Goodness factor
The goodness factor is a metric developed by Eric Laithwaite to determine the 'goodness' of an electric motor.[1][2] Using it he was able to develop efficient magnetic levitation induction motors.[3]
where
- G is the goodness factor (factors above 1 are likely to be efficient)
- Ae, Am are the cross sections of the electric and magnetic circuits
- le, lm are the lengths of the electric and magnetic circuits
- μ is the permeability of the core
- ω is the angular frequency the motor is driven at
- σ is the conductivity of the conductor
From this he showed that the most efficient motors are likely to be relatively large. However, the equation only directly relates to non-permanent magnet motors.
Laithwaite showed that for a simple induction motor this gave:
where p is the pole pitch arc length, ρr is the surface resistivity of the rotor and g is the air gap.
References
- ^ ER Laithwaite (1965). "The Goodness of a Machine". Electronics and Power. 11 (3): 101–103. doi:10.1049/ep.1965.0071.
- ^ DJ Patterson; CW Brice; RA Dougal; D Kovuri (2003). "The "goodness" of small contemporary permanent magnet electric machines" (PDF). IEEE International Electric Machines and Drives Conference, 2003. IEMDC'03. Vol. 2. pp. 1195–1200. doi:10.1109/IEMDC.2003.1210392. ISBN 0-7803-7817-2. S2CID 14563810.
- ^ ER Laithwaite (1965). "Electromagnetic levitation". Electronics and Power. 11 (12): 408–410. doi:10.1049/ep.1965.0312.