Programming (GEP) to estimate the relationship between furan concentration ... production increases with increasing degree of degradation and a total yield of ...
A Novel Application of Gene Expression Programming in Transformer Diagnostics A.Abu-Siada, Lai Sin Pin and Syed Islam Curtin University of Technology, Australia
Abstract-Furans are the major degradation of insulating paper in transformer oil. Hence the concentration of furans in oil can be used as a good indicator of paper deterioration. Furan concentration in transformer oil is currently measured using High-Performance Liquid Chromatography (HPLC) or Gas Chromatography-Mass Spectrometry (GC/MS). Both methods provide accurate and reliable results in detecting furan concentration. However, the two methods need very expensive equipments and take long time to get the result for one sample. Moreover it requires a trained expert to perform and interpret the results. This paper introduces a novel approach for detecting furan concentration in transformer oil through measuring its spectral response. The Ultraviolet-to-Visible (UV-Vis) spectral response of transformer oil can be measured instantly with relatively cheap equipment and does not need an expert person to conduct the test. Results show that there is a good correlation between oil spectral response and its furan contents. Also, the paper introduces a novel application for Gene Expression Programming (GEP) to estimate the relationship between furan concentration and spectral response of transformer oil.
I.
INTRODUCTION
Power transformers are a vital link in a power system. Monitoring and diagnostic techniques are essential to decrease maintenance and improve reliability of the equipment. Currently there are several of chemical and electrical diagnostic techniques applied for power transformers[1]. As the entire energized and high temperature transformer components are immersed in the transformer oil, the transformer oil is a key source to detect incipient faults, fast developing faults, insulation trending and generally reflects the health condition of the transformer. The electrical windings in a power transformer consist of paper insulation immersed in insulating oil. Paper insulation is composed of approximately 90% of cellulose, 6-7% hemi-cellulose and 3-4% of lignin. Due to electrical and thermal stresses, oil and cellulose decomposition occurs evolving gases that will decrease the heat dissipation capability and the dielectric strength of the oil. When degradation of paper insulation occurs, the cellulose molecular chains get shorter and chemical products such as furanic derivatives are produced and dissolve in the oil. Furans are the major degradation of paper in oil and the 2-furaldehyde in oil is the most prominent component of paper decomposition. The increase in furans concentration in the oil corresponds to the decrease in the tensile strength and the degree of polymerization (DP) of the paper. De Pablo reported the following relation between furfural and Degree of polymerization based on viscosity DPv[2] :
DPV =
7100 8.88 + 2 FAL
(1)
where 2FAL is the furfural concentration in mg/kg of oil. Then the concentration of 2-furfuraldehyde in the oil can be used as a good indicator of paper deterioration. It has been estimated that new paper, under normal running conditions will generate furfural at the rate of 1.7 ng/g of paper/h. The rate of production increases with increasing degree of degradation and a total yield of 0.5 mg of furfural/g of paper is expected in 100000 h of running (15-20 years)[3-5]. Furan level in a transformer can be correlated with paper DP, and therefore an in-service assessment of the mechanical strength of the paper insulation can be made. Furans concentration is measured by High-Performance Liquid Chromatography (HPLC) or Gas Chromatography-Mass Spectrometry (GC/MS) based on American Society for Testing and Materials (ASTM D5837, Standard Specifications for Mineral Insulating Oil in Electrical Apparatus)[6]. Both analysis methods provide accurate and reliable results in detecting the concentration of furan derivatives; 2- furfural (2-FAL), 2-Furfurol (2-FOL), 5-Hyroxy methyl-2-furfural (5-HMF), 5-Methyl-2-furfural (5-MEF), and 2-Acetylfuran (2-ACF). However, these two methods need very expensive equipments and take long time to get the results in addition it requires for an expert person to perform and interpret the results. The technique for furan testing is described in IEC, but there is no guideline for interpretations. This paper presents a novel approach for determination of furan concentration in transformer oil through measuring its spectral response. The Ultraviolet-to-Visible (UV-Vis) spectral response of transformer oil can be measured instantly with relatively cheap equipment and does not need an expert person to conduct the test. Results show that there is a good correlation between oil spectral response and its furan contents. II. LABORATORY AGED OIL The study has been performed on in-service as well as laboratory aged transformer oil. Laboratory aged insulating oil is prepared by utilizing the heating process available in IEC 61125[7]. Section of new craft paper (20mmx280mm) was cut and wrapped around copper strips (3mmx10mm) then it was impregnated in 25ml of new transformer oil (shell Diala B). All samples were heated up to 100°C in a thermostaticallycontrolled aluminum alloy block heater for 7 days. Oxygen
2008 Australasian Universities Power Engineering Conference (AUPEC'08)
Paper P-054 page 1
flow at a rate of 1 l/hr was supplied into each dry tube to further accelerate the aging process. III. FURAN ANALYSIS All samples were prepared in accordance to standard ASTM D 5837 and tested using GC/MS system for furan derivatives identification and quantification. Table I shows furan derivative concentration in particle per million (ppm) for different oil samples using GC/MS. Results show that the 2furaldehyde (2-FAL) is the most prominent component of paper decomposition. Therefore, the level of 2-furaldehyde in transformer oil can be used as an indicator for paper deterioration.
Where Aλ is the absorbance, S is the sample intensity at wavelength λ , D is the dark intensity at wavelength λ , R is the reference intensity at wavelength λ . Same oil samples used for furan concentration measurement using GC/MS were tested using a laboratory grade spectrophotometer for absorbance spectrophotometry. The experiment procedure was set up in reference to ASTM E275[10]. Figure 1 shows the lab set up for measuring spectral response for one oil sample. Figure 2 shows the spectral response (absorbance) for different oil samples with different furan concentration.
Table I Furan concentration result by GC/MS Test Sample
