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How to use electronic megohmmeter

time:2020/11/2   source:华天电力  reading:250 time

There are three terminals for the digital megohmmeter: one is "L" which is the wire end, one "E" is the ground terminal, and the other "G" is the shielding terminal (also called the protection ring). Generally, the insulation resistance under test is all It is connected between the "L" and "E" terminals, but when the surface leakage of the insulator under test is serious, the shield ring of the test object or the part that does not need to be measured must be connected to the "G" terminal. In this way, the leakage current flows directly back to the negative terminal of the generator via the shielded terminal "G" to form a loop, instead of flowing through the measuring mechanism (moving coil) of the digital megohmmeter. This fundamentally eliminates the effect of surface leakage current. It should be particularly noted that when measuring the insulation resistance between the cable core and the surface, the shield terminal button "G" must be connected, because when the air humidity is high or the cable is insulated When the surface is not clean, the leakage current on the surface will be very large. In order to prevent the leakage of the measured object from affecting its internal insulation measurement, a metal shielding ring is generally added to the outer surface of the cable. G" terminal is connected.

Insulation Resistance Tester.png

When using a digital megohmmeter to measure the insulation resistance of electrical equipment, you must pay attention to the "L" and "E" terminals cannot be reversed. The correct connection method is: "L" wire terminal button is connected to the conductor of the device under test, "E" "The ground terminal button is grounded to the equipment shell, and the "G" shield terminal is connected to the insulated part of the device under test. If the "L" and "E" are connected reversely, the leakage current flowing through the insulator and the surface will be collected to the ground through the shell, and flow from the ground to the measuring coil through the "L", so that the "G" will lose the shielding effect and give the measuring tape There is a big error. In addition, because the degree of insulation between the internal lead of the "E" end and the case is lower than that between the "L" end and the case, when the digital megohmmeter is used on the ground and the correct wiring method is used, the "E" end is opposite to the instrument The insulation resistance of the shell and the shell to the ground is equivalent to a short circuit and will not cause errors. When the "L" and "E" are reversed, the insulation resistance of the "E" to the ground is connected in parallel with the measured insulation resistance, and the measurement result Too small, will bring greater error to the measurement.

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