A wind farm sending line protection scheme based on same-name traveling wave waveform trend covariance

Abstract

The application discloses a kind of based on same name wave waveform trend covariance wind farm sending-out line protection scheme, comprising: step 1, select AC zero sequence current rate of change as starting criterion;Step 2, analysis bus place fold reflection coefficient;Step 3, when positive direction fault, the same name wave waveform change trend detected by two-side protection device is similar, and the covariance value obtained by calculation is smaller;Step 4, when reverse direction fault, the same name wave waveform change trend detected by two-side protection device is opposite, and the covariance value obtained by calculation is larger;Step 5, covariance value obtained by calculation is compared with preset threshold value, and fault direction is discriminated according to comparison result;Step 6, according to fault direction discrimination result, corresponding protection action is executed, the application utilizes the covariance difference of same name wave waveform trend at line two ends after fault to discriminate fault direction, and it is high in reliability, direction discrimination is clear, and it is suitable for the fast protection of wind farm sending-out line.

Description

Technical Field

[0001] This invention relates to the field of power protection technology, and in particular to a protection scheme for wind farm transmission lines based on the trend covariance of the same traveling wave waveform. Background Technology

[0002] Wind farm transmission lines are the "main arteries" connecting wind farms to the main power grid. Their safe and stable operation directly affects the power generation efficiency of wind farms and the grid's acceptance capacity, and is of great significance to ensuring my country's energy transition and the achievement of its "dual carbon" goals. Because wind farm transmission lines typically have long distances, complex operating environments, high failure rates, and fault characteristics greatly influenced by wind turbine control strategies, traditional protection schemes based on power frequency electrical quantities suffer from poor adaptability and slow response speed.

[0003] Traveling wave (TW) protection has been widely studied in high-voltage transmission lines due to its insensitivity to system oscillations, transition resistance, and current transformer (CT) saturation, as well as its potential for ultra-high-speed operation. However, existing TW protection schemes mostly focus on fault location using single-ended or double-ended TWs, or on direction determination using single characteristic quantities such as amplitude and polarity of the TW. Their reliability needs improvement when dealing with situations such as weak feeders and complex frequency-varying characteristics in wind farms. Accurately and quickly identifying internal and external faults in wind farm transmission lines, especially accurately determining the fault direction, is a current technical challenge. Therefore, this paper proposes a wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform, so as to solve the problems mentioned in the background art.

[0005] This invention is achieved through the following technical solution: A wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform includes the following steps: Step 1, Startup Criteria: Real-time acquisition of electrical quantities at the protection devices on both sides of the line. When a sudden change in electrical quantity is detected that meets the preset startup conditions, the protection is activated. Step 2, Obtain the traveling wave: After the protection is started, extract the traveling wave waveform data of the same name detected by the protection devices on both sides of the line within the specified time window; Step 3, Reference waveform selection: Select the same traveling wave waveform detected by one of the protection devices as the reference waveform; Step 4, calculate covariance: Based on the reference waveform and the same traveling wave waveform detected by the other protection device, calculate the covariance value used to characterize the difference in the trend of change of the two waveforms. Step 5, Fault direction determination: Compare the calculated covariance value with a preset threshold, and determine the fault direction based on the comparison result; Step 6, Execute protection: Based on the fault direction determination result, execute the corresponding protection action.

[0006] Furthermore, in step 1, the activation criterion is the rate of change of AC zero-sequence current, the expression of which is: , ,in The zero-sequence current is an alternating current synthesized from three-phase currents. , The preset startup threshold Furthermore, in step 2, the traveling wave of the same name is the voltage or current traveling wave that propagates from the fault point to the busbars at both ends of the line during the initial stage of the fault.

[0007] Furthermore, when a fault occurs in the forward direction of the line, the traveling wave generated at the fault point propagates to both ends of the line simultaneously, and the waveform changes of the same traveling wave detected by the protection devices on both sides of the line are the same or similar.

[0008] Furthermore, when a fault occurs in the opposite direction of the line, the traveling wave detected by the fault-side protection device is a traveling wave refracted from the opposite bus, while the traveling wave detected by the opposite-side protection device is a traveling wave reflected from the opposite bus. The waveforms of the two devices have opposite or significantly different trends.

[0009] Furthermore, in step 4, the formula for calculating the covariance is: ,in and These are the data sequences of the reference waveform and the corresponding traveling wave waveform detected by the protection device on the other side, respectively, where n is the total number of sampling points within the time window. and Sequences and The mean.

[0010] Furthermore, in step 5, the criterion for determining the fault direction is as follows: if the covariance value is greater than a preset threshold, it is determined to be a fault in the positive direction of the line; if the covariance value is less than or equal to the preset threshold, it is determined to be a fault in the reverse direction of the line.

[0011] Furthermore, the preset threshold is adjusted by comprehensively considering the refractive index of the line boundary, the line length, and the sampling rate.

[0012] Furthermore, the proposed scheme is applicable to AC systems, and the extracted electrical quantities are one or more of zero-sequence voltage, zero-sequence current, phase voltage, or phase current.

[0013] Furthermore, the specified time window comprises several sampling points from the arrival of the first traveling wave surge at the protection device after the fault occurs, and the length of the time window at least covers the first wavefront of the traveling wave.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention uses the trend similarity (covariance) of the entire waveform of the same traveling wave at both ends of the line after a fault for discrimination, rather than a single feature (such as amplitude or polarity). It can more comprehensively reflect the fault information contained in the waveform, has stronger anti-interference ability, and higher reliability.

[0015] This invention is based on the essential differences in the propagation paths and reflection processes of traveling waves during faults in the forward and reverse directions, which lead to drastically different waveform trends at both ends. The covariance value can clearly and accurately quantify this difference, thereby reliably determining the fault direction.

[0016] This invention does not rely on precise line parameters and complex communication synchronization, and has good adaptability to complex operating conditions such as weak feed and frequency variation characteristics of wind farms, and can provide effective protection for wind farm transmission lines. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The flowchart provided by this invention is a protection scheme for wind farm transmission lines based on the trend covariance of the same traveling wave waveform.

[0019] Figure 2 This invention provides a positive direction fault traveling wave refraction diagram for a wind farm transmission line protection scheme based on the covariance of the same traveling wave waveform trend.

[0020] Figure 3 This invention provides a schematic diagram of the positive direction fault traveling wave propagation process of a wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform.

[0021] Figure 4 The image provided by this invention shows the forward traveling wave waveform detected by the protection device M1 under a positive direction fault in a wind farm transmission line protection scheme based on the covariance of the same traveling wave waveform trend.

[0022] Figure 5 The image provided by this invention shows the forward traveling wave waveform detected by the protection device M2 under a positive direction fault in a wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform.

[0023] Figure 6 The present invention provides an equivalent circuit diagram for a reverse fault protection scheme for wind farm transmission lines based on the trend covariance of the same traveling wave waveform.

[0024] Figure 7 The diagram shows the AC zero-sequence voltage forward traveling wave waveform detected by the protection device M1 under a reverse fault in a wind farm transmission line protection scheme based on the covariance of the same traveling wave waveform trend, which is provided by the present invention.

[0025] Figure 8 The diagram shows the AC zero-sequence voltage forward traveling wave waveform detected by the protection device M2 under a reverse fault in a wind farm transmission line protection scheme based on the covariance of the same traveling wave waveform trend, which is provided by the present invention.

[0026] Figure 9 This is a typical wind farm transmission line topology diagram for the application of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0028] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0029] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0031] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Optional embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0032] See Figure 1-9 A wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform includes the following steps: Step 1, Startup Criteria: Real-time acquisition of electrical quantities at the protection devices on both sides of the line. When a sudden change in electrical quantity is detected that meets the preset startup conditions, the protection is activated. Step 2, Obtain the traveling wave: After the protection is started, extract the traveling wave waveform data of the same name detected by the protection devices on both sides of the line within the specified time window; Step 3, Reference waveform selection: Select the same traveling wave waveform detected by one of the protection devices as the reference waveform; Step 4, calculate covariance: Based on the reference waveform and the same traveling wave waveform detected by the other protection device, calculate the covariance value used to characterize the difference in the trend of change of the two waveforms. Step 5, Fault direction determination: Compare the calculated covariance value with a preset threshold, and determine the fault direction based on the comparison result; Step 6, Execute protection: Based on the fault direction determination result, execute the corresponding protection action.

[0033] In step 1, the starting criterion is the rate of change of AC zero-sequence current, and its expression is: , ,in The zero-sequence current is an alternating current synthesized from three-phase currents. , The preset startup threshold In step 2, the same-named traveling wave is the voltage or current traveling wave that propagates from the fault point to the busbars at both ends of the line during the initial stage of the fault.

[0034] When a fault occurs in the forward direction of the line, the traveling wave generated at the fault point propagates to both ends of the line simultaneously, and the waveform changes of the same traveling wave detected by the protection devices on both sides of the line are the same or similar.

[0035] When a fault occurs in the opposite direction of the line, the traveling wave detected by the fault-side protection device is a traveling wave refracted from the opposite bus, while the traveling wave detected by the opposite-side protection device is a traveling wave reflected from the opposite bus. The waveforms of the two devices have opposite or significantly different trends.

[0036] In step 4, the formula for calculating covariance is: ,in and These are the data sequences of the reference waveform and the corresponding traveling wave waveform detected by the protection device on the other side, respectively, where n is the total number of sampling points within the time window. and Sequences and The mean.

[0037] In step 5, the criterion for determining the fault direction is as follows: if the covariance value is greater than a preset threshold, it is determined to be a fault in the positive direction of the line; if the covariance value is less than or equal to the preset threshold, it is determined to be a fault in the reverse direction of the line.

[0038] The preset threshold is adjusted by comprehensively considering the refractive index of the line boundary, the line length, and the sampling rate.

[0039] The proposed scheme is applicable to AC systems, and the extracted electrical quantities are one or more of zero-sequence voltage, zero-sequence current, phase voltage, or phase current.

[0040] The specified time window consists of several sampling points from the arrival of the first traveling wave surge at the protection device after the fault occurs, and the length of the time window must at least cover the first wavefront of the traveling wave.

[0041] For example, this embodiment is applied to, Figure 9 The topology of a typical wind farm transmission line is shown. Protection devices M1 and M2 are installed at the busbars on both sides of the line to collect the voltage and current signals of the line.

[0042] Step 1: Start Criterion The protection device monitors the electrical quantities of the line in real time. In this embodiment, the rate of change of AC zero-sequence current is selected as the activation criterion, and its expression is: (1) (2) in, Let be the zero-sequence AC current at time t, which is determined by the three-phase current. , , synthesis: . The starting threshold is set based on the principle of reliably avoiding the maximum fluctuation of the AC zero-sequence current during normal operation. For example, it can be set to... ( (Rated current) The sampling interval is given. Protection is activated when equation (2) is satisfied.

[0043] Step 2: Analysis of busbar reflection coefficient Understanding the laws governing reflection and refraction of traveling waves at the generatrix is ​​fundamental to this scheme. Figure 2 Taking the positive direction fault shown as an example, the line The wave impedance is The equivalent surge impedance of the parallel equipment on the busbar is When the amplitude is When the incident voltage traveling wave reaches the busbar, the refracted voltage and reflected voltage It can be calculated using the following formula: refractive index (3) Reflectance coefficient (4) Refracting voltage (5) Reflected voltage (6) Similarly, there is a corresponding reflection and refraction relationship for traveling current waves.

[0044] Step 3: Forward Fault Characteristic Analysis like Figure 3 As shown, assume the fault occurs in the positive direction of Line 1 (i.e., inside the line, such as point f1). The initial traveling wave generated by the fault will propagate simultaneously to both ends of the line, M1 and M2. The expression for the forward traveling wave detected by M2 can be written as:

[0045] in, The initial traveling wave at the fault point, Distance from the fault point distance, For the total length of the line, For traveling wave speed, Let be the traveling wave propagation function. As the propagation constant, although the amplitude may differ due to varying attenuation and time delay, they all originate from the same initial traveling wave. The overall trend of their waveform changes is basically the same, such as Figure 4 and Figure 5As shown, therefore, in the case of a fault in the positive direction, the waveforms of the traveling waves at both ends are highly similar, and the calculated covariance value is relatively small.

[0046] Step 4: Analysis of Fault Characteristics in the Reverse Direction by Figure 6 shown In the opposite direction (i.e., outside the line, such as...) Taking a point-based fault as an example, the fault occurs... Outside the side busbar, Detected traveling wave Traveling wave from fault Refractive index Decide: (9) The traveling wave continued towards Lateral propagation, reaching Reflection occurs when the side busbar is exposed. Detected traveling wave This is the reflected wave: (10) Its waveform and In comparison, there is not only a time delay, but also a difference due to the reflection coefficient. The effect of this can cause the waveform trend to reverse, such as... Figure 7 and Figure 8 As shown, in the case of a fault in the opposite direction, and The detected traveling wave waveforms showed significant differences, with opposite trends or weak correlation, resulting in large calculated covariance values.

[0047] Step 5: Waveform trend quantification based on covariance To quantify the similarity between two waveforms, this invention introduces covariance, assuming... The detected waveform sequence is , The detected waveform sequence is Then Based on, and covariance Defined as: (11) in, and Sequences and The absolute values ​​of the mean and covariance reflect the degree of synchronization between the changing trends of the two waveforms. When two waveforms change in the same direction (both increasing or decreasing), the covariance is a large positive value.

[0048] When two waveforms change in opposite directions, the covariance is a negative value with the larger absolute value.

[0049] When two waveforms are not strongly correlated, the absolute value of the covariance is close to 0.

[0050] In this embodiment, the absolute value of the covariance is used for discrimination, that is, the calculation is performed. .

[0051] Step 6: Fault direction identification and protection action Based on the above analysis, the following fault direction discrimination criteria are proposed: like If so, it is determined to be a fault in the positive direction of the line; like If so, it is judged as a fault in the reverse direction of the line.

[0052] in, The threshold is set as a preset threshold. Considering the waveform distortion caused by noise, measurement errors, and line losses in the actual system, the threshold is set reasonably. It can reliably distinguish between positive and negative faults, and the threshold setting can be optimized through offline simulation or on-site waveform data.

[0053] The protection device performs the corresponding operation based on the judgment result: If the fault is determined to be a positive fault (within the zone), the protection device will immediately send a trip command to the circuit breaker to isolate the faulty line.

[0054] If the fault is determined to be in the opposite direction of the line (outside the zone), the protection device will reliably lock out and not operate.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform, characterized in that, Includes the following steps: Step 1, Startup Criteria: Real-time acquisition of electrical quantities at the protection devices on both sides of the line. When a sudden change in electrical quantity is detected that meets the preset startup conditions, the protection is activated. Step 2, Obtain the traveling wave: After the protection is started, extract the traveling wave waveform data of the same name detected by the protection devices on both sides of the line within the specified time window; Step 3, Reference waveform selection: Select the same traveling wave waveform detected by one of the protection devices as the reference waveform; Step 4, calculate covariance: Based on the reference waveform and the same traveling wave waveform detected by the other protection device, calculate the covariance value used to characterize the difference in the trend of change of the two waveforms. Step 5, Fault direction determination: Compare the calculated covariance value with a preset threshold, and determine the fault direction based on the comparison result; Step 6, Execute protection: Based on the fault direction determination result, execute the corresponding protection action.

2. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, In step 1, the starting criterion is the rate of change of AC zero-sequence current, and its expression is: , ,in The zero-sequence current is an alternating current synthesized from three-phase currents. , This is the preset startup threshold.

3. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, In step 2, the same-named traveling wave is the voltage or current traveling wave that propagates from the fault point to the busbars at both ends of the line during the initial stage of the fault.

4. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, When a fault occurs in the forward direction of the line, the traveling wave generated at the fault point propagates to both ends of the line simultaneously, and the waveform changes of the same traveling wave detected by the protection devices on both sides of the line are the same or similar.

5. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, When a fault occurs in the opposite direction of the line, the traveling wave detected by the fault-side protection device is a traveling wave refracted from the opposite bus, while the traveling wave detected by the opposite-side protection device is a traveling wave reflected from the opposite bus. The waveforms of the two devices have opposite or significantly different trends.

6. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, In step 4, the formula for calculating covariance is: ,in and These are the data sequences of the reference waveform and the corresponding traveling wave waveform detected by the protection device on the other side, respectively, where n is the total number of sampling points within the time window. and Sequences and The mean.

7. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1 or 6, characterized in that, In step 5, the criterion for determining the fault direction is as follows: if the covariance value is greater than a preset threshold, it is determined to be a fault in the positive direction of the line; if the covariance value is less than or equal to the preset threshold, it is determined to be a fault in the reverse direction of the line.

8. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 7, characterized in that, The preset threshold is adjusted by comprehensively considering the refractive index of the line boundary, the line length, and the sampling rate.

9. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, The proposed scheme is applicable to AC systems, and the extracted electrical quantities are one or more of zero-sequence voltage, zero-sequence current, phase voltage, or phase current.

10. The wind farm transmission line protection scheme based on the trend covariance of the same traveling wave waveform as described in claim 1, characterized in that, The specified time window consists of several sampling points from the arrival of the first traveling wave surge at the protection device after the fault occurs, and the length of the time window must at least cover the first wavefront of the traveling wave.

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