Discharge characteristics in short rod-plane gaps with dielectric-covered rod under lightning impulse voltages

Results are presented concerning both prebreakdown phenomena and the breakdown mechanism in short rod-plane gaps with dielectric-covered rod under positive standard lightning impulse voltages. Characteristic discharge parameters, namely first and second corona inception time and voltage, and time and voltage to breakdown were measured, through multiple level tests, with the gap length as a parameter. The simple air gaps i.e. without any insulating covers were considered as reference cases. In the presence of the dielectric cover breakdown occurs at higher applied voltages as a result of increased both corona inception voltages and discharge path. Interpretation of the results is made based on the discharge development pattern and electric field calculations.