Insulation Design of the 160 kV DC Superconducting Fault Current Limiting Winding

Superconducting fault current limiter (SFCL) is a promising device for limiting the short-circuit current of the power system. A 160-kV SFCL is developed for protecting the voltage source converter-based high-voltage direct current (VSC-HVdc) transmission system in Nanao of China. The main insulation and longitudinal insulation design of the 160-kV superconducting fault current-limiting winding are presented, where the liquid nitrogen (LN
₂
) is used as the cooling and insulation medium. The main insulation simulation results show that the maximum electric field strength of the SFCL winding could be restricted to 1.2 kV/mm during the 252-kV dc voltage withstand test by using optimized grading and shielding ring. The SFCL winding is composed of 96 noninductive-type superconducting bifilar coils, and the turn-to-turn insulation of the bifilar coil is a combination of LN
₂
and polytetrafluoroethylene (PTFE). The turn-to-turn distance of the bifilar coil is optimized based on the longitudinal insulation analysis under the 550-kV lightning impulse withstand voltage test, 450-kV switching impulse withstand voltage test, and 16-kA power switching test. According to the simulation and experimental results, the maximum voltage drop occurs on the first turn of the bifilar coil.