Conditioning of Series Vacuum Interrupters (VIs) for Medium Voltage by Applying High-Frequency (HF) Current to Increase the Dielectric Strength of VIs

According to well known standards e.g. IEC 62271-100, vacuum circuit breakers and especially vacuum interrupters (VIs) have to fulfil miscellaneous forms of dielectric strength requirements depending on the rated voltage. Besides conventional conditioning methods e.g. with alternating current (AC), further techniques have to be investigated in the case of higher voltage levels. This work describes the high frequency (HF) current conditioning method with the objective to increase the dielectric strength of modern and very compact VIs for medium voltage applications. A test set-up for conditioning of VIs in the kHz range is presented. The conditioning current has peak values up to 10 kA with durations of microseconds and voltages up to 135 kV (peak). The dielectric properties of investigated VIs are described with emphasis on the obtainable lightning impulse withstand voltage level after one or more HF-sequences. Additionally the surface microtopography and roughness of contact surfaces are analysed by means of atomic force microscopy before and after applying HF-conditioning.