Simulation Method for Identifying A Harmonic Offender in a Power System Containing Multiple Six-Pulse Drives

The focus of this paper is to define and identify a harmonic offender and develop a simulation method to investigate this concept in an interconnected power system containing multiple six-pulse drives. The IEEE 519 recommended practice provides indices to determine distortion as well as recommending limits within which systems containing harmonics should operate. However, no specific method is provided for determining whether or not the harmonic spectrum magnitudes and phase angles of a new drive that is to be installed in a system that already contains more than one six-pulse drive will be a harmonic offender or not. When only one drive is present in a system, its harmonic spectrum phase angles has no effect on the distortion index results. Only harmonic magnitudes influence distortion. However, when multiple drives are connected in a system, the harmonic currents from each source add vectorially at the point of common coupling. As a result, the harmonic distortion is highly dependant on the method in which the harmonic current spectrum angles are modelled. Whether a drive is a harmonic offender or not in a given system thus depends upon the modelling of drives taking into account the harmonic spectrum phase angles. To enhance the understanding of modelling harmonic spectrum phase angles, the two methods (voltage and current method) are compared and a recommendation as to which method should be used is made. Three case studies are conducted to show the usefulness of the developed method.