Molded Case Electronically Assisted Circuit Breaker for DC Power Distribution Systems

This article introduces a new dc hybrid circuit breaker (HCB) concept termed electronically assisted circuit breaker (EACB). A conventional ac mechanical molded case circuit breaker (MCCB) is used to interrupt dc fault currents with the assistance of an electronic commutation circuit, which is activated for a short time period only during the late phase of the breaking process. Unlike other prior art HCB concepts, the EACB uses a conventional thermal-magnetic MCCB baseline design with minimal modification on the actuation mechanism, arc chamber, or form factor, and uses an electronic commutation circuit, which only needs to commutate a fault current far below its peak value for a very short duration (~100 μs), both contributing to significant cost savings. Other advantages of the EACB concept include self-powered and autonomous operation, simple installation, inherently low on-resistance, and galvanic isolation. While an EACB does not facilitate arc-free or ultrafast breaking, it does provide a simple and cost-effective way to enhance the dc current interruption capability of the conventional ac MCCBs, which currently dominate the low voltage circuit breaker market. The EACB concept has been validated both experimentally and by simulation. Several 600Vdc/250A (nominal) EACB prototypes are designed and tested. They have experimentally demonstrated a fault current interruption capability of over 8000 A at a dc voltage of 600 V within 6 ms.