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Insulation resistance test

time:2021/2/5   source:华天电力  reading:341 time

Electricity safety problems exist in the process of electricity consumption, in electrical equipment, such as motors, cables, and household appliances. One of their normal operations is the degree of insulation of their insulating materials, that is, the value of 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 value changes 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. When the polarization starts, 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 capacitive current (polarization current) that decays quickly, the absorption current that changes slowly with time, and the conduction current (leakage current) that does not change with time. Generally, the larger the equipment capacity, this phenomenon The more obvious.


Insulation Resistance Tester (3).png


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 increase 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.

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