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High-voltage cable is a type of high-voltage power cable for transmission and distribution. It is a power cable used to transmit power between 10 kV and 35 kV (1 kV = 1000 V) and is mostly used in the main roads of power transmission. The components of high-voltage cable from inside to outside include: conductor, insulation, inner sheath, filler (armor), and outer insulation. In addition, the cable should meet the performance requirements of low-halogen and low-smoke or halogen-free and smoke-free flame-retardant cables and have radial waterproofness.
In the traction power supply system, high-voltage cables are mostly used for power transmission between 27.5 kV gas-insulated metal-enclosed switchgear (GIS switchgear for short) and online disconnectors, traction transformers, and self-use transformers. Because high-voltage cables occupy less space and require less maintenance, they have more advantages than overhead lines in natural disasters such as lightning protection, bird protection, and pollution flash protection. They can directly improve the overall safety and reliability of the traction power supply system. Special high-voltage cables for electrified railways are widely used in traction substations.
The main types of medium voltage cables are YJV cables, VV cables, YJLV cables, and VLV cables.
YJV cable is the full name of cross-linked polyethylene insulated PVC sheathed power cable (copper core)
VV cable is the full name of polyvinyl chloride insulated PVC sheathed power cable (copper core)
YJLV cable is the full name of cross-linked polyethylene insulated PVC sheathed aluminum core power cable
VLV cable is the full name of polyvinyl chloride insulated PVC sheathed aluminum core power cable
Due to the excellent conductivity of copper conductors, more and more projects use copper core power cables as the main power supply system, while aluminum core power cables are less used, especially in the higher voltage power system, the more copper core cables are selected.
The components of high voltage cables from inside to outside include: conductor, insulation, inner sheath, filler (armor), and outer insulation. Of course, armored high-voltage cables are mainly used for underground burial, which can resist high-intensity compression on the ground and prevent damage from other external forces.
NA-YJV, NB-YJV, cross-linked polyethylene insulated PVC sheathed A (B) class fire-resistant power cables can be laid indoors, tunnels and pipelines where fire resistance is required.
NA-YJV22, NB-YJV22, cross-linked polyethylene insulated steel belt armored PVC sheathed A (B) class fire-resistant power cables are suitable for underground laying when fire resistance is required, but not suitable for laying in pipelines.
NA-VV, NB-VV, PVC insulated PVC sheathed A (B) class fire-resistant power cables can be laid indoors, tunnels and pipelines where fire resistance is required.
NA-VV22, NB-VV22, PVC insulated steel tape armored PVC sheathed A (B) class fire-resistant power cables are suitable for underground laying when fire resistance is required, but not suitable for laying in pipelines.
WDNA-YJY23, WDNB-YJY23, cross-linked polyethylene insulated steel tape armored polyolefin sheathed A (B) class halogen-free low-smoke fire-resistant power cables are suitable for underground laying when halogen-free, low-smoke and fire resistance are required, but not suitable for laying in pipelines.
ZA-YJV, ZA-YJLV, ZB-YJV, ZB-YJLV, ZC-YJV, ZC-YJLV, cross-linked polyethylene insulated PVC sheathed A (B, C) class flame-retardant power cables can be laid indoors, in tunnels and pipelines where flame retardancy is required.
ZA-YJV22, ZA-YJLV22, ZB-YJV22, ZB-YJLV22, ZC-YJV22, ZC-YJLV22, cross-linked polyethylene insulated steel tape armored PVC sheathed A (B, C) class flame-retardant power cables are suitable for underground laying when flame retardancy is required, and are not suitable for laying in pipelines.
ZA-VV, ZA-VLV, ZB-VV, ZB-VLV, ZC-VV, ZC-VLV, PVC insulated PVC sheathed A (B, C) class flame-retardant power cables can be laid indoors, in tunnels and pipelines where flame retardancy is required.
ZA-VV22, ZA-VLV22, ZB-VV22, ZB-VLV22, ZC-VV22, ZC-VLV22, PVC insulated steel tape armored PVC sheathed Class A (B, C) flame retardant power cables are suitable for underground laying when flame retardancy is required, and are not suitable for laying in pipelines.
WDZA-YJY, WDZA-YJLY, WDZB-YJY, WDZB-YJLY, WDZC-YJY, WDZC-YJLY, cross-linked polyethylene insulated polyolefin sheathed Class A (B, C) flame retardant power cables can be laid indoors, in tunnels and pipelines where flame retardancy, halogen-free and low-smoke are required.
WDZA-YJY23, WDZA-YJLY23, WDZB-YJY23, WDZB-YJLY23, WDZC-YJY23, WDZC-YJLY23,
Cross-linked polyethylene insulated, steel tape armored, polyolefin sheathed Class A (B, C) flame-retardant power cable is suitable for underground laying when flame retardancy, halogen-free and low-smoke are required, and is not suitable for laying in pipelines.
VV, VLV, copper (aluminum) core PVC insulated PVC sheathed power cables are laid indoors, in tunnels and pipelines or on outdoor brackets, and do not bear pressure and mechanical external forces
VY, VLY, copper (aluminum) core PVC insulated polyethylene sheathed power cables
VV22, VLV22, copper (aluminum) core PVC insulated steel tape armored PVC sheathed power cables are laid indoors, in tunnels, cable trenches and directly buried in soil. The cables can withstand pressure and other external forces
VV23, VLV23, copper (aluminum) core PVC insulated steel tape armored polyethylene sheathed power cables
This product is suitable for fixed granary lines for transmission and distribution of AC rated voltage of 35KV and below. The maximum long-term working temperature of the cable conductor is 90 degrees. When short-circuited (the maximum time does not exceed 5S), the maximum temperature of the cable conductor does not exceed 250 degrees.
1.8kV and below are low-voltage cables; 3.6KV~35KV are medium-voltage cables; 35KV~110KV are high-voltage cables; 110~220KV are ultra-high voltage cables;
Ultra-high voltage cable is a type of power cable that has emerged with the continuous development of cable technology. Ultra-high voltage cable is generally used as a hub in a large-scale power transmission system. It is a type of high-voltage cable with high technical content and is mainly used for long-distance power transmission.
The cable is a bridge between power supply equipment and power equipment, and plays the role of transmitting electrical energy. It is widely used, so failures often occur. The following is a brief analysis of the causes of common problems in high-voltage cables. According to the causes of the failure, they are roughly divided into the following categories: manufacturer manufacturing reasons, construction quality reasons, design unit design reasons, and external force damage.
Manufacturer manufacturing reasons are divided into three categories according to the different locations of occurrence, namely, cable body reasons, cable joint reasons, and cable grounding system reasons.
Reasons for cable body manufacturing
Generally, problems that are prone to occur during the cable production process include insulation eccentricity, uneven insulation shield thickness, impurities in the insulation, protrusions on the inner and outer shields, uneven cross-linking, cable dampness, poor sealing of the cable metal sheath, etc. Some serious cases may cause failures during the completion test or shortly after commissioning. Most of them exist in the form of defects in the cable system, posing serious hidden dangers to the long-term safe operation of the cable.
Reasons for cable joint manufacturing
High-voltage cable joints used to be wrapped, molded, and molded. The workload required for on-site production was large, and because of the limitations of on-site conditions and the production process, there would inevitably be air gaps and impurities between the insulation tape layers, so problems were prone to occur. The types commonly used in China are assembly and prefabricated types.
Cable joints are divided into cable terminal joints and cable intermediate joints. Regardless of the joint form, cable joint failures generally occur at the cable insulation shielding fracture, because this is the location where electrical stress is concentrated. The reasons for cable joint failures due to manufacturing reasons include manufacturing defects of the stress cone body, insulation filler problems, and oil leakage of the sealing ring.
Cable grounding system
The cable grounding system includes cable grounding box, cable grounding protection box (with sheath protector), cable cross interconnection box, sheath protector and other parts. The main problem that is prone to occur is that the box is not well sealed and water enters, resulting in multiple grounding points, causing excessive induced current in the metal sheath. In addition, the unreasonable selection of sheath protector parameters or poor quality of zinc oxide crystal instability can also easily cause damage to the sheath protector.
There are many examples of high-voltage cable system failures due to construction quality. The main reasons are as follows: First, the site conditions are relatively poor. The environment and process requirements for cables and joints are very high when they are manufactured in the factory, and the temperature, humidity and dust at the construction site are not easy to control. Second, during the cable construction process, it is inevitable that small scratches will be left on the insulation surface. Semi-conductive particles and sand on the emery cloth may also be embedded in the insulation. In addition, during the joint construction process, the insulation is exposed to the air, and moisture will be absorbed into the insulation, which will leave hidden dangers for long-term safe operation. Third, the installation was not strictly carried out in accordance with the process or the process regulations did not take into account possible problems. Fourth, the DC withstand voltage test was used for the completion acceptance, which caused the formation of a reverse electric field in the joint and led to insulation damage. Fifth, it was caused by poor sealing. The intermediate joint must adopt a sealing structure with a metal copper shell plus a PE or PVC insulation anti-corrosion layer. The lead seal must be dense during on-site construction, which effectively ensures the sealing and waterproof performance of the joint.
The cable is squeezed and broken down due to the thermal expansion of the cable. When the cross-linked cable is loaded with high load, the core temperature rises, the cable expands due to heat, and the cable is pressed against the bracket facade at the turning point in the tunnel. The long-term high-load operation of the cable has a large creeping force, which causes the bracket facade to crush the cable outer sheath and metal sheath, squeeze into the cable insulation layer, and cause the cable to break down.
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