CN109119977A - Multiterminal flexible direct current power grid DC line fast protection method and system based on single ended voltage - Google Patents

Multiterminal flexible direct current power grid DC line fast protection method and system based on single ended voltage Download PDF

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Publication number
CN109119977A
CN109119977A CN201811098051.7A CN201811098051A CN109119977A CN 109119977 A CN109119977 A CN 109119977A CN 201811098051 A CN201811098051 A CN 201811098051A CN 109119977 A CN109119977 A CN 109119977A
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China
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line
voltage
current
limiting reactor
direct current
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CN109119977B (en
Inventor
邹贵彬
张烁
魏秀燕
黄强
谢仲润
孙辰军
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State Grid Corp of China SGCC
Shandong University
State Grid Hebei Electric Power Co Ltd
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State Grid Corp of China SGCC
Shandong University
State Grid Hebei Electric Power Co Ltd
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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
    • 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
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • 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
    • H02H7/265—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 making use of travelling wave theory
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

Abstract

The invention discloses a kind of multiterminal flexible direct current power grid DC line fast protection method and system based on single ended voltage, comprising: acquisition direct current positive and negative electrode route current-limiting reactor two sides voltage signal in real time；Constitute low-voltage start-up criterion；Line mode voltage on the current-limiting reactor being calculated carries out wavelet transformation, calculates wavelet modulus maxima；Data validation is carried out, the size and symbol of the first wavelet modulus maxima for meeting data validity condition are recorded；Fault identification criterion is established, the fault identification based on single ended voltage traveling wave wavelet modulus maxima symbol and amplitude difference is carried out；Failure pole identical criterion is constructed, the failure pole identification based on voltage traveling wave transient state energy difference in size is carried out.The mentioned line protection method of the present invention is reliable under various failure primary condition, rapidly identifies fault direction, and the factors such as transition resistance, abort situation and fault in ac transmission system have little effect Protection criteria, and reliability, sensitivity are high.

Description

Multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage and System
Technical field
The present invention relates to DC grid line fault protection technical fields, more particularly to the multiterminal based on single ended voltage are flexible DC grid DC line fast protection method and system.
Background technique
Compared to AC network and conventional high-pressure DC transmission system, the multiterminal flexible direct current based on voltage source converter Power grid has great advantage in terms of extensive new-energy grid-connected, regional power grid interconnection and central concentrated load.But Since the damping of flexible direct current system is smaller, after DC side failure fault progression quickly, several milliseconds of internal fault electric currents will on It is raised to great value, jeopardizes the safety of entire DC grid.Therefore, in order to by fault clearance, guarantee before converter station is latched The safe and reliable operation of sound circuit after failure, it is necessary to faulty line be isolated in transient process after the failure occurred.
Currently, DC Line Fault isolation technology has been achieved for significant progress, including dc circuit breaker, failure self-cleaning change Flow device etc..Since in existing Fault Isolation technology, only dc circuit breaker can be cut off in the case where converter station is not stopped transport Failure guarantees that the sound circuit in soft straight power grid continues to run, therefore the Fault Isolation technology based on dc circuit breaker is considered It is the best solution of soft straight power grid DC line fault.But this method needs to be accurately positioned event in a very short period of time Hinder route, the method that there is no reliable maturation at present, therefore need a kind of soft straight power grid selectivity and rapidity of can satisfy Route protection new principle.
The prior art proposes the guard method based on both-end amount, although this method has preferable selectivity, by In it, there are communication delay, it is difficult to meet the requirement of quick-action, therefore cannot function as the main protection of soft straight power network line.
The prior art proposes the guard method based on low-voltage, overcurrent and current differential, voltage derivative, this method It can satisfy the requirement of quick-action, but due to the influence of the factors such as transition resistance, the sensitivity of above-mentioned protection philosophy is difficult to protect Card, while the excision of adjacent faulty line may also lead to the malfunction of this route protection.
Summary of the invention
In order to limit the rate of climb of DC side fault current in soft straight power grid, strive for for protection and dc circuit breaker movement Time, DC line both ends are usually mounted with current-limiting reactor.The thought of conventional high-tension DC power transmission line boundary protection is used for reference, It can be with establishing protective criterion using current-limiting reactor as boundary element.
The present invention analyzes the communication process of false voltage traveling wave after DC line fault first, has derived internal fault external fault In the case of two side line mode voltage traveling wave of current-limiting reactor expression formula, and then the line mode voltage being calculated on current-limiting reactor. Secondly, discovery is when frequency is greater than a certain specific by the amplitude-frequency characteristic of current-limiting reactor line mode voltage when analysis internal fault external fault When frequency (present invention is defined as break frequency f0), frequency component voltage magnitude when troubles inside the sample space on current-limiting reactor will Greater than external area error.Accordingly, DC line internal fault external fault identical criterion is constructed, and then is proposed accordingly based on single-ended electricity The multiterminal flexible direct current power grid DC line fast protection method of pressure, this method can quickly and effectively identify faulty line, and And the factors such as fault type, transition resistance and abort situation determine that result has little effect to protection.
To achieve the goals above, the present invention adopts the following technical scheme:
Multiterminal flexible direct current power grid DC line disclosed in one or more kinds of embodiments based on single ended voltage Fast protection method, comprising:
(1) voltage signal of direct current positive and negative electrode route current-limiting reactor two sides is acquired in real time, and collected voltage is believed It number is filtered；
(2) it is opened according to the relationship construction low-voltage between the voltage in current-limiting reactor line side and DC grid voltage rating Dynamic criterion, judges whether current-limiting reactor line side voltage meets low-voltage entry condition, if it is, event occurs for DC line Barrier, into next step；Otherwise, return step (1)；
(3) the two side line mode voltage traveling wave of direct current positive and negative electrode route current-limiting reactor after calculating failure in setting time, from And the line mode voltage on current-limiting reactor is calculated；
(4) the line mode voltage on the current-limiting reactor that step (3) is calculated carries out wavelet transformation, calculates the first scale Wavelet modulus maxima；
(5) wavelet modulus maxima obtained to step (4) carries out data validation, records and first meets data The symbol and size of the wavelet modulus maxima of effectiveness condition；
(6) fault identification criterion is established, wavelet modulus maxima symbol and the size letter being calculated using step (5) Breath identified based on single ended line mode voltage wavelet modulus maxima symbol and the internal fault external fault of difference in size；
(7) if step (6) is identified as troubles inside the sample space, according to the positive electrode and negative electrode voltage traveling wave of DC power transmission line one end Transient state energy and, construct failure pole identical criterion, carry out based on voltage traveling wave transient state energy difference in size failure pole identification, from And identify fault type.
Further, low according to the relationship construction between the voltage in current-limiting reactor line side and DC grid voltage rating Voltage starting criterion, specifically: when the absolute value or direct current of the voltage for meeting direct-flow positive pole route current-limiting reactor line side When the absolute value of the voltage in anode circuit current-limiting reactor line side is less than the DC grid voltage rating of setting multiple, hair is determined Raw failure, protection starting.
Further, the two side line mode voltage of direct current positive and negative electrode route current-limiting reactor after calculating failure in setting time Traveling wave, specifically:
The line mode voltage traveling wave for defining route one end current-limiting reactor line side and bus bar side is respectively Δ UR,lineAnd Δ UR,bus, then:
In formula, Up,lineAnd Un,lineRespectively current-limiting reactor line side positive electrode and negative electrode voltage sample value, Up,busWith Un,busRespectively current-limiting reactor bus bar side positive electrode and negative electrode voltage sample value, n are current sampling point, and h indicates to adopt in data window The number of sampling point.
Further, the line mode voltage on current-limiting reactor is calculated, specifically:
Defining the line mode voltage on the current-limiting reactor of route one end is Δ UR, then:
ΔUR(n)=Δ UR,line(n)-ΔUR,bus(n)
Wherein, Δ UR,lineWith Δ UR,busThe respectively line mode voltage in route one end current-limiting reactor line side and bus bar side Traveling wave.
Further, wavelet transformation is carried out to the line mode voltage on current-limiting reactor, calculates the first scale wavelet transform mould Maximum, specifically:
In formula, a0It (k) is original signal, h0、h1Respectively low pass and high-pass filter；aj(k)、djIt (k) is original signal The smooth Coefficients of Approximation of jth layer and detail coefficients, respectively representing from sample rate is fsOriginal signal in 0~f of frequency range for extractings/2j +1And fs/2j+1~fs/2jSignal component；
Wavelet modulus maxima dj(kn) is defined as: | dj(kn)|≥|dj(k)|；
Wherein, djIt (k) is the jth layer smooth detail coefficient of original signal.
Further, data validation is carried out to wavelet modulus maxima, records and first meets data validity The symbol and size of the wavelet modulus maxima of condition, specifically:
Set setting valve Mmax, taking wavelet modulus maxima to be greater than the data of the setting valve is valid data；
In formula, setting valve MmaxIt can be got most according to the wavelet modulus maxima being calculated in sampling time window Big value determines.
Further, fault identification criterion is established, specifically:
Defining the first scale to meet first wavelet modulus maxima is M1If M1Meet
In formula, M0Maximum value for the wavelet modulus maxima that can be obtained when external area error, KrelFor safety factor, It is taken as 1.2；If meeting above-mentioned condition, protection is determined as troubles inside the sample space.
Further, then according to the positive electrode and negative electrode voltage traveling wave transient state energy of DC power transmission line one end and building event Hinder pole identical criterion, specifically:
The ratio for defining bipolar line one end positive electrode and negative electrode voltage traveling wave transient state energy sum is λ, sets safety factor k (0 < k < 1), then λ calculating formula are as follows:
In formula, h is the number of sampled point in sampling time window.
Further, the failure pole identification based on voltage traveling wave transient state energy difference in size is carried out, so that identification is out of order Type.Specifically:
If λ >=1+k, judge that plus earth failure occurs；
If λ≤1-k, judge that cathode ground fault occurs；
If 1-k < λi< 1+k then judges that intereelectrode short-circuit failure occurs；
Wherein, λ is the ratio of bipolar line one end positive electrode and negative electrode voltage traveling wave transient state energy sum, and k is safety factor.
Multiterminal flexible direct current power grid DC line disclosed in one or more kinds of embodiments based on single ended voltage Rapid protection system, including server, the server include memory, processor and storage on a memory and can handle The computer program run on device, the processor are realized above-mentioned any based on the more of single ended voltage when executing described program Hold flexible direct current power grid DC line fast protection method.
Compared with prior art, the beneficial effects of the present invention are:
(1) using the line mode voltage polarity and amplitude identification internal fault external fault on current-limiting reactor, two pole tension rows are utilized The transient state energy sum of wave ratio identification troubles inside the sample space failure pole, test model is only needed 20kHz sample frequency and Judgement can be completed in the data window of 1ms, and quick-action is strong；
(2) under various failure primary condition it is reliable, rapidly identify fault direction, transition resistance, abort situation and The factors such as fault in ac transmission system have little effect Protection criteria, and reliability, sensitivity are high；
(3) the Protection criteria only relating to parameters with protected circuit and current-limiting reactor, and with other parameters in system It is unrelated；
(4) mentioned method does not need system communication, merely with single ended voltage measurement data can be realized internal fault external fault with And the identification of failure pole；
(5) recognition methods principle is simple, clear, and identification is accurate, is easy to Project Realization, and the sample rate required protection is opposite It is lower, and improving for protection sensitivity can be realized by improving the sample rate of protective device, practical value with higher.
Detailed description of the invention
The accompanying drawings constituting a part of this application is used to provide further understanding of the present application, and the application's shows Meaning property embodiment and its explanation are not constituted an undue limitation on the present application for explaining the application.
Tetra- end flexible direct current power system simulation model of Fig. 1；
The symmetrical bipolar converter station topological structure of Fig. 2；
Typical fault schematic diagram inside and outside the line areas Fig. 3；
Fig. 4 simplifies equivalent network；
Amplitude-versus-frequency curve when Fig. 5 current-limiting reactor is 200mH；
Fig. 6 multiterminal flexible direct current power network line Non-unit protection program flow chart；
Fig. 7 F2Line mode voltage waveform when failure；
Fig. 8 F2Wavelet modulus maxima waveform when failure；
Fig. 9 F1Line mode voltage waveform when failure；
Figure 10 F1Wavelet modulus maxima waveform when failure；
Figure 11 F3Line mode voltage waveform when failure；
Figure 12 F3Wavelet modulus maxima waveform when failure；
Amplitude-versus-frequency curve when Figure 13 current-limiting reactor is 100mH.
Specific embodiment
It is noted that following detailed description is all illustrative, it is intended to provide further instruction to the application.Unless another It indicates, all technical and scientific terms used herein has usual with the application person of an ordinary skill in the technical field The identical meanings of understanding.
It should be noted that term used herein above is merely to describe specific embodiment, and be not intended to restricted root According to the illustrative embodiments of the application.As used herein, unless the context clearly indicates otherwise, otherwise singular Also it is intended to include plural form, additionally, it should be understood that, when in the present specification using term "comprising" and/or " packet Include " when, indicate existing characteristics, step, operation, device, component and/or their combination.
The invention discloses a kind of multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage, such as Shown in Fig. 6, comprising the following steps:
(1) DC line current-limiting reactor two sides positive and negative electrode voltage signal is acquired in real time, and collected signal is carried out Filtering processing；
(2) low-voltage start-up criterion is constituted using the voltage in current-limiting reactor line side, only when current-limiting reactor route When side voltage meets low-voltage entry condition, subsequent step just be will do it；
(3) the two side line mode voltage traveling wave of direct current positive and negative electrode route current-limiting reactor after calculating failure in certain time, from And the line mode voltage on current-limiting reactor is calculated；
(4) the line mode voltage on the current-limiting reactor that step (3) is calculated carries out wavelet transformation, calculates the first scale Wavelet modulus maxima；
(5) wavelet modulus maxima obtained to step (4) carries out data validation, records and first meets data The symbol and size of the wavelet modulus maxima of effectiveness condition；
(6) fault identification criterion is established, wavelet modulus maxima symbol and the size letter being calculated using step (5) Breath identified based on single ended line mode voltage wavelet modulus maxima symbol and the internal fault external fault of difference in size；
(7) if step (6) is identified as troubles inside the sample space, according to the positive electrode and negative electrode voltage traveling wave of DC power transmission line one end Transient state energy and, construct failure pole identical criterion, carry out based on voltage traveling wave transient state energy difference in size failure pole identification, from And identify fault type.
In step (2), the protection starting pinciple based on low-voltage are as follows:
Before carrying out faulty line and failure pole identical criterion, need to establish corresponding protection start-up criterion.This protection Used fault initiating criterion is the starting of current-limiting reactor line side low-voltage, and specific criterion is as follows:
|Ua,line| < 0.9Udc (1)
In formula, Ua,lineIndicate that pole a current-limiting reactor line side measures voltage, a indicates anode or cathode, UdcFor direct current Power grid voltage rating just starts as long as there is a pole to meet formula (1) protection.
In step (6), inside and outside the area based on line mode voltage wavelet transformation the first scale modulus maximum on current-limiting reactor The recognition principle of failure are as follows:
Assuming that the protection of the both ends DC line MN is R in Fig. 3MWith RN, protection scope is identical, i.e. both ends current-limiting reactor DC line between device, below to protect RMFor analyzed.
For protecting RM, the failure that back side occurs is reverse fault, it can be easy to distinguish by polarity of voltage, It will be described below.Fault signature situation the faintest is F in the case of all troubles inside the sample spaces1High resistant monopole ground connection occurs for place Failure, and fault signature situation the most obvious is F in the case of all external area errors3Metallicity intereelectrode short-circuit failure occurs for place. If it is possible to quickly and accurately faulty line just can be accurately positioned in above-mentioned two situations differentiation by establishing protective criterion, Meets the needs of soft straight power grid is for DC line protection.The present invention is as breach, to F1、F2、F3When place breaks down Voltage traveling wave communication process is analyzed in detail.
After DC line breaks down, fault point can generate voltage and current traveling wave, and from fault point to route two sides It propagates.Since soft straight power grid mostly uses greatly between bipolar DC link and positive and negative anodes circuit there are coupling effect, for convenience The propagation characteristic for analyzing traveling wave in DC line, first decouples bipolar line.Common decoupling method is phase-model transformation, as follows Shown in formula:
In formula, Up、UnIndicate positive electrode and negative electrode line voltage distribution, U0、U1Zero mould and line mode voltage component after indicating decoupling； Ip、InIndicate positive electrode and negative electrode line current, I0、I1Zero mould and line mould current component after indicating decoupling.
By formula (2) with formula (3) it is found that zero _exit only exists in positive and negative anodes circuit electrical quantity asymmetry, therefore pole Between short trouble when zero _exit is not present, zero _exit is very big when monopole failure.When monopolar grounding fault occurs for route, Zero mode voltage traveling wave Δ U of fault pointF0With line mode voltage traveling wave Δ UF1Calculation method are as follows:
In formula, Z0、Z1Indicate zero mould of DC line and the impedance of line mould；RfIndicate fault point transition resistance；UdcIndicate direct current Net voltage rating.
When intereelectrode short-circuit failure occurs for DC line, each mode voltage Δ U of fault pointF0、ΔUF1It is respectively as follows:
Zero _exit is not present when due to bipolar failure, while the attenuation degree of zero _exit is remote when propagating same distance Greater than Aerial mode component, therefore in order to reduce the influence that traveling wave decays for protection philosophy, the present invention chooses line mode voltage construction and protects Protect criterion.
After DC line breaks down, converter station mainly undergoes two failure phases.First stage is MMC before IGBT is latched Submodule capacitor discharge regime, second stage be IGBT because after self-protection function locking AC system to DC side feed-in electric current rank Section.
In order to cut off failure in the case where converter station is not stopped transport after guaranteeing soft straight grid collapses, it is necessary to assure Faulty line is identified and is removed by one stage.The converter station fault progression first stage is mainly shown as that submodule capacitor discharged Journey, can be with Approximate Equivalent for RLC series arm.Capacitor C in equivalent series brancheqRepresent the equivalent of each bridge arm submodule capacitor Capacitor, LeqFor equivalent, the R of bridge arm reactanceeqFor IGBT on-state equivalent resistance, value is respectively as follows:
Therefore, converter station equivalent impedance ZconvAre as follows:
After DC line breaks down, initial traveling wave can be propagated from fault point to route both ends, and not connected in wave impedance Catadioptric occurs for continuous place.Fig. 4 is the simplification equivalent network for the typical soft straight grid line mode voltage in four ends of analysis chart 1, due to this Equivalent circuit shown in Fig. 4 can be used merely with the initial traveling wave of line mode voltage in invention.
In Fig. 4, dotted line frame indicates that communication process of the initial line mode voltage traveling wave in DC line, this process are mainly wrapped The time delay that the attenuation process and traveling wave for including traveling wave are propagated, can be indicated with following formula:
ΔUj(s)=Δ Ui(s)·e-γl (8)
In formula, l indicates traveling wave propagation distance；γ indicates the propagation constant of line line wave, and real part α and imaginary part β distinguish table Levy the attenuation constant and phase constant of traveling wave in the line；Zs、ZmRespectively DC line series impedance matrix is major and minor diagonal Element, Ys、YmThe respectively major and minor diagonal element of DC line shunt admittance matrix.ΔUiIndicate fault point initial line mould electricity Press traveling wave, Δ UjIndicate initial line mode voltage traveling wave Δ UiThe incident ray mould at protection point is reached after DC line is propagated Voltage traveling wave.
When traveling wave travels to line end by fault point, since there are current-limiting reactors, converter station for DC line end And other outlets, therefore catadioptric occurs in DC line end.The incident voltage wave Δ U of line end is transmitted in Fig. 4j After catadioptric occurs, available current-limiting reactor two sides voltage Δ UR,lineWith Δ UR,busIt is respectively as follows:
In formula, Γ (s) is line mode voltage traveling wave reflection coefficient, ZsFor equivalent resistance of the protection R back side system at frequency f It is anti-, ZconvIndicate the equivalent impedance of converter station.
By the line mode voltage of formula (10) and formula (11) available current-limiting reactor are as follows:
For F on DC bus in Fig. 42The intereelectrode short-circuit failure at place, it is assumed that transition resistance zero, available Δ UR,bus With Δ UR,lineAre as follows:
The line mode voltage Δ U of current-limiting reactor at this timeR,F2Are as follows:
By formula (15) it can be seen that Δ UR,F2For positive polarity.
Work as F1When monopole high resistance earthing fault occurs for place, fault traveling wave travels to guarantor via lkm transmission line of electricity by fault point Simultaneously catadioptric occurs for line port where shield, herein Δ Ui(s) the Δ U being equal in formula (4)F1It (s), can by formula (8) and formula (13) To obtain the line mode voltage of current-limiting reactor are as follows:
As F on the DC bus of route opposite end3When metallicity intereelectrode short-circuit failure occurs for place, the initial traveling wave of failure is by fault point It first passes around current-limiting reactor and reaches DC line, hereafter fault traveling wave communication process and F1It is identical to locate failure, herein Δ Ui(s) Equal to the Δ U in formula (15)R,line(s), by the line mode voltage of formula (8) and formula (13) available current-limiting reactor are as follows:
Comparison expression (16) and formula (17), formula (18) are it can be found that F2Locate current-limiting reactor line mode voltage and F when failure1、F3 Locate polarity when failure on the contrary, can be very easily by protection R back side reverse fault and positive fault distinguish using this feature.Cause This, as long as F can be distinguished1With F3Locating failure just being capable of locating bad lines.In order to compare two kinds of offline mode voltages of fault condition Difference draws F1With F3The Bode figure of line mode voltage when failure on current-limiting reactor is to compare the offline mould electricity of two kinds of failure situations The amplitude-frequency characteristic of pressure.
Comparison expression (17) and formula (18) are it can be found that the difference between two formulas is mainly reflected in the second of constant coefficient and denominator On a factor, G is used1(s) and G2(s) it indicates are as follows:
Zero mould wave impedance Z of DC line in formula (19)0, line mould wave impedance Z1Although not being resistance form, its imaginary part compared with It is small, it is idealized in qualitative analysis and regards resistance as, then the effect of the factor is identical as constant coefficient, has for full rate component There is identical amplitude attenuation to act on.In Z1In the case where being approximately resistance, denominator is equivalent to as system introducing one-in formula (20) Z1The pole of/L has biggish attenuation for high fdrequency component.For low frequency component, current-limiting reactor is considered as short Road, therefore the amplitude of formula (17) will be much smaller than formula (18).During frequency component is by low frequency to high frequency variation, formula (18) Amplitude due to pole there are attenuation degrees gradually to become by force, and the amplitude attenuation degree of formula (17) has almost no change, therefore must Surely there is a certain frequency makes two formula amplitudes identical, is defined as break frequency f in the present invention0, Fig. 5 show using straight in Fig. 1 Flow Line L12With converter station S1The formula (17) that is calculated of parameter and formula (18) amplitude-versus-frequency curve, wherein formula (17) transition Resistance is taken as 500 Ω.
As shown in Figure 5, when frequency is lower than break frequency f0When, | Δ UR,F1(s)|<|ΔUR,F3(s)|；It is turned when frequency is greater than Dot frequency f0When, | Δ UR,F1(s)|>|ΔUR,F3(s)|.Therefore, corresponding Protection criteria can be constructed based on this feature.
Based on the above analysis, internal fault external fault deterministic process proposed by the present invention is as follows:
(1) according to break frequency f0Choose suitable sample frequency, it is desirable that minimum in the signal band that the first scale extracts Frequency component be greater than break frequency f0；
(2) the positive and negative anodes circuit current-limiting reactor two sides voltage data in certain time is extracted, is counted respectively using formula (21) Calculate line side and bus side line mode voltage Δ UR,line、ΔUR,bus:
In formula, h is the number of sampled point in sampling time window.
(3) by route side line mode voltage Δ UR,lineSubtract bus side line mode voltage Δ UR,busObtain the line of current-limiting reactor Mode voltage Δ UR, as shown in formula (22):
ΔUR(n)=Δ UR,line(n)-ΔUR,bus(n) (22)
(4) to Δ URWavelet transformation is carried out, the first modulus maximum M of the first scale is extracted1, it is desirable that M1Meet
M1> 0.5Mmax (23)
In formula, MmaxFor the maximum value of wavelet modulus maxima in time window.
Therefore, internal fault external fault identical criterion are as follows:
In formula, M0For adjusting threshold, maximum first scale wavelet transform modulus maximum when positive external area error is represented, it can M when metallicity intereelectrode short-circuit failure occurs on the bus of line taking road opposite end1；KrelFor safety factor, the present invention is set as 1.2.If Protect the M calculated1Meet formula (24), then the protection of this side is identified as that troubles inside the sample space occurs.
In step (7), the failure pole recognition principle based on voltage traveling wave transient state energy and difference are as follows:
After occurring due to monopole failure, much larger than pole is perfected, this is primarily due to perfect the temporary of pole failure pole transient state energy State energy is that route coupling generates, and positive and negative anodes are failure pole when bipolar failure, and transient state energy is roughly the same.Therefore Failure pole may be implemented using the difference to identify, define parameter λ first:
In formula, h is number of sampling points, Up,lineAnd Un,lineThe current-limiting reactor that respectively positive and cathode protection arrives Line side voltage.
Therefore, failure pole identical criterion is as follows:
In formula, k is Reliability factor, is taken as 0.2.
Flexible direct current power system simulation model is constructed using PSCAD, simulating, verifying is carried out to mentioned method:
1) model is established
Relevant parameter of the present invention according to Zhangbei County's flexible direct current demonstration project, has built in PSCAD/EMTDC such as Fig. 1 institute The soft straight power system simulation model in tetra- end ± 500kV shown.Converter station is symmetrical dipolar configuration in Fig. 1, and each converter station includes two MMC, topological structure is as shown in Fig. 2, the major parameter of converter station is shown in table 1.Current-limiting reactor is mounted on every direct current in Fig. 1 The both ends of transmission line of electricity, RijIndicate the protective device for being installed on the end DC line ij, which includes measurement current-limiting reactor The measuring unit R of device line side and bus bar side voltageij,lAnd Rij,b.Direct current overhead transmission line is used according to frequency model in simulation model. Using four ends MMC flexible direct-current electric network model shown in FIG. 1, mentioned guard method is verified, chooses protection R12As grinding Study carefully object.According to the amplitude-versus-frequency curve of Fig. 5, R is protected in available Fig. 112Break frequency f0For 4.2kHz.Due to requiring The signal low-limit frequency f that the first scale of wavelet transformation extractss/ 4 are higher than critical frequency f0, therefore it is required that protection sample rate fsIt is greater than 4f0, for protecting R in simulation model used in the present invention12For 16.8kHz.Therefore in order to protect can action message, select protection Sample rate is 20kHz, 0.5ms after 0.5ms to protection starting before wavelet transformation analysis data window selects protection to start.
1 converter station major parameter of table
2) fault simulation inside and outside Typical Areas
A. reverse fault F2.Assuming that failure betides F in Fig. 12Point, fault type are metallicity intereelectrode short-circuit failure, Fig. 7 For line mode voltage Δ U after failureR12Waveform, Fig. 8 are corresponding first scale wavelet transform modulus maximum.For ease of description, waveform 0 moment of time shaft represents the initial time of analysis data window.
As shown in Figure 8, initial line mode voltage is positive polarity, and modulus maximum is equally positive, determine the failure for reverse fault, It is identical as theory analysis.
B. positive external area error F3.Assuming that failure betides F in Fig. 13Point, fault type are metallicity intereelectrode short-circuit failure, Fig. 9 and Figure 10 is respectively line mode voltage waveform and its first scale wavelet transform modulus maximum.
By Fig. 9 and 10 it is found that initial line mode voltage is negative polarity, modulus maximum is equally negative, and determines the failure for forward direction Failure.M is calculated according to formula (23)1It is -42.89, and then protection R is calculated by formula (24)12Faulty line identification sentence According to threshold value be 51.47.Therefore, which is identified as external area error.
C. troubles inside the sample space F1.Assuming that failure betides F in Fig. 11Point, fault type are through 500 Ω transition resistance plus earths Failure, Figure 11 and 12 are respectively line mode voltage waveform and its first scale wavelet transform modulus maximum.
By Figure 11 and 12 it is found that initial line mode voltage is negative polarity, modulus maximum is equally negative, and determines the failure for forward direction Failure.M is calculated according to formula (23)1It is -66.86, absolute value is greater than protection R12Threshold value (51.47), therefore it is determined as area Internal fault.It is 11.298 by the failure pole criterion λ that sampled data is calculated, therefore is determined as positive electrode fault.As it can be seen that when being protected When high resistance earthing fault occurs for line end, Protection criteria still is able to sensitive reliably identify troubles inside the sample space and its failure classes Type.
3) different faults scene simulation is verified
A. different faults scene simulation in area.Table 2 show route L12It is upper that Protection criteria under different faults scene occurs Identify that situation, abort situation are set as 5%, 50% and 95% (distance protection installation place) of total track length.By 2 simulation result of table It is found that mentioned Protection criteria can correctly identify, and have for the failure that different location and transition resistance occur in area Higher sensitivity.
Protection identification situation under different faults scene in 2nd area of table
B. different faults scene simulation outside area.Table 3 show route L13And L24Head end and end, converter station S3、S4Outlet The identification situation of Protection criteria when metallicity intereelectrode short-circuit failure occurs for bus and AC system.By 3 simulation result of table it is found that For the failure of different location and transition resistance occurs outside area, mentioned Protection criteria can be correctly identified.
Protection identification situation under different faults scene outside 3rd area of table
4) influence of current-limiting reactor inductance value
The inductance value for changing DC line both ends current-limiting reactor will affect break frequency f0Size, inductance value gets over Small, corresponding break frequency is higher.Figure 13, which is shown, is reduced to transmission function after 100mH for current-limiting reactor inductance value in Fig. 1 Amplitude-versus-frequency curve.
As seen from Figure 13, break frequency is increased to 8.2kHz by the 4.2kHz in Fig. 3, therefore only needs by that will adopt Sample rate is increased to greater than 4f0, i.e. 32.8kHz.Using the simulation model in Fig. 1, current-limiting reactor inductance value is reduced by 200mH After 100mH, protection threshold value becomes 40.00, M when line end passes through 500 Ω ground fault1It is -56.83.Therefore, it protects Action message still is able under worst operating condition.
The pole of line mode voltage when the present invention utilizes DC power transmission line area internal and external fault on line end current-limiting reactor Property and amplitude Characteristics, seek the line mode voltage on current-limiting reactor first with line modular transformation and carry out wavelet transformation, acquire line mould The first wavelet modulus maxima of first scale of voltage, later through its polarity and amplitude compared with threshold value, into And cog region internal and external fault, the identification of failure pole is carried out by comparing the difference of the two poles of the earth voltage transient energy sum.Simulation analysis table Bright, under various fault conditions, the present invention can correctly identify internal fault external fault, failure pole, and high sensitivity is highly reliable.Separately Outside, which only needs the data window of 1ms to be calculated, and does not need to carry out data communication, quick action.
Above-mentioned, although the foregoing specific embodiments of the present invention is described with reference to the accompanying drawings, not protects model to the present invention The limitation enclosed, those skilled in the art should understand that, based on the technical solutions of the present invention, those skilled in the art are not Need to make the creative labor the various modifications or changes that can be made still within protection scope of the present invention.

Claims (10)

1. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage characterized by comprising
(1) in real time acquisition direct current positive and negative electrode route current-limiting reactor two sides voltage signal, and to collected voltage signal into Row filtering processing；
(2) sentenced according to the relationship construction low-voltage starting between the voltage in current-limiting reactor line side and DC grid voltage rating According to, judge whether current-limiting reactor line side voltage meets low-voltage entry condition, if it is, DC line breaks down, Into in next step；Otherwise, return step (1)；
(3) the two side line mode voltage traveling wave of direct current positive and negative electrode route current-limiting reactor after calculating failure in setting time, to count Calculation obtains the line mode voltage on current-limiting reactor；
(4) the line mode voltage on the current-limiting reactor that step (3) is calculated carries out wavelet transformation, calculates the first multi-scale wavelet Convert modulus maximum；
(5) wavelet modulus maxima obtained to step (4) carries out data validation, records that first to meet data effective The symbol and size of the wavelet modulus maxima of property condition；
(6) fault identification criterion is established, the wavelet modulus maxima symbol and size information being calculated using step (5), Identified based on single ended line mode voltage wavelet modulus maxima symbol and the internal fault external fault of difference in size；
(7) if step (6) is identified as troubles inside the sample space, according to the positive electrode and negative electrode voltage traveling wave transient state of DC power transmission line one end Energy and, construct failure pole identical criterion, carry out based on voltage traveling wave transient state energy difference in size failure pole identification, to know Be not out of order type.
2. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, according to the relationship construction low-voltage starting between the voltage in current-limiting reactor line side and DC grid voltage rating Criterion, specifically: when the absolute value or direct current anode circuit of the voltage for meeting direct-flow positive pole route current-limiting reactor line side When the absolute value of the voltage in current-limiting reactor line side is less than the DC grid voltage rating of setting multiple, determine to break down, Protection starting.
3. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, the two side line mode voltage traveling wave of direct current positive and negative electrode route current-limiting reactor after calculating failure in setting time, specifically Are as follows:
The line mode voltage traveling wave for defining route one end current-limiting reactor line side and bus bar side is respectively Δ UR,lineWith Δ UR,bus, Then:
In formula, Up,lineAnd Un,lineRespectively current-limiting reactor line side positive electrode and negative electrode voltage sample value, Up,busAnd Un,busPoint Not Wei current-limiting reactor bus bar side positive electrode and negative electrode voltage sample value, n is current sampling point, and h indicates sampled point in data window Number.
4. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, the line mode voltage on current-limiting reactor is calculated, specifically:
Defining the line mode voltage on the current-limiting reactor of route one end is Δ UR, then:
ΔUR(n)=Δ UR,line(n)-ΔUR,bus(n)
Wherein, Δ UR,lineWith Δ UR,busThe respectively line mode voltage traveling wave in route one end current-limiting reactor line side and bus bar side.
5. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, wavelet transformation is carried out to the line mode voltage on current-limiting reactor, calculate the first scale wavelet transform modulus maximum, tool Body are as follows:
In formula, a0It (k) is original signal, h0、h1Respectively low pass and high-pass filter；aj(k)、djIt (k) is the jth layer of original signal Smooth Coefficients of Approximation and detail coefficients, respectively representing from sample rate is fsOriginal signal in 0~f of frequency range for extractings/2j+1With fs/2j+1~fs/2jSignal component；
Wavelet modulus maxima dj(kn) is defined as: | dj(kn)|≥|dj(k)|；
Wherein, djIt (k) is the jth layer smooth detail coefficient of original signal.
6. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, data validation is carried out to wavelet modulus maxima, records and first meets the small of data validity condition The symbol and size of wave conversion modulus maximum, specifically:
Set setting valve Mmax, taking wavelet modulus maxima to be greater than the data of the setting valve is valid data；
In formula, setting valve MmaxThe maximum value that can be got according to the wavelet modulus maxima being calculated in sampling time window It determines.
7. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, establishes fault identification criterion, specifically:
Defining the first scale to meet first wavelet modulus maxima is M1If M1Meet
In formula, M0Maximum value for the wavelet modulus maxima that can be obtained when external area error, KrelFor safety factor, it is taken as 1.2；If meeting above-mentioned condition, protection is determined as troubles inside the sample space.
8. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, then according to the positive electrode and negative electrode voltage traveling wave transient state energy of DC power transmission line one end and the identification of building failure pole Criterion, specifically:
Define bipolar line one end positive electrode and negative electrode voltage traveling wave transient state energy sum ratio be λ, setting safety factor k (0 < k < 1), then λ calculating formula are as follows:
In formula, h is the number of sampled point in sampling time window.
9. the multiterminal flexible direct current power grid DC line fast protection method based on single ended voltage as described in claim 1, It is characterized in that, the failure pole identification based on voltage traveling wave transient state energy difference in size is carried out, to identify fault type.Specifically Are as follows:
If λ >=1+k, judge that plus earth failure occurs；
If λ≤1-k, judge that cathode ground fault occurs；
If 1-k < λi< 1+k then judges that intereelectrode short-circuit failure occurs；
Wherein, λ is the ratio of bipolar line one end positive electrode and negative electrode voltage traveling wave transient state energy sum, and k is safety factor.
10. the multiterminal flexible direct current power grid DC line rapid protection system based on single ended voltage, which is characterized in that including service Device, the server include memory, processor and storage on a memory and the computer program that can run on a processor, The processor realizes the described in any item multiterminal flexible direct currents based on single ended voltage of claim 1-9 when executing described program Power grid DC line fast protection method.
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