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Modeling and Control of the Starter Motor and Start-Up Phase for Gas Turbines

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Modeling and Control of the Starter Motor and Start-Up Phase for Gas Turbines electronics Article Modeling and Control of the Starter Motor and Start-Up Phase for Gas Turbines Soheil Jafari 1,* , Seyed Alireza Miran Fashandi 2 and Theoklis Nikolaidis 3 1 Propulsion Engineering Centre, School of Aerospace Transport and Manufacturing, Cranfield University, Cranfield MK43 0AL, UK 2 Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran; [email protected] 3 Propulsion Engineering Centre, School of Aerospace Transport and Manufacturing, Cranfield University, Cranfield MK43 0AL, UK; t.nikolaidis@cranfield.ac.uk * Correspondence: s.jafari@cranfield.ac.uk; Tel.: +44-(0)-1234-750111 (ext. 5106) Received: 18 February 2019; Accepted: 19 March 2019; Published: 25 March 2019 Abstract: Improving the performance of industrial gas turbines has always been at the focus of attention of researchers and manufacturers. Nowadays, the operating environment of gas turbines has been transformed significantly respect to the very fast growth of renewable electricity generation where gas turbines should provide a safe, reliable, fast, and flexible transient operation to support their renewable partners. So, having a reliable tools to predict the transient behavior of the gas turbine is becoming more and more important. Regarding the response time and flexibility, improving the turbine performance during the start-up phase is an important issue that should be taken into account by the turbine manufacturers. To analyze the turbine performance during the start-up phase and to implement novel ideas so as to improve its performance, modeling, and simulation of an industrial gas turbine during cold start-up phase is investigated this article using an integrated modular approach. During this phase, a complex mechatronic system comprised of an asynchronous AC motor (electric starter), static frequency converter drive, and gas turbine exists. The start-up phase happens in this manner: first, the clutch transfers the torque generated by the electric starter to the gas turbine so that the turbine reaches a specific speed (cranking stage). Next, the turbine spends some time at this speed (purging stage), after which the turbine speed decreases, sparking stage begins, and the turbine enters the warm start-up phase. It is, however, possible that the start-up process fails at an intermediate stage. Such unsuccessful start-ups can be caused by turbine vibrations, the increase in the gradients of exhaust gases, or issues with fuel spray nozzles. If, for any reason, the turbine cannot reach the self-sustained speed and the speed falls below a certain threshold, the clutch engages once again with the turbine shaft and the start-up process is repeated. Consequently, when modeling the start-up phase, we face discontinuities in performance and a system with variable structure owing to the existence of clutch. Modeling the start-up phase, which happens to exist in many different fields including electric and mechanical application, brings about problems in numerical solutions (such as algebraic loop). Accordingly, this study attempts to benefit from the bond graph approach (as a powerful physical modeling approach) to model such a mechatronic system. The results confirm the effectiveness of the proposed approach in detailed performance prediction of the gas turbine in start-up phase. Keywords: industrial gas turbine; electric starter; cold start-up phase; dynamic modeling; bond graph; mechatronic approach; integrated modeling approach Electronics 2019, 8, 363; doi:10.3390/electronics8030363 www.mdpi.com/journal/electronics Electronics 2019, 8, 363 2 of 25 1. Introduction Electronics 2019, 8, x FOR PEER REVIEW 2 of 27 Current focuses of industrial gas turbine manufacturers are on minimizing costs, enhancing flexibilityCurrent and focuses capacity, of whileindustrial retaining gas turbine the reliability. manufacturers This has are motivated on minimizing well-known costs, companiesenhancing includingflexibility and Siemens capacity, [1], GE while [2], retaining and Alstom the [reliability.3] to work This on a has set ofmotivated what is knownwell-known as performance companies enhancementincluding Siemens methods [1], toGE be [2] able, and to yieldAlstom more [3] profit.to work on a set of what is known as performance enhancementIn order tomethods increase to thebe able flexibility to yield of more industrial profit. gas turbine, improving the start-up phase is of considerableIn order importance to increase since the flexibility the start-up of phaseindustrial in most gas utilized turbine, gas improving turbines hasthe createdstart-up challenges phase is inof gasconsiderable transmission importance line stations since in the certain start countries,-up phase resultingin most utilized in trip in gas the turbines turbine has [4]. created The reason challenges behind suchin gas unsuccessful transmission start-ups line stations could in be certain attributed countries, to turbine resulting vibrations, in trip the in increasethe turbine in the[4]. gradients The reason of exhaustbehind such gases, unsuccessful or problems start in fuel-ups spray could nozzles. be attributed If the turbine to turbine is unable vibrations, to attain the the increase self-sustained in the speedgradients and of its exhaust speed fallsgases, below or problems a certain in limit, fuel the spray clutch nozzles. engages If the with turbine the turbine is unable shaft to once attain more the andself-sustained the start-up speed process and isits repeated. speed falls This below in turna certain increases limit, thethe turbineclutch engages start-up with duration the turbine and incurs shaft expensesonce more for and repair the start and- maintenance.up process is Therefore,repeated. This appropriately in turn increases performing the turbine the start-up start- processup duration and reducingand incurs its expenses time have for always repair been and consideredmaintenance. by Therefore, manufacturers. appropriately Since the performing performance the of start the gas-up turbineprocess duringand reducing the start-up its time phase have has always direct been impacts considered on its lifespan by manufacturers. as well as the Since time the required performance for its repair,of the gas the importanceturbine during of this the notion start-up becomes phase muchhas direct more impacts significant. on its For lifespan instance, as Siemenswell as the believes time thatrequired as the for market its repair, continues the importance to grow, faster of this start-ups notion becomes become asmuch important more significant. as recurring For ones. instance, As a result,Siemens Siemens believes launched that as athe project market named continues FACY, abbreviatedto grow, faster from start fast- cyclingups become (Figure as1 ),important to integrate as everyrecurring engineering ones. As thought a result, into Siemens a comprehensive launched a plantproject concept. named The FACY, purpose abbreviated was to devise from fast a plant cycling that could(Figure increase 1), to integrate the frequency every of engineering starts while thought decreasing into their a comprehensive duration and keepingplant concept. the requirements The purpose of otherwas to components devise a plant to athat minimum could increase including the the frequency steam generator of starts while usedfor decreasing heat recovery their duration at warm and hotkeeping start-ups the requirements [4]. of other components to a minimum including the steam generator used for heat recovery at warm and hot start-ups [4]. Figure 1.1. ImprovingImproving thethe start-upstart-up process process in in Siemens Siemens combined-cycle combined-cycle power power plant plant (GT: (GT: Gas Gas Turbine, Turbine, ST: SteamST: Steam Turbine). Turbine). Additionally, investigation and implementation of improving the performance of start-up phase Additionally, investigation and implementation of improving the performance of start-up phase were carried out by GE company researchers. For instance, the start-up phase of a normal industrial were carried out by GE company researchers. For instance, the start-up phase of a normal industrial gas turbine, GE LM6000, which takes 10 min is displayed in Figure2. gas turbine, GE LM6000, which takes 10 min is displayed in Figure 2. The start-up phase of the GE LM6000 industrial gas turbine is reduced to less than 5 min by implementing the following actions (Figure3 shows the new start-up process of this gas turbine): • No LLP (Life Limited Parts) penalty when used less than 4 times a year • Two cycles per 1 penalty when used more than 4 times a year • Observation and measurement manual should be checked when used more than 4 times a year. Electronics 2019, 8, x FOR PEER REVIEW 3 of 27 Electronics 2019, 8, 363 3 of 25 Electronics 2019, 8, x FOR PEER REVIEW 3 of 27 Figure 2. Normal start-up process of GE LM6000 industrial gas turbine (HPC: High Pressure Compressot) [5]. The start-up phase of the GE LM6000 industrial gas turbine is reduced to less than 5 min by implementing the following actions (Figure 3 shows the new start-up process of this gas turbine): • No LLP (Life Limited Parts) penalty when used less than 4 times a year • FigureTwoFigure 2.cycles 2.Normal Normal per 1 start-up penaltystart-up process whenprocess u ofsed of GE moreGE LM6000 LM6000 than industrial4 industrialtimes a gasyear gas turbine turbine (HPC: (HPC: High High Pressure Pressure • Compressot)ObservationCompressot) [5]. [5]and. measurement manual should be checked when used more
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