High voltage cable is a kind of power cable, refers to the transmission of 1kv-1000kv between the power cable, mainly used in power transmission and distribution, high voltage cable in the laying of the air chamber space of the building. The product implementation standard of high voltage cable is GB12706.3-2002. High voltage lines usually refer to transmission lines that transport more than 10KV(including 10KV), and high voltage usually does not include 1000V.
High voltage cable is a kind of power cable, high voltage cable is laid in the air chamber space of the building. High voltage cables are sheathed with flame retardant plastic sheaths of low smoke polyvinyl chloride (PVC) or fluorinated vinyl polymer (FEP).
Species
YJV cable full name XLPE insulated PVC sheathed Power cable (copper core)
VV cable full name Polyvinyl chloride insulated polyvinyl chloride sheathed power cable (copper core)
YJLV cable full name crosslinked polyethylene insulated polyvinyl chloride sheathed aluminum core power cable
VLV cable full name PVC 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 road of the power supply system, while the application of aluminum core power cables is less, especially in the higher voltage power system, the more copper core cables are selected.
NA-YJV, NB-YJV, cross-linked polyethylene insulated polyvinyl chloride sheathed Class A(B) fire-resistant power cables can be laid in indoor, tunnel and pipeline where fire resistance is required.
NA-YJV22, NB-YJV22, cross-linked polyethylene insulated steel tape armored polyvinyl chloride sheathed Class A(B) fire-resistant power cables are suitable for buried laying when fire resistance is required, not suitable for pipeline laying.
NA-VV, NB-VV, PVC insulated PVC sheathed Class A(B) fire-resistant power cables can be laid in indoor, tunnel and pipeline requirements for fire resistance.
NA-VV22, NB-VV22, PVC insulated steel tape armouring PVC sheathed A(B) class fire-resistant power cable suitable for fire resistance requirements when buried laying, not suitable for pipeline laying.
WDNA-YJY23, WDNB-YJY23, crosslinked polyethylene insulated steel tape armouring polyolefin sheathed Class A(B) halogen-free low-smoke refractory power cable suitable for halogen-free low-smoke and fire resistance requirements buried laying, not suitable for pipeline laying.
ZA-YJV, ZA-YJLV, ZB-YJV, ZB-YLV, ZB-YJV, ZC-YJLV, crosslinked polyethylene insulated polyvinyl chloride sheathed A(B, C) class flame retardant power cables can be laid in the indoor, tunnel and pipeline requirements for flame retardant.
ZA-YJV22, ZA-YJLV22, ZB-YJV22, ZB-YJLV22, ZC-YJLV22, ZC-YJLV22, crosslinked polyethylene insulated steel tape armored polyvinyl chloride sheathed A(B, C) class flame retardant power cable suitable for flame retardant requirements when buried laying, not suitable for pipeline laying.
ZA-VV, ZA-VLV, ZB-VV, ZB-VLV, ZC-VLV, PVC insulation PVC sheathed A(B, C) class flame retardant power cables can be laid in the indoor, tunnel and pipeline requirements for flame retardant.
ZA-VV22, ZA-VLV22, ZB-VV22, ZB-VLV22, ZC-VV22, ZC-VLV22, PVC insulated steel tape armored PVC sheathed A(B, C) class flame retardant power cable suitable for flame retardant requirements when buried laying, not suitable for pipeline laying.
WDZA-YJY, WDZA-YJLY, WDZB-YJY, WDZC-YJLY, crosslinked polyethylene insulated polyolefin sheathed Class A(B, C) flame retardant power cables can be laid in indoor, tunnel and pipeline with flame retardant and halogen-free low smoke requirements.
WDZA-YJY23, WDZA-YJLY23, WDZB-YJY23, WDZB-YJLY23, WDZC-YJY23, WDZC-YJLY23, WDZC-YjLY23, WDZC-YjLY23,
Crosslinked polyethylene insulated steel tape armouring polyolefin sheathed A(B, C) class flame retardant power cable suitable for flame retardant and halogen-free low smoke requirements buried laying, not suitable for pipeline laying.
VV, VLV, copper (aluminum) core PVC insulation PVC sheathed power cable laying indoors, tunnels and pipelines or outdoor bracket laying, do not withstand pressure and mechanical external force
VY, VLY, copper (aluminum) core PVC insulated polyethylene sheathed power cable
VV22, VLV22, copper (aluminum) core PVC insulated steel tape armouring PVC sheathed power cables laid in indoor, tunnel, cable trench and directly buried in the soil, the cable can withstand pressure and other external forces
VV23, VLV23, copper (aluminum) core PVC insulated steel tape armoured polyethylene sheathed power cable
Advantages: Occupy less ground and space, little affected by weather and external environment, can improve the system power factor, is conducive to personal safety, operation and maintenance is simple and convenient, is conducive to urban planning, is conducive to environmental protection.
Disadvantages: The construction investment cost is large, the cable line is not easy to change, the branch technology is complex, the cable joint requires specialized technology, the cost is high, the fault finding is difficult, and the repair time is long.
Structure
Technical Knowledge
First of all, ensure that the electrical parameters of the stress tube must meet the above standard values in order to work reliably. It is necessary to fill the air gap of the cable insulation semi-conductive layer with silicone grease to eliminate gas and achieve the purpose of reducing partial discharge. Due to poor internal stress handling, the cross-linked cable will shrink greatly during operation. Therefore, when installing accessories, pay attention to the stress tube and the insulation shield cover not less than 20mm to prevent the stress tube from separating from the insulation shield during shrinkage. Due to the small elasticity of the heat shrink attachment, the interface may produce an air gap when the heat expands and cold shrinks during operation, so the sealing technology is very important to prevent moisture immersion.
Fault Manifestation
The performance of high voltage cable damage mainly includes cable outer sheath damage, cable trench collapse and cable body breakdown, etc. The consequences may be: transmission, transformer, power supply system paralysis, construction machinery and equipment burning, serious may be: inflation equipment burst, resulting in the expansion of the accident or chain disaster, and even a major safety accident leading to life danger. Therefore, the necessary high voltage cable line inspection and protective measures are very important.
According to the cause of the failure, it is roughly divided into four categories: manufacturer manufacturing, construction quality, design unit design and external damage.
Manufacturer reason
According to different manufacturing reasons, manufacturers can be divided into cable bodies, cable joints and cable grounding systems.
Ontological cause
In general, the problems prone to occur in the cable production process include insulation eccentricity, uneven insulation shield thickness, insulation impurities, internal and external shielding protrusions, uneven cross-linking, cable moisture, and poor cable metal sheath sealing. In some cases, failures may occur shortly after completion tests or operation, and most cable systems have defects that pose serious risks to the long-term safe operation of the cable.
Reason for joint
In the past, high-voltage cable joints used winding, mold casting, molding and other types, and the on-site production workload was large. Due to the limitations of site conditions and production processes, there will inevitably be gaps and impurities between the insulation tape layers, so it is prone to problems. The commonly used types in China are prefabricated and prefabricated.
Cable joints are divided into cable terminal joints and cable intermediate joints. Regardless of the joint form, the cable joint failure generally occurs at the cable insulation shield fracture, because it is the part of the electrical stress concentration. The causes of cable joint failure include stress cone manufacturing defects, insulation packing problems, sealing ring oil leakage, etc.
Grounding system
The cable grounding system includes a cable grounding box, a cable grounding protection box (with a protective layer protector), a cable cross-interconnection box, and a protective layer protector. The general problem is mainly due to the poor seal of the box, resulting in multi-point grounding, resulting in excessive induction current of the metal protective layer. In addition, the parameter selection of the protective layer protector is unreasonable or the quality is poor, and the zinc oxide crystal is unstable, which is also easy to cause damage to the protective layer protector.
Construction reason
There are many cases of high voltage cable system failure caused by construction quality, the main reasons are as follows
First, the site conditions are poor, the environment and process requirements are high when the cable and joint are manufactured in the factory, and the temperature, humidity and dust on the construction site are difficult to control.
Second, during the construction of the cable, small slip marks will inevitably be left on the insulation surface, and semi-conductive particles and sand particles on the emery cloth may also be embedded in the insulation. In addition, because the insulation is exposed to the air, the moisture in the joint construction process will also be inhaled, leaving hidden dangers for long-term safe operation.
Third, the problems that may occur in the installation process are not strictly considered in accordance with the process construction or process regulations.
Fourth, the DC voltage withstand test is used for completion acceptance, resulting in the formation of anti-electric field in the joint, resulting in insulation damage.
Fifth, the sealing is not handled well. The sealing structure of the intermediate joint must be added with metal copper shell PE or PVC insulation anticorrosive layer to ensure the sealing of the lead seal in the field construction, and effectively ensure the sealing and waterproof performance of the joint.
Design reason
Cable extrusion damage due to thermal expansion of the cable. When the cross-linked cable load is high, the core temperature rises, and the cable is heated and expanded. The top of the cable at the tunnel bend is located on the support facade. The creep force of the cable with long-term heavy load operation is very large, which causes the support facade to destroy the outer sheath and metal sheath of the cable, and extrude the cable insulation layer, resulting in cable breakage.
For the protection measures of high-voltage cables, in general, the construction quality must be ensured during construction, especially the production quality of the cable head, which must meet the regulations and requirements; In addition, to strengthen the protection of cable lines in construction, the following methods are commonly used:
First, isolation protection: cable line buried deep and close to the pile foundation or foundation pit cable protection method, can be through steel sheet pile, root pile, deep mixing pile, etc. to form an isolation body, limit the displacement of soil around the underground cable line, to prevent squeezing or vibration cable line; For the cable line buried depth is not large, it can also be dug isolation groove method, isolation groove location can be selected between the construction point and the cable line, can also be excavated in the cable part, or the cable line can be dug out of the hanging. Note that the isolation groove must be dug deep to the point of the pipeline in order to play the role of isolating extrusion pressure and vibration force.
Second, suspension protection: excavation of the foundation pit within the scope of the cable protection area needs to be hollowing out the cable trench to protect the safety of the cable trench, so that the cable pipeline will be exposed to the foundation pit, and the middle of the cable pipeline can not be set up to support, in this case, the cable pipeline can be fixed by the suspension method. Among them, attention must be paid to: 1, the exposed cable must be protected by buckle; 2, when the cable box culvert is emptied, it should be suspended every 1 to 1.5 meters, and the steel plate should be placed in the cable box culvert to ensure that the cable box culvert is evenly stressed; 3. The deformation length of the sling and the fixed point position of the sling should not be affected by soil deformation.
Support protection: If the cable pipeline needs to be suspended, a number of support points can also be set up along the line to support the line, including temporary support bodies such as steel sheet piles, piers, etc., which are convenient for construction and removal, and can also be used as permanent buildings for permanent installation of support points.
Fourth, cable trench reinforcement protection: considering the construction of large heavy machinery within the protection scope of the cable corridor, the cable trench is generally reinforced and protected, and a layer of "protective shell" is added around the original box culvert, so that the load of the original cable trench is all unloaded onto the newly built cable trench, to achieve the unloading protection of the cable box culvert, and the load around the cable box culvert is removed.
In addition, after the cable line installation is completed, it is necessary to strengthen the cable operation monitoring to avoid the cable overload operation, and at the same time, the cable should be tested in accordance with a certain period of time. If the abnormal problem is found, corresponding measures should be taken immediately to deal with it in time. The cable trench should be kept dry to prevent the cable from getting damp, resulting in decreased insulation and causing short circuit.
Important reminder: It is necessary to regularly clean the accumulated dust on the high-voltage cable, prevent these dust from naturally causing the cable fire, and strengthen the regular verification and maintenance of the cable circuit switch and protection to ensure its reliability.