Metodologija eksperimentalnoga istraživanja dielektričkih naprezanja u uljno-barijernoj izolaciji transformatora

doctoral thesis

• Title (english): Methodology of experimental research of dielectric stress in oil-barrier transformer insulation
• Author: Petar Gabrić
• Mentor: Damir Ilić (mentor)
• Mentor: Antun Mikulecky (komentor)
• Committee member: Damir Ilić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; (Department of Electrical Engineering Fundamentals and Measurements); Zagreb
• Defense date and country: 2017, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering; Electromechanical Engineering
• Universal decimal classification (UDC): 621.3 - Electrical engineering

Abstract

Vijek trajanja i pouzdanost rada energetskih transformatora u pogonu u najvećoj mjeri određuje stanje izolacijskog sustava transformatora, a transformator može biti u pogonu sve dok izolacija transformatora može izdržati naprezanja. U ovom radu istražuje se glavna izolacija transformatora, odnosno uljno-barijerni izolacijski sustav. Priznata i provjerena teorija proboja uljnih kanala ne postoji pa se kriteriji za dimenzioniranje izolacije temelje na ispitivanjima modela izolacije i iskustvu. Istraživanje prema kojem se danas često dimenzionira glavna izolacija transformatora proveo je Kappeler prije više od 50 godina. Istraživanje je provedeno u homogenom el. polju, s papirom izoliranim elektrodama, u otplinjenom i naplinjenom ulju, za širine uljnih kanala od 0,5 mm do 6 mm. Danas se Kappelerovi rezultati ekstrapoliraju i za širine uljnih kanala veće od 100 mm, a opravdanost ovakve ekstrapolacije nije dokazana u literaturi. U ovom radu predložen je i eksperimentalno potvrđen koncept za istraživanje podnosivih dielektričkih naprezanja u uljno-barijernom izolacijskom sustavu transformatora, tj. predložen je postupak proširenja Kappelerovih istraživanja na uljne kanale širine do 30 mm. Definirana je fizička izvedba modela s papirom izoliranim elektrodama, pogodna za istraživanje uljno-barijerne izolacije, koja ne pokazuje problem „ranog“ nastanka parcijalnih izbijanja. Predložen je postupak visokonaponskog ispitivanja modela izolacije koji se temelji na cenzuriranju, tj. zaustavljanju ispitivanja bez pojave PI ili proboja, i postupak statističke obrade eksperimentalnih rezultata koji rezultira zadovoljavajućom točnošću procjene parametara matematičkog modela podnosivih naprezanja kod jednominutnog ispitivanja AC naponom. Procijenjena je mjerna nesigurnost eksperimentalnih rezultata detaljnom analizom utjecajnih veličina na mjernu nesigurnost geometrije modela, te analizom utjecaja ispitnog postupka i nesigurnosti mjerenja napona. U konačnici je, ispitivanjem dvaju prototipova modela, provedena eksperimentalna provjera kojom je potvrđena primjenjivost predloženog koncepta istraživanja za definiranje podnosivih naprezanja u uljno-barijernom izolacijskom sustavu.

Abstract (english)

The service life and operation safety of power transformers depend largely on the condition of a transformer insulation system. The transformer can be in service until its insulation system is able to withstand all kinds of service stresses. In this thesis, main transformer insulation (in a form of oil-barrier insulation system) is in focus. Due to a fact that well-proven and widely accepted breakdown theory in liquids has not yet been found, permissible el. stress values in transformer insulation are derived from experimental studies. One of the basic, and the most often applied, experimental results related to AC permissible stress in oil-barrier insulation are Kappeler’s results, published more than 50 years ago. Kappeler performed research in homogeneous el. field, with paper insulated electrodes, in degassed and gas saturated oil, for oil gap widths between 0,5 mm and 6 mm. Nowadays, results of Kappeler research are extrapolated up to 100 mm and more, despite the fact that validation of this extrapolation, according to the authors’ knowledge, is not published in the literature. The aim of this thesis is to present a concept for experimental research of dielectric stress in oil-barrier insulation system. In other words, Kappeler results are checked and extended to the larger oil gap widths (up to 30 mm). The insulation model concept with wrapped paper insulation is defined. In presented model geometry “early PD inception“ problem is not detected, which means the concept is suitable for further oil-barrier insulation research. Also, procedure for high voltage testing of insulation models is proposed as well as statistical analysis approach for experimental research with a small number of insulation models. High voltage testing procedure is based on test censoring (testing is stopped at predefined stress level without PD inception or breakdown registered). Furthermore, experimental results uncertainty is estimated by performing detailed analysis of related influencing factors (uncertainties of model geometry, high voltage testing procedure and voltage measurement). Finally, experimental verification is done by high voltage testing of two model prototypes. Obtained results confirm that proposed model concept is appropriate for experimental research of oil-barrier insulation permissible stress.

• Keywords: transformator; uljno-barijerna izolacija; Kappelerovo istraživanje; model izolacije; proračun faktora sigurnosti; cenzuriranje visokonaponskog ispitivanja; Monte Carlo simulacije; parcijalna izbijanja
• Keywords (english): transformer; oil-barrier insulation; Kappeler research; insulation model; safety factor calculation; censoring of high voltage testing; Monte Carlo experiments; partial discharges
• Language: croatian
• URN:NBN: urn:nbn:hr:168:669787
• Study programme: Title: Electrical Engineering and Computing; Study programme type: university; Study level: postgraduate; Academic / professional title: Doktor znanosti elektrotehnike i računarstva (Doktor znanosti elektrotehnike i računarstva)
• Type of resource: Text
• Extent: 156 str. ; 30 cm.
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2019-04-05 13:21:22