Study of the Impact of Degree of Polymerization on the Remnant Life of Transformer Insulation

In South Africa, transformers are the most critical links in the power system's generation, transmission, and distribution. Their insulation system is comprised of dielectric oil and cellulose paper. The aging of the insulating system is influenced by several factors including high loading profile, temperature rise, and short circuits. Many diagnostic tests can be performed, and correctional measures may be taken to guarantee that consumers receive uninterrupted power supply. The remaining life of the transformer's cellulose paper insulation determines when the transformer's useful life ends. The mechanical or tensile strength of the solid insulation determines the aging of the paper insulation, which is calculated in terms of its Degree of Polymerization (DP). The direct method, which involves actual paper samples and is thus expensive and invasive, is the conventional method for calculating DP. Recently, a non-intrusive indirect approaches has been used to estimate the DP value from the furan compounds dissolved in the dielectric oil. In this work, the impact of the DP on the remnant life of four different transformer cellulose insulating materials is studied. An analysis of various cellulose insulation DP models are employed in estimating the DP and consequently the remnant life. The study further propose new formulae correlating 2-furalde hyde (2FAL) and DP in relation to the ageing process using regression analysis on a fleet of collected transformer oil samples. The results are compared with measured DP values and yield an estimation error of less than 3% and 4% respectively.