Understanding the Effects of Electrical Sliding Speed on Contact Characteristics of On-Load Tap Changers

This paper analyzes the influence of sliding speed on the electrical contact performance and tribological characteristics of on-load tap changer (OLTC) contacts. The current-carrying friction and wear test of copper-tinned and copper contact couple in an insulating oil medium is carried out to simulate a real oil-immersed on-load tap changer's contact switching and operation process to reveal the contact deterioration and wear mechanism. The results show that the contact resistance between contacts increases with sliding speed. When the sliding speed is 119 mm/s, the maximum contact resistance is 0.3 Ω. At the same time, the average contact resistance presents a “U”-shaped curve change, which increases slowly in the initial stage, decreases gradually after 50 mm/s, and reaches the minimum at 76 mm/s-95 mm/s. Then it increases rapidly, and the arc erosion phenomenon turns to be intensified. The micromorphology and element analysis shows that the surface wears mechanism of moving contact changes from abrasive wear, adhesive wear, and delamination wear to abrasive wear, adhesive wear, delamination wear, and arc erosion large erosion pits on the surface. In addition, about 95 mm/s is a critical threshold. Below this threshold speed, the increase of contact resistance is mainly caused by mechanical wear. Beyond this threshold, non-mechanical factors such as arc erosion and chemical oxidation aggravate the deterioration of the contact surface, increasing contact resistance.