A Critical Review of Homopolar Generators: Design, Efficiency, Modelling, and Practical Viability

Abstract

This review critically examines the operating principles, design considerations, efficiency trade offs, modelling approaches, and practical viability of homopolar generators (HPGs), direct current machines that generate very high currents at low voltages. Starting with the theoretical background of electromagnetic induction, such as the Faraday paradox and Lorentz force explanation, the review follows how conceptual arguments have been used in subsequent engineering practices. The literature on rotor-stator designs, magnet approaches, and current-collection schemes is reviewed to demonstrate how efficiency, durability and scalability are influenced by design trade-offs. Reported uses of HPGs in pulsed-power systems, welding, electromagnetic launchers, and fusion experiments illustrate their niche application, but also recurring problems including low terminal voltage, resistive heating, and brush wear. The development of computational modelling and materials has enhanced the accuracy of performance predictions, but experimental validation over long periods of time is lacking. Throughout the literature, trends of consensus, unresolved issues, and future research directions can be summarized as the necessity of scalable, reliable, and manufacturable HPG designs. This review highlights gaps in empirical testing, lifecycle assessment, and integration with other pulsed-power systems, and suggests future work that can combine advanced materials, better contact technologies, and design-for-manufacturing principles to realize the full potential of homopolar generators.