A new energy source end grid sending line protection method and system

Abstract

The present application relates to a kind of new energy source end grid sending line protection method and system, belong to the technical field of power system relay protection, solve the existing technology in new energy source end grid sending line protection there is for the poor transition resistance ability when in-zone fault, the problem of easy misoperation when out-zone fault.It includes after sending line fault occurs, respectively collect the voltage, current high frequency component of sending line wind farm side and direct current side protection installation;Based on the voltage, current high frequency component of sending line wind farm side and direct current side protection installation, obtain the 1 module high frequency impedance variance of sending line wind farm side and direct current side;Based on the 1 module high frequency impedance variance of wind farm side and direct current side and fault identification criterion, determine the sending line fault type, if fault type is sending line in-zone fault, then protection trip, realize sending line protection.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method and system for protecting the transmission lines of new energy source grids. Background Technology

[0002] After large-scale new energy sources are integrated into the power grid through power electronic equipment, their fault transient response characteristics change due to the influence of converter control strategies, etc., which are characterized by limited amplitude, non-power frequency, and controlled phase angle, which are quite different from synchronous power sources. Among them, the line longitudinal protection designed based on the short-circuit characteristics of pure AC systems faces great challenges.

[0003] Longitudinal protection systems are widely used in the main protection of transmission lines due to their simple principle and rapid operation. Existing AC line longitudinal protection systems are mainly divided into two types: those based on electrical quantities and those based on logic quantities. Electrical quantity-based longitudinal protection uses the instantaneous values ​​of current transmitted between cables and optical fiber channels to construct protection criteria to distinguish between internal and external faults. Logic quantity-based longitudinal protection uses signals from both sides, such as power direction and measured impedance, to comprehensively distinguish between internal and external faults. However, due to factors such as wind farm fault-crossing control strategies, fault conditions, and load current, the short-circuit characteristics of wind farms change, leading to decreased sensitivity or even failure to operate of traditional protection systems. Existing protection systems for new energy source-end power grid transmission lines suffer from poor withstand resistance during internal faults and are prone to false tripping during external faults. Summary of the Invention

[0004] Based on the above analysis, the embodiments of the present invention aim to provide a method and system for protecting the transmission lines of new energy source-end power grids, in order to solve the problems of poor withstand capability of transition resistance when the fault is within the zone and easy to malfunction when the fault is outside the zone in the existing protection of transmission lines of new energy source-end power grids.

[0005] On one hand, embodiments of the present invention provide a method for protecting the transmission lines of a new energy source grid, comprising the following steps:

[0006] After a fault occurs in the transmission line, high-frequency components of voltage and current are collected at the protection installation points on the wind farm side and DC side of the transmission line, respectively.

[0007] Based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line, the first-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained.

[0008] Based on the variance of the 1-mode high-frequency impedance and the fault identification criteria on the wind farm side and the DC side, the fault type of the transmission line is determined. If the fault type is a fault within the transmission line area, the protection trips to achieve transmission line protection.

[0009] Furthermore, the fault identification criteria include:

[0010] If the variance of the first-mode high-frequency impedance on the wind farm side of the transmission line is not greater than the threshold value of the first-mode high-frequency impedance variance on the wind farm side, and the variance of the first-mode high-frequency impedance on the DC side of the transmission line is greater than the threshold value of the first-mode high-frequency impedance variance on the DC side, then it is determined that the transmission line has an internal fault.

[0011] If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an out-of-area fault has occurred on the wind farm side of the transmission line.

[0012] If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is not greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an external fault has occurred on the DC side of the transmission line.

[0013] Furthermore, the first-mode high-frequency impedance variance of the transmission line on the wind farm side and the DC side is obtained by performing the following steps:

[0014] Based on the high-frequency components of voltage and current at the wind farm side and DC side protection installation point of the transmission line at each sampling point, the first-mode high-frequency voltage and current at the corresponding sampling point at the wind farm side and DC side protection installation point of the transmission line are obtained.

[0015] Based on the mode 1 voltage and current at the protection installation points on the wind farm side and DC side of the transmission line within half a cycle after the fault, the mode 1 high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained.

[0016] Furthermore, the 1-mode high-frequency voltage U at the wind farm side protection installation point of the sending line at the k-th sampling point... W1 (k) Mode 1 high-frequency current I W1 (k) are respectively represented as:

[0017]

[0018]

[0019] In the formula, U WA (k), U WB (k), U WC (k) represent the high-frequency components of the A, B, and C phase voltages at the wind farm side protection installation point of the k-th sampling point, respectively; I WAY (k), I WBY (k), I WCY (k) represent the high-frequency components of the A, B, and C phase currents at the wind farm side protection installation point of the sending line at the kth sampling point, respectively;

[0020] The mode high-frequency impedance variance V on the wind farm side of the transmission line w , is represented as:

[0021]

[0022] In the formula, Z w1 N represents the 1-mode high-frequency impedance on the wind farm side of the transmitting line; T This represents the total number of sampling points within one sampling period after the fault.

[0023] Furthermore, the 1-mode high-frequency voltage U at the DC side protection installation point of the output line at the k-th sampling point... R1 (k) Mode 1 high-frequency current I R1 (k) are respectively represented as:

[0024]

[0025]

[0026] In the formula, U RA (k), U RB (k), U RC (k) represent the high-frequency components of the A, B, and C phase voltages at the DC side protection installation point of the sending line at the k-th sampling point; I RA (k), I RB (k), I RC (k) represent the high-frequency components of the A, B, and C phase currents at the DC side protection installation point of the sending line at the kth sampling point;

[0027] The 1-mode high-frequency impedance variance V on the DC side of the transmitting line r , is represented as:

[0028]

[0029] In the formula, Z l1 This indicates the impedance of the mode 1 high-frequency line of the transmitting line.

[0030] Furthermore, the 1-mode high-frequency impedance Z on the wind farm side of the transmission line w1 , is represented as:

[0031] Z W1 =(jωL r +Z pmsg1 / / ... / / Z pmsgi / / ... / / Z pmsgN )

[0032] in,

[0033]

[0034] In the formula, Z pmsgi The first-order high-frequency impedance of the i-th wind turbine on the wind farm side of the transmission line is represented by N; N represents the total number of wind turbines on the wind farm side of the transmission line; ω represents the angular frequency; Lr This represents the inductance of the wind farm's main transformer referred to the Y-connected side; k w Indicates the turns ratio of the main transformer in the wind farm; R 1i L 1i R represents the converter-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line, respectively; 2i L 2i R represents the grid-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line, respectively; 3i C 1i Let represent the filter damping resistance and capacitance of the i-th wind turbine on the wind farm side of the transmission line, respectively.

[0035] Furthermore, the impedance Z of the first-mode high-frequency line of the transmitting line... l1 , is represented as:

[0036] Z l1 =Z l11 +Z l12

[0037] in,

[0038] Z l11 =R l11 +jωL l11 ,

[0039] Z l12 =R l12 +jωL l12 ,

[0040] In the formula, Z l11 Z l12 R represents the Mode 1 high-frequency line impedance on the wind farm side and the DC side of the transmitting line, respectively; l11 L l11 These are the equivalent resistance and inductance on the wind farm side of the transmission line, respectively; R l12 L l12 These are the equivalent resistance and inductance on the DC side of the transmitting line, respectively.

[0041] Furthermore, it also includes:

[0042] If the fault type is an outgoing line fault, the protection will not operate.

[0043] Furthermore, the threshold values ​​for the 1-mode high-frequency impedance variance on both the wind farm side and the DC side of the transmission line are set to 50.

[0044] On the other hand, embodiments of the present invention provide a protection system for power grid transmission lines at the source of a new energy source, comprising:

[0045] The data acquisition module is used to collect the high-frequency components of voltage and current at the wind farm side and DC side protection installation points of the transmission line after a fault occurs.

[0046] The 1-mode high-frequency impedance variance acquisition module is used to obtain the 1-mode high-frequency impedance variance of the wind farm side and DC side of the transmission line based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line.

[0047] The fault identification and protection start-up module is used to determine the fault type of the transmission line based on the 1-mode high-frequency impedance variance and fault identification criteria on the wind farm side and DC side. If the fault type is a fault within the transmission line area, the protection trips to realize the protection of the transmission line.

[0048] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0049] This invention provides a method and system for protecting power transmission lines at the source end of a new energy grid.

[0050] First, this invention obtains the first-mode high-frequency impedance variance of the wind farm side and DC side protection installation points by collecting and processing the high-frequency components of voltage and current at the wind farm side and DC side of the transmission line. Then, it determines the fault type based on the fault identification criteria and the first-mode high-frequency impedance variance of the wind farm side and DC side. When the fault type is a fault within the transmission line occurrence zone, the protection trips. The above process makes full use of the sensitive characteristics of high-frequency components based on the harmonic characteristics of wind turbine units, which can realize the rapid and accurate determination of the fault type of the transmission line. It effectively solves the problem that existing protection technologies are difficult to identify faults in the transmission lines of the new energy source grid, and improves the reliability and stability of the new energy source grid.

[0051] Second, by analyzing the topology of the wind farm grid-side converter and DC rectifier under different conduction conditions after a fault, and combining the transient characteristics of the components in the high-frequency section, this invention constructs a 1-mode high-frequency equivalent model of the new energy source-end transmission system, avoiding the impact of wind farm control strategies on protection. On this basis, according to the matching characteristics of different fault scenarios and the 1-mode high-frequency impedance variance on both sides of the transmission line, a protection criterion based on high-frequency impedance variance is constructed, realizing rapid and accurate identification of faults inside and outside the area.

[0052] Third, the present invention is not affected by transition resistance, fault location and fault type, has high sensitivity and low sampling frequency, and is easy to implement in engineering; and only needs to transmit the identification results of the fault direction between the two ends of the output line, without exchanging electrical quantity information between the two ends, the fault identification is not affected by synchronization error, and the requirements for communication devices are low.

[0053] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0054] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0055] Figure 1 This is a flowchart illustrating the protection method for the power grid transmission line at the source end of a new energy source provided in Embodiment 1 of the present invention.

[0056] Figure 2 This is a schematic diagram of the wiring of the new energy source-end power grid transmission system in Embodiment 1 of the present invention;

[0057] Figure 3 This is a structural diagram of the grid-side converter for a direct-drive wind turbine in Embodiment 1 of the present invention;

[0058] Figure 4 This is the high-frequency model of the wind farm side of the transmission line in Embodiment 1 of the present invention;

[0059] Figure 5 This is a structural diagram of the DC rectifier-side converter in Embodiment 1 of the present invention;

[0060] Figure 6 (a) and (b) are the 1-mode models of the D-bridge converter in Embodiment 1 of the present invention with two converter valves and three converter valves turned on.

[0061] Figure 7 (a) and 7(b) are the 1-mode models of the Y-bridge converter with two converter valves and three converter valves in operation in Embodiment 1 of the present invention;

[0062] Figure 8 This is a structural diagram of the AC filter and reactive power compensation device in Embodiment 1 of the present invention;

[0063] Figure 9 (a), 9(b), 9(c), and 9(d) are the 1-mode high-frequency models of DC-side combinations one, two, three, and four of the transmitting line in Embodiment 1 of the present invention;

[0064] Figure 10 This is the general-purpose 1-mode high-frequency model for the DC side of the transmission line in Embodiment 1 of the present invention;

[0065] Figure 11 This is a 1-mode high-frequency model of the transmission system in the case of an in-zone fault in Embodiment 1 of the present invention;

[0066] Figure 12 This is the high-frequency model of the transmission system in the wind field side zone outside the fault in Embodiment 1 of the present invention;

[0067] Figure 13 This is the first-mode high-frequency model of the power supply system in Embodiment 1 of the present invention when there is an external fault on the DC side.

[0068] Figure 14 This is a schematic diagram of the protection system structure of the power grid transmission line at the new energy source end in Embodiment 2 of the present invention;

[0069] Figure 15 (a) and 15(b) are the mode high-frequency impedance variances of the wind farm side and DC side when the transmission line passes through different transition resistances at 50% of the transmission line in Embodiment 3 of the present invention.

[0070] Figure 16 (a) and 16(b) are the mode high-frequency impedance variances of the wind farm side and DC side when there is a fault at different locations of the transmission line in Embodiment 3 of the present invention.

[0071] Figure 17 (a) and 17(b) are the mode high-frequency impedance variances of the wind farm side and DC side when the wind farm side of the transmission line experiences faults with different transition resistances in Embodiment 3 of the present invention.

[0072] Figure 18 (a) and (b) represent the mode high-frequency impedance variance of the wind farm side and the DC side when the DC side of the transmission line experiences faults with different transition resistances in Embodiment 3 of the present invention. Detailed Implementation

[0073] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0074] Example 1

[0075] A specific embodiment of the present invention discloses a method for protecting the transmission lines of a new energy source grid, such as... Figure 1 As shown, it includes the following steps:

[0076] S1. After a fault occurs in the transmission line, the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line are collected respectively.

[0077] S2. Based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line, the first-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained.

[0078] During implementation, in step S2, the first-mode high-frequency impedance variance of the transmission line on the wind farm side and the DC side is obtained by performing the following steps:

[0079] S21. Based on the high-frequency components of voltage and current at the wind farm side and DC side protection installation point of the transmission line at each sampling point, obtain the first-mode high-frequency voltage and current at the corresponding sampling point at the wind farm side and DC side protection installation point of the transmission line.

[0080] In practice, the 1-mode high-frequency voltage U at the wind farm side protection installation point of the sending line at the k-th sampling point W1 (k) Mode 1 high-frequency current I W1 (k) are respectively represented as:

[0081]

[0082]

[0083] In the formula, U WA (k), U WB (k), U WC (k) represent the high-frequency components of the A, B, and C phase voltages at the wind farm side protection installation point of the k-th sampling point, respectively; I WAY (k), I WBY (k), I WCY (k) represent the high-frequency components of the A, B, and C phase currents at the wind farm side protection installation point of the sending line at the kth sampling point.

[0084] In practical implementation, the 1-mode high-frequency voltage U at the DC side protection installation point of the sending line at the k-th sampling point R1 (k) Mode 1 high-frequency current I R1 (k) are respectively represented as:

[0085]

[0086]

[0087] In the formula, U RA (k), U RB (k), U RC (k) represent the high-frequency components of the A, B, and C phase voltages at the DC side protection installation point of the sending line at the k-th sampling point; I RA (k), I RB (k), I RC (k) represent the high-frequency components of the A, B, and C phase currents at the DC side protection installation point of the sending line at the kth sampling point.

[0088] S22. Based on the 1-mode high-frequency voltage and current at the protection installation points on the wind farm side and DC side of the transmission line at all sampling points within half a cycle after the fault, the 1-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained.

[0089] In specific implementation, the mode 1 high-frequency impedance variance V on the wind farm side of the transmission line w , is represented as:

[0090]

[0091] In the formula, Z w1 N represents the 1-mode high-frequency impedance on the wind farm side of the transmitting line; T This represents the total number of sampling points within one sampling period after the fault.

[0092] In specific implementation, the variance V of the first-mode high-frequency impedance on the DC side of the transmitting line is... r , is represented as:

[0093]

[0094] In the formula, Z l1 This indicates the impedance of the mode 1 high-frequency line of the transmitting line;

[0095] Specifically, the 1-mode high-frequency impedance Z on the wind farm side of the transmitting line w1 , is represented as:

[0096] Z w1 =(jωL r +Z pmsg1 / / ... / / Z pmsgi / / ... / / Z pmsgN (7)

[0097] in,

[0098]

[0099] In the formula, Z pmsgi The first-order high-frequency impedance of the i-th wind turbine on the wind farm side of the transmission line is represented by N; N represents the total number of wind turbines on the wind farm side of the transmission line; ω represents the angular frequency; L r This represents the inductance of the wind farm's main transformer referred to the Y-connected side; k w Indicates the turns ratio of the main transformer in the wind farm; R 1i L 1i R represents the converter-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line, respectively; 2i L 2i R represents the grid-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line, respectively; 3i C 1i Let represent the filter damping resistance and capacitance of the i-th wind turbine on the wind farm side of the transmission line, respectively.

[0100] Specifically, the 1-mode high-frequency line impedance Z of the transmitting line l1 , is represented as:

[0101] Z l1 =Z l11 +Z l12 (8)

[0102] in,

[0103] Z l11 =R l11 +jωL l11 ,

[0104] Z l12 =R l12 +jωL l12 ,

[0105] In the formula, Z l11 Z l12 R represents the Mode 1 high-frequency line impedance on the wind farm side and the DC side of the transmitting line, respectively; l11 L l11 These are the equivalent resistance and inductance on the wind farm side of the transmission line, respectively; R l12 L l12 These are the equivalent resistance and inductance on the DC side of the transmitting line, respectively.

[0106] S3. Based on the variance of the 1-mode high-frequency impedance and the fault identification criteria on the wind farm side and the DC side, determine the fault type of the transmission line. If the fault type is a fault within the transmission line area, the protection trips to achieve transmission line protection.

[0107] In implementation, the fault identification criteria include:

[0108] If the variance of the first-mode high-frequency impedance on the wind farm side of the transmission line is not greater than the threshold value of the first-mode high-frequency impedance variance on the wind farm side, and the variance of the first-mode high-frequency impedance on the DC side of the transmission line is greater than the threshold value of the first-mode high-frequency impedance variance on the DC side, then it is determined that the transmission line has an internal fault.

[0109] If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an out-of-area fault has occurred on the wind farm side of the transmission line.

[0110] If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is not greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an external fault has occurred on the DC side of the transmission line.

[0111] In specific implementation, the threshold value of the 1-mode high-frequency impedance variance on both the wind farm side and the DC side of the transmission line is set to 50.

[0112] In practice, the method of this embodiment also includes:

[0113] S4. If the fault type is an outgoing line fault, the protection will not operate.

[0114] In this embodiment, based on the harmonic characteristics of the wind turbine, the characteristic harmonic of the turbine is 6h±1, and the higher the harmonic order, the lower the harmonic content. Considering all factors, this embodiment selects the 11th harmonic order, i.e., h is 2. At this time, the selected high-frequency component is the component of the 11th harmonic.

[0115] It should be noted that the protection method for the power grid transmission line at the source of new energy in this embodiment is derived based on the following derivation:

[0116] First, the topology of the grid-side converter of the wind farm directly driven by the power grid at the source of new energy is analyzed to obtain a 1-mode high-frequency model of the wind farm side of the transmission line.

[0117] Specifically, Figure 2 Wiring diagram for the power grid transmission system of new energy sources. Figure 3 for Figure 2 The diagram shows the structure of the grid-side converter for the i-th direct-drive wind turbine on the wind farm side of the transmission line, where i ranges from 1 to N, and N represents the total number of direct-drive wind turbines on the wind farm side of the transmission line. This embodiment uses vector analysis in the frequency domain, where C... di R is the DC capacitor of the i-th wind turbine on the wind farm side of the transmission line; 1i and L 1i The converter-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line; R 2i and L 2i The grid-side resistance and inductance of the i-th wind turbine on the wind farm side of the transmission line; C 1i R is the filter capacitor for the i-th wind turbine on the wind farm side of the transmission line; 3i The damping resistance of the filter for the i-th wind turbine on the wind farm side of the transmission line; I agi I bgi I cgi Let I be the three-phase current flowing from the grid-side converter of the i-th wind turbine; ahi I bhi I chi Let I be the three-phase current flowing through the damping resistor and filter capacitor of the i-th fan; awi I bwi I cwi U is the three-phase current flowing into the secondary side of the main converter from the i-th wind turbine; ai U bi U ci U represents the three-phase voltage to ground of the LCL filter of the i-th wind turbine; awd U bwd U cwd U is the three-phase voltage on the secondary side of the main transformer in the wind farm. di Let be the voltage across the DC capacitor of the i-th fan.

[0118] The grid-side converter for direct-drive wind turbines is a three-phase voltage-source PWM inverter. During normal operation, adjacent IGBTs are turned on with a 60° phase difference. Each IGBT conducts for 180° of electrical angle (half a cycle), meaning that at any given moment, three adjacent arms are in the conducting state. This results in six possible conduction conditions: Condition 1) Arms 1, 2, and 3 are conducting; Condition 2) Arms 2, 3, and 4 are conducting; Condition 3) Arms 3, 4, and 5 are conducting; Condition 4) Arms 4, 5, and 6 are conducting; Condition 5) Arms 5, 6, and 1 are conducting; and Condition 6) Arms 6, 1, and 2 are conducting. When a fault occurs in the transmission line, the conduction conditions of the IGBTs and diodes are determined by the PWM voltage and the three-phase current flowing through the grid-side converter. Since the upper and lower arms connected to the same phase conduct complementaryly, the conduction conditions during a fault are similar to those during normal operation, with three adjacent arms still conducting.

[0119] Taking the conduction of bridge arms 1, 2, and 3 of the grid-side converter as an example, a high-frequency model of the grid-side converter for a direct-drive wind turbine is constructed. Figure 2 It can be seen that the relationship between the three-phase voltage and current of the grid-side converter at this time is:

[0120]

[0121]

[0122]

[0123] in,

[0124] In the formula, U 0i Let ω be the voltage between the negative terminal of the grid-side converter of the i-th wind turbine and ground, and let ω represent the angular frequency.

[0125] When the direct-drive wind turbine is in the other three adjacent arm positions, its three-phase voltage and current relationship has a similar form.

[0126] Depend on Figure 2 It can be seen that the three-phase current flowing into the secondary side of the main transformer of the direct-drive wind farm is:

[0127]

[0128] Since the main transformer of the wind farm has a Ynd11 wiring structure, the three-phase voltage and current on both sides of the transformer satisfy the following relationship:

[0129]

[0130]

[0131] The three-phase voltage at the wind farm side protection installation point of the transmission line is:

[0132]

[0133] In the formula, k w For the main transformer ratio of the wind farm, U awd U bwd U cwd U is the three-phase voltage on the delta-connected side of the wind farm's main transformer. AWY U BWY U CWY I represents the three-phase voltage on the Y-connected side of the main transformer in the wind farm. WAY I WBY I WCY L represents the three-phase current flowing through the Y-connected side of the main transformer in the wind farm. r This is the inductance of the main transformer of the wind farm, referred to the Y-connected side.

[0134] According to fault analysis theory, a three-phase circuit can be decoupled into three modules for analysis, and the calculation formula is as follows:

[0135]

[0136] In the formula, F a F b F c F1, F2, and F0 represent the three-phase electrical quantities, respectively, and represent the decoupled 1-mode, 2-mode, and 0-mode electrical quantities.

[0137] Substituting the three-phase voltage and current on the wind farm side (W side) of the transmission line into equation (16), we can obtain:

[0138]

[0139]

[0140] Substituting equations (13), (14), and (15) into equations (17) and (18) respectively, we get:

[0141]

[0142]

[0143] Substituting equations (9), (10), and (11) into equations (19) and (10) respectively, we get:

[0144] U W1 =k w (U ai -U ci -3k w 2 (R 2i +jωL 2i )I wi1-jωL r I W1 (twenty one)

[0145]

[0146] k w (U ai -U ci )=k w U di -3k w 2 (R 1i +jωL 1i )I gi1 (twenty three)

[0147] in,

[0148] When the grid-side converter is operating with the other three adjacent bridge arms conducting, following the above derivation process, the 1-mode voltage and current expressions similar to equations (21) to (23) can be derived. The difference is that when the grid-side converter is operating in conditions 2 and 5, k in equation (23) w U di The value becomes 0; when the grid-side converter is in operating condition 3 and operating condition 4, k in equation (23) becomes 0. w U di The value becomes -k w U di When the grid-side converter is in operating condition 6, k in equation (11) w U di The value remains unchanged.

[0149] Depend on Figure 3 Therefore, the frequency domain expression for the voltage across the DC capacitor is:

[0150]

[0151] Among them, I dci (ω) flows into DC capacitor C di The frequency domain signal of the current value; U di (ω) represents the frequency domain signal of the voltage across the DC capacitor; ω represents the angular frequency.

[0152] To support the DC voltage, the DC capacitor C di The parameters are generally set to large values, so when in the high-frequency range, the denominator of equation (24) is very large, and the DC capacitor branch can be regarded as a short circuit. Thus, a 1-mode high-frequency model of the wind power side of the transmission line can be constructed, such as Figure 4 As shown.

[0153] Second, the topology of the DC side of the power grid transmission line at the source of new energy is analyzed to obtain a 1-mode high-frequency model of the DC side of the transmission line.

[0154] Specifically, Figure 5 This is a structural diagram of the DC rectifier-side converter. The location of the Y / Δ connected converter transformer is defined as the D-bridge, and the location of the Y / Y connected converter transformer is defined as the Y-bridge. Wherein, U... A U B U C The three-phase voltage of the converter bus; I ad I bd I cd For the three-phase current of the valve-side winding of the Y / Δ connected converter transformer; I ay I by I cy For the three-phase current of the valve-side winding of the Y / Y connected converter transformer; k yd k yy These represent the turns ratios of the Y / Δ connected converter transformer and the Y / Y connected converter transformer, respectively; L rd L ry These are the inductances of the Y / Δ and Y / Y connected converter transformers referred to the converter bus side, respectively.

[0155] When a fault occurs in the outgoing line, the operating conditions of the D-bridge converter on the DC rectifier side are as follows: Condition 1) VD1 and VD2 are conducting; Condition 2) VD1, VD2, and VD3 are conducting; Condition 3) VD2 and VD3 are conducting; Condition 4) VD2, VD3, and VD4 are conducting; Condition 5) VD3 and VD4 are conducting; Condition 6) VD3, VD4, and VD5 are conducting; Condition 7) VD4 and VD5 are conducting; Condition 8) VD4, VD5, and VD6 are conducting; Condition 9) VD5 and VD6 are conducting; Condition 10) VD5, VD6, and VD1 are conducting; Condition 11) VD6 and VD1 are conducting; Condition 12) VD6, VD1, and VD2 are conducting. The operating conditions of the Y-bridge converter are similar. This paper analyzes the scenario of the D / Y bridge converter under the above-mentioned conduction conditions and constructs a 1-mode high-frequency model of the DC side of the transmission line.

[0156] When the D-bridge converter is in conduction condition 1, i.e., VD1 and VD2 are conducting, the current relationship of the DC rectifier side converter is as follows:

[0157]

[0158] In the formula, I d This refers to the DC current in a high-voltage direct current transmission system.

[0159] When the D-bridge converter is in conduction condition 4, i.e., VD2, VD3, and VD4 are conducting, the voltage and current relationship of the DC rectifier side converter is as follows:

[0160]

[0161] In the formula, U d1 U is the DC voltage at point d1, the common anode of the D-bridge converter. d2 The DC voltage at point d2, where the D-bridge converter and the Y-bridge converter are connected, is... Figure 5 Voltages to ground at points d1 and d2.

[0162] Substituting the three-phase voltage and current of the D-bridge converter on the DC side of the output line, i.e., the R side, into equation (16), we can obtain:

[0163]

[0164]

[0165] In the formula, I Rd1 This refers to the high-frequency current of the DC-side D-bridge converter on the transmission line, in module 1.

[0166] Converting the voltage and current in equations (25) and (26) to the sending line side and substituting them into equations (27) and (28), we can obtain:

[0167]

[0168] U R1 +jωL rd I Rd1 =-k yd (U d1 -U d2 )=h1(U d1 -U d2 (30)

[0169] From equations (29) and (30), we can obtain the 1-mode height model of the D-bridge converter as follows: Figure 6 As shown in (a) and 6(b), when the DC rectifier-side D-bridge converter is in different conduction conditions, it can be equivalent to a controlled current source branch or a controlled voltage source and an inductor series branch. When the D-bridge converter is in the operating condition where other converter valves are turned on, the converter 1-mode high-frequency voltage and current relationship can be obtained according to the above derivation process. The difference is that when the D-bridge converter is in operating conditions 3 and 7, g1 in equation (29) takes the value of 1 / 3; when the D-bridge converter is in operating condition 5, g1 takes the value of 2 / 3; when the D-bridge converter is in operating condition 9, g1 takes the value of -1 / 3; when the D-bridge converter is in operating condition 11, g1 takes the value of -2 / 3; when the D-bridge converter is in operating conditions 2 and 8, h1 in equation (30) takes the value of 0; when the D-bridge converter is in operating condition 6, h1 takes the value of -k ydWhen the D-bridge converter is in operating conditions 10 and 12, h1 takes the value k. yd .

[0170] When the Y-bridge converter is in conduction condition 1, i.e., VY1 and VY2 are conducting, the current relationship of the DC rectifier side converter is as follows:

[0171]

[0172] When the Y-bridge converter is in conduction condition 4, i.e., VY2, VY3, and VY4 are turned on, the voltage and current relationship of the rectifier-side converter is as follows:

[0173]

[0174] Substituting the three-phase voltage and current of the Y-bridge converter on the DC R side of the transmission line into equation (8), we get:

[0175]

[0176]

[0177] In the formula, I Ry1 This is the high-frequency current of the first mode of the Y-bridge converter on the DC side of the transmission line.

[0178] Converting the voltage and current in equations (31) and (32) to the sending line side and substituting them into equations (33) and (34), we can obtain:

[0179] I Ry1 =-I d =g2I d (35)

[0180]

[0181] From equations (35) and (36), we can obtain the first-mode high-frequency model of the Y-bridge converter as follows: Figure 7 As shown in (a) and 7(b), when the DC rectifier-side Y-bridge converter is in different conduction conditions, it can be equivalent to a controlled current source branch or a controlled voltage source and an inductor series branch. When the Y-bridge converter is in the operating condition where other converter valves are turned on, the converter 1-mode high-frequency voltage and current relationship can be obtained according to the above derivation process. The difference is that when the Y-bridge converter is in operating conditions 3 and 9, g2 in equation (35) takes the value of 0; when the Y-bridge converter is in operating conditions 5 and 7, g2 takes the value of 1; when the Y-bridge converter is in operating condition 11, g2 takes the value of -1; when the Y-bridge converter is in operating conditions 2 and 10, h2 in equation (36) takes the value of 1 / 3k. yy When the Y-bridge converter is operating under conditions 4 and 8, h2 is -1 / 3k. yyWhen the Y-bridge converter is operating under condition 6, the value of h2 is -2 / 3k. yy When the Y-bridge converter is operating under condition 12, the value of h2 is 2 / 3k. yy .

[0182] Figure 5 The topology of the AC filter and reactive power compensation device in the middle is as follows: Figure 8 As shown, C2, C3, C4, and C5 are the capacitor parameters of the AC filter, R4, R5, and R6 are the resistor parameters of the AC filter, and L3 and L4 are the inductor parameters of the AC filter.

[0183] Depend on Figure 8 It can be seen that the impedance Z corresponding to the AC filter and reactive power compensation device is... ac Represented as:

[0184]

[0185] The three-phase voltage of the converter bus and the three-phase current flowing through the AC filter satisfy the following relationship:

[0186]

[0187] In the formula, I Afilter I Bfilter I Cfilter This refers to the three-phase current flowing through the AC filter.

[0188] Substituting the three-phase voltage and current of the AC filter into equation (16), we get:

[0189]

[0190]

[0191] In the formula, I filter1 This represents the first-mode high-frequency current of the AC filter.

[0192] Substituting equation (38) into equations (39) and (40), we get:

[0193] U R1 (ω)=Z ac (ω)I filter1 (ω) (41)

[0194] The high-frequency voltage-current relationship of the D / Y bridge converter is transformed into a combination, and combined with equation (41), the following four high-frequency models of the DC side of the transmission line can be obtained. Combination 1: The high-frequency model of the D / Y bridge converter is the high-frequency model of the two converter valves with adjacent serial numbers when they are turned on, such as Figure 9As shown in (a); Combination 2: The D-bridge converter has two adjacent converter valves turned on, and the Y-bridge converter has three adjacent converter valves turned on, forming a 1-mode high-frequency model, as shown in (a). Figure 9 (b) shows the following combination: Combination 3: When the D-bridge converter has three adjacent converter valves turned on, and the Y-bridge converter has two adjacent converter valves turned on, it is a 1-mode high-frequency model, as shown in Figure 3. Figure 9 (c) shows; Combination 4: The D / Y bridge converters are all 1-mode high-frequency models with three converter valves of adjacent serial numbers in operation, such as Figure 9 As shown in (d), since all four of the above-mentioned 1-mode high-frequency models include AC filters, reactive power compensation branches, and controlled current source branches or controlled voltage source and inductor series branches, the difference lies in the different parameters of each equivalent branch. Therefore, a general 1-mode high-frequency model for the DC side of the transmission line can be constructed, such as... Figure 10 As shown.

[0195] Third, construct an additional network when the transmission line fails, derive the mode 1 voltage and current relationship between the wind farm side and DC side of the transmission line under each fault scenario, and then obtain the relationship between the mode 1 high-frequency impedance variance of the wind farm side and DC side of the transmission line and each fault scenario, thereby obtaining the fault identification criteria.

[0196] When a fault occurs in the wind power transmission line within the region, a one-mode high-frequency model of the transmission system under the fault condition can be constructed by combining the one-mode high-frequency impedance models of the wind farm side and the DC side of the transmission line, such as... Figure 11 As shown. Figure 11 In the middle, Z w1 For the 1-mode high-frequency impedance of the wind farm side of the transmission line, Z l11 Z l12 Z represents the 1-mode high-frequency line impedance on the wind farm side and the DC side of the transmitting line, respectively. l11 =R l11 +jωL l11 Z l12 =R l12 +jωL l12 Among them, R l11 L l11 These are the equivalent resistance and inductance on the wind farm side of the transmission line, respectively; R l12 L l12 These are the equivalent resistance and inductance on the DC side of the transmitting line, respectively; R f This is the fault transition resistor.

[0197] Depend on Figure 11 It can be concluded that, under this fault scenario, the mode 1 high-frequency voltage and current on the wind farm side of the transmission line satisfy the following relationship:

[0198]

[0199] Among them, the mode 1 high-frequency impedance Z on the wind field sidew1 The expression is:

[0200] Z w1 =(jωL r +Z pmsg1 / / ... / / Z pmsgi / / ... / / Z pmsgN (43)

[0201] in,

[0202]

[0203] Taking N=2 as an example, in this case,

[0204]

[0205] In the formula, a0, ..., a 11 b0、...、b 10 These are constants calculated based on the parameters of each component.

[0206] According to equation (42), when a fault occurs in the transmission line, a certain equivalent resistance value of the first mode high frequency (the ratio of the first mode high frequency voltage and current) can be obtained from the voltage and current at the wind farm side protection installation point. At this time, the variance of the first mode high frequency impedance formed by the first mode high frequency equivalent resistance value at the wind farm side protection installation point and the first mode high frequency impedance remains basically unchanged, that is, it is 0.

[0207] Depend on Figure 11 Therefore, the 1-mode voltage-current relationship on the DC side of the transmitting line under this fault scenario is as follows:

[0208]

[0209] Since there are controlled voltage sources and controlled current sources, the equivalent resistance value of the first mode high frequency on the DC side of the transmission line calculated by equation (45) cannot be represented by a definite value. At this time, the variance of the first mode high frequency impedance formed by the first mode high frequency impedance and the first mode high frequency line impedance at the DC side protection installation location is theoretically greater than 0.

[0210] When an out-of-area fault occurs on the back side of wind field W in the transmission line, the mode 1 high-frequency model of the transmission system is as follows: Figure 12 As shown.

[0211] Depend on Figure 12 Therefore, the mode 1 high-frequency voltage-current relationship on the wind farm side of the transmission line under this fault scenario is as follows:

[0212]

[0213] The voltage-current relationship of the first-mode high-frequency circuit on the DC side of the transmitting line is as follows:

[0214]

[0215] Since there are controlled voltage sources and controlled current sources, the equivalent resistance values ​​of the first mode high frequency calculated by equations (46) and (47) cannot be represented by a definite value. At this time, the variance of the first mode high frequency impedance formed by the first mode high frequency impedance and the first mode high frequency line impedance at the wind farm side and DC side protection installation location is theoretically greater than 0.

[0216] When an out-of-area fault occurs on the DC R back side of the transmission line, the mode 1 high-frequency model of the transmission system is as follows: Figure 13 As shown.

[0217] Depend on Figure 13 Therefore, the mode 1 voltage-current relationship on the wind farm side of the transmission line under this fault scenario is as follows:

[0218]

[0219] The voltage-current relationship on the DC side of the transmitting line is as follows:

[0220]

[0221] From equations (48) and (49), we can obtain a definite equivalent resistance value of the 1-mode high frequency at both the wind farm side and the DC protection installation point of the transmission line. At this time, the variance of the 1-mode high frequency impedance formed by the equivalent resistance value of the 1-mode high frequency at the wind farm side and the DC protection installation point, the 1-mode high frequency impedance, and the 1-mode high frequency line impedance remains basically unchanged, i.e., it is 0.

[0222] Therefore, in this embodiment, the variance of the first-mode high-frequency impedance, which is composed of the first-mode high-frequency equivalent resistance value calculated using the voltage and current at the protection installation points on the wind farm side and DC side of the line, the first-mode high-frequency impedance, and the first-mode high-frequency line impedance, is expressed as follows:

[0223]

[0224] To ensure the accuracy of the results, this embodiment averages the calculation results from multiple sampling points, thereby guaranteeing a more accurate result. The expression is as follows:

[0225]

[0226] This implementation is based on the matching between the 1-mode high-frequency impedance variance obtained at the protection installation points on the wind farm side and DC side of the transmission line and the fault scenario, and takes into account the influence of factors such as measurement errors. It sets threshold values ​​for the 1-mode high-frequency impedance variance on both the wind farm side and DC side of the transmission line to construct fault identification criteria. Preferably, the threshold values ​​for the 1-mode high-frequency impedance variance on both the wind farm side and DC side of the transmission line are set to 50.

[0227] In practice, the matching between the first-mode high-frequency impedance variance obtained at the wind farm side and DC side protection installation points of the transmission line and the fault scenario is as follows:

[0228] When a fault occurs in the transmission line, the variance of the first-mode high-frequency impedance on the wind farm side of the transmission line is not greater than the threshold value of the first-mode high-frequency impedance variance on the wind farm side, and the variance of the first-mode high-frequency impedance on the DC side of the transmission line is greater than the threshold value of the first-mode high-frequency impedance variance on the DC side.

[0229] When an outgoing line experiences an external fault on the wind farm side, the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the outgoing line is greater than the corresponding first-mode high-frequency impedance variance threshold value.

[0230] When an out-of-area fault occurs on the DC side of the transmission line, the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line shall not exceed the corresponding first-mode high-frequency impedance variance threshold value.

[0231] In practice, the protection criterion is specifically as follows:

[0232] If the variance of the first-mode high-frequency impedance on the wind farm side is not greater than the threshold value of the first-mode high-frequency impedance variance on the wind farm side, and the variance of the first-mode high-frequency impedance on the DC side is greater than the threshold value of the first-mode high-frequency impedance variance on the DC side, then the fault is determined to be a fault within the transmission line area, and the protection trips; otherwise, it is determined to be a fault outside the area, and the protection does not operate.

[0233] Compared with existing technologies, this embodiment provides a protection method for transmission lines of new energy power grids. It collects and processes the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line to obtain the first-mode high-frequency impedance variance on the wind farm side and DC side. Based on fault identification criteria and the first-mode high-frequency impedance variance on the wind farm side and DC side, it determines the fault type. When the fault type is a fault within the transmission line's fault zone, the protection trips. This process, based on the harmonic characteristics of wind turbines, fully utilizes the sensitive characteristics of high-frequency components, enabling rapid and accurate determination of the fault type of the transmission line. It effectively solves the problem that existing protection technologies struggle to identify faults in transmission lines of new energy power grids, thus improving the reliability and stability of the new energy power grid. Through analysis... The topology of the grid-side converter and DC rectifier of the wind farm under different conduction conditions after a fault was constructed. Combined with the transient characteristics of the components in the high-frequency range, a one-mode high-frequency equivalent model of the new energy source-end transmission system was built to avoid the influence of wind farm control strategy on protection. On this basis, according to the matching characteristics of the one-mode high-frequency impedance variance on both sides of the transmission line under different fault scenarios, a protection criterion based on high-frequency impedance variance was constructed, realizing rapid and accurate identification of faults inside and outside the zone. Moreover, the embodiment is not affected by transition resistance, fault location and fault type, has high sensitivity, low sampling frequency and is easy to implement in engineering. Furthermore, it only requires the two ends of the transmission line to transmit the identification results of the fault direction, without exchanging electrical quantity information between the two ends. Fault identification is not affected by synchronization error and has low requirements for communication devices.

[0234] Example 2

[0235] A specific embodiment 2 of the present invention provides a protection system for the power grid transmission line at the source end of a new energy source, such as... Figure 14 As shown, it includes:

[0236] The data acquisition module is used to collect the high-frequency components of voltage and current at the wind farm side and DC side protection installation points of the transmission line after a fault occurs.

[0237] The 1-mode high-frequency impedance variance acquisition module is used to obtain the 1-mode high-frequency impedance variance of the wind farm side and DC side of the transmission line based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line.

[0238] The fault identification and protection start-up module is used to determine the fault type of the transmission line based on the 1-mode high-frequency impedance variance and fault identification criteria on the wind farm side and DC side. If the fault type is a fault within the transmission line area, the protection trips to realize the protection of the transmission line.

[0239] The specific implementation process of this invention can be found in the above method embodiments, and will not be repeated here.

[0240] Since this embodiment shares the same principle as the method embodiments described above, this system also possesses the corresponding technical effects of the method embodiments described above.

[0241] Example 3

[0242] To verify the correctness of embodiments 1 and 2 of the present invention, a specific embodiment 3 of the present invention is constructed as follows. Figure 2 The system simulation model is shown. The main parameters of the new energy source-end power grid transmission system are shown in Table 1, and in this embodiment, the time of fault occurrence is taken as time zero.

[0243] Table 1 Main parameters of the new energy source-end power grid transmission system

[0244]

[0245] Considering the location of the fault and the influence of the transition resistance, the simulation verification is divided into the following four parts.

[0246] Part 1: Simulation Verification Results of Faults with Different Transition Resistances in the Transmission Line Area

[0247] A phase C fault is set at 50% of the WR of the transmitting line, with the transition resistance varying from 0 to 300Ω. In the above fault scenario, the high-frequency voltage and current on both sides of the transmitting line are extracted and substituted into equation (51) to obtain the high-frequency impedance variance V. w and V r ,like Figure 15 As shown in (a) and (b). From Figure 15 (a) It can be seen that as the transition resistance gradually increases, the high-frequency impedance variance V on the W side increases. w There is a trend of first decreasing and then increasing. When a C-phase fault occurs in the transmitting line WR and the transition resistance is 300Ω, at t = 0.02ms, V w Taking the maximum value, 1.6613, is still far less than the threshold value of 50. According to... Figure 15 (b) It can be seen that as the transition resistance gradually increases, the high-frequency impedance variance V on the R side increases. r There is a gradual decreasing trend. When the transition resistance is 250Ω and t = 0.18ms, V r The minimum value is 152.9064, which is greater than the threshold value of 50.

[0248] Based on the above analysis, it can be seen that when a high-resistance fault occurs in the line area, the protection of this invention can operate correctly, regardless of the fault type, and has high sensitivity and rapid identification capability.

[0249] Part Two: Simulation Verification Results of Faults Occurring at Different Locations within the Transmission Line Area

[0250] A phase-to-phase fault (AB) is set at different locations on the transmitting line WR, with a transition resistance of 300Ω. In the above fault scenario, the high-frequency voltage and current on both sides of the transmitting line are extracted and substituted into equation (51) to obtain the high-frequency impedance variance V. w and V r ,like Figure 16 As shown in (a) and (b). From Figure 16 (a) It can be seen that when a fault occurs at different locations on the AC line, the high-frequency impedance variance V on the W side... w It exhibits a certain degree of volatility. When an AB phase-to-phase fault occurs at the WR outlet of the transmitting line, at t = 8.20 ms, V w Taking the maximum value, 0.3033, is much smaller than the threshold value of 50. According to... Figure 16 (b) It can be seen that as the transition resistance gradually increases, the high-frequency impedance variance V on the R side increases. r There is a gradual decreasing trend. When an AB phase-to-phase fault occurs at the WR outlet of the transmitting line, at t = 1.02 ms, V r Taking the minimum value of 1367.4, it is still far greater than the threshold value of 50. In the above fault scenario, the high-frequency impedance variance V w and V r If the criteria for determining a fault within the area are met, it is determined that a fault has occurred within the area of ​​the sending line.

[0251] The simulation results show that the protection criterion proposed in this invention is not affected by the fault location and still has high sensitivity when a high-resistance fault occurs at the end of the line.

[0252] Part Three: Simulation Verification Results of Faults with Different Transition Resistances Occurring on the Wind Farm Side Outside the Transmission Line Area

[0253] A three-phase fault is set on the back side of the wind farm W of the transmission line, with the transition resistance varying from 0 to 300Ω. In the above fault scenario, the high-frequency voltage and current on both sides of the transmission line are extracted and substituted into equation (51) to obtain the high-frequency impedance variance V. w and V r ,like Figure 17 As shown in (a) and (b). From Figure 17 (a) It can be seen that as the transition resistance gradually increases, the high-frequency impedance variance V on the W side increases. w There is a gradually increasing trend. When an A / B phase-to-phase fault occurs in the transmitting line WR and the transition resistance is 100Ω, at t = 8.66ms, V w The minimum value is 307.8844, but it is still greater than the threshold value of 50. According to... Figure 17 (b) It can be seen that when the transition resistance is 50Ω and t=0.02ms, V r Taking the minimum value, 9000.3, which is much larger than the threshold value of 50, in the above fault scenario, the high-frequency impedance variance V... w and Vr The criteria for determining an in-zone fault are not met, therefore it is determined that the fault occurred outside the zone on the sending line.

[0254] As can be seen from the above analysis, when a fault occurs outside the wind farm side of the transmission line through different transition resistors, the method proposed in this invention can accurately identify the occurrence of the fault outside the zone and prevent the protection from malfunctioning.

[0255] Part 4: Simulation Verification Results of Faults Occurring on the DC Side Outside the Transmission Line Area via Different Transition Resistances

[0256] A three-phase fault is set on the back side of the DC R of the transmission line, and the transition resistance varies from 0 to 300Ω. In the above fault scenario, the high-frequency voltage and current on both sides of the transmission line are extracted and substituted into equation (51) to obtain the high-frequency impedance variance V. w and V r ,like Figure 18 As shown in (a) and (b). From Figure 18 (a) It can be seen that as the transition resistance gradually increases, the high-frequency impedance variance V on the W side increases. w There is a gradual decreasing trend. When a three-phase fault occurs in the transmitting line WR and the transition resistance is 0Ω, at t = 2.84ms, V w The maximum value is 8.9098, but this is far less than the threshold of 50. According to... Figure 18 (b) It can be seen that when the transition resistance is 0Ω and t=0.02ms, V r Taking the maximum value, 8.3424, which is much smaller than the threshold value of 50, the high-frequency impedance variance V0 in the above fault scenario is... w and V r The criteria for determining an in-zone fault are not met, therefore it is determined that the fault occurred outside the zone on the sending line.

[0257] As can be seen from the above analysis, when a fault occurs outside the DC side of the transmission line through different transition resistors, the method proposed in this invention can accurately identify the occurrence of the fault outside the zone and prevent the protection from malfunctioning.

[0258] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0259] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for protecting the transmission lines of a new energy source grid, characterized in that, Includes the following steps: After a fault occurs in the transmission line, high-frequency components of voltage and current are collected at the protection installation points on the wind farm side and DC side of the transmission line, respectively. Based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line, the first-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained. Based on the variance of the 1-mode high-frequency impedance and the fault identification criteria on the wind farm side and the DC side, the fault type of the transmission line is determined. If the fault type is a fault within the transmission line area, the protection trips to achieve transmission line protection. The fault identification criteria include: If the variance of the first-mode high-frequency impedance on the wind farm side of the transmission line is not greater than the threshold value of the first-mode high-frequency impedance variance on the wind farm side, and the variance of the first-mode high-frequency impedance on the DC side of the transmission line is greater than the threshold value of the first-mode high-frequency impedance variance on the DC side, then it is determined that the transmission line has an internal fault. If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an out-of-area fault has occurred on the wind farm side of the transmission line. If the variance of the first-mode high-frequency impedance on both the wind farm side and the DC side of the transmission line is not greater than the corresponding first-mode high-frequency impedance variance threshold, then it is determined that an out-of-area fault has occurred on the DC side of the transmission line. The following steps are performed to obtain the 1-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line: Based on the high-frequency components of voltage and current at the wind farm side and DC side protection installation point of the transmission line at each sampling point, the first-mode high-frequency voltage and current at the corresponding sampling point at the wind farm side and DC side protection installation point of the transmission line are obtained. Based on the 1-mode high-frequency voltage and current at the protection installation points on the wind farm side and DC side of the transmission line at all sampling points within half a cycle after the fault, the 1-mode high-frequency impedance variance on the wind farm side and DC side of the transmission line is obtained. No. k The mode high-frequency voltage at the wind farm-side protection installation point of the transmission line at each sampling point. 1-mode high-frequency current They are represented as follows: ； ； In the formula, , , They represent the first k The wind farm side protection installation point of the transmission line at each sampling point A , B , C High-frequency components of phase voltage; , , They represent the first k The wind farm side protection installation point of the transmission line at each sampling point A , B , C High-frequency components of phase current; The mode-1 high-frequency impedance variance of the wind farm side of the transmission line , represented as: ； In the formula, This represents the 1-mode high-frequency impedance on the wind farm side of the transmitting line; This represents the total number of sampling points within one sampling period after the fault occurs. No. k The mode high-frequency voltage at the DC side protection installation point of the transmission line at each sampling point. 1-mode high-frequency current They are represented as follows: ； ； In the formula, , , They represent the first k The DC side protection installation point of the transmission line at each sampling point A , B , C High-frequency components of phase voltage; , , They represent the first k The DC side protection installation point of the transmission line at each sampling point A , B , C High-frequency components of phase current; The mode-1 high-frequency impedance variance on the DC side of the transmitting line , represented as: ； In the formula, This indicates the impedance of the mode 1 high-frequency line of the transmitting line.

2. The method for protecting the power transmission line of a new energy source-end grid according to claim 1, characterized in that, The 1-mode high-frequency impedance of the wind farm side of the transmission line , represented as: ； in, ； ； In the formula, Indicates the first wind farm side of the transmission line i The 1-mode high-frequency impedance of a typhoon generator; N Indicates the total number of wind turbines on the wind farm side of the transmission line; Indicates angular frequency; This represents the inductance of the wind farm's main transformer referred to the Y-connected side; Indicates the turns ratio of the main transformer in the wind farm; , These represent the wind farm side of the transmission line, respectively. i The inverter-side resistance and inductance of the typhoon generator; , These represent the wind farm side of the transmission line, respectively. i The grid-side resistance and inductance of a typhoon generator; , These represent the wind farm side of the transmission line, respectively. i The damping resistor and capacitor of the typhoon generator's filter.

3. The method for protecting the power transmission line of a new energy source-end grid according to claim 2, characterized in that, The 1-mode high-frequency line impedance of the transmitting line , represented as: ； in, ， ， In the formula, , These represent the 1-mode high-frequency line impedances on the wind farm side and the DC side of the transmitting line, respectively. , These are the equivalent resistance and inductance on the wind farm side of the transmission line, respectively; , These are the equivalent resistance and inductance on the DC side of the transmitting line, respectively.

4. The method for protecting the power transmission line of a new energy source-end grid according to claim 1, characterized in that, Also includes: If the fault type is an outgoing line fault, the protection will not operate.

5. The method for protecting the power transmission line of a new energy source-end grid according to claim 1, characterized in that, The threshold values ​​for the 1-mode high-frequency impedance variance on both the wind farm side and the DC side of the transmission line are set to 50.

6. A new energy source-end power grid transmission line protection system based on the new energy source-end power grid transmission line protection method according to any one of claims 1-5, characterized in that, include: The data acquisition module is used to collect the high-frequency components of voltage and current at the wind farm side and DC side protection installation points of the transmission line after a fault occurs. The 1-mode high-frequency impedance variance acquisition module is used to obtain the 1-mode high-frequency impedance variance of the wind farm side and DC side of the transmission line based on the high-frequency components of voltage and current at the protection installation points on the wind farm side and DC side of the transmission line. The fault identification and protection start-up module is used to determine the fault type of the transmission line based on the 1-mode high-frequency impedance variance and fault identification criteria on the wind farm side and DC side. If the fault type is a fault within the transmission line area, the protection trips to realize the protection of the transmission line.

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