1. What is circuit preparation?
A: Indicates the current path composed of various components, devices, and devices.
2. What is the low voltage line?
Answer: It is responsible for the distribution of electric power overhead lines or cable lines, and the voltage is less than 1KV. Typical is a 220V/380V power line.
3. What is a low voltage electrical appliance?
Answer: It is used for rated voltage AC 1000V or DC 1500V and below. It is an electric appliance that protects, controls, regulates, converts and turns on and off in a circuit consisting of a power supply system and a power supply device.
4. What is a low-voltage complete set?
Answer: It is a complete set of low-voltage switchgear and control appliances.
5. Which two types of low-voltage complete sets are included?
A: There are two types of electronic control equipment and power distribution equipment (or power distribution equipment).
6. What is a power distribution device?
A: Refers to a variety of equipment for power, distribution and lighting in low-voltage power distribution systems in power plants, substations and factories and mines.
7. What are the working steps when the power distribution and power failure work?
A: Disconnect the power supply, check the power, install the temporary grounding wire, hang the nameplate and install the barrier.
8. What are the main components of low voltage primary equipment?
Answer: There are mainly low-voltage fuses; low-voltage knife switches; low-pressure knife fuse switches and load switches; low-voltage circuit breakers.
9. What are the main functions of the low voltage fuse?
A: Mainly to achieve short-circuit protection of low-voltage distribution systems, and some can also achieve overload protection.
10. What are the main functions of the low pressure knife switch?
A: No load operation, used as a disconnector.
11. What are the main functions of the low-pressure knife fuse switch and load switch?
Answer: The low-pressure knife fuse switch has the dual functions of a knife switch and a fuse. The main function of the load switch can effectively cut off the load current and provide short-circuit protection.
12. What are the main functions of the low voltage circuit breaker?
Answer: It can not only load and unload the circuit, but also automatically trip in short circuit, overload and voltage loss.
13. What is a clearance?
Answer: The shortest distance between the two adjacent conductors with potential difference in the electrical equipment.
14. What is the role of the circuit breaker arc shield?
Answer: (1) Guide the arc to blow out longitudinally, thereby preventing phase-to-phase short-circuiting; (2) Bring the arc into contact with the insulating wall of the arc-extinguishing chamber, thereby rapidly cooling, increasing the de-free action, increasing the arc-column pressure drop, and forcing the arc to extinguish.
15. Why do shunt compensation capacitors be used in industrial and mining enterprises?
Answer: The shunt compensation capacitor is used to compensate the reactive power required by the inductive load of the power system to achieve: (1) Improve the grid voltage quality. (2) Improve the power factor. (3) Reduce line loss. (4) Improve the output of transformers and lines.
16. What is electrical safety? What aspects does it include?
Answer: Electrical safety refers to the quality of electrical products, as well as no accidents during installation, use and maintenance, such as personal death, equipment damage, electrical fires, electrical explosions, etc. Electrical safety includes both personal safety and equipment safety. Personal safety refers to the personal safety of electricians and other participating workers; equipment safety refers to the safety of electrical equipment and its ancillary equipment and facilities.
17. What are the commonly used arc extinguishing methods?
Answer: Commonly used arc extinguishing methods are: speed pull arc extinguishing method, cooling arc extinguishing method, arc arc extinguishing method, long arc cutting short arc extinguishing method, narrow groove or slit arc extinguishing method, vacuum arc extinguishing method and hexafluoride Sulphur arc extinguishing method.
18. What is the meaning of low-voltage switchgear and control equipment (referred to as complete sets of equipment)?
A: There are one or more low-voltage switchgear and related control, measurement, signal, protection, adjustment and other equipment. The manufacturer is responsible for all internal electrical and mechanical connections, and is completely assembled with structural components. A combination.
19. What is the meaning of the main circuit and auxiliary circuit in the complete set of equipment?
A: The main circuit is all the conductive loops that carry electrical energy; all the control, measurement, signal and control loops outside the main loop of the auxiliary circuit.
20. What standards should the low voltage distribution cabinet design meet?
A: IEC4391 (low-voltage switchgear and control equipment), GB7251 (low-voltage switchgear), ZBK36001 (low-voltage withdrawable switchgear)
21. What is the main circuit?
A: All conductive parts on a circuit used to transfer electrical energy in a complete set of equipment.
22. What is an auxiliary circuit?
A: All the conductive parts on the circuit for control, measurement, signal and regulation, data processing, etc. in the complete set of equipment (except the main circuit).
23. What is the level of protection?
A: Prevent the human body from approaching the live parts or the outer casings, partitions that touch the moving parts, and the degree of protection that should be provided to prevent solid objects from entering the equipment.
24. What is the meaning of working grounding?
Answer: Working grounding refers to the connection of some equipment in the power system to the earth metal directly or through arc suppression coils, reactors, resistors, etc., called working ground.
25. What is the meaning of protection grounding?
A: The protective grounding is to connect the metal casing of the electrical equipment to the grounding body.
26. What is the rated insulation voltage?
A: The standard voltage value used to measure the insulation strength, clearance and creepage distance of different potential parts of electrical appliances and their components under specified conditions.
27. What are the safety of the power distribution cabinet?
A: Voltage pass rate, power supply reliability.
28. What are the main functions of the circuit breaker?
Answer: It can connect, carry and disconnect the current under normal circuit conditions, and can also be connected, carry a certain time and break current under the specified abnormal circuit.
29. How is the phase sequence of the busbar specified?
A: When arranged from left to right, the left side is phase A, the middle is phase B, and the right side is phase C.
When arranged from top to bottom, the upper side is the A phase, the middle is the B phase, and the lower side is the C phase.
When arranged from far to near, it is far from phase A, with phase B in the middle and nearly phase C.
30. How is the phase color coloring of the busbar specified?
Answer: A phase yellow, B phase green, C phase red, PE black, PEN yellow and green alternating color, positive - ochre, negative - blue.
The device has a high voltage above ground (250V) and a low voltage below (250V).
31. What is overcurrent protection?
Answer: When a short circuit occurs, one of the important features is that the current in the line increases sharply. When the current flows through a predetermined value, the protection device that acts in response to the increase in current is called overcurrent protection.
32. What is the safety distance?
A: The minimum distance that must be maintained between a person and a charged body to prevent electric shock and short-circuit accidents, between the charged body and the ground and other objects.
33. What is protection and zero?
Answer: The protection system of the metal casing of the electrical equipment connected to the working zero line is called zero-connection protection.
34. What is feedback?
A: It is called feedback to send some or all of the input power (voltage or current) back to its input and participate in the control output together with the input signal.
35. What is a switchgear?
A: A general term for the combination of control, detection, protection and regulation equipment associated with power generation, transmission, distribution and power conversion.
36. What is a control device?
Answer: It is a general term used to control the switching devices of powered devices and the combination of control, detection, protection and regulating devices associated with these switching devices.
37. What is the use of the isolating switch?
Answer: A. Separate the electrical equipment from the live power grid; B. Change the operating mode; C. Connect and disconnect the small current circuit.
38. The main technical parameters of the fuse?
Answer: A. rated voltage; B. rated current; C. breaking capacity; D. melting characteristics; E. overvoltage.
39. What are the main products of low-voltage power distribution equipment?
A: Low-voltage power distribution panel, switch cabinet, switch board, lighting box, power box and motor control center.
40. What is current protection and what is the operating principle?
Answer: When a short circuit occurs, one of the important features is that the current in the line increases sharply. When the current flows through a predetermined value, the protection device that acts in response to the current rise is called overcurrent protection. The operating current is considered in terms of the maximum load current, and the choice is based on the stepped time limit.
41. What are the main differences between electronic control equipment and power distribution equipment?
Answer: The functions of the electronic control equipment are mainly controlled, and the functions of the power distribution equipment are mainly transmission.
42. What is a relay protection device?
A: A device that can respond to a fault or abnormal operation of an electrical device in a power system and act on a switch trip or signal.
43. What kinds of relays are commonly used?
A: Current relays, voltage relays, signal relays, time relays, intermediate relays, differential relays, and gas relays.
44. What are the requirements for relay protection?
A: In order to correct the fault correctly and quickly, relay protection is required to have sufficient selectivity, speed, sensitivity and reliability.
45. Which electrical equipment must be grounded or zero-protected?
Answer: 1. Base and outer casing of generator, transformer, motor, high and low voltage electrical appliances and lighting equipment; 2. Secondary coil of transformer; 3. Frame of switchboard and control panel; 4. Transmission of electric equipment; Metal structure of the distribution equipment inside and outside the house, concrete frame and metal fence; 6, cable head and cable box casing, cable sheath and threaded steel pipe; 7, power line tower and switchgear and capacitors installed on the distribution line pole.
46. ​​What are the classifications of transformers?
A: Transformers are divided into power transformers and special transformers. Power transformers are divided into oil immersed and dry. At present, oil-immersed transformers are used as step-up transformers, step-down transformers, tie transformers, and distribution transformers. Dry-type transformers are only used in some distribution transformers.
47. What are the components of the transformer?
Answer: Generally, it consists of five main parts: iron core, winding, oil tank, insulating sleeve and cooling system.
48. What are the losses in the operation of the transformer?
A: There is copper consumption and iron consumption.
49. Why can the transformer tapping function?
Answer: The voltage of the power system changes with the operation mode and the load size. If the voltage is too high or too low, it will affect the service life of the equipment. Therefore, in order to ensure the quality of the power supply, it must be adjusted according to the system voltage changes. Changing the tap is to change the number of turns of the coil, that is, to change the change of the transformer, and also change the voltage, so it plays a role of voltage regulation.
50. What types of common relays are divided according to the principle of action?
A: Electromagnetic, inductive, electric, and magnetoelectric.
51. What is electrical safety equipment?
A: It refers to the tools and utensils necessary to protect the safe operation of electrical work and personal safety. They can prevent accidents such as electric shock, arc burns and falling from high altitude.
52. What are the electrical safety uses?
A: Insulating safety equipment (insulated boots, insulated gloves, insulated operating rods, insulating pliers), electroscopes, sudden incoming protective equipment, temporary ground lines, signage, aerial work safety equipment (climbing boards, buckles) and other safety equipment .
53. What is the cause of the short circuit?
Answer: The reason for the short circuit: (1) wiring error; (2) insulation damage; (3) operation error; (4) mechanical damage.
54. What is the danger of short circuit?
Answer: Because the current does not pass through the load during the short circuit, it only flows inside the power supply. The internal resistance is very small, which makes the current large. The strong current will generate a large thermal effect and mechanical effect, which may damage the power supply or the circuit or cause a fire.
55. Can short circuits be used in production?
Answer: The electric welder uses a short circuit to generate a large current to weld between the welding rod and the workpiece. When the motor starts, the current is very large. The switch connected in parallel with the ammeter can be closed, the meter is short-circuited, and the motor starting current does not pass through the ammeter. Protection, disconnect the switch after starting.
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