Wire and cable science knowledge

1. What kinds of insulated wires are there?
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Answer: Common insulated wires are as follows: PVC insulated wire, PVC insulated flexible wire, nitrile polyvinyl chloride mixture insulated flexible wire, rubber insulated wire, agricultural underground direct buried aluminum core plastic insulated wire, rubber insulated cotton yarn Textile flexible wires, PVC insulated nylon sheathed wires, PVC insulated flexible wires for electricity and lighting, etc.
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2. What kind of occasion is the cable tray suitable for?
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Answer: The cable bridge is suitable for the indoor and outdoor overhead laying of power cables and control cables in general industrial and mining enterprises, and can also be used for indoor and outdoor erection of telecommunications, radio and television departments.
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3. What are the types of commonly used wires and cables according to their uses?
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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.
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4. What are the cable accessories?
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Answer: Commonly used electrical accessories include cable terminal junction box, cable intermediate junction box, connecting pipe and terminal, steel plate junction groove, cable tray, etc.
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5. What is a cable intermediate joint?
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Answer: The device that connects the conductor, insulation shielding layer and protective layer of the cable to the cable to connect the cable line is called the cable intermediate joint.
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6. What is the electrical main wiring?
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Answer: Electrical main wiring is the connection method between main electrical equipment and busbars in power plants and substations, including the connection method between main busbars and plant power systems according to certain functional requirements.
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7. What regulations should be followed when selecting the section of the power cable?
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Answer: The selection of power cables should follow the following principles:
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(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;
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(2) The continuous allowable current of the cable should be equal to or greater than the maximum continuous current of the power supply load;
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(3) The cross section of the wire core should meet the stability requirements when the power supply system is short-circuited;
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(4) Check whether the voltage drop meets the requirements according to the cable length;
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(5) The minimum short-circuit current at the end of the line should enable the protective device to operate reliably.
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8. What are the advantages of XLPE cables and oil-paper cables?
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Answer: (1) Easy to install, because it allows a small minimum bending radius and light weight;
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(2) Not affected by line drop;
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(3) Good thermal performance, high allowable working temperature and large transmission capacity;
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(4) The cable accessories are simple and all of them are of dry structure;
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(5) Simple operation and maintenance, no oil leakage;
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(6) The price is lower;
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(7) High reliability and low failure rate;
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(8) The manufacturing process is less, the process is simple, and the economic benefit is remarkable.
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9. What are the requirements for clamps for fixing AC single-core cables? Why?
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Answer: The clamp should have no iron parts to form a closed magnetic circuit. This is because when the cable core passes current, magnetic force lines are generated around it, and the magnetic force lines are proportional to the current passing through the core. If magnetic materials such as iron parts are used, according to Electromagnetic induction shows that eddy currents will be generated in the iron parts to heat the cable, or even burn the cable. Therefore, iron parts cannot be used as fixing fixtures for single-core AC cables.
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10. What are the biggest features and advantages of the following heat-shrinkable cable head accessories?
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Answer: The biggest feature of the heat-shrinkable attachment is that it replaces the traditional stress cone with a stress tube. 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, has superior performance, and saves metal. The heat-shrinkable cable accessories combine the pouring type and the dry-packing type, and combine the advantages of these two types of accessories.
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11. What inspections should be done before cable laying?
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Answer: (1) The brackets should be complete and the paint should be complete.
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(2) The cable type, voltage and specification conform to the design.
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(3) The cable insulation is good. When there is any doubt about the seal of the oil-paper cable, it should be judged by moisture; 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.
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(4) The oil pressure of the oil-filled cable should not be lower than 1.47MPa.
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12. When there is doubt about the sealing of oil-paper insulated power cables, how to check whether the cable insulation paper is damp with a simpler method?
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Answer: Ignite the cable insulation paper or put it in cable oil at about 150°C for inspection. If there is no "hissing" sound or white foam, it means that it is not damp.
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13. What should be indicated on the cable sign board? What are the requirements for writing?
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Answer: The cable line design number, cable model, specification and starting point should be indicated on the signboard, and the cables used in parallel should have sequence numbers. The writing is required to be clear and not easy to fall off.
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14. Where should the orientation marks of direct buried cables be set?
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A: At both ends of the cable, at the cable connector at 50-100m of the straight section of the cable, and at the bend where the cable changes direction.
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15. For the yellow wax ribbons, black glass lacquer ribbons, and alkali-free glass ribbons used to make cable joints, how should moisture be removed before construction?
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Answer: (1) Constant temperature drying method: Roll the insulating tape into a small roll with a diameter of 25~30mm, put it in a constant temperature drying oven at 110~120°C for 4~5 hours, cool and dry, take it out, and put it in a dry sealed cylinder.
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(2) Oil immersion dehumidification method: Put the small roll of insulating tape into the cable oil at a constant temperature of 120~130°C, keep a distance of 30mm from the bottom of the pot, take it out after a certain period of time after the oil surface no longer produces foam, and put it into the storage In the barrel with cable oil, the oil level should exceed all loaded objects and seal it.
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16. What is the function of the outer sheath of the cable?
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Answer: Protect the inner sheath from mechanical damage and chemical corrosion, and enhance the mechanical strength.
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17. What requirements should the outdoor cable trench meet?
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Answer: The upper part of the cable trench should be slightly higher than the ground, covered with a concrete cover, the cables should be laid flat on the support, and there should be good drainage pipes.
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18. What is the function of the cable inner sheath?
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Answer; Keep the insulation layer from contacting with water, air or other objects, prevent the insulation from getting damp and the insulation layer from mechanical damage.
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19. What should be paid attention to when using wire cutters?
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Answer: Before use, be sure to check whether the insulation of the insulating handle is intact. During use, it is not allowed to use wire cutters to cut metal wires that exceed the specifications, and it is forbidden to use wire cutters instead of hammers to hit tools to avoid damage.
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20. What is dielectric strength?
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Answer: Insulating substances in the electric field will be broken down when the electric field strength increases to a certain limit. The electric field strength that leads to insulation breakdown is called dielectric strength.