The voltage on the distribution line is, in most cases, distorted even at no load of the transformer, This is due to the "backgrouud" distortion on the medium-voltage line caused by the large number of single-phase nonlinear loads, such as PC's, TV's, VCR's, etc. This paper proposes a method to mis single-phase and three-phase nonlinear loads and reduce the harmonic currents significantly The dependence of the phase angle of the harmonic currents as a function of the short-circuit impedance is investigated using SABER for the three-phase and the single-phase diode rectifier both with and without dc-link inductance. The phase angle of the fifth harmonic current of a three-phase diode rectifier is always in counterphase with the fifth harmonic current of a single-phase diode rectifier. This leads to the conclusion that adding three-phase rectifier load can actually improve the power quality at the transformer, This is also validated by a number of on-site measurements in several applications of three-phase adjustable-speed drives.
