100. Dissolved Gas Analysis for Transformers

The transformer is one of the most important and costly apparatus in a power system. The reliable and efficient fault-free transformer has a decisive role in the availability of electricity supply. In a transformer, oil and paper insulation get degraded under a combination of thermal, electrical, chemical, mechanical, and environmental stresses during its operation. Whena power transformer is subject to electrical and thermal stresses, characteristic gases (such as H2, CH4, C2H2, C2H4, C2H6, CO, CO2) will be generated in the transformer oil. These stresses also change the properties of the paper and oil, which ages the insulation system. M.K. Pardhan assessed the status of insulation during thermal & electrical stresses on a transformer prototype. A number of properties (such as dissipation factor, capacitance, breakdown voltage [BDV] of oil & paper, degree of polymerization [DP], total combustible gases [TCG], furan contents etc.) have been identified as being reasonably sensitive indices of degradation. According to Mitchinson et al, the characteristics of the aged oils were also determined by using various analytical techniques such as Ultra-violet/visible (UV/Vis) spectroscopy, infra-red (IR) spectroscopy, acid number and water content test, and dielectric spectroscopy. A significant factor in ageing is chemical action through moisture, metal contaminants and oxidation. Dissolved gas analysis (DGA) is widely used to detect incipient faults in oil-filled electrical equipment. But according to Michel Duval & James J. Dukarm, some inaccuracy is always associated with laboratory DGA measurements of transformer oil, which may affect the gas ratios, and other calculations. Consequently a technique based on artificial intelligence were proposed by various researchers.