Design and implementation of a test environment to study late-breakdowns in high voltage vacuum circuit breakers

In the last decades, the vacuum switching technology has established itself as the standard in the medium voltage level (Us <= 52kV). However, at higher voltages, this technology is not yet competitive to the current SF6 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 a vacuum circuit breaker and tested widely. However, the interpretation of these tests are difficult due to the absence of suitable diagnostic tools. Therefore, the present thesis deals with the development of a suitable 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 of restrikes two main requirements have been derived: 1. The synthetic test circuit needs to be realized using only test transformers. This is necessary to achieve a high number of test series because the use of power transformers is limited and not economical. In case of a capacitive switching duty, this limitation effects the generation of the recovery voltage and how it is applied to the test object. The recovery voltage itself consists in equal parts of a direct and alternating voltage component and must be applied precisely during its voltage zero crossing. This has been realized using two independent voltage sources and a voltage-making switch that has been specially designed for this purpose. 2. A simultaneous detection of field-emission currents and charged micro-particles is needed. Both phenomena can cause restrikes but are not necessarily independent from each other. To measure field-emission currents, a proven concept from the medium voltage level has been adapted towards a high number of capacitive switching operations in rapid succession. This has been achieved by exploiting the separate generation of current and voltage of a synthetic test circuit. Based on their identical interaction with the test circuit, micro-particles have been detected using partial discharge measurement equipment. As a consequence, the whole test environment must have a low partial discharge level to enable this detection. Within this work, the measurement systems as well as the test circuit have been commissioned and tested. It was possible to demonstrate the simultaneous detection of micro-particles and field-emission currents (>= 100 μA). Furthermore, a best practice has been defined for future investigations. Based on first 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 μs) at the voltage zero crossing with an additional voltage-making switch. Thus, the main negative aspect in their generation, which arise from the use of test transformers, can be compensated