Investigation on Noise Pollution Comprehensive Treatment of Distribution Transformer in Living Area

In the current paper,which deals with the noise pollution excited by distribution transformers in the living area,a comprehensive treatment scheme is put forward for the purpose of reducing the sound pressure level emitting into the environment.In accordance with the associated test standard,the sound pressure levels of distribution transformer and surrounding environment are not only tested but analyzed as well.The measurements were carried out with the frequency analysis of the 1/3 octave resolution,with the center frequencies at 125 Hz,250 Hz,400 Hz,and 500 Hz.As illustrated,on the basis of the measurement results,the frequency of noise at 500 Hz of distribution transformer causes the major noise pollution in the surrounding environment.This measurement result is in line with the noise frequency characteristics of distribution transformer.There are two transmission routes of noise:(i)the noise excited by distribution transformer transmits by means of the wall of distribution room,and (ii)part of noise spreads through the ground of distribution room.Accordingly,acoustic shield and vibration isolation device are applied for the reduction of the low frequency noise emitted through the above two paths.Aimed at applying the appropriate acoustic material and vibration mounting,the evaluation of the noise reduction and vibration absorption is carried out in accordance with the sound and vibration insulation theory.Following the noise treatment,the transformer and environment noise are measured again.The corresponding findings shed light on the fact that the sound level satisfied the requirement of limits of the ordinance.The proposed noise treatment scheme can be applied to the existing power distribution facilities for controlling the sound levels that reach a point where it is comparatively more unobjectionable.

Modeling and acoustic analysis of irregular sound enclosure by using Chebyshev-variational method

A modeling method for irregular sound enclosures was proposed based on the Chebyshev-variational theory. A rectangular space was first assumed to bound the irregular sound space and the sound pressure in the rectangular space expressed as a triple-Chebyshev series. Next, a coordinate transformation was performed and the Lagrangian functional of the irregular sound space obtained. Finally, the Lagrangian functional was solved under the Ritz method framework, and the enclosure＇s acoustic characteristic equation deduced and the eigenpairs obtained. The accuracy of the present method was validated according to agreement between the present results and finite element results for an enclosure with a curved surface.Furthermore, the acoustic characteristics of a trapezoidal enclosure and an enclosure with an inner groove were investigated. The results showed that the mode shapes of the trapezoidal sound space changed with increased inclination angle and the natural frequencies, except the first order, of the sound space with a rectangular inner groove decreased with increased groove depth.