Voltage Unbalance Numerical Evaluation and Minimization: Estimation by Incremental Sensitivity Analysis and Analytical Solutions;pp. 87-135
Authors: (Diogo C. Garcia, Anesio L.F. Filho, Jorge Andres Cormane Angarita, Onivaldo A. Fernandes, Fransicso A. do Nascimento, Universidade de Brasilia, Brazil, and others)
Abstract: Voltage unbalance is one of the parameters analyzed in power quality studies and represents the difference between the magnitudes of the voltages of a tri-phase electrical system and the phase shifts between them. It is desirable to have sinusoidal voltages with identical magnitudes and 120 electrical degree phase shifts between them. However in practice, there is always a deviation from this ideal case due to characteristics such as poor distribution of single-phase loads and the presence of transformers, transmission lines and capacitor banks with assembly differences between phases. These differences cause losses to both the consumer and to the energy supplier, such as reduced efficiency of tri-phase induction motors. In order to determine the influence of the network’s parameters (magnitudes and phase shifts of the three phases) on voltage unbalance and the values required to reduce or even eliminate it, the present chapter develops and presents two analysis methods. The influence of each parameter is determined through incremental sensitivity calculations and the changes needed for reduction are calculated by analytical solutions. The quantification index considered is the symmetrical components method. All methods developed were implemented in software and their validity was tested for a series of unbalance situations.