51. Why does a storage battery self-discharge?
A: The main reason for the self-discharge of a storage battery is due to impurities in the plates, forming local small batteries. The two poles of the small batteries form a short-circuit loop, causing the storage battery to self-discharge. In addition, due to the different densities of the electrolyte in the storage battery, the electromotive force on the upper and lower parts of the plates is uneven, which will also cause the self-discharge of the storage battery.
 

52. Why is it necessary to regularly charge and discharge the storage battery?
A: Regular charging and discharging, also known as verification charging and discharging, means that for storage batteries operating under float charging, after a certain period of time, the substances on the plates should undergo a larger charging and discharging reaction to check the battery capacity and identify aging batteries for timely maintenance to ensure normal operation. Regular charging and discharging is generally carried out at least once a year.
   

53. Why is a resistor connected in series with the traffic light and DC power supply monitoring light?
A: The purpose of connecting a resistor in series with the traffic light is to prevent the lamp socket from short-circuiting and causing the switch to trip and close. The purpose of connecting a resistor in series with the DC power supply monitoring light is to prevent the filament or lamp socket from short-circuiting and causing a short circuit in the DC power supply, as well as to prevent the high voltage from burning out the DC power supply monitoring light.
 

54. How is the load rate of equipment calculated?
A: Load rate = (Average value of daily load curve / Maximum value of daily load curve) * 100%
   

55. Why must the neutral point of 110kV and above transformers be grounded before power outage and power supply?
A: China's 110kV power grid generally adopts a neutral point directly grounded system. During operation, in order to meet the requirements of relay protection device sensitivity matching, the neutral points of some transformers are not grounded. However, because the overvoltage caused by the asynchronous operation of the circuit breaker will endanger the insulation of these transformers, it is required to directly ground the neutral point of the transformer when switching 110kV and above unloaded transformers.
   

56. What is voltage instantaneous overcurrent protection?
A: When a short-circuit fault occurs on the line, the bus voltage drops sharply. When the voltage drops to the voltage protection setting value, the low-voltage relay operates and trips the circuit breaker, instantly cutting off the fault. This is voltage instantaneous overcurrent protection.
    

57. What is distance protection?
A: Distance protection refers to a protective device that uses impedance elements to reflect short-circuit faults. The impedance value of the impedance element is the ratio of the voltage and current connected to the element: U/I=Z, which is the impedance value from the short-circuit point to the protection installation location. Because the impedance value of the line is proportional to the distance, it is called distance protection or impedance protection.
 

58. What is a synchronizing circuit?
A: Usually, a substation only installs one or two sets of common synchronizing devices, so it is necessary to install a synchronizing busbar. The AC voltage is taken from both sides of the circuit breaker using voltage transformers, and then connected to the synchronizing busbar through the synchronizing handle of each circuit breaker. The synchronizing busbar is then connected to the synchronizing device. The secondary circuit and the wiring of the synchronizing device are called the synchronizing circuit.
 

59. What is high-frequency protection? What are its advantages?
A: High-frequency protection includes phase-difference high-frequency protection and power directional interlock high-frequency protection. Phase-difference high-frequency protection measures and compares the phases of the current on both sides of the protected line, using the power line carrier communication method to transmit the phases of the current on both sides. Power directional interlock high-frequency protection compares the direction of power on both sides of the protected line. The power direction from the busbar to a certain line is defined as positive, and the direction to the busbar is negative. In case of a line internal fault, the power direction on both sides is from the busbar to the line, and the protection operates to trip. The signal transmission method is the same. The biggest advantage is that it can cut off various faults from both sides of the protected line without time limit; it does not need to cooperate with the protection of adjacent lines; phase-difference high-frequency protection is not affected by system oscillations.

 

60. What are the main physical properties of SF6 gas?
A: SF6 gas is a colorless, odorless, non-toxic, non-flammable inert gas with excellent insulation properties. It does not age or deteriorate, its specific gravity is about 5.1 times that of air, and it liquefies at -62 degrees under standard atmospheric pressure.
 

61. What are the regulations for installing gas relays on transformers and plant transformers?
A: Transformers with oil cushions of 800KVA and above, and plant transformers of 400KVA for thermal power plants and 180KVA and above for hydropower plants should be equipped with gas relays.
 

62. Why is the temperature rise of the windings of Class A insulated transformers specified as 65 degrees?
A: Iron loss and copper loss are generated during the operation of the transformer, and these two parts of loss are all converted into heat, causing the iron core and windings to heat up, the insulation to age, and affecting the service life of the transformer. Therefore, international regulations stipulate that the insulation of transformer windings mostly uses Class A insulation, and the temperature rise of the windings is specified as 65 degrees.
 

63. What are the five main components of a resistor-limited on-load tap-changing switch? What are their uses?
A: The components and functions of the resistor-limited on-load tap-changing switch are as follows: (1) Switching switch: Used to switch the load current; (2) Selector switch: Used to select the pre-selected tap; (3) Range switch: Used to change direction or roughly adjust the tap; (4) Operating mechanism: The power part of the tap-changing switch, with interlocking, limit, and counting functions; (5) Fast mechanism: Quickly switches according to the predetermined program.
 

64. What is the function of the thermal siphon filter installed on one side of the transformer oil tank?
A: Transformer oil will gradually become dirty and oxidized during operation. To extend the service life of the oil and enable the transformer to operate under better conditions, it is necessary to maintain good oil quality. The thermal siphon filter can keep the transformer oil quality good during operation without severe aging. In this way, the oil can be used for many years without special regeneration treatment.
 

65. What is the unbalanced current of a transformer? What are the requirements?
A: The unbalanced current of a transformer refers to the current difference between the windings of a three-phase transformer. In a three-phase four-wire transformer, the unbalance of each phase load is not allowed to exceed 20%. In a three-phase four-wire transformer, the unbalanced current-induced neutral line current must not exceed 25% of the rated current of the low-voltage winding. If the above regulations are not met, the load should be adjusted.
 

66. Why is it necessary to measure the slope of the connection pipe between the transformer cover and the oil cushion after the transformer is newly installed or overhauled? What is the standard?
Answer: There are two slopes on the gas relay side of the transformer. One is the slope of the transformer cover in the direction of the gas relay, which should be 1%-1.5%. The slope of the transformer cover should be padded from the bottom during the installation of the transformer. The other is the slope from the transformer tank to the oil cushion connecting pipe, which should be 2%-4% (this slope is manufactured by the manufacturer). These two slopes are, firstly, to prevent air from being stored in the transformer, and secondly, to facilitate the rapid and reliable entry of gas into the gas relay in case of a fault, ensuring the correct operation of the gas relay.
 

67. Which part of the transformer winding is the hottest during normal operation?
Answer: The temperature of both the winding and the core is higher at the top and lower at the bottom. For a general structure oil-immersed transformer winding, it has been verified that the hottest point is located at 70%-75% of the height and one-third of the radial distance from the inner diameter of the winding. The hottest point of each transformer winding should be determined by testing.
 

68. What is the role of a static var compensator (SVC) in a power system?
Answer: The function of an SVC is to supply reactive power to the system, improve the power factor, reduce network losses, and has a good effect on adjusting network voltage and improving power quality.
 

69. What are the basic requirements for electrical main busbars?
Answer: (1) Reliable power supply. (2) Operational safety and flexibility. (3) Simple and convenient operation. (4) Economic construction and operation. (5) The possibility of future expansion should be considered.
 

70. What are the measures to improve the static stability of the power system?
Answer: (1) Reduce the reactance of the system components. (2) Use automatic voltage regulator (AVR). (3) Use frequency-sensitive load shedding devices. (4) Increase the active and reactive power reserve capacity of the power system.
 

71. What grade of current transformers should be equipped for various energy meters in substations?
Answer: For active energy meters, current transformers with an accuracy class of 1.0 or 2.0 should be equipped; for reactive energy meters, current transformers with an accuracy class of 2.0 or 3.0 should be equipped; for the energy meters of transformers, station service transformers, and lines, and other energy meters used for electricity billing, current transformers with an accuracy class of 0.5 or 1.0 should be equipped.
 

72. What is dual rectifier? What are the common types of dual rectifiers?
Answer: A dual rectifier is composed of a voltage source (voltage source) connected to the voltage system and a rectifier power supply (current source) connected to the current system, which are reasonably matched by series and parallel methods to ensure the provision of reliable and reasonable control power under various operating modes and fault conditions of the primary system. Common dual rectifiers include single-phase and three-phase types. Single-phase dual rectifiers are further divided into parallel and series connections.
 

73. What are the dangers of sub-harmonic resonance overvoltage?
Answer: Sub-harmonic resonance is quite dangerous to the system. Under the action of sub-harmonic resonance voltage and power frequency voltage, the magnetic flux density of the PT core is rapidly saturated, and the excitation current increases rapidly, which will cause the PT winding to overheat and be damaged (all PTs in the same system are threatened), and even cause busbar faults, resulting in large-scale power outages.
 

74. What factors are related to the change of transformer oil level?
Answer: Under normal circumstances, the oil level of the transformer changes with the change of oil temperature, because the change of oil temperature directly affects the volume of the transformer oil, causing the oil level in the oil gauge to rise or fall. Factors affecting oil temperature changes include load changes, ambient temperature changes, internal faults, and the operation of cooling devices.
 

75. What are the causes of on-load tap changer (OLTC) failures?
Answer: (1) The transition resistance in the auxiliary contacts is broken down and burned during switching. (2) The tap changer is not tightly sealed, and water ingress causes interphase short circuits. (3) Due to the jamming of the contact roller, the tap changer stops at the transition position, causing inter-turn short circuits and burning. (4) The tap changer oil tank is short of oil. (5) Encountering fault current during tap changing.
 

76. What are the causes of on-load tap changer (OLTC) malfunction?
Answer: (1) The operating power supply voltage disappears or is too low. (2) The motor winding is broken and burned, and the starting motor is de-energized. (3) Poor contact of the interlock contacts. (4) The rotating mechanism is disengaged and the pins are dropped.
 

77. What should be paid attention to when replacing the desiccant in the transformer breather?
Answer: (1) The heavy gas protection should be changed to signal. (2) When removing the breather, the connecting pipe should be plugged to prevent back suction of air. (3) After replacing the dry desiccant, the oil seal should cover the vent to seal the breather.
 

78. Can the operating condition of a running transformer be judged according to its sound?
Answer: The operating condition of a transformer can be judged according to its sound. Place one end of a wooden stick on the transformer tank and the other end on your ear to listen carefully to the sound. If the continuous humming sound is heavier than usual, check the voltage and oil temperature. If there is no abnormality, it is mostly due to loose core. When a squeaking sound is heard, check whether there is any flashover phenomenon on the surface of the bushing. When a crackling sound is heard, it is an internal insulation breakdown phenomenon.

 

79. What are the basic requirements for relay protection?
Answer: According to the tasks undertaken by relay protection devices in the power system, relay protection devices must meet the following four basic requirements: selectivity, speed, sensitivity, and reliability.
 

80. Why is it required that the relay protection device operate quickly?
Answer: Because the rapid operation of the protection device can quickly cut off the fault, prevent the expansion of the accident, prevent the equipment from being more seriously damaged, and can also reduce the time of fault-free users working under low voltage and the power outage time, and accelerate the process of restoring normal operation.
 

81. What is high-speed reclosing?
Answer: When a fault occurs on the protected line, the protection device selectively cuts off the faulty line. At the same time, the reclosing action is performed once. If the reclosing is performed on a permanent fault, the protection device immediately acts again to disconnect the circuit breaker without time limit and selectivity. This protection device is called high-speed reclosing, which can generally be achieved by adding an intermediate relay.
 

82. What is auto-reclosing?
Answer: A device that allows a circuit breaker to automatically reclose quickly after tripping without manual operation is called an auto-reclosing device.
 

83. What are the characteristics of ground distance protection?
Answer: (1) It can protect against various ground faults using only one distance relay, simplifying wiring. (2) It can tolerate large ground transition resistances. (3) The protection action is fast and has good operating characteristics. (4) It is less affected by changes in system operating modes.
 

84. What are the characteristics of plate sulfation in battery operation?
Answer: (1) Bubbles appear prematurely during charging or immediately at the beginning of charging. (2) The voltage is too high during charging and lower than normal during discharging. (3) The positive plate appears brown with white spots.
 

85. What are the reasons for transformer oil shortage?
Answer: (1) Long-term oil seepage or large oil leakage from the transformer. (2) Oil was drained during transformer maintenance and not replenished in time. (3) The oil pillow capacity is small and cannot meet operational requirements. (4) The temperature is too low, and the oil pillow's oil storage is insufficient.
 

86. What are the characteristics of plate short circuits in battery operation?
Answer: (1) The voltage is relatively low (sometimes zero) during charging or discharging. (2) The electrolyte specific gravity cannot increase during charging. (3) Few bubbles appear during charging, and the bubbles appear late.
 

87. What are the characteristics of plate bending in battery operation?
Answer: (1) Plate bending. (2) Plate cracking. (3) The negative plate lead wool swells and forms moss-like tumors.
 

88. What are the "5-8", "6-7", and "2-4" contacts on the general circuit breaker operating handle? In what position of the operating handle are they closed? In what position are they open?
Answer: 5-8 are closing contacts, closed in the "closing" position and open in the "closed" position; 6-7 are tripping contacts, closed in the "tripping" position and open in the "tripped" position; 2-4 are reclosing discharge contacts, closed in the "prepare to trip" and "tripped" positions and open in the "prepare to close" position.
 

89. What is the function of relay protection?
Answer: Relay protection devices can detect equipment faults and abnormal operating conditions and automatically and quickly isolate the faulty equipment from the system selectively by operating the circuit breaker, ensuring that fault-free equipment continues to operate normally, limiting accidents to the minimum range, improving system reliability, and maximizing the safety of power supply to users.
 

90. What is the time delay characteristic of overcurrent protection?
Answer: The relationship curve between the short-circuit current flowing through the overcurrent protection device and the operating time is called the time delay characteristic of the protection device. The time delay characteristic is divided into definite time delay characteristic and inverse time delay characteristic. The operating time of the definite time delay is fixed and is independent of the magnitude of the short-circuit current. The operating time of the inverse time delay is related to the magnitude of the short-circuit current. The larger the short-circuit current, the shorter the operating time; the smaller the short-circuit current, the longer the operating time. The short-circuit current and the operating time limit have a certain curve relationship.
 

91. What are the basic principles of the Electricity Law?
Answer: (1) The principle that the electric power industry should develop appropriately ahead of the needs of national economic and social development. (2) The principle that the state encourages domestic and foreign economic organizations and individuals to invest in and develop power sources and establish power generation enterprises according to law, implementing the principle of whoever invests benefits. (3) The principle that power facilities and electricity are protected by the state. (4) The principle that power construction and power generation should protect the environment and prevent pollution according to law. (5) The principle that the state encourages and supports the use of renewable and clean energy for power generation. (6) The principle that power enterprises operate independently, are self-sufficient, and accept supervision according to law. (7) The principle that the state assists and supports the development of the electric power industry in minority ethnic areas, remote areas, and impoverished areas. (8) The principle that the state encourages the use of advanced science and technology and management methods to develop the electric power industry.
  

92. What are the basic principles of power grid operation and management?
Answer: (1) The power grid implements unified dispatching and hierarchical management. (2) No unit or individual may illegally interfere with power grid dispatching.

 

93. What is the main content of the Electricity Law?
Answer: The Electricity Law has ten chapters and seventy articles. The main content includes: The general provisions section defines the legislative purpose, scope of application, basic principles for developing the electric power industry, and the electric power management system. The specific provisions section includes power construction, power generation and grid management, power supply and use, electricity prices and fees, rural power construction and rural electricity use, power facility protection and supervision and inspection, legal liabilities, etc., comprehensively regulating the construction and development of the electric power industry. The supplementary provisions stipulate the effective date of the Electricity Law, which is April 1, 1996.
 

94. What are the main contents of the power safety production management system?
Answer: According to Article 19 of the Electricity Law, power enterprises must strengthen safety production management and establish and improve a safety production responsibility system, including the following specific systems: (1) Safety production responsibility system; (2) Production duty system; (3) Operation ticket system; (4) Work permit system; (5) Operation supervision system; (6) Work interruption, transfer, and termination system; (7) Safety production education system; (8) Regular inspection and maintenance system for power facilities.
 

95. What should be considered in anti-accident drills?
Answer: Lessons learned from accidents and abnormal phenomena in this enterprise and other enterprises. (2) Major defects and weaknesses in equipment. (3) Accidents that may occur before and after the introduction of new equipment, as well as seasonal accidents that affect the safe operation of equipment. (4) Weak links in special operating modes and operating techniques. (5) Major and complex operations of equipment systems.
 

96. What training work is specifically responsible for the team trainer?
Answer: (1) Develop team training plans, earnestly implement them under the leadership of the team leader, and strive to complete various training tasks assigned by the sub-station and county bureau. (2) Organize team members to learn the technical specifications of the equipment they manage, familiarize themselves with the equipment situation and regulations, etc. (3) Rely on team members and conduct team training activities based on the characteristics of the team. (4) Assist the team leader in daily team training work, such as on-site questioning, safety knowledge Q&A, technical explanation, technical Q&A, accident prediction, etc. (5) Assist the team leader in arranging the on-the-job training of new personnel, supervise and inspect the implementation of the master-apprentice contract, and conduct questioning and testing of new personnel. (6) Timely manage the registration of various trainings and summarize them regularly, reporting the implementation situation to the sub-station and county bureau training engineers.
 

97. What are the basic contents of the training for newly recruited production personnel?
Answer: (1) Political ideology and fine traditions, factory history and discipline education. (2) Electricity industry professional ethics education. (3) Education on observing laws and disciplines and civilized manners. (4) Education on relevant laws, regulations, and safety production knowledge.
 

98, What are the training steps for new on-duty personnel before taking up their posts?
Answer: Before new on-duty personnel can independently work on duty, they must go through three training stages: on-site basic system learning, on-the-job learning, and trial duty learning. A training plan needs to be developed for each stage, and training should be conducted according to the plan.
 

99, What is the purpose of anti-accident drills?
Answer: (1) Regularly check the ability of operating personnel to handle accidents. (2) Enable production personnel to master the correct methods for quickly handling accidents and abnormal phenomena. (3) Implement anti-accident measures and help production personnel further master on-site procedures and be familiar with equipment operating characteristics.
 

100, What are the contents of technical learning for operating personnel?
Answer: (1) Electricity safety work regulations, operation procedures, accident handling procedures, technical grade standards, job specifications, and relevant regulations and systems. (2) Compilation of accident, obstacle, and equipment abnormality data accumulated over the years that have occurred in this bureau, and anti-accident technical measures, etc. (3) Weak links and anti-accident measures and countermeasures exposed in anti-accident drills. (4) The structure, principle, parameters, performance, system layout, and operation methods of current and new equipment. (5) Safe and economical operation methods and advanced work methods. (6) Equipment maintenance and operation methods after changes and new technology operation. (7) The impact of seasonal changes on operating equipment and preventive measures. (8) Demonstration of operational professional theories or skills, etc. (9) Relevant parts of dispatching regulations.