Current Status and Future Trend of Controlled Switching System

1. Introduction Life-cycle cost reduction of transmission and distribution systems is becoming increasingly important to adapt to global changes resulting from factors such as electricity market liberalization, electricity industry deregulation , environmental protection issues, as well as various emerging technologies developed using information technology advances. Technical requirements for power equipment have also been changing. For instance, the development of high-voltage and large-capacity equipment has advanced to ensure stable power supply in the context of growing electricity demand. However, the most important requirement in this period of severe competition brought about by liberalization and deregulation is to develop more reliable and cost-effective equipment. As emerging technologies such as controlled switching, remote monitoring diagnostic techniques and digital controls became practical, CIGRE (International Council on Large Electric Systems) have conducted extensive investigations on field experience of these technologies as well as international surveys on the reliability and maintenance practices of high voltage equipment. In the 1990s, market demands for extending the life while reducing life-cycle cost drove research and development towards further compactness, reliability and reduced operating energy. These efforts led to the 550kV one-break gas circuit breaker (GCB) and the 1100kV two-break GCB. Controlled switching has become an economical substitute for a closing resistor and is commonly used to reduce switching surges. The number of installations using controlled switching has increased rapidly due to satisfactory service performance since the late 1990s. Currently, it is often specified for shunt capacitor and shunt reactor banks because it can provide several economic benefits such as elimination of closing resistors and extension of a maintenance interval for nozzle and contact. It also provides various technical benefits such as improved power quality and suppression of transients in transmission and distribution systems. Recently, an advanced controller considering the residual flux in a transformer core has been installed and has demonstrated good performance in the field. This controller can significantly suppress overvoltage induced by inrush currents in case of transformer energization and