What Is a Protection Relay Tester and How Does It Work?
Published · 2 min read
A protection relay watches the power system and trips a circuit breaker when something goes wrong. A protection relay tester is how you prove, before a real fault, that it will.
Why relays must be tested
A relay may sit idle for years and then have a fraction of a second to act. A wrong setting, a drifting component or a wiring mistake would go unnoticed until a fault, when the damage is largest. Regular testing finds these problems while the plant is still safe.
How a relay tester works
The tester replaces the signals the relay normally gets from the current and voltage transformers. It generates precise three-phase currents and voltages, applies them to the relay inputs (secondary injection) and watches the relay's contacts. It records whether the relay picked up, how long it took to trip and at what value.
The result is compared with the relay's settings and with the limits in its manual or the utility's standard. A pass proves the relay would act as intended; a fail tells you which function to correct.
What is tested
A modern test set covers more than relays:
- Overcurrent, distance, differential and other protection functions
- Circuit breakers (timing, contact resistance and motor current)
- Energy meters and transducers
- Current transformers (CT) and capacitor voltage transformers (CVT)
- Power transformers (ratio, vector group, no-load current, winding resistance)
The software matters as much as the box
Most of the work happens in the software: choosing the test, entering the relay's settings, running a sequence of points and printing a report. Good software repeats a test exactly the same way every year, which is what makes results comparable over time.
Next step
Vebko's AMT testers are run by AMTPro software and cover the tests above; which of them are available depends on the device and the software package. The related pages below show the tester, the software and the training videos.