Roberto J. Cabral

Improvement of an overhead distribution feeder performance against lightning considering the wire-guard protection

This paper presents a study about the influence of the wire-guard as a protection system in overhead distribution line in comparison with unprotected topology against lightning. A real feeder was considered as a case study using ATP-EMTP software. Practical aspects related to the modeling of a distribution line are presented. Simulation results show that the shielding configuration ensures a protection significantly better than the actual topology, around 10 times in terms of lightning peak current. Thus, the wire-guard can improve the immunity of distribution system against atmospheric discharges.

Fatores que afetam a performance da comunicação mediada por computador

This work describes an analysis of factors affecting performance in computer mediated communication used in distance education. The study aimed to identify and measure indexes representing impacting factors on communication and consequences on group performance using Social Psychology and Theory of Positive Emotions. Some results derived from analysis of communication in virtual communities of learning are presented as examples of evidences for the conclusions of the work. Resumo. O presente estudo descreve uma analise dos fatores que afetam a performance da comunicacao mediada por computador em cursos de educacao a distância. O estudo visou determinar e medir atraves de indicadores representativos dos fatores que tem impacto na comunicacao e consequencias na performance do grupo como um todo utilizando subsidios de teorias da Psicologia Social e da Teoria das Emocoes Positivas. Alguns resultados derivados da analise da comunicacao em comunidades virtuais de aprendizagem sao apresentados como exemplos de evidencias das conclusoes .

Comparative performance of impulsive grounding systems embedded in concrete: An experiment in reduced scale

This paper presents a comparative study of impulsive grounding systems encased in concrete (namely UFER grounding). Several topologies used in transmission and distribution networks as well as in industrial plants were evaluated considering soils with different properties. Scale measurements (in an electrolytic tank with soil) were carried out in order to quantify the performance of this grounding system. The study discusses the performance of different grounding configurations: 1 rod; 2 rods; counterweight; cross and grid embedded in concrete. The results show that the use of UFER grounding can reduce significantly the value of the grounding impulsive impedance both in soils with low and high resistivity for the different evaluated configurations.

Initial results from a prototype corresponding to an induction water heater

It is clear that the development of new methodologies that increase the electrical systems efficiency and the welfare of users, avoiding pollution as best as possible, are highly desired by researchers and utilities. In this context, in Ecuador, basic service elements like water heaters are usually used by population. Where, currently water heaters based on Liquefied Petroleum Gas (LPG) are used. However, these devices are harmful for the countrys economy. In this research, a novel prototype corresponding to an induction water heater is proposed. This has three operation stages corresponding to rectification, filtering, and controlling single-phase inverter by sinusoidal pulse width modulation (SPWM). In order to validate the proposed work, different test at each operation state, were developed. Results show an acceptable performance. Therefore, the prototype can be considered as an alternative to traditional devices.

System unbalance effect on faulted distribution systems: A numerical study

This paper presents a numerical study of the system unbalance effect on system voltage and current calculation during asymmetrical faults. Two different system operational conditions are tested considering a voltage imbalance at the substation bus: balanced system loads and voltage imbalance equal to 3.65% due to system loads. Five fault impedances are simulated. Two fault analysis methods, the symmetrical components and phase component algorithms are implemented and analyzed based on numerical simulations of asymmetrical faults on the IEEE 13 bus test feeder. The results show the accuracy of each fault analysis method and how the errors may vary according to the system pre-fault unbalance operation condition and the fault impedance.

Resonant investor in SPWM switching, used for a solar photovoltaic installation connected to the network

In the investigation of new methodologies and technologies, with the purpose of developing a major efficiency in the Electrical Systems of Power, whilst also finding methods to mitigate or minimize the disadvantages or risks to the environment; they have found ways to innovate new unconventional techniques of securing the electrical energy to implement to the electrical service network (to sell to the distribution network) or for autoconsumption (isolated systems of the network). In addition, due that in Ecuador is implementing a new program of efficient cooking, based on the replacement of kitchens and heaters Liquefied Petroleum Gas (LPG) per Efficient Electrical Systems and between other projects that significantly will change the curve of daily demand in the country, becoming a problem in regulating. For those two significant reasons, this research proposes an Inverter with Sinusoidal Pulse Width Modulation (SPWM), which transforms the energy received by the Photovoltaic generators to the voltage required to inject energy to the Low Voltage grid (LV), with acceptable levels of harmonic distortion (THD). Results show that the work has an acceptable performance. The design can be considered an alternative for current problems, making an analysis and calculation of necessary panels to implement this energy to the low voltage grid.

Combined TACS-MODELS for Footing Tower Resistance considering ground ionization

Voltages produced by atmospheric discharges are considered the main causes of electric power outages. The study of atmospheric discharges should be analyzed and studied in order to make good insulator coordination. In this context, Footing Tower Resistance (FTR) is a crucial parameter in lightning strokes studies. FTR performance is variable with the time, thus their value is not constant. Therefore, it is necessary to visualize the impedance change when a lightning hits overhead lines. This paper presents a model implemented using Transient Analysis of Control Systems (TACS)-MODELS to determine the impedance value considering their non-linear performance. Taking the impedance value equation and considering the current value, the FTR value is estimated during contingency simulation. The model considers a threshold current value for ground ionization phenomena initiation. Results show that the proposed model is effective, emulating with high precision the non-linear ground resistance behavior.