Circuit breakers are mechanically sophisticated devices designed to carry load current under normal power system conditions, direct current flow between desired sections of an electric power system, and interrupt current flow under abnormal power system events and conditions, such as faults.
The proper functioning of a circuit breaker is reliant on a number of individual components, including the interrupter, the operating mechanism, and the auxiliary contacts and coils, which have to be tested at regular intervals.
Mechanical wear and lubrication often affects the performance of breakers, so being able to trend mission critical parameters and compare these with factory thresholds helps to verify proper breaker function.
Recommended circuit breaker tests include tests common to all types of circuit breakers (such as time & travel, contact resistance, minimum pick-up, and coil current), tests that depend on the circuit breaker technology being implemented, (pre/post insertion resistors, grading capacitors, dynamic resistance), the medium that insulates the breaker contacts, including air/gas, vacuum, and oil (such as gas density, air pressure, etc), and tests that depend on network design which ultimately dictates the necessity and presence of pre-insertion resistors or synchronous switching as well as shunt capacitors for the circuit breaker.