Clearing faults near shunt capacitor banks

Fault interrupting tests on high-voltage circuit breakers confirmed the problems of breaking a short-circuit current, which can occur in substations with shunt capacitor banks. Research was conducted on the behavior of different extinguishing media. Tests show that all types of circuit breakers (including the restrike-free breakers) have reignitions after the interruption of faults in the vicinity of a shunt capacitor bank. This is caused by the low rate of rise of the recovery voltage which gives the circuit breaker an opportunity to clear at short arcing times. Reignitions occur because of the low dielectric withstand capability of the small contact gap. Both tests and computer calculations show high overvoltages when the circuit breaker interrupts at one of the superimposed high-frequency current zeros which are created after reignition. Some breakers interrupt at a high-frequency current zero and thus create overvoltages. Other breakers do not interrupt at a high-frequency current zero and wait for a current zero of the power-frequency current, thus prolonging the arcing time. The overvoltages in three-phase circuits are higher than in single-phase circuits.<
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