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1. What are the common types of wires and cables classified by their uses? Answer: Based on their purpose, they can be classified into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc. 2. What are the types of insulated wires? Answer: The common types of insulated wires include: polyvinyl chloride insulated wires, polyvinyl chloride insulated flexible wires, nitrile-polyvinyl chloride mixture insulated flexible wires, rubber-insulated wires, aluminum-core plastic-insulated wires for underground use in agricultural applications, rubber-insulated cotton yarn woven flexible wires, polyvinyl chloride insulated wires with nylon sheaths, and polyvinyl chloride insulated flexible wires for power and lighting purposes. 3. In what situations are cable trays suitable? Answer: Cable trays are suitable for the overhead installation of power cables and control cables in indoor and outdoor areas of general industrial and mining enterprises; they can also be used in industries such as telecommunications and radio and television for similar purposes. 4. What are the cable accessories? Answer: Common electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connection pipes and terminals, steel plate wiring troughs, cable trays, etc. 5. What is a cable intermediate joint? Answer: A device that connects the conductors, insulation shielding layers, and protective layers of cables together to enable the connection of cable circuits is called a cable splice. 6. What is the main electrical wiring? Answer: The electrical main wiring is the method of connecting the main electrical equipment and busbars in power plants and substations, including the connection between the main busbars and the plant service system according to certain functional requirements. 7. What regulations should be followed when selecting the cross-sectional area of power cables? Answer: The selection of power cables should follow these principles: (1) The rated voltage of the cable must be greater than or equal to the rated voltage of the power supply system at the installation site ； (2) The continuous allowable current of the cable shall be equal to or greater than the maximum continuous current of the powered load ； (3) The cross-sectional area of the conductor core must meet the stability requirements in the event of a short circuit in the power supply system ； (4) Check whether the voltage drop meets the requirements based on the cable length ； (5) The minimum short-circuit current at the end of the line should be sufficient to ensure reliable operation of the protective devices. 8. What are the advantages of cross-linked polyethylene cables compared to oil-paper cables? Answer: (1) It is easy to install, as it allows for a small minimum bending radius and is lightweight ； (2) Not affected by line elevation differences* ； (3) Good thermal performance, allowing high operating temperatures and large transmission capacity ； (4) The cable accessories are simple, all being of dry-type design ； (5) Simple operation and maintenance, with no oil leakage issues ； (6) Lower price ； (7) High reliability and low failure rate ； (8) It has few manufacturing steps and a simple process, resulting in significant economic benefits. 9. What are the requirements for the clamps used to secure single-core AC cables? Why? Answer: The fixture should not contain any iron components that could form a closed magnetic circuit. This is because when current flows through the cable core, magnetic field lines are generated around it, and the strength of these magnetic field lines is proportional to the magnitude of the current flowing through the core. If magnetic conductive materials such as iron are used, electromagnetic induction dictates that eddy currents will be generated in those materials, causing the cable to heat up and even getting it damaged. Therefore, iron parts cannot be used as fixing clamps for single-core AC cables. 10. What are the main features and advantages of the accessories for the following heat-shrinkable cable terminals? Answer: The main advantage of heat-shrinkable fittings is the use of stress tubes in place of traditional stress cones. This not only simplifies the installation process but also reduces the size of the joint ends. They are easy to install, save time and labor, offer superior performance, and help conserve metal. The heat-shrinkable cable accessories combine the poured and dry-pack types, integrating the advantages of both types of accessories. 11. What inspections should be carried out before cable laying? Answer: (1) The brackets should be complete and the paint should be intact. (2) The cable model, voltage, and specifications meet the design requirements. (3) The cable has good insulation; when there are doubts about the sealing of oil-paper cables, a moisture detection should be carried out ； Direct-buried cables and low-bottom cables must pass the DC withstand voltage test ； The oil sample from the oil-filled cable must pass the tests. (4) The oil pressure of the oil-filled cable should not be lower than 1.47 MPa. 21. What are the advantages of cross-linked heat-shrinkable cable accessories? Answer: This is a new type of material. Compared to other types of accessories currently available, it offers advantages such as superior electrical properties, small size, light weight, easy installation, and compatibility with various materials. Additionally, it exhibits resistance to weather conditions, anti-contamination properties, and flame retardancy with self-extinguishing capabilities. 12. When there are doubts about the sealing of oil-paper insulated power cables, how can one use a simple method to check whether the cable’s insulating paper is damp? Answer: Ignite the cable insulation paper or place it in cable oil at around 150°C for inspection. If there is no “hissing” sound or appearance of white foam, it indicates that the insulation is not damp. 13. What information should be indicated on cable nameplates? What are the requirements for writing? Answer: The design number of the cable route, cable type, specifications, and starting point should be indicated on the signboard. Cables used in parallel should have sequence numbers. The writing must be clear and not easily smudged. 14. Where should the orientation markers for directly buried cables be placed? Answer: At both ends of the cable, at points 50~100m along the straight section of the cable, as well as at the bends where the cable changes direction. 15. For materials such as yellow waxed tape, black glass enamel tape, and alkali-free glass fiber tape used for making cable joints, how should moisture removal be carried out before installation? Answer: (1) Constant-temperature drying method: Roll the insulating tape into small rolls with a diameter of 25–30 mm, place them in a constant-temperature drying oven at 110–120°C for 4–5 hours. After cooling, remove them and place them in a dry, sealed container. (2) Oil immersion dehumidification method: Place small rolls of insulating tape in cable oil kept at a constant temperature of 120–130°C, maintaining a distance of 30 mm from the bottom of the tank. After a certain period of time, once no more foam appears on the surface of the oil, remove the tapes and place them in a barrel filled with cable oil; the oil level should be above all the items placed inside, and then seal the barrel. 16. What is the function of the cable’s outer protective layer? Answer: To protect the inner lining from mechanical damage and chemical corrosion, and to enhance its mechanical strength. 17. What requirements should outdoor cable trenches meet? Answer: The upper part of the cable trench should be slightly higher than the ground level, and it should be covered with a concrete cover. The cables should be laid flat on supports, with proper drainage systems in place. 18. What is the function of the inner shielding layer of a cable? Answer ； Prevent the insulation layer from coming into contact with water, air, or other objects, thereby avoiding moisture damage to the insulation and protecting it from mechanical damage. 19. What should be noted when using wire cutters? Answer: Before use, be sure to check that the insulation of the insulated handle is intact. Do not use wire cutters to cut metal wires beyond the limits specified; also, avoid using wire cutters as a substitute for a hammer in order to prevent damage. 20. What is insulation strength? Answer: In an electric field, insulating materials will break down when the electric field strength increases to a certain limit. The electric field strength that causes this breakdown of insulation is known as the insulation strength. 22. What are the requirements for the mechanical strength of cable conductor connection points? Answer: The mechanical strength of the connection points is generally lower than the tensile strength of the cable conductors themselves. For power cables that are installed fixedly, the tensile strength required of the connection points must be no less than 60% of the tensile strength of the conductors. 23. What are the main properties that the insulation material of power cables should possess? Answer ； It should possess the following main properties: (1) high breakdown strength ； (2) Low dielectric loss ； (3) Relatively high insulation resistance ； (4) Excellent discharge resistance ； (5) It possesses a certain degree of flexibility and mechanical strength ； (6) The insulation performance remains stable over the long term. 24. What are the regulations regarding the pulling force when mechanically laying cables? Answer: For copper core cables, the allowable pulling strength when pulling the head is 70 N/cm ； For aluminum core cables, the allowable pulling strength when pulling the head is 40 N/cm ； When pulled using a wire mesh sleeve, the allowable strength of lead-sheathed cables is 10 N/cm ； The lead sheathed cable is 40 N/cm. 25. What are the regulations regarding cable protection pipes? Answer: (1) When cables need to be laid in protective pipes, the inner diameter of the pipe should be no less than 1.5 times the outer diameter of the cable; the inner diameter of concrete pipes, clay pipes, asbestos, or cement pipes should be no less than 100 mm ； (2) The bending radius of the cable conduit shall comply with the regulations regarding the bending radius of the cables passed through it ； (3) Each pipe should have no more than three elbows, and no more than 2 right-angle bends. 26. How to measure the outer diameter of a cable jacket? Answer: At five evenly distributed points around the circumference of the sleeve, the outer diameter of the sleeve and its average value are measured; the average outer diameter is the outer diameter of the sleeve. 27. How to connect copper core cables with different cross-sections? Answer: For connecting copper-core cables with different cross-sections, open-type weak-back copper connectors can be used and joined by soldering; alternatively, pure copper rods can be shaped into copper connectors according to the respective cross-sectional requirements and connected by crimping. 28. Briefly describe the process of manufacturing indoor terminal fittings for 10KV cross-linked cables using heat-shrink methods? Answer ； (1) Preparation stage: Check whether the heat-shrinkable cable accessories are complete and of matching models; after checking and confirming that the cable is free of moisture, inspect the cable. (2) Cut off the excess cables, and determine the cable length based on the site conditions. (3) Remove the protective layer. (4) Weld the grounding wire by welding it to the steel strip. (5) Fill the triangular joint and apply wrapping sealant. (6) Install the three-core branch sheath, pull the sheath over the root part, and shrink it starting from the middle, first towards the root and then towards the fingers. (7) Strip the copper tape and the outer semiconductive layer; cut away the copper tape at the three-core branch connection point by more than 20 mm. It is strictly prohibited to damage the main insulation, and the semiconductive layer must be removed completely. (8) Install the stress tube; after the branch sleeves at the tube ends are connected, heat-shrink them. (9) Install the terminal blocks. (10) Install the insulating tube. (11) Install the seal tube. (12) Install the phase color tube after phasing. 29. What are the installation steps for indoor and outdoor prefabricated terminals? Answer: (1) Position the cable in the designated location, secure it, and clean its surface; then peel off the outer sheath according to the instructions. If necessary, the length of the outer sheath that is peeled off can be adjusted. Two sets of ground wires are drawn out from the copper strip and the outer sheath armor, respectively. (2) Measure the required length starting from the outer sheath opening, cut off the excess cable, and pull on a heat-shrinkable sleeve to the base of the three-pronged section; heat it from the middle to cause contraction. Then measure the specified length starting from the upper opening of the sleeve (350–380 mm for 35 kV). Remove the excess copper strip (leave 20mm), retain the predetermined position of the semiconductor, and crimp the wire terminals for sealing. 30. The applications of wires and cables are mainly divided into three categories: (1) Power systems. The wires and cables used in power systems include overhead bare wires, busbars, power cables (plastic cables, oil-paper insulated cables – which have been largely replaced by plastic power cables, rubber-sheathed cables, overhead insulated cables), branch cables (which replace some busbars), magnet wire, as well as wires and cables for electrical equipment used in power systems. (2) Information transmission systems: The wires and cables used in information transmission systems include local telephone cables, television cables, electronic cables, radio frequency cables, fiber optic cables, data cables, electromagnetic wires, power communication cables, or other composite cables. (3) Mechanical equipment and instrumentation systems: Almost all products in this category are used, with the exception of overhead bare wires; the main ones include power cables, electromagnetic wires, data cables, and instrumentation cables. 31. Wire and cable products are mainly divided into five categories: (1) Bare wires and bare conductor products. The main characteristic of these products is that they consist of pure conductive metal, without any insulation or coating layers, such as aluminum-clad steel wires, copper-aluminum busbars, and electric locomotive wires ； The processing techniques mainly involve pressure processing, such as melting, rolling, drawing, stranding/squeezing stranding, etc ； The products are mainly used in suburban areas, rural regions, customer main lines, switchgear, etc. (2) The main characteristic of power cables is that an insulating layer is extruded (wound) around the conductor; this applies to overhead insulated cables. In some cases, several conductors are stranded together (corresponding to the phase wires, neutral wire, and ground wire in electrical systems), as in overhead insulated cables with two or more conductors. Additionally, a protective sheath layer may be added, as in plastic/rubber-sheathed wires and cables. The main processing techniques include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, and sheath extrusion; the combination of these processes varies depending on the type of product. The product is primarily used for the transmission of high-voltage electrical power in power generation, distribution, transmission, transformation, and supply circuits, where it handles large currents (ranging from dozens of amperes to several thousand amperes) and high voltages (from 220V to 500kV and above). (3) Wires and cables for electrical equipment: These products are characterized by a wide variety of types and specifications, as well as a broad range of applications. They are mostly used at voltages of 1 kV or less. New products continue to be developed for special applications, such as fire-resistant cables, flame-retardant cables, low-smoke zero-halogen/low-smoke low-halogen cables, cables resistant to termites and rats, oils, cold, heat, and wear, as well as medical, agricultural, and mining cables, and thin-walled wires. (4) Communication cables and optical fibers (brief introduction): With the rapid development of the communication industry over the past two decades or so, these products have also seen astonishing growth. From the simple telephone and telegraph cables of the past, they have evolved to include thousands of pairs of cables, coaxial cables, optical fibers, data cables, and even combined communication cables. The structural dimensions of such products are usually small and uniform, with high requirements for manufacturing precision. (5) Electromagnetic wires (winding wires) are mainly used in various motors, instruments, and equipment. Derivatives/new products of wires and cables: Derivatives/new products of wires and cables arise mainly from the need to meet different application scenarios and requirements, as well as the demands for improved convenience in equipment use and reduced equipment costs. This is achieved by using new or special materials, altering the product structure, raising the standards for manufacturing processes, or combining different types of products together. Different materials are used, such as flame-retardant cables, low-smoke zero-halogen/low-smoke low-halogen cables, termite- and rodent-resistant cables, as well as oil-resistant/cold-resistant/heat-resistant cables ； Changing the product structure, such as fire-resistant cables, etc ； Raise process requirements such as medical cables, etc ； Composite products such as OPGW, etc ； It facilitates installation and reduces equipment costs, such as prefabricated branch cables. 32. What inspections should be carried out after the busbar installation is completed? Answer: The following inspections should be carried out: (1) The processing, fabrication, welding, and screwing of metal components must comply with the regulations ； (2) All bolts, washers, split pins and other components must be complete and reliable ； (3) The busbar configuration and mounting frame shall comply with the regulations, and the electrical distances between phases and to ground shall meet the requirements ； (4) The porcelain parts, iron parts, and joints should be intact; the oil-filled sleeves should show no oil leakage, and the oil level should be normal ； (5) The paint is intact, the color is correct, and the grounding is good. 33. In 35 kV and lower voltage power cable joints, what are several methods to improve the electric field distribution at the jacket separation points? (Please list five methods) and briefly describe them. Answer: (1) Flared mouth: At the cut site of the lead wrap, pry up the edges of the lead wrap to form a flared shape; these edges should be smooth, rounded, and symmetrical. (2) Reserved overall insulation: A section of overall insulating paper is left between the cut in the lead sheath and the point where the cable core wires separate. (3) Cut the semiconductive paper: Cut the semiconductive paper below the flared end. (4) Enveloping stress cone: A cone shape is formed using insulating tape and conductive metal materials, artificially expanding the shielding layer to improve the electric field distribution. (5) Equipotential method: For dry-type or cross-linked polyethylene cable terminations, a metal strip is wrapped around the insulation surface of each conductor core, and these strips are connected together. (6) Installation of stress control tube: For 35kV cables with heat-shrinkable cable terminals, first, two layers of semiconductor tape are wrapped around the core insulation starting from the end of the core’s copper shielding layer using a semiconductor tape; then, a stress control tube of the appropriate specification is fitted over the end of the copper shielding and heat-shrunk into shape. 34. What requirements must be met for the processing of cable supports? Answer: (1) The steel should be straight with no obvious twisting; the cutting error should be within 5 mm, and the cut edges should have no burrs or ridges ； (2) The bracket shall be welded firmly without visible deformation, and the vertical clear distance between the cross braces shall not deviate from the design value by more than 5 mm ； (3) Metal supports must be treated to prevent corrosion; in areas with high humidity and moisture, salt, fog, or chemical corrosion, special anti-corrosion treatments shall be applied as specified in the design. 35. List the cable trays you are familiar with. Answer: Welded E-frame, assembled E-frame, bridge-type cable tray, cable bracket, hook-type support, single-cable bracket, etc. 36. What requirements must be met when laying cables? Answer: The following requirements should be met: (1) In terms of safe operation, various external damages should be avoided as much as possible to improve the reliability of power supply for cable lines ； (2) Economically, considering the option with the lowest investment costs ； (3) In terms of construction, the route of the cable lines must facilitate installation as well as maintenance after operation. 37. What are the insulating materials used for making cable terminations or intermediate connections? Answer: There are insulating glue, insulating tape, insulating tubes, insulating gloves, insulating resin, etc. 38. Briefly describe the general procedure for manufacturing cable terminals. Answer: (1) Preparations before production: including ○1 reading the installation instructions ； ○2 Inspect the scene ； ○3 Material preparation ； ○4 Cable Sealing Test ； ○5 Pre-production testing, etc. (2) Joint fabrication process: includes ○1 cutting off excess cable ； ○2 Stripping of the cable protective layer ； ○3-conductor connection ； ○4 Wrapping insulation (or shrink tubing) ； ○5 Install the connector housing ； ○6 Insulating agent pouring ； ○7 Perform sealing and other treatments. (3) Electrical testing after production. 39. What requirements must be met for the processing of cable protection pipes? Answer: (1) The pipe opening should be ridged and have sharp corners; it is advisable to make the pipe opening in a trumpet shape. (2) After bending, the cable conduit shall have no cracks or significant dents, and the degree of bending shall not exceed 10% of the conduit’s outer diameter ； The bending radius of the cable conduit should not be less than the minimum allowable bending radius of the cable passed through it. (3) Metal pipes should be coated with anti-corrosion paint on their outer surface, and anti-corrosion paint should also be applied to those areas of galvanized pipes where the zinc coating has peeled off. 40. What are the requirements for the arrangement of cables? Answer: (1) Power cables and control cables should not be installed on the same layer of support. (2) High-voltage and low-voltage cables, as well as strong-current and weak-current control cables, should be arranged in layers in the appropriate order; generally, this should be from top to bottom. However, when high-voltage cables of 35 kV or higher are introduced into the cabinets, the cables can be arranged from bottom to top in order to meet the requirements regarding the bending radius. 41. What is the method for laying cables in a cable trench? Answer: The method of laying cables in a cable trench is similar to that of laying cables directly in the ground. Generally, pulleys can be placed in the trench; after laying, the cables are placed on the bottom of the trench or on supports, and cable tags are tied to them. 42. What are the common equipment used for cable laying? Answer: (1) Air compressors, mainly used to damage the road surface in preparation for laying cables later ； (2) Electric winch or cable tractor, mainly used for pulling cables ； (3) Cable conveyor, used in conjunction with a tractor to overcome high friction forces and reduce damage to the cables ； (4) Cable reel unwinding bracket ； (5) Roller mechanism; (6) Twist prevention to reduce twisting of the steel wire rope ； (7) Cable reel braking device ； (8) Tensimeter. 43. What are the requirements for the installation spacing of supports in cable trenches? Answer: Cables are fixed to the walls of cable trenches and tunnels. When installed horizontally, if the outer diameter of the cable is 50 mm or less, a support should be placed every 1 meter ； Cables with an outer diameter greater than 50 mm shall be fitted with a support every 0.6 m ； For single cables arranged in a triangular pattern, they should be secured with straps every 1 meter; when installed vertically, they need to be fixed every 1 to 1.5 meters. 44. How to handle the installation of power cables and control cables on the same tray? Answer: Power cables and control cables should generally not be installed in the same tray. When there are few cables and it is necessary to install both types of cables in the same tray, they should be separated by a partition. 45. How to install grounding wires in cable tunnels? Answer: Continuous grounding wires should be installed along the entire length of the tunnel and ditch; these grounding wires should be connected to all supports, with their ends connected to the grounding electrodes. The specifications of the grounding wire shall meet the design requirements. In addition to meeting insulation requirements, the cable lead sheaths and armoring shall all be interconnected with each other as well as with the ground wire; both the cable trays and the ground wire should be coated with anti-rust paint or galvanized. 46. What are the requirements for fire sealing of cable openings? Answer: For larger cable penetration openings, such as those where cables pass through floor slabs, when using fireproof sealing materials for sealing, it is necessary to apply four to six layers of fireproof coating on the surface of the cable, over a length of about 1.5 meters starting from below the opening. Afterwards, a plate made of fire-resistant material should be used to support the sealing material, ensuring that the seal is secure and easy to remove when the cable needs to be replaced. The seal must be tight and free of gaps in order to effectively prevent smoke and fire from spreading. 47. What checks should be performed before lighting a blowtorch? Answer: The following checks should be carried out: (1) Check whether the pump has oil leaks or seepages, and whether there are leaks or air leaks at the oil tank and nozzle ； (2) Is the amount of oil in the tank exceeding 3/4 of the tank’s capacity, and is the filling screw plug tightened? 48. What precautions should be taken when using a blowtorch? Answer: (1) The maximum oil filling volume for the blowtorch is 3/4 of the tank’s capacity ； (2) Do not use too high a pressure when inflating; once the flame changes from yellow to blue after ignition, it can be used ； (3) There should be no flammable materials in the vicinity, and the air must circulate ； (4) When shutting it down, first turn off the control switch. After the flame is extinguished, slowly loosen the oil port cover to release air. Once all the air has been released, turn off the control switch; wait until it has cooled completely before loosening the port cover ； (5) Kerosene burners and gasoline burners should be used separately. 49. What is the purpose of a manual hydraulic clamp? How to operate it? Answer: To connect two wires, the ends of the wires are usually inserted into crimping tubes made of the same material, and a crimping tool is used to create several indentations, thereby joining the wires together. During crimping, when the handle is lifted upward, the plunger moves outward, creating a vacuum in the lower chamber of the oil inlet valve; as a result, the oil from the oil tank enters the plunger chamber. When the handle is pressed down, the plunger moves inward; under pressure, the oil causes the inlet valve to close while the outlet valve opens, allowing oil pressure to enter the hydraulic cylinder and push the piston as well as the male die. A crimping tube is placed between the male and female dies. When the depth of the depression created by crimping reaches a certain value, the return valve is opened, causing the piston to return automatically. After one depression has been crimped, the crimping tool is moved to crimp the next one. 50. According to the differences in insulation and protective layers, into which main categories can common low-voltage power cables be divided? Answer: (1) Oil-impregnated paper-insulated lead-coated (or aluminum-coated) power cable ； (2) Oil-impregnated paper-insulated power cable without dripping oil ； (3) Polyvinyl chloride insulated, polyvinyl chloride sheathed power cable ； (4) Cross-linked polyvinyl chloride insulated, polyethylene sheathed power cable ； (5) Cross-linked polyvinyl chloride insulated, polyvinyl chloride sheathed power cable ； (6) Rubber-insulated power cable. 51. What are the categories of common insulating materials? Give an example? Answer: (1) Inorganic insulating materials: include mica, asbestos, marble, porcelain, glass, etc ； (2) Organic insulating materials: including resins, rubbers, paper, hemp, cotton yarn, etc ； (3) Composite insulating materials: Various insulating materials manufactured using the above insulating materials. 52. In what situations is pipe tray installation used? What are the advantages? Answer: Pipe trunking is generally used at locations where it intersects with other buildings, roads, or railways, and is sometimes also employed in areas with a high density of buildings. The main advantages are low space requirement, the ability to bear heavy loads, no interference between cables, and high safety. 53. What is the long-term allowable current-carrying capacity of a cable? Answer: The long-term allowable current-carrying capacity of a cable refers to the current value at which, when a specified current flows through the cable, the cable conductors reach their long-term allowable operating temperature after thermal stabilization. 54. What are the factors that determine the long-term allowable current-carrying capacity of a cable? Answer: It is determined by the following three factors: (1) the long-term allowable operating temperature of the cable ； (2) Heat dissipation performance of the cable itself ； (3) Condition of the cable installation and heat dissipation conditions in the surrounding environment. 55. How many ways are there to lay cables? Answer: There are several options: (1) Bury it directly underground ； (2) Installed in the cable trench ； (3) Installed in underground tunnels ； (4) Installed on interior walls or ceilings of buildings ； (5) Installed on the bridge frame ； (6) Laid inside the exhaust pipe ； (7) Laid on the seabed. 56. How to carry out the connection of cable ducts? Answer: When connecting cable conduits, clamps and pipe fittings must be used for connection. If welding is employed, direct welding is not allowed; instead, a section of thicker pipe should be fitted over the connection point before welding, to prevent weld slag from falling into the conduit. 57. What are the requirements for bending the cable core wires up and down when making cable terminals? Answer: When bending the core, the paper insulation must not be damaged, and the bending radius of the core wire must be no less than 10 times that of the cable core. Special care must be taken during production to ensure that the bent parts of the wire core are subjected to even stress; otherwise, the insulating paper is very likely to be damaged. 58. Briefly describe the heat-shrink sealing method for plastic cables. Answer: The heat-shrink method is suitable for sealing medium and low-voltage rubber and plastic cable joints and terminations; it can also be used for cables with non-dripping and viscous impregnated insulation. Two main types of heat-shrinkable tubes are used: those made of cross-linked polyethylene and those made of silicone rubber, both of which can contract uniformly when exposed to heat. This type of tube is fitted over the designated bonding and sealing area, and hot melt adhesive is applied to that area. When heated to a certain temperature, the heat-shrink tube contracts while the hot melt adhesive melts; once it cools down naturally, a good sealing layer is formed. 59. What should be noted when bending cable protection tubes using an electric pipe bender? Answer: (1) The pipe bender should be operated by personnel who understand its performance and are familiar with the operating procedures ； (2) Inspection must be carried out before use; buttons, control levers, and limit switches must be in good condition, and the pipe bender must be reliably grounded ； (3) Select a mold that meets the requirements and determine the required bending radius ； (4) There should be sufficient space for movement around the construction site ； (5) Before use, wait until it is running smoothly at idle speed before starting it under load. During operation, it is strictly prohibited to touch its rotating parts with hands or feet ； (6) The power should be turned off promptly after the work is completed to release the oil pressure. 60. What is the content of the cable inventory, and what do the cable numbers mean? Answer: The cable inventory serves as a basis for laying cables and guiding construction, as well as an archive for operation and maintenance. The number, starting point, model, specifications, and length of each cable should be listed, and the total length should be calculated through classification. For cable management, the spare cores of each cable should also be specified. The cable number is a identifier for the cable; therefore, it is required that the numbers used throughout the plant be unique, and that they have a certain meaning and pattern that allows them to reflect the characteristics of the cable. 61. How many categories can the current methods of cable laying be divided into? Answer: (1) Manual laying, that is, using a mass workforce strategy, with one or more people coordinating and directing the process to carry out the laying as specified ； (2) Mechanized laying, that is, the use of rollers, pullers, and conveyors controlled by a synchronous power supply, which is relatively safe ； (3) A combination of manual labor and machinery is used; in some sites where there are many turns and construction is difficult, it is challenging to rely solely on machinery, which is why this method is adopted. 62. What requirements should be met for the wiring of secondary circuits? Answer: (1) The wiring was done correctly according to the diagram ； (2) The electrical connection of the wires should be firm and reliable ； (3) There should be no joints in the wires inside the cabinets, and the wire cores must be undamaged ； (4) The end of the cable core wire shall be marked with its circuit number; the number must be correct, the writing clear, and resistant to fading ； (5) The wiring should be neat, clear, and aesthetically pleasing; the wire insulation should be in good condition with no damage ； (6) There should be one wire connected to each side of each terminal, with a maximum of two wires. 63. What are the requirements for cable trays? Answer: (1) The distance from the top of the pipe rack to the ground is 0.2 m inside the factory building, 0.5 m under walkways, and 0.7 m in general areas ； (2) Pipe shafts shall be installed at both the direction change points and branch points; shafts shall also be added when the length exceeds 30 mm ； (3) The depth of the pit shall be not less than 0.8 m, and the diameter of the manhole shall be not less than 0.7 m ； (4) The drain pipes should have a drainage slope of 0.5% to 1% leading toward the pit. 64. What are the requirements for the resistance at the cable conductor connection points? Answer: It is required that the resistance at the connection points be low and stable. The ratio of the resistance at these connection points to that of a conductor of the same length and cross-section should not exceed 1 for newly installed terminal and intermediate connectors ； For operating terminal heads and intermediate heads, this ratio should not be greater than 1.2. 65. What requirements must the design of cable joints and intermediate connectors meet? Answer: The requirements that must be met are: (1) high voltage resistance and good conductor connection ； (2) High mechanical strength and low dielectric loss ； (3) Simple structure with strong sealing performance. 66. What is a cable fault? What are the common types? Answer: A cable fault refers to a failure in which the cable experiences insulation breakdown during preventive testing, or during operation, insulation breakdown or wire burnout leads to the interruption of power supply in that cable circuit. Common faults include ground fault, short-circuit fault, open-circuit fault, flashover fault, and mixed faults. 67. How to handle single-phase ground faults in cable lines? Answer: In the case of a single-phase ground fault in a cable line, the damage to the cable conductors is usually only localized. If the damage is mechanical and the soil near the fault site is dry, it is generally possible to carry out local repairs by adding a fake connector; in other words, the cable core does not need to be cut, and the insulation at the fault site can simply be strengthened and sealed. 68. What tests and inspections should be carried out on power cables before installation? Answer: Before installation, it is necessary to check whether the cable’s model, specifications, and length meet the requirements, as well as to determine if there are any external damages. For low-voltage cables, an 1000V megohmmeter is used to measure the insulation resistance, with a value generally not lower than 10 MΩ. For high-voltage cables, a 2500V megohmmeter is used, and the resistance value should generally be no less than 400 MΩ. 69. What should generally be noted when laying cables in the main plant? Answer: When laying cables in the main plant, the following points should generally be noted: (1) Control cables leading to the control room should preferably be laid overhead ； (2) 6KV cables should be laid in tunnels or conduit; in areas with high groundwater levels, they can also be laid overhead or in conduit ； (3) For 380V cables, when the cable ends are at zero height, tunnels, ditches, or conduit systems should be used; when the equipment is on one end and at the other end it is below ground level, the cables can be laid partially in the air. When the groundwater level is high, it is advisable to lay the cables in the air. 70. Where are the inner and outer shielding layers of an power cable located? What materials to use? What is its function? Answer: To ensure good contact between the insulating layer and the cable conductor, and to eliminate the increase in electric field strength on the conductor’s surface caused by irregularities on its surface, an inner shielding layer made of metallized paper or semiconductor tape is generally used around the conductor’s surface. To ensure good contact between the insulating layer and the metal sheath, an outer shielding layer is generally wrapped around the outer surface of the insulating layer. The outer screen layer and the inner screen layer are made of the same material; sometimes copper strips or woven copper wires are also used on the outside. 71. Briefly describe the composition and properties of epoxy resin composites. Answer: An epoxy resin composite is composed of epoxy resin along with a curing agent, fillers, toughening agents, and diluents. It has the following properties: (1) Sufficient mechanical strength ； (2) Excellent electrical performance ； (3) Stable electrical performance ； (4) Sufficient adhesion to non-ferrous metals ； (5) Good corrosion resistance ； (6) When used outdoors, it is resistant to rain, light, and humid heat. 72. Why is it necessary to install a return wire running parallel to the cable in the grounding method for one end of the single-core cable jacket? Answer: In cable systems where one end of the metal shield is grounded, in order to ensure that the induced voltage within the shield does not exceed the allowable limits, it is necessary to install a conductor that runs parallel to the cable line, with both ends of this conductor grounded; such a conductor is called a return wire. When a single-phase ground fault occurs, the ground short-circuit current can flow back to the system’s center point through the return path. Since the magnetic flux generated by the ground current flowing through the return path cancels out part of the magnetic flux produced by the ground current in the cable conductors, the induced voltage in the sheath during a short-circuit fault can be reduced. 73. How many categories can cable engineering be divided into? Answer: (1) Site transportation: includes the loading, unloading, and transport of construction materials from the warehouse to the construction site, as well as the return trip with an empty vehicle. (2) Local works: including road surface excavation, tunnel, and channel construction, etc. (3) Laying work: includes laying, intermediate joint fabrication, cover plate installation, pipe burial, level adjustment, pulling head fabrication, etc. (4) End-end works: including the fabrication and installation of support and suspension cable trays and their foundations, the fabrication of terminal fittings, the installation of hydraulic and signaling devices, and various electrical performance tests. (5) Sealing work: includes the fabrication of oil-filled cable sealing heads, as well as the installation of fuel tanks, automatic drainage systems, and signaling devices. (6) Grounding works: including insulated joints, commutation boxes, protectors, and the installation of grounding boxes. 74. What inspections should be carried out for the acceptance of cable lines? Answer: (1) The cable specifications should meet the requirements; they should be arranged neatly, without any damage, and the labels should be complete, correct, and clear ； (2) The fixed bending radius of the cable, relevant distances, and the wiring of the metal sheath of single-core power cables shall meet the requirements ； (3) Cable terminals and intermediate joints shall not leak oil, be firmly installed; the oil pressure of oil-filled cables and the setting values of gauges shall meet the requirements ； (4) Good grounding ； (5) The phase colors of the cable terminals are correct, and the metal components such as brackets are properly painted ； (6) Cable trenches, tunnels, and bridge decks should be free of debris, with all covers in place. 75. What are the requirements during the measurement of the positive-sequence impedance of cable lines? Answer: The phasor sum of the AC resistance of the cable conductor and the phase voltages of the three-phase inductive reactance of the cable is called the positive-sequence impedance. The positive-sequence impedance of cable lines can generally be measured directly on the cable reel. A low voltage is usually used for this measurement, so a step-down transformer is required to reduce the voltage. The transformer is connected in star configuration, with a capacity of at least 10 kVA, and it offers a wide range of voltage adjustment capabilities. The AC power supply used for measurement should be stable enough to ensure that the current meets the specified requirements. The reading on the voltmeter must represent the voltage at the cable end. It is advisable for the test current to be close to the cable’s long-term allowable current rating. When reading the values from the various meters, the current should be turned on first, and then the values of all three meters should be recorded simultaneously. 76. According to the Regulations on Safety in Electrical Production, what qualifications must electrical workers possess? Answer: The following conditions must be met: (1) To be deemed healthy by a doctor, with no illnesses that would prevent working ； (2) Possess the necessary electrical knowledge, master the relevant regulations, professional techniques, and safety operation procedures appropriate to their position and job nature, and pass the relevant examinations ； (3) Master first-aid methods for electric shock. 77. What precautions should be taken when transporting and handling cables? Answer: (1) During transportation and handling, the cables and cable reels must not be damaged; it is strictly prohibited to push the cable reels directly off a vehicle. Cables should generally not be transported or stored in a horizontal position. (2) Before transporting or rolling the cable reel, it is necessary to ensure that the reel is secure, the cables are tightly wound, and the oil pipes connecting the oil-filled cables to the pressure oil tank are fixed and not damaged. The pressure oil tank must also be stable, and the pressure indication must meet the required standards. 78. What are the measures to prevent cable fires? Answer: (1) Use flame-retardant cables ； (2) Use fire-resistant cable trays ； (3) Use fire-resistant coating ； (4) Install fire partitions and fire barriers at cable tunnels, mezzanine exits, etc ； (5) Aerial cables should be kept away from oil pipelines and explosion-proof doors; otherwise, local conduit installation or thermal and fire protection measures should be taken. 79. What factors should be considered when selecting the cross-sectional area of an electrical cable? Answer: The following aspects should be considered: (1) The maximum allowable operating current of the cable over the long term ； (2) Thermal stability during short circuit ； (3) The voltage drop on the line must not exceed the allowable operating range. 80. What are the advantages of power cables over overhead lines? Answer: (1) It operates reliably; since it is installed in concealed locations such as underground, it is less susceptible to external damage, has fewer chances of malfunctioning, ensures a stable power supply, and poses no risk to human safety ； (2) Low maintenance workload, no need for frequent inspections ； (3) No need to erect towers ； (4) Helps to improve the power factor.