Transient Current and Voltage Waveforms When Switching on a Capacitive Circuit with a Vacuum Circuit Breaker

The article contains a description of a model of a vacuum circuit breaker that is used for the analysis of transient phenomena when switching on a capacitive circuit. The most important element when designing the model was to take into account the occurrence of the phenomenon of the bouncing of contacts during the circuit switching process. The proposed circuit breaker model is controlled based on the following parameters: chopping current, comparison of return voltage with the voltage of contact gap strength, and also the value of the slope of the current increase. The model takes into account the phenomenon of contact bounces and their asynchronous closure. This model is used to analyse voltage and current waveforms on both a switched capacitor bank and on a circuit breaker itself. Due to the autonomous nature of the vacuum circuit breaker model, it can be used both in the analysis of currents and voltages during switching processes in capacitive and inductive circuits, as well as in power system models. It is adapted for analyses at a medium voltage ranging from 6 to 36kV.

I. Introduction

Vacuum circuit breakers, due to their properties, are the leading switches that are used at medium voltage. They are used in switching processes and as an effective safety device during surge phenomena. When discussing the topic of vacuum circuit breakers, their advantages [1], which distinguish these types of switches, should be mentioned, namely: •

during natural transitions through zero, the are switches off naturally and the contact gap strength is then rebuilt very quickly;

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very long operation time at low costs - the required inspection takes place every 10 years or 10,000 operations;

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limited negative impact on the natural environment - there are no gas emissions during switching processes;

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the use of a vacuum chamber allows harmful gases (e.g. SF₆) to be avoided, which significantly reduces the cost of recycling;

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the use of a vacuum chamber allows harmful gases (e.g. SF₆) to be avoided, which significantly reduces the cost of recycling;

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the durability of vacuum circuit breakers is estimated at 2,000 cycles for rated current and 100 cycles for breaking current.