Effect of Source Phase Difference on Static Transfer Switch Performance

A thyristor-based static transfer switch (STS) provides a continuous supply for a voltage sensitive load through fast transfer between two sources when the main source does not meet load voltage requirements. This paper investigates the impact of phase difference between the corresponding voltages of the two sources on the load transfer performance achieved by an STS. The studies are performed on the IEEE benchmark STS-1 system using the power system computer-aided design/electromagnetic transient dc simulation software. The studies indicate that the impact of phase difference on the STS load transfer time is insignificant when the sensitive load is a passive (e.g., RL) load. However, if the load can operate in a regenerative mode (e.g., a motor load), the effect of phase difference on the transfer time is noticeable. The studies show that a phase difference of 25deg can increase the load transfer time by about 2 ms