Asymmetric Three-phase Asynchronous Generator Running

A practical power distribution system has always a certain degree of unbalance which can be caused by one or several factors such as the single-phase load, unbalanced three-phase loads, unequal impedances of transformer windings and asymmetrical series impedances of power lines or cables. Further, the excitation capacitances of an SEIG may also be unbalanced because of manufacturing inaccuracy, ageing or failure of some capacitors. So, the problems of SEIG under unbalanced operation deserve to be further research, which will be a good technical guide for the safety and stability operation of the SEIG in practice.According to a A-connected induction generator building-up voltage under single excitation capacitor without load, the analysis is based on the symmetrical component method, deriving the single-phase loop impedance. Supposing the loop impedance is zero, then solving the three-phase's no-load voltages with the optimization method. By the validation of the experiments, finding that a A-connected induction generator with single capacitor can establish terminal voltages successfully, and the no-load voltages increase as the increment of the excitation capacitor. The voltage in which phase the excitation capacitor locates is the maximum.The steady-state operation of Y-connected three-phase induction generator with single-phase load is analyzed basing on the theories of two-port network equivalent circuit. The calculated results verify that the load voltage increases with the balance capacitor growing and decreases as the increment of the excitation capacitor when the SEIG feeds the R-load. As the SEIG services the R-L load, the load voltage is larger with the balanced capacitor rising, but the voltage increases firstly, up to the maximum, and then decreases quickly with the excitation capacitor increasing.By contrasting the affection of the short-shunt connection of capacitors, long-shunt connection of capacitors and parallel connection of capacitor on the load voltage, finding that parallel connection and long-shunt connection of capacitor are not the ideal scheme for reactive power compensation, which have an impact of shunt and voltage-dividing on load. The short-shunt connection of capacitor goes against the stabilization of the R-load voltage, but it supplies capacitive current and reactive power for the R-L load, which can improve the capacity for carrying load.Based on the theories of two-port network method and the new equivalent circuit, the steady-state operation of the self-excited induction generator with three-phase unbalanced loads is analyzed, which transforms the abstract and complicated rotate magnetic field problems of generator into the concrete and simple circuit problems. The variety of voltages and currents of the SEIG with asymmetrical loads is calculated. The calculated values well match the experimental values, which verify the availability and accuracy of this presented method. At the same time, according to the gained unbalanced load voltages and currents, the asymmetrical degree of the SEIG can be analyzed, which makes reference for the reactive power compensation.