I. Applicable standards and definitions of cable accessories
There are three main levels of applicable standards for cable accessories:
Level 1: IEC standards
IEC62076 power cable systems for extruded insulated power cables and their accessories with rated voltage from 150kV(Um=170kV) up to 500kV(Um=550kV) -- test methods and requirements
IEC60840 test methods and requirements for extruded insulated power cables and their accessories with rated voltage from 30kV(Um=36kV) to 150kV(Um=170kV)
IEC60859 Cable Connection Device for Gas-Insulated Metal Enclosed Switches with Rated Voltage of 72.5kV and Above
IEC60502 Extruded insulated Power Cables and Accessories with Rated Voltage from 1kV(Um=1.2kV) to 30kV(Um=36kV)
IEC60055 Paper insulated metal sheathing (with copper or aluminum body but excluding pressurized gas and oil-filled cables) rated Voltage up to and including 18/30kV - Part 1 - Cable and Accessory Tests chapter 7: Type tests for accessories
IEC61442 - test method for accessories of power cables with rated voltage from 6kV(Um= 7.2kv) to 30kV(Um=36kV)
Level 2: National standard (GB standard)
Rated Voltage 220kV(Um=250kV) Crosslinked polyethylene Insulated Power Cable and Its Accessories
GB/Z11017 Crosslinked Polyethylene Insulated Power Cables and Accessories with Rated Voltage 110kV
GB5589 Test Method for Cable Accessories
GB9327 Test Methods for Cable Conductor Compression and Mechanical Connection Joints
GB14315 Crimped Copper and Aluminum Terminals and Connecting Pipes for Wire and Cable Conductors
Note: GB11033 "basic technical requirements for power cable accessories with rated voltage 26, 35kV and below" has been lowered to JB/T8144
Level 3: Industry standards
JB standard (Machinery Industry Association Standard)
JB/T8144 basic Technical Requirements for Power Cable Accessories with Rated Voltage 26/35kV and below GB11033
JB6464 Straight Winding Connector for Power Cables with Rated Voltage 26/35kV and Below
JB6465 "Indoor type and Outdoor Type Porcelain Bushing is terminal for Power Cables with Rated Voltage 26/35kV and Below"
JB6466 Indoor and Outdoor Porcelain Bushing Terminal of Power Cables with Rated Voltage 8.7/10kV and Below
JB6468 Indoor and Outdoor Wrapped Terminal of Power Cables with Rated Voltage 26/35kV and Below
JB7829 "Indoor and Outdoor Thermal Shrinkage Terminals of Power Cables with Rated Voltage 26/35kV and Below"
JB7830 Straight Type Thermal shrinkage Joint for Power Cables with Rated Voltage 26/35kV and Below
JB7831 "Indoor and Outdoor Gating Terminals of Power Cables with Rated Voltage 8.7/10kV and Below"
JB7832 "Rated Voltage 8.7/10kV and Below Power Cable through Type Pouring Joint"
JB/T8501.1 Indoor and Outdoor Prefabricated Terminal of Plastic Insulated Power Cables with Rated Voltage up to and including 26/35kV
JB/T8503.2 Indoor and Outdoor Prefabricated Terminal of Plastic Insulated Power Cables with Rated Voltage up to and including 26/35kV
Cable accessories refer to all kinds of cable terminals and joints in cable lines.
A cable terminal head is a device installed at the end of a cable line and connected to overhead lines or electrical equipment.
A cable joint is a device that connects a cable to a cable.
The development of cable accessories started from the wrapping type, followed by porcelain sleeve type, pouring type, heat shrinkable type, prefabricated type, cold shrinkable type.
Attachment cable terminal electric stress control is to use the Hi - K of the dielectric constant of 25 and made, the dielectric constant of the material, dielectric strength, insulation resistance and dielectric loss factor compared to maintain long-term, stable running, through this kind of stress control method, high electric field intensity on the surface of the terminal can be reduced to 15 v/mil safety within the scope of high potential is moving to the ends of the cable, rather than focusing on cable shielding to cut off the place nearby, so that the cable terminal external insulation tend to be divergent, uniform electric field distribution.
Therefore, the discharge voltage of external insulation is increased, the diameter of the whole cable terminal is reduced, and the shape coefficient of cable accessories is increased, which also increases the discharge voltage.
Features of cable accessories:
Cable accessories (cold shrink) cable terminal insulation material is made of high quality silicone rubber material, it has a good hydrophobic performance, when water droplets on the above, at any time rolling, no conductive water film, and has hydrophobic self-healing properties.
In addition, it has a strong insulation, electrical resistance, corrosion resistance and uv resistance linear, the biggest advantage is to ensure long-term use performance stability.
Long service life, same with the cable body.
The function of cable accessories
At the cable terminal and joints, due to the disconnect of the cable metal sheath and shielding layer, the electric field distribution is much more complex than that of the cable body, and there is axial stress in the electric field at the cable terminal. Therefore, it is necessary to use cable accessories to realize the continuity and connection of the cable, that is, a connection device that can meet certain insulation and sealing requirements.
Cable conductor, insulation, shielding and covering the four main structure layer, cable accessories, as an integral part of the cable line cable terminal in the head, middle joint, must make the four layer structure of the cable has continued, respectively, and can realize good conductor, insulation and reliable, good seal and adequate mechanical strength, to ensure the quality of cable terminals and cable connector, to ensure that the entire cable power supply reliability of distribution network.
The cable accessory terminal head has unique material formulation and manufacturing technology, making it closely attached to the main insulation of the cable, providing constant and lasting radial pressure to the cable body, small partial discharge, high initial voltage, insulation impact level higher than the existing standard level, good waterproof sealing, and "breathing" with the cable body.
Cold shrinkage technology and cable accessories
Cold shrink technology also known as pre-expansion technology, elastic rubber in the elastic range in advance, set into the plastic core to join fixed.
During installation, the elastomer will rapidly shrink and tighten on the cable body as long as the wire core is removed.
No need for fire and special tools, and no trouble of piece-by-piece fitting.
The main products are 1, cold shrink indoor terminal 2, cold shrink outdoor terminal 3, cold shrink middle joint 4, cold shrink three finger sets.
Advantages of cold shrink cable accessories
One, from the construction technology comparison
1) Cold shrinkage construction:
A the cold-shrink cable accessories can reduce too much human factors. In the construction, the cold-shrink can automatically shrink as long as the plastic core is removed. In the shrinkage process, the non-uniform shrinkage of the insulation pipe will not occur due to human factors.
Thus ensuring the quality of construction.
B Cold shrinkage is the contraction from one end to the other end in accordance with the program, which cannot be changed to ensure that no bubbles will appear during the contraction process.
C in the dangerous situation of petrochemical industry.
The construction of cold shrinkage avoids the use of heat source and becomes safe.
2) Thermal shrinkage construction:
The thermal shrinkage of A is greatly affected by the construction level. Uneven heating will lead to uneven shrinkage and thickness of the insulation pipe, or even some parts will not shrink at all, resulting in uneven shrinkage and thickness, and the thin places are prone to breakdown and other problems
In the process of heat shrinkage and heating, It is easy for B to burn the insulation pipe due to poor control of heating degree, which greatly affects the insulation performance of the insulation pipe.
In the heating process, heat shrinkage of C can be heated from one end to the other or from the middle to both ends, which will easily lead to bubbles appearing in the shrinkage process.
D is for places where open fires and other heat sources are prohibited, such as petrochemical and chemical industries. If the use of open fires increases the danger, it may lead to serious accidents.
Ii. In use
1) The cold-shrink cable accessories will keep synchronous respiration with the cable as the cable expands and contracts in heat, so that the cable and accessories can always keep a good combination.
2) Heat-shrinkable cable accessories will not change with the thermal expansion and cooling of the cable, and a long period of operation will easily lead to the gap between the cable and accessories, leading to accidents.
Contrast in quality
1) Due to the inherent advantages of cold shrink, the application of cold shrink cable accessories is constantly developing towards high voltage. Currently, 110KV cold shrink cable accessories are available.
2) The inherent disadvantages of heat-shrinkable cable accessories make the application of heat-shrinkable cable accessories hover below 35KV voltage class for a long time. However, at 35KV voltage class, heat-shrinkable cable accessories have become an important reason for frequent accidents in cable operation.
Price comparison
1) The price of cold shrinkage is expensive. At present, the price of cold shrinkage is about 4-10 times or more than that of hot shrinkage. However, from the perspective of long-term operation cost, more considerations can be given to cold shrinkage over 10KV, especially over 35KV, which will reduce long-term operation cost.
2) The thermal shrinkage is cheap. At present, the thermal shrinkage is most widely used in the fields below 35KV, and the 35KV level has gradually been excessive to the cold shrinkage. The 10KV and 1KV fields are still widely used due to the low price.
To sum up, in the field above 10KV, the long-term operation cost of using cold shrinkage is lower than that of hot shrinkage, so it is recommended to use cold shrinkage.
At 10KV and below, it is economical to use heat shrink.
Cold shrinkage as long as a bit of damage is easy to insulation bad easy to accident!
At present, most of the accessories used for 6 ~ 35kV extruded insulated power cables are cold-shrinkable cable accessories and heat-shrinkable cable accessories.
The two structural types of products have different characteristics.
1) Product features of cold-shrinkable cable accessories.
The cold-shrink cable accessories are made of high elastic special silicone rubber by injection molding.
The electric stress control unit is geometric: stress cone, high temperature and high pressure vulcanization molding process and insulation body prefabricated into a whole, reliable shape and size, stable electrical performance.
When installed, it is fastened to the cable and becomes one with the cable.
2) Product features of heat-shrinkable cable accessories.
The heat-shrinkable cable accessories are extruded from rubber and plastic composites (polymers), cross-linked by high-energy irradiation, and cooled and shaped when expanding and expanding to the required geometry size before leaving the factory.
In the field installation, it is necessary to heat up to a certain temperature, and make use of the "elastic memory" property of the polymer to shrink back to the correct position, so as to tighten the cable cutting and installation part to meet the requirements of insulation sealing.
The electrical stress control unit is of parameter type.
3) Features of cold-shrinkable cable accessories (compared with heat-shrinkable cable accessories).
Compared with heat-shrinkable cable accessories, cold-shrinkable cable accessories have the following characteristics:
Good electrical properties of materials.
Cold-shrinkable cable accessories are made of silicone rubber with high elasticity, good insulation, anti-leakage, hydrophobicity, weather resistance and ultraviolet aging resistance.
The material used in the heat-shrinkable cable accessories is rubber and plastic composite material (polymer). The material itself has no elasticity, only the function of "elastic memory".
(2) Stable performance of electric stress control unit.
The electric stress control unit of the cold-shrink cable accessories is geometric: stress cone, which relies on geometric curves to improve electric field distortion. Its shape has been formed in the company, so the performance of the electric stress control unit is stable.
Heat shrinkable cable accessories electric stress control unit for the parameter type, the electric stress control unit is the high dielectric constant and the volume resistivity between insulating material and semiconducting material material molding, special parameters of the material is difficult to control and easy to change, in the process of molding and construction lead to unstable electric stress control unit performance.
The structural type is more ideal.
The stress cone and insulation part of the cold-shrinkable cable accessories are prefabricated as a whole in the factory through high temperature and high pressure molding process. During installation, the accessories only need to be set on the treated cable. The product quality can be controlled in the factory, and the on-site installation workload is less.
The structure of heat-shrinkable cable accessories is pipes: stress pipes, internal and external insulation pipes, and semi-conductive pipes overlap. It is hard to avoid small air gap between all kinds of pipes, and it is difficult to guarantee the partial discharge performance of the intermediate joints.
More convenient installation: no need of fire.
Due to the limitation of structure type, in some fire-free situations, heat-shrinkable cable accessories are not applicable;
The cold-shrinkable cable accessories are not subject to this limitation, and there is no need for fire and other special tools during installation. Only the skeleton in the main body can be pulled out or the main body can be put in by hand.
(5) Good interface characteristics.
The cold-shrinkable cable accessory is made of high elastic silicone rubber, and the accessory is an elastic body. After installation, the accessory is always tightly bound on the cable, which becomes an integral part of the cable. Meanwhile, it has great pressure on the interface, good interface characteristics and good partial discharge performance.
Since the materials of heat-shrinkable cable accessories are not elastic at room temperature after heating, the bending and kneading of the cable will cause the separation between the heat-shrinkable cable accessories and the cable after installation.
In the process of cable operation, the change of ambient temperature will also create a gap between the heat-shrinkable accessory and the cable, which will result in poor interface performance between the accessory and the cable and poor partial discharge performance in actual operation, especially for 35kV voltage class.
Reliable sealing performance.
The cold-shrinkable cable accessory is made of high elastic silicone rubber material. After installation, the accessory and the cable become one. When the cable expands and contracts due to temperature, the accessory will expand and contract accordingly.
The sealing of heat-shrinkable cable accessories is mainly achieved by hot-melt adhesive and systolic compression stress.
After the installation of thermal shrinkage accessories, when the temperature drops, the cable will contract (thermal expansion and cold shrinkage), just good shrinkage of thermal shrinkage components stable structure, no longer have elasticity, so the cable lost the elastic compression force, sealing all depends on sealant, sealing performance is not reliable.
Materials and production cost comparison.
The material cost of the domestic cold-shrink type middle head (outdoor) is 6-7 times that of the heat-shrink type, and the material price is about 6,500 yuan (some differences between different specifications);
Domestic heat shrinkable type terminal head (outdoor) material price is 4-5 times of heat shrinkable type, material price is about 3000 yuan (the specification is different some difference).
Other consumable materials differ little.
The production cost (i.e. the labor cost used in the production) is slightly higher than the production cost of the hot shrinkage.
Price comparison
1) The price of cold shrinkage is expensive. At present, the price of cold shrinkage is about 4-10 times or more than that of hot shrinkage. However, from the perspective of long-term operation cost, more considerations can be given to cold shrinkage over 10KV, especially over 35KV, which will reduce long-term operation cost.
2) The thermal shrinkage is cheap. At present, the thermal shrinkage is most widely used in the fields below 35KV, and the 35KV level has gradually been excessive to the cold shrinkage. The 10KV and 1KV fields are still widely used due to the low price.
To sum up, in the field above 10KV, the long-term operation cost of using cold shrinkage is lower than that of hot shrinkage, so it is recommended to use cold shrinkage.
At 10KV and below, it is economical to use heat shrink.
Cold shrinkage as long as a bit of damage is easy to insulation bad easy to accident!
At present, most of the accessories used for 6 ~ 35kV extruded insulated power cables are cold-shrinkable cable accessories and heat-shrinkable cable accessories.
The two structural types of products have different characteristics.
1) Product features of cold-shrinkable cable accessories.
The cold-shrink cable accessories are made of high elastic special silicone rubber by injection molding.
The electric stress control unit is geometric: stress cone, high temperature and high pressure vulcanization molding process and insulation body prefabricated into a whole, reliable shape and size, stable electrical performance.
When installed, it is fastened to the cable and becomes one with the cable.
2) Product features of heat-shrinkable cable accessories.
The heat-shrinkable cable accessories are extruded from rubber and plastic composites (polymers), cross-linked by high-energy irradiation, and cooled and shaped when expanding and expanding to the required geometry size before leaving the factory.
In the field installation, it is necessary to heat up to a certain temperature, and make use of the "elastic memory" property of the polymer to shrink back to the correct position, so as to tighten the cable cutting and installation part to meet the requirements of insulation sealing.
The electrical stress control unit is of parameter type.
3) Features of cold-shrinkable cable accessories (compared with heat-shrinkable cable accessories).
Compared with heat-shrinkable cable accessories, cold-shrinkable cable accessories have the following characteristics:
Good electrical properties of materials.
Cold-shrinkable cable accessories are made of silicone rubber with high elasticity, good insulation, anti-leakage, hydrophobicity, weather resistance and ultraviolet aging resistance.
The material used in the heat-shrinkable cable accessories is rubber and plastic composite material (polymer). The material itself has no elasticity, only the function of "elastic memory".
(2) Stable performance of electric stress control unit.
The electric stress control unit of the cold-shrink cable accessories is geometric: stress cone, which relies on geometric curves to improve electric field distortion. Its shape has been formed in the company, so the performance of the electric stress control unit is stable.
Heat shrinkable cable accessories electric stress control unit for the parameter type, the electric stress control unit is the high dielectric constant and the volume resistivity between insulating material and semiconducting material material molding, special parameters of the material is difficult to control and easy to change, in the process of molding and construction lead to unstable electric stress control unit performance.
The structural type is more ideal.
The stress cone and insulation part of the cold-shrinkable cable accessories are prefabricated as a whole in the factory through high temperature and high pressure molding process. During installation, the accessories only need to be set on the treated cable. The product quality can be controlled in the factory, and the on-site installation workload is less.
The structure of heat-shrinkable cable accessories is pipes: stress pipes, internal and external insulation pipes, and semi-conductive pipes overlap. It is hard to avoid small air gap between all kinds of pipes, and it is difficult to guarantee the partial discharge performance of the intermediate joints.
More convenient installation: no need of fire.
Due to the limitation of structure type, in some fire-free situations, heat-shrinkable cable accessories are not applicable;
The cold-shrinkable cable accessories are not subject to this limitation, and there is no need for fire and other special tools during installation. Only the skeleton in the main body can be pulled out or the main body can be put in by hand.
(5) Good interface characteristics.
The cold-shrinkable cable accessory is made of high elastic silicone rubber, and the accessory is an elastic body. After installation, the accessory is always tightly bound on the cable, which becomes an integral part of the cable. Meanwhile, it has great pressure on the interface, good interface characteristics and good partial discharge performance.
Since the materials of heat-shrinkable cable accessories are not elastic at room temperature after heating, the bending and kneading of the cable will cause the separation between the heat-shrinkable cable accessories and the cable after installation.
In the process of cable operation, the change of ambient temperature will also create a gap between the heat-shrinkable accessory and the cable, which will result in poor interface performance between the accessory and the cable and poor partial discharge performance in actual operation, especially for 35kV voltage class.
Reliable sealing performance.
The cold-shrinkable cable accessory is made of high elastic silicone rubber material. After installation, the accessory and the cable become one. When the cable expands and contracts due to temperature, the accessory will expand and contract accordingly.
The sealing of heat-shrinkable cable accessories is mainly achieved by hot-melt adhesive and systolic compression stress.
After the installation of thermal shrinkage accessories, when the temperature drops, the cable will contract (thermal expansion and cold shrinkage), just good shrinkage of thermal shrinkage components stable structure, no longer have elasticity, so the cable lost the elastic compression force, sealing all depends on sealant, sealing performance is not reliable.
Materials and production cost comparison.
The material cost of the domestic cold-shrink type middle head (outdoor) is 6-7 times that of the heat-shrink type, and the material price is about 6,500 yuan (some differences between different specifications);
Domestic heat shrinkable type terminal head (outdoor) material price is 4-5 times of heat shrinkable type, material price is about 3000 yuan (the specification is different some difference).
Other consumable materials differ little.
The production cost (i.e. the labor cost used in the production) is slightly higher than the production cost of the hot shrinkage.
Heat-shrinkable power cable accessories
Heat-shrinkable power cable accessories are characterized by small size, light weight, easy installation and excellent performance-to-price ratio. They are suitable for terminal treatment and intermediate connection of power cables of 1kV, 10kV and 35kV.
1KV cable accessories can be divided into two core, three core, four core, five core terminal and intermediate connection, terminal opening distance is 600mm;
10kV and 35kV cable accessories can be divided into single core, three core indoor terminal, outdoor terminal and intermediate connection, indoor terminal opening distance is 650mm, outdoor terminal opening distance is 800mm.
There are many manufacturers of thermal shrinkage cable accessories, and the installation size and structure of the products are slightly different.
1. Thermal shrinkage cable terminal head
The stripping diagram of 10kV three-core cable terminal head is shown in the figure.
In the figure, the work is sheath stripping Figure 5 -- 110kV three-core cable terminal head cable stripping figure cutting length, indoor is 550mm, outdoor is 750mm.
J is 10 10mm deep of terminal hole.
1) Cable stripping: Strip the outer sheath, steel strip (if any) and inner sheath of the cable according to the dimensions shown in the drawing.
The stripping length of outer sheath of 35kV single-core cable is 780mm, plus the terminal hole depth and 10mm.
(4) Peel off shielded copper strip and semi-conductive layer (for 10kV three-core cable) : peel off shielded copper strip from 50mm above the end of branch sheath finger.
The remaining 20mm semi-conductive layer shall be retained and stripped off. The end of the retained semi-conductive layer shall be disposed according to the general procedures and requirements of the installation process.
(5) Stripping insulation of the end of the tangential core: strip the insulation of the end of the wire core by adding 10mm to the depth of the terminal hole;
For 35kV cable, the insulation end shall be cut into a 30mm long cone.
(6) Crimping terminal: Remove burrs and flaps after crimping.
(7) Installation of stress tube: wipe the insulating surface with cleaning agent.
Note: Wipe the semi-conductive layer clean