Effects of rotor eccentricity on acoustic noise from induction machines

Abstract

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 <f> = 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

Development of ultralow noise motors by using windings as a sensor (Noise reduction of motors by realizing an eccentricity of under one micrometer)

“…基本理論が検討され (Ellison and Yang, 1971) ，それらが体系的にまとめられた (Yang, 1981 Fig. 2 Configuration of the experimental apparatus.…”

The Detection and Suppression of Unbalanced Magnetic Pull in Wound Rotor Induction Motors Using Pole-Specific Search Coils and Auxiliary Windings

“…Noise monitoring is carried out by measuring and analyzing the acoustic noise spectrum. In [16], Ellison and Yang carried out tests in an anechoic chamber. It was found that slot harmonics in the acoustic noise spectra from an induction motor were functions of static eccentricity.…”

Modeling and measurement of airgap harmonics of single-phase induction motors

“…Consider the first-order permeance equation due to stator-rotor slotting, given by (3). The effective permeance wave is obtained by taking into account the mutuals by the multiplication procedure and can be written as …”

“…Also, there is a trend to use these results in the designing of online monitoring of motors in industrial plants. A considerable amount of detailed information on the airgap harmonics of three-phase induction motors is available in the literature [1]- [3]. On the contrary, the available papers on the single-phase motors is rather limited.…”