Ten Important Knowledges of Wire and cable

- Jun 05, 2020-

electric cable (8)


1. What types of commonly used wires and cables are classified according to their uses?


Answer: 

It can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, radio frequency cable, etc.


2. What kinds of insulated wires are there?


Answer: 

Common insulated wires include the following: PVC insulated wires, PVC insulated flexible wires, butyronitrile and PVC mixture insulated flexible wires, rubber insulated wires, agricultural underground directly buried aluminum core plastic insulated wires, rubber insulated cotton yarn Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.


3. What regulations should be followed when selecting the cross-section of the power cable?


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 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.


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

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answer:


(1) Easy to install, because it allows the minimum bending radius to be small and light weight;


(2) Not subject to line drop restrictions;


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


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


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


(6) The price is low;


(7) High reliability and low failure rate;


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



5. 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 to replace 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 accessory integrates the perfusion type and the dry-pack type, and combines the advantages of these two accessories.



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


answer:


(1) The bracket should be complete and painted.


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


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


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




7. 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?


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.



8. What should be indicated on the cable sign? What are the requirements for writing?


Answer: 

The design number, cable type, specification and starting point of the cable line should be indicated on the sign board, and the cables used in parallel should have sequential numbers. The handwriting should be clear and not easy to fall off.



9. 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) Constant temperature drying method: roll the insulation tape into small rolls with a diameter of 25-30mm, put them in a constant temperature drying oven at 110~120℃, bake them for 4~5h, cool them and take them out, put them in a dry sealed cylinder


(2) Oil immersion moisture removal method: Put a small coil 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 time, the oil surface no longer produces foam, take it out, and put it into storage In drums with cable oil, the oil level should exceed all enclosed objects and seal them.



10. What is the role of the inner sheath of 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.


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