Differential protection method, system, device and storage medium for low-frequency transmission line

Abstract

The present invention discloses a differential protection method, system, device and storage medium for a low-frequency power transmission line. The method comprises the following steps: collecting line current; taking R1 sampling points on the current, and if the current values ​​of S1 sampling points accumulated among the R1 sampling points are greater than a first threshold value, then criterion one is satisfied; taking consecutive sampling points on the positive and negative half-cycles of the current, and if the current values ​​of S2 sampling points continuously among the sampling points are greater than a second threshold value, then criterion two is satisfied; taking R3 sampling points between two zero-crossing points of the current, and if the current values ​​of S3 sampling points continuously among the R3 sampling points are greater than the first threshold value, then criterion three is satisfied; taking sampling points on the current, and if the current values ​​of the sampling points are greater than a conventional steady-state differential current and a low-ratio braking action threshold, then criterion four is satisfied; and if at least one of criterion one, criterion two and criterion three is satisfied, and criterion four is satisfied, then differential protection is actuated. The present invention can realize fast and accurate actuation of differential protection.

Description

Technical Field

[0001] The present invention relates to a differential protection method, system, device and storage medium for a low-frequency transmission line, and belongs to the technical field of relay protection. Background Art

[0002] Traditional current phasor differential protection has a simple principle and high sensitivity. It can adapt to various complex working conditions such as system oscillation and non-full phase. It is suitable for power networks with various grid structures, has a natural phase selection capability, and is widely used in power systems.

[0003] However, when a fault occurs within the line area, the regulation of the power electronic devices (M3C) at both ends of the low-frequency transmission line limits the amplitude of the fault current at both ends of the line and exhibits certain ride-through characteristics, causing the sensitivity of traditional differential protection to decrease or even refuse to operate, seriously affecting the normal operation of the low-frequency transmission system; and as the frequency of the low-frequency transmission system decreases, the calculation data window of the phasor differential protection becomes correspondingly longer, and the protection's speed will be reduced. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a differential protection method, system, device and storage medium for low-frequency transmission lines. Aiming at the problem of abnormal operation of differential protection of low-frequency transmission lines, a differential protection criterion is constructed based on the differential principle of sampled values ​​to achieve fast and accurate operation of differential protection.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides a differential protection method for a low-frequency transmission line, comprising:

[0007] Collect current from low-frequency transmission lines;

[0008] Take R1 current sampling points on the current. If the current values ​​of S1 current sampling points accumulated among the R1 current sampling points are greater than the preset first threshold value, then the first judgment condition is met.

[0009] Continuous current sampling points are taken on the positive and negative half cycles of the current. If the current values ​​of S2 consecutive current sampling points among the current sampling points are greater than the preset second threshold value, then the second judgment condition is met;

[0010] R3 current sampling points are taken between the two zero-crossing points of the current. If the current values ​​of S3 current sampling points among the R3 current sampling points are continuously greater than the preset first threshold value, then the third judgment is met;

[0011] Take a current sampling point on the current. If the current value at the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, then criterion four is met.

[0012] If at least one of the first, second and third criteria is met, and the fourth criterion is met, the differential protection will be activated.

[0013] Optionally, the number of current sampling points S1>N / 4, where N is the number of sampling points of one current cycle at the rated low frequency; and the number of current sampling points R1≥S1+2.

[0014] Optionally, the number of current sampling points S3 ≥ N / 10, where N is the number of sampling points of one current cycle at the rated low frequency; and the number of current sampling points S3 and R3 satisfy: S3 / R3 ≥ 50%.

[0015] Optionally, the current values ​​of the current sampling points in the first, second, third and fourth criteria are all i d =|i m +i n |,i m 、i n are the current values ​​of the current sampling points on this side and the opposite side respectively; the conventional steady-state differential current is 0.15i r ,i r =|i m -i n |.

[0016] In a second aspect, the present invention provides a differential protection system for a low-frequency transmission line, comprising:

[0017] Current acquisition module, used to collect current from low-frequency transmission lines;

[0018] A criterion module 1 is used to select R1 current sampling points on the current. If the current values ​​of S1 current sampling points accumulated among the R1 current sampling points are greater than a preset first threshold value, then the criterion 1 is met;

[0019] The second criterion module is used to take consecutive current sampling points on the positive and negative half cycles of the current. If the current values ​​of S2 consecutive current sampling points among the current sampling points are greater than the preset second threshold value, the second criterion is met;

[0020] A criterion three module is used to select R3 current sampling points between two current zero-crossing points. If the current values ​​of S3 consecutive current sampling points among the R3 current sampling points are greater than a preset first threshold value, then the criterion three is met;

[0021] The criterion four module is used to take a current sampling point on the current. If the current value of the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, the criterion four is established;

[0022] The differential protection module is used to activate the differential protection if at least one of the first criterion, the second criterion, and the third criterion is satisfied, and the fourth criterion is satisfied.

[0023] Optionally, the number of current sampling points S1>N / 4, where N is the number of sampling points of one current cycle at the rated low frequency; and the number of current sampling points R1≥S1+2.

[0024] Optionally, the number of current sampling points S3 ≥ N / 10, where N is the number of sampling points of one current cycle at the rated low frequency; and the number of current sampling points S3 and R3 satisfy: S3 / R3 ≥ 50%.

[0025] Optionally, the current values ​​of the current sampling points in the first, second, third and fourth criteria are all i d =|i m +i n |,i m 、i n are the current values ​​of the current sampling points on this side and the opposite side respectively; the conventional steady-state differential current is 0.15i r ,i r =|i m -i n |.

[0026] In a third aspect, the present invention provides a differential protection device for a low-frequency transmission line, comprising a processor and a storage medium;

[0027] The storage medium is used to store instructions;

[0028] The processor is configured to operate according to the instructions to execute the steps of the above method.

[0029] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when executed by a processor.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention provides a differential protection method, system, device and storage medium for a low-frequency transmission line. To address the problem of abnormal differential protection operation of a low-frequency transmission line, a differential protection criterion is constructed based on the sampling value differential principle, wherein criterion one is a classic sampling point differential criterion, which is adapted to a relatively standard low-frequency sinusoidal current waveform; criterion two utilizes the characteristic setting of sampling points with large continuous amplitudes of the fault current before electronic device adjustment, and has high sensitivity to metallic faults within the zone; criterion three utilizes the condition that two zero-crossing points directly and continuously meet the threshold to solve the problem of frequency deviation; criterion four uses conventional amplitude-based low-ratio differential operation as the gatekeeper condition for the above three criteria, ensuring that there will be no false operation in the event of a fault outside the zone, and also ensuring sensitivity to faults within the zone; in summary, the present invention can ensure that the differential protection operates quickly and correctly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a differential protection method for a low-frequency transmission line provided in Example 1 of the present invention;

[0033] Figure 2 is a schematic diagram of a typical double-terminal power transmission line provided in the first embodiment of the present invention;

[0034] Figure 3 Schematic diagram of a low-frequency power transmission system model based on an M3C inverter provided in the first embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of current sampling and differential current at both ends of a three-phase short circuit at the midpoint of a line provided by the first embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the operation of the line midpoint three-phase short-circuit differential criterion provided in the first embodiment of the present invention;

[0037] Figure 6 A schematic diagram of current sampling and differential current at both ends of a line midpoint A grounded, provided by the first embodiment of the present invention;

[0038] Figure 7 Schematic diagram of the operation of the differential criterion for phase grounding at the midpoint A of the line provided in the first embodiment of the present invention;

[0039] Figure 8 Schematic diagram of current sampling and differential current at both ends of phase A grounded outside the line area provided by embodiment 1 of the present invention;

[0040] Figure 9 Schematic diagram of the operation of the differential criterion for grounding of phase A outside the line area provided by the first embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0042] Example 1:

[0043] like Figure 1 As shown, an embodiment of the present invention provides a differential protection method for a low-frequency transmission line, comprising:

[0044] 1. Collect the current of low-frequency transmission lines.

[0045] 2. Take R1 current sampling points on the current. If the current values ​​of S1 current sampling points accumulated among the R1 current sampling points are greater than the preset first threshold value, then the first judgment condition is met;

[0046] The judgment of each current sampling point is:

[0047] i d >i set1

[0048] like Figure 2 As shown, i d is the current value at the current sampling point:

[0049] i d =|i m +i n |

[0050] i m 、i n are the current values ​​of the current sampling points on this side and the opposite side respectively; i set1 is the preset first threshold value;

[0051] At the same time, the following must be met:

[0052] The number of current sampling points S1>N / 4, where N is the number of sampling points for one current cycle at the rated low frequency; the number of current sampling points R1≥S1+2.

[0053] 3. Take consecutive current sampling points on the positive and negative half-cycles of the current. If the current values ​​of S2 consecutive current sampling points among the current sampling points are greater than the preset second threshold value, then the second judgment criteria is met;

[0054] The judgment of each current sampling point is:

[0055] i d >i set2

[0056] i set2 is the preset second threshold value.

[0057] 4. Take R3 current sampling points between the two current zero-crossing points. If the current values ​​of S3 consecutive current sampling points among the R3 current sampling points are greater than the preset first threshold value, then the third judgment is met;

[0058] The judgment of each current sampling point is:

[0059] i d >i set1

[0060] At the same time, the following must be met:

[0061] The number of current sampling points S3 ≥ N / 10, where N is the number of sampling points of one current cycle at the rated low frequency; the number of current sampling points S3 and R3 satisfy: S3 / R3 ≥ 50%.

[0062] 5. Take a current sampling point on the current. If the current value at the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, then criterion 4 is met;

[0063] The judgment of each current sampling point is:

[0064]

[0065] i r is the braking current, i r =|i m -i n |;i set3 is the preset third threshold value.

[0066] 6. If at least one of the criteria 1, 2, and 3 is true, and criterion 4 is true, the differential protection will be activated.

[0067] When a computer executes a differential protection method for a low-frequency transmission line provided in this embodiment, the process is as follows:

[0068] (1) Collect the current of low-frequency transmission lines;

[0069] (2) Determine whether both the preset first and second criteria are met. If both are met, the differential protection is activated.

[0070] The first category of criteria includes criteria one, criteria two and / or criteria three. If any one of the criteria in the first category is satisfied, the first category of criteria is satisfied. The conditions for satisfaction include:

[0071] Take R1 current sampling points on the current. If the current values ​​of S1 current sampling points accumulated among the R1 current sampling points are greater than the preset first threshold value, then the first judgment condition is met.

[0072] Continuous current sampling points are taken on the positive and negative half cycles of the current. If the current values ​​of S2 consecutive current sampling points among the current sampling points are greater than the preset second threshold value, then the second judgment condition is met;

[0073] R3 current sampling points are taken between the two zero-crossing points of the current. If the current values ​​of S3 current sampling points among the R3 current sampling points are continuously greater than the preset first threshold value, then the third judgment is met;

[0074] The second type of criteria includes Criterion 4. If Criterion 4 is established, the second type of criteria is established. The conditions for establishment include:

[0075] A current sampling point is taken on the current. If the current value at the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, then criterion four is met.

[0076] Combining the above methods, the following simulation example is provided for a low-frequency transmission system model:

[0077] Use RTDS to build Figure 3 The low-frequency transmission system model based on the M3C inverter is shown in the figure. The length of the protected low-frequency line is 13.2 km, the rated frequency is 20 Hz, and the component and line parameters are shown in Tables 1 and 2.

[0078] Table 1 Simulation system component parameters

[0079]

[0080] Table 2 Simulation system line parameters

[0081]

[0082]

[0083] Assuming that the sampling rate of electrical quantities at both ends of the low-frequency line is 1200Hz, then N is 60; the value of S1 in criterion 1 is 12, i set1 is 686A; in the second criterion, the value of the continuous current sampling point R2 is 60, the value of S2 is 30, i set2 is 600A. A fault point is set at the beginning, middle and end of the low-frequency line of the simulation model, that is, Figure 3 Points F1 to F3 in the figure are used to calculate the satisfaction of the protection criteria when a three-phase short circuit occurs at each fault point. Due to their similar characteristics, this paper only uses phase A at the fault point F2 as the reference phase for analysis. The simulation results are shown in Figures 4-5 , the action time is shown in Table 3.

[0084] Depend on Figure 5 It can be seen that the differential protection principle combined with sampling values ​​proposed in this paper can all operate correctly. Among them, criterion 1 has good operating characteristics due to the relatively large amplitude of the fault current in the first half of the cycle. Criterion 2 cannot be well met due to the decreasing trend of the fault current and the small number of sampling points greater than the threshold value in the second half of the cycle. Criterion 3, due to its adaptive nature, can identify faults under different operating conditions and has good operating characteristics. The steady-state differential current threshold and low-ratio braking equation as control conditions can also correctly identify fault conditions.

[0085] Table 3 Symmetrical fault operation within the zone

[0086]

[0087] In order to study the applicability of the new differential protection criterion when an asymmetric fault occurs in the low-frequency line area, a fault point is set at the beginning, middle and end of the low-frequency line in the simulation model, and the satisfaction of the protection criterion when a phase A grounding fault occurs at each fault point is calculated. This paper selects the fault phase when the F2 point fault occurs for analysis, and the simulation results are shown in Figures 6-7 .

[0088] Depend on Figure 6 、 7 It can be seen that after a fault occurs, the differential protection principle combined with the sampling value proposed in this paper can also operate correctly. The operation time is shown in Table 4.

[0089] Table 4 Asymmetric fault operation in the zone

[0090]

[0091] In order to study the applicability of the new differential protection criterion when a fault occurs outside the low-frequency line area, a fault point is set at each low-frequency line F4 in the simulation model, and the satisfaction of the protection criterion when a single-phase grounding fault occurs at each fault point is calculated. This paper selects the fault phase for analysis, and the simulation results are shown in Figure 8 、 9 .

[0092] Depend on Figure 8 、 9 It can be seen that when a fault occurs outside the low-frequency line area, the differential protection will not operate reliably because there is no differential current between the phases.

[0093] Example 2:

[0094] The present invention provides a differential protection system for a low-frequency transmission line, comprising:

[0095] Current acquisition module, used to collect current from low-frequency transmission lines;

[0096] A criterion module 1 is used to select R1 current sampling points on the current. If the current values ​​of S1 current sampling points accumulated among the R1 current sampling points are greater than a preset first threshold value, then the criterion 1 is met;

[0097] The second criterion module is used to take consecutive current sampling points on the positive and negative half cycles of the current. If the current values ​​of S2 consecutive current sampling points among the current sampling points are greater than the preset second threshold value, the second criterion is met;

[0098] A criterion three module is used to select R3 current sampling points between two current zero-crossing points. If the current values ​​of S3 consecutive current sampling points among the R3 current sampling points are greater than a preset first threshold value, then the criterion three is met;

[0099] The criterion four module is used to take a current sampling point on the current. If the current value of the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, the criterion four is established;

[0100] The differential protection module is used to activate the differential protection if at least one of the first criterion, the second criterion, and the third criterion is satisfied, and the fourth criterion is satisfied.

[0101] Specifically:

[0102] The number of current sampling points S1>N / 4, where N is the number of sampling points for one current cycle at the rated low frequency; the number of current sampling points R1≥S1+2.

[0103] The number of current sampling points S3 ≥ N / 10, where N is the number of sampling points of one current cycle at the rated low frequency; the number of current sampling points S3 and R3 satisfy: S3 / R3 ≥ 50%.

[0104] The current values ​​of the current sampling points in Criteria 1, 2, 3 and 4 are all i d =|i m +i n |,i m 、i n are the current values ​​of the current sampling points on this side and the opposite side respectively; the conventional steady-state differential current is 0.15i r ,i r =|i m -i n |.

[0105] Example 3:

[0106] Based on the first embodiment, the present invention provides a differential protection device for a low-frequency transmission line, including a processor and a storage medium;

[0107] The storage medium is used to store instructions;

[0108] The processor is configured to operate according to the instructions to execute the steps of the above method.

[0109] Example 4:

[0110] Based on the first embodiment, the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when executed by a processor.

[0111] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0112] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0113] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0114] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A differential protection method for a low-frequency transmission line, characterized in that: include: Collect current from low-frequency transmission lines; Take the current Current sampling points, if There are accumulated current sampling points If the current value of a current sampling point is greater than a preset first threshold value, the first judgment condition is met; Take continuous current sampling points on the positive and negative half cycles of the current. If there are continuous current sampling points If the current value of the current sampling point is greater than the preset second threshold value, the second judgment condition is met; Take the current between the two zero crossing points Current sampling points, if There are continuous current sampling points If the current value of the current sampling point is greater than the preset first threshold value, then the third criterion is met; Take a current sampling point on the current. If the current value at the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, then criterion four is met. If at least one of the criterion 1, criterion 2, and criterion 3 is true, and criterion 4 is true, the differential protection will be activated; Among them, the number of current sampling points , The number of sampling points for a current cycle at the rated low frequency; the number of current sampling points ; The number of current sampling points , The number of sampling points for a current cycle at the rated low frequency; the number of current sampling points and satisfy: .

2. A differential protection method for a low-frequency power transmission line according to claim 1, characterized in that: The current values ​​of the current sampling points in the first, second, third and fourth criteria are all , are the current values ​​of the current sampling points on this side and the opposite side respectively; The conventional steady-state differential current is , .

3. A differential protection system for low-frequency transmission lines, characterized in that: include: Current acquisition module, used to collect current from low-frequency transmission lines; Judgment module 1, used to take the current Current sampling points, if There are accumulated current sampling points If the current value of the current sampling points is greater than the preset first threshold value, the first judgment is established; wherein the number of current sampling points , The number of sampling points for a current cycle at the rated low frequency; the number of current sampling points ; The second criterion module is used to take continuous current sampling points on the positive and negative half cycles of the current. If there are continuous current sampling points If the current value of the current sampling points is greater than the preset second threshold value, the second criterion is established; wherein the number of current sampling points , The number of sampling points for a current cycle at the rated low frequency; the number of current sampling points and satisfy: ; The third criterion module is used to select the value between the two zero crossing points of the current. Current sampling points, if There are continuous current sampling points If the current value of the current sampling point is greater than the preset first threshold value, then the third criterion is met; The criterion four module is used to take a current sampling point on the current. If the current value of the current sampling point is greater than the conventional steady-state differential current and the low-ratio braking action threshold, the criterion four is established; The differential protection module is used to activate the differential protection if at least one of the first criterion, the second criterion, and the third criterion is satisfied, and the fourth criterion is satisfied.

4. A differential protection system for low-frequency power transmission lines according to claim 3, characterized in that: The current values ​​of the current sampling points in the first, second, third and fourth criteria are all , are the current values ​​of the current sampling points on this side and the opposite side respectively; The conventional steady-state differential current is , .

5. A differential protection device for a low-frequency transmission line, characterized in that: including processors and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to claim 1 or 2.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to claim 1 or 2 are implemented.

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