Series Connection of Gas and Vacuum Circuit Breakers as a Hybrid Circuit Breaker in High-Voltage Applications

Possible sulfur hexafluoride (SF6) gas alternatives have been the focus of research and development in science and industry for many years. After the revision of the European F-Gas regulation 517/2014, the investigation has been even more intensified. One option for an approach for realizing an environmentally friendly switchgear for the high-voltage level is a combination of gas circuit breaker (GCB) and vacuum circuit breaker (VCB) in a series connection. Both switching concepts have advantages: the VCB can withstand very steep rising transient recovery voltages after current zero (CZ), while the GCBs are able to withstand high amplitudes of recovery voltage. In this investigation, the coupling and interaction of a series connection of a VCB and a GCB filled with carbon dioxide (CO2) is experimentally characterized in a basic study. The postarc current of the axial-magnetic-field-type VCB is identified as an important parameter influencing the interaction between both circuit breakers in the series connection and subsequently in the focus of the investigation. The different CZ behavior of a single VCB and a hybrid circuit breaker is compared. The voltage distribution across the two circuit breakers is the main assessment criterion for a series connection. In the first phase after CZ, the postarc current has a dominant influence on the voltage distribution; after that, a transition phase leads to capacitive voltage division phase. In order to control the voltage distribution, both capacitive and resistive voltage controls are investigated.