School of
Information Technology and Electrical Engineering

Condition Monitoring of Natural Ester Filled Transformer

Kapila BandaraTue, 26/11/2013 - 09:00
Dr. Chandima Ekanayake

Majority of the power transformers installed in electric power systems around the world are insulated with cellulose paper based products and mineral oil, owing their low cost, availability, excellent dielectric properties, and better compatibility. Performance of mineral oil as insulating liquid in HV transformers appears to be limited due to their poor biodegradability and lower fire point. Due to supreme biodegradable property and higher fire point, vegetable oil based natural esters are recognized as a potential alternative for mineral oil, and it has been prevalent in distribution level during the last decade. However, to ensure safe operation of natural ester filled power transformers, it is necessary to understand primary differences between mineral oil and natural ester in diagnosis, ageing, processing issues and cost.

During the transformer operation, cellulose insulation degrades due to thermal and electrical stresses. The paper degradation is significant at higher temperatures and when oxygen and moisture content is high in the insulation. Due to degradation paper eventually loses its mechanical strength, which increases the risk of failure even under normal operation condition. Therefore, accurate information about the insulation condition is essential to plan maintenance, and indeed to avoid catastrophic failures, which may lead to cost millions of dollars for utilities. Dielectric spectroscopy based measurements and chemical based techniques such as Dissolved Gas Analysis (DGA) have effectively been used to characterize degradation of insulation and to identify incipient faults in mineral oil filled transformers. Therefore, this research aims to ensure that conventional electrical and chemical based techniques can still be used, when transformers are filled with natural esters. Moreover, applicability of Fourier Transform Infrared spectroscopy (FTIR) to assed the degradation of cellulose and furfural content in oil is also verified.

During the first phase of this research, a comparative study between one commercially available natural ester and mineral oil has been performed under controlled condition at laboratory scale. It is aimed to understand and compare the degradation of cellulose impregnated with natural ester to that of the mineral oil. The impact of thermal and electrical faults in natural esters on DGA interpretation techniques and dielectric spectroscopy measurements has also been assessed. Moreover, the degradation of cellulose was also assessed with FTIR spectroscopy.

According to the primary results, natural esters showed different dielectric behaviour compared to that of mineral oil, and degradation of cellulose immersed in ester was also dissimilar. It appeared that similar gassing behaviour in natural ester and mineral oil for electrical faults, but different gassing characteristics for thermal faults. In addition to that, DGA interpretation techniques successfully identified faults in both type of oil. Aging of cellulose reflected on FTIR spectroscopy, particularly wave number relevant to cellulose back bone and hydroxyl group. The preliminary results revealed that FTIR is a potential tool for identifying the aging status of transformer insulation.

In next stage of this research study, frequency and time domain dielectric spectroscopy of natural ester impregnated cellulose will be modelled with appropriate relaxation functions. Further, influence of moisture and aging status on these model parameters will be investigated. Finally, the study will be focused on accurately identifying the condition of natural ester filled transformer insulation.


Kapila Bandara  completed his B.Sc.Eng. (2004) and M.Sc. Eng. (2009) degrees in Electrical and Electronics Engineering at the University of Peradeniya, Sri Lanka. He has been working as an Electrical Engineer at the Ceylon electricity Board, Sri Lanka, since 2005. He has received commonwealth professional fellowship to conduct research at Cardiff School of Engineering UK for three months. In 2012, Kapila received IPRS scholarship to continue his studies towards PhD at School of Information Technology and Electrical Enginering in The University of Queensland, Australia. His research interests is condition monitoring of power transformers and power system controls. He has been a member of IEEE & PES since 2009.

Seminar Type: 

PhD Confirmation Seminar