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the purpose of this paper is to study the influence of the type of winding -double layer or single layer -to the global noise level of the machine. For this purpose, two variable speed induction motors have been studied, of the type M3AA 71 B4/8 manufactured by Electroprecizia S.A. Săcele, Romania, with Dahlander windings, star connected -for the low speed and double star connected -for the high speed. The motors are modelled from magnetic and mechanical point of view with finite element softwares. The investigated motors were placed in the semi-anechoic chamber in order to determine the noise-tofrequency characteristics (spectrograms).

The aim of this paper is to analyze the magnetic noise produced by an three phase induction motor power of 7.5kW, 1000 rpm simple layer windings produced by the company Electroprecizia Sacele located in Brasov Romania.It was chosen this engine knowing that from 2015 it will be adopted the standard IEC 60034-30 IE3 category which provides noise limits for these induction motors. A second reason for choosing this type of motor 7.5kW -1000rpm is connected to the fact that its functioning in normal regime is very silent, the total noise produced has low values, the higher value of noise is given by the electromagnetic noise.In this paper we have considered the direct network feed because these are the only conditions in which this motor function. This category of induction motors are used most frequently, almost every time, without inverter.The simulation was performed considering supply voltage 400 V (nominal voltage) and fixed frequency 50Hz. Engine speed is fixed and induction motor is directly connected from the grid without inverter (at no load). For the simulation was used a finite element program Flux 2D , and experimental measurements were performed in a semi-anechoic chamber located in the research laboratory of the company which making the induction motor.

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