Controlled switching technologies, state-of-the-art

Controlled switching has become an economical solution and is commonly applied to reduce switching surges. The number of installations has increased rapidly due to satisfactory service performance since the late 1990s. However, some problems seem to exist before it becomes an alternative solution of a conventional closing resistor for transformer and line switching. CIGRE WG13.07 published an application guide based on their international surveys of the field experience. The guide emphasizes the importance of compensation for the variations of the operating times because controlled switching system requires accurate operation consistency. The research reveals some hydraulic operating mechanisms generate a considerable delay of the closing time at operation after a few hour idle times. Accordingly, the idle time compensation is essential to even daily-operated system. Controlled transformer energization taking into account the residual flux as well as important requirements for different switching applications is described.