168 / 2024-04-15 14:52:09

Performance of vacuum circuit breaker in frequently capacitor bank switching

: VACUUM CIRCUIT BREAKER, CAPACITOR SWITCHING, VACUUM INTERRUPTER, RESTRIKE, FREQUENT SWITCHING

Power system reactive power compensation is of great significance to improve the power factor of the grid, reduce line losses and improve the quality of electric energy. In shunt capacitor compensation is widely used in medium voltage power systems. Usually, the rated current of capacitor compensation device does not exceed 1000A, and with daily switching of the compensation device, the opening and closing operation of the compensation circuit is more frequent.

Medium-voltage power systems always use vacuum circuit breakers to switch capacitor banks, in the process of capacitive current switching, the closing inrush current will cause the vacuum interrupter contacts to melt and weld, which increase the probability of re-strike. The process for verifying the performance of circuit breakers for capacitive current opening and closing is stipulated in IEC 62271-100, which requires that the C2 level be 104 operations, and the actual operations of vacuum circuit breakers used in the compensation circuit of capacitor banks is far more than 104.

The new “K-type” vacuum interrupter was developed for frequent switching of capacitor banks. The interrupter contacts have higher resistance to fusion welding, and the closing inrush current of circuit has less effect on the contact surface. Vacuum circuit breakers using “K-type” interrupters have successfully passed three rounds of back-to-back capacitor bank switching tests of class C2 (40.5kV, 1250A) with totally 264 operations in accordance with the test procedure stipulated in IEC62271-100. Based on the influence of frequent capacitor bank switching on contacts of vacuum interrupter and the problems of existing products on customer site, combined with the back to back capacitor switching test data of 40.5kV, 1250A with “K-type” vacuum interrupter. The paper shows the detail information of the cumulative frequency of the pre-ignition electric field strength and the form and energy distribution of the inrush current during the whole testing. After 264 tests, the insulation performance of “K-type” vacuum interrupter meets the relevant requirements of GB/IEC standards, and the surface roughness and micro-welding of contactors are significantly improved.