Design and test results of a novel quench protection circuit for a HTS ship propulsion motor

This paper describes a novel configuration of a quench protection circuit for a high-temperature superconducting (HTS) ship propulsion motor that can protect the HTS coils from an unexpected outage in its cryogenic cooling system. The quench protection circuit consists of conductor parts placed adjacent to the HTS coils and dump resistors and diodes placed in the cryogenic-temperature and normal-temperature areas, respectively. The conductor parts are shaped and arranged such that the magnetic coupling with the HTS coil is extremely large. Thereby, the current of the HTS coils can be instantaneously attenuated immediately after the quench protection is activated. With this configuration, the electromagnetic energy of the HTS coils can be absorbed in the dispersed parts. This can make the dump resistors smaller and make it easier to install them on a HTS ship propulsion motor. By analysing the equivalent electric circuit model of the protection circuit, we derived the conditions under which instantaneous current attenuation of the HTS coil occurs. In accordance with the conditions, we have fabricated a quench protection circuit that protects one HTS field pole of the 3 MW HTS motor developed by Kawasaki Heavy Industries. The fabricated circuit was empirically evaluated and proved to be highly effective in quench protection. The present quench protection circuit technology contributes to the practical application of HTS ship propulsion motors.