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A new technique for measuring the transient potential distribution of electrical discharge is proposed. The measuring system consists of a Bi4Ge3O12 Pockels crystal, an Ar ion laser, a beam expander, a streak camera and a charge-coupled device camera. The potential profile of the discharge along a linear path of 50 mm in length is measured in the range of 0∼±36 kV. The temporal and spatial resolutions of this system are estimated to reach 2 ns and 0.1 mm, respectively. The potential distribution of a surface discharge creeping on a dielectric material is measured to clarify its developing mechanism. The tip of the propagating surface discharge has a high potential close to an applied potential. The maximum value of electric fields of a negative surface streamer exceeds 16 kV/cm in the direction of the streamer propagation.

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The Pockels sensing system has been developed for directly measuring the potential and electric field distribution on a dielectric material. The system consists of an Ar ion laser, a Nd:YAG laser, a streak camera, and charge coupled device cameras. With this system, both the transient change in the potential distribution along a linear path of 50 mm in maximum length and the instantaneous two-dimensional potential distribution on a 25 mm square area can be measured simultaneously. The minimum resolution of this system reaches up to 0.2 ns. This article describes the transient change in potential distribution with a surface discharge in atmospheric air. The transient change of potential distribution with a propagating negative surface discharge in atmospheric air is measured with this system. The propagating direction component of the electric field Ex near the tip of the propagating streamer exceeds 3 MV/m.

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