Principles of Insulation Coordination and Recent Activity on Reduction of Insulation Level in Japan

The standard for test voltages (JEC-0102) in Japan, which is a basic standard for withstand voltage tests on electric power equipment, was revised in 2010. In this revision, the reduced test voltages for lightning impulse withstand voltage tests have been standardized in the range from 66/77 kV to 550 kV. This paper describes the estimation process for overvoltages caused by surge phenomena and the process of determining the additional test voltages. Moreover, the test voltages for 1100 kV (UHV) systems were established in JEC-0102 in 2010. For UHV systems, insulation rationalization was realized by employing new techniques for surge suppression. Moreover, to standardize the test voltages, the latest knowledge, such as the lightning conditions adopted for lightning overvoltage analysis,…