Characteristics and Applications of Catenary Wires

Catenary wires must be flexible, capable of withstanding high tension, and exhibit minimal changes in sag due to temperature fluctuations.
Structurally, a catenary wire consists of a multi-layered stranded conductor, formed by wrapping several layers of metal wire around a central core wire. To ensure a compact structure, the winding direction of each layer is opposite to that of the layer beneath it; this prevents the layers from loosening when subjected to external forces, particularly torsional stress. In accordance with standard operational practices, the outermost layer is wound in a right-hand direction.
Serving the dual purpose of power transmission and supporting the contact wires of an overhead catenary system, the catenary wire acts as the "lifeline" of an electrified railway. Given the unique operational conditions and environments of railways, catenary wires are subject to stringent performance requirements. They must possess high electrical conductivity and excellent current-carrying capacity, ensuring reliable power transmission across diverse geographic regions, throughout all four seasons, and under varying climatic conditions. Furthermore, they must be corrosion-resistant and durable, capable of withstanding chemical pollutants-such as acids, alkalis, salts, and sulfur compounds-often present in the atmosphere. They also need to offer high mechanical strength combined with a low self-weight, ensuring minimal deformation and uniform sag after installation, while effectively enduring vibrations caused by passing locomotives as well as external loads from wind, ice, rain, and snow. Additionally, they should be easy to install, simple to maintain and repair, and cost-effective.
Copper catenary wires offer superior electrical conductivity, allowing them to serve as a path for traction current; by operating in parallel with the contact wire, they help reduce voltage drop and energy loss. They also exhibit excellent corrosion resistance. However, copper catenary wires consume a significant amount of copper, resulting in higher costs. Moreover, they possess relatively low mechanical strength, limiting their ability to withstand high tension, and they are prone to significant changes in sag as temperatures fluctuate. Common specifications include types such as TJ-95 and TJ-120. Steel catenary wires are made of galvanized steel strands; they offer high strength and high tensile capacity, exhibit minimal sag (with little variation in sag), and are both cost-effective and economical in their use of non-ferrous metals. However, they have high electrical resistance and poor conductivity, and are therefore generally used as non-current-carrying catenary wires. Since steel catenary wires are not corrosion-resistant, anti-corrosion measures must be implemented during their use. Common specifications include types such as GJ-100, GJ-80, and GJ-70, where "GJ" denotes steel strands, and the number represents the cross-sectional area of ​​the strand. Specifically, GJ-100 is used for 3T-class suspension systems, while GJ-70 is used for 2.5T-class suspension systems (referring to the combined tension of the contact wire and the catenary wire, totaling 3 tons or 2.5 tons, respectively).
Aluminum-clad steel catenary wires are composed of aluminum-clad steel wires stranded together with aluminum wires. The steel core of the aluminum-clad steel wires bears the tension, while the aluminum cladding and the additional aluminum wires carry the current. This configuration provides good electrical conductivity, high mechanical strength, and superior corrosion resistance. Aluminum-clad steel catenary wires are typically designated by the symbol "GLZ," where "G" stands for the steel core, "L" for the aluminum-clad steel strand, and "Z" for a current-carrying catenary wire.
A wide variety of catenary wires are in use, with significant differences in their technical performance. Internationally, the types of catenary wires used are relatively standardized, with copper or copper-alloy strands being the most common choice. From a technical perspective, using the same material for both the catenary wire and the contact wire improves the performance of the overhead contact system, simplifies construction, enhances installation precision, eliminates the need for special treatment of electrical connection clamps, and reduces the workload for operation and maintenance. Operational experience in China has also demonstrated that catenary wires made of copper or copper-alloy offer reliable technical performance and a high level of safety. To ensure the safety and reliability of the system, copper or copper-alloy strands are generally used for catenary wires on electrified main-line railways, while other types of strands may be employed for secondary lines (such as those for mining railways or dedicated local industrial lines).