The megohmmeter, also known as a megger, is composed of a high-voltage hand-cranked generator and a magnetoelectric double-coil ratio meter. It features stable output voltage, accurate readings, low noise, easy cranking, and is equipped with a shielding device to prevent leakage current in the measuring circuit and independent terminals.
1. Before measurement, correctly select the specification of the meter so that its rated voltage matches the rated voltage of the electrical equipment under test. For equipment with a rated voltage of 500V or below, generally choose a 500-1000V megohmmeter; for equipment above 500V, use a 2500V megohmmeter; for high-voltage equipment, select a 2500-5000V megohmmeter.
2. When using the megohmmeter, first check whether it is in good condition. Without connecting the test object, crank the megohmmeter; the pointer should rise to the "∞" position. Then short-circuit the two terminals and slowly crank the megohmmeter; the pointer should point to "0". If it meets the above conditions, the megohmmeter is good; otherwise, it cannot be used.
3. During use, it must be placed horizontally and kept away from external magnetic fields.
4. The two wires between the terminals and the test object must not be twisted together; they should be connected separately to prevent poor insulation of twisted wires from affecting the readings.
5. When measuring, turn the handle gradually from slow to fast and maintain a speed of 150 r/min. After the governor slides, a stable reading is obtained. Generally, take the stable value after 1 minute. If the pointer indicates zero, continuous cranking is not allowed to prevent coil damage.
6. During thunderstorms or when there are high-voltage conductors nearby, it is forbidden to use the instrument for measurement. Measurement can only be performed when the equipment is de-energized and cannot be energized by induced electricity.
7. Before and after measurement, the test object must be fully discharged to ensure equipment and personal safety.
8. When measuring the insulation resistance of capacitive electrical equipment, after obtaining a stable reading, first remove the test leads, then stop turning the handle. Immediately after measurement, ground and discharge the tested equipment.
9. Avoid severe and prolonged vibration to prevent damage to the meter's pivot and jewel, which could affect scale indication.
10. When not in use, the instrument should be stored in a fixed place. The ambient temperature should not be too hot or too cold, and it should not be placed on damp or dirty ground. Also, avoid placing it near corrosive air.
