Low-voltage load shedding configuration method adapting to new voltage stability standard

Abstract

The invention provides a low-voltage load shedding configuration method adaptive to a new voltage stability standard. The method comprises the following steps: identifying a voltage instability problem region and a voltage instability fault type; determining a load shedding station and a total load shedding amount in combination with the voltage instability problem region and the voltage instability fault type; determining a recovery voltage level of the voltage instability problem region based on the new voltage stability standard; calculating a P-V curve of a key site in the voltage instability problem region; determining specific implementation parameters of a voltage load shedding configuration scheme of the voltage instability problem region based on the load shedding station, the total load shedding amount, the recovery voltage level and a P-V curve; and for the voltage instability problem region, performing simulation verification on the voltage load shedding configuration scheme, and taking the voltage load shedding configuration scheme passing the verification as the configuration scheme of the corresponding region. The invention provides a low-voltage load shedding configuration method which can effectively cope with new standards and has good regional adaptability, and the safety and stability of a power system are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power system stability control, and in particular relates to a low-voltage load reduction configuration method adapted to a new voltage stability standard. Background Art

[0002] As my country's power grid expands and becomes more complex, the power system faces more challenges in terms of safety and stability. In particular, under high-load operation, problems such as tight backup capacity and critical lines approaching their maximum power limits increase the risk of voltage instability after a fault.

[0003] Voltage stability is crucial for the reliable operation of power systems. It is divided into two types: small disturbances (static) and large disturbances (transient), which focus on the ability to maintain voltage under slight changes and after severe faults, respectively. In order to prevent large-scale power outages caused by voltage collapse, low-voltage load shedding has been widely studied as an important measure.

[0004] At present, as experts and scholars continue to deepen their analysis and understanding of system voltage stability issues, the criteria for voltage instability have been revised. The original national standard for voltage stability is: the system voltage central point bus voltage drops below 0.75 pu for no more than 1 second during transient and dynamic processes, and the central point bus voltage of 220kV and above voltage levels is not less than 0.9pu after the dynamic process subsides. According to the "Guidelines for Safety and Stability of Power Systems" (GB 38755-2019) and "Code for Safety and Stability Calculation of Power Systems" (GB / T 40581-2021), the system transient voltage stability must meet the following requirements: "In the transient process after the power system is subjected to a large disturbance, the load bus voltage should recover to above 0.80pu within 10s (taking the average rated voltage as the voltage reference value), and the load bus voltage should recover to above 0.90pu after the transient process ends.

[0005] The changes in voltage transient stability standards have the following impacts on the three types of safety and stability standard faults and the corresponding defense lines:

[0006] (1) For the first type of fault, if the system can operate stably after the fault under the old standard system, it can also operate stably under the new standard system, but the opposite is not true. In this way, the power grid can have more abundant operating modes under the new standard system.

[0007] (2) For the second type of fault, if stabilization measures can be taken after the fault under the old standard system within the original operation mode, then there is no need to take stabilization measures if it can be stabilized under the new standard system. Then, the original third line of defense (low voltage load reduction) configured for stabilization refusal should also be adjusted synchronously to ensure that the third line of defense will not malfunction.

[0008] For operating modes other than the original operating mode, it is necessary to calculate and analyze the adaptability of the original stability control system after the failure, as well as the coordination issues of the third line of defense.

[0009] (3) For the third type of faults, within the original operating mode, on the one hand, it should cooperate with the stability control and avoid the action of the third line of defense for the original unstable fault to become stable; on the other hand, in response to the change of stability standards, the low-voltage load reduction plan can be optimized simultaneously to adjust the load shedding amount and action time, and cooperate with other third lines of defense to avoid mismatch of the third line of defense.

[0010] In view of the above-mentioned impacts, it is necessary to study the low-voltage load reduction configuration method that adapts to the new voltage stability standards. Summary of the invention

[0011] In view of this, the present invention aims to provide a low-voltage load reduction configuration method adapted to the new voltage stability standard, so as to solve the above-mentioned problems existing in the existing low-voltage load reduction measures in response to the new voltage stability standard.

[0012] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0013] The present invention provides a low voltage load reduction configuration method adapted to the new voltage stability standard, comprising the following steps:

[0014] Identify voltage instability problem areas and voltage instability fault types;

[0015] Determine load shedding sites and the total amount of load shedding based on the voltage instability problem area and the voltage instability fault type;

[0016] Determine the restoration voltage level of the voltage instability problem area based on the new voltage stability standard;

[0017] Calculate the PV curves of key sites in the voltage instability problem area;

[0018] Determine specific implementation parameters of the voltage load reduction configuration scheme for the voltage instability problem area based on the load-shedding sites and the total load shedding amount, the recovery voltage level, and the PV curve;

[0019] For the voltage instability problem area, the voltage load reduction configuration scheme is simulated and verified, and the voltage load reduction configuration scheme that passes the verification is used as the configuration scheme for the corresponding area.

[0020] Furthermore, a heavy load operation mode is adopted to identify the voltage instability fault type, and the voltage instability fault type at least includes rare and serious faults defined by the third level safety and stability standard.

[0021] Furthermore, the voltage load shedding configuration scheme includes at least: voltage load shedding control method, installation location, action conditions, time delay and load shedding amount.

[0022] Furthermore, specific implementation parameters of the voltage load reduction configuration scheme for the voltage instability problem area are determined based on the load-shedding sites and the total load shedding amount, the recovery voltage level, and the PV curve, including:

[0023] For the installation site, select the load-shedding site that meets the higher sensitivity condition as the priority configuration site;

[0024] For the above mentioned operating conditions, the operating voltage setting range of the low voltage load shedding relay is 8% to 15% lower than the minimum voltage allowed in normal operation;

[0025] For the time delay, the time delay of low-voltage load shedding is determined according to load characteristics;

[0026] For the load shedding amount, the relative proportion of load shedding at each load shedding site is determined based on sensitivity analysis, and then the load shedding amount of each site is determined using a PV curve analysis method.

[0027] Furthermore, the time delay of low voltage load shedding is determined according to the load characteristics, including:

[0028] For a motor type load, determining a first time delay;

[0029] For a load of the constant impedance type, a second time delay is determined, the second time delay being greater than the first time delay.

[0030] Furthermore, the load shedding amount of the determined voltage load reduction configuration scheme is not less than 10%~20% of the load in the region.

[0031] Furthermore, the voltage load reduction configuration scheme is configured according to the hierarchical and regional principles, and the setting parameters of each level and each area include at least: the number of basic rounds and the action voltage and action delay of each round.

[0032] Furthermore, the set action voltage and action delay actually meet the requirements for enabling the voltage load reduction measure to avoid the low voltage process that may exist during the normal fault removal time and avoid the action time of the second line of defense safety and stability control device.

[0033] Furthermore, the first round of action voltage of the basic round is lower than the lowest voltage allowed by the system in the long term, and the last round of action voltage is higher than the critical voltage of the system static voltage instability.

[0034] Furthermore, to address transient voltage stability issues, the basic number of wheels of the automatic low-voltage load reduction device installed in the system is set at 2 to 5, and a special wheel with a long delay is provided. To address long-term voltage stability issues, the number of wheels and action delay are increased.

[0035] In summary, the present invention provides a low-voltage load reduction configuration method that adapts to the new voltage stability standard, including identifying voltage instability problem areas and voltage instability fault types; determining the load-shedding sites and the total amount of load shedding in combination with the voltage instability problem areas and the voltage instability fault types; determining the recovery voltage level of the voltage instability problem area based on the new voltage stability standard; calculating the PV curve of the key sites in the voltage instability problem area; determining the specific implementation parameters of the voltage load reduction configuration scheme in the voltage instability problem area based on the load-shedding sites and the total amount of load shedding, the recovery voltage level and the PV curve; for the voltage instability problem area, performing simulation verification on the voltage load reduction configuration scheme, and using the verified voltage load reduction configuration scheme as the configuration scheme for the corresponding area. The present invention proposes to provide a low-voltage load reduction configuration method that can effectively respond to the new standard and has good regional adaptability, which significantly improves the safety and stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 A flow chart of a low voltage load reduction configuration method adapted to the new voltage stability standard provided by an embodiment of the present invention;

[0038] Figure 2 This is the PV curve diagram of some stations in a certain area;

[0039] Figure 3 Add corresponding PV curves for some site loads in a certain area;

[0040] Figure 4 This is a time domain simulation curve of voltage recovery caused by double-line tripping of a transmission line in a certain area. DETAILED DESCRIPTION

[0041] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Based on some practical experience of domestic and foreign power grids, the following issues need to be considered in the low-voltage load shedding configuration setting: operation mode and fault, installation location, action conditions, time delay, and load shedding amount. These issues are first introduced below.

[0043] (1) Operation mode and failure

[0044] The domestic "Guidelines for the Safety and Stability of Power Systems" divides the safety and stability standards of the power system's ability to withstand large disturbances into three levels: the first level standard is a common single fault, requiring the system to maintain stable operation and normal power supply when such a fault occurs; the second level standard is a more serious fault, requiring the system to correctly operate protection, switches and reclosing after such a fault occurs, maintain stable operation, and allow stable control measures such as cutting the machine or load when necessary; the third level standard is a rare serious fault. When such a fault occurs and causes stability to be destroyed, the system must take measures to prevent system collapse, avoid long-term large-scale power outages and catastrophic power outages for the most important users, and minimize load losses. The power system should resume normal operation as soon as possible. The measures taken for these three levels of standards are the three lines of defense to ensure the safe and stable operation of the power system.

[0045] It is generally believed that low-voltage load shedding belongs to the measures in the third line of defense. Therefore, the low-voltage load shedding configuration mainly considers the rare and serious faults defined by the third-level safety and stability standards.

[0046] Since voltage collapse accidents basically occur under heavy load conditions, the operating mode that needs to be considered for low-voltage load reduction configuration is mainly the heavy load operating mode.

[0047] (2) Installation location

[0048] For low-voltage load shedding with centralized control, it is mainly necessary to install monitoring devices at some key nodes (generally important hub substations). For low-voltage load shedding devices with decentralized control, they need to be installed first at nodes with weak voltage stability, so that a smaller load shedding amount can be used to effectively prevent system voltage collapse.

[0049] Common methods for identifying nodes with weak voltage stability in the system are:

[0050] 1) Identify weak nodes directly based on voltage levels;

[0051] 2) Use the Jacobian matrix of the power flow equation to perform modal analysis and identify weak nodes based on the size of the participation factor;

[0052] 3) Identify weak nodes based on the size of the singular vectors of the Jacobian matrix of the power flow equation;

[0053] 4) Identify weak nodes based on the load margin of the nodes;

[0054] 5) Identify weak nodes using power mismatch in power flow calculations;

[0055] 6) Use node assessment methods to identify weak nodes, etc.

[0056] Since the voltage stability weak nodes change with the system operation mode, the generator output, load distribution, maintenance mode, etc. all have a certain impact on the system weak nodes. Therefore, it is necessary to consider various operation modes and use different methods in combination to find relatively accurate and universal weak nodes.

[0057] (3) Action conditions

[0058] The action conditions and time delay are the key to the setting of the low-voltage load reduction device. It is necessary to comprehensively consider the influence of various factors to ensure the correct action of the low-voltage load reduction device and maintain the stability of the system voltage.

[0059] Low-voltage load shedding with centralized control can adopt relatively complex load shedding action conditions. For example, Tokyo Electric Power Company of Japan adopts three standards as action conditions: long-term voltage collapse standard, short-term voltage collapse standard and slow voltage recovery standard. Quebec of Canada has added the integral rule as an action condition on the basis of three rounds of load shedding.

[0060] When using decentralized control to reduce low voltage loads, the local voltage level is generally used as the basis for load shedding due to limited conditions.

[0061] The operating voltage of the low-voltage load reduction device should be lower than the minimum voltage during normal operation. The proportion of the operating voltage lower than the minimum voltage during normal operation can be determined based on actual conditions, generally around 8% to 15%.

[0062] (4) Time delay

[0063] Types of stability. Since different types of voltage instability have different mechanisms and manifestations, low-voltage load shedding can only operate correctly in various types of voltage instability with a reasonable time delay.

[0064] The dynamic process of voltage instability and voltage collapse can last from 1s to 10min. According to the length of the duration, voltage instability accidents can be divided into short-term and long-term. These two time domain processes can basically be strictly distinguished.

[0065] For small disturbance voltage stability, the node voltage continues to slowly decrease as the system load increases. After reaching the critical point, the system voltage collapses and the voltage drops rapidly, causing a large-scale power outage in the system, which generally lasts for more than a few minutes. For large disturbance and long-term voltage instability, the system can reach a voltage stability state in a short time after the disturbance occurs, but due to the action of other automatic adjustment or control devices in the system, the system voltage slowly decreases and eventually voltage collapse occurs. This instability may last for tens of seconds. For the above voltage instability problems, the delay time of low-voltage load shedding action can be relatively long.

[0066] For short-term voltage instability caused by large disturbances, the voltage of each node changes rapidly within a few seconds after the disturbance occurs, and eventually the voltage collapses. For the above voltage instability problems, low-voltage load shedding requires fast action.

[0067] For example, the low-voltage load shedding device installed in Tennessee, USA, is mainly used to prevent short-term voltage drop instability in areas with a large number of air-conditioning loads. The device operates in 9 161kV substations with the same operating voltage in 5 rounds, with a short delay time of 0.9 to 2.1s. The low-voltage load shedding device installed in the Puget Sound area of ​​the Pacific Electric Company of the United States is mainly used to prevent long-term voltage instability problems, so the time delay is longer, 3.5 to 8s. The low-voltage load shedding device installed by Tokyo Electric Power Company of Japan comprehensively considers the two time domain characteristics of short-term voltage collapse and long-term voltage collapse in the action delay time.

[0068] In addition, the action delay time is also closely related to the load composition of the installation node. If the load is mainly a motor load with a constant power nature, the low-voltage load reduction speed should be fast. If the load is mainly lighting or electric heating devices, the low-voltage load reduction speed delay can be longer. For constant impedance type loads, when the system voltage still cannot be restored after removing part of the load, it is necessary to add some rounds to restore the system voltage to an acceptable level.

[0069] (5) Load shedding

[0070] Whether the low-voltage load reduction measures can effectively prevent voltage collapse depends on the load shedding amount. Different voltage instability problems have different requirements for load shedding. The action delay time also affects the load shedding amount. If the load shedding amount is not enough, the voltage collapse cannot be prevented. If the load shedding amount is too large, overvoltage is likely to occur. How to grasp this, there is currently no recognized appropriate method.

[0071] Common methods for load shedding include first determining the relative proportion of load shedding at the load shedding nodes based on sensitivity analysis, and then determining the load shedding amount at each node using methods such as PV curve analysis. Alternatively, the expected voltage value of the node after load shedding can be given first, and then a load shedding amount can be calculated to ensure that the node voltage returns to a required level after load shedding.

[0072] The load required for the low-voltage load shedding scheme should be sufficient to meet the system voltage recovery requirements after the low-voltage load shedding action under various fault modes. In general, the low-voltage load shedding amount arranged should not be less than 10% to 20% of the load in the area.

[0073] Based on the above analysis, combined with the national standard "GB / T40588-2021 Technical Regulations for Automatic Low-voltage Load Reduction in Power Systems", the embodiment of the present invention proposes a low-voltage load reduction configuration method that adapts to the new voltage stability standard. The specific steps can be seen in Figure 1 :

[0074] S1: Identify voltage instability problem areas and voltage instability fault types.

[0075] It should be noted that voltage instability refers to the state when the power system cannot maintain a sufficient voltage level to meet the load demand after being disturbed. Voltage instability fault types include but are not limited to transient stability problems and static stability problems.

[0076] This step can use the data collected by online monitoring equipment to detect abnormal voltage patterns through real-time data analysis algorithms. Historical data can also be compared with the current operating status to identify potential risk areas. In addition, artificial intelligence techniques (such as machine learning models) can be used to predict and classify different types of voltage instability.

[0077] S2: Determine the load shedding sites and the total amount of load shedding based on the voltage instability problem area and voltage instability fault type.

[0078] It should be noted that load shedding sites refer to power consumption points that can be safely disconnected from the power grid without affecting the supply of critical services (such as hospitals, traffic lights, etc.). The total amount of load shedding is the total amount of electricity consumption that needs to be reduced in order to restore grid stability.

[0079] This step can use optimization algorithms (such as linear programming and mixed integer programming) to determine the optimal load reduction strategy based on the grid topology and the importance of each node. The optimization algorithm can consider a variety of constraints, such as minimizing the impact of user interruptions and maintaining power supply to key facilities.

[0080] S3: Determine the restoration voltage level in the voltage instability problem area based on the new voltage stability standard.

[0081] It should be noted that the new voltage stability standard refers to the latest technical guidance documents on voltage stability such as the "Guidelines for Safety and Stability of Power Systems". In this embodiment, the national standard "GB / T40588-2021 Technical Regulations for Automatic Low-voltage Load Reduction of Power Systems" is selected to determine the recovery voltage level. According to regulations, the minimum operating voltage of 500kV is 0.95, and the minimum operating voltage of 220kV is 0.9pu.

[0082] S4: Calculate the PV curves of key sites in the voltage instability problem area.

[0083] It should be noted that the PV curve is used to describe the impact of active power changes on node voltage.

[0084] S5: Determine the specific implementation parameters of the voltage load reduction configuration plan in the voltage instability problem area based on the load shedding sites and the total amount of load shedding, the recovery voltage level and the PV curve.

[0085] It should be noted that the voltage load reduction configuration plan is a specific action plan to reduce the load according to preset time and action conditions.

[0086] S6: For the voltage instability problem area, the voltage load reduction configuration scheme is simulated and verified, and the voltage load reduction configuration scheme that passes the verification is used as the configuration scheme for the corresponding area.

[0087] It should be noted that the actual performance of the load shedding scheme is tested using professional power system simulation tools. If the results meet expectations, they are formally adopted; otherwise, the parameters need to be adjusted until they are satisfactory.

[0088] During simulation verification, the load model should adopt a detailed model that reflects the actual dynamic characteristics, taking into account the low voltage ride-through characteristics of new energy, the impact of low voltage tripping on the load side, and the coordination of the three lines of defense.

[0089] This embodiment provides a low-voltage load reduction configuration method that adapts to the new voltage stability standard. By identifying the voltage instability problem area and fault type, the recovery voltage level is determined in combination with the new voltage stability standard, and specific implementation parameters are formulated based on detailed PV curve analysis and simulation verification, thereby providing a low-voltage load reduction configuration method that can effectively respond to the new standard and has good regional adaptability, significantly improving the safety and stability of the power system.

[0090] In one embodiment, a heavy load operation mode is adopted to identify the voltage instability fault type, and the voltage instability fault type mainly considers the rare and serious faults defined in the third level safety and stability standard.

[0091] In one embodiment, the voltage load shedding configuration scheme includes at least: a voltage load shedding control method, an installation location, an action condition, a time delay, and a load shedding amount.

[0092] Among them, the voltage load shedding control method can include centralized control and decentralized control. Centralized control usually uses a central control system to decide when and how to cut the load; decentralized control is to install independent low-voltage load shedding devices at each key node, and decide whether to start load shedding based on the local voltage level. The installation location is the specific location of the low-voltage load shedding device in the power grid. The action condition is the specific condition that triggers the start of the low-voltage load shedding device. The time delay refers to the time interval from detecting that the voltage is lower than the threshold to the actual load shedding. The load shedding amount refers to the total amount of load that needs to be shelved under specific conditions.

[0093] In one embodiment, specific implementation parameters of the voltage load reduction configuration scheme for the voltage instability problem area are determined based on the load shedding sites and the total load shedding amount, the recovery voltage level, and the PV curve, including:

[0094] S51: For the installation site, a load-shedding site with a higher sensitivity that meets higher conditions is selected as a priority configuration site.

[0095] S52: For the operating conditions, the operating voltage setting range of the low-voltage load shedding relay is 8% to 15% lower than the minimum voltage allowed during normal operation.

[0096] S53: For the time delay, determine the time delay of low voltage load shedding according to the load characteristics.

[0097] S54: For the load shedding amount, the relative proportion of the load shedding of each load shedding site is determined according to the sensitivity analysis, and then the load shedding amount of each site is determined by using the PV curve analysis method.

[0098] In a further embodiment, the time delay of low voltage load shedding is determined according to load characteristics.

[0099] For example, if the load is mainly motor load, the voltage reduction has a greater impact on it, so the load shedding speed should be fast, and the time delay generally does not exceed 1.5s; if the load is mainly lighting or electric heating equipment with constant impedance characteristics, the load shedding delay can be longer, such as 3s to 6s; for constant impedance type loads, when the voltage drops to a certain level and part of the load is cut off, the system voltage still does not return to the normal operating requirements, and some special wheels need to be added to restore the system voltage to normal levels.

[0100] In a further embodiment, the load shedding amount of the determined voltage load shedding configuration scheme is not less than 10% to 20% of the load in the region.

[0101] In one embodiment, the voltage load reduction configuration scheme is configured according to the hierarchical and regional principles, and the setting parameters of each level and each area include at least: the number of basic rounds and the action voltage and action delay of each round.

[0102] Specifically, the configuration of automatic low-voltage load reduction measures should follow the principle of layering and zoning to solve the problem of local power grid voltage stability. According to the specific situation of voltage stability problems in different regions, the action voltage and delay time of each round should be reasonably set, and each round should not skip the action. Considering some unpredictable situations, a special action round with a long delay should be added so that the voltage in some areas of the power grid will not be suspended at a low level for a long time. The action voltage of the additional special long-delay round can be repeated with the basic round or slightly higher than the basic round.

[0103] In a further embodiment, when a fault occurs in the power system, the automatic low-voltage load reduction measure should avoid the low voltage process that may exist during the normal fault removal time to prevent load loss caused by malfunction of the device. The automatic low-voltage load reduction measure should also avoid the actual operation of the second line of defense safety and stability control device. The action voltage and delay of the automatic low-voltage load reduction measure are reasonably set. When the voltage stability criterion is met after the fault, the automatic low-voltage load reduction device does not operate.

[0104] In a further embodiment, the first round of action voltage of the basic round is lower than the lowest voltage allowed by the system in the long term, and the last round of action voltage is higher than the critical voltage of the system static voltage instability.

[0105] In a further embodiment, in order to solve the problem of transient voltage stability, the basic round number of the automatic low-voltage load reduction device set in the system can be set to 2~5, and a special round with a long delay can be set. In order to solve the problem of long-term voltage stability, the round number and action delay can be appropriately increased. It is recommended that the basic round voltage difference be (2%~5%)Un, the action delay of each round is 0.2s~5s, the action delay of the special round is 10s~20s, and the load reduction amount is determined by calculation and analysis based on the power grid situation.

[0106] In addition, the low voltage load reduction configuration setting also needs to follow the following principles:

[0107] (1) After the automatic low-voltage load reduction measure is activated, the voltage of all load buses in the system should be restored to above 0.9 pu as soon as possible during the transient process.

[0108] (2) Automatic low-voltage load reduction measures should meet the requirements of system stability and voltage recovery under different disturbances. The load reduction amount should be sufficient, while excessive load reduction should be avoided as much as possible.

[0109] (3) When configuring automatic low-voltage load reduction measures, they should be coordinated with the system's existing automatic low-voltage disconnection, out-of-step disconnection, low-frequency load reduction and other measures to reduce unnecessary load losses and avoid further impact on the system.

[0110] Taking a certain load-intensive area as an example, the following low-voltage load reduction configuration scheme is designed to adapt to the new voltage stability standard.

[0111] (1) Selection of low voltage load shedding configuration location

[0112] By increasing the overall load of the area in equal proportion, the PV curves of each area in the entire region are calculated to determine the low-voltage load reduction configuration location. Figure 2 shown.

[0113] The greater the voltage drop at the node, the more sensitive the load is to the voltage, and low-voltage load shedding should be configured first. At present, the low-voltage load shedding plan is configured according to 30% of the load in the area, and the low-voltage load shedding capacity of a single site is reconfigured according to the voltage drop sorting and the load that can be cut at a single node does not exceed 60% of the maximum load ratio.

[0114] (2) Setting of load shedding amount

[0115] To set the load shedding amount, it is necessary to calculate the PV curve corresponding to the load increase of a single site, such as Figure 3 shown.

[0116] Figure 3 It is shown in the figure that after the node voltage is lower than the inflection point voltage (generally 0.8-0.7pu), a slight increase in the load will cause the voltage to drop rapidly. To ensure the effectiveness of the low-voltage load reduction action, the voltage of the last round of action should be greater than the voltage collapse point or consider a certain margin greater than the inflection point voltage. At the same time, the voltage of the first round is lower than the minimum voltage allowed by the system for a long time, that is, less than 0.9 pu. In addition, considering that the national standard recommends a difference of 2%~5%, the middle value can be selected as 4%. In this way, two rounds of low-voltage load reduction are set, which are 0.87pu and 0.83pu respectively.

[0117] Considering that the target recovery voltage after low-voltage load reduction action is 0.92pu, the load reduction rate relationship table of different node action voltages of 0.87pu and 0.83pu is shown below.

[0118] Table 1 Relationship between load and voltage at different load nodes

[0119]

[0120] In order to adapt to the PV characteristics of all nodes, the load shedding amount of the low-voltage load reduction scheme can be selected to be 10%~30%.

[0121] (2) Setting of action delay

[0122] Considering that the low-voltage load reduction scheme should avoid the first and second type of faults, the action time should be longer than the voltage recovery time after the first and second type of faults and the stabilization action.

[0123] The optimization principles for setting the action delay are as follows:

[0124] (a) In case of N-1 fault, low voltage load shedding should not be activated;

[0125] (b) When a double-circuit line on the same tower trips, the low-voltage load reduction should not be performed at a higher level (before the stability control system is activated);

[0126] (c) When multiple complex faults cause system stability to be destroyed, low-voltage load reduction should be able to fully play its role to prevent the accident from expanding and reduce load losses.

[0127] Under the original voltage standard, the low voltage load reduction plan is:

[0128] The first round was 0.83pu, delay 0.5s, and removal volume 15%;

[0129] The second round is 0.80pu, delay 0.5s, and resection volume 15%; it works independently.

[0130] In order to ensure that the action delay can reliably avoid the above fault conditions, it is necessary to consider the situation where all double-line tripping faults in the area cause the slowest voltage recovery.

[0131] Depend on Figure 4 It can be seen that the time from the most serious fault of all double-line tripping in this area to the voltage recovery to 0.87pu is about 2.57s (node ​​11), and the time from the voltage recovery to 0.83pu is about 2.43s. Considering a certain margin, the first round of action time can be set to 3.0s. Considering the coordination between the rounds of low-voltage load shedding, the second round of action should be after the first round of action. The action time can be set to 0.5s with reference to the existing fixed value, and a new solution is designed:

[0132] According to the PV curve and the relevant first and second type fault simulation characteristics, a new low voltage load reduction scheme can be proposed: the first round is 0.87pu, delay 3.0s, and cut-off amount is 15%; the second round is 0.83pu, delay 0.5s, and cut-off amount is 15%, and they take effect in sequence.

[0133] In addition, considering that if the recovery voltage is suspended between 0.87pu and 0.9pu for a long time after a fault, the existing low-voltage load reduction scheme will not work, which is not conducive to the safe and stable operation of the system. Therefore, it is possible to consider adding a special round scheme. The special round 1 is set to 0.9pu, with a delay of 20s and a load shedding of 10%.

[0134] The first round was 0.87 pu, delay 3.0 s, and resection volume 15%;

[0135] The second round is 0.83pu, delay is 3.0s, and the removal amount is 15%.

[0136] Special round 1: 0.9pu, delay 20s, load shedding 10%.

[0137] The new solution adopts a long delay wheel to avoid false low-voltage load reduction caused by faults in the same-tower lines.

[0138] Now the proposed solution is calculated in combination with the actual fault in the area and compared with the original solution.

[0139] (1) N-1 fault verification

[0140] An N-1 fault check was carried out on the 220kV and above lines in the area. The system voltage was stable and neither the new nor the old scheme would lead to load shedding.

[0141] (2) Double-line tripping fault verification

[0142] The 500kV double-line tripping fault in this area was checked and the results are as follows:

[0143] Table 2 Calculation results of 500kV double-line tripping fault under different schemes

[0144]

[0145] It can be seen from the table that according to the old criterion, it is transient voltage instability, but according to the new voltage stability criterion, the system can maintain voltage stability without taking stability control measures. The action behaviors of each scheme are as follows:

[0146] The new scheme will not cause low-voltage load reduction. Since the original scheme is equipped with a short-delay 0.5s action wheel, low-voltage load reduction action will be triggered during fault recovery. The maximum action amount is 4637MW, which does not meet the coordination principle of the second and third lines of defense.

[0147] (2) Complex fault verification

[0148] The 500kV switch refusal to operate fault in this area was checked and the results are as follows:

[0149] Table 3 Calculation results of 500kV switch failure under different schemes

[0150]

[0151] In the switch refusal 2 example, if the low-voltage load reduction measures are not taken, the system voltage will be unstable. After taking measures, the original solution and the three solutions proposed in this patent will all be activated, and the system will remain stable after the action, but the load loss of load reduction is different: the new solution < the original solution.

[0152] Several other groups of switches failed to operate, and the system voltage was stable. The original solution had a short-delay action wheel that would quickly operate and cut off a large amount of load, while the new solution had a long-delay action wheel that would not operate to cut the load.

[0153] After comparing the above solutions, we can draw the following conclusions:

[0154] Table 4 Comparison of schemes

[0155]

[0156] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low voltage load shedding configuration method adapted to the new voltage stability standard, characterized in that: The steps include: Identify voltage instability problem areas and voltage instability fault types; Determine load shedding sites and the total amount of load shedding based on the voltage instability problem area and the voltage instability fault type; Determine the restoration voltage level of the voltage instability problem area based on the new voltage stability standard; Calculate the PV curves of key sites in the voltage instability problem area; Determine specific implementation parameters of the voltage load reduction configuration scheme for the voltage instability problem area based on the load-shedding sites and the total load shedding amount, the recovery voltage level, and the PV curve; For the voltage instability problem area, the voltage load reduction configuration scheme is simulated and verified, and the voltage load reduction configuration scheme that passes the verification is used as the configuration scheme for the corresponding area.

2. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 1 is characterized in that: The voltage instability fault type is identified by adopting a heavy load operation mode, and the voltage instability fault type includes at least rare and serious faults defined by the third level safety and stability standard.

3. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 1 is characterized in that: The voltage load shedding configuration scheme at least includes: voltage load shedding control method, installation location, action conditions, time delay and load shedding amount.

4. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 3 is characterized in that: The specific implementation parameters of the voltage load reduction configuration scheme in the voltage instability problem area are determined based on the load-shedding sites and the total load shedding amount, the recovery voltage level, and the PV curve, including: For the installation site, select the load-shedding site that meets the higher sensitivity condition as the priority configuration site; For the above mentioned operating conditions, the operating voltage setting range of the low voltage load shedding relay is 8% to 15% lower than the minimum voltage allowed in normal operation; For the time delay, the time delay of low-voltage load shedding is determined according to load characteristics; For the load shedding amount, the relative proportion of load shedding at each load shedding site is determined based on sensitivity analysis, and then the load shedding amount of each site is determined using a PV curve analysis method.

5. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 4 is characterized in that: Determine the time delay of low voltage load shedding based on load characteristics, including: For a motor type load, determining a first time delay; For a load of the constant impedance type, a second time delay is determined, the second time delay being greater than the first time delay.

6. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 4 is characterized in that: The load shedding amount of the determined voltage load reduction configuration plan shall not be less than 10%~20% of the load in the area.

7. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 1 is characterized in that: The voltage load reduction configuration scheme is configured according to the hierarchical and regional principles, and the setting parameters of each level and each area at least include: the number of basic rounds and the action voltage and action delay of each round.

8. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 7 is characterized in that: The set action voltage and action delay are actually sufficient to enable the voltage load reduction measure to avoid the low voltage process that may exist during the normal fault removal time and avoid the action time of the second line of defense safety and stability control device.

9. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 7, characterized in that: The first round of action voltage of the basic round is lower than the minimum voltage allowed by the system for a long time, and the last round of action voltage is higher than the critical voltage of the system static voltage instability.

10. The low voltage load shedding configuration method adapted to the new voltage stability standard according to claim 7, characterized in that: To address transient voltage stability issues, the basic number of wheels for the automatic low-voltage load reduction device in the system is set at 2 to 5, and a special wheel with a long delay is also provided. To address long-term voltage stability issues, the number of wheels and action delay are increased.

Images