Condition monitoring of biodegradable oil filled transformer

Abstract

Natural and synthetic ester insulating oils have higher fire points and excellent biodegradable characteristics. Therefore, in order to reduce the adverse environmental impact and to improve the fire safety of transformers, there is an increasing demand for natural and synthetic ester insulating liquids as a transformer insulating oil. However, present understanding on ageing behaviour of ester oil-paper composite insulation system and knowledge on application of existing condition monitoring tools for ester based insulation systems are inadequate. This impedes the cost effective and reliable field applications of ester insulating oils, particularly application of natural esters. To reduce this knowledge gap, series of controlled ageing experiments are performed in this research project to provide a better and comprehensive understanding on ageing behaviour of ester oil-paper insulation systems. Furthermore, applicability of existing chemical and electrical based condition monitoring techniques for ester oil-paper insulation systems is systematically investigated in this research project.In this thesis, ageing behaviour of dry pressboard insulation in mineral and three different ester insulating oils under simulated transformer operating environment is investigated. Moreover, the ageing behaviour of natural ester-pressboard composite insulation in moisture rich environment is also compared with that of mineral oil-pressboard system. Degree of polymerisation of pressboard samples measured at different ageing interval is used in this research to determine the ageing condition of pressboard. Moreover, applicability of oil related diagnostic parameters such as concentration of dissolved furanic compounds, acidity value, Dielectric Dissipation Factor (DDF), viscosity and colour to assess the degree of degradation of both ester and mineral insulating oils is thoroughly investigated in this research project. The potential of FTIR (Fourier Transform Infrared spectroscopy) techniques for characterising the degree of degradation of paper insulation is also discussed in this thesis. In addition, this thesis concentrates on characterisation of the charge dynamic in insulating oil through modelling of their dielectric responses.The comparison of gassing behaviour of ester and mineral insulating oils under two different low temperature faults and low energy electric discharge condition is also presented in this thesis.Dissolved Gas Analysis (DGA) results presented in this thesis depicts that faults gases detected in ester and mineral oil samples subjected to a similar fault are akin in type but quantitatively different. The quantity of fault gases produced in two different natural ester oils is also dissimilar.For example, soy-based natural ester produces a large quantity of ethane (C2H6) under low temperature overheating condition than sunflower oil based natural ester. Therefore, this research project investigates the applicability of well-established DGA interpretation schemes namely Duval II | P a g e triangle, IE...

Measurements on pressboard to understand the effect of solid insulation condition on monitoring of power transformer winding clamping pressure

“…A linear multiple regression model defined by (7) was used to model the calculated data for B. This model defines the moisture, temperature, and ageing dependency of B.…”

Investigation on heat transfer characteristics of nano titania added transformer oil with hotspot temperature

“…Hotspot in transformers is one of the major concern and the temperature can rise up to 200°C [2] In addition, it affects the loading capacity of transformers [3]. In order to reduce the size, weight and meet the growing population demand, there is a need for the development of a class of insulation system which can provide enhanced dielectric and heat transfer properties.…”

Understanding the moisture temperature and ageing dependency of power transformer winding clamping pressure

“…The orientation of cellulose fibres is parallel to the surface of the paper sheets. As a result, pressboard structure has pores of different sizes in between the paper layers [55,67]. When compressed along the through-thickness direction, the pores structure of pressboard collapses causing material densification [55,70].…”

“…As a result, pressboard structure has pores of different sizes in between the paper layers [55,67]. When compressed along the through-thickness direction, the pores structure of pressboard collapses causing material densification [55,70]. Therefore, densification due to compaction of pores is a factor that decides the through-thickness compressive stress-strain behaviour of pressboard.…”

“…These strong hydrogen bonds provide the mechanical strength of cellulose based solid insulation materials such as paper and pressboard[59,60]. Physically, cellulose has a semi-crystalline structure, which has both highly crystalline regions and amorphous regions as shown inFigure 3.2[55,61,62]. The typical crystallinity index of cellulose is about 50%-70%[63].…”