A Coupled Inductor based Hybrid Circuit Breaker Topology for Subsea HVDC Transmission Systems

Reliability of a typical DC power system largely dependent on the fault interruption capability of the switchgear. In AC power system, steady-state fault current incurs natural zero crossing which is not available for fault in a DC system. Instead, in DC systems, the fault current increases from its steady state value rapidly, the rate of rise of fault current is being decided by the lumped value of network inductance. Hence, fault interruption time for HVDC circuit breaker should be minimal in order to immediately isolate the faulty section and prevent any damage to the DC grid. Fast fault interruption is achieved by employing solid state circuit breakers (SSCB). However, substantially large power loss due to higher on-state voltage drop of the semiconductor devices limits the application of SSCBs. Hybrid circuit breakers combining the features of mechanical breakers and SSCB have shown better performance in terms of efficiency but de-magnetization of network inductance during voltage blocking state of mechanical breaker remains a pivotal challenge. This paper presents two coupled inductor based hybrid HVDC circuit breaker topologies to address the above mentioned problems of DC switchgears. The coupled inductor and capacitor are designed to form a resonant circuit during the fault to provide an artificial zero crossing of fault current. The added advantage of the proposed topologies is that, they do not require external charging circuitry to pre-charge the capacitor, and also eliminate the requirement of surge arrester which are employed for suppressing the energy stored in the network inductance during fault. Analysis and design of the proposed circuit breaker topologies are presented along with corresponding simulation results.