Key points analysis of installing cable joints in power construction

In the installation of power engineering, cable terminals and intermediate cable joints are important components of power equipment in transmission and transformation cable lines. Their function is to disperse the electric field at the external shielding and cutting point of the cable terminal, protect the cable from breakdown, as well as provide internal and external insulation and waterproofing. More than 60% of accidents in cable lines are caused by accessories, so the quality of joint accessories plays a very important role in the reliability of the entire power transmission and transformation.

1. The connection of conductors requires low resistance and sufficient mechanical strength, and there should be no sharp corners at the connection. The commonly used method for connecting conductors in medium and low voltage cables is crimping, which should pay attention to:

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

(2) The clearance between the inner diameter of the pressure tube and the outer diameter of the connected wire core should be set at 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 with equal cross-section, and the tensile strength of the copper conductor joint should not be less than 60N/mm2;

(4) Before crimping, apply conductive adhesive to the outer surface of the conductor and the inner surface of the connecting pipe, and use a wire brush to damage the oxide film;

(5) Sharp corners, burrs, etc. on connecting pipes, wire core conductors, etc. should be smoothed with a file or sandpaper.

2. If the cable body has an internal shielding layer, the internal shielding layer of the crimping tube conductor part should be restored when making the joint. A portion of the internal semiconductor shielding of the cable should be left to ensure that the internal shielding of the connection head on the connecting tube can be connected to each other, ensuring the continuity of the internal semiconductor and evenly distributing the field strength at the joint connection.

3. The treatment of external semiconductor shielding. External semiconductor shielding is a semiconducting material that provides a uniform electric field outside the insulation of cables and cable joints. Like internal semiconductor shielding, it plays a very important role in cables and joints. The outer semiconductor port should be neat and uniform, and it is also required to have a smooth transition with insulation. Semiconductor tape should be added to the cable joint to connect with the outer semiconductor shielding of the cable body.

4. The processing and construction of cable reaction force cones require accurate and precise shape and size of the reaction force cone. The potential distribution on the entire cone surface is equal. When making cross-linked cable reaction cones, cutting tools are generally used, or slightly heated with low heat and cut with a fast knife. After the basic shape is formed, it is scraped with 2mm thick glass and polished with sandpaper from coarse to fine until smooth.

5. Metal shielding and grounding treatment. The main function of metal shielding in cables and joints is to conduct cable fault short-circuit currents and shield electromagnetic interference from nearby communication equipment. In operation, the metal shielding is at zero potential in a well grounded state. When the cable fails, it has the ability to conduct short-circuit currents in a very short period of time. The grounding wire should be reliably welded, and the metal shielding and armor tape on both ends of the cable body should be firmly welded. The grounding of the terminal should be reliable.

6. The sealing and mechanical protection of joints are essential to ensure their reliable operation. Moisture and moisture should seep into the cable joints, and joint protection grooves or cement protection boxes should be built or installed at the joint positions.