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NEETRAC PROJECT #: 13-169
Date Closed: 8/1/2016
Accurate ratings for overhead and underground lines require an accurate knowledge of the conductor ac resistance. Unfortunately, the ac resistance is difficult to measure. A longstanding pragmatic approach is to calculate the parameters that impact ac resistance - skin effect and the proximity effect. Concerns with this approach include lack of agreement with experimental data and the use of experimental data that is not directly applicable for today's conductors. This includes very large (1600 mm2 +) sizes for underground cables and twisted pair, insulated strands and composite cores for overhead conductors. Overhead conductors have geometries that are difficult to calculate and there are additional computational difficulties with new composite core materials. Additionally, experimental measurement procedures are not straightforward. In this project, NEETR.AC reviewed existing approaches to measuring the ac resistance of conductors and performed limited tests in the laboratory to determine the most practical approach. The tests established a proof of concept for a thermal and an electrical method. It was found that thermal method appears to be an appropriate and practical approach because it yields values that match expectations and it allows for comparisons between standard designs and different novel designs. The electrical measurement methods yielded results that were not in agreement with accepted values.