To measure electrical equipment and objects of different voltage levels, a megohmmeter of the corresponding voltage level should be selected. For measuring electrical equipment below 500V, a 500V megohmmeter should be used. For equipment above 500V and below 3000V, a 1000V megohmmeter should be used. For equipment above 3000V and above, a 2500V megohmmeter should be used. Also pay attention to the measurement range of the megohmmeter, so that the qualified insulation resistance value of the measured object falls within the measurement range of the instrument.

Digital Megohmmeter

Before measurement, open circuit and short circuit tests should be conducted on the instrument to check the quality of the megohmmeter. The open circuit experiment involves separating the instrument wires and shaking the dial to 120 revolutions per minute, at which point the pointer should be at infinity; The short circuit experiment is to first short-circuit the two meter wires, shake the handle (slowly at the beginning) to 120 revolutions per minute, and the instrument pointer should be at zero position.

2. The megohmmeter has three terminals, labeled as L.E and G. During measurement, L is connected to the conductor of the measured object; Connect the E terminal to the outer shell of the equipment or another phase conductor insulated from the tested live phase; The G end is designed to prevent measurement errors caused by leakage current on the tested insulation surface. It is connected to the insulation material where the L end of the tested object is connected and wrapped with 3-5 turns of soft bare wire.

When measuring, the shaking speed of the shaking table should be around 120 revolutions per minute. Generally, connect the E.G end first, and then connect the L end after shaking the meter. After one minute, the instrument pointer will stabilize before reading.

After reading, the L line of the instrument should be disconnected first, and then the shaking of the meter should be stopped. This is particularly important for measuring devices with considerable capacitance, such as capacitors. Otherwise, the shaking meter may be damaged due to reverse power transmission from the tested object to the instrument. After testing, immediately manually discharge the tested object.

Due to the fact that the shake meter measures high resistance insulation resistance, there are high requirements for the test line. otherwise The leakage current of the test line will affect the accuracy of the measurement. The testing line must be used. A single insulated soft copper wire with high insulation strength should not be replaced with ordinary soft copper stranded wire.

Before measurement, it is necessary to manually discharge the object being measured, especially capacitive equipment.

7. Pay attention to the usage environment, try to stay away from strong magnetic fields, and do not shake the insulation resistance in rainy weather. When the environmental humidity is high, the impact of humidity should be considered.