Ensaios de resistência dinâmica em disjuntores: análise de sensibilidade da corrente e da velocidade de abertura dos contatos.

Abstract

The dynamic resistance measurement (DRM) is a diagnostic technique used to assess the operative state of circuit breaker contacts, that stands out for being able to analyze both the main and arcing contacts. In this research, an analysis of the result reproducibility of DRM tests is presented, which was implemented with speed reduction of the contact opening process, as well as an analysis of the test current level influence on DRM results. To evaluate the methodology, a comparison was made using the coefficient of determination (R2) between the results of the DRM tests carried out with speed reduction and at rated speed. To perform the tests, an alternative system was adopted, which consists of a digital oscilloscope, a stationary battery, current and voltage sensors and resistors made of chrome aluminum iron. The proposed system allows the injection of a direct current up to 300 A. To achieve the speed reduction of the contact opening process, a speed reducer was coupled with an asynchronous motor, which was triggered by a frequency inverter. From the obtained results with the samples studied, it can be verified that: the results of DRM tests carried out with rated speed of contact opening do not repeat themselves on similar tests; DRM tests carried out with rated speed of contact opening and using the minimum levels of test current indicated by IEC and ANSI standards are highly affected by the interference of oil films, thus, providing masked and unreliable results; DRM tests carried out with reduced speed of contact opening provides results with better reproducibility; for DRM tests carried out with reduced speed of contact opening, higher levels of test current help to increase the result reproducibility, however, this effect is not as noticeable as the opening speed increases.