EPSS test

The goal of an EPSS test is to confirm that the EPSS system can transfer the load from normal supply to emergency supply in the specified amount of time. Normal supply could be utility power, while emergency supply could be backup generator power.

To start a test, the Automatic Transfer Switch (ATS) is set into Test mode. This triggers a sequence of events that start the generators and transfers the load to emergency supply. To end the test, the ATS is set to Normal mode, which transfers the load back to normal supply and stops the generators.

EPSS test performance is evaluated based on the time it takes to successfully transfer the load after the start of the ATS test mode. Different standards define different acceptable transfer times for EPSS systems. See Emergency Power Supply Systems for more information on standard compliance.

The following diagram shows the test sequence of events. It shows the ATS status (Normal, Test, Emergency), the generator status (Stop, Start, Running), and the status transitions that control the logging of generator electrical (load) and engine data for EPSS reporting.