The growing complexity of modern marine electrical power systems through the extensive and ever-increasing use of electrical machines and power electronic systems together with the demand for electrical integration between the propulsion, service, weapon and/or cargo systems means that the impact of any waveform distortion needs to be carefully assessed early in the vessel's design stage to ensure proper functioning of the vessel's electrical system at sea. Waveform distortion is generally caused by non-linearity effects present in the electrical distribution system that cause energy imbalances. Analysis of distorted waveforms in vessels and offshore platforms generally shows such energy is present at many different frequencies; at exact multiple frequencies of the fundamental and at other frequencies which may be classified as being sub-harmonics and non-integer harmonics. In this paper, the author examines the types of harmonics in marine electrical systems citing a typical arrangement using a commonly employed propulsion drive to suggest that the true impact of harmonics in any marine electrical system can only really be appreciated by decomposing each harmonic into its positive, negative and zero sequence components.
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