Production Technology Of Cold-shrinkable Cable Terminal

- Oct 08, 2019-

Cold-shrinkable cable terminal is a part of cable accessories, which is made of elastomer material (commonly used silicone rubber and ethylene propylene rubber) and vulcanized by injection in the factory. It is then expanded and lined with plastic spiral support. When installed on site, the pre-expansion parts are packed at the end or joint of the treated cable, and the plastic spiral bars (supports) which are internally supported are pulled out and pressed on the cable insulation to form the cable accessories. Because it relies on elastic retraction force at room temperature, rather than heat shrinkage cable accessories, it is commonly known as cold shrinkage cable accessories. In the early stage, the cold-shrinkable cable terminals were only insulated by silicone rubber cold-shrinkable components, and the electric field treatment still adopted the stress cone type or the stress band wrapping type.

At present, cold shrinkage stress control tubes are widely used, with voltage levels ranging from 10 kV to 35 kv. The cold shrinkable cable terminal adopts cold shrinkable insulating tube as reinforcement insulation in 1kV level and cold shrinkable insulating joint with semi-conductive shielding layer inside and outside in 10kV level. The cold shrinkage branching sleeve is used at the bifurcation of the three-core cable terminal.

The cold shrinkable cable terminal has the advantages of small size, convenient operation, rapid, no special tools, wide application range and less product specifications. Compared with heat-shrinkable cable accessories, there is no need for fire heating, and after installation, moving or bending will not be as dangerous as heat-shrinkable cable accessories, because the end of cold-shrinkable cable depends on elastic compression force. Compared with the prefabricated cable accessories, although the internal interface characteristics are guaranteed by elastic compression force, 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 the components of prefabricated cable accessories have no tension before they are installed on the cable, while the terminal of the cold-shrinkable cable is in the state of high tension. Therefore, it must be ensured that the cold-shrinkable components should not have obvious long-term deformation or elastic stress relaxation during the storage period, otherwise the elastic compression force will not be enough after they are installed on the cable. Ensure good interface characteristics.

Following is a brief introduction to the structure, installation process and precautions of 10 LV and 35 kV cold-shrinkable cable terminals and 10 kV cold-shrinkable cable terminals.

1.10 kV three-core cable cold-shrinkable cable terminal

(1) Strip the cable outer sheath, steel strip (if there is steel strip), inner sheath and filler between cores according to the dimensions specified in the installation instructions provided by the manufacturer. (Strip stripping length is mainly determined by the allowable bending radius of cores and the prescribed distance between phases, but it is necessary to consider the length of cold shrinkage sheath sleeve on the cores provided by the manufacturer.) The inner protective layer is 10 mm and the steel strip is 25 mm. Then the cable end is about 50mm long and a section of outer protective layer is scrubbed clean.

(2) Installation of grounding wires. Ground braided copper wire and three copper strips are fixed on the wire core copper shield above 65 mm with a constant force spring. If the steel strip is required to be grounded separately from the core shield, another 10 mm2 braided copper wire should be fixed on the steel strip with a constant force spring, then covered with an insulating tape wrapped, and then the core shielded grounded braided copper wire should be connected with three core grounded copper strips to lead out.

Note: There is no electrical connection between the steel belt grounding wire and the shielded core grounding wire in the terminal head. In order to prevent water vapor from entering the cable along the grounding line, two layers of waterproof tape are wrapped on the outer protective layer, the grounding wire is clamped in the middle, and two layers of waterproof tape are wrapped on the outside.

(3) Install cold shrinkage branching sleeve. The cold shrinkage branching sleeve is placed at the bifurcation of the core. First, the plastic spiral bars in the lower end are pulled out, and then three plastic spiral bars in the inner finger tube are pulled out to shrink and compress at the bifurcation of the core.

(4) Install cold shrinkage casing. The three cold shrinkage sleeves are respectively sheathed on the top and bottom of the three cores to cover the branch sheath finger tubes with 15mm. The plastic spiral strips in the tubes are extracted and contracted and compressed on the copper shield of the cores. In order to lengthen the indoor terminal, the second cold shrinkage casing is contracted by the same method. The lower end of the casing is overlapped with the ** root by 15mm. The length from the end of the casing to the end of the core shall be equal to the size specified in the installation instructions.

(5) Leave a copper shield upward from the casing opening (45 mm for outdoor terminal and 30 mm for indoor terminal), and peel off the rest.

Leave 10 mm semi-conductive layer, the rest of the semi-conductive layer peeled off, and according to the terminal hole deep 1 OMM peeled off the core end insulation.

(6) The semi-conductive tape should be wrapped around the end of the steel shielding tape at 10 mm until the cable insulation is covered at 10 mm. Then the semi-conductive tape should be returned to the copper shielding tape. The transition between the semi-conductive tape and the insulation should be smooth (without obvious steps).

(7) crimping terminal.

(8) Installation of cold shrinkage insulators. First, wipe the cable insulation and the junction end at the pressure joint with a cleaning agent, and coat a little silicone grease around the semi-conductive tape and the nearby insulation surface. Insert the cold-shrinkable insulator into the position specified in the installation instructions, pull out the plastic spiral bar, shrink and compress the cable insulation (if the width of the terminal plate is larger than the inner diameter of the cold-shrinkable insulator, the cold-shrinkable insulator should be installed first, and then press the connection terminal).

(9) Insulated rubber tape is used to wrap the gap between terminal and core insulation, and the leak-proof strip is wrapped outside.

(10) The phase-color marking band is wrapped around the branch finger tube of the three-phase core.

2.35 kV Single core cable terminal

Compared with the 10 kV three-core cable terminal, the structure and process are simpler. No branching sleeve and protective sleeve on the core are needed. The rest are basically the same as the three-core cable terminal.

3.10 kV three-core cable joint

Its installation process is similar to that of prefabricated joints, but the following differences should be noted:

(1) When the main body of the cold shrinkage joint is sleeved on the long stripped cable core, the tap of the plastic spiral bar should be directed towards the bifurcation of the cable core at that end.

(2) After all the parts concerned are covered in the core of the cable, the conductor of the two ends of the cable and the crimping nozzle need not be crimped twice as the joint of the prefabricated parts.

(3) Before moving the main body of the cold-shrinkable joint to the middle of the joint, uniformly coat the semi-conductive layer at the junction with insulation and the insulating surface with the special mixture provided by the manufacturer.

(4) Installation of shielded copper mesh bridge crossing line and steel strip crossing connection, usually fixed by constant force spring.

(5) The cold shrinkage joint is wrapped with a waterproof band by half-lap, and the outer sheath of the cable is covered with 60 mm at both ends. Then the whole surface of the joint is wrapped with armoured band, which has good mechanical protection after solidification. This kind of pin belt is preimpregnated curable black polyurethane fiberglass ribbon, vacuum packaging. Open the package before use, pour water 15 seconds later and pour out the water, then use it. Other suitable protective layers or boxes can also be used.