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Transformer insulation resistance test method

time:2020/10/10   source:华天电力  reading:787 time

By testing the insulation resistance of the transformer, the degree of insulation aging can be roughly understood. The measurement of insulation resistance includes measuring the insulation resistance of the primary and secondary windings to ground and the insulation resistance between the primary and secondary windings. The test methods are as follows: 

(1) Use a 2500V megohmmeter for windings with a rated voltage above 1kV, and use a 1000V or 2500V megohmmeter for those below 1kV.

(2) Before the measurement, clean the transformer bushing to avoid leakage current and affect the accuracy of the measurement result.

(3) The non-measured winding should be grounded during measurement. Ground the transformer shell and high voltage winding to measure the low voltage winding; then ground the transformer shell and low voltage winding to measure the high voltage winding.

Insulation Resistance Tester.png

(4) When measuring, if the hand-cranked megohmmeter is used, the handle should be rotated at a speed of 120r/min to gradually increase the pointer until the pointer is stable and then record the reading.

(5) The insulation resistance should be based on the value obtained when the transformer winding is immersed in oil (referring to the oil-immersed transformer). After the transformer is filled with oil, it should be left standing for 5-6 hours before measuring. Compare the measurement result with the value before putting it into operation. If the drop is significant (less than 70%), a test should be carried out to make a comprehensive analysis.

(6) Matters needing attention:

① The measurement should be carried out under good weather conditions, and the temperature of the transformer under test and the environment should not be lower than 5.

②When measuring, the environmental humidity should not be greater than 75%, because the humidity has a greater impact on the surface leakage current and reduces the insulation resistance.

③After each insulation resistance measurement, discharge the charge (short-circuit the terminal with a wire); otherwise, the insulation resistance will increase in the second measurement.

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