News from Japan

Switchgear is an essential component of electric power networks for transmitting and distributing power and is installed in all related facilities. More than 100 years have passed since it was introduced. Air-insulated switchgear, which was vulnerable to dust and humidity, was used until the 1970s. Then a new gas-insulated switchgear (GIS) using sulfur hexafluoride (SF6) gas, much superior in electrical insulating performance, was developed. However, in recent years SF6 has been designated as a greenhouse gas, and the electric power industry has been working to reduce its use. One way is to use highpressure air for insulation. However, such devices are inevitably bigger than the corresponding SF6 devices, and they require pressure vessels. Another option is to use solid insulation. The electric strength of a typical epoxy compound is three times that of SF6, and so smaller body size is practicable in an environmentally friendly solid-insulated switchgear (SIS). However, because of the difference in the coefficients of thermal expansion between ceramic and epoxy compounds, conventional epoxy compounds have insufficient mechanical strength to withstand internal stresses caused by differential expansion. Thus it is necessary to develop a highperformance epoxy compound that can be directly molded into a vacuum interrupter consisting of ceramic tubes.