Cold shrink cable accessories are made of elastomer materials (silicone rubber and ethylene propylene rubber are commonly used) injected and vulcanized in the factory, and then expanded and lined with plastic spiral supports to form various cable accessories Parts. When installing on-site, put these pre-expansion pieces on the end of the cable after treatment or at the joint, draw out the internally supported plastic spiral strip (support), and press it on the cable insulation to form a cable accessory. Because it relies on elastic retraction at room temperature, instead of using fire to shrink as heat shrinkable cable accessories, it is commonly called cold shrinkable cable accessories. Early cold-shrinkable cable terminal heads only used silicone rubber cold-shrinkable parts for additional insulation, and the electric field treatment still adopted the stress cone type or the stress band wrapping type.

The cold shrinkage stress control tube is generally used, and the voltage level is from 10kv to 35kv. For cold-shrinkable cable accessories, 1kv class uses cold-shrinkable insulating tubes for reinforced insulation, and 10kv class uses cold-shrinkable joints with inner and outer semi-conductive shielding layers. Cold-shrinkable branch sleeves are used at the bifurcation of the three-core cable terminal.

Model

Molded cable accessories are mainly used for straight-through joints of cross-linked cables of 35kv and above. It is a joint formed by using radiation crosslinked or chemically crosslinked polyethylene film strips to wrap around the cable joint after treatment, press it with the help of a special mold (aluminum mold or heat-resistant tension band), and heat it to form a joint. In the production process, the radiation cross-linked polyethylene strip is pre-stretched (stretched at 100c for 30%, then cooled and cut), wrapped into a joint, and then heated to retract to make the wrapped strip The air gap between the layers is compressed, thereby increasing the discharge voltage of the air gap. This type of connector has a higher level of partial discharge and is suitable for making cable connectors with higher voltage levels. Due to the long winding and heating time, this type of connector is generally not used for cables below 35kv. Even if the 35kv cable connector, because the wrapping type and the prefabricated connector process are more convenient, the molded connector is not used much.

The 35kv cable molded joint is formed on-site. Therefore, in addition to requiring the operator to strictly follow the dimensions and requirements specified in the drawing, it is also related to the environmental conditions during construction (humidity, dust, etc.). The humidity should not be too high. The construction site should have rain and dustproof tents, and rubber gloves should be worn when wrapping the bag.

Casting

The materials used for cast-type cable accessories include epoxy resin, polyurethane and acrylate, etc. Polyurethane is mostly used for extruded insulated cables, which are mainly used as straight-through joints and branch joints. The cured polyurethane has higher elasticity, and its expansion coefficient is relatively close to that of the extruded cable insulation material, which is very beneficial to improve the interface characteristics of the cable insulation and the reinforced insulation in the joint. Polyurethane and polyurethane have a strong binding force, so it is more advantageous to use as a polyurethane insulated cable joint.

The structure and installation process of cast-type cable joints vary from manufacturer to manufacturer, but the cable stripping process and operating points are basically the same as other cable joints. There are two methods for treating the electric field at the cut-off part of the semi-conductive shielding layer outside the cable: one is to wrap the stress control tape there; the other is to wrap the stress cone.

For 35kv cable joints, ethylene-propylene rubber self-adhesive tape is usually wrapped around the cable insulation surface as a transition layer. The connector shell is usually provided by the factory, and the metal shielding layer in the shell should be reliably connected with the cable shielding layers at both ends.

If it is cast with a mold, the insulating surface of the joint should be wrapped with a semi-conductive self-adhesive tape after demolding, and then a shielded copper mesh should be applied. The copper mesh should be reliably connected to the cable shielding layers at both ends. Then, install the joint over the bridge wire and the outer protective layer of the joint (usually a heat shrinkable sheath).

The correctness of the pouring process has a great influence on the performance of the cable accessories, so special attention should be paid. Firstly, check whether the casting agent used exceeds the storage period (instructions on the package). The two components of the casting agent should be fully stirred before pouring, and then poured slowly from the pouring to l to avoid bubbles.

Advantages: Cold-shrinkable cable accessories have the advantages of small size, convenient and fast operation, no special tools, wide application range and few product specifications.

Compared with heat-shrinkable cable accessories, it does not need to be heated by fire, and after installation, moving or bending will not cause the danger of disconnection between the internal layers of the accessory like heat-shrinkable cable accessories (because cold-shrinkable cable accessories rely on elastic compression Tightness). Compared with prefabricated cable accessories, although they rely on elastic compression force to ensure the internal interface characteristics, it does not correspond to the cable section one by one like the prefabricated cable accessories, and has many specifications.

It must be pointed out that before installing on the cable, the parts of the prefabricated cable accessories are not under tension, while the cold shrinkable cable accessories are under high tension. Therefore, it must be ensured that the cold shrinkable components should not be There is obvious permanent deformation or elastic stress relaxation, otherwise sufficient elastic pressing force cannot be guaranteed after installation on the cable, so that good interface characteristics cannot be guaranteed.

Applicable standards:

IEC standard

IEC62076 "Power cable system with rated voltage above 150kV (Um=170kV) to 500kV (Um=550kV) extruded insulated power cables and accessories-Test methods and requirements"

IEC60840 "Test Methods and Requirements for Extruded Insulated Power Cables and Accessories from 30kV (Um=36kV) and 150kV (Um=170kV)"

IEC60859 "Cable connection device for gas-insulated metal-enclosed switch with rated voltage 72.5kV and above"

IEC60502 "Rated voltage 1kV (Um=1.2kV) above to 30kV (Um=36kV) extruded insulated power cable and its accessories"

IEC60055 "Rated voltage 18/30kV and below paper-insulated metal sheath (with copper or aluminum body, but not including compressed gas and oil-filled cables)" Part 1 "Cable and accessory test" Chapter 7: Type test of accessories

IEC61442 "Test Method for Power Cable Accessories from 6kV (Um=7.2kV) to 30kV (Um=36kV)"

National standard

GB/Z18890 "Rated voltage 220kV (Um=250kV) XLPE insulated power cable and its accessories"

GB/Z11017 "Rated voltage 110kV XLPE insulated power cable and its accessories"

GB5589 "Test Method for Cable Accessories"

GB9327 "Cable conductor compression and mechanical connection joint test method"

GB14315 "Crimp type copper and aluminum terminal blocks and connecting pipes for wire and cable conductors"

Note: GB11033 "Basic technical requirements for power cable accessories with rated voltages of 26, 35kV and below" has been delegated to JB/T8144

Industry Standard

JB Standard (Mechanical Industry Association Standard)

JB/T8144 "Basic Technical Requirements for Power Cable Accessories with Rated Voltage 26/35kV and Below" formerly GB11033

JB6464 "Rated voltage 26/35kV and below power cable straight-through wrap-around connector"

JB6465 "Rated voltage 26/35kV and below power cable indoor type, outdoor type porcelain sleeve is the terminal"

JB6466 "Indoor and outdoor porcelain sleeve terminals for power cables with rated voltages of 8.7/10kV and below"

JB6468 "Rated voltage 26/35kV and below power cable indoor type, outdoor type wrapping type terminal"

JB7829 "Rated voltage 26/35kV and below power cable indoor and outdoor heat shrinkable terminal"

JB7830 "Rated voltage 26/35kV and below power cable straight-through heat shrinkable joint"

JB7831 "Rated voltage 8.7/10kV and below power cable indoor type, outdoor type cast-in terminal"

JB7832 "Rated voltage 8.7/10kV and below power cable straight-through cast joint"

JB/T8501.1 "Indoor and outdoor prefabricated assembled terminals for plastic insulated power cables with rated voltages of 26/35kV and below"

JB/T8503.2 "Indoor and outdoor prefabricated prefabricated terminals for plastic insulated power cables with rated voltages of 26/35kV and below"