An algorithm for prioritizing the maintenance of power transformers

Transcription

1 Eergy Productio ad Maagemet i the 21st Cetury, Vol A algorithm for prioritizig the maiteace of power trasformers I. V. Davideko & E. D. Halikova Ural Power Egieerig of Ural Federal Uiversity, Russia Abstract This report presets a algorithm that takes ito accout power trasformer (PT) techical coditios ad their potetial for failure risk assessmet to help determie maiteace precedece. The techical coditio itegrated idex is assessed through the weighted average of coditio idexes determied by the results of PT traditioal ad special cotrol methods. Each cotrol type idex is the three-dimesioal space vector where the coordiates are ext: X damage seriousess, Y damage developmet speed, Z damage developmet duratio. The traditioal cotrol method defect idetificatio ad coordiate determiatio are carried out by a expert system without ay specialist participatio. Risk failure assessmet icludes: damages of suppliers ad to cosumers of electricity; trasformer desig features; lifetime; ES trasformer uit (system) failure potetial. The PT uit failure potetials were calculated usig the flows of failures ad damage statistics of 350 reliable facts of PT damage accumulated by the ES for 20 years of operatio. Firstly, priority rakig for serviceable trasformer operatioal activities are excluded from the sample. The there are calculated coordiates o each of the remaiig trasformers. It coordiates the poits, which are marked by the PT plae. The plae icludes three zoes: additioal scheduled ispectios ad emergecy repairs. The ES raks PT by the distace from the origi withi each zoe. Keywords: power trasformers, prioritized maiteace activities, assessmet of techical coditio, probability damage, risk of failure, weight idexes. 1 Itroductio Every eterprise has fiacial, persoel ad time resource limitatios. The ecessary volume of techical service ad maiteace (TSM) frequetly doi: /eq140331

2 336 Eergy Productio ad Maagemet i the 21st Cetury, Vol. 1 exceeds the available compay resources. Therefore the questio of TSM actios order icludig equipmet chage is rather importat for every compay. The urgecy of correct decisios icrease because it becomes more difficult to provide the ecessary reliability of equipmet work i the coditios of prevailig equipmet ageig over reovatio. Furthermore, with the implemetatio of ew techologies ito the productio, cosumers lay fiacial claims to the low quality ad ureliable eergy supply agaist compaies. This report presets the solutio of choosig order of ecessary actios that takes ito accout the rakig of power trasformer (PT) o techical coditios ad possible cosequeces of their failures. The give algorithm ca be applied to differet types of equipmet but i this report we pay attetio to PT. The algorithm is the twety-year result of developmet ad implemetatio of expert-diagoses ad iformatioal system (EDIS) Albatros ad the statistic collectio of damaged equipmet. At preset the system EDIS is used at 367 workplaces i Russia ad States of the former Soviet Uio. There are collected more tha 350 cases of PT damage developmet proved by the equipmet usealig i databases. 2 Russia experiece of power trasformers rakig o techical coditio I the article [1] it was offered to coduct PT rakig with the help of high qualified experts. They determie the ecessary set of cotrollable parameters for PT expert-diagostics. Next, the experts with high experiece of aalog work coduct rakig of PT rage o the basis of expert-diagostics results accoutig characteristics of trasformer costructio ad assessmet of quality level ad coditios of operatio. The advatages of this approach are record of characteristic costructio, level ad coditio of PT operatio. Ufortuately, there are ot eough high qualified specialists ad that is why this approach is ot rather efficiet ad does ot allow ecompassig the etire equipmet rage of Russia. Besides, a expert approach is more expesive tha PT computer rakig. I the report [2] icluded the ew methodology which couted the idex of PT techical coditio as rated sum criteria values of equipmet uit multiplied by their weight idexes. i K V V M 100, where K criterio value; V weight idex; M maximum criterio value. Methodology covered the rage of basic parameters for the PT assessmet. The criterio with udefied value was ot take ito accout either i the umerator or i the deomiator of the formula 1. The assessmet of PT techical coditio idex had to iclude test results, the load modes, uit (1)

3 Eergy Productio ad Maagemet i the 21st Cetury, Vol coditios lifetime ad the possible cosequeces i the case of a accidet. Durig data assessmet by experts, 5 level criterio values were used: very good, good, satisfactory, below satisfactory; poor. The determiat factors of techical coditio idex were the test results, which were system assessed at 3-step scale. Disadvatages of this approach: Simplicity of the model ad therefore its iadequacy to such a complex obect as PT; The eergy compay expert must participate i the parameters assessmet that reduces efficiecy ad eutrality of the PT rakig because of possible mistakes ad low expert qualificatio; A formal approach to the parameters assessmet of exceedig their maximum acceptable values that leads to the 1st ad 2d type errors; Igorig lack of iformatio (the less parameters are assessed, the better techical coditio idex). I 2012 i the report [3] it was proposed to calculate the techical coditio idex of the multi-compoet obect, as the weighted average umber of idices of the coditio of hardware compoets. Weight idices that are take with other compoets i the calculatio of the coditio idex of multicompoet obect are defied by the expert aalysis o the compoet importace for the multicompoet obect fuctioig. Thus, to calculate the coditio idex of multicompoet obects we use the ext formula: I imo i W i i W I i where I imo coditio idex of multicompoet obect; W i i compoet weight; I i i compoet coditio idex. Thus, each maor uit was give its weight idex ad the coditio idex was calculated for each of these uits. At preset the methodology is ot implemeted i corpore. Techical coditio idex is calculated o the basis of PT measuremets itself, excludig coditio idices of its high-voltage bushigs ad tap-chager ad other uits. Firstly techical coditio idices are calculated for each type of measuremet, ad the there is calculated (2) the resultig idex. The calculatio icludes all measuremets types regulated by maagemet directive (MD) [4] for power trasformers, without remoteess limitatio of their executio. Disadvatages of this approach: i, (2) A formal approach to the cotrolled parameters of exceedig their maximum acceptable values uder the RD [4], igorig most parameters treds ad the PT costructio characteristics that leads to the 1st ad 2d type errors;

4 338 Eergy Productio ad Maagemet i the 21st Cetury, Vol. 1 igorig the fact that the measuremet results that were carried out several years ago, may ot reflect the curret techical coditio of PT; Igorig the results of special diagosis methods (e.g. vibratio ispectio, partial discharges measuremet). 3 The assessmet of the techical coditio of the power trasformer The peculiarity of proposed assessmet of PT techical coditio is that durig the calculatig of techical coditio idex of Im obect is used the assessmet output of expert system ( EDIS Albatros ), but ot the evaluatio of cotrolled parameters themselves [5]. The aalysis of the EDIS measuremets results cosists of two stages: the assessmets of cotrolled parameters values ad their treds; type defect idetificatio ad evaluatio of its developmet. For performig the 1st diagosis stage EDIS uses 2 levels of values (permissible ad maximum permissible) for all cotrolled parameters ad their treds. These assessmet criteria were derived by system developers durig te-year research work. As the derived criteria parameters assessmets ad their treds (i cotrast to [4]) are differetiated o desig features ad PT lifetime, it reduces the 1st ad 2d type errors. Next we will show the importace of techical coditio idex for Im 2d stage diagosis determiig. Imagie that there is exceedig of regulated values for two PTs for the followig gases cocetratios: C 2 H 6, C 2 H 4, C 2 H 2. But oe trasformer has gas pairs ratio C 2 H 6 /C 2 H 4 ad C 2 H 2 /C 2 H 4 diagosed as low heat ad i the other as arc. It is obvious that PT are i differet techical coditios, but from the methodological poit of view [2,3] the techical coditio idex of these trasformers o DGA results will be the same. I additio, we propose to take ito accout the speed ad defect developmet duratio i the assessmet of the techical coditio idex. Summarizig the foregoig facts, we propose to calculate the techical coditio idex as a vector of -dimesioal space, where m is the umber of measuremet types. Im 1 x M y max 2 1 z 2 100%, (3)

5 Eergy Productio ad Maagemet i the 21st Cetury, Vol where M max the maximum vector legth of i dimesio; the measuremets umber. I tur, each measuremet idex is represeted by a vector, which is the evaluatio result of a 3-coordiate (x, y, z): x the idex of heaviess assessmet, the defect dager. The idex value depeds o the defect type that is idetified by EDIS; y the idex of speed assessmet of defect developmet. The idex depeds o the treds assessmet of cotrolled parameters ad determiatio of defect type coducted by EDIS; z the idex of workig period assessmet ad duratio of defect developmet observatio. The idex depeds o the coducted ad recommeded by EDIS TSM operatios, as well as legth of defect developmet observatio. For differet measuremets values M max, x, y, z are differet, because measuremets have differet sesitivity degree ad accuracy of defect idetificatio. Coditio assessmet made by other programs with special methods (vibratio ispectio, low-voltage pulses, PD cotrol ad thermal cotrol), are fed ito the system by experts. EDIS Albatros aalyzes each PT accordig to the followig iformatio: aalysis of gases dissolved i oil (DGA); physico-chemical oil aalysis, icludig surface tesio ad oil isulativity, its clarity, color ad Vrmaa idex; the moister cotet of solid isulatio ad degree of its polymerizatio; isulatig characteristics of solid isolatio; widigs ohm resistace; short-circuit resistace; coducted ad plaed TSM operatios; descriptio of the exteral iflueces o the equipmet, coditios ad work modes; lifetime ad costructio features of the equipmet. Thus, EDIS diagoses each type of measuremet accordig to the supposed defect ature, the degree of its developmet ad, if possible, its localizatio. Moreover, the system makes recommedatios to the persoel for further work, takig ito accout the diagosis result ad history of trasformer operatio as a set of TSM operatios icludig additioal tests. The idex values (x, y, z) for each type of measuremet (icludig for special kids of measuremets), diagosis, maiteace ad TSM operatios ad others are stored i the database of EDIS. They were determied by expert evaluatio durig the algorithm creatig.

6 340 Eergy Productio ad Maagemet i the 21st Cetury, Vol. 1 4 Risk assessmet of power trasformer failure The specific feature of the proposed risk assessmet failure of PT is that it is examied the cosequeces of failure both for the provider ad cosumer of electricity. Also, there are take ito accout equipmet costructio features, its lifetime, probability of failure ad the supposed place (uit, system) of PT damage. Failure probability of PT uits was calculated by values of failure flows of trasformers ad the statistics of their defectiveess. The calculatio was based o more tha 350 reliable damage facts of kV PT accumulated by EDIS Albatros for 20 years of its operatio i the power compaies of the Russia Federatio. Assessig the risk of PT failure it is desirable to take ito accout the potetial ecoomic, evirometal, social cosequeces ad possible huma losses, compay's image deterioratio, lost profit of provider ad cosumer of electricity, the duratio ad cost of repairs, operatig coditios, the cosumer category. I practice to take all these factors ito accout is ot possible due to lack of (privacy) fiacial iformatio. Aimig at the retetio of comprehesive approach to the assessig of trasformer risk failure we propose to calculate the risk by the followig formula: 1 H Pk U Pmax P (4) k Pk 1 Pk Urepair N K heatt off Crate Ucos, V V Pmax where H risk; P k probability of k uit damage; ΣU total loss; N power trasformer power; ΔU repair = U urget U plaed the price differece betwee repairs of differet urgecy; K heat load idex; t off iterruptig time of eergy supply; C rate the rate for cosumer; V the umber of backup lies; U cos fiacial cosumer claims at power failure (e.g. due to the productio loss, break of the techological cycle, etc). Determiig probability of PT failure authors pay attetio to several importat factors. First, you eed to take ito accout that the flow size of PT damage chages with the operatio time of trasformer. Based o the aalysis of damage flows depedece o the trasformer lifetime, we sigled out five periods: the ruig-i period, the oe of high reliability, mid-life ad overhauls oes, the after recovery oe ad the period of rapid loss of residual efficiecy. Secod, it is essetial to remember of PT costructio features, for example class voltage. It is kow that PTs with high voltage classes have higher failure probability. Furthermore, the PTs of differet voltage classes have differet costructio weakesses. For example, for PT 35 kv are highly typical damages associated with dyamic widig istability ad for PT 110 kv damages of tap chager ad bushigs [5]. Tap chager of PT kv are rarely damaged. Third, calculatig the risks it must be take ito accout that PT systems ad uits are damaged with differet frequecy. The ext formula is used for calculatig the probability of trasformer uits failure:

7 Eergy Productio ad Maagemet i the 21st Cetury, Vol P k = N k F, (5) where P k failure probability of trasformer k uit %; N k k uit damage frequecy (%); F the value of failure flow depedig o the trasformer age. Based o the failure flow values of PT failures ad statistics of their defectiveess [5] were calculated probabilities of idividual uits. Table 1 shows the calculatio results of damage probability of PT idividual uits for differet ages ad voltage classes obtaied by the authors. Table 1: The probability of various uits damage of kV trasformers with differet lifetimes. 35 kv 110 kv 0-5 years years 0-5 years years Widig ad isolatio 1.03% 0.78% 1.41% 0.93% Tap chager 0.51% 0.39% 0.40% 0.56% Bushigs 0.26% 0.00% 0.40% 0.26% Core 0.00% 0.00% 0.10% 0.11% Oil protectio system 0.00% 0.00% 0.00% 0.13% Tak ad fittigs 0.00% 0.00% 0.00% 0.08% Coolig systems 0.51% 0.91% 0.00% 0.03% The data i Table 1 illustrates the eed i differetiatio durig PT risk assessmet the damage probability depedig o the operatio period, the class voltage ad uit. The calculatio was based o the 339 damage facts of PT kV accumulated by the database EDIS Albatros durig its operatio. The sample reliability is quite high, because every damage fact was examied by experts o the result compliace of techical coditio assessmet accordig to descriptio measuremets of detected damage durig PT usealig. Thus, the assessmet of PT risk failure is performed by EDIS Albatros by the formula 3. Firstly expert system o the base of PT measuremets evaluates techical coditio ad idetifies the proposed damage locatio (uit ). The the system chooses the appropriate probability Pk value from the database depedig o the PT age, class voltage ad the supposed damage place. 5 Algorithm of trasformers rakig o the order of TSM operatios For PT rakig o the sequece of TSM operatios from the sample of cosidered trasformers are excluded obects that are i good coditio. The, the itegral idicator of Im techical coditio ad its risk failure Hm are calculated for each remaiig i the sample obect.

8 342 Eergy Productio ad Maagemet i the 21st Cetury, Vol. 1 These coordiates (Hm; Im) idicate the obect o the graph show i Figure 1, where the ordiate axis shows techical coditios idicator, ad the abscissa the risk amout. Next system EDIS coducts trasformers rakig o the distace from the poit with coordiates (Hm; Im) to the poit (0, 0). The greater the distace, the more eed of TSM operatios. Figure 1: Example of displayig the rakig results of EDIS Albatros. The graph is divided ito three zoes: additioal ispectio ( there is developig defect i the trasformer, it is take uder frequet cotrol ad additioal test ca be assiged to clarify the defect ature ad its localizatio); curret repairs ( there is a defect i the trasformer but ot hiderig its efficiecy ad requirig routie repairs); emergecy repairs (there is a defect i the trasformer, which will soo lead to the loss of its fuctioality ad requirig mid-life or overhaul repairs or equipmet replacemet). Figure 1 shows us that the areas vary greatly i the umber of PT, that are marked. This distributio, obtaied by system EDIS, correspods to the data give i the reports of egieerig ceters i Russia, i the percetage of PT requirig immediate withdrawal of work, curret maiteace ad additioal ivestigatio. If trasformers have the same coordiates (Hm; Im), the idicator of costly maiteace is used to determie the order. The idicator of costly maiteace is the specific cost of PT service of homogeeous group for the give power compay. Homogeeous group icludes idetical trasformers i costructio features, close terms of lifetime ad quality of materials ad maufacturig techologies. Primarily TSM operatios are carried out for such PTs which service costs more for a eergy compay.

9 Eergy Productio ad Maagemet i the 21st Cetury, Vol Coclusios I the paper the algorithm for rakig PT o the order of TSM operatios based o their techical coditio ad assessmet risk of failures was proposed. This algorithm was verified i practice. Beefits of the proposed algorithm i terms of assessig the techical coditio of PT are the followig: techical coditio is calculated by the system without huma participatio; i idex calculatig are used ot the marks of cotrolled parameters but system diagoses; idex calculatig uses system recommedatios accoutig the history of the damage developmet ad coducted TSM operatios. Beefits i terms of risk assessmet of PT failures are the followig: There are examied failure cosequeces both for the provider ad cosumer of electricity; probability of failure is selected o the basis of techical coditio assessmet with supposed defect(s) ature ad place of its developmet; failure probability depeds o the lifetime ad class voltage. Oe of the bottleecks i the evaluatio of risk failure is the lack of iformatio about the fiacial claims of cosumers, as well as the accuracy of the iformatio about the losses of eergy compaies. Usig the proposed algorithm, icludig the structure of the iformatioal ad aalytical systems i eterprises operatig with PTs i egieerig ceters ad maiteace orgaizatios will icrease efficiecy ad eutrality, reduce error of maagemet operatio, which i tur will reduce the risks of eterprises, ehace the lifetime ad reliability of trasformers. Refereces [1] Sokolov V.V. The ew methodology of trasformers equipmet diagosis with rakig o the techical coditio. VIII Collected book, Symposium of electrical techology 2010 (Travek), May, [2] System of strategic plaig repairs. PC FNC FGCˮ. Methodology of expert evaluatio of the equipmet techical coditio. Versio 0.3. Moscow [3] Methodology of techical coditio evaluatio of the mai etwork equipmet. Appedix 1 to the model stadard PC IRNC Holdig Compayˮ of maagemet of idustrial assets of subsidiaries ad affiliates. Moscow, 2012.

10 344 Eergy Productio ad Maagemet i the 21st Cetury, Vol. 1 [4] MD Cotet ad stadards for electrical equipmet testsˮ, M., publisher SC ENAS, [5] Davideko I.V. Doctoral thesis Developmet of multiple-aspect system of techical coditio assessmet ad servicig of high- oil-filled electric equipmet [6] Davideko I.V., Ovchiikov K.V., Khalikova E.D., Questios of aalysis reliability of trasformer equipmet kv Jue 2013 Moscow Iteratioal Associatio Travek, VEI. Report 1.18 Magazie EergoIfo. 2013, 9. pp