Time to Breakdown on Large Electrodes Tested with Positive Switching Impulses

In high voltage equipment like bus terminals and interconnectors, it is common the use of large rounded electrodes to control high electric fields and improve the air insulation strength. A lot of information has been gathered from experimental campaigns during the last decades, where the main task focused on measuring the U50% breakdown voltage for several common electrode arrangements, and based on that, predict the behavior of similar electrode configurations existing in substations, transmission lines, etc. One special case occurs when small conductive protrusions are located on the surface of large electrodes. It has been observed before that the measured U50% is reduced compared with the case of an electrode without protrusions. In the present work, we analyze experimental results regarding the time-to-breakdown in switching impulse tests on large electrodes considering the presence of protrusions. A relation between the time-to-breakdown, the electrode type and the gap length was analyzed comparing different experimental data.