Design and Fabrication of a Ferrofluid-Gap Test Rig for Radial Flux Electrical Machines

This paper presents the design and fabrication of a novel ferrofluid-gap test rig and reports preliminary experimental results on the magnetic behavior of a ferrofluidgap in open-load conditions. A ferrofluid-gap is an unconventional approach for reducing the magnetic reluctance of the air-gap region in electrical machines by filling it with magnetically permeable ferrofluid. With a particular focus on the application of ferrofluid-gaps to direct-drive wind turbine generators, a test rig was designed to characterize both the magnetic and mechanical behavior of ferrofluid-gaps across a broad range of conditions. This includes turbulence and shear rates exceeding what could be expected in full-scale multimegawatt machines. The experimental results demonstrate that the magnetic behavior of a ferrofluid-gap remains unaffected by turbulence and shear. Additionally, the observed increase in test rig open-load voltage output with a ferrofluid-gap is compared against predictions from finite element method simulations, showing good agreement between experiment and theory.