70 / 2018-08-23 09:23:05

Analysis of conductor sag change after bare overhead conductor is covered with insulation material

Insulated conductor,Stress Analysis,Conductor sag change,Catenary equation

Bare conductor has been widely used in overhead transmission lines due to its good electrical conductivity and physical and mechanical properties. However, with the rapid development of the distribution network, the shortcomings of the original overhead bare conductor are also gradually exposed during operation. For example, when the bare conductor crosses the area with trees and vegetation, the branches with certain conductivity may make the conductor short-circuited, which poses new challenges to the safety operation of distribution networks. Compared with bare conductor, insulated conductor can greatly reduce the occurrence of distribution network accidents and the scope of power distribution accidents, improve the reliability of power supply and the safety level of distribution network effectively. Meanwhile, the price is much cheaper than buried cables. It has been widely used in 6-35kV transmission lines in China, and in Russia, covered conductors for 110 kV overhead lines have been designed when constructing and reconstructing transmission lines.
However, compared with the bare conductor, the tensile strength of the insulated conductor is much lower than that of the bare conductor, and since the self-load of the insulated wire with steel core is at least 30% heavier than the bare conductor of the same specification, it is easy to form the image that the insulated skin layer shrinks to the middle of the sag, which will accelerate the aging and deterioration of the skin layer. At present, the insulation transformation, as an efficient way to cover bare conductor with insulation material, usually selects some liquid coating material which can be quickly constructed and can be cured at ambient temperature, with the cooperation of automatic coating device, to realize the rapid automatic coating in a long distance. Therefore, how to evaluate the influence of insulation material and its thickness on the conductor sag during the insulation transformation process correctly and efficiently, whether the conductor is within the safety operation range, and how to take measures to anticipated accidents timely are urgent problems to be solved.
Based on the assumption:
1. The conductor is a ductile chain articulated everywhere. And it only subjects to axial tensile stress and the bending torque is not considering.
2. All the load on the wire points to the same direction and distributes averagely along with the conductor for the insulation material is coated averagely.
3. The tension of the conductor conforms to the Hooke's law.
This paper formulates the catenary equation of the insulated conductor and evaluates the variation of conductor sag after insulation transformation by analyzing the stress on the conductor, focusing on the influence of the insulation material and its thickness on the sag of the conductor; finally, the finite element model is established to simulate with COMSOL and the result of force analysis and sag change above are verified by the model.