Magnetic Noise of Polyphase Induction Motors

Abstract

The demand for quieter machines has led to a general procedure for calculation of sound pressure levels of polyphase induction motors. The origin of the magnetic driving forces which are responsible for the motor noise, and the method of calculating the mechanical response of the motor structure, are described in this paper. A method is developed to calculate the sound pressure levels of the magnetic noise at a specified point near the motor. The paper gives numerical results of calculations, and the corresponding sound pressure levels for a particular 4-pole, 30-horsepower polyphase induction motor of open frame construction under different operating conditions. The agreement is unexpectedly good.

Acoustic Noise Characterization of Space Vector Modulated Induction Motor Drives – An Experimental Approach

“…The magnitude of noise at each frequency is measured by the noise measurement system in terms of sound pressure level (SPL), which is related to sound intensity level (SIL) as shown by (1).…”

“…E LECTROMAGNETICALLY induced acoustic noise, radiated by electric machines, has been a subject of long and intensive research [1]- [5]. The flux harmonics in the airgap of an ac machine cause radial forces on the stator structure.…”

“…The major causes for the harmonics in the air-gap flux are [6]- [9]: 1) Spatial mmf harmonics due to non-sinusoidal distribution of stator and rotor windings [6] 2) Harmonics in the air-gap permeance, which depend on: a) Numbers of the stator and rotor slots [7], [8] b) Geometry of slots and teeth in stator as well as rotor [8], [9] c) Saturation in the iron core [10] 3) Harmonic currents in the stator winding [6] Long and extensive research in the area of acoustic noise [1]- [5] has led to valuable design guidelines with regard to number of stator slots, number of rotor slots, and the design of stator and rotor windings to reduce (and keep at a minimum) the adverse effects of the spatial mmf harmonics and permeance harmonics [3]. Recent research works have focused on reduction in acoustic noise through improved rotor design [11] and skewing [12].…”

“…The structural subsystem models the vibration response of the stator structure to these electromagnetic forces [25], [26]. The acoustic subsystem quantifies the acoustic noise caused by vibrations of the stator structure [1], [22], [24].…”

“…Pioneering works on the vibration behavior have modeled the stator core as a beam [1] or as a ring [27]. Experimental studies have shown significant differences between the vibration behaviors of a steel ring and a steel ring with slots as in a stator core [27].…”