Corona Charge Injection Prior to Sparkover in an Inversed Rod-Plane Gap Under Composite Voltages

Research on the sparkover characteristics of long air gaps under composite voltages has important significance on the design and operation of transmission lines and equipment. In this paper, corona charge injection prior to sparkover in an inversed rod-plane gap under composite voltages was studied. The variation of charge injection to the initiation of leader and breakdown was measured by a capacitor divider. Two photomultipliers were positioned to study corona development at two positions between the tip of the rod and the plane, from which the light output could be compared with the charge injected into the gap. When a positive prestress voltage is employed at the plane, charge injection is enhanced and leader inception and breakdown occur at lower voltages than with prestress voltage of opposite polarity. The U_50% sparkover voltages are in inverse proportion to the charge and power inputs up to the time of the leader initiation. The results of corona charge injection to sparkover are helpful for understanding the physical process of the gap breakdown in depth.