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The correct test method of megohmmeter

time:2021/4/11   source:华天电力  reading:495 time

When the megohmmeter measures the insulation resistance of electrical equipment to ground, the correct wiring should be: "E" terminal is grounded, and "L" terminal is connected to the device under test. The grounding mentioned here, of course, refers to the case where the measured object is grounded.

According to the principle of the megohmmeter, the “E” terminal is connected to the positive pole of the generator, the “L” terminal is connected to the measuring coil, and the shielding terminal “G” is connected to the negative pole of the generator. When the meter is correctly wired to measure the insulation resistance of the device under test to the ground, the leakage current of the insulation surface flows directly back to the negative pole of the generator via "G", and does not flow through the measuring coil, so it can play a shielding role.

Insulation Resistance Tester.png

2. The leads cannot be twisted together during the measurement of the megohmmeter:

When measuring the insulation resistance of electrical equipment with a megohmmeter, in order to reduce the measurement error, two separate leads are required. The main reason is: the voltage of the megohmmeter is relatively high. If the two leads are twisted together for measurement, when the wire insulation is poor, it is equivalent to connecting a resistor in parallel to the electrical equipment under test, which will seriously affect the measurement. Data results.

3. The requirements for the shaking test time of the megger to measure the insulation resistance:

When measuring the insulation resistance with a megohmmeter, it is generally stipulated that the reading after 1 minute of shaking shall prevail. Because after applying a DC voltage to the insulation resistance, the current flowing through the insulation resistance gradually decreases with time, and the DC resistivity of the insulation resistance is determined according to the steady-state conduction current, and the insulation resistance of different materials passes through it. The decay time of the current is also different. Tests have proved that the current on most insulating materials has stabilized after one minute, so it is stipulated that the insulation performance of the insulator is determined by the insulation resistance value after applying the voltage for one minute.

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