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. These devices safeguard assets and maintain power stability by swiftly detecting and isolating faults. 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. Protection relays are indispensable components of modern power systems, ensuring the reliability, safety, and stability of electrical networks.