Electric field and current density in the impulse corona discharge in a rod/plane gap

Abstract

Measurements have been made of corona discharges in positive rod/earthed plane systems subjected to impulse voltages up to 200 kV. For this an electrostatic fluxmeter for the examination of electric fields and charge densities present in the corona has been developed and used. Measurements of electric fields and current densities so obtained during the discharge are compared with conventional measurements of total current densities. These show that the transient at the centre of the plane is a double pulse of time separation 0.1 to 1.0 μ s. The first pulse is shown by the fluxmeter to be due to induced charge on the plane surface and the second to electron emission from the surface. At the plane electrode the space charge electric field can be as great as 8 kV/cm, and the conduction current density in the corona 45 A/m 2 . The duration of the decaying space-charge field is several seconds. The construction, calibration and synchronization of the fluxmeter, which can measure electric fields down to 10 V/cm with a time resolution of 0.5 ms, are described. The principles of the device in separating the displacement and conduction current com­ponents in the discharge process are discussed.