Abstract
During the development of a commercial vacuum interrupter for application in HV (high voltage) switchgear at a rated voltage of 145kV, we investigated the behavior of vacuum arcs controlled by axial magnetic fields (AMF). AMF arc control is already extensively used in medium voltage (1-52kV) applications, the key difference is the 2-3 times larger contact gap and the corresponding reduction of the AMF strength for HV applications. We conducted several stress tests with short circuit currents up to 40kA, thus not only testing the interrupting capability, but also the electrical endurance of such a contact system. We also investigated the dielectric behavior of the vacuum interrupter by testing the capacitive switching duty. Overall, the contacts were used in about 40 operations at high currents. Despite this large number of operations, they showed a minimal amount of contact erosion and damage and demonstrated behavior very similar to the extensive experience with MV vacuum interrupters. In line with simulation results, we conclude that even at high contact gaps and currents, a diffuse vacuum arc was maintained which distributed the arc energy evenly over the contacts.
Highlights
Vacuum interrupters (VI) have been used in high voltage (HV) applications above 52 kV from the start of practical VI manufacturing in the late 1950’s and early 1960’s
During the development of a commercial vacuum interrupter for application in HV switchgear at a rated voltage of 145 kV, we investigated the behavior of vacuum arcs controlled by axial magnetic fields (AMF)
Vacuum interrupters are the dominant technology for circuit breakers in medium voltage applications based on the long electrical life at load and shortcircuit currents, as well as being maintenance-free and offering minimal contact erosion during operation
Summary
Vacuum interrupters (VI) have been used in high voltage (HV) applications above 52 kV from the start of practical VI manufacturing in the late 1950’s and early 1960’s. Circuit breaker designs successfully achieved ratings up to 145 kV/40 kA [1] and 132 kV/3500 MVA [2] in type tests, and achieved some limited field use. A concerted focus on HV VI development in Japan resulted in the field installation of approximately 8300 circuit breakers using VI from the late 1970’s to 2010 [3]. 99% of these circuit breakers were for 72 kV and lower system voltages Many of these designs, especially in later years, used a single VI or at most two VI in series instead of the previous multiple VI systems. Even in Japan only a very small percentage of the installed base of HV circuit breakers used vacuum
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