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A Review of Online Partial Discharge Measurement of Large Generators

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A Review of Online Partial Discharge Measurement of Large Generators energies Review AReview Review of Online Partial Discharge Measurement ofA Large Review Generators of Online Partial Discharge Measurement of Large Generators Yuanlin Luo 1,*, Zhaohui Li 2 and Hong Wang 3 1Yuanlin School of Luo Hydropower1,* ID , Zhaohui and Inform Li 2ationand HongEngineering, Wang Huazhong3 University of Science and Technology, Wuhan 430074, China 1 School of Hydropower and Information Engineering, Huazhong University of Science and Technology, 2 State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Wuhan 430074, China Huazhong University of Science and Technology, Wuhan 430074, China; [email protected] 2 State Key Laboratory of Advanced Electromagnetic Engineering and Technology, 3 Three Gorges Hydropower Plant, China Yangtze Power Corporation, Yichang 443002, China; Huazhong University of Science and Technology, Wuhan 430074, China; [email protected] [email protected] 3 Three Gorges Hydropower Plant, China Yangtze Power Corporation, Yichang 443002, China; * Correspondence: [email protected]; Tel.: +86-180-0717-7889 [email protected] Received:* Correspondence: 24 September [email protected];2017; Accepted: 22 October Tel.: 2017; +86-180-0717-7889 Published: 25 October 2017 Received: 24 September 2017; Accepted: 22 October 2017; Published: 25 October 2017 Abstract: Online partial discharge (PD) measurements have long been used as an effective means toAbstract: assess theOnline condition partial of the discharge stator windings (PD) measurements of large generators. have long An been increase used in as the an use effective of PD means online to measurementassess the condition systems ofduring the stator the la windingsst decade ofis evident. large generators. Improvemen An increasets in the detection in the use capabilities of PD online aremeasurement partly the reason systems for during the increased the last decadepopulari isty. evident. Another Improvements reason has been in the the detection development capabilities of digitalare partly signal the processing reason for techniques. the increased In popularity.addition, rapid Another progress reason is hasbeing been made the developmentin automated of single digital PDsignal source processing classification. techniques. However, In addition, there are rapid still progress some factors is being hindering made in automatedwider application single PD of source the system,classification. such as However, the complex there PD are mechanism still some factors and hinderingPD pulse widerpropagation application in stator of the windings, system, such the as presencethe complex of detrimental PD mechanism noise and and PD pulsedisturbances propagation on-site, in stator and windings, multiple the PD presence sources of occurring detrimental simultaneously.noise and disturbances To avoid on-site, repetition and multipleof past work PD sources and to occurringprovide an simultaneously. overview for fresh To avoid researchers repetition inof this past area, work this and paper to providepresents ana comprehensive overview for fresh survey researchers of the state-of-the-art in this area, knowledge this paper presentson PD mechanism,a comprehensive PD pulse survey propagation of the state-of-the-art in stator windings, knowledge PD on signal PD mechanism, detection methods PD pulse and propagation signal processingin stator windings,techniques. PD Areas signal for detection further research methods are and also signal presented. processing techniques. Areas for further research are also presented. Keywords: large generator; stator winding insulation; partial discharge (PD); PD mechanism; propagationKeywords: characteristics;large generator; signal stator detection winding methods; insulation; signal partial processing discharge techniques (PD); PD mechanism; propagation characteristics; signal detection methods; signal processing techniques 1. Introduction 1. IntroductionThe reliability and availability of large generators depends critically on the condition of their stator windingThe reliability insulation, and availability which is ofexposed large generators to a combination depends criticallyof thermal, onthe electrical, condition ambient of their and stator mechanicalwinding insulation, (TEAM) effects, which isi.e., exposed ageing to astresses, combination that contribute of thermal, significantly electrical, ambient to large and generator mechanical failures(TEAM) [1,2], effects, as shown i.e., ageing in Figure stresses, 1. Partial that discharge contribute (PD) significantly is known to as large both generatora main cause failures and [an1,2 ], indicatoras shown of stator in Figure winding1. Partial insulation discharge deficiencies, (PD) is and known thus as is bothefficient a main in indicating cause and insulation an indicator latent of defectsstator and winding faults. insulation PD measurements deficiencies, are and more thus effect is efficientive than in most indicating dielectric insulation measurements latent defects when andit comesfaults. to PD early measurements detection of are sudden more effective faults, and than ha mostve been dielectric applied measurements with a considerable when it comes degree to earlyof successdetection [3–5]. of sudden faults, and have been applied with a considerable degree of success [3–5]. 24% Insulation damage 3% Thermal damage 56% 17% Bearing damage Mechanical damage FigureFigure 1. 1.FailureFailure statistics statistics based based on on data data presented presented in in[1]. [1 ]. Energies 2017, 10, 1694; doi:10.3390/en10111694 www.mdpi.com/journal/energies Energies 2017, 10, 1694; doi:10.3390/en10111694 www.mdpi.com/journal/energies Energies 2017, 10, 1694 2 of 31 Energies 2017, 10, 1694 2 of 32 PD is a localized electrical discharge that only partially bridges the insulation between conductors, accompanied by charge movement, acoustic emission, light radiation and chemical reactionPD isetc. a localized [6]. Utilizing electrical these discharge physical that characteristics only partially bridgesof the PD the insulationprocesses, betweenPD signals conductors, can be accompanieddetected by many by charge methods movement, and systems, acoustic including emission, electrical light radiation detection, and chemicalacoustic reactiondetection, etc. light [6]. Utilizingdetection theseand chemical physical characteristicsdetection method of the[6,7]. PD Among processes, them, PD the signals electrical can beone detected is based by on many the methodsmeasurements and systems, of electrical including signals. electrical It can either detection, evaluate acoustic the global detection, condition light detectionof insulation and system chemical by detectionmonitoring method PD statistics [6,7]. Amongor assess them, the most the deteriorated electrical one site is basedof the in onsulation the measurements through analysis of electrical of each signals.PD pulse, It canand either thereby evaluate has become the global the conditionmost preval ofent insulation detection system method by monitoring [8,9] and the PD focus statistics of the or assessremainder the most of this deteriorated paper. site of the insulation through analysis of each PD pulse, and thereby has becomePD theonline most measurement prevalent detection consists method of two [key8,9] steps: and the PD focus signal of thedetection remainder and interpretation. of this paper. The formerPD can online be implemented measurement at consists the high of voltage two key (H steps:V) or neutral PD signal terminals detection of the and generator interpretation. with Thevarious former sensors can [7,9]. be implemented After that, the at PD the signal high voltageis processed (HV) by or hardware neutral terminals and software of the techniques, generator withincluding various pre-processing sensors [7,9 ].by After hardware that, themodules, PD signal digitization, is processed denoising by hardware by software-based and software techniques,techniques and including subsequent pre-processing PD source by identification hardware modules, using feature digitization, extraction denoising and pattern by software-based recognition techniquestechniques and[9,10], subsequent as shown PD in Fi sourcegure 2. identification Recently, an using increase feature in the extraction use of PD and online pattern measurement recognition techniquessystems is evident [9,10], as [11–13]. shown Improvem in Figure2ents. Recently, in the detection an increase capabilities in the use are of PDpartly online the measurementreason for the systemsincreased is popularity evident [11 [5,13,14].–13]. Improvements Another reason in the has detection been the capabilitiesdevelopment are of partlydigital the signal reason processing for the increasedtechniques, popularity including [ 5various,13,14]. Anothersoftware-based reason hasdenoising been the techniques development which of improve digital signal the reliability processing of techniques,the measurement including results various in the software-based presence of noise denoising and disturbances. techniques whichIn addition, improve rapid the progress reliability is ofbeing the measurementmade in feature results extraction in the and presence single ofPD noise source and classification disturbances. [10]. In However, addition, the rapid report progress [15] provided is being madeby International in feature extractionCouncil of andLarge single Electric PD Systems source classification (CIGRE) indicated [10]. However, that the increase the report is mostly [15] provided caused by Internationaltoo many generators
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