Power Transformers and Partial Discharges

The ageing of the transformer oil and insulation may cause partial discharge in power transformers. So it is recommended that partial discharge test be conducted during periodical maintenance of transformers. The link below will give good idea about the Multi Channel Digital PD detector.

http://www.ldic.de/media/files/Media/Techpapers/14-Russwurm-Dirk-Partial_Disch.pdf

The following link gives the on site online partial discharge measurements on power transformers.

http://www.transformerscommittee.org/meetings/s2001_Amsterdam/dp_transfo.pdf

Thank you sir, its a good coment.

Binod Kumar Panda

I only have experience in Partial discharge tests of cast resin distribution and power transformers ranging from 300Kva to 15,000Kva. This is a type test and routine test for many (not all,not even some very big ones) manufacturers.Under IEC 726,the maximum amout of partial discharge allowed is 20 pC or pico coulumb.

This test is done in factory enviroment where external interference are eliminated. The partial discharge amount indicate the the initial good condition of the fully assembled new transformer.If there are air bubbles or some sharp/pointed conductors in the rsin insulated element not visible by our eyes, the value of the pC will increase immediately.This is the best we can have to know the condition of the cast resin transformer when it is about to be shipped out of the factory.The normal value is about 5 to 10 pC for a 2000Kva transformer.

However after commisioning,over time,may be in 1 to 5 years, this condition can change for the worse due to the degeneration,ionisation and eventual oxydation of solid impurity/dust contamination or colour pigments,fire retardant (France Transfo )that are added to the molten resin/silica or resin prepragnated reinforced glass fibre ( ABB ).This will cause the failure of the coil insulation and failure of complete transformer in the form of a flash-over.

Regards,

Khor.

OK, Thank you sir,

Regards

Binod Panda