Measurement of power transformer insulation resistance and absorption ratio, or polarization index, to check the overall condition of the insulation transformer with high sensitivity, can effectively check out the transformer overall insulation damp, wet or dirty part surface, as well as cross-cutting defects.
 When the insulating power transformers throughout between poles, measure the insulation resistance when there will be significant changes, both in order to be sensitive to detect defects by measurement.


      When measuring the insulation resistance of power transformers, using idle winding grounding method, the advantage can be measured on the test section is insulated ground portion and different voltage section between the windings can avoid measurement errors caused by the remaining charge.