Investigation on compatibility of insulating materials in on-load tap changer with insulating oil

The insulation system of On-load tap changer (OLTC) is composed of insulating oil and the solid insulating materials in OLTC. The compatibility of solid insulating materials in OLTC with mineral insulating oil is one of the most important factors to decide the long-term reliable operation of OLTC. However, the compatibility of OLTC insulating components with mineral insulating oil is seldom studied. In this work, the effect of insulating materials, such as Epoxy Phenolic Glass Cloth Laminates (EPGCL3248), Epoxy Glass Fiber (EGF), Reinforced Nylon (PA66), Polyformaldehyde (POM) on the electrical and physicochemical properties of insulating oil were analyzed. The solid insulating materials were immersed in 800 mL insulating oil separately, and aged at 90 degrees C, 100 degrees C, 110 degrees C, and 130 degrees C. The aging time is 20 h, 41 h, 82 h, and 164 h, respectively. After the thermal aging, the water content, breakdown voltage, dielectric loss and acidity of insulating oil samples were tested, and the compatibility between the insulating oil and the solid insulating materials was analyzed. Among the solid insulating materials used in OLTC, the Nylon PA66 exhibits poor compatibility with mineral oil. The research results provide useful advises for the selection, optimization and replacement of OLTC solid insulating materials.