Design Concepts for a Fluid-Filled Three-Phase Axial-Peg-Style Electrostatic Rotating Machine Utilizing Variable Elastance

Rotating electric machinery is usually constructed of iron/steel laminations, copper windings, and permanent magnets. This paper investigates fluid-filled, electrostatic rotating machines for the ultimate ambition of transitioning fundamental magnetic materials to dielectrics in order to reduce production costs. The study of the axial-peg-style electrostatic rotating machine focuses on basic geometric and material knowledge and the creation of design tools. An axial-peg machine possesses interdigitated pegs (cylinders) that come into, and out of, radial alignment as the machine rotates causing variable capacitance between the stator and rotor. A prototype with peak torque of 0.7 Nm and gap field strength of 15 kV/mm was constructed. The specific torque density of the machine is 0.101 Nm/kg, comparable to fractional horsepower NEMA class induction machines. This was achieved by filling the machine with a dielectric fluid, whose relative permittivity is 7.1, rather than the ultra-high vacuum typically employed in canonical electrostatics. Experimental measurements presented include angular capacitance, peak torque, and torque-per-volt under stall conditions. Construction techniques are discussed in detail.