The main purpose of having Power Circuit Breakers on the substations is to protect the equipment from destructive short-circuit current surges. However, partial discharges/arcing, mechanical and thermal faults can be developed inside the unit due to different factors such as contamination, lack of use, manufacturing defect, etc.
A combination of Acoustic Emission and Vibration techniques (AE/VA) is an excellent way to detect incipient faults before they develop into significant problems. Similar to Load Tap Changers, ciruit breakers are evaluated while out of service by performing Acoustic Emission testing while Vibration testing is used while the circuit breakers are in service, the evaluation when the circuit breaker is not being operated is to perform by Acoustic Emission and the assessment when having an operation is done through the vibration technique.