Effect of regenerative load on a Static Transfer Switch performance

A Thyristor-based Static Transfer Switch (STS) is used to connect an altern ate source of ac power to a sensitive load when the main source fails. A ma in criterion for performance evaluation of a STS is the transfer time from the main to the alternate source. The transfer time depends upon the commut ation process of the outgoing and incoming switches which in turn depends o n the system parameters and the load characteristics. This paper investigat es the effect of a regenerative load on the transfer time/total load-transf er time of a STS and identifies the worst case scenario(s) in which maximum transfer time occurs. The IEEE STS benchmark models STS-1 and STS-2 are ch osen to demonstrate the STS performance under various fault, disturbance co nditions in a medium-voltage distribution system and a low-voltage experime ntal set-up system. The simulations are performed using the PSCAD/EMTDC pac kage. The paper-shows that a hybrid load can operate in regenerative mode d epending on the load parameters and fault/disturbance characteristics.