The influence of the air pressure on propagation characteristics of a local discharge occuring on wet polluted surfaces

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An electrolytic solution surface was used to simulate the surface of wet polluted insulators. The solution was set in a Pyrex glass chamber to simulate the surface of wet polluted insulators in transmission lines which pass altitudes. The air pressure in the chamber was changed from 27 to 101 kPa. As the applied voltages, three kinds of impulse voltages, 2/80 mu s simulating a lightning surge, 101800 mu s and 100/2500k mu s simulating a switching surge, were used and were applied between the point and plane electrodes placed on the solution. The resistivity of the solution, the aqueous solution of potassium chloride, was changed from about 170 to 740 OMEGAcm. A local discharge propagates on the solution surface when an impulse voltage is applied to the surface. To observe the propagation velocity of the local discharge and the intensity of a line spectrum of light from the local discharge tip, a monochrometer and photomultipliers were set round the solution surface. The influence of the air pressure and the resistivity of the solution on relations between the propagation velocity of the local discharge and the intensity of a line spectrum of light from the local discharge tip was examined. As a result, it was found that (1) the propagation velocity increases with the intensity of a line spectrum, (2) the propagation velocity for a given intensity of a line spectrum increases with the resistivity of the solution, (3) the influence of the air pressure on the relations is very small, and (4) the influence of the applied voltage waveform on the relations is very small.