Abstract
Almost all today electrical loads are considered non-linear such as switch mode power supply (SMPS) for powering computer and mobile phone or variable speed drive (VSD) for driving home and industrial electric motors. These loads generate ac non-sinusoidal current containing a lot of harmonics as indicated by its high total harmonics distortion (THD) figure. Current harmonics bring negative effects into all electrical power system components, including three-phase generator. This paper provides analysis of load current harmonics effects on vibration of three-phase generator. Three different laboratory experiments have been conducted i.e. three-phase linear resistive loading, non-linear loading with a three-phase ac/dc converter and non-linear loading with three single-phase capacitor filtered ac/dc converters. Results show that the higher load current harmonics content the higher is vibration of the three-phase generator. Non-linear loading with a three-phase ac/dc converter that generate about 24.7% THD gives an increase of 4.3% and 5.5% in average of vertical and horizontal vibrations of the three-phase generator respectively. Further, non-linear loading with three single-phase capacitor filtered ac/dc converters that generate THD as high as 74.9% gives significant increase of 28.1% and 23.6% in average of vertical and horizontal vibrations respectively.
Highlights
Many electrical loads are classified as nonlinear such as switch mode power supply (SMPS) for powering computer as well as mobile phone and variable speed drive (VSD) for powering ac three-phase motor commonly used in water pump unit, compressor, belt conveyor, escalator and lift or robotic arms in an industrial production unit [1], [2], [3]
The second one is non-linear loading with a three-phase ac/dc converter and the last one is non-linear loading with three single-phase capacitor filtered ac/dc converters connected as perphase load of the three-phase generator output terminal
Results from laboratory experiment show that non-linear loading with a three-phase ac/dc converter that has about 24.7% total harmonic distortion figure (THDi) in average gives an increase of 4.3% in vertical vibration and 5.5% in horizontal vibration as compared to linear loading with about 17.6% THDi in average
Summary
Many electrical loads are classified as nonlinear such as switch mode power supply (SMPS) for powering computer as well as mobile phone and variable speed drive (VSD) for powering ac three-phase motor commonly used in water pump unit, compressor, belt conveyor, escalator and lift or robotic arms in an industrial production unit [1], [2], [3]. SMPS and VSD use single-phase ac/dc converter and three-phase ac/dc converter respectively at the input/ac side [4] Switching of these converters produces ac non-sinusoidal current containing a lot of harmonics as indicated by the high total harmonic distortion figure (THDi). If a linear load is connected harmonics free ac sinusoidal current will flow in generator three-phase armature windings. If a non-linear load is connected ac non-sinusoidal current with harmonics will flow in generator three-phase armature windings. Effect of load current harmonics generated by non-linear loads on generator performance, on its vibration, is investigated throughout this paper. Generator vibration on nonlinear loading differs according to current harmonics content generated by the non-linear load
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