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Questions and Answers on Power Dispatching Technology - Short Answer Question Series 6 126. What is automatic generation control (AGC)? Answer: Automatic power generation control, referred to as AGC, is an important part of the energy management system (EMS). Instructions are sent to the relevant power plants or units according to the control objectives of the power grid dispatch center, and automatic control of the generator power is realized through the automatic control and adjustment devices of the power plants or units. 127. How many control modes does AGC have? answer: There are two AGC control modes: primary control mode and secondary control mode. The primary control mode is divided into three types: 1. Fixed frequency control mode ； 2. Fixed tie line power control mode ； 3. Frequency and tie line deviation control mode ； The secondary control mode is divided into two types: 1. Time error correction mode ； 2. Tie line accumulated power error correction mode. 128. In regional power grids, how should the grid and provincial AGC control modes be selected? In large district networking, how should the AGC control mode be selected? Answer: In regional power grids, network regulation is generally responsible for the task of system frequency regulation, and its AGC control mode should select fixed frequency control mode. ； Provincial dispatch should be ensured to be dispatched according to the tie line plan, and its AGC control mode should select the fixed tie line control mode. In the regional interconnected power grid, the frequency and tie line exchange power of the interconnected power grid should be jointly controlled by the power grids participating in the interconnection, and the AGC control mode should select the frequency and tie line deviation control mode. 129. What is a power source? Answer: The power generation source is a control object of AGC, which can be one unit, several units running in parallel, an entire power plant or several power plants running in parallel. The set point control instructions issued by the AGC software package are all targeted at the power generation source. 130. On what principle is the set point power of the power generation source calculated? Answer: The power set point power is calculated according to different principles according to the size of ACE. ACE is divided into dead zone, normal allocation area, allowed control area and emergency support area according to its size. There are different allocation strategies for different regions. In the dead zone, only the pairwise allocation strategy is implemented for the power generation sources whose power deviates greatly from the ideal value, and new set points are calculated. The power of the other power generation sources is not reallocated. In the normal allocation area, ACE is allocated to each power source according to the normal economic participation factor, and its set point power is calculated. In the allowed control area, only the power generation sources that can reduce ACE are restricted to participate in the control, and their set point power is calculated. In the emergency support area, ACEs are allocated according to the speed of the adjustment rate of the power source, and its set point power is calculated, that is, the power source with the fastest adjustment rate is allowed to bear more adjustment power. 131. What are the two operating modes of the network analysis software in the EMS system? What is the difference from offline computing software? answer: There are two operating modes of the network analysis software in the EMS system: 1. Real-time mode: The original data of the running software is continuously refreshed based on the real-time measurement data and calculated in real time or calculated regularly in a certain period. Such as real-time network topology, state estimation, dispatcher flow, etc. 2. Research mode: The original data of the running software is not refreshed. It can be a real-time snapshot of data from a certain time section or manually inserted data. It can be used to study the operating status of the power grid, such as dispatcher power flow, safety analysis, etc. There are certain differences between network analysis software in EMS and offline computing software. First, it is real-time. Even in research mode, snapshots can be taken from the real-time system for analysis and research. The second is its rapidity requirement. In order to meet the rapidity, there is no offline calculation software that considers the mathematical model more comprehensively. 132. Describe the concept of network topology analysis? Answer: The topology of the power grid describes the graphical connection relationship of various electrical components in the power grid. The power grid is composed of several live electrical islands, and each electrical island is composed of many busbars and electrical components connected between the busbars. Each busbar is composed of several bus line elements connected through switches and knives. Network topology analysis is based on the remote signaling status of each switch and blade in the power grid, and uses a certain search algorithm to connect each bus line element into a certain bus, and form an electrical island with the bus and connected electrical components to perform network wiring identification and analysis. 133. What is state estimation? What is its purpose? What basic conditions must be met for operating status estimation? answer: Power system state estimation utilizes the redundancy of the real-time measurement system and applies estimation algorithms to detect and eliminate bad data. Its function is to improve data accuracy and maintain data consistency, and provide reliable real-time power flow data for network analysis. The use of state estimation must ensure that the inside of the system is observable, and the system measurements must have a certain degree of redundancy. State estimates made in the absence of measurements are unusable. 134. What is security analysis, static security analysis, and dynamic security analysis? Answer: Security analysis is based on the N-1 principle for a running network or a network under a certain research state, and studies the security situation and safety margin of the network after each operating component exits operation due to failure. Static safety analysis is to study whether the components are overloaded and whether the bus voltage exceeds the limit. Dynamic safety analysis studies whether the line power exceeds the stable limit. 135. Functionally speaking, how is safety analysis divided? Answer: From a functional perspective, safety analysis is divided into two major modules: one is for sorting faults, that is, automatically sorting according to N-1 fault severity ； One is safety assessment. For static safety analysis, it is to carry out power flow calculation analysis, and for dynamic safety analysis, it is to carry out stability calculation analysis. 136. What is the difference between optimal power flow and traditional economic dispatch? Answer: Traditional economic dispatch only optimizes active power. Although line loss correction is considered, it only considers the optimization of line losses caused by active power. Traditional economic dispatch generally does not consider bus voltage constraints, and it is generally difficult to consider safety constraints. In addition to optimizing active power and consumption, the optimal power flow also optimizes reactive power and network loss. In addition, the optimal power flow also takes into account the bus voltage constraints and the safety constraints of the line power flow. 137. What is the role of the Dispatcher Training Simulation System (DTS)? Answer: The dispatcher training simulation system is mainly used for dispatcher training. It can provide a simulation system of the power grid through which dispatchers can simulate on-site operations and system anti-accident simulations. * , thereby improving the effectiveness of dispatcher training and accumulating experience in power grid operation and accident handling. 138. What are the basic requirements for a dispatcher training simulation system? The dispatcher simulation training system should try to meet the following three requirements: 1. Authenticity: The power system model has the same dynamic and static characteristics as the actual power system, and the actual power system should be reproduced as realistically as possible for training. 2. Consistency: The environment of the student station should be as consistent as possible with the environment of the actual power grid dispatching and control center, so that the students can have a sense of presence when being trained. 3. Flexibility: The training can be flexibly controlled at the instructor's desk, and various operations and failures of the power system can be flexibly simulated. 139. Briefly describe what is a single operation instruction? Answer: A single operation instruction refers to an operation instruction issued by the on-duty dispatcher for only one unit and with only one operation content and completed by the subordinate on-duty dispatcher or on-site operation personnel. 140. Briefly describe the subsystems and their functions of the power system communication network? Answer: The subsystems of the power system communication network are: (1. Dispatching communication subsystem, which provides power grid dispatching services. (2. Data communication subsystem. This system provides channels for various data transmissions such as dispatch automation, relay protection, safety automatic devices, and computer networking. (3. Exchange communication subsystem. This system serves information exchange between power production, infrastructure and management departments. 141. What information does dispatch automation provide to dispatchers that reflects the current status of the system? answer: 1. Provide accurate and reliable real-time information for safe monitoring of power grid operation conditions, including relevant load and power generation conditions, load conditions of transmission lines, voltage, active and reactive power flows, stability limits, system frequency, etc. 2. When important deviations occur in power grid operating conditions, timely and automatic alarms are issued, and corrective measures are indicated or initiated at the same time. 3. When the power grid is disconnected, a display is given and the location of the disconnection is pointed out. 142. What is an energy management system (EMS)? What are its main functions? Answer: EMS energy management system is the general name of modern power grid dispatching automation system (including hardware and software). Its main functions consist of two parts: basic functions and application functions. Basic functions include: computer, operating system and EMS support system. The application functions include: data collection and monitoring (SCADA), automatic power generation control (AGC) and planning, and network application analysis. 143. What are the advanced application software of power grid dispatching automation system? Answer: Advanced application software for power grid dispatching automation systems generally includes: load forecasting, power generation planning, network topology analysis, power system status estimation, power system online power flow, optimal power flow, static safety analysis, automatic power generation control, dispatcher training simulation system, etc. 144. What is the role of the power grid dispatching automation SCADA system? Answer: The power grid information collected by the dispatch center must be processed by application software before it can ultimately serve dispatch production in various ways. With the support of application software, dispatchers can monitor the operating status of the power grid, quickly and effectively analyze the safety and economic level of the power grid operation, quickly complete judgments and decisions in case of accidents, and implement effective remote control and remote adjustment of remote plants and stations. At present, the basic functions and functions of SCADA systems used in domestic dispatch operations are: 1) Data collection and transmission ； (2) Security monitoring, control and alarm ； (3) Tabulation printing ； (4) Special operations ； (5) Recollection of the accident. 145. What is automatic generation control (AGC)? Answer: Automatic power generation control, referred to as AGC, is an important part of the energy management system (EMS). Instructions are sent to the relevant power plants or units according to the control objectives of the power grid dispatch center, and automatic control of the generator power is realized through the automatic control and adjustment devices of the power plants or units. 146. What is state estimation? What is its purpose? What basic conditions must be met for operating status estimation? answer: Power system state estimation utilizes the redundancy of the real-time measurement system and applies estimation algorithms to detect and eliminate bad data. Its function is to improve data accuracy and maintain data consistency, and provide reliable real-time power flow data for network analysis. The use of state estimation must ensure that the inside of the system is observable, and the system measurements must have a certain degree of redundancy. State estimates made in the absence of measurements are unusable. 147. What is security analysis, static security analysis, and dynamic security analysis? Answer: Security analysis is based on the N-1 principle for a running network or a network under a certain research state, and studies the security situation and safety margin of the network after each operating component exits operation due to failure. Static safety analysis is to study whether the components are overloaded and whether the bus voltage exceeds the limit. Dynamic safety analysis studies whether the line power exceeds the stable limit. 148. Functionally speaking, how is security analysis divided? Answer: From a functional perspective, safety analysis is divided into two major modules: one is for sorting faults, that is, automatically sorting according to N-1 fault severity ； One is safety assessment. For static safety analysis, it is to carry out power flow calculation analysis, and for dynamic safety analysis, it is to carry out stability calculation analysis. 149. What is the difference between optimal power flow and traditional economic dispatch? Answer: Traditional economic dispatch only optimizes active power. Although line loss correction is considered, it only considers the optimization of line losses caused by active power. Traditional economic dispatch generally does not consider bus voltage constraints, and it is generally difficult to consider safety constraints. In addition to optimizing active power and consumption, the optimal power flow also optimizes reactive power and network loss. In addition, the optimal power flow also takes into account the bus voltage constraints and the safety constraints of the line power flow. 150. What is the role of the Dispatcher Training Simulation System (DTS)? Answer: The dispatcher training simulation system is mainly used for dispatcher training. It can provide a simulation system of the power grid through which dispatchers can simulate on-site operations and system anti-accident simulations. * , thereby improving the effectiveness of dispatcher training and accumulating experience in power grid operation and accident handling. Questions and Answers on Power Dispatching Technology - Short Answer Question Series 7 151. What are the basic requirements for a dispatcher training simulation system? Answer: The dispatcher simulation training system should try to meet the following three requirements: 1. Authenticity: The power system model has the same dynamic and static characteristics as the actual power system, and the actual power system should be reproduced as realistically as possible for training. 2. Consistency: The environment of the student station should be as consistent as possible with the environment of the actual power grid dispatching and control center, so that the students can have a sense of presence when being trained. 3. Flexibility: The training can be flexibly controlled at the instructor's desk, and various operations and failures of the power system can be flexibly simulated. 152. Briefly describe what is a single operation instruction? Answer: A single operation instruction refers to an operation instruction issued by the on-duty dispatcher for only one unit and with only one operation content and completed by the subordinate on-duty dispatcher or on-site operation personnel. 153. Briefly describe what is an item-by-item operation instruction? Answer: Item-by-item operation instructions refer to the operation instructions that the dispatcher on duty issues one by one in the order of operating tasks, and the ordered unit executes them one by one in the order of the instructions. Generally used for operations involving two or more units, such as line outage and power supply, etc. Dispatchers must write operation task tickets in advance according to operating principles. During operation, the on-duty dispatcher issues operation instructions item by item, and the on-site personnel on duty operate item by item in the order of instructions. 154. What is a comprehensive operation instruction? Answer: A comprehensive instruction is a comprehensive operation task issued by the on-duty dispatcher to a unit. The specific operation items and sequences are filled in by the on-site operators according to regulations, and the operation can be carried out after obtaining the permission of the on-duty dispatcher. Generally used for operations involving only one unit, such as switching busbars in substations and power outages in transformers. 156. Under what circumstances is it necessary to conduct a nuclear examination? Why nuclear phase? answer: For newly put into production lines or changed lines, the phase and phase sequence must be checked. If the secondary circuit related to paralleling has been modified during maintenance, the phase and phase sequence must also be checked. If AC power supplies with different phases or phase sequences are paralleled or connected, a large current will be generated. The huge current will cause damage to generators or electrical equipment, so phase verification is required. For correct paralleling, not only the primary phase sequence and phase must be correct, but also the secondary phase and phase sequence must be correct, otherwise non-synchronous paralleling will also occur. 157. * * What is the standard frequency of the power system and its allowable deviation? answer: * * The standard frequency of the power system is 50HZ. For systems with a capacity of 3000MW and above, the allowable frequency deviation is 50±0.2HZ, and the deviation between the electric clock indication and the standard time is not greater than 30 seconds. ； For systems with a capacity below 3000MW, the allowable frequency deviation is 50±0.5HZ, and the deviation between the electric clock indication and the standard time is not more than 1 minute. 158. How many common methods are there for power system voltage adjustment? answer: The system voltage must be adjusted according to the specific requirements of the system, using different methods at different plants and stations. Commonly used voltage adjustment methods include the following: 1. Increase or decrease reactive power for voltage regulation, such as voltage regulation by generators, condensers, shunt capacitors, and shunt reactors ； 2. Change the distribution of active power and reactive power to regulate voltage, such as voltage regulating transformer, changing transformer tap to regulate voltage. ； 3. Change network parameters for voltage regulation, such as connecting capacitors in series, switching on and off parallel operation transformers, switching on and off no-load or light-load high-voltage line voltage regulation. Under special circumstances, the voltage is sometimes adjusted by adjusting the electrical load or limiting power. 159. What are the main peak-shaving power supplies in the power system? Answer: Peak-shaving power supplies used in power systems are generally: conventional hydropower units, pumped storage units, gas turbine units, conventional steam turbine generator units and other new forms of peak-shaving power supplies. 160. How many ways are there to adjust the grid voltage? What is reverse voltage regulation? Answer: Voltage adjustment methods are generally divided into three types: reverse voltage regulation, constant voltage regulation, and forward voltage regulation. Reverse voltage regulation refers to the adjustment of the power supply voltage of the power grid within the allowable voltage deviation range so that the voltage of the power grid at peak load is higher than the voltage at valley load, making the user's voltage peaks and valleys relatively stable. 161. What is the sequence of power outage and power supply operations? What should you pay attention to when operating? answer: The sequence of operations for a line power outage is: open the switches at both ends of the line, open the line side gate knife, open the bus side gate knife, and connect the grounding knife (or hang the ground wire) at each end of the line that may receive power. The order of the line power supply operation is: open the grounding blades at each end of the line (or remove the grounding wire), close the busbar side blades and line side blades at both ends of the line, and close the switch. Notes: 1. Prevent the voltage at the end of the line from rising above the allowable value when there is no load. 2. When putting in or removing empty lines, excessive fluctuations in the grid voltage should be avoided. 3. Avoid self-excitation when the generator is put into the no-load line under no-load conditions. 162. What matters should be paid attention to when shutting down and transmitting power to a power transformer? Answer: Generally, all relay protections should be put into use when charging the transformer. In order to ensure the stability of the system, the active power of the relevant lines should be reduced before charging. Before charging or shutting down the transformer, the neutral point grounding switch must be closed. Under normal circumstances, when there are power supplies on both the high and low voltage sides of the 220KV transformer, the high voltage side should be charged during power transmission, and the low voltage side should be paralleled. ； In the event of a power outage, the system will be decoupled at the low voltage side first. When operating the transformer of the ring network system, the charging end should be selected correctly to reduce the voltage difference at the parallel point. When transformers are operated in parallel, they should meet the conditions for parallel operation. 163. What conditions should be met for the closed-loop operation of the power grid? answer: 1. The phases of the loop closing points should be consistent. If the phase change may occur after the first loop closing or maintenance, it must be measured to prove that the phases on both sides of the loop closing point are consistent. ； 2. If it is an electromagnetic ring network, the difference between the transformer wiring groups in the ring network is zero. ； Under special circumstances, after calculation and verification, the relay protection will not malfunction and the relevant loop equipment will not be overloaded. The loop closing operation is allowed when the transformer wiring difference is 30°. ； 3. After ring closing, it will not cause overload of components in the ring network. ； 4. The voltage of each bus bar should not exceed the specified value ； 5. Relay protection and safety automatic devices should adapt to the ring network operation mode ； 6. The power grid is stable and meets the specified requirements. 164. What issues should be paid attention to when de-looping the power grid? Answer: Before the deloop operation, the active and reactive power flows at the deloop point should be checked to ensure that the power grid voltage quality after deloop is within the specified range, the power flow changes do not exceed the control range in terms of grid stability, equipment capacity, etc., and the cooperation with relay protection and safety automatic devices ； Contact relevant parties before and after unwinding. 165. Briefly describe what is an item-by-item operation instruction? Answer: Item-by-item operation instructions refer to the operation instructions that the dispatcher on duty issues one by one in the order of operating tasks, and the ordered unit executes them one by one in the order of the instructions. Generally used for operations involving two or more units, such as line outage and power supply, etc. Dispatchers must write operation task tickets in advance according to operating principles. During operation, the on-duty dispatcher issues operation instructions item by item, and the on-site personnel on duty operate item by item in the order of instructions. 166. What is a comprehensive operation instruction? Answer: A comprehensive instruction is a comprehensive operation task issued by the on-duty dispatcher to a unit. The specific operation items and sequences are filled in by the on-site operators according to regulations, and the operation can be carried out after obtaining the permission of the on-duty dispatcher. Generally used for operations involving only one unit, such as switching busbars in substations and power outages in transformers. 167. Under what circumstances is it necessary to conduct a nuclear examination? Why nuclear phase? answer: For newly put into production lines or changed lines, the phase and phase sequence must be checked. If the secondary circuit related to paralleling has been modified during maintenance, the phase and phase sequence must also be checked. If AC power supplies with different phases or phase sequences are paralleled or connected, a large current will be generated. The huge current will cause damage to generators or electrical equipment, so phase verification is required. For correct paralleling, not only the primary phase sequence and phase must be correct, but also the secondary phase and phase sequence must be correct, otherwise non-synchronous paralleling will also occur. 168. * * What is the standard frequency of the power system and its allowable deviation? answer: * * The standard frequency of the power system is 50HZ. For systems with a capacity of 3000MW and above, the allowable frequency deviation is 50±0.2HZ, and the deviation between the electric clock indication and the standard time is not greater than 30 seconds. ； For systems with a capacity below 3000MW, the allowable frequency deviation is 50±0.5HZ, and the deviation between the electric clock indication and the standard time is not more than 1 minute. 169. How many common methods are there for power system voltage adjustment? answer: The system voltage must be adjusted according to the specific requirements of the system, using different methods at different plants and stations. Commonly used voltage adjustment methods include the following: 1. Increase or decrease reactive power for voltage regulation, such as voltage regulation by generators, condensers, shunt capacitors, and shunt reactors ； 2. Change the distribution of active power and reactive power to regulate voltage, such as voltage regulating transformer, changing transformer tap to regulate voltage. ； 3. Change network parameters for voltage regulation, such as connecting capacitors in series, switching on and off parallel operation transformers, switching on and off no-load or light-load high-voltage line voltage regulation. Under special circumstances, the voltage is sometimes adjusted by adjusting the electrical load or limiting power. 170. What are the main peak-shaving power supplies in the power system? Answer: Peak-shaving power supplies used in power systems are generally: conventional hydropower units, pumped storage units, gas turbine units, conventional steam turbine generator units and other new forms of peak-shaving power supplies. 171. How many ways are there to adjust the grid voltage? What is reverse voltage regulation? answer: Voltage adjustment methods are generally divided into three types: reverse voltage regulation, constant voltage regulation, and forward voltage regulation. Reverse voltage regulation refers to the adjustment of the power supply voltage of the power grid within the allowable voltage deviation range so that the voltage of the power grid at peak load is higher than the voltage at valley load, making the user's voltage peaks and valleys relatively stable. 172. What is the sequence of power outage and power supply operations? What should you pay attention to when operating? answer: The sequence of operations for a line power outage is: open the switches at both ends of the line, open the line side gate knife, open the bus side gate knife, and connect the grounding knife (or hang the ground wire) at each end of the line that may receive power. The order of the line power supply operation is: open the grounding blades at each end of the line (or remove the grounding wire), close the busbar side blades and line side blades at both ends of the line, and close the switch. Notes: 1. Prevent the voltage at the end of the line from rising above the allowable value when there is no load. 2. When putting in or removing empty lines, excessive fluctuations in the grid voltage should be avoided. 3. Avoid self-excitation when the generator is put into the no-load line under no-load conditions. 173. What matters should be paid attention to when shutting down and transmitting power to a power transformer? answer: Generally, all relay protections should be put into use when charging the transformer. In order to ensure the stability of the system, the active power of the relevant lines should be reduced before charging. Before charging or shutting down the transformer, the neutral point grounding switch must be closed. Under normal circumstances, when there are power supplies on both the high and low voltage sides of the 220KV transformer, the high voltage side should be charged during power transmission, and the low voltage side should be paralleled. ； In the event of a power outage, the system will be decoupled at the low voltage side first. When operating the transformer of the ring network system, the charging end should be selected correctly to reduce the voltage difference at the parallel point. When transformers are operated in parallel, they should meet the conditions for parallel operation. 174. What conditions should be met for the closed-loop operation of the power grid? answer: 1. The phases of the loop closing points should be consistent. If the phase change may occur after the first loop closing or maintenance, it must be measured to prove that the phases on both sides of the loop closing point are consistent. ； 2. If it is an electromagnetic ring network, the difference between the transformer wiring groups in the ring network is zero. ； Under special circumstances, after calculation and verification, the relay protection will not malfunction and the relevant loop equipment will not be overloaded. The loop closing operation is allowed when the transformer wiring difference is 30°. ； 3. After ring closing, it will not cause overload of components in the ring network. ； 4. The voltage of each bus bar should not exceed the specified value ； 5. Relay protection and safety automatic devices should adapt to the ring network operation mode ； 6. The power grid is stable and meets the specified requirements. Questions and Answers on Power Dispatching Technology - Short Answer Question Series 8 176. What issues should be paid attention to in the power grid deloop operation? Answer: Before the deloop operation, the active and reactive power flows at the deloop point should be checked to ensure that the power grid voltage quality after deloop is within the specified range, the power flow changes do not exceed the control range in terms of grid stability, equipment capacity, etc., and the cooperation with relay protection and safety automatic devices ； Contact relevant parties before and after unwinding. 177. What issues should be paid attention to during the power grid closing operation? Answer: During the loop closing operation, it must be ensured that the phases on both sides of the loop closing point are the same, and the voltage difference and phase angle should comply with regulations. ； It should be ensured that in the closed loop network, the power flow changes do not exceed the limitations of grid stability, equipment capacity, etc. For the operation of more complex loop networks, calculations or verification should be performed first, and relevant parties should be contacted before and after the operation. 178. What are the conditions for power system parallelism at the same time? answer: 1. The phase sequence and phase on both sides of the parallel switch are the same. 2. The frequencies on both sides of the parallel switch are equal. When adjustment is difficult, the allowable frequency difference is not greater than the regulations of this website. 3. The voltages on both sides of the parallel switch are equal. When adjustment is difficult, the allowable voltage difference is not greater than the regulations of this network. 179. What are the precautions for power system disconnection operation? Answer: The precautions for the power system splitting operation are: Adjust the active power flow at the splitting point to zero and the current to the minimum. If there are difficulties in adjustment, the small grid can transmit a small amount of power to the large grid to avoid large changes in the frequency and voltage of the small grid after splitting. 180. In the power grid, what operations are allowed to be performed directly with a knife? answer: 1. When there is no ground fault in the power grid, close the voltage transformer ； 2. Close the lightning arrester when there is no lightning activity ； 3. Combine the capacitive current of the busbars of 220KV and below and the equipment directly connected to the busbars, and combine the circulating current of the 500KV no-load bus and the combined 3/2 connection busbar allowed by the test ； 4. When there is no ground fault in the power grid, close the neutral point grounding knife or arc suppression coil of the transformer. ； 5. The bypass knife connected in parallel with the switch can pull the bypass current of the switch when the switch is closed. ； 6. Pull together no-load transformers and reactors whose excitation current does not exceed 2 amps and no-load lines whose capacitive current does not exceed 5 amps (but for power grids of 20KV and above, outdoor three-phase linkage switches should be used). 181. What should you pay attention to when activating or deactivating high-frequency protection? Why? Answer: Before the high-frequency protection is put into tripping, the high-frequency signals on both sides of the line must be exchanged. After confirming that they are normal, both sides of the high-frequency protection of the line can be put into tripping at the same time. For high-frequency protection of lines in ring network operation, both sides must be enabled for tripping or deactivated at the same time during normal operation. It is not allowed to enable tripping on one side and deactivate the other side. Otherwise, when there is a fault outside the area, the high-frequency protection side that is deactivated cannot send a blocking signal to the opposite side, which will cause the high-frequency protection action of unilateral tripping to trip. 182. Can the transformer neutral point zero-sequence overcurrent protection and gap overvoltage protection be enabled at the same time? Why? Answer: The transformer neutral point zero-sequence overcurrent protection and gap overvoltage protection cannot be enabled at the same time. The zero-sequence overcurrent protection of the transformer neutral point can only be activated when the neutral point is directly grounded, while the gap overvoltage protection can only be activated when the neutral point of the transformer is grounded through the discharge gap. If both are activated at the same time, it may cause malfunction of the above protection. 183. What is a power system accident? What are the main causes of accidents? Answer: The so-called power system accident refers to an event in which power system equipment failure or personnel work errors affect the quantity or quality of power supply beyond the specified range. There are many reasons for power system accidents, such as natural disasters, equipment defects, improper management and maintenance, poor maintenance quality, external damage, unreasonable operation methods, relay protection malfunctions and personnel errors, etc. 184. From the perspective of accident scope, how many categories can power system accidents be divided into? What do the various types of accidents mean? answer: Power system accidents can be divided into two categories based on the scope of the accident, namely local accidents and system accidents. Local accidents refer to events in which individual components in the system fail, causing changes in power grid operation and power quality in local areas, and affecting users' power consumption. System accident refers to an event in which the main tie line in the system trips or loses large power supply, causing drastic changes in the frequency and voltage of the entire system, causing the quantity or quality of the power supply to exceed the specified range, and even causing system collapse or large-scale power outage. 185. What are the general principles for handling power system accidents? answer: When an accident occurs in the power system, the operating personnel of each unit handle the accident under the command of the superior on-duty dispatcher and do the following: 1. Limit the development of the accident as soon as possible, eliminate the root cause of the accident and eliminate threats to personal and equipment safety, and prevent system stability from damage or collapse. 2. Use all possible methods to keep the equipment running, first ensuring the self-use power of power plants and hub substations. ； 3. Restore power supply to users who have lost power as soon as possible, especially to restore power supply to important users with security power supply. ； 4. Adjust the system operation mode to restore it to normal. 186. When an accident occurs in the system, what are the main requirements that the accident and the operating personnel of the relevant units must report to the dispatch immediately? Answer: When an accident occurs in the system, the accident and the relevant units should immediately and accurately report the situation to the relevant superior on-duty dispatcher. The report content includes the time and phenomenon of the accident, switch displacement, operation of relay protection and safety automatic devices, changes in frequency, voltage, power flow, and equipment status, etc. After the situation is clarified, a detailed report will be made quickly. 187. What accidents can the accident unit handle first and then report without waiting for dispatch instructions? answer: In the event of the following situations, the accident unit may handle the incident on its own without waiting for dispatch instructions and then report: 1. When there is a threat to people and equipment, take measures according to on-site procedures. ； 2. When all or part of the self-consumption power of power plants and substations is out of power, use other power sources to restore self-consumption power. ； 3. When the frequency decreases due to system accidents, each power plant will increase unit output and deploy backup generating units and integrate them into the system. ； 4. When the system frequency is as low as the load shedding and low-frequency decoupling device should operate according to the frequency, and the device does not operate, immediately manually cut off the switch that the device should operate after confirming that it is correct. ； 5. The dispatch procedures and on-site procedures clearly stipulate that accidents can be handled by oneself without waiting for instructions from the dispatcher on duty. 188. Under what circumstances must the on-site personnel on duty ask the on-duty dispatcher for instructions before forcibly transmitting power? Answer: In the following situations, on-site operators must ask the dispatcher on duty and obtain permission before forcibly transmitting power: 1. When the line trips due to a busbar failure and no obvious fault point is found ； 2. Ring network line fault tripping ； 3. One circuit of the double circuit fails and trips. ； 4. It may cause non-synchronized closing of circuits to trip. 189. After the accident is handled, what should the dispatch personnel do? Answer: When the accident handling comes to an end, the dispatch personnel on duty should quickly report the accident situation to the relevant leaders and report to the superior dispatch in a timely manner in accordance with relevant regulations. After handling the line fault trip (regardless of successful reclosure or not), the maintenance management department should be notified to check the line. After the accident is handled, the accident situation and handling process should be recorded in detail, and the accident report should be filled out within 72 hours. 190. What is frequency abnormality? What is frequency accident? Answer: For systems with a capacity of 3000MW and above, a frequency deviation exceeding 50±0.2HZ is a frequency abnormality. If the frequency deviation exceeds 1 hour, it is a frequency accident. A frequency deviation exceeding 50±1HZ is an accident frequency. If the frequency deviation exceeds 15 minutes, it is a frequency accident. For systems with a capacity below 3000MW, frequency deviation exceeding 50±0.5HZ is a frequency abnormality, and its duration exceeding 1 hour is a frequency accident. ； If the frequency deviation exceeds 50±1HZ, it is an accident frequency, and its duration shall not exceed 15 minutes, which is a frequency accident. 191. What are the methods to deal with low-frequency accidents in the system? Answer: Maintaining the balance of system power supply and consumption at any time is the main measure to prevent low-frequency accidents. Therefore, the main methods when dealing with low-frequency accidents are: 1. Call out the spinning reserve ； 2. Quickly start the backup unit ； 3. Incident support for networked systems ； 4. Remove the load when necessary (execute according to the pre-established accident power supply sequence table). 192. What are the methods to deal with high-frequency operation of the system? answer: The main methods to deal with the high-frequency operation of the system are: 1. Adjust the power output: give priority to reducing the output of hydropower units that are not running with water abandonment until they are shut down for standby. Reduce the output of thermal power units to the minimum allowable technical output ； 2. Start the pumping operation of the pumped storage unit ； 3. Reduce the force on the hydropower unit running without water until it stops. ； 4. Thermal power units are shut down for backup. 193. What are the main measures to prevent system frequency collapse? answer: 1. The operation of the power system should ensure sufficient and reasonably distributed spinning reserve capacity and emergency reserve capacity. ； 2. Hydropower units adopt low-frequency self-starting devices and pumped storage units are equipped with low-frequency pump cutting and low-frequency automatic power generation devices. ； 3. Use important power supply emergency load-shedding devices ； 4. Low-frequency automatic load-shedding devices with sufficient capacity should be installed and put into use in the power system. ； 5. Formulate measures to ensure power supply for power plants and supply power to important loads in nearby areas ； 6. Develop a system accident power-up sequence table and manually cut off the load when necessary. 194. What are the standards for voltage abnormalities and accidents at power grid monitoring control points in my country? answer: The standards stipulated in our country are: Voltage abnormality: It exceeds ±5% of the voltage curve value specified by power system dispatching and lasts for more than 1 hour, or exceeds ±10% of the specified value and lasts for more than 30 minutes, which is classified as voltage abnormality. Voltage accident: It exceeds ±5% of the voltage curve value specified by power system dispatching and lasts for more than 2 hours, or exceeds ±10% of the specified value and lasts for more than 1 hour, which is designated as a voltage accident. 195. When the voltage at the power grid monitoring control point drops beyond the specified range, what measures should the dispatcher on duty take? answer: When the voltage at the grid monitoring control point drops beyond the specified range, the following measures should be taken: 1. Rapidly increase the reactive power output of the generator ； 2. Install reactive power compensation capacitor (there should be a certain lead time) ； 3. Try to change the reactive power flow distribution of the system ； 4. Conditions allow to reduce the active power output of the generator and increase the reactive power output. ； 5. Start the backup unit to regulate pressure when necessary ； 6. Remove the parallel reactor ； 7. When there is no voltage regulation capability, the power will be cut off. 196. What basic measures should be taken to deal with excess reactive power and high voltage in local power grids? Answer: 1. Run the generator with high power factor and generate as little reactive power as possible. ； 2. Some generators run in phase and absorb the reactive power of the system. ； , remove the parallel capacitor ； 4. Put in parallel reactor ； 5. Control the reactive power supply of the low-voltage power grid to the Internet ； 6. Change the operating mode when necessary and conditions permit. ； 7. Improved phase operation of the camera unit. 197. What are the main reasons for power outage in the substation bus? What is the general basis for determining whether a busbar is faulty? What should I pay attention to? answer: The main reasons for the power outage of the substation busbar are: failure of the busbar itself ； The components connected to the bus are faulty, and the protection or switch refuses to operate. ； The external power supply is completely shut down, etc. Whether there is a busbar failure should be based on: instrument indications, protection and automatic device actions, switch signals and accident phenomena (such as fire, explosion sounds, etc.), etc. to determine the accident situation and take effective measures quickly. During the accident handling process, you should pay attention and must not