Power System Harmonics

Abstract

The proliferation of nonlinear loads such as power converters, fluorescent bulbs, and adjustable speed drives (ASDs) in the power distribution system gives rise to harmonic distortions in voltage and current waveforms. While drawing a fundamental current from the supply system, a nonlinear load injects non-sinusoidal currents back to the supply system. The distorted load current interacts with the system impedance and in turn distorts the utility’s supply voltage. As a result, other loads connected to the same distribution system end up drawing distorted currents as well. Significant voltage distortion increases the system losses and adversely affects the operation of end-user loads. In this chapter, the concept of power system harmonics is introduced and the approaches to analyze the distribution circuit in the presence of nonlinear loads are discussed. The power quality issues due to harmonic distortions and power system indices to quantify them are summarized as well. The voltage–current characteristics and the circuit models for several non-linear loads are discussed, followed by circuit modeling in the presence of harmonics. Several methods for harmonic power flow study are presented. A harmonic power flow study calculates active and reactive power flows, voltages, and currents at each node for each harmonic frequency. Several methods to mitigate power system harmonics using active and passive filters are also discussed.