Supercapacitor-assisted Arc Management (SCA2M) technique for DC circuit breakers in low-voltage applications

Abstract

Direct Current (DC) circuits are gaining popularity due to their compatibility with renewable energy. However, their development is hindered by the lack of mature DC protection, such as circuit breakers. Unlike alternating current (AC), DC lacks natural zero-crossing points, making arc extinction harder and causing severe contact degradation. Additionally, DC fault currents rise faster than AC, emphasising the need for effective arc extinguishing in DC circuit breaking.

Three types of DC circuit breakers (DCCB) exist: mechanical, solid-state, and hybrid. Mechanical DCCBs use mechanical switches, solid-state DCCBs rely on semiconductor switches, and hybrid DCCBs combine both. Despite extensive research, no technologies have achieved viable commercial-scale production due to high costs and technological immaturity. As a cost-effective alternative, manufacturers modify mechanical AC circuit breakers for DC applications by connecting multiple poles in series. However, this approach increases power loss, contact resistance, and overall switch size. For small-scale DCCBs, permanent neodymium magnets are incorporated within the circuit breaker to aid in arc extinguishment as a simple supplementary technique.

This research is the initial step taken by the Waikato Power Electronics Research Group (WaiPER) in New Zealand to address the DCCB arcing issue, with promising experience gathered from two decades of past work based on non-traditional supercapacitor applications known as supercapacitor-assisted (SCA) techniques, achieving multiple patents and industry products.

This thesis aims to develop an electric arc-management technique for mechanical contact-pair based DCCBs using the rapid discharge capability of commercial supercapacitors (SC). A transformer-based circuit reduces the DC loop current during circuit breaker opening, thereby decreasing arcing time, arc energy and contact degradation while extending breaker lifespan. A 2-kW, 80-A prototype demonstrates the concept for approximately 50% arcing time reduction with 55% arc energy reduction, with visual and analytical comparisons of arcing with and without the SC-based technique. The technique is further developed for better performance, achieving 64% reduction in arcing time and 67% reduction in arc energy using a two-transformer-based implementation. Tests were further conducted for multiple circuit breakers of the same rating for different voltage and current values. Successful current reduction in the DC loop is based on a low-voltage SC–MOSFET combination which eliminates the need for high-voltage auxiliary circuits and forced cooling, thus keeping costs low. Also, since the SC-MOSFET loop is galvanically isolated from the main DC loop, the prototype is intrinsically protected from natural events such as lightning overvoltage and current surges.