Results of an investigation on the overvoltages due to a vacuum circuit-breaker when switching an HV motor

The results of a study of overvoltages arising when an HV motor is switched by a vacuum circuit breaker are presented. A laboratory test circuit was devised that would reproduce the actual network conditions in a generating plant, and special measurement and acquisition systems were used to enable the switching-surge amplitude and waveform to be recorded with accuracy. Statistical processing of the data was followed by estimation of the probability of occurrence of overvoltages and by evaluation of the number of the surges impinging on the motor-winding during its operating life. The results are discussed, and a number of conclusions are drawn