CN110071483B

CN110071483B - Bridge difference protection anti-misoperation lockout judgment method based on mutual approximation entropy algorithm

Info

Publication number: CN110071483B
Application number: CN201910399364.4A
Authority: CN
Inventors: 翁汉琍; 贾永波; 刘雷; 黄景光; 李振兴; 万毅
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2019-05-14
Filing date: 2019-05-14
Publication date: 2021-02-19
Anticipated expiration: 2039-05-14
Also published as: CN110071483A

Abstract

A bridge difference protection anti-misoperation lockout judgment method based on a mutual approximation entropy algorithm comprises the following steps: acquiring current sequence I measured by current transformer TA on secondary side of Y/Y converter transformer_12a、I_12bAnd I_12cAnd current sequence I measured by secondary side TA of Y/delta converter transformer_22a、I_22bAnd I_22c(ii) a Formula delta I is determined by using bridge difference protection amplitude_Y＝I_ac‑I_acYAnd Δ I_D＝I_ac‑I_acDForming a Y bridge criterion sequence delta I_YD-bridge criterion sequence delta I_D(ii) a Judgment amplitude criterion Delta I_Y>I_setOr Δ I_D>I_setWhether the result is true or not; judging whether the switch is in no-load switch-on; three groups of current sequences I for calculating TA measurement of secondary side of Y/delta converter transformer_22a、I_22bAnd I_22cThe mutual approximate entropy between each two is the value of Capen (m, r, N); the amplitude criterion and the locking criterion form a new action logic of bridge difference protection. The method can effectively prevent the phenomenon of bridge differential protection maloperation caused by excitation inrush current generated by no-load closing and recovery inrush current generated by external fault removal while ensuring the performance of the bridge differential protection action.

Description

Bridge difference protection anti-misoperation lockout judgment method based on mutual approximation entropy algorithm

Technical Field

The invention relates to the technical field of converter station bridge difference protection, in particular to a bridge difference protection anti-misoperation lockout determination method based on a mutual approximation entropy algorithm.

Background

The converter bridge difference protection is backup protection for protecting a direct current system by tripping off a network side breaker when a converter bridge has a valve commutation fault or a trigger fault.

The converter transformer is easy to generate serious inrush current with unconventional characteristics in the no-load switching-on and external fault removal and power restoration processes, and the frequent occurrence and new characteristics of the serious inrush current can cause misoperation of bridge differential protection of the converter. When the direct current high slope converter station is over the direct current high slope, the bridge difference II section protection misoperation is triggered due to the standby switching locking operation of the converter transformer, the direct current single pole locking is caused, and direct impact is caused on a plurality of devices and even systems of the converter station.

The current countermeasures for preventing the bridge differential protection unwanted operation include: and TA with better transient characteristics is used, a protection fixed value is optimized, and zero sequence circulation at the delta side of the Y/delta converter transformer is introduced into a starting criterion to serve as braking quantity.

The method has certain guiding significance for preventing the bridge difference protection misoperation, but still has a plurality of defects in practical application: the replacement of the TA increases the cost and is easily restricted by the installation location; increasing the protection rating may reduce the sensitivity and snap-action of converter bridge differential protection to in-zone faults.

The bridge difference protection criterion is analyzed, and the fact that excitation inrush current generated by converter transformer during no-load closing and recovery inrush current generated by external fault removal both generate large zero-sequence circulating current in a delta side ring of the Y/delta converter transformer is found, when the zero-sequence circulating current flows through a certain phase winding TA with large remanence, the phase TA is saturated, TA transmission characteristics are degraded, the current magnitude adopted by protection is mistakenly measured, and bridge difference protection misoperation is caused.

The false action reason is analyzed, the current sequence of the TA saturated phase and the current sequence of other normal phases have obvious difference in similarity degree, and the mutual approximation entropy algorithm has obvious advantage in processing sequence similarity. Therefore, the similarity degree between the current sequences is calculated by utilizing a mutual approximation entropy algorithm, and a bridge difference protection anti-misoperation locking criterion is formed.

Disclosure of Invention

The method is characterized in that saturation of a certain phase winding TA is easily caused when the Y/delta converter is switched into the idle load and switched on and external faults are removed, and the TA saturated phase and the secondary side current sequence of the normal phase have obvious difference in the similar degree. The invention provides a bridge difference protection anti-misoperation lockout determination method based on a mutual approximation entropy algorithm, which can effectively identify the difference between a TA saturated phase and a normal phase current sequence and can effectively solve the problem of bridge difference protection misoperation caused by TA saturation of a winding of a converter transformer.

The technical scheme adopted by the invention is as follows:

the bridge difference protection anti-misoperation lockout judgment method based on the mutual approximation entropy algorithm comprises the following steps:

step 1: under a certain sampling frequency, obtaining a current sequence I measured by a secondary side current transformer TA of a Y/Y converter transformer_12a、I_12bAnd I_12cAnd current sequence I measured by secondary side TA of Y/delta converter transformer_22a、I_22bAnd I_22c(ii) a Formula delta I is determined by using bridge difference protection amplitude_Y＝I_ac-I_acYAnd Δ I_D＝I_ac-I_acDForming a Y bridge criterion sequence delta I_YD-bridge criterion sequence delta I_D. Wherein, I_acY＝max{I_aY，I_bY，I_cY}、I_acD＝max{I_aD，I_bD，I_cD}、I_ac＝max{I_acY，I_acD}；

I_aY、I_bYAnd I_cYAre each equal to I_12a、I_12bAnd I_12c；

I_aD、I_bDAnd I_cDAre each equal to I_22a-I_22b、I_22b-I_22cAnd I_22c-I_22a。

Step 2: judgment amplitude criterion Delta I_Y>I_setOr Δ I_D>I_setIs established, wherein I_setIf the bridge difference protection action setting value is established, starting a misoperation prevention locking criterion to step 3; otherwise, returning to continuously judge the inequality.

And step 3: judging whether the switching-on is carried out in an idle load mode, and if the switching-on is carried out in the idle load mode, executing the step 4; otherwise, the current sequence is subjected to standardization processing.

And 4, step 4: three groups of current sequences I for calculating TA measurement of secondary side of Y/delta converter transformer_22a、I_22bAnd I_22cMutually approximate entropy Capen (m, r, N) values between every two, and convert the three groups of results obtained by calculation into corresponding three groups of C values; the specific method comprises the following steps: by the formula

Calculating the value of the Capen (m, r, N) between the two sequences, wherein r is the similarity tolerance; b and A are respectively the similarity of two sequence sampling values under the tolerance r, and are marked as events A and B, P_i(B | A) is the probability of similarity in the sense of tolerance r; n is the sample length; m is a modeDimension number, and then C ═ e is taken as the calculated value of CApEn (m, r, N)^{-CApEn(m,r,N)}Conversion is performed so that the obtained result is in the interval (0, 1)]And (4) the following steps.

And 5: the amplitude criterion and the locking criterion form a new action logic of bridge difference protection, when the amplitude criterion is met, the action quantity output is 1, otherwise, the action quantity output is 0; when there are two or more groups C<C_set，C_setWhen the locking criterion setting value is set, the locking criterion action output quantity is 0, otherwise, the locking criterion action output quantity is 1; when the amplitude criterion action quantity and the locking criterion action quantity are both 1, the bridge difference protection acts; otherwise, locking is performed.

A bridge difference protection anti-misoperation lockout judgment method based on a mutual approximation entropy algorithm is characterized in that a mutual approximation entropy algorithm is adopted to calculate the value of a Capen (m, r, N) between every two phases of a current sequence of a Y/delta converter transformer three-phase TA secondary side, and the result is converted into a value of C.

The invention discloses a bridge difference protection anti-misoperation lockout judgment method based on a mutual approximation entropy algorithm, which has the following technical effects:

1: the method compares the similarity degree between every two phases of the three-phase current sequence of the secondary side of the Y/delta converter transformer TA, has better anti-noise capability and can deal with strong interference which is generated occasionally.

2: the invention does not need to describe the complete picture of the signal sequence, and only describes the similarity of the sequence from the statistical perspective, so that the data window is flexible to select, and a stable statistical value can be obtained by using less data.

3: the invention is used as the bridge difference protection locking criterion, can effectively prevent the protection maloperation caused by excitation surge current and recovery surge current when no-load switching-on and external fault removal, and has high reliability.

Drawings

FIG. 1(a) is a waveform diagram of primary side current of three-phase TA of Y/delta converter transformer during no-load closing;

fig. 1(b) is a waveform diagram of the secondary side current of three-phase TA of the Y/Δ converter transformer during no-load closing.

FIG. 2(a) is a waveform diagram of primary side current of three-phase TA of Y/delta converter transformer when external fault is removed;

fig. 2(b) is a waveform diagram of secondary side current of three-phase TA of Y/Δ converter transformer when external fault is removed.

Fig. 3(a) is a C-value comparison graph between two phases of three-phase current on the delta side of the Y/delta converter when the circuit breaker is closed in no-load.

Fig. 3(b) is a diagram of the output of the three-phase current bridge difference protection action quantity on the delta side of the Y/delta converter transformer during no-load closing of the invention.

Fig. 4(a) is a C-value comparison graph between two phases of three-phase current on the delta side of the Y/delta converter when an external fault is removed according to the present invention.

Fig. 4(b) is a graph showing the output of the three-phase current bridge differential protection operation amount on the delta side of the Y/delta converter transformer when the external fault is removed.

Fig. 5(a) is a C-value comparison graph between two phases of three-phase current on the delta side of the Y/delta converter in the case of an internal fault according to the present invention. .

Fig. 5(b) is a graph showing the operation amount of the three-phase current bridge difference protection on the delta side of the Y/delta converter transformer at the time of the internal failure of the present invention.

FIG. 6 is a flow chart of a novel scheme of bridge difference protection anti-false-operation blocking based on mutual approximation entropy algorithm.

Detailed Description

As shown in fig. 6, the method for determining the bridge difference protection anti-false-operation locking based on the mutual approximation entropy algorithm includes the following steps:

step 1: at a certain sampling frequency, taking 4kHz as an example, obtaining a current sequence I measured by a secondary side TA of the Y/Y converter transformer_12a、I_12bAnd I_12cAnd current sequence I measured by secondary side TA of Y/delta converter transformer_22a、I_22bAnd I_22c。

Formula delta I is determined by using bridge difference protection amplitude_Y＝I_ac-I_acYAnd Δ I_D＝I_ac-I_acDForming a Y bridge criterion sequence delta I_YD-bridge criterion sequence delta I_D。

Wherein, I_acY＝max{I_aY，I_bY，I_cY}、I_acD＝max{I_aD，I_bD，I_cD}、I_ac＝max{I_acY，I_acD}；I_aY、I_bYAnd I_cYAre each equal to I_12a、I_12bAnd I_12c；I_aD、I_bDAnd I_cDAre each equal to I_22a-I_22b、I_22b-I_22cAnd I_22c-I_22a。

Step 2: judgment amplitude criterion Delta I_Y>I_setOr Δ I_D>I_setIs established, wherein I_setAnd setting a bridge difference protection action value. If yes, starting the false action prevention locking criterion provided by the invention, and going to step 3; otherwise, returning to continuously judge the inequality.

And 4, step 4: three groups of current sequences I for calculating TA measurement of secondary side of Y/delta converter transformer_22a、I_22bAnd I_22cAnd (3) mutually approximating entropy Capen (m, r, N) values between every two, and converting three groups of results obtained by calculation into corresponding three groups of C values.

The specific method comprises the following steps: by the formula

Calculating the value of the CApEn (m, r, N) between the two sequences,

wherein r is a similarity tolerance; b and A are respectively the similarity of two sequence sampling values under the tolerance r, and are marked as events A and B, P_i(B | A) is the probability of similarity in the sense of tolerance r; n is the sample length; m is the mode dimension. Then, the calculated value of CApEn (m, r, N) is set as C ═ e^{-CApEn(m,r,N)}Conversion is performed so that the obtained result is in the interval (0, 1)]And (4) the following steps.

And 5: the amplitude criterion and the locking criterion form a new action logic of bridge difference protection. When the amplitude criterion is satisfied, the output of the motion quantity is 1, otherwise, the output is 0; when there are 2 groups and above C<C_set，C_setAnd when the locking criterion setting value is the locking criterion setting value, the locking criterion action output quantity is 0, otherwise, the locking criterion action output quantity is 1. When the amplitude criterion action quantity and the locking criterion action quantity are both 1, the bridge difference protection acts; otherwise, locking is performed.

1. When no-load switching-on and external fault removal are carried out, the current magnitude characteristics of the primary side and the secondary side of the Y/delta converter transformer TA are as follows:

for bridge difference protection, when any one of the Y bridge and the D bridge reaches a bridge difference protection amplitude criterion and meets a delay criterion, the protection acts. When no-load switching-on and external fault removal occur, the combined action of zero sequence circulating current generated in a delta side ring of a Y/delta converter transformer and residual magnetism of a winding causes the TA of a certain phase to be saturated, so that the measurement of the protection electricity consumption of the phase is wrong, and the misoperation of bridge difference protection is caused. The original judgment data cannot distinguish the situations that the bridge difference protection amplitude criterion exceeds the setting value during no-load closing, external fault removal and internal fault, but the TA saturated phase caused by inrush current and the TA secondary side current sequence of other normal phases have obvious difference in the similarity degree, and the difference can be used for judgment.

Assuming that residual magnetism exists in the phase a of the winding TA on the delta side of the Y/delta converter transformer, fig. 1(a) and 1(b) are graphs of primary and secondary side current waveforms of the three phases TA of the Y/delta converter transformer during no-load switching, and when t is 0.1s, the time-load switching is performed. Fig. 2(a) and 2(b) are waveform diagrams of primary and secondary side currents of the Y/Δ converter three-phase TA when an external fault is removed, where the external fault occurs when t is 0.1s, and the fault is removed when t is 0.2 s. When zero-sequence loop current generated by excitation surge current and recovery surge current flows in a loop at the delta side of a Y/delta converter transformer, the zero-sequence loop current and the residual magnetism of a winding act together to cause TA saturation of an A phase, so that the waveform of the transformed current is distorted; while the other two phases TA are not affected and normally transmit. This makes the current waveform sequence of the saturated phase and the normal phase in the TA secondary side three-phase current have difference.

2. Mutual approximation entropy algorithm:

mutual approximation entropy is a quantity that represents the degree of complexity between two discrete sequences. It analyzes the sequence from the view point of sequence complexity to generate new pattern probability, and judges the similarity degree by calculating the conditional probability of the same pattern existing between two sequences.

The mutual approximate entropy method is used for expressing the similarity degree of two sequences, namely finding the similar mode of the two sequences, and the mutual approximate entropy value is defined as:

in the formula: r is a similarity tolerance; b and A are respectively the similarity of two series sampling values in a tolerance r, and are marked as events A and B, P_i(B | A) is the probability of similarity in the sense of tolerance r; n is the sample length, and the mutual approximation entropy can obtain a stable value only by comparing relatively few data points; m is the mode dimension, and in practical application, m is 2.

Calculating a mutual approximation entropy value according to the following steps:

(1) and sequentially carrying out vector reconstruction on the two current sequences to be compared to obtain vectors corresponding to the two currents. Firstly, a current sequence is divided into a plurality of one-dimensional time sequences with the length of N, i_x＝{i_x(n) } and i_y＝{i_y(N), wherein N is 1, … N. Reconstructing m-dimensional vectors according to the formula (2) and the formula (3), and respectively recording the two current sequences as I_x(j) And I_y(k)。

I_x(j)＝[i_x(j),…,i_x(j+m-1)],j＝1,…,N-m+1 (2)

Where N is the sample length, m is the mode dimension, typically 2, and j is the current sequence I_xNumber of (1), i_x(j) For a sequence of currents i_x(n) } j-th point, i_x(j + m-1) is a current sequence i_x(n) } j + m-1 th point, I_x(j) Is the jth m-dimensional vector.

I_y(k)＝[i_y(k),…,i_y(k+m-1)],k＝1,…,N-m+1 (3)

Where N is the sample length, m is the mode dimension, typically 2, and k is the current sequence I_yNumber of (1), i_y(k) For a sequence of currents i_y(n) } the k-th point, i_y(k + m-1) is the current sequence i_y(n) } the k + m-1 th point in the center, I_y(k) Is the k-th m-dimensional vector.

When current sequence i_xAnd i_yWhen the amplitude difference is large, the current sequence is generally standardized firstly, and the specific method is as follows:

since the sequence has already been standardized, r may be 0.2. Wherein,

for normalized current sequences i_x(n)，mean(i_x) As a sequence of currents i_xAverage value of i_x(n) is a current sequence i_xPoint n of middle, SD (i)_x) As a sequence of currents i_xThe standard deviation of (a) is determined,

for normalized current sequences i_yN-th point of (1), i_y(n) is a current sequence i_yThe nth point in middle, mean (i)_y) As a sequence of currents i_yAverage value of (d), SD (i)_y) As a sequence of currents i_yStandard deviation of (2).

(2) Calculating the similar tolerance according to the two groups of current sequences, wherein r is the current sequence i_x(n) and i_y(n) 0.2 times the covariance, i.e. r 0.2 × COV (i)_x(n),i_y(n)), wherein

(3) Defining the distance between two sequences as I_x(j) And I_y(k) Corresponding to the maximum value of the difference of the currents, the maximum difference expression is as follows:

wherein j is a current sequence I_xK is the current sequence I_yP is 0 and 1, m is the mode dimension, typically 2, I_x(j + p) is the (j + p) th current sequence, I_y(k + p) is the (k + p) th current sequence.

(4) And counting d (I) for each j and k according to the set value r of the similarity margin_x(j),I_y(k) A number smaller than r) and calculating the ratio of the number of r to the total number of vectors N-m +1, denoted as C_m,rThe value is twoThe approach probability of the m-dimensional mode in the sequence under the condition of the similar tolerance r is specifically expressed as follows:

C_m,r＝[d(I_x(j),I_y(k))<number of r]/(N-m+1) (5)

(5) To C_m,rObtaining I by calculating the logarithm and then the average_x(j) And I_y(k) Mutual similarity of (D) is denoted as T_m,r[d(I_x(j),I_y(k))]The specific expression is as follows:

(6) and when the embedding dimension is changed into m +1, repeating the steps (1) to (4) to obtain C with the dimension of m +1_m+1,rAnd T_m+1,r[d(I_x(j),I_y(k))]Will T_m,r[d(I_x(j),I_y(k))]And T_m+1,r[d(I_x(j),I_y(k))]And (3) obtaining a final mutual approximation entropy value of the two currents by difference, wherein the expression is as follows:

CApEn(m,r,N)＝T_m,r[d(I_x(j),I_y(k))]-T_m+1,r[d(I_x(j),I_y(k))] (7)

according to the steps, the mutual approximate entropy value of the two sequences can be obtained.

Analyzing according to the steps, and finding that if the similarity degree of the two sequences is higher, the mutual approximation entropy value obtained according to the formula (7) is almost 0; if they are not similar, the mutual approximation entropy is larger. Therefore, the calculated mutual approximation entropy ranges from the value of Capen (m, r, N) E [0, + ∞). The range of the value is too wide, which is not beneficial to forming effective setting value to divide the similarity of the two waveform sequences. Therefore, further processing of the mutual approximation entropy values is required. According to y ═ e^-xAs a result, when x ∈ [0 ] + ∞ ], y ∈ [0, 1 ]]Therefore, the value C is defined as the similarity discrimination value of the present invention, and the specific formula is:

C＝e^{-CApEn(m,r,N)} (8)

extracting current sequence I measured by three-phase TA of secondary side of Y/delta converter transformer_22a、I_22bAnd I_22cThree sets of comparison sequences (I)_22aAnd I_22b、I_22bAnd I_22c、I_22cAnd I_22a)。

Substituting the two sequences to be compared into an algorithm calculation formula by utilizing a mutual approximation entropy algorithm_xAnd I_yThe value of CApEn (m, r, N) between the two sequences was calculated and the result was converted to a C value. Fig. 3(a), fig. 4(a), and fig. 5(a) are C values between every two phases of the secondary side three-phase current of the Y/Δ converter transformer when the converter transformer is switched on under no load, removed under external fault, and failed internally (A, B interphase fault), respectively, because the new criterion of false-operation-prevention locking is started simultaneously with the criterion of bridge difference protection amplitude, the C value before the criterion of bridge difference protection amplitude is started is set to 1.

As can be seen from fig. 3(a), fig. 4(a) and fig. 5(a), when no-load switching and external fault removal are performed, two groups of C values in the three groups of C values are smaller than the setting value of 0.65, and when an internal fault occurs, the three groups of C values are all above the setting value of 0.65.

3. A novel bridge difference protection anti-misoperation lockout scheme based on a mutual approximation entropy algorithm comprises the following steps:

obtaining current sequence I measured by TA of secondary side of Y/Y converter transformer under certain sampling frequency_12a、I_12bAnd I_12cAnd current sequence I measured by secondary side TA of Y/delta converter transformer_22a、I_22bAnd I_22c. Y-bridge criterion sequence delta I is formed by using bridge difference protection amplitude criterion_YD-bridge criterion sequence delta I_D. Judgment of Delta I_YOr Δ I_DAnd if any item is greater than the setting value, starting the new scheme provided by the invention. After a novel bridge difference protection anti-misoperation locking scheme is started, firstly, whether the current sequence is in no-load closing or not is judged, if the current sequence is in the no-load closing condition, the current sequence is directly calculated, and otherwise, the current sequence is subjected to standardization processing. Then three groups of current sequences (I) of TA measurement of secondary side of Y/delta converter transformer are calculated_22a、I_22bAnd I_22c) The value of CApEn (m, r, N) between each two, and the 3 sets of results obtained by calculation are converted into the corresponding 3 sets of C values. The specific method comprises the following steps: by the formula

Calculating the value of the CApEn (m, r, N) between the two sequences, and then taking the calculated value of the CApEn (m, r, N) as C ═ e^{-CApEn(m,r,N)}Conversion is performed so that the obtained result is in the interval (0, 1)]And (4) the following steps.

Through setting reasonable C_setAnd the internal fault can be effectively distinguished from other conditions. The amplitude criterion and the locking criterion form a new action logic of bridge difference protection. When the amplitude criterion is satisfied, the output of the motion quantity is 1, otherwise, the output is 0; when there are 2 groups and above C<C_set，C_setAnd when the locking criterion setting value is the locking criterion setting value, the locking criterion action output quantity is 0, otherwise, the locking criterion action output quantity is 1. Judging whether the amplitude criterion action quantity and the locking criterion action quantity meet the requirement of 1 at the same time, if so, judging that the internal fault occurs, and performing bridge difference protection action; if not, judging that false action current caused by TA saturation of the Y/delta converter transformer winding is detected, and locking the bridge difference protection. The novel bridge differential protection misoperation-preventing locking scheme based on the mutual approximation entropy algorithm can effectively prevent the phenomenon of bridge differential protection misoperation caused by excitation inrush current generated by no-load switching-on and recovery inrush current generated when external faults are removed. The flow chart of the novel scheme of the bridge difference protection anti-misoperation lockout based on the mutual approximation entropy algorithm is shown in FIG. 6.

The new scheme is utilized to calculate the C value between every two phases of the secondary side three-phase current sequence of the Y/delta converter transformer TA when the converter transformer has no-load closing, external fault removal and internal fault (A, B interphase fault), and whether the bridge difference protection acts or not is judged according to new action logic, and the result is shown in fig. 3(b), fig. 4(b) and fig. 5(b), wherein C is_setTake 0.65.

It can be clearly seen that:

(1): and when no-load switching-on and external fault removal are carried out, the locking criterion is started, the action output quantity of the amplitude criterion is 1, but two groups of C values in the three groups of C values obtained by calculation are less than 0.65 setting value, and the action output quantity of the C value criterion is 0. Therefore, the bridge difference protection action output quantity does not satisfy the action logic. The protection can be locked reliably at the moment, and misoperation cannot occur.

(2): and when an internal fault occurs, the C value between every two phases of the secondary side three-phase current of the TA of the Y/delta converter is greater than 0.65 setting value. At the moment, the action output quantity of the amplitude criterion and the action output quantity of the C value criterion are both 1, and the new criterion action logic is met. At the moment, the internal fault can be reliably identified, and the protection is continuously opened.

The invention discloses a bridge difference protection anti-misoperation lockout judgment method based on a mutual approximation entropy algorithm, which can effectively prevent the misoperation problem caused by TA saturation of a winding while ensuring the performance of bridge difference protection actions.

Claims

1. The bridge difference protection anti-misoperation lockout determination method based on the mutual approximation entropy algorithm is characterized by comprising the following steps of:

step 1: under a certain sampling frequency, obtaining a current sequence I measured by a secondary side current transformer TA of a Y/Y converter transformer_12a、I_12bAnd I_12cAnd current sequence I measured by secondary side TA of Y/delta converter transformer_22a、I_22bAnd I_22c(ii) a Formula delta I is determined by using bridge difference protection amplitude_Y＝I_ac-I_acYAnd Δ I_D＝I_ac-I_acDForming a Y bridge criterion sequence delta I_YD-bridge criterion sequence delta I_D；

Wherein, I_acY＝max{I_aY，I_bY，I_cY}、I_acD＝max{I_aD，I_bD，I_cD}、I_ac＝max{I_acY，I_acD}；

I_aY、I_bYAnd I_cYAre each equal to I_12a、I_12bAnd I_12c；

I_aD、I_bDAnd I_cDAre each equal to I_22a-I_22b、I_22b-I_22cAnd I_22c-I_22a；

Step 2: judgment amplitude criterion Delta I_Y>I_setOr Δ I_D>I_setIs established, wherein I_setIf the bridge difference protection action setting value is established, starting a misoperation prevention locking criterion to step 3; otherwise, returning to continuously judge the inequality;

and step 3: judging whether the switching-on is carried out in an idle load mode, and if the switching-on is carried out in the idle load mode, executing the step 4; otherwise, the current sequence is subjected to standardization treatment;

Calculating the value of the Capen (m, r, N) between the two sequences, wherein r is the similarity tolerance; b and A are respectively the similarity of two sequence sampling values under the tolerance r, and are marked as events A and B, P_i(B | A) is the probability of similarity in the sense of tolerance r; n is the sample length; m is the mode dimension, and then the calculated value of CApEn (m, r, N) is taken as C ═ e^{-CApEn(m,r,N)}Conversion is performed so that the obtained result is in the interval (0, 1)]Internal;

2. The bridge difference protection anti-false-operation locking judgment method based on the mutual approximation entropy algorithm is characterized in that:

in step 4, the mutual approximation entropy is calculated according to the following steps:

sequentially carrying out vector reconstruction on the two current sequences to be compared to obtain vectors corresponding to the two currents; firstly, a current sequence is divided into a plurality of one-dimensional time sequences with the length of N, i_x＝{i_x(n) } and i_y＝{i_y(N), wherein N is 1, … N; reconstructing m-dimensional vectors according to the formula (2) and the formula (3), and respectively recording the two current sequences as I_x(j) And I_y(k)；

I_x(j)＝[i_x(j),…,i_x(j+m-1)],j＝1,…,N-m+1 (2)

Where N is the sample length, m is the mode dimension, 2, j is the current sequence I_xNumber of (1), i_x(j) For a sequence of currents i_x(n) } j-th point, i_x(j + m-1) is a current sequence i_x(n) } j + m-1 th point, I_x(j) Is the jth m-dimensional vector;

I_y(k)＝[i_y(k),…,i_y(k+m-1)],k＝1,…,N-m+1 (3)

where N is the sample length, m is the mode dimension, is 2, and k is the current sequence I_yNumber of (1), i_y(k) For a sequence of currents i_y(n) } the k-th point, i_y(k + m-1) is the current sequence i_y(n) } the k + m-1 th point, I_y(k) Is the k-th m-dimensional vector;

when current sequence i_xAnd i_yWhen the amplitude difference is large, the current sequence is firstly standardized by the specific method

Since the sequence has been standardized, r is taken to be 0.2;

wherein,

for normalized current sequences i_yN-th point of (1), i_y(n) is a current sequence i_yThe nth point in middle, mean (i)_y) As a sequence of currents i_yAverage value of (d), SD (i)_y) As a sequence of currents i_yStandard deviation of (d);

step (2) calculating the similar capacitance according to the two groups of current sequencesLimit, r is a current sequence i_x(n) and i_y(n) 0.2 times the covariance, i.e. r 0.2 × COV (i)_x(n),i_y(n)), wherein,

step (3) defining the distance between the two sequences as I_x(j) And I_y(k) Corresponding to the maximum value of the difference of the currents, the maximum difference expression is as follows:

wherein j is a current sequence I_xK is the current sequence I_yP is 0 and 1, m is the mode dimension and is 2, I_x(j + p) is the (j + p) th current sequence, I_y(k + p) is the (k + p) th current sequence;

step (4), according to the set value r of the similarity tolerance, d (I) is counted for each j and k_x(j),I_y(k) A number smaller than r) and calculating the ratio of the number of r to the total number of vectors N-m +1, denoted as C_m,rThe value is the approaching probability of the m-dimensional mode in the two sequences under the condition of the similar tolerance r, and the specific expression is as follows:

C_m,r＝[d(I_x(j),I_y(k))<number of r]/(N-m+1) (5)

Step (5), for C_m,rObtaining I by calculating the logarithm and then the average_x(j) And I_y(k) Mutual similarity of (D) is denoted as T_m,r[d(I_x(j),I_y(k))]The specific expression is as follows:

and (6) when the embedding dimension is changed into m +1, repeating the steps (1) to (4) to obtain C when the dimension of m +1 is changed_m+1,rAnd T_m+1,r[d(I_x(j),I_y(k))]Will T_m,r[d(I_x(j),I_y(k))]And T_m+1,r[d(I_x(j),I_y(k))]And (3) obtaining a final mutual approximation entropy value of the two currents by difference, wherein the expression is as follows:

CApEn(m,r,N)＝T_m,r[d(I_x(j),I_y(k))]-T_m+1,r[d(I_x(j),I_y(k))] (7)