In modern power systems, high-voltage cables play a vital role. From underground power grids in cities to long-distance transmission lines across mountains and rivers, high-voltage cables ensure efficient, stable and safe transmission of electric energy. This article will explore in depth the various technologies related to high-voltage cables, including their structure, classification, manufacturing process, performance characteristics, installation and maintenance.
1.Basic structure of high-voltage cables
High-voltage cables are mainly composed of conductors, insulation layers, shielding layers and protective layers.
The conductor is the transmission channel for current and is usually made of copper or aluminum. Copper has good conductivity and ductility, while aluminum is relatively low in cost and light in weight. These conductors are generally in the form of multi-strand twisted wires to increase flexibility.
The insulation layer is a key part of the high-voltage cable, which plays a role in preventing current leakage and isolating the conductor from the outside world. Common insulating materials include cross-linked polyethylene (XLPE), oil paper, etc. XLPE has excellent electrical properties, heat resistance and mechanical strength, and is widely used in modern high-voltage cables.
The shielding layer is divided into inner shielding and outer shielding. The inner shield is used to make the electric field uniform and prevent local discharge from damaging the insulation layer; the outer shield can reduce the interference of the external electromagnetic field on the cable, and also prevent the cable from having an electromagnetic impact on the outside world.
The protective layer mainly protects the cable from damage by external factors such as mechanical damage, chemical corrosion and water intrusion. It is usually composed of metal armor and outer sheath. The metal armor can provide mechanical strength, and the outer sheath has waterproof and anti-corrosion functions.
2. Classification of high-voltage cables
According to the voltage level, high-voltage cables can be divided into medium-voltage cables (generally 3-35kV), high-voltage cables (35-110kV), ultra-high-voltage cables (110-500kV) and ultra-high-voltage cables (above 500kV). Cables of different voltage levels differ in structural design, insulation requirements, etc.
From the perspective of insulating materials, in addition to the XLPE cables and oil-paper cables mentioned above, there are also ethylene-propylene rubber cables. Oil-paper cables have a long history, but due to their high maintenance costs and other reasons, they have gradually been replaced by XLPE cables. Ethylene propylene rubber cable has good flexibility and weather resistance, and is suitable for some special occasions.
3. Manufacturing process of high-voltage cable
The manufacturing of high-voltage cable is a complex and delicate process.
The manufacturing of conductors first requires the copper or aluminum raw materials to be stretched, twisted and other processes to ensure the dimensional accuracy and mechanical properties of the conductor. During the twisting process, the strands of the strands must be closely arranged to improve the conductivity of the conductor.
The extrusion of the insulation layer is one of the key steps. For the XLPE insulation layer, the XLPE material is extruded at high temperature and evenly wrapped on the conductor. During the extrusion process, parameters such as temperature, pressure and extrusion speed must be strictly controlled to ensure the quality and thickness uniformity of the insulation layer.
The shielding layer is usually made by metal wire weaving or metal tape wrapping. The manufacturing processes of the inner and outer shields are slightly different, but both need to ensure the integrity of the shielding layer and good electrical connection.
Finally, the production of the protective layer includes the laying of the metal armor and the extrusion of the outer sheath. The metal armor should fit tightly on the cable, and the extrusion of the outer sheath should ensure a smooth appearance without defects such as bubbles and cracks.
4. Performance characteristics of high-voltage cables
In terms of electrical performance, high-voltage cables need to have high insulation resistance, low dielectric loss and good voltage resistance. High insulation resistance can effectively prevent current leakage, low dielectric loss reduces the loss of electric energy during transmission, and good voltage resistance ensures that the cable can operate safely in a high-voltage environment.
In terms of mechanical properties, the cable should have sufficient tensile strength, bending radius and impact resistance. During installation and operation, the cable may be subjected to stretching, bending and external force impact. If the mechanical properties are insufficient, it is easy to cause cable damage.
Thermal performance is also an important aspect. The cable will generate heat during operation, especially when running under high load. Therefore, the cable needs to have good heat resistance and be able to work normally within a certain temperature range without problems such as insulation aging. XLPE cable has relatively good heat resistance and can operate for a long time at higher temperatures.
5. Installation and maintenance of high-voltage cables
In terms of installation, the first thing to do is to plan the path to ensure that the cable laying path is reasonable and safe. During the laying process, care should be taken to avoid excessive stretching, bending and extrusion of the cable. For long-distance cable laying, equipment such as cable conveyors are usually used to assist construction.
The production of cable joints is a key link in the installation process. The quality of the joint directly affects the operating reliability of the cable. When making joints, the cable needs to be stripped, cleaned, connected and insulated. Each step needs to be carried out strictly in accordance with the process requirements to ensure that the electrical and mechanical properties of the joint meet the requirements.
Maintenance work is essential for the long-term stable operation of high-voltage cables. Regular inspections can promptly detect whether the cable appearance is damaged or the sheath is damaged. At the same time, some testing equipment can also be used to test the insulation performance and partial discharge of the cable. If problems are found, they should be repaired or replaced in time.
6. Failure and detection of high-voltage cables
Common failures of high-voltage cables include insulation breakdown, conductor disconnection, and joint failure. Insulation breakdown may be caused by insulation aging, partial discharge, or external overvoltage. Conductor disconnection is usually caused by mechanical external force or long-term overload. Joint failure may be caused by poor joint manufacturing process or severe heating during operation.
In order to detect these faults, there are many detection methods. Partial discharge detection is a commonly used method. By detecting the signal generated by partial discharge in the cable, it can be determined whether there are insulation defects inside the cable. The withstand voltage test can detect the withstand voltage capacity of the cable and find potential insulation problems. In addition, infrared thermal imaging technology can detect the temperature distribution on the surface of the cable, so as to find out whether the cable has problems such as local overheating.
7.Application and development trend of high-voltage cables in power systems
In power systems, high-voltage cables are widely used in urban power grid transformation, outgoing lines of large power stations, submarine cable transmission and other fields. In urban power grids, due to limited space, the use of underground cables can save space and improve the beauty of the city. The outgoing lines of large power stations require the use of high-voltage cables to transmit electricity to distant substations. Submarine cable transmission can realize cross-sea power transmission and provide stable power supply for islands and coastal areas.
With the continuous development of power technology, high-voltage cables have also shown some development trends. One is the research and development and application of cables with higher voltage levels. With the increase in demand for long-distance power transmission, the development of ultra-high voltage cables will become a focus. The second is the intelligence of cables. By integrating sensors and other equipment into the cable, real-time monitoring of the cable’s operating status and fault warning can be achieved, thereby improving the operating reliability of the cable. The third is the development of environmentally friendly cables. As people’s requirements for environmental protection increase, the research and development of low-pollution, recyclable cable materials will be a future development direction.
Post time: Sep-24-2024