20 common cable knowledge questions and answers

There are many types of wire and cable, and there is a lot of knowledge about wire and cable. If you want to understand the knowledge of wire and cable, you must learn more. The following is the basic knowledge about wire and cable organized for you. help!

20 cases of common knowledge of wire and cable, worth collecting!

1. Under what circumstances is the use of pipe laying? What are the advantages?

Answer: The laying of drain pipes is generally used where it intersects with other buildings, roads or railways, and is sometimes used in areas with dense buildings. The main advantage is that it occupies less area and has a higher bearing capacity. The cables do not interfere with each other and are safer.

2. What is the long-term allowable current carrying capacity of the cable?

Answer: The long-term allowable current-carrying capacity of the cable refers to the current value when the cable conductor reaches the long-term allowable working temperature after the specified current is passed through the cable after thermal stability.

3. What are the factors that determine the long-term allowable current carrying capacity of the cable?

Answer: The following three factors determine:

(1) The long-term normal working temperature of the conductor;

(2) The heat dissipation characteristics of the cable itself;

(3) Cable installation environment and heat dissipation conditions.

4. How many cables are laid?

Answer: There are the following:

(1) Directly buried underground;

(2) Fixed installation in the cable trench;

(3) Installed in underground tunnel;

(4) Installed on the internal wall of the building or on the ceiling;

(5) Installed on the bridge;

(6) Laying in the exhaust pipe;

(7) Lay on the bottom of the water.

5. How to connect the cable tube?

Answer: When connecting the cable pipe, you need to use a buckle and a pipe joint to connect. If welding is used, direct butt welding cannot be used. A thick pipe should be put on the connection before welding to prevent the welding slag from falling into the pipe.

6. What is the main electrical wiring?

Answer: The electrical main wiring is the connection method of the main electrical equipment and busbar in the power plant and substation, including the connection method of the main busbar and the factory power system according to certain functional requirements.

7. What rules should be followed when choosing the cross section of power cables?

Answer: (1) The rated voltage of the cable cannot be lower than the rated voltage of the power supply system at the installation point;

(2) The working current allowed by the cable cannot be lower than the maximum continuous current of the power supply load;

(3) The cross section of the wire core must meet the stability requirements of the power supply system when short-circuited;

(4) Check whether the voltage drop meets the requirements according to the cable length;

(5) The minimum short-circuit current at the end of the line should enable reliable operation of the protection device.

8. What are the advantages of cross-linked polyethylene cable and oil-paper cable?

Answer: (1) It is easy to install because its material is light and the degree of bending is small during installation;

(2) There is no upper and lower limit between lines;

(3) Good thermal performance, allowing high working temperature and large transmission capacity;

(4) The cable accessories are simple and all are dry structure;

(5) Simple operation and maintenance, no oil leakage;

(6) The price is lower;

(7) High reliability and low failure rate;

(8) The manufacturing process is few, the process is simple, and the economic benefit is remarkable.

9. What are the requirements for the clamps for fixing AC single-core cables? Why?

Answer: The clamp must not have a conductive object to form a closed magnetic circuit, to prevent electromagnetic effects from occurring around the cable core when the current passes through. The magnetic force line is proportional to the current passing through the core. It can be known from the magnetic induction that eddy current will be generated in the iron to heat the cable and even burn the cable. Therefore, it is not possible to use conductive objects when acting as a fixing.

10. What are the biggest features and advantages of the following heat-shrinkable cable head accessories?

Answer: The biggest feature of the heat shrinkable attachment is that it discards the original stress cone and replaces it with a stress tube. It simplifies the construction difficulty, reduces the terminal size of the joint, is convenient to install, saves time and labor, has superior performance, and saves metal. The heat-shrinkable cable accessory combines the characteristics of the infusion type and the dry package type, and enjoys the advantages of both.

11. What inspection work should be carried out before the cable is laid?

Answer: (1) Tools for installing fixed cables should be prepared.

(2) Check whether the cable model, voltage and specifications are consistent with the requirements.

(3) The cable is well insulated. When there is doubt about the sealing of the oil-paper cable, it should be judged by moisture; direct buried cables and small bottom cables should be difficult to pass the DC withstand voltage test; oil samples of oil-filled cables should be tested.

(4) The oil pressure of the oil-filled cable should not be lower than 1.47MPa.

12. When there is doubt about the sealing of oil-paper insulated power cables, how can I use a simpler method to check whether the cable insulation paper is damp?

Answer: Ignite the cable insulation paper or put it into the cable oil at about 150 ℃ to check, no "hiss" or white foam appears, indicating that it is not wet.

13. How to deal with the moisture treatment before the construction of the yellow wax ribbon, black glass lacquer ribbon and alkali-free glass ribbon used for the cable joint?

Answer: (1) Drying method: arrange the insulation layer into small rolls with a diameter of 25 to 30mm, and then put them in a constant temperature drying oven at 110 to 120 ℃ for 4 to 5 hours. After cooling and drying, take them out and put them in a dry sealed cylinder .

(2) Oil immersion and moisture removal method: put a small roll of insulation tape in cable oil with a constant temperature of 120 ~ 130 ℃, keep a distance of 30mm from the bottom of the pot, after a certain period of time, the oil surface no longer produces foam, then take it out and store it In drums with cable oil, the oil level should exceed all enclosed objects and seal them.

14. What is the role of the outer sheath of the cable?

Answer: Protect the cable components inside from mechanical damage and chemical corrosion by other external forces, enhance mechanical strength and corrosion resistance.

15. What is the role of the inner sheath of the cable?

Answer: Avoid direct contact of the insulating layer with water, air or other corrosive objects, and protect the insulating layer from corrosive gases or mechanical damage.

16. What should be paid attention to when using wire cutters?

Answer: Before use, pay attention to check whether there is any damage to the insulated handle. In the middle of use, you can not cut the metal material outside the allowable specifications, and it is forbidden to use other hammering tools.

17. What is insulation strength?

Answer: In the power circuit, the insulation substance will be broken down when the strength of the circuit increases to a certain limit. This electric strength that causes insulation breakdown is called insulation strength.

18. What are the advantages of cross-linked heat shrinkable cable accessories?

A: This is a newly invented material today. It has excellent electrical properties compared with other materials currently used, and has the advantages of small size, light weight, easy installation, matching materials, etc. In addition, it has weather resistance and pollution resistance Performance, flame retardant and self-extinguishing capabilities.

19. What are the requirements for the mechanical strength of cable conductor connection points?

Answer: The mechanical strength of the connection is mostly less than the mechanical strength of the cable conductor itself. Especially for the cable fixed at a certain place, the tensile strength of the connection point is not less than 60 of the tensile strength of the conductor itself.

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