Results of Japan's First In-Grid Operation of 200-MVA Superconducting Cable System

A high-temperature superconducting (HTS) power cable demonstration project was started in 2007 to evaluate the cable's performance, stability, and reliability. This project aims to operate a 66-kV 200-MVA HTS cable system in a real power grid of the Tokyo Electric Power Company. A 240-m-long HTS cable was successfully installed, and other system components, such as a cable-to-cable joint, terminations, and a cooling system, were also constructed at the Asahi Substation in Yokohama. After several completion and performance tests on the system, the HTS cable was connected to a real grid from October 29, 2012 to December 25, 2013. The in-grid operation had continued for more than one year without any accidental interruption of the operation or troubles of this system. The temperatures and pressures of liquid nitrogen flowing in the HTS cable were controlled to within the target values. After the in-grid operation, the critical current of the HTS cable was measured, and it was confirmed that there was no degradation compared with the initial results. In addition, no partial discharge was observed in periodical measurements. It is concluded that the HTS cable system has good performance and stability for long-term in-grid operation.