Tan Delta of 22KV to 415V transformer

[camo1978]

Can anyone provide information on conducting PF/DF tests on lower rated transformers. Specifically in regards to voltages and frequencies to be applied and which tests are required for a two winding transformer. (GST,GST ga, UST etc) It appears that 10KV is a recognised acceptable voltage but obviously im not going to apply this to the LV terminals of a 415V Transformer.
Thanks in advance for your help

 

[amps21]

I dont think u need to apply 10kV. You can test the winding @ 1000V and then extrapolate it to 10kV.

I do not think that the frequency of the test voltage can be changed. Your tester shall have test voltage @ 60Hz. Since P=V^2w.C.Tandelta, frequency will increase your insulation PF.

The normal tests would be GST (grounded speciment test- where the ground current is measured (eg.HV to LV+Gnd)

GSTg (Guarded) - Guard the circuit that does not need to be measured (eg. HV to Gnd - LV guarded)

UST(ungrounded specimen test) - No ground current (eg. HV to LV only).

Tan Delta ( as u know) is temperature dependent.

You should be able to get more info from the test kit operation manual about specific connections etc.

 

[unclebob]

May be you already know, but don't forget to test the HV
bushings also. They should have a nameplate indicating
a tandelta and capacitance (c1) values.