Primary current injection testing is usually associated with high current and high voltage power distribution systems found in an electrical substation, or in a large industrial installation. The principle is very straightforward: a test current is injected into the primary side of a system to determine how the system behaves at particular levels of current. By injecting a predetermined current into the circuit breaker, it is possible to determine whether the relay will trip at this current and, if so, how long the current needs to flow before the trip is initiated.
One popular circuit breaker tester is the Electrical Test Instruments PI-6000 Circuit Breaker Test Set. The ETI PI-6000 is an advanced primary injection test set capable of testing circuit breakers up to 6000 amperes frame size. Incorporating an output transformer with dual primaries to facilitate its use on power sources of 480 VAC as well as 240 and 208 VAC, and dual secondaries to provide optimal impedance matching to a wide range of breaker sizes, the ETI PI-6000, offers an internal voltage sensor that automatically configures the AC control power section to be energized only when properly configured for the applied voltage.