Thermal Model of Electrical Contacts Based on Experimental Data

The paper presents statistical analysis of experimental results received in direct temperature measurement of energized electrical contacts of low voltage circuit breaker in laboratory setup. Thermal study was performed on electrical contacts of 3200 Amp low voltage circuit breaker in good conditions and in artificially "aged" conditions. Experimental data have been collected on four contact points on each of three phases of circuit breaker loaded in the range from 50 to 105% of maximum rated current with 5% increment. The points of direct temperature measurement have been located at different distances from "aged" contact. The goal was to find mathematical model that could reliably define the relationship between temperature rise on electrical connections and current changing in wide range. Data analysis showed that with high degree of confidence the temperature-current relationship could be described using relatively simple function. This approach allows defining a single factor changing with connection deterioration resulting in resistance rise, which in turn makes possible to develop an algorithm for the diagnostic of the change of energized electrical contact physical condition in timely manner.