DC breakdown voltage characteristics of small air gaps with insulating barriers in non-uniform field

In this study, the influence of insulating barriers on the breakdown voltage of air in non-uniform field is experimentally and theoretically investigated. Tests were conducted in order to determine the positive and negative DC breakdown voltage of small air gaps (up to 50 mm) formed by energized rod and grounded plane electrodes with an insulating barrier between them. The dielectric behaviour of the barriers is also examined by using various disc type insulating barriers with three different materials such as rubber, colored and transparent PVC (polyvinyl chloride) with diameters of 37.5, 75 and 150 mm. In addition, the experiments are simulated with FEMM 4.0 (Finite Element Method Magnetics) analysis program by computer. A comparison was made between the test results and the computer application. As a result, the breakdown voltage varies due to the size of the barriers, the maximum flashover voltages were observed when the barriers were positioned at the nearest point to the rod electrode and the small sized barriers become effective only in very small air gaps. The test results are in accordance with the application and the breakdown voltage of the negative polarity is always higher than the positive polarity tests.