Investigations on the dielectric behavior of vacuum circuit breakers after switching operations

The dielectric behaviour of vacuum interrupters (VI) before and after switching operations has been investigated. At first, switching operations with different intensities of load with short circuit currents at 50Hz frequency were performed. The test objects were a standard VI with a rated voltage of 12kV, a rated current of 1250A and a short circuit interruption current of 20kA. In order to simulate switching operations as they are performed under ordinary technical conditions with these VIs, a standard switchgear has been modified. The three, by default assembled VI poles of this switchgear have been replaced by one test setup pole, which allows an easy exchange of a single vacuum interrupter. The switchgear is connected to a high power test field, where the necessary 50Hz half cycles with 20kA rms of current intensity can be generated. The different current intensities were chosen in steps of 5kA in order to simulate different operational demands. It is known, that the dielectric performance of VIs can be affected and decreased by switching operations [1]. The dielectric behaviour of VIs that haven't been and the VIs that have been switched with different amounts of current, have been tested with lightning impulse voltage. Furthermore, the VIs have been opened and the traces of the switching operations have been investigated.