CN110504658B - Transformer differential protection method based on two-dimensional space reconstruction current characteristic track - Google Patents
Transformer differential protection method based on two-dimensional space reconstruction current characteristic track Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
- H02H7/045—Differential protection of transformers
- H02H7/0455—Differential protection of transformers taking into account saturation of current transformers
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Abstract
A transformer differential protection method based on two-dimensional space reconstruction current characteristic track collects a current sequence I measured by current transformers TA on two sides of a transformer under a certain sampling frequency1And I2In a period data window, the number of sampling points is N, I1＝{I1(1),I1(2),…,I1(i),…,I1(N)}，I2＝{I2(1),I2(2),…,I2(i),…,I2(N) }, two sets of current sequences I to be collected1And I2The trajectories are reconstructed in a two-dimensional coordinate system to form a sequence of reconstructed trajectories L, L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N. And calculating the percentage K of the number of the points in the reconstructed track sequence L falling into the first quadrant and the third quadrant of the two-dimensional coordinate system in the total number. The calculated K value and K are comparedsetComparison, wherein KsetFor protection action setting, if K>KsetIf so, judging that the fault is in the area and protecting the action; if K<KsetThen it is judged as an out-of-area fault and protection is locked. According to the method, current information on two sides is reconstructed into a characteristic track in a two-dimensional coordinate system, and quadrant characteristics of the track under different fault types are subjected to quantitative analysis so as to identify the fault type under the condition of TA saturation.
Description
Technical Field
The invention discloses a transformer differential protection method based on a two-dimensional space reconstructed current characteristic track, and relates to the technical field of transformer differential protection.
Background
The transformer is an important device in power system transmission, and the correctness of the protection action of the transformer is particularly important. Conventionally, a transformer differential protection is widely used in an actual field as a main protection of a transformer because the principle is simple and only the current amount is used to distinguish the fault type. Whether the transformer differential protection can operate correctly depends on whether the two sides TA can transmit current information correctly. When one side TA is saturated, it transmits false current information that may cause the differential protection to malfunction.
At present, a ratio braking method, a second harmonic braking method, a time difference method, a wavelet method, a morphology method, a virtual braking current method and the like are generally adopted for differential protection of the transformer to cope with the influence of TA saturation on the differential protection. These methods have good effects in identifying TA saturation and improving the performance of differential protection operation, but still have some disadvantages: by using a ratio braking method, the protection is influenced by too high or too low braking coefficient; the accurate positioning of the fault moment and the difference stream occurrence moment by adopting a time difference method is difficult to realize, so that the reliability cannot be guaranteed; the second harmonic braking method may delay the operation due to the occurrence of a large amount of harmonic components; the wavelet method is used for detecting the difference of maximum values of TA secondary current, but larger deviation occurs at certain critical positions or zero-crossing points; the criteria provided by the morphology method require a large amount of calculation time, and the protection action may be delayed; the virtual brake current method requires the incorporation of other criteria. Therefore, it is necessary to explore a new method for solving the influence of TA saturation on the differential protection of the transformer.
The quadrant characteristics of the reconstructed track under different working conditions are analyzed, the influence of the TA state on the quadrant characteristics is small, and the fault characteristics are easy to quantify. Therefore, the current at two sides of the transformer is reconstructed by using the two-dimensional space reconstruction current characteristic track, and a new transformer differential protection criterion is formed.
Disclosure of Invention
Under the influence of fault current, TA on two sides of the transformer differential protection is easy to saturate, so that the waveform of transmitted and transformed current is distorted, and the action performance of the transformer differential protection is seriously influenced. Aiming at the problem of false operation or failure operation of transformer differential protection caused by TA saturation, the invention provides a transformer differential protection method based on a two-dimensional space reconstructed current characteristic track.
The technical scheme adopted by the invention is as follows:
the transformer differential protection method based on the two-dimensional space reconstruction current characteristic track comprises the following steps:
step 1: under a certain sampling frequency, collecting a current sequence I measured by current transformers TA on two sides of a transformer1And I2In a period data window, the number of sampling points is N,
I1＝{I1(1),I1(2),…,I1(i),…,I1(N)}，I2＝{I2(1),I2(2),…,I2(i),…,I2(N)}，
where i is a count symbol of the number of sampling points, i is 1,2, …, N.
Step 2: two groups of current sequences I collected in the step 11And I2The trajectories are reconstructed in a two-dimensional coordinate system to form a sequence of reconstructed trajectories L, L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N.
And step 3: and calculating the percentage K of the number of the points in the reconstructed track sequence L falling into the first quadrant and the third quadrant of the two-dimensional coordinate system in the total number.
And 4, step 4: the calculated K value and K are comparedsetComparison, wherein KsetFor protection action setting, if K>KsetIf so, judging that the fault is in the area and protecting the action; if K<KsetThen it is judged as an out-of-area fault and protection is locked.
In step 2, taking the ith sampling point of a certain sampling moment as an example, the current sequence I is divided into1Is sampled by1(i) As the abscissa of the two-dimensional space, corresponding to the current sequence I of the ith sampling point at the same time2Is sampled by2(i) As an ordinate of the two-dimensional space, an i-th feature point L (i) of a reconstruction trajectory L is formed in a two-dimensional coordinate system, and then, within one period data window, the number of sampling points is N, and a reconstruction trajectory sequence L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N is formed in the two-dimensional coordinate system.
In step 3, in a period duration data window, the number of sampling points is N, and K is set as the percentage of the number of points of the reconstructed feature track point appearing in the first quadrant and the third quadrant of the two-dimensional space coordinate system to the total number of points in the data window, that is:
in the formula, n13Representing the number of points in the reconstruction track sequence L in the first quadrant and the third quadrant, and N representing the total number of points of the reconstruction track sequence L in the data window;
and forming a K value calculation sequence by extracting secondary current sequences of TA (time advance) on two sides of the transformer in real time and moving a data window along with a real-time reconstructed characteristic track.
A transformer differential protection method based on a two-dimensional space reconstruction current characteristic track reconstructs tracks of current sequences on two sides of a transformer in a two-dimensional space coordinate system, and quadrant characteristics of the reconstructed tracks are utilized to identify fault types.
The invention discloses a transformer differential protection method based on a two-dimensional space reconstruction current characteristic track, which has the following technical effects: 1. the method calculates the percentage of points positioned in the first quadrant and the third quadrant in the reconstructed track to the total number, the influence of the loss of individual data points on the calculation result is very little, and the method has stronger capacity of resisting data loss.
2. The data window is flexible to select, and the quadrant characteristics of the reconstructed track can be calculated by using less data.
3. The invention is used as the criterion for the differential protection of the transformer, can effectively prevent the problem of protection maloperation or refusal operation caused by TA saturation, and has high reliability.
Drawings
Fig. 1(a) is a reconstructed characteristic trace diagram of the transformer according to the present invention when an internal fault occurs.
Fig. 1(b) is a reconstructed characteristic trace diagram of the transformer in the case of an out-of-zone fault according to the present invention.
Fig. 1(c) is a characteristic trace diagram reconstructed when a fault in a transformer area is accompanied by TA saturation according to the present invention.
Fig. 1(d) is a characteristic trace diagram reconstructed when the transformer out-of-area fault is accompanied by TA saturation according to the present invention.
Fig. 2(a) is a waveform diagram of both-side current at the time of an intra-zone fault.
Fig. 2(b) is a graph showing the calculation result of the criterion K value at the time of the intra-area fault according to the present invention.
Fig. 3(a) shows the waveform of the current flowing through both sides in the case of an out-of-range fault.
Fig. 3(b) is a graph showing the calculation result of the criterion K value at the time of the out-of-area fault according to the present invention.
Fig. 4(a) is a waveform diagram of the current at both sides when the intra-zone fault TA is saturated.
Fig. 4(b) is a graph of the calculation result of the criterion K value when the TA in-zone fault is saturated according to the present invention.
Fig. 5(a) is a waveform diagram of the current at both sides when the out-of-band fault TA is saturated.
Fig. 5(b) is a graph of the calculated result of criterion K value when the out-of-range fault TA is saturated according to the present invention.
Fig. 6 is a flowchart of a transformer differential protection algorithm for reconstructing a current characteristic trajectory in a two-dimensional space according to the present invention.
Detailed Description
A transformer differential protection method based on a two-dimensional space reconstruction current characteristic track utilizes phase characteristic difference of currents on two sides of a transformer under different disturbance conditions, reconstructs the currents on the two sides in a two-dimensional space coordinate system to obtain a characteristic track after reconstruction of the currents on the two sides, and utilizes the characteristic difference of a two-dimensional space quadrant of the reconstructed characteristic track under different disturbances to construct a new criterion of transformer differential protection. The new criterion can overcome the problems of the traditional TA saturation refusal during the internal fault of the differential protection area and the TA saturation misoperation during the external fault of the differential protection area.
As shown in fig. 6, the method comprises the following steps:
step 1: under a certain sampling frequency, collecting a current sequence I measured by current transformers TA on two sides of a transformer1And I2，
In a period data window, the number of sampling points is N,
I1＝{I1(1),I1(2),…,I1(i),…,I1(N)}，I2＝{I2(1),I2(2),…,I2(i),…,I2(N)}，
where i is a count symbol of the number of sampling points, i is 1,2, …, N.
Step 2: two groups of current sequences I collected in the step 11And I2Reconstructing a rail in a two-dimensional coordinate systemAnd tracing to form a reconstructed track sequence L.
Taking the ith sampling point of a certain sampling moment as an example, the current sequence I1Is sampled by1(i) As the abscissa of the two-dimensional space, corresponding to the current sequence I of the ith sampling point at the same time2Is sampled by2(i) As an ordinate of the two-dimensional space, an i-th feature point L (i) of the reconstruction trajectory L is formed in the two-dimensional coordinate system, and then a reconstruction trajectory sequence L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N is formed in the two-dimensional coordinate system within one period data window (the number of sampling points is N).
And step 3: and calculating the percentage K of the number of points in the reconstructed track sequence L in the period, which fall into the first quadrant and the third quadrant of the two-dimensional coordinate system, in the total number.
In a period duration data window, the number of sampling points is N, and K is set as the percentage of the number of points of the reconstructed characteristic track point appearing in the first quadrant and the third quadrant of the two-dimensional space coordinate system to the total number of points in the data window. Namely:
in the formula, n13The number of points in the reconstruction track sequence L in the first quadrant and the third quadrant is shown, and N represents the total number of points in the data window of the reconstruction track sequence L. And forming a K value calculation sequence by extracting secondary current sequences of TA (time advance) on two sides of the transformer in real time and moving a data window along with a real-time reconstructed characteristic track.
And 4, step 4: the calculated K value and K are comparedsetComparison of where KsetFor protection action setting, if K>KsetJudging the fault in the area and protecting the action; if K<KsetThen it is judged as an out-of-area fault and protection is locked.
1. Reconstructing a current characteristic track in a two-dimensional space:
when the transformer has an internal fault, the waveform sequences of the currents on the two sides are basically in the same phase; and when an out-of-range fault occurs, the waveform sequences of the currents on the two sides are inverted. Then the in-phase characteristics of the two-sided current waveform sequences at the time of the in-zone fault can be considered as a positive correlation, while the anti-phase characteristics of the two-sided current waveform sequences at the time of the out-of-zone fault can be considered as a negative correlation. Therefore, the sampling value of one side current at a certain moment can be taken as the abscissa of the two-dimensional space, the sampling value of the other side current corresponding to the same moment can be taken as the ordinate of the two-dimensional space, and the correlation of the currents at the two sides can be represented by the reconstructed track characteristics in the two-dimensional space. Namely, when currents on two sides of a fault in a region are in positive correlation, the reconstructed characteristic tracks of the two sides of the fault basically fall in the first quadrant and the third quadrant of a two-dimensional space; when the two sides of the external fault are in negative correlation, the reconstructed characteristic tracks of the two sides of the external fault basically fall into the second quadrant and the fourth quadrant of the two-dimensional space.
2. Reconstructing a current characteristic track in a two-dimensional space under different working conditions:
for the differential protection of the transformer, the protection acts when the differential current is larger than the protection setting value. When the system generates transient disturbance, TA for differential protection is saturated to generate false difference flow, which is easy to cause protection misoperation. The traditional differential protection criterion is easily influenced by the TA state, but the TA saturation has little influence on the phase characteristics of the current waveform, so that the current phase characteristics of the internal fault and the external fault still have great difference, and the difference can be used for judging the fault.
FIG. 1(a) is a reconstructed characteristic trace of a fault in a transformer area; FIG. 1(b) is a reconstructed characteristic trace of a transformer in case of an out-of-zone fault; FIG. 1(c) is a reconstructed characteristic trace of a fault in a transformer area when TA saturates; fig. 1(d) is a reconstructed characteristic trace when the transformer out-of-zone fault is accompanied by TA saturation.
As can be seen from fig. 1(a), 1(b), 1(c), and 1 (d): when the transformer area has a fault, because the currents on the two sides are basically in the same phase, the characteristic track reconstructed into the coordinate system basically appears in the first quadrant and the third quadrant, and the number of points contained in the second quadrant and the fourth quadrant is less; when an out-of-range fault occurs, currents on two sides are basically reversed, and the reconstructed characteristic tracks basically only appear in the second quadrant and the fourth quadrant. When the TA on one side is saturated along with the fault in the area, a small number of reconstructed characteristic points fall into the second quadrant, but the proportion of the deviated characteristic points in a cycle to the total number is low, and the characteristic that most of the points are positioned in the first quadrant and the third quadrant can be still maintained; similarly, when an out-of-band fault is accompanied by the saturation of TA on one side, the current on the saturated TA side is distorted, so that a part of points fall into the first quadrant, but most of characteristic points in one cycle are still positioned in the second and fourth quadrants.
3. The transformer differential protection algorithm for reconstructing the current characteristic track in the two-dimensional space comprises the following steps:
under a certain sampling frequency, collecting a current sequence I measured by current Transformers (TA) at two sides of a transformer1And I2Within a period data window (number of sampling points is N), I1＝{I1(1),I1(2),…,I1(i),…,I1(N)}，I2＝{I2(1),I2(2),…,I2(i),…,I2(N), where i is a count sign of the number of sample points, i is 1,2, …, N. Two sets of current sequences I to be collected1And I2And reconstructing the track in the two-dimensional coordinate system to form a reconstructed track sequence L. Taking the ith sampling point of a certain sampling moment as an example, the current sequence I1Is sampled by1(i) As the abscissa of the two-dimensional space, corresponding to the current sequence I of the ith sampling point at the same time2Is sampled by2(i) As an ordinate of the two-dimensional space, an i-th feature point L (i) of the reconstruction trajectory L is formed in the two-dimensional coordinate system, and then a reconstruction trajectory sequence L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N is formed in the two-dimensional coordinate system within one period data window (the number of sampling points is N). And calculating the percentage K of the number of points in the reconstructed track sequence L in the period, which fall into the first quadrant and the third quadrant of the two-dimensional coordinate system, in the total number. And forming a K value calculation sequence by extracting secondary current sequences of TA (time advance) on two sides of the transformer in real time and moving a data window along with a real-time reconstructed characteristic track.
Through setting reasonable KsetThe fault types can be effectively distinguished and are not influenced by the TA state. By judging K>KsetWhether or not to complete the fault discrimination, wherein KsetAnd setting a protection action value. When K is satisfied>KsetJudging the fault in the area and performing protection action; and if the fault does not meet the requirement, judging that the fault is out of the area, and protecting and locking. The flow of the transformer differential protection algorithm for reconstructing the current characteristic trace in the two-dimensional space is shown in fig. 6.
The waveforms of the currents at the two sides of the transformer in which the internal fault, the external fault, the internal fault TA saturation and the external fault TA saturation occur are shown in fig. 2(a), 3(a), 4(a) and 5(a), and the faults all occur when t is 0.4s, wherein the solid line represents the high-voltage-side current I1The dotted line represents the low-side current I2. The K value of the reconstructed trajectory in the above cases is calculated by the proposed algorithm, and the result is shown in FIGS. 2(b), 3(b), 4(b) and 5(b), where K issetTaking 50 percent.
It can be clearly seen that:
(1) and when an intra-area fault occurs, the calculated K value exceeds a setting value of 50% in 11ms (about half cycle) after the fault occurs, and the protection can be rapidly and reliably operated.
(2) And when an out-of-area fault occurs, the calculated K value is always close to 0 and is far smaller than the action setting value, and the protection can be reliably locked.
(3) When the TA in the area is saturated, although the value of the criterion K is reduced compared with the normal transmission of the TA in the area, the value of the criterion K still exceeds the setting value of 50% 11ms (about half cycle) after the fault occurs, so that the protection can act correctly.
(4) When TA (fault area) of the outside area is saturated, even if the K value is increased when the fault occurs, the K value still does not exceed 50% of the setting value, so that the protection can still be locked reliably.
The transformer differential protection algorithm for reconstructing the current characteristic locus in the two-dimensional space can overcome the problems of false operation caused by TA saturation during the external fault and refusal operation caused by TA saturation during the internal fault of the traditional transformer differential protection.
Claims (2)
1. The transformer differential protection method based on the two-dimensional space reconstruction current characteristic track is characterized by comprising the following steps of:
step 1: under a certain sampling frequency, collecting a current sequence I measured by current transformers TA on two sides of a transformer1And I2In a period data window, the number of sampling points is N,
I1＝{I1(1),I1(2),…,I1(i),…,I1(N)}，I2＝{I2(1),I2(2),…,I2(i),…,I2(N)}，
wherein i is a counting symbol of the number of sampling points, i is 1,2, …, N;
step 2: two groups of current sequences I collected in the step 11And I2Reconstructing the track in a two-dimensional coordinate system to form a reconstruction track sequence L, L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N;
and step 3: calculating the percentage K of the number of points in the reconstructed track sequence L falling into the first quadrant and the third quadrant of the two-dimensional coordinate system in the total number;
and 4, step 4: the calculated K value and K are comparedsetComparison, wherein KsetFor protection action setting, if K>KsetIf so, judging that the fault is in the area and protecting the action; if K<KsetJudging as an out-of-area fault, and protecting and locking;
in step 2, taking the ith sampling point of a certain sampling moment as an example, the current sequence I is divided into1Is sampled by1(i) As the abscissa of the two-dimensional space, corresponding to the current sequence I of the ith sampling point at the same time2Is sampled by2(i) As an ordinate of the two-dimensional space, an i-th feature point L (i) of a reconstruction trajectory L is formed in a two-dimensional coordinate system, and then, within one period data window, the number of sampling points is N, and a reconstruction trajectory sequence L ═ { L (1), L (2), …, L (i), …, L (N) }, i ═ 1,2, …, N is formed in the two-dimensional coordinate system.
2. The transformer differential protection method based on the two-dimensional space reconstruction current characteristic track according to claim 1, is characterized in that: in step 3, in a period duration data window, the number of sampling points is N, and K is set as the percentage of the number of points of the reconstructed feature track point appearing in the first quadrant and the third quadrant of the two-dimensional space coordinate system to the total number of points in the data window, that is:
in the formula, n13Indicates the number of points in the reconstructed trajectory sequence L in the first and third quadrants, NRepresenting the total number of points of the reconstruction track sequence L in the data window; and forming a K value calculation sequence by extracting secondary current sequences of TA (time advance) on two sides of the transformer in real time and moving a data window along with a real-time reconstructed characteristic track.
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