Impedance characteristic-based longitudinal protection method for wind farm transmission line

Abstract

The application discloses a kind of wind farm sending out line pilot protection method based on impedance characteristic, belong to wind farm sending out line protection field.First, the positive sequence voltage and current extracted to wind farm sending out line protection installation are carried out data preprocessing, and the positive sequence impedance is calculated using the positive sequence voltage and current after data processing.Second, whether it meets the fault starting condition is judged according to the positive sequence short-circuit current and the calculation result of positive sequence impedance, if it meets, the abnormal sampling data of positive sequence impedance amplitude sequence is eliminated based on BIRCH clustering, and the clustering characteristics of positive sequence impedance amplitude sequence without abnormal sampling data are calculated.Then, according to the difference of double-end positive sequence impedance amplitude under wind farm sending out line area fault and area fault, the line pilot protection criterion is constructed.Finally, considering the influence of data measurement error and data delay transmission, the pilot protection starting criterion and protection criterion setting are determined, and the area fault and area fault are judged according to the comparison between the calculated value and the setting value of protection criterion.The advantages of the application are: it can solve the problem of unreliable traditional pilot protection method caused by frequency deviation characteristic, data delay transmission and abnormal sampling data, is not affected by wind farm operating condition and transition resistance, has strong resistance to data delay transmission and abnormal data, the protection method is simple and easy to operate, has good reliability, has low requirement for line sampling device, and is suitable for wind power integration system.

Description

[0001] This invention belongs to the field of wind farm transmission line protection, and specifically relates to a method for longitudinal protection of wind farm transmission lines. Background Technology

[0002] Driven by energy transition and the increasing maturity of power electronics technology, large-scale wind power integration into the power system is an inevitable trend. The fault characteristics of wind power differ from those of conventional power grids, posing adaptation challenges for power frequency protection systems. Traditional longitudinal protection systems, despite their numerous advantages as the main protection for wind farm transmission lines, are inherently susceptible to failure to operate or maloperation due to the impact of large-scale wind power integration. Summary of the Invention

[0003] This invention addresses the unreliability of traditional longitudinal protection methods for wind farm transmission lines caused by frequency offset characteristics, data delay transmission, and abnormal sampling data. It effectively distinguishes between faults within and outside the designated protection zone of wind farm transmission lines, applies the BIRCH clustering method to eliminate abnormal sampling data, and combines the differences in the amplitude characteristics of the two-terminal positive sequence impedance to form a longitudinal protection criterion for the line. This impedance-based longitudinal protection method for wind farm transmission lines can reliably distinguish between faults within and outside the designated protection zone, is unaffected by wind farm operating conditions and transition resistance, and has strong resistance to data delay transmission and abnormal data. It is suitable for wind power grid integration systems and has promising application prospects.

[0004] The technical solution of this invention is as follows: A longitudinal protection method for wind farm transmission lines based on impedance characteristics is provided. When a fault occurs in the wind farm transmission line, firstly, the positive sequence voltage and current at both ends of the transmission line are sampled. Secondly, the sampled data is preprocessed, and the positive sequence short-circuit current is used to calculate the positive sequence impedance amplitude to determine whether the fault initiation conditions are met. Then, BIRCH clustering is used to remove abnormal data in the positive sequence impedance amplitude sequence at both ends and its clustering characteristics are calculated. Finally, the difference factor δ of the positive sequence impedance amplitude at both ends is calculated. p Finally, a setting value δ was determined that takes into account the effects of measurement errors and data delay transmission. pset , using δ p With the set value δ pset The comparison is used to determine whether the fault is inside or outside the zone.

[0005] A longitudinal protection method for wind farm transmission lines based on impedance characteristics, characterized by the following specific steps:

[0006] Step 1. Extract the positive sequence voltage and current signals at the installation point of the wind farm's transmission line protection. Preprocess the extracted positive sequence voltage and current signal data and use the preprocessed positive sequence voltage and current to calculate the positive sequence impedance amplitude.

[0007] Step 2. Determine whether the fault initiation conditions are met based on the positive sequence short-circuit current and the positive sequence impedance amplitude;

[0008] Step 3. Use BIRCH clustering to remove outlier sampled data from the two-terminal positive sequence impedance amplitude sequence, and calculate the clustering characteristics of the two-terminal positive sequence impedance amplitude sequence after removing the outlier sampled data;

[0009] Step 4. Calculate the difference factor δ of the positive sequence impedance amplitude at both ends. p Establish setting values ​​that take into account the effects of measurement errors and data delay transmission;

[0010] Step 5. Adjust the difference factor δ of the positive sequence impedance amplitude at both ends. p With the set value δ pset In comparison, determine whether the fault is inside or outside the zone.

[0011] Further, in step 1, when a fault occurs in the wind farm's transmission line, the positive sequence voltage and current signals at the protection installation point of the wind farm's transmission line are collected, with a data window of 10ms. A bandpass filter is used to filter out data outside the 35Hz-65Hz range from the extracted signal, and the power frequency signal in the filtered data is extracted using the Prony algorithm. The positive sequence impedance is calculated by the ratio of the voltage fault component to the current fault component. The positive sequence impedance amplitude is calculated as follows:

[0012]

[0013] In the formula: U M1 I M1 These are the positive sequence voltage and current signals collected during the transient period of a fault in the wind power transmission line, U. M1|0| I M1|0| These represent the positive sequence voltage and current signals collected before the fault in the wind power transmission line, and the amplitude of the system-side back-side impedance |Z. N1 |Calculation method is the same as|Z M1 |

[0014] Furthermore, in step 2, it is determined whether the fault initiation conditions are met based on the positive sequence short-circuit current and the positive sequence impedance amplitude, specifically as follows:

[0015] By utilizing the difference in positive sequence impedance amplitude under forward and reverse faults on the wind power side transmission line, the fault initiation condition on the wind power side is set to the positive sequence impedance amplitude |Z. M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 |;The system side selects a positive-sequence abrupt change current starting element, when ΔI N1 ≥0.2I N1 If the conditions are met, proceed to the next step; otherwise, continue the test.

[0016] Furthermore, in step 3, BIRCH clustering is a comprehensive hierarchical clustering algorithm with advantages such as low memory consumption, fast clustering speed, and strong scalability, and it also has the function of detecting outlier data. Using BIRCH clustering, outlier sampled data of the two-terminal positive sequence impedance amplitude sequence are removed and clustering features are calculated, specifically as follows:

[0017] Cluster feature trees (CF Trees) can be built based on clustering characteristics. The maximum number of discrete points in a non-leaf node of a CF Tree is B, and the spatial threshold is T, which is usually the radius r.

[0018] By analyzing the fault time series globally and combining it with clustering features, the centroid x0 and radius r of the fault time series can be derived as follows:

[0019]

[0020]

[0021] Fault time series clustering steps based on the BIRCH algorithm:

[0022] (1) Scan all data of the fault time series, calculate the radius r of the fault time series, and build a CF Tree;

[0023] (2) Take the first discrete data input as the root node of the leaf node. After the subsequent fault time series data is input, determine whether the distance between it and the root node is less than T. If it is less than T and the total number of discrete points of the leaf node does not exceed B, then merge it into the leaf node. Otherwise, use it as the root node of the new leaf node for clustering.

[0024] (3) Scan the CF Tree after the clustering is completed, delete the abnormal leaf nodes that contain only a small number of discrete points, and complete the clustering of the fault time series.

[0025] After removing outlier sampled data, |Z M1 |and|Z N1 The formula for calculating cluster features SS is as follows:

[0026]

[0027] Further, in step 4, δ is calculated. p The setting value is determined considering the impact of measurement errors and data delay transmission, specifically as follows:

[0028] When a fault occurs in the transmission line of a wind farm within the area, |Z M1 |far greater than|Z N1 |;When an outbound fault occurs in the wind farm's transmission line,|Z M1 |and|Z N1|Approximately equal, utilizing this property, combined with |Z after removing outlier sampled data. M1 |and|Z N1 By calculating the clustering feature SS, the formula for the two-terminal positive sequence impedance magnitude difference ratio factor can be obtained:

[0029]

[0030] When a fault occurs in the transmission line of a wind farm within the affected area, the difference factor δ of the positive sequence impedance amplitude at both ends... p Approaching 1, when an external fault occurs in the wind farm's transmission line, the difference factor δ of the positive sequence impedance amplitude at both ends is... p Approaching 0.

[0031] Under ideal conditions, the fault in the wind farm's transmission line area meets δ p =1. Considering the influence of factors such as CT and PT measurement errors and data transmission delays, a reliability coefficient is introduced to mitigate the impact of these factors. The setting value is determined as follows:

[0032] δ pset =K1K2δ pb (6)

[0033] In the formula: K1 is the reliability coefficient taking into account the measurement error factors of CT and PT, usually taken as 0.85. K2 is the reliability coefficient taking into account the abnormal data factor, usually taken as 0.95. Considering the faults inside and outside the wind farm transmission line area, δ p Feature differences, select δ pb =1. The setpoint δ can be calculated. pset =0.8.

[0034] Furthermore, in step 5, when the difference factor δ of the positive sequence impedance amplitude at both ends... p Greater than the set value δ pset If the fault occurs at a certain time, the wind farm's transmission line will experience a fault within the designated area; otherwise, the wind farm's transmission line will experience a fault outside the designated area. Attached Figure Description

[0035] Figure 1 This is a flowchart of the present invention.

[0036] Figure 2 This is the topology of a large-scale wind turbine connected to the power system in an embodiment of the present invention.

[0037] Figure 3 This invention describes the characteristic of the difference ratio of the positive sequence impedance at both ends in the fault location f1 within the wind farm transmission line fault zone, f2 on the system side outside the fault zone, and f3 on the main transformer side outside the fault zone.

[0038] Figure 4This invention addresses the impact of data delay transmission on the longitudinal protection performance of wind farm transmission lines based on impedance characteristics when an AG fault occurs.

[0039] Figure 5 This invention addresses the impact of abnormal sampling data on the longitudinal protection performance of wind farm transmission lines based on impedance characteristics when an AG fault occurs. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1: Create as shown in the attached document Figure 2 The large-scale wind turbine integration into the power system shown is used as a simulation model. The wind farm consists of 33 1.5MW doubly-fed wind turbines. The equivalent positive-sequence impedance of the main transformer T1 is Z. T1 =j0.12; The equivalent positive sequence impedance of the wind farm's transmission line is Z. L1 =0.164+j0.479; the equivalent positive sequence impedance of the power grid system is Z. S1 =j0.065. The system reference voltage is 220kV, and the reference capacity is 1000MWA. AG faults are set at f1 within the wind farm's transmission line area, f2 on the system side outside the area, and f3 on the main transformer side outside the area.

[0042] When an AG fault occurs at f1, the positive sequence voltage and current signal data of the wind farm's outgoing line are preprocessed, and the positive sequence impedance amplitude is calculated to obtain |Z. M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 | After removing outlier samples using BIRCH clustering, the positive-sequence impedance amplitude difference ratio factor δ is calculated. p δ can be obtained p Approaching 1; when an AG fault occurs at f2, the positive sequence impedance magnitude can be calculated to obtain |Z M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 | Calculate the difference factor δ of the positive sequence impedance amplitude at both ends. p δ can be obtained p Approaching 0; when an AG fault occurs at f3, the positive sequence impedance magnitude can be calculated to obtain |Z M1 | Less than 1.24 times the positive sequence impedance amplitude of the wind farm's transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 The fault start-up conditions are not met. The calculation results are attached. Figure 3 .

[0043] Example 2: Create as shown in the attached document Figure 2 The large-scale wind turbine integration into the power system shown is used as a simulation model. The wind farm consists of 33 1.5MW doubly-fed wind turbines. The equivalent positive-sequence impedance of the main transformer T1 is Z. T1 =j0.12; The equivalent positive sequence impedance of the wind farm's transmission line is Z. L1 =0.164+j0.479; the equivalent positive sequence impedance of the power grid system is Z. S1 =j0.065. The system reference voltage is 220kV, and the reference capacity is 1000MWA. A-phase ground faults are assumed to occur at points f1 within the wind farm's transmission line zone, and f2 and f3 outside the zone. Considering the maximum transition resistance of the 220kV transmission line is 100Ω, transition resistances of 75Ω and 150Ω are set.

[0044] pass Figure 1 The process yields the impact of transition resistance on the longitudinal protection of wind farm transmission lines based on impedance characteristics, as shown in Table 1.

[0045] Table 1. Performance verification of transition resistance for longitudinal protection of wind farm transmission lines based on impedance characteristics.

[0046]

[0047] As shown in Table 1, when different fault locations and transition resistances are set on the wind farm transmission lines, the proposed longitudinal protection method can correctly identify faults inside and outside the zone and has good resistance to transition resistance.

[0048] Example 3: Create as shown in the attached document Figure 2 The large-scale wind turbine integration into the power system shown is used as a simulation model. The wind farm consists of 33 1.5MW doubly-fed wind turbines. The equivalent positive-sequence impedance of the main transformer T1 is Z. T1 =j0.12; The equivalent positive sequence impedance of the wind farm's transmission line is Z. L1 =0.164+j0.479; the equivalent positive sequence impedance of the power grid system is Z. S1 =j0.065. The system reference voltage is 220kV, and the reference capacity is 1000MWA. Taking a phase-A ground fault occurring at point f1 in the wind farm's transmission line area as an example, this paper discusses the impact of data delay transmission on protection performance. |Z M1 |Fault time sequence delay 5ms, 10ms,|Z N1 The fault time series was transmitted normally.

[0049] (1) When |Z M1 |During the transmission of the fault time sequence with a 5ms delay, the acquired positive-sequence voltage and current signal data of the sending line are preprocessed, and the positive-sequence impedance amplitude is calculated|Z M1 |。 We can get |Z after 5ms M1|Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 |, Two-terminal positive sequence impedance magnitude difference factor δ p If the value is greater than 0.8, the protection system can correctly identify faults after a 5ms delay compared to normal data transmission.

[0050] (2) When |Z M1 |When transmitting the fault time sequence with a 10ms delay, the acquired positive-sequence voltage and current signal data of the sending line are preprocessed, and the positive-sequence impedance amplitude is calculated|Z M1 |。 We can get |Z after 5ms M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 |, Two-terminal positive sequence impedance magnitude difference factor δ p If the value is greater than 0.8, the protection system can correctly identify faults after a 10ms delay compared to normal data transmission.

[0051] The calculation results are attached. Figure 4 .

[0052] Example 4: Create as shown in the attached document Figure 2 The large-scale wind turbine integration into the power system shown is used as a simulation model. The wind farm consists of 33 1.5MW doubly-fed wind turbines. The equivalent positive-sequence impedance of the main transformer T1 is Z. T1 =j0.12; The equivalent positive sequence impedance of the wind farm's transmission line is Z. L1 =0.164+j0.479; the equivalent positive sequence impedance of the power grid system is Z. S1 =j0.065. The system reference voltage is 220kV, and the reference capacity is 1000MWA. The fault type is set to AG fault, the fault point is set at f1 of the wind farm's transmission line, and the voltage and current signals of the wind farm's transmission line are set to have a data loss or false pulse once every 5ms.

[0053] (1) When the voltage and current signals of the wind power transmission line are missing once every 5ms, the positive sequence voltage and current signal data of the collected transmission line are preprocessed, and the positive sequence impedance amplitude |Z is calculated. M1 |。 We can obtain |Z M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 |, Two-terminal positive sequence impedance magnitude difference factor δ p A value greater than 0.8 protects against data loss.

[0054] (2) When a virtual pulse appears every 5ms in the voltage and current signals of the wind power side transmission line, the collected positive sequence voltage and current signal data of the transmission line are preprocessed, and the positive sequence impedance amplitude |Z is calculated. M1 |。 We can obtain |Z M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's outgoing transmission line|Z L1 |Z Positive sequence impedance magnitude in minimum power grid operating mode| S1 |, Two-terminal positive sequence impedance magnitude difference factor δ p If the value is greater than 0.8, the protection is not affected by virtual pulses.

[0055] The calculation results are attached. Figure 5 .

[0056] Example 5: Create as shown in the attached document Figure 2 The large-scale wind turbine integration into the power system shown is used as a simulation model. The wind farm consists of 33 1.5MW doubly-fed wind turbines. The equivalent positive-sequence impedance of the main transformer T1 is Z. T1 =j0.12; The equivalent positive sequence impedance of the wind farm's transmission line is Z. L1 =0.164+j0.479; the equivalent positive sequence impedance of the power grid system is Z. S1 =j0.065. The system reference voltage is 220kV, and the reference capacity is 1000MWA. The fault type is set to AG fault, the fault point is set at f1 of the wind farm's transmission line, and the noise is selected as Gaussian white noise with signal-to-noise ratios of 10, 20, 30, and 40dB, respectively, added to |Z M1 |and|Z N1 Fault time series.

[0057] Table 2 Verification of the longitudinal protection method for wind farm transmission lines based on impedance characteristics in the face of noise interference.

[0058]

[0059] As shown in Table 2, when different fault locations and noise interference are set on the wind farm transmission lines, the proposed longitudinal protection method can reliably distinguish between faults inside and outside the zone and has good noise resistance performance.

Claims

1. A longitudinal protection method for wind farm transmission lines based on impedance characteristics, characterized in that, The specific steps are as follows: Step 1. Extract the positive sequence voltage and current signals at the installation point of the wind farm's transmission line protection. Preprocess the extracted positive sequence voltage and current signal data and use the preprocessed positive sequence voltage and current to calculate the positive sequence impedance amplitude. Step 2. Determine whether the fault initiation conditions are met based on the positive sequence short-circuit current and the positive sequence impedance amplitude; Step 3. Use BIRCH clustering to remove outlier sampled data from the two-terminal positive sequence impedance amplitude sequence and calculate the clustering characteristics; Step 4. Calculate the difference factor of the positive sequence impedance amplitude at both ends. δ p Establish setting values ​​that take into account the effects of measurement errors and data delay transmission; Step 5. δ p Compare with the set value to determine whether the fault is inside or outside the zone; In step 3, BIRCH clustering is used to remove outlier sampled data from the two-terminal positive sequence impedance amplitude sequence and to calculate clustering features. The specific steps are as follows: Clustering feature trees (CF Trees) can be built based on clustering characteristics. The maximum number of discrete points in a non-leaf node of a CF Tree is... B The spatial threshold is T , radius is r ; The centroid of the fault time series can be derived through global analysis of the fault time series and by combining clustering features. ,radius r They are respectively: (2) (3) Fault time series clustering steps based on the BIRCH algorithm: (1) Scan all data of the fault time series and calculate the radius of the fault time series. r Build a CF Tree; (2) Take the first discrete data point as the root node of the leaf node, and determine whether the distance between the subsequent fault time series data and the root node is less than 1. T If less than and the total number of discrete points of the leaf node does not exceed B If the result is positive, it is merged into the leaf node; otherwise, it is used as the root node of the new leaf node for clustering. (3) Scan the CF Tree after clustering and delete the abnormal leaf nodes that contain only a small number of discrete points to complete the clustering of the fault time series; After removing outlier sampled data, |Z M1 |and|Z N1 Calculate cluster features SS The formula is as follows: (4) In step 4, calculate δ p The steps for setting the adjustment value, taking into account the impact of measurement error and data delay transmission, are as follows: When a fault occurs in the transmission line of a wind farm within the area, |Z M1 |far greater than|Z N1 |;When an outbound fault occurs in the wind farm's transmission line,|Z M1 |and|Z N1 |Approximately equal, utilizing this property, combined with |Z after removing outlier sampled data. M1 |and|Z N1 Calculate cluster features SS The formula for the positive sequence impedance amplitude difference ratio factor can be obtained as follows: (5) When a fault occurs in the area of ​​the wind farm's transmission line, the difference ratio of the positive sequence impedance amplitude at both ends is... δ p Approaching 1, when an external fault occurs in the wind farm's transmission line, the difference factor of the positive sequence impedance amplitude at both ends is... δ p Approaching 0; Ideally, the fault conditions within the wind farm's transmission line area should meet the following requirements. δ p =1. Considering the influence of factors such as CT and PT measurement errors and data transmission delays, a reliability coefficient is introduced to avoid the impact of these factors; the setting value is determined as follows: (6) In the formula: K 1 is the reliability coefficient taking into account the error factors of CT and PT measurements, which is taken as 0.85; K 2 represents the reliability coefficient taking into account abnormal data factors, taken as 0.95; considering faults within and outside the wind farm transmission line area. δ p Feature differences, selection δ pb =1, calculate the setpoint. δ pset =0.8075; In step 1, when a fault occurs in the wind farm's transmission line, the positive sequence voltage and current signals at the protection installation point of the wind farm's transmission line are collected, with a data window of 10ms. A bandpass filter is used to filter out data outside the 35Hz~65Hz range from the extracted signals, and the power frequency signal in the filtered data is extracted using the Prony algorithm. The positive sequence impedance is calculated by the ratio of the voltage fault component to the current fault component. The positive sequence impedance amplitude is calculated as follows: (1) In the formula: U M1 , I M1 These are the positive sequence voltage and current signals collected during the transient period of a fault in the wind power transmission line. U M1|0| , I M1|0| These represent the positive sequence voltage and current signals collected before the fault in the wind power transmission line, and the positive sequence impedance amplitude |Z on the N side. N1 The calculation method is the same.

2. The method according to claim 1, characterized in that, In step 2, the fault initiation conditions are determined based on the positive sequence short-circuit current and the positive sequence impedance amplitude. The specific steps are as follows: By utilizing the difference in positive-sequence impedance amplitude under forward and reverse faults on the wind power side transmission line, the fault initiation condition on the wind power side is set to the positive-sequence impedance amplitude | Z M1 |Greater than or equal to 1.24 times the positive sequence impedance amplitude of the wind farm's transmission line| Z L1 |Positive sequence impedance magnitude in minimum power grid operating mode| Z S1 |;The system side selects a positive-sequence abrupt change current starting element, when If all conditions are met, proceed to the next step; otherwise, continue testing.

3. The method according to claim 1, characterized in that, In step 5, when the difference factor of the positive sequence impedance amplitude at both ends... δ p Greater than the set value δ pset If the fault occurs at a certain time, the wind farm's transmission line will experience a fault within the designated area; otherwise, the wind farm's transmission line will experience a fault outside the designated area.

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