The surface discharge of electricity on the solid insulation is investigatcd for the case:-
(1) In air, various insulating plates are used, and tests are made under a number of different conditions, including momentary application of pressure, and damped and sustained oscillations.
Under 50 cycle a. c. supply, it is found that the negative surface-spark-corona takes a circuler path a certain distance apart from the electrode, and the critical voltage, which separates two distinct type of discharge, i. e. the luminous pole-brush and the spark-corona, is proportional to square root of thickness of insulating materials, and its proportional constant depends on the insulating materials.
(2) In transformer oil, the distinct pole-brush can not be traced, and the difference of positive and negative surface-spark-corona is not so distinct as in air.
From the microscopic investigation of the image made on the film by the luminosity of the discharge, it is ascertained that the sensitive film has no important influence on the formation of discharge. (july 1924)
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