1) Before measuring, cut off the power supply of the device under test, connect the conductive part of the device to the earth, and discharge it fully to ensure safety. Electrical equipment that has been measured with a megohmmeter should also be grounded and discharged in time before re-measurement. (2) Before measuring, check whether the megohmmeter is in good condition, that is, before the megohmmeter is connected to the measured object, shake the handle to make the generator reach the rated rotation. 1) Before measuring, cut off the power supply of the measured device, and The conductive part of the equipment is connected to the earth and fully discharged to ensure safety. The electrical equipment that has been measured with a megohmmeter should also be grounded and discharged in time before the measurement can be performed again. (2) Before measuring, check whether the megohmmeter is in good condition, that is, before the megohmmeter is connected to the measured object, shake the handle to make the generator reach the rated speed (120r/min), and observe whether the pointer points to the position of the scale. Short-circuit the terminal line (L) and ground (E), slowly shake the handle, and observe whether the pointer points to the 0 position of the scale. If the pointer cannot point to the position of the finger, it indicates that the megohmmeter is faulty and should be used after repair. (3) The wiring must be correct. There are generally three terminals on the megohmmeter, marked with L (line), E (ground) and G (shield). Among them, L is connected to the conductor part of the measured object and the ground, E is connected to the shell or earth of the measured object, and G is connected to the shield of the measured object or the part that does not need to be measured. Terminal G is used to shield the surface current. For example, when measuring the insulation resistance of a cable, due to the leakage current on the surface of the insulating material, the measurement result will be inaccurate, especially in the case of high humidity and the cable insulation surface is not clean, which will cause a large measurement error. In order to avoid the influence of surface current, a metal shielding ring is added on the surface of the object to be measured and connected to the shielding terminal of the megohmmeter. In this way, the surface leakage current IB starts from the positive pole of the generator and flows back to the negative pole of the generator via the terminal G to form a loop. IB no longer passes through the measuring mechanism of the megohmmeter, so the effect of surface leakage current is fundamentally eliminated. (4) The wire connecting the terminal and the device under test cannot use double-strand insulated wire or twisted wire. It should be connected separately with single-stranded wire to avoid errors caused by poor insulation of the stranded wire. In order to obtain correct measurement results, the surface of the device under test should be wiped clean with a clean cloth or cotton yarn. (5) Shaking the handle should be slower and faster. If you find that the pointer is pointing to zero, it means that the insulation under test may have a short circuit. At this time, you cannot continue to shake the handle to prevent heating and damage to the coil in the watch. The hand-cranked generator should maintain a constant speed, and the pointer should not keep swinging quickly and slowly. Usually the most suitable speed is 120r/min. (6) Measure the insulation resistance of equipment with large capacitance. Do not stop shaking the megohmmeter immediately after reading, otherwise the charged capacitor will discharge the megohmmeter, which may burn the megohmmeter. After reading, reduce the speed of the handle on the one hand, and remove the ground terminal wire on the other. Before the megger stops rotating and the test object is fully discharged, the conductive part of the device under test should not be touched. (7) When measuring the insulation resistance of the equipment, the temperature, humidity, and the relevant conditions of the test object during the measurement should also be noted in order to analyze the measurement results
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