The Interruption of Charging Current at High Voltage

The switching of high-voltage transmission lines and underground cables occasionally produces overvoltage surges on electric power systems. While operating experience generally has been satisfactory voltages of 66 kv and below, there have been transient disturbances of considerable magnitude at the higher voltages. The length of many of the transmission lines and the importance of maintaining continuity of service on heavily loaded interconnections have stimulated a critical analysis of the problem. However, in contrast to the extreme overvoltages predicted by theoretical studies, a review of several hundred field tests over the past ten years, including many tests with voltage records by cathode ray oscillographs, discloses practically no cases of line or bus surge voltages on solidly grounded systems reaching transient peaks as high as 2¿ times normal line-to-ground crest voltage. This paper attempts to evaluate the effect of both the circuit constants and the characteristics of the various types of interrupters used in modern high voltage oil circuit breakers on the magnitude of switching surges. Particular attention is given to the advantages and disadvantages of such oil flow pistons or low ohmic value resistors in parallel with the main arc extinguishing devices.