Acoustic-noise measurements on nominally identical small electrical machines

Ellison, A.J.; Yang, S.J.

doi:10.1049/piee.1970.0110

Cited by 4 publications

(1 citation statement)

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“…In a recent paper, 2 it is seen that the noise data vary considerably between nominally identical small machines, and this variation is most likely to be caused by the variations of the dimensions of parts between the tolerance limits in mass production. For electric machines with small air gaps, these slight variations in the dimensions of the stator, rotor, end shields and bearings may lead to a considerable variation of the air gap at different angular positions between the stator and rotor.…”

Section: List Of Principal Symbolsmentioning

confidence: 99%

Effects of rotor eccentricity on acoustic noise from induction machines

Ellison

Yang

1971

Proc. Inst. Electr. Eng. UK

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The variations of acoustic-noise power radiated from electric machines, having varying degrees of eccentricity of the rotor in the stator bore, were studied using a specially constructed rig in an anechoic chamber. A series of noise components, which were found in expsriments to vary considerably with rotor eccentricity, were identified analytically from the expressions for the mode numbers and frequencies of the magneticforce waves, taking into account the stator and rotor slotting, eccentricity and iron saturation. A method is presented for calculating the variation of important noise components with eccentricity. The effects on the noise power of different numbers of stator parallel paths and of different ways of connecting them were investigated using specially wound machines. Information is given concerning the choice of parallel paths and connections for noise reduction. List of principal symbolsA rd = amplitude of radial displacement, m a = outer radius of stator, m B = flux density, T b = halflength of the cylindrical part of machine, m c = speed of sound, m/s £" = modified Young's modulus, i.e. E/(l -y 2 ) N/m 2 , F = m.m.f., A / = frequency, Hz g = mean air-gap length, m g' = effective mean air-gap length, m h = parameter in sound power expression / = any integer J,(JC) = Bessel function of the first kind K,(x) = modified Bessel function k = order of m.m.f. space harmonic (Section 3.1) k = wave number, i.e. o»/c (Section 3.3) m = mode of vibration P = sound power, W p = number of pole pairs q -order of current time harmonic r 0 = radius of neutral layer, m r c = radius of stator core at the bottom of slot, m t = time, s Y/(x) = Bessel function of the second kind Z = number of slots z = axial distance (z -0 at centre of machine) a = angle of skew, rad 8 -logarithmic decrement e = relative eccentricity (infinitesimal quantity in eqn. 29) e' = effective relative eccentricity 6 = angle, rad A = permeance, Wb/A y -Poisson's ratio [Mo = permeability of free space, H/m p 0 = density of air, kg/m 3 a ra = radial force per unit area, N/m 2 = angular position, rad ifi -phase angle of m.m.f. wave co = angular frequency, rad/s Subscripts 1 supply c core dy dynamic ec eccentricity

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Section: List Of Principal Symbolsmentioning

confidence: 99%