Physics:Goodness factor
From HandWiki
Short description: Metric for determining the efficiency of an electric motor
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]
- [math]\displaystyle{ G = \frac {\omega} {\mathrm{resistance} \times \mathrm{reluctance}} = \frac {\omega \mu \sigma A_\mathrm{m} A_\mathrm{e}} {l_\mathrm{m} l_\mathrm{e}} }[/math]
where
- G is the goodness factor (factors above 1 are likely to be efficient)
- Am, Ae are the cross sections of the magnetic and electric circuit
- lm, le are the lengths of the magnetic and electric 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:
- [math]\displaystyle{ G \propto \frac {\omega \mu_0 p^2} {\rho_\mathrm{r} g} }[/math]
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". IEEE International Electric Machines and Drives Conference, 2003. IEMDC'03.. 2. pp. 1195–1200. doi:10.1109/IEMDC.2003.1210392. ISBN 0-7803-7817-2. http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf.
- ↑ ER Laithwaite (1965). "Electromagnetic levitation". Electronics and Power 11 (12): 408–410. doi:10.1049/ep.1965.0312. https://ieeexplore.ieee.org/document/5176480.
 |  |
