Connecting Leaders in a Nonuniform Spark Gap

Still photographs of discharge events reveal a multitude of phenomena, most of them well known, but sometimes, an unexpected phenomenon appears. Here, a photograph where leaders meet midgap in a positive 1-m rod-to-plane electrode configuration subjected to a switching impulse voltage is presented. The appearance of a connecting negative leader originating from the plane electrode was not expected. The positive leader propagating from the rod is inhibited by a large series resistor in the discharge circuit, thereby giving a negative connecting leader time to develop from the plane electrode.