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Three misunderstandings of megohmmeter

time:2021/1/9   source:华天电力  reading:516 time

The megohmmeter is a commonly used measuring instrument, mainly used to check the insulation resistance of electrical equipment, household appliances or electrical circuits to the ground and between phases. The function is to ensure that the equipment, electrical appliances and circuits work under normal conditions to avoid electric shock injuries. And equipment damage. The three misunderstandings about the use of megohmmeters are summarized as follows:

Misunderstanding 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 to test the high-voltage and low-voltage coils of the transformer; apply AC 2kV as the withstand voltage test voltage to the insulation of the 0.4kV side coil, and there will be no abnormal conditions such as breakdown or flashover within 60s, while 10kV is applied with AC 42kV is used 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, a megohmmeter with a range of 2500V and above should be used. Only a 500V or 1000V megohmmeter can be used for the low voltage on the 0.4kV side to the ground. If 500V and 1000V megohmmeters are used to measure the high voltage side with a rated voltage higher than 500V and 1000V, the measurement results will have errors. If a megohmmeter with too high rated voltage is used to measure the insulation resistance of the low voltage side, the insulation may be damaged.

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Misunderstanding 2:

There is no measurement method of two people working together. "After reading the above values, disconnect the tested product without stopping the rotation of the handle, and then stop the shaking to prevent damage to the megohmmeter due to the charge feedback discharge of the charge accumulation of the test product." This is a general use. Common usage methods are introduced in the manual or teaching materials, but quite a lot of testers will shake the test after wiring, so many megohmmeter components are damaged, or the megohmmeter is scrapped and repaired after one or two use. When we use the megohmmeter, we take the two-person operation method to measure. After connecting the test line, one person is responsible for turning the megohmmeter handle and reading, and the other person takes the test end and aligns the test sample and listens to the operator who turns the megohmmeter handle. Command; "Lap test product, pull open, discharge" command.

Misunderstanding 3:

It is an extremely non-standard practice to use general floral thread and rubber woven thread instead of the special thread for megohmmeter. Because the insulation value of general floral and rubberized wires is far lower than that of special test wires. The special test wire will not affect the insulation value due to the overlap of the test product by holding the end. On the contrary, the general fancy wire and rubber braided wire may also hurt the operator during the shaking test. At the same time, keep the dedicated test line properly.

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