Materials Science Forum Vol. 856

Abstract: This paper compares thin film photovoltaic technologies’ productivity for different installation sites and surface positions. The aim is to guide architects to increase the energy yield during the design of buildings with integrated photovoltaic panels by providing information on the appropriate inclination and orientation of the panels. Meteorological data from ten sites from the Equator to the Arctic Circle are used. Two types of input solar radiation (extraterrestrial and real) are referenced, from horizontal to an arbitrary oriented surface, and are introduced in Durisch’s model to estimate the energy production for various surface inclinations and orientations. Thus 3D surfaces are obtained which allows the architects to choose an appropriate compromise between the aesthetic and the practical.

Abstract: In this paper, statistical data regarding off-grid inverter faults are presented, derived from the maintenance records of a major service center in Greece. Several commercial types of inverters for autonomous photovoltaic (PV) systems have been examined, presenting different types of faults and malfunctions. The service procedures recorded encompass fault diagnosis, specific failed parts, symptoms indicating malfunction and estimated cause of failure for each case. The statistical analysis undertaken leads to useful conclusions about the robustness and weak points for off-grid equipment, as well as the common failure causes and malfunction indications.

Abstract: Parameterized computer models of photovoltaic (PV) cells and modules are proposed in the paper. Four-and five-parameter one-diode models, two-diode model, as well as behavioral models of the PV cell are considered. The temperature-dependence of the model parameters is taken into account. Parameter extraction approach is developed to determine the model parameters, based on nullor equivalent circuit and datasheet characteristics of the PV cells and modules. PSpice description of the developed PV model is given in the form of parameterized block. The accuracy of the computer PV models is investigated by comparison to the datasheet characteristics.

Abstract: This paper contains a strategy to minimize the power losses in the electrical distribution network of Kosovo. In order to develop the strategy, a model was constructed to simulate an electrical distribution network, and different parameters were included that helped in estimation of the technical power losses in the medium voltage (MV) distribution network. The main objective of this paper is to present approach to minimize technical and non-technical losses in power systems. The analysis of the Kosovo electric power system was performed by means of PSS/E 3.3 software. The results indicate options for reduction of the loses by replacement of old type of transformers and preparation of the MV system for upgrade and change the voltage level from 10 kV to 20 kV. As a first step new 110/10kV transformers can be installed, designed to be reconnected in the future to 110/20kV.

Abstract: The paper is devoted to the development of electrical current sensor, comparable with one pole of protective-switching apparatus of electric network for the voltage up to 1 kV. It is defined, that variation of mass, dimensions and electrical characteristics of the sensor generates a nominal row of currents of the device, protecting from sparks.

Abstract: Harmonic analysis studies have become an important component of power system analysis and design on recent years. They are used to quantify the distortion in voltage and current waveform and avoid them to propagate through the AC network. Harmonics are created mainly by nonlinear loads in power systems. Thus, in this paper are analyzed the harmonics created by industrial loads and other electronic devices and their effects.

Abstract: The aim of this paper is to explore new approaches of monitoring, diagnosis, condition evaluation, and possibility of extending the life of transformers. Research, emphasizing to experimental work, is conducted on a 1.5 KVA single-phase transformer to measure the internal temperature of the primary and secondary winding, using reliable instruments. Special consideration is given to the convenience in the acquisition and management of experimental data, so that the proposed monitoring system can be exploited for all kinds of thermal tests and various loading conditions. The transformer under study is designed and constructed from scratch, according to particular technical specifications. Having completed the transformer construction with the temperature sensors linked in each coil, our aim is to apply various types of loads and record the temperature variation inside the transformer. A process of acquisition and processing of data related to various parameters of transformers is developed so as to predict the behavior and prevent the failure of a transformer.

Abstract: This paper presents the results of experimental work on thin piezoelectric polyvinylidene fluoride (PVDF) film, used as active layer in piezoelectric transformer. PVDF film was deposited by spray deposition technique on flexible polyethylene terephthalate (PET) substrate and its thickness was measured to be 2 μm. Aluminum (Al) bottom and top contacts were deposited by vacuum thermal evaporation. The transfer function of the transformer was measured at different frequencies in the range 50 Hz – 4 MHz. It was observed that at input frequency of 1 MHz, the transfer function started to decrease, which supposed low-frequency AC/AC transformer. Dielectric losses, which characterize piezoelectric devices’ quality, were less that 0.09 in the whole frequency range. This is proof for the efficient energy conversion and stable operation of the microstructure. The work shows that the PVDF transformer performance is comparable to the existing piezoceramic based transformers, which however suffer of high dielectric losses, signal distortions and relatively low boundary frequency.

Abstract: In this paper, the performance of silicon (Si) and silicon carbide (SiC) power MOSFETs during short circuits is investigated. The response of both semiconductors is examined under hard switch fault and fault under load conditions using a short circuit tester board. In addition, their failure mechanism is recorded and analyzed. Examination results show that the SiC MOSFET fails in the energy limiting mode, due to gate oxide rupture, while the Si MOSFET is destructed during the power limiting mode, at the beginning of the fault. The electro-thermal characterization of these devices is performed through three-dimensional finite element analysis, utilizing the experimentally extracted power dissipation for each transistor. Simulation results confirm the exceptional ruggedness that SiC power MOSFETs exhibit outside their safe operating area.

Abstract: The paper presents a computer model, developed in the software programme Comsol, for studying the influence of the ventilation apertures on low voltage (LV) switchboard heating. Results have been obtained, concerning the distribution of the LV switchboard thermal field and air velocity field in cases of closed LV switchboards and switchboards with ventilation apertures both at natural and forced ventilation. The influence of the ventilation apertures location, as well as of the air velocity at forced ventilation, on heating the current carrying circuits in the LV switchboard has been studied.