On the processing of harmonics and interharmonics in electrical power systems

A recent IEC standard draft gives new definitions and methods for measurement and interpretation of results for harmonics and interharmonics, in particular introducing the concept of the harmonic and interharmonic groups. This paper analyses the spectral leakage problems due to a nonsynchronization of the analyzed waveforms with the window width, deriving from both fundamental frequency deviations and nonsynchronized interharmonics. Improvements of the signal processing recommended by IEC are introduced: the utilization of the classical Hanning Window, in place of the rectangular, and the doubling of the window width. In order to show the usefulness of the proposed improvements, the measurement results on a modern high power AC locomotive are reported and analyzed.