CN111641196A - High-voltage direct-current line pilot protection method based on branch current characteristics - Google Patents
High-voltage direct-current line pilot protection method based on branch current characteristics Download PDFInfo
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- H—ELECTRICITY
- 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
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
Abstract
The invention relates to a high-voltage direct current line pilot protection method based on branch current characteristics, which comprises the following steps of: step 1: collecting electric quantity data of a detection point; step 2: judging whether the line meets pilot protection starting criteria or not according to the data collected in the step 1, if so, executing the step 3, otherwise, returning to the step 1; and step 3: extracting harmonic current; and 4, step 4: judging whether the line meets the intra-area fault criterion, if so, judging that the line has an intra-area fault, then executing the step 5, otherwise, judging that the line has an extra-area fault, and protecting and resetting the line; and 5: calculating a positive and negative electrode current waveform slope ratio coefficient P, and executing a pole selection criterion to obtain a fault pole; step 6: and executing protection action on the fault pole to complete the pilot protection of the line. Compared with the prior art, the method has the advantages of reliability, economy, quick action, high accuracy and the like.
Description
Technical Field
The invention relates to the technical field of high-voltage direct-current transmission line protection, in particular to a high-voltage direct-current line pilot protection method based on branch current characteristics.
Background
At present, a high-voltage direct-current transmission system generally takes traveling wave protection as main protection, the protection action is fast, but the anti-interference capability is poor under the condition of high grounding impedance. The pilot protection is used as a backup protection, so that high-resistance faults can be effectively identified and the full length of the power transmission line is protected. However, under the influence of distributed capacitance of an out-of-area fault, the pilot protection delay reaches the second level, and the requirement on the quick action of relay protection is difficult to guarantee.
The method for improving the reliability of pilot protection in the prior art comprises three methods of using a wavelet transformation principle, an inverse wave amplitude value and a direct current filter impedance characteristic, and the method has the following defects: the reliability of the high-voltage direct-current transmission line can be improved by combining the wavelet transformation principle with the voltage and current sudden change phase angle difference of the S transformation structure, but the calculation is too complex, and the practical engineering use value is not large; the internal and external faults of the region can be distinguished by utilizing the integral of the amplitude of the reverse traveling wave, the protection action speed can be improved, but the transmission span is too long, and the reverse traveling wave attenuation is difficult to ensure that the protection range covers the full length; the fault area can be quickly identified by using the impedance frequency characteristic of the direct current filter, but the extraction of the characteristic value is very difficult. The three methods either need to be subjected to complex wavelet transformation or need to be specially invested in a large number of special detection instruments, and the reliability, the economy and the quick-acting performance of the methods cannot be considered at the same time. For example, chinese patent CN105098738B discloses a pilot protection method for an hvdc transmission line based on S transformation, which identifies faults inside and outside the area by transforming a phase angle difference based on a voltage and current break variable S. Although the reliability of the power transmission line is improved, the method needs to calculate the phase angle difference of the sudden change, has large calculation amount, more complex calculation, longer time delay and slower protection speed, and is difficult to ensure the requirement of the pilot protection speed.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a pilot protection method for a high-voltage direct-current line based on branch current characteristics, which has the advantages of reliability, economy, quick action and high accuracy.
The purpose of the invention can be realized by the following technical scheme:
a pilot protection method for a high-voltage direct-current line based on branch current characteristics is a program embedded in a computer and comprises the following steps:
step 1: collecting electric quantity data of a detection point;
step 2: judging whether the line meets pilot protection starting criteria or not according to the data collected in the step 1, if so, executing the step 3, otherwise, returning to the step 1;
and step 3: extracting harmonic current;
and 4, step 4: judging whether the line meets the intra-area fault criterion, if so, judging that the line has an intra-area fault, then executing the step 5, otherwise, judging that the line has an extra-area fault, and protecting and resetting the line;
and 5: calculating a positive and negative electrode current waveform slope ratio coefficient P, and executing a pole selection criterion to obtain a fault pole;
step 6: and executing protection action on the fault pole to complete the pilot protection of the line.
Preferably, the starting criterion in step 2 is specifically:
D＝max(DM，DN)＞Dset
wherein D isMAnd DNRespectively averaging the slope of the detected current waveform at a rectification side detection point M and an inversion side detection point N; n issThe number of sampling points in a sampling time window is shown; i isM(i) And IN(i) Respectively obtaining the current value of the rectification side and the current value of the inversion side at the ith sampling point; dsetIs a preset starting threshold value.
Preferably, the starting criterion in step 2 is subjected to anti-shake processing for preventing disturbance caused by lightning stroke.
More preferably, the anti-shake treatment specifically comprises: and judging the starting criterion once every set time, if the judging results of two adjacent times are different, judging that the current judging result is invalid, returning to the step 1, and executing the step 3 until the line faults are judged in the two adjacent times.
More preferably, the set time is 3 milliseconds.
Preferably, the step 3 specifically comprises: harmonic currents of 600Hz are extracted from the current information of the line by S-conversion.
Preferably, the in-zone fault criterion is specifically:
wherein n issThe number of sampling points in a sampling time window is shown; i isr(i) A current value corresponding to the ith sampling point of the smoothing reactance branch at the rectifying side; i isi(i) The current value corresponding to the ith sampling point of the inverter side smoothing reactance branch circuit is obtained; j. the design is a squaresetA threshold is determined for the intra-zone and the inter-zone faults.
More preferably, the in-zone and out-zone fault discrimination threshold JsetAnd the value is smaller than the minimum value of the smoothing reactance branch current of the rectifying side and the smoothing reactance branch current of the inverting side in fault.
Preferably, the method for calculating the slope proportionality coefficient P of the positive and negative electrode current waveforms in step 5 comprises:
wherein n issThe number of sampling points in a sampling time window is shown; i isMp(i) The current value corresponding to the ith sampling point of the positive electrode at the rectifying side is obtained; i isMn(i) And the current value corresponding to the ith sampling point of the negative electrode on the rectifying side is obtained.
Preferably, the pole selection criterion is specifically:
wherein P is the positive and negative electrode current waveform slope proportionality coefficientset1And Pset2Two preset thresholds.
Compared with the prior art, the invention has the following advantages:
firstly, considering reliability, economy and quick action: the pilot protection method only needs to collect the electric quantity of a detection point on a system circuit and the current data of a harmonic reactance branch circuit, and can accurately judge a fault occurrence area and a fault pole through various criteria by means of S conversion calculation of current.
Secondly, the accuracy is high: the pilot protection method of the invention sets an anti-shake processing flow in order to prevent disturbance caused by lightning stroke, and by setting the anti-shake processing flow, misjudgment of line faults is greatly reduced, and accuracy is improved.
Drawings
FIG. 1 is a schematic flow diagram of a pilot protection method of the present invention;
FIG. 2 is an equivalent circuit diagram of an intra-area fault network according to an embodiment of the present invention;
FIG. 3 is an equivalent circuit diagram of an out-of-range fault network in an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a bipolar hvdc transmission system in accordance with an embodiment of the present invention;
FIG. 5 is a value diagram of a fault criterion J in a region before and after a fault occurs in an embodiment of the present invention;
fig. 6 is a schematic value diagram of P when a fault occurs in the positive electrode region in the embodiment of the present invention;
fig. 7 is a schematic value diagram of P when a fault occurs in the negative electrode region in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
A pilot protection method for a high-voltage direct current line based on branch current characteristics is a program embedded in a computer, and the flow schematic of the method is shown in figure 1, and comprises the following steps:
step 1: collecting electric quantity data of a detection point and current data of a smoothing reactance branch;
step 2: judging whether the line meets pilot protection starting criteria or not according to the data collected in the step 1, if so, executing the step 3, otherwise, returning to the step 1;
the structure of the bipolar hvdc transmission system is shown in fig. 4, when the line is operating normally, the currents I at the points M and N of detection of the electrical quantitiesMAnd INAll the current waveforms have sharp rise or fall, and at the moment, the pilot protection starting criterion can be formed only by detecting the average value of the slopes of the current waveforms, specifically:
D＝max(DM，DN)＞Dset
wherein D isMAnd DNRespectively averaging the slope of the detected current waveform at a rectification side detection point M and an inversion side detection point N; n issThe number of sampling points in a sampling time window is shown; i isM(i) And IN(i) Respectively obtaining the current value of the rectification side and the current value of the inversion side at the ith sampling point; dsetFor the preset starting threshold, it is generally chosen according to the impedance characteristics of the line, Dset＝1.6×106。
In order to prevent the disturbance caused by the lightning strike, the present embodiment further introduces an anti-shake process, specifically: and judging the starting criterion once every set time, if the judging results of two adjacent times are different, judging that the current judging result is invalid, returning to the step 1, and executing the step 3 until the line faults are judged in the two adjacent times. The set time in this embodiment is selected to be 3 milliseconds.
And step 3: extracting harmonic current, specifically: harmonic currents of 600Hz are extracted from the current information of the line by S-conversion. The S transformation method used in this embodiment is a mature technique, so the step of S transformation is not described in detail.
And 4, step 4: judging whether the line meets the intra-area fault criterion, if so, judging that the line has an intra-area fault, then executing the step 5, otherwise, judging that the line has an extra-area fault, and protecting and resetting the line;
firstly, analyzing the internal and external fault characteristics of a high-voltage direct-current power transmission area: assuming that the line has an intra-area fault, an equivalent circuit diagram as shown in fig. 2 is obtained according to the superposition principle. As can be seen from the figure, the current I of the smoothing reactance branch at the rectifying side when the zone fault occursrAnd the inversion side current IiComprises the following steps:
wherein Z is1bImpedance of the direct current filtering link; zmIs the inverter impedance; zpIs the smoothing reactor impedance; i isMA detection value of a current detection point at the rectifying side; i isNAnd detecting the point detection value for the inversion current.
In the DC filtering link, Z is at different frequencies1bVery small, especially at 600Hz Z1bClose to 0, so IrAnd IiAre all close to 0. Therefore, when an in-zone fault occurs, the DC filter branch approaches a short-circuit state, IrAnd IiThe branch is provided with almost no harmonic current.
When an out-of-range fault occurs, its equivalent circuit diagram is shown in fig. 3. The smoothing reactance branch current I of the direct current side and the inversion side can be known according to the shunt relationrComprises the following steps:
wherein, UMIs a measured value of a voltage measuring point on the rectifying side; rfIs the transition resistance. According to different grounding points, the transition resistance RfThe value is about 5-500 omega; zmAbout 1000 omega, so that the smoothing reactance branch current IrMuch greater than 0, clearly distinguishes the intra-zone fault current criterion.
In the embodiment, the current magnitude of a smoothing reactance branch close to an inverter or a rectification branch in a direct current filtering link in the high-voltage direct current transmission line is used as a criterion for distinguishing the internal fault from the external fault in the area.
Calculation of IrAnd IiAverage over time:
wherein n issThe number of sampling points in a sampling time window is shown; i isr(i) A current value corresponding to the ith sampling point of the smoothing reactance branch at the rectifying side; i isi(i) The current value corresponding to the ith sampling point of the smoothing reactance branch at the inversion side is obtained.
According to the characteristics of the flat wave reactance branch circuit when the fault occurs inside and outside the current generation area, when the fault occurs inside the area, the current quantity of the flat wave reactance branch circuit is very small and close to 0, so that a threshold value J is set by considering the impedance of the branch circuit and the engineering error marginset. When an in-zone fault occurs, the amount of current is less than the threshold, and when an out-of-zone fault occurs, the amount of current is much greater than this certain value. The start-up criteria are thus specifically set to:
threshold JsetThe value of the direct current filter impedance and the engineering margin of a specific line are integrated, and the value of the direct current filter impedance and the engineering margin is required to be smaller than the minimum value of the smoothing reactance branch current of the rectifying side and the smoothing reactance branch current of the inverting side during fault. In the embodiment, one fifth of the current values of the smoothing reactance branch circuits on the rectifying side and the inverting side at the fault moment is selected to ensure reliable judgment, and at the moment, JsetThe calculation method comprises the following steps:
extracting harmonic current component of 600Hz, selecting 400mH for smoothing reactor, and Jset＝40。
And 5: calculating a positive and negative electrode current waveform slope ratio coefficient P, and executing a pole selection criterion to obtain a fault pole;
in the bipolar hvdc transmission system as shown in fig. 4, the ratio of the current waveform slopes of the positive and negative electrodes can be used as the basis for judging the positive and negative electrodes. When a single-pole fault occurs, the slope of the current waveform of the non-fault pole is smaller than that of the fault pole, so that the ratio of the slope of the current waveform of the positive pole to the slope of the current waveform of the upper negative pole is defined as a proportionality coefficient P, and the specific calculation method comprises the following steps:
wherein n issThe number of sampling points in a sampling time window is shown; i isMp(i) The current value corresponding to the ith sampling point of the positive electrode at the rectifying side is obtained; i isMn(i) And the current value corresponding to the ith sampling point of the negative electrode on the rectifying side is obtained.
Selecting proper pole selection criterion threshold value Pset1And Pset2The available pole selection criterion is specifically as follows:
in consideration of attenuation effects of high-resistance grounding and long-distance lines, P is selected in the embodimentset1＝1.4，Pset2＝0.6。
Step 6: and executing protection action on the fault pole to complete the pilot protection of the line.
In order to verify the effectiveness of the pilot protection method, a +/-800 kV bipolar high-voltage direct-current transmission engineering simulation model is built by utilizing PSCAD/EMTDC software, the transmission power is 6000MW, and the total length of a line is 2000 km. 2/12/39 three-regulation DC filters are installed at both ends of the DC line. The sampling frequency was 10 kHz. The data window time selected in this embodiment is 5 ms. The model adopts a 500 omega high-impedance ground fault model, and selects several typical fault type simulation experiments to ensure the effectiveness of protection under various extreme conditions.
Internal faults of the positive electrode area and the negative electrode area: if a fault point occurs in the zone at 5s and a fault in the positive electrode zone and a fault in the negative electrode zone are separately input, whether the protection method is established is analyzed according to the two conditions. When a fault occurs, a schematic diagram of the value change of the fault criterion J in the area before and after the fault occurs is shown in fig. 5.
From the time period (4.98 s-5.015 s) in the figure, after the fault occurs, most of the harmonic wave of 600Hz flows into the ground through the direct current filter, and almost no harmonic wave of 600Hz passes through the smoothing reactance branch at the rectifying side and the smoothing reactance branch at the inverting side. The value of the fault identification criterion J is far smaller than the set value 40, so that the fault is judged to be an intra-area fault.
Whether the internal fault occurs in the positive electrode or the negative electrode can be analyzed according to the change condition of the pole selection criterion P, the value of P when the internal fault occurs in the positive electrode area is shown in figure 6, and the value of P when the internal fault occurs in the negative electrode area is shown in figure 7. The data window given in fig. 6 (4.98 s-5.015 s) indicates that after a fault occurs, the current in the positive pole suddenly rises rapidly and much faster than the rising speed of the negative pole current, resulting in the derivative of the positive pole current waveform being much larger than the derivative of the negative pole current waveform. That is, the pole selection criterion P exceeds the upper limit of the set value, and the positive fault occurs at the moment as known by the criterion formula.
The data window (4.98 s-5.02 s) presented in fig. 7 shows that after the fault occurs, the current of the negative pole suddenly rises rapidly and is much faster than the rising speed of the current of the positive pole, resulting in the derivative of the negative pole current waveform being much larger than that of the positive pole current waveform. That is, the pole selection criterion P exceeds the lower limit of the set value, and the criterion formula shows that the in-zone negative-level fault occurs at the moment.
Through the simulation, the effectiveness of the pilot protection method is verified, and meanwhile, the method is proved to have higher reliability and accuracy.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A pilot protection method for a high-voltage direct-current line based on branch current characteristics is a program embedded in a computer, and is characterized by comprising the following steps:
step 1: collecting electric quantity data of a detection point;
step 2: judging whether the line meets pilot protection starting criteria or not according to the data collected in the step 1, if so, executing the step 3, otherwise, returning to the step 1;
and step 3: extracting harmonic current;
and 4, step 4: judging whether the line meets the intra-area fault criterion, if so, judging that the line has an intra-area fault, then executing the step 5, otherwise, judging that the line has an extra-area fault, and protecting and resetting the line;
and 5: calculating a positive and negative electrode current waveform slope ratio coefficient P, and executing a pole selection criterion to obtain a fault pole;
step 6: and executing protection action on the fault pole to complete the pilot protection of the line.
2. The pilot protection method for the high-voltage direct-current line based on the branch current characteristics of claim 1, wherein the starting criterion in the step 2 is specifically as follows:
D＝max(DM，DN)＞Dset
wherein D isMAnd DNRespectively averaging the slope of the detected current waveform at a rectification side detection point M and an inversion side detection point N; n issThe number of sampling points in a sampling time window is shown; i isM(i) And IN(i) Respectively obtaining the current value of the rectification side and the current value of the inversion side at the ith sampling point; dsetIs a preset starting threshold value.
3. The pilot protection method for the high-voltage direct-current line based on the branch current characteristics of claim 1, wherein the starting criterion in the step 2 is subjected to anti-shake processing to prevent disturbance caused by lightning stroke.
4. The pilot protection method for the high-voltage direct-current line based on the branch current characteristic of claim 3, wherein the anti-shake treatment specifically comprises: and judging the starting criterion once every set time, if the judging results of two adjacent times are different, judging that the current judging result is invalid, returning to the step 1, and executing the step 3 until the line faults are judged in the two adjacent times.
5. The pilot protection method for the high-voltage direct current line based on the branch current characteristics of claim 4, wherein the set time is 3 milliseconds.
6. The pilot protection method for the high-voltage direct current line based on the branch current characteristic of claim 1, wherein the step 3 specifically comprises: harmonic currents of 600Hz are extracted from the current information of the line by S-conversion.
7. The pilot protection method for the high-voltage direct-current line based on the branch current characteristics of claim 1, wherein the in-zone fault criterion is specifically as follows:
wherein n issThe number of sampling points in a sampling time window is shown; i isr(i) A current value corresponding to the ith sampling point of the smoothing reactance branch at the rectifying side; i isi(i) The current value corresponding to the ith sampling point of the inverter side smoothing reactance branch circuit is obtained; j. the design is a squaresetA threshold is determined for the intra-zone and the inter-zone faults.
8. The method according to claim 7, wherein the inter-area and inter-area fault discrimination threshold J is set as a high-voltage direct-current line pilot protection method based on branch current characteristicssetAnd the value is smaller than the minimum value of the smoothing reactance branch current of the rectifying side and the smoothing reactance branch current of the inverting side in fault.
9. The high-voltage direct current line pilot protection method based on branch current characteristics according to claim 1, wherein the calculation method of the positive and negative electrode current waveform slope proportionality coefficient P in the step 5 is as follows:
wherein n issThe number of sampling points in a sampling time window is shown; i isMp(i) The current value corresponding to the ith sampling point of the positive electrode at the rectifying side is obtained; i isMn(i) And the current value corresponding to the ith sampling point of the negative electrode on the rectifying side is obtained.
10. The method for pilot protection of the high-voltage direct-current line based on the branch current characteristics according to claim 1, wherein the pole selection criterion is specifically as follows:
wherein P is the positive and negative electrode current waveform slope proportionality coefficientset1And Pset2Two preset thresholds.
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| CN114069577A (en) * | 2021-11-18 | 2022-02-18 | 国网江苏省电力有限公司连云港供电分公司 | Pilot protection method for power transmission line |
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| CN112803478A (en) * | 2021-01-05 | 2021-05-14 | 湖南大学 | Active injection type single-end protection method for micro-grid based on phase polarity characteristics |
| CN114069577A (en) * | 2021-11-18 | 2022-02-18 | 国网江苏省电力有限公司连云港供电分公司 | Pilot protection method for power transmission line |
| CN114069577B (en) * | 2021-11-18 | 2024-01-09 | 国网江苏省电力有限公司连云港供电分公司 | Pilot protection method for power transmission line |
| CN114243659A (en) * | 2021-12-23 | 2022-03-25 | 天津大学 | High-voltage direct-current transmission line pilot protection based on wave impedance measurement under tuned frequency |
| CN114243659B (en) * | 2021-12-23 | 2023-07-07 | 天津大学 | Pilot protection method for high-voltage direct-current transmission line based on wave impedance measurement under tuning frequency |
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