Impact of acidity on the degradation of the solid insulation of power transformer

Summary

Power transformers which represent about 60% of the investment cost of a transformer substation are very important equipment in any power grids. It is therefore, essential to maintain the insulation system in pristine condition to ensure reliability on this important asset. Oil in service degrades and in turn affects not only its own properties (dielectric, physicochemical), but also the solid insulation’s degradation rate. During the aging of oil/ paper insulation system, acids are produced. The acids built-up are absorbed by the paper and therefore accelerate the degradation of the whole insulation system. This contribution summarizes some results onto the influence of the initial oil acidity on the paper degradation rate. Three acids were considered, i.e. acetic, formic and levulinic acids, either individually or combined. Accelerated thermal aging of oil/paper insulation were performed according to ASTM1934 standard under laboratory-controlled conditions. In addition to aged oil’s properties, three parameters were measured to assess the degradation rate of the insulation paper: the degree of polymerization (DPv) according to ASTM D4243, the dissipation factor (tand) according to the ASTM D928 and moisture content, according to ASTM D1533. From the obtained results, it was noticed that the oil sample which contains formic acid degrades much more the insulating paper than acetic and levulinic ones.

Additional informations

Authors

L. CISSE, I. Fofana, Y. HADJADJ, D.K. AMBROISE, K.M.L. YAPI

Keywords

power transformers, acidity, aged insulation, solid insulation