Diagnóstico de disjuntores: aplicação da transformada Wavelet a sinais de resistência dinâmica de contato.

Abstract

The objective of this work is to propose a classification technique for contact degradation level of circuit breakers, providing an indication of their operation status, in order to determine the most appropriate time to carry out interventions and, thereby, contributing to reduce interruptions. The dynamic resistance measurement (DRM) is a diagnostic technique used to evaluate this degradation. The same is shown capable of analyzing both the main and arcing contacts. All tests performed for this thesis used DRM curves generated with reduced contact opening speed, and various test current levels. For the tests, an alternative measurement system was adopted, consisting of a digital oscilloscope, a stationary battery, voltage and current sensors and chromealuminum- iron resistors. The system is able to determine the resistance values since the beginning of the contact opening process until its total separation, allowing the application of a test current up to 300 A. To reduce the contact opening speed, a new system was designed, which consists of a speed reducer coupled to an asynchronous motor, which is controlled through a frequency converter. The classification of the contact degradation level was done in this work using Wavelet transform. The results obtained using the Wavelet transform were compared to those using as a criterion the prior knowledge of each sample degradation level. The results analysis highlights the Coiflet 6 Wavelet as the most suitable for the classification of contact degradation level of high voltage circuit breakers.