CN111371074A - CT saturation identification method based on dynamic fuzzy identification - Google Patents
CT saturation identification method based on dynamic fuzzy identification Download PDFInfo
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Abstract
The invention discloses a CT saturation identification method based on dynamic fuzzy identification, which comprises the steps of accurately judging the initial moment of CT saturation in starting judgment, introducing a CT saturation criterion, respectively calculating respective weight values by using a transient-steady-state asynchronous identification principle and a waveform depression harmonic identification principle, voting according to the weight values, judging whether the CT is saturated, and simultaneously combining different working conditions and using various unlocking criteria to realize quick response unlocking. The method is simple and reliable, has good effect, and can ensure the bus protection device to reliably act.
Description
Technical Field
The invention relates to a method for identifying CT saturation depth, and belongs to the technical field of power system relay protection.
Background
The current input of the relay protection device is usually taken from a Current Transformer (CT) near the circuit breaker, so accurate transmission of the CT is a reliable guarantee of correct operation of the protection device. Moreover, bus protection maloperation is likely to cause serious accidents of total station power failure. In order to ensure the stable operation of the power system, reduce the malfunction of the microcomputer type bus protection device and improve the reliability of the protection device, the CT saturation criterion must be ensured to be reliable.
At present, in order to identify CT saturation, there are generally a synchronous identification method, an additional braking region method, a time difference method, a dynamic analog magnetic flux method, a waveform symmetry method, a harmonic braking method, and the like. Some methods need relatively complex coefficients, some methods are inconvenient to implement, some methods have certain limitations in use, and a simple, practical, high-reliability and good-effect CT saturation identification scheme cannot be provided.
Disclosure of Invention
The invention provides a CT saturation identification method based on dynamic fuzzy identification, which aims to: the CT saturation identification scheme is simple, practical, high in reliability and good in effect, and ensures that the bus protection device reliably acts.
The technical scheme of the invention is as follows:
a CT saturation identification method based on dynamic fuzzy identification is characterized in that: comprehensively judging whether the CT saturation is caused by an out-of-area fault by using a transient and steady state asynchronous identification method and a waveform sag harmonic identification method; and judging whether the unlocking condition is met or not according to the unlocking criterion, and unlocking according to the judgment result.
As a further improvement of the method, the method comprises the following specific steps:
acquiring original sampling current signals of each branch and voltage signals of each bus section;
step two, identifying faults by using a sum current sampling value mutation element and a difference current out-of-limit element; if the fault starting moment is identified through the sum current sampling value abrupt variable element, turning to the step three; if the fault is identified through the differential flow out-of-limit element, the step four is carried out;
step three, transient state identification is carried out by utilizing a T/4 data window, if CT saturation caused by an external fault is detected, the external fault mark is set to be 1, then the step four is carried out, and if not, the method is not locked and is ended;
step four, judging unlocking criteria, if the unlocking criteria are met, releasing the lock and ending, otherwise, turning to step five;
step five, introducing steady-state identification and waveform depression harmonic identification, respectively calculating the weight values of the steady-state identification and the waveform depression harmonic identification, voting according to the weight values, and further judging whether the CT saturation is caused by an out-of-area fault; if the CT saturation caused by the external fault is judged, firstly setting the external fault mark as 1, locking two cycles, and then returning to the fourth step; otherwise, directly turning to the step four.
As a further improvement of the method: setting a sampling period as T, and counting the number N of sampling points in each sampling period;
the specific method of transient recognition in step three is as follows: and judging whether each sampling point in the T/4 data window meets the following formula or not by utilizing the T/4 data window:
in the formula, idn is the nth differential current sampling point value, Idset is the fixed value of the differential protection starting current, ijFor each jth branch current sampling value, m is the total number of branches, and ksat1 is a first saturation identification braking coefficient;
and judging whether the CT saturation caused by the out-of-area fault is caused according to whether the number of the sampling points continuously meeting the formula in the T/4 data window exceeds a preset threshold value.
As a further improvement of the method: the unlocking criterion of the step four is three items, and the locking can be released when any one item is met:
(1) criterion one
And automatically releasing CT saturation blocking if the sampling values in 1.25 continuous sampling periods meet the following unlocking conditions:
in the above formula, Idn is a differential current power frequency full-period effective value, Irn is a sum current power frequency full-period effective value, ksat2 is a second saturation identification braking coefficient, and Idset is a differential protection starting current fixed value;
(2) criterion two
On the basis of the first criterion, a saturation recognition braking coefficient ksat3 larger than ksat2 is used for replacing ksat2, the continuous time meeting the condition is set to be a numerical value smaller than 1.25 sampling periods, and other conditions are unchanged;
(3) criterion three
And if the sampling values in the continuous 0.5 sampling periods meet the following unlocking conditions, automatically releasing the saturation latch:
in the above formula, Id1 is a differential current power frequency fundamental wave quantity, Id2 is a differential current second harmonic wave quantity, and Id3 is a differential current third harmonic wave quantity; k2 and k3 are predetermined thresholds for harmonic content.
As a further improvement of the method: the specific method for steady state identification in the step five is as follows: and returning to the fault or disturbance after the initial time T, circularly using the T data window, and judging whether each sampling point in each T data window meets the following formula:
and setting the weight value of the transient and steady asynchronous identification principle as A according to the number of the sampling points which continuously meet the formula in the T data window, wherein the value range of the weight value of A is 0-1, and the weight value A is larger as the number is larger.
As a further improvement of the method: the specific method for identifying the waveform depression harmonic wave in the fifth step comprises the following steps: and circularly using the T data windows, and performing the following calculation according to the data in each T data window:
in the above formula, Id1 is a differential current power frequency fundamental wave quantity, Id2 is a differential current second harmonic wave quantity, and Id3 is a differential current third harmonic wave quantity;
and setting the weight value of the waveform depression harmonic recognition principle as B, taking the value of B according to the sizes of B1 and B2, wherein the value range of the weight value of B is 0-1, and the larger the values of B1 and B2 are, the larger the weight value of B is.
As a further improvement of the method: the "voting by weight value" in the fifth step means:
calculating a comprehensive weight value A + B of steady-state identification and waveform depression harmonic identification; setting a threshold value C1 of a total confidence weighted value, a threshold value C2 of an absolute confidence weighted value of steady asynchronous recognition and a threshold value C3 of an absolute confidence weighted value of waveform depression harmonic recognition;
when any one of the following three conditions is satisfied: and A + B is more than or equal to C1, or A is more than or equal to C2, or B is more than or equal to C3, and CT saturation caused by an out-of-range fault is judged.
Compared with the prior art, the invention has the following positive effects: the method respectively calculates respective weighted values by using a transient-steady state asynchronous recognition principle and a waveform depression harmonic recognition principle, and then compares the weighted values with respective threshold values and the threshold values of the weighted values and the threshold values, thereby judging whether the CT is saturated, ensuring that a protection device can rapidly act when an external fault is converted into an internal fault, and simultaneously combining different working conditions, using various unlocking criteria, rapidly responding to unlocking, opening protection action conditions and timely removing the internal fault. The method is simple and reliable, has good effect, and can ensure the bus protection device to reliably act.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings:
referring to fig. 1, a CT saturation recognition method based on the dynamic fuzzy recognition principle includes the following steps:
the method comprises the steps of firstly, collecting original sampling current signals of each branch and voltage signals of each bus section at regular intervals of N points per cycle, and using the sampling frequency of the sampling data as basic sampling data, wherein the sampling frequency is N × fe, fe is the rated frequency of a power system, N is the number of sampling points per cycle of the rated frequency, and T is the sampling period.
In this embodiment, the setting device performs sampling calculation at 40 points per cycle, and in order to ensure accurate capture of the start time, the start determination is performed during sampling interruption, and the start counter dw87BPickCnt is set.
And step two, in the initial stage of the fault or disturbance, identifying the fault by using a sum current sampling value mutation element and a difference current out-of-limit element. If the fault starting moment is identified through the sum current sampling value abrupt variable element, turning to the step three; if a fault is identified by the "differential flow off-limit element", then go to step four.
Step three, transient recognition is carried out: and (3) detecting the magnitude of the differential current, the delay condition of the current and the CT saturation blocking ratio characteristic by using the sampling value of a T/4 data window by taking the starting time of the fault as a base point until the end of the first T/4 period (namely when dw87BPickCnt is less than or equal to 10), obtaining the point-by-point distribution rate of the T/4 data window, and identifying whether the initial stage is the CT saturation caused by an out-of-range fault.
The specific judgment method of the T/4 data window is as follows: judging whether each sampling point in the T/4 data window respectively meets the following formula:
in the formula, idn is the nth differential current sampling point value, Idset is the fixed value of the differential protection starting current, ijFor each jth branch current sample, m is the total number of branches and ksat1 is the first saturation identification braking coefficient.
Setting the weight value of the temporary steady state asynchronous recognition principle as A, and taking the value of A according to the number of continuous sampling points meeting the judgment formula, wherein the specific strategy is as follows:
n∈0，A＝0％
n∈1，A＝10％
n∈2，A＝30％
n∈3，A＝40％
n∈4，A＝60％
n∈5～6，A＝70％
n∈7，A＝80％
n∈8，A＝90％
n∈9～10，A＝100％。
taking "n ∈ 8, a is 90%" as an example, the meaning is that if there are 8 consecutive sampling points in the T/4 data window satisfying the judgment formula of the T/4 data window, a is 90%.
The threshold value C2 of the absolute confidence weight value of the transient steady-state asynchronous recognition principle is set to 0.6. And when A is larger than or equal to C2, judging that the CT caused by the out-of-range fault is saturated, setting the out-of-range fault mark as 1 and the inherent delay of 2T, and then turning to the fourth step.
If A < C2, CT saturation due to internal fault is identified, the out-of-range fault flag is still 0, no lock is applied, and the method ends.
When a fault occurs in the bus generating area, the differential flow is actually reflected and generated synchronously, and the braking coefficient of the differential flow immediately enters the action area, so that the CT saturation identification condition cannot be met.
And step four, when dw87BPickCnt is larger than 40, after CT saturation confirmation is caused by the outside fault, and when the outside fault is converted into the inside fault, unlocking is quickly responded by adopting various criteria according to different working conditions, the protection action condition is opened, and the inside fault is timely removed.
Judging whether any one of the following unlocking criteria is met: and if the unlocking criterion is met, unlocking, and then finishing the method, otherwise, turning to the fifth step.
The unlocking criteria include:
(1) criterion one
After the criteria identify that an out-of-area fault causes CT saturation, a high value differential stream will be generated immediately upon the conversion of the fault to an in-area fault. If the sampling values in the continuous 1.25T all meet the following unlocking conditions, the CT saturation blocking of the criterion is automatically released:
in the above formula, Idn is a difference current power frequency full-period effective value, Irn is a sum current power frequency full-period effective value, and ksat2 is a second saturation identification braking coefficient.
The validity period of the criterion is after T delay for fault starting, and when the condition that CT saturation is caused by an out-of-area fault is identified.
(2) Criterion two
And taking ksat3 as a saturation identification braking coefficient larger than ksat2 on the basis of the first criterion, and taking the continuous time meeting the condition to be smaller than 1.25T, wherein other conditions are unchanged.
(3) Criterion three
If the sampling values within the continuous 0.5T all meet the following unlocking conditions, the CT saturation blocking of the criterion is automatically released:
in the above formula, Id1 is the differential current power frequency fundamental wave quantity, Id2 is the differential current second harmonic wave quantity, Id3 is the differential current third harmonic wave quantity, and k2 and k3 are harmonic content thresholds.
Step five, when dw87BPickCnt is larger than 80, introducing steady state identification and waveform depression harmonic identification, voting through weight values, and further judging whether CT saturation caused by an out-of-area fault is caused:
(1) and (3) steady state identification: and after the starting time T, returning to the fault or disturbance, detecting the magnitude of the differential current, the delay condition of the current and the CT saturation blocking ratio characteristic by circularly utilizing the sampling value of the T data window to obtain the point-by-point distribution rate of the T data window, and identifying whether the CT saturation is caused by the out-of-area fault or not after the first T data window.
And setting a certain linear transmission and transformation area in the T data window, wherein the CT saturation in the area can be quickly recovered, and identifying whether the CT saturation is caused by an out-of-area fault or not according to the linear transmission and transformation area, wherein the inherent delay is 2T.
The specific judgment method of the T data window is to judge whether each sampling point in the T data window meets the following formula:
setting the weight value of the temporary steady state asynchronous recognition principle as A, and taking the value of A according to the number of continuous sampling points meeting the judgment formula, wherein the specific strategy is as follows:
n∈0，A＝0％
n∈1～3，A＝10％
n∈4～6，A＝30％
n∈7～9，A＝40％
n∈10～11，A＝50％
n∈11，A＝55％
n∈12，A＝60％
n∈13～14，A＝65％
n∈15～16，A＝70％
n∈17～20，A＝80％
n∈20～30，A＝90％
n∈30～40，A＝100％。
taking "n ∈ 12, a is 60%" as an example, the meaning is that if there are 12 consecutive samples in the T data window satisfying the judgment formula of the T data window, a is 60%.
(2) Waveform depression harmonic identification: although the CT saturation waveform caused by the fault is severely distorted, there is a certain significant characteristic that the current can still be correctly transmitted at the moment of the starting transient and near the zero crossing point of each cycle, so that the differential current also has a waveform dent or defect characteristic. Even if CT saturation occurs in the internal fault, the difference flow caused by the internal fault is large, the harmonic content of the internal fault is not too large, and the external fault CT saturation identification criterion is not met. The waveform depression harmonic identification principle is that by utilizing the remarkable characteristics, a second harmonic component and a third harmonic component in the differential flow are analyzed, and when the ratio of the second harmonic component to the power frequency fundamental wave quantity is respectively larger than a preset value, the continuity identification of the waveform is assisted, so that whether the CT saturation caused by the external fault is identified or not can be identified.
And circularly using the T data windows, and performing the following calculation according to the data in each T data window:
in the above formula, Id1 is a differential power frequency fundamental wave quantity, Id2 is a differential second harmonic quantity, and Id3 is a differential third harmonic quantity. And starting to calculate the harmonic wave after the current mutation amount starts one cycle, and calculating the second harmonic wave and the third harmonic wave by adopting a Fourier algorithm. The data window of the algorithm of the present principle is still T, and its inherent delay is 2T.
The values of the ratio coefficients k2 and k3 were set to 0.2 and 0.1, respectively.
Setting the weight value of the waveform depression harmonic recognition principle as B, and taking the B value according to the relation between B1 and B2 and the ratio coefficients k2 and k3, wherein the concrete strategy is as follows:
B1∈k2×0～10％、B2∈k3×0～10％，B＝0％
B1∈k2×10％～50％、B2∈k3×10％～50％，B＝30％
B1∈k2×50％～70％、B2∈k3×50％～70％，B＝40％
B1∈k2×80％～90％、B2∈k3×80％～90％，B＝50％
B1∈k2×90％～110％、B2∈k3×90％～110％，B＝60％
B1∈k2×110％～140％、B2∈k3×110％～140％，B＝70％
B1∈k2×140％～180％、B2∈k3×140％～180％，B＝80％
B1∈k2×180％～220％、B2∈k3×180％～220％，B＝90％
B1∈k2×220％～、B2∈k3×220％～，B＝100％。
for example, when B1 ∈ k2 × 90% to 110%, B2 ∈ k3 × 90% to 110%, and B is 60% ", B1 and B2 are in the corresponding ranges, respectively, B is 60%.
(3) Calculating a comprehensive weight value of steady-state identification and waveform depression harmonic identification: and A + B.
The threshold value C1 of the total confidence level weight value is set to 1, the threshold value C2 of the absolute confidence level weight value of the transient-steady asynchronous recognition principle is set to 0.6, and the threshold value C3 of the absolute confidence level weight value of the waveform notch harmonic recognition principle is set to 0.6. When any one of the following three conditions is satisfied: a + B is larger than or equal to C1, or A is larger than or equal to C2, or B is larger than or equal to C3, CT saturation caused by the external fault is judged, the external fault mark is set to be 1, two cycles are locked, and then the step four is returned; otherwise, directly turning to the step four.
Claims (7)
1. A CT saturation identification method based on dynamic fuzzy identification is characterized in that: comprehensively judging whether the CT saturation is caused by an out-of-area fault by using a transient and steady state asynchronous identification method and a waveform sag harmonic identification method; and judging whether the unlocking condition is met or not according to the unlocking criterion, and unlocking according to the judgment result.
2. The CT saturation identification method based on the dynamic fuzzy identification as claimed in claim 1, characterized by comprising the following steps:
acquiring original sampling current signals of each branch and voltage signals of each bus section;
step two, identifying faults by using a sum current sampling value mutation element and a difference current out-of-limit element; if the fault starting moment is identified through the sum current sampling value abrupt variable element, turning to the step three; if the fault is identified through the differential flow out-of-limit element, the step four is carried out;
step three, transient state identification is carried out by utilizing a T/4 data window, if CT saturation caused by an external fault is detected, the external fault mark is set to be 1, then the step four is carried out, and if not, the method is not locked and is ended;
step four, judging unlocking criteria, if the unlocking criteria are met, releasing the lock and ending, otherwise, turning to step five;
step five, introducing steady-state identification and waveform depression harmonic identification, respectively calculating the weight values of the steady-state identification and the waveform depression harmonic identification, voting according to the weight values, and further judging whether the CT saturation is caused by an out-of-area fault; if the CT saturation caused by the external fault is judged, firstly setting the external fault mark as 1, locking two cycles, and then returning to the fourth step; otherwise, directly turning to the step four.
3. The CT saturation identification method based on the dynamic fuzzy identification as claimed in claim 2, characterized in that: setting a sampling period as T, and counting the number N of sampling points in each sampling period;
the specific method of transient recognition in step three is as follows: and judging whether each sampling point in the T/4 data window meets the following formula or not by utilizing the T/4 data window:
in the formula, idn is the nth differential current sampling point value, Idset is the fixed value of the differential protection starting current, ijFor each jth branch current sampling value, m is the total number of branches, and ksat1 is a first saturation identification braking coefficient;
and judging whether the CT saturation caused by the out-of-area fault is caused according to whether the number of the sampling points continuously meeting the formula in the T/4 data window exceeds a preset threshold value.
4. The CT saturation identification method based on the dynamic fuzzy identification as claimed in claim 2, characterized in that: the unlocking criterion of the step four is three items, and the locking can be released when any one item is met:
(1) criterion one
And automatically releasing CT saturation blocking if the sampling values in 1.25 continuous sampling periods meet the following unlocking conditions:
in the above formula, Idn is a differential current power frequency full-period effective value, Irn is a sum current power frequency full-period effective value, ksat2 is a second saturation identification braking coefficient, and Idset is a differential protection starting current fixed value;
(2) criterion two
On the basis of the first criterion, a saturation recognition braking coefficient ksat3 larger than ksat2 is used for replacing ksat2, the continuous time meeting the condition is set to be a numerical value smaller than 1.25 sampling periods, and other conditions are unchanged;
(3) criterion three
And if the sampling values in the continuous 0.5 sampling periods meet the following unlocking conditions, automatically releasing the saturation latch:
in the above formula, Id1 is a differential current power frequency fundamental wave quantity, Id2 is a differential current second harmonic wave quantity, and Id3 is a differential current third harmonic wave quantity; k2 and k3 are predetermined thresholds for harmonic content.
5. The CT saturation identification method based on the dynamic fuzzy identification as claimed in claim 3, characterized in that: the specific method for steady state identification in the step five is as follows: and returning to the fault or disturbance after the initial time T, circularly using the T data window, and judging whether each sampling point in each T data window meets the following formula:
and setting the weight value of the transient and steady asynchronous identification principle as A according to the number of the sampling points which continuously meet the formula in the T data window, wherein the value range of the weight value of A is 0-1, and the weight value A is larger as the number is larger.
6. The CT saturation identification method based on dynamic fuzzy identification as claimed in claim 5, characterized in that: the specific method for identifying the waveform depression harmonic wave in the fifth step comprises the following steps: and circularly using the T data windows, and performing the following calculation according to the data in each T data window:
in the above formula, Id1 is a differential current power frequency fundamental wave quantity, Id2 is a differential current second harmonic wave quantity, and Id3 is a differential current third harmonic wave quantity;
and setting the weight value of the waveform depression harmonic recognition principle as B, taking the value of B according to the sizes of B1 and B2, wherein the value range of the weight value of B is 0-1, and the larger the values of B1 and B2 are, the larger the weight value of B is.
7. The CT saturation identification method based on dynamic fuzzy identification as claimed in claim 6, characterized in that: the "voting by weight value" in the fifth step means:
calculating a comprehensive weight value A + B of steady-state identification and waveform depression harmonic identification; setting a threshold value C1 of a total confidence weighted value, a threshold value C2 of an absolute confidence weighted value of steady asynchronous recognition and a threshold value C3 of an absolute confidence weighted value of waveform depression harmonic recognition;
when any one of the following three conditions is satisfied: and A + B is more than or equal to C1, or A is more than or equal to C2, or B is more than or equal to C3, and CT saturation caused by an out-of-range fault is judged.
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| CN104466903A (en) * | 2014-11-26 | 2015-03-25 | 济南大学 | Current transformer saturation recognition method for differential protection |
| US20160006240A1 (en) * | 2013-04-07 | 2016-01-07 | Youyi Li | A method for detecting fault and current differential protection system thereof |
| CN109149518A (en) * | 2018-07-31 | 2019-01-04 | 中国电力科学研究院有限公司 | A kind of method and system based on sampled value Sudden Changing Rate identification CT saturation |
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| US20160006240A1 (en) * | 2013-04-07 | 2016-01-07 | Youyi Li | A method for detecting fault and current differential protection system thereof |
| CN103323698A (en) * | 2013-05-24 | 2013-09-25 | 西安交通大学 | Novel current transformer saturation identification method |
| CN104466903A (en) * | 2014-11-26 | 2015-03-25 | 济南大学 | Current transformer saturation recognition method for differential protection |
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