Due to high mechanical inertia and rapid variations in wind speed over time, at variable wind speeds, the problem of operation in the optimal energetic area becomes complex and in due time it is not always solvable. No work has been found that analyzes the energy-optimal operation of a wind system operating at variable wind speeds over time and that considers the variation of the wind speed over time. In this paper, we take into account the evolution of wind speed over time and its measurement with a low-power turbine, which operates with no load at the mechanical angular velocity ω_MAX. The optimal velocity is calculated. The energy that is captured by the wind turbine significantly depends on the mechanical angular velocity. In order to perform a function in the maximum power point (MPP) power point area, the load on the electric generator is changed, and the optimum mechanical velocity is estimated, ω_OPTIM, knowing that the ratio ω_OPTIM/ω_MAX does not depend on the time variation of the wind speed.

At the beginning, this article details the manufacturing procedures for varistor materials. Starting from the initial composition of two large series of varistors (those with two additive oxides and those with five additive oxides), there is a major overview of the main stages of the technological process and the equipment used for the production, emphasizing the technological changes that were made. The article continues with the study of the influence of the sintering pressure and the sintering temperature on the electrical properties of the varistor materials made before. There were two experimental series of 7 varistors, one series based on 2 additive oxides and one based on 5 additive oxides. Each varistor of these series was sintered at another temperature, the fundamental purpose being to determine an optimal sintering temperature for each chemical composition. A second activity consisted of manufacturing two more series of varistors with the same chemical composition (2 oxides and 5 additive oxides), which were sintered at two different pressures, for having a set of conclusions on the influence of sintering pressure on the electric performances. All conclusions are underlying a new process for manufacturing metal oxide based varistors.

Metal oxide varistors are applied today inside modern surge arresters for overvoltage protection for all voltage levels. Their main issue is the thermal activation of their crossing current, which could lead to complete destruction by thermal runaway. This article presents a new technological solution developed in order to increase the thermal stability of metal oxide varistors. It consists in connecting in parallel two or more similar varistors (for dividing their current), having a thermal coupling between them (for equalizing their temperatures and forcing them to act together and simultaneously as much as possible). Starting from a finite element computer model performed for each situation (varistor standalone or parallel), up to real measurements, the thermal stability of the equipment was analyzed in permanent and impulse regime. Experiments were carried out in the same conditions. Experimental data obtain from two disk varistors corresponds very well to simulations, proving that parallel connection of varistors, combined with a thermal exchange between them is an efficient technical solution for thermal stability improvement, even if not apparently economically justified.

This paper presents a laboratory method and an original control solution used in order to compute the influence of High Voltage Lines and Equipment on Low Voltage ones at 20 kV. All voltage lines taken in consideration could be either regular 400/230 V AC supply lines or even classic telecommunication lines belonging to the HV power station or to other TC companies. High voltage overhead lines are parallel or crossed in the proximity of low voltage lines, so, they could produce strong electric/magnetic fields or resistive modifications on the low voltage facilities. These influences can induce interferences and could cause fatal injuries to humans operating on low voltage equipment (even on domestic appliances) or great damages to all electronic equipment (IT, TV, TC, domestic). Our goal is to present, first of all, an analytic method used to assess the values of some parameters like the capacitive current, the capacitive voltage, the psofometrical voltage, the longitudinal induced voltage as well as the resistive voltage component. This laboratory equipment could be used for teaching purposes and for studies and recommendations demanded for designing electrical lines. Conceived for industrial use, it was already tested in the university, as didactic tool. On the second part of our paper, we will describe the architecture of that system, both as hardware, as well as from the software applied.