Static transfer switch: advances in high speed solid-state transfer switches for critical power quality and reliability applications

The static transfer switch (STS) selects, at high speeds, between two or more sources of power and provides the best available power to the electrical load downstream. The STS is a solid-state switch based on the silicon controlled rectifier (SCR) device. While the STS has been commercially available since 1971, advances in the sensing of power anomalies and in the control of SCRs have provided enhanced power reliability to critical sites in industries as diverse as process control applications in petrochemical and fiber related industries; data processing in large data centers; semiconductor manufacturing; and hospitals. This paper presents the fundamentals of the solid-state technology that is the foundation of the STS; and examines the results of subjecting the STS to a three-phase upstream fault.