The dynamic change of copper terminal contact resistance is affected by many factors, and the study of its laws and influencing factors is of great significance to the stable operation of electrical systems.
First, the dynamic change law of copper terminal contact resistance is closely related to the contact process. In the initial contact stage, since the surface is not absolutely flat at the microscopic level, the actual contact area is much smaller than the apparent area, and only some discrete conductive spots are in contact. As the contact pressure is applied, these conductive spots undergo elastic-plastic deformation, and the contact resistance gradually decreases. When the contact pressure reaches a certain level, the downward trend of the contact resistance slows down and tends to be stable. During operation, the contact resistance will fluctuate due to factors such as the thermal effect of the current and mechanical vibration. For example, the heat generated when the current passes through will increase the temperature of the contact area, causing the material to expand and the contact state to change, thereby causing dynamic changes in the contact resistance; mechanical vibration may cause the contact point to loosen or displace, which also causes fluctuations in the contact resistance.
Second, contact pressure is one of the key factors affecting the contact resistance of copper terminal. When the contact pressure increases, on the one hand, the microscopic protrusions on the contact surface are flattened, the actual contact area increases, the conductive path increases, and the contact resistance decreases. On the other hand, a sufficiently large contact pressure can destroy the oxide film and contamination layer on the contact surface, so that good direct contact is formed between the metals, further reducing the contact resistance. However, the greater the contact pressure, the better. When the pressure is too large, it may cause plastic deformation to the copper terminal, or even damage the terminal structure, which will affect the contact performance and lead to unstable contact resistance.
Third, the influence of the surface state on the contact resistance of the copper terminal cannot be ignored. The roughness, cleanliness and oxidation degree of the copper terminal surface will affect the contact resistance. When the surface roughness is large, the actual contact area is reduced and the contact resistance increases; when there are pollutants such as oil and dust on the surface, an insulating layer will be formed on the contact surface, which will hinder the conduction of current and significantly increase the contact resistance. Copper is easily oxidized in the air to form an oxide film, which has poor conductivity and will increase the contact resistance. Moreover, as time goes by, the oxide film continues to thicken and the contact resistance will continue to rise. Therefore, keeping the surface of the copper terminal clean and smooth and preventing oxidation are important measures to reduce the contact resistance.
Fourth, the operating temperature has a complex effect on the contact resistance of the copper terminal. When the temperature rises, on the one hand, the resistivity of the metal material will increase, resulting in an increase in contact resistance; on the other hand, the temperature increase will cause the material on the contact surface to expand thermally, which may improve the contact state and reduce the contact resistance. In actual operation, when current passes through the copper terminal, the Joule heat generated by the contact resistance will increase the temperature of the contact area, forming a vicious cycle. If the heat dissipation conditions are not good and the temperature continues to rise, the contact resistance will increase further, and may even cause contact point ablation, affecting the normal operation of the electrical system.
Fifth, the current size is also a factor that affects the dynamic change of the copper terminal contact resistance. When the current passing through the copper terminal is small, the contact resistance is relatively stable. However, as the current increases, significant Joule heat will be generated, causing the temperature to rise, which in turn affects the contact resistance. In addition, large currents may also lead to the generation of electromotive force. Under the action of electromotive force, the contact point may be displaced or deformed, changing the contact state and causing the contact resistance to change. In the case of high current faults such as short circuits, the change in contact resistance is more drastic, which may cause serious damage to electrical equipment.
Sixth, material properties have a fundamental impact on the contact resistance of copper terminals. Copper terminals of different materials have different properties such as resistivity, hardness, and oxidation resistance, which leads to differences in contact resistance. Copper with higher purity has lower resistivity, which is conducive to reducing contact resistance; materials with moderate hardness can better form a good contact surface under contact pressure and reduce contact resistance. In addition, adding alloy elements can improve the properties of copper, such as improving oxidation resistance and enhancing mechanical strength, thereby indirectly affecting contact resistance. Appropriate material selection is crucial to controlling the contact resistance of copper terminals.
Seventh, environmental factors will also affect the contact resistance of copper terminals. A humid environment will accelerate the oxidation and corrosion of copper terminals, increasing contact resistance; an environment containing corrosive gases (such as sulfur dioxide, hydrogen sulfide, etc.) will react chemically with copper to form corrosion products on the surface, seriously affecting contact performance. In addition, in high-altitude areas, due to the thin air and poor heat dissipation conditions, the temperature of the contact point is easy to rise, which will also cause changes in contact resistance. Therefore, it is necessary to take corresponding protective measures, such as sealing and coating protective layers, for different environmental conditions to ensure the stability of the contact resistance of copper terminals.
