Browsing by Author "Lombard, Charles Henry Ochse"

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    Analysis of gearbox loads in large air-cooled condensers.
    (Stellenbosch : Stellenbosch University, 2017-03) Lombard, Charles Henry Ochse; Els, Daniel Nicolaas Johannes; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Operational gearbox loading, in an air-cooled condenser (ACC), is measured and analysed in this investigation. Measurements are recorded during the start, stop and normal operational periods of the gearbox. Interaction between gearbox input and output torsion and bending experienced by the output shaft, are the primary focus of the study. Secondary areas of investigation include gearbox vibration, temperature, shaft speeds and power consumption of the motor. Correlations are also drawn between gearbox loading and wind conditions. Industry has noted that the gearboxes used in the ACC of large coal red power stations, are responsible for most of the unit down-time, which motivated the above mentioned investigation. This investigation is part of a collaboration between Stellenbosch University and various industry partners. The knowledge gained from this study may be used to optimize selection criteria, design of ACC gearbox components, and to improve operation and maintenance information. Previous research has not yet published data that was obtained from the input shaft of such a gearbox, as working conditions complicate this task. A previously developed measurement system is customized to meet the requirements of this investigation. Strain gauges are used to measure torsion on both gearbox shafts as well as bending on the output shaft. The data is transmitted from the rotating shafts by means of radio frequency and it is recorded by using a very specialized data acquisition system. Gearbox shaft speed, vibration and temperature are measured with proximity sensors, accelerometers and a thermal camera. The power supply of the motor is measured with an oscilloscope and current transformers. The data from the various sensors are time synchronized before recording. The accelerometers and the thermal camera were calibrated beforehand, while the same was not possible for the strain gauges. Fundamental strain theory was used to determine the measured torsion and bending on the output shaft. The accuracy of the input shaft measurements are quanti ed by means of nite element analysis, statistical analysis and laboratory testing. Vibration analysis is then also performed on the input shaft to investigate the relationship between temperature and elastic modulus. Firstly, start-up measurements showed that the induction motor draws up to 7:89 times the rated power. During this period, gearbox torque was measured to be roughly four times higher than the operational torque. Secondly, analysis of the normal operational data showed that strain measurement is a ected by shaft temperature, while frequency spectrum analysis proved that torsional vibrations are transferred through the gearbox. Correlations were also drawn between output shaft bending and varying wind conditions. Lastly, stop period measurements were able to show reverse loading of the gearbox, as the fan drives the motor during that period. This study succeeded in acquiring and analysing data from the input shaft of an operational ACC gearbox , which has never been done before. It was also established that absolute strain gauge measurements are not possible without knowing the exact material properties of the test sample.