Voltage distortion of rotary UPS and standby engine generator sets

Methods for calculating the voltage distortion produced by nonlinear loads, and design concepts for reducing the distortion are described. The impact of reducing saliency in the rotor construction and in the damper windings on the impedance of the generator to harmonic currents is analyzed. It is shown that generator voltage distortion under nonlinear loads can be controlled by either one of two methods, overrating the generator to make the nonlinear load a smaller percentage of the generator rating, or reducing the internal impedance of the generator to the harmonics of the nonlinear load current.<>