Simulation Test and Analysis of Defects for SF6/CF4 Mixed Gas Circuit Breaker

With the characteristic of superior resistance to low temperature liquefaction, SF/CF
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mixed gas insulation circuit breaker (mixed gas circuit breaker) has been extensively applied in the severe cold areas of Inner Mongolia. However, after suddenly temperature decreasing in the Xilin Gol in early 2019, the defects of low-pressure alarm or blocking for eight SF
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/CF
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mixed gas insulation circuit breaker of various manufacturers occurred. The diagnostic tests were conducted onsite for the defective circuit breaker, for instance, leak test, $\mathrm{S}F_{6}$ decomposition test, and density meter verification. Nevertheless, the test results indicated no abnormalities. In order to research the reasons of the defects, mixed gas composition test for defective circuit breaker will be conducted in this paper. Simultaneously, the parameters of the mixed gas circuit breaker in Xilin Gol will be inspected. The process of low-pressure defects for $\mathrm{S}F_{6}/\mathrm{C}F_{4}$ mixed gas circuit breaker under low temperature operating condition will be simulated combining the test platform. The simulation test illustrates that incorrect filling ratio of $\mathrm{S}F_{6}$ to $\mathrm{C}F_{4}$, mismatch of the parameters of the mixed gas density meter, and excessive pressure in tank may lead to low-pressure defects for $\mathrm{S}F_{6}/\mathrm{C}F_{4}$ mixed gas circuit breaker under low temperature operating condition. Thus, a number of technical suggestions will be proposed in this paper. For instance, the requirements of onsite mixed gas composition test and the onsite collation of mixed gas density meter parameters should be supplemented to the relevant regulations. Additionally, leak test under low temperature operating condition should be implemented for release test.