Wire and cable knowledge quiz 80

Wire and cable are inextricably linked with us in weak construction. Today we will take a look at common problems in wire and cable.

Wire and Cable 80 Questions and Answers

1. What types of commonly used wires and cables are divided by purpose?

Answer: According to purpose, it can be divided into bare wire, insulated wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, and radio frequency cable.

2. What are the types of insulated wires?

Answer: The common insulated wires are the following: PVC insulated wire, PVC insulated cord, nitrile PVC mixture insulated cord, rubber insulated wire, agricultural 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, cable bridge for what kind of occasion?

Answer: Cable trays are suitable for general laying of power cables and control cables for indoor and outdoor use by industrial and mining companies. They can also be used for indoor and outdoor installations in telecommunications, broadcasting and television departments.

What are the cable accessories?

Answer: The commonly used electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connecting pipes and terminals, steel wiring slots, and cable trays.

5, what is the cable middle connector?

Answer: The device that connects the cable with the cable conductor, insulation shield and protective layer to connect the cable line is called the cable middle connector.

6, what is the main electrical wiring?

Answer: The main electrical connection is the connection mode of the main electrical equipment and busbars in power plants and substations, including the main busbars and plant power systems according to certain functional requirements.

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

A: 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 supply load;

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

(4) Verify that the voltage drop meets the requirements based on the length of the cable;

(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 cable and oil-paper cable?

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

(2) Not subject to line drop*;

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

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

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

(6) Lower prices;

(7) High reliability and low failure rate;

(8) There are few manufacturing processes, simple processes, and significant economic benefits.

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

A: The fixture should be composed of no iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic lines are generated around it. The magnetic force line is proportional to the current flowing through the core. If using magnetic materials such as iron, according to Electromagnetic induction shows that eddy currents will be generated in the iron to heat the cable and even burn the cable. Therefore, it is not allowed to use iron pieces as fixing fixtures for single-core AC cables.

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

A: The most important feature of the heat-shrinking attachment is the use of a stress tube instead of the traditional stress cone. 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 superior in performance, saving metal. The heat-shrinkable cable accessory sets the pouring type and the dry bag type, and combines the advantages of these two types of accessories.

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

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

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

(3) The cable is well insulated. When there is doubt about the sealing of the oil-paper cable, it should be judged by moisture; the buried cable and the small-bottom cable should pass the DC voltage test and pass the 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.

21, crosslinked heat shrinkable cable accessories What are the advantages?

A: This is a new type of material. Compared with other types of accessories nowadays, it has the advantages of superior electrical performance, small size, low quality, easy installation, and matching materials. It also has weather resistance, contamination resistance, flame retardance, self-extinguishing, etc. ability.

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

A: Insulate the cable insulation paper or put it in the cable oil of about 150°C. Check that there is no “click” or white foam, indicating that it is not wet.

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

Answer: The cable design number, cable type, specification and starting point should be indicated on the signboard. The serial cable should be used in parallel. Requires clear writing and easy to fall off.

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

Answer: At both ends of the cable, the cable connector 50~100m at the cable connector changes the direction of the cable.

15. To make yellow ribbons, black glass lacquer ribbons, and alkali-free glass ribbons for cable joints, how do you handle the tide before construction?

answer:

(1) Constant temperature drying method: The insulating tape is rolled into a small roll with a diameter of 25~30mm, placed in a constant temperature drying box at 110~120°C for 4~5h, cooled and dried, and put into a dry sealed tube.

(2) Oil immersing and draining tide method: Put the small coil of insulating tape into the cable oil at a constant temperature of 120~130°C, and 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 it will be taken out and stored. In tanks with cable oil, the oil level should exceed all enclosed objects and seal it.

16. What is the role of the cable sheath?

A: The inner sheath is protected from mechanical damage and chemical corrosion, enhancing mechanical strength.

17, outdoor cable ditch should meet what requirements?

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

18. What is the role of the sheath in 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.

19, when using wire cutters should pay attention to what?

A: Before use, be sure to check the insulating handle insulation is intact, use wire cutters can not be cut over the specifications allow the metal wire, and the use of wire cutters instead of a hammer to beat the tool to avoid damage.

20, what is the dielectric strength?

A: In the electric field, when the electric field strength increases to a certain limit, the insulation material will be broken down. This electric field strength that causes insulation breakdown is called the insulation strength.

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

A: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For a fixedly installed 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 insulating material for power cables?

A; should have the following main features:

(1) High breakdown strength;

(2) Low dielectric loss;

(3) High insulation resistance;

(4) Excellent resistance to discharge performance;

(5) Has a certain degree of flexibility and mechanical strength;

(6) Long-term stability of insulation performance.

24. When laying cables, what are the requirements for traction strength?

A: For copper core cables, when pulling the head, the allowable traction strength is 70N/cm; for the aluminum core cable, when the head is pulled, the allowable traction strength is 40N/cm; if the wire mesh cover is used for traction, the lead protection Set cable allowable strength is 10N/cm;

Lead sheathed cable is 40N/cm.

25. What are the regulations for cable protection tubes?

Answer: (1) When the cable needs to wear a protective tube, the inner diameter of the pipe should not be less than 1.5 times the outer diameter of the cable, and the inner diameter of the concrete pipe, clay pipe, asbestos, cement pipe should 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 should not exceed a maximum of three elbows and no more than two right angle bends.

26, how to measure the outer diameter of the cable jacket?

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

27, how to connect different sections of copper cable?

Answer: The copper cables with different cross-sections can be connected by using open weak copper back-ends and connected by soldering. Copper can also be connected by pure copper rods according to different cross-section requirements and connected by crimping.

28. Summarize the process of heat-shrinking a 10KV cross-connect cable to make an indoor terminal.

Answer: (1) Preparation phase: Check whether the heat shrinkable cable accessories are complete and whether the model is matched. After checking and confirming whether there is moisture in the cable, check the cable.

(2) Exclude excess cables, and determine the cable length according to site conditions.

(3) Strip the cover.

(4) Weld the ground wire and solder the ground wire to the strip.

(5) Fill the trifurcation and wrap the sealant.

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

(7) Strip the copper strip and the outer semiconductive layer, strip the copper strip with more than 20mm of the three-core branch sleeve, and do not damage the main insulation and remove the clean semiconductive layer.

(8) Install the stress tube and heat shrink the joints at the end of the nozzle.

(9) Install the terminal block.

(10) Install the insulation tube.

(11) Install the sealing tube.

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

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

Answer: (1) Place the cable in position, fix it, clean the surface according to the predetermined position, and remove the sheath with reference to the instruction manual. If special requirements are required, the length of the outer sheath stripping can be adjusted, and the copper strip and the outer sheath can be installed separately. 2 ground lines.

(2) From the outer jacket mouth up to take the required size, remove the excess cable, insert the heat shrinkable three-finger sleeve to the root of the three-forked mouth and heat the middle heat shrinkage, and measure up from the upper mouth of the finger cuff to the specified size (35kv to 350~380mm ). Remove the excess copper tape (retain 20mm), and then keep the semiconductor at a predetermined position, crimping the outlet terminal seal.

30. The application of wire and cable is mainly divided into three categories:

(1) Power system

The wire and cable products used in the power system mainly include bare overhead wires, busbars (bus bars), power cables (plastic cables, oil-paper cables (substituted by plastic power cables), rubber sheath cables, overhead insulated cables), and branch cables. (Replace some of the busbars), electromagnetic wires, and electrical equipment.

(2) Information transmission system

The wire and cable used for information transmission systems mainly include local telephone cables, television cables, electronic cables, radio frequency cables, optical fiber cables, data cables, electromagnetic wires, power communication or other composite cables.

(3) Machinery and Instrumentation System

Except for the bare overhead wires, this part has applications for almost all other products, but mainly power cables, electromagnetic wires, data cables, instrumentation cables, etc.

31, wire and cable products are mainly divided into five categories:

(1), bare wires and bare conductor products

The main features of this type of product are: pure conductive metal, non-insulating and sheathing layers, such as ACSR, copper and aluminum busbars, electric locomotive lines, etc.; the processing technology is mainly pressure processing, such as smelting, rolling, pulling System, stranded/pressed stranded, etc.; products are mainly used in suburban areas, rural areas, user main lines, switch cabinets, etc.

(2) Power cable

The main characteristics of this type of product are: Extruding (wrapping) the insulation around the conductor, such as overhead insulated cables, or strands (corresponding to the phase, neutral and ground of the power system), such as overhead insulation cables with more than two cores , Or increase the jacket layer, such as plastic / rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, sheath extrusion, etc. There are certain differences in the different process combinations of various products.

The products are mainly used in the transmission of electricity, electricity, electricity, electricity, electricity, and electricity in high-voltage transmission lines, with large currents (tens of amps to several thousand amps) and high voltages (220 V to 500 kV and above).

(3) Wire and cable for electrical equipment

The main features of this type of product are: variety of specifications, a wide range of applications, the use of voltage in 1kV and below, in the face of special occasions continue to derive new products, such as fire-resistant cables, flame-retardant cables, low smoke and halogen-free / low Smoke low-halogen cable, termite-proof, rat-proof cable, oil/cold resistance/temperature/wear resistant cable, medical/agricultural/mine cable, thin-walled wire, etc.

(4) Communication cables and optical fibers (brief introduction)

With the rapid development of the communications industry over the past two decades, the products have also been developing at an alarming rate. From the simple telephone telegraph cable in the past to the development of thousands of pairs of voice cables, coaxial cables, optical cables, data cables, and even composite communication cables.

The size of such products is usually small and uniform, and the manufacturing precision is high.

(5) Magnet wire (winding wire)

Mainly used for various motors, instruments and meters.

Wire and cable derivatives/new products

The derivative/new products of wire and cable are mainly due to the requirements of different applications, different application requirements, and the convenience of equipment and the reduction of equipment costs. New materials, special materials, or changes in product structure, or improvement of process requirements, or different The products of the varieties are combined and produced.

Use different materials such as flame-retardant cables, low-smoke and halogen-free/low-smoke and low-halogen cables, termite-proof cables, rat-proof cables, oil/cold resistance/temperature resistant cables, etc.;

Change product structure such as: fire-resistant cables;

Improve process requirements such as: medical cables;

Combination products such as: OPGW;

Easy to install and reduce equipment costs such as: prefabricated branch cables.

32. What inspections should be performed after the bus device is completed?

Answer: The following inspections should be conducted:

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

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

(3) The busbar preparation and installation rack should comply with the regulations, and the electrical distance between phases and earth should meet the requirements;

(4) Porcelain pieces, iron pieces and gluing joints shall be complete, and the oil-filled casing shall be free from oil leakage and normal oil level;

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

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

Answer: (1) Swelling flare: The edge of the lead package should be pounded at the cut-off position of the lead package and should be horn-shaped. Its edge should be smooth, round and symmetrical.

(2) Retained package insulation: There is a piece of turn-up insulating paper between the lead-bag cuts and the separation point of the cable core.

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

(4) Enveloping the stress cone: Tapering the tape with an insulating tape and a conductive metal material artificially expands the shielding layer to improve the electric field distribution.

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

(6) Install the stress control tube: For the 35kv and send the heat shrinkable tube cable end, firstly surround the two layers of semiconductor tape from the direction of the end of the copper core shield layer through the semiconductor tape to the insulation of the core, and then make the corresponding specification of the stress The tube, sleeved at the end of the copper shield, is heat-shrink molded.

34, cable bracket processing should meet the requirements?

Answer: (1) The steel should be straight, without obvious distortion, the blanking error should be in the range of 5mm, and the cut should have no curling or burrs;

(2) The brackets should be firmly welded without any significant deformation. The vertical distance between the cross braces and the design deviation should not exceed 5 mm;

(3) The metal stent must be treated with anti-corrosion treatment. When it is located in hot and humid areas, salt, fog, and chemically corroded areas, it should be designed for special anti-corrosion treatment.

35. List the cables you are familiar with.

A: Welded E-frames, assembled E-frames, bridged cable racks, cable trays, hook-type brackets, single-wire brackets, etc.

36. What requirements should be fulfilled for laying cables?

Answer: The following requirements should be met:

(1) In terms of safe operation, all kinds of external damage should be avoided as much as possible, and the reliability of power supply for the cable line should be improved;

(2) In terms of economy, consider from the perspective of the most investment;

(3) For construction, the route of the cable line must be easy for maintenance after rotation and maintenance.

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

Answer: There are insulating adhesives, insulating tapes, insulating tubes, insulating gloves, and insulating resins.

38, a brief description of the general operation of the cable head production process.

Answer: (1) Preparation before production: Including ○ 1 reading installation instructions; ○ 2 viewing site; ○ 3 stock preparation; ○ 4 cable trial tide;

(2) Manufacturing process of joints: Including ○1 to cut excess cable; ○2 Stripping of protective layer of cable; ○3 Conductor connection; ○4 Wrap around insulation (or shrink pipe); ○5 Install joint housing; ○6 Insulated insulation Agent; ○ 7 sealing treatment.

(3) Post-production electrical testing.

39, cable protection tube processing should meet the requirements?

Answer: (1) The nozzle should be sharp and sharp, and the nozzle should be made into a trumpet shape.

(2) After the cable pipe is bent, there shall be no cracks and significant indentations. The degree of bending shall not be greater than 10% of the outside diameter of the pipe; the bending radius of the cable pipe shall not be less than the minimum allowable bending radius of the cable penetrated. .

(3) The metal pipe shall be painted with anticorrosive paint or leaching on the exterior, and the galvanized pipe shall be painted with anticorrosive paint on the zinc layer.

40, the cable arrangement meets what requirements?

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

(2) For high and low voltage cables, the strong and weak electric control cables should be arranged hierarchically in order. The general situation should be from top to bottom, but when the high voltage cable with more than 35kv is introduced into the panel, in order to meet the bending radius, the following can be used: Configuration.

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

Answer: The method of laying the cable in the cable trench is similar to that of laying the buried cable. Generally, the pulley can be placed in the trench. After the casting is completed, place the cable on the bottom of the trench or the bracket and bind the cable label on the cable.

42. What are the common equipment for laying cables?

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

(2) Electric winches or cable traction machines, mainly used to pull cables;

(3) The cable conveyor is used with a traction machine to overcome the huge friction and reduce the damage to the cable;

(4) cable tray payout bracket;

(5) Roller device;

(6) Flood prevention, reducing the distortion of the wire rope;

(7) cable disc brake device;

(8) Tensiometer.

43. What are the requirements for the installation distance of brackets in cable trenches?

A: The cable is fixed on the wall of the cable trench and the tunnel. When the horizontal device is installed, when the outer diameter of the cable is equal to or less than 50mm, a support shall be added every 1m. The cable with an outer diameter larger than 50mm shall be added every 0.6m to support; The triangular single cable is fastened with a strap every 1m. When it is vertical, it is fixed every 1~1.5m.

44. How to handle the installation of power cables and control cables in the same bracket?

A: The 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, separate the partitions.

45. How to install a grounding cable in a cable tunnel?

Answer: The whole length of the tunnel and ditch should be installed with a continuous grounding wire. The grounding wire should be connected to all the supports, and the two ends should be connected to the grounding electrode. The specifications of the ground wire should meet the design requirements. In addition to insulation requirements, cable lead packages and armored equipment shall all be connected to each other and connected to the grounding cable. The cable racks and grounding cables shall be painted with antirust paint or galvanized.

46. ​​What are the requirements for fire blocking of cable holes?

A: For larger cable penetration holes, such as cables running through the floor, when using fire blocking materials to block, according to the actual situation, should be painted on the surface of the cable four to six layers of fire retardant coating, the length of about 1.5m below the hole, and then Refractory materials are used to process the board fireproof plugging material with certain strength to ensure that the plugging is firm and easy to replace when the cable is replaced. The plugging is dense and non-porous to effectively block the fire and block the fire.

47, torch light before ignition should pay attention to what inspection?

Answer: The following items should be checked:

(1) Whether the pump is leaking oil or leaking oil, leaking oil or gas at the oil barrel or nozzle;

(2) Whether the amount of oil in the drum exceeds 3/4 of the capacity of the drum and if the screw plug for refueling is tightened.

48. What should be noted when using torches?

Answer: (1) The maximum fuel injection volume of the torch is 3/4 of the volume of the oil cylinder;

(2) The starting pressure should not be too large. After the ignition, the flame can be used from yellow to blue;

(3) There must be no flammable materials around and the air must circulate;

(4) Turn off the adjustment switch when it is deactivated. After the fire is extinguished, slowly loosen the oil hole cover and let go of air. After the air is released, it is necessary to loosen the adjustment switch, and then completely cool and then loosen the hole cover;

(5) Kerosene burners and gasoline burners should be used separately.

49, what is the use of manual hydraulic clamp? How to operate?

A: The connection of two wires is usually made by inserting two wire ends into a pressure tube made of the same material. Several pits are pressed with crimping pliers to connect the wires together. When the handle is lifted up during crimping, The plunger moves outwards, creating a vacuum in the lower chamber of the oil valve, and the oil in the fuel tank enters the plunger chamber. When the handle is pressed down, the plunger moves inward. After the oil is pressurized, the oil inlet valve is closed, the oil outlet valve is opened, the oil pressure enters the hydraulic cylinder, the piston and the male mold are pushed, and a pressure pipe is placed between the male and female molds. When the crimped crater is deep enough to reach a certain value, the oil return valve is opened and the piston automatically returns. After pressing a pit, the pressure pliers are moved and the next one is pressed.

50, commonly used low-voltage power cables according to the different insulation and protection layer, which can be divided into several categories?

Answer: (1) Oil-impregnated paper insulated lead (or aluminum) power cable;

(2) Non-dripping oil-impregnated paper-insulated power cables;

(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 insulation 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 materials: Insulating materials of the type that are formed by the above insulating materials.

52. In what kind of situation is the cascading pipe laid? What are the advantages?

A: The laying of pipes is generally used where they intersect with other buildings, roads or railways, and is sometimes used in areas where buildings are dense. The main advantage is that it occupies less space and can withstand large loads. The cables do not affect each other and are relatively safe.

53. What is the long-term allowable ampacity of the cable?

Answer: The long-term allowable ampacity of the cable refers to the current value when the cable conductor reaches the long-term allowable operating temperature after the heat is stabilized in the cable through the specified current.

54. What are the factors that determine the long-term allowable ampacity of the cable?

A: There are three factors that determine:

(1) The long-term allowable operating temperature of the cable;

(2) The thermal performance of the cable itself;

(3) Condition of the cable device and the heat dissipation conditions of the surrounding environment.

55, there are several ways to lay the cable?

A: There are the following types:

(1) buried directly underground;

(2) installed in the cable trench;

(3) Installed in an underground tunnel;

(4) Installed on the interior wall or ceiling of a building;

(5) Installed on the bridge;

(6) laying in the pipe;

(7) Laid under water.

56, how to connect the cable pipe work?

Answer: When the cable pipe is connected, it must be connected with the buckle and the pipe joint. If welding is adopted, direct butt welding is not allowed. The joint should be covered with a thick pipe and then welded so as to prevent the welding slag from falling into the pipe.

57, when making cable heads, what are the requirements for twisting the cable cores up and down?

Answer: When pulling the core, the paper insulation must not be damaged. The bending radius of the core wire must not be less than 10 times that of the cable core. Special care must be taken in the production, so that the bent part of the core should be evenly subjected to force, otherwise the insulating paper can be easily damaged.

58, a brief description of the plastic cable heat shrink seal method.

A: The heat shrink method is applicable to the sealing of middle and low pressure rubber and plastic cable joints and terminal heads. It can also be applied to non-dripping and viscous impregnated insulated cables. Two types of cross-linked polyethylene and silicone rubber heat shrinkable tubes that shrink evenly when heated. The tube is placed over a predetermined adhesive seal, and a hot melt adhesive is applied to the adhesive site. When heated to a certain temperature, the heat shrinkable tube shrinks, and the hot melt adhesive melts. After being naturally cooled, the tube is formed. Good seal seal.

59. What should you pay attention to when bending a cable protection tube with an electric bending machine?

Answer: (1) Benders should be operated by personnel who understand their capabilities and are familiar with operational knowledge.

(2) Inspection must be performed before use. Buttons, operating handles, and travel switches should be in good condition. Bender must be reliably grounded.

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

(4) There should be sufficient activity range around the construction site;

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

(6) Power outage should be promptly completed after work is completed to release oil pressure.

60. What is the meaning of cable inventory and cable number?

Answer: The cable inventory is the basis for laying out the cable and guiding the construction, operation and maintenance of the file information. Should be included in each cable number, starting point, model, size, length, and statistics of the total length of the classification, control cable should also list the spare core of each cable.

The cable number is a sign of the identification cable, so the whole plant number is not repeated, and there are certain meanings and laws that can express the characteristics of the cable.

61. The current laying methods of cables can be divided into several categories.

A: (1) Artificially laid, that is, employing human-sea tactics, under the coordination and command of one or more people, laying according to regulations;

(2) mechanized laying, that is, the use of rollers, tractors, conveyors, through a synchronous power control, more secure;

(3) The combination of labor and machinery, some sites due to more turns, construction is difficult, full use of machinery is more difficult, so use this method.

62, control the secondary circuit wiring should meet the requirements?

Answer: (1) According to the figure, the wiring is correct;

(2) The electrical connection of the wire should be solid and reliable;

(3) The wires in the cabinet shall not have joints, and the core wires shall be free of damage;

(4) The end of the cable core should be marked with the loop number, the number should be correct, the writing is clear and it is not easy to decolorize;

(5) The wiring shall be neat, clear and beautiful, and the insulation of the conductor shall be good and non-destructive;

(6) The wiring on each side of each terminal should be a single wire, with a maximum of two wires.

63, what are the requirements of the cable pipe?

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

(2) Well pits shall be installed in the direction of change and at the branch, and pits shall also be provided when the length exceeds 30mm;

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

(4) The drainage pipe should have a slope gradient of 0.5% to 1% in the pit.

64, what are the requirements for the resistance of the cable conductor connection point?

Answer: It is required that the resistance of the connection point is small and stable, and the ratio of the resistance of the connection point to the conductor of the same length and the same cross-section should not be greater than 1 for newly installed terminal heads and intermediate terminals; for the terminal heads and intermediate heads in operation This ratio should not exceed 1.2.

65, cable connector and the middle of the design should meet what requirements?

Answer: The requirements that should be met are:

(1) high pressure strength, good conductor connection;

(2) Large mechanical strength and small medium loss;

(3) Simple structure and strong sealing.

66. What is a cable fault? There are several common types?

Answer: The cable fault refers to the breakdown of the cable line due to the breakdown of the cable during the preventive test or the operation of the cable due to the breakdown of the cable and the burning of the cable. Common faults include ground faults, short-circuit faults, disconnection faults, flashover faults, and hybrid faults.

67, how to deal with single-phase earth fault cable line?

A: Single-phase earth fault of cable line In general, the damage of cable conductor is only partial. If it is a mechanical damage, and the soil near the fault point is relatively dry, partial repair can be done normally and a false joint can be added. Do not cut the cable core, only the insulation of the fault point can be sealed.

68. What tests and inspections should be conducted before the power cable is laid?

Answer: Before laying, check whether the cable's type, size and length are in compliance with the requirements. Is there any external damage? The low-voltage cable uses a 1000V Megohmmeter to measure the insulation resistance. The resistance is generally not lower than 10MΩ. The high-voltage cable is measured with a 2500V megohmmeter. The resistance generally does not reach 400MΩ.

69. What should you pay attention to when laying cables in the main building?

A: When laying cables in the main building, you should generally pay attention to:

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

(2) 6KV cables are to be laid by tunnels or pipes, and the groundwater level may be elevated or laid by cascading pipes;

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

70. What are the inner and outer shield layers of the power cable? What material is used? What is the role?

Answer: In order to make the insulation layer and the cable conductor have better contact and eliminate the increase of the electric field strength on the surface of the conductor caused by the non-smooth surface of the conductor, the inner shield layer of the metalized paper or semiconductor tape is generally wrapped on the surface of the conductor. In order to make the insulating layer and the metal sheath have better contact, generally the outer layer of the insulating layer is covered with an outer shield layer. The material of the outer screen layer and the inner screen layer are the same, and sometimes the copper tape or the braided copper ribbon is also used.

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

A: Epoxy resin composites consist of epoxy resin, hardener, filler flexibilizer, and thinner. Has the following properties:

(1) Have sufficient mechanical strength;

(2) Excellent electrical performance;

(3) Stable electrical performance;

(4) Adequate adhesion with non-ferrous metals;

(5) good corrosion resistance;

(6) It is resistant to rain, light and moisture when it is used outdoors.

72. Why should a single-core cable jacket grounded in one end be installed with a reflow line running parallel to the cable?

Answer: In the cable grounding at one end of the metal sheath, in order to ensure that the induced voltage in the 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 back Streamline. When a single-phase ground fault occurs, the ground short-circuit current can flow back to the center of the system through the return line, and the magnetic flux generated by the ground current through the return line cancels the magnetic flux generated by the ground current of a part of the cable conductor and can be reduced. The induced voltage of the sheath in the event of a short circuit.

73, cable engineering can be divided into several projects?

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

(2) Local projects: including road excavation, tunnels, and trench construction.

(3) Laying project: including laying, intermediate head making, flipping cover plate, buried pipe, school tide, traction head making and so on.

(4) Both ends of the project: including the production and installation of supports, suspension bridges and their foundations, the production of terminal heads, the installation of oil pressure and signal devices, and the testing of electrical properties.

(5) Plug and stop works: including the production of oil-filled cable plugs and heads, installation of fuel tanks, automatic drainage, and signal devices.

(6) Grounding engineering: Including insulation joints, transposition boxes, protectors, and grounding box installation.

74. What inspections should be performed on the acceptance of cable lines?

Answer: (1) The cable specifications should conform to the regulations, the arrangement should be neat, no damage, complete signs, correct and clear;

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

(3) The cable terminal and the middle head are not leaking oil, and the installation is firm. The oil pressure of the oil-filled cable and the setting value of the meter should meet the requirements;

(4) Good grounding;

(5) The cable terminal is in correct color, and the metal components such as brackets are complete;

(6) There should be no debris in the cable trench, in the tunnel and on the bridge, and the cover is complete.

75. What are the requirements in the process of measuring the positive sequence impedance of cable lines?

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

The positive sequence impedance of the cable line can be measured directly on the cable tray. Generally, lower voltages are used during measurement. Therefore, step-down transformers are required to perform step-down voltages. The voltage drop device uses star-type wiring, and the capacity is generally more than 10 kVA. For wider voltage adjustment range, the AC power supply should be relatively stable during measurement to ensure that the current reaches the specified requirements during measurement. The reading of the actual voltmeter must be the voltage at the cable end. The test current is preferably close to the long-term allowable ampacity of the cable. For each meter value, the three tables are read at the same time after closing the current.

76. According to the "Safety Regulations for the Production of Electric Power Industry", what are the necessary conditions for electricians?

Answer: The following conditions must be met:

(1) A medically certified illness that does not interfere with work;

(2) Having the necessary electrical knowledge, according to their duties and the nature of their work, mastering relevant regulations, professional techniques and safe operating techniques, and passing the examination;

(3) Proficiency in emergency methods for electric shock.

77. What should you watch out for during cable transportation?

Answer: (1) In the process of transportation and loading, cables and cable trays should not be damaged. It is forbidden to push cable trays directly from the vehicle. Cables should not be transported flat and stored flat.

(2) Before transporting or rolling cable trays, it must be ensured that the cable trays are securely fastened, and the oil conduits between the oil-filled cables and the pressurized oil tanks should be fixed and not damaged. The pressure oil tanks should be firm and the pressure indicators should meet the requirements.

78, cable fire prevention measures?

Answer: (1) Use flame-retardant cables;

(2) Use fireproof cable brackets;

(3) using fire retardant paint;

(4) Fireproof partition walls and fire dampers are installed at cable tunnels, mezzanine exits, etc.;

(5) Overhead cables should avoid oil pipes and explosion-proof doors. Otherwise, fire protection measures should be taken for local pipes or heat insulation.

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

A: The following aspects should be considered:

(1) Operating current allowed to pass through the cable for a long period of time;

(2) Thermal stability in the event of a short circuit;

(3) The voltage drop on the line must not exceed the allowable operating range.

80, what are the advantages of power cables and overhead lines?

A: (1) Operation is reliable. Because it is installed in a hidden place such as underground, it is damaged by external forces, there is less chance of failure, and the power supply is safe. It will not cause any harm to the human body.

(2) Maintenance workload is small, and frequent inspections are not required;

(3) No erection of towers;

(4) Helps increase power factor.