Basic cable knowledge

The core prompts: 1, commonly used wire, cable according to the use of what types? Answer: According to the purpose, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, and communication power. 1. What types of wires and cables are used according to their purposes?

Answer: According to purpose, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, and radio frequency cable.

2. What are the types of insulated wires?

Answer: The common insulated wires are the following: PVC insulated wire, PVC insulated cord, PVC mixture insulated cord, rubber insulated cord, agricultural buried aluminum core plastic insulated wire, rubber insulated cotton yarn Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.

3, cable bridge for what kind of occasion?

Answer: Cable trays are suitable for general laying of power cables and control cables for indoor and outdoor use by industrial and mining companies. They can also be used for indoor and outdoor installations in telecommunications, broadcasting and television departments.

What are the cable accessories?

Answer: The commonly used electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connecting pipes and terminals, steel wiring slots, and cable trays.

5, what is the cable middle connector?

Answer: The device that connects the cable with the cable conductor, insulation shield and protective layer to connect the cable line is called the cable middle connector.

6, what is the main electrical wiring?

Answer: The main electrical connection is the connection mode of the main electrical equipment and busbars in power plants and substations, including the main busbars and plant power systems according to certain functional requirements.

7. What rules should be followed when selecting the section of a power cable?

A: The selection of power cables should follow the following principles:

(1) The rated voltage of the cable shall be greater than or equal to the rated voltage of the power supply system at the installation point;

(2) The continuous allowable current of the cable shall be equal to or greater than the maximum continuous current of the supply load;

(3) The cross-section of the core must meet the requirements for the stability of the short circuit of the power supply system;

(4) Verify that the voltage drop meets the requirements based on the length of the cable;

(5) The minimum short-circuit current at the end of the line should enable the protection device to operate reliably.

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

A: (1) Easy to install because it allows a small minimum bending radius and light weight;

(2) Not subject to line drop restrictions;

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

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

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

(6) Lower prices;

(7) High reliability and low failure rate;

(8) There are few manufacturing processes, simple processes, and significant economic benefits.

9. What are the requirements for the clamp of a fixed AC single-core cable? why?

A: The fixture should be composed of no iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic lines are generated around it. The magnetic force line is proportional to the current flowing through the core. If using magnetic materials such as iron, according to Electromagnetic induction shows that eddy currents will be generated in the iron to heat the cable and even burn the cable. Therefore, it is not allowed to use iron pieces as fixing fixtures for single-core AC cables.

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

A: The most important feature of the heat-shrinking attachment is the use of a stress tube instead of the traditional stress cone. It not only simplifies the construction process, but also reduces the size of the terminal of the joint. It is easy to install, saves time and labor, and is superior in performance, saving metal. The heat-shrinkable cable accessory sets the pouring type and the dry bag type, and combines the advantages of these two types of accessories.

11. What inspections should be performed before the cable is laid?

Answer: (1) The bracket should be complete and painted.

(2) The cable model, voltage, and specifications meet the design.

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

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

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

A: Insulate the cable insulation paper or put it in the cable oil of about 150°C. Check that there is no “click” or white foam, indicating that it is not wet.

13. What should be indicated on the cable signboard? What are the requirements for writing?

Answer: The cable design number, cable type, specification and starting point should be indicated on the signboard. The serial cable should be used in parallel. Requires clear writing and easy to fall off.

14. Where should the orientation mark of the buried cable be located?

Answer: At both ends of the cable, the cable connector 50~100m at the cable connector changes the direction of the cable.

15. To make yellow ribbons, black glass lacquer ribbons, and alkali-free glass ribbons for cable joints, how do you handle the tide before construction?

Answer: (1) Constant temperature drying method: The insulating tape is rolled into a small roll with a diameter of 25~30mm, placed in a constant temperature drying box at 110~120°C for 4~5h, cooled and dried, and put into a dry sealed tube.

(2) Oil immersing and draining tide method: Put a small roll of insulating tape into the cable oil at a constant temperature of 120~130°C, and keep a distance of 30mm from the bottom of the pot. After a certain period of time, the oil is no longer foamed, then it is taken out and stored. In tanks with cable oil, the oil level should exceed all enclosed objects and seal it.

16. What is the role of the cable sheath?

A: The inner sheath is protected from mechanical damage and Chemical corrosion, enhancing mechanical strength.

17, outdoor cable ditch should meet what requirements?

Answer: The upper part of the cable trench should be slightly higher than the ground. Covers should be covered with concrete. The cable should be laid flat on the bracket and have a good drain.

18. What is the role of the sheath in the cable?

Answer: The insulation layer will not be in contact with water, air or other objects to prevent the insulation from moisture and the insulation layer from mechanical damage.

19, when using wire cutters should pay attention to what?

A: Before use, be sure to check the insulating handle insulation is intact, use wire cutters can not be cut over the specifications allow the metal wire, and the use of wire cutters instead of a hammer to beat the tool to avoid damage.

20, what is the dielectric strength?

A: In the electric field, when the electric field strength increases to a certain limit, the insulation material will be broken down. This electric field strength that causes insulation breakdown is called the insulation strength.

21, crosslinked heat shrinkable cable accessories What are the advantages?

A: This is a new type of material. Compared with other types of accessories nowadays, it has the advantages of superior electrical performance, small size, low quality, easy installation, and matching materials. It also has weather resistance, contamination resistance, flame retardance, self-extinguishing, etc. ability.

22. What are the requirements for the mechanical strength of the cable conductor connection point?

A: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For a fixedly installed power cable, the tensile strength of the connection point is not less than 60% of the tensile strength of the conductor itself.

23. What are the main properties of the insulating material for power cables?

A; should have the following main features:

(1) High breakdown strength;

(2) Low dielectric loss;

(3) High insulation resistance;

(4) Excellent resistance to discharge performance;

(5) Has a certain degree of flexibility and mechanical strength;

(6) Long-term stability of insulation performance.

24. When laying cables, what are the requirements for traction strength?

A: For copper core cables, when pulling the head, the allowable traction strength is 70N/cm; for the aluminum core cable, when the head is pulled, the allowable traction strength is 40N/cm; if the wire mesh cover is used for traction, the lead protection Set cable allowable strength is 10N/cm;

Lead sheathed cable is 40N/cm.

25. What are the regulations for cable protection tubes?

Answer: (1) When the cable needs to wear a protective tube, the inner diameter of the pipe should not be less than 1.5 times the outer diameter of the cable, and the inner diameter of the concrete pipe, clay pipe, asbestos, cement pipe should not be less than 100mm;

(2) The bending radius of the cable tube shall comply with the provisions of the bending radius of the cable.

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