Voltage Distribution Characteristic of the D-Shaped Coil of HTS-SMES Under High-Frequency Impulse

The application of D-shaped coils to large-scale toroidal high-temperature superconducting magnetic energy storage (HTS-SMES) magnets can effectively suppress the large bending moment caused by uneven tension and reduce the section stress. The HTS-SMES system may be subjected to high-frequency transient overvoltage due to lightning impulse or switching operations. Transient overvoltages can potentially result in insulation failure or breakdown, which seriously endangers the safety of equipment and the stability of the power system. To investigate the transient voltage distribution characteristic of the D-shaped coil under transient impulse, a calculation method of the D-shaped double-pancake (DP) coil is proposed in this article, which is based on the equivalent circuit and lumped parameter model. In this method, each turn of the coil is represented as a lumped parameter unit. In addition, a small-size D-shaped DP coil was wound for verification. The voltage distribution under the lightning impulse voltage was measured at room temperature and liquid nitrogen at 77 K, respectively. The results indicate that the proposed method can calculate the transient voltage distribution of the D-shaped DP coil quickly and accurately. Then, we investigated the effects of the turn-to-turn insulation thickness and the height between the upper and lower pancake of the HTS-SMES D-shaped DP coil on the transient voltage distribution.