Design of stand-by generators for non-linear loads

The author discusses the causes of the problems and the design changes possible in the generator to minimize the voltage waveform distortion. A method for calculating the additional losses in the generator due to harmonic currents is presented. The discussion refers specifically to generators of the salient pole type in the 10-2000 kW range, but the general principles apply to all types of rotating field machines. Optimum generator design depends on the system connection. For generators connected directly to balanced line to neural loads, a 2/3 pitch machine with low zero sequence reactance minimizes triplen voltage harmonic distortion. For balanced three-phase loads, lower subtransient reactances and, consequently, lower voltage harmonic distortion can be obtained by using a longer coil pitch