Impact of subcycle transfer switches on distribution system reliability

Certain electric energy customers require extremely high levels of reliability. Even if they experience a momentary interruption, processes can be ruined and many thousands of dollars lost. These customers have historically had to satisfy their own reliability needs by installing uninterruptible power supplies and emergency generation equipment. In the age of deregulation, however, utilities still experience increasing pressure to satisfy customer reliability needs. Luckily, modern power electronic devices are giving utilities the tools they need to accomplish this task. An example of such a device is a subcycle transfer switch. This device has the potential to greatly improve the reliability of a targeted customer, but assessing its overall impact to system reliability is a nontrivial problem. This paper describes a method of including subcycle transfer switches in predictive distribution system reliability assessment methods. It then applies this method to a four feeder test system and discusses the results