Guillermo Aponte

Obtaining the Electrical Impedance Using Wavelet Transform From the Time Response

This letter presents a new mathematical concept for electrical impedance based on the transient response, by means of the coefficients energy of the continuous wavelet transform. To validate the new proposed method, signals were simulated in the Alternative Transients Program, and the experimental results were compared with the short time Fourier transform. This contribution has been particularly applied to power transformers in order to identify possible damages from just analyzing the transient responses in the wavelet domain.

Implementación de un Modelo de un Transformador Eléctrico para el Análisis de su Respuesta en Frecuencia

This article presents the implementation of a model for the analysis of the frequency behavior of a transformer. The model is obtained from the Frequency Response Test (FRA). This test consists basically of obtaining the characteristics of the transformer and comparing the results with those of a reference transformer, which are previously known and considered as normal- The differences indicate that the transformer has certain damage. The article describes the model, its implementation, the procedure to obtain its parameters and its application in the analysis of the curve variations obtained by the FRA tests. This model represents a good tool that can be used as support to identify some type of mechanical problem in the transformer.

Selección de una wavelet madre para el análisis frecuencial de señales eléctricas transitorias usando WPD

This paper proposes a method to select an appropriate mother wavelet for the frequency analysis of electrical transient signals, based on the wavelet properties and considering the needs of the application case. The Wavelet Packet Decomposition (WPD) was used to analyze wavelets as filters and to quantify the information leakage by evaluating the performance of different families included in the Matlab’s libraries. To validate the method proposed, an application case is presented where the effective value (RMS) is estimated for a transient signal. The selection method used provides a clear scope on how to exploit the wavelet properties to select the appropriate one depending on the particular application.

Índice de Salud para Transformadores de Potencia Inmersos en Aceite Mineral con Voltajes entre 69kV y 230kV usando Lógica Difusa

This article provides a methodology for calculating the health index for oil-paper insulation system in power transformers with rated voltage between 69kV and 230kV, using fuzzy logic. The article also provides a detailed review of the existing limits of acceptance, according to the present standards and for each of the six input variables: moisture content, acidity, dielectric strength, dissipation factor oil, dissolved gas and furan content. With this information, the membership functions are obtained and the six input values are related to the output value, which represents the health index of the transformer. Using data provided by a company of the Colombian electricity sector for 18 power transformers the health index is calculated and the results are analyzed. The health index could be useful for establishing a ranking of the state of power transformers with the aim of better assigning resources and maintenance activities.

Panorama de la Gestión de Activos para Transformadores de Potencia

This article presents an overview of the conceptual framework related to the asset management of power transformers, and to the assessment of risks associated with transformer failures. The risk index is an essential tool for developing the management of this asset, especially because it supports the asset manager in the decision-making process. The risk index is composed by two indicators: i) consequence factor, which assesses the impacts that could arise in the event of equipment failure, and ii) the probability of failure, which is determined from the results of tests for transformer functioning, operating history, and failure history, among others. General aspects of asset management according to international standards are presented, to then deal with specific aspects related to evaluation of the transformer risk index, found in the literature.

Compensación Paralelo de Reactivos Durante la Prueba de Aptitud al Cortocircuito en Transformadores de Distribución

This article presents a strategy for using parallel reactive compensation with capacitors to increase the capacity of the short circuit test field at the Universidad del Valle. Transformers are key elements to maintain the electrical supply service. For that reason they must have an adequate capacity to withstand the mechanical, thermal and electrical stresses that occur during a short circuit. The High Voltage testing laboratory of the Universidad del Valle (Cali, Colombia), carries out short circuit tests for single phase distribution transformers up to 100kVA and for three phase transformers up to 300kVA. The short circuit withstand test at the laboratory is limited by the distribution network current capacity and the test can only be done at a fixed voltage, defined by the electrical network. The results show that parallel reactive compensation is a good alternative to reduce capacity requirements in short circuit tests.

Medición de Campos Electromagnéticos en la Ciudad de Cali, Colombia

This paper shows a measurement methodology of the electromagnetic field produced by radio and telecommunications installations and presents results obtained in the evaluation of 50 measurement sites in the city of Cali in Colombia. This work was done because people’s concern about proliferation of radio base stations in urban areas, and their fear about the possible dangerous effects of the electromagnetic fields on human health. The evaluation was carried out to determine and quantify the levels of electromagnetic field that exist in the environment of the city. In general, the values found were lower than 0.5% of the limit established by the International Commission for Non-Ionizing Radiation Protection, ICNIRP (0.2 mW/cm 2 ). However, in two sites the measured values exceeded