Modern life is changing with each passing day, and people cannot do without electricity for a moment. In the process of using electricity, there are problems with electricity safety. In electrical equipment, such as motors, cables, household appliances, etc. One of their normal operations is the degree of insulation of their insulating material, that is, the value of the insulation resistance. When heated and damp, the insulating material ages. The insulation resistance is reduced. As a result, electrical equipment leakage or short-circuit accidents occur. In order to avoid accidents, it is required to frequently measure the insulation resistance of various electrical equipment.

The difference in insulation performance of objects of different materials will be more obvious, and the trend of changes in the value during the test will also be different.

Some insulating objects, such as plastic and porcelain, can reach a stable value at the moment of conduction under the action of DC voltage. However, for generators, motors, cables, etc., their insulation is composed of composite media. Under the action of DC voltage, there will be more Kind of polarization phenomenon. At the beginning of polarization, the current is very large. As time increases, the current decreases and the resistance value increases accordingly. This phenomenon is called absorption. In the absorption phenomenon, the fastest attenuation is the capacitive current (polarization current), the absorption current that changes slowly with time, and the current that does not change with time is the conduction current (leakage current). Generally, the larger the equipment capacity, the more obvious this phenomenon.

Three currents of the insulation resistance tester during the insulation test:

1. Capacitance current i1: This part of the current is caused by the capacitance effect of the medium. When the sample under test is pressurized, rapid polarization occurs inside the medium, which is equivalent to the current generated by charging the capacitor; it is instantaneous and attenuates high speed;

2. Absorption current i2: This part of the current is caused by the slow polarization inside the medium, which decays slowly over time;

3. Conductive current i3: This part of the current is caused by the conductance of the medium itself, and its current value is constant.

Therefore, when the insulated cable tester measures the insulation value of electrical equipment, with the gradual decrease of the test current, the insulation resistance will rise rapidly, and then the trend of change will slow down; generally, the value at 60s is used as a reference, which can be compared with Compare the insulation requirements of the equipment to determine whether the insulation of the equipment is qualified.