Expert System of Fault Diagnosis for Gear Box in Wind Turbine

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1 Available olie at Systems Egieerig Procedia 4 (202) The 2 d Iteratioal Coferece o Complexity Sciece & Iformatio Egieerig Expert System of Fault Diagosis for Gear Box i Wid Turbie YANG Zhi-Lig, WANG Bi, DONG Xig-Hui, LIU Hao North Chia Electric Power Uiversity, Beijig,02206, Chia Abstract Gear box is oe of the key compoets i wid turbie. To make timely ad accurate diagosis for gear box, a expert system based o fault tree aalysis is developed i this paper. Firstly, a fault tree model is established i accordace with the structural features of wid turbie gearbox. O basis of the fault tree model, qualitative aalysis ad quatitative aalysis of the gearbox faults are carried out afterwards. Fially,a Web-orieted expert system is developed by C# o the.net platform which will save the fault diagosis time sigificatly ad make the expert solutio for the fault of gear box to achieve the precise ad quick maiteace more effectively Published Published by by Elsevier Elsevier Ltd. Ltd. Selectio Selectio ad ad peer-review peer-review uder uder resposibility resposibility of Desheg of Desheg Dash Dash Wu Wu. Ope access uder CC BY-NC-ND licese. Keywords: expert system, fault diagosis, idustrial egieerig, gear box, wid turbie;. Itroductio Gear box is oe of the key compoets i wid turbie ad the fault of gear box will lead to wid turbie shut dow ievitably. So what must be doe is makig timely ad accurate diagosis to gear box. However, due to rapid developmet of wid power idustry, there is o fault diagosis system specifically for wid turbie gearbox o the market i Chia. Curretly, durig the wid turbie gearbox fault diagosis, workers geerally aalyze the pheomeo by rule of thumb. This fault diagosis approach will sped more time ad the accuracy is low. Statistics show that the determiig time for the fault diagosis takes up 70% to 90% of the total time, while the repair time takes up oly about 0% to 30%[]. Fault diagosis systems have bee successfully applied i may kids of techical processes to improve operatio reliability ad safety. Wu itroduced a expert system for fault diagosis i iteral combustio egies usig wavelet packet trasform ad eural etwork[2]. Lei proposed a ew multidimesioal hybrid itelliget diagosis method to idetify differet categories ad levels of gear damage automatically[3]. Saravaa dealt with the effectiveess of wavelet-based features for fault diagosis usig support vector machies ad proximal support vector machies[4]. I aother paper, he itroduced the use of decisio tree for selectig best statistical features that discrimiate the fault coditios of the gear box from the sigals extracted ad the decisio tree was also used to geerate the rules automatically from the feature set [5]. Correspodig author. address: yzhil@cepu.edu.c Published by Elsevier Ltd. Selectio ad peer-review uder resposibility of Desheg Dash Wu. Ope access uder CC BY-NC-ND licese. doi:0.06/j.sepro

2 90 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 (202) Fault diagosis systems are relatively ew ad are flourishig o a rapid scale i wid eergy techology, especially for the developmet of large-scale wid turbies. Barszcz presets the applicatio of the spectral kurtosis techique for detectio of a tooth crack i the plaetary gear of a wid turbie[6]. Tag presets a wid turbie fault diagosis method based o the Morlet wavelet trasformatio ad Wiger-Ville distributio[7]. Jiag applied a ew deoisig method based o adaptive Morletwavelet ad sigular value decompositio (SVD) to feature extractio for wid turbie vibratio sigals[8]. Hussai proposed a ovel method for real time fault detectio i gearboxes by usig adaptive features extractio algorithm to deal with o-statioary faulty sigals[9]. This paper applies the fault diagosis system o wid turbie gear box, i order to make timely, accurate diagosis for gear box ad provide timely solutios. I this way, it ca ot oly meet the requiremets of rapid respose to wid turbie fault diagosis, but also prevet the emergece of huma error, the valuable experiece of experts ca be retaied to prevet lost, too. Fault tree aalysis is a ituitive, clear, logical, ad applicable system compares to the relatively simple oes. The gear box of wid turbie has less hierarchical structure, so fault tree is used to aalyze the compoet faults ad express their reasos, ad a expert system based o fault tree aalysis is chose to make diagosis o wid turbie gear box i this paper. 2. Fault Tree of Gear Box i Wid Turbie 2.. Fault Tree Aalysis Fault tree aalysis is a graphical iterpretatio method which ca refie the system fault causes from whole to part by dedrite progressively. It is also a importat method of aalyzig system reliability ad safety. Fault tree is draw through aalyzig a variety of factors (icludig hardware, software, eviromet, huma factors, etc.) which should cause system fault, refiig system fault evet from whole to part by dedrite progressively, idetifyig the cause of system fault, determiig the probability of fault, ad evaluatig the importat degree related to the cause[0]. Fault tree model is a behavior ad qualitative causal model based o studyig the structure ad fuctioal characteristics of fault. The top evet is the evet which is to be avoided firstly. The basic evets are those ca cause top evet while the itermediate evets are the odes. Fault tree is a dedritic logic diagram which shows relevace betwee evets by usig logic gates. As show i Fig.. System fault or Module A fault Module B fault or ad C C2 C3 C4 Fig. Fault tree diagram

3 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 ( 202 ) I Fig., the top evet is system fault caused by itermediate evets of compoet A fault or compoet B fault. Compoet A fault is caused by basic evet of part fault or part 2 fault. The basic evets of part 3 fault ad part 4 fault happe will cause the compoet B fault Fault Tree of Gear Box i Wid Turbie From the curret structural characteristics of gear box i wid turbie ad its actual fault coditios, faults usually occur i parts such as gears, shafts, bearigs ad box. But i order to perfect the fault tree, fasteer fault ad oil seal fault are added to the fault tree. I the fault tree of gear box, wid turbie gear box fault is the top evet; the itermediate evets iclude gear fault, shaft fault, bearig fault, the box fault, fasteers fault, seals fault ad other evets which ca be further refied; the damage of parts or improper operatio is take as the basic evet. As fault of ay compoet of the gear box will cause a system fault, the mai logical relatioship betwee the fault is "or". The fial fault tree is show i Figure 2(M stads for itermediate evet, while C stads for basic evet). Wid turbie gear box fault Gear fault fault Bearig fault Box fault Fasteer fault Seal fault... M C C2... misaligmet bedig loose C3 C4 C5 C6 C7 C8 C9 C0 C0 C assemblig error deformatio Ueve settlemet Bearig wear or deformatio Box wear or deformatio w w2 w3 w4 w5 Uequal selectio Improper placemet Heatig less Speed too fast Load too large Fig.2 Wid turbie gear box fault tree diagram I order to get a exteded fault tree, auxiliary iformatio icludig the weight ad solutio of fault is added to each basic evet. Fig.2 oly shows correspodig weight of itermediate evet M3. The relatioship of weights is: () I which, ω i stads for the correspodig weight of basic evet C. Fially the diagostic kowledge base is obtaied by usig productio rules to put the fault tree iformatio ito kowledge base []. Accordig to the diagostic kowledge base, ot oly the specific locatios ad causes of fault ca be obtaied, but also the referece solutio ca be give by experts.

4 92 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 (202) Fault Aalysis Based o Fault Tree 3.. Qualitative Aalysis The task of qualitative aalysis is to idetify the possible causes of system top evet fault, or to fid out the miimal cut sets of the fault tree [2]. The method of fidig the miimum cut set is maily upstream ad dowstream. Accordig to logical relatioship betwee faults of gear box i wid turbie, this paper adopts dowstream. The idea of dowstream is: accordig to the two adjacet terms i the fault tree, logic "or" gate icreases the umber of cut sets ad logic "ad" gate icreases the capacity of the cut set [3]. Startig from the top evet, the cut sets of fault tree is obtaied by replacig the previous evets ito the ext level evet, writig evet vertically whe meetig "or" gate, util the gates are all coverted ito the top evet. Fig. 3 shows the miimal cut sets are gotte by qualitative aalysis which take the gearbox fault, axis fault ad axis bedig as the mai lie. The miimal cut sets of other compoets fault ca be obtaied by the same method. Due to the structural characteristics of gear box, the resultig cut sets are all the miimal cut sets, which are {C},{C2},{C3},{C4},{C5},{C6},{C7},{...}. Miimal cut sets are idepedet of each other. Gear fault Uequal selectio Bearig fault misaligmet Improper placemet Gear box fault fault bedig Heatig less Box fault loose Speed too fast... Load too large. Fig.3 Qualitative aalysis of gear box fault 3.2. Quatitative aalysis After obtaiig all miimal cut sets, if there is eough data which ca support iferrig probability of each basic evet, the further quatitative aalysis ca be made [4]. The mai purpose of quatitative aalysis is to fid the characteristic quatities of the top evet (such as the top evet probability ad system reliability) ad the importace of the basic evet, which ca determie the weakesses i the system. ) Calculate the probability of top evet The probability of occurrece of top evet with "ad" gate ca be calculated by followig formula: px ( ) = px ( i) = px ( i) The probability of occurrece of top evet with "or" gate ca be calculated by followig formula: px ( ) = px ( ) = [ px ( )] i i (2) (3)

5 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 (202) I which, p(x) is probability of the fault tree top evet, p(xi) is probability of the i-th miimal cut set of fault tree, is the total umber of fault tree miimal cut set. 2) Importace aalysis of basic evet Importace aalysis is to aalyze the cotributio of fault, which occurred i the miimal cut sets of a compoet, to the probability of top evet. Probability importace degree of basic evet describes the extet of probability chage of top evet caused by the probability chage of i-th basic evet fault, which is expressed by the formula as follow: p( x) Ii ( x) =, i =... p( xi ) (4) Ii(x) is probability importace degree of i-th basic evet, p(x) is probability of the tree top evet fault, p(xi) is probability of the i-th miimal cut set of fault tree, is the amout of miimal cut set i the fault tree. 4. Expert System of Fault Diagosis O the basis of fault tree aalysis for gear box, a Web-orieted expert system for fault diagosis of gear box is developed. The system is desiged to have three grades, icludig symptoms page, fault causes page, solutios page. After eterig the system, the default page is a symptoms page. As show i Fig. 4. Fig.4 Qualitative aalysis of gear box fault This system is developed by C# o the.net platform. The overall framework of the system is as show i Fig. 4. Accordig to the structural of the gear box, the left side of page is made to accordio style, i which the six compoets fault of gear box are defied to the category ame; the right side of the page defaults symptoms page, i which the previous colum of symptoms colum displays correspodig fault category ad the ext colum liks possible causes. ) To query fault symptom I the symptoms page, the user ca query page by page or do fuzzy query by writig keywords i the search box, ad click the search butto to get the results you wat. 2) To query reaso of fault

6 94 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 (202) The user ca get correspodig possible causes of fault symptom by clickig o the details lik of possible cause colum i the above list. They ca also directly click o the correspodig fault symptom i accordio structure to get a list of correspodig reasos. The query result is ordered by the weight of reaso ad the reaso whose weight is large is sorted i the top of the list. 3) To query solutio of fault After gettig the list of fault reaso, the user ca click o the details lik of solutio colum to get the recommeded solutio give by expert. Recommeded solutio will be ordered from top to bottom, if there are multiple. Maiteace staff ca choose differet solutios accordig to the circumstaces. 5. Coclusio Gear box is oe of the key compoets of wid turbie, whose fault will directly affects the safety ad the operatio of the overall wid turbie. This paper develops a expert system of fault diagosis for gearbox i wid turbie based o fault tree aalysis. With the gradual accumulatio of fault ad repair istace about wid turbie gear box, the expert system based o fault tree aalysis will play a better role i the fault diagosis of wid turbie gear box. Ackowledgemets This study is supported by the Fudametal Research Fuds for the Cetral Uiversities (09MG23). Refereces []WANG Yi, FENT Xiaoyu. Electric locomotive fault diagosis expert system based o fault tree. Electric Locomotives & Mass Trasit Vehicles 2004; 27: [2]Jia-Da Wu, Chiu-Hog Liu. A expert system for fault diagosis i iteral combustio egies usig wavelet packet trasform ad eural etwork. Expert Systems with Applicatios 2009; 36: [3]Yaguo Lei, Mig J. Zuo, Zhegjia He, Yayag Zi. A multidimesioal hybrid itelliget method for gear fault diagosis. Expert Systems with Applicatios 200; 37: [4]N. Saravaa, V.N.S. Kumar Siddabattui, K.I. Ramachadra. A comparative study o classificatio of features by SVM ad PSVM extracted usig Morlet wavelet for fault diagosis of spur bevel gear box. Expert Systems with Applicatios 2008; 35: [5]N. Saravaa, S. Cholairaja, K.I. Ramachadra. Vibratio-based fault diagosis of spur bevel gear box usig fuzzy techique. Expert Systems with Applicatios 2009; 36: [6]Tomasz Barszcz, RobertB Radall. Applicatio of spectral kurtosis for detectio of a tooth crack i the plaetary gear of a wid turbie. Mechaical Systems ad Sigal Processig 2009; 23: [7]Baopig Tag, Weyi Liu, Tao Sog. Wid turbie fault diagosis based o Morlet wavelet trasformatio ad Wiger-Ville distributio. Reewable Eergy 200; 35: [8]Yoghua Jiag, Baopig Tag, Yi Qi, Weyi Liu. Feature extractio method of wid turbie based o adaptive Morlet wavelet ad SVD. Reewable Eergy 20; 36: [9]Sajid Hussai, HossamA.Gabbar. A ovel method for real time gear fault detectio based o pulse shape aalysis. Mechaical Systems ad Sigal Processig 20; 25: [0]ZHU Xueju,CHEN Yu. The research of itelliget fault diagosig methods based o FTA. Microcomputer Iformatio 2005; 2(6): []YANG Bi,DING Hui,LUO Weimi,ZHANG Xiaofei.( 2002) Expert system of trasformer fault diagosis based o kowledge, Proceedigs of the CSEE, 22(0): 2-24.

7 YANG Zhi-Lig et al. / Systems Egieerig Procedia 4 (202) [2]YU Aihua. Fault tree aalysis ad applicatio to hydraulic system maiteace. Hoistig ad Coveyig Machiery 2006; 6: [3]CHEN Yogwag. Applicatio of fault tree aalysis method i fault diagosis for 6V280 diesel egie fuel system. Mechaical Research & Applicatio 200;2(3): [4]SHI Dighua,WANG Sogrui. Fault tree aalysis methods ad theories. Beijig Normal Uiversity Press 993:.

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