Abstract
At the supporting point of an insulated wire in a high voltage areal distribution system, there appears the compound insulation system consisting of an insulator and the insulation layer of the wire. Hence, complicated discharge phenomenon is to occur at the supporting point due to the penetrated overvoltage by the lightning, as reported in the earlier work.
Recently it has been found that polarities of successive lightnings in the districts along the Japan sea in winter were frequently intermingled with the positive and the negative. With such successive lightnings the discharge phenomenon is supposed to be much more complicated.
In this work, two successive impulse voltages whose polarities were intermingled with positive and negative, were impressed on the wire, and they were intermitted in time interval of 30s. Under these conditions, the leaders progressing from the tip of binding wire along the surface of the insulated wire were observed. In consequence, it was clarified that there were remarkable differences in the progression characteristics of the leaders in comparison with those due to a single stroke of lightning.
Finally it is pointed out that it is necessary to take care of the weak point of insulation layer of the wire not only in the neighborhood of the supporting point, but also in the farther range.
