No abstract

The quality of electricity is a problem of major interest, making it necessary to analyze the factors and causes that result in the worsening of the electric energy quality. An important aspect of electricity quality is the introduction of current and voltage harmonics in the alternating current network by non-linear consumers. The paper analyzes the deforming regime introduced by the drive systems of a bucket wheel excavator within a technological line at an open pit mine. Methods. The paper presents the measurements of power quality in a laboratory experimental study and measurements of an upgraded technological line at a lignite open pit. In this sense, the present the study of a distorting regime introduced by the drive systems formed from a static frequency converter and an asynchronous motor, as well as the results of quality power measurements introduced by the drive systems in the electric network. Findings. The paper presents analysis of the voltage and current harmonics introduced in the alternating current network of static converter-asynchronous motor drive systems, which is necessary to establish the deformation factor. The values of the deforming regime are essential to obtain the harmonic compensation solutions. Originality. The originality of the paper consists in the approach to the measurements performed and the analysis of the deforming regime introduced by the electric drive systems. Practical implications. The values of the current and voltage harmonics were determined both by the laboratory measurements and by measurements made on the supply line of a bucket wheel excavator in different operating regimes.

Purpose. Electrical equipment for explosion-threatening environments in mines at risk of explosion communicates with the external environment through intrinsic safety barriers that limit the values of currents to values below the methane ignition, limit that exceeds the allowable concentration in the atmosphere. This avoids work accidents due to under-ground explosions, avoiding the risk of explosion through electric equipment. Methods. Experimental research has been based on the geomechanical characterization of the coal and surrounding rocks in the Jiu Valley Basin and measurements obtained in situ was researched by statistic methods. Three methods of studying barriers based on the use of the MATLAB program were used. The first method is based on MATLAB programming, the second involves the barrier study using the Simulink model and the third method is based on the use of the SimPowerSystems software package. In all three cases studied, the variation of the voltage at the output of the barrier and current through the barrier are analyzed considering two operating modes, the aperiodic and the oscillating regimes. Findings. The paper is a study of the intrinsic security barriers, based on which a correct dimensioning can be made. Originality. The originality of the paper consists in the analysis of the barriers with intrinsic safety, using the simulation with the MATLAB-Simulink program packages. Practical implications. All the methods addressed lead to obtaining the diagrams of variation of the voltage at the exit of the barrier and of the current through the barrier in two possible regimes: the aperiodic regime and the oscillating regime.

This paper presents a new and a modern method for study the inductive-capacitive circuits which are connected to an AC power source, using modern methods based on digital technology and software used in engineering applications. The capacitive circuits which are switched on an AC power source at the initial moment are presented below. We can determine the capacitor current variation forms, the capacitor voltage in a transient regime by using virtual mediums, in two different regimes: the oscillating regime and the-periodic regime. Each presented case contains an analytical presentation of the phenomenon, but it also contains the diagrams of current and voltage capacitors. The diagrams were obtained by two methods, which use MATLAB package. These diagrams are compared with experimental measurements obtained with a data-acquisition system produced by National Instruments using LABVIEW software.

Abstract. The paper presents a method of extinguishing the electric arc that occurs between the contacts of direct current breakers. The method consists of using an LC type extinguishing group to be optimally sized. From this point of view is presented a theoretical approach to the phenomena that occurs immediately after disconnecting the load and the specific diagrams are drawn. Using these, the elements extinguishing group we can choose. At the second part of the paper there is presented an analyses of the circuit switching process by decomposing the process in particular time sequences. For every time interval there was conceived a numerical simulation model in MATLAB-SIMULINK medium which integrates the characteristic differential equation and plots the capacitor voltage variation diagram and the circuit dumping current diagram.