Measure the insulation resistance of the final screen and the ground end (N) of the voltage transformer against the enclosure (ground). The insulation resistance should not be less than 1000MQ.When the insulation resistance of the final panel to ground is less than 1000MQ, its TA value should not be greater than 2% when measured.4.Insulation resistance shall be measured using a 2500V megohm meter.6.2.Polarity Inspection:Test the wiring group and polarity of the current transformer and they should conform to the design requirement and be consistent with the name plate and sign.Refer to standard GB50150-2016.Item10.0.9Check the wiring winding group and polarity of the transformer, which should meet the design requirements and conform to the nameplate and mark.6.3.Measurement of CT Ratio:The permissible error of the transformer ratio at the rated tapping position ±0.5%.(According to the accuracy level)Refer to standard GB50150-2016.Item10.0.10