CN104155572B - Fault line selection method for same-tower double-circuit direct current transmission line - Google Patents

Abstract

The invention discloses a fault line selection method for a same-tower double-circuit direct current transmission line. The fault line selection method comprises the following steps: calculating linear modal wave and ground modal wave of the current circuit of the double-circuit according to the polar line voltage and current of the current circuit; calculating ground modal wave change rate; judging whether the ground modal wave change rate is larger than a minimum setting valve or not, if yes, obtaining squared value of the linear modal wave and the ground modal wave respectively, then performing integration, and calculating the integral ratio of the linear modal wave and the ground modal wave, and if not, continuing to judge; distinguishing the fault circuit and the non-fault circuit according to the ratio; distinguishing the fault polar and the non-fault polar in the fault circuit according to the integral value of the ground modal wave. The method has the advantages of high sensitivity, small operation amount, requirement of current circuit information, no communication between different circuits, short determining time, low influence by transition resistance, capability of quickly determining the fault circuit of the same-tower double direct current transmission line without misjudgement and the like.

Description

A kind of same-tower double-circuit direct-current transmission line fault line selection

Technical field

The present invention relates to a kind of power system HVDC Transmission Technology, particularly to a kind of event of common-tower double-return DC power transmission line Barrier selection method.

Background technology

Chinese natural energy resources skewness and the energy are with the asymmetric present situation of population distribution so that D.C. high voltage transmission Technology has open application prospect at home.Compare high-voltage AC transmission technology, high voltage dc transmission technology has unit and makes The advantages of valency is low, through-put power is big, two ends exchange need not run simultaneously, control to adjust rapid, therefore uses D.C. high voltage transmission Technology is conducive to improving economic indicator, flexibility of technical indicator, reliability of operation and scheduling of power system etc..

In order to ensure the safe and reliable operation of power system, the protection of HVDC transmission line is significant.Mesh Before, HVDC transmission line protection in the world adopts traveling-wave protection mostly, using the voltage electricity traveling to protection point Popular wave characteristic carries out fault distinguishing, and protection detection time is short.But, because the increase of transmission line capability and transmission of electricity corridor are nervous, Common-tower double-return DC power transmission line just increasingly puts into operation.Multiple-circuit on same tower has two loop line roads, each loop line road have positive pole, Negative pole, the polar curve on arbitrary loop line road breaks down, and all can sense in the positive pole on another loop line road and negative pole in traveling wave communication process Fault electric parameters, unfavorable to the traveling-wave protection based on single back line or one pole line, the false protection that non-faulting is returned may be caused.For Ensure that the reliability of transmission line of electricity route selection will improve circuit setting valve, but can due to voltage x current during high resistance earthing fault Inconspicuous etc. electric parameters fault signature, also easily tripping in fault-line selecting method.Traditional mould based on single back line design Measure after traveling-wave protection is applied to common-tower double-return DC power transmission line although the line mould ripple being coupled to non-faulting is very little, but by In there being three different Aerial mode components on multiple-circuit on same tower, non-faulting returns the line mould ripple of sensing with transition resistance and fault The change of distance, may make line mould ripple rate of change and line mould ripple change amplitude be more than setting valve and cause malfunction.

Content of the invention

It is an object of the invention to overcoming shortcoming and the deficiency of prior art, provide a kind of common-tower double-return DC power transmission line Fault-line selecting method, the method is that the information based on each time of double-circuit line for the fault signature for multiple-circuit on same tower provides one It is adaptable to there is existing common-tower double-return DC power transmission line and spirit in the selection method planting common-tower double-return direct current transmission line fault Sensitivity is high, be not susceptible to erroneous judgement, and tolerance transition resistance ability is strong.

The purpose of the present invention is achieved through the following technical solutions：A kind of common-tower double-return direct current transmission line fault route selection side Method, comprises the steps of：

(1) take a certain particular moment instantaneous voltage before current time as reference quantity, by the electricity of current time Pressure instantaneous value deducts the voltage variety that reference quantity obtains four polar curves, and wherein four polar curves are represented with 1P, 1N, 2P, 2N, 1P, The 1N electrode line on the first loop line road, negative line respectively, 2P, 2N respectively electrode line on the second loop line road and negative line, then four The voltage variety of polar curve is respectively Δ u_1P、Δu_1N、Δu_2P、Δu_2N；Current change quantity is respectively Δ i_1P、Δi_1N、Δi_2P、Δ i_2N.

(2) based on single back line line mould ripple and topotype ripple ask for define, calculate the dummy line mould ripple on each loop line road respectively With virtual topotype ripple, computing formula is as follows：

Wherein P₁、G₁Represent the dummy line mould ripple on the first loop line road and virtual topotype ripple respectively；G₂、P₂Represent second respectively The dummy line mould ripple on loop line road and virtual topotype ripple.

(3) calculate the rate of change dG of the virtual topotype ripple in the first loop line road₁The change of the virtual topotype ripple of/dt and the second loop line road Rate dG₂/ dt, and take absolute value respectively.

(4) start when the absolute value of the virtual topotype ripple rate of change on this loop line road exceedes setting valve virtual to this loop line road Integrate after line mould ripple P and virtual topotype ripple G is squaredAnd ask for integrated square ratioWithS is individually integrated obtaining to the virtual topotype ripple G on every loop line road simultaneously_G.

(5) carry out fault according to ratio result in given time window T to select back：

If aFor non-faulting loop line, this time route protection of locking；

If bFor fault loop line, complete fault and select back.

(6) virtual topotype ripple integrated value S according to fault loop_GCarry out Judging fault and the positive pole returning in fault occurs still Negative pole.

If a is S_G>Δ_s, it is the positive electrode fault that fault is returned；

If b is S_G<-Δ_s, it is the negative pole fault that fault is returned.

Preferably, in step (1), the voltage variety on four described loop line roads is before current instantaneous value deducts 10ms Value, to guarantee that what in the 10ms after line failure line voltage distribution deducted is the steady-state value before fault occurs, obtains circuit Voltage failure amount, is calculated using following formula：

Wherein, u_1P(t)、i_1PT () represents polar curve 1P in the instantaneous voltage of t, current instantaneous value, Δ u respectively_1P、Δ i_1PRepresent voltage jump amount after protection starts for the circuit 1P, jump-value of current respectively, the rest may be inferred by analogy for it, and Δ t=10ms is current Moment and the time interval of particular moment.

Preferably, in step (3), the numerical method asking for virtual topotype ripple rate of change is to ask for the Backward divided difference of three points The maximum of numerical differentiation value, asks for formula as follows：

Wherein, t_dFor sampling time interval.

When circuit is short-circuited fault, the false voltage traveling wave of short dot and current traveling wave are propagated to circuit two ends, by Can be distorted in circuit communication process in traveling wave and decay, when reaching circuit two ends, wavefront is frequently not rectangular wave, institute So that the fault characteristic amount of correlation must could be obtained, therefore takes topotype ripple numerical differentiation by catching the maximum of wavefront Maximum contribute to obtaining more accurate data, accuracy is high.

Preferably, in step (4), the setting valve reaching the absolute value of the topotype ripple rate of change of distinguishing rule as traveling wave sets For 100kv/ms, ensure that topotype rate of change still can start when circuit occurs high resistance ground with relatively low setting valve, thus Judging fault traveling wave can reach protection point.

And the integration of dummy line mould ripple square value and virtual topotype popin side value often takes a point to be all multiplied by a coefficientt_d、T_IFor the parameter setting, to carry out gain or scaling to integrated value, and lower limit of integral is set to 1 it is ensured that dummy line mould Ripple is not 0 with the denominator of the integrated square ratio of virtual topotype ripple, and computing formula is：

It is respectively the integrated square value of dummy line mould ripple and virtual topotype ripple, t_dFor sampling time interval 0.1ms, T_IFor integration time constant 2ms.

The principle of the failure line selection of the present invention is as follows：When circuit symmetrically replaces, the dummy line mould ripple that fault is returned has necessarily Amplitude, and the dummy line mould wave amplitude that non-faulting is returned is 0.When the asymmetric transposition of circuit, feature is similar to, only because actual meaning The inconsistent dummy line mould wave amplitude causing non-faulting to return of Aerial mode component of justice is not 0.If conventionally utilizing virtual The rate of change of line mould ripple and change amplitude carry out fault and select Hui Ze to be subject to transition Resistance Influence than larger.Hence with virtual topotype ripple Carry out ratio method differentiation with dummy line mould ripple, then the ratio that fault is returned can be smaller, and the ratio that non-faulting is returned can be than larger.This Outward, during positive electrode fault, the virtual topotype ripple that fault is returned is toward positive polarity direction change；During negative pole fault, the virtual topotype that fault is returned Ripple, toward negative polarity direction change, therefore can carry out the failure line selection after fault is selected back.

Practical Project circuit asymmetric transposition, multiple-circuit on same tower has three Aerial mode components and a ground mold component, but It is because the difference of three Aerial mode components is less, although therefore non-faulting returns calculated dummy line mould ripple is not exclusively 0, Very little, impact can be reduced after therefore taking integration, return for Judging fault and return with non-faulting.Additionally, three Aerial mode components Difference also makes fault return to be calculated each instantaneous value of virtual topotype ripple and just might not be entirely or be entirely negative, but can So that impact is reduced by integration.Again because the virtual topotype ripple that non-faulting is returned contains the Aerial mode component being of practical significance and topotype divides Amount, the polar orientation of the two is contrary, and as shown in Figure 2 a and 2 b, therefore first squared value integrates and is conducive to increase non-faulting to return Virtual topotype ripple and virtual topotype ripple ratio.

In sum, following computing formula can be chosen as route selection criterion：

As the absolute value abs (dG/dt) of the topotype ripple change setting valve G extremely low more than₀When, start to dummy line mould The square value P of ripple², the square value G of virtual topotype ripple², virtual topotype ripple G and being integrated, obtain integrated value And S_G, and calculating integral valueWithRatio, if in limited time window,Exceed setting valve K, then for Non-faulting is returned, and by this loop line road locking, another loop line road not locking is fault and returns.If in limited time window, fault is returned Topotype ripple integrated value be more than a positive setting valve Δ_sIt is then positive electrode fault；If the topotype ripple integrated value that fault is returned is less than one Individual negative setting valve-Δ_sIt is then negative pole fault.It is because while that the not quite identical of three Aerial mode components causes virtually Mould ripple integrated value is not exclusively to be just or not exclusively negative, but when positive electrode fault, the integrated value of virtual topotype ripple is toward negative direction Deviate abscissa very little, can be differentiated with a relatively low positive setting valve；And when negative pole fault, the integration of virtual topotype ripple It is worth very little toward positive direction deviation abscissa, can be differentiated with a relatively low negative setting valve of absolute value.

Setting principle；

The setting valve of absolute value topotype ripple rate of change should be taken into account still can be with action, simultaneously during circuit generation high resistance ground In order to reflect that circuit traveling wave reaches this information, setting valve suitably can be reduced on the basis of meeting previous condition again.This Literary composition is verified under circuit 500 Ω transition resistance ground fault condition with meeting, and the setting valve of therefore topotype ripple rate of change should be Different faults are apart from lower 0.97 times that minimum topotype ripple rate of change absolute value during 500 Ω transition resistance earth fault occurs.

Fault in the case of the adjusting by various line-to-ground faults of K is returned the ratio being returned with non-faulting and is verified, in order to Ensure that fault returns reliable not locking, non-faulting returns reliable locking, and in order to ensure occurring still can realize during 500 Ω transition resistance Correct route selection, takes fault to return ratio and the polar curve 2N of maximum and occurs 500 Ω transition resistance ground fault condition to be adjusted, K value is taken to return 2 times of virtual topotype ripple and dummy line mould ripple integral square ratio for fault under this failure condition.Additionally, by a large amount of Emulation understand, when positive electrode fault, virtual topotype ripple integrated value that fault is returned only can in the initial 1ms after traveling wave arrival Can change toward positive direction always afterwards to negative offset, the size of the therefore negative setting valve of topotype ripple integration should be greater than positive electrode fault Maximum negative offse amount is to ensure that during positive electrode fault, reliability is not judged to negative pole fault；When negative pole fault, the topotype ripple that fault is returned Initial 1ms only after traveling wave arrival for the integrated value may change toward negative direction, therefore topotype afterwards always toward positive direction change The size of the positive setting valve of ripple integration should be greater than negative pole fault maximum positive offset amount to ensure that during negative pole fault, reliability is not judged to Positive electrode fault.

With regard to the selection of time window, because virtual topotype ripple contains the Aerial mode component being of practical significance, therefore at least to elect as After traveling wave reaches, 2ms has all been reached and Aerial mode component differentia influence reduction in integral and calculating with ensureing three Aerial mode components, with When also ensure to have enough time so that topotype ripple and the integrated square ratio feature integral process of line mould ripple display；Additionally, Do not exceed the 6ms after traveling wave reaches, to ensure the impact of the now not yet controlled system of circuit electric parameters, travelling waves are yet Feature after fault generation, simultaneously in order that protecting quick acting, this method chooses 3ms.

The present invention has such advantages as with respect to prior art and effect：

Firstth, sensitivity is high；The present invention adopts circuit virtual topotype popin side integrated value and line mould popin side integrated value Ratio is selected, and non-faulting returns ratio all considerably beyond adjusting in many cases.

Secondth, do not need to communicate between different times；The present invention only needs to use the electric parameters such as the voltage x current on this loop line road, Only need to same time line-internal to be communicated, and only can carry out lateral communications it is not necessary to different loop line road in same one end Communication, be conducive to that Practical Project is realized and reliability is high.

Secondth, operand is few；The inventive method is only needed to extract voltage variety, is subtracted each other by the addition of voltage x current and ask for Dummy line mould ripple and virtual topotype ripple, numerical value cumulative realization integration, ratio calculation be can achieve to be returned using fault and returned with non-faulting Dummy line mould ripple and the feature difference of virtual topotype ripple and positive electrode fault and the virtual topotype ripple of negative pole fault opposite polarity Realize failure line selection, operand is little, it is easy to accomplish.

3rd, required time window is short；The taken window of the inventive method is shorter, just reaches in protection point 3ms in traveling wave Enable fault to select back, for end fault, the criterion that in the 7ms after fault occurs, non-faulting is returned just can reach setting valve, It is advantageously implemented quick failure line selection.

4th, tolerance transition resistance is big；Under high transition resistance, virtual topotype ripple rate of change remains to open the inventive method Move, and virtual topotype ripple is barely affected with the integrated square ratio feature of line mould ripple, the polarity of virtual topotype ripple is also constant.

Brief description

Fig. 1 is a kind of stream of the same-tower double-circuit direct-current transmission line fault line selection based on single time local message of the present invention Cheng Tu.

Fig. 2 a is the dummy line mould ripple and virtual topotype ripple figure that the symmetrical lower fault that replaces is returned.

Fig. 2 b is the dummy line mould ripple and virtual topotype ripple figure that the symmetrical lower non-faulting that replaces is returned.

Fig. 3 is structure common-tower double-return double back DC power transmission line model according to frequency parameter model figure.

Specific embodiment

With reference to embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention do not limit In this.

Embodiment

As shown in figure 1, a kind of same-tower double-circuit direct-current transmission line fault line selection, comprise the steps of：

(1) take a certain particular moment instantaneous voltage before current time as reference quantity, by the electricity of current time Pressure instantaneous value deducts the voltage variety that reference quantity obtains this time polar curve, and wherein four polar curves are represented with 1P, 1N, 2P, 2N, 1P, 1N represents the electrode line of the 1st loop line, negative line respectively, and 2P, 2N represent electrode line and the negative line of the 2nd loop line respectively, then four The voltage variety of polar curve is respectively Δ u_1P、Δu_1N、Δu_2P、Δu_2N, the voltage variety respectively Δ i on four loop line roads_1P、Δ i_1N、Δi_2P、Δi_2N, calculate formula as follows：

Wherein, u_1P(t)、i_1PT () represents circuit 1P in the instantaneous voltage of t, current instantaneous value, Δ u_1P、Δi_1PTable Show the voltage jump amount after the generation of polar curve 1P fault, jump-value of current, the rest may be inferred by analogy for it, Δ t is current time and particular moment Time interval, Δ t is taken as 10ms and obtains voltage x current fault amount to guarantee the 10ms after fault generation；

(2) computing formula of the line mould ripple based on single back line and topotype ripple asks for dummy line mould ripple and the void on each loop line road Intend topotype ripple, computing formula is as follows：

Wherein, line mould wave impedance and topotype wave impedance are chosen for 245.8 Ω/m and 630.6 respectively according to practical implementation Ω/m；

(3) calculate the integration ratio of virtual topotype ripple and dummy line mould ripple square value：

(4) choose the time window of 3ms, returned according to the ratio result locking non-faulting in time window 3ms：

If a is R₁>K, locking the first loop line road, judge the second loop line road as fault loop；

If b is R₂>K, locking the second loop line road, judge the first loop line road as fault loop；

Wherein, K represents the setting valve of virtual topotype ripple and dummy line mould ripple integrated square ratio；

(5) virtual topotype ripple integrated value S according to time window 3ms internal fault loop_GSelect fault pole：

If a is S_G>0.1p.u., fault extremely positive pole；

If b is S_G<- 0.1p.u., fault extremely negative pole.

Using PSCAD/EMTDC simulation software, cross the systematic parameter of DC engineering with reference to small stream Lip river, build common-tower double-return direct current Transmission system model.Common-tower double-return double back DC power transmission line model builds using according to frequency parameter model, total track length 1254km, Overhead line structures parameter is as shown in Figure 3.The trapezoidal distribution of multiple-circuit on same tower, upper strata polar curve is 1P, 2N, and lower floor's polar curve is 1N, 2P, G1, G2 are respectively ground wire, and horizontal range l3 of two ground wires is 28.4m, and horizontal range l1 of polar curve 1P and 2N is 14.5m, pole Horizontal range l2 of line 1N and 2P is 19.2m, lower floor's polar curve and ground apart from h1 be 18m, upper strata polar curve and lower floor's polar curve Vertical range h2 is 15m, and ground wire is 22m with vertical range h3 of upper strata polar curve.Additionally, the cross-line depth of transmission line of electricity is 18m, The cross-line depth of ground wire is 17m.Then, on the basis of this DC transmission system model, according to fault provided by the present invention Selection method, is based respectively on each single back line and builds each revolving line voltage current change quantity computing module, the change of virtual topotype ripple Rate judge module, fault select back criterion module and failure line selection criterion module, thus constituting its failure line selection model, sampling Frequency is 10kHz, is arranging earth fault respectively, fault resistance includes metallic earthing at rectification side different distance With high resistance earthing fault (500 Ω).Observe the output result that fault selects back model, (table 1 is metallicity event as shown in Table 1 and Table 2 Barrier route selection result, the failure line selection result that table 2 is 500 Ω for transition resistance).S in Tables 1 and 2_G/S_PData fault return and be Maximum in 3ms after traveling wave arrival, non-faulting returns the maximum in 3ms after reaching, S for traveling wave_GAfter then choosing traveling wave arrival Maximum in 3ms and minimum of a value, just can learn differentiation result by the data in these time windows.

Table 1

Table 2

Verified under circuit 500 Ω transition resistance ground fault condition with meeting herein, due to when away from 90%, top Topotype ripple rate of change absolute value minimum 104kv/ms during raw 500 Ω transition resistance earth fault, therefore takes 104kv/ms's 0.97 times of setting valve for topotype ripple rate of change absolute value, this setting valve is 100kv/ms.

It is can be found that by the simulation result of table 2：Limit 2N occurs fault during transition resistance 500 Ω earth fault to return virtually Mould ripple is maximum with dummy line mould ripple integrated square ratio, and up to 5.744, therefore setting valve is taken as 11.488, additionally, by substantial amounts of Emulation understands, when positive electrode fault, the virtual topotype ripple integrated value that fault is returned only may in the initial 1ms after traveling wave arrival To negative offset, change toward positive direction always afterwards, and the maximum offseting toward negative direction is -0.01 order of magnitude perunit value；When negative During the fault of pole, topotype ripple integrated value that fault the is returned initial 1ms only after traveling wave arrival may toward positive direction change, afterwards one Directly toward negative direction change, and toward positive direction skew maximum be 0.01 order of magnitude perunit value, therefore choose 0.1p.u. and- 0.1p.u. carries out, in returning for fault, the setting valve that fault selects pole.

Carry out the event of other metallicity faults and 500 Ω transition resistance situations using the setting valve obtaining according to setting principle Barrier differentiates and fault selects pole, and discovery can be correctly completed fault and select pole, and effect is fine.

Above-described embodiment is the present invention preferably embodiment, but embodiments of the present invention are not subject to above-described embodiment Limit, other any Spirit Essences without departing from the present invention and the change made under principle, modification, replacement, combine, simplify, All should be equivalent substitute mode, be included within protection scope of the present invention.

Claims (6)

1. a kind of same-tower double-circuit direct-current transmission line fault line selection is it is characterised in that comprise the steps of：

(1) take the ginseng as respective polar curve for the voltage x current instantaneous value of each polar curve of a certain particular moment before current time respectively Consider, obtain the voltage of each polar curve by the reference quantity that the voltage x current instantaneous value of each polar curve of current time deducts respective polar curve Variable quantity and current change quantity；

(2) the dummy line mould ripple P of line mould ripple and the first loop line in the formula calculating double-circuit line of topotype ripple is asked for based on single loop line₁、 The virtual topotype ripple G of the first loop line₁, the dummy line mould ripple P of the second loop line₂Virtual topotype ripple G with the second loop line₂；

(3) calculate the absolute value of the rate of change of each loop line road virtual topotype ripple, and whether judge the rate of change absolute value of topotype ripple Meet protection definite value, if the rate of change absolute value of topotype ripple meets protects definite value, execution step (4), otherwise, return to step (3)；

(4) integrate after every loop line road dummy line mould ripple and virtual topotype wavelength-division are not carried out in T time window with squared value, obtain Integrated square value to dummy line mould rippleIntegrated square value with virtual topotype rippleAnd calculate the ratio of the two

(5) carry out fault according to ratio result to select back；IfThis loop line road is non-faulting loop, this time of locking Circuit, this loop line road fault distinguishing terminates；IfThis loop line road is fault loop, this loop line road of not locking, Then execution step (6), K represents the setting valve of virtual topotype ripple and dummy line mould ripple integrated square ratio；

(6) compare topotype ripple integrated value S of fault loop_GSize：If S_G>Δ_s, then represent the just extremely fault of fault loop Pole；If S_G<-Δ_sThen it represents that the negative pole of fault loop is fault pole, Δ_sFor positive electrode fault.

2. same-tower double-circuit direct-current transmission line fault line selection according to claim 1 is it is characterised in that step (1) In, the described voltage variety of each polar curve and current change quantity are calculated using below equation：

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{1P}=u_{1P}\left(t\right)-u_{1P}\left(t-\mathrm{\&Delta;}t\right)\\ {\mathrm{\&Delta;u}}_{1N}=u_{1N}\left(t\right)-u_{1N}\left(t-\mathrm{\&Delta;}t\right)\\ {\mathrm{\&Delta;u}}_{2P}=u_{2P}\left(t\right)-u_{2P}\left(t-\mathrm{\&Delta;}t\right)\\ {\mathrm{\&Delta;u}}_{2N}=u_{2N}\left(t\right)-u_{2N}\left(t-\mathrm{\&Delta;}t\right)\end{array}\right.,$

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{1P}=i_{1P}\left(t\right)-i_{1P}(t-\mathrm{\&Delta;}t)\\ {\mathrm{\&Delta;i}}_{1N}=i_{1N}\left(t\right)-i_{1N}(t-\mathrm{\&Delta;}t)\\ {\mathrm{\&Delta;i}}_{2P}=i_{2P}\left(t\right)-i_{2P}(t-\mathrm{\&Delta;}t)\\ {\mathrm{\&Delta;i}}_{2N}=i_{2N}\left(t\right)-i_{2N}(t-\mathrm{\&Delta;}t)\end{array}\right.,$

Wherein, u_1P(t), i_1PT () represents circuit 1P in the instantaneous voltage of t and current instantaneous value, Δ u respectively_1P、Δi_1P Represent voltage jump amount and the jump-value of current of circuit 1P respectively, by that analogy, between Δ t is for the time before current time and fault Every taking 10ms to guarantee to calculate the voltage jump amount of gained and jump-value of current as fault component.

3. same-tower double-circuit direct-current transmission line fault line selection according to claim 1 is it is characterised in that in step (3), in, the numerical method asking for virtual topotype ripple rate of change is the maximum of the Backward divided difference numerical differentiation value asking for three points, Ask for formula as follows：

${\mathrm{dG}}_1/dt\left(t\right)=max\left\{\frac{G_1\left(t\right)-G_1\left(t-t_d\right)}{t_d},\frac{G_1\left(t-t_d\right)-G_1\left(t-2t_d\right)}{t_d},\frac{G_1\left(t-2t_d\right)-G_1\left(t-3t_d\right)}{t_d}\right\},$

${\mathrm{dG}}_2/dt\left(t\right)=max\left\{\frac{G_2\left(t\right)-G_2\left(t-t_d\right)}{t_d},\frac{G_2\left(t-t_d\right)-G_2\left(t-2t_d\right)}{t_d},\frac{G_2\left(t-2t_d\right)-G_2\left(t-3t_d\right)}{t_d}\right\},$

Wherein, t_dFor sampling time interval, then again topotype ripple rate of change is taken absolute value.

4. same-tower double-circuit direct-current transmission line fault line selection according to claim 1 is it is characterised in that in step (4) in, the integration of line mould ripple and topotype ripple chooses following computing formula, and is output as 1 when integrated value is less than 1, calculates public Formula is：

$S_P\left(t\right)=\left\{\begin{array}{cc}{S}_P(t-t_d)+\frac{t_d}{T_I}*P\left(t\right)& \left(S_p\right(t)>1)\\ 1& \left(S_p\right(t)<1)\end{array}\right.,$

$S_G\left(t\right)=\left\{\begin{array}{cc}{S}_G(t-t_d)+\frac{t_d}{T_I}*G\left(t\right)& \left(S_G\right(t)>1)\\ 1& \left(S_G\right(t)<1)\end{array}\right.,$

P is dummy line mould ripple, and G is virtual topotype ripple, S_PAnd S_GIt is respectively the integrated value of line mould ripple and topotype ripple, t_dFor during sampling Between be spaced, T_IFor integration time constant.

5. same-tower double-circuit direct-current transmission line fault line selection according to claim 1 is it is characterised in that step (2) In, take a certain particular moment instantaneous voltage before current time as reference quantity, by the instantaneous voltage of current time Deduct the voltage variety that reference quantity obtains this time polar curve, wherein four polar curves are represented with 1P, 1N, 2P, 2N, 1P, 1N table respectively Show electrode line, the negative line of the 1st loop line, 2P, 2N represent electrode line and the negative line of the 2nd loop line respectively, then the electricity of four polar curves Pressure variable quantity is respectively Δ u_1P、Δu_1N、Δu_2P、Δu_2N, the voltage variety respectively Δ i on four loop line roads_1P、Δi_1N、Δi_2P、 Δi_2N, calculate the dummy line mould ripple P of the first loop line in described double-circuit line₁With virtual topotype ripple G₁And second loop line virtual Line mould ripple P₂With virtual topotype ripple G₂Computing formula as follows：

$\left\{\begin{array}{c}{P}_1=0.5*\&lsqb;({\mathrm{\&Delta;i}}_{1P}-{\mathrm{\&Delta;i}}_{1N})*Z_{cl}-({\mathrm{\&Delta;u}}_{1P}-{\mathrm{\&Delta;u}}_{1N})\&rsqb;\\ G_1=0.5*\&lsqb;({\mathrm{\&Delta;i}}_{1P}+{\mathrm{\&Delta;i}}_{1N})*Z_{c0}-({\mathrm{\&Delta;u}}_{1P}+{\mathrm{\&Delta;u}}_{1N})\&rsqb;\end{array}\right.,$

$\left\{\begin{array}{c}{P}_2=0.5*\&lsqb;({\mathrm{\&Delta;i}}_{2P}-{\mathrm{\&Delta;i}}_{2N})*Z_{cl}-({\mathrm{\&Delta;u}}_{2P}-{\mathrm{\&Delta;u}}_{2N})\&rsqb;\\ G_2=0.5*\&lsqb;({\mathrm{\&Delta;i}}_{2P}+{\mathrm{\&Delta;i}}_{2N})*Z_{c0}-({\mathrm{\&Delta;u}}_{2P}+{\mathrm{\&Delta;u}}_{2N})\&rsqb;\end{array}\right.,$

Wherein, Z_clFor circuit line mould wave impedance, Z_c0For circuit topotype wave impedance.

6. same-tower double-circuit direct-current transmission line fault line selection according to claim 1 is it is characterised in that step (1) In, described polar curve includes the electrode line 1P of the 1st loop line, negative line 1N of the 1st loop line, the electrode line 2P of the second loop line and second time Negative line 2N of line, the electrode line 1P of described 1st loop line, negative line 1N of the 1st loop line, the electrode line 2P and second of the second loop line The voltage variety of negative line 2N of loop line is respectively Δ u_1P、Δu_1N、Δu_2PWith Δ u_2N, the electrode line 1P of described 1st loop line, The current change quantity of negative line 2N of negative line 1N of the 1st loop line, the electrode line 2P of the second loop line and the second loop line is respectively Δ i_1P、Δi_1N、Δi_2PWith Δ i_2N.