In a national project that began in 2007, Tokyo Electric Power Company (TEPCO), Sumitomo Electric Industries (SEI) and Mayekawa Mfg. Corporation (MYCOM) aim to operate a 66 kV, 200 MVA HTS cable system in a power grid to demonstrate its reliability and stable operation. In order to verify the validity of the cable design, a 30 m HTS cable system was constructed and subjected to various tests. After the confirmation of the nominal current and voltage performance, a long-term operation test was performed to verify whether the HTS cable system is capable of handling the rated current and voltage for thirty years. A 250 m cable was manufactured for the in-grid demonstration, and shipping tests were successful. The cable system construction was completed at the Asahi substation (Yokohama, Kanagawa), and the in-grid demonstration will start in 2012.