CN104155572A - 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 common-tower double-return direct current transmission line fault selection method

Technical field

The present invention relates to a kind of electric system HVDC Transmission Technology, particularly a kind of common-tower double-return direct current transmission line fault selection method.

Background technology

China's natural energy resources skewness and the energy and the asymmetric present situation of population distribution, make high voltage dc transmission technology have at home open application prospect.Compare high-voltage AC transmission technology, high voltage dc transmission technology has that unit price is low, through-put power is large, two ends exchange without advantages such as synchronous operation, regulating and controlling are rapid, therefore uses high voltage dc transmission technology to be conducive to improve the dirigibility etc. of economic target, technical indicator, reliability of operation and the scheduling of electric system.

In order to ensure the safe and reliable operation of electric system, the protection of HVDC (High Voltage Direct Current) transmission line is significant.At present, HVDC (High Voltage Direct Current) transmission line protection in the world adopts traveling-wave protection mostly, utilizes the electric current and voltage travelling waves that propagates into protection point to carry out fault distinguishing, and protection is short detection time.But because increase and the transmission of electricity corridor of transmission line capability are nervous, common-tower double-return DC power transmission line puts into operation just day by day.Common-tower double-return circuit has two loop line roads; there are positive pole, negative pole in each loop line road; the polar curve on arbitrary loop line road breaks down; the ripple communication process of being expert at all can be in positive pole and the negative pole sense faults electric parameters on another loop line road; unfavorable to the traveling-wave protection based on single back line or one pole line, may cause the protection malfunction that non-fault is returned.In order to guarantee that the reliability of transmission line of electricity route selection will improve circuit setting valve, but the electric parameters fault signature such as electric current and voltage is not obvious can be due to high resistance earthing fault time, and tripping also easily appears in fault-line selecting method.Traditional modulus traveling-wave protection based on single back line design is applied to after common-tower double-return DC power transmission line; although it is very little to be coupled to the line mould ripple of non-fault; but owing to there being three different Aerial mode components on common-tower double-return circuit; non-fault is returned the line mould ripple of induction along with the variation of transition resistance and fault distance, may make line mould ripple rate of change and line mould ripple change amplitude and be greater than setting valve and cause malfunction.

Summary of the invention

The shortcoming that the object of the invention is to overcome prior art is with not enough, a kind of common-tower double-return direct current transmission line fault selection method is provided, the method is that a kind of selection method of common-tower double-return direct current transmission line fault is provided based on each information of returning of double-circuit line for the fault signature of common-tower double-return circuit, be applicable to exist existing common-tower double-return DC power transmission line and highly sensitive, difficult erroneous judgement by accident, tolerance transition resistance ability is strong.

Object of the present invention is achieved through the following technical solutions: a kind of common-tower double-return direct current transmission line fault selection method, comprises following steps:

(1) get before current time a certain particular moment instantaneous voltage as with reference to amount, instantaneous voltage by current time deducts the voltage variety that reference quantity obtains four polar curves, wherein four 1P for polar curve, 1N, 2P, 2N represent, 1P, 1N be electrode line, the negative line on the first loop line road respectively, 2P, 2N are respectively electrode line and the negative line on the second loop line road, and the voltage variety of four polar curves is respectively Δ u _1P, Δ u _1N, Δ u _2P, Δ u _2N; Current change quantity is respectively Δ i _1P, Δ i _1N, Δ i _2P, Δ i _2N.

(2) definition of asking for based on single back line line mould ripple and topotype ripple, calculates respectively dummy line mould ripple and the virtual topotype ripple on each loop line road, and computing formula is as follows:

$\left\{\begin{array}{c}{P}_1=0.5*[({\mathrm{\Δi}}_{1P}-{\mathrm{\Δi}}_{1N})*Z_{\mathrm{cl}}-({\mathrm{\Δu}}_{1P}-{\mathrm{\Δu}}_{1N})]\\ G_1=0.5*[({\mathrm{\Δi}}_{1P}+{\mathrm{\Δi}}_{1N})*Z_{c0}-({\mathrm{\Δu}}_{1P}+{\mathrm{\Δu}}_{1N})]\end{array}\right.,$

$\left\{\begin{array}{c}{P}_2=0.5*[({\mathrm{\Δi}}_{2P}-{\mathrm{\Δi}}_{2N})*Z_{\mathrm{cl}}-({\mathrm{\Δu}}_{2P}-{\mathrm{\Δu}}_{2N})]\\ G_2=0.5*[({\mathrm{\Δi}}_{2P}+{\mathrm{\Δi}}_{2N})*Z_{c0}-({\mathrm{\Δu}}_{2P}+{\mathrm{\Δu}}_{2N})]\end{array}\right.,$

P wherein ₁, G ₁the dummy line mould ripple and the virtual topotype ripple that represent respectively the first loop line road; G ₂, P ₂the dummy line mould ripple and the virtual topotype ripple that represent respectively the second loop line road.

(3) calculate the rate of change dG of the first virtual topotype ripple in loop line road ₁the rate of change dG of/dt and the second virtual topotype ripple in loop line road ₂/ dt, and take absolute value respectively.

(4) when surpassing setting valve, the absolute value of the virtual topotype ripple rate of change on this loop line road starts this loop line road dummy line mould ripple P and the squared rear integration of virtual topotype ripple G to obtain and ask for integrated square ratio with the virtual topotype ripple G on every loop line road is carried out separately to integration simultaneously and obtain S _g.

(5) in given time window T, according to ratio result, carrying out fault selects back:

If a for non-fault loop line, this time route protection of locking;

If b for fault loop line, complete fault and select back.

(6) according to the virtual topotype ripple integrated value S of fault loop _gcarry out Judging fault and occur in positive pole or the negative pole that fault is returned.

If a is S _g> Δ _s, the positive electrode fault returning for fault;

If b is S _g<-Δ _s, the negative pole fault of returning for fault.

Preferably, in step (1), the voltage variety on four described loop line roads is that current instantaneous value deducts the value before 10ms, with what guarantee in the 10ms after line failure that line voltage distribution deducts, is the steady-state value before fault occurs, obtain line voltage distribution fault amount, adopt following formula to calculate:

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

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

Wherein, u _1P(t), i _1P(t) represent that respectively polar curve 1P is at t instantaneous voltage, current instantaneous value constantly, Δ u _1P, Δ i _1Prepresent respectively voltage jump amount, the jump-value of current of circuit 1P after protection starting, the rest may be inferred by analogy for it, and Δ t=10ms is the time interval of current time and particular moment.

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

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

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

Wherein, t _dfor sampling time interval.

When circuit is short-circuited fault, the capable ripple of false voltage and the current traveling wave of short dot are propagated to circuit two ends, because row ripple, in circuit communication process, distortion and decay can occur, while arriving circuit two ends, wavefront is not often rectangular wave, so must be by catching the maximum value of wavefront, could obtain relevant fault characteristic amount, the maximum value of therefore getting topotype ripple numerical differentiation contributes to obtain data more accurately, and degree of accuracy is high.

Preferably; in step (4); the setting valve of absolute value that arrives the topotype ripple rate of change of distinguishing rule as row ripple is made as 100kv/ms; with lower setting valve, guarantee that topotype rate of change still can start when the circuit generation high resistance ground, thereby can arrive protection point by the capable ripple of Judging fault.

And the integration of dummy line mould ripple square value and virtual topotype popin side value is often got a point and is all multiplied by a coefficient t _d, T _ifor the parameter setting, so that integrated value is gained or convergent-divergent, and lower limit of integral is made as 1, guarantees that the denominator of the integrated square ratio of dummy line mould ripple and virtual topotype ripple is not 0, and computing formula is:

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

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

be 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 failure line selection of the present invention is as follows: when the symmetrical transposition of circuit, the dummy line mould ripple that fault is returned has certain amplitude, but not the dummy line mould wave amplitude that fault is returned is 0.When the asymmetric transposition of circuit, seemingly, just because the Aerial mode component of practical significance is inconsistent, cause the dummy line mould wave amplitude that non-fault is returned is not 0 to feature class.If utilize the rate of change of dummy line mould ripple and change amplitude according to classic method, carry out fault to select Hui Ze affected by transition resistance larger.Therefore utilize virtual topotype ripple and dummy line mould ripple to carry out ratioing technigue differentiation, the ratio that fault is returned can be smaller, and the ratio that non-fault is returned can be larger.In addition,, during positive electrode fault, the virtual topotype ripple that fault is returned changes toward positive polarity direction; During negative pole fault, the virtual topotype ripple that fault is returned changes toward negative polarity direction, therefore can carry out the failure line selection after fault is selected back.

Practical Project circuit asymmetric transposition, common-tower double-return circuit has three Aerial mode components and a ground mold component, but because the difference of three Aerial mode components is less, therefore although to return the dummy line mould ripple calculating be not exclusively 0 to non-fault, but very little, therefore after getting integration, can reduce impact, for Judging fault, return with non-fault and return.In addition, the difference of three Aerial mode components also makes fault return to calculate each instantaneous value of virtual topotype ripple just might not be entirely or be entirely negative, but can reduce impact by integration.The virtual topotype ripple returning due to non-fault again contains Aerial mode component and the ground mold component being of practical significance, the opposite polarity directions of the two, as shown in Figure 2 a and 2 b, therefore first squared value again integration be conducive to increase virtual topotype ripple that non-fault returns and the ratio of virtual topotype ripple.

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

The absolute value abs (dG/dt) changing when topotype ripple surpasses an extremely low setting valve G ₀time, start the square value P to dummy line mould ripple ², virtual topotype ripple square value G ², virtual topotype ripple G and carry out integration, obtain integrated value and S _g, and calculating integral value with ratio, if in limited time window, surpass setting valve K, for non-fault, return, by this loop line road locking, another loop line not locking of road is fault and returns.If in limited time window, the topotype ripple integrated value that fault is returned is greater than a positive setting valve Δ _sit is positive electrode fault; If the topotype ripple integrated value that fault is returned is less than a negative setting valve-Δ _sit is negative pole fault.Although this be because the not quite identical virtual topotype ripple integrated value causing of three Aerial mode components not exclusively for just or not exclusively for bearing, but when positive electrode fault, it is very little that the integrated value of virtual topotype ripple departs from horizontal ordinate toward negative direction, with a lower positive setting valve, can differentiate; And when negative pole fault, it is very little that the integrated value of virtual topotype ripple departs from horizontal ordinate toward positive dirction, with a lower negative setting valve of absolute value, can differentiate.

Setting principle;

The setting valve of absolute value topotype ripple rate of change still can move while should be taken into account circuit generation high resistance ground, simultaneously in order to reflect that the capable ripple of circuit arrives this information, setting valve can met to suitably reduction again on the basis of last condition.Herein to meet under circuit 500 Ω transition resistance ground fault condition, carry out verification, so 0.97 times of the minimum topotype ripple rate of change absolute value of the setting valve of topotype ripple rate of change while should be the lower generation 500 Ω transition resistance earth fault of different faults distance.

The adjusting of K returned by the fault in various line-to-ground fault situations the ratio returning with non-fault and carried out verification, in order to guarantee fault, return reliably not locking, non-fault is returned reliable locking, and still can realize correct route selection during in order to ensure generation 500 Ω transition resistance, get fault and return ratio and occur that peaked polar curve 2N 500 Ω transition resistance ground fault condition occurs and adjusts, get K value and return virtual topotype ripple and dummy line mould ripple integral square ratio 2 times for fault under this failure condition.In addition, from a large amount of emulation, when positive electrode fault, in the initial 1ms that the virtual topotype ripple integrated value that fault is returned is only expert at after ripple arrival, may move to negative bias, past positive dirction variation always, so the size of the negative setting valve of topotype ripple integration afterwards is not reliably judged to be negative pole fault in the time of should being greater than the maximum negative side-play amount of positive electrode fault with assurance positive electrode fault; When negative pole fault, the initial 1ms that the topotype ripple integrated value that fault is returned is only expert at after ripple arrival may change toward positive dirction, past negative direction variation always, so the size of the positive setting valve of topotype ripple integration afterwards is not reliably judged to be positive electrode fault in the time of should being greater than the maximum positive side-play amount of negative pole fault with assurance negative pole fault.

About choosing of time window, because virtual topotype ripple is containing the Aerial mode component being of practical significance, therefore after at least will electing row ripple as and arriving, 2ms, to guarantee three Aerial mode components and all arrived and Aerial mode component differentia influence in integral and calculating reduces, also ensures time enough the integrated square ratio feature integral process of topotype ripple and line mould ripple is displayed simultaneously; In addition, also do not surpass the 6ms after row ripple arrives, to guarantee the now impact of the not yet controlled system of line electricity tolerance, travelling waves is the feature after fault occurs, and simultaneously in order to make to protect quick acting, this method is chosen 3ms.

The present invention has following advantage and effect with respect to prior art:

The first, sensitivity is high; The present invention adopts the ratio of the virtual topotype of circuit popin side's integrated value and line mould popin side integrated value to select, and in a lot of situations, non-fault is returned ratio all considerably beyond adjusting.

The second, between different returning, do not need communication; The present invention only need to use the electric parameters such as electric current and voltage on this loop line road, only needs same time line-internal to communicate, and can only in same one end, carry out lateral communications, does not need the communication on different loop lines road, is conducive to Practical Project realization and reliability high.

The second, operand is few; The inventive method only needs to extract voltage variety, by the addition of electric current and voltage, is subtracted each other and asked for that dummy line mould ripple and virtual topotype ripple, numerical value are cumulative realizes that integration, ratio calculation can be realized the dummy line mould ripple that utilizes fault to return to return with non-fault and the opposite polarity of the feature difference of virtual topotype ripple and the virtual topotype ripple of positive electrode fault and negative pole fault is realized failure line selection, operand is little, is easy to realize.

Three, required time window is short; Window that the inventive method takes is shorter, just can realize fault and select back in the ripple of being expert at arrival protection point 3ms, and for end fault, the criterion that in the 7ms after fault occurs, non-fault is returned just can reach setting valve, is conducive to realize failure line selection fast.

Four, tolerance transition resistance is large; The inventive method is under high transition resistance, and virtual topotype ripple rate of change still can start, and the integrated square ratio feature of virtual topotype ripple and line mould ripple is influenced hardly, and the polarity of virtual topotype ripple is also constant.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of a kind of common-tower double-return direct current transmission line fault selection method based on single time local message of the present invention.

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

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

Fig. 3 is the parameter model figure frequently that complies with that builds common-tower double-return double back DC power transmission line model.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited to this.

Embodiment

As shown in Figure 1, a kind of common-tower double-return direct current transmission line fault selection method, comprises following steps:

(1) get before current time a certain particular moment instantaneous voltage as with reference to amount, instantaneous voltage by current time deducts the voltage variety that reference quantity obtains this time polar curve, wherein four 1P for polar curve, 1N, 2P, 2N represent, 1P, 1N represent respectively electrode line, the negative line of the 1st loop line, 2P, 2N represent respectively electrode line and the negative line of the 2nd loop line, and the voltage variety of four polar curves is respectively Δ u _1P, Δ u _1N, Δ u _2P, Δ u _2N, the voltage variety on four loop line roads is respectively Δ i _1P, Δ i _1N, Δ i _2P, Δ i _2N, calculate formula as follows:

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

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

Wherein, u _1P(t), i _1P(t) represent that circuit 1P is at t instantaneous voltage, current instantaneous value constantly, Δ u _1P, Δ i _1Prepresent voltage jump amount, jump-value of current after polar curve 1P fault occurs, the rest may be inferred by analogy for it, and Δ t is the time interval of current time and particular moment, and Δ t is taken as 10ms and obtains electric current and voltage fault amount to guarantee the 10ms after fault occurs;

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

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

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

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

(3) calculate the integration ratio of virtual topotype ripple and dummy line mould ripple square value: $\left\{\begin{array}{c}{R}_1=S_{{G1}^2}/S_{{P1}^2}\\ R_2=S_{{G2}^2}/S_{{P2}^2}\end{array}\right.;$

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

If a is R ₁>K, locking the first loop line road, judges that the second loop line road is fault loop;

If b is R ₂>K, locking the second loop line road, judges that the first loop line road is fault loop;

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

(5) according to the virtual topotype ripple integrated value S in time window 3ms internal fault loop _gselect the fault utmost point:

If a is S _g>0.1p.u., fault is very anodal;

If b is S _g<-0.1p.u., fault negative pole very.

Adopt PSCAD/EMTDC simulation software, the systematic parameter of crossing DC engineering with reference to small stream Lip river, builds common-tower double-return DC transmission system model.Common-tower double-return double back DC power transmission line model adopts according to frequency parameter model and builds, total track length 1254km, and overhead line structures parameter is as shown in Figure 3.Common-tower double-return circuit is trapezoidal profile, upper strata polar curve is 1P, 2N, lower floor's polar curve is 1N, 2P, G1, G2 are respectively ground wire, and the horizontal range l3 of two ground wires is 28.4m, and the horizontal range l1 of polar curve 1P and 2N is 14.5m, the horizontal range l2 of polar curve 1N and 2P is 19.2m, the distance h 1 on lower floor's polar curve and ground is 18m, and the vertical range h2 of upper strata polar curve and lower floor's polar curve is 15m, and the vertical range h3 of ground wire and upper strata polar curve is 22m.In addition, the cross-line degree of depth of transmission line of electricity is 18m, and the cross-line degree of depth of ground wire is 17m.Then, on the basis of this DC transmission system model, according to fault-line selecting method provided by the present invention, based on each single back line, build each revolving line voltage current change quantity computing module, virtual topotype ripple rate of change judge module, fault respectively and select back criterion module and failure line selection criterion module, thereby form its failure line selection model, sample frequency is 10kHz, apart from rectification side different distance place, earth fault is being set respectively, fault resistance comprises metallic earthing and high resistance earthing fault (500 Ω).Observe the Output rusults that fault is selected back model, as shown in Table 1 and Table 2 (table 1 is metallicity failure line selection result, table 2 for transition resistance be the failure line selection result of 500 Ω).S in table 1 and table 2 _g/ S _pdata fault return into row ripple arrive after maximal value in 3ms, non-fault return into row ripple arrive after maximal value in 3ms, S _gchoose row ripple and arrive maximal value and the minimum value in rear 3ms, by the data in these time windows, just can learn differentiation result.

Table 1

Table 2

To meet under circuit 500 Ω transition resistance ground fault condition, carry out verification herein, due to when apart from top, 90% ripple of topotype while there is 500 Ω transition resistance earth fault rate of change absolute value minimum is 104kv/ms, therefore 0.97 times that gets 104kv/ms is the setting valve of topotype ripple rate of change absolute value, and this setting valve is 100kv/ms.

Simulation result by table 2 can be found: when transition resistance 500 Ω earth fault occurs limit 2N, fault is returned virtual topotype ripple and dummy line mould ripple integrated square ratio maximum can reach 5.744, therefore setting valve is taken as 11.488, in addition, from a large amount of emulation, when positive electrode fault, in the initial 1ms that the virtual topotype ripple integrated value that fault is returned is only expert at after ripple arrival, may move to negative bias, toward positive dirction, change afterwards always, and be-0.01 order of magnitude perunit value toward the maximal value of negative direction skew; When negative pole fault, the initial 1ms that the topotype ripple integrated value that fault is returned is only expert at after ripple arrival may change toward positive dirction, toward negative direction, change afterwards always, and the maximal value toward positive dirction skew is 0.01 order of magnitude perunit value, therefore choose 0.1p.u. and-0.1p.u. carries out the setting valve that fault is selected the utmost point during fault is returned.

The setting valve that utilization obtains according to setting principle carries out fault distinguishing and the fault of other metallicity faults and 500 Ω transition resistance situations and selects the utmost point, and discovery can correctly complete fault and select the utmost point, and effect is fine.

Above-described embodiment is preferably embodiment of the present invention; but embodiments of the present invention are not restricted to the described embodiments; other any do not deviate from change, the modification done under Spirit Essence of the present invention and principle, substitutes, combination, simplify; all should be equivalent substitute mode, within being included in protection scope of the present invention.

Claims (6)

1. a common-tower double-return direct current transmission line fault selection method, is characterized in that, comprises following steps:

(1) get respectively before current time a certain particular moment each polar curve electric current and voltage instantaneous value as the reference quantity of polar curve separately, the electric current and voltage instantaneous value of each polar curve by current time deducts the electric current and voltage variable quantity that the reference quantity of polar curve separately obtains each polar curve;

(2) formula of asking for line mould ripple and topotype ripple based on single loop line calculates the dummy line mould ripple P of the first loop line in double-circuit line ₁, the first loop line virtual topotype ripple G ₁, the second loop line dummy line mould ripple P ₂virtual topotype ripple G with the second loop line ₂;

(3) calculate the absolute value of the rate of change of each virtual topotype ripple in loop line road, and the whether satisfied protection definite value of the rate of change absolute value of judgement ground modulus, if the rate of change absolute value of ground modulus meets protection definite value, perform step (4), otherwise, return to step (3);

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

(5) according to ratio result, carrying out fault selects back; If this loop line Lu Weifei fault loop, this loop line road of locking, this loop line road fault distinguishing finishes; If this loop line road is fault loop, this loop line road of not locking, execution step (6);

(6) compare the topotype ripple integrated value S of fault loop _gsize: if S _g> Δ _s, represent the just very fault utmost point of fault loop; If S _g<-Δ _s, the negative pole that represents fault loop is the fault utmost point.

2. common-tower double-return direct current transmission line fault selection method according to claim 1, is characterized in that, in step (1), the voltage variety of each described polar curve and current change quantity adopt following formula to calculate:

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

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

Wherein, u _1P(t), i _1P(t) represent that respectively circuit 1P is at t instantaneous voltage and current instantaneous value constantly, Δ u _1P, Δ i _1Pthe voltage jump amount and the jump-value of current that represent respectively circuit 1P, by that analogy, Δ t is the time interval before current time and fault, gets 10ms and take and guarantee to obtain voltage jump amount in the 10ms after fault occurs and jump-value of current is fault component.

3. common-tower double-return direct current transmission line fault selection method according to claim 1, it is characterized in that, in step (3), the numerical method of asking for topotype ripple rate of change is to ask for the maximal value of the Backward divided difference numerical differentiation value of three points, asks for formula as follows:

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

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

Wherein, t _dfor sampling time interval, and then topotype ripple rate of change is taken absolute value.

4. common-tower double-return direct current transmission line fault selection method according to claim 1, is characterized in that, in step (4), the integration of line mould ripple and topotype ripple is chosen following computing formula, and when integrated value is less than 1, is output as 1, and computing formula is:

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

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

S _pand S _gbe respectively the integrated value of line modulus and ground modulus, t _dfor sampling time interval, T _ifor integration time constant.

5. common-tower double-return direct current transmission line fault selection method according to claim 1, is characterized in that, in step (2), calculates the dummy line mould ripple P of the first loop line in described double-circuit line ₁with virtual topotype ripple G ₁and the dummy line mould ripple P of the second loop line ₂with virtual topotype ripple G ₂computing formula as follows:

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

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

Wherein, Z _clfor circuit line mould wave impedance, Z _c0for circuit topotype wave impedance.

6. common-tower double-return direct current transmission line fault selection method according to claim 1, it is characterized in that, in step (1), described polar curve comprises the electrode line 1P of the 1st loop line, the electrode line 2P of the negative line 1N of the 1st loop line, the second loop line and the negative line 2N of the second loop line, and the voltage variety of the electrode line 1P of described the 1st loop line, the negative line 1N of the 1st loop line, the electrode line 2P of the second loop line and the negative line 2N of the second loop line is respectively Δ u _1P, Δ u _1N, Δ u _2Pwith Δ u _2N, the current change quantity of the electrode line 1P of described the 1st loop line, the negative line 1N of the 1st loop line, the electrode line 2P of the second loop line and the negative line 2N of the second loop line is respectively Δ i _1P, Δ i _1N, Δ i _2Pwith Δ i _2N.