Investigation of AC Resistance on Winding Conductors in Slot According to Strands Configuration

Owing to the high speed and frequency required in electric machine industry, the significance of ac resistance has been increasing. This study investigates the ac resistance of windings according to the configuration of strands. The mechanism of generating the ac resistance in winding conductors was investigated with respect to the slot leakage flux and eddy current. Then, when applying the strands to the winding, the concept of unbalanced impedance was introduced to characterize the additional ac resistance due to circulating current. The analytic method to calculate ac resistance describing the above phenomena is derived and verified by FEA results. Afterward, the ac resistances of varying numbers and arrangements of strands were separately studied via finite element analysis. In addition, a method to avoid increasing the ac resistance was suggested based on impedance equalization when applying strands. Finally, experiments were conducted to verify the effect of the strand configuration on ac resistance. An E- and I- shaped core, which can be the rendering of common electric machines, such as motors, generators, and transformers, was manufactured and tested with winding specimens. Consequently, the test results showed a similar trend as the analytical results.