Method, device and program for busbar protection against power frequency magnetic field interference

Abstract

The application discloses a method, device and program for bus protection device anti-power frequency magnetic field interference, comprising: collecting sampling data of all current branches of the device; screening non-interference branches without current based on three-phase current instantaneous value, zero sequence current instantaneous value and absolute value of zero sequence current instantaneous value power frequency variation; performing interference mutation judgment on the screened branches combined with three-phase current instantaneous value, three-phase interphase current instantaneous value, three-phase current instantaneous value power frequency variation, and absolute value of zero sequence current instantaneous value power frequency variation to obtain disturbance branches; monitoring whether the disturbance branches satisfy disturbance keeping state; judging disturbance state of non-disturbance branches combined with disturbance state and disturbance keeping state of the previous sampling period; performing device disturbance judgment based on the number of disturbance branches, and filtering respective superimposed currents of all branches of the device when the device is in the disturbance state. The method of the application can accurately identify interference branches when the branches are interfered to different degrees, and improve protection reliability.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment testing technology, specifically relating to methods, equipment, and procedures for busbar protection devices to resist power frequency magnetic field interference. Background Technology

[0002] Busbar faults are among the most serious faults in a power grid. When a fault occurs, the protection device must quickly trip all branch circuit breakers connected to the faulty busbar to prevent the accident from escalating. Therefore, busbar protection devices have extremely high requirements for reliability, speed, and sensitivity. The electromagnetic environment in which the protection device operates is extremely complex, and is closely related to multiple factors such as interference sources, device installation location, and system faults. Electromagnetic interference can interfere with the sampling circuit of the protection device, affecting the accuracy of the analog quantities acquired by the device. Busbar differential protection devices need to simultaneously acquire current signals from more than 20 branches. Electromagnetic interference may generate weak interference signals on each current transformer (CT). The superposition of interference from more than 20 branches can lead to false tripping or failure to trip of the busbar protection.

[0003] Chinese invention patents CN106055757B and CN105206408B demonstrate that hardware optimizations such as transformer design, transformer layout, and PCB optimization can enhance the device's anti-interference capability. These methods improve the power frequency magnetic field immunity, but cannot completely eliminate power frequency interference.

[0004] Chinese invention patent CN109740105B (hereinafter referred to as Patent 1) determines whether the device is under power frequency magnetic field interference by judging whether the number of branches with current changes and the number of branches with zero-sequence current abrupt changes are equal to the total number of branches of the protection device. Finally, the current of each branch is filtered to remove the superimposed current caused by power frequency magnetic field interference. Chinese invention patent CN110808575B (hereinafter referred to as Patent 2) identifies power frequency magnetic field interference in the spare interval, records the spare interval number and the current magnitude of each phase of the spare interval under power frequency magnetic field interference, and calculates the average interference current value of each phase; the total power frequency magnetic field interference value is obtained by using the average interference current value of each phase; the actual differential current value is obtained by subtracting the total power frequency magnetic field interference value from the original differential current, and is used for protection logic calculation.

[0005] The two methods described above identify and compensate for power frequency magnetic field interference using software algorithms. However, they still have the following problems: the bus protection device has a large number of branches, and the impact of magnetic field interference on each CT varies greatly. Patent 1, by judging whether the number of branches with current changes and the number of branches with zero-sequence current mutations are equal to the total number of branches of the protection device, may lead to an error in the power frequency magnetic field interference status, ultimately causing the device to be unable to determine the power frequency magnetic field status. Similarly, Patent 2, which uses an average compensation method, may lead to undercompensation or overcompensation, ultimately causing the device to malfunction or fail to operate. Summary of the Invention

[0006] The present invention aims to overcome the defects existing in the prior art and provide a method, device and procedure for bus protection devices to resist power frequency magnetic field interference. When the magnetic field interference only affects part of the bay, the method can identify and eliminate the influence of power frequency magnetic field interference on differential current, prevent differential protection from maloperation and failure to operate due to accumulated power frequency magnetic field interference, and increase the reliability of bus protection.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for resisting power frequency magnetic field interference in busbar protection devices, the method comprising:

[0009] Collect sampling data from all current branches of the busbar protection device;

[0010] Based on the sampling data of each branch, branches that meet the following conditions are selected: the instantaneous values ​​of the three-phase current and the instantaneous value of the zero-sequence current are both less than the first threshold, the absolute value of the power frequency change of the instantaneous value of the zero-sequence current is less than the second threshold, and the duration exceeds the first time threshold.

[0011] The selected branches are subjected to interference mutation judgment: if the instantaneous values ​​of the three-phase current and the three-phase interphase current are both less than the third threshold, the power frequency change of the instantaneous value of the three-phase current is greater than the fourth threshold, and the absolute value of the power frequency change of the instantaneous value of the zero-sequence current is greater than the fifth threshold, the corresponding data point is marked; if the number of marked data points in a sampling period of a certain branch exceeds the preset number, the branch is marked as a disturbance branch.

[0012] Monitor whether the disturbed branch meets the disturbance hold-up condition; if the branch is not marked as a disturbed branch, but was a disturbed branch in the previous sampling period and met the disturbance hold-up condition, then the branch is marked as a disturbed branch.

[0013] If the number of disturbed branches in the device exceeds half of the total number of branches, the device is determined to be in a disturbed state, and the superimposed current after the sudden change is filtered out from the current of all branches.

[0014] In some embodiments of the present invention, the first threshold, the second threshold, the third threshold, the fourth threshold, and the fifth threshold are set based on the rated secondary current of the current transformer combined with the strength of hardware interference capability.

[0015] In some embodiments of the present invention, the third threshold is greater than the first threshold.

[0016] In some embodiments of the present invention, the disturbance holding state of the disturbance branch is monitored in the following way:

[0017] Monitor the instantaneous values ​​of the three-phase current, the three-phase phase-to-phase current, and the zero-sequence current of the disturbed branch. If the instantaneous values ​​of the three-phase current and the three-phase phase-to-phase current are less than the third threshold, the instantaneous value of the zero-sequence current is greater than the sixth threshold, and the duration exceeds the second time threshold, then the disturbed branch meets the disturbance hold-up state.

[0018] In some embodiments of the present invention, a branch status identifier is set for each branch, and different branch statuses are marked by assigning values ​​to the branch status identifiers; the subsequent filtering and judgment process is performed based on the values ​​of the branch status identifiers.

[0019] In some embodiments of the present invention, the disturbance branch is marked as follows:

[0020] Set a disturbance status flag and assign the value 'a' to the marked disturbance branch;

[0021] For the disturbance branch with disturbance state identifier 'a', assign the disturbance judgment identifier 'b' and perform a disturbance hold-up state judgment. If the disturbance hold-up state is satisfied, assign the disturbance hold-up state identifier 'c'.

[0022] For branches whose disturbance status identifier is not a, determine whether they satisfy the condition that the disturbance judgment identifier in the previous sampling period was b and the disturbance hold status identifier was c. If they satisfy the condition, assign the value b to the disturbance judgment identifier of the branch.

[0023] The branch marked with disturbance judgment 'b' is used as the disturbance branch for device disturbance judgment.

[0024] In some embodiments of the present invention, if the number of data points marked in a branch exceeds 3 in a sampling period, the branch is marked as a disturbance branch.

[0025] The present invention further provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above method.

[0026] The present invention further provides a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0027] The present invention further provides a computer program product, including a computer program / instruction that, when executed by a processor, implements the steps of the above-described method.

[0028] The method of this invention calculates the characteristics of the sampled values ​​of all branches, identifies power frequency magnetic field interference through multi-step criteria, and compensates for the power frequency magnetic field interference when calculating the differential current, thus preventing bus protection from maloperating or failing to operate. This method can accurately identify interfering branches when they are subjected to varying degrees of interference, improving protection reliability. Attached Figure Description

[0029] Figure 1 This is a flowchart of the method of the present invention.

[0030] Figure 2 This is an interference state diagram for different branches.

[0031] Figure 3 These are comparison images before and after interference was filtered out. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] The process of the anti-power frequency magnetic field interference method described in this invention is as follows: Figure 1 As shown, the specific steps include the following:

[0035] 1. Collect sampling data from all current branches of the busbar protection device;

[0036] 2. Based on the sampled data, determine whether each branch is in a no-current and non-interference state. When the instantaneous values ​​of the three-phase currents of the branch are all less than The instantaneous value of zero-sequence current is less than The absolute value of the instantaneous value of zero-sequence current and the change in power frequency. Less than If the branch current continuously meets the above conditions for more than 40ms, it is determined that the branch is in a non-operational, non-interference state, and an indicator is set. Used to characterize branches In non-operational, non-interference state, the identifier of this branch is as follows. Assign a value of 1 and expand the width by 20ms. This is the branch number. The formula for determining a no-flow and non-interference state is as follows:

[0037] and and

[0038]

[0039]

[0040] in , , These are the instantaneous values ​​of phase currents A, B, and C of branch circuit, respectively. This is the instantaneous value of the zero-sequence current. For the current instantaneous data sampling point, For an instantaneous data sampling point one cycle ago, This is the rated secondary current value of the CT.

[0041] The above threshold data , In practical applications, adjustments can be made based on the strength of the hardware's anti-interference capabilities.

[0042] 3. For non-operational, non-interference states ( For a branch with a current of 1), determine the abrupt change state of the branch. Only when the branch is disturbed in a no-flow state can the branch enter a disturbed state.

[0043] Considering the varying degrees of interference experienced by different branches, this invention sets a relatively low threshold for the abrupt change in phase current (0.002In), while also introducing the abrupt change in zero-sequence current and using the simultaneous in-phase magnetic field of the three phases of the power frequency magnetic field as criteria. This allows for accurate identification of branches experiencing different degrees of interference. The criteria for determining the branch interference state are as follows:

[0044] The instantaneous values ​​of the three-phase currents in the branch are all less than The instantaneous values ​​of the three-phase interphase currents in the branch are all less than The instantaneous values ​​of the three-phase currents in the branch circuit and the power frequency variation are all greater than 100%. The absolute value of the instantaneous value of zero-sequence current and the change in power frequency. Greater than .

[0045] If a branch simultaneously meets the above conditions, the instantaneous disturbance is marked. The value is 1. Within a data window of one sampling period, if there are at least 3 data points... If the value is 1, then the branch disturbance status flag for that branch is... The value is assigned to 1.

[0046]

[0047]

[0048] and and

[0049] and and

[0050] and and

[0051]

[0052]

[0053] in , , These are the phase-to-phase currents of phases AB, BC, and AC of the branch, respectively; count is the count value.

[0054] The above threshold data In practical applications, adjustments can be made based on the strength of the hardware's anti-interference capabilities.

[0055] 4. If the branch disturbance status indicator If the value is 1, then the disturbance judgment flag of the output of this branch is... If the value is 1, the disturbance judgment flag participates in the determination of the device disturbance state, and determines whether the branch has met the holding condition within 10ms. The holding condition is as follows:

[0056] and and

[0057] and and

[0058]

[0059] in This represents the amplitude of the zero-sequence current in that branch.

[0060] If the branch disturbance status indicator If the value is 0, then the disturbance judgment flag and disturbance hold status of the branch in the previous sampling period are considered: if the disturbance judgment flag of the branch in the previous sampling period is 0... If the value is 1 and the disturbance hold condition is met, then the disturbance judgment flag of the output of this branch is... It is 1 if it is true, otherwise it is 0.

[0061] The above threshold data In practical applications, adjustments can be made based on the strength of the hardware's anti-interference capabilities.

[0062] 5. Based on comprehensive judgment, when the number of disturbed branches ( If the number of branches with a value of 1 is greater than half the total number of branches in the device, the device is in a disturbance state.

[0063]

[0064] 6. If the device is under disturbance, the superimposed current after the sudden change in the current of each branch is filtered out, and the load current before the disturbance is obtained according to the following formula. In the formula For the load current before the interference, For power frequency magnetic field interference current, This is the superimposed current after the interference.

[0065]

[0066] The impact of magnetic field interference on various CT scans varies considerably, such as... Figure 2 In the event of interference, this invention can accurately identify and eliminate the impact of power frequency magnetic field interference on differential current, preventing differential protection from maloperation and failure to operate due to accumulated power frequency magnetic field interference, thereby increasing the reliability of bus protection.

[0067] The national standard stipulates that the device should not malfunction or fail to operate under power frequency interference of 1000 A / m, provided the excitation amount is 0.95 A and the setpoint is 1 A. After processing with the method of this invention, under power frequency interference far exceeding the standard value of 1200 A / m, with the excitation amount applied being 0.18 A and the setpoint 0.2 A, the superimposed interference value of all branches of the device is less than 0.02 A. After adopting the method of this invention, the overall anti-interference capability of the device is improved from 0.05 A to 0.02 A, greatly improving the reliability of the device under interference. Figure 3 ).

Claims

1. A method for resisting power frequency magnetic field interference in busbar protection devices, characterized in that, The method includes: Collect sampling data from all current branches of the busbar protection device; Based on the sampling data of each branch, branches that meet the following conditions are selected: the instantaneous values ​​of the three-phase current and the instantaneous value of the zero-sequence current are both less than the first threshold, the absolute value of the power frequency change of the instantaneous value of the zero-sequence current is less than the second threshold, and the duration exceeds the first time threshold. The selected branches are subjected to interference mutation judgment: if the instantaneous values ​​of the three-phase current and the three-phase interphase current are both less than the third threshold, the power frequency change of the instantaneous value of the three-phase current is greater than the fourth threshold, and the absolute value of the power frequency change of the instantaneous value of the zero-sequence current is greater than the fifth threshold, the corresponding data point is marked; if the number of marked data points in a sampling period of a certain branch exceeds the preset number, the branch is marked as a disturbance branch. Monitor whether the disturbed branch meets the disturbance hold-up condition; if the branch is not marked as a disturbed branch, but was a disturbed branch in the previous sampling period and met the disturbance hold-up condition, then the branch is marked as a disturbed branch. If the number of disturbed branches in the device exceeds half of the total number of branches, the device is determined to be in a disturbed state, and the superimposed current after the sudden change is filtered out from the current of all branches.

2. The method according to claim 1, characterized in that, The first threshold, second threshold, third threshold, fourth threshold, and fifth threshold are set based on the rated secondary current of the current transformer combined with the strength of hardware interference capability.

3. The method according to claim 1, characterized in that, The third threshold is greater than the first threshold.

4. The method according to claim 1, characterized in that, The method for monitoring the disturbance hold-up status of the disturbance branch is as follows: Monitor the instantaneous values ​​of the three-phase current, the three-phase phase-to-phase current, and the zero-sequence current of the disturbed branch. If the instantaneous values ​​of the three-phase current and the three-phase phase-to-phase current are less than the third threshold, the instantaneous value of the zero-sequence current is greater than the sixth threshold, and the duration exceeds the second time threshold, then the disturbed branch meets the disturbance hold-up state.

5. The method according to claim 1, characterized in that, A branch status identifier is set for each branch, and different branch statuses are marked by assigning values ​​to the branch status identifiers; the subsequent filtering and judgment process is based on the values ​​of the branch status identifiers.

6. The method according to claim 5, characterized in that, The marking method for the disturbance branch is as follows: Set a disturbance status flag and assign the value 'a' to the marked disturbance branch; For the disturbance branch with disturbance state identifier 'a', assign the disturbance judgment identifier 'b' and perform a disturbance hold-up state judgment. If the disturbance hold-up state is satisfied, assign the disturbance hold-up state identifier 'c'. For branches whose disturbance status identifier is not a, determine whether they satisfy the condition that the disturbance judgment identifier in the previous sampling period was b and the disturbance hold status identifier was c. If they satisfy the condition, assign the value b to the disturbance judgment identifier of the branch. The branch marked with disturbance judgment 'b' is used as the disturbance branch for device disturbance judgment.

7. The method according to claim 1, characterized in that, If the number of data points marked in a branch exceeds 3 within a sampling period, then the branch is marked as a disturbance branch.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method according to any one of claims 1 to 7.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method according to any one of claims 1 to 7.

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