Commonly used high-voltage cables are generally single-core cables or three-core cables. Single-core cables are usually used to transmit one-way AC and DC power as well as oil-filled lines of 60kV and above. And three-core cables are mainly used in three-way AC grids and in various high-voltage lines.
According to the actual application, there are many differences in the scope of application, laying environment, manufacturing, installation and price of these two types of cables.
Single-core cable is suitable for indoor, tunnel and cable trench. It cannot withstand mechanical external force. Considering heat dissipation, it is not suitable for direct burial and is not allowed to be laid in magnetic pipes such as steel pipes.
Three-core cable is suitable for indoor and outdoor, tunnel and cable trench. It can withstand certain mechanical external forces and tensile forces. The armored three-core cable can be laid in direct burial or in various pipes containing magnetic pipes.
Single-core cables have a smaller outer diameter and are lighter in weight. Therefore, the cable manufacturing length can be independent of the cable tray and weight limitation. For example, the length of 400mm² single core cable can be 1000m long.
The manufacturing and transportation of three-core cables is limited by the weight of the cable tray and the cable itself. Therefore, each cable tray cannot be made too long. Generally, 400mm² cable length is not more than 500m.
Single-core cables are easy to lay. However, the laying length is three times longer than that of a three-core cable. Therefore, the overall construction time is longer. When single-core cables are connected to terminals, the electrical safety spacing is more generous because crossings can be reduced. In long line works, single-core cables can reduce the use of cable joints. This enhances the reliability of transmission line operation.
Three-core cables (cables de multiconductor) are not easy to lay. However, the laying length is 1/3 of the single-core cable, so the overall construction time is shorter. When the cable is connected to the indoor distribution device, the three-core cable termination is influenced by the size of the cable bin of the distribution device and the torque of the cable itself at the laying position.
Single-core cable is more strict for laying environment because it does not allow steel band armored (banda de acero blindada) with magnetism. General external force that may cause damage to the cable. The metal shield of single-core cable normally needs to be grounded on one side or cross interconnected. If grounded directly, the metal shield will generate a large loop current, which will burn the cable.
Three-core cable has more relaxed requirements for laying environment because of the steel belt armor protection. There is some protection against general external damage. The three phases of the three-core cable are wrapped together and rely on the insulation material for insulation. If the insulation material moisture, deterioration will easily cause a phase short circuit.
The price of single-core cable is cheaper than three-core cable for the same cross-sectional area of high-voltage cable. But the purchase should still consider the actual use of demand. In general, for 500mm² and below cross-sectional cables, it is more appropriate to choose three-core cables. This is because the three-core cable is much safer.