Japan's first in-grid operation of a 66 kV - 200 MVA superconducting cable system

T. Mimura, S. Honjo, T. Masuda, A. Machida, T. Hara

Research output: Contribution to conferencePaperpeer-review

1 Citation (Scopus)


High Temperature Superconducting (HTS) cables can transmit large amounts of electricity in a small size with minimal losses. Therefore, it is expected to save the construction cost of underground lines in urban areas and decrease transmission losses. Several HTS cables have recently been demonstrated in networks around the world, and full-scale commercialization is expected in the near future. In Japan, the development of compact HTS cables suitable for urban deployment has been underway since the early 1990s. In 2007, a national project was begun to verify their operational performance and long-term reliability in the grid. The HTS cable being used has a capacity of 200 MVA at 66 kV, and contains three cores in a cryostat. The conductor is wound from Bi-based HTS wires with a critical current of 200 A per wire at liquid nitrogen (LN2) temperature. Their electrical insulation is polypropylene laminated paper (PPLP) impregnated with subcooled LN2. The cryostat has double corrugated stainless steel pipes separated by a vacuum to decrease heat invasion from the environment. Verification tests were conducted on a 30 m cable system with a joint and terminations. The tests included voltage tests, load cycle tests, and fault current tests, and their success confirmed the soundness of the cable design. The conditions of the voltage test satisfied Japanese regulations for 66 kV oil-filled cable. Shipping tests were also successfully completed using sample cables cut from the whole cable. An HTS cable 240 m long was installed at the Asahi substation of the Tokyo Electric Power company (TEPCO) in Yokohama; then a joint, terminations and cooling system were constructed in 2011. After successful performance tests of critical current measurement, DC voltage, and partial discharge measurement, the cable was connected to the grid for the first time in Japan, and delivered electricity to 70,000 households in October 2012. This trouble-free in-grid service has now continued for over a year. The temperature and pressure of LN2 for the cable were controlled within target limits. Some refrigerators and circulation pumps have received scheduled maintenance while the system remaining in operation. After nine months of operation, the critical current of the cable was checked and showed no change from its initial value. In addition, no partial discharge was observed in periodic measurements. We can conclude that the HTS cable system performs well and has possibility of the stable operation for long-term in the grid.

Original languageEnglish
Publication statusPublished - 2014
Externally publishedYes
Event45th International Conference on Large High Voltage Electric Systems 2014, CIGRE 2014 - Paris, France
Duration: 2014 Aug 242014 Aug 30


Conference45th International Conference on Large High Voltage Electric Systems 2014, CIGRE 2014


  • Critical current
  • Cryostat
  • Partial discharge
  • Superconducting cable

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Fuel Technology


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