How to measure the insulation of the transformer's high and low winding by the ohmmeter?
When measuring, such as using hand type ohmmeter, the handle should be rotated at 120r / min speed, so that the pointer rises gradually until the pointer indicates stability and then records the readings.
Before measuring, the transformer bushing is cleaned so as not to cause leakage current, which will affect the accuracy of the measurement results. (3) when measuring the non measured winding should be grounded. First, the transformer shell and high voltage winding ground, measuring low voltage winding; then the transformer shell and low-voltage winding ground, measuring high-voltage winding.
By testing the insulation resistance of the transformer, the degree of insulation aging can be generally understood. The measurement of insulation resistance includes measuring the insulation resistance of the primary and secondary windings to the ground and the insulation resistance between the two and the two windings. Test methods are as follows: (1) measuring voltage of more than 1kV winding using 2500V trillion European table, 1kV below 1000V or 2500V European table.
The insulation resistance shall be based on the value obtained when the transformer winding is immersed in oil (oil immersed transformer). After the transformer is filled with oil, it should be placed 5 to 6h for static measurement. Compare the measurements with the values before they are put into operation. If significant drops (less than 70%) are observed, tests should be carried out to make a thorough analysis.
