Answer: Adjust the tap and reduce it in several steps to make its voltage meet the requirements.
Note: If the tidal current direction is 500kV to 220kV at that time, the tap-changer has little influence on the voltage of 500kV system.
If the tidal current was from 220kV to 500kV at that time, the tap changer had a great influence on the voltage of the 500kV system.
2. Why can't thunderstorm weather be close to lightning arrester and lightning rod?
A: Thunderstorm weather, there are many lightning strikes. When lightning strikes lightning arrester or lightning rod, lightning current enters the earth through grounding device. Due to the grounding resistance of the grounding device, the potential will rise very high when lightning current passes, which may cause counterattack or step voltage to nearby equipment or personnel and threaten personal safety. Therefore, thunderstorm weather can't be near lightning arrester or lightning rod.
3. What is internal overvoltage? What is atmospheric overvoltage? What is the harm to the equipment?
Answer: Internal overvoltage refers to the overvoltage that is harmful to the power system when the state of the power system suddenly changes due to operation, accidents or improper coordination of power grid parameters.
Atmospheric overvoltage, also known as external overvoltage, is induced lightning overvoltage caused by direct lightning strike on equipment or lightning strike near equipment.
Internal overvoltage and atmospheric overvoltage are both very high, which is easy to cause flashover of weak insulation points and damage or even burn the insulation of electrical equipment.
4. What is the grounding resistance of substation grounding grid?
Answer: the grounding resistance of the large current grounding system should satisfy r ≤ 2000/I Ω, when I >; R ≤ 0.5 Ω can be selected at 4000A.
When the small current grounding system is used for the equipment below 1000V, the grounding resistance should satisfy r ≤125/i Ω, and when it is used for the equipment above 1000V, the grounding resistance r ≤ 250/i Ω should not be greater than10 Ω under any circumstances.
5. What is the grounding resistance of lightning rod?
Answer: The grounding resistance of independent lightning rods is generally not greater than10Ω, and the centralized grounding resistance of lightning rods installed on the frame is generally not greater than10Ω.
6. What is the function of the disconnector?
Answer; 1. Obvious disconnection point
2. Cut off the small current
3. Change the operation mode
7. What is the duty of the working ticket licensor?
Answer: 1. Responsible for reviewing whether the safety measures listed in the working ticket are correct and complete, and whether they meet the site conditions;
2. Whether the safety measures at the job site are perfect;
3. Be responsible for checking whether there is any danger of suddenly calling the power-off equipment;
4. Even if you have any questions about the contents listed in the working ticket, you must ask the working ticket issuer clearly and make detailed supplements when necessary.
8. What are the organizational measures to ensure safety?
A: 1. Working ticket system;
2. Work permit system;
3. Work guardianship system;
4. Work interruption, transfer and termination system.
9. What jobs need to be filled in the first job?
Answer: 1. Working on high-voltage equipment requires total or partial power failure;
2. High-voltage equipment needs to be powered off or safety measures should be taken for secondary wiring and lighting in the high-voltage room.
10. Which jobs need to fill in the second working ticket?
Answer: 1. Live working and working on the shell of live equipment;
2. Control panel and low-voltage distribution box. Distribution box Working on the main power supply line;
3. It is not necessary to cut off the high-voltage equipment when working on the secondary wiring circuit;
4. Rotating generator. The operation of excitation circuit of synchronous phase modulator or rotor resistance circuit of high voltage motor;
5. Non-duty personnel are on duty to phase with insulating rods and voltage transformers or to measure the high voltage circuit current with clamp ammeter.
1 1. What should the work permit holder do after completing the site safety measures?
Answer: 1. Go to the site with the person in charge of the work to check the safety measures taken again, and touch the test by hand to prove that the maintenance equipment has no voltage;
2. Point out the location and matters needing attention of live equipment to the working director;
3. Sign the working ticket with the person in charge.
12. What should I pay attention to when the working ticket is finally accepted?
Answer: The person in charge of the work records the repaired items, problems found, test results and existing problems, and checks the equipment status (line shifting, pressure plate, etc.). ) and the person in charge of the work, whether there are remnants, whether the site is clean, etc. , and then fill in the working ticket end time, signed by both parties to terminate the working ticket.
13. What technical measures are there to ensure safety?
Answer: 1. The power went out.
Check the power
3. Install grounding wire
4. Hang signs and install fences
14. What are the procedures for changing the person in charge of the work on the work ticket?
Answer: When it is necessary to change the person in charge of the work, the work signatory should record the change on the work ticket.
15. What are the symbols in this book and explain the purpose of each one?
A: There are six signs:
1. The operating handles of switches and knife switches should be hung with the sign "No closing, someone is working". Once closed, power can be sent to the work place.
2. If someone is working on the line, a sign "No closing, the line is occupied" should be hung on the line knife and switch operating handle.
3. On the fence of the construction site near the live equipment and on the fence of the outdoor operation site; In the forbidden aisle; Commercial stress testing ground; The outdoor shelf says "Stop, high pressure danger!" " Should be hung on the beam near the live equipment in the workplace. Signboard.
4. Hang the "Henceforth" sign on the iron shelves and ladders where the staff get up and down.
5. Hang the sign "Work here" in the workplace.
6. Hang "No climbing, high pressure danger!" On the iron frame where the staff get up and down, close to another iron frame that may get up and down, or on a ladder that runs transformers and other equipment. Signboard.
16. How long are the first and second working tickets valid?
Answer: The valid time of the first and second working tickets is limited to the maintenance period approved by the dispatching.
17. What are the main reference materials to prevent electrical misoperation?
Answer: 1) Safety work regulations for power industry.
2) Twenty-five key requirements for preventing major accidents in power production (Guodian Company)
3) Minutes of National Professional Work Conference on Preventing Electrical Misoperation (No.96.49 of Ministry of Electric Power)
4) Regulations on Prevention of Electrical Misoperation Devices (No.90.110 of the Ministry of Energy)
5) Summary Meeting Minutes of East China Power Grid Anti-misoperation Mutual Check (East China Power Generation Office No.96.036)
6) Several Provisions on Substation Operation and Management (enterprise standard of provincial companies Q/ZDL24107001-2000a)
7) Minutes of 99 Bureau's Meeting on Error Prevention (Hangzhou Diansheng 99.067)
8) The Company's management system for the use of error prevention devices.
18. What are the assessment rules for switching operation tickets?
A: Our institute conducts labor competition according to the requirements of Guodian East China Company.
19. What are the requirements for the sign of substation equipment?
Answer: 1) The primary, secondary and tertiary equipment on the substation site must have standardized, complete, clear and accurate naming marks, including junction box, control box and power box.
2) The names of secondary pressure plates, terminals, small switches, small knives, buttons and other components must be clearly identifiable, and strictly conform to the standard tickets and on-site operation procedures.
3) There should be a clear dividing line behind the control screen and protection screen of multiple units, and the unit name should be indicated.
4) The upper part of the terminal strip of each unit behind the control screen and protection screen shall indicate the name of the unit.
5) The casing of the tripping outlet relay shall be clearly marked with no touching.
6) The naming mark of the equipment shall be installed in strict accordance with the equipment, which is not limited by time. Dismantling is strictly prohibited during operation. If the equipment needs to be temporarily removed due to painting and other work, the accuracy of the position must be strictly checked when reinstalling.
20. How to manage the task execution process of switching operation?
Answer: 1) The switching operation shall be carried out in strict accordance with the requirements of the Eight-step Implementation Specification for Switching Operation (Hangdiansheng No.98.0234) of our bureau.
2) pour brake operation should strictly implement the scheduling command. For a group of commands containing multiple operation tasks, it is strictly forbidden to change the order between tasks without authorization; For an operation task, it is strictly forbidden to change the order of each operation step on the operation ticket without authorization.
3) In case of any doubt or obstacle in operation (such as the knife can't be operated due to mechanism defect, etc.). ), immediately stop the operation, report to the dispatcher and leadership, find out the reason, it is strictly prohibited to modify the operation ticket or dismantle the locking device at will.
4) If the operation is interrupted for some reason (for example, go back to the main control room to get the unlock key, etc.). ), when the operation is resumed, please be sure to re-check the contents of the current operation steps and the equipment logo.
5) For the operation of the substation (such as power system), the person in charge on duty must issue an operation command, and the rest are the same as the formal operation of dispatching.
6) The competent unit of substation operation shall conduct spot checks on the implementation of switching operation procedures of this substation, and operate the task at least once a month. The results of spot checks are reported to the Bureau of Biotechnology together with the monthly report.
2 1. In terms of preventing misoperation, what should I pay attention to after the main equipment works?
Answer: 1) If the maintenance unit dismantles or affects the anti-misoperation device and its loop during the work, the maintenance unit shall be responsible for restoring it before the end of the work, and the operation unit shall be responsible for acceptance.
2) The maintenance unit shall ensure that the relevant auxiliary contacts are in good condition after the switch and knife are overhauled, and the relevant error-proof circuit is complete, and the operation unit shall be responsible for the acceptance.
3) For new construction, expansion and reconstruction projects, the anti-misoperation device shall be designed, constructed and accepted simultaneously with the main equipment.
22. What should be the installation rate of error prevention devices?
A: 100%.
23. What should be the elimination rate of anti-misoperation devices?
Answer: The vacancy elimination rate should reach 100% within 30 days.
24. Can I unlock it in an emergency?
Answer: In an emergency (when there is a direct threat to people, systems and equipment), after confirming that the operation steps are correct and the current operating equipment is correct, with the consent of the person in charge on duty, you can unlock the operation first, and then go through the unlocking procedures afterwards.
25. Briefly describe the configuration principle of 220kV line protection.
Answer: For 220kV lines, when it is difficult to set and cooperate according to the stability requirements or backup protection, two sets of quick-acting protection should be installed for the whole line. The ground short circuit backup protection can be configured with phase or inverse time zero sequence current protection, and can also be supplemented by ground distance protection with phase or inverse time zero sequence current protection. Phase-to-phase short-circuit backup protection should generally be equipped with subsection distance protection.
26. Briefly describe the configuration principle of 500kV line protection.
Answer: For 500kV lines, two complete and independent quick-acting main protections should be installed. Ground short circuit backup protection can be configured with subsection or inverse time zero sequence current protection. Grounding distance protection can also be used, supplemented by phasing or inverse time zero sequence current protection. Phase-to-phase short-circuit backup protection can be equipped with subsection distance protection.
27. What is "far backup"?
Answer: "Remote backup" means that when a component fails and its protective device switch refuses to operate, the protective devices of adjacent components on the power supply side will operate to remove the fault.
28. What is a "near backup"?
Answer: "Near Backup" strengthens the protection of the component itself through dual configuration, 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 move, the high-voltage switch of the same substation bus can be started, or the opposite side switch can be cut remotely.
29. What are the characteristics of line longitudinal protection?
Answer: When the line fails, the line longitudinal protection is a protection device that makes the switches on both sides trip quickly at the same time, and it is the main protection of the line. It takes the specific relationship between the discriminators on both sides of the line as the criterion, that is, the two sides transmit the discriminator to the other side through the channel, and then, according to the relationship between the other side and our discriminator, the two sides identify the fault in the area or the fault outside the area respectively.
Therefore, discriminant quantity and channel are the main components of longitudinal protection device.
(1) direction high-frequency protection is to judge whether it is an internal fault or an external fault by comparing the fault directions seen at both ends of the line. If the fault direction seen when the protected line fails internally is the positive direction, then when the protected line fails externally, one side will always see the opposite direction. Characterized in that:
A) it is required that the positive discrimination starting element has enough sensitivity to the fault at the end of the line;
B) Dual-band transceiver must be used.
(2) Phase difference high-frequency protection is a high-frequency protection that compares the phases of power frequency currents on both sides of the protected line. When the fault currents on both sides are in the same phase, the protection is locked, and when the current phases on both sides are opposite, the protection trips. Characterized in that:
A) It can deal with all kinds of symmetrical and asymmetrical faults in full-phase state, and the device is relatively simple;
B) no response to system oscillation. The protection can continue to operate under the condition of non-full-phase operation and single-phase reclosing;
C) circuit disconnection which is not affected by voltage;
D) When the channel or transceiver stops working, the whole protection will stop running, so a separate backup protection is needed.
(3) The high-frequency locking distance protection is based on the directional distance protection device installed on the line, and the corresponding transceiver equipment is added to form the longitudinal distance protection through the channel. Characterized in that:
A) Be sensitive enough to deal with all kinds of symmetrical and asymmetrical faults quickly;
B) still keep the backup protection function;
C) When the voltage secondary circuit is disconnected, the protection will malfunction, so it is necessary to take disconnection locking measures to stop the protection from running.
30. What is the important role of longitudinal protection in power grid?
Answer: Because the pilot protection can realize full-line quick action in the power grid, it can ensure the stability of parallel operation of power systems, improve transmission power, reduce losses caused by faults and improve the coordination performance between backup protections.
3 1. How many kinds of longitudinal protection channels can be divided into?
A: It can be divided into the following categories:
(1) power line carrier pilot protection (short for high frequency protection).
(2) Microwave longitudinal protection (referred to as microwave protection).
(3) Optical fiber longitudinal protection (referred to as optical fiber protection).
(4) longitudinal protection (referred to as longitudinal protection).
32. What are the signals of longitudinal protection?
Answer: There are three signals for longitudinal protection:
(1) lock signal. This is a signal to prevent the protection from tripping. In other word, that absence of locking signal is a necessary condition for protection trip. Only when the two conditions of local protection element action and no locking signal are met at the same time, the protection will trip.
(2) Allow signal. This is a signal that allows the protection action to trip. In other words, the permission signal is a necessary condition for the protection action to trip. Only when two conditions of local protection element action and permission signal are met at the same time, the protection will trip.
(3) Trip signal. It is a signal that directly leads to tripping. At this time, it has nothing to do with whether the protection element acts or not. As long as the trip signal is received, the protection will act on the trip, and the remote trip protection is to use the trip signal.
33. Briefly describe the basic working principle of directional comparison high frequency protection.
Answer: The basic working principle of directional comparison high-frequency protection is to comprehensively judge whether it is an internal fault or an external fault of the protected line by comparing the fault directions seen on both sides of the line. If the fault direction seen during the internal fault of the protected line is the positive direction, then when the external fault of the protected line occurs, there is always a situation where the reverse direction is seen. Therefore, the discriminating element in directional comparison high frequency protection is directional element or current element, and its action value can distinguish forward and reverse faults. The so-called comparison of the fault direction of the line is to compare the behavior of specific discrimination between the two sides.
34. The advantages and disadvantages of high frequency locking distance protection?
A: This protection has the following advantages:
(1) can respond to all kinds of symmetrical and asymmetrical faults sensitively and quickly.
(2) It can still maintain the function of remote backup protection (when there is sensitivity).
(3) It is not affected by the distributed capacitance of the line.
Disadvantages are as follows:
Series compensation capacitor (1) will make the high frequency distance protection malfunction or refuse to operate.
(2) Failure will occur when the voltage secondary circuit is disconnected. Break line locking measures should be taken to stop the protection from running.
35. What problems should be paid attention to in the operation of zero sequence current protection?
Answer: The following problems should be paid attention to in the operation of zero sequence current protection:
(1) When the current loop is disconnected, it may cause protection misoperation. This is a common fault of general sensitive protection, which needs to be prevented in operation. As far as the disconnection probability is concerned, it is far less than the disconnection probability of the distance protection voltage circuit. If necessary, the method of zero-sequence current locking of adjacent current transformers can be used to prevent this misoperation.
(2) There will also be zero-sequence current when the power system is operating asymmetrically, such as asymmetric operation caused by different three-phase parameters of the transformer, two-phase operation in the process of single-phase reclosing, three-phase switches in different periods during three-phase reclosing and manual closing, zero-sequence circulation caused by inconsistent contact resistances of the switches when the buses are switched in parallel, and unbalanced excitation inrush current caused by the operation time of the air-dropped transformer.
(3) When one of the parallel lines is geographically close, when one of the lines fails, it may cause the other line to generate induced zero current, which may lead to the misoperation of the opposite zero-sequence directional relay. If this is really possible, negative sequence directional relay can be used to prevent the misoperation and judgment of the above directional relay.
(4) Because there is no zero-sequence current and zero-sequence voltage in the AC circuit of zero-sequence directional relay at ordinary times, the circuit disconnection is not easy to be found; When the relay zero-sequence voltage transformer is open on the triangle side, it is not easy to use a more intuitive simulation method to check the correctness of its direction, so it is more likely to cause protection refusal and misoperation when the AC circuit fails.
36. When phase difference high-frequency protection and high-frequency locking protection are used in conjunction with single-phase reclosing, why should phase difference high-frequency protection stop when tripping for three times and high-frequency locking protection stop when tripping for one time?
Answer: On the line with single-phase reclosing, when the phase difference is not complete, all high-frequency starting elements may not return. At this time, if there is a single trip stop signal on both sides, the side with slow signal stop after single-phase fault trip will mistakenly jump three phases, because intermittent waves are still emitted during non-full-phase operation. Therefore, after a single-phase fault trip, the phase difference high-frequency protection cannot be stopped. However, after the three-phase trip, the phase difference high-frequency protection loses its operating power and sends out a continuous wave, which will lock the opposite phase difference high-frequency protection. Therefore, it is necessary to implement three trip stop signals to speed up the trip of the opposite phase difference high frequency protection and remove the fault. In addition, when the bus protection is in action, if the switch fails, the three-trip stop signal can make the opposite high-frequency protection act and cut off quickly. High-frequency blocking protection must be single-tripped, because when the single-phase fault side of the line jumps first and then the protection will return, the starting element of high-frequency blocking protection will not return, and the transceiver will start sending letters, which will block the high-frequency blocking protection on the opposite side. Therefore, after single-phase tripping, it is necessary to stop communication and accelerate the tripping of high-frequency blocking protection on the opposite side.
37. A line has two sets of microcomputer protection, and the line is single-phase reclosing. How to use two sets of microcomputer to protect reclosing?
Answer: Two sets of microcomputer reclosing selector switches are switched to single position, and only one set of reclosing outlet is connected. If two sets of reclosing outlets are connected, the switches may overlap twice in a short time.
38. Microcomputer fault recorder generally records what electrical quantities?
Answer: For voltage systems of 220kV and above, microcomputer fault recorder generally takes in voltages UA, UB, UC and 3U0, and currents IA, IB, IC and 3I0；; High-frequency protection switch signals such as high-frequency signal amount, protection action and switch position.
39. What are the characteristics of transformer inrush current?
Answer: Surge current has the following characteristics:
(1) contains a large number of aperiodic components, which tend to bias the inrush current to one side of the time axis.
(2) It contains a lot of higher harmonic components, mainly second harmonic.
(3) There is discontinuity between the influx waveforms.
40. What are the methods to prevent the influence of inrush current in current differential protection?
Answer: The way to prevent inrush current is to use differential relay with fast saturated iron core.
4 1.500kV shunt reactor should be installed with what protection and its function?
Answer: The high-voltage shunt reactor shall be equipped with the following protection devices:
(1) high impedance differential protection. Protect the phase-to-phase and grounding faults of reactor winding and bushing.
(2) Turn-to-turn protection. Protection reactor turn-to-turn short circuit fault.
(3) Gas protection and temperature protection. Protect the reactor from all kinds of faults, oil level drop and temperature rise.
(4) Over-current protection. Overcurrent caused by phase-to-phase or grounding fault between reactor and lead.
(5) overload protection. Prevent the reactor winding from being overloaded.
(6) Neutral point overcurrent protection. The external grounding fault of protective reactor causes small reactance overcurrent of neutral point.
(7) Gas protection and temperature protection of small reactance of neutral point. Protect all kinds of faults, oil level reduction and temperature increase in small reactance.
42. Please describe the characteristics of medium impedance fast bus protection.
Answer: Fast bus protection is a medium impedance bus differential protection with braking, and its selection element is a medium impedance current differential relay with proportional braking characteristics, which solves the misoperation problem of bus differential protection when the current transformer is saturated and causes out-of-area faults. Measurement and comparison of protection device based on instantaneous current value. When there is an internal fault of the bus, the starting element and the selecting element of the protection device can act before the current transformer is saturated, so the action speed is very fast. Characteristics of medium impedance fast bus protection device;
(1) Two buses run in parallel, and one bus fails. In any case, the protective device is highly selective.
(2) When the two buses run in parallel, the two buses fail one after another, and the protection device can trip all the connecting elements on the two buses one after another.
(3) If the bus has internal fault, the whole action time of the protection device shall not exceed10 ms. ..
(4) The double busbar is operating normally and the protection device is reliable.
(5) Bus internal fault during double-bus switching operation; If two sets of knives of a line cross two sets of buses at the same time, the bus will fail, and the protection device can quickly cut off all the connecting elements on the two sets of buses. If two sets of knives of a line cross two sets of buses at the same time, the buses will fail, and the protection device still has high selectivity.
(6) External bus fault, regardless of whether the line current transformer is saturated or not, the protection device is reliable and does not maloperation.
(7) During normal operation or switching operation, if the AC current circuit of busbar protection is disconnected, the protection device will block the whole set of protection after setting delay, and send out an alarm signal for AC current circuit disconnection.
(8) In substations with similar switches or similar switch trip times, the protection device can ensure that the bus coupler switch trips first when the bus bar fails.
(9) For the fault between the bus-bar switch current transformer and the bus-bar switch, the bus protection and the switch failure protection successively trip all the connecting elements of the two groups of buses.
(10) On the 500kV bus, the transient current transformer is used. When the double-bus connection switch is double-span, the starting element may not have braking characteristics. On the 220kV bus, in order to prevent the misoperation of the protection when the double-bus contact knife crosses two spans, the starting element and the selecting element have the same ratio braking characteristics.
43. In the bus current differential protection, why do you want to use voltage locking element?
Answer: In order to prevent the differential relay from misoperation or touching the outlet intermediate relay by mistake, a voltage locking element is adopted.
44. How to realize the voltage locking element?
Answer: The voltage lockout element is realized by a low-voltage relay and a zero-sequence overvoltage relay connected to the secondary side of the voltage transformer on each bus. Three low-voltage relays respond to various phase-to-phase short-circuit faults, and zero-sequence overvoltage relays respond to various ground faults.
45. Why do you want to set the bus charging protection?
Answer: Bus differential protection should ensure that the faulty bus can be quickly and selectively disconnected when a group of buses or a section of buses are closed for charging. In order to cut off the fault on the live bus more reliably, current or zero sequence current protection is set on the bus coupler switch or bus section switch as bus charging protection.
Bus charging protection has simple wiring and high sensitivity in setting value. If conditions permit, this protection can be used as a temporary protection to charge the special bus with new lines alone.
Bus charging protection is only put into use when the bus is charging, and should be stopped in time after charging is good.
46. What is "two votes three system"?
A: Two tickets refer to the working ticket and the operation ticket;
"Three systems" refers to the system of shift handover, patrol inspection, regular test and rotation of equipment.
47. What is the state of the equipment in the power system?
Answer: The equipment state of power system is generally divided into four states: operation, hot standby, cold standby and maintenance.
48. What are the operating systems of the power system?
Answer: The dispatcher on duty in the power system should abide by the following rules when operating:
Operation ticket system, repeated operation ticket system, guardianship system and record system.
49. What are the forms of scheduling operation instructions?
Answer: The forms of dispatching operation instructions are: single instruction, item-by-item instruction and comprehensive instruction.
50. What conditions should be met for closed loop operation of power grid?
Answer: (1) The phase should be consistent. If the phase change may be caused after the first loop closing or overhaul, it must be proved that the phases on both sides of the loop closing point are consistent through measurement.
(2) If it belongs to the electromagnetic ring network, the difference between transformer wiring groups in the ring network is zero; Under special circumstances, after calculation and verification, the relay protection will not malfunction, and the related loop equipment will not be grounded, allowing the transformer wiring difference of 30 degrees for loop closing operation.
(3) After the ring is closed, all elements in the ring network will not be overloaded.
(4) Bus voltage should not exceed the specified value.
(5) The relay protection and safety automatic device should adapt to the ring network operation mode.
(6) Stability meets the specified requirements.