100 pieces of key knowledge of motor industry for you

1. The highest stator voltage of the generator shall not be greater than (110%) of the rated voltage, and the lowest voltage shall generally not be lower than (90%) of the rated voltage, and shall meet the requirements of (plant) voltage.

2. The normal operating frequency of the generator shall be maintained at (50) Hz, and the allowable variation range is (± 0.2) Hz. The generator can operate continuously according to the rated capacity. When the frequency changes, the stator current, excitation current and temperature of each part shall not exceed (rated value).

3. The generator stator voltage is allowed to change within the rated value range (± 5%). When the power factor is the rated value, its rated capacity remains unchanged, that is, when the stator voltage changes within this range, the stator current can change inversely in proportion. However, when the generator voltage is lower than the rated value (95%;) The long-term allowable value of stator current shall not exceed the rated value (105%).

4. The hydrogen purity of the generator shall not be less than (96%), and the oxygen content shall be less than (2%).

5. The rated power factor of generator is (0.85). For generators that have not undergone the leading phase test, when the excitation regulator device is put into automatic operation, the power factor is allowed to operate for a long time within the late phase (0.95-1) range; When the power factor changes, the active and reactive power under the power factor shall not exceed the range of the (P-Q) output curve under the hydrogen pressure at that time.

6. After the generators are paralleled, the increase speed of active load depends on (steam turbine), and the increase speed of reactive load (unlimited), but the stator voltage change shall be monitored.

7. The insulation resistance of the generator rotor winding shall be measured with a (500V) megger, and the insulation value shall not be less than (0.5M Ω).

8. When three-phase current of stator is unbalanced, (negative sequence) current will be generated.

9. During the voltage rise of the generator, check that the three-phase voltage of the stator should rise (steadily) and the rotor current should not exceed (no-load value).

The insulation of 10.6KV motor shall be measured with a (2500V) volt megger, and the measured insulation resistance shall be greater than (6) M Ω.

11. Under normal conditions, the motor with squirrel cage rotor is allowed to be started (2 times) in cold state, and the time interval of each time is not less than (5) minutes. It is allowed to start (1 time) in hot state. Only the motor with accident handling or starting time not exceeding (2~3) seconds can be started more than once.

The insulation resistance of 12.6KV high-voltage auxiliary motor shall be measured under the same environment and temperature. If this measurement is lower than (1/3~1/5) times of the last measurement value, the reason shall be checked, and the absorption ratio “R60/R15” must be measured, which shall be greater than (1.3).

13. The motor can operate within the change of power frequency (± 1%) under rated voltage, with its rated output unchanged.

14. The main transformer cooler (full stop) is allowed to operate under the rated load limit. If the load is small and the upper oil temperature of the main transformer does not reach the specified value, it is allowed to rise to the specified value, but the maximum operation time of the main transformer shall not exceed (60) minutes.

15. The three-phase unbalanced current of AC motor shall not exceed (10%) of the rated value, and the current of any phase shall not exceed (rated value).

16. For transformers with oil immersed self cooling and oil immersed air cooling, the maximum allowable value of the upper oil temperature shall not exceed (95) ℃, and generally shall not exceed (85) ℃.

17. When the gas protection secondary circuit is grounded at one point, the heavy gas protection should be switched to the (signal) position.

18. The upper oil temperature of transformer with forced oil circulation air cooling generally does not exceed (75) ℃, and the maximum does not exceed (85) ℃.

19. The applied primary voltage of the transformer shall not exceed (105%) of the rated value of the tap generally. At this time, the secondary side of the transformer can carry the rated current.

20. Generally, double bus connection is adopted in power plants. During normal operation, one element (grounding) shall be guaranteed on each screen line. The main transformer is generally grounded through (grounding switch), and the neutral point of start-up standby transformer is generally (directly) grounded.

21.6KV switch cabinets are equipped with “five prevention” mechanical locking devices. Generally, the locking functions of the forced mechanical locking devices are (the trolley switch cannot be moved when it is closed), (the trolley switch cannot be pushed into the working position when the grounding switch is closed), (the grounding switch cannot be closed when the switch is in the working position), (the grounding switch cannot be opened when the switch is not in the working position), and (the grounding switch cannot be opened because it is not suitable).

22. After all disconnectors are closed, it must be checked that (three-phase contacts) are in good contact.

23. Before closing the grounding knife switch, it must be confirmed that the power switch on each side is in the (off) position, and it shall be carried out after verification (no voltage).

24. In case of loaded broach switch, it shall be quickly (closed) before the arc is broken. If the arc is broken, it is strictly prohibited to close it again. In case of on load closing, it is strictly prohibited to re (disconnect).

25. If there is no switch in the loop, the disconnecting switch can be used to equalize the loop current with the pull in voltage not exceeding 10KV and the current below (70A).

26. The normal working voltage of the cable line shall not exceed (15%) of the rated voltage of the cable.

27. Under normal circumstances, electrical equipment is not allowed to operate (without protection). If necessary, partial protection can be disabled, but (main protection) cannot be disabled at the same time; It is forbidden to open the cabinet door of the protection device during operation, and it is forbidden to use (wireless) communication equipment in the relay protection room of the central control room.

28.The insulation resistance of AC and DC low-voltage auxiliary motors below 380V shall be measured with (500) V megger. The insulation resistance of the motor shall not be less than (0.5) M Ω.

29. The definite time overload protection of the generator reflects the size of the generator (stator current).

30. The overvoltage protection of generator stator winding reflects the magnitude of (terminal voltage).

31. The generator definite time negative sequence overcurrent protection reflects the size of the generator stator (negative sequence current) to prevent the generator (rotor surface) from overheating.

32. The four limiting factors on the P-Q curve of the generator are (stator winding heating, rotor winding heating, stator end core heating, and stable operation limit).

33. Generator reverse power protection, for protection (turbine).

34. The order of installing the grounding wire is to install it first (grounding terminal) and then (conductor terminal).

35. Under normal operation mode, electrical insulation materials are classified according to the maximum allowable working (temperature).

36. The current value indicated by the AC ammeter represents the (effective) value of the current.

37. The safe distance of equipment without power failure is (0.7) m for 6kV, (1.5) m for 110KV and (5) m for 500KV.

38. In the power plant, the phase sequence of three-phase bus is represented by a fixed color, and (yellow), (green) and (red) are specified to represent phase A, phase B and phase C respectively.

39. Low voltage equipment refers to equipment whose voltage to ground is below (250) V, so the 380V auxiliary power system we often refer to is (low-voltage equipment).

40. During the normal operation of the generator, the three-phase unbalance value of the stator current shall not exceed (10%) of the rated value of the stator generally.

41. The phase difference high-frequency protection uses (high-frequency) signals to compare the current (phase) at both ends of the protected line.

42. If the disconnector is found to be hot, the equipment (load) shall be reduced until it is not hot, and the ventilation at the place shall be strengthened to cool down. If the heat is serious, the equipment shall be (stopped) for treatment after operation.

43. When the temperature difference between the highest and lowest temperature of the stator bar layers of the water-cooled generator reaches (8) ℃ or the water temperature difference of the stator bar water diversion pipe reaches (8) ℃, an alarm shall be given and the cause shall be found out. At this time, it can be handled (by reducing the load).

44. When the temperature difference of the stator bar of the water-cooled generator reaches (14) ℃ or the temperature difference of the outlet water of the stator water diversion pipe reaches (12) ℃, or the temperature of the interlayer temperature measuring element in any sub slot exceeds (90) ℃ or the outlet water temperature exceeds (85) ℃, after confirming that the temperature measuring element is correct, in order to avoid serious accidents, immediately (shut down), carry out (backwashing) and relevant inspection and handling.

45. The product of the effective value of the total voltage and the effective value of the current in a sinusoidal AC circuit contains both (active power) and (reactive power). We call it (apparent power).

46. In a circuit, the current flowing into a node (equal to the current flowing out of the node) is Kirchhoff (the first law).

47. Starting from any point in the circuit and circulating along the circuit for one week, the sum of potential increases (equal to) the sum of potential decreases, which is Kirchhoff (the second law).

48. The (branch current) method is the most basic method for calculating complex circuits.

49. In the (inductive) circuit, the voltage is ahead of the current; In a (capacitive) circuit, the voltage lags behind the current.

50. In the power system, shunt reactors are commonly used to absorb redundant (reactive) power and reduce (system voltage).

51. In a three-phase AC circuit, the line voltage (equal to) the phase voltage of the triangular connected power supply or load.

52. The total power of symmetrical three-phase AC circuit is equal to (3) times of single-phase power.

53. For symmetrical three-phase AC circuit, the neutral point voltage is equal to (zero).

54. In the power system, the so-called short circuit refers to an abnormal connection between (phase to phase) or (phase to ground) through arc or other small impedance.

55. The storage battery is an energy storage device, which can convert (electric) energy into (chemical) energy for storage; When it is used, it converts (chemical) energy into (electrical energy) and releases it through the external circuit.

56. The size of conductor resistance is not only related to the conductor’s (length) and (sectional area), but also to the conductor’s (material) and temperature.

57. In a closed circuit, voltage is the condition for generating current. The size of current is related to both the (resistance) and (terminal voltage) of the circuit.

58. In a series circuit, the voltage distribution at both ends of the load is proportional to the resistance of each load; In a parallel circuit, the current distribution of each branch is inversely proportional to the resistance of each branch.

59. When the (current) in the coil changes, the two ends of the coil will generate (self induced) electromotive force.

60. After the conductor is energized, the direction of the electromagnetic force received in the magnetic field is determined by (left-hand rule), while the direction of the induced electromotive force generated when the conductor moves to cut the magnetic line of force in the magnetic field is determined by (right-hand rule).

61. The number of alternating current periodic changes per second is called (frequency), which is represented by the letter (f), its unit name is (Hz), and its unit symbol is (Hz).

62. The maximum instantaneous value of sinusoidal alternating current in a cycle is called the (maximum) value of alternating current, also called (amplitude) or (peak value).

63. The effective value of alternating current is divided by the maximum equivalent dry value (√ 2).

64. In the circuit composed of resistance, inductance and capacitance, only (resistance) components consume electric energy, while (inductance) components and (capacitance) components exchange energy without consuming electric energy.

65. The power supply mode of star connection not led out at the neutral point is (three-phase three wire) system, and its current relationship is that the line current is equal to (phase current).

66. The greater the current passing through a coil, the stronger the (magnetic field) generated, and the more (magnetic) lines passing through the coil.

67. The current carrying coil can generate magnetic field, and its (strength) is in direct proportion to the current passing through the current carrying conductor.

68. The voltage between three-phase end lines is called (line voltage); The voltage between the terminal line and the neutral point is (phase voltage); In a star connected symmetrical circuit, the line voltage is equal to (√ 3) times the phase voltage.

69. The main reason for short circuit in the power system is that the current carrying part (insulation) of electrical equipment is damaged.

70. The hazards of short circuit to electrical equipment mainly include: (1) the current (thermal effect) causes the equipment to burn or damage the insulation; (2) (Electric power) deforms and destroys electrical equipment.

71. The electrical equipment and current carrying conductor must have sufficient (mechanical) strength, be able to withstand the electrodynamic action during short circuit, and have sufficient thermal (stability).

72. The transformer changes the voltage and current of an alternating current into the same (frequency) but different (value) voltage and current according to the (electromagnetic induction) principle.

73. The principle of induction motor is that when the three-phase symmetrical AC current flows through the three-phase fixed winding, a (rotating) magnetic field is generated. The magnetic line of the magnetic field cuts the wire on the rotor and induces (current). Because of the interaction between the stator magnetic field and the rotor current, electromagnetic (torque) is generated and it rotates.

74. The copper wire and aluminum wire are connected by conversion joint. If they are directly connected, there is (potential difference) between the copper wire and aluminum wire. If there is moisture at the connection, it will form (ionization) action and cause electric corrosion.

75. When insulating materials are placed near transmission lines, (induced) charges will be generated, which is called (electrostatic) induction of transmission lines.

76. Sulfur hexafluoride (SF6) is a (colorless), (odorless) and incombustible gas with very stable performance.

77. As the DC power supply (for control) and (for protection) in the power plant, the battery has the advantages of stable voltage, reliable power supply, etc.

78. The active substance on the (positive) plate of the battery is lead dioxide, and the active substance on the (negative) plate is sponge lead.

79. The capacity of a group of storage batteries is 1200AH. If the current is discharged at 100A, the continuous power supply time is (12 hours).

80. Under normal conditions, electrical equipment only bears its (rated) voltage. Under abnormal conditions, the voltage may rise a lot, which is dangerous to the insulation of electrical equipment. We call it (overvoltage).

81. In power system, external overvoltage is also called (atmospheric) overvoltage, which can be divided into (direct) lightning overvoltage and (induced) lightning overvoltage according to the form of overvoltage.

82. In power system, internal overvoltage can be divided into (operation) overvoltage, (arc grounding) overvoltage and (electromagnetic resonance) overvoltage according to the causes of overvoltage.

83. The terminals of the megger are L, E and G, which represent L (line), E (grounding) and G (shielding).

84. When measuring the insulation resistance of electrical equipment, it is generally judged by measuring the absorption ratio. When the absorption ratio is greater than 1.3, it means (good insulation); When it is close to 1, it means (insulation is affected with damp).

85. The head of the multimeter is the main component of the multimeter. It is a highly sensitive (magnetoelectric) DC (ampere) meter.

86. The purpose of the circuit breaker is to (make) or (break) the circuit normally; In case of fault, it can automatically (cut off) the fault current, and can automatically (reclose) when necessary, playing the role of control and protection.

87. The functions of oil in the circuit breaker are (arc extinguishing) and (insulation).

88. The role of high-voltage disconnector is: (1) to connect or disconnect (allow) the load circuit; (2) Create an obvious (disconnection) point to ensure personal safety; (3) Cooperate with (circuit breaker) to switch the operation mode.

89. The insulation of high-voltage disconnector mainly includes: (to ground) insulation; Insulation (fracture).

90. The primary main wiring of the power plant shall meet the requirements of (safety) reliability, (mode) flexibility and (maintenance) convenience.

91. The secondary rated voltage of voltage transformer is generally (100) V, and the secondary rated current of current transformer is generally (5) A.

92. The insulating material has good (dielectric) performance, i.e. high (insulation) resistance and withstand voltage strength.

93. The substances in nature are classified into three categories (conductor), (semiconductor) and (insulator) according to their conductivity.

94. When charged bodies are close to each other, they will have a strong effect. When objects with similar charges are close to each other, their effect is (mutual exclusion); The action of objects with opposite charges is (attract each other) when they approach.

95. When two coils flow in or out of current from a fixed end respectively, the (magnetic flux) generated by them is mutually reinforcing, then the two ends are called (homonymous) ends.

96. The capacitive reactance of the capacitor element to (high frequency) current is very small, while to (direct current) it can be regarded as an open circuit, so the capacitor has (isolation) effect in the circuit.

97. The unit of active power is watt, the unit of reactive power is var, and the unit of apparent power is volt ampere.

98. In a single-phase circuit, the apparent power is equal to the product of the rms of (voltage) and (current).

99. In order to increase the cross-sectional current of the bus, the number of parallel buses is commonly used. However, the more the number of parallel buses is, the more (uneven) the current distribution is. The current flowing through the middle bus is (small), and the current flowing through the buses on both sides is (large).

100. Circuit breakers can be divided into (gas) dielectric circuit breakers, (liquid) dielectric circuit breakers, (vacuum) circuit breakers, etc. according to the arc extinguishing medium.