CN104979809A - Method for projecting traveling wave of same-tower double-circuit HVDC transmission line - Google Patents

Abstract

The invention discloses a method for projecting traveling wave of a same-tower double-circuit HVDC transmission line. The method includes employing different criteria for and setting the upper and lower layers of pole wires respectively, eliminating outer-zone faults of the upper-layer pole wire through voltage change rate and current direction, eliminating outer-zone faults of the lower-layer pole wire through ground-mode change rate, employing voltage integration ratio to distinguish the fault of the very pole wire, for the upper-layer pole wire, from that of the other pole wire, and employing voltage integration ratio and modulus integration ratio to distinguish the fault of the very pole wire, for the lower-layer pole wire, from that of the other pole wire. The method has the advantage of high sensitivity, less operation burden and short determination time, the information of the very round is needed, communication between different rounds is not required, and influence of transition resistance is minimal. The fault pole wire of a same-tower double-circuit DC transmission line can be rapidly determined, and misjudgement hardly occurs.

Description

A kind of common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method

Technical field

The present invention relates to a kind of electric power system HVDC (High Voltage Direct Current) transmission line Protection Technology; in particular to a kind of common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method, the method a kind ofly can meet setting value when different polar curve, different circuit distance break down by different Protection criteria and realize protecting the common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection scheme of action message.

Background technology

Along with the development of electrical network scale, HVDC (High Voltage Direct Current) transmission system is applied to Practical Project more and more widely, have also appeared common-tower double-return HVDC (High Voltage Direct Current) transmission system simultaneously.DC transmission system is taked the mode of double-circuit line wiring on the same tower to compare only to adopt single back line transmission of electricity to be more conducive to saving transmission of electricity corridor and improving power delivery capacity; but; owing to there is coupling in various degree between many polar curves; and many long distance direct current transportation polar curves carry out exact sodution coupling there will be multiple modulus; once break down; traveling wave fault characteristic relative complex, will make row wave property analyze and protection seting more difficult.

Conventional high-tension DC transmission system adopts single back line power transmission; there is the low problem of tolerance transition resistance ability, sensitivity in the traveling-wave protection of single back line; trace it to its cause; mainly because the contradiction that other polar curve generation near terminal faults are large in this polar curve coupling amount and this polar curve generation far-end high resistance earthing fault amount is little; if setting value arranges improper; other polar curve near terminal faults then may be caused to cause this pole coupling amount to exceed definite value and malfunction, or be that less being not enough to of this polar curve far-end high resistance earthing fault amount makes the action of this polar curve and tripping.Also effectively do not solve for this problem in single time HVDC (High Voltage Direct Current) transmission line protection at present, improve protection definite value often and ensure the reliable not malfunction of non-faulting polar curve.Equally also there is the indifferent problem of tolerance transition resistance in the traveling-wave protection of common-tower double-return HVDC (High Voltage Direct Current) transmission line.In addition; common-tower double-return HVDC (High Voltage Direct Current) transmission line has two loop line roads; line arrangement mode is asymmetric; different polar curve fault is different in the coupling amount of other polar curves, and therefore the row wave property that obtains of different line fault is different, and fault type increases relatively; if still adopt the Protection criteria of single time DC power transmission line; protected by the rate of change of voltage traveling wave or modulus traveling-waves and amplitude, then protection seting process is more complicated, and reliability is not high.If the fault characteristic of common-tower double-return HVDC (High Voltage Direct Current) transmission line can be made full use of, realize near terminal fault and far-end fault and meet setting value and action by different Protection criteria, just can design more safe and reliable common-tower double-return HVDC (High Voltage Direct Current) transmission line protection.

Summary of the invention

The object of the invention is to overcome the shortcoming of prior art and deficiency, a kind of common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method is provided, this guard method can meet different faults polar curve, different faults distance protection still action message and tolerance higher transition resistance, and for the fault signature of multiple-circuit on same tower, different protection schemes is adopted respectively to upper strata polar curve and lower floor's polar curve, and for the fault characteristic of lower floor's polar curve, adopt two Protection criteria realizing said function simultaneously, arbitrary Protection criteria meets this link of protection and action, be applicable to existing common-tower double-return HVDC (High Voltage Direct Current) transmission line and highly sensitive, not easily judge 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 HVDC (High Voltage Direct Current) transmission line traveling-wave protection method, comprises following steps:

Different layers polar curve takes different fault initiating modes: not strong with being coupled of other polar curves during the polar curve fault of upper strata, take voltage change ratio can distinguish inverter side external area error, and tolerance transition resistance ability is enough strong, adopt average current magnitude can distinguish rectification side external area error simultaneously; Lower floor's line voltage rate of change tolerance transition resistance is indifferent, then adopt topotype ripple rate of change as start-up criterion:

For upper strata polar curve:

(1) calculate this line voltage rate of change and take absolute value,

$|du/dt\left(t\right)|=\left|\frac{u\left(t\right)-u(t-T)}{T}\right|,$

Du/dt (t) is the voltage change ratio of moment t, and u (t) is the magnitude of voltage of moment t, and T is the time scale asking for voltage change ratio, can be chosen for sampling time t _dintegral multiple.The absolute value of voltage change ratio is polar curve protection start-up criterion, starts setting value, make this moment be t if at a time meet _a.

(2) get electric current and voltage mean value in certain a period of time before start-up criterion meets setting value as stable state reference quantity, deduct reference quantity by the instantaneous voltage of current time and current instantaneous value, obtain voltage variety Δ u _1P, Δ u _1N, Δ u _2P, Δ u _2Nwith current change quantity Δ i _1P, Δ i _1N, Δ i _2P, Δ i _2N.Wherein, 1P, 1N are respectively electrode line, the negative line on the first loop line road, and 2P, 2N are respectively electrode line and the negative line on the second loop line road.

(3) mean value of calculating current i in certain hour window:

$avg\left(i\right)=\frac{1}{n}\underset{i=1}{\overset{n}{\Σ}}\mathrm{\Δ}i,$

Avg (i) is the current average of window seclected time, and the sampling number that n is electric current in seclected time window, △ i is current change quantity.

(4) carry out integration by change time window to this line voltage variable quantity with to line voltage variable quantity, and ask for the maximum of the two integration ratio, polar curve is referred to and this polar curve another root polar curve on same loop line road, then time window w _iinterior voltage integrating meter ratio is:

$K_{E_{ul}/E_{ul\_op}}\left(w_i\right)=\frac{E_{ul}\left(w_i\right)}{E_{ul\_op}\left(w_i\right)},$

E _ul(w _i) be time window w _iinterior line voltage integrated value, E _{ul_op}(w _i) be time window w _iinterior to pole line voltage integrated value.Then the maximum of the two integration ratio is:

$K_{E_{ul}/E_{ul\_op}.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_{ul}/E_{ul\_op}}\left(w_i\right),$

T ₀for the time span of maximum duration window.

(5) if current average avg (i) and voltage integrating meter ratio meet Protection criteria, then protection act simultaneously.Protection criteria is:

When this polar curve is electrode line:

$\left\{\begin{array}{c}avg\left(i\right)>0\\ K_{E_{u_l}/E_{u_{l\_op}},\max }>{\mathrm{\&Delta;}}_1\end{array}\right.,$

When this polar curve is negative line:

$\left\{\begin{array}{c}avg\left(i\right)<0\\ K_{E_{u_l}/E_{u_{l\_op}},\max }>{\mathrm{\&Delta;}}_1\end{array}\right.,$

For lower floor's polar curve:

(6) for loop, place, this polar curve road, the absolute value of topotype ripple rate of change is calculated,

$|dG/dt\left(t\right)|=\left|\frac{G\left(t\right)-G(t-T)}{T}\right|,$

The topotype ripple rate of change that dG/dt (t) is moment t, the topotype ripple that G (t) is moment t, T is the time scale asking for topotype ripple rate of change, can be chosen for sampling time t _dintegral multiple.The absolute value of topotype ripple rate of change is polar curve protection start-up criterion, starts setting value, make this moment be t if at a time meet _a, the computing formula of G (t) is:

G(t)＝(i _P(t)+i _N(t))*Z _c0-(u _P(t)+u _N(t))，

I _p(t), i _nt () is respectively electrode line, negative line transient current, u _p(t), u _nt () is respectively electrode line, negative line instantaneous voltage, Z _c0for topotype wave impedance.

(7) get electric current and voltage mean value in certain a period of time before start-up criterion meets setting value as stable state reference quantity, deduct reference quantity by the instantaneous voltage of current time and current instantaneous value, obtain voltage variety Δ u _1P, Δ u _1N, Δ u _2P, Δ u _2Nwith current change quantity Δ i _1P, Δ i _1N, Δ i _2P, Δ i _2N.Wherein, 1P, 1N are respectively electrode line, the negative line on the first loop line road, and 2P, 2N are respectively electrode line and the negative line on the second loop line road.

(8) defined the line mould ripple variable quantity P and topotype ripple variable quantity G that ask for each loop line road of common-tower double-return DC line by the line mould ripple and topotype ripple that singly return DC power transmission line, computing formula is as follows:

$\left\{\begin{array}{c}\mathrm{\&Delta;}P=({\mathrm{\&Delta;i}}_P-{\mathrm{\&Delta;i}}_N)*Z_{cl}-({\mathrm{\&Delta;u}}_P-{\mathrm{\&Delta;u}}_N)\\ \mathrm{\&Delta;}G=({\mathrm{\&Delta;i}}_P+{\mathrm{\&Delta;i}}_N)*Z_{c0}-({\mathrm{\&Delta;u}}_P+{\mathrm{\&Delta;u}}_N)\end{array}\right.,$

Wherein, Δ i _p, Δ i _nbe respectively the current change quantity of this time positive and negative polar curve, Δ u _p, Δ u _nbe respectively the voltage variety of this time positive and negative polar curve, Z _cl, Z _c0be respectively line mould wave impedance and topotype wave impedance.

(9) carry out integration by change time window to this line voltage variable quantity with to line voltage variable quantity, and ask for the maximum of the two integration ratio.

$K_{E_{ul}/E_{ul\_op}}\left(w_i\right)=\frac{E_{ul}\left(w_i\right)}{E_{ul\_op}\left(w_i\right)},$

E _ul(w _i) be time window w _iinterior line voltage integrated value, E _{ul_op}(w _i) be time window w _iinterior to line voltage integrated value, then the maximum of the two integration ratio is:

$K_{E_{ul}/E_{ul\_op}.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_{ul}/E_{ul\_op}}\left(w_i\right),$

T ₀for the time span of maximum duration window.

If voltage integrating meter ratio maximum meet protection seting value Δ ' ₁, then protection act, otherwise proceed to step (10), Protection criteria is:

$K_{E_{u_l}/E_{u_{l\_op}},max}>{{\mathrm{\&Delta;}}^{\&prime;}}_1$

(10) by change time window, integration is carried out to the line mould ripple P on this loop line road and topotype ripple G, and asks for the maximum of the two integration ratio:

$K_{E_G/E_P}\left(w_i\right)=\frac{E_G\left(w_i\right)}{E_P\left(w_i\right)},$

E _g(w _i) be time window w _ithe topotype ripple integrated value on interior loop line road, E _p(w _i) be time window w _ithe line mould ripple integrated value on interior loop line road.

Then the topotype ripple G of this loop line and the integration ratio maximum of line mould ripple P are:

$K_{E_G/E_P.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_G/E_P}\left(w_i\right),$

If modulus integration ratio maximum meets Protection criteria, then protection act, Protection criteria is:

$\left\{\begin{array}{c}{K}_{E_{u_l}/E_{u_l\_op},\max }>1\\ K_{E_G/E_P.\max }<{\mathrm{\&Delta;}}_2\end{array}\right.,$

Preferably; in step (2) and (7); the voltage on four described loop line roads, current change quantity are voltage, current average in certain a period of time before current instantaneous value deducts protection startup; with voltage, the current value guaranteeing to obtain after Protection criteria starts be current voltage, current value deducts the stationary value before fault; obtain line voltage distribution, current change quantity, adopt following formula to calculate:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{1P}=u_{1P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{u}_{1P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{1N}=u_{1N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{u}_{1N}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{2P}=u_{2P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{u}_{2P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{2N}=u_{2N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{u}_{2N}(t_a-i*t_d)}{20}\end{array}\right.,$

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{1P}=i_{1P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{i}_{1P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{1N}=i_{1N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{i}_{1N}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{2P}=i_{2P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{i}_{2P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{2N}=i_{2N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\mathrm{\&Sigma;}}}{i}_{2N}(t_a-i*t_d)}{20}\end{array}\right.,$

Wherein, u _1P(t), i _1Pt () represents instantaneous voltage, the current instantaneous value of polar curve 1P in t respectively, Δ u _1P, Δ i _1Prepresent the voltage variety of polar curve 1P after protection starting, current change quantity respectively, the rest may be inferred by analogy for it.T _afor start-up criterion meets the setting value moment, t _dfor sampling time interval.

Preferably, in step (4), (9), by following this line voltage of formulae discovery and the integrated value to line voltage:

$E_{u_l}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_l\left(i\right),E_{u_{l\_op}}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_{l\_op}\left(i\right),$

Δ u _lfor this line voltage variable quantity, Δ u _{l_op}for to pole line voltage variable quantity, N _ifor time window w _iin number of samples.

Preferably, in step (10), the integrated value by following formulae discovery topotype ripple and line mould ripple:

$E_G\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}G\left(i\right),E_P\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}P\left(i\right),$

Δ G is the topotype ripple variable quantity in loop, this polar curve place, and Δ P is the line mould ripple variable quantity in loop, this polar curve place, N _ifor time window w _iin number of samples.

Preferably, in step (4), (9) and (10), for each time window w _i, initial time is always t _a, finish time is then t _a+ (pt _d) * i, p be increase coefficient, should choose less as far as possible; The number of time window can be selected as required, should choose multiple as far as possible.

In step (9) and (10), fault signature for different faults distance takes different Protection criteria: during lower floor's polar curve near terminal fault, same time this polar curve, with comparatively large to the voltage ratio of polar curve, for judging this polar curve fault, but can reduce during far-end fault; During lower floor's polar curve far-end fault same loop line topotype ripple and line mould Bob value less, effectively can distinguish this line down and another line down, but comparatively large during near terminal fault, and during this polar curve fault, this polar curve with always 1 is greater than to the voltage ratio of polar curve.Therefore, the Protection criteria of lower floor's polar curve be chosen for voltage integrating meter ratio be greater than setting value Δ ' ₁then protection act, or voltage integrating meter ratio is greater than 1 and modulus integration ratio is less than setting value Δ ₂then protection act.

In step (9) and (10); the setting method of lower floor's polar curve is not exclusively protected head end according to the criterion of circuit symmetry transposition model based on two or relation or is not exclusively protected end to adjust; the protection range of two criterions is made to have lap; setting method has theoretical foundation, and protection is more reliable.Setting principle is: voltage integrating meter ratio incomplete protective wire modulus and the distinct far-end fault of ground modulus; And the incomplete protective wire modulus of modulus integration ratio and the complete overlapping near terminal fault of ground modulus; Namely for lower floor's polar curve, voltage integrating meter ratios delta ' ₁adjust as when the lower topotype ripple of symmetry transposition separates completely with line mould ripple, the voltage ratio of fault pole and non-faulting pole is multiplied by a safety factor (1.5 times); And modulus integration ratios delta ₂adjust for symmetry transposition roll off the production line Mo Bo and topotype ripple complete overlapping time the fault integration ratio that returns topotype ripple and line mould ripple be multiplied by a safety factor (0.8 times).

In step (4), (9) and (10), utilize the mode of the integration ratio of voltage or modulus as criterion, efficiently solve the problem that amplitude affects by transition resistance, the integration ratio of voltage or modulus does not affect by transition resistance substantially.

In step (4), (9) and (10), become time window and integration is carried out to voltage and modulus: the time window getting multiple different time length asks for voltage integrating meter ratio and modulus integration ratio, and ask for maximum, to eliminate the impact that fault distance brings.Such as: can be chosen for the modulus integrated value that 5 progressive time windows ask for this line voltage integrated value and this loop line respectively, these 5 progressive time windows are respectively 5,10,15,20 and 25 sampled points (comprising the sampled point that start-up criterion meets the setting value moment) from start-up criterion meets the setting value moment.

Protection philosophy of the present invention is as follows: for upper strata polar curve; when the positive direction of rated current is for flow to inverter side from rectification side; then can determine whether rectification side external area error by sense of current; but DC line fault or inverter side external area error can not be distinguished, therefore also need voltage change ratio criterion to distinguish inverter side external area error.For electrode line, if survey current change quantity direction for just, then may be line fault or inverter side external area error; If to survey current change quantity direction be negative, be then rectification side external area error.For negative line, if to survey current change quantity direction be negative, then may be line fault or inverter side external area error; If survey current change quantity direction for just, be then rectification side external area error.Protect when voltage change ratio and the sense of current two criterions therefore can be utilized to ensure rectification side and inverter side external area error and be failure to actuate.And for lower floor's polar curve, adopt topotype ripple rate of change to start, if topotype ripple rate of change meets setting value, then can get rid of rectification side external area error and inverter side external area error simultaneously.

When the transposition of circuit symmetry, for the first loop line 1P fault, the electric current and voltage of fault polar curve and non-faulting polar curve can be expressed as:

$\left\{\begin{array}{c}{u}_{1P}=-3u_l-u_0,i_{1P}=-3u_l/Z_{cl}-u_0/Z_{c0},\\ u_{1N}=u_l-u_0,i_{1N}=u_l/Z_{cl}-u_0/Z_{c0},\end{array}\right.$

U _1P, u _1Nfor the voltage of polar curve 1P, 1N, i _1P, i _1Nfor the electric current of polar curve 1P, 1N.U _lfor line mould wave amplitude, u ₀for topotype wave amplitude, and u ₀/ u _l=Z ₀/ Z _l.But line mould ripple is different with topotype wave propagation characteristic, the two also non-concurrent superposition.

From above formula, because three Aerial mode components are completely the same, the superposition in the same way of fault very three Aerial mode components, is 3 times of Aerial mode component; And non-faulting very the non-of three Aerial mode components superpose in the same way, be 1 times of Aerial mode component, when only having Aerial mode component at wavefront place, the row wave amplitude size of fault pole is 3 times of the row wave amplitude size of non-faulting pole, as shown in Figure 2.When considering far-end fault; first line mould ripple arrives protection point; the voltage variety of fault pole is 3 times of the voltage variety of non-faulting pole; therefore this line voltage variable quantity and the integration ratio to line voltage variable quantity is utilized; when integration ratio exceedes setting value then protection act when can make this pole fault, and during other polar curve faults, this line voltage variable quantity and the integration ratio to line voltage variable quantity are no more than 3 times and protection is failure to actuate.

Meanwhile, the line mould ripple in loop, fault polar curve place and topotype ripple can be expressed as:

$\left\{\begin{array}{c}P=4u_l\\ G_1=(1+Z_0/Z_l)*u_l+2u_0\\ P_2=0,\\ G_2=(1-Z_0/Z_l)*u_l+2u_0\\ Z_0/Z_l\&ap;2.6\end{array}\right.,$

P ₁, G ₁be line mould ripple and the topotype ripple on the first loop line road, P ₂, G ₂be line mould ripple and the topotype ripple on the second loop line road.

From above formula, the line mould ripple that fault is returned has certain amplitude, and the line mould wave amplitude that non-faulting is returned is 0, as shown in Figure 3 a and Figure 3 b shows.Therefore the topotype ripple that returns of fault and line mould ripple integration ratio are certain value; the integration ratio of the topotype ripple that non-faulting is returned and line mould ripple then ideal situation is a very large value; utilize the integration ratio of topotype ripple and line mould ripple; this time protection act when can make this time polar curve fault, and during the polar curve fault on another loop line road, protection is failure to actuate.When considering near terminal fault, topotype ripple superposes with line mould ripple, and the topotype ripple that fault is returned and line mould Bob value are G ₁/ P ₁=2.2; When considering far-end fault, topotype ripple not yet arrives, and ratio is then 0.9.

Practical Project circuit asymmetric transposition, multiple-circuit on same tower has three Aerial mode components and a ground mold component, Non-completety symmetry transposition causes three Aerial mode components not completely the same, therefore the change in voltage amplitude of fault pole is not 3 times of Aerial mode component, and the change in voltage amplitude of non-faulting pole also differs and is decided to be 1 times of Aerial mode component.Especially, during upper strata polar curve (as 1P) fault, as shown in fig. 4 a, larger time transposition than circuit full symmetric with the row wave amplitude difference in size of non-faulting pole in fault pole, protection action message in this pole when being conducive to adopting voltage ratio to make this pole fault, and this pole protection during the fault of pole is failure to actuate; During lower floor's polar curve (as 1N) fault; as shown in Figure 4 b; little time transposition than circuit full symmetric with the row wave amplitude difference in size of non-faulting pole in fault pole; only utilize voltage ratio, if setting value chooses improper this pole false protection when relay fail or other polar curve faults when just may make this pole fault.But during lower floor's polar curve near terminal fault, as shown in Figure 5, the voltage magnitude of fault pole and non-faulting pole is widely different, voltage ratio still may be used for Judging fault pole and non-faulting pole very greatly, and different faults distance under, during the fault of this pole this pole tension variable quantity with always 1 is greater than to the ratio of pole tension variable quantity.

For line mould ripple and topotype ripple, under asymmetric transposition (for 1P fault), as shown in Figure 6 a, compared with the waveform (as shown in Figure 3 a) when the line mould ripple that fault is returned replaces with full symmetric with topotype ripple, difference is little.But as shown in Figure 6 b, be not entirely 0 compared with the waveform (as shown in Figure 3 b) when the line mould ripple that non-faulting is returned replaces with full symmetric, the integration ratio of the topotype ripple that non-faulting is returned and line mould ripple is not very large under some failure condition.Equally, during 1N polar curve fault, the line mould ripple that non-faulting is returned also not is entirely 0, unfavorable to protection.In addition, for the near terminal fault situation (for 1N fault) that fault is returned, as shown in Figure 7a, topotype ripple is obviously large than line mould wave amplitude, the integration ratio of the topotype ripple that fault is returned and line mould ripple is then relatively large near terminal fault situation, the integration ratio of the topotype ripple utilizing fault to return and line mould ripple is less to carry out differentiation fault and returns when returning with non-faulting, and the near terminal fault situation reliability of returning for fault is not high.But; for far-end fault; as shown in Figure 7b; the row wave amplitude of the topotype ripple that fault is returned and line mould ripple closer to; the integration ratio of the topotype ripple that fault is returned and line mould ripple is less; therefore far-end fault is conducive to utilizing the integration ratio of topotype ripple and line mould ripple be less than setting value and make this time polar curve fault this time protection act, and this time protection of another time line fault is failure to actuate.Utilize this polar curve and this polar curve action when can make this time this polar curve fault to the integration ratio of line voltage variable quantity and the relation of 1, and this time is failure to actuate to this polar curve during polar curve fault simultaneously.Therefore for lower floor's polar curve, protection action message to be realized in conjunction with voltage ratio and modulus ratio simultaneously.

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

For upper strata polar curve, the criterion that protection act need meet is:

For positive electrode fault, after voltage change ratio criterion starts:

$\left\{\begin{array}{c}avg\left(i\right)>0\\ K_{E_{u_l}/E_{u_{l\_op}},\max }>{\mathrm{\&Delta;}}_1\end{array}\right.,$

For negative pole fault, the criterion that protection act need meet is:

$\left\{\begin{array}{c}avg\left(i\right)<0\\ K_{E_{u_l}/E_{u_{l\_op}},\max }>{\mathrm{\&Delta;}}_1\end{array}\right.,$

Avg (i) is the current average of window seclected time, for the maximum of voltage integrating meter ratio, Δ ₁for the setting value of upper strata line voltage integration ratio.

For lower floor's polar curve, the criterion that protection act need meet is:

$K_{E_{u_l}/E_{u_{l\_op}},max}>{{\mathrm{\&Delta;}}^{\&prime;}}_1,$

Or:

$K_{E_{u_l}/E_{u_{l\_op}},\max }>1$ And $K_{E_G/E_P.\max }<{\mathrm{\&Delta;}}_2,$

for the maximum of voltage integrating meter ratio, for the maximum of modulus integration ratio, Δ ' ₁for the setting value of lower floor's line voltage integration ratio, Δ ₂for the setting value of lower floor's polar curve modulus integration ratio.

For upper strata polar curve, after voltage change ratio starts, need current average to distinguish rectification side external area error simultaneously, guarantee troubles inside the sample space; And for lower floor's polar curve, the external area error of rectification side and inverter side can reliably be got rid of by topotype ripple rate of change simultaneously.

For upper strata polar curve, because the amount of the coupling difference of the fault amount of this polar curve fault and other polar curves is comparatively large, directly utilize this polar curve with the voltage integrating meter ratio returned polar curve this polar curve fault can be judged whether.If exceeding setting value is then this polar curve fault.

For lower floor's polar curve, due under some failure condition the fault amount of this polar curve fault and the amount of the coupling difference of other polar curves less, only select voltage integrating meter ratio then protection reliability is not high; Need applied voltage integration ratio simultaneously with modulus integration ratio during near terminal fault, comparatively large, can be greater than setting value Δ ' ₁and action; During far-end fault, less, but still be greater than 1, Ke Yiyou be less than setting value Δ ₂and safety action.

The setting principle that the present invention adopts:

The absolute value of voltage change ratio: owing to utilizing upper strata polar curve to utilize the sense of current can effectively distinguish rectification side external area error, the absolute value of voltage change ratio only need avoid the maximum of the voltage change ratio absolute value that inverter side external area error obtains.

The absolute value of topotype ripple rate of change: the absolute value of topotype ripple rate of change need avoid the maximum of the voltage change ratio absolute value that inverter side external area error obtains.

For upper strata polar curve, want large compared with when voltage variety ratio replaces with symmetry, therefore the setting value of voltage variety integration ratio is the voltage traveling wave variable quantity ratio that the lower far-end fault situation fault pole of symmetrical transposition and wavefront place, non-faulting pole only contain Aerial mode component;

For lower floor's polar curve, owing to making protection act when voltage integrating meter ratio is used near terminal fault, and make protection act when the integration ratio of topotype ripple and line mould ripple is used for far-end fault.In order to ensure no matter which point break down protection can action message, therefore will there is overlapping region in the protection range of the two.Setting principle is: voltage integrating meter ratio incomplete protective wire modulus and the distinct far-end fault of ground modulus; And the incomplete protective wire modulus of modulus integration ratio and the complete overlapping near terminal fault of ground modulus.Namely voltage integrating meter ratio is adjusted as when the lower topotype ripple of symmetry transposition separates completely with line mould ripple, the voltage ratio 3 of fault pole and non-faulting pole is multiplied by safety factor (1.5 times); And modulus integration ratio adjust for symmetry transposition roll off the production line Mo Bo and topotype ripple complete overlapping time the fault integration ratio 2.2 that returns topotype ripple and line mould ripple be multiplied by a safety factor (0.8 times).

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

The first, high sensitivity and high reliability is had concurrently; The present invention adopts line voltage distribution integration ratio or topotype ripple and line mould ripple integration ratio to select, and under a lot of failure condition, ratio all has larger nargin with setting value, and less by the influence of fluctuations of indivedual point.

The second, sample information amount is few, the voltage and current electric parameters of this time two polar curves only needing rectification side head end to record; The present invention only needs to use the electric parameters such as the electric current and voltage on this loop line road, only needs same time line-internal to communicate, and only can carry out lateral communications in same one end, does not need the communication on different loop line road, is conducive to Practical Project and realizes and reliability is high.

Three, operation method is simple, easily realizes; The inventive method only need to extract voltage variety, by the addition of electric current and voltage subtract each other ask for line mould ripple and topotype ripple, numerical value add up realize integration, ratio calculation can realize utilizing the voltage characteristic difference of fault pole and non-faulting pole, fault returns line mould ripple and the topotype ripple returned with non-faulting feature difference realizes fault polar curve protection act; operand is little, is easy to realize.

Three, required time window is short, becomes time window and just on the basis of previous time window, increases minority amount of information; Window that the inventive method takes is shorter, even if for end fault, the 7ms internal fault polar curve after fault occurs just can action message.

Four, transition resistance is tolerated large; Because voltage change ratio is only for distinguishing inverter side external area error, the inventive method still can start under high transition resistance, and voltage integrating meter ratio and modulus integration ratio feature affect by transition resistance hardly, and tolerance transition resistance ability is strong.

Accompanying drawing explanation

Fig. 1 is the flow chart of common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method.

Fig. 2 is the voltage waveform of point failure in 1P generation under the Bei Ruilong circuit model of full symmetric transposition.

Fig. 3 a is the modulus traveling-waves that the fault of point failure in 1P generation under the Bei Ruilong circuit model of full symmetric transposition is returned.

Fig. 3 b is the modulus traveling-waves that the non-faulting of point failure in 1P generation under the Bei Ruilong circuit model of full symmetric transposition is returned.

Fig. 4 a is the voltage waveform according to point failure in 1P generation under frequency circuit model do not replaced.

Fig. 4 b is the voltage waveform according to point failure in 1N generation under frequency circuit model do not replaced.

Fig. 5 is the voltage waveform according to polar curve 1N generation near terminal fault under frequency circuit model do not replaced.

Fig. 6 a is the modulus traveling-waves returned according to the fault of point failure in 1P under frequency circuit model do not replaced.

Fig. 6 b is the modulus traveling-waves returned according to the non-faulting of point failure in 1P under frequency circuit model do not replaced.

Fig. 7 a is the modulus traveling-waves returned according to frequency circuit model 1P near terminal fault fault do not replaced.

Fig. 7 b is the modulus traveling-waves returned according to frequency circuit model 1P far-end fault fault do not replaced.

Fig. 8 is the polar curve arrangement architecture figure of double-circuit line.

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 thereto.

Embodiment

As shown in Figure 1, a kind of common-tower double-return high voltage direct current transmission line fault selection method based on single time local message, comprises following steps:

For upper strata polar curve:

(1) this line voltage rate of change absolute value du/dt (t) is calculated in real time,

$|du/dt\left(t\right)|=\left|\frac{u\left(t\right)-u(t-T)}{T}\right|,$

U (t) is real-time voltage sampled value, and T is the time scale asking for voltage change ratio, is chosen for T=t _d.The absolute value of voltage change ratio is polar curve protection start-up criterion, if this line voltage rate of change absolute value reaches setting value, protection starts, and start subsequent step, this Startup time is designated as t _a.

(2) the voltage and current mean value getting 20 sampled points before start-up criterion meets setting value in certain a period of time as with reference to amount, deducts reference quantity by the instantaneous voltage of current time and current instantaneous value, obtains this line voltage variation delta u _lwith current change quantity Δ i _l, with returning pole line voltage variation delta u _{l_op}with current change quantity Δ i _{l_op}.

${\mathrm{\&Delta;u}}_l\left(t\right)=u_l\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_l(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;u}}_{l\_op}\left(t\right)=u_{l\_op}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{l\_op}(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;i}}_l\left(t\right)=i_l\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_l(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;i}}_{l\_op}\left(t\right)=i_{l\_op}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{l\_op}(t_a-i*t_d)}{20},$

U _l(t), u _{l_op}t () is respectively this polar curve and to line voltage instantaneous value, i _l(t), i _{l_op}t () is respectively this polar curve and to polar curve current instantaneous value.T _afor start-up criterion meets the setting value moment, t _dfor sampling time interval.

(3) mean value of electric current in time window that this polar curve road start-up criterion meets 20 sampled points after setting value is asked for.

$Avg\left(i\right)=\frac{1}{20}\underset{i=1}{\overset{20}{\&Sigma;}}\mathrm{\&Delta;}i(t_a+i*t_d),$

If this polar curve is electrode line and Avg (i) >0, go to step (4);

If this polar curve is electrode line and Avg (i) <0, protection is failure to actuate, and exits computing;

If this polar curve is negative line and Avg (i) <0, go to step (4);

If this polar curve is negative line and Avg (i) >0, protection is failure to actuate, and exits computing;

(4) choose 5 progressive time windows and ask for this line voltage integrated value respectively and to line voltage integrated value, these 5 progressive time windows are respectively 5,10,15,20 and 25 sampled points (comprising the sampled point that voltage change ratio meets criterion) from voltage change ratio meets criterion.In each time window, the integration of voltage is asked for formula and is:

$E_{u_l}=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_l\left(i\right),E_{u_{l\_op}}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_{l\_op}\left(i\right),$

Calculate this polar curve and the voltage integrating meter ratio to polar curve in each time window:

$K_{E_{ul}/E_{ul\_op}}\left(w_i\right)=\frac{E_{ul}\left(w_i\right)}{E_{ul\_op}\left(w_i\right)},$

And ask the maximum of the integration ratio in all time windows:

$K_{E_{ul}/E_{ul\_op}.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_{ul}/E_{ul\_op}}\left(w_i\right),$

If the maximum of voltage integrating meter ratio be greater than setting value, the protection act of this polar curve; Otherwise protection is failure to actuate, and exits computing.

For lower floor's polar curve:

(1) place, this polar curve road loop line topotype ripple rate of change absolute value is calculated in real time | dG/dt (t) |:

$|dG/dt\left(t\right)|=\left|\frac{G\left(t\right)-G(t-T)}{T}\right|,$

T is the time scale asking for voltage change ratio, is chosen for T=t _d.G (t) for real-time topotype ripple, computing formula is:

G(t)＝(i _P(t)+i _N(t))*Z _c0-(u _P(t)+u _N(t))，

I _p(t), i _nt () is the electric current of the positive and negative polar curve in loop, place, u _p(t), u _nt () is the voltage of the positive and negative polar curve in loop, place, the absolute value of topotype ripple rate of change is polar curve protection start-up criterion, if this loop line topotype ripple rate of change reaches setting value, protection starts, and start subsequent step, this Startup time is designated as t _a.

(2) the voltage and current mean value getting 20 sampled points before start-up criterion meets setting value in certain a period of time as with reference to amount, deducts reference quantity by the instantaneous voltage of current time and current instantaneous value, obtains this line voltage variation delta u _lwith current change quantity Δ i _l, to line voltage variation delta u _{l_op}with current change quantity Δ i _{l_op}(polar curve being to another root polar curve in loop, this polar curve place):

${\mathrm{\&Delta;u}}_l\left(t\right)=u_l\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_i(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;u}}_{l\_op}\left(t\right)=u_{l\_op}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{l\_op}(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;i}}_l\left(t\right)=i_l\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_l(t_a-i*t_d)}{20},$

${\mathrm{\&Delta;i}}_{l\_op}\left(t\right)=i_{l\_op}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{l\_op}(t_a-i*t_d)}{20},$

(3) choose 5 progressive time windows and ask for this line voltage integrated value respectively and to line voltage integrated value, these 5 progressive time windows are respectively 5,10,15,20 and 25 sampled points (comprising that sampled point that voltage change ratio meets criterion) from topotype ripple rate of change meets criterion.In each time window, the integration of voltage is asked for formula and is:

$E_{u_l}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_l\left(i\right),E_{u_{l\_op}}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_{l\_op}\left(i\right),$

Δ u _l, Δ u _{l_op}be respectively this polar curve and the voltage variety to polar curve.

Calculate this polar curve and the voltage integrating meter ratio to polar curve in each time window:

$K_{E_{ul}/E_{ul\_op}}\left(w_i\right)=\frac{E_{ul}\left(w_i\right)}{E_{ul\_op}\left(w_i\right)},$

And ask the maximum of the integration ratio in all time windows:

$K_{E_{ul}/E_{ul\_op}.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_{ul}/E_{ul\_op}}\left(w_i\right),$

If the maximum of voltage integrating meter ratio be greater than setting value, the protection act of this polar curve; Otherwise turn to step (4).

(4) line mould ripple and the topotype ripple variation delta P and Δ G in loop, this polar curve place is asked for,

$\left\{\begin{array}{c}\mathrm{\&Delta;}P=({\mathrm{\&Delta;i}}_P-{\mathrm{\&Delta;i}}_N)*Z_{cl}-({\mathrm{\&Delta;u}}_P-{\mathrm{\&Delta;u}}_N)\\ \mathrm{\&Delta;}G=({\mathrm{\&Delta;i}}_P+{\mathrm{\&Delta;i}}_N)*Z_{c0}-({\mathrm{\&Delta;u}}_P+{\mathrm{\&Delta;u}}_N)\end{array}\right.,$

Δ i _p, Δ i _nfor the both positive and negative polarity line current variable quantity in loop, place, Δ u _p, Δ u _nfor the positive and negative polar curve voltage variety in loop, place, Z _cl, Z _c0be respectively line mould wave impedance and topotype wave impedance.

(5) choose 5 progressive time windows and ask for this time former ripple integrated value and topotype ripple integrated value respectively, these 5 progressive time windows are respectively 5,10,15,20 and 25 sampled points (comprising that sampled point that voltage change ratio meets criterion) from topotype ripple rate of change meets criterion.In each time window, modulus integration is asked for formula and is:

$E_P\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}P\left(i\right),E_G\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}G\left(i\right),$

Δ P, Δ G are respectively line mould ripple and topotype ripple variable quantity.

Calculate topotype ripple and the line mould ripple integration ratio on this loop line road in each time window:

$K_{E_G/E_P}\left(w_i\right)=\frac{E_G\left(w_i\right)}{E_P\left(w_i\right)},$

Then the maximum of the topotype ripple variation delta G of this loop line and the integration ratio of line mould ripple variation delta P is:

$K_{E_G/E_P.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_G/E_P}\left(w_i\right),$

If the maximum of voltage integrating meter ratio be greater than 1 and the maximum of modulus integration ratio be less than setting value, then protection act, otherwise protection is failure to actuate, and exits computing.

Adopt PSCAD/EMTDC simulation software, cross the system parameters of DC engineering with reference to small stream Lip river, build one-tower double-circuit DC transmission system model.

Common-tower double-return double back DC power transmission line model adopts variable parameter model frequently to build, and total track length 1254km, overhead line structures parameter as shown in Figure 8.Multiple-circuit on same tower 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 h1 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 is 16m, and the cross-line degree of depth of ground wire is 11m.

Then, on the basis of this DC transmission system model, sample to fault data with the sample frequency of 10kHz, arrange earth fault at distance rectification side different distance place respectively, fault resistance comprises metallic earthing and high resistance earthing fault (250 Ω and 500 Ω).According to the Protection Scheme for Transmission Line that patent of the present invention is carried, respectively protection scheme program is write to upper strata polar curve and lower floor's polar curve, fault data is processed, comprise the voltage change ratio computing module of upper strata polar curve and the integration ratio of voltage variety, the topotype ripple rate of change computing module of lower floor's polar curve, the integration ratio of voltage variety integration ratio and line mould ripple and topotype ripple, observe the protection act situation of this polar curve when different polar curve breaks down, as shown in table 4 (a), for upper strata polar curve failure line selection emulated data 1P relay testing information slip (wherein, “ ?" represent that voltage change ratio criterion is not activated), table 4 (b) for upper strata polar curve 2N relay testing information slip (wherein, “ ?" represent that voltage change ratio criterion is not activated), table 4 (c) for lower floor polar curve 1N relay testing information slip (wherein, “ ?" represent that topotype ripple rate of change criterion is not activated), table 4 (d) for lower floor polar curve 2P relay testing information slip (wherein, "-" represents that topotype ripple rate of change criterion is not activated), table 4 (e) for external area error test case table (wherein, "-" represents that voltage change ratio or topotype ripple rate of change criterion are not activated).In table 4 with value be result of calculation in 25 sampled points (i.e. the time window of 2.5ms) after row ripple arrives after start-up criterion response, and current average after to be row ripple arrive start-up criterion respond after the result of calculation of 20 sampled points (i.e. the time window of 2ms).

Table 4 (a)

Table 4 (b)

Table 4 (c)

Table 4 (d)

Table 4 (e)

To upper strata polar curve, 1.2 times 0.67 (p.u.) adjusting as avoiding all this line voltage of polar curve inverter side fault rate of change maximums of voltage change ratio, voltage integrating meter ratio is then the minimum value of the voltage ratio of the lower fault pole of symmetrical transposition and non-faulting, i.e. 3 (doubly).For lower floor with regard to line, 2 times 2.13 (p.u.) adjusting as avoiding all this loop line of polar curve inverter side fault topotype ripple rate of change maximums of topotype ripple rate of change, voltage integrating meter ratio is then 1.5 times of the minimum value of the voltage ratio of the lower fault pole of symmetrical transposition and non-faulting, i.e. 4.5 (doubly), modulus integration ratio is then 0.8 times of symmetrical transposition calculating modulus ratio maximum, i.e. 1.76 (doubly).

The setting value obtained according to setting principle is utilized to carry out the protection act situation of other metallicity faults, 250 Ω and each polar curve of 500 Ω transition resistance situation, respond well, and upper strata polar curve can distinguish inverter side external area error by voltage change ratio during external area error, rectification side external area error can be distinguished by the sense of current; And lower floor's polar curve topotype ripple rate of change can distinguish external area error.

Above-described embodiment is the present invention's preferably execution mode; but embodiments of the present invention are not restricted to the described embodiments; change, the modification done under other any does not deviate from Spirit Essence of the present invention and principle, substitute, combine, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.

Claims (10)

1. a common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method, is characterized in that, comprises following steps:

(1) for upper strata polar curve, the absolute value of line voltage rate of change is asked for, as start-up criterion, and calculating current mean value avg (i); For lower floor's polar curve, based on the topotype ripple in this loop, polar curve place of formulae discovery of single back line topotype ripple, and ask for the absolute value of topotype ripple rate of change, as start-up criterion;

(2) for upper strata polar curve, judge whether voltage change ratio meets Protection criteria, if voltage change ratio and current average avg (i) meet Protection criteria simultaneously, then proceed to step (3), otherwise, return step (1); For lower floor's polar curve, judge whether topotype ripple rate of change meets Protection criteria, if meet, then proceed to step (3), otherwise, return step (1);

(3) get electric current and voltage mean value in certain a period of time before start-up criterion meets setting value respectively as stable state reference quantity, the reference quantity deducting respective polar curve by the electric parameters instantaneous value of each polar curve of current time obtains the electric current and voltage variable quantity of each polar curve; For lower floor's polar curve, try to achieve line mould ripple and topotype ripple variable quantity by electric current and voltage variable quantity simultaneously;

(4) for upper strata polar curve, each time window of this polar curve w is asked for _ivoltage integrating meter value with to line voltage integrated value and ask for this time window w _ivoltage integrating meter ratio for lower floor's polar curve, ask for each time window of this polar curve w _ivoltage integrating meter value with to line voltage integrated value and ask for this time window w _ivoltage integrating meter ratio meanwhile, loop, place each time window w is asked for _iline mould ripple integrated value E _p(w _i) and topotype ripple integrated value E _g(w _i) and this time window w _imodulus integration ratio

(5) for upper strata polar curve, the maximum of the voltage integrating meter ratio of all time windows is asked for for lower floor's polar curve, ask for the maximum of the voltage integrating meter ratio of all time windows with the maximum of the modulus integration ratio of all time windows

(6) for upper strata polar curve, if the maximum of the voltage integrating meter ratio of all time windows meet Protection criteria setting value, then this polar curve protection act; For lower floor's polar curve, if the maximum of the voltage integrating meter ratio of all time windows be greater than setting value Δ ' ₁or be greater than 1 and the maximum of the topotype ripple of all time windows and line mould ripple integration ratio be less than setting value Δ ₂, then this polar curve protection act.

2. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1, is characterized in that, in step (1), the formula of described single back line topotype ripple is:

G(t)＝(i _P(t)+i _N(t))*Z _c0-(u _P(t)+u _N(t))，

Wherein, G (t) is topotype ripple instantaneous value, i _p(t) _,i _n(t) _,u _p(t) and u _nt electrode line current instantaneous value that () is same loop line, negative line current instantaneous value and electrode line instantaneous voltage and negative line instantaneous voltage, Z _c0for topotype wave impedance.

3. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1; it is characterized in that; in step (1); upper strata polar curve utilizes voltage change ratio to be combined with current polarity jointly to differentiate reliably gets rid of rectification side external area error, and the computing formula of described voltage change ratio absolute value is:

$|du/dt\left(t\right)|=\left|\frac{u\left(t\right)-u(t-T)}{T}\right|,$

Wherein, du/dt (t) is the voltage change ratio of moment t, and u (t) is for this polar curve is at the instantaneous voltage of moment t, and T is the time scale asking for voltage change ratio, can be chosen for sampling time t _dintegral multiple, the absolute value of voltage change ratio is polar curve protection start-up criterion, starts setting value, make this moment be t if at a time meet _a;

In certain hour window, the computing formula of current average is:

$Avg\left(i\right)=\frac{1}{n}\underset{i=1}{\overset{n}{\&Sigma;}}\mathrm{\&Delta;}i,$

Wherein, Avg (i) is current average, and Δ i is current change quantity, the sampling number that n is current change quantity in seclected time window;

If this is electrode line very, after voltage change ratio criterion starts, have Avg (i) >0 then for polar curve internal fault, if or this very negative line, after voltage change ratio criterion starts, having Avg (i) <0 is then polar curve internal fault; Otherwise be rectification side external area error.

4. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1; it is characterized in that; in step (1); lower floor's polar curve adopts topotype ripple rate of change; even if still can start under higher transition resistance; and get rid of rectification side external area error and inverter side external area error simultaneously, in stable situation, lower floor's polar curve topotype ripple rate of change calculated in real time and taken absolute value:

$|dG/dt\left(t\right)|=\left|\frac{G\left(t\right)-G(t-T)}{T}\right|,$

Wherein, the topotype ripple rate of change that dG/dt (t) is moment t, the topotype ripple instantaneous value that G (t) is moment t, T is the time scale asking for voltage change ratio, can be chosen for sampling time t _dintegral multiple.

5. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1, is characterized in that, in step (3), the variable quantity acquiring method for electric current and voltage is:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{1P}=u_{1P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{1P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{1N}=u_{1N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{1N}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{2P}=u_{2P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{2P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;u}}_{2N}=u_{2N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{u}_{2N}(t_a-i*t_d)}{20}\end{array}\right.,$

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{1P}=i_{1P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{1P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{1N}=i_{1N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{1N}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{2P}=i_{2P}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{2P}(t_a-i*t_d)}{20}\\ {\mathrm{\&Delta;i}}_{2N}=i_{2N}\left(t\right)-\frac{\underset{i=21}{\overset{40}{\&Sigma;}}{i}_{2N}(t_a-i*t_d)}{20}\end{array}\right.,$

Wherein, u _1P(t), i _1Pt () represents that polar curve 1P is at the instantaneous voltage of t and current instantaneous value respectively, Δ u _1P, Δ i _1Prepresent voltage variety and the current change quantity of polar curve 1P respectively, all the other by that analogy; t _afor start-up criterion meets the Protection criteria moment, t _dfor sampling time interval;

Variable quantity acquiring method for line mould ripple and topotype ripple is:

$\{\begin{array}{c}\mathrm{\&Delta;}P=({\mathrm{\&Delta;i}}_P-{\mathrm{\&Delta;i}}_N)*Z_{cl}-({\mathrm{\&Delta;u}}_P-{\mathrm{\&Delta;u}}_N)\\ \mathrm{\&Delta;}G=({\mathrm{\&Delta;i}}_P+{\mathrm{\&Delta;i}}_N)*Z_{cl}-({\mathrm{\&Delta;u}}_P+{\mathrm{\&Delta;u}}_N)\end{array},$

Wherein, Δ P, Δ G are line mould ripple variable quantity and topotype ripple variable quantity, Δ i _p, Δ i _nfor try to achieve this loop line electrode line, negative line current change quantity, Δ u _p, Δ u _nfor try to achieve this loop line electrode line, negative line voltage variety.

6. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1; it is characterized in that; in step (4), utilize the mode of the integration ratio of voltage or modulus as criterion, this polar curve and the voltage integrating meter ratio to polar curve are:

$K_{E_{ul}/E_{ul\_op}}\left(w_i\right)=\frac{E_{ul}\left(w_i\right)}{E_{ul\_op}\left(w_i\right)},$

Wherein, for time window w _iinterior polar curve and the voltage integrating meter ratio to polar curve, E _ul(w _i) be time window w _ithe voltage integrating meter value of interior polar curve, E _{ul_op}(w _i) be time window w _iin with this polar curve in the voltage integrating meter value to polar curve of same loop line;

The topotype ripple of this loop line and the integration ratio of line mould ripple are:

$K_{E_G/E_P}\left(w_i\right)=\frac{E_G\left(w_i\right)}{E_P\left(w_i\right)},$

Wherein, for the topotype ripple in loop, this polar curve place and line mould ripple are at time window w _iinterior integration ratio, E _g(w _i) for the topotype ripple in loop, this polar curve place is at time window w _iinterior integrated value, E _p(w _i) for the line mould ripple in loop, this polar curve place is at time window w _iinterior integrated value.

7. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1; it is characterized in that; in step (4); become time window and integration is carried out to voltage and modulus: the time window getting multiple different time length asks for voltage integrating meter ratio and modulus integration ratio; and ask for maximum; in each time window, the integration of voltage is asked for formula and is:

$E_{u_l}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_l\left(i\right),E_{u_{l\_op}}\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}{\mathrm{\&Delta;u}}_{l\_op}\left(i\right),$

Wherein, be respectively this polar curve and to polar curve at time window w _iinterior voltage integrating meter value, Δ u _l, Δ u _{l_op}be respectively this polar curve and to polar curve at time window w _iinterior voltage variety, N _ifor time window w _iinterior sampling number;

Calculate this polar curve and the voltage integrating meter ratio to polar curve in each time window, and ask the maximum of the integration ratio in all time windows:

$K_{E_{ul}/E_{ul\_op}.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_{ul}/E_{ul\_op}}\left(w_i\right),$

Wherein, for the maximum of voltage integrating meter ratio in all time windows, for time window w _iinterior voltage integrating meter ratio;

The formula of asking for of modulus integration is:

$E_G\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}G\left(i\right),E_P\left(w_i\right)=\underset{i=1}{\overset{N_i}{\&Sigma;}}\mathrm{\&Delta;}P\left(i\right),$

Wherein, E _p(w _i), E _g(w _i) be respectively time window w _iinterior line mould ripple integrated value and topotype ripple integrated value, Δ P, Δ G are respectively line mould ripple and topotype ripple variable quantity;

Calculate modulus integration ratio, and ask the maximum of the integration ratio in all time windows:

$K_{E_G/E_P.max}\left(w_i\right)=\underset{w_i<t_0}{max}{K}_{E_G/E_P}\left(w_i\right),$

Wherein, for the maximum of modulus integration ratio in all time windows, for time window w _iinterior modulus integration ratio.

8. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1, it is characterized in that, in step (6), for differentiation this polar curve fault and other polar curve faults, upper strata polar curve and lower floor's polar curve adopt different protection scheme: upper strata polar curve gets final product action when voltage integrating meter ratio meets, otherwise, be failure to actuate; Lower floor's polar curve is when the satisfied then action of voltage integrating meter ratio, or voltage integrating meter ratio is greater than 1 and the satisfied then action of modulus integration ratio, otherwise, be failure to actuate;

The Protection criteria that upper strata polar curve is distinguishing this polar curve fault and other polar curve faults is:

$K_{E_{u_l}/E_{u_{l\_op}},max}>{\mathrm{\&Delta;}}_1,$

Wherein, for this polar curve and the maximum to line voltage integration ratio, Δ ₁for the setting value of upper strata line voltage integration ratio;

The Protection criteria that lower floor's polar curve is distinguishing this polar curve fault and other polar curve faults is:

$K_{E_{u_l}/E_{u_{l\_op}},max}>{{\mathrm{\&Delta;}}^{\&prime;}}_1$ Or

$K_{E_{u_l}/E_{u_{l\_op}},max}>1$ And $K_{E_G/E_P.max}<{\mathrm{\&Delta;}}_2,$

Wherein, for the maximum of voltage integrating meter ratio, for the maximum of modulus integration ratio, Δ ' ₁for the setting value of lower floor's line voltage integration ratio, Δ ₂for the setting value of lower floor's polar curve modulus integration ratio.

9. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1, is characterized in that, in step (6), for lower floor's polar curve, the criterion that protection act need meet is:

For lower floor's polar curve near terminal fault, voltage integrating meter ratio meets criterion:

$K_{E_{u_l}/E_{u_{l\_op}},max}>{{\mathrm{\&Delta;}}^{\&prime;}}_1,$

Wherein, for the maximum of voltage integrating meter ratio, Δ ' ₁for the setting value of lower floor's line voltage integration ratio;

For lower floor's polar curve far-end fault, modulus integration ratio meets criterion:

$K_{E_{u_l}/E_{u_{l\_op}},max}>1$ And $K_{E_G/E_P.max}<{\mathrm{\&Delta;}}_2,$

Wherein, for the maximum of voltage integrating meter ratio, for the maximum of modulus integration ratio, Δ ₂for the setting value of lower floor's polar curve modulus integration ratio.

10. common-tower double-return HVDC (High Voltage Direct Current) transmission line traveling-wave protection method according to claim 1, is characterized in that, in step (6), and voltage integrating meter ratio incomplete protective wire modulus and the distinct far-end fault of ground modulus; And the incomplete protective wire modulus of modulus integration ratio and the complete overlapping near terminal fault of ground modulus; Namely for lower floor's polar curve, voltage integrating meter ratios delta ' ₁adjust as when the lower topotype ripple of symmetry transposition separates completely with line mould ripple, the voltage ratio of fault pole and non-faulting pole is multiplied by the safety factor of 1.5 times; And modulus integration ratios delta ₂adjust for symmetry transposition roll off the production line Mo Bo and topotype ripple complete overlapping time the fault integration ratio that returns topotype ripple and line mould ripple be multiplied by the safety factor of 0.8 times.