Abstract
The voltage on the distribution line is, in most cases, distorted even at no load of the transformer. This is due to the "background" distortion on the medium-voltage line caused by the large number of single-phase nonlinear loads, such as PCs, TVs, VCRs, etc. This paper proposes a method to mix 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.
I. INTRODUCTION
The exploding use of personal computers and electric loads controlled by power electronic has lead to a severe increase of current harmonics drawn from the distribution line. These harmonic currents can in worst cases result in:
Overheating or derating of transformer
Overheating of wiring
Damaging of capacitor banks
Resonance
Malfunction of electronic equipment
Communication interference
Distorted supply voltage.
