Transformer no load losses
Transformer no load losses
(OP)
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?
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?






RE: Transformer no load losses
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.
RE: Transformer no load losses
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
RE: Transformer no load losses
The thing should be considered is the total value shouldn't be more than guaranteed factory values.
Batu
RE: Transformer no load losses
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.
RE: Transformer no load losses
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.
RE: Transformer no load losses
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.
RE: Transformer no load losses
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.
RE: Transformer no load losses