How to measure the insulation resistance correctly?

Insulation resistance refers to the resistance to the ground of the live part of the device. In order to prevent the device from burning or damaging due to grounding under pressure, this resistance is generally high, in the mega-ohm range. The grounding resistance is for the safe operation of the equipment and the safety of the person. The equipment needs to be grounded safely. However, the grounding resistance is connected to the indirect live part of the device. The grounding resistance is the resistance between the protective casing of the device and the earth. This value is relatively small, generally ohmic, so that the device casing can be effectively grounded to ensure the device casing. The voltage is in a safe range and the like. The shaker we use is for rough measurement, the applied voltage is small, and the sound of the ground capacitance is large, and the measurement error range is large, and it is only suitable for devices with mega-level or higher. If you measure small resistance, you can use a multimeter if accuracy is not required. The high requirements of the general use of the bridge, the measurement range will be smaller and more accurate.

How to measure the insulation resistance correctly?
There are electrical safety issues in the process of electricity use, in electrical equipment, such as motors, cables, household appliances, and so on. One of their normal operations is the degree of insulation of the insulating material, ie the value of the insulation resistance. When heated and damp, the insulation ages. Its insulation resistance is reduced. This causes electrical equipment leakage or short-circuit accidents. In order to avoid accidents, it is required to constantly measure the insulation resistance of various electrical equipment. Determine if the insulation level meets the needs of the equipment. Common resistance measurements are usually measured at low voltage and at high voltage. The insulation resistance is higher due to the general value (generally megaohms). Measurements at low voltages do not reflect true insulation resistance values ​​operating at high voltages. The megohmmeter is also called an insulation resistance meter. It is the most commonly used meter for measuring insulation resistance. It has a high-voltage power supply when measuring the insulation resistance, which is the difference between it and the resistance meter. The megohmmeter is convenient and reliable for measuring insulation resistance. However, if it is used improperly, it will bring unnecessary errors to the measurement. We must use the megohmmeter insulation resistance for measurement. When the megohmmeter is working, it generates high voltage itself, and the measuring object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents.

Before using, you must first make the following preparations:
(1) Before the measurement, the power of the device under test must be cut off, and the ground should be short-circuited. The device must not be energized for measurement to ensure the safety of the person and equipment.
(2) For equipment that may induce high voltage, the possibility must be eliminated before measurement can be made.
(3) The surface of the object to be tested should be cleaned to reduce the contact resistance and ensure the correctness of the measurement results.
(4) Before the measurement, check whether the megohmmeter is in normal working condition, mainly check the two points of “0” and “∞”. That is, the handle is shaken to make the motor reach the rated speed. The megger should be in the “0” position when it is short-circuited and “∞” when it is open.
(5) The megohmmeter should be placed in a stable and stable place and away from large external current conductors and external magnetic fields. After the above preparations are made, the measurement can be carried out. When measuring, pay attention to the correct wiring of the megohmmeter, otherwise it will cause unnecessary errors or even errors.

There are three terminals of the megohmmeter: one is “L”, that is, the line end, one “E” is the ground end, and another “G” is the shield end (also called the protection ring). Generally, the insulation resistances to be tested are connected. Between the "L" and "E" ends, but when the surface of the insulator to be tested is seriously leaky, the shield ring of the test object or the portion not to be measured must be connected to the "G" end. Thus, the leakage current flows directly back through the shield end "G".

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