Optimization of a PV-Wind Hybrid Power Supply Structure with Electrochemical Storage Intended for Supplying a Load with Known Characteristics

An important aspect of the off-grid utilization of hybrid generation systems is the integration of energy storage facilities into their structures, which allows for improved power supply reliability. However, this results in a significant increase in the cost of such systems. Therefore, it is justified to use optimization resulting in the minimization of the selected economic indicator taking into account the most important technical constraints. For this reason, this work proposes an algorithm to optimize the structure of a hybrid off-grid power distribution system (with electrochemical energy storage), designed to supply a load with known daily energy demand. The authors recommend genetic algorithm utilization as well as a modified criterion for evaluating the quality of solutions based on the Levelized Cost of Energy (LCOE) index. Several technical and economic analyses were presented, including unit costs, power distribution of the wind and solar sections, nominal battery capacity, SSSI index (System Self-Sufficiency Index), etc. The model of the system includes durability of the elements which have a significant impact on the periodic battery replacement. The tests were carried out for two types of loads and two types of electrochemical batteries (NMC-Lithium Nickel Manganese Cobalt Oxide; and PbO2-Lead-Acid Battery), taking into account the forecast of an increased lifetime of NMC type batteries and decreasing their price within five years. The proposed synthesis method of photovoltaic-wind (PV-wind) hybrid off-line systems leads to limiting the energy capacity of electrochemical storages. Based on the analyses, the authors proposed recommended methods to improve (reduce) the value of the criterion index (LCOE) for PV-wind off-grid systems while maintaining the assumed level of power supply reliability.Fil: Kasprzyk, Leszek. Poznań University of Technology; PoloniaFil: Tomczewski, Andrzej. Poznań University of Technology; PoloniaFil: Pietracho, Robert. Poznań University of Technology; PoloniaFil: Nadolny, Zbigniew. Poznań University of Technology; PoloniaFil: Mielcarek, Agata. Poznań University of Technology; PoloniaFil: Tomczewski, Krzysztof. Opole University of Technology; PoloniaFil: Trzmiel, Grzegorz. Poznań University of Technology; PoloniaFil: Alemany, Juan Manuel. Universidad Nacional de Río Cuarto. Facultad de Ingeniería. Departamento de Electricidad y Electrónica. Instituto de Protecciones de Sistemas Eléctricos de Potencia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Electric Field Distribution and Dielectric Losses in XLPE Insulation and Semiconductor Screens of High-Voltage Cables

This article presents the electric field distribution E and dielectric losses ΔPdiel. in the insulation system of high-voltage cables. Such a system consists of inner and outer semiconductor screens and XLPE insulation. The aim of this study was to compare the values of E and ΔPdiel. between semiconductor screens and XLPE insulation. The objects of the research were high-voltage cables of 110 kV, 220 kV, 400 kV, and 500 kV. The geometrical dimensions of the cables, especially the radii of individual layers of insulation, as well as the electrical properties of the screens and XLPE, were taken from the literature. Semiconductor screens and XLPE insulation were treated as a system of three concentric cylinders. When determining the electric field distribution, both the electrical permittivity and electrical conductivity, which, in the case of semiconductor screens, play important roles, were taken into account. The obtained results prove that both the electric field distribution E and dielectric losses Pdiel. are significantly larger in XLPE insulation than in semiconductor screens. The intensity E in XLPE insulation is about four orders of magnitude greater than the intensity in semiconductor screens. Dielectric losses ΔPdiel. in XLPE insulation are about eight orders of magnitude greater than the losses occurring in semiconductor screens

Impact of Changes in Limit Values of Electric and Magnetic Field on Personnel Performing Diagnostics of Transformers

Electric and magnetic fields accompany technical personnel in their working environment (work exposure). That is why many countries have the appropriate regulations. The impact of electric and magnetic fields on humans is still not fully recognized. This is the reason why the limit values of its intensity in many countries differs significantly. The article presents changes in the stress limits of the electric and magnetic fields in Poland at the turn of the last dozen years. The last such change was the result of a Directive of the European Union (2013/35/EU). The effects of changes in limit values on the working conditions of technical personnel performing diagnostics of high voltage transformers or working in the immediate vicinity of such transformers are presented. The article shows that recent changes have improved the working conditions of technical personnel in relation to the electric field and worsened the conditions taking into account the magnetic field

Design and Optimization of Power Transformer Diagnostics

From year to year, humanity’s dependence on electricity supplies is growing, which affects virtually all areas that improve the comfort of people’s lives [...

Electro-Insulating Nanofluids Based on Synthetic Ester and TiO2 or C60 Nanoparticles in Power Transformer

The article discusses thermal properties of synthetic ester admixed with nanoparticles. The analyzed thermal properties were: thermal conductivity λ, kinematic viscosity υ, density ρ, specific heat cp, and the thermal expansion factor β- all obtained by means of measurements. On the basis of these, the authors calculated the heat transfer factor α, which determines the ability of the liquid to heat transport. The authors used nanoparticles of fullerene C60 and titanium oxide TiO2. The analysis of the thermal properties was done for the temperatures of 25, 40, 60 and 80 °C. The authors analyzed the impact of nanoparticles C60 and TiO2 on thermal properties of synthetic ester. They proved that fullerene C60 in principle had no influence on heat transfer factor α of the ester, while titanium oxide TiO2 had some positive influence on the factor, the value of which increased about 1–3%

Determination of Dielectric Losses in a Power Transformer

The article presents a method of determining dielectric losses that occur in insulating materials in a power transformer. These losses depend mainly on the electric field stress, pulsation, dielectric loss coefficient, and electrical permittivity of insulating materials. These losses were determined by integrating an expression describing unit losses. The determined dielectric losses were compared with the total losses of the transformer. It turned out that dielectric losses are a fraction of a percent of the total losses. The influence of the electrical permittivity of the insulating liquid and paper insulation on the value of dielectric losses was investigated. This influence was ambiguous, which is characteristic of stratified systems made of materials with different permittivity. An analysis of the influence of the dielectric loss coefficient tan(delta) on the value of dielectric losses in the transformer was carried out. The impact of this coefficient on the amount of dielectric losses turned out to be directly proportional

Thermal properties of mixtures of mineral oil and natural ester in terms of their application in the transformer

The article describes research results of thermal properties of mineral oil and natural ester. Percentage proportions of both the liquids were as follows: 100/0, 95/5, 80/20, 50/50, 20/80, 0/100. The authors present measurement results of thermal conductivity, viscosity, specific heat, density, and thermal expansion of the created mixtures. The measurements were taken in a relatively wide temperature range: 25 °C, 40 °C, 60 °C, and 80 °C. On the basis of the measurement results, convection heat transfer coefficient α was calculated and the most advantageous proportion of both the components of the mixture was pointed in terms of cooling effectiveness of the transformer

Heat transfer coefficient α of insulation liquid used in power transformers, based on measurements

Proper work of the power transformer is determined by many factors. One of them is relatively low operating temperature of the transformer. Too high temperature has many negative consequences, such as fast aging process of the insulation system. The temperature depends on the load of transmission line, losses and heat exchange in transformer. Heat exchange depends on heat transfer factor α of insulation liquid, which is a component of insulation system of transformer. This factor depends on many factors: the type of insulation liquid, the length of the heating element (windings), temperature, winding surface heat load, the winding position (vertical, horizontal), place on the winding (upper, middle or bottom part). The article presents the results of the measurement of heat transfer factor α as a function of type of insulation liquid, winding surface heat load, and place on the windings. The results will be used by designers and operators of power transformers

Electro-Insulating Nanofluids Based on Synthetic Ester and TiO2 or C60 Nanoparticles in Power Transformer

The article discusses thermal properties of synthetic ester admixed with nanoparticles. The analyzed thermal properties were: thermal conductivity λ, kinematic viscosity υ, density ρ, specific heat cp, and the thermal expansion factor β- all obtained by means of measurements. On the basis of these, the authors calculated the heat transfer factor α, which determines the ability of the liquid to heat transport. The authors used nanoparticles of fullerene C60 and titanium oxide TiO2. The analysis of the thermal properties was done for the temperatures of 25, 40, 60 and 80 °C. The authors analyzed the impact of nanoparticles C60 and TiO2 on thermal properties of synthetic ester. They proved that fullerene C60 in principle had no influence on heat transfer factor α of the ester, while titanium oxide TiO2 had some positive influence on the factor, the value of which increased about 1–3%