Positive sequence equivalent impedance pilot protection method suitable for new energy transmission line

Abstract

The invention provides a positive-sequence equivalent impedance pilot protection method suitable for a new energy transmission line, and the method comprises the steps: when protection is started, carrying out the pilot protection of the positive-sequence equivalent impedance on the basis of the new energy transmission line; line impedance, first equivalent impedance, namely positive-sequence equivalent impedance measured at the new energy side protection installation position, and second equivalent impedance, namely positive-sequence equivalent impedance measured at the flexible direct-current power transmission side protection installation position are obtained respectively; adding the first equivalent impedance and the second equivalent impedance to obtain sum impedance; obtaining a sum impedance amplitude and a sum impedance angle according to the sum impedance; respectively obtaining a line impedance amplitude and a line impedance angle according to the line impedance; judging the fault type according to the sum impedance amplitude, the line impedance amplitude, the sum impedance angle and the line impedance angle; and determining whether protection acts according to the fault type. According to the method, the problem of insufficient sensitivity of current differential protection in a new energy transmission line is solved, and the protection reliability is improved by constructing a protection criterion based on the impedance amplitude and the impedance angle.

Description

Technical Field

[0001] The present invention relates to the technical field of AC line fault identification in a flexible DC system with new energy access, and particularly relates to a positive sequence equivalent impedance pilot protection method applicable to new energy transmission lines. Background Art

[0002] Since the 21st century, problems such as global warming and energy shortage have become increasingly prominent. To address issues such as global climate change and energy security, new energy power sources represented by wind power and photovoltaic power in China have developed rapidly. The flexible DC transmission technology does not have the problem of commutation failure and can independently control active and reactive power. Connecting new energy to the grid through flexible DC can improve the operating conditions of the power grid.

[0003] When a fault occurs in the AC side line of a flexible DC system with new energy access, both ends of the line are power electronic converters, and their fault characteristics are quite different from those of synchronous generators. The short-circuit current amplitudes on both sides are limited and the phase angles are controlled. The above characteristics may challenge the adaptability of protection principles designed based on synchronous machine characteristics, and there are risks of refusal to operate and misoperation in traditional protection principles such as current differential protection, distance protection, and direction elements, seriously affecting the accurate identification and rapid isolation of faults.

[0004] Existing research mainly proposes new protection schemes from two aspects. On the one hand, by fully exploring the fault transient quantity information, a new protection principle based on traveling waves and time-domain information is constructed; on the other hand, considering the fault characteristics of a flexible DC system with new energy access, the traditional power frequency quantity protection scheme is improved.

[0005] Prior art: Chinese Patent Application No. CN201110175930.7 discloses a fault location method based on single - end ranging. When a short - circuit fault occurs on a transmission line, the power - frequency voltage and current of the busbar at the local end of the line are obtained by using a traveling - wave fault ranging device for the transmission line, the impedance is calculated to determine the fault point area, and the transition resistance is estimated; then, by analyzing the transient voltage / current traveling waves through wavelet transform, if it is determined as a common short - circuit fault, the single - end traveling - wave method combined with the line length is used to directly calculate the fault point location; if it is determined as a special short - circuit fault, the single - end fault ranging method for transmission lines combining the impedance method and the traveling - wave method is used to calculate the fault point location. Chinese Patent Application No. CN202410568747.0 discloses a pilot protection method based on time - domain model identification applicable to a wind - power - integrated system. After a fault occurs, the three - phase voltage and current at the protection installation location of the transmission line are collected and phase - mode transformation is performed; if the mutation of the 1 - mode voltage and current satisfies the protection startup criterion, first, the three - phase differential voltage and differential current of the line are calculated and zero - sequence compensation is performed, and then the three - phase correlation coefficients are calculated by using the first - order derivative of the three - phase voltage and the differential current. If the correlation coefficient is greater than the protection setting value, it is considered that an in - zone fault has occurred. Chinese Patent Application No. CN201410030636.0 discloses a pilot protection based on fault - component virtual - impedance differential and its method. After a fault occurs, the virtual sequence impedance of the line is calculated by using the collected line characteristic sequence impedance, line sequence propagation coefficient, voltage and current fault sequence components on both sides of the line, and then a ratio - restraint criterion is constructed by using the sum of the virtual impedances at the mid - point of the line and the smaller value of the virtual impedances; finally, the fault is identified by analyzing the different characteristics presented by this criterion under various in - zone and out - of - zone faults. Chinese Patent Application No. CN202310800031.4 discloses a protection method for improving the sensitivity of differential protection considering new - energy access. This protection method needs to record the fault current and voltage data of 40 ms before and after the fault at the protection installation locations on both sides of the transmission line with new - energy access; after the protection starts, first, the fault occurrence range is preliminarily judged according to the phase difference and amplitude ratio of the currents on both sides of the line; if it is judged as a non - out - of - zone fault, the transmission - line impedance and new - energy equivalent - system impedance are further calculated by using the voltage and current data before and after the fault, the current deviation angle on the new - energy side is calculated according to the line impedance and new - energy equivalent - system impedance, the phase of the fault current on the new - energy side is adjusted in real - time, and finally, the in - zone and out - of - zone faults are judged based on the ratio - restraint equation of pilot differential protection.

[0006] However, in the above-mentioned prior art, the technical solutions based on traveling waves have high requirements for equipment. If the sampling rate of the measuring equipment is insufficient, it is difficult for the sampling points to accurately capture the transient information at the moment of fault occurrence; most of the technical solutions based on time-domain information use similarity algorithms to extract the differential characteristics of electrical quantities during internal and external faults, and it is difficult to distinguish the fault area in the case of high-resistance faults; the technical solutions based on power-frequency quantity information make full use of the amplitude and phase characteristics of voltage and current under different control strategies to construct protection criteria, but they may face the risk of failure after the control strategy changes. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a positive-sequence equivalent impedance pilot protection method applicable to new energy transmission lines, which solves the problem of insufficient sensitivity of current differential protection in new energy transmission lines, and improves the protection reliability by constructing protection criteria based on impedance amplitude and impedance angle.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows: A positive-sequence equivalent impedance pilot protection method applicable to new energy transmission lines, comprising the following steps: When the protection is started, based on the new energy transmission line, the line impedance, the first equivalent impedance and the second equivalent impedance are respectively obtained, where the first equivalent impedance is the positive-sequence equivalent impedance measured at the protection installation location on the new energy side, and the second equivalent impedance is the positive-sequence equivalent impedance measured at the protection installation location on the flexible DC transmission side;

[0009] The sum impedance is obtained by adding the first equivalent impedance and the second equivalent impedance; the sum impedance amplitude and the sum impedance angle are respectively obtained according to the sum impedance; the line impedance amplitude and the line impedance angle are respectively obtained according to the line impedance;

[0010] The fault type is discriminated according to the sum impedance amplitude, the line impedance amplitude, the sum impedance angle and the line impedance angle; it is judged whether the protection operates according to the fault type.

[0011] In some embodiments, the steps of obtaining the first equivalent impedance and the second equivalent impedance are as follows:

[0012] The first voltage mutation, the first current mutation, the second voltage mutation and the second current mutation are obtained, where the first voltage mutation is the positive-sequence voltage mutation before and after the fault measured at the protection installation location on the new energy side, the first current mutation is the positive-sequence current mutation before and after the fault measured at the protection installation location on the new energy side, the second voltage mutation is the positive-sequence voltage mutation before and after the fault measured at the protection installation location on the flexible DC transmission side, and the second current mutation is the positive-sequence current mutation before and after the fault measured at the protection installation location on the flexible DC transmission side;

[0013] Obtain the first equivalent impedance according to the ratio of the first voltage mutation amount to the first current mutation amount;

[0014] Obtain the second equivalent impedance according to the ratio of the second voltage mutation amount to the second current mutation amount.

[0015] In some embodiments, when the distributed capacitance of the transmission line is not considered:

[0016] The first voltage mutation amount is the first difference, and the first difference is the value obtained by subtracting the second positive-sequence voltage from the first positive-sequence voltage; the first positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side after the fault, and the second positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side before the fault;

[0017] The first current mutation amount is the second difference, and the second difference is the value obtained by subtracting the second positive-sequence current from the first positive-sequence current; the first positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side after the fault, and the second positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side before the fault;

[0018] The second voltage mutation amount is the third difference, and the third difference is the value obtained by subtracting the fourth positive-sequence voltage from the third positive-sequence voltage; the third positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side after the fault, and the fourth positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side before the fault;

[0019] The second current mutation amount is the fourth difference, and the fourth difference is the value obtained by subtracting the fourth positive-sequence current from the third positive-sequence current; the third positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side after the fault, and the fourth positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side before the fault.

[0020] In some embodiments, when the distributed capacitance of the transmission line is considered:

[0021] The first voltage mutation amount is the first difference, and the first difference is the value obtained by subtracting the second positive-sequence voltage from the first positive-sequence voltage; the first positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side after the fault, and the second positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side before the fault;

[0022] The first current mutation quantity is the fifth difference, the fifth difference is the value obtained by subtracting the sixth difference from the second difference, the second difference is the value obtained by subtracting the second positive-sequence current from the first positive-sequence current, and the sixth difference is the value obtained by subtracting the sixth positive-sequence current from the fifth positive-sequence current; the first positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side after the fault, the second positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side before the fault, the fifth positive-sequence current is the positive-sequence current flowing through the distributed capacitance branch on the new energy side after the fault, and the sixth positive-sequence current is the positive-sequence current flowing through the distributed capacitance branch on the new energy side before the fault;

[0023] The second voltage mutation quantity is the value obtained by subtracting the fourth positive-sequence voltage from the third positive-sequence voltage; the third positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side after the fault, and the fourth positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side before the fault;

[0024] The second current mutation quantity is the seventh difference, the seventh difference is the value obtained by subtracting the eighth difference from the fourth difference, the fourth difference is the value obtained by subtracting the fourth positive-sequence current from the third positive-sequence current, and the eighth difference is the value obtained by subtracting the eighth positive-sequence current from the seventh positive-sequence current; the third positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side after the fault, the fourth positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side before the fault, the seventh positive-sequence current is the positive-sequence current flowing through the distributed capacitance branch on the flexible DC transmission side after the fault, and the eighth positive-sequence current is the positive-sequence current flowing through the distributed capacitance branch on the flexible DC transmission side before the fault.

[0025] In some embodiments, the steps of discriminating the fault type according to the sum impedance amplitude, the line impedance amplitude, the sum impedance angle, and the line impedance angle are as follows:

[0026] Obtain a first protection criterion and a second protection criterion;

[0027] Judge whether the first protection criterion holds according to the sum impedance amplitude and the line impedance amplitude;

[0028] Judge whether the second protection criterion holds according to the sum impedance angle and the line impedance angle;

[0029] When only the first protection criterion holds, or only the second protection criterion holds, or both the first protection criterion and the second protection criterion hold, the fault type is an in-zone fault;

[0030] When both the first protection criterion and the second protection criterion do not hold, the fault type is an out-of-zone fault. In some embodiments, the first protection criterion is:

[0031] |abs(Zeq.W +Z eq.M ) - abs(Z L )| > K set1 ;

[0032] Wherein, abs represents the amplitude value, and Z eq.W is the first equivalent impedance, and Z eq.M is the second equivalent impedance, and Z L is the line impedance, and K set1 is the amplitude setting value.

[0033] In some embodiments, the amplitude setting value is 2.

[0034] In some embodiments, the second protection criterion is:

[0035] |arg(Z eq.W + Z eq.M ) - arg(Z L )| > K set2 ;

[0036] Wherein, arg represents the phase angle, and Z eq.W is the first equivalent impedance, and Z eq.M is the second equivalent impedance, and Z L is the line impedance, and K set2 is the impedance angle setting value.

[0037] In some embodiments, the impedance angle setting value is 1.

[0038] In some embodiments, when the fault type is a fault within the zone, the protection operates; when the fault type is a fault outside the zone, the protection does not operate.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present disclosure provides a positive sequence equivalent impedance pilot protection method applicable to new energy transmission lines, which solves the problem of insufficient sensitivity of current differential protection in new energy transmission lines, and improves the reliability of protection by constructing protection criteria based on impedance amplitude and impedance angle. This scheme also considers the influence of distributed capacitance on the proposed protection method and improves the calculation accuracy of positive sequence equivalent impedance. It is analyzed that the protection method can operate correctly under various fault conditions, and has high sensitivity and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic flow chart of the positive sequence equivalent impedance pilot protection method applicable to new energy transmission lines of the present disclosure;

[0042] Figure 2 is a topological structure diagram of a new energy transmission system via a flexible DC;

[0043] Figure 3 It is the equivalent circuit diagram when the new energy is transmitted through the flexible DC transmission system under normal operation;

[0044] Figure 4 It is the positive sequence component network diagram when a short - circuit fault occurs at point f1 outside the new energy side area of the new energy transmission line;

[0045] Figure 5 It is the positive sequence component network diagram when a short - circuit fault occurs at point f2 outside the flexible DC output side area of the new energy transmission line;

[0046] Figure 6 It is the positive sequence component network diagram when a short - circuit fault occurs at point f3 within the line area;

[0047] Figure 7 It is the protection action logic diagram based on the first protection criterion and the second protection criterion;

[0048] Figure 8 It is the comparison diagram of the sum impedance and the line impedance parameters when a single - phase grounding fault occurs at point f1 outside the new energy side area;

[0049] Figure 9 It is the comparison diagram of the sum impedance and the line impedance parameters when a two - phase inter - phase fault occurs at point f1 outside the new energy side area;

[0050] Figure 10 It is the comparison diagram of the sum impedance and the line impedance parameters when a two - phase grounding fault occurs at point f1 outside the new energy side area;

[0051] Figure 11 It is the comparison diagram of the sum impedance and the line impedance parameters when a three - phase fault occurs at point f1 outside the new energy side area;

[0052] Figure 12 It is the comparison diagram of the sum impedance and the line impedance parameters when a single - phase grounding fault occurs at point f2 outside the flexible DC output side area;

[0053] Figure 13 It is the comparison diagram of the sum impedance and the line impedance parameters when a two - phase inter - phase fault occurs at point f2 outside the flexible DC output side area;

[0054] Figure 14 It is the comparison diagram of the sum impedance and the line impedance parameters when a two - phase grounding fault occurs at point f2 outside the flexible DC output side area;

[0055] Figure 15 It is the comparison diagram of the sum impedance and the line impedance parameters when a three - phase fault occurs at point f2 outside the flexible DC output side area;

[0056] Figure 16 It is the comparison diagram of the sum impedance and the line impedance parameters when a single - phase grounding fault occurs at point f3 within the line area;

[0057] Figure 17 It is a comparison diagram of the sum impedance and the line impedance parameters when a two-phase phase-to-phase fault occurs at point f3 within the line area;

[0058] Figure 18 It is a comparison diagram of the sum impedance and the line impedance parameters when a two-phase grounding fault occurs at point f3 within the line area;

[0059] Figure 19 It is a comparison diagram of the sum impedance and the line impedance parameters when a three-phase fault occurs at point f3 within the line area. Specific implementation manner

[0060] Aiming at the problems in the background technology, the protection performance can be improved by fully exploiting the post-fault electrical quantity information and improving the traditional power frequency quantity protection. As a kind of power frequency quantity protection, pilot protection has advantages such as good selectivity and fast action, and is usually applied to the main protection of transmission lines and transformers. By introducing the positive sequence equivalent impedance information to improve the traditional pilot protection method, it can be effectively applied to the new energy power system.

[0061] To clearly illustrate the technical features of this solution, the following will combine the drawings and embodiments to detail the implementation manner of this application, 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. The embodiments of this application and each feature in 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.

[0062] See Figure 1 , this disclosure provides a positive sequence equivalent impedance pilot protection method applicable to new energy outgoing lines, including the following steps: collecting voltage and current data, judging whether the protection starts according to the voltage and current data. When the protection does not start, repeat collecting the voltage and current data. When the protection starts, judge whether the protection acts through the following steps;

[0063] Based on the new energy outgoing line, respectively obtain the line impedance Z L , the first equivalent impedance Z eq.W and the second equivalent impedance Z eq.M , the first equivalent impedance Z eq.W is the positive sequence equivalent impedance measured at the protection installation location on the new energy side, and the second equivalent impedance Z eq.M is the positive sequence equivalent impedance measured at the protection installation location on the flexible DC transmission side;

[0064] According to the first equivalent impedance Z eq.W and the second equivalent impedance Z eq.M add them to obtain the sum impedance (Z eq.W +Z eq.M) Obtain the sum impedance magnitude abs(Z eq.W +Z eq.M ) and the sum impedance angle arg(Z eq.W +Z eq.M ) respectively according to the sum impedance (Z eq.W +Z eq.M );Obtain the line impedance magnitude abs(Z L ) and the line impedance angle arg(Z L ) respectively according to the line impedance Z L );

[0065] Discriminate the fault type according to the sum impedance magnitude abs(Z eq.W +Z eq.M ), the line impedance magnitude abs(Z L ), the sum impedance angle arg(Z eq.W +Z eq.M ) and the line impedance angle arg(Z L );Judge whether the protection operates according to the fault type, and realize the protection of the new energy transmission line. In some embodiments, when the fault type is an internal fault, the protection operates; when the fault type is an external fault, the protection does not operate.

[0066] In some embodiments, the steps to obtain the first equivalent impedance Z eq.W and the second equivalent impedance Z eq.M are as follows:

[0067] Obtain the first voltage mutation the first current mutation the second voltage mutation and the second current mutation The first voltage mutation is the positive sequence voltage mutation before and after the fault measured at the protection installation location on the new energy side, and the first current mutation is the positive sequence current mutation before and after the fault measured at the protection installation location on the new energy side. The second voltage mutation is the positive sequence voltage mutation before and after the fault measured at the protection installation location on the flexible DC transmission side, and the second current mutation is the positive sequence current mutation before and after the fault measured at the protection installation location on the flexible DC transmission side;

[0068] Obtain the first equivalent impedance according to the ratio of the first voltage mutation to the first current mutation;

[0069]

[0070] Obtain the second equivalent impedance according to the ratio of the second voltage mutation to the second current mutation:

[0071]

[0072] Wherein, is the positive-sequence equivalent impedance on the new energy side, is the positive-sequence equivalent impedance on the VSC-HVDC side.

[0073] In some embodiments, when the capacitive reactance of the transmission line distributed capacitance is not considered:

[0074] The first voltage mutation is the first difference The first difference is the first positive-sequence voltage minus the second positive-sequence voltage The value; the first positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side after the fault, and the second positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the new energy side before the fault;

[0075] The first current mutation is the second difference The second difference is the first positive-sequence current minus the second positive-sequence current The value; the first positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side after the fault, and the second positive-sequence current is the positive-sequence current measured at the protection installation location on the new energy side before the fault;

[0076] The second voltage mutation is the third difference The third difference is the third positive-sequence voltage minus the fourth positive-sequence voltage The value; the third positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the VSC-HVDC side after the fault, and the fourth positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the VSC-HVDC side before the fault;

[0077] The second current mutation is the fourth difference The fourth difference is the third positive-sequence current minus the fourth positive-sequence current The value; the third positive-sequence current is the positive-sequence current measured at the protection installation location on the VSC-HVDC side after the fault, and the fourth positive-sequence current is the positive-sequence current measured at the protection installation location on the VSC-HVDC side before the fault.

[0078] The new energy is sent out through the VSC-HVDC system as Figure 2 shown, Figure 2 where A is the new energy station, B is the VSC-HVDC converter, and C is the external system. In the sending-end system, the new energy station is collected and stepped up to 220V through the main transformer, and then enters the VSC-HVDC converter station on the wind farm side after passing through a section of AC line; the receiving-end system mainly realizes the power transmission from the DC bus to the external AC system through the grid-side converter. In Figure 2In the network topology, M and W represent the busbars on the VSC side and the new energy side respectively, f1 represents an external fault at the outlet of the new energy side, f2 represents an external fault at the outlet of the VSC-HVDC side, and f3 represents the fault point of an internal fault. The research object is the line MW.

[0079] The equivalent circuit diagram of the new energy transmission system via VSC-HVDC is as Figure 3 shown. Under normal operating conditions, the voltage value measured at the installation location of the new energy side protection is and the current value measured at the installation location of the new energy side protection is The voltage value measured at the installation location of the VSC-HVDC side protection is and the current value measured at the installation location of the VSC-HVDC side protection is

[0080] The positive sequence component network when a short-circuit fault occurs in the new energy transmission line is as Figures 4 - 6 shown. Under fault conditions, the positive sequence voltage phasor measured at the installation location of the new energy side protection is and the positive sequence current phasor measured at the installation location of the new energy side protection is The positive sequence voltage phasor measured at the installation location of the VSC-HVDC side protection is and the positive sequence current phasor measured at the installation location of the VSC-HVDC side protection is

[0081] That is, when not considering the capacitive reactance of the transmission line distributed capacitance:

[0082]

[0083] In some of these embodiments, when considering the capacitive reactance of the transmission line distributed capacitance:

[0084] The first voltage mutation is the first difference The first difference is the value obtained by subtracting the second positive sequence voltage from the first positive sequence voltage; the first positive sequence voltage is the positive sequence voltage measured at the installation location of the new energy side protection after the fault, and the second positive sequence voltage is the positive sequence voltage measured at the installation location of the new energy side protection before the fault;

[0085] The first current mutation is the fifth difference, and the fifth difference is the second difference minus the sixth difference The value, the second difference is the value obtained by subtracting the second positive sequence current from the first positive sequence current, and the sixth difference is the fifth positive sequence current minus the sixth positive sequence current The value; the first positive sequence current is the positive sequence current measured at the installation location of the new energy side protection after the fault, the second positive sequence current is the positive sequence current measured at the installation location of the new energy side protection before the fault, the fifth positive sequence current is the positive sequence current flowing through the distributed capacitance of the new energy side after the fault, and the sixth positive sequence current is the positive sequence current flowing through the distributed capacitance of the new energy side before the fault;

[0086] The second voltage mutation is the third difference The third difference is the value obtained by subtracting the fourth positive-sequence voltage from the third positive-sequence voltage; the third positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side after the fault, and the fourth positive-sequence voltage is the positive-sequence voltage measured at the protection installation location on the flexible DC transmission side before the fault;

[0087] The second current mutation is the seventh difference, and the seventh difference is the fourth difference minus the eighth difference The value, the fourth difference is the value obtained by subtracting the fourth positive-sequence current from the third positive-sequence current, and the eighth difference is the seventh positive-sequence current minus the eighth positive-sequence current The value; the third positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side after the fault, the fourth positive-sequence current is the positive-sequence current measured at the protection installation location on the flexible DC transmission side before the fault, the seventh positive-sequence current is the positive-sequence current flowing through the distributed capacitance on the flexible DC transmission side after the fault, and the eighth positive-sequence current is the positive-sequence current flowing through the distributed capacitance on the flexible DC transmission side before the fault.

[0088] When the object of study is a new energy transmission line, the π model is adopted for the transmission line. Generally, it is considered that the capacitive reactance of the distributed capacitance of the transmission line is large, and the shunt current of the capacitive branch is very small compared with the load current and the fault current. Therefore, the shunt current of the capacitive branch has little influence on the calculation of the positive-sequence equivalent impedance, and the first equivalent impedance and the second equivalent impedance can be calculated according to Equations (1) and (2). However, to further improve the calculation accuracy of the first equivalent impedance and the second equivalent impedance, considering the influence of the shunt current of the distributed capacitance, according to Kirchhoff's Current Law (KCL), the capacitive current compensation is performed on the load current flowing through the protection installation location, and the current flowing through the transmission line is obtained as:

[0089]

[0090] In the formula, is the current flowing through the distributed capacitance on the new energy side under normal operating conditions, is the current flowing through the distributed capacitance on the flexible DC transmission side under normal operating conditions; is the current flowing through the protection installation location on the new energy side under normal operating conditions, is the current flowing through the protection installation location on the flexible DC transmission side under normal operating conditions;

[0091] Similarly, during a short-circuit fault, the capacitive current compensation is performed on the fault current flowing through the protection installation location, and the short-circuit current flowing through the transmission line is:

[0092]

[0093] In the formula, is the positive-sequence current flowing through the shunt capacitance on the new energy side after a fault, is the positive-sequence current flowing through the shunt capacitance on the flexible DC transmission side after a fault; is the positive-sequence current flowing through the protection installation location on the new energy side after a fault, is the positive-sequence current flowing through the protection installation location on the flexible DC transmission side after a fault.

[0094] The current expressions flowing through the capacitance branch before and after a fault are:

[0095]

[0096] In the formula, is the reactance of the shunt capacitance, f is the power frequency, f = 50Hz, and C1 is the positive-sequence capacitance parameter of the π-type equivalent circuit.

[0097] Generally, the reactance of the transmission line shunt capacitance is large, and the current flowing through the capacitance branch is very small in magnitude compared with the load current and fault current. When calculating the first equivalent impedance and the second equivalent impedance, the influence of the shunt of the shunt capacitance can be ignored; in special cases, in order to improve the protection reliability, the capacitance parameters of the transmission line can be considered when calculating the first equivalent impedance and the second equivalent impedance to improve the calculation accuracy of the first equivalent impedance and the second equivalent impedance.

[0098] Considering the influence of the shunt capacitance of the AC line on the impedance calculation, the positive-sequence measured impedance at the protection installation location on the new energy side and the positive-sequence measured impedance at the protection installation location on the flexible DC output side are respectively:

[0099]

[0100] When different short-circuit fault types occur at different positions, there are large differences in the equivalent sequence network diagrams of the system, and there are large differences in the positive-sequence voltage and positive-sequence current measured at the protection installation location. Therefore, when analyzing the adaptability of protection methods, it will be described separately according to different short-circuit fault types occurring at different positions.

[0101] When a fault occurs at different positions, as shown in the new energy transmission line in Figure (1), the π model is adopted for the transmission line. Among them, M and W represent the busbars on the flexible converter side and the new energy side respectively, f1 represents the out-of-zone fault at the outlet of the new energy side, f2 represents the out-of-zone fault at the outlet of the flexible DC transmission side, and f3 represents the fault point of the in-zone fault. The research object is the line MW, and the influence of the line shunt capacitance is ignored; the positive-sequence equivalent impedance on the new energy side is The positive-sequence equivalent impedance on the flexible DC output side is The positive-sequence impedance of the line MW is Add the positive-sequence equivalent impedance value on the new energy side to the positive-sequence equivalent impedance value on the flexible DC output side to obtain the sum of the positive-sequence impedance measurement values for the following three fault scenarios:

[0102] (1) When a short-circuit fault occurs at point f1 at the outlet of the new energy side of the transmission line, the positive-sequence impedance value measured at the location of the new energy side protection is The positive-sequence impedance value measured at the location of the flexible DC output side protection is Meanwhile At this time, according to Figure 3 and Figure 4 Write the loop voltage equation between the locations of the new energy side and flexible DC output side protections:

[0103]

[0104] By combining the loop voltage equation with equations (1) and (2), we can further obtain:

[0105]

[0106] At this time, the positive-sequence impedance value measured at the location of the new energy side protection and the positive-sequence impedance value measured at the location of the flexible DC output side protection The sum is equal to the positive-sequence impedance of the line The sum impedance has the same magnitude as the line impedance and the same impedance angle as the line impedance;

[0107] (2) When a short-circuit fault occurs at point f2 at the outlet of the VSC side of the transmission line, the positive-sequence impedance value measured at the location of the new energy side protection is The positive-sequence impedance value measured at the location of the flexible DC output side protection is Meanwhile At this time, according to Figure 3 and Figure 5 Write the loop voltage equation between the two protection locations:

[0108]

[0109] By combining the loop voltage equation with the definition expression of the positive-sequence equivalent impedance, we can further obtain:

[0110]

[0111] At this time, the positive-sequence impedance value measured at the location of the new energy side protection and the positive-sequence impedance value measured at the location of the flexible DC output side protection The sum is equal to the positive-sequence impedance of the line The sum impedance magnitude is the same as the line impedance magnitude, and the sum impedance angle is the same as the line impedance angle.

[0112] (3) When a fault occurs at point f3 within the transmission line area, the positive-sequence impedance value measured at the protection installation location on the new energy side is The positive-sequence impedance value measured at the protection installation location on the flexible DC output side is At this time This condition is no longer satisfied, and according to Figure 3 、 Figure 6 Write the loop voltage equation between the two protection installation locations:

[0113]

[0114] By combining the positive-sequence equivalent impedance definition expression, we can further obtain:

[0115]

[0116] In most cases, the sum impedance magnitude is not the same as the line impedance magnitude and the sum impedance angle is not the same as the line impedance angle. Affected by the control strategy, the positive-sequence equivalent impedance on the new energy side after the fault may exhibit negative impedance characteristics. In special cases, there may be a situation where one of the sum impedance magnitude and the line impedance magnitude, and the sum impedance angle and the line impedance angle is approximately equal.

[0117] Based on the above analysis, it can be known that

[0118] It is possible to use the magnitude and impedance angle of the sum of the positive-sequence impedance value measured at the protection installation location on the new energy side after the fault and the positive-sequence impedance value measured at the protection installation location on the flexible DC output side, that is, the sum impedance magnitude and the sum impedance angle, and whether they are equal to the line positive-sequence impedance magnitude and the line positive-sequence impedance angle as a criterion to distinguish between in-zone faults and out-of-zone faults:

[0119] When an out-of-zone fault occurs on the outgoing line, the sum impedance magnitude is equal to the line impedance magnitude, and the sum impedance angle is equal to the line impedance angle; when an in-zone fault occurs, the sum impedance magnitude is not equal to the line impedance magnitude and the sum impedance angle is equal to the line impedance angle. A double-ended quantity protection criterion can be constructed based on the difference characteristics of the positive-sequence equivalent impedance inside and outside the zone to distinguish between in-zone faults and out-of-zone faults. However, in special cases, there may be a situation where the sum impedance is approximately equal to the line impedance. At this time, if a protection criterion is constructed using the absolute value of the difference between the sum impedance and the line impedance, it may cause the protection to refuse to operate in the zone.

[0120] In some of these embodiments, the steps for distinguishing the fault type according to the sum impedance magnitude, the line impedance magnitude, the sum impedance angle, and the line impedance angle are:

[0121] Obtain the first protection criterion and the second protection criterion; the first protection criterion is:

[0122] |abs(Z eq.W +Z eq.M ) - abs(Z L )| > K set1 ;

[0123] In the formula, abs represents the amplitude value, Z eq.W is the first equivalent impedance, Z eq.M is the second equivalent impedance, Z L is the line impedance, K set1 is the amplitude setting value;

[0124] The second protection criterion is:

[0125] |arg(Z eq.W +Z eq.M ) - arg(Z L )| > K set2 ;

[0126] In the formula, arg represents the phase angle, Z eq.W is the first equivalent impedance, Z eq.M is the second equivalent impedance, Z L is the line impedance, K set2 is the impedance angle setting value.

[0127] Judge whether the first protection criterion is established according to the amplitude of the sum impedance and the amplitude of the line impedance;

[0128] Judge whether the second protection criterion is established according to the angle of the sum impedance and the angle of the line impedance;

[0129] When only the first protection criterion is established, or only the second protection criterion is established, or both the first protection criterion and the second protection criterion are established, the fault type is an in - zone fault;

[0130] When the first protection criterion is established and the second protection criterion is not established, the fault type is an out - of - zone fault.

[0131] The protection logic is as Figure 7 shown. In the figure, is the sum impedance.

[0132] Taking into account the influence of distributed capacitance, etc., the amplitude setting value is 2, and the impedance angle setting value is 1.

[0133] Example 1

[0134] In Figure 2 the typical topology structure diagram of the new energy transmitted through the flexible DC system, taking the line WM as the research object, the fault occurs at 1.0 s. When an out - of - zone fault occurs on the new energy side (at f1), as Figures 8 - 11 shown. Figure 8The magnitude and angle of the sum impedance when a phase - to - ground fault occurs, Figure 9 The magnitude and angle of the sum impedance when a short - circuit fault occurs between phases b and c, Figure 10 The magnitude and angle of the sum impedance when a phase - to - ground short - circuit fault occurs between phases b and c, and Figure 11 The magnitude and angle of the sum impedance when a three - phase ground fault occurs, and compare it with the magnitude and angle of the line impedance. Figure 8 When a single - phase ground fault through a transition resistance occurs (Rf = 200Ω), the magnitude and angle of the sum impedance measured and calculated at the protection installation points on both sides. After 20 ms of the fault, the magnitude of the sum impedance stabilizes at 48.92Ω, and the angle of the sum impedance stabilizes at 80.93°. While the magnitude of the line impedance is 48.9Ω and the angle of the line impedance is 80.9°. The absolute value calculated according to the first protection criterion is 0.02Ω, which is less than the magnitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.03°, which is less than the impedance - angle setting value K set2 , and the protection operates correctly without tripping. Figure 9 When a two - phase short - circuit fault through a transition resistance occurs (Rf = 200Ω), the magnitude and angle of the sum impedance measured and calculated at the protection installation points on both sides. After 20 ms of the fault, the magnitude of the sum impedance stabilizes at 48.8Ω, and the angle of the sum impedance stabilizes at 81.25°. While the magnitude of the line impedance is 48.9Ω and the angle of the line impedance is 80.9°. The absolute value calculated according to the first protection criterion is 0.1Ω, which is less than the magnitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.35°, which is less than the impedance - angle setting value K set2 , and the protection operates correctly without tripping. Figure 10 The absolute value calculated according to the first protection criterion is 0.14Ω, which is less than the magnitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.05°, which is less than the impedance - angle setting value K set2 ; Figure 11 The absolute value calculated according to the first protection criterion is 0.2Ω, which is less than the magnitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.1°, which is less than the impedance - angle setting value K set2 , and the above situations do not meet the protection operation conditions, and the protection operates correctly without tripping.

[0135] Example 2

[0136] In Figure 2 a typical topology structure diagram of a new - energy power transmission system via a flexible DC transmission system, taking line WM as the research object, the fault occurs at 1.0 s. When an external fault occurs on the flexible - DC side (at f2), as Figures 12 - 15 shown. Figure 12The sum impedance amplitude and sum impedance angle when a phase - to - ground fault occurs, Figure 13 The sum impedance amplitude and sum impedance angle when a short - circuit fault occurs between phases b and c, Figure 14 The sum impedance amplitude and sum impedance angle when a b - c phase - to - ground short - circuit fault occurs, and Figure 15 The sum impedance amplitude and sum impedance angle when a three - phase ground fault occurs, and compare them with the line impedance amplitude and line impedance angle. Figure 12 When a single - phase ground fault through a transition resistance occurs (Rf = 200Ω), the sum impedance amplitude and sum impedance angle measured and calculated at both sides of the protection installation. After 20ms of the fault, the sum impedance amplitude stabilizes at 48.7Ω, and the sum impedance angle stabilizes at 80.8°. While the line impedance amplitude is 48.9Ω and the line impedance angle is 80.9°. The absolute value calculated according to the first protection criterion is 0.2Ω, which is less than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.1°, which is less than the impedance angle setting value K set2 , and the protection operates correctly without tripping. Figure 13 When a two - phase - to - two - phase fault through a transition resistance occurs (Rf = 200Ω), the sum impedance amplitude and sum impedance angle measured and calculated at both sides of the protection installation. After 20ms of the fault, the sum impedance amplitude stabilizes at 48.89Ω, and the sum impedance angle stabilizes at 80.71°. While the line impedance amplitude is 48.9Ω and the line impedance angle is 80.9°. The absolute value calculated according to the first protection criterion is 0.01Ω, which is less than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.19°, which is less than the impedance angle setting value K set2 , and the protection operates correctly without tripping. Figure 14 The absolute value calculated according to the first protection criterion is 0.6Ω, which is less than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.3°, which is less than the impedance angle setting value K set2 ; Figure 15 The absolute value calculated according to the first protection criterion is 0.4Ω, which is less than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 0.01°, which is less than the impedance angle setting value K set2 , and the above situations do not meet the protection operation conditions, so the protection operates correctly without tripping.

[0137] Example 3

[0138] In Figure 2 the typical topology structure diagram of a new - energy power transmission system through a flexible DC transmission system, taking line WM as the research object, when the fault occurs at 1.0s. Figures 16 - 19When a zone fault occurs at 50 km (at f3) from the measuring point R1 of the MW line distance protection, the measured values of the sum impedance amplitude, impedance angle at both protection installation locations, and the actual values of the positive sequence impedance amplitude and impedance angle of the MW line are presented. Figure 16 The sum impedance amplitude and sum impedance angle during an a-phase ground fault; Figure 17 The sum impedance amplitude and sum impedance angle during a bc-phase short circuit fault; Figure 18 The sum impedance amplitude and sum impedance angle during a bc-phase ground short circuit fault, and Figure 19 The sum impedance amplitude and sum impedance angle during a three-phase ground fault, and they are compared with the line impedance amplitude and line impedance angle. Figure 16 When a single-phase ground fault through a transition resistance occurs (Rf = 200 Ω), the measured and calculated sum impedance amplitude and sum impedance angle at both protection installation locations. After 20 ms of the fault, the sum impedance amplitude stabilizes at 599.5 Ω, and the sum impedance angle stabilizes at -82.5°. While the line impedance amplitude is 48.9 Ω and the line impedance angle is 80.9°. The absolute value calculated according to the first protection criterion is 550.6 Ω, which is much larger than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 163.4°, which is much larger than the impedance angle setting value K set2 , meeting the protection operation conditions, and the protection operates correctly. Figure 17 When a two-phase short circuit fault through a transition resistance occurs (Rf = 200 Ω), the measured and calculated sum impedance amplitude and sum impedance angle at both protection installation locations. After 20 ms of the fault, the sum impedance amplitude stabilizes at 641 Ω, and the sum impedance angle stabilizes at -87.2°. While the line impedance amplitude is 48.9 Ω and the line impedance angle is 80.9°. The absolute value calculated according to the first protection criterion is 592.1 Ω, which is much larger than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 168.1°, which is much larger than the impedance angle setting value K set2 , meeting the protection operation conditions, and the protection operates correctly. Figure 18 The absolute value calculated according to the first protection criterion is 324 Ω, which is much larger than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 110°, which is much larger than the impedance angle setting value K set2 ; Figure 19 The absolute value calculated according to the first protection criterion is 216.5 Ω, which is much larger than the amplitude setting value K set1 ; The absolute value calculated according to the second protection criterion is 106°, which is much larger than the impedance angle setting value K set2 , and all the above situations meet the protection operation conditions, and the protection operates correctly.

[0139] The present disclosure provides a positive-sequence equivalent impedance pilot protection method adapted to a new energy transmission line. This method calculates the positive-sequence equivalent impedances on both sides, namely the first equivalent impedance and the second equivalent impedance, based on the voltage and current change amounts at the protection installation points on both sides of the new energy transmission line before and after a fault. On this basis, considering the amplitude differences of the sum impedance when a fault occurs inside or outside the zone: when a fault occurs outside the zone of the transmission line, the amplitude of the sum impedance is equal to the amplitude of the line impedance; when a fault occurs inside the zone, the amplitude of the sum impedance is not equal to the amplitude of the line impedance. Finally, considering that in special cases when a fault occurs inside the zone, the sum impedance may be approximately equal to the line impedance, to improve the reliability of the protection, when constructing the protection criterion, the information of the positive-sequence equivalent impedance amplitude and impedance angle is fully utilized to form a pilot protection criterion based on the characteristic differences of the positive-sequence equivalent impedance, so as to realize the discrimination between internal faults and external faults.

[0140] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A positive sequence equivalent impedance pilot protection method applicable to a new energy transmission line, characterized in that: The following steps are involved: When the protection is started, based on the renewable energy transmission line, the line impedance, the first equivalent impedance and the second equivalent impedance are respectively obtained, wherein the first equivalent impedance is the positive sequence equivalent impedance measured at the protection installation on the renewable energy side, and the second equivalent impedance is the positive sequence equivalent impedance measured at the protection installation on the flexible direct current transmission side; Obtain a sum impedance by adding the first equivalent impedance and the second equivalent impedance; obtain a sum impedance amplitude and a sum impedance angle respectively according to the sum impedance; obtain a line impedance amplitude and a line impedance angle respectively according to the line impedance; The fault type is determined according to the sum impedance amplitude, the line impedance amplitude, the sum impedance angle and the line impedance angle; and whether protection is actuated is determined according to the fault type.

2. According to claim 1, the positive sequence equivalent impedance pilot protection method applicable to the new energy transmission line is characterized in that: The steps of obtaining the first equivalent impedance and the second equivalent impedance are: Obtain a first voltage mutation, a first current mutation, a second voltage mutation, and a second current mutation, wherein the first voltage mutation is a positive-sequence voltage mutation before and after the fault measured at the protection installation on the new energy side, the first current mutation is a positive-sequence current mutation before and after the fault measured at the protection installation on the new energy side, the second voltage mutation is a positive-sequence voltage mutation before and after the fault measured at the protection installation on the flexible direct current transmission side, and the second current mutation is a positive-sequence current mutation before and after the fault measured at the protection installation on the flexible direct current transmission side; Obtaining the first equivalent impedance according to the ratio of the first voltage mutation amount to the first current mutation amount; The second equivalent impedance is obtained according to the ratio of the second voltage mutation amount to the second current mutation amount.

3. The positive sequence equivalent impedance pilot protection method applicable to the renewable energy transmission line according to claim 2 is characterized in that: When the distributed capacitance of the transmission line is not considered: The first voltage mutation amount is the first difference, which is the value of the first positive sequence voltage minus the second positive sequence voltage; the first positive sequence voltage is the positive sequence voltage measured at the protection installation on the new energy side after the fault, and the second positive sequence voltage is the positive sequence voltage measured at the protection installation on the new energy side before the fault; The first current mutation amount is the second difference, and the second difference is the value of the first positive sequence current minus the second positive sequence current; the first positive sequence current is the positive sequence current measured at the protection installation on the new energy side after the fault, and the second positive sequence current is the positive sequence current measured at the protection installation on the new energy side before the fault; The second voltage mutation amount is the third difference, and the third difference is the value of the third positive sequence voltage minus the fourth positive sequence voltage; the third positive sequence voltage is the positive sequence voltage measured at the protection installation on the flexible direct current transmission side after the fault, and the fourth positive sequence voltage is the positive sequence voltage measured at the protection installation on the flexible direct current transmission side before the fault; The second current mutation amount is the fourth difference, and the fourth difference is the value of the third positive sequence current minus the fourth positive sequence current; the third positive sequence current is the positive sequence current measured at the protection installation on the flexible DC transmission side after the fault, and the fourth positive sequence current is the positive sequence current measured at the protection installation on the flexible DC transmission side before the fault.

4. The positive sequence equivalent impedance pilot protection method applicable to the renewable energy transmission line according to claim 2 is characterized in that: When considering the distributed capacitance of transmission lines: The first voltage mutation amount is the first difference, which is the value of the first positive sequence voltage minus the second positive sequence voltage; the first positive sequence voltage is the positive sequence voltage measured at the protection installation on the new energy side after the fault, and the second positive sequence voltage is the positive sequence voltage measured at the protection installation on the new energy side before the fault; The first current mutation amount is the fifth difference, the fifth difference is the value of the second difference minus the sixth difference, the second difference is the value of the first positive sequence current minus the second positive sequence current, and the sixth difference is the value of the fifth positive sequence current minus the sixth positive sequence current; the first positive sequence current is the positive sequence current measured at the protection installation on the new energy side after the fault, the second positive sequence current is the positive sequence current measured at the protection installation on the new energy side before the fault, the fifth positive sequence current is the positive sequence current flowing through the distributed capacitor on the new energy side after the fault, and the sixth positive sequence current is the positive sequence current flowing through the distributed capacitor on the new energy side before the fault; The second voltage mutation amount is the value of the third positive sequence voltage minus the fourth positive sequence voltage; the third positive sequence voltage is the positive sequence voltage measured at the protection installation on the flexible DC transmission side after the fault, and the fourth positive sequence voltage is the positive sequence voltage measured at the protection installation on the flexible DC transmission side before the fault; The second current mutation amount is the seventh difference, the seventh difference is the value of the fourth difference minus the eighth difference, the fourth difference is the value of the third positive sequence current minus the fourth positive sequence current, and the eighth difference is the value of the seventh positive sequence current minus the eighth positive sequence current; the third positive sequence current is the positive sequence current measured at the protection installation on the flexible DC transmission side after the fault, the fourth positive sequence current is the positive sequence current measured at the protection installation on the flexible DC transmission side before the fault, the seventh positive sequence current is the positive sequence current flowing through the distributed capacitor on the flexible DC transmission side after the fault, and the eighth positive sequence current is the positive sequence current flowing through the distributed capacitor on the flexible DC transmission side before the fault.

5. The positive sequence equivalent impedance pilot protection method applicable to the renewable energy transmission line according to claim 1 is characterized in that: The steps of determining the fault type according to the sum impedance amplitude, the line impedance amplitude, the sum impedance angle and the line impedance angle are as follows: Acquire a first protection criterion and a second protection criterion; Determining whether the first protection criterion is established according to the sum impedance amplitude and the line impedance amplitude; Determining whether the second protection criterion is established according to the sum impedance angle and the line impedance angle; When only the first protection criterion is satisfied, or only the second protection criterion is satisfied, or both the first protection criterion and the second protection criterion are satisfied, the fault type is an intra-zone fault; When the first protection criterion is met and the second protection criterion is not met, the fault type is an out-of-zone fault.

6. The positive sequence equivalent impedance pilot protection method applicable to the new energy transmission line according to claim 5 is characterized in that: The first protection criterion is: |abs(Z eq.W +Z eq.M )-abs(Z L )|>K set1 ; In the formula, abs represents the amplitude, Z eq.W is the first equivalent impedance, Z eq.M is the second equivalent impedance, Z L is the line impedance, K set1 is the amplitude setting value.

7. The positive sequence equivalent impedance pilot protection method applicable to the new energy transmission line according to claim 6 is characterized in that: The amplitude setting value is 2.

8. The positive sequence equivalent impedance pilot protection method applicable to the new energy transmission line according to claim 5 is characterized in that: The second protection criterion is: |arg(Z eq.W +Z eq.M )-arg(Z L )|>K set2 ; In the formula, arg represents the phase angle, Z eq.W is the first equivalent impedance, Z eq.M is the second equivalent impedance, Z L is the line impedance, K set2 is the impedance angle setting value.

9. The positive sequence equivalent impedance pilot protection method applicable to the new energy transmission line according to claim 8 is characterized in that: The impedance angle setting value is 1.

10. The positive sequence equivalent impedance pilot protection method applicable to a new energy transmission line according to any one of claims 5 to 9, characterized in that: When the fault type is an internal fault, the protection is activated; when the fault type is an external fault, the protection is not activated.

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