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Reasons for the change in insulation value

time:2020/12/3   source:华天电力  reading:253 time

With the rapid economic development and the continuous improvement of living standards, people cannot do without electricity for a moment. There are problems with electricity safety in the process of using electricity. In electrical equipment, such as motors, cables, and household appliances, they are normal. One of the operations is the degree of insulation of the insulating material, that is, the value of the insulation resistance. When heated and damp, the insulating material will age and its insulation resistance will decrease, resulting in electrical equipment leakage or short-circuit accidents. 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.


Insulation Resistance Tester (3).png


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 This kind of polarization phenomenon, the current is very large at the beginning of polarization, and the current decreases with the increase of time, and the resistance value increases accordingly. This phenomenon is called absorption phenomenon. In the absorption phenomenon, the capacitive current (polarization current ), the current that changes slowly with time is the absorption current, 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 conductivity of the medium itself, and its current value is constant.


Therefore, when the insulation resistance 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.


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Transformer measuring short-circuit impedance  | 2020/12/4 | reading253time Principle of Insulation Resistance Test  | 2020/12/3 | reading259time return