Transition Modes for Automatic Transfer Switches - Part 2

When selecting an Automatic Transfer Switch (ATS), it is necessary to specify the load transition mode that will best meet the needs of the application. The load transition mode indicates the sequence and timing of the operations that will transfer load between power sources.

Load transition modes can be categorized by whether they transfer between sources with or without power interruption to the load. Open Transition and Delayed Transition switching produce short-duration power interruptions each time load is transferred from one source to another. These modes were described in Transition Modes for Automatic Transfer Switches - Part 1. Two additional transition modes complete transfers without power interruption, and are known as Closed Transition and Soft Load transition modes. The following narrative provides additional detail about these two modes.