1. What are the types of commonly used wires and cables according to their use?
Answer: According to the purpose, it can be divided into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.
2. What kinds of insulated wires are there?
Answer: There are the following types of commonly used insulated wires: PVC insulated wires, PVC insulated cords, nitrile and PVC compound insulated cords, rubber insulated wires, direct buried aluminum core plastic insulated wires for agricultural use, and rubber insulated cotton yarn Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.
3. What kind of occasion is the cable tray suitable for?
Answer: The cable tray is suitable for laying power cables and control cables indoors and outdoors in general industrial and mining enterprises, and can also be used for indoor and outdoor installations in telecommunications, radio and television departments.
4. What are the cable accessories?
Answer: Commonly used electrical accessories include cable terminal junction box, cable intermediate junction box, connecting pipe and terminal block, steel plate junction box, cable tray, etc.
5. What is a cable intermediate connector?
Answer: The device that connects the cable and the cable's conductor, insulation shielding layer and protective layer to connect the cable line is called the cable intermediate joint.
6. What is electrical main wiring?
Answer: The electrical main wiring is the connection method of the main electrical equipment and the bus bar in power plants and substations, including the connection method of the main bus bar and the auxiliary power system according to certain functional requirements.
7. When choosing the cross-section of the power cable, which regulations should be followed?
Answer: The selection of power cables should follow the following principles:
(1) The rated voltage of the cable should 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 should be equal to or greater than the maximum continuous current of the power supply load;
(3) The cross-section of the core must meet the requirements for stability of the power supply system when it is 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 the protection device to operate reliably.
8. What are the advantages of cross-linked polyethylene cables and oil-paper cables?
Answer: (1) Easy to install, because it allows a small minimum bending radius and light weight;
(2) Not limited by line drop;
(3) Good thermal performance, high allowable working temperature and large transmission capacity;
(4) The cable accessories are simple, all of which are dry structure;
(5) Simple operation and maintenance, no oil leakage problem;
(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 fixing AC single-core cables? Why?
Answer: The clamp should have no iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic lines of force are generated around it. The magnetic line of force is proportional to the current passing through the core. If iron and other magnetic materials are used, according to Electromagnetic induction knows that eddy currents will be generated in the iron to heat the cable and even burn the cable. Therefore, iron pieces cannot be used as fixing fixtures for single-core AC cables.
10. What are the biggest features and advantages of the following heat shrinkable cable head accessories?
Answer: The biggest feature of heat-shrinkable accessories is the use of stress tubes instead of traditional stress cones. It not only simplifies the construction process, but also reduces the size of the joint terminal, which is convenient to install, save time and labor, and is easy to install.
Can be superior and save metal. The heat-shrinkable cable accessory integrates the perfusion type and the dry pack type into one, which combines the advantages of these two types of accessories.
11. What inspection work should be carried out before cable laying?
Answer: (1) The bracket should be complete and the paint should be complete.
(2) The cable type, voltage, and specifications conform to the design.
(3) The cable insulation is good. When there is doubt about the sealing of the oil-paper cable, the damp judgment should be made; the direct-buried cable and the small-bottom cable should pass the DC withstand voltage 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 1.47MPa.
12. When there are doubts about the sealing of oil-paper insulated power cables, how to check whether the cable insulation paper is damp in a simpler way?
Answer: Ignite the cable insulation paper or put it in the cable oil at about 150℃ to check, there is no "hissing" sound or white foam, indicating that it is not damp.
13. What should be indicated on the cable sign? What are the requirements for writing?
Answer: The cable circuit design number, cable model, specification and starting point should be indicated on the sign, and the cables used in parallel should have a sequence number. The handwriting is required to be clear and not easy to fall off.
14. Where should the azimuth signs of directly buried cables be set?
Answer: At both ends of the cable, the cable connector is at 50~100m in the straight section of the cable and the corner where the cable changes direction.
15. Yellow wax ribbon, black glass lacquer tape, alkali-free glass ribbon, etc. used to make cable joints, how to remove moisture before construction?
Answer: (1) Constant temperature drying method: roll the insulating tape into a small roll with a diameter of 25~30mm and put it in
Bake in a constant temperature drying oven at 110~120℃ for 4~5h, cool and dry, take it out, and put it into a dry sealed cylinder.
(2) Oil immersion and moisture removal method: Put the small coil of insulating tape into the cable oil at 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 will no longer produce foam, then take it out and put it in storage. In the barrel with cable oil, the oil level should exceed all the loaded objects and seal it.
16.What is the function of the outer sheath of the cable?
Answer: Protect the inner protective layer from mechanical damage and chemical corrosion, and enhance the mechanical strength.
17.What are the requirements for outdoor cable trenches?
Answer: The upper part of the cable trench should be slightly higher than the ground, covered with a cover made of concrete, the cable should be laid flat on the support, and there should be a good drainage pipe.
18. What is the function of the cable inner sheath?
Answer: Keep the insulating layer from contact with water, air or other objects to prevent the insulation from being damp and the insulating layer from mechanical damage.
19. What should I pay attention to when using wire cutters?
Answer: Before use, be sure to check whether the insulation of the insulating handle is intact. Do not use wire cutters to cut metal wires that exceed the specifications. It is forbidden to use wire cutters to replace hammers to avoid damage.
20. What is dielectric strength?
Answer: Insulating materials will be broken down in an electric field when the electric field strength increases to a certain limit. This electric field strength that causes insulation breakdown is called dielectric strength.
21. What are the advantages of cross-linked heat shrinkable cable accessories?
Answer: This is a new type of material. Compared with other types of accessories, it has better electrical performance.
It has many advantages, such as small size, low quality, easy installation, and supporting materials. In addition, it also has the ability of weather resistance, anti-fouling, flame retardant and self-extinguishing.
22. What are the requirements for the mechanical strength of the cable conductor connection point?
Answer: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For fixedly laid power cables, the tensile strength of the connection point is required to be no less than 60% of the tensile strength of the conductor itself.
23. What are the main properties of the insulation material of the power cable?
Answer: It should have the following main properties:
(1) High breakdown strength;
(2) Low dielectric loss;
(3) Quite high insulation resistance;
(4) Excellent discharge resistance;
(5) It has a certain degree of flexibility and mechanical strength;
(6) Long-term insulation performance is stable.
24. When laying cables mechanically, what are the requirements for traction strength?
Answer: For copper core cables, when the head is towed, the allowable traction strength is 70N/cm; for aluminum core cables, when the head is towed, the allowable traction strength is 40N/cm; if the wire mesh sleeve is used for traction, the lead protection The allowable strength of the sheathed cable is 10N/cm; the lead sheathed cable is 40N/cm.
25. What are the regulations for cable protection tubes?
Answer: (1) When the cable needs to be laid through a protective tube, the inner diameter of the tube should not be less than the outer diameter of the cable
1.5 times, the inner diameter of concrete pipe, clay pipe, asbestos, cement pipe should not be less than 100mm;
(2) The bending radius of the cable tube should meet the requirements of the bending radius of the cable inserted;
(3) Each pipe should not exceed three elbows at most, and there should be no more than two right-angle bends.
26. How to measure the outer diameter of the cable sheath?
Answer: At five points evenly distributed on the circumference of the sheath, measure the outer diameter of the sheath and its average value. The average outer diameter is the outer diameter of the sheath.
27. How to connect copper core cables with different cross-sections?
Answer: The copper core cables of different cross-sections can be connected by open weak backed copper pipes and connected by soldering method, or pure copper rods can be connected into copper pipes according to different cross-section requirements and connected by crimping method.
28. Briefly describe the process of 10KV cross-linked cable heat shrinkable indoor terminal head?
Answer; (1) Preparation stage: Check whether the heat-shrinkable cable accessories are complete and the models match. After checking and confirming whether there is moisture in the cable, check the cable.
(2) Cut off the excess cables, and determine the cable length according to the site conditions.
(3) Strip off the protective layer.
(4) Weld the ground wire, and weld the ground wire to the steel strip.
(5) Fill the three-pronged mouth and wrap sealant.
(6) Install the three-core branch sheath, insert the sheath into the root, and shrink from the middle, first to the root, and then to the fingers.
(7) Strip the copper tape and the outer semi-conductive layer, and peel and cut the copper tape with a three-core branch sleeve over 20mm. It is strictly forbidden to damage the main insulation and remove the semi-conductive layer.
(8) Install the stress tube, and heat shrink after the butt joint at the end of the tube.
(9) Install wiring terminals.
