This study investigates the relationship between void size and insulation lifetime due to partial discharges (PDs) in internal voids. Experimental results clearly show that the larger the void size, the shorter the insulation lifetime, which decreases the lifetime nvalue index of the voltage-time characteristics. The results also show a clear relationship between the insulation lifetime of a solid insulator having void defects and the PD energy generated in the void, which is related to the cumulative PD energy density per cycle. Therefore, we propose estimating the insulation lifetime of an insulator with voids by calculating the cumulative PD energy density per cycle.

A new electromagnetically actuated vacuum circuit breaker (VCB) has been designed and developed on the basis of the transient electromagnetic analysis coupled with motion. The VCB has three advanced bistable electromagnetic actuators, which control each phase independently. The VCB serves as a synchronous circuit breaker as well as a standard circuit breaker. In this work, the flux delay due to the eddy current is analytically formulated using the delay time constant of the actuator coil current, thereby leading to accurate driving behavior. With this analytical method, the electromagnetic mechanism for a 24 kV rated VCB has been optimized; and as a result, the driving energy is reduced to one fifth of that of a conventional VCB employing spring mechanism, and the number of parts is significantly decreased. Therefore, the developed VCB becomes compact, highly reliable and highly durable.

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A new electromagnetically actuated vacuum circuit breaker (VCB) has been developed for a 72 kV rated switchgear. Each phase of this VCB has a plurality of compact electromagnetic actuators linked mechanically providing the required driving energy. The mechanical linkage working as a lever magnifies an actuator stroke to the required stroke of a 72 kV rated vacuum interrupter. An electromagnetic analysis coupled with motion, which considers the mechanical linkage of the plural actuators, has been developed for designing the driving behavior of this VCB. Using this analytical method and a quality engineering method known as the Taguchi method, we have clarified effective parameters to reduce the time difference of the driving behavior for tolerance specifications. Moreover, analyzing the oscillatory behavior closing the contacts, a structure of this VCB has been designed to reduce the bounce duration. The developed new VCB has been confirmed that a time difference is short enough and bounce duration is reduced. This VCB is highly reliable against variations in manufacturing and environment.

SUMMARY The vacuum circuit breaker (VCB) achieves the high current interrupting capability in the pressure lower than 10 Pa to 5 Pa. When gas pressure increases, the breakdown voltage of a VCB decreases according to Paschen's law, and in the case of small leak, the partial discharge will occur in the VCB and the high frequency electromagnetic waves are radiated. So, we have developed the partial discharge detection system using an antenna with the region from 200 MHz to 300 MHz placed inside the VCB. However, if the partial discharge occurs outside the VCB, the detection system leads to misdetection as the partial discharge inside the VCB. In order to improve the performance of partial discharge detection, the outputs of antenna voltages inside and outside the VCB are investigated.