Breakdown in air gaps with solid insulating barrier under impulse voltage stress

The influence of solid insulating barriers to the impulse strength of air gaps has been investigated by few researchers. It is well known that thin insulating materials increase considerably the breakdown voltage, sometimes two to three times. Some researchers performed thorough investigations for the determination of the parameters of the barrier effect that influence the impulse level for the breakdown. The distance of the barrier from the high voltage electrode is the most important parameter. The field distribution is also important as well as the shape of the insulating sheet. The experimental investigations led to some theoretical models for the breakdown process. This paper analyzes and discusses those models and spots the points where they agree as well as the differences between them. Finally, it attempts to compose a model that sheds light on the barrier effect and complies with all the experimental and theoretical analyses.