CN108599116A - A kind of DC line protection method suitable for alternating current-direct current mixing power distribution network - Google Patents
A kind of DC line protection method suitable for alternating current-direct current mixing power distribution network Download PDFInfo
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- CN108599116A CN108599116A CN201810369746.8A CN201810369746A CN108599116A CN 108599116 A CN108599116 A CN 108599116A CN 201810369746 A CN201810369746 A CN 201810369746A CN 108599116 A CN108599116 A CN 108599116A
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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
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/263—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 involving signal transmission between at least two stations involving transmissions of measured values
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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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- Emergency Protection Circuit Devices (AREA)
Abstract
The invention discloses a kind of DC line protection methods suitable for alternating current-direct current mixing power distribution network, including main protection, nearly back-up protection and remote back-up protection.Main protection is made of current differential protection, overcurrent protection and unbalanced current protection.Nearly back-up protection is made of directional current protection and under-voltage protection, and not by transition Resistance Influence, protection domain is total track length.Remote back-up protection is made of directional current protection, voltage across poles protection, unstable voltage protection and differential unstable voltage protection.After reducing AC fault, especially single-line to ground fault, harmonics tripping leads to DC grid operation exception, AC fault can be isolated by remote back-up protection.
Description
Technical field
The present invention relates to Relay Protection Technology in Power System fields, more particularly to suitable for alternating current-direct current mixing power distribution network
DC line protection method.
Background technology
In DC line, to protect power electronic devices, current conversion station that generally there is overcurrent blocking function, improve to direct current
The quick-action requirement of route protection.Because the delay time of failure current traveling wave and false voltage traveling wave is usually no more than 1ms, meet
Quick-action requirement, therefore generally use traveling-wave protection and voltage jump amount protection cooperation, the main protection as DC line.But as
The traveling-wave protection of single-end electrical quantity protection, there are setting valves to be not easy to determine, it is difficult to the problem of distinguishing area's internal and external fault, and received
It is larger to cross Resistance Influence, needs to make improvements.To weaken influence of the transition resistance to protection, at present by analysis be not easy by
The fault current time to peak that transition resistance influences identifies fault type, and matches realization protection circuit using two sections of protections
Overall length, but it is similar with traveling-wave protection, determining problem is difficult to there is also setting valve.Using voltage characteristic failure judgement type, but
This method can not determine abort situation.Also it can realize fault location by analyzing the modes such as fault traveling wave feature.Such as by circuit two
The anti-traveling wave amplitude at end integrates ratio, as DC line area internal and external fault criterion.Or when using area's internal and external fault, AC line
Road both sides voltage jump amount is different from the direction character of jump-value of current, failure judgement position.But using modular multilevel
In the DC distribution net of transverter (modular multilevel converter, MMC), be generally not provided with smoothing reactor and
Filter reactance, and DC distribution web frame is various, current-limiting reactor size and installation site and disunity, DC line both ends are simultaneously
Differ and has established a capital physical boundary.Therefore it is not particularly suited for the mixing of the alternating current-direct current containing MMC using the protection scheme that physical boundary is arranged and matches
Power grid.
In addition, the Protection Scheme for Transmission Line currently used for DC distribution net, only considers the protection of this section of circuit mostly, to being protected
It is less to protect the considerations of circuit is influenced with adjacent lines cooperation and AC fault, and is divided without specific protection zone.
Thus, it is desirable to have a kind of DC line protection method suitable for alternating current-direct current mixing power distribution network solves in the prior art
There are the problem of.
Invention content
The purpose of the present invention is to provide a kind of DC line protection method suitable for alternating current-direct current mixing power distribution network, packets
It includes：Including complete main protection, nearly back-up protection and remote back-up protection.
The main protection is made of current differential protection, overcurrent protection and the protection of positive and negative electrode current imbalance.Its
In, current differential protection is used for failure judgement position, and overcurrent protection and current imbalance protect fault type for identification.Protection
Ranging from, whole section of DC line.
The nearly back-up protection is made of directional current protection and under-voltage protection, and directional current protection determines faulty section
Domain, under-voltage protection failure judgement type.Not by transition Resistance Influence, protection domain is total track length.
The remote back-up protection is by the directional current protection for determining abort situation, and for determining fault type
Voltage across poles protection, unstable voltage protection and differential unstable voltage protection composition.When downstream is also direct current by protection equipment
When circuit, remote back-up protection ranging from this section of circuit and subordinate's circuit.When downstream is transverter by protection equipment, remote standby is protected
Shield range exchanges exit from this section of circuit beginning to transverter.
Preferably, the main protection includes the following steps：
Step 1 is determined according to total poor stream criterion whether there is failure inside protected circuit；
The total continuous n times of poor stream criterion (generally taking 3~5 times) of regulation are set up, then are judged to protected circuit troubles inside the sample space.It is described
Shown in total poor stream criterion such as formula (1)：
idcDiff＞ Iset1.1 (1)
Wherein, Iset1.1For total difference current definite value, calculated by principle shown in formula (2)：
Iset1.1=Kset1.1max{|IdcD.sup|, | IdcD.sub|, | IdcD.nor|} (2)
Wherein, Kset1.1For the safety factor more than 1；IdcD.sup、IdcD.sub、IdcD.norRespectively upstream AC line is short out
Road, the short circuit of downstream DC line and when normal operation, this section of DC line begin, the maximum difference stream of end current, and max { } expressions take
Maximum value；The upstream refers to adjacent with by protection DC line, close to the side of power supply or equivalent power supply.The line end
It refer to the one end of circuit far from power supply or equivalent power supply.
idcDiffFor total poor stream, shown in computational methods such as formula (3)：
idcDiff=| ipDiff|+|inDiff| (3)
Wherein, ipDiff、inDiffThe respectively difference current of protected circuit anode and cathode, computational methods such as formula (4) institute
Show：
Wherein, A, B indicate the both ends of a DC line respectively.ipARectify electrode current, i for ApBRectify electrode current for B,
inAFor the ends A cathodal current, inBFor the ends B cathodal current.
After step 2 is determined as protected circuit troubles inside the sample space, judged by current imbalance protection and overcurrent protection
Failure pole.
Line one-end positive and negative electrode current imbalance factor KIdiffIt is calculated by formula (5)：
Wherein, inAnd ipRespectively by the measurement electric current of protection DC line the same end cathode and anode.
The rule of the failure judgement pole includes the following steps：
If 1) | KIdiff- 1 | ＞ KsetIdAnd KIdiff＞ 1 meets simultaneously, then is judged to anode circuit ground short circuit.
Wherein KsetIdFor monopole fault threshold values, calculated according to formula (6)：
KsetId=Kset1.3max{|KId.nor- 1 |, | KId.PNF-1|} (6)
Wherein, Kset1.3For the safety factor more than 1；KId.nor、KId.PNFRespectively intereelectrode short-circuit in normal operation and area
When, line one-end positive and negative electrode current imbalance factor.
If 2) | KIdiff- 1 | ＞ KsetIdAnd KIdiff＜ 1 meets simultaneously, then is judged to positive circuit ground short circuit；
If 3) KIdiff=1, then judge that failure is not had by protection DC line, or interpolar failure has occurred.And further
It is calculated by the difference current i at protection DC line one end (such as ends A) according to formula (7)dcA：
idcA=| ipA|+|inA| (7)
Wherein, ipA、inARespectively DC line A rectify, cathodal current.
If idcA＞ Iset1.2, then it is judged to interpolar failure.Wherein Iset1.2For threshold value, calculate as shown in formula (8)：
Iset1.2=Kset1 2max{IdcA.SpF, IdcA.nor} (8)
Wherein, IdcA.SpF、IdcA.norMonopole short circuit grounding and when normal operation respectively in area, circuit A rectifies, negative electricity
The maximum value of the sum of flow measure；Kset1.2For the safety factor more than 1.
Preferably, the nearly back-up protection includes the following steps：
Step 1 passes through the t that is delayedset2, realize the cooperation of nearly back-up protection and main protection.To escape AC fault, tset2Value
More than or equal to 1/4 power frequency period, that is, it is more than 5ms.
Step 2 is to improve to judge speed, while judging whether directional current criterion and low voltage criterion are true.Wherein, if
This grade of circuit and downstream line direction are satisfied by directional current criterion in continuous 3 sampling periods, then it is assumed that directional current criterion
It sets up, failure is happened at this section of circuit.
The directional current criterion includes：
1) line one-end (such as ends the A) poles i fault current direction is denoted as SiA(i=p, n, and p represent anode, and n represents cathode),
Its value is calculated by formula (9)：
Wherein, iiAFor the ends A i electrode current measured values；iiA0For normal operation when, the ends A i electrode currents；Iset2.1For over-current adjusting
Value is calculated by formula (10)：
Wherein, Kset2.1It is slightly over 1 safety factor；IiA0.max、IiA0.minRespectively normal operation when, the ends A i electrode currents
Maxima and minima.
If 2) this section of circuit beginning fault current direction SiA, with downstream line beginning fault current direction SisubMeet formula
(11), then it is judged to that troubles inside the sample space occurs.
SiASisub=-1 (11)
The case where step 3 is set up according to low voltage criterion determines whether troubles inside the sample space, and determines fault type.If
tset2Interior, only cathode voltage meets low voltage criterion always, then is plus earth short circuit；If in tset2Inside only cathode voltage is always
Meet low voltage criterion, is then cathode ground short circuit；If in tset2Interior positive and negative electrode voltage meets always low voltage criterion, then
For intereelectrode short-circuit.
Shown in the low voltage criterion such as formula (12)：
Wherein, upA、unARectify for circuit A, cathode voltage；Uset2.2For low-voltage threshold value.When protected circuit downstream
For DC line when, Uset2.2It is calculated by formula (13)；When protected circuit downstream is transverter, Uset2.2It is calculated by formula (14).
Uset2 2=Kset2 2U0A min (13)
Wherein, Kset2.2For the safety factor of under-voltage protection, value is slightly larger than 1；U0A.minFor normal operation when circuit begin
Hold minimum voltage；U0AFor circuit beginning rated voltage.
Preferably, the remote back-up protection includes the following steps：
Step 1 is when subordinate is also DC line, remote back-up protection ranging from this section of circuit and subordinate's circuit.When subordinate is
When transverter, remote back-up protection range exchanges exit (connection transformer valve side) from this section of circuit beginning to transverter, at this point,
Remote back-up protection, which is applied not only to DC Line Fault caused by preventing DC current fast tripping protection, nearly back-up protection tripping, to be isolated,
After AC fault can also being reduced, especially after AC single phase ground short circuit, harmonics are failure to actuate the shadow to direct current tolerance
It rings.
The remote back-up protection of step 2 includes the directional current protection for determining abort situation, and for determining failure classes
Voltage across poles protection, unstable voltage protection and the differential unstable voltage protection of type.
Step 3 when being still DC line by protection DC line downstream, the judgement flow of directional current protection with it is close after
Directional current protection judgment rule is identical in standby protection.When subordinate is current conversion station, then pass through this section of circuit beginning current direction
Coordinate with voltage protection, whether failure judgement is happened in area.The voltage protection includes voltage across poles criterion, unbalance voltage
Criterion and differential unbalance voltage criterion.Wherein, shown in voltage across poles criterion such as formula (15), unbalance voltage criterion such as formula (16)
It is shown, shown in differential unbalance voltage criterion such as formula (17).To prevent fault type from judging by accident, voltage across poles criterion, uneven electricity
Pressure criterion and differential unbalance voltage criterion need to continuously meet at least 1/2 power frequency period, i.e. 10ms, be just judged to the criterion at
It is vertical.
udc＜ Uset3.2 (15)
|upn| ＞ Uset3.3 (16)
Wherein, udcFor DC line voltage across poles；upnFor unbalance voltage, it is equal to DC line positive and negative electrode voltage vector
With；Uset3.2、Uset3.3、Uset3.4As shown in formula (18).
Wherein, Kset3.2、Kset3.3、Kset3.4For safety factor, Kset3.2Value is slightly less than 1, Kset3.3、Kset3.4Value is bigger
In 1；Udc.nor.minFor normal operation when minimum voltage across poles；Upn.nor.maxFor normal operation when maximum unbalance voltage；When
When subordinate is still DC line, UpnD.AC.maxFor the maximum differential unbalance voltage of exchange side short circuit, at this point, the criterion is for preventing
Only false protection after transverter exchange terminal short-circuit；When subordinate is transverter, UpnD.AC.maxSubordinate for current conversion station connection hands over
The maximum differential unbalance voltage of Flow Line short circuit, at this point, the criterion is for preventing false protection after AC line short circuit.
Advantageous effect：The invention discloses a kind of DC line protection methods suitable for alternating current-direct current mixing power distribution network, contain
Complete main protection, nearly back-up protection and remote back-up protection are covered, protection's dead-zone is avoided.The change of current is included in transverter exchange outlet
In the remote back-up protection range of device higher level's circuit, guarantor is exchanged after reducing transverter exchange terminal short-circuit, especially single-phase short circuit
Protect influence of the tripping to DC line normal operation.In addition, protection has good selectivity and rapidity.
Description of the drawings
Fig. 1 is that photovoltaic DC collects access system topological diagram.
Fig. 2 is DC line main protection flow chart.
Fig. 3 is the nearly back-up protection flow chart of DC line.
Fig. 4 is AC line great distance back-up protection flow chart.
Specific implementation mode
The present invention provides a kind of DC line protection method suitable for alternating current-direct current mixing power distribution network, including complete main guarantor
Shield, nearly back-up protection and remote back-up protection.
Main protection is made of current differential protection, overcurrent protection and the protection of positive and negative electrode current imbalance.Wherein, electric
It flows differential protection and is used for failure judgement position, overcurrent protection and current imbalance protect fault type for identification.Protection domain
For whole section of DC line.
Nearly back-up protection is made of directional current protection and under-voltage protection, and directional current protection determines fault zone, low
Voltage protection failure judgement type.Not by transition Resistance Influence, protection domain is total track length.
Remote back-up protection is by the directional current protection for determining abort situation, and the interpolar for determining fault type
Voltage protection, unstable voltage protection and differential unstable voltage protection composition.When downstream is also DC line by protection equipment
When, remote back-up protection ranging from this section of circuit and subordinate's circuit.When downstream is transverter by protection equipment, remote back-up protection model
Enclose the exchange exit from this section of circuit beginning to transverter.
To keep the purpose, technical scheme and advantage that the present invention is implemented clearer, below in conjunction in the embodiment of the present invention
Attached drawing, technical solution in the embodiment of the present invention is further described in more detail.In the accompanying drawings, identical from beginning to end or class
As label indicate same or similar element or element with the same or similar functions.Described embodiment is the present invention
A part of the embodiment, instead of all the embodiments.The embodiments described below with reference to the accompanying drawings are exemplary, it is intended to use
It is of the invention in explaining, and be not considered as limiting the invention.Based on the embodiments of the present invention, ordinary skill people
The every other embodiment that member is obtained without creative efforts, shall fall within the protection scope of the present invention.
The embodiment of the present invention is described in detail below in conjunction with the accompanying drawings.
It is illustrated so that photovoltaic DC shown in Fig. 1 collects access system as an example.Straight-flow system is 5MW photovoltaic plants, exchange
System voltage is 35kV.Twolink is the 30kV direct current cables of 10km, line impedance Z1=0.45 Ω/km.Grid-connected converter
It stands and is made of modularization multi-level converter (MMC) and connection transformer.MMC uses 129 level with blocking function to mix
Type MMC, half-bridge submodule are 1: 1 with full-bridge submodule number ratio.Transformer Dyn11 transformers are connected, and through 1000 Ω resistance
Ground connection, no-load voltage ratio 1: 1.1.Photovoltaic plant is controlled using maximal power tracing, and MMC is using reactive power and determines DC voltage conduct
The current decoupled control of outer shroud.
The flow of main protection is as shown in Figure 2.Wherein, sign (y) be symbol decision function, when y be timing, functional value 1,
It is that functional value is -1 when bearing that functional value, which is 0, y, when y is 0.Judge speed to improve, while judging first three in Fig. 2 criterion, and remembers
Number is set up in record.It continuously sets up 3 times and thinks that the criterion is set up, according still further to Fig. 2 flow failure judgement types.
In addition to beginning, for other positions metallic short circuit, to analyze circuit AB beginnings, end electricity after failure on circuit AB
Pressure, electric current.After monopole short circuit, voltage across poles is constant, and photovoltaic output current is basically unchanged, the extremely corresponding MMC half-bridges submodule of failure
Block capacitance forms discharge loop with line capacitance.Begin, end fault extra current ifA、ifBMainly determined by line distribution capacitance,
And positive and negative electrode fault current direction is identical, then after failure, positive and negative electrode current imbalance.After intereelectrode short-circuit, by fault point interpolar
Voltage is reduced to 0 influence, begins, terminal voltage declines and close to 0.By photovoltaic output characteristics it is found that photovoltaic output current increases,
And about short circuit current, MMC submodule capacitances discharge.Compared with monopole short circuit, beginning fault current ifAAlso include that photovoltaic exports
Short circuit current, end fault electric current ifBAlso include MMC capacitance discharge currents.
If the beginnings circuit AB are short-circuit, since photovoltaic plant is directly connected with beginning, therefore ifAOnly by photovoltaic output short circuit current
It determines.Because photovoltaic output maximum short circuit current be 1kA, and electric current have one-way, can only be flowed out from photovoltaic plant, cause just,
Cathodal current degree of unbalancedness is relatively low.Therefore after circuit AB beginning short circuits, current quick may be failure to actuate.
When emulating 1s, respectively in k1 to k4 setting plus earth short circuits and intereelectrode short-circuit, ac short circuit is set in k5, k6.
Sample frequency 20kHz handles simulation data data in Matlab, verifies protection scheme.For circuit AB, Iset1.1It need to escape
Maximum difference stream 1.7748kA after the monopole short circuit of the beginnings circuit BC, enables Kset1.1=1.05, then Iset1.1=1.86kA；Iset1.2It needs
The maximum current 3.2kA after this section of line monopole short circuit is escaped, K is enabledset1.2=1.1, then Iset1.2=3.52kA；Iset1.3It need to hide
The maximum imbalance current coefficient 0.0016 after this section of circuit intereelectrode short-circuit is crossed, K is enabledset1.3=1.1, then Iset1.3=0.00176.
For circuit BC, Iset1.1The maximum difference stream 1.966kA after the monopole short circuit of MMC direct currents exit need to be escaped, K is enabledset1.1=1.1,
Then Iset1.1=2.16kA；Iset1.2The maximum current 2.88kA after this section of line monopole short circuit need to be escaped, K is enabledset1.2=1.1, then
Iset1.2=3.17kA；Iset1.3The maximum imbalance current coefficient 0.003 after this section of circuit intereelectrode short-circuit need to be escaped, K is enabledset1.3
=1.1, then Iset1.3=0.0033.The verification of current quick scenario outcomes is as shown in table 1.
Wherein, XfA、XfBDistance (the unit of respectively circuit AB and circuit BC failures to this section of circuit beginning：Km), PF generations
Table anode short circuit, PNF represent intereelectrode short-circuit, and acF represents ac short circuit, RfFor transition resistance.
The test result of 1 main protection of table
As shown in Table 1, for metallic short circuit, the protection of circuit BC can accurately identify the failure of this section of circuit.Due to
Directly it is connected with photovoltaic plant, circuit AB can be identified in addition to beginning, the short circuit of other positions.But for high resistive fault, electric current
Fast tripping protection is difficult to.In order to reduce the influence of transition resistance and photovoltaic plant short circuit curve to fault identification, protection is improved
Reliability, need setting that can protect the nearly back-up protection of this section of total track length.
Fig. 3 show the nearly back-up protection flow of DC line.Pass through the t that is delayedset2, realize nearly back-up protection and this section of electric current
The cooperation of fast tripping protection prevents main protection from acting backup false protection.Judge speed to improve, while judging that directional current is sentenced
According to whether true with low voltage criterion.Wherein, if this grade of circuit and subordinate's line direction are satisfied by continuous 3 sampling periods,
Then think that directional current criterion is set up, failure is happened at this section of circuit.The case where being set up further according to low voltage criterion judges whether
For troubles inside the sample space, and determine fault type.If in tset2Interior, only cathode voltage meets always, then is plus earth short circuit；If
tset2Inside only cathode voltage meets always, then is cathode ground short circuit；If in tset2Interior positive and negative electrode voltage meets always, then for
Intereelectrode short-circuit.
In photovoltaic DC access system model, by taking the protection of circuit AB as an example, the beginnings circuit AB, BC electricity after failure is analyzed
Flow direction.On circuit AB after any point k2 failures, the fault current at the beginnings circuit AB is mainly received by photovoltaic plant and line electricity
Electricity provides, and the fault current at the beginnings circuit BC is mainly MMC capacitance discharge currents, and with the beginnings AB fault current direction on the contrary, i
Electrode current direction SiA=1, SiB=-1 or SiA=-1, SiB=1, directional current criterion is set up, and is troubles inside the sample space, is continued to judge AB
Beginning voltage determines failure pole.When circuit AB higher level's k1 point failures, circuit AB, BC beginning electric currents are carried by the electric discharge of MMC capacitances
For SiA、SiBIt is 1 or -1, directional current criterion is invalid, is external area error, and protection is failure to actuate.When k3 points event on circuit BC
When barrier, the beginnings circuit AB, BC electric current is provided by photovoltaic plant, SiA、SiBIt is 1 or -1, directional current criterion is invalid, is
External area error, protection are failure to actuate.
For circuit AB, after the short circuit of circuit beginning, current quick is failure to actuate, and as shown in Table 1, and main protection is set up
Time up to 0.4ms, therefore enable tset2=0.5ms, Kset2.1=1.1, take the beginnings AB overcurrent definite value Iset2.1.A=0.0128kA,
The beginnings BC overcurrent definite value Iset2.1.B=0.0177kA.Enable Kset2.2=0.9, take the minimum voltage U for allowing operation0A.min=
28.5kV, then Uset2.2=26.65kV.
For circuit BC, the beginnings BC overcurrent definite value Iset2.1.BThe beginning=0.0128kA, CD overcurrent definite value Iset2.1.C=
0.0177kA.As shown in Table 1, in addition to high resistant short circuit, time up to 1.4ms is set up in main protection, therefore enables tset2=5ms, Kset2.1
=0.9, circuit rated voltage U0A=30kV, then Uset2.2=7.9kV.When low voltage criterion setting valve is formula (14), by table 1
It is found that time up to 15.7ms is set up in main protection, therefore enable tset2=20ms, Uset2.2Value is identical as AB sections.Nearly back-up protection
Test result such as table 2.
The test result of 2 nearly back-up protection scheme of table
As shown in Table 2, the nearly back-up protection being made of directional current protection and under-voltage protection, can accurately identify whole
Short circuit in section circuit, and external area error not malfunction.Because of Protection criteria only related, therefore the transition resistance shadow by normal operating condition
The quick-action for ringing protection, has no effect on the reliability of protection.In addition, in directional current protection, next stage circuit beginning need to be acquired
Current direction signal causes the quick-action of protection also by communication delay.Compared to main protection, back-up protection is to quick-action
It is required that it is relatively low, and the protection reliability is higher, therefore can be used for the back-up protection of DC line.
Remote back-up protection flow chart as indicated at 4, wherein tset3For the time definite value of remote back-up protection.To prevent fault type
Erroneous judgement, voltage across poles criterion, unbalance voltage criterion and differential unbalance voltage criterion need to continuously meet at least 1/2 power frequency week
Phase, i.e. 10ms are just judged to criterion establishment.
Photovoltaic DC shown in Fig. 1 collects in access system, by taking BC sections of remote back-up protections as an example, AC and DC in analysis area
After failure, BC sections of beginning voltage characteristics.In area after interpolar metallic short circuit, circuit beginning voltage across poles udcBust and close to 0, by
Equal in fault point in positive and negative pole tension, circuit is uniform transmission line, therefore circuit beginning unbalance voltage upn=0.Monopole gold
After attribute short circuit, it is contemplated that instant of failure, capacitor charge and discharge influences in photovoltaic plant, voltage across poles udcRestore to failure after fluctuation
Preceding value, but unbalance voltage upnVoltage across poles is sported by 0.After transverter exchanges exit k5 point short circuits, in MMC submodules
Under capacitor charge and discharge effect, the fluctuation of MMC DC side voltage across poles, under its influence, circuit voltage across poles udcFluctuation.And due to straight
Galvanic electricity briquetting component containing AC sine, unbalance voltage upnB1Also include sinusoidal component.The uneven electricity of the differential at the beginnings circuit BC
Pressure is less than setting valve, and protection is failure to actuate.
The test result of 3 remote back-up protection scheme of table
For circuit AB, remote back-up protection need to coordinate in nearly back-up protection with circuit BC's, and as shown in Table 2, circuit BC is close
Back-up protection actuation time is up to 20.6ms, therefore takes tset3=25ms.Enable Kset3.1The beginning=1.1, AB overcurrent definite value Iset3.1.A
The end=0.0128kA, BC overcurrent definite value Iset3.1.B=0.0159kA.Enable Kset3.2=Kset3.3=Kset3.4=1.1, take Uset3.2
=55kV, Uset3.3=51.3kV, Uset3.4=3.828.For circuit BC, remote back-up protection need to be protected with MMC exchange side matches
It closes, tset3Value need to escape the exchange side nearly back-up protection maximum actuation time.Enable Kset3.1=1.1, take the beginnings BC overcurrent definite value
Iset3.1.B=0.0128kA.Enable Kset3.2=Kset3.3=Kset3.4=1.1, acquire Uset3.2=55kV, Uset3.3=51.3kV,
Uset3.4=0.048.
Remote back-up protection scenario outcomes verification such as table 3, wherein it includes action delay t that criterion, which sets up the time not,set3, AF A
Phase ground short circuit, BCF B, C line to line fault, BCGF B, C two-phase grounding faults, ABCF is three-phase shortcircuit.
As shown in Table 3, when subordinate is still DC line, remote back-up protection can accurately identify this section and subordinate's circuit is short
Road.When subordinate is transverter, remote back-up protection can identify the direct-current short circuit of this section of circuit and Converter DC-side, Yi Jihuan
Device exchange side single-line to ground fault is flowed, and after transverter subordinate AC fault, protects not malfunction.
In summary, which has good reliability.
It is last it is to be noted that：The above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations.To the greatest extent
Present invention has been described in detail with reference to the aforementioned embodiments for pipe, it will be understood by those of ordinary skill in the art that：It is still
Can be with technical scheme described in the above embodiments is modified, or which part technical characteristic is equally replaced
It changes；And these modifications or replacements, the essence for various embodiments of the present invention technical solution that it does not separate the essence of the corresponding technical solution
God and range.
Claims (7)
1. a kind of DC line protection method suitable for alternating current-direct current mixing power distribution network, which is characterized in that include the following steps：
1) it proposes main protection judgment method, formulates the composition and judgment rule of main protection.The main protection by current differential protection,
Overcurrent is protected and positive and negative electrode current imbalance protection composition；Wherein, current differential protection is used for failure judgement position, mistake
Stream protection and current imbalance protect fault type for identification；Protection domain is whole section of DC line；
2) it proposes nearly back-up protection judgment method, formulates the composition and judgment rule of nearly back-up protection；The nearly back-up protection by
Directional current protection and under-voltage protection composition, directional current protection determine fault zone, under-voltage protection failure judgement type；
Not by transition Resistance Influence, protection domain is total track length；
3) it proposes remote back-up protection judgment method, formulates the composition and judgment rule of remote back-up protection.The remote back-up protection by
Directional current protection for determining abort situation, and voltage across poles protection, unbalance voltage for determining fault type
Protection and differential unstable voltage protection composition；When downstream is also DC line by protection equipment, remote back-up protection is ranging from
This section of circuit and subordinate's circuit；When downstream by protection equipment be transverter when, remote back-up protection range from this section of circuit beginning to
Transverter exchanges exit；At this point, remote back-up protection is applied not only to prevent direct current main protection, nearly back-up protection tripping from leading to not
The case where isolated DC failure, after can also reducing AC fault, especially after AC single phase ground short circuit, harmonics are failure to actuate
Influence to direct current tolerance；
The downstream refers to side adjacent with by protection DC line, far from power supply or equivalent power supply；The circuit beginning is
Refer to circuit close to power supply or one end of equivalent power supply.
2. method according to claim 1, which is characterized in that current differential protection judges rule in the main protection described in step 1)
Include then：
Total continuous n times of poor stream criterion (generally taking 3~5 times) are set up, then are judged to protected circuit troubles inside the sample space；Total poor stream is sentenced
According to shown in such as formula (1)：
idcDiff＞ Iset1.1 (1)
Wherein, Iset1.1For total difference current definite value, calculated by principle shown in formula (2)：
Iset1.1=Kset1.1max{|IdcD.sup|, | IdcD.sub|, | IdcD.nor|} (2)
In formula (2), Kset1.1For the safety factor more than 1；IdcD.sup、IdcD.sub、IdcD.norRespectively upstream DC line short circuit,
When the short circuit of downstream DC line and normal operation, this section of DC line begin, the maximum difference stream of end current；Max { } expressions take most
Big value；The upstream refers to adjacent with by protection DC line, close to the side of power supply or equivalent power supply；The line end is
Refer to the one end of circuit far from power supply or equivalent power supply；
In formula (1), idcDiffFor total poor stream, shown in computational methods such as formula (3)：
idcDiff=| ipDiff|+|inDiff| (3)
Wherein, ipDiff、inDiffThe respectively difference current of protected circuit anode and cathode, shown in computational methods such as formula (4)：
Wherein, A, B indicate the both ends of a DC line respectively；ipARectify electrode current, i for ApBRectify electrode current, i for BnAFor A
Hold cathodal current, inBFor the ends B cathodal current.
3. method according to claim 1, which is characterized in that current imbalance protection and electricity in the main protection described in step 1)
Flowing overcurrent protection judgment rule includes：
After being determined as protected circuit troubles inside the sample space, failure judgement pole is protected by current imbalance protection and overcurrent；Its
In, current imbalance protection is judged using line one-end positive and negative electrode current imbalance factor, and overcurrent protection uses circuit one
The difference current at end judges；
The line one-end positive and negative electrode current imbalance factor KIdiffIt is calculated by formula (5)：
In formula (5), inAnd ipRespectively by the measurement electric current of protection DC line the same end cathode and anode；
The rule of the failure judgement pole includes the following steps：
If 1) | KIdiff- 1 | ＞ KsetIdAnd KIdiff＞ 1 meets simultaneously, then is judged to anode circuit ground short circuit；
Wherein KsetIdFor monopole fault threshold values, calculated according to formula (6)：
KsetId=Kset1.3max{|KId.nor- 1 |, | KId.PNF-1|} (6)
Wherein, Kset1.3For the safety factor more than 1；KId.nor、KId.PNFRespectively in normal operation and area when intereelectrode short-circuit, line
The single-ended positive and negative electrode current imbalance factor in road；
If 2) | KIdiff- 1 | ＞ KsetIdAnd KIdiff＜ 1 meets simultaneously, then is judged to positive circuit ground short circuit；
If 3) KIdiff=1, then judge that failure is not had by protection DC line, or interpolar failure has occurred；And further according to
Formula (7) is calculated by the difference current i at protection DC line one end (such as ends A)dcA：
idcA=| ipA|+|inA| (7)
Wherein, ipA、inARespectively DC line A rectify, cathodal current；
If idcA＞ Iset1.2, then it is judged to interpolar failure；Wherein Iset1.2For threshold value, calculate as shown in formula (8)：
Iset1.2=Kset1.2max{IdcA SpF, IdcA nor} (8)
Wherein, IdcA.SpF、IdcA.norMonopole short circuit grounding and when normal operation respectively in area, circuit A rectifies, cathodal current is surveyed
The maximum value of the sum of magnitude；Kset1.2For the safety factor more than 1.
4. method according to claim 1, which is characterized in that directional current protection is sentenced in the nearly back-up protection described in step 2)
Disconnected rule includes：
1) pass through the t that is delayedset2, realize the cooperation of nearly back-up protection and main protection；To escape AC fault, tset2Value be more than etc.
In 1/4 power frequency period, that is, it is more than 5ms；
2) it is to improve to judge speed, while judging whether current direction criterion and low voltage criterion are true；Wherein, if continuous 3
This grade of circuit and downstream line direction are satisfied by current direction criterion in sampling period, then it is assumed that and current direction criterion is set up, therefore
Barrier is happened at this section of circuit；
3) the case where being set up further according to low voltage criterion determines whether troubles inside the sample space, and determines fault type；If in tset2It is interior,
Only cathode voltage meets low voltage criterion always, then is plus earth short circuit；If in tset2Inside only cathode voltage meet always it is low
Voltage criterion is then cathode ground short circuit；If in tset2Interior positive and negative electrode voltage meets always low voltage criterion, then is interpolar
Short circuit.
5. method according to claim 4, which is characterized in that the current direction criterion includes：
1) line one-end (such as ends the A) poles i fault current direction is denoted as SiA(i=p, n, and p represent anode, and n represents cathode), takes
Value is calculated by formula (9)：
Wherein, iiAFor the ends A i electrode current measured values；iiA0For normal operation when, the ends A i electrode currents；Iset2.1For over-current adjusting value, press
Formula (10) calculates：
Wherein, Kset2.1It is slightly over 1 safety factor；IiA0.max、IiA0.minRespectively normal operation when, the ends A i electrode currents are most
Big value and minimum value；
If 2) this section of circuit beginning fault current direction SiA, with downstream line beginning fault current direction SisubMeet formula (11),
It is then judged to that troubles inside the sample space occurs；
SiASisub=-1 (11)
6. method according to claim 4, which is characterized in that shown in the low voltage criterion such as formula (12)：
Wherein, upA、unARectify for circuit A, cathode voltage, Uset2.2For low-voltage threshold value；When protected circuit downstream is direct current
When circuit, Uset2.2It is calculated by formula (13)；When protected circuit downstream is transverter, Uset2.2It is calculated by formula (14)；
Uset2.2=Kset2.2U0A.min (13)
Wherein, Kset2.2For the safety factor of under-voltage protection, value is more than 1；U0A.minFor normal operation when circuit beginning it is minimum
Voltage；U0AFor circuit beginning rated voltage.
7. method according to claim 1, which is characterized in that the remote back-up protection judgment rule described in step 3) includes：
1) when subordinate is also DC line, remote back-up protection ranging from this section of circuit and subordinate's circuit；When subordinate is transverter
When, remote back-up protection range exchanges exit (connection transformer valve side) from this section of circuit beginning to transverter, at this point, remote standby
Protection is applied not only to DC Line Fault caused by preventing DC current fast tripping protection, nearly back-up protection tripping and can not be isolated, can be with
After reducing AC fault, especially after AC single phase ground short circuit, harmonics are failure to actuate the influence to direct current tolerance；
2) remote back-up protection includes the directional current protection for determining abort situation, and the interpolar for determining fault type
Voltage protection, unstable voltage protection and differential unstable voltage protection；
3) when being still DC line by protection DC line downstream, in the judgement flow and claim 5 of directional current protection
It is described identical；
When subordinate is current conversion station, then coordinated by this section of circuit beginning current direction and voltage protection, whether failure judgement is sent out
In the areas Sheng；The voltage protection includes voltage across poles criterion, unbalance voltage criterion and differential unbalance voltage criterion,
In, shown in voltage across poles criterion such as formula (15), shown in unbalance voltage criterion such as formula (16), differential unbalance voltage criterion such as formula
(17) shown in；To prevent fault type from judging by accident, voltage across poles criterion, unbalance voltage criterion and differential unbalance voltage criterion need
It is continuous to meet at least 1/2 power frequency period, i.e. 10ms, just it is judged to criterion establishment；
udc＜ Uset3.2 (15)
|upn| ＞ Uset3.3 (16)
Wherein, udcFor DC line voltage across poles；upnFor unbalance voltage, be equal to DC line positive and negative electrode voltage vector and；
Uset3.2、Uset3.3、Uset3.4As shown in formula (18)：
Wherein, Kset3.2、Kset3.3、Kset3.4For safety factor, Kset3.2Value is slightly less than 1, Kset3.3、Kset3.4Value is slightly larger than 1；
Udc.nor.minFor normal operation when minimum voltage across poles；Upn.nor.maxFor normal operation when maximum unbalance voltage；Work as subordinate
When being still DC line, UpnD.AC.maxFor the maximum differential unbalance voltage of exchange side short circuit, at this point, the criterion is for preventing from changing
It flows device and exchanges false protection after terminal short-circuit；When subordinate is transverter, UpnD.AC.maxFor subordinate's AC line of current conversion station connection
The maximum differential unbalance voltage on short out road, at this point, the criterion is for preventing false protection after AC line short circuit.
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