More than 30 years of research and development of high quality electric cables
Advantages, disadvantages, and model specifications of power cables
2020-07-10
1、 Main characteristics of cables
Advantages: It occupies less ground and space, and is less affected by weather and external environment. It can improve the system power factor, which is conducive to personal safety, operation and maintenance. It is simple and convenient, which is conducive to urban planning and environmental protection
Disadvantages: The construction investment cost is high, and the cable line is difficult to change. The branch technology is complex, and the cable joint requires specialized technology, which is expensive. Fault detection is difficult, and the repair time is long
Especially suitable for situations where cable networks are used Important office spaces:
Party and government organs; Research institutes; International institutions; Embassy and consulate
Places with dense lines: such as substations and distribution rooms located in urban areas; power plant; Within large enterprises; commercial centre; CBD area; financial center; City square; High rise building; Scenic spots in residential areas; Important crossings in cultural relics protection areas: crossing railways; Crossing highways; Crossing rivers.
2、 Basic knowledge of power cables
① What is a power cable?
A special wire that is insulated and wrapped around the metal wire core, shielded and sealed with protective materials, and capable of transmitting electrical energy. Mainly including wire core, insulation, protection, and sealing.
② Classified by voltage level:
Low voltage power cables: 3kV and below;
Medium voltage power cable: 6kV~35kV;
High voltage power cable: 66kV~110kV;
Ultra high voltage power cable: 220kV~500kV;
Ultra high voltage power cable: 750kV; 1000kV。
3、 Cable types are classified according to insulation materials:
1. Cross-linked polyethylene insulated cable
2. Polyvinyl chloride (PVC) insulated cable
3. Polyethylene (PE) insulated cable
4. Rubber insulated cable
5. Viscous oil paper insulated cable
6. Non drip oil paper insulated cable
7. Oil filled cable
8. Inflatable cable
4、 The meaning of cable specifications and models
Advantages: It occupies less ground and space, and is less affected by weather and external environment. It can improve the system power factor, which is conducive to personal safety, operation and maintenance. It is simple and convenient, which is conducive to urban planning and environmental protection
Disadvantages: The construction investment cost is high, and the cable line is difficult to change. The branch technology is complex, and the cable joint requires specialized technology, which is expensive. Fault detection is difficult, and the repair time is long
Especially suitable for situations where cable networks are used Important office spaces:
Party and government organs; Research institutes; International institutions; Embassy and consulate
Places with dense lines: such as substations and distribution rooms located in urban areas; power plant; Within large enterprises; commercial centre; CBD area; financial center; City square; High rise building; Scenic spots in residential areas; Important crossings in cultural relics protection areas: crossing railways; Crossing highways; Crossing rivers.
2、 Basic knowledge of power cables
① What is a power cable?
A special wire that is insulated and wrapped around the metal wire core, shielded and sealed with protective materials, and capable of transmitting electrical energy. Mainly including wire core, insulation, protection, and sealing.
② Classified by voltage level:
Low voltage power cables: 3kV and below;
Medium voltage power cable: 6kV~35kV;
High voltage power cable: 66kV~110kV;
Ultra high voltage power cable: 220kV~500kV;
Ultra high voltage power cable: 750kV; 1000kV。
3、 Cable types are classified according to insulation materials:
1. Cross-linked polyethylene insulated cable
2. Polyvinyl chloride (PVC) insulated cable
3. Polyethylene (PE) insulated cable
4. Rubber insulated cable
5. Viscous oil paper insulated cable
6. Non drip oil paper insulated cable
7. Oil filled cable
8. Inflatable cable
4、 The meaning of cable specifications and models
For example: ZC-YJV23-8.7/10kV-3 × 240 ① The first half represents the model: ZC-YJV23 flame-retardant Class C cross-linked polyethylene insulation (copper core), PVC inner sheath, double steel strip armor, polyethylene outer sheath. ② The latter half represents specifications: 8.7/10kV-3 × The phase voltage U0 designed for 240 cables is 8.7kV; The designed line voltage U of the cable is 10kV; Three wire cores, each with a nominal cross-sectional area of 240 mm2.
Two voltage concepts in cable networks
① Power system voltage: The rated voltage of the power system during normal operation. For example, 220V, 380V, 10kV, 35kV, 110kV, 220kV, 500kV, etc Cable product voltage: expressed as U0/U (Um). For example; 6/10(12)kV、8.7/10(12)kV、21/35(40.5)kV、26/35(40.5)kV、64 /110(126)kV。 Among them: U0: phase voltage; U: Line voltage; Um: The maximum value (maximum voltage) of the "highest system voltage" that the device can withstand.
5、 Basic structure of power cables
The function of wire core ① is to transmit electrical energy, and commonly used materials are copper and aluminum. ② Sectional area (unit of measurement: square millimetre): In order to facilitate the manufacture and use of cable sections, standard series specifications are adopted. The regulations in China are: 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630, 800, 1000, 1200, 1400, 1600, 2000, 2500, etc. ③ Wire core structure: Multiple fine wires are twisted into bundles, and then compressed by a mold to increase the compression coefficient from 0.73 to above 0.9, which is conducive to crimping connection Cable conductor resistance: The conductor itself has resistance and generates heat when passing through the current, and its temperature rise value is a key factor limiting the current carrying capacity of the cable. We hope that the smaller the resistance of the conductor, the better.
Conductor shielding layer (also known as inner shielding layer or inner semi conductive layer): ① The conductor shielding layer is a non-metallic layer extruded onto the cable conductor, with equal potential to the conductor and a volume resistivity of 100-1000 Ω • m. Equipotential with conductor. ② Generally, low voltage cables of 3kV and below do not have a conductor shielding layer, while medium and high voltage cables of 6kV and above must have a conductor shielding layer The main function of the conductor shielding layer is to eliminate pits and unevenness on the surface of the conductor; Eliminate the tip effect on the conductor surface; Eliminate pores between conductors and insulation; Make close contact between conductors and insulation; Improve the electric field distribution around the conductor; The shielding layer of cross-linked cable conductors also has the effect of inhibiting the growth of electrical trees and thermal shielding.
Insulation layer (also known as main insulation) ① The main insulation of the cable has a specific function of withstanding system voltage. During the service life of the cable, it must withstand the rated voltage and overvoltage during system faults, lightning impulse voltage for a long time, to ensure that there is no phase to ground or phase to phase breakdown short circuit under working heating conditions. Therefore, the main insulation material is the key to the quality of the cable Crosslinked polyethylene is a good insulation material that is now widely used, with a color of cyan white and semi transparent. Its characteristics are: high insulation resistance; Capable of withstanding high power frequency and pulse electric field breakdown strength; Lower tangent value of dielectric loss angle; Stable chemical performance; Good heat resistance, with a long-term allowable operating temperature of 90 ℃; Good mechanical properties, easy to process and process.
Insulation shielding layer (also known as outer shielding layer or outer semi conductive layer) ① The insulation shielding layer is a non-metallic layer extruded onto the main insulation of the cable, and its material is also a cross-linked material with semi conductive properties, with a volume resistivity of 500-1000 Ω • m. Equipotential with grounding protection. ② Generally, low voltage cables of 3kV and below do not have an insulation shield layer, while medium and high voltage cables of 6kV and above must have an insulation shield layer The function of the insulation shielding layer: the transition between the main insulation of the cable and the grounding metal shield, providing close contact and eliminating pores between the insulation and grounding conductors; Eliminate the tip effect on the surface of the grounding copper strip; Improve the electric field distribution around the insulation surface. ④ Insulation shielding can be divided into peelable and non peelable types according to the process. Generally, for medium voltage cables, peelable types are used for 35kV and below. Good peelable insulation shielding has good adhesion and there are no semi conductive particles left after peeling. 110kV and above shall be of non stripping type. The combination of non stripping shielding layer and main insulation is closer, and the construction process requirements are higher.
Metal shielding layer ① The metal shielding layer is wrapped outside the insulation shielding layer, and the metal shielding layer generally uses copper tape or wire. It is a key structure that limits the electric field inside the cable and protects personal safety. It is also a grounding shielding layer that protects cables from external electrical interference In case of grounding or short circuit fault in the system, the metal shielding layer is the channel of short circuit grounding current, and its cross-sectional area shall be calculated and determined according to the system short circuit capacity and neutral point grounding mode. Generally, the cross-sectional area of the shielding layer calculated for 10kV systems is recommended to be no less than 25 square millimetre. ③ In 110kV and above cable lines, the metal shielding layer is composed of a metal sheath, which has both electric field shielding and waterproof sealing functions, as well as mechanical protection functions The material and structure of metal sheaths generally use corrugated aluminum sheaths; Corrugated copper sheath; Corrugated stainless steel sheath; Lead sheath, etc. Another type of composite sheath is a structure that uses aluminum foil attached to PVC and PE sheaths, which is commonly used in European and American products.
The armor layer ① is wrapped with a metal armor layer outside the inner lining layer, generally using double-layer galvanized steel strip armor. Its function is to protect the interior of the cable and prevent mechanical external forces from damaging the cable during construction and operation. It also has the function of grounding protection The armor layer has various structures, such as steel wire armor, stainless steel armor, non-metallic armor, etc., used for special cable structures. The outer sheath ① is the outermost protection of the cable, usually made of polyvinyl chloride (PVC) and polyethylene (PE), which are insulation materials and are formed by extrusion. According to technical requirements, flame retardant polyvinyl chloride (PVC) is generally used. Adapt to the requirements of cold winter and hot summer, without cracking or softening The main function of the outer sheath is to seal and prevent moisture intrusion, protect the armor layer from corrosion, and prevent the expansion of fire caused by cable faults On the outer sheath, there is also printed the characteristic information of the cable, such as specification, model, production year, manufacturer, continuous meter length, etc.
Insulation layer (also known as main insulation) ① The main insulation of the cable has a specific function of withstanding system voltage. During the service life of the cable, it must withstand the rated voltage and overvoltage during system faults, lightning impulse voltage for a long time, to ensure that there is no phase to ground or phase to phase breakdown short circuit under working heating conditions. Therefore, the main insulation material is the key to the quality of the cable Crosslinked polyethylene is a good insulation material that is now widely used, with a color of cyan white and semi transparent. Its characteristics are: high insulation resistance; Capable of withstanding high power frequency and pulse electric field breakdown strength; Lower tangent value of dielectric loss angle; Stable chemical performance; Good heat resistance, with a long-term allowable operating temperature of 90 ℃; Good mechanical properties, easy to process and process.
Insulation shielding layer (also known as outer shielding layer or outer semi conductive layer) ① The insulation shielding layer is a non-metallic layer extruded onto the main insulation of the cable, and its material is also a cross-linked material with semi conductive properties, with a volume resistivity of 500-1000 Ω • m. Equipotential with grounding protection. ② Generally, low voltage cables of 3kV and below do not have an insulation shield layer, while medium and high voltage cables of 6kV and above must have an insulation shield layer The function of the insulation shielding layer: the transition between the main insulation of the cable and the grounding metal shield, providing close contact and eliminating pores between the insulation and grounding conductors; Eliminate the tip effect on the surface of the grounding copper strip; Improve the electric field distribution around the insulation surface. ④ Insulation shielding can be divided into peelable and non peelable types according to the process. Generally, for medium voltage cables, peelable types are used for 35kV and below. Good peelable insulation shielding has good adhesion and there are no semi conductive particles left after peeling. 110kV and above shall be of non stripping type. The combination of non stripping shielding layer and main insulation is closer, and the construction process requirements are higher.
Metal shielding layer ① The metal shielding layer is wrapped outside the insulation shielding layer, and the metal shielding layer generally uses copper tape or wire. It is a key structure that limits the electric field inside the cable and protects personal safety. It is also a grounding shielding layer that protects cables from external electrical interference In case of grounding or short circuit fault in the system, the metal shielding layer is the channel of short circuit grounding current, and its cross-sectional area shall be calculated and determined according to the system short circuit capacity and neutral point grounding mode. Generally, the cross-sectional area of the shielding layer calculated for 10kV systems is recommended to be no less than 25 square millimetre. ③ In 110kV and above cable lines, the metal shielding layer is composed of a metal sheath, which has both electric field shielding and waterproof sealing functions, as well as mechanical protection functions The material and structure of metal sheaths generally use corrugated aluminum sheaths; Corrugated copper sheath; Corrugated stainless steel sheath; Lead sheath, etc. Another type of composite sheath is a structure that uses aluminum foil attached to PVC and PE sheaths, which is commonly used in European and American products.
The armor layer ① is wrapped with a metal armor layer outside the inner lining layer, generally using double-layer galvanized steel strip armor. Its function is to protect the interior of the cable and prevent mechanical external forces from damaging the cable during construction and operation. It also has the function of grounding protection The armor layer has various structures, such as steel wire armor, stainless steel armor, non-metallic armor, etc., used for special cable structures. The outer sheath ① is the outermost protection of the cable, usually made of polyvinyl chloride (PVC) and polyethylene (PE), which are insulation materials and are formed by extrusion. According to technical requirements, flame retardant polyvinyl chloride (PVC) is generally used. Adapt to the requirements of cold winter and hot summer, without cracking or softening The main function of the outer sheath is to seal and prevent moisture intrusion, protect the armor layer from corrosion, and prevent the expansion of fire caused by cable faults On the outer sheath, there is also printed the characteristic information of the cable, such as specification, model, production year, manufacturer, continuous meter length, etc.
6、 Packaging, transportation, and storage of cables
1. The packaging of cables requires the use of cable reels, including iron reels, wooden reels, and iron framed wooden reels. The outer diameter of the reels has a significant impact on the cost of transportation and storage. It is recommended to use reels with a diameter of less than 3.2 meters and a width of no more than 2.2 meters for 10kV and below cables. For cables exceeding 3.5 meters, special transport vehicles should be used.
2. The weight of each cable reel is related to the specification, model, and length of the cable. Generally, the single reel length of medium and low voltage cables is around 500 meters, and the weight is 3-10 tons.
3. During transportation and loading and unloading, cables and cable trays should not be damaged. It is strictly prohibited to push the cable reel directly from the vehicle. Cable trays should not be transported or stored flat.
4. Before transporting or rolling the cable reel, it is necessary to ensure that the cable reel is secure and the cable is tightly wound. When rolling, it is necessary to follow the arrow on the cable reel or the tightening direction of the cable.
5. The cable head should be protected and reliably sealed during transportation and storage to prevent moisture and water ingress. When there is suspicion in the appearance inspection, moisture judgment or testing should be carried out. Any damage to the head during storage should be dealt with immediately.
6. Cable storage should be centralized and classified, and the model, voltage, specification, and length should be indicated. There should be channels between cable trays. The foundation should be solid, and when restricted by conditions, pads should be added under the tray, and the storage area should not accumulate water. When the cable reel is damaged, it should be replaced in a timely manner.
7. Oil filled cables should be kept in good condition during transportation and storage, including pressure tanks, oil pipes, valves, and pressure gauges. During the storage period, the oil pressure should be regularly checked and recorded, and the oil pressure should not drop to the lowest value. When the oil pressure drops to zero or a vacuum occurs, it should be handled promptly.
1. The packaging of cables requires the use of cable reels, including iron reels, wooden reels, and iron framed wooden reels. The outer diameter of the reels has a significant impact on the cost of transportation and storage. It is recommended to use reels with a diameter of less than 3.2 meters and a width of no more than 2.2 meters for 10kV and below cables. For cables exceeding 3.5 meters, special transport vehicles should be used.
2. The weight of each cable reel is related to the specification, model, and length of the cable. Generally, the single reel length of medium and low voltage cables is around 500 meters, and the weight is 3-10 tons.
3. During transportation and loading and unloading, cables and cable trays should not be damaged. It is strictly prohibited to push the cable reel directly from the vehicle. Cable trays should not be transported or stored flat.
4. Before transporting or rolling the cable reel, it is necessary to ensure that the cable reel is secure and the cable is tightly wound. When rolling, it is necessary to follow the arrow on the cable reel or the tightening direction of the cable.
5. The cable head should be protected and reliably sealed during transportation and storage to prevent moisture and water ingress. When there is suspicion in the appearance inspection, moisture judgment or testing should be carried out. Any damage to the head during storage should be dealt with immediately.
6. Cable storage should be centralized and classified, and the model, voltage, specification, and length should be indicated. There should be channels between cable trays. The foundation should be solid, and when restricted by conditions, pads should be added under the tray, and the storage area should not accumulate water. When the cable reel is damaged, it should be replaced in a timely manner.
7. Oil filled cables should be kept in good condition during transportation and storage, including pressure tanks, oil pipes, valves, and pressure gauges. During the storage period, the oil pressure should be regularly checked and recorded, and the oil pressure should not drop to the lowest value. When the oil pressure drops to zero or a vacuum occurs, it should be handled promptly.
Related news
■
TEl：
Cases：
More than 30 years focus on high quality cable development and manufacturing
Address：
Guantun Village, Shaha Subdistrict, Sujiatun District, Shenyang City
Copyright shenyang electric power cable factory. All rights reserved
Note: some of the materials are from the Internet, if you have any questions, please contact us