Semiconductive products have significant applications in high-voltage and ultra-high-voltage cables. The following is an introduction to them from aspects such as their types, working principles, and specific application locations:
Types of semiconductive products
Common semiconductive products include semiconductive shielding materials and semiconductive tapes.
Semiconductive shielding materials: They are classified into cross-linkable and non-cross-linkable types, and are generally composed of high-molecular polymers (such as polyethylene, etc.), conductive carbon black, additives, etc. Through reasonable formula design, it is made to have an appropriate electrical conductivity.
Semiconductive strip: A strip-shaped product made of semiconductive materials, some of which are also combined with other reinforcing materials to meet different usage requirements.
Principle of operation
During the process of transmitting electrical energy in high-voltage and ultra-high-voltage cables, there will be an electric field around the conductors. If the electric field distribution is uneven, it may lead to excessively high local electric field intensity, accelerate the aging and damage of insulating materials, and even cause insulation breakdown. Semiconductive products have a certain electrical conductivity, which can make the electric field distribution inside the cable more uniform, thereby reducing the local electric field intensity and ensuring the safe and reliable operation of the cable.
Specific application location
– Conductor shielding layer: Located between the conductor and the insulating layer, it is formed by coating the surface of the conductor with semiconductive shielding material through a high-temperature extrusion process. On the one hand, it can eliminate the microscopic unevenness on the surface of the conductor and make the electric field distribution on the surface of the conductor more uniform. On the other hand, it can be in close contact with the conductor, effectively reducing the interfacial resistance between the conductor and the insulating layer and preventing the occurrence of partial discharge.
– Insulating shielding layer: On the outside of the insulating layer, it is also formed by extrusion of semiconductive shielding material or winding of semiconductive tape. Its function is to evenly distribute the electric field on the outer surface of the insulating layer and prevent partial discharge between the insulating layer and the metal sheath. In addition, when a cable malfunctions, the insulating shielding layer can serve as a channel for fault current, facilitating the detection and location of the fault point.
– Joints and terminals: At the joints and terminals of high-voltage and ultra-high-voltage cables, semiconductive tapes are often used to handle insulation interfaces, improve electric field distribution, and enhance insulation performance. For instance, when making cable joints, using semiconductive tape wound around the insulation break can effectively alleviate the problem of electric field concentration, enhance the electrical performance and long-term operational stability of the joint.
The impact on cable performance
– Electrical performance: Significantly enhance the electrical insulation performance of cables, reduce partial discharge levels, and extend the service life of cables. For instance, by rationally using semiconductive products, the partial discharge starting voltage of cables can be raised to a relatively high level, reducing the risk of insulation aging.
– Mechanical properties: Semiconductive shielding materials and tapes can also enhance the mechanical properties of cables to a certain extent, such as improving the flexibility and bending resistance of cables and reducing insulation damage caused by external forces.
Thermal performance: It helps dissipate heat inside the cable. As the semiconductive material has a certain thermal conductivity, it can promptly conduct the heat generated during the operation of the cable away, reducing the operating temperature of the cable.