Tan Delta test kit rating

[power2020]

1. Any one pl. suggest us that how to calculate the current rating of Tan-Delta test- kit for testing of 16.5kV, 260MVA Generator / 400/16.5kV 260MVA transformer (for both HT and LT).

2. For transformer bushing tan-delta testing, why should not inject rated voltage of the busing?

Advanced thanks,

 

[electricpete]

1 - As I rememer, the Doble test set was limited to 300 milliAmps at 10kv test voltage. (3kva). If the device you are testing draws more current than the capability of the test set, then you have to reduce your test voltage to remain within the capability of the test set.

2 –
2A - For one thing you are limited by the capability of your test set, generally 10kvac.
2B – For another thing you want to compare your results to other tests at standard voltage, generally 10kv or less.
2C - It's been awhile since I looked at the setup of the test taps. I remember there were two different varieties. If you did have the capability to put full line-to-ground voltage, you want to doublecheck to make sure you are not overstresing portions of the insulation system. Maybe someone else can refresh my memory on this.

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[edison123]

I use 12 KV inductors in parallel with the gen/motor windings get my 100 mA TD kit up to 3 Amps.


* Basically, I would like a full-time job on part-time basis *

 

[power2020]

1st queiry is clear.
Pl discuss regarding 2nd queiry.
Thanks...

 

[prc]

No problem .You can inject full rated voltage to bushing and measure tan delta at that voltage.But then you require a standard capacitor of that voltage to measure tandelta.Doble kit normally is with a 10 kV capacitor and hence measuremet at that voltage.In fact bushing manufacturer will be measuring tan delta not only at rated voltage, but also at full test voltage.

 

[power2020]

Thanks Mr. PRC, I have seen in many sites that Doble test of HV bushings is carried with 2.5kV however Doble kit rating is upto 10kV. Any specific reason?

 

[prc]

Doble kit is provided with a 12 kV power source and hence all site testsare done at voltages below this.In case you want at a higher voltage, you require a voltage source, a standard capacitor and an additional instrument accessory from Doble.
Reason of selecting 2.5 kv may be availability of earlier bench mark values at that voltage.Some utilities have standardised at 10 kV.