Backup protection method for new energy transmission line

Abstract

A backup protection method for a new energy transmission line comprises the steps of firstly collecting three-phase current, zero-sequence current and three-phase voltage at a line protection installation position and calculating phasors, then calculating inter-phase potential of an equivalent power supply, then judging a fault direction based on an included angle between the inter-phase potential of the equivalent power supply and the positive-sequence voltage at the installation position, and if the fault is a forward fault, judging the fault direction; if yes, further judging whether the fault is a forward internal fault and preventing steady-state override, and if a specific criterion is met, triggering a backup protection action; according to the design, the equivalent potential of the new energy power supply is calculated by using the electrical quantity at the protection installation position after the fault, the fault direction is judged according to the angle between the positive sequence voltage at the protection installation position and the potential of the new energy apparent power supply, and the protection action area is further calculated according to the angle between the positive sequence voltage at the protection installation position and the potential of the new energy apparent power supply. Therefore, the fault of the new energy transmission line can be accurately identified, and the problem that the backup protection of the new energy transmission line is incorrect due to the new energy power supply control response is effectively solved.

Description

Technical Field

[0001] The invention relates to a backup protection means, belongs to the technical field of relay protection, and in particular to a backup protection method for a new energy transmission line. Background Art

[0002] In recent years, the installed capacity and power generation of wind power and photovoltaic new energy have grown rapidly, and the proportion of new energy power generation in total power generation has continued to increase; large-scale new energy is transmitted through the AC system. When the AC transmission line fails, the short-circuit current provided by the new energy power supply is affected by its control strategy. Compared with the conventional power supply, the short-circuit current amplitude is significantly reduced. Among them, the negative-sequence current suppression strategy will reduce the negative-sequence current component during asymmetric line faults, and the low-voltage ride-through strategy will reduce the positive-sequence current after the fault. The equivalent source impedance and system power angle increase, and the new energy power supply presents typical weak power supply characteristics after the AC line fault, which in turn affects the backup protection of the new energy transmission line, especially the action performance of the distance protection.

[0003] Phase-to-phase distance protection using positive-sequence voltage as polarization voltage has been widely used in power grids at home and abroad, and is the most important backup protection for renewable energy AC transmission lines. When the system power angle is greater than 90 degrees, the positive-sequence polarization voltage phase-to-phase distance protection will refuse to operate or malfunction; after a fault occurs in the renewable energy transmission line, the renewable energy control response causes the system power angle to increase, seriously affecting the transmission of renewable energy and the safe and stable operation of the power grid.

[0004] At present, there is no effective solution to the problem of incorrect operation of distance protection of renewable energy transmission lines. Generally, the method of withdrawing distance protection is adopted to prevent incorrect operation of protection. However, this will cause the renewable energy transmission line to lose backup protection. When the main protection of the line is also withdrawn, the line fault will not be able to be quickly removed, which will lead to large-scale disconnection of renewable energy and damage to the stability of the power system. Therefore, there is an urgent need for a backup protection method that can accurately identify the fault of renewable energy transmission lines to solve the above-mentioned defects in the prior art. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects and problems of inaccurate protection actions in the prior art and to provide a backup protection method for a new energy transmission line that can accurately identify faults in the new energy transmission line.

[0006] To achieve the above objectives, the technical solution of the present invention is: a backup protection method for a new energy transmission line, comprising:

[0007] S1, collect the three-phase current i at the line protection installation a (t), i b (t), i c (t), zero sequence current i 0 (t) and three-phase voltage ua (t),u b (t),u c (t); and calculate the phase quantities of the three-phase currents at the line protection installation Phase of zero sequence current And the phasors of the three-phase voltages

[0008] S2. Calculate the interphase potential of the new energy equivalent power source based on the phasors of the three-phase current, zero-sequence current and three-phase voltage;

[0009] S3. Based on the phase-to-phase potential of the new energy equivalent power source, calculate the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, and determine the fault location of the new energy transmission line; the determination result includes any one of the following:

[0010] The first type: if 0°<α≤95°, it is judged as a forward fault and the process goes to step S4;

[0011] The second type: if α≥125°, it is judged as an out-of-zone fault and the backup protection does not operate;

[0012] The third type: if 125°>α>95°, proceed to step S5 for further determination;

[0013] S4. If 0°<α<95°, after judging it as a forward fault, it is necessary to further judge the fault in the forward zone and prevent the steady-state overrunning when the fault occurs outside the forward zone;

[0014] The judgment basis includes any one or any combination of the following:

[0015] The criterion for faults in the forward zone is as follows:

[0016]

[0017] in: To protect the positive sequence voltage between phases at the installation location; is the phase-to-phase operating voltage, Z set is the setting impedance; β is the angle margin;

[0018] The criterion for preventing steady-state overrunning during a fault outside the forward zone is as follows:

[0019]

[0020] in: θ is the angle of the new energy equivalent power source, is the amplitude of the potential of the new energy equivalent power source, It is the positive sequence voltage amplitude between phases at the installation location of the line protection;

[0021] If any of the above two criteria is met, the backup protection action is triggered;

[0022] S5. If 125°>α>95°, the fault identification criteria include any of the following:

[0023] The first one:

[0024] Second type:

[0025] The third type:

[0026] If the above three criteria are met at the same time, the backup protection action is triggered.

[0027] In step S2, the calculation formula of the phase potential of the new energy equivalent power source is as follows:

[0028]

[0029] in: are the phase-to-phase potentials of the three phases of the new energy equivalent power supply, They are the phase-to-phase voltages of the three-phase equivalent power supply of new energy, are the phase-to-phase currents of the three-phase equivalent power supply of new energy, Z ab , Z bc , Z ca They are the phase-to-phase impedances of the three-phase equivalent power supply of the new energy source.

[0030] The calculation formula for calculating the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location is as follows:

[0031]

[0032] Where: α is the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, is the phase potential of the new energy equivalent power source, It is the interphase positive sequence voltage at the installation location of the line protection; The value can be any one of ab, bc, and ca.

[0033] In step S5, the first criterion uses the sudden change direction element to judge the forward and reverse faults, which is as follows:

[0034] If the mutation direction element satisfies It is judged as a reverse fault;

[0035] If the mutation direction element does not satisfy It is judged as a forward fault;

[0036] in: is the interphase sudden change voltage, is the phase angle of the phase current, is the load current before the fault, and j is the imaginary part of the complex number.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. In a backup protection method for a new energy transmission line of the present invention, firstly, the three-phase current, zero-sequence current and three-phase voltage at the line protection installation are collected, and the corresponding phasors are calculated, and then the interphase potential of the new energy equivalent power supply is calculated, and then the fault direction is judged based on the angle between the interphase potential of the new energy equivalent power supply and the positive sequence voltage at the line protection installation. If it is a forward fault, it is further judged whether it is a fault in the forward area and prevents steady-state overstepping. If a specific criterion is met, the backup protection action is triggered to isolate the fault part and ensure the stable operation of the power system; in the application of this design, the equivalent potential of the new energy apparent power supply is calculated by using the electrical quantity at the protection installation after the fault, and the fault direction is judged according to the angle between the positive sequence voltage at the protection installation and the apparent power supply potential of the new energy equivalent power supply, and the protection action area is further calculated according to the angle between the positive sequence voltage and the apparent power supply potential of the new energy equivalent power supply, so that the fault of the new energy transmission line can be accurately identified, and the problem of incorrect action of the backup protection of the new energy transmission line caused by the control response of the new energy power supply is effectively solved. Therefore, the present invention can ensure the correct action of the backup protection of the new energy transmission line.

[0039] 2. In a backup protection method for a new energy transmission line of the present invention, the phase-to-phase potential and angle are calculated to provide accurate numerical results, enhance the accuracy of system analysis, and comprehensively consider the three-phase characteristics for systematic analysis, thereby improving the applicability of the interaction between the new energy system and the power grid, as well as the flexibility of flexibly selecting parameters according to actual conditions.

[0040] 3. In a backup protection method for a new energy transmission line of the present invention, a sudden change direction element is used to determine the fault direction, which can quickly and accurately distinguish between forward faults and reverse faults, and simplifies the fault judgment process, reduces the possibility of misoperation, and helps to improve the stability and safety of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of the steps of the method of the present invention.

[0042] Figure 2 It is a schematic diagram of the relationship between the angle margin and the included angle in Example 1 of the present invention.

[0043] Figure 3 This is a logical diagram of the backup protection action in Example 1 of the present invention.

[0044] Figure 4 This is a schematic diagram of a new energy transmission line fault in Example 1 of the present invention.

[0045] Figure 5 It is a schematic diagram of the existing distance protection on the M side refusing to operate during a short circuit fault in Example 1 of the present invention.

[0046] Figure 6 It is a schematic diagram of the correct operation of the backup protection of the M side in this scheme during a short circuit fault in Example 1 of the present invention.

[0047] Figure 7 It is a schematic diagram of malfunction of the existing distance protection on the N side during a short circuit fault in Example 1 of the present invention.

[0048] Figure 8 This is a schematic diagram showing that the backup protection of the N side of the present invention does not operate correctly when a short circuit fault occurs in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0050] A backup protection method for a new energy transmission line, comprising:

[0051] S1, collect the three-phase current i at the line protection installation a (t), i b (t), i c (t), zero sequence current i 0 (t) and three-phase voltage u a (t),u b (t),u c (t); and calculate the phase quantities of the three-phase currents at the line protection installation Phase of zero sequence current And the phasors of the three-phase voltages

[0052] S2. Calculate the interphase potential of the new energy equivalent power source based on the phasors of the three-phase current, zero-sequence current and three-phase voltage;

[0053] S3. Based on the phase-to-phase potential of the new energy equivalent power source, calculate the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, and determine the fault location of the new energy transmission line; the determination result includes any one of the following:

[0054] The first type: if 0°<α≤95°, it is judged as a forward fault and the process goes to step S4;

[0055] The second type: if α≥125°, it is judged as an out-of-zone fault and the backup protection does not operate;

[0056] The third type: if 125°>α>95°, proceed to step S5 for further determination;

[0057] S4. If 0°<α≤95°, after judging it as a forward fault, it is necessary to further judge the fault in the forward zone and prevent the steady-state overrunning when the fault occurs outside the forward zone;

[0058] The judgment basis includes any one or any combination of the following:

[0059] The criterion for faults in the forward zone is as follows:

[0060]

[0061] in: To protect the positive sequence voltage between phases at the installation location; is the phase-to-phase operating voltage,

[0062] Z set is the setting impedance; β is the angle margin;

[0063] The criterion for preventing steady-state overrunning during a fault outside the forward zone is as follows:

[0064]

[0065] in: θ is the angle of the new energy equivalent power source, is the amplitude of the potential of the new energy equivalent power source, It is the positive sequence voltage amplitude between phases at the installation location of the line protection;

[0066] If any of the above two criteria is met, the backup protection action is triggered;

[0067] S5. If 125°>α>95°, the fault identification criteria include any of the following:

[0068] The first one:

[0069] Second type:

[0070] The third type:

[0071] If the above three criteria are met at the same time, the backup protection action is triggered.

[0072] In step S2, the calculation formula of the phase potential of the new energy equivalent power source is as follows:

[0073]

[0074] in: are the phase-to-phase potentials of the three phases of the new energy equivalent power supply, They are the phase-to-phase voltages of the three-phase equivalent power supply of new energy, are the phase-to-phase currents of the three-phase equivalent power supply of new energy, Z ab , Z bc , Z ca They are the phase-to-phase impedances of the three-phase equivalent power supply of the new energy source.

[0075] The calculation formula for calculating the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location is as follows:

[0076]

[0077] Where: α is the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, is the phase potential of the new energy equivalent power source, It is the interphase positive sequence voltage at the installation location of the line protection; The value can be any one of ab, bc, or ca.

[0078] In step S5, the first criterion uses the sudden change direction element to judge the forward and reverse faults, which is as follows:

[0079] If the mutation direction element satisfies It is judged as a reverse fault;

[0080] If the mutation direction element does not satisfy It is judged as a forward fault;

[0081] in: is the interphase sudden change voltage, is the phase angle of the phase current, is the load current before the fault, and j is the imaginary part of the complex number.

[0082] Embodiment 1:

[0083] See also Figure 1 , a backup protection method for a new energy transmission line, comprising:

[0084] S1, collect the three-phase current i at the line protection installation a (t), i b (t), i c (t), zero sequence current i 0 (t) and three-phase voltage u a (t),u b (t),u c(t); and calculate the phase quantities of the three-phase currents at the line protection installation Phase of zero sequence current And the phasors of the three-phase voltages

[0085] Furthermore, the calculation formula for the phase-to-phase potential of the new energy equivalent power supply is as follows:

[0086]

[0087] in: are the phase-to-phase potentials of the three phases of the new energy equivalent power supply, They are the phase-to-phase voltages of the three-phase equivalent power supply of new energy, are the phase-to-phase currents of the three-phase equivalent power supply of new energy, Z ab , Z bc , Z ca They are the phase-to-phase impedances of the three-phase equivalent power supply of the new energy source.

[0088] Preferably, the phase-to-phase potential can be obtained by measurement or by calculating the single-phase potential. The expression of the single-phase potential is as follows:

[0089]

[0090] in: are the single-phase potentials of the three-phase equivalent power supply of new energy, k is the zero-sequence compensation coefficient, Z a , Z b , Z c They are the single-phase impedance of the three-phase equivalent power supply of new energy;

[0091] S2. Calculate the interphase potential of the new energy equivalent power source based on the phasors of the three-phase current, zero-sequence current and three-phase voltage;

[0092] Furthermore, the calculation formula for calculating the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location is as follows:

[0093]

[0094] Where: α is the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, is the phase potential of the new energy equivalent power source, It is the interphase positive sequence voltage at the installation location of the line protection; The value can be any one of ab, bc, or ca.

[0095] S3. Based on the phase-to-phase potential of the new energy equivalent power source, calculate the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, and determine the fault location of the new energy transmission line; the determination result includes any one of the following:

[0096] The first type: if 0°<α≤95°, it is judged as a forward fault and the process goes to step S4;

[0097] The second type: if α≥125°, it is judged as an out-of-zone fault and the backup protection does not operate;

[0098] The third type: if 125°>α>95°, proceed to step S5 for further determination;

[0099] S4. If 0°<α≤95°, after judging it as a forward fault, it is necessary to further judge the fault in the forward zone and prevent the steady-state overrunning when the fault occurs outside the forward zone;

[0100] The judgment basis includes any one or any combination of the following:

[0101] The criterion for faults in the forward zone is as follows:

[0102]

[0103] in: To protect the positive sequence voltage between phases at the installation location; is the phase-to-phase operating voltage,

[0104] Z set is the setting impedance; β is the angle margin;

[0105] In this scheme, the criterion is to compare the phase-to-phase working voltage The phase difference between the positive sequence voltage and the phase-to-phase voltage is used to determine whether it is a forward zone fault. If the phase difference is between 0° and 90°+β, it is determined to be a forward zone fault, and β can be used to provide the accuracy of the judgment.

[0106] The criterion for preventing steady-state overrunning during a fault outside the forward zone is as follows:

[0107]

[0108] in: θ is the angle of the new energy equivalent power source, is the amplitude of the potential of the new energy equivalent power source, It is the positive sequence voltage amplitude between phases at the installation location of the line protection;

[0109] In this scheme, the criterion is used to ensure that the backup protection device of the power system will not malfunction when a fault occurs outside the forward zone of the line (i.e., a fault occurring downstream of the protection device). Specifically, this criterion compares the phase-to-phase working voltage and the positive sequence voltage between phases at the line protection installation location The amplitude of is used to determine whether it is a fault outside the forward zone.

[0110] When α<90°, if the absolute value of the difference between the amplitude of the phase-to-phase working voltage and the amplitude of the phase-to-phase positive sequence voltage is greater than It is considered that a fault outside the forward zone has occurred and the backup protection device should not operate.

[0111] When α≥90°, in addition to the amplitude difference condition, the influence of the angle θ of the equivalent power source needs to be considered. If the absolute value of the difference between the amplitude of the phase-to-phase working voltage after considering the phase angle and the amplitude of the phase-to-phase positive sequence voltage is also greater than It is also considered that a fault outside the forward zone has occurred and the backup protection device should not operate.

[0112] A fault outside the forward zone of the backup protection causes the protection to malfunction, which is called "override".

[0113] If any of the above two criteria is met, the backup protection action is triggered, that is, the "OR" gate exit of the two; Figure 2 As shown, the relationship between the angle margin β and the included angle α is as follows:

[0114]

[0115] S5. If 125°>α>95°, the backup protection criterion includes any of the following:

[0116] The first one:

[0117] Furthermore, the first criterion uses the sudden change direction element to judge the forward and reverse faults, as follows:

[0118] If the mutation direction element satisfies It is judged as a reverse fault;

[0119] If the mutation direction element does not satisfy It is judged as a forward fault;

[0120] in: is the interphase sudden change voltage, is the phase angle of the phase current, is the load current before the fault, and j is the imaginary part of the complex number.

[0121] In this scheme, the criterion is to compare the phase angle of the fault impedance The direction of the fault is determined by comparing the phase angle of the complex number (1-j2)50Ω. If the phase angle difference between the two is between -75° and 45°, it is considered a reverse fault; (1-j2)50Ω is a reference impedance used to adjust the range of the phase angle.

[0122] Second type:

[0123] In this scheme, the criterion determines the direction of the fault by comparing the phase difference between the phase-to-phase working voltage and the phase-to-phase positive sequence voltage at the line protection installation. If the phase difference is between 0° and 105°, it is judged as a forward fault. It is the reference voltage used to adjust the range of phase difference.

[0124] The third type:

[0125] Where: θ is the angle of the new energy equivalent potential;

[0126] In this scheme, the criterion prevents the protection from overrunning malfunction in the case of a fault outside the forward zone by comparing the amplitude difference between the phase-to-phase working voltage and the phase-to-phase positive sequence voltage. It is judged as a fault in the forward zone; θ is used to adjust the phase angle.

[0127] If the above three criteria are met at the same time, the backup protection action is triggered.

[0128] In this embodiment, by adjusting the phase of the polarization voltage and the protection action area, it is possible to prevent the backup protection from refusing to operate when a two-phase short circuit fault occurs in the forward direction of the line, and to prevent the backup protection from malfunctioning when a two-phase short circuit fault occurs in the reverse direction of the line. In order to address the problem of steady-state overshooting caused by changes in the action area, protection criteria for preventing steady-state overshooting are added, which significantly improves the reliability of backup protection for new energy transmission lines.

[0129] In this embodiment, Figure 3 This is a schematic diagram of the backup protection action logic of this scheme; this embodiment simulates the fault of the new energy transmission line and compares the protection logic of this scheme with the existing scheme. The fault schematic diagram is shown in FIG. Figure 4 shown.

[0130] Figure 5 for Figure 4 The figure shows the action behavior of the existing distance protection on the M side when a two-phase metallic short-circuit fault occurs at point F1 of the new energy transmission line. It can be seen from the figure that the existing distance protection will refuse to operate when there is a fault in the area; Figure 6 This is the backup protection action behavior proposed by the present invention. As can be seen from the figure, the backup protection principle proposed by the present invention can operate correctly when there is a fault in the area.

[0131] Figure 7 for Figure 4 The figure shows the action behavior of the existing distance protection on the N side when a two-phase metallic short-circuit fault occurs at point F2 of the new energy transmission line. It can be seen from the figure that the existing distance protection will malfunction when a fault occurs outside the reverse zone; Figure 8 This is the backup protection action behavior proposed by the present invention. As can be seen from the figure, the backup protection principle proposed by the present invention can operate correctly when a fault occurs outside the reverse zone.

[0132] Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A backup protection method for a new energy transmission line, characterized in that: include: S1, collect the three-phase current i at the line protection installation a (t), i b (t), i c (t), zero-sequence current i0(t) and three-phase voltage u a (t),u b (t),u c (t); and calculate the phase quantities of the three-phase currents at the line protection installation Phase of zero sequence current And the phasors of the three-phase voltages S2. Calculate the interphase potential of the new energy equivalent power source based on the phasors of the three-phase current, zero-sequence current and three-phase voltage; S3. Based on the phase-to-phase potential of the new energy equivalent power source, calculate the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, and determine the fault location of the new energy transmission line; the determination result includes any one of the following: The first type: if 0°<α≤95°, it is judged as a forward fault and the process goes to step S4; The second type: if α≥125°, it is judged as an out-of-zone fault and the backup protection does not operate; The third type: if 125°>α>95°, proceed to step S5 for further determination; S4. If 0°<α≤95°, after judging it as a forward fault, it is necessary to further judge the fault in the forward zone and prevent the steady-state overrunning when the fault occurs outside the forward zone; The judgment basis includes any one or any combination of the following: The criterion for faults in the forward zone is as follows: in: To protect the positive sequence voltage between phases at the installation location; is the phase-to-phase operating voltage, Z set is the setting impedance; β is the angle margin; The criterion for preventing steady-state overrunning during a fault outside the forward zone is as follows: in: θ is the angle of the new energy equivalent power source, is the amplitude of the potential of the new energy equivalent power source, It is the positive sequence voltage amplitude between phases at the installation location of the line protection; If any of the above two criteria is met, the backup protection action is triggered; S5. If 125°>α>95°, the fault identification criteria include any of the following: The first one: Second type: The third type: If the above three criteria are met at the same time, the backup protection action is triggered.

2. The backup protection method for the new energy transmission line according to claim 1 is characterized in that: include: In step S2, the calculation formula of the phase potential of the new energy equivalent power source is as follows: in: are the phase-to-phase potentials of the three phases of the new energy equivalent power supply, They are the phase-to-phase voltages of the three-phase equivalent power supply of new energy, are the phase-to-phase currents of the three-phase equivalent power supply of new energy, Z ab , Z bc , Z ca They are the phase-to-phase impedances of the three-phase equivalent power supply of the new energy source.

3. The backup protection method for the new energy transmission line according to claim 2 is characterized in that: include: The calculation formula for calculating the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location is as follows: Where: α is the angle between the potential of the new energy equivalent power source and the positive sequence voltage at the line protection installation location, is the phase potential of the new energy equivalent power source, It is the interphase positive sequence voltage at the installation location of the line protection; The value can be any one of ab, bc, and ca.

4. The backup protection method for the new energy transmission line according to claim 1 is characterized in that: include: In step S5, the first criterion uses the sudden change direction element to judge the forward and reverse faults, which is as follows: If the mutation direction element satisfies It is judged as a reverse fault; If the mutation direction element does not satisfy It is judged as a forward fault; in: is the interphase sudden change voltage, is the phase angle of the phase current, is the load current before the fault, and j is the imaginary part of the complex number.

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