A wind farm main transformer longitudinal protection method based on waveform dissimilarity factor

Abstract

The invention discloses a method for longitudinal protection of main transformer of wind farm based on waveform dissimilarity factor, comprising the following steps: collecting current at protection installation places on both sides of transformer and performing phase correction and per-unit processing on the current; calculating Hausdorff distance between phase currents on both sides in data window in real time; judging the interval where Hausdorff distance between phase currents on both sides is located, if it is between reward threshold and penalty threshold, assigning reward and penalty coefficient to 0, if it is less than penalty threshold, assigning reward and penalty coefficient to -1, except for the above situation, assigning reward and penalty coefficient to 1; calculating waveform dissimilarity factor between phase currents on both sides in data window in real time by reward and penalty coefficient, when it is greater than setting threshold, it is determined as fault in zone. The invention is not affected by frequency offset characteristic of wind farm, and has good anti-excitation surge current and current transformer saturation capability, and has obvious superiority compared with traditional transformer current differential protection.

Description

Technical Field

[0001] The invention relates to a wind farm main transformer longitudinal protection method based on waveform dissimilarity factor, belonging to the technical field of power system relay protection. Background Art

[0002] my country is accelerating the transition from a fossil energy system to a low-carbon energy system. Wind power generation, as an important clean energy generation method, has developed rapidly. However, the topology and control strategy of wind turbines are different from those of traditional synchronous power sources. After large-scale wind power is connected to the grid, the fault current characteristics in wind farms are quite different from those in traditional synchronous power grids. Affected by factors such as fault current frequency offset, magnetizing inrush current, current transformer saturation, and abnormal data, the transformer differential protection scheme based on second harmonic braking has the risk of refusal or malfunction in wind power generation systems, threatening the safe and stable operation of the power system. Summary of the invention

[0003] In view of the risk of refusal to operate or malfunction of traditional transformer current differential protection methods in wind power generation systems, the present invention provides a wind farm main transformer longitudinal protection method based on waveform dissimilarity factors.

[0004] A method for longitudinal protection of a main transformer of a wind farm based on waveform dissimilarity factor comprises the following steps:

[0005] Step 1: Perform phase correction and standardization on the current sampled at the protection installation on both sides of the wind farm main transformer. After processing, the three-phase currents on the wind farm side and the grid side of the main transformer are i mx and i nx ; x = A, B, C, representing phases A, B, and C respectively;

[0006] Step 2: Real-time calculation of the three-phase current i on both sides of the main transformer after normalization in the data window mx and -i nx The Hausdorff distance H(i mx ,-i nx );

[0007] Step 3: Determine H(i mx ,-i nx ) is in the interval, if H Pthr ≤H(i mx ,-i nx )≤H Rthr , assign RPC to 0, that is, RPC = 0, and then execute step 6; if it is not within the interval, execute step 4; where RPC is the reward and punishment coefficient;

[0008] Step 4: Determine H(i mx ,-inx ) is in the interval, if H(i mx ,-i nx )<H Pthr , then assign RPC to -1, that is, RPC = -1, and then execute step 6; if it is not within the interval, execute step 5;

[0009] Step 5: Assign RPC a value of 1, i.e., RPC = 1, and then execute step 6;

[0010] Step 6: Real-time calculation of the three-phase current i on both sides of the transformer after normalization in the data window mx and -i nx The waveform dissimilarity factor WDF value between them;

[0011] Step 7: Determine the interval of the waveform dissimilarity factor WDF. If WDF>WDF thr , it is determined to be an internal fault; if WDF≤WDF thr , it is determined to be a non-intra-zone fault and returns to step 1.

[0012] The present invention discloses a wind farm main transformer longitudinal protection method based on waveform dissimilarity factor, which has obvious advantages over the traditional transformer current differential protection method. The present invention is not affected by the frequency offset characteristics of the wind farm, has good anti-excitation inrush current, CT saturation and abnormal data capabilities, and does not need to be used in conjunction with the second harmonic braking principle. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of wind power generation system connected to the grid;

[0014] Figure 2 The figure is a flow chart of the longitudinal protection method for the main transformer of a wind farm based on waveform dissimilarity factor. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] A method for longitudinal protection of a main transformer of a wind farm based on waveform dissimilarity factor comprises the following steps:

[0017] Step 1: If Figure 1 and Figure 2 , the phase correction processing is performed on the sampling current at the protection installation on both sides of the main transformer of the wind farm. The specific calculation formula is:

[0018]

[0019]

[0020] in, They are the three-phase sampling currents of A, B, and C on the grid side of the main transformer, They are the three-phase currents A, B and C on the grid side of the main transformer after phase correction; They are the three-phase sampling currents of A, B, and C on the wind farm side of the main transformer, They are the three-phase currents A, B and C on the wind farm side of the main transformer after phase correction.

[0021] The three-phase currents on both sides of the main transformer after phase correction are normalized to per unit. The specific calculation formula is:

[0022]

[0023]

[0024] in, are the three-phase current reference values ​​of the main transformer grid side and wind farm side after phase correction; i nx and i mx They are the three-phase currents on the grid side and wind farm side of the main transformer after normalization; x=A, B, C, representing the three phases A, B, and C respectively.

[0025] Step 2: Real-time calculation of the three-phase current i on both sides of the main transformer after normalization in the data window mx and -i nx The Hausdorff distance H(i mx ,-i nx ), the specific calculation formula is:

[0026] H(i mx ,-i nx )=max[h(i mx ,-i nx ),h(-i nx ,i mx )] (5)

[0027] Among them, h(i mx ,-i nx ) and h(-i nx ,i mx ) is the current on both sides of the main transformer after normalization mx with -i nx The single-phase Hausdorff distance between mx ,-i nx ) is the bidirectional Hausdorff distance, which means the single-phase Hausdorff distance h(i mx ,-i nx ) and h(-i nx ,i mx ) is the maximum value between .

[0028] Suppose there are two sets A={a1,a2,...,a p},B={b1,b2,...,b q}, set A and set B represent the current i on both sides of the main transformer after normalization. mx with -i nx A time series. Any point a in set A i There is a point b in set B with the shortest distance to it. j , a i and b j The distance between i The minimum distance to set B. The minimum distance calculation formula is:

[0029] ||a i -b j ||≤||a i -b k ||(1≤k≤q and k≠j) (6)

[0030] Here, ||·|| represents the Euclidean distance between the subsets in set A and the subsets in set B.

[0031] Element a in set A i The maximum value of the minimum distance to all points in set B is the single-phase Hausdorff distance h(A,B) from set A to set B. Similarly, the maximum value of the minimum distance to all points in set B is h(A,B). i The maximum value of the minimum distance to all points in set A is the single-phase Hausdorff distance h(B,A) from set B to set A.

[0032] Single-phase Hausdorff distance h(i mx ,-i nx ) and h(-i nx ,i mx ) The calculation formulas are:

[0033]

[0034]

[0035] Step 3: If Figure 2 , judge H(i mx ,-i nx ) is in the interval, if H Pthr ≤H(i mx ,-i nx )≤H Rthr , assign RPC to 0, that is, RPC = 0, and then execute step 6; if it is not within the interval, execute step 4; where RPC is the reward and punishment coefficient;

[0036] Step 4: If Figure 2 , judge H(i mx ,-i nx ) is in the interval, if H(i mx ,-i nx )<H Pthr , assign RPC to -1, that is, RPC = -1, and then execute step 6; if it is not within the interval, then execute step 5;

[0037] Step 5: If Figure 2 , assign RPC a value of 1, i.e., RPC = 1, and then execute step 6;

[0038] Step 6: If Figure 2 , real-time calculation of the three-phase current i on both sides of the transformer after normalization in the data window mx and -i nx The waveform dissimilarity factor WDF value between them is calculated as follows:

[0039]

[0040] Wherein, N is the number of sampling points in the power frequency cycle, and k is the current moment.

[0041] Step 7: If Figure 2 , determine the interval of the waveform dissimilarity factor WDF, if WDF>WDF thr , it is determined to be an internal fault; if WDF≤WDF thr , it is determined to be a non-intra-zone fault and returns to step 1.

[0042] The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements, substitutions, modifications and embellishments can be made without departing from the principle and purpose of the present invention. These improvements, substitutions, modifications and embellishments should also be regarded as the scope of protection of the present invention.

[0043] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A method for longitudinal protection of a main transformer of a wind farm based on waveform dissimilarity factor, comprising the following steps: Step 1: Perform phase correction and standardization on the current sampled at the protection installation on both sides of the wind farm main transformer. After processing, the three-phase currents on the wind farm side and the grid side of the main transformer are i mx and i nx ; x = A, B, C, representing phases A, B, and C respectively; Step 2: Real-time calculation of the three-phase current i on both sides of the main transformer after normalization in the data window mx and -i nx The Hausdorff distance H(i mx ,-i nx ); Step 3: Determine H(i mx ,-i nx ) is in the interval, if H Pthr ≤H(i mx ,-i nx )≤H Rthr , assign RPC to 0, that is, RPC = 0, and then execute step 6; if it is not within the interval, execute step 4; where RPC is the reward and punishment coefficient; Step 4: Determine H(i mx ,-i nx ) is in the interval, if H(i mx ,-i nx )<H Pthr , then assign RPC to -1, that is, RPC = -1, and then execute step 6; if it is not within the interval, execute step 5; Step 5: Assign RPC a value of 1, i.e., RPC = 1, and then execute step 6; Step 6: Real-time calculation of the three-phase current i on both sides of the transformer after normalization in the data window mx and -i nx The waveform dissimilarity factor WDF value between them; Step 7: Determine the interval of the waveform dissimilarity factor WDF. If WDF>WDF thr , it is determined to be an internal fault; if WDF≤WDF thr , it is determined to be a non-intra-zone fault and returns to step 1.

2. A method for longitudinal protection of main transformers in a wind farm based on waveform dissimilarity factor according to claim 1, characterized in that: The specific calculation formula for phase correction of the three-phase sampled current at the protection installation on both sides of the main transformer in step 1 is: in, They are the three-phase sampling currents of A, B, and C on the grid side of the main transformer, They are the three-phase currents A, B and C on the grid side of the main transformer after phase correction; They are the three-phase sampling currents of A, B, and C on the wind farm side of the main transformer, They are the three-phase currents A, B and C on the wind farm side of the main transformer after phase correction.

3. The method for longitudinal protection of main transformers in a wind farm based on waveform dissimilarity factor according to claim 1 is characterized in that: The specific calculation formula for normalizing the three-phase sampled current at the protection installation on both sides of the main transformer after phase correction in step 1 is: in, are the three-phase current reference values ​​of the main transformer grid side and wind farm side after phase correction; i nx and i mx They are the three-phase currents on the grid side and wind farm side of the main transformer after normalization; x=A, B, C, representing the three phases A, B, and C respectively.

4. The method for longitudinal protection of main transformers in a wind farm based on waveform dissimilarity factor according to claim 1 is characterized in that: The specific calculation formula of the Hausdorff distance algorithm described in step 2 is: Among them, h(i mx ,-i nx ) and h(-i nx ,i mx ) is the current on both sides of the main transformer after normalization mx with -i nx The single-phase Hausdorff distance between mx ,-i nx ) is the bidirectional Hausdorff distance, which means the single-phase Hausdorff distance h(i mx ,-i nx ) and h(-i nx ,i mx ), Suppose there are two sets A={a1,a2,...,a p },B={b1,b2,...,b q }, set A and set B represent the current i on both sides of the main transformer after normalization. mx with -i nx A time series, any point a in set A i There is a point b in set B with the shortest distance to it. j , a i and b j The distance between i The minimum distance to set B. The minimum distance calculation formula is: ||a i -b j || ≤ ||a i -b k || (1 ≤ k ≤ q and k ≠ j) (6) Among them, ||·|| represents the Euclidean distance between the subsets in set A and the subsets in set B, Element a in set A i The maximum value of the minimum distance to all points in set B is the single-phase Hausdorff distance h(A,B) from set A to set B. Similarly, the maximum value of the minimum distance to all points in set B is h(A,B). i The maximum value of the minimum distance to all points in set A is the single-phase Hausdorff distance h(B,A) from set B to set A. Single-phase Hausdorff distance h(i mx ,-i nx ) and h(-i nx ,i mx ) The calculation formulas are: 。 5. According to the method for longitudinal protection of main transformer of wind farm based on waveform dissimilarity factor according to claim 1, it is characterized by: The waveform dissimilarity factor WDF calculation formula in step 6 is: Wherein, N is the number of sampling points in the power frequency cycle, and k is the current moment.

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