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What are the pitfalls of megohm meter operation?

time:2020/7/8   source:华天电力  reading:286 time

Abstract: For the measurement of the insulation value of a 10kV transformer, ZC series portable megohmmeters are used, and some of them have three misunderstandings. The rated voltage of the megohmmeter does not match the voltage of the electrical equipment under test, and no two people are used to cooperate. The measurement method of the standard method is to use general flower thread and rubber woven thread instead of the megger special thread.


For the measurement of the insulation value of 10kV transformers, ZC series portable megohmmeters are used, and there are three misunderstandings:


Insulation Resistance Tester.png


Myth 1:

The rated voltage of the megohmmeter does not match the voltage of the electrical equipment under test. That is, different megohmmeters should be used for the high-voltage and low-voltage coils of the test transformer; 2kV AC is applied to the insulation of the 0.4kV side coil as the withstand voltage test voltage, and there are no abnormal conditions such as breakdown and flashover within 60s, while 10kV is applied AC 42kV as the withstand voltage test voltage. Therefore, to measure the insulation resistance of high-voltage to low-voltage, high-voltage to ground and iron core to ground, use a 2500V megohmmeter with a range of more than 2500MΩ. The low voltage on the 0.4kV side can only use a 500V or 1000V megohmmeter to ground. If a 500V and 1000V megohmmeter is used to measure the high-voltage side with a rated voltage higher than 500V and 1000V, the measurement result has errors. If a megohmmeter with a too high rated voltage is used to measure the insulation resistance value on the low voltage side, the insulation may be destroyed.


Myth 2:

There is no measurement method in which two people cooperate. "After reading the above values, the test article should be disconnected without turning the handle, and then the shaking can be stopped to prevent damage to the megohmmeter due to the charge feedback discharge of the accumulated electrical charge of the test article." This is the general use The common usage methods in the instruction manual or textbook are introduced, but quite a few testers shake the test after wiring, so many megohmmeter components are damaged, or after one or two use, the megohmmeter is scrapped and repaired. When using the megohmmeter, take the operation method of two people to measure. After connecting the test line, one person is responsible for turning the megohmmeter handle and reading, and the other hand is holding the test end to the test sample to obey the order of the operator who turns the megohmmeter handle. ; The password of "lap test, pull apart, discharge". Due to the method of using the megohmmeter in conjunction with the operation, it is not easy to damage the ZC series megohmmeter.


Myth 3:

It is extremely irregular to use general flower thread and rubber woven thread instead of megger dedicated thread. Because the insulation value of general flower wire and rubber woven wire is much lower than that of special test wire. The special test wire will not affect the insulation value due to the overlapping of the test specimens. On the contrary, the general flower wire and rubber yarn may also hurt the operator during the shake test. At the same time, special test lines must be properly kept, including special power lines and test probes for ZC48 electronic megger.


It is recommended to use an electric shaker to avoid the above problems. HT2671 and HT2500 series megohmmeters are ideal substitutes for ZC series equipment.


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