In-depth decryption of the motor industry, 100 key pieces of knowledge for you

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

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

    3. The stator voltage of the generator 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 proportionally inversely. . But when the generator voltage is lower than the rated value (95%;), the long-term allowable value of the stator current shall not exceed the rated value (105%.).

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

    5. The rated power factor of the generator is (0.85). For generators that have not undergone phase advance tests, when the excitation regulator device is turned on automatically, the power factor is allowed to operate in the late phase (0.95~1) range for a long time; when the power factor changes, the power factor should be adjusted to have and without the power factor. The work power does not exceed the (P-Q) output curve range under the hydrogen pressure at that time.

    6. After the generator is paralleled, the active load increase speed depends on the (steam turbine) and the reactive load increase speed (not limited), but the stator voltage changes should be monitored.

    7. Use a (500V) megger to measure the insulation resistance of the generator rotor winding. The insulation value shall not be less than (0.5MΩ).

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

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

    When measuring the insulation of a 10.6KV motor, a (2500V) volt megger should be used to measure it, and the measured insulation resistance should be greater than (6) MΩ.

    11. Under normal circumstances, the squirrel-cage rotor motor is allowed to be started (2 times) in the cold state, and the time interval between each time is not less than (5) minutes. It is allowed to be started (1) time in the hot state, only in the event of an accident. Motors whose processing or starting time does not exceed (2 to 3) seconds can be started one more time.

    The insulation resistance of the 12.6KV high-voltage factory motor is measured in the same environment and temperature. If the current measurement is lower than (1/3~1/5) times the last measurement value, the reason should be checked and the absorption must be measured. Ratio "R60/R15", this value should be greater than (1.3).

    13. The motor can operate under the rated voltage and within the change of power frequency (±1%), 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 operating time of the main transformer shall not exceed (60 )minute.

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

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

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

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

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

    20. Generally, power plants use double busbar wiring. During normal operation, there should be one element (grounding) on ​​each line. The main transformer is generally grounded through (grounding knife switch), and the neutral point of the starter transformer is generally (directly) grounded.

    21.6KV switch cabinets are all equipped with "five-proof" mechanical locking devices. The locking functions of the forced mechanical locking device are generally (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 It cannot be pushed into the working position), (when the switch is in the working position, the grounding knife switch cannot be closed), (the grounding knife switch is not closed, and the back baffle of the switch cabinet cannot be opened).

    22. After all isolating switches are closed, check (three-phase contacts) for good contact.

    23. Before closing the grounding switch, you must confirm that the power switch on each side is in the (off) position, and proceed after verifying (no voltage).

    24. If a loaded broach gate occurs, it should be closed quickly before the arc is broken. If the arc has been broken, it is strictly prohibited to close it again. If closing with load occurs, re-opening is strictly prohibited.

    25. When there is no switch in the loop, the isolation switch can be used to balance the loop current with a voltage not exceeding 10KV and a current below (70A).

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

    27. Under normal circumstances, electrical equipment is not allowed to operate (without protection). Partial protection can be deactivated when necessary, but (main protection) is not allowed to be deactivated at the same time; it is prohibited to open the protection device cabinet door during operation, and it is prohibited to continue operating in the centralized control room. (Wireless) communication equipment is used indoors.

    Use a (500) V megger to measure the insulation resistance of AC and DC low-voltage factory motors below 28.380V. The insulation resistance value of the motor shall not be less than (0.5) MΩ.

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

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

    31. The fixed-time negative sequence overcurrent protection of the generator reflects the size of the generator stator (negative sequence current) and prevents the generator (rotor surface) from overheating.

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

    33. Generator reverse power protection, used to protect (steam turbine).

    34. The order of installing grounding wires is to install them first (ground end) and then (conductor end).

    35. In normal operating 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 safe distance for equipment without power outage is (0.7) m for 6kV, (1.5) m for 110KV, and (5) m for 500KV.

    38. In power plants, the phase sequence of the three-phase busbar is represented by fixed colors. It is stipulated that (yellow), (green), and (red) represent phase A, phase B, and phase C respectively.

    39. Equipment with a voltage to ground below (250) volts is considered low-voltage equipment, so the 380V factory power system we often refer to is (low-voltage equipment).

    40. When the generator is operating normally, the three-phase unbalance value of the stator current generally cannot exceed the stator rating (10%).

    41. The working principle of phase differential high-frequency protection is to use (high-frequency) signals to compare the current (phase) at both ends of the protected line.

    42. When it is found that the isolating switch is overheating, the equipment (load) should be reduced until it stops producing heat, and ventilation and cooling should be strengthened. If the heat is severe, the equipment should be stopped (stopped) for treatment.

    43. When the temperature difference between the highest and lowest temperatures between the stator bar layers of a water-cooled generator reaches (8) °C or the water temperature difference at the outlet of the stator bar water pipe reaches (8) °C, an alarm should be made and the cause should be identified. At this time, you can ( load reduction) processing.

    44. The temperature difference of the stator bar of the water-cooled generator reaches (14) ℃ or the water outlet temperature difference of the stator water pipe reaches (12) ℃, or the temperature of the interlayer temperature measuring element in any stator slot exceeds (90) ℃ or the outlet water temperature exceeds ( 85)℃, after confirming that the temperature measuring element is correct, in order to avoid major accidents, (stop) and perform (backwashing) and related inspections should be carried out immediately.

    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). We call it (apparent power).

    46. ​​In a circuit, the current flowing into a node is (equal to) the current flowing out of the node. This is Kirchhoff's (First Law).

    47. Starting from any point in the loop and circulating along the loop, the sum of the increase in potential is (equal to) the sum of the decrease in potential. This is Kirchhoff's (second law).

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

    49. In (inductive) circuits, voltage leads current; in (capacitive) circuits, voltage lags behind current.

    50. In power systems, parallel reactors are commonly used to absorb excess (reactive) power and reduce (system voltage).

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

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

    53. For a 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. A battery is an energy storage device that can convert (electrical) energy into (chemical) energy and store it; when used, it converts (chemical) energy into (electrical energy) and releases it through an external circuit.

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

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

    58. In a series circuit, the distribution of voltage across the load is (proportional) to the size of each load resistance; in a parallel circuit, the distribution of current in each branch is (inversely proportional) to the size of each branch resistance.

    59. When the (current) in the coil changes, a (self-induced) electromotive force is generated at both ends of the coil.

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

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

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

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

    64. In a circuit composed of resistors, inductors, and capacitors, only the (resistance) element consumes electric energy, while the (inductor) element and the (capacitor) element exchange energy and do not consume electric energy.

    65. The power supply mode of the star connection that does not lead out at the neutral point is a (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) produced and the more (magnetic) lines passing through the coil.

    67. A current-carrying coil can generate a magnetic field, and its (strength) is (proportional to) the magnitude of the current passing through the current-carrying conductor.

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

    69. The main cause of short circuit in the power system is the destruction of the (insulation) of the current-carrying part of the electrical equipment.

    70. The main hazards of short circuit to electrical equipment are: (1) the current (thermal effect) causes the equipment to burn or damages the insulation; (2) (electric power) causes the electrical equipment to deform and destroy.

    71. Electrical equipment and current-carrying conductors must have sufficient (mechanical) strength, be able to withstand the electrodynamic force during short circuit, and have sufficient thermal (stability).

    72. The transformer is based on the principle of (electromagnetic induction) to change the voltage and current of an alternating current into voltages and currents with the same (frequency) but different (value).

    73. The principle of induction motor is that when three-phase symmetrical alternating current flows through the three-phase stator winding, a (rotating) magnetic field is generated. The magnetic lines of the magnetic field cut the wires on the rotor and induce (current). Due to the interaction between the stator magnetic field and the rotor current, Produces electromagnetism (torque) and rotates.

    74. Copper wires and aluminum wires are connected using conversion joints. If they are directly connected, there will be a (potential difference) between the copper and aluminum wires. If there is moisture and moisture at the connection, (ionization) will occur and electric corrosion will occur.

    75. If insulators are placed near transmission lines, (induced) charges will be generated. This phenomenon is called (electrostatic) induction of transmission lines.

    76. Sulfur hexafluoride (SF6) is a (colorless), (odorless) non-flammable gas with very stable properties.

    77. The battery is used as a DC power source for (control) and (protection) in power plants. It has the advantages of stable voltage and reliable power supply.

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

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

    80. Under normal circumstances, electrical equipment can only withstand its (rated) voltage. Under abnormal circumstances, the voltage may rise more, and the voltage rise that is dangerous to the insulation of electrical equipment is called (overvoltage).

    81. In the power system, external overvoltage is also called (atmospheric) overvoltage. According to the form of overvoltage, it can be divided into: (direct) lightning overvoltage and (induction) lightning overvoltage.

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

    83. There are three terminals of the megohmmeter: L, E, and G. They represent: L (line), E (ground), and G (shield).

    84. When measuring the insulation resistance of electrical equipment, the moisture content of the insulation is generally determined 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 damp).

    85. The meter head of a multimeter is the main component of the multimeter. It is a high-sensitivity (magnetoelectric) DC (current) meter.

    86. The purpose of a circuit breaker is to (connect) or (disconnect) a circuit under normal conditions; when a fault occurs, it can automatically (cut off) the fault current, and when necessary, it can automatically (reclose), playing both control and protection roles. .

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

    88. The functions of the high-voltage isolation switch are: (1) to connect or disconnect the (permitted) load circuit; (2) to create an obvious (disconnection) point to ensure personal safety; (3) to cooperate with the (circuit breaker) for switching Operation mode.

    89. The insulation of high-voltage isolating switch mainly includes: (ground) insulation; (fracture) insulation.

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

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

    92. Insulating materials have good (dielectric) properties, that is, they have high (insulation) resistance and voltage resistance.

    93. People classify substances in nature into three categories: (conductor), (semiconductor) and (insulator) according to their ability to conduct electricity.

    94. When charged objects are close to each other, there will be a strong effect. When objects with the same charge are close, the action is (mutual repulsion); when objects with opposite charges are close, the action is (mutual attraction).

    95. When current flows into or out of two coils from a fixed end respectively, the (magnetic flux) they generate strengthens each other, then the two ends are called (same name) ends.

    96. The capacitive reactance of the capacitive element to (high-frequency) current is extremely small, and it can be regarded as an open circuit to (DC), so the capacitor plays a (DC blocking) role in this circuit.

    97. The units of active power are used (watts), the units of reactive power are used (vahr), and the units of apparent power are used (volt-amperes).

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

    99. In order to increase the cross-sectional current of the busbar, the number of parallel busbars is often used to solve the problem. However, the more parallel busbars, the more (uneven) the current distribution. The current flowing through the middle busbar is (small), and the current flowing through the busbars on both sides is smaller. Current (large).

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