Key points in the manufacture and installation of cable connectors

These problems often occur when making and installing joints: the peeling marks are too deep, the ports are not neat; the insulating surface is too much impurities, there are dents or protrusions; the grounding wire is not firmly connected; the sealing of the accessories is poor; the terminal and the connecting pipe are pressed The connection is not good, the sealing is not strict; the shielding layer is not well connected.

The emergence of these problems is closely related to the skill level of the producers. To solve the problem completely, you can break them down into key points in the operation.

1. sawing steel shovel

If the fracture is not correct when sawing the steel shovel, there is a burr left, which is easy to cause the tip discharge during operation and puncture the protective layer. Pay attention to the depth during sawing. Do not cut through the lower steel shovel. The burrs should be sharpened with a trowel or tapped with a tool.

2. Connect the ground wire

The metal shield is connected to the grounding system to eliminate surface corona and shield electromagnetic fields from electromagnetic interference from nearby communication equipment. The metal shield connected to the grounding system in operation is at zero potential, and it has the ability to conduct short-circuit currents in a very short time after a cable failure. The grounding wire is not firmly connected to the steel shovel and the metal shielding layer, and is not resistant to vibration, which may cause the accessory to burn out.

The grounding wire should be soldered or fixed reliably. The metal shielding and armoring tape on the cable body at both ends should be firmly connected. The grounding of the terminal should be firm and not loose. The grounding wire should be fixed on the steel shovel and the metal shielding layer with a spring steel belt, or the welding should be firm, and the welding should not be burnt or soldered.

3. Do the grounding wire moisture-proof section

If the sealant is not tightly wrapped around the moisture-proof section of the grounding wire, the middle solder is not tightly filled, and moisture will penetrate into the gap, causing the cable insulation water tree to age and even explode.

The middle part of the grounding wire should be filled with solder in the middle, and a layer of sealing glue should be wrapped around the outer sheath of the cable, and then the grounding wire is pressed onto the tape, and then a layer of sealing glue is wrapped. Finally sealed with a sheathed tube.

4. Stripping the metal shielding layer, the outer shielding layer and the insulating layer

When the stripping is performed, the lower knife is likely to be too deep, and the next layer of material is cut, resulting in an increase in local electric field strength, partial discharge, and breakdown of insulation.

In the peeling, you must grasp the depth of the lower knife, do not cut through, wrap it with PVC tape and then tear it along the edge. Try to use a special stripping tool for stripping.

5. Polish and clean the insulation

When polishing, it is easy to bring the conductive particles in the shielding layer into the insulating layer, or the protrusions on the surface of the insulating layer are not completely removed, which may cause partial discharge and breakdown insulation.

To use a sandpaper that is thick and thin, and carefully sanded, now only one piece of sandpaper is provided in the accessory box, which can be polished with the front side and then polished with the back side. When wiping with a cleaning towel, from the insulating layer to the shielding layer, never wipe repeatedly, leaving black conductive particles on the insulating layer.

6. Stress tube in the heat shrinkable attachment

The stress tube does not overlap well with the metal shielding layer and the insulating shielding layer, and the electrical stress cannot be evenly distributed, which may cause cable insulation breakdown short circuit. This link is very important in the installation of the accessories. It is often the case that the cable is burnt due to poor bonding of the stress tube, and it must be given sufficient attention during production.

7. Connection of terminal block and connecting pipe conductor

The basic requirements for conductor connection are low and stable resistance, sufficient mechanical strength, resistance to galvanic corrosion, vibration resistance, and no burrs at the joint. Medium and low voltage cable conductors of 10kV and below are commonly connected by crimping. The operational points are:

(1) After stripping the insulation of sufficient length, remove the dirt and oxide film on the surface of the conductor, and apply the conductive paste before inserting it into the connecting tube.

(2) The center of the nip of the forming edge or the pit pressure of the confining pressure during crimping shall be on the same plane or straight line. Each time the mold is closed, it should stay for 10~15 seconds, so that the plastic deformation of the metal in the crimping part is basically stable.

(3) The resistance value of the connection point should not be greater than 1.2 times the conductor resistance of the same section and the same length. The tensile strength of the cable connection point of the fixed laying is not less than 60% of the tensile strength of the conductor itself.

(4) After the crimping, the connecting tube, the sharp corners on the core conductor, the burrs, etc., are smoothed with a trowel or sandpaper.

(5) Fill the crimping gap with semi-conductive tape and connect with the conductor shielding layer; be clear about the use place and use requirements of various strips; wrap according to the regulations.

8. Inner semi-conductive shielding treatment

The cable body with the inner shield must restore the inner shield of the joint of the crimped tube conductor portion when making the intermediate joint. A part of the inner semi-conductive shield of the cable should be left so that the inner shields of the joints on the connecting pipe can communicate with each other to ensure the continuity of the inner semi-conductive layer, so that the electric field strength at the joint connecting pipe is evenly distributed.

9. Treatment of the outer semi-conductive shielding layer

The outer semi-conductive shielding layer is a semi-conductive material that acts as a uniform electric field attached to the outside of the cable insulation. Like the inner semi-conductive shielding layer, it plays an important role in cables and joints. The outer semi-conductive layer port must be neat and uniform, with a smooth transition from insulation, the step can be ground flat or the step can be filled with a semi-conductive tape. When making the intermediate joint, the semiconductor strip is wound around the joint and connected to the external semiconductor shield of the cable.

10. Cable reaction cone processing

The reaction cone with correct shape and size during construction has the same potential distribution on the entire cone surface, which can effectively improve the electric field distribution at the core break. The reaction cone curve is shown in Figure 1. Since the standard complex logarithmic curve is not easy to be cut, the end of the insulating layer is often cut into a pencil head to make the curved surface a tapered surface. When making a cross-linked cable reaction cone, it is usually cut with a special cutting tool, or scraped with a knife or glass. After basic molding, it is scraped with 2mm thick glass, and finally sanded from coarse to fine until smooth. . For 35kV and below cable terminals, this is generally not the case, and the cross section can be directly cut.

11. Sealing and mechanical protection of the joint

The sealing and mechanical protection of the joint is a guarantee for the safe and reliable operation of the joint. The joint should be prevented from infiltrating moisture and moisture. The joint is smoothed with a sealant and then placed in a sealed tube for sealing. A joint protection groove or a protective box should be installed at the joint position.

12. Construction in rain, snow, fog, windy weather

Temperature, humidity and dust control at the construction site should be carried out during construction in extreme environments. The air humidity during construction shall not exceed 70%, and the northern ambient temperature shall not be lower than zero degrees Celsius. In windy weather, the dust is too large, and falling on the insulation layer will cause partial discharge and cause insulation breakdown. The solution is to place the cable accessories in a closed tent and control the temperature and humidity before making the installation.