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

The deregulation of energy markets holds out new prospects for contract 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 sources detection is one of the main problems, because of equipment sensibility and the proliferation of loads which absorb non-sinusoidal 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 voltages 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.