High and low voltage power distribution, 100 knowledge!

1. What is electricity?

A: there are phenomena of charge existence and charge change. Electricity is an important energy source.

2. What is an electric field?

A: the field formed around the charged body can transfer the interaction between the charged bodies.

3. What is charge?

A: the positive or negative charge carried by an object or a particle constituting an object.

4. What is potential?

A: the energy of a unit positive charge at a certain point is called the potential at that point.

5. What is voltage? What are its basic and common units?

A: the potential difference between two points in the circuit is called voltage. Its basic unit is the volt. Abbreviation: volt, symbol V, common units: kilovolt (kV), millivolt (MV).

6. What is current?

A: the directional movement of charge under the action of electric field force is called current.

7. What is resistance? What are its basic units and common units?

A: when current flows in a conductor, it must be subject to a certain resistance, which is called the resistance of the conductor. Its basic unit is Ohm, which is abbreviated as ohm. The symbol is expressed as Ω. The commonly used units are kiloohm (K Ω) and megaohm (m Ω)

8. What are conductors, insulators and semiconductors?

A: objects that easily conduct current are called conductors. An object that can hardly conduct an electric current under normal conditions is called an insulator. An object whose conductivity is between a conductor and an insulator is called a semiconductor.

9. What is capacitance? What is its basic unit and common unit?

A: the capacity of a capacitor to store charge under a certain voltage is called capacitance. Its basic unit is farad, the symbol is f, and common symbols include micro method (MF), Pico farad (PF), 1F = 106mf = 1012mmf (PF).

10. What is a capacitor?

Answer: the circuit element of a container that stores charge and electric energy (potential energy).

11. What is inductance? What are its basic and common units?

A: the ability of the coil to generate self induced potential through a certain amount of variable current is called the inductance of the coil. Inductance for short. Its common unit is milliliter, the symbol is h, and the common unit is milliheng (MH). 1H=103MH

12. What is the function of inductance?

A: inductance does not play a role in DC circuit. It plays a role in resisting current change for abrupt load and AC circuit.

13. What is capacitive reactance, inductive reactance, reactance and impedance? What is their basic unit?

A: the blocking effect of capacitance on AC in the circuit is called capacitive reactance.

The blocking effect of inductance on AC in the circuit is called inductive reactance.

The blocking effect of capacitance and inductance on AC in a circuit is generally called reactance.

The resistance, capacitance, and inductance of a circuit to an alternating current.

Their basic unit is Ohm (Ω).

14. What is a circuit?

Answer: the path of current in the electrical device. The circuit is usually composed of power supply, switch, load and direct conductor.

15. What is DC circuit and AC circuit?

A: the circuit containing DC power supply is called DC circuit.

A circuit containing an AC power supply is called an AC circuit.

16. What is a circuit diagram?

A: a diagram showing the current path composed of various components, devices and devices. Or use the words and regulations stipulated by the state

17. What is a power plant?

A: it is a factory that converts all kinds of primary energy contained in nature into electric energy (secondary energy).

18. What are the types of power plants?

Answer: thermal power plant; Hydropower plant; Thermal power plant; Nuclear power plants; Wind power plant; Solar power plant, etc.

19. What is the composition of the power system?

Answer: it is composed of generators, transformers, power lines and electrical equipment.

20. What is a power grid?

A: it is a network connecting transmission lines of various voltage levels and various types of substations.

21. What are the types of substation and distribution substation?

Answer: there are outdoor substation, indoor substation, underground substation, mobile substation, box substation and outdoor simple substation.

22. What is the task of the distribution substation?

Answer: receiving and distributing electric energy.

23. What is the task of the substation?

Answer: accept electric energy, change voltage and distribute electric energy.

24. What is the role of power lines?

A: transmit and distribute electric energy.

25. What are the components of overhead lines?

Answer: it mainly includes tower, insulator, conductor, cross arm, hardware, grounding device and foundation, etc.

26. What are the types of towers?

A: there are usually cement poles and metal poles (iron tower, steel pipe pole, section steel pole, etc.).

27. What are the types of insulators?

A: there are needle type, butterfly type, suspension type and porcelain cross arm type.

28. What are the three main types of conductors?

Answer: single strand conductor, multi strand stranded wire and composite multi strand stranded wire.

29. What is the material and structure of the conductor and its representation?

Answer: l aluminum conductor; T copper conductor; G. steel conductor; LG steel cored aluminum conductor; J multi strand strand; TMY copper bus; Lmy aluminum bus.

30. What are the common electrical equipment for overhead lines?

Answer: A. drop fuse; B. Disconnector; C. High voltage column switch (load switch); D. Lightning arrester; E. Power container on column, etc.

31. What is a high voltage line?

Answer: overhead lines or cable lines responsible for the transmission and distribution of electric energy, power lines with voltage of 3 ~ 35kV and above.

32. What is a low voltage line?

Answer: the power line with voltage below 1kV, which is responsible for distributing electric energy overhead line or cable line. Typical is 220V / 380V power line.

33. What is the role of the power supply bureau?

Answer: implement power management, distribution, maintenance and technical support for power grid.

34. What is a power distribution room?

Answer: it is a place where high-voltage and low-voltage complete sets of devices are centrally controlled to receive and distribute electric energy.

35. What is the role of high voltage apparatus in power system?

A: it plays the role of control, protection and measurement in the process of power production, transmission and distribution.

36. What is a high voltage package?

A: it is a complete set of electrical appliances based on switches. It is used in the power distribution system to receive and distribute electric energy. Control, measure, protect and adjust the line.

37. What is a low voltage appliance?

Answer: it is an electrical appliance with rated voltage of AC 1000V or DC 1500V and below, which plays the role of protection, control, regulation, conversion and on-off in the circuit composed of power supply system and electrical equipment.

38. What is a low voltage package?

A: it is a complete set of equipment composed of low-voltage switchgear and control appliances.

39. What are the two types of low voltage packages?

Answer: electric control equipment; There are two types of power distribution equipment (or power distribution device).

40. What is electronic control equipment? What is its purpose?

A: it refers to the electric drive control equipment of various production machinery, and most of its direct control objects are motors. It is mainly used in metallurgy, mining, locomotives, ships, various production machinery, hoisting and transportation machinery, etc.

41. What is power distribution equipment?

Answer: it refers to all kinds of complete sets of equipment for power, power distribution and lighting in the low-voltage distribution system of power plants, substations and factories and mining enterprises.

42. What are the working steps for power transformation and distribution outage?

Answer: disconnect the power supply, check the power, install temporary grounding wire, hang signs and install barriers.

43. What are the main high-voltage primary equipment?

Answer: there are mainly high-voltage fuses; High voltage disconnector; High voltage load switch; High voltage circuit breaker.

44. What are the main functions of high voltage fuse?

A: it is a protective appliance that melts the melt and disconnects the circuit when the passing current exceeds the specified value. Its function is mainly to protect the circuit and the equipment in the circuit from short circuit.

45. What are the main functions of the high voltage disconnector?

A: it is mainly to isolate the high-voltage power supply to ensure the safe maintenance of other electrical equipment (including lines). Because there is no special arc extinguishing structure, the load current and short-circuit current cannot be cut off.

46. What are the main functions of high voltage load switch?

Answer: it has a simple arc extinguishing device, which can turn on and off a certain load and overload current, but can not turn off the short-circuit current. At the same time, it also has the function of isolating high-voltage power supply and ensuring safety.

47. What are the main functions of high voltage circuit breaker?

A: the main function is not only to turn on and off the normal load current, but also to turn on and withstand the short-circuit current for a certain time, and to automatically trip and remove the short-circuit fault under the action of the protection device.

48. What are the main low-voltage primary equipment?

Answer: there are mainly low-voltage fuses; Low voltage knife switch; Low voltage knife melting switch and load switch; Low voltage circuit breaker.

49. What are the main functions of low voltage fuse?

Answer: it is mainly to realize the short-circuit protection of low-voltage distribution system, and some can also realize its overload protection.

50. What are the main functions of low voltage knife switch?

Answer: no load operation, used as disconnector.

51. What are the main functions of low-voltage knife fuse switch and load switch?

Answer: the low-voltage knife fuse switch has the dual functions of knife switch and fuse. The main function of load switch can effectively turn on and off load current and carry out short-circuit protection.

52. What are the main functions of low voltage circuit breaker?

Answer: it can not only make and break the circuit with load, but also automatically trip in case of short circuit, overload and voltage loss.

53. What is a DC motor?

A: the rotating motor whose output or input is DC electric energy is called DC motor.

54. Where are DC motors used?

Answer: it is used in large steel rolling equipment, large precision machine tools, mine hoists, trams and other places.

55. What is the basic structure of DC motor?

Answer: it is mainly composed of stator and rotor.

56. What are the two excitation modes of DC motor?

A: there are two types: separately excited type and self excited type.

57. What is an asynchronous motor?

A: also known as induction motor, it is an AC motor that generates electromagnetic torque by the interaction between air gap rotating magnetic field and rotor winding induced current, so as to realize electromechanical energy conversion.

58. What are the two types of asynchronous motors according to rotor structure?

Answer: there are squirrel cage and wound asynchronous motors.

59. What is the basic structure of asynchronous motor?

A: it is composed of two basic parts. The stationary part is called the stator and the rotating part is called the rotor. There is a certain air gap between stator and rotor.

60. What are the two connection methods of asynchronous motor?

Answer: there are two methods: Star (y) connection and triangle (△) connection.

61. What are the general protections for small and medium capacity asynchronous motors?

Answer: A. short circuit protection: fuse is generally used as short circuit protection device; B. Loss of voltage protection: the electromagnetic coil of the magnetic starter plays the role of loss of voltage protection in the control circuit of the starting motor. Automatic air switch and self coupling step-down compensator are generally equipped with voltage loss tripping device. C. overload protection: thermal relay is generally used as overload protection device of motor.

62. For a three-phase asynchronous motor, the nameplate indicates that the rated voltage is 220 / 380V. How should it be connected?

Answer: when the voltage of the power line is 220V, the triangular (△) connection method is adopted

When the voltage of the power line is 380, the star (y) connection method is adopted.

63. What is soft start of motor?

A: make the motor input voltage rise gradually from zero with a preset functional relationship until the end of starting, and give the motor full voltage, that is, soft starting. In the process of soft starting, the motor starting torque and speed increase gradually.

64. What are the soft start modes?

Answer: (1) ramp boost soft start.

(2) Slope constant current soft start.

(3) Step start.

(4) Impulse starting.

65. What is a soft starter?

A: soft starter is a new equipment used to control squirrel cage asynchronous motor. It is a novel motor control device integrating motor soft start, soft stop, light load energy saving and various protection functions.

66. Application scope of soft starter?

Answer: in principle, the cage asynchronous motor can be applied to various applications where speed regulation is not required. The current application range is AC 380V (or 660V), and the motor power ranges from thousands of watts to 800KW. The soft starter is especially suitable for various pump loads or fan loads where soft start and soft stop are required.

67. What is the difference between soft start and traditional decompression start?

Answer: (1) no impulse current. When the soft starter starts the motor, the starting current of the motor increases linearly from zero to the set value. It has no impact on the motor, improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

(2) It has soft shutdown function, i.e. smooth deceleration and gradual shutdown. It can overcome the disadvantages of instantaneous power failure and shutdown, reduce the impact on heavy-duty machinery, avoid the water hammer effect of elevation water supply system and reduce equipment damage.

(3) The starting parameters are adjustable, and can be freely and steplessly adjusted to the best starting current according to the selection of load conditions and power grid relay protection characteristics.

68. What is a frequency converter?

A: the device that converts AC with fixed voltage and frequency into AC with variable voltage or frequency is called "frequency converter".

69. What are the main differences between soft starter and frequency converter?

A: the frequency converter is used where speed regulation is required. Its output not only changes the voltage, but also changes the frequency at the same time; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage and does not change the frequency. The frequency converter has all the functions of soft starter, but its price is much more expensive and its structure is much more complex than that of soft starter.

70. What is a transformer?

A: it is an electrical equipment used to change the AC voltage. According to the principle of electromagnetic induction, one level of AC voltage is transformed into another level of AC voltage to meet the needs of different loads.

71. What are the classifications of transformers?

Answer: transformers are divided into power transformers and special transformers. Power transformers are divided into oil immersed and dry-type. At present, oil immersed transformers are used as step-up transformers, step-down transformers, interconnection transformers and distribution transformers, and dry-type transformers are only used in some distribution transformers.

72. What parts does the transformer consist of?

A: it is generally composed of five main parts: iron core, winding, oil tank, insulating sleeve and cooling system.

73. What are the losses of transformer during operation?

Answer: copper consumption and iron consumption.

74. Why can the transformer tap play a regulating role?

A: the voltage of the power system changes with the operation mode and load. Too high or too low voltage will affect the service life of the equipment. Therefore, in order to ensure the power supply quality, it must be adjusted according to the change of system voltage. Changing the tap is to change the number of turns of the coil, that is, to change the change of the transformer and the voltage, so it plays the role of voltage regulation.

75. What kinds of power cables are commonly used?

Answer: oil paper insulated cable, plastic insulated cable (PVC insulated cable, polyethylene insulated cable), cross-linked polyethylene insulated cable, rubber insulated cable, etc.

76. What protective devices are generally installed on 3 ~ 10kV High voltage power lines?

Answer: common relay protection devices in 3 ~ 10kV substation include overcurrent protection, current quick break protection and transformer gas protection
1. What is electricity?

A: there are phenomena of charge existence and charge change. Electricity is an important energy source.

2. What is an electric field?

A: the field formed around the charged body can transfer the interaction between the charged bodies.

3. What is charge?

A: the positive or negative charge carried by an object or a particle constituting an object.

4. What is potential?

A: the energy of a unit positive charge at a certain point is called the potential at that point.

5. What is voltage? What are its basic and common units?

A: the potential difference between two points in the circuit is called voltage. Its basic unit is the volt. Abbreviation: volt, symbol V, common units: kilovolt (kV), millivolt (MV).

6. What is current?

A: the directional movement of charge under the action of electric field force is called current.

7. What is resistance? What are its basic units and common units?

A: when current flows in a conductor, it must be subject to a certain resistance, which is called the resistance of the conductor. Its basic unit is Ohm, which is abbreviated as ohm. The symbol is expressed as Ω. The commonly used units are kiloohm (K Ω) and megaohm (m Ω)

8. What are conductors, insulators and semiconductors?

A: objects that easily conduct current are called conductors. An object that can hardly conduct an electric current under normal conditions is called an insulator. An object whose conductivity is between a conductor and an insulator is called a semiconductor.

9. What is capacitance? What is its basic unit and common unit?

A: the capacity of a capacitor to store charge under a certain voltage is called capacitance. Its basic unit is farad, the symbol is f, and common symbols include micro method (MF), Pico farad (PF), 1F = 106mf = 1012mmf (PF).

10. What is a capacitor?

Answer: the circuit element of a container that stores charge and electric energy (potential energy).

11. What is inductance? What are its basic and common units?

A: the ability of the coil to generate self induced potential through a certain amount of variable current is called the inductance of the coil. Inductance for short. Its common unit is milliliter, the symbol is h, and the common unit is milliheng (MH). 1H=103MH

12. What is the function of inductance?

A: inductance does not play a role in DC circuit. It plays a role in resisting current change for abrupt load and AC circuit.

13. What is capacitive reactance, inductive reactance, reactance and impedance? What is their basic unit?

A: the blocking effect of capacitance on AC in the circuit is called capacitive reactance.

The blocking effect of inductance on AC in the circuit is called inductive reactance.

The blocking effect of capacitance and inductance on AC in a circuit is generally called reactance.

The resistance, capacitance, and inductance of a circuit to an alternating current.

Their basic unit is Ohm (Ω).

14. What is a circuit?

Answer: the path of current in the electrical device. The circuit is usually composed of power supply, switch, load and direct conductor.

15. What is DC circuit and AC circuit?

A: the circuit containing DC power supply is called DC circuit.

A circuit containing an AC power supply is called an AC circuit.

16. What is a circuit diagram?

A: a diagram showing the current path composed of various components, devices and devices. Or use the words and regulations stipulated by the state

17. What is a power plant?

A: it is a factory that converts all kinds of primary energy contained in nature into electric energy (secondary energy).

18. What are the types of power plants?

Answer: thermal power plant; Hydropower plant; Thermal power plant; Nuclear power plants; Wind power plant; Solar power plant, etc.

19. What is the composition of the power system?

Answer: it is composed of generators, transformers, power lines and electrical equipment.

20. What is a power grid?

A: it is a network connecting transmission lines of various voltage levels and various types of substations.

21. What are the types of substation and distribution substation?

Answer: there are outdoor substation, indoor substation, underground substation, mobile substation, box substation and outdoor simple substation.

22. What is the task of the distribution substation?

Answer: receiving and distributing electric energy.

23. What is the task of the substation?

Answer: accept electric energy, change voltage and distribute electric energy.

24. What is the role of power lines?

A: transmit and distribute electric energy.

25. What are the components of overhead lines?

Answer: it mainly includes tower, insulator, conductor, cross arm, hardware, grounding device and foundation, etc.

26. What are the types of towers?

A: there are usually cement poles and metal poles (iron tower, steel pipe pole, section steel pole, etc.).

27. What are the types of insulators?

A: there are needle type, butterfly type, suspension type and porcelain cross arm type.

28. What are the three main types of conductors?

Answer: single strand conductor, multi strand stranded wire and composite multi strand stranded wire.

29. What is the material and structure of the conductor and its representation?

Answer: l aluminum conductor; T copper conductor; G. steel conductor; LG steel cored aluminum conductor; J multi strand strand; TMY copper bus; Lmy aluminum bus.

30. What are the common electrical equipment for overhead lines?

Answer: A. drop fuse; B. Disconnector; C. High voltage column switch (load switch); D. Lightning arrester; E. Power container on column, etc.

31. What is a high voltage line?

Answer: overhead lines or cable lines responsible for the transmission and distribution of electric energy, power lines with voltage of 3 ~ 35kV and above.

32. What is a low voltage line?

Answer: the power line with voltage below 1kV, which is responsible for distributing electric energy overhead line or cable line. Typical is 220V / 380V power line.

33. What is the role of the power supply bureau?

Answer: implement power management, distribution, maintenance and technical support for power grid.

34. What is a power distribution room?

Answer: it is a place where high-voltage and low-voltage complete sets of devices are centrally controlled to receive and distribute electric energy.

35. What is the role of high voltage apparatus in power system?

A: it plays the role of control, protection and measurement in the process of power production, transmission and distribution.

36. What is a high voltage package?

A: it is a complete set of electrical appliances based on switches. It is used in the power distribution system to receive and distribute electric energy. Control, measure, protect and adjust the line.

37. What is a low voltage appliance?

Answer: it is an electrical appliance with rated voltage of AC 1000V or DC 1500V and below, which plays the role of protection, control, regulation, conversion and on-off in the circuit composed of power supply system and electrical equipment.

38. What is a low voltage package?

A: it is a complete set of equipment composed of low-voltage switchgear and control appliances.

39. What are the two types of low voltage packages?

Answer: electric control equipment; There are two types of power distribution equipment (or power distribution device).

40. What is electronic control equipment? What is its purpose?

A: it refers to the electric drive control equipment of various production machinery, and most of its direct control objects are motors. It is mainly used in metallurgy, mining, locomotives, ships, various production machinery, hoisting and transportation machinery, etc.

41. What is power distribution equipment?

Answer: it refers to all kinds of complete sets of equipment for power, power distribution and lighting in the low-voltage distribution system of power plants, substations and factories and mining enterprises.

42. What are the working steps for power transformation and distribution outage?

Answer: disconnect the power supply, check the power, install temporary grounding wire, hang signs and install barriers.

43. What are the main high-voltage primary equipment?

Answer: there are mainly high-voltage fuses; High voltage disconnector; High voltage load switch; High voltage circuit breaker.

44. What are the main functions of high voltage fuse?

A: it is a protective appliance that melts the melt and disconnects the circuit when the passing current exceeds the specified value. Its function is mainly to protect the circuit and the equipment in the circuit from short circuit.

45. What are the main functions of the high voltage disconnector?

A: it is mainly to isolate the high-voltage power supply to ensure the safe maintenance of other electrical equipment (including lines). Because there is no special arc extinguishing structure, the load current and short-circuit current cannot be cut off.

46. What are the main functions of high voltage load switch?

Answer: it has a simple arc extinguishing device, which can turn on and off a certain load and overload current, but can not turn off the short-circuit current. At the same time, it also has the function of isolating high-voltage power supply and ensuring safety.

47. What are the main functions of high voltage circuit breaker?

A: the main function is not only to turn on and off the normal load current, but also to turn on and withstand the short-circuit current for a certain time, and to automatically trip and remove the short-circuit fault under the action of the protection device.

48. What are the main low-voltage primary equipment?

Answer: there are mainly low-voltage fuses; Low voltage knife switch; Low voltage knife melting switch and load switch; Low voltage circuit breaker.

49. What are the main functions of low voltage fuse?

Answer: it is mainly to realize the short-circuit protection of low-voltage distribution system, and some can also realize its overload protection.

50. What are the main functions of low voltage knife switch?

Answer: no load operation, used as disconnector.

51. What are the main functions of low-voltage knife fuse switch and load switch?

Answer: the low-voltage knife fuse switch has the dual functions of knife switch and fuse. The main function of load switch can effectively turn on and off load current and carry out short-circuit protection.

52. What are the main functions of low voltage circuit breaker?

Answer: it can not only make and break the circuit with load, but also automatically trip in case of short circuit, overload and voltage loss.

53. What is a DC motor?

A: the rotating motor whose output or input is DC electric energy is called DC motor.

54. Where are DC motors used?

Answer: it is used in large steel rolling equipment, large precision machine tools, mine hoists, trams and other places.

55. What is the basic structure of DC motor?

Answer: it is mainly composed of stator and rotor.

56. What are the two excitation modes of DC motor?

A: there are two types: separately excited type and self excited type.

57. What is an asynchronous motor?

A: also known as induction motor, it is an AC motor that generates electromagnetic torque by the interaction between air gap rotating magnetic field and rotor winding induced current, so as to realize electromechanical energy conversion.

58. What are the two types of asynchronous motors according to rotor structure?

Answer: there are squirrel cage and wound asynchronous motors.

59. What is the basic structure of asynchronous motor?

A: it is composed of two basic parts. The stationary part is called the stator and the rotating part is called the rotor. There is a certain air gap between stator and rotor.

60. What are the two connection methods of asynchronous motor?

Answer: there are two methods: Star (y) connection and triangle (△) connection.

61. What are the general protections for small and medium capacity asynchronous motors?

Answer: A. short circuit protection: fuse is generally used as short circuit protection device; B. Loss of voltage protection: the electromagnetic coil of the magnetic starter plays the role of loss of voltage protection in the control circuit of the starting motor. Automatic air switch and self coupling step-down compensator are generally equipped with voltage loss tripping device. C. overload protection: thermal relay is generally used as overload protection device of motor.

62. For a three-phase asynchronous motor, the nameplate indicates that the rated voltage is 220 / 380V. How should it be connected?

Answer: when the voltage of the power line is 220V, the triangular (△) connection method is adopted

When the voltage of the power line is 380, the star (y) connection method is adopted.

63. What is soft start of motor?

A: make the motor input voltage rise gradually from zero with a preset functional relationship until the end of starting, and give the motor full voltage, that is, soft starting. In the process of soft starting, the motor starting torque and speed increase gradually.

64. What are the soft start modes?

Answer: (1) ramp boost soft start.

(2) Slope constant current soft start.

(3) Step start.

(4) Impulse starting.

65. What is a soft starter?

A: soft starter is a new equipment used to control squirrel cage asynchronous motor. It is a novel motor control device integrating motor soft start, soft stop, light load energy saving and various protection functions.

66. Application scope of soft starter?

Answer: in principle, the cage asynchronous motor can be applied to various applications where speed regulation is not required. The current application range is AC 380V (or 660V), and the motor power ranges from thousands of watts to 800KW. The soft starter is especially suitable for various pump loads or fan loads where soft start and soft stop are required.

67. What is the difference between soft start and traditional decompression start?

Answer: (1) no impulse current. When the soft starter starts the motor, the starting current of the motor increases linearly from zero to the set value. It has no impact on the motor, improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

(2) It has soft shutdown function, i.e. smooth deceleration and gradual shutdown. It can overcome the disadvantages of instantaneous power failure and shutdown, reduce the impact on heavy-duty machinery, avoid the water hammer effect of elevation water supply system and reduce equipment damage.

(3) The starting parameters are adjustable, and can be freely and steplessly adjusted to the best starting current according to the selection of load conditions and power grid relay protection characteristics.

68. What is a frequency converter?

A: the device that converts AC with fixed voltage and frequency into AC with variable voltage or frequency is called "frequency converter".

69. What are the main differences between soft starter and frequency converter?

A: the frequency converter is used where speed regulation is required. Its output not only changes the voltage, but also changes the frequency at the same time; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage and does not change the frequency. The frequency converter has all the functions of soft starter, but its price is much more expensive and its structure is much more complex than that of soft starter.

70. What is a transformer?

A: it is an electrical equipment used to change the AC voltage. According to the principle of electromagnetic induction, one level of AC voltage is transformed into another level of AC voltage to meet the needs of different loads.

71. What are the classifications of transformers?

Answer: transformers are divided into power transformers and special transformers. Power transformers are divided into oil immersed and dry-type. At present, oil immersed transformers are used as step-up transformers, step-down transformers, interconnection transformers and distribution transformers, and dry-type transformers are only used in some distribution transformers.

72. What parts does the transformer consist of?

A: it is generally composed of five main parts: iron core, winding, oil tank, insulating sleeve and cooling system.

73. What are the losses of transformer during operation?

Answer: copper consumption and iron consumption.

74. Why can the transformer tap play a regulating role?

A: the voltage of the power system changes with the operation mode and load. Too high or too low voltage will affect the service life of the equipment. Therefore, in order to ensure the power supply quality, it must be adjusted according to the change of system voltage. Changing the tap is to change the number of turns of the coil, that is, to change the change of the transformer and the voltage, so it plays the role of voltage regulation.

75. What kinds of power cables are commonly used?

Answer: oil paper insulated cable, plastic insulated cable (PVC insulated cable, polyethylene insulated cable), cross-linked polyethylene insulated cable, rubber insulated cable, etc.

76. What protective devices are generally installed on 3 ~ 10kV High voltage power lines?

Answer: common relay protection devices in 3 ~ 10kV substation include overcurrent protection, current quick break protection and transformer gas protection1. What is electricity?

A: there are phenomena of charge existence and charge change. Electricity is an important energy source.

2. What is an electric field?

A: the field formed around the charged body can transfer the interaction between the charged bodies.

3. What is charge?

A: the positive or negative charge carried by an object or a particle constituting an object.

4. What is potential?

A: the energy of a unit positive charge at a certain point is called the potential at that point.

5. What is voltage? What are its basic and common units?

A: the potential difference between two points in the circuit is called voltage. Its basic unit is the volt. Abbreviation: volt, symbol V, common units: kilovolt (kV), millivolt (MV).

6. What is current?

A: the directional movement of charge under the action of electric field force is called current.

7. What is resistance? What are its basic units and common units?

A: when current flows in a conductor, it must be subject to a certain resistance, which is called the resistance of the conductor. Its basic unit is Ohm, which is abbreviated as ohm. The symbol is expressed as Ω. The commonly used units are kiloohm (K Ω) and megaohm (m Ω)

8. What are conductors, insulators and semiconductors?

A: objects that easily conduct current are called conductors. An object that can hardly conduct an electric current under normal conditions is called an insulator. An object whose conductivity is between a conductor and an insulator is called a semiconductor.

9. What is capacitance? What is its basic unit and common unit?

A: the capacity of a capacitor to store charge under a certain voltage is called capacitance. Its basic unit is farad, the symbol is f, and common symbols include micro method (MF), Pico farad (PF), 1F = 106mf = 1012mmf (PF).

10. What is a capacitor?

Answer: the circuit element of a container that stores charge and electric energy (potential energy).

11. What is inductance? What are its basic and common units?

A: the ability of the coil to generate self induced potential through a certain amount of variable current is called the inductance of the coil. Inductance for short. Its common unit is milliliter, the symbol is h, and the common unit is milliheng (MH). 1H=103MH

12. What is the function of inductance?

A: inductance does not play a role in DC circuit. It plays a role in resisting current change for abrupt load and AC circuit.

13. What is capacitive reactance, inductive reactance, reactance and impedance? What is their basic unit?

A: the blocking effect of capacitance on AC in the circuit is called capacitive reactance.

The blocking effect of inductance on AC in the circuit is called inductive reactance.

The blocking effect of capacitance and inductance on AC in a circuit is generally called reactance.

The resistance, capacitance, and inductance of a circuit to an alternating current.

Their basic unit is Ohm (Ω).

14. What is a circuit?

Answer: the path of current in the electrical device. The circuit is usually composed of power supply, switch, load and direct conductor.

15. What is DC circuit and AC circuit?

A: the circuit containing DC power supply is called DC circuit.

A circuit containing an AC power supply is called an AC circuit.

16. What is a circuit diagram?

A: a diagram showing the current path composed of various components, devices and devices. Or use the words and regulations stipulated by the state

17. What is a power plant?

A: it is a factory that converts all kinds of primary energy contained in nature into electric energy (secondary energy).

18. What are the types of power plants?

Answer: thermal power plant; Hydropower plant; Thermal power plant; Nuclear power plants; Wind power plant; Solar power plant, etc.

19. What is the composition of the power system?

Answer: it is composed of generators, transformers, power lines and electrical equipment.

20. What is a power grid?

A: it is a network connecting transmission lines of various voltage levels and various types of substations.

21. What are the types of substation and distribution substation?

Answer: there are outdoor substation, indoor substation, underground substation, mobile substation, box substation and outdoor simple substation.

22. What is the task of the distribution substation?

Answer: receiving and distributing electric energy.

23. What is the task of the substation?

Answer: accept electric energy, change voltage and distribute electric energy.

24. What is the role of power lines?

A: transmit and distribute electric energy.

25. What are the components of overhead lines?

Answer: it mainly includes tower, insulator, conductor, cross arm, hardware, grounding device and foundation, etc.

26. What are the types of towers?

A: there are usually cement poles and metal poles (iron tower, steel pipe pole, section steel pole, etc.).

27. What are the types of insulators?

A: there are needle type, butterfly type, suspension type and porcelain cross arm type.

28. What are the three main types of conductors?

Answer: single strand conductor, multi strand stranded wire and composite multi strand stranded wire.

29. What is the material and structure of the conductor and its representation?

Answer: l aluminum conductor; T copper conductor; G. steel conductor; LG steel cored aluminum conductor; J multi strand strand; TMY copper bus; Lmy aluminum bus.

30. What are the common electrical equipment for overhead lines?

Answer: A. drop fuse; B. Disconnector; C. High voltage column switch (load switch); D. Lightning arrester; E. Power container on column, etc.

31. What is a high voltage line?

Answer: overhead lines or cable lines responsible for the transmission and distribution of electric energy, power lines with voltage of 3 ~ 35kV and above.

32. What is a low voltage line?

Answer: the power line with voltage below 1kV, which is responsible for distributing electric energy overhead line or cable line. Typical is 220V / 380V power line.

33. What is the role of the power supply bureau?

Answer: implement power management, distribution, maintenance and technical support for power grid.

34. What is a power distribution room?

Answer: it is a place where high-voltage and low-voltage complete sets of devices are centrally controlled to receive and distribute electric energy.

35. What is the role of high voltage apparatus in power system?

A: it plays the role of control, protection and measurement in the process of power production, transmission and distribution.

36. What is a high voltage package?

A: it is a complete set of electrical appliances based on switches. It is used in the power distribution system to receive and distribute electric energy. Control, measure, protect and adjust the line.

37. What is a low voltage appliance?

Answer: it is an electrical appliance with rated voltage of AC 1000V or DC 1500V and below, which plays the role of protection, control, regulation, conversion and on-off in the circuit composed of power supply system and electrical equipment.

38. What is a low voltage package?

A: it is a complete set of equipment composed of low-voltage switchgear and control appliances.

39. What are the two types of low voltage packages?

Answer: electric control equipment; There are two types of power distribution equipment (or power distribution device).

40. What is electronic control equipment? What is its purpose?

A: it refers to the electric drive control equipment of various production machinery, and most of its direct control objects are motors. It is mainly used in metallurgy, mining, locomotives, ships, various production machinery, hoisting and transportation machinery, etc.

41. What is power distribution equipment?

Answer: it refers to all kinds of complete sets of equipment for power, power distribution and lighting in the low-voltage distribution system of power plants, substations and factories and mining enterprises.

42. What are the working steps for power transformation and distribution outage?

Answer: disconnect the power supply, check the power, install temporary grounding wire, hang signs and install barriers.

43. What are the main high-voltage primary equipment?

Answer: there are mainly high-voltage fuses; High voltage disconnector; High voltage load switch; High voltage circuit breaker.

44. What are the main functions of high voltage fuse?

A: it is a protective appliance that melts the melt and disconnects the circuit when the passing current exceeds the specified value. Its function is mainly to protect the circuit and the equipment in the circuit from short circuit.

45. What are the main functions of the high voltage disconnector?

A: it is mainly to isolate the high-voltage power supply to ensure the safe maintenance of other electrical equipment (including lines). Because there is no special arc extinguishing structure, the load current and short-circuit current cannot be cut off.

46. What are the main functions of high voltage load switch?

Answer: it has a simple arc extinguishing device, which can turn on and off a certain load and overload current, but can not turn off the short-circuit current. At the same time, it also has the function of isolating high-voltage power supply and ensuring safety.

47. What are the main functions of high voltage circuit breaker?

A: the main function is not only to turn on and off the normal load current, but also to turn on and withstand the short-circuit current for a certain time, and to automatically trip and remove the short-circuit fault under the action of the protection device.

48. What are the main low-voltage primary equipment?

Answer: there are mainly low-voltage fuses; Low voltage knife switch; Low voltage knife melting switch and load switch; Low voltage circuit breaker.

49. What are the main functions of low voltage fuse?

Answer: it is mainly to realize the short-circuit protection of low-voltage distribution system, and some can also realize its overload protection.

50. What are the main functions of low voltage knife switch?

Answer: no load operation, used as disconnector.

51. What are the main functions of low-voltage knife fuse switch and load switch?

Answer: the low-voltage knife fuse switch has the dual functions of knife switch and fuse. The main function of load switch can effectively turn on and off load current and carry out short-circuit protection.

52. What are the main functions of low voltage circuit breaker?

Answer: it can not only make and break the circuit with load, but also automatically trip in case of short circuit, overload and voltage loss.

53. What is a DC motor?

A: the rotating motor whose output or input is DC electric energy is called DC motor.

54. Where are DC motors used?

Answer: it is used in large steel rolling equipment, large precision machine tools, mine hoists, trams and other places.

55. What is the basic structure of DC motor?

Answer: it is mainly composed of stator and rotor.

56. What are the two excitation modes of DC motor?

A: there are two types: separately excited type and self excited type.

57. What is an asynchronous motor?

A: also known as induction motor, it is an AC motor that generates electromagnetic torque by the interaction between air gap rotating magnetic field and rotor winding induced current, so as to realize electromechanical energy conversion.

58. What are the two types of asynchronous motors according to rotor structure?

Answer: there are squirrel cage and wound asynchronous motors.

59. What is the basic structure of asynchronous motor?

A: it is composed of two basic parts. The stationary part is called the stator and the rotating part is called the rotor. There is a certain air gap between stator and rotor.

60. What are the two connection methods of asynchronous motor?

Answer: there are two methods: Star (y) connection and triangle (△) connection.

61. What are the general protections for small and medium capacity asynchronous motors?

Answer: A. short circuit protection: fuse is generally used as short circuit protection device; B. Loss of voltage protection: the electromagnetic coil of the magnetic starter plays the role of loss of voltage protection in the control circuit of the starting motor. Automatic air switch and self coupling step-down compensator are generally equipped with voltage loss tripping device. C. overload protection: thermal relay is generally used as overload protection device of motor.

62. For a three-phase asynchronous motor, the nameplate indicates that the rated voltage is 220 / 380V. How should it be connected?

Answer: when the voltage of the power line is 220V, the triangular (△) connection method is adopted

When the voltage of the power line is 380, the star (y) connection method is adopted.

63. What is soft start of motor?

A: make the motor input voltage rise gradually from zero with a preset functional relationship until the end of starting, and give the motor full voltage, that is, soft starting. In the process of soft starting, the motor starting torque and speed increase gradually.

64. What are the soft start modes?

Answer: (1) ramp boost soft start.

(2) Slope constant current soft start.

(3) Step start.

(4) Impulse starting.

65. What is a soft starter?

A: soft starter is a new equipment used to control squirrel cage asynchronous motor. It is a novel motor control device integrating motor soft start, soft stop, light load energy saving and various protection functions.

66. Application scope of soft starter?

Answer: in principle, the cage asynchronous motor can be applied to various applications where speed regulation is not required. The current application range is AC 380V (or 660V), and the motor power ranges from thousands of watts to 800KW. The soft starter is especially suitable for various pump loads or fan loads where soft start and soft stop are required.

67. What is the difference between soft start and traditional decompression start?

Answer: (1) no impulse current. When the soft starter starts the motor, the starting current of the motor increases linearly from zero to the set value. It has no impact on the motor, improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

(2) It has soft shutdown function, i.e. smooth deceleration and gradual shutdown. It can overcome the disadvantages of instantaneous power failure and shutdown, reduce the impact on heavy-duty machinery, avoid the water hammer effect of elevation water supply system and reduce equipment damage.

(3) The starting parameters are adjustable, and can be freely and steplessly adjusted to the best starting current according to the selection of load conditions and power grid relay protection characteristics.

68. What is a frequency converter?

A: the device that converts AC with fixed voltage and frequency into AC with variable voltage or frequency is called "frequency converter".

69. What are the main differences between soft starter and frequency converter?

A: the frequency converter is used where speed regulation is required. Its output not only changes the voltage, but also changes the frequency at the same time; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage and does not change the frequency. The frequency converter has all the functions of soft starter, but its price is much more expensive and its structure is much more complex than that of soft starter.

70. What is a transformer?

A: it is an electrical equipment used to change the AC voltage. According to the principle of electromagnetic induction, one level of AC voltage is transformed into another level of AC voltage to meet the needs of different loads.

71. What are the classifications of transformers?

Answer: transformers are divided into power transformers and special transformers. Power transformers are divided into oil immersed and dry-type. At present, oil immersed transformers are used as step-up transformers, step-down transformers, interconnection transformers and distribution transformers, and dry-type transformers are only used in some distribution transformers.

72. What parts does the transformer consist of?

A: it is generally composed of five main parts: iron core, winding, oil tank, insulating sleeve and cooling system.

73. What are the losses of transformer during operation?

Answer: copper consumption and iron consumption.

74. Why can the transformer tap play a regulating role?

A: the voltage of the power system changes with the operation mode and load. Too high or too low voltage will affect the service life of the equipment. Therefore, in order to ensure the power supply quality, it must be adjusted according to the change of system voltage. Changing the tap is to change the number of turns of the coil, that is, to change the change of the transformer and the voltage, so it plays the role of voltage regulation.

75. What kinds of power cables are commonly used?

Answer: oil paper insulated cable, plastic insulated cable (PVC insulated cable, polyethylene insulated cable), cross-linked polyethylene insulated cable, rubber insulated cable, etc.

76. What protective devices are generally installed on 3 ~ 10kV High voltage power lines?

Answer: common relay protection devices in 3 ~ 10kV substation include overcurrent protection, current quick break protection and transformer gas protection1. What is electricity?

A: there are phenomena of charge existence and charge change. Electricity is an important energy source.

2. What is an electric field?

A: the field formed around the charged body can transfer the interaction between the charged bodies.

3. What is charge?

A: the positive or negative charge carried by an object or a particle constituting an object.

4. What is potential?

A: the energy of a unit positive charge at a certain point is called the potential at that point.

5. What is voltage? What are its basic and common units?

A: the potential difference between two points in the circuit is called voltage. Its basic unit is the volt. Abbreviation: volt, symbol V, common units: kilovolt (kV), millivolt (MV).

6. What is current?

A: the directional movement of charge under the action of electric field force is called current.

7. What is resistance? What are its basic units and common units?

A: when current flows in a conductor, it must be subject to a certain resistance, which is called the resistance of the conductor. Its basic unit is Ohm, which is abbreviated as ohm. The symbol is expressed as Ω. The commonly used units are kiloohm (K Ω) and megaohm (m Ω)

8. What are conductors, insulators and semiconductors?

A: objects that easily conduct current are called conductors. An object that can hardly conduct an electric current under normal conditions is called an insulator. An object whose conductivity is between a conductor and an insulator is called a semiconductor.

9. What is capacitance? What is its basic unit and common unit?

A: the capacity of a capacitor to store charge under a certain voltage is called capacitance. Its basic unit is farad, the symbol is f, and common symbols include micro method (MF), Pico farad (PF), 1F = 106mf = 1012mmf (PF).

10. What is a capacitor?

Answer: the circuit element of a container that stores charge and electric energy (potential energy).

11. What is inductance? What are its basic and common units?

A: the ability of the coil to generate self induced potential through a certain amount of variable current is called the inductance of the coil. Inductance for short. Its common unit is milliliter, the symbol is h, and the common unit is milliheng (MH). 1H=103MH

12. What is the function of inductance?

A: inductance does not play a role in DC circuit. It plays a role in resisting current change for abrupt load and AC circuit.

13. What is capacitive reactance, inductive reactance, reactance and impedance? What is their basic unit?

A: the blocking effect of capacitance on AC in the circuit is called capacitive reactance.

The blocking effect of inductance on AC in the circuit is called inductive reactance.

The blocking effect of capacitance and inductance on AC in a circuit is generally called reactance.

The resistance, capacitance, and inductance of a circuit to an alternating current.

Their basic unit is Ohm (Ω).

14. What is a circuit?

Answer: the path of current in the electrical device. The circuit is usually composed of power supply, switch, load and direct conductor.

15. What is DC circuit and AC circuit?

A: the circuit containing DC power supply is called DC circuit.

A circuit containing an AC power supply is called an AC circuit.

16. What is a circuit diagram?

A: a diagram showing the current path composed of various components, devices and devices. Or use the words and regulations stipulated by the state

17. What is a power plant?

A: it is a factory that converts all kinds of primary energy contained in nature into electric energy (secondary energy).

18. What are the types of power plants?

Answer: thermal power plant; Hydropower plant; Thermal power plant; Nuclear power plants; Wind power plant; Solar power plant, etc.

19. What is the composition of the power system?

Answer: it is composed of generators, transformers, power lines and electrical equipment.

20. What is a power grid?

A: it is a network connecting transmission lines of various voltage levels and various types of substations.

21. What are the types of substation and distribution substation?

Answer: there are outdoor substation, indoor substation, underground substation, mobile substation, box substation and outdoor simple substation.

22. What is the task of the distribution substation?

Answer: receiving and distributing electric energy.

23. What is the task of the substation?

Answer: accept electric energy, change voltage and distribute electric energy.

24. What is the role of power lines?

A: transmit and distribute electric energy.

25. What are the components of overhead lines?

Answer: it mainly includes tower, insulator, conductor, cross arm, hardware, grounding device and foundation, etc.

26. What are the types of towers?

A: there are usually cement poles and metal poles (iron tower, steel pipe pole, section steel pole, etc.).

27. What are the types of insulators?

A: there are needle type, butterfly type, suspension type and porcelain cross arm type.

28. What are the three main types of conductors?

Answer: single strand conductor, multi strand stranded wire and composite multi strand stranded wire.

29. What is the material and structure of the conductor and its representation?

Answer: l aluminum conductor; T copper conductor; G. steel conductor; LG steel cored aluminum conductor; J multi strand strand; TMY copper bus; Lmy aluminum bus.

30. What are the common electrical equipment for overhead lines?

Answer: A. drop fuse; B. Disconnector; C. High voltage column switch (load switch); D. Lightning arrester; E. Power container on column, etc.

31. What is a high voltage line?

Answer: overhead lines or cable lines responsible for the transmission and distribution of electric energy, power lines with voltage of 3 ~ 35kV and above.

32. What is a low voltage line?

Answer: the power line with voltage below 1kV, which is responsible for distributing electric energy overhead line or cable line. Typical is 220V / 380V power line.

33. What is the role of the power supply bureau?

Answer: implement power management, distribution, maintenance and technical support for power grid.

34. What is a power distribution room?

Answer: it is a place where high-voltage and low-voltage complete sets of devices are centrally controlled to receive and distribute electric energy.

35. What is the role of high voltage apparatus in power system?

A: it plays the role of control, protection and measurement in the process of power production, transmission and distribution.

36. What is a high voltage package?

A: it is a complete set of electrical appliances based on switches. It is used in the power distribution system to receive and distribute electric energy. Control, measure, protect and adjust the line.

37. What is a low voltage appliance?

Answer: it is an electrical appliance with rated voltage of AC 1000V or DC 1500V and below, which plays the role of protection, control, regulation, conversion and on-off in the circuit composed of power supply system and electrical equipment.

38. What is a low voltage package?

A: it is a complete set of equipment composed of low-voltage switchgear and control appliances.

39. What are the two types of low voltage packages?

Answer: electric control equipment; There are two types of power distribution equipment (or power distribution device).

40. What is electronic control equipment? What is its purpose?

A: it refers to the electric drive control equipment of various production machinery, and most of its direct control objects are motors. It is mainly used in metallurgy, mining, locomotives, ships, various production machinery, hoisting and transportation machinery, etc.

41. What is power distribution equipment?

Answer: it refers to all kinds of complete sets of equipment for power, power distribution and lighting in the low-voltage distribution system of power plants, substations and factories and mining enterprises.

42. What are the working steps for power transformation and distribution outage?

Answer: disconnect the power supply, check the power, install temporary grounding wire, hang signs and install barriers.

43. What are the main high-voltage primary equipment?

Answer: there are mainly high-voltage fuses; High voltage disconnector; High voltage load switch; High voltage circuit breaker.

44. What are the main functions of high voltage fuse?

A: it is a protective appliance that melts the melt and disconnects the circuit when the passing current exceeds the specified value. Its function is mainly to protect the circuit and the equipment in the circuit from short circuit.

45. What are the main functions of the high voltage disconnector?

A: it is mainly to isolate the high-voltage power supply to ensure the safe maintenance of other electrical equipment (including lines). Because there is no special arc extinguishing structure, the load current and short-circuit current cannot be cut off.

46. What are the main functions of high voltage load switch?

Answer: it has a simple arc extinguishing device, which can turn on and off a certain load and overload current, but can not turn off the short-circuit current. At the same time, it also has the function of isolating high-voltage power supply and ensuring safety.

47. What are the main functions of high voltage circuit breaker?

A: the main function is not only to turn on and off the normal load current, but also to turn on and withstand the short-circuit current for a certain time, and to automatically trip and remove the short-circuit fault under the action of the protection device.

48. What are the main low-voltage primary equipment?

Answer: there are mainly low-voltage fuses; Low voltage knife switch; Low voltage knife melting switch and load switch; Low voltage circuit breaker.

49. What are the main functions of low voltage fuse?

Answer: it is mainly to realize the short-circuit protection of low-voltage distribution system, and some can also realize its overload protection.

50. What are the main functions of low voltage knife switch?

Answer: no load operation, used as disconnector.

51. What are the main functions of low-voltage knife fuse switch and load switch?

Answer: the low-voltage knife fuse switch has the dual functions of knife switch and fuse. The main function of load switch can effectively turn on and off load current and carry out short-circuit protection.

52. What are the main functions of low voltage circuit breaker?

Answer: it can not only make and break the circuit with load, but also automatically trip in case of short circuit, overload and voltage loss.

53. What is a DC motor?

A: the rotating motor whose output or input is DC electric energy is called DC motor.

54. Where are DC motors used?

Answer: it is used in large steel rolling equipment, large precision machine tools, mine hoists, trams and other places.

55. What is the basic structure of DC motor?

Answer: it is mainly composed of stator and rotor.

56. What are the two excitation modes of DC motor?

A: there are two types: separately excited type and self excited type.

57. What is an asynchronous motor?

A: also known as induction motor, it is an AC motor that generates electromagnetic torque by the interaction between air gap rotating magnetic field and rotor winding induced current, so as to realize electromechanical energy conversion.

58. What are the two types of asynchronous motors according to rotor structure?

Answer: there are squirrel cage and wound asynchronous motors.

59. What is the basic structure of asynchronous motor?

A: it is composed of two basic parts. The stationary part is called the stator and the rotating part is called the rotor. There is a certain air gap between stator and rotor.

60. What are the two connection methods of asynchronous motor?

Answer: there are two methods: Star (y) connection and triangle (△) connection.

61. What are the general protections for small and medium capacity asynchronous motors?

Answer: A. short circuit protection: fuse is generally used as short circuit protection device; B. Loss of voltage protection: the electromagnetic coil of the magnetic starter plays the role of loss of voltage protection in the control circuit of the starting motor. Automatic air switch and self coupling step-down compensator are generally equipped with voltage loss tripping device. C. overload protection: thermal relay is generally used as overload protection device of motor.

62. For a three-phase asynchronous motor, the nameplate indicates that the rated voltage is 220 / 380V. How should it be connected?

Answer: when the voltage of the power line is 220V, the triangular (△) connection method is adopted

When the voltage of the power line is 380, the star (y) connection method is adopted.

63. What is soft start of motor?

A: make the motor input voltage rise gradually from zero with a preset functional relationship until the end of starting, and give the motor full voltage, that is, soft starting. In the process of soft starting, the motor starting torque and speed increase gradually.

64. What are the soft start modes?

Answer: (1) ramp boost soft start.

(2) Slope constant current soft start.

(3) Step start.

(4) Impulse starting.

65. What is a soft starter?

A: soft starter is a new equipment used to control squirrel cage asynchronous motor. It is a novel motor control device integrating motor soft start, soft stop, light load energy saving and various protection functions.

66. Application scope of soft starter?

Answer: in principle, the cage asynchronous motor can be applied to various applications where speed regulation is not required. The current application range is AC 380V (or 660V), and the motor power ranges from thousands of watts to 800KW. The soft starter is especially suitable for various pump loads or fan loads where soft start and soft stop are required.

67. What is the difference between soft start and traditional decompression start?

Answer: (1) no impulse current. When the soft starter starts the motor, the starting current of the motor increases linearly from zero to the set value. It has no impact on the motor, improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

(2) It has soft shutdown function, i.e. smooth deceleration and gradual shutdown. It can overcome the disadvantages of instantaneous power failure and shutdown, reduce the impact on heavy-duty machinery, avoid the water hammer effect of elevation water supply system and reduce equipment damage.

(3) The starting parameters are adjustable, and can be freely and steplessly adjusted to the best starting current according to the selection of load conditions and power grid relay protection characteristics.

68. What is a frequency converter?

A: the device that converts AC with fixed voltage and frequency into AC with variable voltage or frequency is called "frequency converter".

69. What are the main differences between soft starter and frequency converter?

A: the frequency converter is used where speed regulation is required. Its output not only changes the voltage, but also changes the frequency at the same time; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage and does not change the frequency. The frequency converter has all the functions of soft starter, but its price is much more expensive and its structure is much more complex than that of soft starter.

70. What is a transformer?

A: it is an electrical equipment used to change the AC voltage. According to the principle of electromagnetic induction, one level of AC voltage is transformed into another level of AC voltage to meet the needs of different loads.

71. What are the classifications of transformers?

Answer: transformers are divided into power transformers and special transformers. Power transformers are divided into oil immersed and dry-type. At present, oil immersed transformers are used as step-up transformers, step-down transformers, interconnection transformers and distribution transformers, and dry-type transformers are only used in some distribution transformers.

72. What parts does the transformer consist of?

A: it is generally composed of five main parts: iron core, winding, oil tank, insulating sleeve and cooling system.

73. What are the losses of transformer during operation?

Answer: copper consumption and iron consumption.

74. Why can the transformer tap play a regulating role?

A: the voltage of the power system changes with the operation mode and load. Too high or too low voltage will affect the service life of the equipment. Therefore, in order to ensure the power supply quality, it must be adjusted according to the change of system voltage. Changing the tap is to change the number of turns of the coil, that is, to change the change of the transformer and the voltage, so it plays the role of voltage regulation.

75. What kinds of power cables are commonly used?

Answer: oil paper insulated cable, plastic insulated cable (PVC insulated cable, polyethylene insulated cable), cross-linked polyethylene insulated cable, rubber insulated cable, etc.

76. What protective devices are generally installed on 3 ~ 10kV High voltage power lines?

Answer: common relay protection devices in 3 ~ 10kV substation include overcurrent protection, current quick break protection and transformer gas protection