Superposition gas breakdown. Final report

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Abstract
Results are described of a research program investigating breakdown in a 76/250 mm coaxial electrode system in compressed SF/sub 6/ as a result of superposition of impulse voltages on the 60 Hz power frequency voltage in the presence of conducting particles. The object of this program was to experimentally determine if impulse superposition is a more severe condition for particle initiated breakdown than the 60 Hz voltage alone, which can result in breakdown as low as only 10% of the dielectric strength of SF/sub 6/. Breakdown voltages were measured for particles both isolated and in contact with the center conductor and also for multiple free conducting particles in the system for impulse voltages, 60 Hz voltage and with impulses superposed on the 60 Hz voltage. The results showed that the lowest values obtained with the superposition of impulse voltages on the 60 Hz voltage were equal to the lowest values of the 60 Hz or impulse voltages alone. The probability for particle initiated breakdown as a result of superposed impulse voltages with realistic magnitudes of the 60 Hz voltage was found to be negligible and was entirely dominated by the 60 Hz breakdown probability. It is therefore concluded that testsmore » using impulses superposed on the 60 Hz voltage does not constitute a more severe test condition for the gas insulation of compressed gas insulated systems than the present 60 Hz test voltages. The voltage combination may be useful as a method of field conditioning long lengths of compressed gas insulated transmission systems. « less

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