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Thesis
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Diagnosticarea şi monitorizarea sistemelor de izolaţie ale transformatoarelor de putere
Bădicu, Laurenţiu-Viorel
2011-10-17
Abstract: ABSTRACT Necesitatea extinderii duratelor de exploatare si reducerii cheltuielilor de mentenanta au condus la cresterea interesului cu privire la monitorizarea si diagnosticarea transformatoarelor de putere. Mai mult, s-a constatat ca o atentie deosebita trebuie acordata starilor sistemelor lor de izolatie – pe baza de hartie celulozica si ulei mineral – deoarece acestea reprezinta cauza principala de defectare a transformatoarelor. Starile sistemelor de izolatie ale transformatoarelor de putere (SITP) pot fi evaluate prin mai multe metode de natura electrica, chimica, acustica etc. In ultima perioada s-a pus din ce in ce mai mult accent pe utilizarea metodelor electrice. In lucrarea de fata sunt prezentate doua metode de monitorizare pe baza masurarii on line a curentilor de absorbtie si resorbtie (CAR) si analiza curbelor lor de variatie in timp precum si a conductivitatii electrice/rezistivitatii de volum, componentelor permitivitatii relative complexe si factorului de pierderi dielectrice. Aceste marimi reprezinta importanti factori de diagnostic utilizati la evaluarea starilor SITP fiind puternic influentati de concentratia de apa, oxigen, acizi, temperatura de functionare si starea de imbatranire a hartiei si uleiului mineral. Rezistivitatea de volum a fost aleasa drept factor de diagnostic pentru determinarea duratei de viata a SITP prin intermediul unei metode bazate pe masurarea energiei de activare corespunzatoare reactiilor principale de degradare a hartiei si uleiului. Aceasta metoda ofera rezultate in intervale de timp mult mai scurte decat metoda clasica bazata pe imbatraniri termice accelerate in laborator utilizata in prezent. Mai mult, conform ghidurilor de incarcare in sarcina au fost determinate duratele de viata consumate si rezervele de durata de viata corespunzatoare sistemelor de izolatie ale transformatoarelor de putere. Metodele de monitorizare prezentate in lucrare permit evaluarea on line a starilor SITP eliminand necesitatea deconectarii transformatoarelor si permitand stabilirea momentului optim de retragere a acestora din serviciu, atunci cand pericolul defectarii este maxim. Aceste metode au fost implementate pe un echipament de monitorizare si diagnosticare a starilor transformatoarelor de putere in care a fost instalata celula de masurare on line a CAR. Astfel, se pot obtine informatii on line, si anume, concentratia de apa atat din ulei cat si din hartie, valoarea conductivitatii electrice/rezistivitatii de volum a izolatiei principale (hartie-ulei) și chiar se poate face evaluarea calitativa a evolutiei principalilor produși de reactie dizolvati in uleiul transformatorului, iar pe baza standardelor in vigoare se poate stabili cu exactitate starea transformatorului. De asemenea, echipamentul dispune de o aplicatie software pentru prelucrarea rezultatelor si stabilirea operatiilor necesare de mentenanta. ABSTRACT The necessity to extend the lifetime of power transformers and to reduce the costs and investments due to maintenance led to an increase of interest concerning the monitoring and diagnosis of power transformers. In addition, it was noticed that a high attention should be given regarding the condition of their insulation systems – based on cellulosic paper and mineral oil – because they are the main cause of transformers failure. The condition of power transformers’ insulation systems (SITP) can be assessed by electrical, chemical, optical methods etc. Lately, the electrical methods are more and more used. In this paper, two monitoring methods based on measurements of absorption and resorption currents (CAR) are presented. The two methods consist in the analysis of the CAR time variation curves and electrical conductivity/volume resistivity. Also, the methods involve the values of the components of complex relative permittivity and dielectric loss factor. These quantities are important diagnostic factors used to assess the SITP condition due to the fact that they are strongly influenced by water content, operation temperature and ageing condition of both mineral oil and paper. The volume resistivity was chosen as a diagnostic factor for SITP lifetime estimation, using a new method based on the activation energy measurement corresponding to the main degradation reactions of the oil and the paper. This method allows the recording of the results in a shorter period of time in comparison with the classic method based on accelerated thermal ageing. Additionally, the loss of life and the remaining lifetime of the power transformers’ insulation systems were determined based on the loading guides for immersed transformers. The proposed monitoring methods, based on CAR measurement, ensure the on line character of SITP condition assessment and allow knowing the optimal moment in time when the transformer must be taken out of service before failure. These methods were implemented on a monitoring and diagnosis equipment. Also, part of this equipment is the on line test cell of CAR measurements. Therefore, important on line information can be obtained, such as the values of oil and paper water concentration, of electrical conductivity/volume resistivity of the main insulation (the insulation between the high voltage and low voltage windings) and even the evolution information of other reaction products (gases, acids etc) which are dissolved in the oil. Next, based on available standards, the condition of the whole transformer can be assessed. A special software was also built in order to analyze the results and to provide the required maintenance operations.
Keyword(s): Transformatoare de putere -- Diagnoză tehnică -- Teză de doctorat ; Materiale izolatoare -- Teză de doctorat
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Record created 2017-03-07, last modified 2017-03-07
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