Abstract Body

We are developing a liquid hydrogen cooled high-temperature superconducting (HTS) generator. To superconduct the field winding of generator of several hundred MW class, several kA-class high-current assembled conductors are required, and we are now developing a prototype conductor and verifying its electrical and mechanical properties¹). It is necessary to perform the kA-class energization tests of assembled conductors under liquid hydrogen cooling, but the capacity of the current leads of the liquid hydrogen test system built at JAXA's Noshiro Rocket Testing Centre is 500 A²), and it is not easy to modify the system to multi kA-class.

One method of testing large-current low-temperature superconducting (LTS) conductors is the current induction method, in which both ends of the target conductor are short-circuited to form a low-inductance secondary coil that is magnetically coupled to a high-inductance primary coil³). By sweeping the current through the primary coil, a large current is induced in the secondary coil. The same method is expected to be used for large-current energization testing of HTS conductors, but there are several issues that need to be improved. These include the accuracy of the induced current measurement using Rogowski coils, the development of ultra-low resistance connection techniques for HTS conductors, and the resetting of the induced current to zero by conductor quenching.

For this reason, we proposed a new energization method in which AC current is applied to the primary coil and conducted a basic study. As a first step, we manufactured a one-turn short-circuit test coil using a single HTS wire and installed it in a fabricated REBCO field coil2), and conducted an inductive energization test. When the excitation frequency was 1 Hz or less, a phenomenon was confirmed in which the phase difference of the Rogowski coil voltage increased rapidly when the peak value of the secondary current exceeded the Ic of the wire, indicating the possibility of determining the Ic of the secondary conductor using this method. Since the Rogowski coil voltage is measured using a lock-in amplifier, it is highly robust to noise and drift, enabling highly accurate inductive current measurement. The next step was to manufacture and verify prototype short-circuited test coils using multiple HTS wires. The test results will be presented at the conference, and the potential of the AC inductive energization method will be discussed.

References

[1] M. Ohya et al., “Current flow simulation of assembled conductors for field coils of liquid hydrogen-cooled high-temperature superconducting generator,” IEEE Trans. Appl. Supercond., Vol. 33, No. 5 (2023) 4603005.

[2] M. Ohya et al., “Energization test apparatus of HTS coils cooled by liquid hydrogen and manufacture of split-type REBCO external field coil,” J. Phys. Conf. ser., Vol. 2776 (2024) 012010.

[3] G. B. J. Mulder et al., “On the inductive method for maximum current testing of superconducting cables,” Proceedings of the 11th International Conference on Magnet Technology (1990) 479-484.

Acknowledgment

This presentation is based on results obtained from a project, JPNP20004, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

This work was also supported by NIFS Collaboration Research program (NIFS23KIIA009).

Figure 1. One-turn short-circuit test coil using an HTS wire installed in a REBCO field coil.

Keywords: High-temperature superconductor, Assembled conductor, Inductive energization test, Liquid hydrogen