The Secondary Injection Test procedure involves injecting a simulated current or voltage signal directly into a protection relay. This helps to test the relay's internal logic, settings, and trip functionalities without applying power to the entire system. That single capability is decisive in parallel feeders, ring networks, and multi-infeed grids, where faults may be fed from both sides. The signals. Verify that your protection relays operate correctly when faults occur using a relay and systems testing solution designed for accurate and reliable secondary injection testing.