100 operation knowledge that the hottest electrica

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100 pieces of operation knowledge that electrical engineers must know

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

2. The normal operation frequency of the generator should be maintained at (50) Hz, and the allowable variation range is (± 0.2) Hz, which can operate continuously according to the rated capacity. When the frequency changes, the stator current, excitation current and the 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 in reverse proportion. But 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 purity of hydrogen during generator operation shall not be lower than (96%), and the oxygen content shall be less than (2%)

5. The rated power factor of the generator is (0.85). When the excitation regulator device is put into automatic operation, the power factor of the generator without phase advance test is allowed to operate for a long time within the late phase (0.95-1); When the power factor changes, the active and reactive power under this power factor should not exceed the range of (P-Q) output curve under the current hydrogen pressure

6. The increase speed of active load after generator paralleling depends on (steam turbine), and the increase speed of reactive load (unlimited), but the change of stator voltage should be monitored

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

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

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

10, 6kV Motors should be measured with a (2500 V) volt megger, and the measured insulation resistance should be greater than (6) m Ω

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

12, the insulation resistance of 6kV high-voltage auxiliary motor is 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 should be checked, and the absorption ratio "r60/r15" must be measured, which should be greater than (1.3)

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

14. The main transformer cooler (full stop) is allowed to operate at the lower limit of the rated load. 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 allowable upper oil temperature shall not exceed (95) ℃ at most, and generally should not exceed (85) ℃

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

18. The upper oil temperature of forced oil circulation air-cooled transformer is generally not more than (75) ℃, and the maximum is not more than (85) ℃

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

20. Generally, power plants adopt double bus connection. During normal operation, there should be an element (grounding) on each wire. The main transformer is generally grounded through (grounding knife switch), and the neutral point of startup and 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 device are (when the trolley switch is in the closing state, it cannot move), (when the grounding knife switch is in the closing state, the trolley switch cannot be pushed into the working position), (when the switch is in the working position, it cannot close the grounding knife switch), (when the grounding knife switch is not in the working position, it cannot open the rear baffle of the switch cabinet)

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, make sure that the power switch on each side is in the (off) position, and carry out after verification (no voltage)

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

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

26. The normal working voltage of the cable line should 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) is not allowed to be disabled at the same time; It is forbidden to open the door of the protection device cabinet 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 generator definite-time overload protection 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 iron core heating, stable operation limit)

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

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

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

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

37. The safety 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 the 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 the equipment whose voltage to ground is below (250) V, so the 380V auxiliary power system we often say is (low voltage equipment)

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

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

42. When the disconnector is found to be heated, the equipment (load) should be reduced until it is not heated, and the ventilation and cooling should be strengthened. If the heating is serious, the equipment should be (stopped) after operation

43. When the temperature difference between the highest and lowest temperature between stator bar layers of water-cooled generator reaches (8) ℃ or the water temperature difference of stator bar water diversion pipe reaches (8) ℃, alarm and find out the cause, and then (reduce the load) treatment can be carried out

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

45. The product of the effective value of the total voltage and the effective value of the current in a sinusoidal AC circuit includes both (active power) and (reactive power), which we call (apparent power)

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

47. Starting from any point of the circuit and circulating along the circuit for a week, the sum of potential increase and (equal to) the sum of potential decrease is Kirchhoff (Second Law)

48. In various methods of calculating complex circuits, (branch current) method is the most basic method

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

50. In power system, shunt reactor is commonly used to absorb excess (reactive) power and reduce (system voltage)

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

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 an arc or other small impedance

55. Battery is an energy storage device, which can convert (electric) energy into (chemical) energy that can eliminate the influence of machine weight on force value; When in use, it converts (chemical) energy into (electrical energy) and releases it through the external circuit

56. The resistance of a conductor is not only related to the (length) and (cross-sectional area) of the conductor, but also to the (material) and temperature of the conductor

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

58. In the 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 (self induced) electromotive force is generated at both ends of the coil

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

61. The number of periodic changes of alternating current per second is called (frequency), which is represented by the letter (f). Its unit name is (Hz), and the 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 known as (amplitude) or (peak)

63, the effective value of AC divided by (√ 2)

64. In the circuit composed of resistance, inductance and capacitance, only (resistance) elements consume electric energy, while (inductance) elements and (capacitance) elements exchange energy and do not consume electric energy

65. The power supply mode of star connection without leading 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, passing through the coil

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