Zero-sequence inverse time limit protection method for single-circuit and double-circuit matched line based on impedance variable-speed factor

Abstract

The invention provides a single-circuit and double-circuit matching line zero-sequence inverse time limit protection method based on an impedance variable-speed factor, and the method comprises the following steps: obtaining a fault type when a fault occurs; based on the fault type, obtaining a sequence current phase at a protection installation position so as to obtain an equivalent phase angle of a voltage phase angle to ground of the fault point; obtaining an impedance variable-speed factor according to an equivalent phase angle of the ground voltage phase angle of the fault point; based on the inverse time characteristic curve, obtaining a protection action equation according to the impedance speed change factor; and protecting the single-circuit and double-circuit matching line according to the protection action equation. According to the method, double-target optimization of quickness and selectivity is realized only by using locally acquired electrical quantity information, maloperation of a non-fault line is avoided, the action time of protection is shortened, and the quickness of protection is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of line protection, and particularly to a zero-sequence inverse-time protection method for single and double-circuit coordinated lines based on an impedance variable speed factor. Background Art

[0002] In engineering applications, the unified inverse-time zero-sequence current protection curve for the entire network and achieving multi-stage coordination through curve translation is a key development direction for relay protection. It has the advantages of simplified setting and strong adaptability, and can effectively improve the overall performance of backup protection.

[0003] With the gradual increase in the scenarios of short lines in series and single and double-circuit coordination in the 220 kV system, the problem of loss of protection selectivity is likely to occur during high-resistance grounding faults. Therefore, the protection curve can be dynamically adjusted based on fault characteristics on the basis of traditional inverse-time protection to improve the protection performance in complex power grid scenarios. However, so far, there is no literature specifically studying the coordination scheme of inverse-time overcurrent protection in short lines. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a zero-sequence inverse-time protection method for single and double-circuit coordinated lines based on an impedance variable speed factor, which realizes the design of a double-objective optimization algorithm for quick action and selectivity only by using the electrical quantity information collected locally by the protection device (without information from the opposite end or the entire network). By introducing an impedance variable speed factor mutation criterion, the misoperation of non-faulty lines in the single and double-circuit coordination scenarios of short lines is improved for the impedance variable speed factor. A secondary acceleration coefficient is introduced in the link of protection re-timing: shortening the protection operation time, improving the quick action of the protection, and preventing the further expansion of the fault.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A zero-sequence inverse-time protection method for single and double-circuit coordinated lines based on an impedance variable speed factor, comprising the following steps: When a fault occurs, obtain the fault type;

[0006] Based on the fault type, obtain the phase angle of the sequence current at the protection installation location, and obtain the equivalent phase angle of the fault point-to-ground voltage phase angle according to the phase angle of the sequence current;

[0007] Obtain the impedance variable speed factor according to the equivalent phase angle of the fault point-to-ground voltage phase angle;

[0008] Based on the inverse-time characteristic curve, obtain the protection operation equation according to the impedance variable speed factor;

[0009] Protect the single and double-circuit coordinated lines according to the protection operation equation.

[0010] In some of the embodiments, the phase angle of the sequence current at the protection installation location at least includes the negative-sequence current phase angle and the zero-sequence current phase angle at the protection installation location.

[0011] In some of these embodiments, the fault types include single-phase ground faults and two-phase ground faults.

[0012] In some of these embodiments, when the fault type is the single-phase ground fault: an equivalent phase angle of the fault point-to-ground voltage phase angle is obtained according to the negative-sequence current phase at the protection installation location;

[0013] When the fault type is the two-phase ground fault: an equivalent phase angle of the fault point-to-ground voltage phase angle is obtained according to the zero-sequence current phase at the protection installation location.

[0014] In some of these embodiments, the steps of obtaining the impedance variable speed factor according to the equivalent phase angle of the fault point-to-ground voltage phase angle are as follows:

[0015] Obtain the length of the protected line where the fault point is located, the first zero-sequence impedance, and the first positive-sequence impedance, where the first zero-sequence impedance is the zero-sequence impedance per unit length of the protected line where the fault point is located, and the first positive-sequence impedance is the positive-sequence impedance per unit length of the protected line where the fault point is located;

[0016] Obtain the zero-sequence current compensation coefficient according to the first zero-sequence impedance and the first positive-sequence impedance;

[0017] When a fault occurs, obtain the first zero-sequence current, the first fault-phase voltage, and the first fault-phase current respectively, where the first zero-sequence current is the zero-sequence current measured at the protection installation location, the first fault-phase voltage is the fault-phase voltage measured at the protection installation location, and the first fault-phase current is the fault-phase current measured at the protection installation location; obtain the line impedance from the protection installation location to the fault point according to the first zero-sequence current, the zero-sequence current compensation coefficient, the equivalent phase angle of the fault point-to-ground voltage phase angle, the first fault-phase voltage, and the first fault-phase current;

[0018] Obtain the impedance variable speed factor according to the line impedance, the length of the protected line, and the first positive-sequence impedance.

[0019] In some of these embodiments, the protection action equation includes a primary protection action equation and a secondary acceleration protection action equation.

[0020] In some of these embodiments, the zero-sequence inverse-time protection method for single and double circuit coordinated lines based on the impedance variable speed factor further includes the following steps:

[0021] Construct an impedance variable speed factor mutation criterion;

[0022] After a fault occurs:

[0023] Starting from the fault occurrence time point, the protection installation location performs a protection action according to the primary protection action equation;

[0024] When the mutation amount of the impedance variable speed factor at the protection installation location satisfies the impedance variable speed factor mutation criterion, starting from the re-timing time point, the protection action occurs at the protection installation location according to the secondary acceleration protection action equation, and the re-timing time point is the time point when the mutation amount of the impedance variable speed factor satisfies the impedance variable speed factor mutation criterion.

[0025] In some embodiments, the impedance variable speed factor mutation criterion is:

[0026]

[0027] In the formula, Z floor is the lower limit of the mutation amount of the impedance variable speed factor, Z ceiling is the upper limit of the mutation amount of the impedance variable speed factor, is the impedance variable speed factor at time t + dt at the protection installation location, is the impedance variable speed factor at time t at the protection installation location.

[0028] In some embodiments, the pre-action protection action equation is:

[0029]

[0030] In the formula, T 0 (3I 0 ) is the zero-sequence inverse-time protection delay starting from the fault occurrence time point, I 0 is the zero-sequence current measured at the protection installation location, I P is the zero-sequence inverse-time current setting value, T P is the zero-sequence inverse-time time setting value, Z Acc is the impedance variable speed factor.

[0031] In some embodiments, the secondary acceleration protection action equation:

[0032]

[0033] In the formula, T 0 (3I 0 ) is the zero-sequence inverse-time protection delay starting from the re-timing time point, I 0 is the zero-sequence current measured at the protection installation location, I P is the zero-sequence inverse-time current setting value, T P is the zero-sequence inverse-time time setting value, k is the secondary acceleration coefficient, Z Acc is the impedance variable speed factor.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention re-times the protection according to the mutation criterion of the impedance variable speed factor: by introducing the mutation criterion of the impedance variable speed factor, the misoperation of the non-faulty line in the short line single- and double-loop cooperation scenario is improved for the impedance variable speed factor.

[0036] 2. The present invention introduces a secondary acceleration coefficient in the link of re-timing the protection: shortens the operation time of the protection, improves the quick-acting performance of the protection, and prevents the further expansion of the fault.

[0037] 3. The present invention only utilizes the electrical quantity information collected locally by the protection device (without the information of the opposite end or the whole network) to realize the design of the dual-objective optimization algorithm for quick-acting performance and selectivity. Description of the Drawings

[0038] Figure 1 is a schematic flow chart of the zero-sequence inverse-time protection method for single- and double-loop cooperative lines based on the impedance variable speed factor of the present invention;

[0039] Figure 2 is the action logic diagram of the inverse-time zero-sequence overcurrent protection in the prior art;

[0040] Figure 3 is a typical structure diagram of short line single- and double-loop cooperation;

[0041] Figure 4 (a) is the decoupling diagram of the typical structure of short line single- and double-loop cooperation, Figure 4 (b) is the zero-sequence equivalent network of the typical structure of short line single- and double-loop cooperation;

[0042] Figure 5 is a typical structure diagram of the faulty line;

[0043] Figure 6 is the phasor diagram of each sequence current and the voltage at the fault point and its variation law trajectory during A-phase single-phase ground short circuit;

[0044] Figure 7 is the vector relationship diagram of the voltage at the protection location and the voltage at the fault point and its variation law trajectory during A-phase single-phase ground;

[0045] Figure 8 is the composite sequence network diagram during two-phase ground short circuit through a transition resistance;

[0046] Figure 9 is the phasor diagram of each sequence current, the voltage at the fault point and its variation law trajectory during BC-phase two-phase ground short circuit;

[0047] Figure 10 is the vector relationship diagram of the voltage at the protection location and the voltage of the faulty phase (B-phase) at the fault point and its variation law trajectory during BC-phase two-phase ground;

[0048] Figure 11The inverse-time overcurrent protection operating time curve with the impedance variable speed factor introduced;

[0049] Figure 12 It is the protection operating logic diagram with the impedance variable speed factor mutation criterion and the secondary acceleration protection operating equation introduced. Specific implementation mode

[0050] The inverse-time overcurrent protection is usually based on the time-current inverse-time characteristic: I r ×t = K, where I is the current, r is the curve type parameter, and K is the time coefficient;

[0051] The curve type parameter r in the formula takes different values according to different usage occasions of the protection: generally, the definite-time overcurrent protection is often adopted when the current change is small at the beginning and end of the protected line. The definite-time limit can be considered a special inverse-time characteristic, that is, r = 0; while when the current change is large at the beginning and end of the line, the very inverse-time characteristic, that is, r = 1, is adopted; usually, the general inverse-time characteristic, that is, 0 < r < 1, is adopted for transmission lines; the overcurrent protection for reflecting the overheat state adopts the special inverse-time characteristic, that is, r = 2.

[0052] In the domestic line system, the time-current characteristic curve of the inverse-time zero-sequence overcurrent protection adopts the general inverse-time characteristic curve in the IEC standard inverse-time characteristic curve as: In the formula: T 0 (3I 0 ) is the zero-sequence inverse-time protection delay; T P is the zero-sequence inverse-time time setting value; I P is the zero-sequence inverse-time current setting value; 3I 0 is the triple zero-sequence current measured by the protection device.

[0053] According to relevant standards, the operating logic of the line inverse-time zero-sequence overcurrent protection is as Figure 2 shown; among them, the zero-sequence inverse-time protection delay T 0 (3I 0 ) is jointly determined by I P and T P , so the operating logic of the zero-sequence inverse-time protection involves a total of T P , I P , T h , T x These 4 setting values. Among them: T 0 (3I 0 ) is achieved through the integration of current and time. When the cumulative amount reaches a specific operating threshold, that is, it meets the starting condition of the T 0 (3I 0 ) element; T h is the zero-sequence inverse-time coordination time, so that the protection maintains the inverse-time characteristic within a certain range;x is the minimum time of the zero-sequence inverse time limit, which is used together with T h to avoid the reclosing, distance protection, and three-phase inconsistency protection times.

[0054] From Figure 2 , the total operating time of the inverse-time zero-sequence overcurrent protection can be expressed as: T all = max{T 0 (3I 0 ), T h} + T x .

[0055] The literature "Huang Jingguang, Zhang Yupeng, Li Jiangxia, et al. A New Scheme of Inverse-Time Overcurrent Protection Based on Impedance Correction [J]. Power System Protection and Control, 2020, 48(09): 88-94." proposed a correction scheme using the percentage of measured impedance and the impedance correction index, but it cannot correctly reflect the operating boundary inside and outside the zone in the case of high-resistance grounding. The literature "Fang Yuchen, Wang Bin, Zhang Liangli. Adaptive Inverse-Time Protection Considering the Generation Output of Distributed Generation [J]. Proceedings of the CSU-EPSA, 2023, 35(10): 9-17." corrected the inverse-time operating characteristic curve using the transition resistance offset angle and the impedance correction coefficient in view of the influence of the distributed generation output on the variation characteristics of the measured impedance. The literature "Huang Jingguang, Li Zhedong, Zhang Yupeng, et al. An Improved Impedance Correction Inverse-Time Overcurrent Protection Setting Method Considering the Optimization Level of Backup Protection [J]. Power System Technology, 2022, 46(07): 2768-2777." improved the denominator of the acceleration factor on the basis of using impedance acceleration and introduced the backup level optimized by the quantum genetic algorithm to accelerate the protection. However, the above schemes do not target the high-resistance grounding fault scenario and have certain limitations.

[0056] Regarding the distribution characteristics of zero-sequence current and the coordination problem of zero-sequence inverse-time overcurrent protection in the double-circuit line scenario, the literature "Zeng Genghui, Cai Zexiang, Chen Qiaoping, et al. Analysis of zero-sequence current distribution characteristics of ground faults on double-circuit lines on the same tower [J]. Power System Technology, 2011, 35(11): 212-217." analyzed the distribution laws of zero-sequence current during external and internal ground faults on double-circuit lines on the same tower under different operating modes, different zero-sequence mutual inductance strengths, and different fault locations. The literature "Lu Xiaoyi, Zheng Tao, Dai Yuxin, et al. Zero-sequence inverse-time current protection introducing root-mean-square value and phase mutation criteria of current [J]. Journal of Xi'an Jiaotong University, 2024, 58(02): 195-206." improved the misoperation situation during double-circuit line faults by introducing the root-mean-square value and phase mutation criteria of zero-sequence current into the inverse-time protection. The literature "Zhang Zijin, Cong Wei, Xiao Jing, et al. Accelerated coordination scheme for zero-sequence inverse-time overcurrent protection of power transmission network with double-circuit lines on the same pole [J]. Electric Power Automation Equipment, 2017, 37(09): 159-165." designed an acceleration scheme based on zero-sequence current change and power direction for the misoperation of protection during internal ground faults on double-circuit lines on the same pole, improving the selectivity and quick-acting performance of the protection, but did not study the influence of transition resistance. The literature "Wu Linlin, Huang Shaofeng. Influence of parallel double-circuit lines on inverse-time zero-sequence current protection and improved algorithm [J]. Power System Technology, 2013, 37(03): 707-712." proposed a voltage-accelerated inverse-time zero-sequence overcurrent protection algorithm based on wide-area information, improving the quick-acting performance of the protection while improving the selectivity, but having a high dependence on the communication system.

[0057] The typical structure of single- and double-circuit coordination is as Figure 3 shown, Figure 3 where the numbers 1-6 in it represent the protection numbers, Line I and Line II are double-circuit lines on the same pole, Z I is the zero-sequence impedance of Line I, Z II is the zero-sequence impedance of Line II, Z m is the zero-sequence mutual impedance between Line I and Line II, Z M is the equivalent zero-sequence impedance of the system on the left side of bus M, Z N is the equivalent zero-sequence impedance of the system on the right side of bus N. Suppose a fault occurs on Line I, and the ratio of the distance from the fault location to bus P to the total length of Line I is α. From Figure 3 through decoupling and network transformation, we get Figure 4 . From Figure 4 (b), it can be seen that when the line impedance satisfies Equation (1), no zero-sequence current flows through Line II. At this time, I N = I QI , I M = I PI , I N is the zero-sequence current flowing from bus N to bus Q, and I QⅠThe zero-sequence current flowing from bus Q to line I, I M The zero-sequence current flowing from bus M to bus P, I PⅠ The zero-sequence current flowing from bus P to line I. The zero-sequence currents flowing through protection 3 and protection 6 are the same, and the zero-sequence currents flowing through protection 1 and protection 2 are the same.

[0058]

[0059] In the formula, Z Ⅰ0 is the zero-sequence impedance of the PQ section of the line, Z N0 is the equivalent zero-sequence impedance of the system on the right side of bus N, Z QN is the zero-sequence impedance of the QN section of the line, Z M0 is the equivalent zero-sequence impedance of the system on the left side of bus M, Z MP is the zero-sequence impedance of the MP section of the line. When the line impedance satisfies equation (2), the direction of the zero-sequence current on line II is the same as that of I PII , I PⅡ is the zero-sequence current flowing from bus P to line II. At this time, I M = I PI +I PII >I PI . The zero-sequence current flowing through protection 1 is greater than the zero-sequence current flowing through protection 2, and the operating time of protection 1 is shorter than that of protection 2, which may cause protection 1 to malfunction.

[0060]

[0061] Similarly, when the line impedance satisfies equation (3), the direction of the zero-sequence current on the line is the same as that of I QII , I QⅡ is the zero-sequence current flowing from bus Q to line II. At this time, the current relationship is I N = I QI +I QII >I QI . The zero-sequence current flowing through protection 6 is greater than the zero-sequence current flowing through protection 3, and the operating time of protection 6 is shorter than that of protection 3, which may cause protection 6 to malfunction.

[0062]

[0063] In summary, in the scenario of single and double circuit cooperation of short lines, when the system parameters and fault point location information meet certain conditions, the protection on the non-fault single circuit line will malfunction and cannot meet the requirements of selectivity.

[0064] To clearly illustrate the technical features of this solution, the following will combine the accompanying drawings and embodiments to elaborate on the implementation manner of this application in detail, so as to fully understand how this application uses technical means to solve technical problems and the implementation process of achieving corresponding technical effects and implement it accordingly. Each feature in the embodiments of this application and the embodiments can be combined with each other on the premise of not conflicting, and the formed technical solutions are all within the protection scope of this application.

[0065] See Figure 1 , the embodiment of the present disclosure provides a zero-sequence inverse-time protection method for single and double circuit coordinated lines based on impedance variable speed factors, including the following steps: when a fault occurs, obtain the fault type;

[0066] Based on the fault type, obtain the phase angle of the sequence current at the protection installation location, and obtain the equivalent phase angle of the fault point-to-ground voltage phase angle according to the phase angle of the sequence current.

[0067] See Figure 5 , Figure 5 is a typical structure diagram of a faulty line. The numbers 1 and 2 in the figure represent protection numbers. When a ground fault occurs at point f in line MN, f is the fault point. is the measured fault phase voltage at the protection location. is the fault phase voltage at the fault point, R g is the equivalent transition resistance of the fault ground;

[0068] In some of the embodiments, the phase angle of the sequence current at the protection installation location includes at least the phase angle of the negative sequence current and the phase angle of the zero sequence current at the protection installation location.

[0069] In some of the embodiments, the fault type includes single-phase ground fault and double-phase ground fault.

[0070] In some of the embodiments, when the fault type is a single-phase ground fault: obtain the equivalent phase angle of the fault point-to-ground voltage phase angle according to the phase angle of the negative sequence current at the protection installation location;

[0071] When the fault type is a double-phase ground fault: obtain the equivalent phase angle of the fault point-to-ground voltage phase angle according to the phase angle of the zero sequence current at the protection installation location.

[0072] Assume that at Figure 5 shown in the line, a phase A ground short circuit occurs at point f through the equivalent transition resistance R of the fault ground g . Before the short circuit, the line is no-load. At this time, the sequence currents at the short circuit point, that is, the fault point, are:

[0073]

[0074] In the formula, is the positive sequence current from the fault point to the ground, is the negative-sequence current of the fault point to the ground, is the zero-sequence current of the fault point to the ground, x 1Σ is the equivalent positive-sequence reactance of the system as seen from the fault point, x 2Σ is the equivalent negative-sequence reactance of the system as seen from the fault point, x 0Σ is the equivalent zero-sequence reactance of the system as seen from the fault point, is the electromotive force of the equivalent power supply of phase A, j is the imaginary unit, the electromotive force of the equivalent power supply and the sequence reactances of each component are all constants and known, and only the fault grounding equivalent transition resistance R g is a variable, and the trajectory of the endpoints of each sequence current vector with the change of the fault grounding equivalent transition resistance R g is a semi-circle related to the equivalent reactance of the system, as Figure 6 shown.

[0075] The current flowing into the ground through the transition resistance is:[[]]

[0076]

[0077] In formula (5), is the fault-phase current when a phase-A ground short circuit occurs at the fault point;

[0078] The sequence voltage can be obtained from the sequence current as:[[]]

[0079]

[0080] In formula (6), is the positive-sequence voltage of the fault point to the ground, is the negative-sequence voltage of the fault point to the ground, is the zero-sequence voltage of the fault point to the ground;

[0081] The fault-phase voltage at the fault point of point f can be obtained from the sequence voltages as:[[]]

[0082]

[0083] In formula (7), is the fault-phase voltage when a phase-A ground short circuit occurs at the fault point;

[0084] At the same time, considering the voltage drop across the transition resistance, the fault-phase voltage at the fault point of point f can also be expressed as:[[]]

[0085]

[0086] It can be seen from formula (7) that the trajectory of the endpoints of the fault-phase voltage vector with the change of the fault grounding equivalent transition resistance R g is a semi-circle related to the zero-sequence current of the fault point to the ground, as Figure 6As shown. Combining with Equation (8), it can be seen that The trajectory of the vector endpoint changing with R g is the same as that of the faulty phase, both being semi - circles.

[0087] When a ground fault occurs in phase A at point f, the measured faulty - phase voltage at the protection installation on the M side of the bus is:

[0088]

[0089] In Equation (9), x S1 is the equivalent positive - sequence impedance of the power source on the left side of bus M, x S0 is the equivalent zero - sequence impedance of the power source on the left side of bus M, c is the shunt coefficient of the current at the bus protection on the M side, the electromotive force of the equivalent power source in phase A and the reactances of each sequence are all constants. The measured faulty - phase voltage at the protection installation on the M side of the bus is a linear function of the positive - sequence current to the ground at the fault point. Combining Equation (9) with Figure 6 it can be seen that the trajectory of the endpoint of the vector changing with R g is a semi - circle as shown in Figure 7 .

[0090] From Equation (4) and Equation (8), it can be seen that when a single - phase ground fault occurs through a transition resistance, the faulty - phase voltage at the fault point and the currents of each sequence at the fault point: the positive - sequence current to the ground at the fault point, the negative - sequence current to the ground at the fault point, and the zero - sequence current I f0 to the ground at the fault point are in the same phase and satisfy:

[0091]

[0092] where Arg represents the phase angle. Considering the influence of the system operation mode on the phase angles of the currents of each sequence, the influence of the negative - sequence current and the zero - sequence current on the system operation mode is smaller than that of the positive - sequence current. And in the negative - sequence network, the equivalent impedance angle of the system is closer to the line impedance angle than in the zero - sequence network. Therefore, the phase angle of the negative - sequence current at the protection installation can be approximated as the phase angle of the negative - sequence current flowing into the fault point:

[0093]

[0094] From Equation (10) and Equation (11), it can be seen that the phase of the faulty negative - sequence current at the protection installation is approximately equal to the phase of the voltage to the ground at the fault point.

[0095]

[0096] Assume that atFigure 5 The fault grounding of point f on the shown line is equivalent to a transition resistance R g A BC-phase ground short circuit occurs. The line is no-load before the short circuit. According to the system wiring diagram, the composite sequence network diagram can be obtained as shown in Figure 8 (a), which is converted into the form as shown in Figure 8 (b) for easy analysis. Figure 8 (a), Figure 8 (b):

[0097]

[0098] In the formula, is Figure 8 the equivalent electromotive force of phase A of the positive-sequence branch and the negative-sequence branch combined and simplified in (a);

[0099] From Figure 8 (b), the zero-sequence current at the short-circuit point can be obtained:

[0100]

[0101] In the formula, x 12Σ is Figure 8 the equivalent reactance of the positive-sequence branch and the negative-sequence branch combined and simplified in (a), is Figure 8 the equivalent branch current of the positive-sequence branch and the negative-sequence branch combined and simplified in (a);

[0102] From formula (15) and Figure 8 (b), the positive-sequence current and the negative-sequence current at the short-circuit point can be obtained respectively as:

[0103]

[0104] The fault-phase current at point f is:

[0105]

[0106] In the formula, α 1 is the first intermediate expression,

[0107]

[0108] The current flowing into the ground through the transition resistance is:

[0109]

[0110] In the formula, is the fault-phase B current when a BC-phase ground short circuit occurs at the fault point, is the fault-phase C current when a BC-phase ground short circuit occurs at the fault point;

[0111] Considering the voltage drop across the transition resistance, the fault-phase voltage at the fault point f is:

[0112]

[0113] In the formula, is the fault-phase B voltage when a BC-phase ground short circuit occurs at the fault point, is the fault-phase C voltage when a BC-phase ground short circuit occurs at the fault point; Similar to Equation (8), Equation (19) shows that and also have trajectories that are semi-circles related to the zero-sequence current to the ground at the fault point. Combining Equations (15) to (19), the trajectories of the endpoints of the sequence currents and the fault-phase voltage vectors at point f with respect to the fault grounding equivalent transition resistance R g can be plotted. The trajectories are all semi-circular, as shown in Figure 9 .

[0114] Taking the grounding of BC phases through a transition resistance as an example, the sequence voltages at the location of the protection installation during a fault are:

[0115]

[0116] In the formula, is the positive-sequence voltage at the location of the protection installation, is the negative-sequence voltage at the location of the protection installation, is the zero-sequence voltage at the location of the protection installation, c 1 is the shunt coefficient of the positive-sequence current at the bus protection on the M side, c 2 is the shunt coefficient of the negative-sequence current at the bus protection on the M side, c 0 is the shunt coefficient of the zero-sequence current at the bus protection on the M side. Combining Equations (13) to (16), the phase voltage

[0117]

[0118] of the fault-phase B at the location of the protection installation on the M side of the bus can be obtained. In the formula, is the electromotive force of the B-phase equivalent power source, is the zero-sequence current at the location of the protection installation. The electromotive force and the sequence reactances are all constants. The phase voltage of the fault-phase B at the location of the protection installation on the M side of the bus is a linear function of the positive-sequence current Figure 9 to the ground at the fault point. Combining Equation (21) with shows that the trajectory of the endpoint of the vector g with respect to the change of R Figure 10 is a semi-circle as shown in

[0119] Similarly, the phase voltage U of the fault-phase C at the location of the protection installation on the M side of the bus can be obtainedMC :

[0120]

[0121] In the formula, is the electromotive force of the C - equivalent power supply. As shown in Equation (19), when a two - phase grounding fault occurs through a transition resistance, the fault - phase voltage at the fault point and the zero - sequence current at the fault point are approximately in the same phase. Therefore, the phase of the voltage between the fault point and the ground can be approximated as the phase of the zero - sequence current of the fault at the protection installation location

[0122]

[0123] The impedance variable - speed factor Z is obtained according to the equivalent phase angle of the voltage phase angle between the fault point and the ground Acc ;

[0124] Based on the inverse - time characteristic curve, the protection operation equation is obtained according to the impedance variable - speed factor;

[0125] The single - and double - circuit coordinated lines are protected according to the protection operation equation.

[0126] In some of these embodiments, the steps of obtaining the impedance variable - speed factor according to the equivalent phase angle of the voltage phase angle between the fault point and the ground are as follows:

[0127] Taking the typical structure of the fault line in Figure 5 as an example, when a grounding fault occurs at line f, the fault - phase voltage measured at the protection installation location of Protection 1 and the fault - phase voltage at the fault point have the following relationship:

[0128]

[0129] Where: is the fault - phase voltage at the fault point; is the fault - phase voltage measured at the protection installation location, is the fault - phase current measured at the protection installation location, is the zero - sequence current measured at the protection installation location, φ is the phase of the voltage, φ = A, B, C phases; Z L is the line impedance from the fault point to the protection; is the zero - sequence current compensation coefficient, z 1 is the positive - sequence impedance per unit length of the transmission line, z 0 is the zero - sequence impedance per unit length of the transmission line; is the line voltage drop,

[0130] Obtain the length of the protected line where the fault point is located, the first zero-sequence impedance and the first positive-sequence impedance, where the first zero-sequence impedance is the zero-sequence impedance per unit length of the protected line where the fault point is located, and the first positive-sequence impedance is the positive-sequence impedance per unit length of the protected line where the fault point is located;

[0131] Obtaining a zero-sequence current compensation coefficient according to a first zero-sequence impedance and a first positive-sequence impedance;

[0132] When a fault occurs, the first zero-sequence current, the first fault phase voltage and the first fault phase current are obtained respectively. The first zero-sequence current is the zero-sequence current measured at the protection installation, the first fault phase voltage is the fault phase voltage measured at the protection installation, and the first fault phase current is the fault phase current measured at the protection installation; the line impedance Z from the protection installation to the fault point is obtained according to the first zero-sequence current, the zero-sequence current compensation coefficient, the equivalent phase angle of the voltage phase angle of the fault point to the ground, the first fault phase voltage and the first fault phase current L ;

[0133] Depend on Figure 7 , Figure 10 The analysis found that the fault phase voltage at the fault point in the case of single-phase grounding through transition resistance and two-phase grounding through transition resistance is Fault phase voltage measured at the protection installation With line voltage drop The vector triangles formed have the following similar characteristics:

[0134] right Three vectors form a vector triangle. Apply the triangle sine theorem and we get:

[0135]

[0136] In the formula, α 2 is the second intermediate expression, β is the third intermediate expression, is the positive sequence impedance phase angle per unit length of the transmission line, Will Substituting into formula (25) we can get:

[0137]

[0138] The impedance speed change factor is obtained according to the line impedance, the length of the protected line and the first positive sequence impedance. The impedance speed change factor is:

[0139]

[0140] In the formula, Z set The setting impedance of the protection, the size of the setting impedance determines the fault range in the area; 1 is the positive sequence impedance per unit length of the line; l is the length of the protected line.

[0141] When a ground fault occurs in the protection zone, i.e., when an internal fault occurs, |Z set |>|Z L |, impedance speed factor Z Acc Less than 1, optimizes the quickness of protection and has an accelerating effect; when a ground fault occurs outside the protection zone, i.e., when an out-of-zone fault occurs, |Z set |<|Z L |, impedance speed factor Z Acc Greater than 1, ensuring the coordination between the upper and lower protection levels. The farther from the fault point, the greater the line impedance Z L The larger the impedance speed factor Z is, the Acc The greater the deviation from 1, the greater the action time difference between the upper and lower protection levels can be expanded through the difference in impedance speed change factors, thereby improving the selectivity of the protection action.

[0142] In some of these embodiments, the protection action equation includes a pre-action protection action equation and a secondary acceleration protection action equation;

[0143] The single-circuit and double-circuit coordinated line zero-sequence inverse time protection method based on impedance speed change factor also includes the following steps:

[0144] Construct the impedance speed change factor mutation criterion;

[0145] After a failure:

[0146] The timing is based on the time when the fault occurs, and the protection installation location takes protective action according to the preemptive protection action equation;

[0147] When the mutation amount of the impedance speed change factor at the protection installation meets the impedance speed change factor mutation criterion, the re-timing time point is used as the timing, and the protection installation takes protection action according to the secondary acceleration protection action equation. The re-timing time point is the time point when the mutation amount of the impedance speed change factor meets the impedance speed change factor mutation criterion.

[0148] In some embodiments, after the protection on one side is actuated, the current phase angle measured by the protection will suddenly change within a few cycles, thereby changing the value of the impedance speed change factor. Based on this, a criterion for detecting the sudden change of the impedance speed change factor is introduced into the action logic of the original inverse time overcurrent protection, and the criterion for the sudden change of the impedance speed change factor is:

[0149]

[0150] In the formula, Z floor is the lower limit of the impedance speed change factor mutation, Z ceiling is the upper limit of the impedance speed change factor mutation, To protect the impedance speed factor at the installation location at time t+dt, It is the impedance speed change factor at the protection installation at time t.

[0151] When the protection on one side is activated, the impedance speed factor mutation of the remaining unactivated protections is smaller than the impedance speed factor mutation generated at the moment of fault occurrence. Setting a suitable upper limit value can avoid the impact of the fault on the impedance speed factor mutation criterion at the moment of fault occurrence.

[0152] The zero-sequence inverse time overcurrent protection action logic after introducing the impedance speed change factor mutation criterion and the secondary acceleration protection action equation is as follows: Figure 12 As shown in the figure, considering that the phase angle values ​​measured in the first few cycles are inaccurate due to the influence of the attenuated DC component at the beginning of the fault, in order to prevent the impedance speed change factor mutation criterion from malfunctioning, a binary delay element is added before re-timing. Only when 3I are always satisfied at the same time within the Δt time 0 >I P The high level can only be output when the following three conditions are met: positive direction, positive direction and impedance speed change factor mutation criterion.

[0153] In some embodiments, the proactive protection action equation is:

[0154]

[0155] Where, T 0 (3I 0 ) is the zero-sequence inverse time protection delay measured at the time of fault occurrence, I 0 The zero-sequence current measured at the protection installation, I P is the zero-sequence inverse time current setting, T P is the zero-sequence inverse time setting, Z Acc is the impedance speed factor.

[0156] The protection action time curve is as follows: Figure 11 As shown, at different impedance speed factors Z Acc Under the action of the protection, the protection action time presents different change rates, so that the speed and selectivity of the protection are optimized.

[0157] In some embodiments, the quadratic acceleration protection action equation is:

[0158]

[0159] Where, T 0 (3I 0 ) is the zero-sequence inverse time protection delay timed at the re-timing time point, I 0 The zero-sequence current measured at the protection installation, I P is the zero-sequence inverse time current setting, T P is the zero-sequence inverse time constant, k is the secondary acceleration coefficient, Z Acc is the impedance speed factor.

[0160] After a fault occurs, the preemptive protection, i.e. the protection action that occurs according to the preemptive protection action equation, will follow the normal inverse time overcurrent protection logic action. After the preemptive protection is activated, the zero-sequence current is redistributed and enters T by retiming. 0 ′(3I 0 ) link calculates the action time and skips the minimum time of zero-sequence inverse time limit to directly make the protection action. The inverse time limit calculation formula entered by re-timing is the secondary acceleration protection action equation;

[0161] The signal sent after retiming is connected with the signal sent by the original protection action logic through "OR" so that the protection effect can be optimized in different fault scenarios. When metallic grounding occurs or the grounding transition resistance is small, the action time difference of each protection is small. After the protection on one side is actuated, although the protection on the other side starts retiming, the time required is longer than the original action time, and the protection action signal is sent through the original action logic channel. When the transition resistance is large, the time difference of the protection actions is large. The latter action, that is, the protection action that occurs according to the secondary acceleration protection action equation, starts retiming for secondary acceleration, and sends an action signal after the timing ends. The time required is less than the time of the original logic channel.

[0162] Calculation example

[0163] According to the ordinary zero-sequence inverse time overcurrent protection method in the IEC standard, the protection setting is considered to avoid the reclosing delay, three-phase inconsistency protection and the action time of the distance protection. h +T x ≥3s, the setting parameters of zero-sequence inverse time overcurrent protection in this article are detailed in Table 1.

[0164] Table 1 Setting of zero-sequence inverse time overcurrent protection

[0165] <![CDATA[Current setting value I P > <![CDATA[Time setting value T P > <![CDATA[Cooperating time T h > <![CDATA[Minimum time T x > 300A 0.4s 0.1s 2.9s

[0166] According to the setting of the impedance variable speed inverse time overcurrent protection method mentioned above, the impedance setting value of the protection is set to the impedance value of the protected line, which can protect the entire length of the line; the secondary acceleration coefficient; the lower limit and upper limit of the impedance variable speed factor mutation are z S1 =0.174+j0.985Ω、z S1 =0.174+j0.985Ω.

[0167] In PSCAD / EMTDC software, Figure 3 The short-circuit single and double-circuit coordination scenarios shown in the figure are analyzed. The system voltage on the M side is 220∠40°kV, the system voltage on the N side is 220∠0°kV, and the positive and zero sequence impedances of the equivalent power sources on the M and N sides are: S1 =0.174+j0.985Ω、z S0=0.766+j0.643Ω, transmission lines MP and QN are single-circuit lines of the same model with a length of 10 km, PQ is a double-circuit line with a length of 10 km on the same tower, the line model is the same as the single-circuit line, the positive sequence impedance and zero sequence impedance of the line are: 1 =0.0178+j0.314Ω / km, z 0 =0.0534+j0.942Ω / km, the mutual inductance between PQ towers is

[0168] z m =0.0267+j0.471Ω / km, all are equipped with zero-sequence inverse time overcurrent protection, the fault time is 1s, and the simulation time is 20s.

[0169] Various types of short-circuit faults are set on the I loop of the double-loop line PQ on the same tower at a distance of 2 km from the P busbar. The protections on the faulty line and the non-faulty single-loop lines on both sides are selected for analysis. The zero-sequence currents at protections 1, 4, 5, and 6, the fault voltage phase angle at the grounding point, and the protection action times of the traditional inverse time, the introduction of impedance speed change factor, and the re-timing are shown in Table 2.

[0170] Table 2 Measurement values ​​and action time of protection on the faulty line and the non-faulty single-circuit lines on both sides in the short-circuit single-circuit and double-circuit coordination scenario

[0171]

[0172] It can be seen from Table 2 that when the traditional inverse time overcurrent protection scheme is adopted, the action of the protection is related to the magnitude of the zero-sequence current. Due to the inherent network structure characteristics of the single-circuit and double-circuit coordination scenarios, the zero-sequence current of protection 1 on the non-fault single-circuit line on one side is greater than the zero-sequence current of protection 3 on the fault line, which will cause protection 1 to malfunction.

[0173] After the introduction of the speed change factor, whether in a metallic grounding fault or a high-resistance grounding fault, the fault voltage phase angle at the grounding point is approximately equal to the equivalent sequence current phase angle at the protection installation location, which verifies the feasibility of replacing the fault phase voltage phase with the negative sequence current phase and zero sequence current phase measured by the protection in the case of single-phase and two-phase grounding faults proposed in the previous article. The impedance speed change factor calculated by the improved measurement impedance can accurately reflect the distance between the fault point and the protection. Taking the grounding fault of phase A through a 90Ω resistor as an example, the speed change factors of protection 2 and protection 3, which are judged as in-zone faults, are less than 1, which reduces the action time. The speed change factors of protection 1 and protection 6, which are judged as out-of-zone faults, are greater than 1, which prolongs the action time. Although the impedance speed change factor plays a positive role in the protection selectivity, it still cannot offset the adverse effect of the zero sequence current flowing through protection 6 being greater than the zero sequence current flowing through protection 3 on the integration time, and protection 6 will still malfunction. After applying the secondary acceleration, the remaining protections are re-timed using the zero-sequence current distribution after the disconnection of protection 2. Obviously, the zero-sequence current flowing through protection 6 will be less than the zero-sequence current flowing through protection 3, so that protection 3 is activated before protection 6, which satisfies the selectivity of protection action. At the same time, the secondary acceleration coefficient less than 1 is used to shorten the action time of the protection and improve the speed of protection. Even in extreme fault situations such as BC two-phase grounding through a 90Ω transition resistor, where the three times zero-sequence current of some protections is less than the current setting and the inverse time overcurrent protection cannot be activated, the remaining unactivated protections can also be re-timed using the secondary acceleration after protection 2 is activated, and the action time is calculated with the help of the redistributed zero-sequence current, and the minimum time T is skipped. x , which can significantly reduce the protection action time while meeting the selectivity.

[0174] In order to verify the influence of fault location on impedance speed change factor and secondary acceleration performance, faults with grounding through 100Ω transition resistance are set at different positions on the I loop of the double-loop line PQ on the same tower. Let α be the ratio of the length of the fault location from the P busbar to the length of the line PQ. The measurement information and action time of the protection on the faulty line and the non-faulty single-loop lines on both sides are shown in Table 3.

[0175] It can be seen from Table 3 that in the short-line single-circuit and double-circuit coordination scenarios, the fault location has little effect on the impedance speed change factor and the secondary acceleration function. Even in the scenario of 100Ω high-resistance grounding, the impedance speed change factor calculated by the phase angle equivalent of the positive direction protection is almost unaffected by the fault location, and can accurately indicate the percentage of the distance between the fault location and the protection to the length of the protected line, thereby accelerating the protection within the area and decelerating it outside the area. After the introduction of secondary acceleration, the protection that meets the impedance speed change factor mutation condition enters re-timing, and the fault can be cleared in a shorter time.

[0176] Table 3 Measured values ​​and action time of protection on faulty line and non-faulty single-circuit lines on both sides when I-circuit is grounded at different positions through 100Ω resistor in double-circuit line PQ on the same tower

[0177]

[0178] Taking the case of a 100Ω grounding fault of phase A at position α=0.9 as an example, the zero-sequence current at protection 1 is greater than the zero-sequence current at protection 2. If the inverse time scheme with the same characteristics is used, protection 1 will malfunction. Although the introduction of the impedance speed change factor has an acceleration effect on protection 2, the acceleration effect of the impedance speed change factor is relatively weak because the fault is far away from protection 2, and protection 1 will still act earlier than protection 2. On this basis, the secondary acceleration re-timing is introduced. After the action of protection 3, the remaining protections use the redistributed zero-sequence current for secondary acceleration, which can make the action time of protection 2 shorter than that of protection 1, meet the selectivity of protection, and improve the speed of protection. In particular, when a 100Ω grounding fault of phase A occurs at position α=0.6, since protection 2 has entered the zero-sequence inverse time minimum time T when the impedance speed change factor mutation criterion is met. x link, so the protection action signal is sent out through the original action logic channel, and the secondary acceleration effect is not achieved. However, the acceleration effect of the impedance speed change factor can still improve the speed of protection.

[0179] This example aims at the problem of non-fault line protection misoperation in the single-circuit and double-circuit coordination scenarios of 220kV short lines using the same characteristic inverse time zero-sequence current curve. In the case of single-phase grounding and two-phase grounding, the negative-sequence current phase and zero-sequence current phase measured by the protection are used to replace the phase voltage phase at the fault point. The impedance value from the protection to the fault point is calculated according to the voltage drop from the protection point to the fault point. The ratio of the corrected measured impedance to the impedance of the protection line constitutes the impedance speed factor. Based on this, a new zero-sequence inverse time current protection scheme that introduces the impedance speed factor mutation criterion is proposed. After the impedance speed factor mutation, the zero-sequence inverse time current protection of the line is re-timed. This method only uses local protection information to achieve the optimization of speed while ensuring the selectivity of the protection. In principle, it eliminates the influence of transition resistance on the protection action performance in the single-circuit and double-circuit coordination scenarios of short lines. Through theoretical analysis and simulation verification based on PSCAD, this scheme has the following characteristics:

[0180] (1) Re-timing by using the impedance speed change factor mutation criterion can effectively prevent the malfunction of the zero-sequence inverse time current protection of the non-fault line. This criterion is still applicable when the line is transitionally grounded.

[0181] (2) In the re-timing stage, a secondary acceleration coefficient less than 1 can be used to reduce the protection action time;

[0182] (3) The scheme only utilizes the local information of the protection without the need for communication and has excellent resistance to transition resistance. It can maintain the ability to respond quickly to faults even under high-resistance ground fault conditions.

[0183] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor, characterized in that: The method comprises the following steps: when a fault occurs, obtaining the fault type; Based on the fault type, obtaining a sequence current phase at the protection installation, and obtaining an equivalent phase angle of the fault point-to-ground voltage phase angle according to the sequence current phase; Obtaining an impedance speed change factor according to an equivalent phase angle of the voltage phase angle of the fault point to the ground; Based on the inverse time characteristic curve, a protection action equation is obtained according to the impedance speed change factor; The single-circuit and double-circuit coordinated lines are protected according to the protection action equation.

2. The method for zero-sequence inverse time protection of single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 1 is characterized in that: The sequence current phase at the protection installation at least includes a negative sequence current phase at the protection installation and a zero sequence current phase at the protection installation.

3. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 2 is characterized in that: The fault types include single-phase grounding fault and two-phase grounding fault.

4. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 3 is characterized in that: When the fault type is the single-phase grounding fault: obtaining an equivalent phase angle of the voltage phase angle of the fault point to the ground according to the negative sequence current phase at the protection installation; When the fault type is the two-phase grounding fault: the equivalent phase angle of the voltage phase angle at the fault point to the ground is obtained according to the zero-sequence current phase at the protection installation.

5. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 1 is characterized in that: The steps of obtaining the impedance speed change factor according to the equivalent phase angle of the voltage phase angle of the fault point to the ground are: Obtaining the length of the protected line where the fault point is located, a first zero-sequence impedance, and a first positive-sequence impedance, wherein the first zero-sequence impedance is the zero-sequence impedance per unit length of the protected line where the fault point is located, and the first positive-sequence impedance is the positive-sequence impedance per unit length of the protected line where the fault point is located; Obtaining a zero-sequence current compensation coefficient according to the first zero-sequence impedance and the first positive-sequence impedance; When a fault occurs, a first zero-sequence current, a first fault phase voltage and a first fault phase current are obtained respectively, wherein the first zero-sequence current is the zero-sequence current measured at the protection installation, the first fault phase voltage is the fault phase voltage measured at the protection installation, and the first fault phase current is the fault phase current measured at the protection installation; Obtaining the line impedance from the protection installation location to the fault point according to the first zero-sequence current, the zero-sequence current compensation coefficient, the equivalent phase angle of the voltage phase angle of the fault point to the ground, the first fault phase voltage and the first fault phase current; The impedance speed change factor is obtained according to the line impedance, the length of the protected line and the first positive sequence impedance.

6. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 1 is characterized in that: The protection action equation includes a pre-action protection action equation and a secondary acceleration protection action equation.

7. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated lines based on impedance speed change factor according to claim 6 is characterized in that: The single-circuit and double-circuit coordinated line zero-sequence inverse time protection method based on impedance speed change factor also includes the following steps: Construct the impedance speed change factor mutation criterion; After a failure: At the time when the fault occurs, the protection installation location performs a protection action according to the proactive protection action equation; When the mutation amount of the impedance speed change factor at the protection installation meets the impedance speed change factor mutation criterion, the retiming time point is used as the timing, and the protection installation takes a protection action according to the secondary acceleration protection action equation. The retiming time point is the time point when the mutation amount of the impedance speed change factor meets the impedance speed change factor mutation criterion.

8. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated transmission lines based on impedance speed change factor according to claim 7 is characterized in that: The impedance speed change factor mutation criterion is: In the formula, Z floor is the lower limit of the impedance speed change factor mutation, Z ceiling is the upper limit of the impedance speed change factor mutation, To protect the impedance speed factor at the installation location at time t+dt, It is the impedance speed change factor at the protection installation at time t.

9. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated transmission lines based on impedance speed change factor according to claim 6 is characterized in that: The preemptive protection action equation is: Where T0(3I0) is the zero-sequence inverse time protection delay measured at the time of fault occurrence, I0 is the zero-sequence current measured at the protection installation, and I P is the zero-sequence inverse time current setting, T P is the zero-sequence inverse time setting, Z Acc is the impedance speed factor.

10. The zero-sequence inverse time protection method for single-circuit and double-circuit coordinated transmission lines based on impedance speed change factor according to claim 6 is characterized in that: The secondary acceleration protection action equation: Where T0(3I0) is the zero-sequence inverse time protection delay measured at the re-timing time point, I0 is the zero-sequence current measured at the protection installation location, and I P is the zero-sequence inverse time current setting, T P is the zero-sequence inverse time constant, k is the secondary acceleration coefficient, Z Acc is the impedance speed factor.

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