Electric machines: a new formulation for the power-mass-efficiency-speed relationship

A novel approach to the classical analysis of the performance of electrical machines is presented. Analysis of an elementary machine model comprising a conductor moving in a magnetic field results in fundamental equations uniquely relating the power-to-mass and torque-to-mass ratios of the elementary machine to operating speed, flux density, efficiency, and the conductor material constants. Allowance is made for nonactive (overhang) conductor material and the remainder of the structural mass of a machine. The approach is applicable to conventional and permanent magnet DC machines, squirrel cage and wound rotor AC machines, and wound rotor and permanent-magnet double cylindrical synchronous machines. Comparison of theoretical and actual specific power values of a few different AC and Dc machines showed very close agreement. The new formulae allow the absolute limits of performance of these machines to be calculated easily