Kerr electro-optic measurements of space charge effects in HV pulsed propylene carbonate

The Kerr electro-optic field mapping technique has been used to study space charge effects in HV pulsed propylene carbonate (C₄H₆O₃) using stainless steel parallel-plane, aluminum blade-plane, and aluminum point-plane electrodes. Measurements presented here were taken using a circular polariscope with aligned polarizers at room temperature (T ∼ 20 to 27°C). Average peak space charge free electric field strengths were E₀ ∼ 52 kV/cm for the parallel-plane electrodes, E₀ ∼ 210 kV/cm at the blade electrode tip and E₀ ∼ 240 kV/cm at the point electrode tip. The measurement times ranged from 10 μs to 1 ms. For the parallel-plane electrodes, the light intensity pictures were analyzed along a line between electrodes in the center of the electrode gap and for the blade-plane and point-plane electrodes the light intensity pictures were analyzed both from the tip of the blade and point, to the plane, and along the plane surface. From the light intensity distribution for the parallel-plane and blade-plane electrodes, the electric field and space charge density were calculated as a function of position and time. The calculated space charge distributions show both positive and negative charge injections from the electrodes as well as bulk charge dissociation and recombination. The light intensity was recorded on Polaroid film for the parallel-plane, blade-plane and point-plane electrode measurements and also with a CCD camera for the point-plane electrodes. A CCD camera was used for the point-plane electrodes to resolve more accurately the gray-scale light intensity distribution because of the short optical path length. All the HV Kerr electro-optic measurements showed significant space charge effects in propylene carbonate because the light intensity distributions differed significantly from the calculated Kerr effect patterns from numerical solutions to Laplace´s equation under space-charge free conditions.