbalance, giving, thus, three different values which do not correspond to values per phase, although their sum really is the sum of power of each phase.
For a more accurate response it should be usefull to know details of the meassurement circuit (preferably circuit diagram) and equipment. Julian

 

[Batu]

No load losses can be different.They can be negative too..
The thing should be considered is the total value shouldn't be more than guaranteed factory values.

Batu

 

[electricpete]

It sounds like the other folks have more familiarity with transformer no-load losses than me.

Julians comment about an expected pattern of two high's and one low current reading rings true. I know that for SINGLE-phase excitation current test of three-phase transformers, that is the expected pattern, based on lower reluctance of the center leg giving higher magnetizing inductance, lower exciting current. I was under the impression that three phase excitation currents can vary in a more complex manner.

 

[jbartos]

Suggestion/question:
1. Have you adhered to any industry standards with your testing and which one?
2. The no load losses and exciting currents are somewhat dependent whether the transformer is new or refurbished.

 

[vtpwringeniero]

To the best of my knowledge, the factory tested this new unit according to IEEE std C.57.12.90-1993.

I've made some further inquiries of TX manufacturers over the past few days. All agree that no-load loss distributions such as shown above occur routinely and that it's the total that matters rather than the distribution. This sets my mind at ease.

 

[jbartos]

Suggestion: There is more recent standard available;
C57.12.90-1999 IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating
Transformers
Print: 88 pages [0-7381-1789-7] [SH94778-NYF] $59.00 * IEEE Mbr: $47.00
PDF: [0-7381-1790-0] [SS94778-NYF] $89.00 * IEEE Mbr: $71.00
however, it may or may not affect the outcome of the posting much since the currents appear to be acceptable.

 

[vtpwringeniero]

Thanks. I'll get a copy of the 1999 version to update our file.