Use of Carter's coefficient with narrow teeth

Abstract

SynopsisThe paper shows that Carter's coefficient gives permeance values almost identical with the true ones for narrow teeth, as established by Carter's later work, unless the tooth width is less than the radial air gap. A small increase in the coefficient is given for tooth widths down to zero. The flux-density distribution obtained by the superposition of waveforms for successive slots as in isolation, is also seen to be indistinguishable in all cases from the true waveforms for near slots, as recently established by Freeman. It is shown that the harmonic content of the ripple is conveniently expressed by a wavelength spectrum.

Modified Carter's Coefficient

“…For path 3, x = r 2 , x 3 = r β , and p 3 (r 2 ) = πr 2 /2 + g + (w ttR − w tbR )/2, and P 3 = 2μ 0 l π ln 1 + πΔr β πd ttR + 2g + w ttR − w tbR (6) where r β , obtained in (11), is the limit of r 2 and Δr β = max(r β − d ttR , 0). For path 4, x 4 = w stR /2 − r β , and p 4 = g + d ttR + d siR , resulting in…”

“…To obtain the magnetomotive force (MMF) drop across the airgap, an effective airgap quantity is determined using Carter's coefficient [1], [5] to account for slotting effects. An empirical coefficient curve is presented for machines with narrow teeth with respect to airgap in [6]. In [1], the flux is assumed to flow in one of two paths.…”