This guide explores the different types of protection relays and their testing procedures, with a focus on tools like secondary injection test sets and three-phase relay test sets. To properly test relays, understanding their classification by design and application is essential. This. How the test-set was measuring it. Acceptance testing, commissioning, and startup will include control power tests, current transformer and potential transformer tests, and any other device testing associated with the protective. From a technician's perspective, master the unique skill of testing protection relays so you can avert undue outages and costly damages to the network.