Analytic Study of the Active Quench Detection Method for High-Temperature Superconducting Magnet Using Resonance Circuit

The combination of a machine's rotation cycle and the unpredictable industrial interference encountered by rotating machinery can generate a time-varying noise signal. Such signals cause difficulty while detecting the quench voltage in superconducting rotating machinery. Quench detection is more difficult in high-temperature superconductors (HTS) than in low-temperature superconductors (LTS) because the normal zone propagation (NZP) velocity of HTS is lower than that of LTS. To detect the quench signal in an HTS, signal wires are widely used for voltage taps. However, owing to the low NZP velocity, it is difficult to detect the quench signal in HTS when the voltage taps are attached at short distances from the HTS devices. Furthermore, there is a possibility of the HTS burning out when voltage taps are attached to both ends of the HTS tape, because the hot spot is scarcely dissipative and thermal runaway may occur in the normal zone. Thus, detecting the quench in HTS rotating machinery is difficult. Moreover, the signal wires used in the voltage taps become twisted when the HTS rotor coil rotates to generate magnetic flux. Therefore, in this paper, a sensitive quench-detection method that uses electromagnetically coupled coils is presented for application to HTS rotating machinery.