Ioan Felea

Researches viewing the loading level on electro insulating oil state from the electric power transformers

The paper has three parts. The first part presents the characteristics of the power transformers that make the object of the analysis and their loading characteristics (load curve, over-voltages, over-currents). The second part shows the state characteristics of the electric insulating oil for each transformer under analysis, in terms of some essential state indicators: dielectric rigidity, tangent to the angle of losses and concentration of the seven essential gases (H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO and CO₂). The third part of the paper makes an analysis of the level of correlation between the power transformer straining degree and the state characteristics of the electric insulating oil and formulating the conclusion with referring of the obtaining results

Decision Support Model for Production Disturbance Estimation

A current modeling framework for disturbance in manufacturing systems (MS) is given by concepts like discrete-event systems, stochastic fluid models and infinitesimal disturbance analysis. The goal of modeling is to achieve control and structural and functional optimization of MS. Objective functions of these optimization models are focused on quantities which reflect the level of reliability, the level of manufactured products, the quality of products or the impact on the environment of MS with disturbances. These models do not allow a dynamic evaluation of consequences of the disturbances which appears in the operation of MS machines and also do not allow an evaluation of the evolution in time of disturbance consequence indicators. Disturbances in technological lines of MS represent local bottlenecks of production with severe economic consequences in what regards production time losses. Good estimation of disturbances dynamics can be very helpful to both technological line designers, who can optimize their projects and production managers who can minimize their losses. Our model allows a dynamic evaluation of consequences of some disturbance of machine operation in MS, using indicators based on time, energy and costs. A MATLAB software package was developed for tests.

On the best adaptive model for web services response time prediction

Quality of Services has an essential role throughout the process of Cloud-based web service composition for faultless and dynamic integration of business applications. Nonetheless, as Cloud-based web services grow, it becomes complicated to make possible service composition rapidly. Because web services response time can be a priceless tool for CWS (Cloud-based web service) composition satisfying end users QoS requirements, in this study we search for the best adaptive model that can do this task.

Consideration on the risk concept for the operating personnel of power systems

The paper represents a reaction to the alarm signal made by the physician of Oradeapsilas Power Distribution Company (S.D. Oradea). The physician noticed above the average values tendency to illness, by the operating personnel from the electric stations. The first part contains some considerations on the risk concept. References are made to risk factors, evaluation of damage level, and risk management in power companies. The second part presents the results of the study made in S.D. Oradea, regarding the electromagnetic pollution in high and medium voltage stations. There are presented maximum values of electric field intensity distribution and the induction of magnetic field; references are made on the riskpsilas influence on the electric station operators.

Modeling the parametrical reliability of power transformers

The paper is structured in three parts. The first part explains the parametrical reliability of the power transformers (PT) in oil in context with its global reliability, taking into account the parameters that defines the state of PT. Is presenting the proposed model to parametrical reliability evaluate of PT. There are given mathematical expressions of the parametrical reliability, in relation with the three parametrical categories, defined for the state of PT viewing the general state of the insulation, the traditional parameters of PT oil, the content of gases in the oil of transformer and its weight. There explains the parametrical risk failure of PT and its global parametrical reliability. In the second part are presented the studies results, effected to a number of 29 PT, the nominal power being between [10 h-25] MVA, located in electric stations of 110 kV/MV within the frame of analyzed power transmission and distribution system (PTDS), administrated by Electric Energy distribution and transmission Branch of Oradea -Romania Distribution Power and Supply (DSPO). There are determinate the paths successions stages by technical diagnosis of PT and there is exemplified the state parameters evolution in time. There gives the values of parametrical reliability function in relation with the three parametrical categories defined for the PT state. There is presented a assessment between the failure risk by derive of parameter and the unexpectedly failure risk by the analyzed PT. The conclusions as well as the recommendations to the analyzed PT exploitation activities are presented in the last part of the paper.

Stochastic approach in study of the effects of photovoltaic sources upon power distribution networks

Issues regarding the influence of the presence of sources of electricity generation, based on renewable resources, the facilities for transportation, distribution and consumption of energy are varied. The effects are more pronounced in the case of solar and wind power, given the specific and variable intermittent electricity production. This paper refers to the effects of the solar sources of power losses on the power grid, resorting to a stochastic approach, motivated by the variability, randomly, to several dimensions, such as pregnancy and solar radiation. It stresses the need for such an approach, then, presents the mathematical model used. The case study presents the results of measurements taken and the results of simulations. The last part contains the conclusions of the study conducted.

Contributions to Modeling and Simulation of Thermal Processes Specific for Greenhouses Heated with Geothermal Energy

Large part of the greenhouse annual energy requirements are for heating purposes, thus having significant influence to the production operational cost. Use of geothermal energy can be an economical solution for their decreasing, however utilization of such source has own specifics in comparison with conventional ones. They can be turned in favor for the concrete use when applied and used in a right way. The paper presents some characteristic problems connected to utilization of low-temperature geothermal waters for heating greenhouses.