Overheating Characteristics of Contact Defects in the Transition Circuit of Oil-immersed Power Transmission Equipment On-Load Tap Changer

Abstract To address the local overheating and ablation problems of fastening connection structures in the transition circuit of oil-immersed power transmission equipment on-load tap changers (OLTCs), this paper proposes a contact-defect simulation method based on Joule-heating energy equivalence. According to the short-duration high-current characteristics during tap-changing operation, the current-carrying process of the transition circuit is equivalently converted into a laboratory current-carrying condition of 258 A for 2 s. A temperature-rise test platform consisting of a programmable AC constant-current source, prototype connection specimens, and an infrared thermal imager is established. Typical contact-defect conditions, including insufficient tightening torque, foreign-particle inclusion, abnormal anti-loosening coating, and uneven contact end surfaces, are designed to investigate the temperature-rise characteristics of the connection structure. The experimental results show that contact defects change the contact state of the conductor-connector interface, reduce the real contact area, increase the contact resistance, and intensify local temperature rise. Furthermore, an electro-thermal coupled simulation model is developed, in which an equivalent contact heat flux is used to characterize the additional interfacial heating caused by contact degradation. The results show that when the equivalent contact heat flux increases from 1.0×105 W/m2 to 1.0×106 W/m2, the simulated additional temperature rise increases from 9.07 ℃ to 103.06 ℃, which is consistent with the experimental trend that contact defects lead to increased temperature rise. The results can provide a reference for assembly quality control and overheating-defect diagnosis of transition circuits in oil-immersed power transmission equipment OLTCs.