CN104979809B - A kind of common-tower double-return HVDC transmission line traveling-wave protection method - Google Patents
A kind of common-tower double-return HVDC transmission line traveling-wave protection method Download PDFInfo
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Abstract
The invention discloses a kind of common-tower double-return HVDC transmission line traveling-wave protection method, comprise the steps of：Different criterions and each Self-tuning System are used to levels polar curve, voltage change ratio and current direction is taken upper strata polar curve to exclude external area error, external area error is excluded using ground mould ripple change rate to lower floor's polar curve, this polar curve failure and other polar curve failures are distinguished using voltage integrating meter ratio to upper strata polar curve, lower floor's polar curve is realized using voltage integrating meter ratio and modulus integration ratio and distinguished this pole failure and other polar curve failures.This protection scheme has high sensitivity, operand is small, it is short without communication, required judgement time between this letter in reply breath, different times only to need; it is small by transition Resistance Influence, the advantages that can quickly being determined to the failure polar curve of the double DC power transmission lines of same tower and be less prone to the situation of erroneous judgement.
Description
Technical Field
The invention relates to a relay protection technology of a high-voltage direct-current transmission line of a power system, in particular to a traveling wave protection method of a same-tower double-circuit high-voltage direct-current transmission line.
Background
With the continuous development of the scale of the power grid, the high-voltage direct-current power transmission system is more and more widely applied to practical engineering, and a same-tower double-circuit high-voltage direct-current power transmission system is also provided. Compared with the mode of erecting double-circuit lines on the same tower, the direct-current power transmission system only adopts single-circuit line power transmission, which is more favorable for saving power transmission corridors and improving the electric energy transmission capacity, however, because of the coupling of different degrees among a plurality of polar lines, and a plurality of moduli can appear when the plurality of long-distance direct-current power transmission polar lines carry out traveling wave decoupling, once a fault occurs, the traveling wave fault characteristics are relatively complex, and the traveling wave characteristic analysis and the protection setting are more difficult.
The traditional high-voltage direct-current power transmission system adopts a single-circuit line to transmit power, the traveling wave protection of the single-circuit line has the problems of poor transition resistance tolerance and low sensitivity, and the reason is mainly because the near-end fault of other polar lines has a large coupling amount at the polar line and a small high-resistance grounding fault amount at the far end of the polar line, if the setting value is not properly set, the near-end fault of other polar lines can cause the misaction of the polar line because the coupling amount of the polar line exceeds a fixed value, or the small high-resistance grounding fault amount at the far end of the polar line is not enough to cause the polar line to act and refuse to act. At present, the problem is not effectively solved in the protection of a single-circuit high-voltage direct-current transmission line, and the protection fixed value is usually improved to ensure that a non-fault polar line is reliable and does not malfunction. The traveling wave protection of the same-tower double-circuit high-voltage direct-current transmission line also has the problem of weak transition resistance tolerance. In addition, the same-tower double-circuit high-voltage direct-current transmission line has two circuits, the arrangement mode of the circuits is asymmetric, and the coupling quantity of different polar line faults on other polar lines is different, so that the traveling wave characteristics obtained by different circuit faults are different, the fault types are relatively increased, if the protection criterion of a single-circuit direct-current transmission line is still adopted, and the protection is carried out by the change rate and the amplitude of voltage traveling waves or modulus traveling waves, the protection setting process is more complicated, and the reliability is low. If the fault characteristics of the same-tower double-circuit high-voltage direct-current transmission line can be fully utilized, the near-end fault and the far-end fault act when different protection criteria meet setting values, and safer and more reliable same-tower double-circuit high-voltage direct-current transmission line protection can be designed.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings of the prior art and provides a traveling wave protection method for a same-tower double-circuit high-voltage direct-current transmission line, which can meet the requirements of protecting different fault polar lines and different fault distances, still reliably acts and tolerates higher transition resistance, adopts different protection schemes for an upper polar line and a lower polar line respectively according to the fault characteristics of the same-tower double-circuit line, adopts two protection criteria for realizing the same function simultaneously according to the fault characteristics of the lower polar line, ensures that any protection criterion meets the protection link, acts, is suitable for the existing same-tower double-circuit high-voltage direct-current transmission line, has high sensitivity, is not easy to generate misjudgment, and has strong capability of tolerating the transition resistance.
The purpose of the invention is realized by the following technical scheme: a traveling wave protection method for a same-tower double-circuit high-voltage direct-current transmission line comprises the following steps:
different layer polar lines adopt different fault starting modes: when the upper layer polar line has a fault, the coupling with other polar lines is not strong, the external fault of the inversion side can be distinguished by adopting the voltage change rate, the capability of enduring transition resistance is strong enough, and the external fault of the rectification side can be distinguished by adopting the average current amplitude; and (3) if the change rate of the lower layer polar line voltage is not strong in the ability of tolerating the transition resistance, adopting the change rate of the ground mode wave as a starting criterion:
for the upper pole line:
(1) Calculating the voltage change rate of the local polar line and taking an absolute value,
du/dt (T) is the voltage change rate of the moment T, u (T) is the voltage value of the moment T, T is the time scale for solving the voltage change rate, and is selected as the sampling time T d Integer multiples of. The absolute value of the voltage change rate is the criterion for the polar line protection starting, and if the absolute value of the voltage change rate meets the starting setting value at a certain moment, the moment is t a 。
(2) Taking the average value of the voltage and the current in a certain period of time before the starting criterion meets the setting value as a steady-state reference quantity, and subtracting the reference quantity from the instantaneous value of the voltage and the instantaneous value of the current to obtain the voltage change quantity delta u 1P 、Δu 1N 、Δu 2P 、Δu 2N And the amount of current change Δ i 1P 、Δi 1N 、Δi 2P 、Δi 2N . Wherein 1P and 1N are respectively the firstThe positive pole line and the negative pole line of the return line, 2P and 2N are respectively the positive pole line and the negative pole line of the second return line.
(3) Calculating the average value of the current i in a certain time window:
avg (i) is the current average value of the selected time window, n is the number of sampling points of the current in the selected time window, and delta i is the current variation.
(4) Integrating the voltage variation of the local polar line and the voltage variation of the opposite polar line by a variable time window, and solving the maximum value of the integral ratio of the voltage variation of the local polar line and the voltage variation of the opposite polar line, wherein the opposite polar line is the other polar line in the same circuit with the local polar line, and the time window w is i The voltage integral ratio in (d) is:
E ul (w i ) Is a time window w i Internal local line voltage integral value, E ul_op (w i ) Is a time window w i The internal epipolar line voltage integral value. The maximum value of the integral ratio of the two is:
t 0 the length of the longest time window.
(5) If the current average value Avg (i) and the voltage integral ratioAnd if the protection criterion is met, the protection is performed. The protection criterion is as follows:
when the polar line is a positive polar line:
when the present line is a negative line:
for the lower layer polar lines:
(6) Calculating the absolute value of the change rate of the earth mode wave for the loop where the polar line is positioned,
dG/dt (T) is the earth-mode wave change rate at the moment T, G (T) is the earth-mode wave at the moment T, T is the time scale for solving the earth-mode wave change rate, and is selected as the sampling time T d An integer multiple of. The absolute value of the change rate of the ground mode wave is the polar line protection starting criterion, and if the absolute value meets the starting setting value at a certain moment, the moment is t a The formula for G (t) is:
G(t)＝(i P (t)+i N (t))*Z c0 -(u P (t)+u N (t))，
i P (t)、i N (t) the instantaneous current of the positive electrode wire and the instantaneous current of the negative electrode wire, u P (t)、u N (t) are the instantaneous voltages of the positive and negative lines, respectively, Z c0 Is the ground mode impedance.
(7) Taking the average value of the voltage and the current in a certain period of time before the starting criterion meets the setting value as a steady-state reference quantity, and subtracting the reference quantity from the instantaneous value of the voltage and the instantaneous value of the current to obtain the voltage change quantity delta u 1P 、Δu 1N 、Δu 2P 、Δu 2N And the amount of current change Δ i 1P 、Δi 1N 、Δi 2P 、Δi 2N . Wherein, 1P, 1N are the positive pole line, the negative pole line of first return circuit respectively, and 2P, 2N are the positive pole line and the negative pole line of second return circuit respectively.
(8) The linear mode wave variation P and the earth mode wave variation G of each circuit of the same-tower double-circuit direct current circuit are obtained by the definition of the linear mode wave and the earth mode wave of the single-circuit direct current transmission line, and the calculation formula is as follows:
wherein, Δ i P 、Δi N Respectively, the current change amount, delta u, of the back positive and negative electrode lines P 、Δu N Respectively, the voltage change amount, Z, of the originally returned positive and negative lines cl 、Z c0 Respectively, line mode wave impedance and earth mode wave impedance.
(9) And integrating the voltage variation of the local polar line and the voltage variation of the opposite polar line by using a variable time window, and solving the maximum value of the integral ratio of the voltage variation of the local polar line and the voltage variation of the opposite polar line.
E ul (w i ) Is a time window w i Internal local line voltage integral value, E ul_op (w i ) Is a time window w i And the maximum value of the integral ratio of the internal pole line voltage integral value to the internal pole line voltage integral value is as follows:
t 0 the length of the longest time window.
If the maximum value of the voltage integral ratio meets the protection setting value delta' 1 If not, the protection action is carried out, otherwise, the step (10) is carried out, and the protection criterion is as follows:
(10) Integrating the line mode wave P and the ground mode wave G of the loop by a variable time window, and solving the maximum value of the integral ratio of the line mode wave P and the ground mode wave G:
E G (w i ) Is a time window w i Integral value of earth mode wave of internal local return line, E P (w i ) Is a time window w i The integral value of the line mode wave of the inner loop line.
The maximum value of the integral ratio of the ground mode wave G and the line mode wave P of the loop is:
if the maximum value of the modulus integral ratio meets the protection criterion, the protection action is carried out, and the protection criterion is as follows:
preferably, in the steps (2) and (7), the voltage and current variation of the four-circuit line is obtained by subtracting the average value of the voltage and current in a certain period of time before the protection is started from the current instantaneous value to ensure that the voltage and current obtained after the protection criterion is started are the current voltage and current minus the stable value before the fault, and the line voltage and current variation is obtained by adopting the following formula:
wherein u is 1P (t)、i 1P (t) represents the instantaneous values of voltage and current, Δ u, of the pole line 1P at time t 1P 、Δi 1P Respectively showing the voltage change amount and the current change amount of the electrode line 1P after the start of protectionVolume, and the rest can be analogized. t is t a Moment t at which the starting criterion satisfies the setting value d Is the sampling time interval.
Preferably, in steps (4) and (9), the integral value of the present line voltage and the counter line voltage is calculated by the following formula:
Δu l delta u being a voltage variation of the principal line l_op For the change of the voltage of the epipolar line, N i Is a time window w i The number of samples in (1).
Preferably, in step (10), the integral values of the ground mode wave and the line mode wave are calculated by the following formula:
Δ G is the variation of ground mode wave of the loop of the local polar line, Δ P is the variation of line mode wave of the loop of the local polar line, N i Is a time window w i The number of samples in (1).
Preferably, in steps (4), (9) and (10), for each time window w i The starting time is always t a And the ending time is t a +(pt d ) I, p is an incremental coefficient, and should be selected as small as possible; the number of the time windows can be selected as required, and a plurality of time windows are selected as much as possible.
In steps (9) and (10), different protection criteria are adopted for fault characteristics of different fault distances: when the near end of the lower polar line fails, the voltage ratio of the same return polar line to the opposite polar line is larger, and the lower polar line is used for judging the failure of the local polar line, but the failure of the far end is reduced; when the far end of the lower polar line fails, the ratio of the ground mode wave to the line mode wave of the same return line is smaller, so that the fault of the return line and the fault of the other return line can be effectively distinguished, but the fault of the near end is larger, and when the polar line fails, the voltage ratio of the polar line to the opposite polar line is always larger than 1. Therefore, the protective criterion of the lower layer polar line is selected as the voltage integral ratioGreater than setting value delta' 1 The protection action is performed, or the voltage integral ratio is larger than 1 and the modulus integral ratio is smaller than the setting value delta 2 The protection is active.
In the steps (9) and (10), the setting method of the lower layer polar line incompletely protects the head end or the tail end of the incomplete protection according to the line symmetric transposition model based on two or relation criteria, so that the protection ranges of the two criteria have an overlapping part, the setting method has a theoretical basis, and the protection is more reliable. The setting principle is as follows: the voltage integral ratio does not completely protect the far-end fault that the line modulus and the ground modulus are completely separated; the modulus integral ratio does not completely protect the near-end fault that the line modulus and the ground modulus are completely overlapped; i.e. the integrated voltage ratio delta 'for the lower layer line' 1 Setting is that the ratio of the voltage quantity of a fault electrode and a non-fault electrode is multiplied by a reliable coefficient (1.5 times) when the earth mode wave and the line mode wave are completely separated under the symmetric transposition; and integral ratio of modulus Δ 2 Setting is to multiply the integral ratio of the fault return ground mode wave and the line mode wave by a reliable coefficient (0.8 times) when the symmetric transposition lower line mode wave and the ground mode wave are completely overlapped.
In the steps (4), (9) and (10), the integral ratio of the voltage or the modulus is used as a criterion, so that the problem that the amplitude is influenced by the transition resistance is effectively solved, and the integral ratio of the voltage or the modulus is basically not influenced by the transition resistance.
In steps (4), (9) and (10), the voltage and modulus are integrated over a variable time window: and (3) obtaining a voltage integral ratio and a modulus integral ratio by taking a plurality of time windows with different time lengths, and obtaining a maximum value to eliminate the influence caused by the fault distance. For example: the voltage integral value of the local line and the modulus integral value of the local loop can be obtained by selecting 5 increasing time windows, wherein the 5 increasing time windows are respectively 5, 10, 15, 20 and 25 sampling points (including the sampling points at the moment that the starting criterion meets the setting value) from the moment that the starting criterion meets the setting value.
The protection principle of the invention is as follows: for the upper-layer polar line, when the positive direction of the specified current flows from the rectifying side to the inverting side, whether the current is an external fault of the rectifying side can be judged according to the direction of the current, but the direct-current line fault or the external fault of the inverting side cannot be distinguished, so that a voltage change rate criterion is also needed to distinguish the external fault of the inverting side. For the positive electrode wire, if the direction of the measured current variation is positive, the line fault or the external fault of the inversion side area can be possible; if the direction of the measured current change is negative, the fault is outside the rectification side area. For the negative electrode wire, if the direction of the change quantity of the measured current is negative, the line fault or the external fault of the inversion side area can be caused; if the direction of the measured current variation is positive, the fault is outside the rectifying side area. Therefore, two criteria of voltage change rate and current direction can be utilized to ensure that the protection does not act when the external fault of the rectifying side and the inversion side occurs. And for the lower layer polar line, the change rate of the ground mode wave is adopted for starting, and if the change rate of the ground mode wave meets a setting value, the external fault of the rectification side and the external fault of the inversion side can be eliminated simultaneously.
When the line is transposed symmetrically, taking the first loop 1P fault as an example, the voltage current of the fault and non-fault pole lines can be expressed as:
u 1P 、u 1N voltages of polar lines 1P, 1N, i 1P 、i 1N The currents of the pole lines 1P, 1N. u. u l Is the amplitude of the line mode wave, u 0 Is the amplitude of the earth mode wave, and u 0 /u l ＝Z 0 /Z l . However, the propagation characteristics of the line mode wave and the ground mode wave are different, and the two waves are not superposed at the same time.
As can be seen from the above formula, since the three line mode components are completely consistent, the fault pole is the same-direction superposition of the three line mode components, which is 3 times of the line mode components; the non-fault pole is a non-homodromous superposition of three line mode components, which is 1 time of the line mode components, and when only the line mode component is arranged at the traveling wave head, the traveling wave amplitude of the fault pole is 3 times of the traveling wave amplitude of the non-fault pole, as shown in fig. 2. When far-end faults are considered, linear mode waves firstly reach a protection point, and the voltage variation of a fault pole is 3 times of that of a non-fault pole, so that the integral ratio of the voltage variation of the local polar line to the voltage variation of the antipole line is utilized, when the local polar line has faults, the protection action is carried out when the integral ratio exceeds a setting value, and when other polar lines have faults, the integral ratio of the voltage variation of the local polar line to the voltage variation of the antipole line is not more than 3 times, the protection action is not carried out.
Meanwhile, the line mode wave and the ground mode wave of the circuit where the fault polar line is located can be expressed as:
P 1 、G 1 line mode waves and ground mode waves, P, of the first loop 2 、G 2 The line mode wave and the earth mode wave of the second loop line.
From the above equation, the line mode wave of the failed loop has a certain amplitude, and the line mode wave of the non-failed loop has an amplitude of 0, as shown in fig. 3a and 3 b. Therefore, the integral ratio of the earth mode wave and the line mode wave of the fault loop is a certain value, while the integral ratio of the earth mode wave and the line mode wave of the non-fault loop is ideally a large value, and by using the integral ratio of the earth mode wave and the line mode wave, the protection of the loop can be operated when the polar line of the loop is in fault, and the protection of the other loop is not operated when the polar line of the loop is in fault. When a near-end fault is considered, the earth mode wave and the line mode wave are superposed, and the ratio of the earth mode wave and the line mode wave returned from the fault is G 1 /P 1 =2.2; when far-end fault is considered, the earth mode wave does not arrive yet, and the ratio is 0.9.
The actual engineering line is not symmetrically transposed, the double-circuit line on the same tower has three line mode components and one ground mode component, and the three line mode components are not completely consistent due to the non-completely symmetric transposition, so that the voltage change amplitude of the fault pole is not 3 times of the line mode components, and the voltage change amplitude of the non-fault pole is not necessarily 1 time of the line mode components. Particularly, when an upper layer polar line (such as 1P) has a fault, as shown in fig. 4a, the difference of the traveling wave amplitude values of a fault pole and a non-fault pole is larger than that of a line when the line is completely symmetrically transposed, so that the adoption of a voltage ratio is facilitated, the protection of the local pole can reliably act when the local pole has a fault, and the protection of the local pole can not act when an opposite pole has a fault; when the lower layer polar line (such as 1N) has a fault, as shown in fig. 4b, the difference of the traveling wave amplitude values of the fault pole and the non-fault pole is smaller than that when the line is completely symmetrically transposed, only the voltage ratio is used, and if the setting value is not properly selected, the protection of the local pole is possibly refused to operate when the local pole has a fault or the local pole is mistakenly operated when other polar lines have a fault. However, when the lower layer polar line has a near-end fault, as shown in fig. 5, the voltage amplitude difference between the fault pole and the non-fault pole is large, the voltage ratio is large, and the voltage variation and the antipodal voltage variation are always greater than 1 when the pole has a fault at different fault distances.
For line mode waves and ground mode waves, under asymmetric transposition (taking 1P fault as an example), as shown in fig. 6a, the line mode waves and ground mode waves of the fault return have little difference compared with the waveforms when completely symmetric transposition is performed (as shown in fig. 3 a). However, as shown in fig. 6b, the non-fault-back line mode wave is not completely 0 compared to the waveform when the position is completely symmetrically shifted (as shown in fig. 3 b), and the integral ratio of the non-fault-back ground mode wave to the line mode wave is not very large in some fault situations. Similarly, when the 1N-pole line fails, the line mode wave that does not fail back is not completely 0, which is disadvantageous for protection. In addition, for the near-end fault condition of the fault loop (taking 1N fault as an example), as shown in fig. 7a, the amplitude of the ground mode wave is significantly larger than that of the line mode wave, the integral ratio of the ground mode wave and the line mode wave of the fault loop is relatively larger in the near-end fault condition, and when the integral ratio of the ground mode wave and the line mode wave of the fault loop is smaller to distinguish the fault loop from the non-fault loop, the reliability of the near-end fault condition of the fault loop is not high. However, for the far-end fault, as shown in fig. 7b, the traveling wave amplitudes of the earth mode wave and the line mode wave of the fault loop are closer, and the integral ratio of the earth mode wave and the line mode wave of the fault loop is smaller, so that the far-end fault is beneficial to the local loop fault which is caused by the fact that the integral ratio of the earth mode wave and the line mode wave is smaller than the setting value to perform the protection operation, and the other loop fault which is caused by the local loop fault does not perform the protection operation. Meanwhile, the integral ratio of the voltage variation of the local polar line and the antipodal line is utilized to be in relation with 1, so that the local polar line can act when the local polar line fails, and the local polar line cannot act when the local polar line fails. Therefore, for the lower layer polar line, the voltage ratio and the modulus ratio are combined at the same time to realize the protection reliable action.
In summary, the following calculation formula can be selected as the line selection criterion:
for the upper polar line, the criterion that the protection action needs to meet is as follows:
for positive faults, after the voltage change rate criterion is initiated:
for negative pole faults, the criterion that the protection action needs to meet is as follows:
avg (i) is the average value of the current for a selected time window,is the maximum value of the voltage integral ratio, Δ 1 The integral ratio of the upper layer electrode line voltage is a setting value.
For the lower layer polar line, the criterion that the protection action needs to meet is as follows:
or:
and is
Is the maximum value of the integrated ratio of the voltages,is integral of modulusMaximum value of the ratio,. DELTA' 1 Is the setting value, delta, of the integral ratio of the lower layer polar line voltage 2 The integral ratio value of the lower polar line modulus is a setting value.
For the upper-layer polar line, after the voltage change rate is started, the current average value is needed to distinguish the external fault of the rectification side, so that the internal fault is ensured; and for the lower layer polar line, the change rate of the earth mode wave can reliably remove the external faults of the rectification side and the inversion side at the same time.
For the upper polar line, because the fault quantity of the fault of the local polar line is greatly different from the coupling quantity of other polar lines, the voltage integral ratio of the local polar line and the same-return antipodal line is directly utilizedIt can be determined whether the local polar line is faulty. If it isAnd if the setting value is exceeded, the fault of the local pole line is determined.
For the lower layer polar line, only the voltage integral ratio is selected because the fault quantity of the fault of the local polar line is slightly different from the coupling quantity of other polar lines under certain fault conditionsThe protection reliability is not high; the voltage integral ratio is applied simultaneouslyIntegral ratio of sum modulusWhen the near-end is in failure,larger, can be larger than a setting value delta' 1 And acts; when the remote end is in a fault,smaller, but still greater than 1, may be prepared fromLess than setting value Delta 2 But ensures action.
The invention adopts a setting principle that:
absolute value of voltage change rate: because the upper layer polar line is utilized to effectively distinguish the external fault of the rectification side area by utilizing the current direction, the absolute value of the voltage change rate only needs to be kept away from the maximum value of the absolute value of the voltage change rate obtained by the external fault of the inversion side area.
Absolute value of rate of change of earth mode wave: the absolute value of the change rate of the ground mode wave needs to avoid the maximum value of the absolute value of the voltage change rate obtained by the fault outside the inversion side area.
For the upper-layer polar line, the ratio of voltage variation is larger than that during symmetric transposition, so the setting value of the integral ratio of the voltage variation is the ratio of the voltage traveling wave variation of which the wave head of the traveling wave of the fault pole and the non-fault pole only contains line mode components under the symmetric transposition under the condition of the far-end fault;
for the lower polar line, the integral ratio of the voltage is used for protecting when the near end is in failure, and the integral ratio of the ground mode wave and the linear mode wave is used for protecting when the far end is in failure. In order to ensure that the protection can reliably act no matter which point has fault protection, the protection ranges of the two points have an overlapping area. The setting principle is as follows: the voltage integral ratio does not completely protect the far-end fault that the line modulus and the ground modulus are completely separated; while the modulus integral ratio does not completely protect against near-end failures where the line and ground moduli completely overlap. Namely, the voltage integral ratio is set as the voltage quantity ratio 3 of a fault pole and a non-fault pole when the earth mode wave and the line mode wave are completely separated under the symmetric transposition and is multiplied by a reliable coefficient (1.5 times); and the modulus integral ratio is set to be 2.2 times of the integral ratio of the fault return ground mode wave and the line mode wave when the symmetric transposition line mode wave and the ground mode wave are completely overlapped by a reliable coefficient (0.8 times).
Compared with the prior art, the invention has the following advantages and effects:
firstly, the device has high sensitivity and high reliability; the invention selects the line voltage integral ratio or the ground mode wave and line mode wave integral ratio, and the ratio and the setting value have larger margin under many fault conditions and are less influenced by the fluctuation of individual points.
Secondly, the sampling information quantity is small, and only the voltage and current electrical quantities of the two polar lines of the loop are measured at the head end of the rectifying side; according to the invention, only the voltage, current and other electric quantities of the circuit are needed, only the internal communication of the same circuit is needed, the transverse communication can be carried out only at the same end, the communication of different circuits is not needed, and the method is beneficial to the realization of practical engineering and has high reliability.
Thirdly, the operation method is simple and easy to realize; the method can realize fault polar line protection action by utilizing the voltage characteristic difference of a fault electrode and a non-fault electrode and the characteristic difference of a fault return line mode wave and a non-fault return line mode wave, and the specific value calculation only by extracting the voltage variation, calculating the line mode wave and the ground mode wave by adding and subtracting the voltage and the current, and accumulating numerical values to realize integration and specific value calculation, and has small operand and easy realization.
Thirdly, the required time window is short, and the time window is changed by only increasing a small amount of information on the basis of the previous time window; the method of the invention requires a shorter time window and even for a terminal fault, the fault polar line can reliably act within 7ms after the fault occurs.
Fourthly, the tolerance transition resistance is large; because the voltage change rate is only used for distinguishing the external faults of the inversion side, the method can still be started under high transition resistance, and the characteristics of the voltage integral ratio and the modulus integral ratio are hardly influenced by the transition resistance, so that the capacity of resisting the transition resistance is strong.
Drawings
Fig. 1 is a flow chart of a traveling wave protection method for a same-tower double-circuit HVDC transmission line.
Fig. 2 is a voltage waveform of a 1P midpoint fault under a completely symmetrically transposed berylon model.
Fig. 3a is modulus traveling waves of fault loops of 1P midpoint faults under the completely symmetrically transposed berylon line model.
Fig. 3b is a modulus traveling wave of a non-fault loop with a 1P midpoint fault under a completely symmetrically transposed berylon model.
Fig. 4a is a voltage waveform of 1P midpoint fault under a frequency-dependent line model without transposition.
FIG. 4b is a voltage waveform of a 1N midpoint fault under a frequency-dependent line model without transposition.
FIG. 5 is a voltage waveform of a near-end fault occurring on a down-line 1N of a line-dependent circuit model without transposition.
Fig. 6a is the modulus traveling wave of the fault loop of the 1P midpoint fault under the frequency-dependent line model without transposition.
FIG. 6b is the modulus traveling wave of the non-fault loop of the 1P midpoint fault under the frequency-dependent line model without transposition.
Fig. 7a is a modulus traveling wave of a near-end fault loop of the frequency-dependent line model 1P without transposition.
Fig. 7b is the modulus traveling wave of the far-end fault loop of the frequency-dependent line model 1P without transposition.
FIG. 8 is a structural diagram of the polar arrangement of the double-circuit line.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Examples
As shown in fig. 1, a single-loop local information-based fault line selection method for a same-tower double-loop high-voltage direct-current transmission line includes the following steps:
for the upper pole line:
(1) Calculating the absolute value | du/dt (t) | of the voltage change rate of the electrode line in real time,
u (T) is a real-time voltage sampling value, T is a time scale for solving the voltage change rate, and T = T is selected d . The absolute value of the voltage change rate is the criterion of the polar line protection starting, if the absolute value of the polar line voltage change rate reaches the setting value, the protection starting is carried out, the subsequent steps are started, and the starting time is marked as t a 。
(2) The average values of voltage and current of 20 sampling points in a certain period of time before the starting criterion meets the setting value are taken as reference values, and the reference values are subtracted from the instantaneous values of the voltage and the current at the current moment to obtain the polar line voltage variation delta u l And the amount of current change Δ i l The voltage variation Deltau of the same-loop antipole line l_op And the amount of current change Δ i l_op 。
u l (t)、u l_op (t) instantaneous values of voltages of the local and opposite poles, i l (t)、i l_op And (t) are instantaneous values of the current of the local polar line and the counter polar line respectively. t is t a Moment t at which the starting criterion satisfies the setting value d Is the sampling time interval.
(3) And calculating the average value of the current in the time window of 20 sampling points after the polar line starting criterion meets the setting value.
If the polar line is a positive polar line and Avg (i) >0, turning to the step (4);
if the polar line is a positive polar line and the Avg (i) <0, the protection is not operated, and the operation is quit;
if the polar line is a negative polar line and Avg (i) <0, go to step (4);
if the polar line is a negative electrode line and the Avg (i) >0, the protection is not operated, and the operation is quit;
(4) And 5 incremental time windows are selected to respectively obtain a voltage integral value of the local pole line and a voltage integral value of the opposite pole line, wherein the 5 incremental time windows are respectively 5, 10, 15, 20 and 25 sampling points (including the sampling points of which the voltage change rates meet the criterion) from the moment that the voltage change rates meet the criterion. The integral of the voltage over each time window is given by:
and calculating the voltage integral ratio of the local polar line and the opposite polar line in each time window:
and the integrated ratio is maximized in all time windows:
if the maximum value of the voltage integral ratioIf the pole line is larger than the setting value, the protection action of the pole line is carried out; otherwise, the protection does not act, and the operation is quitted.
For the lower layer polar lines:
(1) Calculating the absolute value | dG/dt (t) | of the change rate of the ground mode wave of the return line where the polar line is located in real time:
t is a time scale for obtaining the voltage change rate, and is selected to be T = T d . G (t) is real-time ground mode waves, and the calculation formula is as follows:
G(t)＝(i P (t)+i N (t))*Z c0 -(u P (t)+u N (t))，
i P (t)、i N (t) is the current of the positive and negative lines of the loop, u P (t)、u N (t) the voltage of the anode and cathode lines of the loop, the absolute value of the change rate of the earth mode wave is the polar line protection starting criterion, if the change rate of the earth mode wave of the loop reaches the setting value, the protection starting starts, the subsequent step is started, and the starting time is marked as t a 。
(2) The average values of voltage and current of 20 sampling points in a certain period of time before the starting criterion meets the setting value are taken as reference values, and the reference values are subtracted from the instantaneous values of the voltage and the current at the current moment to obtain the polar line voltage variation delta u l And the amount of current change Δ i l Variation amount of line voltage Δ u of the counter electrode l_op And the amount of current change Δ i l_op (the opposite polar line is the other polar line of the loop where the local polar line is located):
(3) And selecting 5 increasing time windows to respectively obtain a voltage integral value of the local polar line and a voltage integral value of the opposite polar line, wherein the 5 increasing time windows are respectively 5 sampling points, 10 sampling points, 15 sampling points, 20 sampling points and 25 sampling points (including the sampling point of which the voltage change rate meets the criterion) from the time when the change rate of the ground mode wave meets the criterion. The integral of the voltage over each time window is calculated as:
Δu l 、Δu l_op the voltage variation of the local line and the opposite line respectively.
And calculating the voltage integral ratio of the local polar line and the opposite polar line in each time window:
and the integrated ratio is maximized in all time windows:
if the maximum value of the voltage integral ratioIf the pole line is larger than the setting value, the protection action of the pole line is carried out; otherwise, turning to the step (4).
(4) Obtaining the variation amount delta P and delta G of the line mode wave and the ground mode wave of the loop where the local line is located,
Δi P 、Δi N delta u is the change of the current of the positive and negative electrode lines of the circuit P 、Δu N Is positive of the circuitNegative line voltage variation amount, Z cl 、Z c0 Line mode wave impedance and ground mode wave impedance, respectively.
(5) 5 increasing time windows are selected to respectively obtain the line modal integral value and the ground modal integral value, wherein the 5 increasing time windows are respectively 5 sampling points, 10 sampling points, 15 sampling points, 20 sampling points and 25 sampling points (including the sampling point of which the voltage change rate meets the criterion) from the time point when the ground modal change rate meets the criterion. In each time window, the modulus integral is calculated as:
and delta P and delta G are respectively line mode wave and ground mode wave variation.
And calculating the integral ratio of the earth mode wave and the line mode wave of the current circuit in each time window:
the maximum value of the integral ratio of the ground mode wave variation Δ G and the line mode wave variation Δ P of the loop is:
if the maximum value of the voltage integral ratioGreater than 1 and maximum value of modulus integral ratioAnd if the value is less than the setting value, protecting the action, otherwise, protecting the non-action, and exiting the operation.
And establishing a same-tower double-circuit direct current transmission system model by adopting PSCAD/EMTDC simulation software and referring to system parameters of the Xiluodie direct current project.
The same-tower double-circuit direct-current transmission line model is constructed by adopting a frequency-dependent parameter model, the total length of the line is 1254km, and the parameters of a line tower are shown in figure 8. The double-circuit lines on the same tower are distributed in a trapezoidal shape, the upper layer polar lines are 1P and 2N, the lower layer polar lines are 1N and 2P, and G1 and G2 are respectively ground lines, the horizontal distance l3 between the two ground lines is 28.4m, the horizontal distance l1 between the polar lines 1P and 2N is 14.5m, the horizontal distance l2 between the polar lines 1N and 2P is 19.2m, the distance h1 between the lower layer polar line and the ground is 18m, the vertical distance h2 between the upper layer polar line and the lower layer polar line is 15m, and the vertical distance h3 between the ground line and the upper layer polar line is 22m. In addition, the overline depth of the power transmission line is 16m, and the overline depth of the ground line is 11m.
Then, on the basis of the dc power transmission system model, the fault data is sampled at a sampling frequency of 10kHz, and ground faults are set at different distances from the rectifying side, respectively, and the fault transition resistances include metallic ground and high-resistance ground faults (250 Ω and 500 Ω). According to the line protection scheme provided by the patent of the invention, protection scheme programs are respectively programmed for an upper layer polar line and a lower layer polar line, fault data are processed, and the protection scheme programs comprise a voltage change rate calculation module and an integral ratio of voltage change of the upper layer polar line, a ground mode wave change rate calculation module, an integral ratio of voltage change and an integral ratio of line mode wave and ground mode wave of the lower layer polar line, and the protection action condition of the lower layer polar line under the condition that different polar lines have faults is observed, as shown in table 4 (a), a 1P protection test condition table of fault line selection simulation data of the upper layer polar line (wherein "-" indicates that the voltage change rate criterion is not started), table 4 (b) is a 2N protection test condition table of the upper layer polar line (wherein "-" indicates that the voltage change rate is not started), table 4 (c) is a 1N protection test condition table of the lower layer polar line (wherein "-" indicates that the ground mode wave change rate criterion is not started), and table 4 (d) is a 2P protection test condition table of the lower layer polar line (wherein "-" indicates that the ground mode wave change rate is not started ", and" test condition table 4 (wherein "-" indicates that the ground mode wave change rate criterion is not started ", and" the fault mode wave change rate criterion is the fault area test condition table (wherein "-" 4 (e) "indicates that the ground wave criterion is not started)" indicates that the fault area change rate or the fault area change rate is not started "). In Table 4Andthe value of (d) is the calculated result in 25 sampling points (i.e., 2.5ms time window) after the start criterion response after the traveling wave arrives, and the current average value is the calculated result in 20 sampling points (i.e., 2ms time window) after the start criterion response after the traveling wave arrives.
TABLE 4 (a)
TABLE 4 (b)
Watch 4 (c)
Watch 4 (d)
TABLE 4 (e)
For the upper layer polar line, the voltage change rate is set to be 1.2 times 0.67 (p.u.) of the maximum value of the voltage change rate of the polar line for avoiding all polar line inversion side faults, and the voltage integral ratio is the minimum value of the voltage ratio of the fault pole to the non-fault pole under the symmetric transposition, namely 3 (times). For the lower layer of the ground wire, the setting of the change rate of the ground mode wave is 2.13 (p.u.) of the maximum value of the change rate of the ground mode wave of the local wire avoiding the faults of all polar lines and inversion sides, the voltage integral ratio is 1.5 (4.5) of the minimum value of the voltage ratio of the fault pole to the non-fault pole under the symmetric transposition, and the modulus integral ratio is 0.8 (1.76) of the maximum value of the modulus ratio under the symmetric transposition.
The protection action conditions of other metallic faults and polar lines under 250 omega and 500 omega transition resistance conditions are carried out by using the setting value obtained according to the setting principle, the effect is good, the external fault of the inversion side can be distinguished by the upper layer polar line through the voltage change rate during the external fault, and the external fault of the rectification side can be distinguished through the current direction; and the change rate of the ground mode wave of the polar line of the lower layer can distinguish the external fault.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such modifications are intended to be included in the scope of the present invention.
Claims (9)
1. A traveling wave protection method for a same-tower double-circuit high-voltage direct current transmission line is characterized by comprising the following steps of:
(1) For the upper-layer polar line, the absolute value of the voltage change rate of the polar line is obtained to serve as a starting criterion, and the average value Avg (i) of the current is calculated; for the lower layer polar line, calculating the ground mode wave of the loop where the polar line is based on a formula of the ground mode wave of the single-loop line, and solving the absolute value of the change rate of the ground mode wave as a starting criterion, wherein the formula of the ground mode wave of the single-loop line is as follows:
G(t)＝(i P (t)+i N (t))*Z c0 -(u P (t)+u N (t))，
wherein G (t) is instantaneous value of earth mode wave, i P (t)、i N (t)、u P (t) and u N (t) instantaneous values of the positive pole wire current, negative pole wire current, positive pole wire voltage and negative pole wire voltage of the same loop, Z c0 Is the earth mode wave impedance;
(2) For the upper-layer polar line, judging whether the absolute value of the voltage change rate meets the protection criterion, if the absolute value of the voltage change rate and the average value Avg (i) of the current meet the protection criterion at the same time, turning to the step (3), and if not, returning to the step (1); judging whether the change rate of the ground mode waves meets the protection criterion or not for the lower layer polar lines, if so, turning to the step (3), otherwise, returning to the step (1);
(3) Respectively taking the average value of the voltage and the current in a certain period of time before the starting criterion meets the setting value as a steady reference quantity, and subtracting the reference quantity of each polar line from the instantaneous value of the electric quantity of each polar line at the current moment to obtain the voltage and current variable quantity of each polar line; for the lower layer polar line, obtaining the variation of linear mode wave and ground mode wave by the voltage and current variation;
(4) For the upper polar line, each time window w of the local polar line is obtained i Voltage integral value ofIntegral value of voltage of sum antipodal lineAnd find the time window w i Voltage integral ratio ofFor the lower layer polar line, each time window w of the local polar line is obtained i Voltage integral value ofIntegral value of voltage of sum antipodal lineAnd find the time window w i Voltage integral ratio ofAt the same time, each time window w of the loop is obtained i Integral value E of linear mode wave P (w i ) And earth mode wave integral value E G (w i ) And the time window w i Integral ratio of modulus of
(5) For the upper polar line, the maximum value of the voltage integral ratio of all time windows is obtainedFor the lower polar line, the maximum value of the voltage integral ratio of all time windows is obtainedAnd maximum value of modulus integral ratio of all time windows
(6) For the upper pole line, if the voltage integral ratio of all time windows is maximumIf the protection criterion setting value is met, the local polar line is protected; for the lower layer polar line, if the maximum value of the voltage integral ratio of all time windowsIs greater than setting value delta' 1 OrMaximum value of integral ratio of earth mode wave to line mode wave of all time windows larger than 1Less than setting value Delta 2 Then, the local line is protected.
2. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, wherein in step (1), the upper-layer polar line is determined and reliably removed from the fault outside the rectifying side area by using the combination of the voltage change rate and the current polarity, and the calculation formula of the absolute value of the voltage change rate is as follows:
wherein du/dt (T) is the voltage change rate of the moment T, u (T) is the voltage instantaneous value of the polar line at the moment T, T is the time scale for obtaining the voltage change rate, and is selected as the sampling time T d Integral multiple of the voltage change rate, the absolute value of the voltage change rate is the polar line protection starting criterion, if the starting setting value is met at a certain moment, the moment is t a ；
The calculation formula of the current average value in a certain time window is as follows:
wherein, avg (i) is the average value of current, Δ i is the current variation, and n is the number of sampling points of the current variation in the selected time window;
if the local pole is a positive pole line, if the voltage change rate criterion is started, if the Avg (i) >0 is present, the internal fault of the polar line is present, or if the local pole is a negative pole line, if the voltage change rate criterion is started, if the Avg (i) <0 is present, the internal fault of the polar line is present; otherwise, the fault is an external fault of the rectifying side.
3. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, characterized in that in step (1), the lower-layer polar line adopts the ground mode wave change rate, can be started even under higher transition resistance, and simultaneously eliminates the rectifying side external fault and the inverting side external fault, and calculates the lower-layer polar line ground mode wave change rate in real time and takes the absolute value under the steady state condition:
wherein dG/dt (t) is the change rate of the ground mode wave at the time t, and G (t) isThe instantaneous value of the earth mode wave at the moment T is the time scale for solving the voltage change rate and is selected as the sampling time T d Integer multiples of.
4. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, wherein in step (3), the method for calculating the variation of the voltage and the current is as follows:
wherein u is 1P (t)，i 1P (t) respectively represent the instantaneous values of voltage and current, Δ u, of the polar line 1P at time t 1P 、Δi 1P Respectively representing the voltage variation and the current variation of the polar line 1P, and the rest are analogized in the same way; t is t a Moment t when the start criterion satisfies the protection criterion d Is a sampling time interval;
the method for solving the variation of the line mode wave and the earth mode wave comprises the following steps:
wherein, Δ P and Δ G are line mode wave variation and ground mode wave variation, and Δ i P 、Δi N For the calculated current change amount of the positive wire and the negative wire of the loop, delta u P 、Δu N For the voltage variation of the positive and negative lines of the loop, Z cl 、Z c0 Line mode wave impedance and ground mode wave impedance, respectively.
5. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, characterized in that in step (4), the integral ratio of the voltage or modulus is used as a criterion, and the integral ratio of the voltage of the local line and the opposite line is:
wherein, the first and the second end of the pipe are connected with each other,is a time window w i Integral ratio of voltages of intrinsic and epipolar lines, E ul (w i ) Is a time window w i Integral value of voltage of intrinsic line, E ul_op (w i ) Is a time window w i The voltage integral value of the opposite polar line of the same loop line with the local polar line;
the integral ratio of the ground mode wave and the line mode wave of the return line is as follows:
wherein the content of the first and second substances,for the earth mode wave and the line mode wave of the loop where the local line is located in the time window w i Inner integral ratio, E G (w i ) Is the earth mode wave of the loop where the local polar line is located in the time window w i Integral value of E P (w i ) Is the linear mode wave of the loop where the local polar line is located in the time window w i The integral value of (2).
6. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, characterized in that in step (4), the voltage and modulus are integrated by a variable time window: and (2) obtaining a voltage integral ratio and a modulus integral ratio by taking a plurality of time windows with different time lengths, and obtaining a maximum value, wherein in each time window, the integral of the voltage is obtained by the following formula:
wherein the content of the first and second substances,respectively the local and opposite polar lines in a time window w i Internal voltage integral value, Δ u l 、Δu l_op Respectively the local and opposite polar lines in a time window w i Internal voltage variation, N i Is a time window w i The number of sampling points;
and calculating the voltage integral ratio of the local polar line and the opposite polar line in each time window, and solving the maximum value of the integral ratio in all the time windows:
wherein, the first and the second end of the pipe are connected with each other,is the maximum value of the voltage integral ratio in all time windows,is a time window w i Internal voltage integral ratio, t 0 The time length of the longest time window;
the equation for the integral of modulus is:
wherein, E P (w i )、E G (w i ) Respectively a time window w i The integral value of the inner linear mode wave and the integral value of the earth mode wave, wherein delta P and delta G are respectively the variable quantity of the linear mode wave and the earth mode wave;
the modulus integral ratio is calculated and the integral ratio is maximized in all time windows:
wherein the content of the first and second substances,the maximum value of the integrated ratio of the quantities in all time windows,is a time window w i Integral ratio of moduli, t 0 The length of the longest time window.
7. The traveling wave protection method for the same-tower double-circuit HVDC transmission line according to claim 1, characterized in that in step (6), for distinguishing the local line fault from other line faults, different protection schemes are adopted for the upper layer line and the lower layer line: the upper layer polar line can act when the voltage integral ratio is satisfied, otherwise, the upper layer polar line does not act; the lower polar line acts when the voltage integral ratio is met, or the voltage integral ratio is greater than 1 and the modulus integral ratio is met, otherwise, the lower polar line does not act;
the protection criterion of the upper layer polar line for distinguishing the fault of the polar line from other polar line faults is as follows:
wherein the content of the first and second substances,is the maximum value of integral ratio of line voltage of local polar line and opposite polar line, delta 1 Setting value of upper layer electrode line voltage integral ratio;
the protection criterion of the lower layer polar line in distinguishing the local polar line fault from other polar line faults is as follows:
or
And is provided with
Wherein the content of the first and second substances,is the maximum value of the integrated ratio of the voltages,is the maximum value of the integrated ratio of moduli, delta' 1 Is a setting value, delta, of the integral ratio of the lower layer polar line voltage 2 The integral ratio value of the polar modulus of the lower layer is a setting value.
8. The same-tower double-circuit HVDC transmission line traveling wave protection method of claim 1, wherein in step (6), the criterion that the protection action should satisfy for the lower-layer polar line is as follows:
for the lower polar line near-end fault, the voltage integral ratio meets the criterion:
wherein the content of the first and second substances,is the maximum value of the integrated ratio of voltages, delta' 1 Setting value of integral ratio of lower layer polar line voltage;
for the lower extreme line far-end fault, the modulus integral ratio meets the criterion:
and is
Wherein the content of the first and second substances,is the maximum value of the integrated ratio of the voltages,maximum value of integral ratio of modulus, delta 2 The integral ratio value of the polar modulus of the lower layer is a setting value.
9. The same-tower double-circuit HVDC transmission line traveling wave protection method defined in claim 1, wherein in step (6), the voltage integral ratio does not completely protect the far-end fault in which the line modulus and the ground modulus are completely separated; the modulus integral ratio does not completely protect the near-end fault that the line modulus and the ground modulus are completely overlapped; i.e. for the lower layer line, the voltage integral ratio delta' 1 Setting is that the ratio of the voltage quantity of a fault electrode and a non-fault electrode is multiplied by a reliable coefficient of 1.5 times when the earth mode wave and the line mode wave are completely separated under the symmetric transposition; and integral ratio of modulus Δ 2 Setting is to multiply the integral ratio of the fault return ground mode wave and the line mode wave by a reliable coefficient of 0.8 time when the line mode wave and the ground mode wave are completely overlapped under the condition of symmetrical transposition.
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