Voltage aided decision-making method and system for coping with new energy oscillation risk and medium

Abstract

The invention discloses a voltage aided decision-making method and system for coping with a new energy oscillation risk and a medium, and relates to the technical field of power system automation, and aims to solve the problem that a new energy unit is easy to repeatedly low-pass under the condition that the voltage supporting capability is weakened after large-scale grid connection of new energy. The method comprises the steps of obtaining multi-source data for monitoring operation of a power grid, generating a current operation mode, performing load flow calculation, and identifying a voltage weak bus in the power grid; determining the voltage sensitivity of a control object by taking electrical equipment in a bus near area with weak voltage as the control object, and screening out an effective control object based on the voltage sensitivity; according to the effective control object, generating a control measure for dealing with repeated low-voltage penetration of the new energy unit; and implementing control measures, and checking the voltage safety to obtain a voltage auxiliary decision. According to the invention, the problem that the new energy repeatedly enters and exits the low-pass filter due to insufficient system voltage support after a large number of conventional units are replaced by the new energy units is solved, and technical support is provided for efficient consumption of the new energy.

Description

Technical Field

[0001] This invention relates to a voltage-assisted decision-making method, system, and medium for addressing the risk of new energy oscillations, belonging to the field of power system automation technology. Background Technology

[0002] With the rapid development of ultra-high voltage direct current (UHVDC) and the large-scale grid connection of new energy sources, the voltage support capacity of the power grid has gradually weakened, the overall dynamic regulation capability of the system has continued to decline, and the trend of "hollowing out" of the main grid has become increasingly obvious. In areas with a high proportion of new energy integration, voltage stability has become one of the core issues restricting the safe and stable operation of the system and the capacity for new energy absorption. In actual power grids, voltage oscillation and instability caused by low-voltage ride-through have occurred many times. This phenomenon often occurs when new energy sources have high output. As the active power output of new energy sources increases, the voltage at the grid connection point gradually decreases to the low-voltage ride-through control threshold. New energy units repeatedly trigger and exit low-voltage ride-through control, causing periodic changes in output power, which in turn causes continuous fluctuations in system voltage. In severe cases, this may lead to large-scale disconnection of new energy sources from the grid.

[0003] To address the issue of repeated low-voltage ride-through by renewable energy units under high-output conditions, existing research mainly proposes solutions from both the grid and renewable energy unit perspectives. On the grid side, the focus is on strengthening the grid structure to improve system strength, while on the renewable energy unit side, the main approach is optimizing the low-voltage ride-through control parameters. However, strengthening the grid structure suffers from poor economic efficiency, and optimizing the low-voltage ride-through control parameters cannot be applied to the infinite number of possible operating modes of renewable energy units under highly uncertain conditions. Therefore, there is an urgent need to propose a voltage-assisted decision generation method based on real-time adjustable resources to address the risk of renewable energy oscillations. Summary of the Invention

[0004] The purpose of this invention is to provide a voltage-assisted decision-making method, system, and medium to address the risk of new energy oscillations, thereby solving the problem of repeated low-voltage breakdowns in new energy units caused by the weakening of voltage support capacity after large-scale grid connection of new energy.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] Firstly, this invention proposes a voltage-assisted decision-making method to address the risk of new energy source oscillations, comprising:

[0007] Acquire multi-source data on the operation of the power grid, generate the current operating mode and perform power flow calculation, and identify the weak voltage bus in the current operating mode based on the power flow calculation results;

[0008] The electrical equipment in the vicinity of the voltage-weak busbar is taken as the control object. The electrical signal sensitivity of the control object is determined based on the electrical signal data of the control object, and effective control objects are screened based on the electrical signal sensitivity.

[0009] Based on the effective control object, generate control measures to address the repeated low-voltage power transmission of new energy units corresponding to the voltage weak bus;

[0010] Implement the aforementioned control measures and verify voltage safety to obtain voltage-assisted decision-making.

[0011] Furthermore, identifying the weak voltage bus in the current operating mode includes:

[0012] Acquire multi-source data on power grid operation;

[0013] The current operating mode scenario is generated based on the multi-source data, and the power flow calculation is performed based on the power flow data corresponding to the current operating mode scenario to obtain the grid connection voltage of the new energy unit;

[0014] Calculate the voltage safety margin when the grid connection point voltage of the i-th new energy unit is lower than the preset voltage, wherein the voltage safety margin Obtained using the following formula:

[0015] (1)

[0016] In the formula, Let be the voltage at the grid connection point of the i-th renewable energy unit; The threshold for the i-th renewable energy unit to enter low voltage ride-through; Preset voltage;

[0017] The grid connection point with the lowest voltage safety margin among those values ​​below the threshold value is selected as the weak voltage bus.

[0018] Furthermore, the multi-source data includes SCADA measurement data and state estimation data.

[0019] Furthermore, the threshold for the i-th new energy unit to enter low voltage ride-through. The voltage safety margin threshold is set to 0.9 pu, the preset voltage is set to 1.0 pu.

[0020] Furthermore, the electrical equipment in the vicinity of the voltage-weak busbar is taken as the control object. Based on the electrical signal data of the control object, the electrical signal sensitivity of the control object is determined. Based on the electrical signal sensitivity, effective control objects are screened, including:

[0021] The electrical signal sensitivity is determined to be voltage sensitivity;

[0022] Centered on the weak voltage bus, the adjustable nodes in the vicinity of the bus and the on-load tap changer of the transformer are taken as the control objects.

[0023] The voltage sensitivity of the controlled object is calculated using the following formula:

[0024] (2)

[0025] In the formula, This indicates the voltage sensitivity of the weak bus to the capacitor being switched on or the reactor being switched off at the j-th node. This represents the capacity at which the capacitor is switched on or the reactor is switched off at the j-th node. Deploy capacity to the j-th node capacitors or de-capacitance The voltage change of the weak busbar after the reactor; This indicates the voltage sensitivity of the k-th transformer turns ratio adjustment to the voltage-weak busbar; This represents the adjustment amount for the turns ratio of the k-th transformer. Adjusting the turns ratio of the kth transformer Voltage change at the weakest busbar;

[0026] Select control objects with voltage sensitivity greater than 0 to form effective control objects.

[0027] Furthermore, the control measures for generating power to address repeated low-voltage power surges of new energy units corresponding to weak voltage busbars include:

[0028] Calculate the voltage boost of a single controlled object l within the effective controlled object. It can be obtained through the following formula:

[0029] (3)

[0030] In the formula, The voltage sensitivity of a single controlled object l. For voltage sensitivity is The corresponding adjustable amount of the controlled object;

[0031] The control measures are sorted in descending order based on the voltage increase after the control object has been executed at its maximum adjustable value.

[0032] The control measures, arranged in descending order, are superimposed sequentially, with each controlled object using its maximum adjustable value, until the constraint of the following calculation formula is met:

[0033] (4)

[0034] Where m is the number of superimposed control objects. This is the lower limit of the busbar safe voltage. Let be the voltage at the grid connection point of the i-th renewable energy unit;

[0035] If all control objects in the effective control objects still do not meet the formula (4) after adopting the maximum adjustable amount, then measures are taken to reduce the active power of the new energy unit corresponding to the voltage weak bus, so as to obtain control measures to deal with the repeated low voltage ride-through of the new energy unit corresponding to the voltage weak bus.

[0036] Furthermore, the measures to reduce the active power of new energy units corresponding to weak voltage buses include:

[0037] The step size for calculating the reduction in active power of new energy generating units, wherein the step size Obtained using the following formula:

[0038] (5)

[0039] in, This represents the actual active power of the new energy generating units corresponding to the low-voltage bus. This is a proportional parameter used to adjust the step size;

[0040] According to the step size Gradually reduce the active power of the new energy units corresponding to the weak voltage bus and perform power flow calculations until the voltage of the weak bus is greater than 100 kWh. .

[0041] Furthermore, the implementation of control measures and the verification of voltage safety to obtain voltage-assisted decision-making include:

[0042] Implement control measures to address the repeated undervoltage surges of new energy units corresponding to weak voltage busbars in the current operating mode;

[0043] Perform power flow calculations and calculate the voltage safety margin at the grid connection point of new energy units in the power grid using Equation (1);

[0044] If the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold, the obtained control measures will be used as voltage auxiliary decisions to deal with repeated low voltage breakdowns of new energy units; otherwise, the above steps will be repeated until the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold.

[0045] Secondly, this invention proposes a voltage-assisted decision-making system to address the risk of new energy source oscillations, comprising:

[0046] The weak voltage bus identification module is used to identify weak voltage busbars in the current operating mode;

[0047] An effective control object screening module is used to calculate the voltage sensitivity of the control object to the voltage-weak bus, and screen out effective control objects based on the voltage sensitivity.

[0048] The repeated undervoltage control module is used to generate control measures for repeated undervoltage of new energy units corresponding to the voltage-weak busbars based on the effective control object.

[0049] The safety verification module is used to implement the control measures and verify the voltage safety to obtain voltage auxiliary decision.

[0050] Thirdly, the present invention proposes a computer-readable storage medium storing a computer program / instruction thereon, which, when executed by a processor, implements the steps of a voltage-assisted decision-making method for addressing the risk of new energy oscillations.

[0051] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0052] This invention achieves voltage safety risk assessment considering the repeated low-voltage charging constraints of renewable energy units. At the same time, it improves the grid connection voltage of renewable energy units through auxiliary decision-making measures such as capacitive reactor commissioning and decommissioning, transformer ratio adjustment, and reduction of active power of renewable energy units. This solves the problem that existing control measures are not economical or cannot adapt to all possible operating scenarios under the uncertainty of strong renewable energy output, and provides technical support for the efficient consumption of renewable energy. Attached Figure Description

[0053] Figure 1 This is a schematic diagram illustrating the steps of a voltage-assisted decision-making method for addressing the risk of new energy oscillations, as provided by the present invention. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use.

[0055] Example 1:

[0056] This embodiment presents a voltage-assisted decision-making method for addressing the risk of new energy source oscillations, such as... Figure 1 As shown, it includes:

[0057] Acquire multi-source data on the operation of the power grid, generate the current operating mode and perform power flow calculation, and identify the weak voltage bus in the current operating mode based on the power flow calculation results;

[0058] The electrical equipment in the vicinity of the voltage-weak busbar is taken as the control object. The electrical signal sensitivity of the control object is determined based on the electrical signal data of the control object, and effective control objects are screened based on the electrical signal sensitivity.

[0059] Based on the effective control objects, generate control measures to address the repeated low-voltage power surges of new energy units corresponding to weak voltage busbars;

[0060] Implement control measures and verify voltage safety to obtain voltage-assisted decision-making.

[0061] In this embodiment, identifying the weak voltage bus in the current operating mode includes:

[0062] Acquire multi-source data on power grid operation;

[0063] The current operating mode scenario is generated based on multi-source data, and the power flow data corresponding to the current operating mode scenario is used to calculate the voltage at the grid connection point of the new energy unit.

[0064] Calculate the voltage safety margin when the grid connection voltage of the i-th new energy unit is lower than the preset voltage. Obtained using the following formula:

[0065] (1)

[0066] in, Let be the voltage at the grid connection point of the i-th renewable energy unit; The threshold for the i-th new energy unit to enter low voltage ride-through is set to 0.9pu; U is the preset voltage, set to 1.0pu.

[0067] The grid connection point with the lowest voltage safety margin among those less than the voltage safety margin threshold is selected as the weak voltage bus, and the voltage margin threshold is set to 0%.

[0068] In this embodiment, the multi-source data includes SCADA measurement data and state estimation data.

[0069] In this embodiment, electrical equipment in the vicinity of a voltage-weak busbar is taken as the control object. Based on the electrical signal data of the control object, the electrical signal sensitivity of the control object is determined. Effective control objects are then selected based on the electrical signal sensitivity, including:

[0070] The electrical signal sensitivity is determined to be voltage sensitivity;

[0071] Centered on the weak voltage bus, the adjustable nodes in the vicinity of the bus and the on-load tap changer of the transformer are taken as the control objects.

[0072] The voltage sensitivity of the controlled object is calculated using the following formula:

[0073] (2)

[0074] in, This indicates the voltage sensitivity of the weak bus to the capacitor being switched on or the reactor being switched off at the j-th node. This represents the capacity at which the capacitor is switched on or the reactor is switched off at the j-th node. Deploy capacity to the j-th node capacitors or de-capacitance The voltage change of the weak busbar after the reactor; This indicates the voltage sensitivity of the k-th transformer turns ratio adjustment to the voltage-weak busbar; This represents the adjustment amount for the turns ratio of the k-th transformer. Adjusting the turns ratio of the kth transformer Voltage change at the weakest busbar.

[0075] Control measures with voltage sensitivity greater than 0 are selected to form effective control targets.

[0076] In this embodiment, the control measures for dealing with repeated low-voltage power surges of new energy units corresponding to weak voltage busbars include:

[0077] Calculate the voltage boost of a single controlled object l within the effective controlled object. It can be obtained through the following formula:

[0078] (3)

[0079] in, The voltage sensitivity of a single controlled object l. For voltage sensitivity is The corresponding control object can be adjusted.

[0080] The control measures are sorted in descending order based on the voltage increase after the control object has been executed at its maximum adjustable value.

[0081] The control measures, arranged in descending order, are superimposed sequentially, with each controlled object using its maximum adjustable value, until the constraint of the following calculation formula is met:

[0082] (4)

[0083] Where m is the number of superimposed control objects. This is the lower limit of the busbar safe voltage. Let be the voltage at the grid connection point of the i-th new energy unit.

[0084] If all control objects in the effective control objects still do not meet the formula (4) after adopting the maximum adjustable amount, then measures are taken to reduce the active power of the new energy unit corresponding to the voltage weak bus, so as to obtain control measures to deal with the repeated low voltage ride-through of the new energy unit corresponding to the voltage weak bus.

[0085] In this embodiment, measures to reduce the active power of new energy units corresponding to weak voltage busbars include:

[0086] The step size for calculating the reduction in active power of renewable energy units. Obtained using the following formula:

[0087] (5)

[0088] in, This represents the actual active power of the new energy generating units corresponding to the low-voltage bus. This is a proportional parameter used to adjust the step size;

[0089] Based on step size Gradually reduce the active power of the new energy units corresponding to the weak voltage bus and perform power flow calculations until the voltage of the weak bus is greater than 100 kWh. .

[0090] In this embodiment, control measures are implemented and voltage safety is checked to obtain voltage-assisted decision-making, including:

[0091] Implement control measures to address the repeated undervoltage surges of new energy units corresponding to weak voltage busbars in the current operating mode;

[0092] Perform power flow calculations and calculate the voltage safety margin at the grid connection point of new energy units in the power grid using Equation (1);

[0093] If the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold, the obtained control measures will be used as voltage auxiliary decisions to deal with repeated low voltage breakdowns of new energy units; otherwise, the above steps will be repeated until the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold.

[0094] Example 2:

[0095] This embodiment provides a system for implementing a voltage-assisted decision-making method to address the risk of new energy oscillations, including:

[0096] The weak voltage bus identification module is used to identify weak voltage busbars in the current operating mode;

[0097] The effective control object screening module is used to calculate the voltage sensitivity of the control object to the voltage weak bus and screen out the effective control objects based on the voltage sensitivity.

[0098] The repeated undervoltage control module is used to generate control measures for repeated undervoltage of new energy units corresponding to weak voltage busbars based on the effective control objects.

[0099] The safety verification module is used to implement control measures and verify voltage safety to obtain voltage auxiliary decision-making.

[0100] Example 3:

[0101] This embodiment proposes a computer-readable storage medium storing a computer program / instruction, which, when executed by a processor, implements the steps of a voltage-assisted decision-making method for addressing the risk of new energy oscillations.

[0102] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0103] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0104] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0105] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0106] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A voltage-assisted decision-making method for addressing the risk of new energy source oscillations, characterized in that, The method includes: Acquire multi-source data on the operation of the power grid, generate the current operating mode and perform power flow calculation, and identify the weak voltage bus in the current operating mode based on the power flow calculation results; The electrical equipment in the vicinity of the voltage-weak busbar is taken as the control object. The electrical signal sensitivity of the control object is determined based on the electrical signal data of the control object, and effective control objects are screened based on the electrical signal sensitivity. Based on the effective control object, generate control measures to address the repeated low-voltage power transmission of new energy units corresponding to the voltage weak bus; Implement the aforementioned control measures and verify voltage safety to obtain voltage-assisted decision-making.

2. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 1, characterized in that, The identification of the weak voltage bus in the current operating mode includes: Acquire multi-source data on power grid operation; The current operating mode scenario is generated based on the multi-source data, and the power flow calculation is performed based on the power flow data corresponding to the current operating mode scenario to obtain the grid connection voltage of the new energy unit; Calculate the voltage safety margin when the grid connection point voltage of the i-th new energy unit is lower than the preset voltage. The voltage safety margin Obtained using the following formula: （1） In the formula, Let be the voltage at the grid connection point of the i-th renewable energy unit; The threshold for the i-th renewable energy unit to enter low voltage ride-through; Preset voltage; The grid connection point with the lowest voltage safety margin among those values ​​below the threshold value is selected as the weak voltage bus.

3. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 2, characterized in that, The multi-source data includes SCADA measurement data and state estimation data.

4. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 2, characterized in that, The threshold for the i-th renewable energy unit to enter low voltage ride-through The voltage safety margin threshold is set to 0.9 pu, the preset voltage is set to 1.0 pu.

5. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 1, characterized in that, The electrical equipment in the vicinity of the voltage-weak busbar is taken as the control object. Based on the electrical signal data of the control object, the electrical signal sensitivity of the control object is determined. Based on the electrical signal sensitivity, effective control objects are screened, including: The electrical signal sensitivity is determined to be voltage sensitivity; Centered on the weak voltage bus, the adjustable node parallel capacitive reactors and on-load taps of the transformers in its vicinity are taken as the control objects; The voltage sensitivity of the controlled object is calculated using the following formula: （2） In the formula, This indicates the voltage sensitivity of the weak bus to the capacitor being switched on or the reactor being switched off at the j-th node. This represents the capacity at which the capacitor is switched on or the reactor is switched off at the j-th node. Deploy capacity to the j-th node capacitors or decommissioning capacity The voltage change of the weak busbar after the reactor; This indicates the voltage sensitivity of the k-th transformer turns ratio adjustment to the voltage-weak busbar; This represents the adjustment amount for the turns ratio of the k-th transformer. Adjusting the turns ratio of the kth transformer Voltage change at the weakest busbar; Select control objects with voltage sensitivity greater than 0 to form effective control objects.

6. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 2, characterized in that, The control measures for responding to repeated undervoltage surges by new energy units corresponding to weak voltage busbars include: Calculate the voltage boost of a single controlled object l within the effective controlled object. It can be obtained through the following formula: （3） In the formula, The voltage sensitivity of a single controlled object l. For voltage sensitivity is The corresponding adjustable amount of the controlled object; The control measures are sorted in descending order based on the voltage increase after the control object has been executed at its maximum adjustable value. The control measures, arranged in descending order, are superimposed sequentially, with each controlled object using its maximum adjustable value, until the constraint of the following calculation formula is met: （4） Where m is the number of superimposed control objects. This is the lower limit of the busbar safe voltage. Let be the voltage at the grid connection point of the i-th renewable energy unit; If all control objects in the effective control objects still do not meet the formula (4) after adopting the maximum adjustable amount, then measures are taken to reduce the active power of the new energy unit corresponding to the voltage weak bus, so as to obtain control measures to deal with the repeated low voltage ride-through of the new energy unit corresponding to the voltage weak bus.

7. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 6, characterized in that, The measures to reduce the active power of new energy units corresponding to weak voltage buses include: The step size for calculating the reduction in active power of new energy generating units, wherein the step size Obtained using the following formula: （5） in, This represents the actual active power of the new energy generating units corresponding to the low-voltage bus. This is a proportional parameter used to adjust the step size; According to the step size Gradually reduce the active power of the new energy units corresponding to the weak voltage bus and perform power flow calculations until the voltage of the weak bus is greater than 100 kWh. .

8. The voltage-assisted decision-making method for addressing the risk of new energy oscillations according to claim 6, characterized in that, The implementation of control measures and the verification of voltage safety to obtain voltage-assisted decision-making include: Implement control measures to address the repeated undervoltage surges of new energy units corresponding to weak voltage busbars in the current operating mode; Perform power flow calculations and calculate the voltage safety margin at the grid connection point of new energy units in the power grid using Equation (1); If the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold, the obtained control measures will be used as voltage auxiliary decisions to deal with repeated low voltage breakdowns of new energy units; otherwise, the above steps will be repeated until the voltage safety margin at the grid connection point of all new energy generating units in the power grid is greater than the voltage safety margin threshold.

9. A voltage-assisted decision-making system for addressing the risk of new energy source oscillations, characterized in that, include: The weak voltage bus identification module is used to identify weak voltage busbars in the current operating mode; An effective control object screening module is used to calculate the voltage sensitivity of the control object to the voltage-weak bus, and screen out effective control objects based on the voltage sensitivity. The repeated undervoltage control module is used to generate control measures for repeated undervoltage of new energy units corresponding to the voltage-weak busbars based on the effective control object. The safety verification module is used to implement the control measures and verify the voltage safety to obtain voltage auxiliary decision.

10. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instruction is executed by the processor, it implements the steps of the voltage-assisted decision-making method for addressing the risk of new energy oscillation as described in any one of claims 1 to 8.

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