Abstracts

In the last decades, the vacuum switching technology has established itself as the standard in the mediumvoltage level (Us <= 52kV). However, at higher voltages, this technology is not yet competitive to the currentSF6 switching technology. Especially during switching of capacitive loads, a high number of restrikes(dielectric breakdowns) occur. This capacitive switching duty is dielectrically the most challenging for avacuum circuit breaker and tested widely. However, the interpretation of these tests are difficult due tothe absence of suitable diagnostic tools. Therefore, the present thesis deals with the development of asuitable test environment to investigate 72.5 kV vacuum circuit breakers.Based on experiences from the medium voltage level and established research findings in the field ofrestrikes two main requirements have been derived:1. The synthetic test circuit needs to be realized using only test transformers. This is necessary toachieve a high number of test series because the use of power transformers is limited and noteconomical. In case of a capacitive switching duty, this limitation effects the generation of therecovery voltage and how it is applied to the test object. The recovery voltage itself consists inequal parts of a direct and alternating voltage component and must be applied precisely duringits voltage zero crossing. This has been realized using two independent voltage sources and avoltage-making switch that has been specially designed for this purpose.2. A simultaneous detection of field-emission currents and charged micro-particles is needed. Bothphenomena can cause restrikes but are not necessarily independent from each other. To measurefield-emission currents, a proven concept from the medium voltage level has been adapted towardsa high number of capacitive switching operations in rapid succession. This has been achieved byexploiting the separate generation of current and voltage of a synthetic test circuit. Based on theiridentical interaction with the test circuit, micro-particles have been detected using partial dischargemeasurement equipment. As a consequence, the whole test environment must have a low partialdischarge level to enable this detection.Within this work, the measurement systems as well as the test circuit have been commissioned andtested. It was possible to demonstrate the simultaneous detection of micro-particles and field-emissioncurrents (>= 100 A). Furthermore, a best practice has been defined for future investigations. Based onfirst measurements, micro-particle activity up to a second after a switching operation could be observed.In addition, it has been shown, that the recovery voltage can be applied to the test object precisely(+-100 s) at the voltage zero crossing with an additional voltage-making switch. Thus, the main negativeaspect in their generation, which arise from the use of test transformers, can be compensated.Advisors/Committee Members: Hinrichsen, Volker (advisor), Smeets, Ren (advisor).