VOLTAGE-TIME CHARACTERISTICS IN SF//6 AND SF//6-N//2 MIXTURES.

In gas-insulated substations, traveling waves with a risetime of only a few ns can be generated by disconnector operation and lightning-induced effects in close proximity to the installation. In case of steep overvoltages due to the operation of surge arresters the availability of primary electrons and the field distribution have the major influence on the time lags of the discharge development. The formative time lags are investigated for different field distributions and primary electron generation mechanisms for SF//6 and N//2 and mixtures of both gases. Optical measurements have been performed to obtain a more detailed information of the ignition processes in the insulating gap. Depending on the intensity of the UV radiation and the relative field strength in front of the cathode, the measured time lags show a more or less significant scatter.