Partial Discharge free Bushing for Thermal Cycling Tests up to 150°C at 10 kV

Published in 2015

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Summary

Lifetime of electrical power apparatus depends on several factors. One important factor is the condition of the insulation system which can be reduced by voids and other defects. Inside these voids discharges may occur which are called partial discharges (PD). Some aspects as voltage level and operating temperature influence the occurrence of PD. Due to higher temperature a higher stress of the insulation system can be expected. Temperature dependent permittivity also leads to reduced PD inception voltages. Thermal cycling leads to further challenges. Alternating temperatures and different thermal expansion coefficients combined with a heat gradient can create cracks inside the insulation. Inside these cracks PD can occur. For PD analysis of samples the measurement setup has to be PD free above the test voltage. For thermal cycling a heat oven needs a special bushing which must handle the different challenges. Also, further challenges exist regarding e.g. dimensions, shielding and thermal conductivity. In this work the conception and construction of a bushing considering these different aspects is done. A test temperature of up to 150°C is required. The bushing for the oven is planned to be PD free up to 10 kV with a noise level of less than 1 pC. The electrically conducting parts are made of brass and the electrical insulation is PTFE. Further restrictions are e.g. limited space and a small amount of heat which is transferred from inside to the outside of the oven. The conditions of the measurement setup and the build-up of the bushing are presented. Also, measurements of the bushing are shown.