1. What is a medium-voltage power cable?
Medium-voltage (MV) power cables are specifically designed for the transmission or distribution of electrical energy. Their voltage level is strictly limited to between 1kV and 35kV. They play a crucial role in the power system, connecting low-voltage (<1kV) cables (used for end-user electrical scenarios such as households and small businesses) and high-voltage (>35kV) cables (used for long-distance, high-capacity power mainline transmission), and are a key component of the distribution network.
2. What are the main components of medium-voltage power cables?
Medium-voltage power cables adopt a layered structure, with each layer having a specific function to ensure safe and stable operation. The core components include:
Conductor: As the carrier for current transmission, it is usually made of copper or aluminum, and can be in the form of solid, stranded, or compacted stranded. The stranded or compacted design can enhance the flexibility of the cable, making it easier to install.
Insulation layer: Wrapped around the conductor, it is the key to preventing current leakage. Common materials include cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR), etc. It must have excellent dielectric properties and resistance to aging.
Semiconductive layer: It is divided into the inner semiconductive layer and the outer semiconductive layer, both of which are in close contact with the insulation layer. The inner semiconductive layer can eliminate the concentration of electric field on the surface of the conductor, while the outer semiconductive layer is closely combined with the insulation layer to reduce the electric field stress between the insulation layer and the shielding layer.
Metal shielding layer: Mostly in the form of copper tape, copper wire, or copper braiding, its function is to confine the electric field inside the cable within the insulation layer, avoiding electromagnetic interference to the outside, and providing a grounding path for short-circuit current in case of a fault.
Outer sheath: The outermost protective structure, the materials are mostly polyvinyl chloride (PVC), polyethylene (PE), or low smoke zero halogen (LSZH) materials, which can resist mechanical damage, chemical corrosion, and ultraviolet radiation.
3. What are the common insulating materials used for medium-voltage power cables?
The selection of insulating materials needs to take into account the usage environment (such as temperature, humidity, and flexibility requirements). Common types include:
Cross-linked Polyethylene (XLPE): The most widely used material at present, it has excellent heat resistance (working temperature up to 90℃), chemical resistance, and flexibility. It is easy to install and has a long service life, suitable for most medium-voltage scenarios.
Ethylene Propylene Rubber (EPR): Good flexibility, strong resistance to temperature, ozone, and moisture, suitable for use in harsh environments (such as underground, damp places), especially performing well in installation scenarios requiring frequent bending.
Polyvinyl Chloride (PVC): Due to its poor heat resistance (only applicable in the lower medium-voltage range of 1-10kV) and the release of toxic gases when burning, it is less used in medium-voltage cables.
4. What are the typical application scenarios of medium-voltage power cables?
Medium-voltage power cables are widely used in power distribution. The main scenarios include:
Urban and suburban power grids (connecting substations and distribution transformers to achieve the distribution of power from the main grid to the regional distribution network).
Industrial facilities (such as factories, oil refineries, etc., providing power for large machinery and production lines).
Commercial complexes (shopping malls, high-rise buildings, etc., for centralized distribution and transmission of internal power).
Renewable energy systems (such as wind farms, solar power stations, connecting the generated power to the public grid).
Underground or underwater power lines (as the main transmission method in urban centers, rivers crossing areas where overhead lines cannot be erected).
5. What are the main causes of faults in medium-voltage power cables?
Common causes of faults include:
Insulation aging: Long-term exposure to high temperatures, humidity, or chemical corrosion leads to a decline in insulation performance; local discharge (local electric field breakdown) within the insulation layer also accelerates aging.
Mechanical damage: Excessive bending during installation, being crushed by heavy equipment, or physical damage caused by soil settlement, rodent gnawing, etc. during operation.
6. What is the typical service life of medium-voltage power cables?
The service life of medium-voltage cables is usually 20-30 years, but it may vary depending on the following factors:
Operating conditions (such as operating temperature, load fluctuations, voltage stability): Long-term overloading can lead to excessively high temperatures, accelerating insulation aging.
Installation quality (such as whether the bending radius requirements are met, whether mechanical stress is effectively avoided): Improper installation can introduce potential faults.
Environmental factors (such as humidity, chemical corrosion, ultraviolet radiation): Harsh environments can shorten the service life.
Maintenance measures (such as regular inspections, timely repair of damages): Scientific maintenance can extend the effective service life of the cables.
