A hybrid DC circuit breaker comprised of a cryogenic contactor in series with a superconductor has recently been developed at NASA Glenn Research Center. This circuit breaker combines mechanical and solid-state technology to meet the needs of certain DC power system applications.

Circuit protectors and other DC protection systems play a key enabling role for the DC power system in applications such as aerospace and the power grid. Despite being a mature technology, conventional electromagnetic circuit breakers are large in size and have a high response time, which makes them unsuitable for, for example, an electrical system in aviation that requires a fast response time. Compared with a mechanical circuit breaker, solid-state circuit breakers based on high power semiconductors can provide a fast response time to make the fault current fully controlled; however, the on resistance of semiconductors creates high conduction loss, which leads to low efficiency. A hybrid solution that combines both mechanical and solid-state technology is desired, and advances in cryogenic contactors and superconductors suggest that the eventual development of cryogenic hybrid DC breakers is likely.

In NASA’s hybrid DC breaker, both the cryogenic contactor and the superconductor can be cooled with the same cryogenic tank. The superconductor can be either resistive type or inductive type. For an inductive superconductor, a core is required, and it could be made bigger or heavier than the resistive superconductor. A solid-state snubber is utilized in parallel to provide transient energy dissipation.

During normal operation, the main current is only fed through the cryogenic contactor and superconductor, which leads to almost zero conduction loss. When a DC short occurs and the short current exceeds the superconductor’s critical current, the resistance or inductance of the superconductor develops rapidly and the current will be bypassed by the parallel semiconductor to protect the superconductor from destructive hot spots during the quench. When the main current going through the cryogenic contactor decreases to a very small value, the contactor will open. Afterward, the gate control signal of the solid-state snubber can be turned off to fully break the fault.

If fast reset function is required, a saturated-core superconductor (one type of inductive superconductor) can be utilized. A saturated-core superconductor doesn’t require the superconductor to perform quench to provide high impedance; therefore, the reset time could be very short.

This work was done by William James Premerlani, Antonio Caiafa, Yan Pan and Ruxi Wang of GE Global Research for Glenn Research Center.