Can oxidation of the contact surface of a copper-aluminum busbar cause overheating or even fire?
Publish Time: 2025-10-02
At the heart of power systems, busbars act like veins, carrying massive currents to deliver energy to every corner. As a critical conductor connecting different electrical devices, the stability of the connection points in a copper-aluminum busbar directly affects the safe operation of the entire system. However, during long-term service, a seemingly minor change—oxidation of the contact surface—can silently create a hidden hazard, eventually leading to serious malfunctions. When people detect a burning smell, blackened contact points, or even charred insulation in a distribution cabinet, the root cause often lies in that barely visible layer of oxide.Both copper and aluminum react with oxygen in the air, forming an oxide layer. Copper oxide is relatively dense and still retains some conductivity, limiting its impact on contact resistance. Aluminum oxidation, however, is quite different. Aluminum is highly reactive and forms a thin layer of aluminum oxide instantly upon exposure to air. This layer is hard, insulating, and extremely stable, unlike copper oxide, which is easily punctured or broken down by current. When a copper-aluminum busbar is connected by bolts or terminals, the ideal scenario is direct metal-to-metal contact for low resistance. But if an oxide layer exists on the aluminum surface, the current path is partially blocked by this insulating layer, significantly reducing the actual conductive area.The reduction in conductive area directly leads to increased contact resistance. According to Joule's law, heat is generated when current flows through a high-resistance area. At low loads, this heat generation may not be noticeable, and the system can still operate. However, as the load increases and the current rises, the heat generation increases non-linearly. The temperature rise, in turn, accelerates the aluminum oxidation process, forming a thicker oxide layer, further increasing the contact resistance. This cycle creates a vicious loop of "temperature rise – oxidation – increased resistance – further temperature rise."Even more complex is the electrochemical corrosion between copper and aluminum. When two metals with different potentials come into contact in a humid environment, a galvanic cell effect is formed, with aluminum, as the more reactive metal, acting as the anode, accelerating corrosion. Corrosion products are typically loose, non-conductive compounds that create gaps at the contact surface, reducing the clamping force of bolted or crimped connections and further impairing electrical contact. This type of corrosion is particularly prevalent in high-humidity, high-salt environments such as coastal areas, chemical plants, and underground substations.Localized hotspots often become weak points in the system. High temperatures can anneal the metal, reducing its mechanical strength and causing the bolt preload to relax, further deteriorating the contact. Surrounding insulation materials age, become brittle, and carbonize under prolonged heat, potentially leading to short circuits or arcing. In extreme cases, localized high temperatures can melt the metal, causing busbar breakage or fires, resulting in widespread power outages or even equipment damage.Preventing these problems hinges on blocking the pathways of oxidation and corrosion. During installation, the aluminum surface must be thoroughly cleaned to remove the oxide layer. A specialized oxide remover or fine sandpaper can be used, followed by immediate connection to prevent re-oxidation. Applying conductive grease to the contact surface fills microscopic irregularities, seals out air to prevent re-oxidation, improves current distribution, and reduces contact resistance. Using copper-aluminum transition terminals or tin-plating minimizes direct contact between the two metals, inhibiting electrochemical corrosion. Torque wrenches must be used to tighten bolts, ensuring uniform and appropriate pressure; too loose results in poor contact, while too tight can damage the soft aluminum.Regular inspections are also crucial. Using an infrared thermal imager to monitor connection temperatures can detect abnormal heating early, preventing potential problems. For equipment that has been in operation for many years, the condition of busbar connections should be closely monitored, with timely maintenance or replacement of aging components.Ultimately, while oxidation of copper-aluminum busbar contacts is a natural phenomenon, it should not be underestimated. It's like a chronic disease, initially without obvious symptoms, but silently eroding system health. Only by remaining vigilant at every stage of design, installation, and operation can we ensure uninterrupted power flow and reliable, silent operation of the power system.
