Electromechanical Characteristics Of Parallel Groove Clamps

According to national standard GB2314 "General Technical Conditions for Power Fittings" and power industry standard DL/T 765.1 "Technical Conditions for Overhead Distribution Line Fittings," the gripping force of non-load-bearing fittings parallel groove clamp on conductors shall not be less than 10% of the calculated breaking strength of the conductor, and the conductivity shall not be lower than the resistance of the contacted conductor.  To ensure stability and reliability, clear requirements are specified for the resistance change after current flow. Meeting these requirements ensures that the fittings parallel groove connector will not fail before the conductor during normal operation, overload, or even short circuits, thus guaranteeing the safety and reliability of the line.
Current conduction between conductors can be analyzed from two aspects: the mechanical contact area of ​​the conductors and the current conduction path. Mechanical contact area of ​​conductors: Microscopically, the conductor surface is composed of countless uneven peaks and valleys. The smoother the conductor surface, the smaller the height difference between the peaks and valleys. When two conductors are brought into contact under external force, the contact mainly exists in the form of peak-to-peak contact. Therefore, the actual mechanical contact area is far less than the nominal contact area designed for the clamp; the true mechanical contact area is approximately 7% of the nominal contact area.
Current conduction path between conductors: First, under external pressure, the active aluminum oxide (Al2O3) layer on the aluminum-aluminum interface of the two conductors is squeezed or rubbed, causing local rupture, allowing aluminum electrons to flow freely between the surface peaks, forming a certain conductivity. The greater the pressure, the more peak-to-peak contact points, and the smaller the contact resistance. In the clamp installation process, it is required to apply conductive grease containing copper and silver ions to the conductor surface to prevent re-oxidation of the ruptured oxide layer. Second, the active Al2O3 itself has a certain conductivity, allowing the undamaged areas to also have a certain conductivity. Simultaneously, under the action of an external power source, the copper and silver ions in the conductive grease further penetrate into the active Al2O3 layer, causing the conductivity of the conductive interface to increase slightly after energized operation compared to the initial value, generally by 0.5%-9%. Thirdly, due to the good plasticity of aluminum, when the two interfaces are pressed together, some of the aluminum in the inner wall of the wire clamp will undergo plastic deformation and enter the stranded gaps of the outer layer of the conductor. This increases the effective contact area and promotes more active inter-molecular penetration. As the number of aluminum atoms in the oxide layer further increases, the conductivity at the electrical interface improves.