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The degradation of surge protector is always presented after long-term operation in low voltage power system, causing the power accidents even fire, it must be regular testing. But the given detection methods in national norms and standards are not perfect, sometimes the product in system cannot be replaced timely even its degradation has been serious, which generates a great deal of security risks.Though the simulation tests of SPD in low voltage power system under different degradation situation, which is based on the Schottky barrier theory and ion migration mechanism, the results indicate that the ZnO varistors after DC are presented polar effects, and the V-I curve disintegration is more serious during negative measurements. After positive and negative DC/AC alternative operations, the polarity effect gradually disappeared, but the disintegration of V-I curve is still existed. The degradation of DC is stronger in AC under the same amplitude current. Though the impact of In, the SPD varistor voltage U1mA experienced three process of increases-stable-sharply decreases by the increase of impact times. The leakage current change very slowly in the beginning, but turn to sharply increases after a certain shocks. These two parameters present obvious inflection effects, but the nonlinear coefficient a is decreased with the increasing impact numbers, overcoming the defects of using the U1mA and leakage current to determine the degree of degradation. The three methods are combined to make a more rational judgment of the degradation of varistor(MOV).Through a large number of experiments, the reasonable parallel MOV can increase the current capacity, reducing the residual pressure, improve the level of voltage protection, to slow down the aging effect. Statistical analysis the simplest way to filter sheet is making use of U1mA, which is to parallel MOVs ranging from±2V, so that the current deviation would be within10%. SnO2varistors internal phase and the grain structure is simpler than ZnO, making its better anti-aging ability in macroscopic electrical characteristics, but the SnO2varistors have not yet reached a mature stage, its residual pressure presents higher under impact current, so its application in the low-voltage surge protection is limited.
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