Insulation resistance refers to the resistance between two parts of conductors separated by insulating materials, and the insulation resistance tester is an instrument used to measure the insulation resistance. In order to ensure the safety of electrical equipment operation, a low requirement should be put forward for the insulation resistance between conductors of different polarities (different phases) or between conductors and the housing.

Many electrical equipment must be regularly tested for insulation resistance during use. For example, during the yellow plum season and thunderstorm weather each year, various electrical equipment of various enterprises, especially high-voltage equipment, will have varying degrees of moisture or partial damage, which will cause electrical damage. The insulation resistance of the equipment is reduced, which directly threatens the safe operation of electrical equipment and the personal safety of staff. In order to prevent accidents, various preventive tests must be performed on electrical equipment regularly. Another example is the safety requirements of household appliances: basic insulation is 2MQ; reinforced insulation is 7MQ, which is for the normal operation of electrical equipment and the personal safety of staff.

Therefore, it is particularly important to understand the insulation characteristics of the equipment. The factors that affect the measured value of insulation resistance are: temperature, humidity, measured voltage and time of action, residual charge in the winding and the surface condition of the insulation, etc. By measuring the insulation resistance of electrical equipment, the following objectives can be achieved:

(1) Understand the insulation performance of the insulation structure. A reasonable insulation structure (or insulation system) composed of insulating materials should have good insulation performance and high insulation resistance;

(2) Understand the insulation quality of electrical products. If the insulation of electrical products is poor, its insulation performance will be significantly reduced;

(3) Understand the damp and contamination of insulation. When the insulation of electrical equipment is damp and contaminated, its insulation resistance will usually decrease significantly;

(4) Check whether the insulation can withstand the withstand voltage test. If the withstand voltage test is performed when the insulation resistance of the electrical equipment is lower than a certain limit, a larger test current will be generated, causing thermal breakdown and damaging the insulation of the electrical equipment. Therefore, various test standards generally stipulate that the insulation resistance should be measured before the withstand voltage test.

It can be seen that the size of the insulation resistance can often sensitively reflect the insulation situation, and can effectively find that the equipment is generally damp, locally severely damp, and penetrating defects. Therefore, measuring the insulation resistance is one of the important means to understand the insulation of the equipment, and it is an indispensable item in the insulation preventive test.