Megohmmeter detailed introduction and precautions
The megohmmeter, also known as the shaker, is an instrument used to measure the insulation resistance and high-value resistance of the device under test. terminal, G: shielding terminal).
1. Selection principle of megohmmeter
(1) Selection of rated voltage level. In general, for equipment with a rated voltage below 500V, a 500V or 1000V megger should be used; for equipment with a rated voltage above 500V, a 1000V~2500V megger should be used.
(2) Choice of resistance range. There are two small black dots on the scale line of the dial of the shaker watch, and the area between the small black dots is the accurate measurement area. Therefore, when selecting a meter, the insulation resistance value of the device under test should be within the accurate measurement area.
2. The use of megohmmeter
(1) Calibration table. Before the measurement, the megger should be subjected to an open circuit and short circuit test to check whether the megohmmeter is in good condition. Open the two connecting wires, shake the handle, the pointer should point to "∞", then short the two connecting wires, the pointer should point to "0", if the above conditions are met, it is good, otherwise it cannot be used.
(2) The device under test is disconnected from the line, and the large-capacitance device must be discharged.
(3) Choose a megohmmeter with a voltage level
(4) When measuring the insulation resistance, generally only the "L" and "E" terminals are used, but when measuring the insulation resistance of the cable to the ground or the leakage current of the device under test is serious, the "G" terminal should be used, and the "G" terminates the shield or housing. After the line is connected, you can turn the handle clockwise. The shaking speed should be slow and fast. When the rotating speed reaches about 120 revolutions per minute (ZC-25 type), keep rotating at a constant speed, read after 1 minute, and Read while shaking, can not stop to read.
(5) Disconnect and discharge. After the reading is completed, shake slowly while removing the wires, and then discharge the device under test. The discharge method is to take the ground wire used for measurement from the megger and short it with the device under test.
4. Precautions
(1) It is forbidden to measure insulation resistance during lightning or near high-voltage equipment. It can only be measured when the equipment is not charged and there is no induced electricity.
(2) During the shaking test, no one can work on the device under test.
(3) The megger wires cannot be twisted together, they should be separated.
(4) Before the megohmmeter stops rotating or the device under test is not discharged, it is strictly forbidden to touch it with hands. When removing the wire, do not touch the metal part of the lead wire.
(5) At the end of the measurement, the large capacitance equipment should be discharged.
(6) Check its accuracy regularly.
