A Continuously Transposed Field Winding for Transient AC-Loss Mitigation in Air-Core Pulsed Alternators

Abstract

Air-core pulsed alternators (APAs) are promising high power density prime power sources for aerospace and defense pulsed-power systems, where compactness, lightweight construction, and transient operational reliability are critical requirements. However, the large conductor cross-sectional area required for high current capability, together with the complex curved racetrack field-winding topology, can induce severe transient AC losses. This loss degrades efficiency and imposes thermal-structural constraints under high-current transient operation. To address this issue, this article adopts a continuously transposed conductor (CTC) configuration and adapts it to the curved racetrack field winding of the APA to mitigate transient losses. First, an analytical 3-D electromagnetic parameter calculation model is proposed for the complex curved racetrack topology, providing a rigorous theoretical foundation. Subsequently, the transient loss mechanisms of different conductor structures are systematically evaluated via 3-D field-circuit coupled finite element analysis. The simulation results show that the CTC limits the strand-to-strand deviations in resistance and self-inductance to below 0.3%. Compared with conventional segmented conductors, the CTC winding reduces the total transient AC-loss energy by 84.0%, including a reduction in circulating-current energy from 98.4 kJ to 424 J. Finally, no-load and field-initiation tests conducted on the APA prototype show good agreement with the simulation results. The peak no-load voltage error is 5.8%, while the errors in the peak field-initiation current and peak time are 0.8% and 0.15%, respectively. These results support the model's ability to reproduce the measured terminal voltage and transient field-current response and confirm the engineering feasibility of the proposed winding scheme.