Installation points of power cable joints

Cable terminal heads and intermediate joints are important components in power transmission and transformation cable lines. Their function is to disperse the electric field at the cut-off part of the outer shield of the cable terminal head, protect the cable from breakdown, and have internal and external insulation and waterproof functions. . In cable lines, more than 60% of accidents are caused by accessories, so the quality of joint accessories plays a very important role in the safety and reliability of the entire power transmission and transformation.

1　Conductor connection

The conductor connection requires low resistance and sufficient mechanical strength, and no sharp corners should appear at the connection. The commonly used connection of medium and low voltage cable conductors is crimping, and crimping should pay attention to:

(1) Choose a conductor connecting pipe with appropriate conductivity and mechanical strength;

(2) The fit gap between the inner diameter of the crimping tube and the outer diameter of the connected core is 0.8～1.4mm;

(3) The resistance value of the joint after crimping should not be greater than 1.2 times that of the conductor of equal cross-section, and the tensile strength of the joint of the copper conductor should not be less than 60N/mm2;

(4) Before crimping, coat the outer surface of the conductor and the inner surface of the connecting pipe with conductive glue, and use a wire brush to destroy the oxide film;

(5) Sharp corners and burrs on the connecting pipe and core conductor should be smoothed with a file or sandpaper.

2　Inner semiconductor shielding treatment

Where the cable body has an inner shielding layer, the inner shielding layer of the conductor part of the crimping tube must be restored when the joint is made, and a part of the inner semiconductor shielding of the cable must be set aside so that the inner shielding of the connector on the connecting tube can communicate with each other. Ensure the continuity of the internal semiconductor, so that the field strength at the junction is evenly distributed.

3　External semiconductor shielding treatment

The outer semiconductor shield is a semi-conductive material that acts as a uniform electric field outside the insulation of the cable and the joint. Like the inner semiconductor shield, it plays a very important role in the cable and the joint. The outer semiconductor port must be neat and uniform, and it also requires a smooth transition with the insulation, and a semiconductor tape is added around the joint to connect with the semiconductor shield outside the cable body.

4　The treatment of cable reaction force cone

During the construction, the shape and the exact size of the reaction force cone have the same potential distribution on the entire cone surface. When making the cross-linked cable reaction cone, a special cutting tool is generally used, or it can be slightly heated with a slight fire and carried out with a sharp knife. After cutting and basic forming, use 2mm thick glass to scrape, and finally use sandpaper to polish from coarse to fine until smooth.

5　Metal shielding and grounding treatment

The role of metal shielding in cables and connectors is mainly to conduct cable fault short-circuit currents and to shield electromagnetic interference from electromagnetic fields on nearby communication equipment. In operation, the metal shield is at zero potential in a well-grounded state. When the cable fails, , It has the ability to conduct short-circuit current in a very short time. The grounding wire should be reliably welded, the metal shields and armor tapes on the cable body of the two ends should be firmly welded, and the grounding of the terminal head should be reliable.

6　Sealing and mechanical protection of joints

The sealing and mechanical protection of the joint are the guarantee to ensure the safe and reliable operation of the joint. Prevent the penetration of moisture and moisture into the joints, and build joint protection grooves or install cement protection boxes at the joints.