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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.

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 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.