CN110119696B - Current transformer tailing current identification method based on waveform characteristic difference - Google Patents
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Abstract
The method comprises the steps of firstly taking an absolute value of 1/2 cycle before the current is sampled by the transformer in real time, calculating a half-wave integral value, a maximum/minimum value and the maximum deviation thereof in the data window, and judging that the sampled current meets the maximum criterion if the maximum deviation is equal to 0. And then taking every three continuous sampling points as a section, judging the increasing and decreasing performance and the concave-convex performance of the sampling points of the section, and judging that the sampling current meets the criterion of the decreasing-concave performance if the number of the sampling sections which are continuously decreased and have concave characteristics exceeds a set threshold value. Further, comprehensively judging that the maximum criterion or the subtractive-concave criterion is met in the data window, and judging that the current of the current transformer is trailing current when the half-wave integral value is smaller than a set threshold value. The recognition algorithm is simple in principle, double in criterion and high in reliability; meanwhile, the method only needs current amount information, and is easy to realize in engineering application.
Description
Technical Field
The invention discloses a current transformer trailing current identification method based on waveform characteristic differences, and belongs to the field of relay protection of power systems.
Background
When the power system fails, the relay protection device sends a tripping command to the corresponding circuit breaker after confirming the failure, and the circuit breaker breaks away the primary side failure part. Through theoretical analysis and field condition verification, since the inductance element exists in the secondary side current loop of the CT, a small part of electric energy can be stored in the inductance element, when the circuit breaker is opened, the exciting winding, the secondary side winding and the secondary load carried by the CT form a loop at the moment, and the energy stored in the inductance of the current loop is released, so that the secondary side loop of the CT still has an attenuated non-periodic direct current component, namely trailing current, after the circuit breaker is opened on the primary side fault equipment.
When the initial current amplitude of the trailing current is higher and the time constant of the CT secondary side is larger, some protection misjudgment can be caused, such as breaker failure, power failure range is enlarged, and the influence on a power system is larger (Jiang Zijiang, liu Jianyong. Nanyang extra-high voltage breaker failure protection research [ J ]. Power system protection and control, 2015, 43 (12): 117-122).
At present, a waveform zero crossing point is generally detected, a cycle time is required, the identification time is long, in addition, once the non-periodic bias current in the fault current is overlarge, the waveform of the fault current can not be in zero crossing point in a cycle even longer, the zero crossing point phenomenon of the original zero-crossing-point-free trailing current can be caused by a transmission error of a CT device, and finally the waveform zero crossing point criterion is invalid (Wu Yani, jiang Weiping, wang Huawei, etc. the research on the delay zero crossing phenomenon of the short circuit current of the 500kV alternating current circuit breaker [ J ]. Electric network technology, 2013, 37 (01): 195-200.) is finally caused.
In order to eliminate the influence of the tailing current on malfunction protection, it is necessary to identify the tailing current and the fault current effectively, quickly and reliably. Therefore, a fast and reliable identification method is needed to be provided for the identification of the trailing current of the current transformer.
Disclosure of Invention
In order to solve the technical problems, the invention provides a current transformer tailing current identification method based on waveform characteristic difference, which compares the difference between the tailing current and fault current in the time domain on the waveform characteristics, such as: increasing and decreasing characteristics, concave-convex characteristics, the maximum deviation, integral value difference and the like, and constructing a trailing current identification criterion. As the criterion only uses a 1/2 cycle data window, the tail current identification is quick, meanwhile, the singleness of the traditional tail current identification criterion can be overcome, and the reliability of the tail current identification is improved.
The technical scheme adopted by the invention is as follows:
a current transformer tailing current identification method based on waveform characteristic differences is characterized in that the fluctuation characteristic, the concave-convex characteristic, the maximum deviation and the integral value difference of sampling current in 1/2 cycle are judged in real time by analyzing the waveform characteristics of the tailing current of the current transformer, a tailing current dual identification criterion is established, and reliable identification of the tailing current is realized.
The trailing current identification method comprises the steps of determining a decreasingly-concave criterion, a maximum criterion, a half-wave integral value criterion and a comprehensive criterion of a sampling current.
A current transformer tailing current identification method based on waveform characteristic difference sequentially obtains absolute values of current instantaneous values in the first 1/2 power frequency period of current measured by a current transformer in real time after a breaker receives a tripping signal of a protection device, and records the absolute values as i 1 ，i 2 ，...，i N/2 The method comprises the steps of carrying out a first treatment on the surface of the In addition, the instantaneous sequence of currents is differentially calculated, y (j) =i (j+ [ N/48 ]]) -i (j), and denoted y 1 ，y 2 ，...，y N/2 At the same time, searching the maximum value of the differential current as y max ＝max{y 1 ，y 2 ，...，y N/2 And the minimum value is y min ＝min{y 1 ，y 2 ，...，y N/2 }. Where N is the number of sampling points in one power frequency cycle, j=1, 2,... The subtractive-concavity criteria are: i is i 1 ，i 2 ，...，i N/2 For the object, every three continuous sampling points are a section, and the increasing and decreasing performance i (j) of the section sampling points is judged>i(j+1)>i(j+2)>0. Convexity and concavity
Where j=1, 2, (N/2) -2; if the number of sampling segments which are continuously decreasing and are concave exceeds a set threshold value, which is set to (N-6)/6, then the decreasing-concave flag η=1 is determined, otherwise η=0.
The maximum criterion is: i is i 1 ，i 2 ，...，i N/2 For the object, the search current maximum value is i max ＝max{i 1 ，i 2 ，...，i N/2 Minimum value i min ＝min{i 1 ，i 2 ，...，i N/2 Calculating the maximum deviation deltai= |i 1 -i max |+|i N/2 -i min I (I); if Δi=0 is satisfied, it is determined that the maximum criterion is satisfied.
The half-wave integral value criterion is: in y 1 ，y 2 ，...，y N/2 For the object, a half-wave integrated value P, p=y is calculated 1 +y 2 +...+y N/2 The method comprises the steps of carrying out a first treatment on the surface of the If P is satisfied<P set And judging that the half-wave integral value criterion is met. Wherein P is set ＝(y max +y min ) N/4 is half-wave integral threshold value.
The comprehensive criteria are as follows: synthesizing the results of the dishing criterion, the maximum criterion and the half-wave integral value criterion, and if eta=1 or delta i=0 is satisfied, and P is the sum of the values of P and P<P set If so, judging that the current transformer current is trailing current at the moment, and otherwise, judging that the current transformer current is fault current.
A current transformer tailing current identification method based on waveform characteristic differences comprises the following steps:
step 1: and after the power transmission line breaker receives the protection tripping command, preprocessing the current instantaneous value in the first 1/2 power frequency period of the current real-time signal. And obtaining a differential value sequence by adopting sequence differential calculation, and searching the maximum value and the minimum value of the differential calculation value sequence.
Step 2: and calculating the maximum deviation of the sampling current, and constructing a maximum criterion. Searching the calculated value sequence can obtain a calculated maximum value and a calculated minimum value, and setting the first value of the calculated values as a value and the last calculated value as a final value. And then subtracting the absolute value sum of the calculated maximum value and the calculated minimum value from the final value by using the value, and meeting the maximum criterion when the sum value is equal to zero.
Step 3: and determining the increase and decrease and the concave-convex characteristics of the sampling current, and constructing a concave-decrease criterion. For the calculated value sequence, according to the fact that every three sampling points are one section, the increasing and decreasing performance and the concave-convex performance of the sampling points of each section are judged, and if the sampling points are continuously decreased and are concave, the judgment that the concave-decreasing performance criterion is met is judged.
Step 4: and constructing a half-wave integral value criterion. Considering that a larger non-periodic current component may exist in the fault current, the fault current is completely deviated from the zero axis to cause the failure of the maximum criterion in the step 2 when the fault current is severe. And calculating a half-wave integral value according to the differential value sequence, and judging that the criterion of the half-wave integral value is met only when the integral value is smaller than a set threshold value.
Step 5: and (3) integrating the results of the subtractive-dishing criterion, the maximum criterion and the half-wave integral value criterion, if any one of the subtractive-dishing criterion and the maximum criterion is met and the half-wave integral value criterion is met, judging that the current of the current transformer is trailing current at the moment, and otherwise, judging that the current transformer is fault current.
The invention discloses a current transformer trailing current identification method based on waveform characteristic differences, which has the beneficial effects that:
(1): only the current information is measured by using the high-voltage transmission line current transformer, other reference quantities are not needed, the required electrical quantity information is less, and the engineering practicability is strong.
(2): the instantaneous current sampling value is not required to be filtered or processed by complex information, and the anti-interference performance is better through multiple comprehensive criteria and threshold setting thereof.
(3): the invention has double trailing current identification criteria, avoids the defect caused by only monotonicity judgment, and has higher reliability.
Drawings
Fig. 1 is a graph showing the difference between the peak time of the trailing current and the fault current waveforms.
Fig. 2 (a) is a diagram showing the difference between the trailing current and the fault current waveforms (the initial value of the trailing current is positive);
fig. 2 b is a diagram showing the difference between the waveform of the tail current and the waveform of the fault current (the initial value of the tail current is negative).
Fig. 3 is a flow chart of a method for identifying the trailing current of a current transformer based on waveform characteristic differences.
Fig. 4 is a diagram of a simulation verification system.
Fig. 5 (a) is a graph of simulation results when the fault current is not saturated and the circuit breaker opens to produce tailing.
Fig. 5 (b) is a graph of simulation results when a small disturbance occurs in the tail current.
Fig. 5 (c) is a graph of simulation results when the fault current is not saturated and the circuit breaker is not opened.
Fig. 5 (d) is a graph of simulation results when the fault current is saturated and the circuit breaker is not opened.
Fig. 5 (e) is a graph of simulation results when the fault current is completely biased above the zero axis.
Detailed Description
The invention provides a current transformer tailing current identification method based on waveform characteristic differences, which specifically comprises the following steps:
step 1: when the circuit breaker of the transmission line receives the tripping signal of the protection device, the instantaneous value of the current in the first 1/2 power frequency period of the current measured by the current transformer in real time is sequentially calculated to obtain an absolute value, and the absolute value is recorded as a calculated value sequence i 1 ，i 2 ，...，i N/2 The method comprises the steps of carrying out a first treatment on the surface of the In addition, the instantaneous sequence of currents is differentially calculated, y (j) =i (j+ [ N/48 ]]) -i (j) and is noted as a sequence of differential values y 1 ，y 2 ，...，y N/2 At the same time, searching the maximum value of the differential current as y max ＝max{y 1 ，y 2 ，...，y N/2 And the minimum value is y min ＝min{y 1 ，y 2 ，...，y N/2 }. Where N is the number of sampling points in one power frequency cycle, j=1, 2,...
Step 2: and calculating the maximum deviation of the sampling current, and constructing a maximum criterion. Searching the calculated value sequence can obtain a calculated maximum value and a calculated minimum value, and setting the first value of the calculated values as a value and the last calculated value as a final value. In contrast to the variability of the occurrence moments of the maximum and minimum values of the tail current and the fault current in this sampling interval, several typical sampling scenarios are shown in fig. 1.
When the sampling current is the trailing current, the maximum value thereof satisfies i max ＝i(t 1 )、i min ＝i(t 2 )。
When the sampling current is fault current, the sampling value in the sampling interval has positive value and negative value, and the sampling value of trailing current has positive value or negative value, so that the fault current is easy to identify. In special cases, the sampled values of the fault current may also be positive or negative, as shown in FIG. 1 IIIIn this case. The fault current 1 indicates that the fault current deviates to the upper part of the 0 axis due to the positive non-periodic component current, and the maximum value generation time of the sampling point and the first sampling value generation time are different, namely i max ≠i(t 1 ). In the same way, the maximum value generation time of the sampling point and the first sampling value generation time are different from each other after the fault current 2 takes the absolute value. The fault current 3 is a situation that the initial non-periodic component current of the fault current is too large, so that the whole fault current waveform is completely deviated to one side of a zero axis, and the maximum value and the minimum value of the sampling point are generated at the same time and are identical to the trailing current, so that the fault current is required to be distinguished from the trailing current by means of other characteristics of the waveform.
After obtaining the instantaneous current calculation value sequence in 1/2 cycle, the maximum value of the sampling current can be calculated as
i max ＝max{i 1 ，i 2 ，...，i N/2 } (1)
The minimum value of the sampling current is
i min ＝min{i 1 ，i 2 ，...，i N/2 } (2)
When the sampling current is the trailing current, the sampling point can satisfy the maximum deviation according to the characteristics of the trailing current waveform
△i＝|i 1 -i max |+|i N/2 -i min |＝0 (3)
Step 3: and determining the increase and decrease and the concave-convex characteristics of the sampling current, and constructing a concave-decrease criterion. When the non-periodic dc component current in the fault current is insufficient to bring the entire fault waveform above the 0 axis and the initial value of the tail current is positive, the waveform is compared with the fault current waveform as shown in fig. 2 (a). As can be seen from fig. 2 (a), the trailing current decays exponentially and its waveform is concave. The waveform of the fault current is changed in a periodic alternating manner with 1/2 cycle. The fault current is partitioned according to a cycle between two wave troughs according to fig. 2 (a), in the six areas, the section of the waveform conforming to the characteristic of the tailing current is only (5) area, and the section size occupied by the (5) area is not more than 1/4 cycle, so that the tailing current and the fault current can be partitioned according to the characteristic in any 1/4 cycle, the characteristic of the concavity and convexity of the fault waveform is changed for preventing the decay of the current of the non-periodic component of the fault current at an excessively high speed, and meanwhile, the identification section is expanded to 1/2 cycle for ensuring the judging result.
Similarly, when the initial value of the tail current is negative, a comparison chart of the tail current waveform and the fault current waveform thereof is shown in fig. 2 (b). As can be seen from fig. 2 (b), the magnitude of the tail current decays exponentially, and its waveform is convex. After the fault current is divided into six sections, the section conforming to the waveform characteristics of the trailing current is only the section (2), and the section size occupied by the section (2) is not more than 1/4 cycle. Therefore, whether the initial value of the tailing current is positive or negative, the tailing current and the fault current can be distinguished in any 1/2 cycle according to the characteristic.
According to the increase and decrease and the concave-convex characteristics of the trailing current, the sampling value of the trailing current can be obtained within 1/2 cycle and can be satisfied after taking absolute value
Decremental: i (j) > i (j+1) > i (j+2) >0 (4)
The product is concave:
where j=1, 2, (N/2) -2, if the number of sampling segments that continuously decrease and are concave in character exceeds the threshold value, set to (N-6)/6, then the de-concavity flag η=1 is determined, otherwise η=0.
Step 4: calculating a half-wave integral value of the sampled instantaneous current value, and constructing a half-wave integral value comparison criterion. When the sampling current is exactly the fault current 3 case shown in fig. 1, a special criterion needs to be constructed to distinguish from the tail current. Considering that a certain amount of sinusoidal current components exist in the fault current, the fault sampling current after the difference still has a small value, and the tailing current is almost filtered after the difference, based on the rule, the fault current and the tailing current are easily distinguished by comparing the integral value of the differential current sequence.
In y 1 ，y 2 ，...，y N/2 For the object, a half-wave integrated value P is calculated,
P＝y 1 +y 2 +...+y N/2 (6)
if P is satisfied<P set And judging that the half-wave integral value criterion is met. Wherein P is set ＝(y max +y min ) N/4 is half-wave integral threshold value;
step 5: synthesizing the results of the dishing criterion, the maximum criterion and the half-wave integral value criterion, and if eta=1 or delta i=0 is satisfied, and P is the sum of the values of P and P<P set If so, judging that the current transformer current is trailing current at the moment, and otherwise, judging that the current transformer current is fault current. The tail current identification flowchart is shown in fig. 3.
Implementation case:
the result verification of the invention is carried out by constructing a system verification power network shown in fig. 4 in PSCAD/EMTDC simulation software. Assuming that the line L1 has an A-phase ground fault at 0.1s, the breaker B2 receives a tripping command at 0.2s, and the current transformer CT has a secondary side current rating I n For 5a, the ct secondary side time constant is 70ms, and the breaker B2 is operated for 90ms. Experiments are carried out under the condition that the circuit breaker B2 is respectively simulated to be correctly tripped and failed, and simulation results of a trailing current half-wave identification method are shown in table 1.
TABLE 1 simulation results of the tail current invention algorithm recognition method
And (3) combining the simulation waveforms obtained by the 5 groups of experiments with tail current identification results of the traditional method and the inventive algorithm to obtain PSCAD simulation experiment result graphs shown in fig. 5 (a), fig. 5 (b) and fig. 5 (c). Fig. 5 (a), 5 (b), and 5 (c): a represents the fault moment, B represents the breaking moment of the breaker B2, C represents the moment when the traditional method recognizes the trailing current, D represents the moment when the invention algorithm recognizes the trailing current, and the displacement moment of each mark of 5 groups of experiments is shown in table 2.
Table 2 time of each marker displacement in the experiment
As shown in fig. 5 (a), at time a, the line is shorted to the ground at phase a, and at time B, B2 is disconnected, resulting in a tail current. Both the traditional method and the inventive algorithm accurately identify the trailing current within 10ms delay of the device. When the tail current is disturbed, as shown in fig. 5 (b), the conventional method cannot accurately identify the tail current in the case that the sampling current is not filtered, and the algorithm of the invention can identify the tail current in the case of smaller disturbance. When the current information collected by the secondary side is fault current, as shown in fig. 5 (c), (d) and (e), the algorithm of the invention can not misjudge the tail current no matter whether the fault current is saturated or not and whether the fault current is completely deviated from the zero axis or not.
Claims (2)
1. The method for identifying the trailing current of the current transformer based on waveform characteristic difference is characterized by comprising the following steps of: by analyzing the trailing current waveform characteristics of the current transformer, the increase and decrease characteristics, the concave-convex characteristics, the maximum deviation and the integral value difference of the sampling current in 1/2 cycle are judged in real time, a double trailing current identification criterion is established, and the reliable identification of the trailing current is realized;
after the breaker receives the tripping signal of the protection device, the instantaneous value of the current in the first 1/2 power frequency period of the current measured by the current transformer in real time is sequentially calculated to obtain the absolute value and is recorded as i 1 ，i 2 ，...，i N/2 The method comprises the steps of carrying out a first treatment on the surface of the In addition, the instantaneous sequence of currents is differentially calculated, y (j) =i (j+ [ N/48 ]]) -i (j), and denoted y 1 ，y 2 ，...，y N/2 At the same time, searching the maximum value of the differential current as y max ＝max{y 1 ，y 2 ，...，y N/2 And the minimum value is y min ＝min{y 1 ，y 2 ，...，y N/2 -a }; wherein N is the number of sampling points in one power frequency period, j=1, 2,/2;
the algorithm comprises determining a sampling current decreasingly-concave criterion, a maximum criterion, a half-wave integral value criterion and a comprehensive criterion, and specifically comprises the following steps: the subtractive-concavity criteria are: i is i 1 ，i 2 ，...，i N/2 For the object, every three continuous sampling points are a section, and the increasing and decreasing performance i (j) of the section sampling points is judged>i(j+1)>i(j+2)>0. Convexity and concavity
Where j=1, 2, (N/2) -2; if the number of sampling sections which are continuously decreased and are concave exceeds a set threshold value and is set to be (N-6)/6, judging a concave-decreasing character eta=1, otherwise eta=0;
the maximum criterion is: i is i 1 ，i 2 ，...，i N/2 For the object, the search current maximum value is i max ＝max{i 1 ，i 2 ，...，i N/2 Minimum value i min ＝min{i 1 ，i 2 ，...，i N/2 Calculating the maximum deviation deltai= |i 1 -i max |+|i N/2 -i min I (I); if Δi=0 is satisfied, judging that the maximum criterion is satisfied;
the half-wave integral value criterion is: in y 1 ，y 2 ，...，y N/2 For the object, a half-wave integrated value P, p=y is calculated 1 +y 2 +...+y N/2 The method comprises the steps of carrying out a first treatment on the surface of the If P is satisfied<P set Judging that the half-wave integral value criterion is met; wherein P is set ＝(y max +y min ) N/4 is half-wave integral threshold value;
synthesizing the results of the dishing criterion, the maximum criterion and the half-wave integral value criterion, and if eta=1 or delta i=0 is satisfied, and P is the sum of the values of P and P<P set If so, judging that the current transformer current is trailing current at the moment, and otherwise, judging that the current transformer current is fault current.
2. The method for identifying the tail current of the current transformer based on the waveform characteristic difference as claimed in claim 1, comprising the following steps:
step 1: when the power transmission line breaker receives a protection tripping command, preprocessing a current instantaneous value in the first 1/2 power frequency period of a current real-time signal; obtaining a differential value sequence by adopting sequence differential calculation, and searching the maximum value and the minimum value of the differential calculation value sequence;
step 2: calculating the maximum value deviation of the sampling current, constructing the maximum value criterion, searching a calculated value sequence to obtain a calculated maximum value and a calculated minimum value, setting the first value of the calculated values as a value, and setting the last calculated value as a final value; and then subtracting the absolute value sum of the calculated maximum value and the calculated minimum value by using the value, and when the sum value is equal to zero, meeting the maximum criterion;
step 3: determining the increasing and decreasing performance and the concave-convex performance of the sampling current, constructing a concave-decreasing performance criterion, and judging the increasing and decreasing performance and the concave-convex performance of sampling points of each section according to each three sampling points as a section aiming at a calculated value sequence, wherein if the sampling points are continuously decreased and are concave, the concave-decreasing performance criterion is judged to be met;
step 4: constructing a half-wave integral value criterion, and considering that a larger non-periodic current component possibly exists in the fault current, and enabling the fault current to completely deviate above a zero axis when serious, so that the maximum value criterion in the step 2 is invalid; calculating a half-wave integral value according to the differential value sequence, and judging that a half-wave integral value criterion is met only when the integral value is smaller than a set threshold value;
step 5: and (3) integrating the results of the subtractive-dishing criterion, the maximum criterion and the half-wave integral value criterion, if any one of the subtractive-dishing criterion and the maximum criterion is met and the half-wave integral value criterion is met, judging that the current of the current transformer is trailing current at the moment, and otherwise, judging that the current transformer is fault current.
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| CN111614061B (en) * | 2020-05-27 | 2022-06-28 | 国网江苏省电力有限公司 | Locking method for differential protection of series transformer |
| CN111610388A (en) * | 2020-07-16 | 2020-09-01 | 三峡大学 | Current transformer trailing current identification method based on current comprehensive characteristics |
| CN113363953A (en) * | 2021-06-17 | 2021-09-07 | 北京四方继保工程技术有限公司 | Method for inhibiting malfunction of fault-removing differential protection by means of hysteresis characteristics |
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