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After filtration BDV Value definitely increase.As IR value is100 Mega-Ohm, then there is no problem, the Transformer is not a new one.You can charge it.
If connections are isolated properly then in this case the10MVA Transformer cannot be energized or in other words it is dysfunctional so need to check the winding inside the shell or replace the transformer or Reinsulating of HV/LV windings along with all accessories can be done.
Dear Sir,
The low IR value (megger value) is due to heigh tan-delta value of your transformer oil.
In the IR results you have obtained, you will find the HT-G showing the least value.
From doing filteration the BDV and ppm values of oil will improve but tan-delta remains the same.
Please conduct a tan-delta test of the transformer oil and verify. Also please inform me rgarding the same
This may be due to sludge deposition on shell winding. Transformer needs oven baking. PPM may be checked also check PI ( Polarisation index of winding)
because insulation test is testing resistance between two points, so, current that megger applied is flow through low resistance. and sample of oil is taken on the bottom transformer. and also winding clearance distance too short.
