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This paper analyzes the effects of voltage sags on the three-phase rectifier of a voltage-source-inverter (VSI)-fed adjustable-speed drive. These effects are dc voltage drop and ac current peaks. As rectifier behavior is univocally characterized by two parameters (which depend on the ac reactance and the dc capacitor), their influence on the dc voltage drop and the ac current peaks is studied. Diagrams in function of these two parameters are presented in order to easily predetermine the worst effects of voltage sags originated by single-phase faults. The results of the study suggest that if the trip levels are correctly adjusted, the drive can ride through the voltage sags produced by single-phase faults (assuming the drive has typical values of L and C). Index Terms--Adjustable-speed drive (ASD), power quality, ridethrough capability, voltage sag.

This paper presents a numerical method for the estimation of induction motor double-cage model parameters from standard manufacturer data: full load mechanical power (rated power), full load reactive electrical power, breakdown torque, and starting current and torque. A model sensitivity analysis for the various electrical parameters shows that stator resistance is the least significant parameter. The nonlinear equations to be solved for the parameters determination are formulated as a minimization problem with restrictions. The method has been tested with 223 motors from different manufacturers, with an average value of the normalized residual error of 1.39*[10.sup.-2]. The estimated parameters of these motors are graphically represented as a function of the rated power. Index Terms--Induction motor, manufacturer data, parameters estimation, parameters indetermination.

This paper proposes a simple, practical PSPICE model of a three-phase, three-legged, saturated transformer with accurate performance. The transformer is modeled with its electric and magnetic equivalent circuits and a simple but reliable characterization of its nonlinear magnetic behavior. Two three-phase transformers of 380/220 V, 7.5 kVA, and 60 kVA, respectively, are studied in order to verify the goodness of the model. The parameters of these transformers are measured in the laboratory, and comparison of the PSPICE model with real measurements has been successful. Index Terms--Magnetizing current, nonlinear model, saturation curve, transformer model.

Multiple harmonic load flow study solutions are mathematically possible but not physically real. The Newton method can provide these false solutions when an ill-conditioned power system is studied. This problem is more usual in the presence of harmonies. This paper analytically studies a kind of false solution in networks with AC/DC converters. These false solutions are easily detected because they present a negative firing angle of the converter. A simple example is studied where the Newton method gives a false solution. Keywords: Harmonic load flow; Newton method.

This paper proposes an algorithm for the approximate calculation of the effects caused by a voltage sag in the induction machine supply system. The algorithm computes the current and torque peaks, and the mechanical speed loss for an extensive range of voltage sags. It has a high calculation speed because it makes two simplifications. The first supposes that speed varies insignificantly during the first cycles after the voltage drop and recovery points to solve analytically the electrical transients in these cycles. The second neglects the electrical transient during the sag duration for a quick evaluation of the speed loss. Machine sensitivity to voltage sags is graphically shown. The curves can be applied to protective relay coordination. Keywords: voltage sag (dip), semianalytic algorithm, exponential matrix, sensitivity curves.

Abstract: The paper proposes an induction motor model for the study of harmonic load flow in balanced and unbalanced conditions. The parameters of this model are obtained from motor manufacturer data and the positive- and negative-sequence equivalent circuits of the single- and double-cage models. An approximate harmonic model based on motor manufacturer data only is also proposed. In addition, the paper includes manufacturer data and the calculated parameters of 36 induction motors of different rated powers. This database is used to analyze the proposed models. [Copyright &y& Elsevier]