AbstractAt substations connected with transmission lines and cables, shunt reactors are sometimes installed to compensate the capacitive current of these lines and cables. It is known that re‐ignitions occur and high‐frequency currents flow during interruption of the shunt reactor currents by switches. When the high‐frequency currents are interrupted immediately after the re‐ignitions (which is called high‐frequency arc extinction), the result is often repetitive re‐ignitions or voltage escalations that produce dangerous overvoltages.The authors investigated the occurrence of high‐frequency arc extinctions in a 550‐kV one‐break SF6 gas circuit breaker during interruption of a 550‐kV shunt reactor current. Computations for a real 550‐kV substation gave a minimum frequency of 290 kHz for the high‐frequency current. However, 550‐kV reactor current interruption tests showed that high‐frequency arc extinctions did not occur even when this frequency was lowered to 26 kHz. Since high‐frequency arc extinction is generally likely to occur at lower frequencies, it was concluded that high‐frequency arc extinction will not occur in a 550‐kV one‐break SF6 gas circuit breaker during interruption of shunt reactor current in real substations. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 18–25, 2001