A self-synchronizing instrument for harmonic source detection in power systems

The deregulation of energy markets holds out new prospects for contracts between customers and utilities, in which the price of energy can depend on voltage quality and load characteristics, as well as on the responsibility for disturbances caused to supply voltage in power systems. In this context, harmonic source detection is one of the main problems because of equipment sensibility and the proliferation of loads which absorb nonsinusoidal currents. In this paper, the authors present a new instrument based on a time-domain method for the detection of harmonic active powers in three-phase systems, which can be usefully applied even in the presence of unbalance or asymmetry. The amplitude and sign of harmonic powers can be measured directly, and no spectral analysis is required for the evaluation of the amplitudes and phase angles of supply currents. Moreover, the instrument is able to synchronize itself with the input signal to measure the total distortion factors of voltages and currents, supply voltage unbalance, and harmonic voltage amplitudes. Theoretical aspects are discussed, the measurement accuracy is evaluated, and the experimental results are presented. Finally, a comparison is made with a commercial instrument.

I. Introduction

IN THE LAST few years, there has been an increase in current and voltage distortion in distribution systems because of the development of loads, such as power electronic devices, which absorb nonsinusoidal currents. In practical situations, harmonic sources can be located both upstream and downstream of the metering section, so that both supply and load may be responsible for harmonic distortion; some harmonics may be produced by the load, others by the network, and others by both load and network. Moreover, in the presence of negative sequence components in currents and voltages, harmonic source detection can be more difficult because of the overlapping of effects due to unbalance and nonlinearity.