In the case of serious power supply asymmetry or three-phase current imbalance, it is suggested the three-wattmeter
method be used to measure the power.
As the electric insulation test and the dielectric strength test have been done for the product before it leaves the
factory, the users don’t have to do such tests again. Moreover, such tests will reduce the insulation and voltage
withstand performance of the product. If such tests are conducted inappropriately, product elements may even be
damaged. If such tests have to be done really, it is suggested they be conducted by the skilled technicians.
If the main circuit voltage withstand test is done, the withstand voltage tester with the time & leakage current settable
and the similar capacity should be used. The test may reduce the life of product. If the main circuit insulation test is
done, the main circuit terminals R, S, T, U, V, W, PB(P1), + and – etc should be short-circuited reliably and then the
meg-ohmmeter with the near voltage grade (250V for 220V, 500V for 380V, and 1000V for 660V) should be used
for measurement. The control circuit should be measured with the resistance shift of the universal meter instead of
the meg-ohmmeter.
For the 380V main circuit, the ground insulation resistance should not be less than 5 MΩ; for the control circuit,
the ground insulation resistance should not be less than 3 MΩ.
8.1.3 Regularly-replaced Elements
To ensure the long-term and reliable operation of frequency inverter, regular care and maintenance should be
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