Fault direction discrimination method and system under serious fault of doubly-fed wind power plant outgoing line
By using technical means such as measurement data, voltage mutations and zero crossing point detection in a double-feed wind farm, the problem of inaccurate judgment of existing directional components when the fault current frequency is offset, the problem of inaccurate judgment of existing directional components is solved. Accurate fault direction identification and fast response are achieved.
Patent Information
- Application Number
- CN202411530597.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-02-14
AI Technical Summary
The existing industrial frequency phasor direction elements cannot operate correctly when the fault current of the double-feed wind farm is offset, resulting in inaccurate determination of the fault direction.
By obtaining the measurement data at the protection installation, using the voltage mutation to select the phase of the fault, conducting zero crossing point detection, and performing similarity calculations within a fixed time window, and using the Pearson correlation coefficient to determine the fault direction.
It realizes accurate fault direction judgment in the case of serious fault failure of the double-feed wind farm transmission and outlet line, improves the reliability and response speed of fault diagnosis, and avoids the risk of wind farm disconnection.
Smart Images
Figure CN119438789A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of relay protection of electric power systems, and in particular to a method and system for determining a fault direction under severe fault conditions of a transmission line of a double-fed wind farm. Background Art
[0002] As an important relay protection element, directional elements have been widely used in directional longitudinal protection and time domain distance protection of transmission lines. They are of great significance for ensuring reliable operation of protection in the event of internal faults and reliable blocking in the event of external faults, and ensuring the selectivity of protection.
[0003] In recent years, the capacity of new energy power generation represented by wind power and photovoltaic power has continued to grow in my country, leading to profound changes in the power structure of the power system. With the increasing proportion of new energy power sources, the positive and negative sequence components of the fault current in the inverter power access system will be affected by the inverter power control strategy, which will affect the positive sequence fault component direction element and the negative sequence direction element; for the double-fed wind turbine AC grid-connected system, when the nearby line fails, the complex dynamic characteristics of the system make it difficult for traditional directional elements to accurately determine the fault direction; further, with the increase in wind power penetration, when the power system fails, the risk of wind turbines being disconnected from the grid also increases, which may lead to larger-scale failures. Summary of the invention
[0004] In view of the above-mentioned problems, the present invention is proposed.
[0005] Therefore, the technical problem solved by the present invention is: to solve the problem that the existing power frequency phasor directional element cannot operate correctly when the frequency of the fault current in the double-fed wind farm is offset.
[0006] In order to solve the above technical problems, the present invention provides the following technical solution: a method for determining the fault direction under a serious fault of a transmission line of a doubly-fed wind farm, which comprises the following steps:
[0007] Obtain the measurement data at the protection installation; use the voltage mutation to select the fault phase; perform zero-crossing detection on the fault phase current and memory voltage according to the real-time sampling rate; take a fixed time window from each zero-crossing point to perform similarity calculation; compare the similarity calculation result with the set value to determine the fault in the area.
[0008] As a preferred solution of the method for determining the fault direction of a double-fed wind farm transmission line under a serious fault in the present invention, the measurement data includes measured voltage and current values.
[0009] After obtaining the measurement data at the protection installation, it is processed by differential filter.
[0010] As a preferred solution of the method for determining the fault direction of a double-fed wind farm transmission line under a serious fault of the present invention, the method of selecting the fault phase by using the voltage mutation includes: using the formula Δu m (t) = u m (t)-u m (tT) Calculate the real-time voltage change Δu on the line side m (t), if a phase satisfies |Δu m (t)|>U set , then the phase is selected as the fault phase. m To protect the installation location, measure the voltage. T is the power frequency period. U set Select the phase threshold for the voltage change.
[0011] As a preferred solution of the method for determining the fault direction of a double-fed wind farm transmission line under a serious fault of the present invention, wherein: the zero-crossing detection includes using formula i m (t)i m (t-Δt)≤0 detects whether the fault current is zero-crossing. If it is detected that i m (t)i m (t-Δt)≤0, then compare |i m (t)|with|i m The time corresponding to the smaller value of (t-Δt)| is taken as t c , and then from t c -3T moment to start looking for satisfaction m (t)u m (t-Δt)≤0 and [u m (t)-u m (t-Δt)][i m (t c )-i m (t c -Δt)]≥0, when the corresponding point is detected, compare |u m (t)|with|u m The time corresponding to the smaller value of (t-Δt)| is taken as t v , where Δt is the sampling time interval, i m To measure current at the protection installation.
[0012] As a preferred solution of the method for determining the fault direction of a double-fed wind farm transmission line under a serious fault of the present invention, the similarity calculation includes selecting a fixed time window and calculating the similarity between i(t) and u(tt) in the time window. c +t v ), the Pearson correlation coefficient is expressed as,
[0013]
[0014] Where r(x,y) is the waveform correlation coefficient of waveform x and waveform y in the data window, and its value range is [-1, 1]. N is the length of the data window. x(i) is the value of waveform x at the i-th sampling point, and y(i) is the value of waveform y at the i-th sampling point. is the average value of waveform x in the data window, is the average value of waveform y in the data window.
[0015] As a preferred solution of the method for determining the fault direction of a double-fed wind farm transmission line under a serious fault of the present invention, wherein: the fault in the determination area includes: according to i(t) and u(tt c +t v ) to determine the fault direction, and the judgment criteria are r(i(t),u(tt c +t v ))≥r set , where r set is the set value, if r(i(t),u(tt c +t v ))≥r set Continuous satisfaction time T set , the fault current is provided by the system side, that is, a reverse fault occurs.
[0016] As a preferred solution of the method for determining the fault direction under severe fault of the transmission line of the doubly-fed wind farm described in the present invention, wherein: the fault in the judgment area also includes: if r(i(t),u(tt c +t v ))<r set , it means that the fault current is provided by the doubly-fed wind farm, that is, a forward fault occurs.
[0017] Another object of the present invention is to provide a system for distinguishing the fault direction of a doubly-fed wind farm transmission line under severe fault conditions, which can solve the problems of inaccurate judgment and untimely response of the existing wind farm transmission line fault diagnosis system under complex fault conditions through accurate fault direction identification and rapid response mechanism.
[0018] In order to solve the above technical problems, the present invention provides the following technical solution: a system for distinguishing the fault direction of a double-fed wind farm transmission line under severe fault conditions, comprising a data acquisition module (100), a fault phase selection module (200), a zero-crossing detection module (300), a similarity calculation module (400) and a fault direction distinguishing module (500).
[0019] The data acquisition module (100) is responsible for acquiring measurement data at the protection installation location and performing differential filter processing on the acquired measurement data.
[0020] The fault phase selection module (200) performs fault phase selection by using the voltage mutation amount, and determines the fault phase by calculating the real-time change amount of the voltage on the line side.
[0021] The zero-crossing detection module (300) performs zero-crossing detection on the fault phase current and the memory voltage to determine the zero-crossing moments of the current and voltage waveforms.
[0022] The similarity calculation module (400) calculates the Pearson correlation coefficient of the fault phase current and the memory voltage within a fixed time window to evaluate the similarity between the waveforms.
[0023] The fault direction determination module (500) compares the similarity calculation result with the set value to determine the fault direction.
[0024] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for determining a fault direction under a serious fault of a transmission line of a doubly-fed wind farm as described above are implemented.
[0025] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for determining the fault direction under a serious fault of a transmission line of a doubly-fed wind farm as described above.
[0026] Beneficial effects of the invention: The criterion proposed in the invention is suitable for serious fault scenarios of the transmission lines of doubly-fed wind farms, has good fast-acting and reliable performance, can effectively solve the problem of misjudgment of the direction of phase-comparison directional elements in new energy scenarios, and is conducive to the reliable removal of new energy transmission line faults. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.
[0028] Figure 1 This is an overall flow chart of a method for determining a fault direction when a transmission line of a doubly-fed wind farm fails seriously according to a first embodiment of the present invention.
[0029] Figure 2 This is an overall framework diagram of a system for determining the fault direction of a double-fed wind farm transmission line under severe fault conditions provided in a second embodiment of the present invention.
[0030] Figure 3A schematic diagram of the structure of a typical new doubly-fed wind farm transmission system in a method for determining a fault direction under a severe fault of a doubly-fed wind farm transmission line provided in a third embodiment of the present invention.
[0031] Figure 4 The third embodiment of the present invention provides a method for determining the fault direction of a double-fed wind farm transmission line under a serious fault. The method provides a correlation coefficient between the fault current and the memory voltage calculated from the zero point when a phase A grounding fault occurs at the forward and reverse outlets of the double-fed wind farm transmission line of a new energy station.
[0032] Figure 5 The third embodiment of the present invention provides a method for determining the fault direction of a double-fed wind farm transmission line under a serious fault, and provides a correlation coefficient between the fault current and the memory voltage calculated from the zero point when a BC phase-to-phase fault occurs at the forward and reverse outlets of the double-fed wind farm transmission line of a new energy station.
[0033] Figure 6 The third embodiment of the present invention provides a method for determining the fault direction of a double-fed wind farm transmission line under a serious fault. The method provides a correlation coefficient between the fault current and the memory voltage calculated from the zero point when a BC two-phase grounding fault occurs at the forward and reverse outlets of the double-fed wind farm transmission line of a new energy station.
[0034] Figure 7 The third embodiment of the present invention provides a method for determining the fault direction of a double-fed wind farm transmission line under a serious fault, and provides a correlation coefficient between the fault current and the memory voltage calculated from the zero point when a three-phase fault occurs at the forward and reverse outlets of the double-fed wind farm transmission line of a new energy station. DETAILED DESCRIPTION
[0035] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.
[0036] Example 1, reference Figure 1 , is an embodiment of the present invention, and provides a method for determining the fault direction of a double-fed wind farm transmission line under severe fault conditions, characterized in that:
[0037] S1: Obtain measurement data at the protection installation.
[0038] The measurement data includes the measured voltage and current values.
[0039] After obtaining the measurement data at the protection installation, it is processed by differential filter.
[0040] S2: Use voltage mutation to select fault phase.
[0041] Using voltage mutation to select fault phase includes using the formula Δu m (t) = u m (t)-u m (tT) Calculate the real-time voltage change Δu on the line side m (t), if a phase satisfies |Δu m (t)|>U set , then the phase is selected as the fault phase. m To protect the installation location, measure the voltage. T is the power frequency period. U set Select the phase threshold for the voltage change.
[0042] S3: According to the real-time sampling rate, the fault phase current and memory voltage are respectively subjected to zero-crossing detection.
[0043] Zero-crossing detection includes using formula i m (t)i m (t-Δt)≤0 detects whether the fault current is zero-crossing. If it is detected that i m (t)i m (t-Δt)≤0, then compare |i m (t)|with|i m The time corresponding to the smaller value of (t-Δt)| is taken as t c , and then from t c -3T moment to start looking for satisfaction m (t)u m (t-Δt)≤0 and [u m (t)-u m (t-Δt)][i m (t c )-i m (t c -Δt)]≥0, when the corresponding point is detected, compare |u m (t)|with|u m The time corresponding to the smaller value of (t-Δt)| is taken as t v , where Δt is the sampling time interval, i m To measure current at the protection installation.
[0044] S4: Starting from the respective zero-crossing points, a fixed time window is taken to perform similarity calculation.
[0045] The similarity calculation includes selecting a fixed time window and calculating the relationship between i(t) and u(tt c +t v ), the Pearson correlation coefficient is expressed as,
[0046]
[0047] Where r(x,y) is the waveform correlation coefficient of waveform x and waveform y in the data window, and its value range is [-1, 1]. N is the length of the data window. x(i) is the value of waveform x at the i-th sampling point, and y(i) is the value of waveform y at the i-th sampling point. is the average value of waveform x in the data window, is the average value of waveform y in the data window.
[0048] S5: Compare the similarity calculation result with the set value to determine the fault in the area.
[0049] Determine the fault in the area, including according to i(t) and u(tt c +t v ) to determine the fault direction, and the judgment criteria are r(i(t),u(tt c +t v ))≥r set , where r set is the set value, if r(i(t),u(tt c +t v ))≥r set Continuous satisfaction time T set , the fault current is provided by the system side, that is, a reverse fault occurs.
[0050] The fault judgment area also includes, if r(i(t),u(tt c +t v ))<r set , it means that the fault current is provided by the doubly-fed wind farm, that is, a forward fault occurs.
[0051] r set The minimum similarity caused by the attenuated DC component at the initial stage of the fault and the sampling interval should be considered when avoiding the reverse fault, T set The reliability and action speed of relay protection should be considered when setting. set =0.95, T set =10ms.
[0052] Example 2, reference Figure 2 , which is an embodiment of the present invention, provides a system for a method for determining a fault direction under a serious fault of a doubly-fed wind farm transmission line, characterized by: a data acquisition module 100, a fault phase selection module 200, a zero-crossing detection module 300, a similarity calculation module 400 and a fault direction determination module 500.
[0053] The data acquisition module 100 is responsible for acquiring the measurement data at the protection installation location and performing differential filter processing on the collected measurement data.
[0054] The fault phase selection module 200 uses the voltage mutation amount to perform fault phase selection and determines the fault phase by calculating the real-time change amount of the voltage on the line side.
[0055] The zero-crossing detection module 300 performs zero-crossing detection on the fault phase current and the memory voltage to determine the zero-crossing moments of the current and voltage waveforms.
[0056] The similarity calculation module 400 calculates the Pearson correlation coefficient of the fault phase current and the memory voltage within a fixed time window to evaluate the similarity between the waveforms.
[0057] The fault direction determination module 500 compares the similarity calculation result with the setting value to determine the fault direction.
[0058] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.
[0059] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.
[0060] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.
[0061] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.
[0062] Example 3: In this example, in order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments. Figure 3 As shown, a typical doubly-fed wind farm transmission system includes an external system equivalent power source us, a relay protection device on the M side of the transmission line, and a doubly-fed wind farm.
[0063] In this embodiment, a single-phase grounding fault occurs at the forward outlet k2 of the outgoing line, and the correlation coefficient between the fault current and the memory voltage calculated from the zero crossing point is calculated as follows: Figure 4 As shown in (a), the protection is activated about 40ms after the fault. A single-phase grounding fault occurs at the forward outlet k1. The correlation coefficient between the fault current and the memory voltage calculated from the zero crossing point is calculated as follows: Figure 4 As shown in (b), the protection is reliable and does not operate.
[0064] In this embodiment, it is assumed that a two-phase interphase fault occurs at the forward outlet k2 of the transmission line, and the correlation coefficient calculation result of the fault current and the memory voltage starting from the zero crossing point is as follows: Figure 5 As shown in (a), the protection is activated about 20ms after the fault; a two-phase phase-to-phase fault occurs at the forward outlet k1, and the correlation coefficient between the fault current and the memory voltage calculated from the zero crossing point is calculated as follows: Figure 5 As shown in (b), the protection is reliable and does not operate.
[0065] In this embodiment, a two-phase grounding fault occurs at the forward outlet k2 of the transmission line, and the correlation coefficient calculation result of the fault current and the memory voltage starting from the zero crossing point is as follows: Figure 6 As shown in (a), the protection is activated about 20ms after the fault. A two-phase grounding fault occurs at the forward outlet k1. The correlation coefficient between the fault current and the memory voltage calculated from the zero crossing point is calculated as follows: Figure 6 As shown in (b), the protection is reliable and does not operate.
[0066] In this embodiment, a three-phase fault occurs at the forward outlet k2 of the transmission line, and the correlation coefficient calculation result between the fault current and the memory voltage starting from the zero crossing point is as follows: Figure 7 As shown in (a), the protection is activated about 30ms after the fault. A three-phase fault occurs at the forward outlet k1. The correlation coefficient between the fault current and the memory voltage calculated from the zero crossing point is calculated as follows: Figure 7 As shown in (b), the protection is reliable and does not operate.
[0067] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.
Claims
1. A method for determining the fault direction of a double-fed wind farm transmission line under severe fault conditions, characterized in that: include: Obtain measurement data at the protection installation; Use voltage mutation to select fault phase; According to the real-time sampling rate, the fault phase current and memory voltage are respectively detected at zero crossing points; A fixed time window is taken from each zero-crossing point to perform similarity calculation; Compare the similarity calculation results with the set values to determine the faults in the area.
2. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 1, characterized in that: The measurement data includes measured voltage and current values; After obtaining the measurement data at the protection installation, it is processed by differential filter.
3. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 2, characterized in that: The method of using voltage mutation to select fault phase includes using the formula Δu m (t) = u m (t)-u m (tT) Calculate the real-time voltage change Δu on the line side m (t), if a phase satisfies |Δu m (t)|>U set , then the phase is selected as the fault phase, where u m To protect the installation location, measure the voltage. T is the power frequency period. U set Select the phase threshold for the voltage change.
4. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 3, characterized in that: The zero-crossing detection includes using formula i m (t)i m (t-Δt)≤0 detects whether the fault current is zero-crossing. If it is detected that i m (t)i m (t-Δt)≤0, then compare |i m (t)|with|i m The time corresponding to the smaller value of (t-Δt)| is taken as t c , and then from t c -3T moment to start looking for satisfaction m (t)u m (t-Δt)≤0 and [u m (t)-u m (t-Δt)][i m (t c )-i m (t c -Δt)]≥0, when the corresponding point is detected, compare |u m (t)|with|u m The time corresponding to the smaller value of (t-Δt)| is taken as t v , where Δt is the sampling time interval, i m To measure current at the protection installation.
5. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 4, characterized in that: The similarity calculation includes selecting a fixed time window and calculating the similarity between i(t) and u(tt c +t v ), the Pearson correlation coefficient is expressed as, Where r(x,y) is the waveform correlation coefficient of waveform x and waveform y in the data window, and its value range is [-1, 1]. N is the length of the data window. x(i) is the value of waveform x at the i-th sampling point, and y(i) is the value of waveform y at the i-th sampling point. is the average value of waveform x in the data window, is the average value of waveform y in the data window.
6. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 5, characterized in that: The fault determination in the area includes: c +t v ) to determine the fault direction, and the judgment criteria are r(i(t),u(tt c +t v ))≥r set , where r set is the set value, if r(i(t),u(tt c +t v ))≥r set Continuous satisfaction time T set , the fault current is provided by the system side, that is, a reverse fault occurs.
7. The method for determining the fault direction of a double-fed wind farm transmission line under a serious fault as claimed in claim 6, characterized in that: The fault determination area also includes: if r(i(t),u(tt c +t v ))<r set , it means that the fault current is provided by the doubly-fed wind farm, that is, a forward fault occurs.
8. A system using the method for determining the fault direction of a double-fed wind farm transmission line under severe fault conditions as claimed in any one of claims 1 to 7, characterized in that: It comprises a data acquisition module (100), a fault phase selection module (200), a zero-crossing point detection module (300), a similarity calculation module (400) and a fault direction determination module (500); The data acquisition module (100) is responsible for acquiring measurement data at the protection installation location and performing differential filter processing on the acquired measurement data; The fault phase selection module (200) performs fault phase selection by using the voltage mutation amount, and determines the fault phase by calculating the real-time change amount of the voltage on the line side; The zero-crossing detection module (300) performs zero-crossing detection on the fault phase current and the memory voltage to determine the zero-crossing moment of the current and voltage waveforms; The similarity calculation module (400) calculates the Pearson correlation coefficient of the fault phase current and the memory voltage within a fixed time window to evaluate the similarity between the waveforms; The fault direction determination module (500) compares the similarity calculation result with the set value to determine the fault direction.
9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for determining the fault direction when a transmission line of a doubly-fed wind farm fails in any one of claims 1 to 7 are implemented.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for determining the fault direction when a transmission line of a doubly-fed wind farm fails are implemented as described in any one of claims 1 to 7.