Position and strength optimization for secondary source of transformer active noise control system

Abstract

The choice of the parameters of the secondary sound source which contain the number、 position and strength is a key part in the design of active noise control system of power transformer. Countering the practical applications environment of noise control of transformer, acoustic radiation model in half-free space is established. After selecting the sum of the squared sound pressures of the observation points as the objective function, the genetic algorithm is used to optimize the position of secondary sound source and the optimal source intensity can be resolved by using the analytical method. By single frequency experiment, the availability of applying optimization scheme of the secondary sound sources to practical transformer noise control is verified. Introduction With the rapid development of the national economy and the city extensions, the high voltage transmission line is introduced into the urban area, and many large capacity and high voltage power transformers are also entered into the urban area. The noise generated by the normal operation of power transformer will have a serious impact on the daily life and rest of the nearby residents, so people pay more and more attention to the noise pollution caused by this problem[1]. The problem of noise control is becoming more and more important. In principle, active noise control (ANC) can be viewed as the superposition of a secondary sound field, generated by the control system, on a primary, disturbing sound field such that the residual sound field is as small as possible. So, basically, the objective of the active control system is to generate a secondary sound field that matches the primary sound field as closely as possible, both in time and in space. Compared with the traditional passive technology, active noise control technique is especially suitable for low frequency noise. An active noise control system is mainly divided into physical and electronic part. The purpose of the physical design is to determine the number of secondary sound sources and its locations and strength in the acoustic field. The choice of the parameters of the secondary sound source not only affects the stability of the whole control system, but also affects the control effect of the noise.A great amount of literature has focused on the control strategies or algorithms, but little research has been conducted in addressing the optimized design of the ANC physical system. In practical engineering applications, there are only some areas have the requirement of noise control such as residential building near the substation. In order to achieve the purpose of local spatial noise cancellation, Mazzanti [5] proposed to use the array type secondary source to achieve the purpose of local spatial noise reduction. In paper[6], the influence of the relative parameters of the secondary sound source array, such as the number of the secondary sound source, the distance between the secondary sound source, and the distance between the secondary sound source and the noise source, is analyzed in theory, and the numerical simulation is carried out. The simulation studies the influence of the relative parameters by a single variable method. A multi-level sub array active control theory is proposed and applied to the local spatial control of the low frequency noise in[7]. In this paper, the influence of the number 3rd International Conference on Machinery, Materials and Information Technology Applications (ICMMITA 2015) © 2015. The authors Published by Atlantis Press 1206 of secondary sound sources and the spatial position of the secondary sound source is obtained by calculation and simulation based on the noise data of the transformer. In paper [8-9], a typical control arrangement with multiple secondary sources and multiple error sensors equally spaced in two parallel lines is proposed and results from computer simulation and experiments in an anechoic chamber show that there exists a range of optimal spacing for the secondary sources and error sensors. But the primary sound source can’t simply be considered as a point sound source, so it is difficult to achieve the design goal in the practical engineering applications. Through referring existed literature, being aimed to the application environment of transformer noise cancellation, the optimization parameter of different number secondary source is obtained by the combination method of analytical method and Genetic algorithm. Experimental results verify the effectiveness of the optimization scheme. Acoustic radiation model of transformer noise field Model of primary and secondary sound sources Given that the noise of power transformer radiated mainly by surface outward, and the size of power transformer is close to the half wavelength of acoustic wave, the radiation model of power transformer can be simplified to the model of the pulse spherical sound source neglecting the harmonic time factor j t e  .And the radiation pressure can be expressed as Eq. 1: