Is the written test topic of recruiting transmission line specialty in China Southern Power Grid the same as electrical engineering and automation? What are you testing?

1. Briefly describe the related concepts and significance of daily load curve.

2. How many common methods are there for system voltage regulation?

3, power system overvoltage is divided into several categories? What are its causes and characteristics?

4. What is an electromagnetic ring network? What are the disadvantages of power grid operation? What's left for the time being?

1. Main protection: meets the requirements of system stability and equipment safety, and can selectively cut off the faults of protected equipment and lines at the fastest speed.

2. High-frequency locking distance protection: High-frequency protection is based on the principle that the starting element and distance direction element of distance protection control the transceiver to send out high-frequency locking signals and lock both sides of protection.

3. Secondary equipment refers to low-voltage electrical equipment that monitors, controls, adjusts and protects the work of primary equipment and provides operating conditions or production command signals for operation and maintenance personnel.

4. Repeated grounding: It is called repeated grounding to connect one or more points on the zero line with the earth again. (Its function is: (1) to reduce the earth voltage of leakage equipment. 2 reduce the risk of electric shock when the zero line is broken. ⑶ Shorten the time of shell contact or ground short circuit. ⑷ Improve the lightning protection performance of overhead lines. )

5. Distance protection: It is a protection device that uses impedance elements to respond to short-circuit faults. Because the impedance element reflects the ratio of voltage to current of the access element (U/I=Z), that is, it reflects the impedance value from the short-circuit fault point to the protection device, and the impedance of the line is proportional to the distance, so this protection is called distance protection or impedance protection.

6. Zero-sequence protection: After the grounding fault occurs in the large short-circuit current grounding system, there will be zero-sequence current, zero-sequence voltage and zero-sequence power. Relay protection devices that use these electrical quantities to protect grounding short circuit are collectively called zero-sequence protection. Zero sequence current protection is a common protection.

7. Backup protection: refers to the protection element that can cut off the faulty element for a long time (relative to the main protection) when the main protection or circuit breaker of a certain element refuses to operate.

8. High-frequency protection: it is a kind of protection that converts the current phase or power direction at both ends of the line into a high-frequency signal after a fault occurs, and then uses the transmission line itself to form a high-frequency current channel and sends this signal to the opposite end to compare the current phase or power direction at both ends.

9. Power system safety automatic device: refers to an automatic protection device to prevent power system instability and large-scale power failure.

10, power system accident: refers to the power system equipment failure or personnel work error, which affects the quantity and quality of power supply and exceeds the specified range.

1 1. resonance overvoltage: some inductance and capacitance elements in the power system can form various oscillation loops when the system is running or faulty, and series resonance will occur under a certain energy source, resulting in serious overvoltage of some elements in the system.

12. Circuit breaker failure protection: when the system fails, the fault element protection acts, and the circuit breaker fails and refuses to operate. The fault element protection acts on the adjacent circuit breakers in this substation to trip. If possible, the wiring of the remote circuit breaker can be tripped simultaneously by using the channel, which is called circuit breaker failure protection.

13. Resonance: If the frequency of the power supply and the parameters of the circuit meet certain conditions, the reactance is equal to zero, the circuit is resistive, and the voltage and current are in phase. This phenomenon is called resonance.

14, comprehensive reclosing: when a single-phase grounding fault occurs, the single-phase reclosing mode is adopted; In case of phase-to-phase short circuit, three-phase reclosing is adopted. A device that comprehensively considers these two reclosing modes is called a comprehensive reclosing device. After the comprehensive reclosing device is switched by the transfer switch, there are generally four operation modes: single-phase reclosing, three-phase reclosing, comprehensive reclosing and direct tripping (that is, if any type of fault occurs in the line, the protection can disconnect the three-phase through the outlet of the reclosing device without reclosing).

15. automatic reclosing: it is an automatic device that automatically turns on the circuit breaker after tripping due to a fault.

16. Electrical equipment in use: refers to all or part of electrical equipment with voltage. Once it is in operation, it will have voltage.

17. Remote backup: refers to that when a component fails and its protection device or switch refuses to operate, the protection devices of adjacent components on each power supply side act to remove the fault.

18, Energy Management System (EMS): It is the general name of modern power grid dispatching automation system. Its main function consists of basic function and application function.

19. Near-backup protection: The dual configuration strengthens the protection of the component itself, so that there is no possibility of refusing to operate when it fails in the area. At the same time, the switch failure protection is installed. When the switch refuses to trip, the high-voltage switch of the same substation bus can be started or the switch on the opposite side can be shaken.

20. Compound voltage over-current protection: it is a voltage compound element composed of negative sequence voltage relay and low voltage relay, which is connected to the interphase voltage. As long as the two relays act and the overcurrent relay also acts, the whole device can be started.

2 1, automatic low-frequency load shedding device: In order to improve the quality of power supply and ensure the reliability of power supply for important users, when the frequency of the system drops due to insufficient active power, according to the degree of frequency drop, some unimportant users are automatically disconnected to prevent frequency drop and make the frequency quickly return to normal. This device is called automatic low frequency load shedding device.

22. Line longitudinal protection: when the line fails, the protection device that makes the switches on both sides trip quickly at the same time is the main protection of the line. It is based on the specific relationship between the discriminators on both sides of the line. That is, the two sides transmit the discriminant quantity to each other through the channel, and then install the relationship between the discriminant quantity of the other side and our side on both sides to distinguish the faults in the area or the faults outside the area.

23. Dynamic stability of power system: refers to the ability of power system to maintain long-term stable operation under the action of automatic regulator and control device after small interference or large interference.

24. The meaning of "permission" in dispatching terminology: Before changing the state of electrical equipment and the operation mode of power grid, according to the relevant regulations, the relevant personnel shall put forward the operation matters, and the dispatcher on duty shall agree to its operation.

25. Comprehensive instruction: it is a comprehensive operation task issued by the on-duty dispatcher to a unit. The specific operation items and sequence shall be filled in by the on-site operators themselves according to the regulations, and can be operated only with the permission of the on-duty dispatcher.

26. One-time adjustment of frequency: The automatic adjustment process of the governor of the generator set without changing the position of the transmission mechanism is one-time adjustment of frequency. This adjustment is differential adjustment, that is, adjusting the frequency deviation caused by the first load change.

27. Secondary frequency modulation: When the power load changes, the primary frequency modulation caused only by the frequency characteristics of the generator speed regulation system cannot restore the original operating frequency. In order to keep the frequency unchanged, the operator needs to manually or automatically operate the governor to make the frequency characteristics of the generator move up and down in parallel, and then adjust the load to keep the frequency unchanged. Keeping the system frequency constant is achieved through primary adjustment and secondary adjustment.

28. Three adjustments of frequency: namely, the economic distribution of active power. According to the optimization criterion, the continuous component of the predicted load is distributed, and the relevant power plants in the system are arranged to generate electricity according to the given load curve, and the active load is optimally distributed between the power plants and the generator sets.

29. Static frequency characteristics of generator speed control system: When the system frequency changes, the speed control system of generator set will automatically change the steam intake of steam turbine or water intake of water turbine to increase or decrease the output of generator set, reflecting the relationship between the output changes of generator set caused by frequency change, which is called static frequency characteristics of generator speed control system.

30. Reverse voltage regulation mode: increase the central point voltage at the maximum load to compensate for the increased voltage loss on the line due to the maximum load, and reduce the central point voltage at the minimum load to prevent the load point voltage from being too high. This central point voltage regulation method is called reverse voltage regulation. At the maximum load, the central point voltage is 5% higher than the rated voltage of the line, and at the minimum load, the central point voltage drops to the rated voltage of the line, which can best meet the user's requirements.

3 1. Constant voltage regulation: If the load changes little, that is, the central point voltage is kept at a value (2%-5%) higher than the rated voltage of the line, the voltage quality of the load point can still be guaranteed without adjusting the central point voltage with the load change. This voltage regulation method is called constant voltage regulation or constant voltage regulation.

32. Parallel voltage regulation: If the load changes little, or the user is in an agricultural power grid with large allowable voltage deviation, the allowable central point voltage is lower at maximum load (not less than 102.5% of the line rated voltage) and higher at minimum load (not more than 107.5% of the line rated voltage). When the reactive power regulation mode is insufficient, this voltage regulation mode can be adopted, but it should generally be avoided.

33. Power dispatching plan change right: refers to the power grid dispatching institution's right to change the daily dispatching plan under special circumstances of the power grid. This right is limited, and it cannot be used to arbitrarily change the scheduling plan, making it lose its seriousness.

34. No-load loss of transformer: the power consumed by the transformer at the rated voltage of the primary side when the transformer is running. This is approximately equal to iron loss.

35. Clock representation of transformer wiring group: take the voltage vector of transformer high voltage side line as minute hand and point to "12", take the voltage vector of low voltage side line as hour hand, and the hour it points to is the group number of the wiring group.

36. Overexcitation of transformer: When the voltage of transformer increases or the frequency decreases, the working magnetic flux density will increase. The saturation of transformer core is called transformer overexcitation.

37. The transformer inrush current refers to the transient current generated in the winding when the transformer is charged at full voltage. Its maximum value can reach 6-8 times of the rated current value of the transformer. When the transformer is put into operation, the maximum inrush current occurs at the moment when the voltage crosses zero.

38. Power system: A unified whole consisting of power generation, transmission, transformation, distribution, electrical equipment and corresponding auxiliary systems is called power system.

39. Power grid: a unified whole consisting of transmission, substation, distribution equipment and corresponding auxiliary systems associated with power generation and consumption is called power grid.

40. Transmission capacity: refers to the maximum allowable transmission power of transmission systems between power systems or from one local system (or power plant) to another local system (or substation) in power systems (generally calculated by the receiving end).

4 1. main network: refers to the highest voltage transmission network, including the initial secondary voltage network, which together with * * * forms the framework of the power grid.

42. Power grid structure: mainly refers to the connection mode of the main network, the power supply and load of the regional power grid, and the power exchange capacity of the tie lines.

43. Line charging power: The reactive power generated by the line-to-ground capacitive current is called line charging power.

44. Submerged supply current: When the fault phase (line) is disconnected from both sides, there is inductive coupling and capacitive coupling between the non-fault phase (line) and the disconnected phase (line), and the current that continues to be supplied to the fault phase (line) is called latent supply current. If its value is large, the reclosing will fail.

45. Wave impedance: When electromagnetic waves propagate in one direction along the line, the ratio of the absolute value of traveling wave voltage to traveling wave current is called wave impedance. Its value is the square root of the ratio of inductance to capacitance per unit line length.

46. Natural power: The transmission line will not only generate reactive power due to distributed capacitance, but also consume reactive power due to series impedance. When a certain fixed active power is transmitted along the line and the two reactive powers on the line can be balanced, this active power is called the natural power of the line. If the transmitted active power is lower than this value, the line will send reactive power to the system; Above this value, the reactive power of the system will be absorbed.

47. Large grounding current system: In the neutral point direct grounding system, when a single-phase grounding fault occurs, the grounding short-circuit current is very large. This system is called large grounding current system.

48. Voltage collapse: The operating voltage corresponding to the tangent point of the voltage characteristic curve of reactive power supply and reactive load in power system is called critical voltage. When the capacity of all reactive power sources in the power system has been adjusted to the maximum, the operating voltage of the system will continue to decrease due to the continuous growth of reactive load. For example, when the working voltage drops to the critical voltage, the voltage of the load will drop due to disturbance, so that the reactive power supply is always smaller than the reactive load, which leads to the continuous voltage drop to zero. This phenomenon that the voltage drops to zero continuously is called voltage collapse. Voltage collapse will lead to a large number of load losses, even a large-scale power outage or system collapse.

49. Frequency collapse: The frequency corresponding to the tangent point of generator frequency characteristic curve and load frequency characteristic curve is called critical frequency. When the operating frequency of the power system is equal to (or lower than) the critical frequency, if the disturbance causes the system frequency to decrease, it will force the generator output to decrease, thus further reducing the system frequency, aggravating the imbalance of active power, forming a vicious circle, and leading to the continuous reduction of the frequency to zero, which is called frequency collapse.

50. Acceleration after reclosing: When the line fails, the protection will selectively remove the fault and then reclose once. If the fault and permanent fault occur at the same time, the protection device will open the short-circuit breaker indefinitely.

5 1. Transformer compound voltage overcurrent protection: This protection is usually used as backup protection of transformer. It is a voltage compound element, which consists of a negative sequence voltage relay and a low voltage relay, and is connected to the interphase voltage. As long as the two relays act and the overcurrent relay also acts, the whole device can be started.

52. Step overvoltage: The current flowing into the ground through the grounding body or grounding grid will form a spatially distributed current field on the surface and deep underground, and generate potential differences at different distances from the grounding body. This potential difference is called step voltage. The step voltage is directly proportional to the intensity of grounding current and inversely proportional to the square of the grounding distance. When the step voltage is high, it is easy to cause harm to people and storage.

53. Counterattack overvoltage: In the substation, if lightning strikes the lightning rod, the lightning current will flow to the ground through the grounding down lead of the building. Due to the existence of structural inductance and grounding resistance, high ground potential will be generated on the structure, which will cause great potential difference to nearby electrical equipment or live wires. If the distance between them is close, it will cause the lightning rod to discharge other equipment or wires, which will lead to the counterattack flashing and cause accidents.

54. System collapse: a state of large-scale power failure accident that is fragmented due to power system stability destruction, frequency collapse, voltage collapse, chain reaction or natural disasters.

55. Chain reaction: refers to the overload or accidental tripping of one transmission line (or a group of transformers), which causes other transmission equipment and generators to trip one after another (including the operation of personnel to prevent equipment damage). Chain reaction is an important reason for the expansion of the accident.

56. Three lines of defense: refers to the requirements for ensuring stable and reliable power supply to the power grid when the power system is disturbed by various kinds. (1) When a high probability common single fault occurs in the power grid, the power system should maintain stable operation and maintain normal power supply to users. (2) When a single fault with serious nature but low probability occurs in the power grid, the power system is required to maintain stable operation, but it is allowed to lose part of the load (or directly cut off part of the load, or naturally reduce the load due to the reduction of system frequency). (3) When the system has rare multiple faults (including single fault and incorrect relay protection). ), the power system may not be able to maintain stable operation, but predetermined measures must be taken to minimize the impact range and shorten the impact time.

57. Differential quick-break protection: When an asymmetric fault occurs inside the transformer, a larger second harmonic component is generated in the differential current, which causes the microcomputer-based longitudinal differential protection of the transformer to brake until the second harmonic component is attenuated. In order to speed up the protection action, it is stipulated that when the differential current is greater than the possible maximum inrush current, the longitudinal differential protection should trip immediately, and the protection set according to the principle of multiple is differential quick-break protection.