A digital measurement scheme for time-varying transient harmonics

This paper presents an enhanced measurement scheme on the harmonics in power system voltages and currents which is not limited to stationary waveforms, but can also estimate harmonics in waveforms with time-varying amplitudes. The paper starts with a review of the common techniques for harmonics measurement based on the fast Fourier transform (FFT). The major pitfalls in the common FFT application techniques are described and the concepts of a new scheme for reducing the picket-fence effect are introduced. The proposed scheme is based on Parseval´s relation and the energy concept which defines a “group harmonic” identification algorithm for the estimation of the energy distribution in the harmonics of time-varying waveforms. The scheme is tested on a portable computer-based harmonic recorder providing on-site harmonic data collection and precise harmonic identification