Low-frequency load shedding protection method and device based on wire inlet current and zero-sequence voltage locking and medium

Abstract

The invention provides a low-frequency load shedding protection method and device based on incoming line current and zero-sequence voltage locking and a medium, and belongs to the technical field of power system automation. The method comprises the following steps: collecting the frequency and amplitude of a three-phase voltage of a high-voltage side bus, each incoming current of a transformer substation and a high-voltage side opening voltage; judging whether the three-phase voltage of the high-voltage side bus meets a starting condition or not; if the starting condition is met, calculating the frequency or amplitude of the three-phase voltage of the high-voltage side bus and whether the change rate of the frequency or amplitude reaches a setting action value or not; if the setting action value is reached, the maximum sampling value of each incoming line current is compared with a locking current constant value, and meanwhile, the high-voltage side opening voltage is compared with an opening voltage locking value; and judging whether the setting outlet acts or not. According to the invention, low-frequency load shedding misoperation is avoided.

Description

Technical Field

[0001] The present invention relates to a low-frequency load shedding protection method, device and medium based on incoming line current and zero-sequence voltage blocking, belonging to the technical field of power system automation. Background Art

[0002] Underfrequency load shedding is a safety control measure that prevents power system frequency collapse. When a power system frequency drops due to a shortfall between power generation and demand, a pre-set portion of the system's secondary loads is sequentially removed according to a pre-set operating frequency. This restores system active power to a balanced state and frequency recovery, playing a crucial role in the safe operation of the power system.

[0003] As the third line of defense for power grid protection, low-frequency load shedding devices have always played a vital role in ensuring safe grid operation. However, with the advancement and maturity of photovoltaic power generation technology, an increasing number of distributed photovoltaic and small photovoltaic power plants have been connected to the grid, leading to profound changes in the operating methods and requirements of the grid system. The original logic of low-frequency load shedding devices is no longer suitable for today's grid development requirements. When the incoming power to a substation trips, the distributed photovoltaic and small photovoltaic power plants carry the entire station load, forming an isolated grid for a short period of time, causing changes in grid frequency and voltage. The low-frequency load shedding device activates when conditions permit, shedding the load. However, when the incoming power to the substation is restored or the backup power supply is successfully switched on, the lost load cannot be restored. This increases the scope of the power outage and negatively impacts the reliability of power supply to users. Therefore, the current protection configuration scheme for low-frequency load shedding devices needs further improvement. There is an urgent need for a low-frequency load shedding device that is suitable for current grid operation to minimize the scope of power outages and ensure continuous power supply. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-frequency load shedding protection method, device and medium based on the locking of incoming line current and zero-sequence voltage. By calculating the locking comparison value of each incoming line current of the substation and comparing it with the locking setting value and the locking setting value of the high-voltage side bus zero-sequence voltage locking value, it is determined whether to operate, thereby avoiding false operation of low-frequency load shedding.

[0005] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking, comprising the following steps: Collect the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage; Determine whether the three-phase voltage of the high-voltage side bus meets the starting conditions; If the starting conditions are met, calculate whether the frequency or amplitude of the three-phase voltage of the high-voltage bus and the rate of change of the frequency or amplitude have reached the set action value; If the set action value is reached, the maximum sampling value of each incoming current will be compared with the locking current set value, and the high-voltage side opening voltage will be compared with the opening voltage locking set value; when the maximum sampling value of each incoming current is less than the locking current set value, the setting outlet will not act, and when the high-voltage side opening voltage is greater than or equal to the opening voltage locking set value, the setting outlet will not act; when the maximum sampling value of each incoming current is greater than or equal to the locking current set value and the high-voltage side opening voltage is less than the opening voltage locking set value, the setting outlet will act, and the outlet will trip all load switches that should be cut off.

[0006] Preferably, the basic locking condition is: <0.15 and or >0.15 , = + + , = + + in, represents the positive sequence voltage, is the negative sequence voltage, Indicates the rated line voltage of the high-voltage side busbar, represents the voltage frequency, Indicates the high-voltage side bus phase A voltage, Indicates the high-voltage side busbar B phase voltage, Indicates the high-voltage side bus phase C voltage, Indicates that the voltage of phase B of the high-voltage side bus rotates 120 degrees clockwise. Indicates that the high-voltage side bus phase C voltage rotates 120 degrees counterclockwise.

[0007] Preferably, the criteria for judging whether the frequency or amplitude of the three-phase voltage of the high-voltage side bus reaches the set action value are as follows: The three-phase voltage-frequency change rate of the high-voltage side bus is less than or equal to the voltage-frequency change rate setting value. Moreover, the voltage frequencies of phase A, phase B, and phase C of the high-voltage side bus are all less than or equal to the voltage frequency starting set value and the voltage frequency action set value.

[0008] Preferably, the criteria for judging whether the rate of change of the three-phase voltage frequency or amplitude of the high-voltage side bus reaches the set action value are as follows: The three-phase voltage amplitude change rate of the high-voltage side bus is less than or equal to the voltage amplitude change rate setting value. Moreover, the voltage amplitudes of phase A, phase B, and phase C of the high-voltage side bus are all less than or equal to the voltage amplitude starting set value and the voltage amplitude action set value.

[0009] In a second aspect, the present invention provides a low-frequency load shedding protection device based on incoming line current and zero-sequence voltage blocking, comprising: The data acquisition module is used to collect the frequency and amplitude of the three-phase voltage of the high-voltage side busbar within a set time; the current of each incoming line of the substation, and the high-voltage side opening voltage; Computer module, used to calculate the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage; A comparison module is used to determine whether low frequency and low voltage occur based on the low frequency load shedding protection sampling value of the incoming line current and the opening voltage lock, and to compare each incoming line current value and the high voltage opening voltage to see whether the lock condition is met; The blocking result output module is used to output the low-frequency load reduction protection output that needs to be blocked based on the incoming line current and opening voltage blocking; Communication module, used for communicating with the substation backend; The output module is used to output abnormal signals and action signals of low-frequency load reduction protection based on incoming line current and zero-sequence voltage blocking.

[0010] A third aspect of the present invention provides a terminal, comprising a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the above method.

[0011] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the above method steps are implemented.

[0012] The advantages of the present invention are: based on the low-frequency load reduction protection method of the incoming line current and the open voltage locking, fault judgment is realized through the sampling values ​​of the incoming line current and the high-voltage open voltage of the substation. When the incoming power supply of the substation trips, the distributed photovoltaic and small photovoltaic power stations form an isolated power grid with the entire station load for a short time, and the grid frequency and voltage change. Due to the locking of the incoming line current and the high-voltage open voltage, the low-frequency load reduction device does not operate and the load is not cut. When the incoming power supply of the substation is successfully reclosed, the lost load is restored to power. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0014] Figure 1 This is a flow chart of the low-frequency load reduction protection method based on incoming line current and opening voltage blocking.

[0015] Figure 2 Schematic diagram of primary wiring of a substation in an embodiment of the present invention.

[0016] Figure 3 This is a flow chart of the low-frequency load shedding protection method based on incoming line current and opening voltage locking in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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 making creative efforts are within the scope of protection of the present invention.

[0018] Example 1, A low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking is applied to a newly constructed power grid that includes a large number of distributed photovoltaic and small photovoltaic stations, including the following steps: S1: collects the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage; S2: Determine whether the three-phase voltage of the high-voltage side bus meets the starting conditions; Specifically, if the conditions are met, the frequency or amplitude of the three-phase voltage of the high-voltage side bus and the rate of change of the frequency or amplitude are calculated to see whether they reach the set action value and step S3 is executed; S3: If the starting conditions are met, calculate whether the frequency or amplitude of the three-phase voltage of the high-voltage bus and the rate of change of the frequency or amplitude have reached the set action value; Specifically, the three-phase voltage frequency or frequency change rate of the high-voltage side bus is calculated and compared with the set value for analysis, and the three-phase voltage amplitude or amplitude change rate of the high-voltage side bus is calculated and compared with the set value for analysis. When the three-phase voltage frequency or frequency change rate of the high-voltage side bus meets the criterion, step S4 is executed; when the three-phase voltage amplitude or amplitude change rate of the high-voltage side bus meets the criterion, step S4 is executed; when the three-phase voltage frequency or amplitude and the frequency or amplitude change rate of the high-voltage side bus meet the criterion at the same time, step S4 is executed; S4: If the set action value is reached, the maximum sampling value of each incoming current will be compared with the locking current set value, and the high-voltage side opening voltage will be compared with the opening voltage locking set value; when the maximum sampling value of each incoming current is less than the locking current set value, the setting outlet will not act, and when the high-voltage side opening voltage is greater than or equal to the opening voltage locking set value, the setting outlet will not act; when the maximum sampling value of each incoming current is greater than or equal to the locking current set value and the high-voltage side opening voltage is less than the opening voltage locking set value, the setting outlet will act, and the outlet will trip all load switches that should be cut off.

[0019] As a refinement of the above embodiment, step S1 specifically includes: sampling of the low-frequency load reduction protection based on the incoming current and zero-sequence voltage blocking includes collecting the three-phase voltage of the high-voltage side bus: U={ , , }, Step 1 specifically includes: sampling of the low-frequency load shedding protection based on the incoming line current and zero-sequence voltage blocking, including the incoming line currents of the substation: I={ , , ...}, Preferably, step 1 specifically includes: sampling of the low-frequency load reduction protection based on the incoming line current and zero-sequence voltage blocking includes the high-voltage side opening voltage: .

[0020] As a refinement of the above embodiment, step S2 specifically includes: the starting condition of the three-phase voltage of the high-voltage side bus is: Positive sequence voltage <0.15 <0.15 and >0.15 If yes, then it is locked, otherwise it goes to step S3; Where, = + + , = + + , The rated line voltage of the high-voltage side bus is 57.7V.

[0021] As a refinement of the above embodiment, step S3 specifically includes: the three-phase voltage frequency of the high-voltage side bus is: , Where: , , They are respectively the voltage frequency of phase A, phase B and phase C of the high-voltage side busbar, and n represents the number of sampling points within the set sampling time.

[0022] High-voltage side bus three-phase voltage frequency change rate { , , }; Where: , , They are respectively the voltage-frequency change rate of phase A of the high-voltage side bus, the voltage-frequency change rate of phase B, and the voltage-frequency change rate of phase C.

[0023] and 、 、 , 、 、 Execute step S4.

[0024] Where: is the voltage-frequency starting setting, Voltage frequency change rate constant, It is the voltage-frequency action constant.

[0025] High-voltage side bus three-phase voltage amplitude: , Where: , , They are respectively the voltage amplitude of phase A, phase B and phase C of the high-voltage side busbar, and n represents the number of sampling points within the set sampling time.

[0026] High-voltage side busbar three-phase voltage amplitude change rate { , , }; Where: , , They are respectively the voltage amplitude change rate of phase A, phase B and phase C of the high-voltage side busbar.

[0027] and 、 、 , 、 、 Go to step 4.

[0028] Where: is the voltage amplitude starting setting, Voltage amplitude change rate constant, It is the voltage amplitude action constant.

[0029] As a refinement of the above embodiment, in step S4, the current sampling of each incoming line of the substation is a discrete value sampling sequence of the current with respect to time: , Where: 、 、 They represent the three-phase currents of the mth incoming line of the substation, and n represents the number of sampling points within the set sampling time.

[0030] As a refinement of the above embodiment, the calculation formula for the current blocking comparison value of each incoming line of the substation is: = , It is the maximum value of the current sampled on each incoming line of the substation, and the positive value is when it points to the high-voltage bus.

[0031] The high-voltage side open-circuit voltage sampling value should be a discrete numerical sequence: = , Where: is the high-voltage side opening voltage, and n is the number of sampling points within the set sampling time.

[0032] When , the setting outlet does not move; Where: It is the constant value of incoming line blocking current.

[0033] ≥ When , the setting outlet does not move; is the opening voltage closing value.

[0034] ≥ and < When the low-frequency load reduction protection based on the incoming current and opening voltage is locked is not locked, and the output is set to operate; the output trips and all load switches that should be cut off are opened.

[0035] like Figure 2When the 110kV Yonghe line fails, the switch on the opposite side trips, and there is no voltage in the incoming line for a short period of time, the 10kV distribution network has a large number of distributed photovoltaic and small photovoltaic power stations. The power generation is roughly equal to the total load of the station. At this time, all the loads of the station will form an island grid. As the load increases or the photovoltaic power generation decreases, the voltage and frequency of the island grid will change. If a conventional low-frequency load reduction device is installed, the frequency or voltage reaches a relatively fixed value. , or , The device will trip the outlets 001 and 002, cutting off the load of the entire station. At this time, even if the 110kV line fault is eliminated and reclosed successfully or other lines are successfully put into standby, even if the busbar is under pressure, the load of the entire station will be lost. The low-frequency load shedding protection based on the incoming current and the open voltage blocking will be turned off when the frequency or voltage reaches a certain value. , or , The device also compares the incoming current setting At this time, there is no forward current in the incoming CT. , or compare the opening voltage , at this time the line is faulty, > , both reached the blocking value, the low-frequency load shedding device blocked, the low-frequency load shedding device did not exit, and no load was removed. The 110kV line fault was eliminated and reclosed successfully, or other lines were successfully put into standby mode, the high-voltage side bus voltage was restored, and the entire station load returned to normal power supply.

[0036] Example 2 A low-frequency load shedding protection device based on incoming line current and zero-sequence voltage blocking, comprising: The data acquisition module is used to collect the frequency and amplitude of the three-phase voltage of the high-voltage side busbar, the current of each incoming line of the substation, and the high-voltage side opening voltage within a set time.

[0037] The computer module is used to calculate the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage.

[0038] The comparison module is used to judge whether low frequency and low voltage occur based on the low frequency load reduction protection sampling value locked by the incoming line current and the opening voltage, and to compare each incoming line current value and the high voltage opening voltage to see whether they meet the locking conditions.

[0039] The blocking result output module is used to output the low-frequency load reduction protection output that needs to be blocked based on the incoming line current and opening voltage blocking.

[0040] Communication module, used to communicate with the substation background.

[0041] The output module is used to output abnormal signals and action signals of low-frequency load reduction protection based on incoming line current and zero-sequence voltage blocking.

[0042] An embodiment of the present disclosure also provides a terminal, including a processor and a storage medium, wherein the storage medium is used to store instructions; the processor is used to operate the low-frequency load reduction protection method based on incoming current and zero-sequence voltage locking according to the instructions.

[0043] The embodiment of the present disclosure further provides a computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are configured to execute the above-mentioned low-frequency load reduction protection method based on incoming line current and zero-sequence voltage blocking.

[0044] The aforementioned computer-readable storage medium may be a transient computer-readable storage medium or a non-transitory computer-readable storage medium.

[0045] The technical solutions of the embodiments of the present disclosure may be embodied in the form of a software product, which is stored in a storage medium and includes one or more instructions for causing a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in the embodiments of the present disclosure. The aforementioned storage medium may be a non-transitory storage medium, including: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, an optical disk, and other media that can store program code, or a transient storage medium.

[0046] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking, characterized in that: The following steps are involved: Collect the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage; Determine whether the three-phase voltage of the high-voltage side bus meets the starting conditions; If the starting conditions are met, calculate whether the frequency or amplitude of the three-phase voltage of the high-voltage bus and the rate of change of the frequency or amplitude have reached the set action value; If the set action value is reached, the maximum sampling value of each incoming current will be compared with the locking current set value, and the high-voltage side opening voltage will be compared with the opening voltage locking set value; when the maximum sampling value of each incoming current is less than the locking current set value, the setting outlet will not act, and when the high-voltage side opening voltage is greater than or equal to the opening voltage locking set value, the setting outlet will not act; when the maximum sampling value of each incoming current is greater than or equal to the locking current set value and the high-voltage side opening voltage is less than the opening voltage locking set value, the setting outlet will act, and the outlet will trip all load switches that should be cut off.

2. The low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking according to claim 1 is characterized in that: The basic locking conditions are: <0.15 and or >0.15 , = + + ， = + + in, represents the positive sequence voltage, is the negative sequence voltage, Indicates the rated line voltage of the high-voltage side busbar, represents the voltage frequency, Indicates the high-voltage side bus phase A voltage, Indicates the high-voltage side busbar B phase voltage, Indicates the high-voltage side bus phase C voltage, Indicates that the voltage of phase B of the high-voltage side bus rotates 120 degrees clockwise. Indicates that the high-voltage side bus phase C voltage rotates 120 degrees counterclockwise.

3. The low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking according to claim 1 is characterized in that: The criteria for judging whether the three-phase voltage frequency or amplitude of the high-voltage side bus reaches the set action value are as follows: The three-phase voltage-frequency change rate of the high-voltage side bus is less than or equal to the voltage-frequency change rate setting value. Moreover, the voltage frequencies of phase A, phase B, and phase C of the high-voltage side bus are all less than or equal to the voltage frequency starting set value and the voltage frequency action set value.

4. The low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking according to claim 3 is characterized in that: The criteria for judging whether the change rate of the three-phase voltage frequency or amplitude of the high-voltage side bus reaches the set action value are as follows: The three-phase voltage amplitude change rate of the high-voltage side bus is less than or equal to the voltage amplitude change rate setting value. Moreover, the voltage amplitudes of phase A, phase B, and phase C of the high-voltage side bus are all less than or equal to the voltage amplitude starting set value and the voltage amplitude action set value.

5. A low-frequency load shedding protection device based on incoming line current and zero-sequence voltage blocking, characterized in that: include: The data acquisition module is used to collect the frequency and amplitude of the three-phase voltage of the high-voltage side busbar within a set time; the current of each incoming line of the substation, and the high-voltage side opening voltage; Computer module, used to calculate the frequency and amplitude of the three-phase voltage of the high-voltage side bus, the current of each incoming line of the substation, and the high-voltage side opening voltage; A comparison module is used to determine whether low frequency and low voltage occur based on the low frequency load shedding protection sampling value of the incoming line current and the opening voltage lock, and to compare each incoming line current value and the high voltage opening voltage to see whether the lock condition is met; The blocking result output module is used to output the low-frequency load reduction protection output that needs to be blocked based on the incoming line current and opening voltage blocking; Communication module, used for communicating with the substation backend; The output module is used to output abnormal signals and action signals of low-frequency load reduction protection based on incoming line current and zero-sequence voltage blocking.

6. A terminal comprising a processor and a storage medium, characterized in that: The storage medium is used to store instructions; the processor is used to operate the low-frequency load reduction protection method based on incoming line current and zero-sequence voltage locking according to any one of claims 1-4 according to the instructions.

7. A computer-readable storage medium, characterized in that A computer program is stored thereon, and when the program is executed by a processor, the low-frequency load shedding protection method based on incoming line current and zero-sequence voltage blocking as described in any one of claims 1 to 4 above is implemented.

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