Jaime Valencia

An efficient procedure for computing lightning induced overvoltages on overhead lines

Overvoltages on electrical power or telecommunications overhead lines due to nearby lightning strokes can cause faults and disturbances in electrical and electronic devices and apparatuses connected to them. It is important to understand these induced overvoltages, because equipments with electronic devices are sensitive to such disturbances. In this paper, lightning radiated electromagnetic fields caused by the return stroke are evaluated with transmission line engineering models, representing the current through the lightning channel. Integral equations are solved by means the Trapezoidal Rule, resulting in an efficient way to compute the radiated electromagnetic field. Also, the coupling between the electromagnetic field radiated by the return stroke and the overhead line is considered by using The Method of Characteristics. In this way, transmission line equations to describe voltages and currents in the overhead line are solved in order to compute the induced overvoltages. Results are compared with others internationally published.

Using genetic algorithm and the simplex method to obtain equivalent circuits of the grounding systems

There are many methodologies that, using the frequency response of a grounding system impedance, permit to get the coefficients of a transfer function or the electrical parameters of a specific circuit, that behave as equivalents of that system. In this paper in the first part, the coefficients of the transfer function and the parameters of the circuit were obtained using the simplex method to optimize the values and minimize the square error between the objective function and the frequency response of the software Gtierras. The results of the methodologies depend on the selection of the initial values (which change for every case evaluated) to start the process. This happens because the simplex method can get local values. In the second part it is proposed a genetic algorithm (global values) to get the initial values of the simplex method and solve the problem. The result of mixing both methods is compared with the vector fitting method, showing that it is possible to obtain a circuit or a transfer function that reproduce successfully the impedance of the grounding systems in the frequency domain.

Análisis de la Medición de la Biomasa en Fermentación en Estado Sólido empleando el Modelo Logístico y Redes Neuronales

Resumen En este trabajo, se llevo a cabo el analisis del crecimiento del Pleurotus pulmonarius en tusa de maiz, empleando redes neuronales artificiales y el modelo logistico. La biomasa se cuantifico a traves de las concentraciones de proteina (metodo Kjeldahl) y ergosterol (cromatografia liquida de alta resolucion). Los datos obtenidos fueron analizados con 2los programas R y Matlab. El mejor r ajustado del modelo logistico fue de 0,9937 en la concentracion de proteina para el analisis ensayo por ensayo. Las redes neuronales artificiales, obtuvieron sumatorias medias de los errores cuadraticos de 0,017 y 11,394 para las concentraciones de proteina y ergosterol respectivamente. Los resultados muestran que el modelo logistico y las redes neuronales artificiales son herramientas utiles para modelar en fermentacion solida. Los mejores ajustes fueron para la concentracion de proteina. Palabras clave: fes, rna, biomasa, modelo logistico , Pleurotus pulmonarius Analysis of Biomass Measurement in Solid-State Fermentation using Neural Networks and a Logistic Model

Transferencia de Impulsos y Ganancia de Tensión en Transformadores Monofásicos de Baja Potencia

The voltage impulse transferences of 1.2/50µs and 3/23µs from the primary to the secondary winding was tested in three single phase transformers used in electronic applications; two transformers of 85W and 18W, and one autotransformer of 50W were used under no load and under resistive load conditions. The autotransformer showed higher damping and lower peak value in the transferred voltage impulse than the other transformers. The maximum voltage value in the secondary winding was obtained at no load condition and the frequency response of the voltage gain of the transformers between 10Hz and 1MHz were analyzed and fitted to transfer functions to model the voltage impulse transferences. The comparison of experimental results with those obtained from transfer functions in the frequency and time domain provides valuable information about the transferred voltage impulses in single phase transformers.

Aplicación de las Redes Neuronales en la Protección Diferencial de Generadores Sincrónicos

En este trabajo se presentan nuevos esquemas para la proteccion diferencial de generadores sincronicos basados en redes neuronales con filtros de respuesta impulsional finita. Adicionalmente se desarrollo y probo experimentalmente un modelo de maquina sincronica. El modelo permite simular fallos internos en los devanados del estator usando el programa de transitorios electromagneticos ATP-EMTP. Esto se hace con el fin de generar los patrones de entrenamiento de las redes neuronales. Los resultados obtenidos permiten concluir que los nuevos esquemas propuestos para la proteccion diferencial son mas efectivos que los conocidos hasta el momento. Con estos nuevos esquemas se logra un tiempo de disparo ante fallos internos del orden de 2.5 microsegundos y una gran capacidad de discriminacion entre fallos internos y fallos externos.

MODIFICACIONES EN UN FLUJO DE CARGA POR LA INCLUSIÓN DE UN CONTROLADOR UNIFICADO DE FLUJOS DE POTENCIA (MODIFICATIONS ON A POWER FLOW DUE TO INCLUSION OF A UNIFIED POWER FLOW CONTROLLER)

El crecimiento de los sistemas de potencia y las condiciones de mercado dadas por los esquemas desregulados han evidenciado las limitantes tecnicas y de operacion que los sistemas electricos de potencia SEP tienen para abastecer la demanda bajo estrictas condiciones de seguridad, calidad de potencia y confiabilidad. Un controlador unificado de flujos de potencia UPFC (unified power flow controller) es uno de los dispositivos de la tecnologia FACTS (Flexible AC Transmission Systems) que ofrece mayor versatilidad en terminos de interaccion con las variables de operacion y control de un SEP y puede ser una solucion optima a las necesidades adicionales de control en un SEP moderno. Este trabajo presenta una formulacion matematica y conceptual para la inclusion de un dispositivo UPFC en el analisis de flujos de carga en un SEP y una metodologia para su inclusion en un software de flujos de carga en estado estable. Para validar la eficiencia de los modelos y metodos propuestos, se selecciona un sistema de potencia de prueba adecuado para ver los efectos esperados de la inclusion del UPFC en el sistema. Abstract: The growth of power systems and the market conditions result of deregulated structures have made evident the operative and technical limitations that electric power systems have for supplying energy demand with strict conditions on security, power quality, and reliability. A unified power flow controller UPFC is one of the flexible AC transmission systems FACTS, devices which offer greater capabilities for interacting with operation and variables of an electric power system, and can be an optimal solution for the additional control requirements on a modern system. This paper presents a mathematical and conceptual formulation for including a UPFC on a load flow analysis, and a methodology for its including on a steady state power flow software. For validating the proficiency of proposed model and methodology, this paper selects a suitable platform system for viewing the expected effects on a load flow by including a UPFC.

Cálculo del Campo Magnético en el Interior de Edificaciones con Sistemas de Protección Contra Rayos

A methodology for the calculation of the magnetic field inside buildings with Lightning Protection System (LPS), is presented. The conductors of the LPS and the lightning channel are considered by using the hybrid electromagnetic model, which is based on the frequency domain of Maxwell’s equations. First, the inductive and capacitive couplings between the different conductors of the LPS are calculated to determine the lightning current distribution in the system. Then, the magnetic field strength is calculated in some points inside the struck structure. Finally, it is presented a characterization of the magnetic strength on different surfaces inside the structure. Results are compared with results of other methodologies proposed in then literature, showing that tool and methodology proposed in this work is adequate to determine the magnetic field inside buildings with LPS.

Load forecasting with Neural Networks for Antioquia-Choco region.

This paper describes a short term load forecasting system based on artificial neural networks and a data pre-processing technique. The forecasting is performed according to the type of week is going to be predicted, based on a given classification. As result of the pre-processing, database are obtained and used to train the neural networks. These networks are evaluated later to generate weekly prediction. The multi layer perceptron (MLP) network presented better results. The neural network inputs are hour demand and day of the classified week and the output is the load forecasting.

Using a grounding system equivalent circuit to evaluate transferred lightning surges trough distribution transformers

Grounding in a distribution system is important to reduce the lightning voltage surges that are transferred from medium voltage to the low voltage network through distribution transformers. These overvoltages produce several damages in equipments connected to distribution system and can cause outages of the electrical power supply bringing economic costs to both electric utility and customer. In this paper, is evaluated the impedance of different grounding geometries in the frequency domain; then, this impedance is used to develop an equivalent circuit of the buried grounding configuration and finally, this equivalent circuit and other models for the distribution system components like transformers, surge arresters, etc, are linked in a circuit model to evaluate the transferred voltages through distribution transformers in the alternative transients program (ATP).