New energy large base AC line single-terminal fault detection method

Abstract

The invention discloses a new energy large base AC line single-terminal fault detection method, and belongs to the technical field of line fault detection. The new energy large base AC line single-terminal fault detection method comprises the following steps: analyzing high-frequency impedance characteristics of power electronic sources in a new energy large base, and determining high-frequency impedance parameters of various power electronic sources under different fault loops; calculating the additional impedance characteristic of the calculated impedance of the high-frequency impedance of the line according to the internal and external fault scenes; based on distance characteristics of high-frequency inductive reactance during internal and external faults, a single-ended fault detection criterion is constructed, and fault detection of a new energy large-base AC line is realized. By adopting the new energy large base AC line single-terminal fault detection method, the problem of low detection precision of the existing detection method can be solved.

Description

Technical Field

[0001] This invention relates to the field of line fault detection technology, and in particular to a method for detecting single-end quantity faults in AC lines of large-scale new energy bases. Background Technology

[0002] In recent years, the installed capacity and power generation of new energy sources have developed rapidly. Due to the inverse distribution of new energy resources and demand in my country, a large number of existing or planned new energy bases and offshore wind farms require long-distance power transmission. Flexible DC transmission technology has become one of the important means of absorbing new energy over medium and long distances. However, in actual new energy flexible DC transmission systems, the performance of distance fault detection deteriorates, and there is even a risk of failure to operate. Therefore, researching single-ended fault detection methods suitable for AC lines in large-scale new energy bases is of great significance.

[0003] Fault detection of single-ended quantities in high-voltage collection lines of AC transmission lines in large-scale new energy bases can be categorized into three main types: fault detection based on control and protection coordination, methods based on improvements to traditional protection, and time-domain distance fault detection methods. For control and protection coordination methods, modifications to the control system are required, leading to system safety and stability issues and making them difficult to apply in engineering projects. For traditional protection improvement methods, which rely heavily on the control strategy of the power electronic source, they have limitations. As for time-domain distance fault detection, which does not rely on control strategies, the lack of information on the opposite side's current results in decreased performance during high-resistance phase-to-phase faults. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting single-ended faults in AC lines of large-scale new energy bases, thereby solving the problem of low detection accuracy in existing methods.

[0005] To achieve the above objectives, this invention provides a method for detecting single-ended faults in AC lines of large-scale new energy bases, comprising the following steps:

[0006] S1. Analyze the high-frequency impedance characteristics of power electronic sources in the new energy base and determine the high-frequency impedance parameters of various power electronic sources under different fault circuits.

[0007] S2. For fault scenarios inside and outside the area, analyze the additional impedance characteristics of the calculated impedance of the line's high-frequency impedance.

[0008] S3. Based on the distance characteristics of high-frequency inductive reactance during faults inside and outside the zone, a single-ended fault detection criterion is constructed to realize fault detection of AC lines in the new energy base.

[0009] Preferably, in S1, the power electronic source includes new energy sources and flexible DC converter stations, and the high-frequency impedance parameters are determined through an equivalent circuit model;

[0010] The high-frequency impedance equivalent circuit of the wind power grid-connected converter in new energy includes filter inductors L1 and L2, filter capacitor C, filter resistors R1 and R2, and DC capacitor C. dc Equivalent resistance R 等值 and equivalent inductance L 等值 Its structure consists of a filter resistor and capacitor connected in parallel with an equivalent resistor and inductor, and then connected in series with the filter resistor and inductor; when the frequency... At that time, the high-frequency impedance of the wind power grid-connected converter is equivalent to an RLC series circuit;

[0011] The high-frequency impedance equivalent circuit of the flexible DC converter station is a bridge structure, including bridge arm resistance R0, bridge arm reactance L0, submodule capacitor C0, and the number of submodule capacitors n connected to each phase bridge arm. px The number of submodule capacitors n connected in each phase lower bridge arm nx x represents three phases A, B, and C, with each branch being an RLC circuit in series; when the frequency... When N is the total number of submodules in one phase bridge arm, the high-frequency impedance of the flexible DC converter station is equivalent to an RL series circuit.

[0012] Preferably, the high-frequency impedance of the wind power grid-connected converter is reduced to the 220kV collection line via the transformer substation and main transformer, with a reduction factor of 10. 5 The high-frequency impedance of the flexible DC converter station is reduced to the 220kV line via the wind farm converter transformer, with a reduction factor of (500 / 220). 2 The reciprocal of.

[0013] Preferably, in step S2, the calculated impedance is calculated by the high-frequency impedance value at the fault point and the high-frequency impedance difference between the two measuring points. The additional impedance of the calculated impedance exhibits resistive characteristics, and the distance is calculated using the high-frequency inductive reactance.

[0014] Preferably, when a fault occurs within the line area, the calculated impedance on the new energy side is:

[0015]

[0016] In the formula, ΔZ w For calculating the impedance on the new energy side, Z k For the high-frequency impedance of the faulty new energy side line in the area, R g For the transition resistance, I mmc For the high-frequency current supplied to the flexible DC converter station side, I pm High-frequency current provided for the new energy side;

[0017] The calculated impedance on the new energy side includes an additional impedance term for the transition resistance, which exhibits resistive characteristics.

[0018] When a fault occurs within the line area, the calculated impedance on the flexible DC converter station side is:

[0019]

[0020] In the formula, ΔZ m For calculating the impedance of the flexible DC converter station, Z L-k The high-frequency impedance of the line on the side of the faulty flexible DC converter station in the area;

[0021] The calculated impedance of the flexible DC converter station includes an additional impedance term for the transition resistance, which exhibits resistive characteristics.

[0022] Preferably, when an out-of-line fault occurs, the calculated impedance on the new energy side is:

[0023]

[0024] In the formula, Z LW Indicates the high-frequency impedance of the transformer box;

[0025] The calculated impedance on the new energy side includes an additional impedance term for the transition resistance, which exhibits resistive characteristics.

[0026] When a fault occurs outside the line zone, the calculated impedance on the flexible DC converter station side is:

[0027]

[0028] In the formula, Z L The high-frequency impedance encompassing the entire length of the line;

[0029] The calculated impedance of the flexible DC converter station includes an additional impedance term for the transition resistance, which exhibits resistive characteristics.

[0030] Preferably, in step S3, the distance from the fault point to both sides is analyzed by calculating the high-frequency inductive reactance from the fault point to both sides. The voltage at the fault point is equivalent to the high-frequency voltage generated when the voltage at the fault detection installation point drops to 0. The formula for calculating the high-frequency inductive reactance distance is:

[0031]

[0032] In the formula, L cal-pm For calculating the high-frequency inductive reactance distance on the new energy side, L cal-mmc For calculating the high-frequency inductive reactance distance on the flexible DC converter station side, U mmc For the high-frequency voltage on the flexible DC converter station side, U pm For the high-frequency voltage of the new energy side, U f L0 is the high-frequency voltage at the fault point, L0 is the line inductance per unit length, and ω is the high-frequency angular frequency.

[0033] Preferably, in step S3, by setting up high-frequency inductive distance fault detection protection lines for sections I and II, the fault detection criterion for section I is as follows:

[0034]

[0035] In the formula, L cal The distance for calculating the high-frequency inductive reactance on the new energy side or the flexible DC converter station side; This is the setting value for section I, which is 80% of the total line length. Indicates the I-segment setting time;

[0036] The fault detection criterion for the high-frequency inductive reactance distance II segment is as follows:

[0037]

[0038] In the formula, This is the setting value for Section II, which is 110% of the total line length. This indicates the setting time for stage II.

[0039] The advantages and positive effects of the single-ended fault detection method for AC lines in a large-scale new energy base as described in this invention are:

[0040] 1. This invention analyzes the high-frequency impedance characteristics of various types of power electronic sources and combines frequency band screening and impedance reduction to make the method applicable to scenarios where power electronic sources account for a high proportion in large-scale new energy bases, thus eliminating the dependence on control strategies.

[0041] 2. This invention is based on the pure resistance characteristics of the high-frequency impedance and the additional impedance when there is a fault inside or outside the zone. It uses high-frequency inductive reactance to calculate the fault distance and can effectively identify the fault location through single-ended quantity detection. It can still operate stably under high-impedance faults, thus improving the reliability and accuracy of fault detection.

[0042] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0043] Figure 1 This is a flowchart of the detection method of the present invention;

[0044] Figure 2 This is the high-frequency circuit diagram of the new energy grid-connected converter of the present invention;

[0045] Figure 3 This is a high-frequency circuit diagram of the flexible DC converter station of the present invention;

[0046] Figure 4 This is a high-frequency loop diagram under fault conditions within the region of this invention;

[0047] Figure 5 This is a high-frequency loop diagram under external fault conditions according to the present invention;

[0048] Figure 6 This is a simulation experiment diagram of the new energy flexible DC grid connection topology of this invention;

[0049] Figure 7 This is the calculated value of the high-frequency inductive reactance on the new energy side at fault F1 in the simulation experiment of this invention;

[0050] Figure 8 This is the calculated high-frequency inductive reactance value of the new energy side at fault F2 in the simulation experiment of this invention;

[0051] Figure 9 This is the calculated high-frequency inductive reactance value of the new energy side at fault F3 in the simulation experiment of this invention;

[0052] Figure 10 The high-frequency inductive reactance of the new energy side at fault F4 in the simulation experiment of this invention is calculated. Detailed Implementation

[0053] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0054] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0055] like Figure 1 As shown, a method for detecting single-ended quantity faults in AC lines of a large-scale new energy base includes the following steps:

[0056] S1. Analyze the high-frequency impedance characteristics of power electronic sources in the new energy base and determine the high-frequency impedance parameters of various power electronic sources under different fault circuits.

[0057] Figure 2 This is the high-frequency circuit diagram of the new energy grid-connected converter of the present invention. (See diagram below.) Figure 2 As shown, although there are various forms of high-frequency impedance fault circuits on the new energy side due to the conduction of thyristors, the main difference between them lies in the different equivalent impedances.

[0058] The high-frequency impedance equivalent circuit of the wind power grid-connected converter in new energy includes filter inductors L1 and L2, filter capacitor C, filter resistors R1 and R2, and DC capacitor C. dc Equivalent resistance R 等值 and equivalent inductance L 等值 Its structure consists of a filter resistor and capacitor connected in parallel with an equivalent resistor and inductor, and then connected in series with the filter resistor and inductor. For the portion in the left box, the capacitive reactance is connected in parallel with the impedance. When the capacitive reactance is less than one-tenth of the impedance, the impedance branch can be ignored.

[0059] When frequency At that time, the branches with different high-frequency impedance structures are ignored, and the high-frequency impedance of the wind power grid-connected converter is equivalent to an RLC series circuit.

[0060] As the selected frequency increases, the high-frequency impedance characteristics of the wind power grid-connected converter will approach inductive characteristics more closely. Furthermore, since the wind power grid-connected converter needs to pass through a transformer substation and a main transformer, if equivalent to a 220kV collection line, its equivalent high-frequency impedance needs to be multiplied by 10. 5 Therefore, its high-frequency impedance exhibits inductive and high-amplitude characteristics.

[0061] Figure 3 This is a high-frequency circuit diagram of the flexible DC converter station of the present invention. Figure 3 As shown, the high-frequency impedance equivalent circuit of the flexible DC converter station is a bridge structure. Taking an A / B phase-to-A fault as an example, it includes the bridge arm resistance R0, bridge arm reactance L0, and submodule capacitor C0. The number of submodule capacitors connected to the bridge arm on each phase is n. px The number of submodule capacitors n connected in each phase lower bridge arm nx x represents the three phases A, B, and C.

[0062] Each branch is an RLC circuit in series. Therefore, considering the extreme case, when the frequency... When N is the total number of sub-modules in a phase arm, that is, all the capacitors on the branch of that phase arm are connected at this time. The selected frequency band can still ensure that each branch of the high-frequency impedance of the flexible DC converter station is inductive. At this time, the high-frequency impedance of the flexible DC converter station is equivalent to an RL series circuit.

[0063] Since the high-frequency impedance of the flexible DC converter station needs to pass through the wind farm converter transformer to be converted to 220kV, its equivalent high-frequency impedance needs to be divided by (500 / 220). 2 It exhibits inductive and low-amplitude characteristics compared to the high-frequency impedance of wind power grid-connected converters.

[0064] S2. For fault scenarios inside and outside the area, analyze the additional impedance characteristics of the calculated impedance of the line's high-frequency impedance.

[0065] The high-frequency impedance values ​​calculated at the fault point under different fault scenarios and the high-frequency impedance difference measured at both ends are used as the calculated impedance of the lines on both sides.

[0066] like Figure 4 As shown, when a fault occurs within the line area, the calculated impedance on the new energy side is:

[0067]

[0068] In the formula, ΔZ w For calculating the impedance on the new energy side, Z k For the high-frequency impedance of the faulty new energy side line in the area, R g For the transition resistance, Immc For the high-frequency current supplied to the flexible DC converter station side, I pm High-frequency current provided for the new energy side.

[0069] Since both the current on the high-frequency renewable energy side and the current on the flexible DC converter station side are inductive, the phase angle difference between the high-frequency currents on both sides is small. Therefore, the additional impedance term of the renewable energy side, which includes the transition resistance, exhibits characteristics close to resistance.

[0070] When a fault occurs within the line area, the calculated impedance on the flexible DC converter station side is:

[0071]

[0072] In the formula, ΔZ m For calculating the impedance of the flexible DC converter station, Z L-k The high-frequency impedance of the line on the side of the flexible DC converter station in the area where a fault occurs.

[0073] Since both the high-frequency current on the renewable energy side and the current on the flexible DC converter station side are inductive, the phase angle difference between the high-frequency currents on both sides is small. Therefore, the additional impedance term of the flexible DC converter station side, which includes the transition resistance, exhibits characteristics close to resistance.

[0074] like Figure 5 As shown, when an external fault occurs, the calculated impedance on the new energy side is:

[0075]

[0076] In the formula, Z LW This indicates the high-frequency impedance of the transformer substation.

[0077] At this point, the additional impedance term in the calculated impedance of the new energy side, which includes the transition resistance, exhibits characteristics close to those of a resistor.

[0078] When a fault occurs outside the line zone, the calculated impedance on the flexible DC converter station side is:

[0079]

[0080] In the formula, Z L This refers to the high-frequency impedance that includes the entire length of the line.

[0081] At this point, the calculated impedance of the flexible DC converter station side, including the additional impedance term of the transition resistance, exhibits characteristics close to that of a resistor.

[0082] Based on the above analysis, it can be concluded that when a fault occurs inside or outside the fault zone, the additional impedance in the calculated high-frequency impedance value exhibits characteristics close to resistance. Therefore, the distance can be calculated using high-frequency inductive reactance.

[0083] S3. Based on the distance characteristics of high-frequency inductive reactance during faults inside and outside the zone, a single-ended fault detection criterion is constructed to realize fault detection of AC lines in the new energy base.

[0084] By calculating the high-frequency inductive reactance from the fault point to both sides, the distance from the fault point to both sides is analyzed. The voltage at the fault point is equivalent to the high-frequency voltage generated when the voltage at the fault detection installation point drops to 0, and I and II segments are set to cooperate.

[0085] The formula for calculating the high-frequency inductive reactance distance is:

[0086]

[0087] In the formula, L cal-pm For calculating the high-frequency inductive reactance distance on the new energy side, L cal-mmc For calculating the high-frequency inductive reactance distance on the flexible DC converter station side, U mmc For the high-frequency voltage on the flexible DC converter station side, U pm For the high-frequency voltage of the new energy side, U f L0 is the high-frequency voltage at the fault point, L0 is the line inductance per unit length, and ω is the high-frequency angular frequency.

[0088] By setting up high-frequency inductive distance fault detection protection lines of sections I and II, the fault detection criterion for section I is as follows:

[0089]

[0090] In the formula, L cal The distance for calculating the high-frequency inductive reactance on the new energy side or the flexible DC converter station side; This is the setting value for section I, which is 80% of the total line length. This indicates the setting time for Stage I. Stage I is an instantaneous action that quickly disconnects the circuit breaker, reducing equipment damage.

[0091] The fault detection criterion for the high-frequency inductive reactance distance II segment is as follows:

[0092]

[0093] In the formula, This is the setting value for Section II, which is 110% of the total line length. This indicates the setting time for Section II. Section II protects the entire length of the line and adjacent lines. By setting a time delay, it avoids competing with Section I for operation, and can also serve as a backup to clear faults when adjacent lines fail to operate.

[0094] Figure 6 The above is a simulation experiment diagram of the new energy flexible DC grid connection topology. The line length is 20km. The external outlet on the sending line station side, the internal outlet on the station side at 2km and 18km, and the external outlet on the system side are respectively denoted as F1, F2, F3, and F4.

[0095] When faults occur at F1, F2, F3, and F4, the calculated values ​​of the high-frequency inductive reactance on the new energy side are as follows: Figure 7 , Figure 8 , Figure 9 , Figure 10 As shown, the high-frequency inductive reactance calculation distances obtained by the method described in this invention are -5.06km, 1.91km, 17.77km, and 24.71km, with errors of 1.20%, 4.50%, 1.28%, and 1.16%, respectively. It exhibits high consistency within the selected frequency band, with an error of less than 5%, and the fault detection can correctly identify the distance to different fault locations and take appropriate action.

[0096] Therefore, the single-end fault detection method for AC lines in large-scale new energy bases described in this invention can solve the problem of low detection accuracy of existing detection methods.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A new energy large base alternating current line single-ended quantity fault detection method, characterized in that, The method comprises the following steps: S1, analyzing the high-frequency impedance characteristics of power electronic sources in a new energy large base, and determining the high-frequency impedance parameters of various power electronic sources under different fault circuits; S2, analyzing the additional impedance characteristics of the calculated impedance of the line high-frequency impedance for internal and external fault scenarios; S3, based on the distance characteristics of the high-frequency inductance under internal and external faults, constructing a single-ended fault detection criterion to realize fault detection of the AC line in the new energy large base.

2. The method according to claim 1, wherein, In S1, the power electronic sources include new energy and flexible DC converter stations, and the high-frequency impedance parameters are determined by an equivalent circuit model; The high-frequency impedance equivalent circuit of the wind power grid-connected converter in new energy includes filter inductors L1 and L2, filter capacitor C, filter resistors R1 and R2, and DC capacitor C. dc Equivalent resistance R 等值 and equivalent inductance L 等值 Its structure consists of a filter resistor and capacitor connected in parallel with an equivalent resistor and inductor, and then connected in series with the filter resistor and inductor; when the frequency... At that time, the high-frequency impedance of the wind power grid-connected converter is equivalent to an RLC series circuit; The high-frequency impedance equivalent circuit of the flexible direct current station is a bridge structure, containing a bridge arm resistor R0, a bridge arm reactance L0, a submodule capacitor C0, a number n of submodule capacitors of each phase upper bridge arm px , a number n of submodule capacitors of each phase lower bridge arm nx , x is A, B and C three phases, each branch is in the form of RLC series; when the frequency , N is the total number of submodules of a phase bridge arm, and the high-frequency impedance equivalent of the flexible direct current station is an RLC series circuit.

3. The method according to claim 2, wherein the method is characterized by: The high frequency impedance of the wind power grid-connected converter is reduced to the 220kV collection line through the transformer and the main transformer, and the reduction coefficient is 10 5 ; the high frequency impedance of the flexible direct current converter station is reduced to the 220kV line through the wind farm converter transformer, and the reduction coefficient is the reciprocal of (500 / 220) 2 .

4. The method according to claim 3, wherein the method is characterized by: In S2, the calculated impedance is calculated by the high-frequency impedance value at the fault point and the difference between the high-frequency impedance values at the two ends, the additional impedance of the calculated impedance presents a resistance characteristic, and the high-frequency inductance is used to calculate the distance.

5. The single-ended fault detection method for the AC line in the new energy large base according to claim 4, characterized in that: when a line internal fault occurs, the new energy side calculated impedance is: In the formula, ΔZ w Z is the impedance of the new energy side, k R is the high-frequency impedance of the line at the new energy side in the fault area, g R is the transition resistance, mmc I is the high-frequency current provided by the flexible direct current converter station side, pm I is the high-frequency current provided by the new energy side. The additional impedance term of the new energy side calculated impedance containing the transition resistance presents a resistance characteristic; when a line internal fault occurs, the flexible DC converter station side calculated impedance is: where ΔZ m is the calculated impedance at the HVDC converter station side, Z L-k is the line high-frequency impedance at the HVDC converter station side for a fault in the zone. The additional impedance term of the flexible DC converter station side calculated impedance containing the transition resistance presents a resistance characteristic.

6. The single-ended fault detection method for the AC line in the new energy large base according to claim 5, characterized in that: when a line external fault occurs, the new energy side calculated impedance is: wherein Z LW represents the high frequency impedance of the tank The additional impedance term of the new energy side calculated impedance containing the transition resistance presents a resistance characteristic; when a line external fault occurs, the flexible DC converter station side calculated impedance is: wherein Z L is the high frequency impedance comprising the full length of the line; The additional impedance term of the flexible DC converter station side calculated impedance containing the transition resistance presents a resistance characteristic.

7. The method according to claim 6, wherein, In S3, the distance from the fault point to both sides is analyzed by calculating the high-frequency inductance from the fault point to both sides, the fault point voltage is equivalent to the high-frequency voltage generated by the voltage drop to 0 at the fault detection installation, and the high-frequency inductance distance calculation formula is: wherein L cal-pm is the distance calculated by the high-frequency inductive reactance on the new energy side, L cal-mmc is the distance calculated by the high-frequency inductive reactance on the HVDC converter station side, U mmc is the high-frequency voltage on the HVDC converter station side, U pm is the high-frequency voltage on the new energy side, U f is the high-frequency voltage on the fault point side, L0 is the line inductance per unit length, and ω is the high-frequency angular frequency.

8. The method according to claim 7, wherein, In S3, the whole length of the protection line is set by setting the high-frequency inductance distance of I and II sections, the fault detection criterion for the high-frequency inductance distance I section is: In the formula, L cal The distance is calculated for the high-frequency inductance of the new energy side or the HVDC converter station side. I is the setting value, and 80% of the full length of the line; I represents the setting time of the I section. The fault detection criterion for the high-frequency inductance distance II section is: wherein is the II segment setting value, which is 110% of the line length; denotes the II segment setting time.

Images