Method for connecting conductors of aluminum - core cable
Aluminum and copper cores are commonly used as cable conductors, but they cannot be directly connected. The main reasons are as follows:
(1) when copper and aluminum core conductors are directly connected, the contact surface of the metal is easy to form electrolyte under the action of water, carbon dioxide and other impurities, so as to form a galvanic battery with aluminum as the negative pole and copper as the positive pole, resulting in electrochemical corrosion of aluminum and increasing contact resistance at the connection of copper and aluminum core.
(2) due to the large difference between the elastic modulus and thermal expansion coefficient of copper and aluminum, after several cold and hot cycles (power on and power off) in operation, there will be a large gap at the contact point, which will affect the contact and increase the contact resistance.
(3) the increase of contact resistance leads to the increase of operating temperature, the intensification of corrosion and oxidation at high temperature, the deterioration of connection quality after vicious cycle, and finally leads to the accident of high temperature, smoke and burning at the contact point.
The code for construction and acceptance of busbar devices for electrical installation engineering clearly stipulates that copper and aluminum transition joints shall be used for connection of copper and aluminum core conductors, and the inner wall of copper pressure pipe shall be tinned if copper pressure pipe is used. The industry standard stipulates that the dc resistance of cu-al transition connection pipe shall not be greater than 1.2 times of the dc resistance of aluminum conductor of the same length and section.
Connection of conductors of different sections
After the adoption of aluminum core cable, the problem is that the connection of copper and aluminum core conductors with different sections is more complicated. For the same type of conductor in construction, the problem can be solved by removing or adding a single conductor wire. However, first of all, removing or adding a single conductor wire causes local large stress when the conductor pipe is pressed, and long-term operation may lead to increased contact resistance.
Second, the removal or addition of single conductor wire usually forms sharp Angle or sharp edge, which may damage the intermediate joint. At this time, the external joint is in a state of tension operation, thus causing mechanical damage. At the same time, the sharp Angle or sharp edge will also cause electric field distortion at the joint part, which will lay a hidden danger for the accident. The connection of conductors of different sections can only be completed by special conductor nozzles with different inner diameters. If copper and aluminum are connected, only copper and aluminum transition joint pipes can be used.
Connection of conductors in aluminum core cable
Aluminum conductor of cable with aluminum core is usually pressed with aluminum pipe, but actually it is also used to be pressed with tin-plated copper pipe. Since nearly 20 years ago, the power system is based on copper cable, the cable installation departments are equipped with the pressure tool is based on the pressure of copper cable, at present, the pressure tool manufacturing enterprises do not produce aluminum cable pressure tool.
The advantage of the point-pressing method of pressing aluminum core cable is that the pressure is small, which is easy to make the local pressing joint contact surface produce metal surface penetration, damage the aluminum core wire and the oxide film on the surface of the connecting pipe, but the connecting pipe is easy to deform after pressing.
The advantage of confining pressure method for copper conductor cable is that the surface shape of the connecting pipe after compression is relatively straight without deformation, and it is easy to solve the problem of electric field concentration at the connecting pipe.
GB/T14315 stipulates that the aluminum pipe is 1 section smaller than the copper pipe. The outer diameter of the aluminum pipe is the same as that of the copper pipe. For example, the outer diameter of the aluminum pipe of 240mm2 and the copper pipe of 300mm2 are the same. Therefore, when copper and aluminum conductor adopt the same series of pressing tools, the pressing mold of aluminum pipe with the same section is one specification larger than that of copper pipe with the same section.
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