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Presented is the dynamic resistance measurement (DRM) method for circuit breakers by using a micro ohmmeter as a power source generating several hundred's amperes. Injecting high DC current through the breaker contacts and simultaneously monitoring the voltage drop across the main contact during the operation of the breaker was reported first in 1993 [1][2]. The DRM test requires a circuit breaker analyzer with a high-resolution measurement. The point of a position change from main to arcing contacts can be observed from the resistance plot. The resistance curve, as a function of a contact travel can be used to reveal potential problems related to the arcing contact condition [3]. Also, the actual length of the arcing contacts can be calculated if measuring the motion. This paper explains the benefit of injecting as high current as possible, but not less than 100A, to provide a reliable voltage drop reading, thus allowing exact detection of the arcing contact performance. After reviewing the characteristics of the dynamic resistance curve, the measuring system and parameters, the paper deals with relevant values that can be extracted from the resistance curve for detecting contact anomalies, wear, and/or misalignment. Finally, case studies are presented and test results are discussed. |
