Transformer testing - Frequency conversion factors / 50Hz to 60Hz 2

[RRaghunath]

50Hz rated transformers are proposed to be tested by the vendor using power supplies rated at 60Hz.
Any advice on the conversion factors to be applied for load loss etc.!!
Thanks in advance.

 

[pie314]

This doesn't sound like a great idea, however if there isn't any other way the conversion factors are as follows:

Load loss -- measure at 60 hz then measure the resistance, using the resistance calculate the I2R losses. Then subtract the I2R losses from the measured loss. The remaining is the eddy and stray loss,however since these were measured @ 60 hz the value must be reduced by (50/60)^2. The sum of the I2R and the corrected eddy loss value will be close to the 50 hz load loss;

Open circuit -- This is more dificult. The best you can do to approximate the 50 hz losses is to test at 83.3% rated voltage. The result will only approximate the 50 hz value.

 

[pie314]

Raghun -- I made a mistake on the open circuit test. You have to increase the voltage by 20%. This will produce the same flux density as rated voltage at 50 hz.

 

[rcw retired EE]

If a temperature rise test is to be perfomred with cooling fans or pumps running, the fans will operate 20% faster and provide a lot more cooling air flow. I do not know of a conversion factor to adjust for that increase.

You could require a 50 Hz fan supply if temperature rise with fans operating is a required test. Additional cost for a VFD to supply the fan power during the test is not that much.

 

[prc]

Raghun,There are many un official conversion factors used by transformer manufacturers.Corrections will be required for 1) Impedance 2)No-load losses 3) Load losses 4) Excitaion current 5) Sound level 6) Insulation power factor 7) Induced voltage test duration.

Official version you can get from draft IEEE Std PC57.12.90-D10 of 2009-02 Annexure B Guide for testing trfs.You can also see a tutorial at

http://www.transformerscommittee.org

by ABB during 2008 fall meeting.

Attached is a summary for 60 to 50 HZ conversion as per IEEE paper(Power Delivery Vol 18 No4 2003-10) "Proposed standards for frequecy conversion factors of trf performance parameters"by Dr Girgis etc of ABB

 

[RRaghunath]

Thanks to you all - pie314, rcwilson and prc.

The cooling fan/pump issue is a good point, rcwilson.

Thanks for the references, prc. I could get the ABB paper and I am still trying for the draft copy of the IEEE. Guess the IEEE would be made official soon. It would be one more step in the process of harmonisation between IEEE and IEC, I think.