Common power cable technology 72 questions! worth collecting!

Common power cable technology 72 questions! worth collecting!

  • Categories:Industry News
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  • Time of issue:2017-08-11 14:48
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(Summary description)According to the use, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, RF cable, etc.

Common power cable technology 72 questions! worth collecting!

(Summary description)According to the use, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, RF cable, etc.

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2017-08-11 14:48
  • Views:0

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

A: According to the use, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, RF cable, etc.

2. What kinds of insulated wires are there?

Answer: There are commonly used insulated wires: polyvinyl chloride insulated wire, PVC insulated wire, nitrile polyvinyl chloride mixture insulated cord, rubber insulated wire, agricultural underground direct 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. 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. It can also be used for erection indoors and outdoors 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 wiring slot, cable tray and so on.

5. What is the cable intermediate connector?

Answer: The device that connects the cable and the conductor of the cable, the insulating shield and the protective layer to connect the cable line is called the cable intermediate connector.

6. What is the electrical main wiring?

Answer: The main electrical 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 plant power system according to certain functional requirements.

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

A: The choice of power cable should follow the following principles:

(1) The rated voltage of the cable is 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 power supply load;

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

(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 XLPE cable and oil-paper cable?

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

(2) not subject to line drop restrictions;

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

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

(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 small, the process is simple, and the economic benefits are remarkable.

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

Answer: The clamp should be free of iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic flux is generated around it. The magnetic flux is proportional to the current passing through the core. If a magnetic material such as iron is used, Electromagnetic induction knows that eddy currents will be generated in the iron parts to heat the cable and even burn the cable. Therefore, iron parts cannot be used as fixing fixtures for single-core AC cables.

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

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, and is

Can be superior and save metal. The heat-shrinkable cable accessory combines a perfusion and a dry-package, combining the advantages of both accessories.

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

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

(2) 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 moisture should be judged; 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 1.47 MPa.

12. When there is any doubt about the sealing of oil-paper insulated power cable, how to check whether the cable insulation paper is damp with a simple method?

Answer: Ignite the cable insulation paper or put it into the cable oil of about 150 °C for inspection. There is no “click” or white foam, indicating that it is not damp.

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

Answer: The cable circuit design number, cable type, specification and starting point should be indicated on the signboard. The cables used in parallel should have a sequence number. Requires clear writing and is not easy to fall off.

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

Answer: At both ends of the cable, at the 50~100m straight section of the cable, the cable connector will change the direction of the corner.

15. How to make moisture-proof treatment before the construction, such as yellow wax ribbon, black glass ribbon, and alkali-free glass ribbon for cable joints.

Answer: (1) Constant temperature drying method: roll the insulation tape into a small volume of 25~30mm in diameter and put it into

Dry in a constant temperature drying oven at 110~120 °C for 4~5h, cool and dry, and put into a dry sealed cylinder.

(2) Oil immersion method: put a small coil of insulation tape into the cable oil at a constant temperature of 120~130 °C, keep a distance of 30mm from the bottom of the pot, after a certain period of time, the oil no longer produces foam and then take it out and put it into storage. In tanks with cable oil, the oil level should exceed all loaded objects and seal them.

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

A: Protect the inner sheath from mechanical damage and chemical corrosion, and enhance mechanical strength.

17. What requirements should the outdoor cable trench meet?

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

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

A: The insulation layer will not come into contact with water, air or other objects to prevent the insulation from being damp and the insulation 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 insulation handle is intact. The wire cutters can not be used to cut the metal wire beyond the specification, and it is forbidden to use the wire cutter instead of the hammer to avoid the damage.

20. What is the insulation strength?

Answer: In the electric field, the insulating material is broken down when the electric field strength increases to a certain limit. The electric field strength that causes the dielectric breakdown is called the dielectric strength.

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

A: This is a new type of material that has superior electrical performance compared to other types of accessories.

The advantages of smaller size, small size, simple installation, convenient materials, and other materials, such as weather resistance, anti-staining, 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 a fixedly laid 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 insulation material of the power cable?

A; should have the following main features:

(1) high breakdown strength;

(2) low dielectric loss;

(3) A fairly high insulation resistance;

(4) Excellent discharge resistance;

(5) has a certain degree of softness and mechanical strength;

(6) The insulation performance is stable for a long time.

24. What are the requirements for traction strength when laying cables?

Answer: For copper core cable, the traction strength is allowed to be 70N/cm when pulling the head; for aluminum core cable, the traction strength is allowed to be 40N/cm when the head is pulled; if it is pulled by steel wire mesh, lead protection The set of cables allows a strength of 10 N/cm; the lead sheathed cable is 40 N/cm.

25. What are the regulations for cable protection?

Answer: (1) When the cable needs to be laid with a protective tube, the inner diameter of the pipe should not be smaller than the outer diameter of the cable.

1.5 times, the inner diameter of concrete pipe, clay pipe, asbestos and cement pipe shall not be less than 100mm;

(2) The bending radius of the cable tube shall comply with the requirements for the bending radius of the cable to be penetrated;

(3) Each pipe shall not exceed a maximum of three bends, and there shall be no more than two right angle bends.

26. How to measure the outer diameter of the cable sheath?

A: At the five points evenly distributed over the circumference of the sheath, the outer diameter of the sheath and its average value are measured, and the average outer diameter is the outer diameter of the sheath.

27. How to connect copper core cables with different cross sections?

Answer: Copper-core cable connections with different cross-sections can be connected by soldering with open weak copper joints. They can also be connected to copper joints by pure copper rods according to different cross-section requirements and connected by crimping.

28. Briefly describe the process of 10KV cross-linked cable heat-shrinking to produce indoor terminal heads?

Answer: (1) Preparation stage: Check whether the heat-shrinkable cable accessories are complete, whether the models match, check and confirm the cable with moisture, and check the cables.

(2) Cut off the excess cable and determine the cable length according to the site conditions.

(3) Stripping the sheath.

(4) Solder the grounding wire and weld the grounding wire to the steel strip.

(5) Fill the three forks and wrap the sealant.

(6) Install the three-core branch sheath, put the sheath into the root, and start to shrink from the middle, first to the root, then to the finger.

(7) Stripping the copper strip and the outer semi-conductive layer, peeling off the copper strip of the three-core branch sleeve 20mm or more, it is strictly forbidden to damage the main insulation and remove the semi-conductive layer.

(8) Install the stress tube, and the sleeve end portion of the tube end is heat-shrinked after docking.

(9) Install the terminal block.

(10) Install the insulation tube.

(11) Install the sealing tube.

(12) Install the color tube after the nuclear phase.

29. What are the installation steps for indoor and outdoor prefabricated terminals?

Answer: (1) Put the cable in place according to the predetermined position, fix and clean the surface, and peel off the outer sheath according to the instruction manual. If there is special need, the outer sheath stripping length can be adjusted, and the copper strip and the outer sheath are respectively led out. 2 sets of ground wire.

(2) Take the required size from the outer sheath opening, cut off the excess cable, insert the heat-shrinking three-finger sleeve to the root of the three-pronged mouth and heat it up by the middle, and measure the specified size from the upper mouth of the finger sleeve (35kv is 350~380mm) ). Remove the excess copper strip (retain 20mm), then retain the predetermined position of the semiconductor, and crimp the outlet terminal seal.

30. Under what circumstances should the motor installed on site be subjected to core inspection?

Answer: When the motor has one of the following conditions, the core inspection should be carried out:

(1) The date of delivery exceeds the manufacturer's warranty period;

(2) Upon visual inspection or electrical test, the quality is suspicious;

(3) When the open motor is suspicious after the end inspection;

(4) If there is an abnormality during the test run.

31. What are the conditions for the generator to be in parallel at the same time?

Answer: The three conditions in which the generator is juxtaposed are that the difference between the voltage, frequency and phase of the generator and the voltage, frequency and phase of the operating system is less than the specified value.

32. What inspections should be carried out after the busbar installation is completed?

A: The following checks should be made:

(1) The processing, preparation and welding of metal components shall comply with the regulations;

(2) All parts such as bolts, washers and split pins shall be complete and reliable;

(3) Busbar preparation and mounting brackets shall comply with the regulations, and the electrical distance between the phases and the ground shall meet the requirements;

(4) Porcelain parts, iron parts and glued parts shall be complete, oil-filled casings shall be free from oil leakage and oil level shall be normal;

(5) The paint is complete, the phase color is correct, and the grounding is good.

33. In power cable joints of 35kv and below, there are several ways to improve the electric field distribution at the gap of the sheath (please list five), and briefly describe the method.

Answer: (1) Expanding the bell mouth: The edge of the lead packet is picked up at the edge of the lead package to form a trumpet shape, and the edge thereof should be smooth, round and symmetrical.

(2) Reserve turnkey insulation: Leave a piece of turnkey insulation paper between the lead package cut and the cable core separation point.

(3) Cut off the semiconductive paper: Cut the semiconductive paper below the bell mouth.

(4) Wrapped stress cone: The insulating tape and the conductive metal material are wrapped into a cone, and the shielding layer is artificially enlarged to improve the electric field distribution.

(5) Equipotential method: For dry-pack or cross-linked polyethylene cable heads, a metal strip is wrapped on the insulation surface of each core and connected together.

(6) Install the stress control tube: For the 35kv and the heat-shrinkable tube cable head, firstly wrap the two-layer semiconductor strip from the end of the core copper shield layer through the semiconductor strip to the core insulation, and then fold the corresponding specifications. The tube is sleeved at the end of the copper shield and heat-shrinked.

34. What requirements should the cable bracket be processed?

Answer: (1) The steel should be straight and there is no obvious distortion. The blanking error should be within 5mm. The incision should be free of curling and burrs;

(2) The bracket should be welded firmly, without obvious deformation, vertical clearance between the cross braces and design deviation

Should not be greater than 5mm;

(3) Metal brackets must be treated with anti-corrosion treatment. When located in areas with damp heat, salt, fog and chemical corrosion, special corrosion protection should be applied according to the design.

35. List the cable holders that you are familiar with.

A: Tailored E-frame, assembled E-frame, bridge cable frame, cable bracket, hook bracket, single cable bracket, etc.

36. What requirements should be met for laying cables?

A: The following requirements should be met:

(1) In terms of safe operation, avoid external damage as much as possible and improve the reliability of power supply of cable lines;

(2) On the economic side, considering the most economical aspects of investment;

(3) In terms of construction, the route of the cable line must be convenient for maintenance after rotation and commissioning.

37. What are the insulation materials for making cable terminations or intermediate joints?

Answer: There are insulating rubber, insulating tape, insulating tube, insulating gloves, insulating resin, etc.

38. Briefly describe the general operating procedures for cable heading.

Answer: (1) Preparation before production: including ○1 reading installation manual; ○2 viewing site; ○3 preparation; ○4 cable test tide; ○5 pre-production test.

(2) The manufacturing process of the joint: including ○1 cutting off excess cable; ○2 stripping of cable protective layer; ○3 conductor connection; ○4 wrapping insulation (or shrinking pipe); ○5 mounting joint shell; ○6 filling insulation Agent; ○7 is subjected to a sealing treatment or the like.

(3) Electrical test after production.

39. What requirements should be met for the processing of cable protection tubes?

Answer: (1) The nozzle should be free of burrs and sharp corners, and the nozzle should be made into a flare.

(2) After the cable tube is bent, there should be no cracks and significant concave sag, and the degree of bending should not be greater than 10% of the outer diameter of the tube; the bending radius of the cable tube should not be less than the minimum allowable bending radius of the cable to be penetrated. .

(3) The metal pipe shall be coated with anti-corrosive paint or leaching table on the outside, and the galvanized pipe shall be coated with anti-corrosive paint.

40. What are the requirements for the arrangement of the cables?

Answer: (1) Power cables and control cables should not be placed on the same shelf.

(2) High and low voltage cables, strong and weak electrical control cables shall be layered according to the order of the order. Generally, the top and bottom should be from the top to the bottom. However, when the high voltage cable containing 35kv or more is introduced into the cabinet, the bending radius can be satisfied. Configuration.

41. What is the method of laying cables in cable trenches?

Answer: The method of laying cables in the cable trench is similar to the laying method of the direct buried cable. Generally, the pulley can be placed in the trench. After the application is completed, the cable is placed on the bottom of the trench or the bracket, and the cable label is tied on the cable.

42. What are the common equipment for cable laying?

Answer: (1) Air compressors are mainly used to damage the road surface and prepare for laying cables later;

(2) Electric hoist or cable traction machine, mainly used for towing cables;

(3) Cable conveyor, used with the tractor to overcome

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