Development and Validation of a Masking System for Mitigation of Low-Frequency Audible Noise from Electrical Substations

Rogerio Regazzi,Carlos Roberto Hall Barbosa,Brunno Cunha,João Vitor Souza,Hugo Villela De Miranda,Carlos Augusto Machado Gomes,Juan José Gómez Acosta,Mauricio Nogueira Frota

doi:10.3390/app11177771

Abstract

Low-frequency audible noise generated by the magnetostriction effect inherent to the operation of power transformers has become a major drawback, especially in cases where the electrical substation is located in urban areas subject to strict environmental regulations that impose noise limits, differing for day and night periods. Such regulations apply a +5 dB penalty if a tonal component of noise is present, which is clearly the case of magnetostriction noise, typically concentrated at twice the industrial frequency (50 Hz or 60 Hz, depending on the country). The strategy used to eliminate the tonal characteristics, therefore contributing to establish compliance with the applicable regulation and to alleviate the discomfort it causes to the human ear, consisted in superimposing to the substation noise a masking sound synthesized from “sounds of nature” with suitable intensities, to flatten the noise spectrum while enhancing the soundscape. The masking system (heavy-duty speakers powered by a microprocessor platform) was validated at an already judicialized urban scenario. Measurement results confirmed that the masking solution was capable of flattening the tonal frequencies, whose beneficial effect yielded the cancellation of the public civil action filed by the neighbors. The proposed solution is ready to be replicated in other scenarios.

Highlights

It is well known that the continuous exposure of the human ear to acoustic noise disturbs and seriously compromises the hearing capacity [1,2] but can endanger the health of those who are exposed to it
In the case of power transformers used in high-voltage electrical substations, the acoustic noise is generated by the periodic expansion and contraction of the steel plates that form the laminated core of the transformer, due to the magnetic field that is induced by the flow of alternating electric current through its coils
This article presented a new approach to mitigating noise pollution acting on the acoustic landscape of external environments, masking emissions that bother or are unpleasant for the population

Summary

Introduction

It is well known that the continuous exposure of the human ear to acoustic noise disturbs and seriously compromises the hearing capacity [1,2] but can endanger the health of those who are exposed to it For this reason, the noise in urban areas is regulated by strict environmental legislation. The active masking system was made possible by superimposing to the global noise (which emanates from the substation’s operation) “sounds of nature”, synthesized in the laboratory, masking the perception of the tonal frequencies (around 120 Hz and first harmonics) by the human ear In this context, the research study represents the response of the electricity utility that has been involved in complaints by residents of the substation neighborhood, who claimed to be disturbed by the annoying noise generated by the operation of the substation. In the case of a continuous noise polluted by intrusive noises, L95 is generally a good descriptor to assess the sound pressure level generated by the functioning of high-voltage transformers, except in cases where the background noise is so high that it masks the specific noise of interest or makes it impossible to be identified

Environmental Regulation

Magnetostriction Noise

Materials and Methods

Characterization of the Substation’s Internal and External Environments

Findings

Conclusions