Sources of distortion-prediction, measurement and compatibility standards for variable speed drive harmonic distortion levels

Variable speed drives are often maligned as the major source of harmonic distortion in a system. It is the purpose of this paper to highlight some of the factors involved when considering the harmonics generated and system compatibility when installing variable speed drives. It also identifies the more important standards and the anomalies that can arise with system incompatibility. Variable speed drives are often installed in a network where they constitute a major portion of the total load. Problems sometimes occur when the drives are first commissioned and the incompatibility of existing parts of the plant is highlighted. Deficiencies in the original equipment are often overlooked and the blame for the problems which occur placed with the drives manufacturer. The author discusses typical current and voltage waveforms for variable speed drives, standards, recommendations and guidelines, system electromagnetic compatibility, network modelling, and harmonic measurements