High-voltage Circuit Breaker Diagnostics

HV circuit breakers play a crucial role in the distribution of electric energy.

With a low duty-cycle but high responsibility in case of faults in the electric network, the demands made on reliability and availability of these components are very high. Adequate maintenance of these components is the key to avoid technical and economical catastrophes while the probability of failure is increasing with increasing lifetime.

 

Contact velocity measurement
The displacement of the contacts is measured by a linear or rotating sensor, depending on the type of circuit breaker and stored in a PC. The related contact velocity and acceleration are subsequently derived in a straightforward manner. These figures often directly display (upcoming) defects mainly related to the operation and tripping mechanism. KEMA has developed recommendations that classify the condition of the component. Because of KEMA’s extensive experience it is relatively easy to develop recommendations for new type of circuit breakers.

 

Vibration measurement
Vibration of the enclosure of the circuit breaker is measured by piezo-electric transducers mounted on the exterior of the circuit breaker. The signals are analyzed in time domain revealing themoment of the start of contact travel, primary contact making and breaking of the contacts. This measurement is non-invasive and consequently, unlike the contact displacement measurement.

 

Coil current measurement
The number of switching operations is generally rather low. However, this causes problems for circuit breakers that are placed in substations where humidity may give rise to problems with the grease of the rotating parts. The tripping coil current gives a useful indication of the state of such mechanisms. KEMA has developed recommendations for several types of tripping coils and opening mechanisms.

 

Partial discharge measurements
The occurrence of partial discharges reveals the existence of dielectric insulation problems within the circuit breaker. Typically the higher the emitted power and frequency of occurrence, the higher the chance of failure by dielectric breakdown. Partial discharges can be measured on-line with a high frequency probe. KEMA possesses a broadband receiver and peak-detector for monitoring applications. Even in several types of metal-enclosed switchgear this technique has been successfully applied.