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The paper deals with the analysis of the particularities of the electric power supply of the railway electric transport systems and the methodology for monitoring and evaluation of the electricity costs in order to develop efficient methods for reducing the losses and, implicitly, reducing the price of energy. The cost methodology for this consumer is analysed, on the basis of which an algorithm is developed and a software module is proposed to monitor the cost of energy needed to power the electric traction system. With the developed methodology and module, the cost of active and reactive energy is calculated and displayed. The results show that the contribution of reactive energy is significant in the total energy cost, which justifies the introduction of the power factor compensation systems, and the active filters to reduce the impact of the harmonics in the supply system.

This paper deals with the development of a model for assessment of the indicators, which characterize the unbalanced and harmonic distorted operation regime in the three-phase low voltage networks. The symmetrical components transformation and the Fourier method are applied, in which each harmonic is decomposed into zero, positive and negative sequence components. The quality indicators in voltage distorted and unbalanced regime are obtained using MathCAD software. The proposed model and procedure is applied for specific case studies. This approach allows the identification and analysis of distorted and unbalanced regime indicators of three-phase low voltage supply system in common coupling point of the consumer, and the procedure can be integrated into a power quality monitoring system.

Nowadays, the role and functionality of power supply system of the consumer (PSC) increases. As interface between the power distribution system and consumer power system, PSC has a strong influence on quality and efficiency of energy and implicitly on the level of energy costs. Besides specific measures for increasing efficiency and reduction of energy costs, the industrial consumer is interested both, in economic and in technical evaluation of power transformer included in PSC, and in its impact on the total energy cost. The paper deals with the methodology of electric energy billing for the case of Romanian industrial consumers. A procedure is proposed for the evaluation of the cost of consumer energy, putting in evidence the losses in PSC when the measurement point is on LV. The loading factor of PSC transformer is determined and the efficiency of PSC transformer replacement is obtained. The application of this procedure is done for a PSC of 100 kVA which supplies an industrial consumer. This procedure can be the basis for development of a system for power control and monitoring with the aim to minimize electricity demand costs.

Currently, major technical challenges linked to the implementation strategy of Distributed Generation (DG) are associated with new studies and researches regarding the impact of renewable energy sources on the parameters of power transmission and distribution networks. To increase the energy efficiency and to reduce the power losses in power distribution networks, specific measures are proposed: increasing the voltage of operation, introduction of control systems, reconfiguration of power networks, energy demand management, etc. Knowing that the impact of DG on power losses is cardinal to substantiate methods of structural improvements in planning distribution networks. In this paper the influence of DG on the low-voltage networks is analyzed, using the facilities offered by the NEPLAN software. Power losses analysis is done on a low voltage test grid of 17 nodes in the cases when a DG unit is connected in the node having the lowest voltage, and in the loading center of consumption. The proposed solution, placing the renewable source in the loading center of consumption, reduces energy losses by up to 57 %. The results and conclusions of this analysis could be extended to any low-voltage radial power distribution network.

The paper deals with the analysis of unbalance regime in three-phase low voltage supply systems. For unbalance evaluation a virtual instrument realized in Java programming language was developed. This tool can be used in protection schema for the electric distribution network, especially in the common point of supplying the industrial consumers, where the electric equipments can be severely affected by continuously functioning in an unbalanced regime of the power supply. The case study includes determination and analyzes of the unbalance indicators for inductive consumers with and without neutral conductor.

Currently, major technical challenges linked to the implementation strategy of smart grids are associated with new studies and researches on the impact of renewables energy sources on the parameters of power transmission and distribution networks. Current dedicated softwares permit the modeling and simulation of power distribution structure which includes different types of renewable energy sources. Thus, new analyses on power flow and voltage drops in the power network nodes and on the stability of both the power distribution networks and transport networks can be done. New solutions are proposed to increase energy efficiency by increasing the value of the rated voltage, automation, introduction of system control and reconfiguration of power networks, optimization, demand management, and others. In this paper the influence of grid-connected photovoltaic power plants is modeled and analyzed, using the facilities offered by the NEPLAN software. Power losses analysis is done on a low voltage test network of 16 nodes in the cases when the network with one or two photovoltaic plants connected. The proposed solution, placing the photovoltaic plants in the center of gravity of consumption, reduces power losses by 55.8%.

This paper analyzes the intrinsic sensitivity of different types of electrical equipment, which is caused by the specific constructive operating principle. In the case of electric motors, their ability to function close to the normal operation regime, even in the case when certain events caused by various electromagnetic disturbances occur, is determined by the electrical and mechanical characteristics of the electric drive. The paper describes the test bench developed within the Electromagnetic Compatibility Laboratory of the Research-Development-Innovation Institute of Transilvania University of Brasov, with a view to establishing the effect of the three-phase voltage dips on the induction motors. The bench allows the generation of three-phase symmetrical dips of abrupt and gradual types with a magnitude ranging between 0 and 90 %. Experimental determinations and measurements of the shape of phase voltages, current, and active power are used to establish the effect of dips supply regimes, and to evaluate the induction motor efficiency.

Phenomena usually associated with neutral conductor interruption are sensitive issues of low voltage electrical networks. These phenomena are now directly related to the power quality, especially in the case of three-phase unbalanced consumers supplied with low balanced/unbalanced three-phase system of voltages. Therefore a detailed analyzes for assessment of the impact of interruption of neutral on the electrical networks and consumers are required. The paper deals with an analytical description of the neutral conductor interruption effect on the unbalanced three single-phase consumers. The simulations for three cases are considered: low voltage supply system with four conductors in normal conditions of operation; the case when the neutral conductor is interrupted in the substation area; the case when the neutral conductor is interrupted in the lines area. It is shown that the neutral displacement voltages and neutral currents depend on the type of fault and on the severity of the three-phase consumer unbalance. The results are useful for appropriate designing of the protection system.

The current waveforms in low voltage electrical networks are frequently harmonic polluted due to actual equipment, most of them being electronically controlled. To reduce the distortions and unbalance effects on the low voltage electrical networks, new methods of monitoring are required, using a more precise set of indicators for power quality analysis. In this paper a modeling of the current waveforms for the three-phase low voltage electrical networks with neutral is done, in conditions of unbalance and distortions, using symmetrical components method. Various studies indicate that deformed and unbalanced regimes are complex processes that require detailed characterization. Using the application developed in Mathcad, the global components of the phase current, unbalance and harmonic distortion indicators are obtained.

The paper deals with an analysis upon the unbalance regime of the three-phase consumers supplied with a sinusoidal voltage system and, upon the voltage and current unbalance indicators. For rapidly calculating the unbalance regime specific indicators, knowing the characteristics of the consumers fed from the three-phase network, a software application in the LabVIEW 8.1 environment was developed. The software is used for obtaining the voltage and current symmetrical components and current of neutral, corresponding to different unbalanced operational regimes of three phase consumers. An application was developed for the particular case consisting of a resistive consumer with/without neutral connection. The voltage unbalance factors range within the admissible limits, however not also the current unbalance factors.

Load curve analysis is an efficient instrument aimed at carrying through studies and planning, necessary for developing electric energy distribution networks and for reducing the electric energy internal consumption. The paper herein presents the analysis of the load curves for an industrial consumer fed from the network of 20 kV, 50 Hz. There are calculated the characteristic parameters for daily and monthly load curves, with the method of statistical analysis for the data measured in real time through data transmission counters. Data analysis indicates the necessity of effecting the measurements in real time, during both winter and summer, as the shape of the load curve characteristics varies.