100 facts about electrical operation knowledge – very comprehensive!

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1. The stator voltage of the generator shall not exceed (110%) of the rated voltage, and the minimum voltage should generally not be lower than (90%) of the rated voltage; it must also meet the requirements regarding (plant) voltage. 2. The normal operating frequency of the generator should be maintained at (50) Hz, with a permissible variation range of (±0.2) Hz; it can operate continuously at its rated capacity. When the frequency changes, the stator current, excitation current, and temperatures of all components must not exceed (the rated values). 3. The stator voltage of the generator may vary within the rated range (±5%). When the power factor is at its rated value, its rated capacity remains unchanged; that is, as the stator voltage varies within this range, the stator current changes in proportion in the opposite direction. But when the generator voltage is below the rated value (95%) ； ) The permanently allowable value of the stator current must not exceed the rated value (105%). 4. The purity of hydrogen used in the operation of the generator must not be less than (96%), and the oxygen content must be less than (2%). 5. The rated power factor of the generator is (0.85). For generators that have not undergone leading-phase tests, when the excitation regulator is set to automatic mode, the power factor is allowed to operate within the lagging phase range (0.95–1) on a long-term basis ； When the power factor changes, the active and reactive powers at that power factor should not exceed the range of the (P-Q) performance curve at the current hydrogen pressure. 6. After the generators are connected in parallel, the rate of increase of the active load is determined by the turbine; there is no limit on the rate of increase of the reactive load, but the changes in stator voltage must be monitored. 7. The insulation resistance of the generator rotor windings shall be measured using a (500V) megohmmeter, and the insulation value must be no less than (0.5MΩ). 8. When the three-phase currents in the stator are unbalanced, (negative sequence) currents will definitely be generated. 9. During the voltage ramp-up process of the generator, the three-phase stator voltages should rise (steadily), and the rotor current must not exceed its (no-load value). 10. The insulation of 6KV motors should be measured using a megohmmeter with a voltage rating of (2500V), and the resulting insulation resistance should be greater than (6) MΩ. 11. Under normal conditions, motors with a squirrel-cage rotor are allowed to be started cold (2 times), with an interval of not less than (5) minutes between each start; they may be started while hot (1 time). Only in the case of accident handling or when the starting time is within (2–3) seconds is an additional start permitted. 12. For the insulation resistance of 6KV high-voltage factory motors, measured under the same environmental and temperature conditions, if the value obtained in this measurement is between (1/3 to 1/5) of the previous measurement value, the cause must be investigated, and the absorption ratio „R60/R15“ must also be measured; this value should be greater than 1.3. 13. The motor can operate at the rated voltage within a range of power supply frequency variations of (±1%), while its rated output remains unchanged. 14. The main transformer cooler (when fully shut down) may operate at the minimum rated load; if the load is low and the oil temperature on the upper side of the main transformer has not reached the specified value, it is allowed to rise to that value, but the maximum operating time of the main transformer shall not exceed (60) minutes. 15. The three-phase unbalanced current of an AC motor shall not exceed (10%) of the rated value, and the current in any one phase shall not exceed the rated value. 16. For transformers cooled by oil immersion with natural convection or forced air cooling, the maximum permissible value of the top oil temperature shall not exceed (95) °C; generally, it should not exceed (85) °C. 17. When there is a single-point ground in the secondary circuit of the gas protection, the heavy gas protection should be switched to the (signal) position. 18. In transformers with forced oil circulation for air cooling, the upper oil temperature generally should not exceed (75)°C, with a maximum of (85)°C. 19. The primary voltage applied to the transformer should generally not exceed 105% of the rated value of that tap; under such conditions, the secondary side of the transformer can carry the rated current. 20. Typical power plants use a double-bus wiring scheme; under normal operation, there should be one component (a ground device) on each bus. The main transformer is generally grounded through a ground switch, while the neutral point of the standby transformer is usually grounded directly. 21. Both 6KV switchgear units are equipped with \"five-prevention\" mechanical interlock devices. The common interlock functions of these mechanical interlock devices are: (the drawer switch cannot be moved when it is in the closed position), (the grounding switch cannot be pushed into the operating position when it is in the closed position), (the grounding switch cannot be closed when the switch is in the operating position), and (the rear panel of the switchgear cannot be opened if the grounding switch is not closed). 22. After all isolating switches are closed, it is necessary to check that the (three-phase contacts) are in good contact. 23. Before closing the grounding switch, it is necessary to ensure that all power switches on the relevant sides are in the (off) position; this should be done only after verifying that there is (no voltage). 24. In the event that a disconnector is pulled under load, it should be quickly closed before the arc is extinguished; however, if the arc has already been extinguished, it is strictly prohibited to close it again. In the event of a closed switch under load, it is strictly prohibited to disconnect it again. 25. When no switch is installed in the circuit, an isolating switch can be used to connect or disconnect the circuit current for balancing, provided that the voltage does not exceed 10 KV and the current is below 70 A. 26. The normal operating voltage of a cable circuit shall not exceed (15%) of the cable’s rated voltage. 27. Under normal circumstances, electrical equipment is not allowed to operate without protection; some protections can be disabled if necessary, but the (main protection) must not be disabled at the same time ； During operation, it is prohibited to open the doors of the protection device cabinets. The use of (wireless) communication devices in the relay protection room within the central control room is also prohibited. 28. For low-voltage AC and DC motors used in plants with voltages below 380V, use a (500)V megohmmeter to measure the insulation resistance. The insulation resistance value of the motor must not be less than 0.5 MΩ. 29. The time-limited overload protection for generators reflects the magnitude of the generator’s current (stator current). 30. The overvoltage protection of the generator stator winding reflects the magnitude of the terminal voltage. 31. The time-limited negative-sequence overcurrent protection for generators reflects the magnitude of the negative-sequence current in the generator stator, thereby preventing overheating of the generator (rotor surface). 32. The four limiting factors on the P-Q curve of a generator are (heating of the stator winding, heating of the rotor winding, heating of the stator end-core, and limits for stable operation). 33. Generator reverse power protection, used to protect (turbine). 34. The sequence for installing grounding wires is to install the (grounding end) first, and then the (conductor end). 35. Under normal operating conditions, electrical insulating materials are classified according to their maximum allowable operating temperature. 36. The current value indicated by an alternating current meter represents the (r.m.s.) value of the current. 37. The safe distance to ensure uninterrupted power supply for equipment is specified as (0.7) m for 6 kV, (1.5) m for 110 kV, and (5) m for 500 kV. 38. In power plants, the phase sequence of three-phase busbars is indicated by fixed colors; yellow, green, and red are specified to represent phases A, B, and C respectively. 39. Equipment with a voltage relative to ground of 250 volts or less is considered low-voltage equipment; therefore, the 380V plant power supply system that we often refer to is (low-voltage equipment). 40. When the generator is operating normally, the three-phase imbalance of the stator current should generally not exceed (10%) of the stator’s rated value. 41. The working principle of differential high-frequency protection is to use (high-frequency) signals to compare the currents (phases) at both ends of the protected line. 42. When it is detected that an isolator is overheating, the load on the equipment should be reduced until the overheating ceases; ventilation and cooling at that location should also be enhanced. In cases of severe overheating, the equipment must be shut down before any corrective measures are taken. 43. An alarm should be triggered when the temperature difference between the highest and lowest temperatures among the stator bar layers of a water-cooled generator reaches (8)°C, or when the temperature difference of the water exiting the stator bar water inlet pipes reaches (8)°C; the cause must be identified, and in such cases the load can be reduced as a solution. 44. When the temperature difference between stator bars of a water-cooled generator reaches (14)°C, or the temperature difference between the inlet and outlet water of the stator cooling water pipes reaches (12)°C; or when the temperature measured by any inter-layer temperature sensor in any stator slot exceeds (90)°C, or the outlet water temperature exceeds (85)°C—after verifying that the temperature sensors are functioning correctly—to prevent serious accidents, the generator must be immediately (shut down), and (backwashing) as well as relevant inspections and corrective measures must be carried out. 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). This product is referred to as (apparent power). 46. In a circuit, the current flowing into a node is equal to the current flowing out of that node; this is Kirchhoff’s first law. 47. Starting from any point in the loop and traveling around it once, the sum of the potential increases equals the sum of the potential decreases; this is Kirchhoff’s second law. 48. Among the various methods for calculating complex circuits, the (branch current) method is the most fundamental one. 49. In (inductive) circuits, voltage leads current ； In (capacitive) circuits, voltage lags behind current. 50. In power systems, shunt reactors are commonly used to absorb excess (reactive) power and reduce the (system voltage). 51. In a three-phase AC circuit, for sources or loads connected in a triangular configuration, the line voltage is equal to the phase voltage. 52. The total power in a symmetrical three-phase AC circuit is equal to (3) times the power of a single phase. 53. In a symmetrical three-phase AC circuit, the voltage at the neutral point is equal to (zero). 54. In power systems, a short circuit refers to an abnormal connection between (phases and phases) or (a phase and ground), through an arc or some other low impedance path. 55. A battery is an energy storage device that can convert electrical energy into chemical energy for storage ； When in use, chemical energy is converted back into electrical energy, which is then released through an external circuit. 56. The resistance of a conductor depends not only on its (length) and (cross-sectional area), but also on its (material) and temperature. 57. In a closed circuit, voltage is the condition that generates current; the magnitude of the current depends both on the (resistance) of the circuit and on the magnitude of the (terminal voltage). 58. In a series circuit, the distribution of voltage across the loads is (directly proportional) to the value of each load resistance ； In a parallel circuit, the distribution of current among the various branches is (inversely proportional) to the resistance of each branch. 59. When the (current) in the coil changes, a (self-inductance) electromotive force is generated across the coil. 60. The direction of the electromagnetic force acting on a conductor when an electric current flows through it in a magnetic field is determined by the (left-hand rule), whereas the direction of the induced electromotive force generated when the conductor moves through the magnetic field, cutting across the magnetic field lines, is determined by the (right-hand rule). 61. The number of times alternating current changes periodically per second is called (frequency), denoted by the letter (f). Its unit is called (hertz), and its symbol is (Hz). 62. The maximum instantaneous value that a sinusoidal alternating current reaches during one cycle is called the (maximum) value of the alternating current, also known as the (amplitude) or (peak value). 63. The effective value of alternating current is the peak value divided by (√2). 64. In a circuit composed of resistors, inductors, and capacitors, only the (resistor) element consumes electrical energy, while the (inductor) and (capacitor) elements exchange energy without consuming any electrical energy. 65. The power supply configuration with a star connection in which the neutral point is not connected is the (three-phase three-wire) system, and the relationship between currents is that the line current equals the (phase current). 66. The greater the current flowing through a coil, the stronger the (magnetic field) generated, and the more (magnetic) flux lines pass through the coil. 67. A current-carrying coil can generate a magnetic field, and its (strength) is (directly proportional) to the magnitude of the current flowing through the conductive wire. 68. The voltage between the three-phase terminal wires is called (line voltage) ； The voltage between the terminal line and the neutral point is (phase voltage) ； In a symmetric circuit with star connections, the line voltage is equal to (√3) times the phase voltage. 69. The main cause of short circuits in power systems is the damage to the (insulation) of the current-carrying parts of electrical equipment. 70. The main hazards of short circuits to electrical equipment include: (1) the (thermal effect) of current, which causes the equipment to burn out or damages its insulation ； (2) (Electromagnetic force) causes electrical equipment to deform and be damaged. 71. Electrical equipment and current-carrying conductors must possess sufficient (mechanical) strength to withstand the electrodynamic forces during a short circuit, as well as adequate thermal (stability). 72. A transformer operates on the principle of (electromagnetic induction) to convert the voltage and current of one type of alternating current into voltage and current with the same (frequency), but different (values). 73. The principle of an induction motor is that when three-phase symmetrical alternating currents flow through the three-phase stator windings, a (rotating) magnetic field is generated. The magnetic flux lines of this field cut across the conductors on the rotor, inducing an (electric current) therein. Due to the interaction between the stator’s magnetic field and the rotor current, electromagnetic (torque) is produced, causing the rotor to rotate. 74. Transition connectors are used for connecting copper and aluminum wires. If they are connected directly, there will be a potential difference between the copper and aluminum wires. Should moisture be present at the connection point, ionization occurs, leading to electrolytic corrosion. 75. Near power transmission lines, if insulating materials are placed there, (induced) charges are generated; this phenomenon is known as (electrostatic) induction by the power transmission lines. 76. Sulfur hexafluoride (SF6) is a (colorless), (odorless) non-flammable gas with very stable properties. 77. In power plants, batteries serve as a DC power source for (control) and (protection), offering advantages such as stable voltage and reliable power supply. 78. The active material on the (positive) plate of a battery is lead dioxide, while the active material on the (negative) plate is sponge lead. 79. The capacity of a set of batteries is 1200 AH. If they are discharged at a current of 100 A, the duration of power supply will be (12 hours). 80. Under normal conditions, electrical equipment is exposed only to its (rated) voltage. In abnormal situations, the voltage can rise significantly; such a voltage increase that poses a risk to the insulation of electrical equipment is referred to as (overvoltage). 81. In power systems, external overvoltage is also known as (atmospheric) overvoltage. Based on its form, it can be divided into: (direct) lightning overvoltage and (induced) lightning overvoltage. 82. In power systems, internal overvoltages can be classified according to the causes of their occurrence as: (operational) overvoltages, (arc grounding) overvoltages, and (electromagnetic resonance) overvoltages. 83. The terminals of a megohmmeter are L, E, and G; their meanings are: L (line), E (ground), G (shield). 84. When measuring the insulation resistance of electrical equipment, the absorption ratio is generally used to determine whether the insulation is damp; when the absorption ratio is greater than 1.3, it indicates (good insulation) ； When it is close to 1, it indicates (insulation moisture absorption). 85. The meter head of a multimeter is its main component; it is a highly sensitive (magnetoelectric) type DC (current) meter. 86. The purpose of a circuit breaker is to (connect) or (disconnect) the circuit under normal conditions ； In the event of a fault, it can automatically cut off the fault current; when necessary, it can also automatically reconnect, serving both control and protection functions. 87. The functions of the oil inside a circuit breaker are (arc extinguishing) and (insulation). 88. The functions of a high-voltage disconnector are: (1) to connect or disconnect the (permissible) load circuit ； (2) Create a distinct (disconnection) point to ensure personal safety ； (3) Switch operating modes in coordination with the (circuit breaker). 89. The insulation of high-voltage isolating switches mainly includes: (insulation to ground) ； (Broken end) Insulated. 90. The primary wiring of a power plant should meet the requirements of being (safe) and reliable, (flexible) in terms of configuration, and convenient for (maintenance). 91. The secondary rated voltage of a voltage transformer is generally (100) V, while the secondary rated current of a current transformer is generally (5) A. 92. Insulating materials possess good (dielectric) properties, namely high (insulation) resistance and voltage withstanding strength. 93. Materials in nature are classified into three categories based on their conductivity: (conductors), (semiconductors), and (insulators). 94. When charged objects come close to each other, a force is exerted between them; when objects with like charges come near, the force exerted is (repulsive) ； When objects with opposite charges come close to each other, the effect is (attraction). 95. When current flows into or out of two coils from a fixed terminal respectively, and the (magnetic flux) generated by them enhances each other, then those two terminals are called (like-named) terminals. 96. The capacitive reactance of a capacitor element to (high-frequency) current is extremely low, while it can be considered an open circuit to (direct current); therefore, the capacitor serves to (block direct current) in such circuits. 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, apparent power is equal to the product of the effective values of (voltage) and (current). 99. To increase the current-carrying capacity of the busbar, it is common to use multiple parallel busbars; however, the more parallel bars there are, the more uneven the current distribution becomes, with less current flowing through the middle busbars and more current flowing through those on the sides. 100. Circuit breakers can be classified according to the arc-quenching medium into: (gas) medium circuit breakers, (liquid) medium circuit breakers, (vacuum) circuit breakers, etc. End Source: Baidu Wenku