This paper presents an analysis of sound pressure levels through theoretical modeling and experimental validation in a 1 kW small wind turbine. The models used in the theoretical analysis are BPM (Brooks, Pope, and Marcolini) and BM (Brooks and Marcolini), where wind turbine blades are divided in sections, and each section has its own contribution with respect to the total emitted sound pressure level. The noise propagation study and its experimental validation were accomplished within the requirements of the standard IEC 61400-11 Ed.3 and the standard NOM-081-SEMARNAT-1994. The comparative study of theoretical and experimental results showed that the BPM and BM methods have a maximum error of 5.5% corresponding to the rated wind speed of 10 m/s. However, at low wind speeds, the theoretical models fit well to experimental data, for example, in the range from 5 to 8 m/s. The experimental data showed that the rotor’s aerodynamic noise is more evident at low wind speed, because under these conditions, environmental noise is much less than wind turbine noise. Finally, to prevent possible negative effects on people’s health, there is a recommended minimum and suitable distance between small wind turbine installations and buildings.

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The Wide Band (WB) or Universal (ULM) Line Model currently is the most general line model available in EMTP for simulating transient responses of power transmission lines and cables. Since this model is still subject to further improvements, an experimenting prototype of it has been developed in Matlab environment. This development is reported here and the paper also offers a comprehensive description of the WB model. Two application examples are provided here, one involving an aerial line and the other one an underground cable. Index Terms-EMTP, frequency dependent parameters, frequency domain, MATLAB, time domain, WB Line Model.

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This paper presents an alternative solution based on infinite series for the accurate and efficient evaluation of cable earth return impedances. This method uses Wedepohl and Wilcox's transformation to decompose Pollaczek's integral in a set of Bessel functions and a definite integral. The main feature of Bessel functions is that they are easy to compute in modern mathematical software tools such as Matlab. The main contributions of this paper are the approximation of the definite integral by an infinite series, since it does not have analytical solution; and its numerical solution by means of a recursive formula. The accuracy and efficiency of this recursive formula is compared against the numerical integration method for a broad range of frequencies and cable configurations. Finally, the proposed method is used as a subroutine for cable parameter calculation in the inverse Numerical Laplace Transform (NLT) to obtain accurate transient responses in the time domain.Keywords: Earth-return impedance, Pollaczek's integral, Wedepohl's integral, infinite series expansion, recursive formula, buried cables, Numerical Laplace Transform (NLT). RESUMENEn este artículo se presenta una solución alternativa basada en series infinitas para la evaluación precisa y eficiente de la impedancia de retorno por tierra en cables subterráneos. En este método se utiliza la transformación de Wedepohl y Wilcox para descomponer la integral impropia de Pollaczek en un conjunto de funciones de Bessel más una integral definida. La característica principal de las funciones de Bessel es que son fáciles de calcular con herramientas modernas de software matemático como Matlab. Las principales contribuciones de este artículo son la aproximación de la integral definida por una serie infinita, dado que no tiene solución analítica, y su evaluación numérica por medio de una fórmula recursiva. La precisión y eficiencia de la fórmula recursiva se compara contra el método de integración numérica para un amplio rango de frecuencias y configuraciones de cables subterráneos. Finalmente, se utiliza el método propuesto como una subrutina de cálculo de parámetros de cables en la Transformada Numérica de Laplace (NLT) para obtener respuestas transitorias precisas en el dominio del tiempo.Palabras clave: Impedancia de retorno por tierra, Integral de Pollaczek, Integral de Wedepohl, serie infinita, fórmula recursiva, cables subterráneos, Transformada Numérica de Laplace (NLT).