Ion Mircea

Power quality impact of energy-efficient electric domestic appliances

Electric domestic appliances are part of our daily life; they improve the quality of life. Concerning energy consumption of domestic appliances, great improvements was achieved these last years. The modern energy-efficient electric domestic appliances are electronically controlled. Generally, in a three-phase system, they constitute an unbalanced and nonlinear load. Their operation may cause power quality problems in low voltage networks. Nonlinear loads draw distorted currents from grid. Different harmonics, especially the third harmonic, in phase and neutral conductors, contribute significantly to the increase of losses in distribution networks having an important contribution to an inefficient operation of line and users. Additionally, the network pollution may decrease the reliability of line. The paper analyses the power quality perturbations produced in distribution networks by energy-efficient electric domestic operation. The conclusions are sustained by a case study.

Study of the influence of lithium batteries on the power network

This article presents the study of connecting a lithium storage battery to the public distribution network. We are following the battery loading and unloading effects from the network and its influence on network parameters, namely : voltage, frequency, short term fliker, the total voltage harmonic distortion (THD-U). The first set of measurements lasts for 24 minutes. In the first 11 minutes the battery is scheduled to discharge 50%, the following minute discharge 100%, the next minute charge 100% and the remaining 11 minutes discharge 50%. Throughout this period the parameters of the distribution network are monitored. Other sets of measurements refers to charging/discharging the battery and reverse and monitoring the network parameters. For each set of measurements were performed as many as 5 tests, the values being approximately equal. The measurement results are compared with the limits of European standard EN 50160. Monitoring of the parameters of the distribution network was performed using analysis software imcPOLARES R1 SP1 V2.2 that allows monitoring in real time of the network parameters and enables generation of a report that compares the measured data with the limits of the international standard EN 50160. When the measurements are complete, we observe that admissible limit values were not exceeded.

Neutral point potential variation from the low voltage distribution electricity grids

In low voltage distribution electricity grids is important to examine how to protect against hazardous voltages and currents that can occur with insulation degradation. It was found that the treatment of neutral defect is important in those regimes, the present paper aim to analyze the networks with isolated neutral. Describing phenomena circuitry directly affected by faulty depend on the network parameters Ciz, Cp and R which are variable in time. Touch voltage and electric currents of earthing in case of failure constitutes selection criteria for the protection system. This is chosen depending on the size of the neutral displacement voltage, fault current and how is the variation of these parameters over time. It is also shows the calculation of the total leakage current, variation of the neutral point and its consequences. The phenomena occurring in the network are identical in the powered equipment ones, they directly influencing the security of the personnel and also of the facilities. The paper also presents how to determine the equations that allow the geometric place plotting of curves for different voltages and network parameters. It is analyzed and the situation when the earthing is done by human body, which passes an electric current whose value, depends directly on resistance Rh of the body. As a conclusion it is found that the leakage current values in the networks with isolated neutral are lower compared to the values that appear in the case of networks with neutral connected directly to the ground, resulting that networks with isolated neutral can be used better in the hazardous environments.

Analysis and monitoring of the compressed air facilities

Compressed air occupies an important place among energy consumers in specialized industry. In this paper, the authors present the results of the monitoring and analysis for the parameters of a compressed air system to an industrial unit, obtained using equipment specialized in monitoring and measurements for compressed air.

The coal conveyor celts functioning modelling of the energy block by 330 MW

In this paper, the authors, with Matlab - Simulink programs help, achieve the energy performances modelling of the mills conveyor belts, that assure the fuel flow require to the energy block functioning by 330 MW, for three characteristic loads: 96%, 82% and 65%. In this purpose, starting up real, functional and constructive parameters of the six coal conveyor belts and, considering the constant transported coal density, with computer simulation help, the variation curves of the power absorbed by gear motors of the coal conveyor belts were traced in function of the usual speed of their functioning. A calculation algorithm, which is based on the simulation, aims at determining idle consumption of the conveyor belt and values for different power consumption categories, such as: for horizontal movement of the material transported, for vertical movement of the material, for overcoming friction between the conveyor belt and the discharge chute guides, for overcoming resistance of the belt unloaders of type two drums. Based on these powers calculated and taking into account the belt transmission speed variation, the variation graphs for the powers absorbed from the electric network have been withdrawn the MATLAB-SIMULINK Program.

The load frequency control simulation in the interconnected electrical power systems

In this article is presented the simulation of the primary control (the load frequency control) for two interconnected power systems in radial network In the paper is described the realization of the mathematical models related to the primary machine composed of the automatic speed regulator model in series with the turbine model. By simulating an imbalance between production and consumption in order to generate a stationary frequency deviation of 200mHz then it follows the dynamic evolution of the frequency according to the dimensional aspect of interconnected systems. On the other hands is interest the place where the disturbance occurs. The used model for simulating the load frequency control between the two interconnected power systems is realized by the interconnection between the primary machine model and the system represented by oscillating equation model of the rotors expressed in relative units of frequency. Depending on the structure Jacobian matrix of the interconnected power systems the model can be developed for interconnected systems in loop network. The modeling and the simulation for two interconnected power systems are realized in MATLAB-SIMULINK program in order to follow the evolution in time of the frequency, the load angle and the power flow deviation on the interconnection tie line.

Tripping overvoltages in HV transmission networks equipped with shunt reactors

Last years meant for Romanian power system huge efforts for increasing of its reliability and stability. A national program sustained financially a large-scale upgrading process of power system components. In this paper the authors present the results of an analysis regarding operation of different versions of equipments included in a HV substation. The performed tests outlined the dependency between the chopping current and the overvoltages rising due to switching-off operation of a shunt reactor in the presence of different types of circuit breakers. Further decisions about upgrading the substation components were based on these test results.

Quality of the electric energy; measurement and analyse methods and system

Abstract The paper presents the equipment used to measure some parameters that characterize the electric energy quality. The proposed equipment performs test and acquisition of analogue data (U and I) and numerical data. The sampled data are recorded when preset thresholds are exceeded by the analogical inputs or when the digital inputs states change. The fixed variant is supplementary provided with 2 analogue outputs and 8 numerical outputs. The operation of equipment is simulated and the corresponding software are exemplified for the case of a highly distorting consumer, a set of electric energy quality parameters being determined for this case. Copyright