Q&A on Electrical Technology

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1. What are the principles to consider when using an isolating switch for operation? 　Answer: When the knife switch opens and closes current, the arc formed does not cause an arcing short circuit. The empirical formula for the arc extension L is as follows:
L = 0.5UI + 30 (when the switching current is less than 100A)
L = 50UI + 30 (when the switching current is greater than 100A)
Where L represents the length of arc extension, in cm ； 　　U —— The effective value of the voltage between the circuit breakers after they are opened, in kV ； 　　I —— The effective value of the current passing through the circuit breaker when it is closed, measured in amps. 2. What are the causes of oil leakage from oil-filled equipment such as oil circuit breakers and transformers? Answer: 1) The rubber gaskets are not resistant to oil. 　　　　2) The oil-resistant rubber gasket is compressed too tightly, causing the rubber to lose its elasticity. 　　　　3) The rubber pad has lost its elasticity after being used for too long. 　　　　4) Overheating causes the gasket to age or carbonize. 　　　　5) The seals at the oil gauge or drain valve, etc., are not tight. 　　　　6) The welding quality of oil pipes at the fuel tank station is poor. 3. What are the common methods used to determine whether equipment is overheating during operation? 　　Answer: 1) Temperature-indicating wax strip monitoring method ； 　　　　2) Hot air current observation method ； 　　　　3) Method for observing changes in colored paint ； 　　　　4) Observe the melting of frost and snow ； 　　　　5) Observe local drying and vapor conditions in the rain ； 　　　　6) Using the wax rod charging test method ； 　　　　7) The method of live monitoring using a temperature detector. 4. What are the common faults of isolating switches and what are their causes? 　　Answer: 1) The contact part is overheating. There are various reasons for overheating; primarily, it is caused by a decrease in the elasticity of the compression spring or by loose bolts on that spring. Secondly, surface oxidation at the contact areas increases resistance, leading to higher temperatures. These high temperatures in turn accelerate oxidation, and this cycle can result in accidents. 　　　　2) The porcelain vase is damaged. Excessive force was applied when operating the isolating switch, or the connection between the isolating switch and the busbar was poor, resulting in the breakage of the porcelain insulator. 　　　　3) The isolation mechanism lacks flexibility in handling separations and reunions. Rust on the operating mechanism of the isolating switch or on the rotating parts of the switch itself can cause problems with its opening and closing functions. If it is winter, then freezing must be taken into account. Severe overheating of the knife switch and the static contact can also cause them to weld together, leading to failure. 5. What are the two methods for determining the dimensions of hard busbar down conductors? Answer: (1) The method of using a suspension line to measure the dimensions and then marking out a sample. 　　(2) Construction method for making prototypes. 6. How to straighten rigid busbars? Answer: The specific methods are as follows: (1) Straighten them on a platform, which can be made of flat materials such as channel steel or rails ； (2) The plane and sides of the busbar should be straightened, which can be done by hitting it with a wooden hammer ； (3) Tools with a hardness greater than that of the aluminum strip, such as hammers, must not be used. 7. Are there any regulations regarding the direction in which bolts of various fittings on insulator strings, conductors, and lightning arresters should be inserted? Answer: (1) Those in a vertical direction must always be inserted from top to bottom. (2) For those in the horizontal direction, pass through on the power-receiving side along the line ； The outer wires on either side of the horizontal conductor pass from the outside toward the inside of the conductor, while the middle phase wire passes from left to right (facing the power-receiving side). For split conductors, they all pass from the outside of the bundle toward the inside of the bundle. (3) Split pins, blind pins; those in the vertical direction pass downward. 8. How to install a gas relay? Answer: (1) Check whether the gas relay is qualified. (2) It should be installed horizontally, with the arrow indicated on the top cover pointing toward the oil reservoir. (3) The pipeline axis of the relay is allowed to be slightly higher at the end facing the oil reservoir, but the inclination from the horizontal plane shall not exceed 4%. (4) The gaskets of each flange must be installed properly. (5) The oil pipeline diameter must not be blocked. 9. Describe the method of manually mixing concrete. Answer: The method of manual mixing is as follows: (1) First, pour the sand on one side of the mixing board, then add the cement on top of the sand and stir it 2-3 times. (2) Mix the sand and cement thoroughly before adding water, then continue mixing 2–3 more times. (3) After mixing evenly, add the stones and stir thoroughly several more times until the stones and mortar are fully combined and the consistency is appropriate. 10. What are the basic requirements when installing strain clamps at both ends of the flexible busbar? Answer: (1) Before disconnecting the wire, wrap 3–4 turns of binding wire around the end of the wire to be disconnected to prevent it from breaking. (2) The position of the wire hanging point should be aligned with the center of the large pin hole in the strain clamp; remember this position when winding the tape. The tape wrapped around the wire should have ends long enough to allow 50 mm of the clamp’s ends to be exposed. The winding direction of the wrapping tape should be consistent with the twist direction of the outer strands of the wire. (3) When selecting a wire clamp, the thickness of the insulation tape should be taken into consideration. The boat-shaped clamping plate of the wire clamp should be kept flat; after the “U”-shaped bolts are tightened, 3–5 threads of the bolt should be visible. (4) When the busbar is short, the suspension holes of the clamps at both ends should be on the same side when the conductor is not under stress. 11. What are the requirements for lifting an isolating switch? Answer: (1) Lift the assembled single-pole isolating switch onto the foundation channel steel. (2) After leveling and aligning it, fix it in place with bolts. (3) The horizontal error of the base should be less than 1%. (4) The switch has a high center of gravity, so measures should be taken to prevent it from tipping over during lifting. 12. Describe the maintenance tasks and technical requirements for isolating switches. Answer: (1) Check whether the insulators of the isolating switch are intact, and whether there is any corona or discharge. Clean the insulators and check the condition of the cement-based connections; any issues found should be addressed or the components replaced promptly. Use a megohmmeter to measure the insulation resistance of the insulators. (2) Check the drive rods and various components of the mechanism for any signs of damage, rust, looseness, or detachment. Regularly inspect the lubrication condition; clean it as necessary and apply lubricant. Remove rust from the base, paint it, and ensure proper grounding. (3) Check whether the contacts are in good contact, whether the compression spring exerts sufficient pressure, and clean the dirt and burn marks on the contact surfaces. Those contact fingers that are severely burned should be replaced; the conductive copper strands must not have any broken or fractured sections. Contact finger springs with insufficient elasticity should also be replaced. A neutral vaseline or conductive silicone grease should be applied to the contact surfaces to reduce oxidation of the contacts. (4) Re-measure the relevant technical parameters of the switch in accordance with the manufacturer’s technical specifications, such as contact insertion depth, synchronization degree, and the opening angle of the spare travel; if they do not meet the requirements, adjustments should be made. 13. What are the requirements for installing lightning arresters? Answer: (1) First, fix the base of the lightning arrester, and then install each unit (section) of the lightning arrester from bottom to top. (2) The arrester has undergone assembly testing and passed it before leaving the factory; it should be assembled at the installation site strictly in accordance with the manufacturer’s specifications, and components cannot be interchanged to avoid changes in its characteristics. (3) For valve arresters with series and parallel resistors, proper selection should be made during installation so that the nonlinear coefficients of the units in the same phase are as similar as possible, with the difference between them not exceeding 0.04. (4) The contact surface of the arrester should be wiped clean to remove oxide films and paint, and a layer of electrical composite grease should be applied. (5) The arrester should be installed vertically, with a verticality deviation of no more than 2%; if necessary, metal sheets can be placed between the flange surfaces to correct this deviation. The centers of the three phases should be on the same line, the nameplates should be located on the same side for easy viewing, the voltage equalizing rings should be installed horizontally, and finally, the gaps should be filled with putty and painted. (6) Tighten the insulator strings to secure them; the tension in each string of the same phase should be even, to prevent the arrester from experiencing additional tensile stress. (7) The discharge counter should be well-sealed, operate reliably, have its three-phase installation positions aligned for easy observation. The grounding is reliable, and the counter indicator returns to zero. (8) The venting passage of the zinc oxide arrester should be unobstructed; during installation, care should be taken to prevent the gases emitted from it from causing inter-phase short circuits or ground flashovers, and these gases must not be directed at other equipment. 14. Explain the steps for vacuum oil filling. Answer: When the vacuum level inside the container reaches the specified value, insulating oil can be slowly injected from below the oil tank through the throttle, without having to relieve the vacuum; the temperature of the oil should be higher than that of the container itself. For voltage levels of 220 kV and above, the oiling time should not be less than 6 hours; for 110 kV, it should not be less than 4 hours. After oiling, the vacuum condition should be maintained for another 4 hours, until all air inside the tank has been completely removed, before the vacuum can be lifted. 15. What issues should be considered when installing a trolley-type high-voltage circuit breaker cabinet? Answer: (1) The ground level should be appropriate to enable the trolley to move smoothly from the ground to the cabinet. (2) The moving contacts of each trolley should be adjusted to be consistent; the moving and fixed contacts should lie on the same center line. The contacts should make firm contact after being inserted, and the insertion depth should meet the requirements. (3) The secondary wiring is correctly and reliably connected with good contact. (4) The electrical or mechanical locking device should be adjusted to be correct and reliable. (5) The relay on the door should have a vibration damping ring. (6) The control cables inside the cabinet should be firmly fixed, without hindering the entry and exit of the trolley. (7) The grounding contacts of the trolley must make good contact, and the voltage transformer serta the grounding points at the bottom of the trolley must be reliably grounded. 16. What are the common faults of busbars? Answer: (1) Poor contact at the joints increases resistance, leading to severe heating that causes the joints to turn red. (2) Poor insulation of the support insulators reduces the insulation resistance of the busbar to ground. (3) When large fault currents pass through the busbar, the electrodynamic forces and arc light cause the busbar to bend, break, or get burned. 17. What are the reasons for flashover discharge in insulators? How should it be dealt with? Answer: The reasons are: (1) Dirt accumulates on the surface of the insulator and inside its porcelain skirt; when moisture is present, the voltage resistance decreases. A discharge path is formed on the surface of the insulator, which increases the leakage current. When this current reaches a certain level, surface breakdown discharge occurs. (2) Even if the dirt on the insulator surface is minimal, certain overvoltages occurring in the power system can cause flashover discharge on the insulator surface due to the effect of these overvoltages. The handling method is as follows: after flashover discharge occurs in an insulator, its surface insulation performance deteriorates significantly; it should be replaced immediately, and the insulators that have not experienced flashover discharge should be cleaned. 18. What are the reasons for heating of the contacts of an isolator? Answer: (1) Overloading of the isolator or poor fit between the contact surfaces reduces the cross-sectional area of the current path, thereby increasing the contact resistance. (2) Oxidation occurs at the contact surface during operation, increasing the contact resistance. Therefore, when current flows through, the contact temperature exceeds the allowable value, and there is even a possibility of it turning red, melting, or even welding together. Under normal conditions, the maximum allowable temperature of the contacts is 75°C; therefore, the contact resistance should be adjusted so that it does not exceed 200μΩ. 19. What components are included in the conductive circuit of the SNl0-10Ⅱ type circuit breaker? What should be the resistance of this circuit after major maintenance? If it does not meet the requirements, which parts need to be addressed? Answer: The conductive circuit includes elements ranging from the lower terminal block, conductive bars, conductive rods, rolling contacts, moving contacts, static contact fingers, static contact blocks, and static contact frames to the upper terminal block. The lower terminal block is fixed in planar contact with the conductive bar by bolts; the rolling contact makes contact with the conductive bar and the conductive rod under the action of a compression spring, while the contact fingers make contact with the moving contact of the conductive rod and the static terminal block under the action of spring plates. The static terminal block is in fixed contact with the contact frame via bolts, and the upper terminal block is in planar contact with the contact frame. 　　After major repairs, the loop resistance should be less than 60μΩ. 　　In the case of non-conformity, it is necessary to check whether the degree of burn on the aforementioned parts meets the requirements, whether the contact is good, especially whether the connection between the upper terminal block and the contact holder is tight; whether there is any deformation or damage to the spring elements installed in the static contact holder; and whether the properties of the spring used for the rolling contacts meet the specified standards. 20. What should be noted when topping up oil in an operating transformer? Answer: (1) The oil to be injected must be qualified oil to prevent mixing of oils. (2) Before adding oil, switch the heavy gas protection to the signal position to prevent accidental tripping. (3) After adding oil, check the gas relay, release air promptly, and then resume normal operation. 21. What electrical testing tasks should substation maintenance workers be able to carry out on their own? Answer: (1) Testing of insulation resistance ； (2) Testing of contact resistance ； (3) Testing of DC resistance ； (4) Motion characteristic test. 22. What are the main factors that affect the contact resistance of conductive connector joints? Answer: The main factors affecting contact resistance include the following: (1) Whether the structure of the joint is reasonable during installation. (2) Is the electrical conductivity of the material good? ； Is the contact performance good? (Manufactured strictly in accordance with the process.) (3) Factors that affect contact resistance include whether the materials used and the contact pressure are appropriate, as well as the degree of oxidation at the contact surface. To prevent the joints from overheating, the impacts of the aforementioned factors should be minimized as much as possible in design and construction. 23. What are the main criteria for adjusting isolating switches? Answer: The main criteria for adjusting isolating switches are as follows: (1) The phase difference among the three phases (i.e., the maximum distance between the blades and the static contacts in an isolating switch with three interconnected poles). The smaller the difference between different periods, the better; this is beneficial for arc extinguishing and reducing mechanical damage when low currents are applied or removed. When the difference is large, it can be resolved by adjusting the depth to which the screw on the insulator of the pull rod is turned, as well as the tightness of the nut on the switch (if the gap of the disconnector was adjusted properly during installation, simply turn the screw 1–2 turns tighter or looser). The adjustment must be carried out carefully and repeatedly. (2) An appropriate residual gap should be maintained after closing (referring to the minimum distance between the bottom surface of the switch blade and the bottom of the static contact). 24. What are the main requirements for installing capacitors? Answer: The requirements for installing capacitors are as follows: (1) When capacitors are installed in layers, there should generally be no more than three layers, and no partitions should be placed between them. The vertical distance between the capacitor busbars and the upper structure should be no less than 20 cm, while the distance from the bottom of the lower capacitors to the ground should be greater than 30 cm. (2) The horizontal distance between capacitor frames should not be less than 0.5 m. The distance between each capacitor should not be less than 50 mm. The capacitor’s nameplate should face the aisle. (3) For capacitors that require grounding, their enclosures shall be grounded together with the metal frame. (4) A thermometer or temperature-indicating wax strip should be installed at an appropriate location on the capacitor to monitor its operating temperature. (5) Capacitor banks shall be equipped with fault protection devices or fuses for inter-phase faults and faults within the capacitor elements. For high-voltage capacitor banks with a capacity of 600 kW or more, differential protection or zero-sequence protection may be installed; alternatively, dedicated fuses can be used for protection on a per-unit basis. (6) The capacitor should be equipped with qualified discharge equipment. (7) Capacitors installed outdoors should be mounted on a platform as much as possible, with the bottom of the platform being at least 3 meters above the ground ； Capacitor banks installed outdoors on the ground should be placed on the concrete surface inside the enclosure of the substation, with the bottom being at a distance of not less than 0.4 m from the ground. At the same time, the capacitor bank should be installed within a fixed enclosure at a height of not less than 1.7 m, with measures in place to prevent small animals from entering. 25. What are the requirements for fixing rectangular busbars on insulators? Answer: The clamps used to fix busbars on insulators are usually made of steel, and they should not form a closed magnetic circuit. If a closed magnetic circuit is formed, a large induced circulating current will be generated in the loop formed by the clamps and bolts, causing the busbars to overheat; this situation is more severe in busbars with high operating currents. 　　To prevent the formation of a closed magnetic circuit, when both clamps are made of iron, one of the fastening bolts should be made of iron and the other of copper. Alternatively, the busbars can be secured using open-type clamps; the two clamps can be one made of iron and the other of aluminum, with both fastening bolts being made of iron. 26. What are the uses of the auxiliary contacts of a circuit breaker? Answer: The circuit breaker uses its own normally open and normally closed contacts, whose positions can be changed, to connect the circuits that control the closing and tripping of the circuit breaker as well as the sound signal circuits. This enables the circuit breaker to open or close circuits, and it also allows for the proper generation of sound signals, as well as the activation of automatic devices and protection interlock circuits. When the auxiliary contacts of a circuit breaker are used in the closing and tripping circuits, they should all have a delay. 27. How to inspect circuit breakers? Answer: (1) Review the commissioning records of the circuit breakers. (2) Inspect the appearance of the circuit breaker, including the oil level and sealing condition; the porcelain parts and grounding system should be in good condition, with no oil leakage in any part. (3) The secondary wiring connections of the equipment should be tight, properly wired, and have good insulation ； The contactor has no sticking and maintains good contact ； The opening distance of the auxiliary circuit breaker is appropriate, and there are no issues with its operating contacts. (4) The hydraulic mechanism should show no oil leakage; all pipeline connections must be tight, all micro-circuit breakers should operate properly without any issues, and the pre-charge pressure must meet the standards. (5) Manual closing is smooth with no resistance, electric opening and closing operate correctly, and the protection indicator lights show the proper signals. (6) Record the problems and defects identified during acceptance, and report them to the relevant departments. 28. How to maintain the opening valve of the hydraulic mechanism (CY3 type)? Answer: (1) After disassembling the opening valve, check the sealing condition between the ball valve and the valve port; the steel ball should be free of any scratches or rust, and the width of the valve seat’s sealing surface should not exceed 0.5 mm. Also, check whether the sealing rings are damaged. Block the ball valve at the valve opening and use a mouth to suck air; if the steel ball can be drawn out, it is qualified ； When it cannot be pulled out, it can be ground with emery sand, or the ball valve can be placed over the valve opening and pressed with a copper rod. (2) Check the return spring for any deformation and to ensure its elasticity is normal; if the elasticity has decreased, it can be replaced. (3) After all inspections show no issues, rinse the valve body, valve seat, and all components with hydraulic oil, and finally assemble them in the reverse order of disassembly. 29. What aspects should be checked after disassembling the pressure reservoir of the CY4-type mechanism? Answer: (1) Check whether there are any scratches, deformations, or rust on the inner wall of the cylinder and the surface of the piston. Minor scratches and rust can be polished using 800-grit sandpaper; those with severe deformation, scratches, or rust should be replaced. (2) Check whether the piston rod is bent, whether its surface is smooth, and whether there is any wear or rust. (3) Check whether the connection plate is deformed. 30. What are the general factors that affect the tripping time of a circuit breaker (electromagnetic mechanism)? Answer: (1) The travel distance of the tripping core ； (2) Condition of the connecting plates in various parts of the breaking mechanism ； (3) Depth of engagement of the disconnection latch with the operator ； (4) Condition of the opening spring ； (5) Conditions of the transmission mechanism, spindle, intermediate static contact mechanism, etc. 31. What should be done if the arc-quenching plates of the SW6-220/110 type circuit breaker become damp? Answer: (1) They can be dried; they should be cleaned thoroughly before drying ； (2) The drying temperature is 80–90℃ ； (3) The heating time shall be no less than 12 hours ； (4) The drying time is 48 hours ； (5) Place it in qualified insulating oil immediately after removal to prevent further moisture absorption ； (6) A voltage withstand test is also required; it can be used only after passing the test. 32. What should be done if the opening and closing speeds of the SNl0 type circuit breaker do not meet the requirements? Answer: (1) If the opening speed is within the acceptable range but at the lower limit, while the closing speed is not satisfactory, it is necessary to check the terminal voltage of the closing coil, whether there is any jamming in the circuit breaker’s mechanism, and whether the DC resistance of the coil is within the specified limits. The issues identified should be addressed promptly. (2) If the opening speed is within the acceptable range and at the upper limit, but the closing speed is not acceptable, the pre-stretch length of the opening spring can be adjusted to make it meet the requirements. (3) If the opening speed is not up to standard, the length of the opening spring can be adjusted to meet the requirement. 33. Describe the items that need to be adjusted and measured after major overhauls of SW2-220Ⅰ and Ⅱ type circuit breakers. Answer: (1) Adjustment and measurement of the total travel distance of the moving contact ； (2) Adjustment and measurement of the moving contact overtravel ； (3) Adjustment and measurement of opening and closing speeds ； (4) Measurement and adjustment of action time ； (5) Measurement of contact resistance in the conductive circuit ； (6) Adjustment of the locking spring. 34. What are the regulations regarding the length of the bent portion when a rectangular busbar is bent horizontally, vertically, or torsionally by 90° each? Answer: (1) When the busbar is bent flat by 900 degrees: for busbars with a specification of 50mmX5mm or less, the bending radius must not be less than 2.5h (where h is the thickness of the busbar) ； For busbars with a specification of 60mm×5mm or larger, the bending radius must not be less than 1.5h. (2) When the busbar is bent vertically at 90°: for busbars with a dimension of 50mm X 5mm or less, the bending radius R must not be less than 1.5b (where b is the width of the busbar) ； For busbars larger than 60mmX5mm, the bending radius must not be less than 2b. (3) When the busbar is twisted (bent) by 90°: the length of the twisted portion should be greater than 2.5 times the width (b) of the busbar. 35. What are the precautions for the operation and maintenance of ZN28-10 type circuit breakers? Answer: (1) Circuit breakers in normal operation should be maintained regularly; dust on the surface of insulating components should be cleaned, and lubricant should be applied to the parts that undergo frictional movement. (2) Periodically, or when a total of 2,000 operations have been performed, check whether the screws in various parts are loose, and take action if necessary. (3) Regularly inspect the closing contactor and auxiliary switch contacts; if they are severely damaged, they should be repaired or replaced promptly. (4) When replacing the arc chamber, it shall not be subjected to bending moment after the fasteners are tightened; the main and secondary parts shall experience significant tensile stress and transverse stress, and the bending deformation of the arc chamber shall not exceed 0.5 mm. After the upper bracket is installed, it must not press down on the arc chamber guide sleeve; a gap of 0.5 to 1.5 mm should be left between them. 36. Describe the steps for disassembling and overhauling the working cylinder of the SW6 type circuit breaker. Answer: (1) Remove the screws used to connect the working cylinder to the mechanism, take off the working cylinder, and place it on a vise; insert protective pads between the jaws of the vise before clamping it. (2) Use a special tool to unscrew the gland sleeve in order to loosen the seal ring. (3) Use a large pipe wrench to unscrew the cylinder head, pull out the piston, and remove the brass washer and sealing ring. (4) Clean the cylinder block and various components with hydraulic oil. (5) Check the inner wall of the cylinder and the surface of the piston rod for any signs of scoring or wear. If there is slight wear, it should be treated with 800-grit emery paper. (6) Check the piston cylinder and cylinder head for any scratches; if any are present, treat them with an oil stone or 800-grit emery paper, and use an oil stone to smooth out the sharp corners at both ends of the piston cylinder. (7) Assembly should be carried out in a clean room to prevent dust from entering the cylinder block. During assembly, all seals must be replaced, and the groove of the bowl-shaped seal should face the inside of the working cylinder. (8) After assembling all the components, manually pull the piston rod to check whether the piston is stuck, and also check the stroke of the cylinder. 37. How to lift the pillar of the LW6-220 type circuit breaker? Answer: It should be lifted in accordance with the following steps and requirements: (1) Use lifting equipment to lift the pillar so that it is in a horizontal position, and attach the two legs to the lower base of the pillar. (2) Lower the pillar so that the two legs attached to it come into contact with the ground; use special wooden blocks to support the flange between the two ceramic sleeves. Then, use a crane to lift the third leg and attach it to the base at the bottom of the pillar. (3) When installing the three connecting plates between the support legs, the smaller one should be placed on the side of the density relay; do not tighten the screws yet. (4) Slowly lift the pillar from a horizontal position to an upright position using a crane (by utilizing the lifting ring on the upper flange of the pillar). (5) Install the pillar on the foundation and tighten all screws in sequence. (6) After the pillar is lifted, it should be well vertical. 38. What is the difference between electromotive force and voltage? How are their directions defined? Answer: Electromotive force is a concept that reflects the work done by an external force to overcome the electric field force, whereas voltage is a concept that reflects the work done by the electric field force. The positive direction of electromotive force is the direction of potential increase, while the direction of voltage is the direction of potential decrease. 39. What is the temperature coefficient of resistance? What is the relationship between a conductor’s resistance and temperature? Answer: The ratio of the increase in a conductor’s resistance for every 1°C rise in temperature to its original resistance is called the temperature coefficient of resistance. Its unit is per degree, and its calculation formula is α = (R2 – R1) / R1 × (t2 – t1). Here, R1 is the resistance value at temperature t1, in ohms ； R2--resistance value at temperature t2, Ω. 40. What is the skin effect? What are its applications? Answer: When an alternating current flows through a conductor, the current tends to flow along the surface of the conductor; this phenomenon is known as the skin effect. To make effective use of conductor materials and facilitate heat dissipation, high-current busbars are often designed in a grooved or diamond shape. Additionally, in high-voltage transmission and distribution lines, steel core stranded wires are used in place of aluminum stranded wires, which not only saves aluminum conductors but also enhances the mechanical strength of the wires. 1. What are the principles to consider when using an isolating switch for operation? 　Answer: When the knife switch opens and closes current, the arc formed does not cause an arcing short circuit. The empirical formula for the arc extension L is as follows:
L = 0.5UI + 30 (when the switching current is less than 100A)
L = 50UI + 30 (when the switching current is greater than 100A)
Where L represents the length of arc extension, in cm ； 　　U —— The effective value of the voltage between the circuit breakers after they are opened, in kV ； 　　I —— The effective value of the current passing through the circuit breaker when it is closed, measured in amps. 2. What are the causes of oil leakage from oil-filled equipment such as oil circuit breakers and transformers? Answer: 1) The rubber gaskets are not resistant to oil. 　　　　2) The oil-resistant rubber gasket is compressed too tightly, causing the rubber to lose its elasticity. 　　　　3) The rubber pad has lost its elasticity after being used for too long. 　　　　4) Overheating causes the gasket to age or carbonize. 　　　　5) The seals at the oil gauge or drain valve, etc., are not tight. 　　　　6) The welding quality of oil pipes at the fuel tank station is poor. 3. What are the common methods used to determine whether equipment is overheating during operation? 　　Answer: 1) Temperature-indicating wax strip monitoring method ； 　　　　2) Hot air current observation method ； 　　　　3) Method for observing changes in colored paint ； 　　　　4) Observe the melting of frost and snow ； 　　　　5) Observe local drying and vapor conditions in the rain ； 　　　　6) Using the wax rod charging test method ； 　　　　7) The method of live monitoring using a temperature detector. 4. What are the common faults of isolating switches and what are their causes? 　　Answer: 1) The contact part is overheating. There are various reasons for overheating; primarily, it is caused by a decrease in the elasticity of the compression spring or by loose bolts on that spring. Secondly, surface oxidation at the contact areas increases resistance, leading to higher temperatures. These high temperatures in turn accelerate oxidation, and this cycle can result in accidents. 　　　　2) The porcelain vase is damaged. Excessive force was applied when operating the isolating switch, or the connection between the isolating switch and the busbar was poor, resulting in the breakage of the porcelain insulator. 　　　　3) The isolation mechanism lacks flexibility in handling separations and reunions. Rust on the operating mechanism of the isolating switch or on the rotating parts of the switch itself can cause problems with its opening and closing functions. If it is winter, then freezing must be taken into account. Severe overheating of the knife switch and the static contact can also cause them to weld together, leading to failure. 5. What are the two methods for determining the dimensions of hard busbar down conductors? Answer: (1) The method of using a suspension line to measure the dimensions and then marking out a sample. 　　(2) Construction method for making prototypes. 6. How to straighten rigid busbars? Answer: The specific methods are as follows: (1) Straighten them on a platform, which can be made of flat materials such as channel steel or rails ； (2) The plane and sides of the busbar should be straightened, which can be done by hitting it with a wooden hammer ； (3) Tools with a hardness greater than that of the aluminum strip, such as hammers, must not be used. 7. Are there any regulations regarding the direction in which bolts of various fittings on insulator strings, conductors, and lightning arresters should be inserted? Answer: (1) Those in a vertical direction must always be inserted from top to bottom. (2) For those in the horizontal direction, pass through on the power-receiving side along the line ； The outer wires on either side of the horizontal conductor pass from the outside toward the inside of the conductor, while the middle phase wire passes from left to right (facing the power-receiving side). For split conductors, they all pass from the outside of the bundle toward the inside of the bundle. (3) Split pins, blind pins; those in the vertical direction pass downward. 8. How to install a gas relay? Answer: (1) Check whether the gas relay is qualified. (2) It should be installed horizontally, with the arrow indicated on the top cover pointing toward the oil reservoir. (3) The pipeline axis of the relay is allowed to be slightly higher at the end facing the oil reservoir, but the inclination from the horizontal plane shall not exceed 4%. (4) The gaskets of each flange must be installed properly. (5) The oil pipeline diameter must not be blocked. 9. Describe the method of manually mixing concrete. Answer: The method of manual mixing is as follows: (1) First, pour the sand on one side of the mixing board, then add the cement on top of the sand and stir it 2-3 times. (2) Mix the sand and cement thoroughly before adding water, then continue mixing 2–3 more times. (3) After mixing evenly, add the stones and stir thoroughly several more times until the stones and mortar are fully combined and the consistency is appropriate. 10. What are the basic requirements when installing strain clamps at both ends of the flexible busbar? Answer: (1) Before disconnecting the wire, wrap 3–4 turns of binding wire around the end of the wire to be disconnected to prevent it from breaking. (2) The position of the wire hanging point should be aligned with the center of the large pin hole in the strain clamp; remember this position when winding the tape. The tape wrapped around the wire should have ends long enough to allow 50 mm of the clamp’s ends to be exposed. The winding direction of the wrapping tape should be consistent with the twist direction of the outer strands of the wire. (3) When selecting a wire clamp, the thickness of the insulation tape should be taken into consideration. The boat-shaped clamping plate of the wire clamp should be kept flat; after the “U”-shaped bolts are tightened, 3–5 threads of the bolt should be visible. (4) When the busbar is short, the suspension holes of the clamps at both ends should be on the same side when the conductor is not under stress. 11. What are the requirements for lifting an isolating switch? Answer: (1) Lift the assembled single-pole isolating switch onto the foundation channel steel. (2) After leveling and aligning it, fix it in place with bolts. (3) The horizontal error of the base should be less than 1%. (4) The switch has a high center of gravity, so measures should be taken to prevent it from tipping over during lifting. 12. Describe the maintenance tasks and technical requirements for isolating switches. Answer: (1) Check whether the insulators of the isolating switch are intact, and whether there is any corona or discharge. Clean the insulators and check the condition of the cement-based connections; any issues found should be addressed or the components replaced promptly. Use a megohmmeter to measure the insulation resistance of the insulators. (2) Check the drive rods and various components of the mechanism for any signs of damage, rust, looseness, or detachment. Regularly inspect the lubrication condition; clean it as necessary and apply lubricant. Remove rust from the base, paint it, and ensure proper grounding. (3) Check whether the contacts are in good contact, whether the compression spring exerts sufficient pressure, and clean the dirt and burn marks on the contact surfaces. Those contact fingers that are severely burned should be replaced; the conductive copper strands must not have any broken or fractured sections. Contact finger springs with insufficient elasticity should also be replaced. A neutral vaseline or conductive silicone grease should be applied to the contact surfaces to reduce oxidation of the contacts. (4) Re-measure the relevant technical parameters of the switch in accordance with the manufacturer’s technical specifications, such as contact insertion depth, synchronization degree, and the opening angle of the spare travel; if they do not meet the requirements, adjustments should be made. 13. What are the requirements for installing lightning arresters? Answer: (1) First, fix the base of the lightning arrester, and then install each unit (section) of the lightning arrester from bottom to top. (2) The arrester has undergone assembly testing and passed it before leaving the factory; it should be assembled at the installation site strictly in accordance with the manufacturer’s specifications, and components cannot be interchanged to avoid changes in its characteristics. (3) For valve arresters with series and parallel resistors, proper selection should be made during installation so that the nonlinear coefficients of the units in the same phase are as similar as possible, with the difference between them not exceeding 0.04. (4) The contact surface of the arrester should be wiped clean to remove oxide films and paint, and a layer of electrical composite grease should be applied. (5) The arrester should be installed vertically, with a verticality deviation of no more than 2%; if necessary, metal sheets can be placed between the flange surfaces to correct this deviation. The centers of the three phases should be on the same line, the nameplates should be located on the same side for easy viewing, the voltage equalizing rings should be installed horizontally, and finally, the gaps should be filled with putty and painted. (6) Tighten the insulator strings to secure them; the tension in each string of the same phase should be even, to prevent the arrester from experiencing additional tensile stress. (7) The discharge counter should be well-sealed, operate reliably, have its three-phase installation positions aligned for easy observation. The grounding is reliable, and the counter indicator returns to zero. (8) The venting passage of the zinc oxide arrester should be unobstructed; during installation, care should be taken to prevent the gases emitted from it from causing inter-phase short circuits or ground flashovers, and these gases must not be directed at other equipment. 14. Explain the steps for vacuum oil filling. Answer: When the vacuum level inside the container reaches the specified value, insulating oil can be slowly injected from below the oil tank through the throttle, without having to relieve the vacuum; the temperature of the oil should be higher than that of the container itself. For voltage levels of 220 kV and above, the oiling time should not be less than 6 hours; for 110 kV, it should not be less than 4 hours. After oiling, the vacuum condition should be maintained for another 4 hours, until all air inside the tank has been completely removed, before the vacuum can be lifted. 15. What issues should be considered when installing a trolley-type high-voltage circuit breaker cabinet? Answer: (1) The ground level should be appropriate to enable the trolley to move smoothly from the ground to the cabinet. (2) The moving contacts of each trolley should be adjusted to be consistent; the moving and fixed contacts should lie on the same center line. The contacts should make firm contact after being inserted, and the insertion depth should meet the requirements. (3) The secondary wiring is correctly and reliably connected with good contact. (4) The electrical or mechanical locking device should be adjusted to be correct and reliable. (5) The relay on the door should have a vibration damping ring. (6) The control cables inside the cabinet should be firmly fixed, without hindering the entry and exit of the trolley. (7) The grounding contacts of the trolley must make good contact, and the voltage transformer serta the grounding points at the bottom of the trolley must be reliably grounded. 16. What are the common faults of busbars? Answer: (1) Poor contact at the joints increases resistance, leading to severe heating that causes the joints to turn red. (2) Poor insulation of the support insulators reduces the insulation resistance of the busbar to ground. (3) When large fault currents pass through the busbar, the electrodynamic forces and arc light cause the busbar to bend, break, or get burned. 17. What are the reasons for flashover discharge in insulators? How should it be dealt with? Answer: The reasons are: (1) Dirt accumulates on the surface of the insulator and inside its porcelain skirt; when moisture is present, the voltage resistance decreases. A discharge path is formed on the surface of the insulator, which increases the leakage current. When this current reaches a certain level, surface breakdown discharge occurs. (2) Even if the dirt on the insulator surface is minimal, certain overvoltages occurring in the power system can cause flashover discharge on the insulator surface due to the effect of these overvoltages. The handling method is as follows: after flashover discharge occurs in an insulator, its surface insulation performance deteriorates significantly; it should be replaced immediately, and the insulators that have not experienced flashover discharge should be cleaned. 18. What are the reasons for heating of the contacts of an isolator? Answer: (1) Overloading of the isolator or poor fit between the contact surfaces reduces the cross-sectional area of the current path, thereby increasing the contact resistance. (2) Oxidation occurs at the contact surface during operation, increasing the contact resistance. Therefore, when current flows through, the contact temperature exceeds the allowable value, and there is even a possibility of it turning red, melting, or even welding together. Under normal conditions, the maximum allowable temperature of the contacts is 75°C; therefore, the contact resistance should be adjusted so that it does not exceed 200μΩ. 19. What components are included in the conductive circuit of the SNl0-10Ⅱ type circuit breaker? What should be the resistance of this circuit after major maintenance? If it does not meet the requirements, which parts need to be addressed? Answer: The conductive circuit includes elements ranging from the lower terminal block, conductive bars, conductive rods, rolling contacts, moving contacts, static contact fingers, static contact blocks, and static contact frames to the upper terminal block. The lower terminal block is fixed in planar contact with the conductive bar by bolts; the rolling contact makes contact with the conductive bar and the conductive rod under the action of a compression spring, while the contact fingers make contact with the moving contact of the conductive rod and the static terminal block under the action of spring plates. The static terminal block is in fixed contact with the contact frame via bolts, and the upper terminal block is in planar contact with the contact frame. 　　After major repairs, the loop resistance should be less than 60μΩ. 　　In the case of non-conformity, it is necessary to check whether the degree of burn on the aforementioned parts meets the requirements, whether the contact is good, especially whether the connection between the upper terminal block and the contact holder is tight; whether there is any deformation or damage to the spring elements installed in the static contact holder; and whether the properties of the spring used for the rolling contacts meet the specified standards. 20. What should be noted when topping up oil in an operating transformer? Answer: (1) The oil to be injected must be qualified oil to prevent mixing of oils. (2) Before adding oil, switch the heavy gas protection to the signal position to prevent accidental tripping. (3) After adding oil, check the gas relay, release air promptly, and then resume normal operation. 21. What electrical testing tasks should substation maintenance workers be able to carry out on their own? Answer: (1) Testing of insulation resistance ； (2) Testing of contact resistance ； (3) Testing of DC resistance ； (4) Motion characteristic test. 22. What are the main factors that affect the contact resistance of conductive connector joints? Answer: The main factors affecting contact resistance include the following: (1) Whether the structure of the joint is reasonable during installation. (2) Is the electrical conductivity of the material good? ； Is the contact performance good? (Manufactured strictly in accordance with the process.) (3) Factors that affect contact resistance include whether the materials used and the contact pressure are appropriate, as well as the degree of oxidation at the contact surface. To prevent the joints from overheating, the impacts of the aforementioned factors should be minimized as much as possible in design and construction. 23. What are the main criteria for adjusting isolating switches? Answer: The main criteria for adjusting isolating switches are as follows: (1) The phase difference among the three phases (i.e., the maximum distance between the blades and the static contacts in an isolating switch with three interconnected poles). The smaller the difference between different periods, the better; this is beneficial for arc extinguishing and reducing mechanical damage when low currents are applied or removed. When the difference is large, it can be resolved by adjusting the depth to which the screw on the insulator of the pull rod is turned, as well as the tightness of the nut on the switch (if the gap of the disconnector was adjusted properly during installation, simply turn the screw 1–2 turns tighter or looser). The adjustment must be carried out carefully and repeatedly. (2) An appropriate residual gap should be maintained after closing (referring to the minimum distance between the bottom surface of the switch blade and the bottom of the static contact). 24. What are the main requirements for installing capacitors? Answer: The requirements for installing capacitors are as follows: (1) When capacitors are installed in layers, there should generally be no more than three layers, and no partitions should be placed between them. The vertical distance between the capacitor busbars and the upper structure should be no less than 20 cm, while the distance from the bottom of the lower capacitors to the ground should be greater than 30 cm. (2) The horizontal distance between capacitor frames should not be less than 0.5 m. The distance between each capacitor should not be less than 50 mm. The capacitor’s nameplate should face the aisle. (3) For capacitors that require grounding, their enclosures shall be grounded together with the metal frame. (4) A thermometer or temperature-indicating wax strip should be installed at an appropriate location on the capacitor to monitor its operating temperature. (5) Capacitor banks shall be equipped with fault protection devices or fuses for inter-phase faults and faults within the capacitor elements. For high-voltage capacitor banks with a capacity of 600 kW or more, differential protection or zero-sequence protection may be installed; alternatively, dedicated fuses can be used for protection on a per-unit basis. (6) The capacitor should be equipped with qualified discharge equipment. (7) Capacitors installed outdoors should be mounted on a platform as much as possible, with the bottom of the platform being at least 3 meters above the ground ； Capacitor banks installed outdoors on the ground should be placed on the concrete surface inside the enclosure of the substation, with the bottom being at a distance of not less than 0.4 m from the ground. At the same time, the capacitor bank should be installed within a fixed enclosure at a height of not less than 1.7 m, with measures in place to prevent small animals from entering. 25. What are the requirements for fixing rectangular busbars on insulators? Answer: The clamps used to fix busbars on insulators are usually made of steel, and they should not form a closed magnetic circuit. If a closed magnetic circuit is formed, a large induced circulating current will be generated in the loop formed by the clamps and bolts, causing the busbars to overheat; this situation is more severe in busbars with high operating currents. 　　To prevent the formation of a closed magnetic circuit, when both clamps are made of iron, one of the fastening bolts should be made of iron and the other of copper. Alternatively, the busbars can be secured using open-type clamps; the two clamps can be one made of iron and the other of aluminum, with both fastening bolts being made of iron. 26. What are the uses of the auxiliary contacts of a circuit breaker? Answer: The circuit breaker uses its own normally open and normally closed contacts, whose positions can be changed, to connect the circuits that control the closing and tripping of the circuit breaker as well as the sound signal circuits. This enables the circuit breaker to open or close circuits, and it also allows for the proper generation of sound signals, as well as the activation of automatic devices and protection interlock circuits. When the auxiliary contacts of a circuit breaker are used in the closing and tripping circuits, they should all have a delay. 27. How to inspect circuit breakers? Answer: (1) Review the commissioning records of the circuit breakers. (2) Inspect the appearance of the circuit breaker, including the oil level and sealing condition; the porcelain parts and grounding system should be in good condition, with no oil leakage in any part. (3) The secondary wiring connections of the equipment should be tight, properly wired, and have good insulation ； The contactor has no sticking and maintains good contact ； The opening distance of the auxiliary circuit breaker is appropriate, and there are no issues with its operating contacts. (4) The hydraulic mechanism should show no oil leakage; all pipeline connections must be tight, all micro-circuit breakers should operate properly without any issues, and the pre-charge pressure must meet the standards. (5) Manual closing is smooth with no resistance, electric opening and closing operate correctly, and the protection indicator lights show the proper signals. (6) Record the problems and defects identified during acceptance, and report them to the relevant departments. 28. How to maintain the opening valve of the hydraulic mechanism (CY3 type)? Answer: (1) After disassembling the opening valve, check the sealing condition between the ball valve and the valve port; the steel ball should be free of any scratches or rust, and the width of the valve seat’s sealing surface should not exceed 0.5 mm. Also, check whether the sealing rings are damaged. Block the ball valve at the valve opening and use a mouth to suck air; if the steel ball can be drawn out, it is qualified ； When it cannot be pulled out, it can be ground with emery sand, or the ball valve can be placed over the valve opening and pressed with a copper rod. (2) Check the return spring for any deformation and to ensure its elasticity is normal; if the elasticity has decreased, it can be replaced. (3) After all inspections show no issues, rinse the valve body, valve seat, and all components with hydraulic oil, and finally assemble them in the reverse order of disassembly. 29. What aspects should be checked after disassembling the pressure reservoir of the CY4-type mechanism? Answer: (1) Check whether there are any scratches, deformations, or rust on the inner wall of the cylinder and the surface of the piston. Minor scratches and rust can be polished using 800-grit sandpaper; those with severe deformation, scratches, or rust should be replaced. (2) Check whether the piston rod is bent, whether its surface is smooth, and whether there is any wear or rust. (3) Check whether the connection plate is deformed. 30. What are the general factors that affect the tripping time of a circuit breaker (electromagnetic mechanism)? Answer: (1) The travel distance of the tripping core ； (2) Condition of the connecting plates in various parts of the breaking mechanism ； (3) Depth of engagement of the disconnection latch with the operator ； (4) Condition of the opening spring ； (5) Conditions of the transmission mechanism, spindle, intermediate static contact mechanism, etc. 31. What should be done if the arc-quenching plates of the SW6-220/110 type circuit breaker become damp? Answer: (1) They can be dried; they should be cleaned thoroughly before drying ； (2) The drying temperature is 80–90℃ ； (3) The heating time shall be no less than 12 hours ； (4) The drying time is 48 hours ； (5) Place it in qualified insulating oil immediately after removal to prevent further moisture absorption ； (6) A voltage withstand test is also required; it can be used only after passing the test. 32. What should be done if the opening and closing speeds of the SNl0 type circuit breaker do not meet the requirements? Answer: (1) If the opening speed is within the acceptable range but at the lower limit, while the closing speed is not satisfactory, it is necessary to check the terminal voltage of the closing coil, whether there is any jamming in the circuit breaker’s mechanism, and whether the DC resistance of the coil is within the specified limits. The issues identified should be addressed promptly. (2) If the opening speed is within the acceptable range and at the upper limit, but the closing speed is not acceptable, the pre-stretch length of the opening spring can be adjusted to make it meet the requirements. (3) If the opening speed is not up to standard, the length of the opening spring can be adjusted to meet the requirement. 33. Describe the items that need to be adjusted and measured after major overhauls of SW2-220Ⅰ and Ⅱ type circuit breakers. Answer: (1) Adjustment and measurement of the total travel distance of the moving contact ； (2) Adjustment and measurement of the moving contact overtravel ； (3) Adjustment and measurement of opening and closing speeds ； (4) Measurement and adjustment of action time ； (5) Measurement of contact resistance in the conductive circuit ； (6) Adjustment of the locking spring. 34. What are the regulations regarding the length of the bent portion when a rectangular busbar is bent horizontally, vertically, or torsionally by 90° each? Answer: (1) When the busbar is bent flat by 900 degrees: for busbars with a specification of 50mmX5mm or less, the bending radius must not be less than 2.5h (where h is the thickness of the busbar) ； For busbars with a specification of 60mm×5mm or larger, the bending radius must not be less than 1.5h. (2) When the busbar is bent vertically at 90°: for busbars with a dimension of 50mm X 5mm or less, the bending radius R must not be less than 1.5b (where b is the width of the busbar) ； For busbars larger than 60mmX5mm, the bending radius must not be less than 2b. (3) When the busbar is twisted (bent) by 90°: the length of the twisted portion should be greater than 2.5 times the width (b) of the busbar. 35. What are the precautions for the operation and maintenance of ZN28-10 type circuit breakers? Answer: (1) Circuit breakers in normal operation should be maintained regularly; dust on the surface of insulating components should be cleaned, and lubricant should be applied to the parts that undergo frictional movement. (2) Periodically, or when a total of 2,000 operations have been performed, check whether the screws in various parts are loose, and take action if necessary. (3) Regularly inspect the closing contactor and auxiliary switch contacts; if they are severely damaged, they should be repaired or replaced promptly. (4) When replacing the arc chamber, it shall not be subjected to bending moment after the fasteners are tightened; the main and secondary parts shall experience significant tensile stress and transverse stress, and the bending deformation of the arc chamber shall not exceed 0.5 mm. After the upper bracket is installed, it must not press down on the arc chamber guide sleeve; a gap of 0.5 to 1.5 mm should be left between them. 36. Describe the steps for disassembling and overhauling the working cylinder of the SW6 type circuit breaker. Answer: (1) Remove the screws used to connect the working cylinder to the mechanism, take off the working cylinder, and place it on a vise; insert protective pads between the jaws of the vise before clamping it. (2) Use a special tool to unscrew the gland sleeve in order to loosen the seal ring. (3) Use a large pipe wrench to unscrew the cylinder head, pull out the piston, and remove the brass washer and sealing ring. (4) Clean the cylinder block and various components with hydraulic oil. (5) Check the inner wall of the cylinder and the surface of the piston rod for any signs of scoring or wear. If there is slight wear, it should be treated with 800-grit emery paper. (6) Check the piston cylinder and cylinder head for any scratches; if any are present, treat them with an oil stone or 800-grit emery paper, and use an oil stone to smooth out the sharp corners at both ends of the piston cylinder. (7) Assembly should be carried out in a clean room to prevent dust from entering the cylinder block. During assembly, all seals must be replaced, and the groove of the bowl-shaped seal should face the inside of the working cylinder. (8) After assembling all the components, manually pull the piston rod to check whether the piston is stuck, and also check the stroke of the cylinder. 37. How to lift the pillar of the LW6-220 type circuit breaker? Answer: It should be lifted in accordance with the following steps and requirements: (1) Use lifting equipment to lift the pillar so that it is in a horizontal position, and attach the two legs to the lower base of the pillar. (2) Lower the pillar so that the two legs attached to it come into contact with the ground; use special wooden blocks to support the flange between the two ceramic sleeves. Then, use a crane to lift the third leg and attach it to the base at the bottom of the pillar. (3) When installing the three connecting plates between the support legs, the smaller one should be placed on the side of the density relay; do not tighten the screws yet. (4) Slowly lift the pillar from a horizontal position to an upright position using a crane (by utilizing the lifting ring on the upper flange of the pillar). (5) Install the pillar on the foundation and tighten all screws in sequence. (6) After the pillar is lifted, it should be well vertical. 38. What is the difference between electromotive force and voltage? How are their directions defined? Answer: Electromotive force is a concept that reflects the work done by an external force to overcome the electric field force, whereas voltage is a concept that reflects the work done by the electric field force. The positive direction of electromotive force is the direction of potential increase, while the direction of voltage is the direction of potential decrease. 39. What is the temperature coefficient of resistance? What is the relationship between a conductor’s resistance and temperature? Answer: The ratio of the increase in a conductor’s resistance for every 1°C rise in temperature to its original resistance is called the temperature coefficient of resistance. Its unit is per degree, and its calculation formula is α = (R2 – R1) / R1 × (t2 – t1). Here, R1 is the resistance value at temperature t1, in ohms ； R2--resistance value at temperature t2, Ω. 40. What is the skin effect? What are its applications? Answer: When an alternating current flows through a conductor, the current tends to flow along the surface of the conductor; this phenomenon is known as the skin effect. To make effective use of conductor materials and facilitate heat dissipation, high-current busbars are often designed in a grooved or diamond shape. Additionally, in high-voltage transmission and distribution lines, steel core stranded wires are used in place of aluminum stranded wires, which not only saves aluminum conductors but also enhances the mechanical strength of the wires.