Analysis of gearbox loads in large air-cooled condensers.

Lombard, Charles Henry Ochse (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANSE OPSOMMING: In hierdie ondersoek word die operasionele lading van 'n ratkas van 'n lugverkoelde kondenseerder (LVK) gemeet en ontleed. Metings word geneem tydens die begin, stop en normale operasionele werkstoestande van die ratkas. Die primêre fokus van hierdie studie is die interaksie tussen die in- en uitree torsie van die ratkas, en die buigmoment van die uitree-as. Sekondêre areas van die ondersoek sluit in ratkas vibrasie, temperatuur, as-spoed en kragverbruik van die motor. Ooreenkomste word ook gemaak tussen die las van die ratkas en windtoestande. Die industrie het opgemerk dat die LVK ratkaste by groot steenkool aangedrewe kragstasies die hoofoorsaak van LVK stilstandtyd is. Dit het hierdie ondersoek gemotiveer en vorm deel van die samewerking tussen die Universiteit van Stellenbosch en vennote in die industrie. Die kennis wat in hierdie studie opgedoen word, kan gebruik word vir die optimering van seleksie standaarde, die ontwerp van LVK ratkas komponente en die verbetering van operasioneleen onderhouds inligting. As gevolg van komplekse werksomstandighede, is vorige navorsings data wat verkry is van die intree-as van hierdie ratkaste, nog nie gepubliseer nie. 'n Reeds bestaande meetstelsel is aangepas om aan die vereistes van hierdie ondersoek te voldoen. Rekstrokies word gebruik om die torsie in beide ratkas asse te meet. Die buiging van die uitree-as word ook deur rekstrokies gemeet. Data word van die roterende asse versend deur middel van radio frekwensie en dit word opgeneem deur 'n gespesialiseerde data opnemingsstelsel. Die ratkas se as-spoed, vibrasie en temperatuur word gemeet met nabyheids sensors, versnellingsmeters en 'n termiese kamera. Die krag toevoer na die motor word gemeet met 'n ossiloskoop en stroom transformators. Die data van die onderskeie sensors word gesinkroniseer voor dit opgeneem word. Die versnellingsmeters en termiese kamera is vooraf gekalibreer, maar dit was nie moontlik vir die rekstrokies nie. Fundamentele vervormingsteorie is gebruik om die torsie en uitree-as buiging vas te stel. Die akkuraatheid van die intree-as se metings word gekwanti seer deur middel van eindige element analise, statistiese analise en laboratorium toetsing. Vibrasie analise word ook uitgevoer op die intree-as om die verwantskap tussen temperatuur en elastisiteits modulus te ondersoek. Hierdie ondersoek se metings toon eerstens dat die induksie motor tydens die begin tydperk 7.89 keer die gespesi seerde drywing trek. Gedurende hierdie tydperk was die ratkas torsie ongeveer vier keer hoër as die operasionele torsie. Tweedens toon die analise van die normale operasionale data dat die vervormingsmeting beïnvloed word deur die as se temperatuur, terwyl frekwensie spektrum analise bewys dat torsie vibrasies deur die ratkas oorgedra word. Ooreenkomste word ook gemaak tussen die buiging van die uitree-as en veranderlike windtoestande. Laastens het die metings van die stopperiode getoon dat omgekeerde belading van die ratkas plaasvind, aangesien die motor in hierdie periode deur die waaier aandryf is. Die ondersoek het daarin geslaag om data van die intree-as van 'n operasionele LVK ratkas te bekom en te ontleed, iets wat nog nie voorheen gedoen is nie. Daar is ook vasgestel dat absolute rekstrokie metings nie moontlik is sonder dat die akkurate materiaal-eienskappe van die toetsmonster bekend is nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101275
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