Measuring insulation resistance is a relatively simple and convenient auxiliary method for checking the insulation status of electrical equipment, and it is also a widely used testing method in the power industry. Nowadays, insulation resistance testers and megohmmeters are commonly used to measure the resistance and absorption ratio of insulation media. The commonly used tools are megohmmeters and insulation resistance testers. More advanced ones can use adjustable high-voltage digital megohmmeters, intelligent insulation resistance testers, and other equipment.

1、 Why measure the insulation resistance of electrical equipment

The function of an insulator is to isolate electricity, including isolation between phase lines (phase to phase insulation) and isolation between phases (ground insulation). The insulation requirement for electrical equipment is non-conductive, which requires a considerable degree of insulation resistance. Ensuring sufficient insulation resistance between phases and to ground is one of the important indicators for the safe operation of any electrical equipment. Therefore, measuring the insulation resistance of electrical equipment is a very important process.

2、 Aging of insulation resistance

During the long-term operation of electrical equipment, it is inevitable that it will be subjected to internal electrical, thermal, and mechanical forces, as well as external atmospheric (such as rain, fog, lightning, etc.), environmental, and external forces. These factors may all cause the aging of insulation resistance in electrical equipment, reducing the isolation capability of electrical equipment. The continuous decrease in insulation capacity will eventually lead to insulation damage. Therefore, regular measurement of insulation resistance and timely investigation of factors causing insulation resistance loss are important guarantees for the safe operation of electrical equipment.

3、 The effectiveness and shortcomings of measuring insulation resistance

By measuring the insulation resistance of electrical equipment, it is possible to effectively reflect defects such as overall moisture damage to the insulation, penetrating channels in the insulation, deterioration of the oil quality of the insulation oil, moisture damage to the insulation caused by water ingress, and cracks in the insulation porcelain sleeve.

However, in some cases, although there are some local defects in the insulation (such as partial discharge), the insulation between phases and relative to ground remains good, and the insulation resistance rarely decreases or even does not lose. Measuring the insulation resistance cannot detect and judge this type of defect, so other testing items need to be used for detection, such as partial discharge detectors, partial discharge monitoring systems, etc. for partial discharge testing. Through comprehensive testing and experimentation, dangerous situations can be avoided.