1. How are the protection ranges of each stage of zero-sequence current protection divided?
Zero-sequence current stage I avoids the maximum zero-sequence current setting of the protection during a short-circuit ground fault at the end of the line; it cannot protect the entire length of the line, but should not be less than 15% to 20% of the total length of the protected line; zero-sequence current stage II generally protects the entire length of the line and extends to the range of stage I of adjacent lines, and coordinates with them. Zero-sequence current stage III is a backup stage for stages I and II, and coordinates with adjacent lines.
2. What are the causes of abnormal noises during the operation of an electric motor?
A: Electrical aspects: (1) Winding grounding or phase-to-phase short circuit; (2) Winding turn-to-turn short circuit; (3) Incorrect polarity connection of winding or part of the coil; (4) Phase loss operation. Mechanical aspects: (1) Fan blades touching the end cover; (2) Severe bearing wear or ball bearing damage; (3) Weak contact between the inner ring of the bearing and the shaft; (4) Stator rubbing.
3. What should I do if the three-phase asynchronous motor fails to start after the power is turned on?
Answer: (1) Use a test pen to check if the power supply is working; (2) Check if the power switch is working properly; (3) Check the motor fuse; (4) Check the connectors on the motor terminal block; (5) Check if the motor is open-circuited; (6) Check if there is a short circuit in the stator and rotor windings.
4. What if the motor cannot be started using the direct starting method?
Answer: (1) Star-delta starter; (2) Autotransformer starter; (3) Resistor and reactance reduced voltage starter.
5. Which electrical devices must be grounded or connected to neutral for protection?
A: 1) Generators, transformers, high and low voltage electrical appliances; 2) Power equipment transmission devices; 3) Instrument transformer secondary coils; 4) Frames of distribution panels and control panels.
6. What is ground fault current? What is voltage to ground?
A: When a phase of an electrical device is grounded, the potential difference between the grounded part and the point where the maximum potential is zero; when a ground short circuit occurs, the short circuit current flows into the ground through the connection point.
7. What should be done if an disconnecting switch is operated incorrectly?
(1) When the disconnecting switch is pulled in the wrong direction, an arc will occur as soon as the switch leaves the stationary contact. If it is pulled in the wrong direction, the switch should be closed immediately to extinguish the arc and avoid an accident. If the switch has been fully opened, the switch that was pulled in the wrong direction should not be closed again.
(2) If the disconnecting switch is opened incorrectly, even if it is closed incorrectly, or even if an arc occurs when closing, it is not allowed to be opened again, because the disconnecting switch under load will cause a three-phase arc short circuit.
8. What is the purpose of a reversing switch?
A: It is mainly used to control small-capacity electric motors to start in both forward and reverse directions under full voltage.
9. What is the function of repeated grounding?
A: 1) Reduce the voltage to ground on the casing of the leaking equipment; 2) Reduce the danger of a broken neutral wire.
10. What should private companies check when the transformer differential protection is put into operation under no-load conditions?
For differential protection of transformers, five no-load tests must be performed on the transformer at rated voltage during new installation. Before no-load energization, the secondary wiring should be checked to ensure it is correct. The no-load energization test should be performed on both the high-voltage and low-voltage sides of the transformer. This is because the system impedance and the transformer's leakage reactance limit the inrush current. The system impedance on the high-voltage side is low, and the low-voltage winding of the transformer is generally inside, resulting in a smaller leakage reactance. Therefore, the inrush current is larger when energizing the high-voltage and low-voltage sides. During the test, the protection device should not trip even once; otherwise, the relay operating current should be increased. 11. What are the different types of overheating in electrical equipment?
A: The main causes are the heat generated by the current, including the following: (1) short circuit; (2) overload; (3) poor contact; (4) core heating; (5) poor heat dissipation.
12. What is the load factor? How can the load factor be improved?
A: The load factor is the percentage of the average active load to the peak active load over a certain period of time. It is used to measure the difference between the average load and the peak load. To improve the load factor, the main approach is to reduce peak load and increase average load.
13. What is protective grounding? What is repeated grounding?
A: In a power distribution system where the neutral point of the low-voltage side of the transformer is grounded, one or more points on the neutral wire are connected to the earth through a grounding device; the metal casing of normally non-energized electrical equipment is connected to the earth through a grounding electrode.
14. What is R, L, C parallel resonance? Answer: In a circuit where a resistor, inductor, and capacitor are connected in parallel, under the action of a sinusoidal power supply of a certain frequency, the circuit terminal voltage and the total current are in phase, and the entire circuit exhibits a special state of resistivity. This state is called parallel resonance.
15. What is a ground fault?
A: When live parts of electrical equipment and power lines in operation come into contact with grounded metal components or become directly connected to the ground due to insulation damage, it is called a grounding short circuit.
16. What is the utilization rate of a transformer?
A: The ratio of the actual output power of a transformer to its rated output power.
17. How do you determine the four basic states of electrical equipment?
A: 1) In the "running" state, the circuit breaker and disconnector are closed, and the power supply is connected to the equipment.
2) "Hot Standby" status: The circuit breaker is open, power is interrupted, and the equipment is shut down, but the disconnecting switches on both sides of the circuit breaker remain closed. 3) "Cold Standby" status: The equipment circuit breaker and disconnecting switches are open. 4) "Under Maintenance" status: The equipment circuit breaker and disconnecting switches are open, and a sign has been hung; there are no barriers, and the grounding wire is connected.
18. How to improve the power factor?
A: Use natural adjustment: (1) Minimize the floating capacity of transformers and motors;
(2) Improve equipment utilization and reduce no-load operation; (3) Change the delta-connected motor to a star-connected motor, manually adjust it, and install a capacitor. This is the most economical and effective method.
19. How to choose the wiring method for a capacitor bank?
A: The selection should be based on the capacitor's voltage, protection method, and capacity. When the capacitor's rated voltage matches the network's rated voltage, a delta connection is used; when the capacitor's rated voltage is lower than the network's rated voltage, a star connection is used.
20. What is overcurrent protection?
A: When a short circuit occurs on a line, its key characteristic is a sharp increase in the current in the line. When the current exceeds a certain predetermined value, the protection device will activate the current switch.
21. What are the components of a secondary circuit?
A: I. According to the nature of the power supply: (1) AC current circuits are all circuits powered by the secondary side of the current transformer. (2) AC voltage circuits are all circuits powered by the secondary side of the voltage transformer, the three-phase five-limb voltage transformer, and the open delta of the transformer.
(3) DC circuit, all circuits of a DC system;
II. Classification by circuit purpose:
(1) Measurement circuit (2) Relay protection circuit
22. What is a capacitor?
A: A capacitor, also known as a capacitive device, is a static electrical device that can store electrical charge. When the charge is released, an electric current is generated, making it an energy storage device.
23. What are electric charge, current, voltage, resistance, circuit, and electric power?
A: Electric charge – The amount of electric charge carried by an object is called electric charge, and its unit is coulomb. Current – The directed movement of electric charge in a conductor forms an electric current, and its unit is ampere. The amount of electricity passing through the cross-sectional area of a conductor in one second is 1 coulomb, and its current intensity is 1 ampere. Voltage – The potential difference between two points in a circuit is called voltage, and its unit is volt. Resistance – The opposition that current encounters in a conductor is called resistance. Its unit is ohm.
A circuit is the path through which electric current flows. A circuit consists of four basic parts: voltage, electrical components, switches, and connecting wires.
A power source is a device that generates electrical energy;
Electrical appliances include light bulbs, electric fans, etc.; connecting wires are used to connect power sources, electrical appliances, and switches, and must be connected to form a circulating circuit. Electrical power—indicates how much work is done by electricity per unit time, abbreviated as power, and the unit is watt. One kilowatt of electrical energy consumed in one hour is called "1 kilowatt-hour".
24. What is an electric motor?
A: An electric motor is an electrical device that converts electrical energy into mechanical energy and outputs that mechanical energy. The most common type is the three-phase AC asynchronous motor. Various types of cotton spinning machinery widely use electric motors for driving.
25. What is a contactor? What is the function of a contactor?
A: A contactor is an automatic electromagnetic switch that uses electromagnetic force to close and open contacts, thus connecting and disconnecting current. Furthermore, contactors also have a low-voltage release function, making them suitable for frequent operation and distance control.
26. What is a fuse?
A: A fuse, also called a circuit breaker or fuse wire, is an effective electrical protection device that can prevent damage from short circuits.
27. What is a thermal relay?
A: Thermal relays are electrical appliances that utilize the current effect to provide overload protection.
28. What are the differences between computer-based protection and traditional relay protection?
A: The main difference is that the original protection input is current and voltage signals, which are directly compared and processed between analog quantities, comparing the analog quantity with the given resistance torque in the device. Computers, however, can only perform digital or logical operations. Therefore, it is first necessary to convert the instantaneous values of the input analog current and voltage into discrete digital quantities before sending them to the computer's central processing unit (CPU). The CPU performs calculations according to a prescribed algorithm and program, constantly comparing the calculation results with the given numbers, and finally determining whether to trip. 29. What is the post-acceleration of reclosing?
A: When a line fault occurs, the protection system operates according to its set value, the line switch opens, and the reclosing device immediately operates. If it is a transient fault, the fault disappears after the line switch opens, reclosing is successful, and power supply to the line is restored. If it is a permanent fault, after reclosing, the protection time element is deactivated, causing it to trip after 0 seconds. This means that the fault has not disappeared after the reclosing operation, accelerating the trip and clearing the fault point. 30. What is a grounding wire?
A: To prevent electric shock due to damage to electrical insulation, electrical wires are usually connected to the ground. This wire is called a protective ground wire.
31. What are the measures for safe electricity use?
A: The live wire must be connected to the switch so that the switch is in the open state and the appliance is not energized.
32. What is a low-voltage electric shock protector?
A: It is an effective protective device to prevent low-voltage electric shock. If an electric shock accident or insulation failure and leakage occurs in a low-voltage network, it will immediately issue an alarm signal or command to cut off the power supply, thus protecting people or equipment.
33. What is air gap?
A: To prevent people from getting too close to live conductors or to prevent vehicles or other objects from colliding with them and getting too close, and to prevent electrical short circuits and fires caused by them, a certain safe distance must be maintained between live conductors and the ground, between live conductors, and between equipment.
34. What is safe voltage?
A: A safe voltage is a voltage that will not cause any damage to any tissues of the human body when it comes into contact with electricity.
35. What are the dangers of unbalanced three-phase power supply?
A: Due to the three-phase voltage imbalance, a reverse-sequence rotating magnetic field will be generated on the stator of the induction motor. At this time, the induction motor will run under the action of both positive and negative magnetic fields. Since the positive-sequence rotating magnetic field is much larger than the negative-sequence magnetic field, the motor rotates in the positive-sequence direction. However, the rotor's reverse-sequence resistance is very small, so the reverse-sequence current is large. Due to the presence of the reverse-sequence current and the magnetic field, a large braking torque is generated, which will reduce the power.
36. What are the three electrical components (electricity, power, and communication)?
A: The three electricity uses refer to planned electricity use, economical electricity use, and safe electricity use.
37. Star-delta (Y-△) reduced voltage starting?
A: For motors that are delta connected when running at a rated voltage of 380V, the stator windings can be first connected in a star configuration, and then connected in a delta configuration after startup. This method is called star-delta reduced voltage starting.
38. What is the earth?
A: When an electrical equipment experiences a grounding fault, the grounding current flows into the ground through the grounding wire and grounding electrode, dissipating in a hemispherical pattern. Near the grounding electrode, the hemisphere is smaller, the resistance is higher, and the voltage drop through this area is also greater, resulting in a higher potential. Further away from the grounding electrode, the hemisphere is larger, the resistance is lower, the voltage drop is smaller, and the potential is lower. With the grounding electrode as the center, the radius of this sphere is approximately 20 meters, and its potential practically approaches zero; this is generally referred to as the earth or ground.
39. What is a grounding electrode?
A: A metal conductor or group of metal conductors that is in direct contact with the earth's soil is called a grounding electrode or grounding group.
40. What are grounding wires and grounding devices?
A: The metal conductor connecting the grounding part of electrical equipment to the grounding electrode is called a grounding wire. The grounding electrode and the grounding wire together are called a grounding system.
41. What is protective grounding?
A: Connect the non-energized metal parts of the electrical equipment to the neutral wire of the electrical grid.
42. What is the function of protective grounding?
A: The neutral point of a transformer or generator grounding system is called the zero point, and the conductor connected to the zero point is called the neutral wire. Protective grounding involves connecting the normally non-energized metal casing of electrical equipment to the neutral wire. However, in power supply systems with a directly grounded neutral point below 1000V, protective grounding is generally not used; instead, protective neutral grounding is employed.
43. What are the key points for connecting to zero?
A: When connecting to neutral, the following requirements should be met: (1) In the same system, it is strictly forbidden to ground one part of the electrical equipment and connect another part of the electrical equipment to neutral, which is extremely unsafe. (2) Switches and fuses are not allowed to be installed on the neutral wire of a three-phase four-wire system. (3) Pay attention to the quality of the neutral wire installation. In order to prevent the neutral wire from breaking, sufficient repeated grounding devices should be installed. The grounding resistance of repeated grounding should not be greater than 10 ohms. (4) All electrical equipment connected to neutral wire should be connected in parallel on the neutral wire or branch line. (5) The cross-sectional area of the neutral wire should not be less than 1/2 of the cross-sectional area of the phase wire.
44. What is a residual current device (RCD)?
A: When a single-phase ground fault occurs in an electrical line or equipment, a residual current is generated. The protective device that uses this residual current to cut off the power supply to the faulty line or equipment is called a residual current device, also known as a leakage current protection device.
45. What is the commonly used three-level protection method for leakage current protection?
A: Overcurrent, grounding, short circuit.
46. What are the causes of electrical leakage? What are the consequences of electrical leakage?
A: Causes: Insulation damage (including aging, environmental factors, mechanical factors, and toxic gases). Consequences: Induces stray currents, causing losses and increasing line losses.
47. What are the causes of leakage in lighting circuits, and what are the methods and steps for checking for leakage?
A: There are two ways for lighting circuits to leak current: one is through damage to the insulation resistance between the live wire and the neutral wire, resulting in leakage; the other is through damage to the insulation between the live wire and the ground, resulting in leakage between the live wire and the ground. The inspection steps are as follows:
(1) First, determine whether there is a leakage. Use a megohmmeter to measure the insulation resistance value, or connect an ammeter to the main switch of the building being inspected, remove all light bulbs, and turn on all light switches. If the ammeter pointer swings, it indicates that there is a leakage.
(2) Determine whether the leakage is between the live wire and the neutral wire, between the live wire and the ground, or both. Taking the connection of an ammeter as an example: disconnect the neutral wire and observe the change in current. If the ammeter reading remains unchanged, the leakage is between the live wire and the ground. If the ammeter reading is zero, the leakage is between the live wire and the neutral wire. If the ammeter reading decreases but is not zero, it indicates that the live wire is the neutral wire, and there is leakage between the live wire and the ground.
(3) Determine the leakage range. Remove the branch circuit breaker or open the knife switch. If the ammeter reading remains unchanged, it indicates that the leakage is in the main circuit. If the ammeter reading decreases but is not zero, it indicates that there is leakage in both the main circuit and the branch circuit. (4) Locate the leakage point. Check each branch circuit one by one, and find and eliminate the leakage point.
48. What are the methods of leakage current protection?
A: Total network protection refers to installing a protector at the low-voltage power source; for mobile electrical equipment, temporary electrical equipment, and household electricity use, final-level protection should be installed; for larger low-voltage power grids, multi-level protection is required. In all three protection methods, the power supply is automatically cut off after the residual current device (RCD) trips.
49. What are electrical safety devices? What are their specific contents?
A: Electrical safety equipment is categorized by function into operating equipment and protective equipment. Operating equipment includes: voltage detectors, insulating rods, and insulating pliers. Protective equipment includes: insulating gloves, insulating boots, insulating mats, insulating platforms, safety barriers, and safety equipment for working at heights.
50. What are the dangers of static electricity?
A: Explosions and fires, electric shocks, and disruptions to production.
51. What measures should be taken when dismantling secondary wiring?
A: When dismantling secondary wiring, a record must be made; upon restoration, it should be cancelled in the logbook. If there are multiple alterations to the secondary wiring, a tag should be attached to each wire end. When dismantling or laying secondary cables, tags should also be attached to the beginning and end of the cable, as well as at bends and intersections along the route. 52. What is a short circuit? What are the consequences of a short circuit?
A: A short circuit occurs when two power lines come into direct contact or touch without passing through a load. A short circuit can cause electrical equipment to overheat, potentially burning it out and causing a fire. The short circuit current also generates a large electrodynamic force, which can damage electrical equipment. Severe short circuits can disrupt system stability and waste electrical energy.
53. How are safe voltage values defined?
A: In my country, the safe voltage values are specified as follows, depending on the specific environmental conditions: 65 volts in buildings with no high risk of electric shock; 36 volts in buildings with a moderate risk of electric shock; and 12 volts in buildings with a particularly high risk of electric shock.
54. What are the safety requirements for grounding and neutral connection? Answer: (1) Continuity of electrical conductivity; (2) Reliable connection; (3) Sufficient mechanical strength;
(4) Sufficient electrical conductivity and thermal stability;
(5) The neutral wire must be grounded repeatedly;
(6) Prevent corrosion; (7) Prevent mechanical damage; (8) The underground installation distance must meet relevant requirements;
(9) The grounding wire and the neutral wire cannot be connected in series.
55. What are the components of ensuring the normal operation of a transformer?
A: This includes observing whether the current, voltage, power factor, oil level, oil color, temperature indication, and contact status are normal; observing whether the equipment and wiring are damaged or severely dirty; observing whether auxiliary facilities such as doors, windows, and fences are intact; listening to whether the sounds are normal, paying attention to whether there are any discharge sounds; and smelling whether there is any burning smell or other abnormal odors.
56. What is screen protection?
A: Shielding is the use of shielding devices to control unsafe factors, that is, using barriers, covers, shields, gates, etc. to isolate live parts from the outside world.
57. What is the main function of transformer oil? What is the function of an automatic air circuit breaker?
A: The main functions of transformer oil are cooling and insulation; automatic air circuit breakers, also known as automatic switches, are important devices for switching circuits in low-voltage distribution networks, and have overcurrent time-limit protection, short-circuit instantaneous protection, and undervoltage protection functions.
58. What are the advantages of using negative-sequence, zero-sequence incremental elements as the starting element for distance protection?
Answer: (1) High sensitivity; (2) Visible starting element for oscillation blocking device; (3) Will not malfunction when the secondary voltage circuit is disconnected; (4) The appearance of symmetrical components is independent of the phase of the fault, so the starting element can be a single relay, which is relatively simple.
59. What are the main types of high-voltage electrical equipment?
A: High-voltage electrical equipment mainly includes high-voltage fuses, high-voltage disconnect switches, high-voltage load switches, high-voltage circuit breakers, high-voltage switchgear, and power transformers.
60. What are the components of a circuit?
A: A circuit is the path through which current flows. It consists of a power source, a load, control and protection devices, and wires.
61. What is Ohm's Law? What is alternating current (AC)?
A: The current through a resistive element is directly proportional to the voltage across the resistor and inversely proportional to the resistance, i.e., I=U/R; Alternating current refers to an electromotive force whose magnitude and direction change periodically with time.
62. Under what conditions can a protective device be classified as a Class I equipment?
A: All protection devices of Class I equipment are in good technical condition, their performance fully meets the requirements for safe operation of the system, and meet the following main conditions: (1) There are no defects in the protection panel, relays, components, auxiliary equipment and secondary circuits. (2) The principle, wiring and setting of the device are correct and comply with the relevant regulations, rules and anti-accident measures. (3) The drawings and data are complete and in line with reality. (4) The operating conditions are good.
63. What is the operating principle of an asynchronous motor?
A: An asynchronous motor works using a magnetic field. When three-phase alternating current is applied to the stator winding of the motor, the magnetic field generated by the constant change of the three-phase current in the stator winding rotates continuously in space. As the rotor conductors cut the magnetic lines of force during the rotation of the magnetic field, and since the two ends of all the rotor conductors are connected by two copper rings, they form a closed loop. Therefore, a rotor current is generated. This current is subjected to electromagnetic force in the rotating magnetic field, which creates an electromagnetic torque on the shaft, causing the rotor to rotate in the direction of the rotating magnetic field.
64. What are some commonly used wireless insulating materials? What are some commonly used organic insulating materials?
A: Mica, porcelain, asbestos, marble, glass, etc. Rubber, resin, quartz sand, silk, etc.
65. What are the inspection items and contents for control switches?
Answer: (1) The outer casing is clean, free of oil stains, and intact. (2) The installation should be firm and not move during operation. (3) The sealing cover should be well sealed. (4) All wiring connections should be firm, not loose, and free of rust. (5) It should rotate flexibly, be in the correct position, and have good contact. (6) Open the sealing cover and check with a flashlight. The inside should be clean, the lubricating grease should not be dry, and the contact points should not be burned. Test the contact piece with an insulating rod; the pressure should be good.
66. What is the importance of the live wire going to the switch?
A: When installing lighting circuits, the light switch must control the live wire. This ensures that the lamp holder is not energized when the switch is off, preventing electric shock when replacing bulbs or repairing lamp holders.
67. What are the reasons for severe overheating of the electric motor?
Answer: (1) The power grid voltage is too low or too high, the driven machinery is stuck or poorly lubricated; (2) The motor is poorly ventilated, and the fan cover is blocked by clothes and debris; (3) The rotor bar is broken; (4) Frequent forward and reverse rotation or too many starts;
(5) Stator and rotor rub against each other; (6) Stator winding has a small-range short circuit or stator winding has a local grounding.
68. What are some commonly used insulating tools?
A: We have insulating rods, insulating pliers, rubber insulating gloves and insulating boots, rubber blankets and insulating platforms.
69. What are the characteristics of a diode?
A: The characteristic of a diode is unidirectional conduction.
70. What are some common lightning protection devices?
A: Lightning rod, lightning wire, lightning protection network, lightning protection strip, lightning arrester.
71. What are the different insulation classes of electric motors? What are their respective temperature ratings?
A: Insulation classes are classified as: A, E, B, F, and H. Class A has a permissible maximum temperature of 105℃ with a temperature rise of 60℃; Class E has a permissible maximum temperature of 120℃ with a temperature rise of 75℃; Class B has a permissible maximum temperature of 130℃ with a temperature rise of 80℃; Class F has a permissible maximum temperature of 155℃ with a temperature rise of 100℃; and Class H has a permissible maximum temperature of 180℃ with a temperature rise of 125℃.
72. What are the components of a handheld power tool?
A: It consists of a drive section, a transmission section, and insulation and mechanical protection sections.
73. What are the different types of lighting methods?
Answer: (1) General lighting; (2) Local lighting; (3) Mixed lighting.
74. What are the installation requirements for lighting switches?
Answer: (1) The height of the lever switch from the ground is 1.2-1.4m and the distance from the cabinet is 150-200mm; (2) The height of the pull switch is 2.2-2.8m and the distance from the cabinet is 150-200mm; (3) The concealed switch is securely installed in the switch box, and the switch box should have a complete cover.
75. What is the minimum cross-sectional area of the suspension wire for incandescent and fluorescent lamps?
A: It should not be less than 0.75 mm2.
76. Braking of a three-phase asynchronous motor?
Answer: (1) Mechanical braking; (2) Reverse braking; (3) Energy-consuming braking.
77. What are the lubrication requirements for electric motor bearings?
A: For motors with a speed of 3000 rpm, it is advisable to fill the motor with oil to a level slightly less than 2/3 full; for motors with a speed of 1500 rpm, it is advisable to fill the motor with oil to a level slightly less than 2/3 full; for motors with a speed of 1500 rpm or higher, it is generally advisable to add calcium-sodium grease high-speed grease; for motors with a speed of less than 1000 rpm low-speed grease, it is usually advisable to add calcium-sodium grease grease.
78. What is the difference between direct current (DC) and alternating current (AC)?
A: Direct current (DC) refers to electric current whose direction does not change with time. In a circuit with constant resistance, applying a power source with constant voltage produces a current whose magnitude and direction remain constant. Alternating current (AC) refers to electric current whose magnitude and direction change periodically with time.
79. What are some common circuit protection devices?
A: Undervoltage protection, short circuit protection, limit protection, overload protection, and interlock protection.
80. What are the different types of guy wires?
Answer: (1) Ordinary guy wire (2) Four-sided guy wire (3) Two-sided guy wire (4) Passageway guy wire (5) Common guy wire (6) V-shaped guy wire (7) Bow-shaped guy wire
81. In what situations is phase determination necessary?
Answer: (1) Newly installed equipment; (2) Two or more incoming cable lines; (3) Two or more overhead lines; (4) One of the two lines after maintenance;
(5) When the transformer is overhauled and operated in parallel with another transformer.
82. How to distinguish between operating lines and decommissioned lines?
Answer: (1) Switch status; (2) Whether there is a voltage indicator; (3) Signal light display status; (4) Direct observation with an electroscope.
83. What are the common types of equipment and line faults?
Answer: (1) Short circuit; (2) Open circuit; (3) Incorrect wiring; (4) Incorrect operation.
84. What are the basic requirements for selecting conductors?
Answer: (1) Select according to the allowable current carrying capacity; (2) Select according to the allowable voltage drop; (3) Select according to the mechanical strength.
85. What are the different types of grounding? What is their function?
A: Methods include protective grounding, functional grounding, shockproof grounding, neutral grounding, and repeated grounding. Purpose: To protect the safety of people and equipment; therefore, electrical equipment needs to be grounded.
86. What are the different types of electric shock?
A: It is divided into single-phase electric shock, two-phase electric shock, and step voltage electric shock.
87. What is phase-to-phase electric shock?
A: When the human body is insulated from the ground, it simultaneously comes into contact with two different phase wires, or the human body simultaneously comes into contact with two live parts of different phases of an electrical device. In this case, the current flows from one phase wire through the human body to the other phase wire.
88. What are safety colors?
A: Safety colors are colors used to convey safety information, such as prohibition, warning, instruction, and reminder. The nationally designated safety colors are red, blue, yellow, and green. Red indicates prohibition or stop; blue indicates instruction or mandatory regulations; yellow indicates warning or caution; and green indicates indication, safe status, or passage.
89. What is the spacing between the lines?
A: Power lines should be placed above communication lines, and high-voltage lines above low-voltage lines. The distance between communication lines and low-voltage lines must not be less than 1.5 meters; between low-voltage lines, not less than 0.6 meters; between low-voltage lines and 10kV high-voltage lines, not less than 1.2 meters; and between 10kV high-voltage lines, not less than 0.8 meters. The distance between 10kV service lines and the ground must not be less than 4.0 meters; the distance between low-voltage service lines and the ground must not be less than 2.5 meters; when low-voltage service lines cross streets with traffic, the distance to the ground must not be less than 6 meters; when crossing streets with difficult traffic or sidewalks, the distance must not be less than 3.5 meters. The burial depth of directly buried cables must not be less than 0.7 meters.
90. What is overload protection?
A: It is a type of protection that can delay cutting off the power supply when the load on a line or device exceeds the allowable range.
91. What are some measures to eliminate the hazards of static electricity?
A: Grounding method, leakage method, neutralization method, and process control method.
