Allowable value of insulation resistance of transformer

After repair, long-term off or standby transformers, before putting into operation, the need to measure insulation resistance. Transformer Insulation Resistance Value Provisions: (1) with the last measurement results, shall not be less than 70% . (2) the insulation resistance shall not be less than 0.5 m below 500V and not less than 1 m per kilovolt above 500V. (3) the absorption ratio of HV and LV winding to ground is not less than 1.3. (4) double winding measurement items: Primary side to ground, secondary side to ground, secondary side to secondary side insulation resistance.