The most complete knowledge of wires and cables in history - 80 Q & A

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

Answer: 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 several kinds of common insulated wires: PVC insulated wire, PVC insulated flexible wire, nitrile PVC mixture insulated wire, rubber insulated wire, agricultural underground directly buried aluminum core plastic insulated wire, rubber insulated cotton yarn textile flexible wire, PVC insulated nylon sheathed wire, PVC insulated flexible wire for power and lighting, etc.

3. What kind of occasion is the cable tray suitable for?

Answer: the cable bridge is applicable to the indoor and outdoor overhead laying of power cables and control cables in general industrial and mining enterprises. It can also be used for the indoor and outdoor erection of telecommunications, radio and television and other departments.

4. What are the cable accessories?

Answer: common electrical accessories include cable terminal junction box, cable intermediate junction box, connecting pipe and terminal, steel plate wiring trough, cable bridge, etc.

5. What is a cable intermediate joint?

A: the device that connects the conductor, insulation shield and protective layer of the cable and the cable to connect the cable line is called the cable intermediate joint.

6. What is the main electrical wiring?

Answer: the main electrical wiring is the connection mode of the main electrical equipment and bus in the power plant and substation, including the connection mode between the main bus and the auxiliary power system according to certain functional requirements.

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

Answer: 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 power supply load;

(3) The cross section of wire core shall meet the requirements of stability in case of short circuit of 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 shall enable the protection device to operate reliably.

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

Answer: (1) easy to install, because it allows small minimum bending radius and light weight;

(2) Not affected by line drop *;

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

(4) Cable accessories are simple and dry structure;

(5) Simple operation and maintenance without oil leakage;

(6) Lower price;

(7) High reliability and low failure rate;

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

9. What are the requirements for fixing the fixture of AC single core cable? Why?

Answer: there should be no iron parts in the clamp to form a closed magnetic circuit, because when the cable core passes through the current, a magnetic line of force will be generated around it, which is directly proportional to the current passing through the core. If magnetic conducting materials such as iron parts are used, according to electromagnetic induction, eddy current will be generated in the iron parts to heat the cable and even burn the cable. Therefore, iron parts cannot be used as the fixing fixture of single core AC cable.

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

A: the biggest feature of heat shrinkable accessories is to replace the traditional stress cone with stress tube. It not only simplifies the construction process, but also reduces the size of the terminal of the joint. It has the advantages of convenient installation, time and labor saving, superior performance and metal saving. The heat shrinkable cable accessory integrates the pouring type and dry package type, which integrates the advantages of these two accessories.

11. What inspections should be carried out before cable laying?

Answer: (1) the support shall be complete and the paint shall be complete.

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

(3) The cable insulation is good. When there is doubt about the sealing of oil paper cable, judge whether it is affected by moisture; The direct current withstand voltage cable and the direct current withstand voltage cable shall pass the test; The oil sample of oil filled cable shall pass the test.

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

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

Answer: check the cable insulation paper or put it in cable oil at 150 degrees or so. No "hissing" or white foam appears, indicating that it is not damp.

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

Answer: the sign board shall indicate the cable line design number, cable model, specification and starting point, and the cables used in parallel shall have sequence number. The handwriting shall be clear and not easy to fall off.

14. Where should the orientation marks of directly buried cables be set?

Answer: at both ends of the cable, at 50 ~ 100m of the straight section of the cable, the cable joint is several bends where the cable changes direction.

15. How to remove moisture before construction of yellow wax ribbon, black glass paint ribbon and alkali free glass ribbon used for making cable joints?

Answer: (1) constant temperature drying method: roll the insulating tape into a small roll with a diameter of 25 ~ 30mm, put it into a constant temperature drying oven at 110 ~ 120 ℃ for 4 ~ 5h, cool and dry it, take it out and put it into a dry sealed cylinder.

(2) oil immersion method: put the insulation tape into the cable oil at constant temperature of 120~130 degrees, keep the 30mm distance from the bottom of the pot. After a certain time, the oil surface will no longer foam and remove into the tank with cable oil. The oil level should be over all the loaded objects and sealed.

16. What is the function of cable outer sheath?

Answer: protect the inner protective layer from mechanical damage and chemical corrosion, and enhance the mechanical strength.

17. What requirements should the outdoor cable trench meet?

Answer: the upper part of the cable trench shall be slightly higher than the ground, covered with a cover plate made of concrete, and the cable shall be laid flat on the support with good drainage pipe.

18. What is the function of cable inner sheath?

Answer; The insulating layer will not contact with water, air or other objects, so as to prevent the insulation from moisture and mechanical damage.

19. What should we pay attention to when using wire pliers?

Answer: before use, be sure to check whether the insulation of the insulating handle is intact. During use, do not use wire pliers to cut metal wires that exceed the specification, and do not use wire pliers instead of hammers to strike tools to avoid damage.

20. What is insulation strength?

A: when the electric field strength of insulating materials in the electric field increases to a certain limit, they will be broken down. The electric field strength leading to insulation breakdown is called insulation strength.

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

A: This is a new type of material. Compared with other types of accessories, it has the advantages of superior electrical performance, small volume, small mass, simple installation, material matching, etc. in addition, it also has the ability of climate resistance, pollution resistance, flame retardant and self extinguishing.

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

Answer: the mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For the fixed power cable, the tensile strength of the connection point shall not be lower than 60% of the tensile strength of the conductor itself.

23. What are the main properties of the insulating layer material of power cable?

Answer; It shall have the following main properties:

(1) High breakdown strength;

(2) Low dielectric loss;

(3) Very high insulation resistance;

(4) Excellent discharge resistance;

(5) It has certain flexibility and mechanical strength;

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

24. What are the provisions on traction strength when laying cables mechanically?

Answer: for copper core cable, when pulling the head, the allowable traction strength is 70N / cm; For aluminum core cable, when pulling the head, the allowable traction strength is 40n / cm; If the steel wire mesh sleeve is used for traction, the allowable strength of lead sheathed cable is 10N / cm;

The lead sheathed cable is 40n / cm.

25. What are the regulations on cable protection tube?

Answer: (1) when the cable needs to be laid through the protective pipe, the inner diameter of the pipe shall not be less than 1.5 times of the outer diameter of the cable, and 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 duct shall comply with the provisions of the bending radius of the penetrated cable;

(3) Each pipe shall not have more than three elbows at most, and no more than two right angle bends.

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

Answer: measure the outer diameter of the sheath and its average value at five points evenly distributed on the circumference of the sheath. The average outer diameter is the outer diameter of the sheath.

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

Answer: for the connection of copper core cables with different sections, the open weak back copper nozzle can be used and connected by tin welding, or the pure copper rod can be connected into copper nozzle according to the requirements of different sections and connected by crimping.

28. Briefly describe the process of heat shrinkable manufacturing indoor terminal of 10kV cross-linked cable?

Answer; (1) Preparation stage: check whether the heat shrinkable cable accessories are complete and whether the models match. After checking and confirming whether the cable has moisture, check the cable.

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

(3) Peel off the protective layer.

(4) Weld the grounding wire and weld the grounding wire on the steel strip.

(5) Fill the Trident and wrapping sealant.

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

(7) Strip the copper strip and the outer semiconducting layer, strip and cut the copper strip with more than 20mm of the three core branch socket, do not damage the main insulation, and remove the semiconducting layer.

(8) Install the stress pipe, and heat shrink after butt joint of the branch sleeve at the end of the pipe orifice.

(9) Install the terminal blocks.

(10) Install insulating pipe.

(11) Install the seal tube.

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

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

Answer: (1) put the cable in place, fix and clean the surface according to the predetermined position, peel off the outer sheath according to the instructions. If there are special needs, the stripping length of the outer sheath can be adjusted, and two groups of ground wires are led out from the copper strip and the outer sheath armor respectively.

(2) Measure the required size upward from the outer sheath mouth, cut off the excess cable, put the heat shrinkable three finger sleeve to the root of the three prong mouth, heat and shrink from the middle, and measure the specified size upward from the upper mouth of the finger sleeve (350 ~ 380mm for 35kV). Remove the excess copper strip (reserve 20mm), reserve the predetermined position of the semiconductor, and crimp the outlet terminal for sealing.

30. The application of wires and cables is mainly divided into three categories:

1. Power system

The wire and cable products used in the power system mainly include overhead bare wires, bus bars (buses), power cables (plastic cables, oil paper power cables (basically replaced by plastic power cables), rubber sheathed cables, overhead insulated cables), branch cables (replacing some buses), electromagnetic wires and electrical equipment wires and cables for power equipment, etc.

2. Information transmission system

The wires and cables used for information transmission system mainly include local telephone cable, TV cable, electronic cable, RF cable, optical fiber cable, data cable, electromagnetic cable, power communication or other composite cables.

3. Mechanical equipment and instrument system

This part is applied to almost all products except overhead bare wires, but mainly power cables, electromagnetic wires, data cables, instrument cables, etc.

31. Wire and cable products are mainly divided into five categories:

1. Bare wire and bare conductor products the main features of this kind of products are: pure conductor metal, no insulation and sheath layer, such as steel cored aluminum strand, copper aluminum bus bar, electric locomotive line, etc; The processing technology is mainly pressure processing, such as melting, calendering, drawing, stranding / compression stranding, etc; The products are mainly used in suburban, rural, user main line, switch cabinet, etc.

2. Power cable

The main features of this kind of products are: extruding (winding) the insulation layer outside the conductor, such as overhead insulated cable, or several cores stranded (corresponding to the phase line, zero line and ground wire of power system), such as overhead insulated cable with more than two cores, or adding sheath layer, such as plastic / rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cable forming, armor, sheath extrusion, etc. different process combinations of various products are different.

The products are mainly used for strong electric energy transmission in power generation, distribution, transmission, transformation and power supply lines, with large current (tens of amps to thousands of AMPS) and high voltage (220V to 500kV and above).

3. Wires and cables for electrical equipment

The main features of these products are: a wide range of varieties and specifications, a wide range of applications, and more use voltages of 1kV and below. In the face of special occasions, new products are constantly derived, such as fire-resistant cables, flame-retardant cables, low smoke halogen-free / low smoke low halogen cables, anti termite, anti mouse cables, oil / cold / temperature / wear-resistant cables, medical / agricultural / mining cables, thin-walled wires, etc.

4. Communication cable and optical fiber (brief introduction)

With the rapid development of the communication industry in the past 20 years, the products also have an amazing development speed. From simple telephone and telegraph cables in the past to thousands of pairs of telephone cables, coaxial cables, optical cables, data cables, and even combined communication cables.

The structural size of this kind of products is usually small and uniform, and the manufacturing accuracy is required to be high.

(5) . electromagnetic wire (winding wire)

It is mainly used for various motors, instruments and meters, etc.

Derivative / new products of wires and cables

The derivative / new products of wires and cables are mainly produced by adopting new materials, special materials, changing product structure, improving process requirements, or combining different kinds of products due to different application occasions, application requirements, convenience of equipment and reducing equipment cost.

Adopt different materials, such as flame retardant cable, low smoke halogen-free / low smoke low halogen cable, anti termite, anti mouse cable, oil / cold / temperature resistant cable, etc;

Change the product structure, such as fire-resistant cable;

Improve process requirements, such as medical cables;

Combined products such as OPGW;

Facilitate installation and reduce equipment cost, such as prefabricated branch cables.

32. What inspections should be carried out after the construction of bus device?

Answer: the following inspections should be carried out:

(1) The processing, preparation, welding and screw connection of metal components shall meet the requirements;

(2) All bolts, washers, cotter pins and other parts shall be complete and reliable;

(3) The bus preparation and installation frame shall meet the requirements, and the electrical distance between phases and to the ground shall meet the requirements;

(4) Porcelain parts, iron parts and glued joints shall be complete, oil filled casing shall be free of oil leakage, and the oil level shall be normal;

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

33. There are several methods to improve the electric field distribution at the disconnection of the sheath in the power cable joint of 35 kV and below (please list five), and briefly describe the methods.

Answer: (1) expanding bell mouth: pry up the edge of the lead package at the cutting point of the lead package into a horn shape, and its edge should be smooth, round and symmetrical.

(2) Reserved turnkey insulation: a section of turnkey insulation paper is reserved between the lead package notch and the separation point of cable core wire.

(3) Cut off the semi conducting paper: cut off the semi conducting paper below the bell mouth.

(4) Wrapping stress cone: wrap the insulating tape and conductive metal material into a cone, and artificially expand the shielding layer to improve the distribution of electric field.

(5) Equipotential method: for dry wrapped or cross-linked polyethylene cable heads, wrap a section of metal tape on the insulation surface of each core and connect them together.

(6) Installation of stress control tube: for the cable head of 35kV and lower heat shrinkable tube, first wrap two layers of semiconductor tape from the end direction of the copper shielding layer of the wire core to the insulation profile of the wire core through the semiconductor tape, and then wrap the stress tube of corresponding specifications at the end of the copper shielding and heat shrinkable.

34. What requirements should the processing of cable support meet?

Answer: (1) the steel should be straight without obvious distortion, the blanking error should be within 5mm, and the incision should be free of curling and burrs;

(2) The support shall be welded firmly without obvious deformation, and the vertical clear distance between each cross brace and the design deviation shall not be greater than 5mm;

(3) The metal support must be subject to anti-corrosion treatment. If it is located in areas with damp heat, salt, fog and chemical corrosion, it shall be subject to special anti-corrosion treatment according to the design.

35. List the cable racks you are familiar with.

Answer: tailor welded E-frame, fabricated E-frame, bridge cable frame, cable bracket, hook support, single cable support, etc.

36. What requirements should be met for laying cables?

Answer: the following requirements shall be met:

(1) In terms of safe operation, try to avoid all kinds of external damage and improve the power supply reliability of cable lines;

(2) In terms of economy, consider the most economical aspect of investment;

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

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

A: there are insulating glue, insulating tape, insulating tube, insulating gloves, insulating resin, etc.

38. Briefly describe the general operation procedure of cable head fabrication. Answer: (1) preparation before production: including ○ 1 reading the installation instructions; ○ 2 inspect the site; ○ 3 material preparation; ○ 4 cable moisture test; ○ 5 pre fabrication test, etc.

(2) Manufacturing process of connector: including ○ 1 cutting off excess cables; ○ 2 stripping and cutting of cable protective layer; ○ 3 conductor connection; ○ 4 wrap insulation (or shrink tubing); ○ 5 install the connector housing; ○ 6 inject insulating agent; ○ 7 sealing treatment, etc.

(3) Electrical test after fabrication.

39. What requirements should the processing of cable protection pipe meet?

Answer: (1) the nozzle should be pricked and sharp corners, and the nozzle should be made into a horn shape.

(2) After bending, the cable pipe shall be free of cracks and obvious concavity, and its bending degree shall not be greater than 10% of the outer diameter of the pipe; The bending radius of the cable duct shall not be less than the minimum allowable bending radius of the penetrated cable.

(3) The metal pipe shall be coated with anti-corrosion paint or asphalt meter on the surface, and the peeling part of the zinc layer of the galvanized pipe shall also be coated with anti-corrosion paint.

40. What requirements does the cable arrangement meet? Answer: (1) power cable and control cable should not be configured on the same layer of support.

(2) High and low voltage cables, strong and weak current control cables shall be configured in layers according to the required sequence. Generally, they should be configured from top to bottom. However, when the high-voltage cables with more than 35kV are introduced into the cabinet, they can be configured from the bottom to the top to meet the bending radius.

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

Answer: the method of laying cables in the cable trench is similar to that of directly buried cables. Generally, the pulley can be placed in the trench. After the laying is completed, the cable shall be placed on the trench bottom or support, and the cable label shall be bound on the cable.

42. What are the common equipment for cable laying?

Answer: (1) the air compressor is mainly used to destroy the road surface and prepare for laying cables in the future;

(2) Electric winch or cable tractor, mainly used to tow cables;

(3) The cable conveyor is used together with the tractor to overcome the huge friction and reduce the damage to the cable;

(4) Cable reel setting out support;

(5) Roller device;

(6) Anti twist, reduce the twist of steel wire rope;

(7) Cable drum braking device;

(8) Tensiometer.

43. What are the requirements for the installation distance of the support in the cable trench? Answer: the cable is fixed on the wall of cable trench and tunnel. When the cable is installed horizontally, when the outer diameter of the cable is equal to or less than 50mm, a support shall be added every 1m; For cables with outer diameter greater than 50mm, add a support every 0.6m; The single cable arranged in a triangle shall be fastened with straps every 1m. When it is installed vertically, it shall be fixed every 1 ~ 1.5m.

44. How to deal with the installation of power cable and control cable in the same bracket?

Answer: generally, power cables and control cables should not be laid in the same bracket. When there are few cables and the control cables and power cables are laid in the same bracket, they should be separated by partitions.

45. How to install grounding wire in cable tunnel?

Answer: the whole length of the tunnel and trench shall be equipped with continuous grounding wire, which shall be connected with all supports, and the two ends shall be connected with the grounding electrode. The specification of grounding wire shall meet the design requirements. In addition to insulation requirements, the lead cladding and armor of cables shall be all interconnected and connected with the grounding wire. The cable rack and grounding wire shall be coated with antirust paint or galvanized.

46. What are the requirements for fireproof sealing of cable holes?

Answer: for larger cable through holes, such as the place where the cable runs through the floor, when plugging with fire-proof plugging material, according to the actual situation, first apply four to six layers of fire-proof coating on the cable surface, with a length of about 1.5m below the hole, and then process the refractory material into a plate support fire-proof plugging material with certain strength, so as to ensure that it is firm after plugging and convenient for disassembly and assembly when replacing the cable, and the plugging is dense without holes, so as to effectively block smoke and fire.

47. What checks should be paid attention to before the blowtorch is ignited?

Answer: the following inspections should be carried out:

(1) Whether there is oil leakage or oil leakage in the air pump, and whether there is oil leakage or air leakage at the oil barrel and nozzle;

(2) Whether the oil volume in the oil barrel exceeds 3 / 4 of the capacity of the oil barrel, and whether the screw plug for refueling is tightened.

48. What should be paid attention to when using blowtorch?

Answer: (1) the maximum oil filling volume of the blowtorch is 3 / 4 of the volume of the oil barrel;

(2) Don't pump too much pressure at the beginning. After lighting, the flame can be used from yellow to blue;

(3) There shall be no combustibles around and the air shall be circulated;

(4) When stopping, turn off the regulating switch first. After the fire is turned off, slowly loosen the oil hole cover to vent. After the air is discharged, loosen the regulating switch and loosen the hole cover after it is completely cooled;

(5) Kerosene blowtorch and gasoline blowtorch shall be used separately.

49. What is the purpose of manual oil pressure Tong? How to operate?

A: the connection of two wires is usually to thread the ends of the two wires into the pressure pipe made of the same material, and squeeze several pits with crimping pliers to connect the wires together. During crimping, when the handle is lifted up, the plunger moves outward, the lower cavity of the oil inlet valve generates vacuum, and the oil in the oil tank enters the plunger cavity. When the handle is pressed down, the plunger moves inward. After the oil is pressed, close the oil inlet valve and open the oil outlet valve to make the oil pressure enter the hydraulic cylinder to push the piston and the male mold. A pressure connecting pipe is placed between the male mold and the female mold. When the pressed pit depth reaches a certain value, open the oil return valve and the piston returns automatically. After pressing a pit, move the pressure clamp and press down another one.

50. What are the main types of common low-voltage power cables according to different insulation and protective layers?

Answer: (1) oil immersed paper insulated lead wrapped (or aluminum wrapped) power cable;

(2) Non trickling oil immersed paper insulated power cable;

(3) PVC insulated PVC sheathed power cable;

(4) Cross linked PVC insulated polyethylene sheathed power cable;

(5) Cross linked PVC insulated PVC sheathed power cable;

(6) Rubber insulated power cable.

51. What are the categories of commonly used insulating materials? For example?

Answer: (1) inorganic insulating materials: Mica, asbestos, marble, porcelain, glass, etc;

(2) Organic insulating materials: resin, rubber, paper, hemp, cotton yarn, etc;

(3) Mixed insulating material: a kind of insulating material formed by processing the above insulating materials.

52. Under what circumstances is pipe laying adopted? What are the advantages?

Answer: pipe laying is generally used in places where it crosses other buildings, roads or railways, and sometimes in areas with dense buildings. The main advantage is that it occupies less land, can bear large load, and the cables do not affect each other, which is relatively safe.

53. What is the long-term allowable current carrying capacity of cable?

Answer: the long-term allowable current carrying capacity of the cable refers to the current value when the cable conductor reaches the long-term allowable working temperature after thermal stability when the specified current passes through the cable.

54. What are the factors that determine the long-term allowable current carrying capacity of the cable?

A: it is determined by the following three factors:

(1) Long term allowable working temperature of cable;

(2) Heat dissipation performance of the cable itself;

(3) Conditions of cable installation and heat dissipation conditions of surrounding environment.

55. How many cable laying methods are there?

A: there are the following:

(1) Buried directly underground;

(2) Installed in cable trench;

(3) Installed in underground tunnel;

(4) Installed on the wall or ceiling inside the building;

(5) Installed on the bridge;

(6) Laid in the drainage pipe;

(7) Laid underwater.

56. How to connect the cable duct?

Answer: when the cable pipe is connected, it must be connected with a buckle and a pipe joint. If welding is adopted, it cannot be directly butt welded. A section of thick pipe should be sleeved at the connection and then welded to avoid welding slag falling into the pipe.

57. What are the requirements for bending the cable core up and down when making the cable head?

Answer: when bending the wire core, the paper insulation shall not be damaged, and the bending radius of the core wire shall not be less than 10 times that of the cable core. Special care shall be taken when making, and the bending part of the wire core shall be stressed evenly, otherwise the insulating paper will be easily damaged.

58. Briefly describe the heat shrinkable sealing method of plastic cable.

Answer: the heat shrinkage method is applicable to the sealing of medium and low voltage rubber and plastic cable joints and terminal heads, as well as non drip and viscous impregnated insulated cables. Two types of heat shrinkable pipes, cross-linked polyethylene type and silicone rubber type, are used, which can shrink evenly when exposed to heat. The pipe is sleeved on the predetermined bonding and sealing part, and the bonding part is coated with hot-melt adhesive. When heated to a certain temperature, the heat shrinkable pipe will shrink and the hot-melt adhesive will melt. After natural cooling, a good sealing layer will be formed.

59. What should be paid attention to when bending cable protection pipe with electric pipe bender?

Answer: (1) the pipe bender shall be operated by personnel who understand its performance and are familiar with operating knowledge;

(2) Before use, the button, operating handle and travel switch must be checked, and the pipe bender must be reliably grounded;

(3) Select the mold that meets the requirements and determine the required bending radius;

(4) There shall be sufficient construction site and surrounding activities;

(5) When in use, it can only work with load after idling is normal. During operation, it is strictly prohibited to touch the rotating part with hands and feet;

(6) After the work is completed, the power shall be cut off in time to release the oil pressure.

60. What are the contents of the cable list and the meaning of the cable number?

Answer: the cable list is the basis for laying cables and guiding construction, as well as the archives of operation and maintenance. The number, starting point, model, specification and length of each cable shall be listed, and the total length shall be counted by classification. The control cable shall also list the spare core of each cable.

The cable number is a sign to identify the cable, so it is required that the number of the whole plant is not repeated, and has a certain meaning and law, which can express the characteristics of the cable.

61. What are the current cable laying methods?

Answer: (1) manual laying, i.e. using the crowd tactics, laying according to the regulations under the coordination and command of one or more people;

(2) Mechanized laying, that is, roller, tractor and conveyor are used to control through a synchronous power supply, which is relatively safe;

(3) Combining labor and machinery, this method is adopted in some sites because there are many turns, the construction is difficult, and it is difficult to use all machinery.

62. What requirements should the control secondary circuit wiring meet?

Answer: (1) according to the construction drawing, the wiring is correct;

(2) The electrical connection of the conductor shall be firm and reliable;

(3) The conductor in the panel and cabinet shall be free of joints, and the conductor core shall be free of damage;

(4) The end of the cable core shall be marked with its circuit number, which shall be correct, legible and not easy to decolorize;

(5) The wiring shall be neat, clear and beautiful, and the conductor insulation shall be good and undamaged;

(6) The wiring on each side of each wiring terminal should be one, no more than two at most.

63. What are the requirements for cable duct?

Answer: (1) the distance from the top of the drainage pipe to the ground is 0.2m in the plant, 0.5m under the sidewalk and 0.7m in general areas;

(2) Drain pits shall be installed at the changed direction and branches, and pits shall also be added when the length exceeds 30mm;

(3) The pit depth shall not be less than 0.8m, and the manhole diameter shall not be less than 0.7mm;

(4) The drainage pipe shall have a drainage slope of 0.5% ~ 1% towards the well pit.

64. What are the requirements for the resistance of cable conductor connection points?

Answer: the resistance of the connection point shall be small and stable. The ratio of the resistance of the connection point to the conductor of the same length and section shall not be greater than 1 for the newly installed terminal head and middle head; For the terminal head and middle head in operation, the ratio shall not be greater than 1.2.

65. What requirements should the design of cable joint and intermediate head meet?

A: the requirements to be met are:

(1) High withstand voltage strength and good conductor connection;

(2) High mechanical strength and small medium loss;

(3) Simple structure and strong sealing.

66. What is a cable fault? How many common types are there?

Answer: cable failure refers to the failure of insulation breakdown of the cable during preventive test or the power failure of the cable line caused by insulation breakdown and wire burning during operation. Common faults include grounding fault, short circuit fault, disconnection fault, flashover fault and mixed fault.

67. How to deal with single-phase grounding fault of cable line?

Answer: Generally speaking, for single-phase grounding fault of cable line, the damage of cable conductor is only local. If it belongs to mechanical damage and the soil near the fault point is dry, it can be repaired locally. Add a fake joint, that is, do not cut off the cable core, but only strengthen the insulation of the fault point and seal it.

68. What tests and inspections should be carried out for power cables before laying?

Answer: before laying, check whether the model, specification and length of the cable meet the requirements and whether there is external force damage. The insulation resistance of the low-voltage cable is telemetered with a 1000V tramegger, and the resistance is generally not less than 10m Ω. The resistance of the high-voltage cable is generally not less than 400m Ω with a 2500V tramegger.

69. What should be paid attention to when laying cables in the main plant?

Answer: when laying cables in the main power house, generally pay attention to:

(1) All control cables leading to the central control room should be laid overhead;

(2) 6kV cables should be laid in tunnels or pipes, and they can also be laid overhead or in pipes at high groundwater levels;

(3) When the cables at both ends of 380V cable are at zero meters, tunnels, ditches or drainage pipes should be used. When the equipment at one end is above and the equipment at the other end is below, it can be partially laid overhead. When the groundwater level is high, it should be overhead.

70. Where are the inner and outer shielding layers of power cables? What materials are used? What does it do?

Answer: in order to make the insulation layer have better contact with the cable conductor and eliminate the increase of electric field intensity on the conductor surface caused by the unsmooth conductor surface, the inner shielding layer of metallized paper or semiconductor paper tape is generally wrapped on the conductor surface. In order to make better contact between the insulating layer and the metal sheath, an outer shielding layer is generally wrapped on the outer surface of the insulating layer. The material of the outer screen layer is the same as that of the inner screen layer, and sometimes copper ribbon or braided copper ribbon is tied outside.

71. Briefly describe the composition and properties of epoxy resin composites.

A: the epoxy resin composite is composed of epoxy resin, hardener, filler, toughener and diluent. It has the following properties:

(1) Sufficient mechanical strength;

(2) Excellent electrical performance;

(3) Stable electrical performance;

(4) Sufficient adhesion with non-ferrous metals;

(5) Good corrosion resistance;

(6) When used outdoors, it is resistant to rain, light, humidity and heat.

72. Why is it necessary to install a return line laid in parallel along the cable in the grounding mode of one end of single core cable sheath?

Answer: in the cable line grounded at one end of the metal sheath, in order to ensure that the induced voltage in the protective sheath does not exceed the allowable standard, a conductor laid in parallel along the cable line must be installed, and both ends of the conductor are grounded. This conductor is called return line. In case of single-phase grounding fault, the grounding short-circuit current can flow back to the central point of the system through the return line. Because the magnetic flux generated by the grounding current through the return line offsets part of the magnetic flux generated by the grounding current of the cable conductor, the induced voltage of the sheath in case of short-circuit fault can be reduced.

73. How many projects can cable engineering be divided into?

A: (1) site transportation: including the loading and unloading, transportation and empty vehicle return of engineering materials from the warehouse to the construction site.

(2) Local works: including pavement excavation, tunnel, ditch construction, etc.

(3) Laying works: including laying, middle head fabrication, cover plate lifting, pipe burying, tide correction, traction head fabrication, etc.

(4) Works at both ends: including fabrication and installation of support and suspension bridge frame and its foundation, fabrication of terminal head, installation of oil pressure and signal device, electrical performance test of famous types, etc.

(5) Plug Engineering: including the production of oil filled cable plug head, the installation of oil supply tank, automatic drainage and signal device, etc.

(6) Grounding works: including installation of insulated joints, transposition boxes, protectors, grounding boxes, etc.

74. What inspections should be carried out for the acceptance of cable lines?

Answer: (1) the cable specification shall comply with the regulations, the arrangement shall be neat without damage, and the signs shall be complete, correct and clear;

(2) The fixed bending radius and relevant distance of the cable and the wiring of the metal sheath of the single core power cable shall meet the requirements;

(3) The cable terminal and middle head shall be free of oil leakage and installed firmly. The oil pressure of oil filled cable and the setting value of meter shall meet the requirements;

(4) Good grounding;

(5) The phase color of cable terminal is correct, and the paint of metal parts such as support is complete;

(6) There shall be no sundries in the cable trench, tunnel and bridge, and the cover plate shall be complete.

75. What are the requirements for positive sequence impedance measurement of cable line?

A: the AC resistance of the cable conductor and the phasor sum of the three same inductive reactances of the cable are called positive sequence impedance.

The positive sequence impedance of the cable line can generally be measured directly on the cable reel. Generally, a lower voltage is used during measurement. Therefore, it is necessary to use a step-down transformer for step-down. The step-down transformer adopts star wiring, with a capacity of more than 10KVA and a wide voltage regulation range. The AC power supply should be relatively stable during measurement to ensure that the current meets the specified requirements during measurement. The reading value of the actual voltmeter must be the voltage at the cable end, The test current should be close to the long-term allowable current carrying capacity of the cable. When measuring and reading the values of each meter, close the current and read the values of three meters at the same time.

76. According to the regulations on production safety of electric power industry, what are the necessary conditions for electrical workers?

Answer: the following conditions must be met:

(1) Certified by the doctor to be in good health without any disease hindering work;

(2) Have necessary electrical knowledge, master relevant regulations, professional technology and safe operation technology according to their position and nature of work, and pass the examination;

(3) Master the first aid method of electric shock.

77. What should be paid attention to during the transportation, loading and unloading of cables?

Answer: (1) in the process of transportation, loading and unloading, the cable and cable reel shall not be damaged. It is strictly prohibited to push the cable reel directly from the vehicle. Generally, the cable shall not be transported and stored horizontally.

(2) Before transporting or rolling the cable reel, it must be ensured that the cable reel is firm, the cable is tightly wound, and the oil pipe between the oil filled cable and the pressure oil tank should be fixed without damage. The pressure oil tank should be firm, and the pressure indication should meet the requirements.

78. What are the measures for cable fire prevention?

Answer: (1) adopt flame retardant cable;

(2) Adopt fireproof cable tray;

(3) Fire retardant coating;

(4) Fire partitions and fire dampers shall be set at cable tunnels, mezzanine exits, etc;

(5) Overhead cables shall avoid oil pipelines and explosion-proof doors, otherwise local pipe threading or thermal insulation and fire prevention measures shall be taken.

79. What aspects should be considered when selecting the section of power cable?

A: the following aspects should be considered:

(1) Allowable working current of cable for a long time;

(2) Thermal stability in case of short circuit;

(3) The voltage drop on the line shall not exceed the allowable working range.

80. What are the advantages of power cable compared with overhead line?

Answer: (1) the operation is reliable. Because it is installed in underground and other hidden places, it is less damaged by external forces and has less chance of failure. The power supply is safe and will not cause harm to people;

(2) The maintenance workload is small and there is no need for frequent inspection;

(3) No tower is required;

(4) It helps to improve the power factor.