Experimental investigation of lightning initiated flashover faults in MV lines

Direct lightning stroke to an overhead line conductor can produce a flashover across insulator causing a fault on the power network. A medium voltage (MV) overhead line with grounded cross arm will experience a single-phase fault whereas a multiphase (two-phase or three phase) fault is likely to occur when the cross arm is ungrounded in the event of a lightning strike. This paper investigates the characteristics of lightning initiated flashover faults in unshielded medium voltage (MV) lines with different types (metallic/wood) and configurations (grounded/ungrounded) of cross arm. The lightning impulse voltage is applied to one phase of a three-phase overhead line and the experimental flashover characteristics of single-phase and two-phase flashover faults are investigated. The total CFO of the line is also calculated using up and down method. The effect of cross arm braces on the flashover path and the variation in the magnitude of voltage build-up in the nearest phase is also analyzed. The tests have been performed under dry and wet conditions with both positive and negative polarities.