Installation and operation procedures for heat shrinkable cable accessories with rated voltage of 36kV and below

I. General Precautions

(1) When shrinking heat-shrinkable components, control the flame carefully to prevent it from becoming too large. During operation, continuously shake the flame and heat evenly along the circumference. Do not heat one spot for an extended period to avoid scalding the heat-shrinkable component. The flame should be fully combusted and free of smoke to prevent carbon particles from adsorbing onto the surface of the heat-shrinkable component and affecting its performance. When shrinking tubing, generally shrink it from the middle to both ends, or from one end to the other, heating evenly and slowly to avoid uneven thickness or air bubbles between layers after shrinkage.

(2) When stripping cables, do not damage the next structural layer. Peelable semiconductive layers can be removed using a scratching method; non-peelable semiconductive layers can be removed using a special tool or a glass scraping method. Regardless of the method used, ensure the insulation layer after removing the semiconductive layer is smooth, round, and free of scratches. Sandpaper used for polishing the insulation shield should not be used to polish the cable insulation again. The cut of the treated shield layer should not have grooves, gaps, or protrusions. (3) Cable accessory fabrication must be a continuous, one-time process from stripping to completion to prevent moisture absorption.

(4) Because heat-shrinkable materials only possess elasticity and compressive force above their shrinkage temperature, the shrunken heat-shrinkable joint should not be bent or flexed after shrinkage; otherwise, interlayer gaps will occur, leading to discharge during operation. If bending or flexing is necessary in practical applications, the material must be reheated and shrunk once after bending or flexing to eliminate any gaps formed.

(5) Mechanical pressure connection is preferred for conductor connections. If compression connection is used, a confined compression crimping method should be employed. If the supplier has special process requirements, those requirements should be followed.

When using the confined compression crimping method for conductor connections, the following requirements must be met:

1) Before crimping, check and verify the connecting hardware and crimping die, and select appropriate terminals, crimping dies, and crimping machines.

2) Before crimping, remove dirt and burrs from the conductor surface.

3) Before crimping, check that the cables at both ends are in a straight line.

4) The conductor insertion length during crimping should meet the process requirements.

5) The crimping sequence can refer to the requirements of Appendix C of GB 14315.

6) Before crimping, check whether the terminals and conductors are straight. After each crimp, pause for 10-15 seconds after the die is fully closed to allow the plastic deformation of the crimped area to stabilize. After crimping, confirm that the extension length of the connector meets the process requirements.

7) At the crimped area, the edges formed by the crimp should each be on the same plane.

8) The compression ratio should be controlled between 15% and 25%.

9) The separator paper between the conductor sections (crimped parts) should be removed before crimping.

10) After crimping, the crimped area should be treated. The surface of the crimped fittings should be smooth, and all metal shavings and crimping marks should be removed. The surface of the crimped fittings should be free of cracks and burrs, and all edges should be free of sharp points. The cable conductor and terminals should be straight and without warping.

II. Accessory Inspection

(1) Check the product manufacturing date and expiration date on the product packaging box. Expired products must not be installed.

(2) Open the product packaging box and check the materials according to the packing list. Ensure that all accessory models, specifications, and quantities are correct.

(3) Cable Inspection

1) Verify the cable conductor cross-section and insulation radius dimensions according to the markings on the cable sheath. Ensure that the accessory models match the cable dimensions.

2) The cable is in good condition, without moisture, water ingress, insulation eccentricity, or other defects. Simultaneously, use a megohmmeter to test the core insulation resistance. For cables of 1kV and below, the resistance should be no less than 100MΩ; for cables of 6kV and above, the resistance should be no less than 200 MΩ.

III. Installation Procedure for Heat-Shrink Terminals

3.1 Cable Stripping

Strip the outer sheath, armor, and inner sheath of the cable according to the dimensions in Figure 1 below.

Figure 1. Schematic diagram of terminal cable stripping

3.2 Securing the Ground Wire

Use sandpaper to remove the anti-corrosion layer from the armor layer and copper shield, exposing the metallic luster. Secure the ground wire to the armor or copper shield using a constant force spring (alternatively, the ground wire can be bound to the position with copper wire, then fully soldered at the binding point with neutral flux and solder; remove burrs after soldering). If the copper shield is copper wire shielding, fold the copper wire back to use it as the ground wire. The two ground wires must not be short-circuited here; shrink a heat-shrink ring or wrap insulating self-adhesive tape around the armor.

Figure 2 Schematic diagram of terminal ground wire fixing

3.3 Shrinking the finger sleeve (this step is not required for single-core cables)

Clean the outer sheath of the cable by grinding down 100mm. Wrap filler adhesive around the cable branch points to fully fill the area. Straighten and parallel the two ground wires along the cable and temporarily secure them with cable ties. Insert the finger sleeve to the branch root and heat to shrink it from the middle towards both ends.

Figure 3. Schematic diagram of terminal finger sleeve retraction

3.4 Core Pretreatment

As shown in Figure 4, the cable shielding layer, semiconducting layer, and insulation layer are stripped (L = terminal hole depth + 5mm), and the cable insulation end is tapered to a length of 30mm.

Figure 4: Dimensions of Terminal Core Pretreatment

3.5 Shrinkage Stress Tube and Insulating Tube

Grind and clean the wire core insulation layer, ensuring no conductive particles remain on the surface. Wrap stress-relieving adhesive around the break in the outer semiconducting layer, overlapping the insulation layer and the outer semiconducting layer by 5mm. Apply a thin, even layer of silicone grease to the surface of the insulation layer, avoiding application to the outer semiconducting layer. Insert the stress tube, overlapping the semiconducting layer by 40mm, and heat-shrink to fix it. Use stress-relieving adhesive to fill the step between the stress tube and the insulator, overlapping by approximately 5mm on each side. Insert the insulating tube (the adhesive-coated end) to the root of the finger sleeve (60mm into the cable sheath for single-core cables), and heat-fix it from the root upwards. If the insulating tube is too long, cut off the excess along the tapered line of the insulation layer after it cools slightly.

3.6 Crimping Terminals

Insert the terminals and crimp them. After crimping, remove burrs and flash (for three-core cables, ensure the terminal end faces are aligned). Filler is wrapped between the break in the insulating tube and the terminal, as well as at the crimping area of ​​the terminal, to create a tapered transition between the break in the insulating tube and the terminal. Then, a layer of sealing strip is wrapped around the outside of it.

Figure 5 Terminal crimping diagram

3.7 Shrink Sealing Tube and Phase Color Tube

Insert the sealing tube and heat to secure it (if a gasket is used, shrink the gasket first). Insert the phase color tube and heat to shrink. The 10kV indoor terminal installation is complete.

3.8 Install Umbrella Skirts

According to the voltage level and terminal type (outdoor/indoor), install the required number of umbrella skirts. The shrink position of the first single-hole umbrella skirt is at the semiconductor layer break. Shrink and secure the other umbrella skirts sequentially according to the dimensions shown in the diagram. Terminal installation is complete.

 Figure 6. Schematic diagram of terminal umbrella skirt installation

04. Heat Shrink Connector Installation Procedure

4.1 Cable Stripping

Strip the outer sheath, armor, and inner sheath of the cable according to the dimensions in Figure 7.

Figure 7. Schematic diagram of cable stripping at the connector.

4.2 Wire core pretreatmen

As shown in Figure 8, strip off the copper shielding layer, semiconducting layer, and insulation layer of the cable (L=1/2 the length of the connecting tube + 2mm), and cut the end of the cable insulation into a 35mm long taper (5mm of which is the exposed inner semiconducting layer).

Figure 8 Schematic diagram of connector core pretreatment

4.3 Shrinkage Stress Tube

Grind and clean the conductor insulation layer, ensuring no conductive particles remain on the surface. Wrap stress-relieving adhesive around the break in the outer semiconductor layer, overlapping the insulation layer and the outer semiconductor layer by 5mm. Apply a thin, even layer of silicone grease to the insulation layer surface, avoiding application to the outer semiconductor layer. Insert the stress tube, overlapping the semiconductor layer C, and heat-shrink to fix it (if the stress tube is a continuous type, it should be fixed after the conductor is connected).

4.4 Inserting the tubing and crimping the terminals:

Substitute the inner and outer sheaths onto the cables at both ends. At the end where the sheath has been stripped longer, insert a set of inner insulation tubing, middle insulation tubing, outer insulation tubing, and semi-conduit for each phase (for cables below 20kV, where there is no middle wall tubing, composite tubing can be used instead of outer insulation tubing and semi-conduit). At the shorter end, insert a section of copper shielding mesh for each phase (this is not necessary if the metal shielding layer is restored by wrapping). Insert the conductors into the connecting tubing according to the original phase sequence and crimp them. Remove burrs and sharp edges from the surface of the connecting tubing and clean away any debris. First, wrap the semi-conducting tape around the surface of the connecting tubing to connect it to the inner semi-conducting layers at both ends. Then, wrap the filler adhesive (for cables above 20kV, wrap with J-30 self-adhesive insulating tape) around the outside of the semi-conducting tape and the insulating cone area, with a thickness 1-2mm higher than the outer diameter of the cable body insulation. Overlap the cable body insulation at both ends by 5mm and transition smoothly.

Figure 9 Schematic diagram of connector crimping

4.5 Installation of Insulating Tubes and Semi-Conduits

Clean the surface of the conductor insulation and stress tubes, wiping from the connection tube towards the stress tube. Use stress-relieving adhesive to fill the step between the stress tube and the insulation, overlapping by approximately 5mm. Apply a layer of silicone grease evenly to the insulation layer, stress tube, and filler adhesive surface, avoiding application to the outer semi-conducting layer. Wrap sealant around the edge of the stress tube, overlapping the stress tube by 20mm and the semi-conducting layer by 10mm. Move the inner insulation tube to the middle of the joint and heat-shrink it from the middle towards both ends to fix it. All three phases can be operated simultaneously, with the heating flame directed in the shrinking direction. After shrinking, wrap a 20mm wide sealing section of sealant around the inner insulation tube 30mm from both ends of the shrunken inner insulation tube. Shrink the other insulating tubes and semi-conduits in the same way. Finally, wrap semi-conducting tape around the end of the semi-conduit, overlapping the copper shield and the semi-conduit by 20mm each.

Figure 10 Schematic diagram of the installation of insulating tubes and semi-conduits

4.6 Installation of Shielding Mesh and Shielding Grounding Wire

Move the pre-installed shielding mesh for each phase to the center of the connector. Evenly stretch the overlapping shielding layers to both sides, ensuring a tight cover over the semiconductor tube (the wrapping method involves wrapping the copper mesh onto the semiconductor layer with an overlap of approximately 1/4). Polish the copper shielding with sandpaper to expose its metallic luster. Secure the grounding wire to the copper shielding using a constant force spring (alternatively, the grounding wire can be tied and fixed in place with copper wire, then fully soldered at the tied position using neutral flux and solder; burrs must be removed after soldering). If the copper shielding is made of copper wire, directly crimp it using a connecting pipe.

Figure 11 Schematic diagram of shielding grounding installation

4.7 Shrinking the Inner Sheath

Bring the three-phase cores together, filling the gaps between phases with the previously cut cable filler, and tightly wrapping the three-phase cores with white cloth strips or tape. Roughen the inner sheath and clean it thoroughly. Wrap approximately 20mm wide and 1-2mm high sealant around both ends of the inner sheath as a water-blocking layer. Move one inner sheath to the steel armor break and heat-shrink it, then move the other inner sheath to the other end of the steel armor break and heat-shrink it. If it is a three-sheath process, wrap approximately 20mm wide and 1-2mm high sealant around the overlap between the two already shrunken sheaths and the third sheath as a water-blocking layer. Move the third sheath to the middle position, overlap the two already shrunken sheaths, and heat-shrink it.

Figure 12 Schematic diagram of inner sheath shrinkage

4.8 Install the armored grounding wire and shrink the outer sheath

Connect the armored grounding wire using the same method as connecting the shielded grounding wire; shrink the outer sheath using the same method as shrinking the inner sheath.

Figure 13. Schematic diagram of armored grounding installation

05. Grounding Requirements

After the terminal is installed, the cable at the lower end of the terminal needs to be fixed. Select a grounding box or grounding protection box according to the line design requirements. The connection between the grounding wire and the grounding wire terminal should be mechanically crimped. The connection between the grounding wire lug and the main grounding should preferably be made with stainless steel or hot-dip galvanized anti-corrosion bolts, and the connection must be reliable. The cable terminal grounding connection wire should be as short as possible.