CN109507534A - One kind being based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods - Google Patents
One kind being based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods Download PDFInfo
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- CN109507534A CN109507534A CN201811444743.2A CN201811444743A CN109507534A CN 109507534 A CN109507534 A CN 109507534A CN 201811444743 A CN201811444743 A CN 201811444743A CN 109507534 A CN109507534 A CN 109507534A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
Abstract
The present invention relates to one kind to be based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, belongs to Relay Protection Technology in Power System field.When single machine ground fault occurs for route; fault current is measured in MMC-HVDC rectification side DC line bus protection installation place; measuring end fault current curve is drawn according to DC line bus protection installation place data obtained; according to the fault current curve waveform of acquisition; utilize wavelet conversion coefficient; it chooses band scale db4 small echo and extracts high-frequency energy D1 and low frequency energy A1, identify line fault as failure criterion using D1 and A1 ratio K q.The present invention detects fault-signal transient using wavelet transformation energy ratio, for identifying failure.In the transient processes such as internal fault external fault and lightning stroke, the feature difference using route transient state mutation energy is obvious, and the transient protection criterion thus constituted has very high sensitivity and selectivity.
Description
Technical field
The present invention relates to one kind to be based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, belongs to electric system relay
Protection technique field.
Background technique
MMC-HVDC system is made of the converter station and DC line at both ends, compared with AC transmission system, DC line
Middle fault progression is quick, and the difficulty of failure removal is also bigger.DC side line-internal failure not only will affect direct current system, to friendship
Streaming system can also have an impact.DC side line-internal failure has seriously endangered the stable operation of power system security.
In the MMC-HVDC system failure, compared with very big load current, the curent change before and after failure is unobvious.Hair
When raw troubles inside the sample space, external area error, the high fdrequency component that system measurements end obtains is widely different.Traditional HVDC system failure inspection
Survey method has very much, such as using the traveling-wave protection of uniform transmission line theory of travelling wave, utilize smoothing reactor and DC filter
The boundary detection method of composition.Wherein traveling wave method is mainly out of order using Current Voltage traveling wave change rate to identify, boundary inspection
The method that high fdrequency component plays detection failure is isolated by physical boundary for survey method, constitutes boundary protection.But in MMC-HVDC
It is lower to the interference of generations such as lightning stroke and the resolution ratio of failure and serious forgiveness in system, be not suitable for utilizing voltage and current change rate
Detect the traveling-wave protection of failure.And in MMC-HVDC system, configuring direct current filter is not needed, so that MMC-HVDC system
The physical boundary of system physical boundary conditions and tradition HVDC system is not quite similar.
Summary of the invention
The technical problem to be solved in the present invention is to provide one kind based on the accident analysis of MMC-HVDC overhead transmission line and identification side
Method, to solve the above problems.
The technical scheme is that a kind of be based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, work as route
When single machine ground fault occurs, fault current is measured in MMC-HVDC rectification side DC line bus protection installation place, according to
DC line bus protection installation place data obtained draw measuring end fault current curve, bent according to the fault current of acquisition
Line waveform chooses band scale db4 small echo and extracts high-frequency energy D1 and low frequency energy A1, utilize D1 using wavelet conversion coefficient
Line fault is identified as failure criterion with A1 ratio K q.
Specific steps are as follows:
(1) when single machine ground fault occurs for route, come in MMC-HVDC rectification side DC line bus protection installation place
Measure electric current；
(2) measuring end fault current curve is drawn according to DC line bus protection installation place data obtained；
(3) select db4 small echo to measuring end event using wavelet conversion coefficient according to the fault current curve waveform of acquisition
Barrier electric current is decomposed, and Naquist frequency f is obtainedn, expression formula are as follows: fs> 2fn, fsFor signal sampling rate；
It (4) is D1 according to the high fdrequency component coefficient obtained in step (3) under jth decomposition scale, low frequency component coefficient is A1,
The information band ranges that the signal component obtain after wavelet energy signal reconstruction is included are as follows:
In formula, DjIndicate the high fdrequency component of jth decomposition scale, AjIndicate the low frequency component of jth decomposition scale
(5) the high-frequency energy D1 and low frequency energy A1 obtained according to step (3) and step (4), utilizes the ratio of D1 and A1
Kq is as failure criterion, MMC-HVDC single-stage ground fault criterion are as follows: Kq=D1/A1.
(6) DC system fault and fault in ac transmission system are differentiated according to whether Kq is greater than setting valve Kset:
If Kq≥Kset, then it is judged as DC system fault；
If Kq<Kset, then it is judged as fault in ac transmission system.
The beneficial effects of the present invention are:
1, the present invention detects fault-signal transient using wavelet transformation energy ratio, for identifying failure.In area
In the transient processes such as inside and outside failure and lightning stroke, the feature difference using route transient state mutation energy is obvious, and what is thus constituted is temporary
State Protection criteria has very high sensitivity and selectivity.
2, the present invention uses wavelet analysis, and wavelet analysis is all may be used with frequency domain and time domain than the advantage of Fourier transformation
The ability for characterizing signal part, detects the transient state in signal, the frequency-portions in signal is showed, convenient for specified
Signal is analyzed.
Detailed description of the invention
Fig. 1 is both ends MMC-HVDC system main circuit canonical topology system model figure in the embodiment of the present invention；
Fig. 2 is fault current set of curves figure when positive line transition resistance is 0 Ω in the embodiment of the present invention；
Fig. 3 is fault current set of curves figure when positive line transition resistance is 300 Ω in the embodiment of the present invention；
Fig. 4 is anode circuit fault current set of curves figure in the embodiment of the present invention；
Fig. 5 is DC line fault Kq distribution map in electrode line road in the embodiment of the present invention；
Fig. 6 is DC line fault Kq distribution map in anode circuit in the embodiment of the present invention；
Fig. 7 is d in the embodiment of the present invention2Frequency band and d7Frequency band comparison diagram；
Fig. 8 is step flow chart of the invention.
Specific embodiment
With reference to the accompanying drawings and detailed description, the invention will be further described.
One kind being based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, when single machine ground fault occurs for route,
Fault current is measured in MMC-HVDC rectification side DC line bus protection installation place, is installed according to DC line bus protection
Locate data drafting measuring end fault current curve obtained and wavelet transformation is utilized according to the fault current curve waveform of acquisition
Coefficient is chosen band scale db4 small echo and extracts high-frequency energy D1 and low frequency energy A1, sentenced using D1 and A1 ratio K q as failure
According to identify line fault.
Specific steps are as follows:
(1) when single machine ground fault occurs for route, come in MMC-HVDC rectification side DC line bus protection installation place
Measure electric current；
(2) measuring end fault current curve is drawn according to DC line bus protection installation place data obtained；
(3) select db4 small echo to measuring end event using wavelet conversion coefficient according to the fault current curve waveform of acquisition
Barrier electric current is decomposed, and Naquist frequency f is obtainedn, expression formula are as follows: fs> 2fn, fsFor signal sampling rate；
It (4) is D1 according to the high fdrequency component coefficient obtained in step (3) under jth decomposition scale, low frequency component coefficient is A1,
The information band ranges that the signal component obtain after wavelet energy signal reconstruction is included are as follows:
In formula, DjIndicate the high fdrequency component of jth decomposition scale, AjIndicate the low frequency component of jth decomposition scale
(5) the high-frequency energy D1 and low frequency energy A1 obtained according to step (3) and step (4), utilizes the ratio of D1 and A1
Kq is as failure criterion, MMC-HVDC single-stage ground fault criterion are as follows: Kq=D1/A1.Corresponding every layer of band scale, rebuilds energy
Signal.Signal wavelet energy under low scale represents high-frequency signal wavelet energy, and the signal wavelet energy under high yardstick represents low
Frequency wavelet energy.
(6) DC system fault and fault in ac transmission system, comprehensive traversal are differentiated according to whether Kq is greater than setting valve Kset
The a large amount of simulation results crossed, Kset consider the nargin in line fault, are set as 0.9.
If Kq≥Kset, then it is judged as DC system fault；
If Kq<Kset, then it is judged as fault in ac transmission system.
The principle of the present invention is:
One, based on the time-domain signal analysis of small wave converting method
Wavelet analysis is that the ability of signal part can be characterized by having frequency domain and time domain all than the advantage of Fourier transformation, inspection
The transient state in signal is measured, the frequency-portions in signal are showed, convenient for analyzing specified signal.
Signal decomposition can be low-frequency range and high band by wavelet decomposition, and wavelet energy is broken down into different frequency bands therewith.
It can will be in multiple subspaces of signal decomposition to different frequency ingredient by multi-level Wavelet Transform analytic method.Each height
There is difference in the specific gravity that gross energy is occupied in space, difference existing for the specific gravity using gross energy in the case of different faults will measure
End current traveling wave decomposes measuring end electric current using small echo, rebuilds energy signal and obtains high fdrequency component, realizes fault branch
Identification.Db4 wavelet function is compact schemes orthogonal wavelet, and time domain compactly supported can be relatively strong and disappears away from small, calculation amount it is opposite and
Speech is simple, meets the requirement of fast detecting failure, therefore carries out wavelet transformation using db4 wavelet function herein.
Two, the single-ended MMC-HVDC magnitude of current distinguishes alternating current-direct current fault identification criterion
Using direct current single end current, the failure of AC and DC side is distinguished using low-and high-frequency current ratio.In MMC-
HVDC rectification side DC line bus protection installation place measures electric current, and a collection of wired foil is preset in completely long range and is connect
Earth fault and route external fault.Measuring end fault current curve is obtained by DC line bus protection installation place, it is suitable to select
Small echo measuring end electric current is decomposed, using input wavelet coefficient, rebuild the high fdrequency component that obtains of energy signal, pass through
The ratio of high and low frequency is to identify line fault.
Three, the identification of alternating current-direct current failure
(1) the fault current curve of measuring end is obtained by DC line bus protection installation place.To fault current curve into
After row wavelet transformation, suitable band scale is chosen as high-frequency energy D1 and low frequency energy A1, is made using D1 and A1 ratio K q
Failure is identified for failure criterion.To sum up, MMC-HVDC plus earth failure criterion are as follows: Kq=D1/A1.
(2) according to KqWhether setting valve K is greater thansetCome differentiate DC side failure with exchange side failure, take Kset be 0.9, if
Kq>=Kset is judged as DC side failure, if Kq<Kset, it is judged as exchange side failure.
Specifically:
MMC-HVDC system model as shown in Figure 1 is built in PSCAD, under 6.4kHz sample rate, line length is
400km.When single-stage ground fault occurs for route, in entire route 10km by closely to remote setting metallic earthing failure, therefore
Barrier transition resistance is respectively adopted 0 Ω, 300 Ω and is used to emulate ordinary failures and high resistive fault.It chooses in fault current curve and occurs
1 point before failure, the temporal current waveform of 32 points after failure.
After carrying out wavelet transformation to fault current curve, 8 frequency bands are decomposed into according to Naquist sampling thheorem, it is corresponding
Frequency range such as the following table 1:
Table 1
Corresponding every layer of band scale, rebuilds energy signal.Signal wavelet energy under low scale represents high-frequency signal small echo
Energy, the signal wavelet energy under high yardstick represent low frequency wavelet energy.It chooses an exchange side fault-signal and carries out small echo change
After changing, as reference value, by identical frequency band, comparison differs biggish height frequency.Consider d1And d8It is interfered in energy scale
Factor selects d2For high-frequency energy scale, d7For low frequency energy energy scale, compare as shown in Figure 7:
In Fig. 1, after singlephase earth fault occurs for exchange side A point, by simulation calculation, the electric current small echo of installation place is protected
Energy low-and high-frequency ratio Kq is 0.5442；After ground fault occurs for B point at rectification side positive DC line bus, transition resistance 0
Ω, protecting the electric current wavelet energy low-and high-frequency ratio Kq of installation place is 3.1817.Comprehensive traversed a large amount of simulation results, Kset are examined
Consider the nargin in line fault, is set as 0.9.After the comparison of low-and high-frequency energy, route single-stage failure ratio is obtained.Simulation result is aobvious
Show, Kq is all larger than equal to Kset, meets expected results.
Exchange after emulation is surveyed fault simulation result and is summarized as shown in table 2:
Table 2
The present invention passes through current characteristics after analysis MMC-HVDC isolated neutral system overhead transmission line monopolar grounding fault, and to it
Simulation analysis is carried out.Using the impedance frequency of MMC inverter, the boundary effect of MMC-HVDC is specified.Wavelet analysis compares Fu
In the advantage of leaf transformation be that the ability of signal part can be characterized by having frequency domain and time domain all, detect the transient state in signal, will
Frequency-portions in signal show, convenient for analyzing specified signal.Therefore wavelet transformation energy ratio is used herein
Fault-signal transient is detected, for identifying failure.In the transient processes such as internal fault external fault and lightning stroke, route is utilized
The feature difference that transient state is mutated energy is obvious, and the transient protection criterion thus constituted has very high sensitivity and selectivity.
It is analyzed by the impedance frequency characteristic to modularization multi-level converter, under different control models, MMC DC side
Impedance operator is essentially identical, and monotonic filter characteristic is presented, and produces apparent decaying to the high fdrequency component in fault-signal and makees
With the single-ended MMC-HVDC guard method based on time-domain coefficients energy ratio being proposed using the characteristic of inverter, in mainstream route
The measuring end of bus protection installation place obtains fault current cluster, after doing normalized, utilizes reconstruction with wavelet signal, construction
Wavelet energy scale chooses suitable dimensions in frequency, obtains failure criterion by high-frequency ratio low frequency to identify failure.Pass through emulation
It is uncomplicated to demonstrate the method calculating, it is swift with judgement and effective.
In conjunction with attached drawing, the embodiment of the present invention is explained in detail above, but the present invention is not limited to above-mentioned
Embodiment within the knowledge of a person skilled in the art can also be before not departing from present inventive concept
Put that various changes can be made.
Claims (2)
1. one kind is based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, it is characterised in that: connect when single machine occurs for route
When earth fault, fault current is measured in MMC-HVDC rectification side DC line bus protection installation place, according to DC line mother
Line protects installation place data obtained to draw measuring end fault current curve, according to the fault current curve waveform of acquisition, benefit
With wavelet conversion coefficient, chooses band scale db4 small echo and extract high-frequency energy D1 and low frequency energy A1, utilize D1 and A1 ratio K q
As failure criterion to identify line fault.
2. according to claim 1 be based on the accident analysis of MMC-HVDC overhead transmission line and recognition methods, it is characterised in that tool
Body step are as follows:
(1) it when single machine ground fault occurs for route, is measured in MMC-HVDC rectification side DC line bus protection installation place
Electric current；
(2) measuring end fault current curve is drawn according to DC line bus protection installation place data obtained；
(3) select db4 small echo to measuring end failure electricity using wavelet conversion coefficient according to the fault current curve waveform of acquisition
Stream is decomposed, and Naquist frequency f is obtainedn, expression formula are as follows: fs> 2fn, fsFor signal sampling rate；
It (4) is D1 according to the high fdrequency component coefficient obtained in step (3) under jth decomposition scale, low frequency component coefficient is A1, is carried out
The information band ranges that the signal component obtained after wavelet energy signal reconstruction is included are as follows:
In formula, DjIndicate the high fdrequency component of jth decomposition scale, AjIndicate the low frequency component of jth decomposition scale
(5) the high-frequency energy D1 and low frequency energy A1 obtained according to step (3) and step (4) is made using the ratio K q of D1 and A1
For failure criterion, MMC-HVDC single-stage ground fault criterion are as follows: Kq=D1/A1；
(6) DC system fault and fault in ac transmission system are differentiated according to whether Kq is greater than setting valve Kset:
If Kq≥Kset, then it is judged as DC system fault；
If Kq<Kset, then it is judged as fault in ac transmission system.
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Cited By (4)
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| CN110995038A (en) * | 2019-11-21 | 2020-04-10 | 中国电力科学研究院有限公司 | MMC (modular multilevel converter) and DC fault isolation method and system based on MMC |
| CN112415304A (en) * | 2020-10-30 | 2021-02-26 | 国网天津市电力公司 | Line identification method based on low-voltage transformer area voltage data curve grouping |
| CN112698155A (en) * | 2020-12-23 | 2021-04-23 | 国网河南省电力公司洛阳供电公司 | Direct-hit line and common fault identification method based on wavelet transformation |
| CN112731060A (en) * | 2020-12-24 | 2021-04-30 | 西安理工大学 | Self-adaptive reclosing method for high-voltage overhead-cable hybrid line |
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| CN110995038A (en) * | 2019-11-21 | 2020-04-10 | 中国电力科学研究院有限公司 | MMC (modular multilevel converter) and DC fault isolation method and system based on MMC |
| CN112415304A (en) * | 2020-10-30 | 2021-02-26 | 国网天津市电力公司 | Line identification method based on low-voltage transformer area voltage data curve grouping |
| CN112415304B (en) * | 2020-10-30 | 2022-08-23 | 国网天津市电力公司 | Line identification method based on low-voltage transformer area voltage data curve grouping |
| CN112698155A (en) * | 2020-12-23 | 2021-04-23 | 国网河南省电力公司洛阳供电公司 | Direct-hit line and common fault identification method based on wavelet transformation |
| CN112731060A (en) * | 2020-12-24 | 2021-04-30 | 西安理工大学 | Self-adaptive reclosing method for high-voltage overhead-cable hybrid line |
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