Investigation of Heating Caused by AC Current Inside Conductor

Abstract

The heating process inside a conductor, produced by the AC current Joule losses is very complex, because of the numerous parameters acting at the same time. For this reason, the experimental verification of calculated results would be welcome and this paper presents an attempt of temperature measurement procedure. First of all, in the laboratories at the Faculty of Technical Sciences in Novi Sad, the appropriate, accurate equipment for temperature measurements does not exist. Hence, the wide range, accurate thermometer should be constructed. Starting with the completely unknown temperature probe, its characteristics were determined. It was found that the probe is based on a NTC resistor and its resistance as the function of temperature was measured and calculated. After that, the NTC probe was applied to measure the time dependent temperature for four different wires; Cu 4 mm2, Cu 6 mm2, Cu 10 mm2 and Al 7.8 mm2. The measurements were performed during 30 minutes and for each wire ten different currents were applied. The measuring results (the resistances) were transferred into the desired results (temperature), applying 1D data interpolation, spline method, called “interp1” in MATLAB. The results are presented graphically, by the time varying conductor’s temperature, depending on time, for 10 different current values as the parameters. Because of the wire’s heating at higher current values, the wire’s resistivity varied significantly and it was difficult to keep the constant current value during the entire measuring intervals. For this reason, an error occurs at the highest temperature values and it is visible in all presented diagrams.