In the installation of power engineering, the cable terminal and the intermediate joint are important power equipment components in the power transmission and transformation cable line. Its function is to disperse the electric field at the outer shielding cut of the cable terminal to protect the cable from breakdown. 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. Connection of conductors
The conductor connection requires low resistance and sufficient mechanical strength, and no sharp corners should appear at the connection. Crimping is commonly used in the connection of medium and low-voltage cable conductors. Attention should be paid to the crimping:
(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 constant cross-section, and the tensile strength of the joint of the copper conductor should not be less than 60N/m㎡;
(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. Internal semiconductor shielding treatment
Where the cable body has an inner shield layer, the inner shield layer of the conductor part of the crimping tube must be restored when the joint is made, and a part of the inner semiconductor shield of the cable must be set aside so that the inner shield 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. Treatment of external semiconductor shielding
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 smooth transition with the insulation is required, and the semiconductor tape is wound around the joint to connect with the semiconductor shield outside the cable body.
4. Treatment of cable reaction force cone
During the construction, the reaction force cone with the exact shape and size has 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 shaping, 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 under 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.
