When considering the standard AC power supply, most people know it as a voltage of 240V or 120V and a frequency of 50Hz or 60Hz and can recognise it in the form of a standard sine wave, which is known as the fundamental. The inherent impedance of the power system restricts the flow of current and causes a slight reduction in voltage, to something like 230V or 220V (or 115V or 110V), but does not, however, cause distortion. Of course, a ship's generators are invariably three-phase and capable of producing much higher voltage and power levels, but the principles of harmonic distortion still apply. If only individual cycles are distorted, caused by, for example, the switching on or off of machinery or electronic components, again, this does not constitute harmonic distortion.
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