Distance protection method and system for new energy transmission line

Abstract

The invention discloses a distance protection method and system for a new energy transmission line, and the method comprises the steps: determining a fault direction and a fault type when protection is started; when the fault direction is a positive direction, determining an additional impedance angle based on the fault type; determining actual fault impedance based on the additional impedance angle; determining a fault position based on the fault actual impedance; and performing a protection action based on the fault position. According to the method, the fault position can be effectively identified, the action is protected, and the problem that distance protection is seriously influenced by transition resistance due to the weak feedback characteristic of the new energy in the scene that the new energy is connected to the alternating current power grid is effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of relay protection technology, and more particularly, to a distance protection method and system for a new energy transmission line. Background Art

[0002] Under the "dual carbon" goal, accelerating the replacement of traditional fossil fuels with renewable energy generation and building a new power system with a growing proportion of renewable energy has become a major development direction for China's power system. Photovoltaic power sources and direct-drive wind turbine generator systems will account for a significant share of this share, and these power sources are connected to the grid via full-power inverters. Their large-scale integration into the power system alters the topology and fault characteristics of the fault network. Consequently, these unique fault characteristics can pose a serious threat to the proper operation of distance protection systems.

[0003] Unlike overcurrent protection, distance protection's protection range is largely unaffected by the grid's operating mode, making it widely used on transmission lines. Compared to traditional synchronous generator power sources, renewable energy sources have a maximum fault current of only 1.2 to 1.5 pu. Due to the limited amplitude and controlled phase angle of inverter-type power sources, the system-side current boosting effect is enhanced. Furthermore, the phase angle difference between the system-side and renewable energy sources can be significant and difficult to predict in advance, leading to inaccurate impedance calculations for traditional amplitude-comparison distance protection. Furthermore, since the positive and negative sequence impedances of renewable energy sources vary depending on factors such as operating mode and fault conditions, and renewable energy stations are nonlinear, multi-coupled control systems, their system impedance cannot be constant. Traditional power frequency sudden change distance protection also faces adaptability issues in the context of renewable energy integration.

[0004] Therefore, a distance protection method for renewable energy transmission lines is needed. Summary of the Invention

[0005] The present invention proposes a distance protection method and system for a renewable energy transmission line to solve the problem that distance protection is seriously affected by transition resistance due to the weak feedback characteristics of renewable energy when renewable energy is connected to the AC power grid.

[0006] In order to solve the above problem, according to one aspect of the present invention, a distance protection method for a new energy transmission line is provided, the method comprising:

[0007] When protection is activated, determine the fault direction and fault type;

[0008] When the fault direction is a positive direction, determining an additional impedance angle based on the fault type;

[0009] determining the actual impedance of the fault based on the additional impedance angle;

[0010] determining a fault location based on the actual fault impedance;

[0011] A protection action is performed based on the fault location.

[0012] Preferably, determining the additional impedance angle based on the fault type comprises:

[0013]

[0014] in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle;

[0015] Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistance is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase;

[0016] When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°;

[0017] When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

[0018] Preferably, the method determines the system-side negative sequence current phase angle in the following manner, including:

[0019]

[0020] in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

[0021] Preferably, determining the actual fault impedance based on the additional impedance angle comprises:

[0022]

[0023] Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

[0024] Preferably, determining the fault location based on the actual fault impedance comprises:

[0025]

[0026] Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

[0027] Preferably, performing a protection action based on the fault location includes:

[0028] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated;

[0029] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time;

[0030] Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

[0031] According to another aspect of the present invention, a distance protection system for a new energy transmission line is provided, the system comprising:

[0032] A fault direction and type determination unit, used to determine the fault direction and fault type when the protection is activated;

[0033] an additional impedance angle determining unit, configured to determine an additional impedance angle based on the fault type when the fault direction is a positive direction;

[0034] a fault actual impedance determining unit, configured to determine the fault actual impedance based on the additional impedance angle;

[0035] a fault location determining unit, configured to determine the fault location based on the actual fault impedance;

[0036] A protection action unit is used to perform a protection action based on the fault location.

[0037] Preferably, the additional impedance angle determining unit determines the additional impedance angle based on the fault type, comprising:

[0038]

[0039] in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle;

[0040] Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistance is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase;

[0041] When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°;

[0042] When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

[0043] Preferably, the additional impedance angle determination unit determines the system-side negative sequence current phase angle in the following manner, including:

[0044]

[0045] in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

[0046] Preferably, the fault actual impedance determining unit determines the fault actual impedance based on the additional impedance angle, comprising:

[0047]

[0048] Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

[0049] Preferably, the fault location determining unit determines the fault location based on the actual fault impedance, comprising:

[0050]

[0051] Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

[0052] Preferably, the protection action unit performs a protection action based on the fault location, including:

[0053] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated;

[0054] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time;

[0055] Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

[0056] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, any step of a distance protection method for a new energy transmission line is implemented.

[0057] According to another aspect of the present invention, the present invention provides an electronic device, including:

[0058] The computer-readable storage medium described above; and

[0059] One or more processors are configured to execute the program in the computer-readable storage medium.

[0060] The present invention provides a distance protection method and system for renewable energy transmission lines, comprising: determining the fault direction and type when protection is activated; determining an additional impedance angle based on the fault type when the fault direction is positive; determining the actual fault impedance based on the additional impedance angle; determining the fault location based on the actual fault impedance; and performing a protection action based on the fault location. This method can effectively identify the fault location and initiate protection action, effectively resolving the issue of distance protection being severely affected by transition resistance due to the weak feed characteristics of renewable energy when connected to the AC power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0062] Figure 1 Flowchart of a distance protection method 100 for a new energy transmission line according to an embodiment of the present invention;

[0063] Figure 2 This is a topology diagram of the system sending out power through AC lines of an inverter-type new energy station according to an embodiment of the present invention;

[0064] Figure 3 is an impedance complex plane according to an embodiment of the present invention;

[0065] Figure 4 is a topological diagram of a phase A ground fault according to an embodiment of the present invention;

[0066] Figure 5 2 is a composite sequence network diagram when a phase A ground fault occurs according to an embodiment of the present invention;

[0067] Figure 6 4. A topological diagram of a BC two-phase fault according to an embodiment of the present invention;

[0068] Figure 7 is a composite sequence network diagram when a BC two-phase fault occurs according to an embodiment of the present invention;

[0069] Figure 8 4. A topological diagram of a BC two-phase grounding fault according to an embodiment of the present invention;

[0070] Figure 9 is an equivalent circuit diagram of a negative sequence network according to an embodiment of the present invention;

[0071] Figure 10 A protection calculation flow chart according to an embodiment of the present invention;

[0072] Figure 11 2 is a diagram showing simulation results under a single-phase grounding fault according to an embodiment of the present invention;

[0073] Figure 12 2 is a diagram showing simulation results under a two-phase fault according to an embodiment of the present invention;

[0074] Figure 13 2 is a diagram showing simulation results under a two-phase grounding fault according to an embodiment of the present invention;

[0075] Figure 14 14 is a schematic structural diagram of a distance protection system 1400 for a new energy transmission line according to an embodiment of the present invention. DETAILED DESCRIPTION

[0076] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0077] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0078] To address the issue of distance protection being severely impacted by transition resistance due to the weak feed-back characteristics of renewable energy when connected to the AC grid, this paper establishes an impedance analytical model and derives an analytical expression for the composite sequence network under asymmetric faults. Taking into account the open circuit characteristics of the renewable energy side in the negative-sequence network, the normalized negative-sequence voltage at the measurement point of the protection installation is used to determine the phase of the current flowing into the transition resistance, thereby solving for the additional impedance angle. Furthermore, the present invention uses the law of sines to calculate the additional impedance and, in turn, solve for the fault distance, enabling distance protection.

[0079] Figure 1 FIG. 1 is a flow chart of a distance protection method 100 for a new energy transmission line according to an embodiment of the present invention. Figure 1 As shown, the distance protection method for renewable energy transmission lines provided in an embodiment of the present invention can effectively identify the fault location and initiate protection, effectively resolving the issue of distance protection being severely affected by transition resistance due to the weak feed characteristics of renewable energy when connected to the AC power grid. The distance protection method 100 for renewable energy transmission lines provided in an embodiment of the present invention begins at step 101. In step 101, when protection is initiated, the fault direction and type are determined.

[0080] In step 102, when the fault direction is a positive direction, an additional impedance angle is determined based on the fault type.

[0081] Preferably, determining the additional impedance angle based on the fault type comprises:

[0082]

[0083] in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle;

[0084] Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistance is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase;

[0085] When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°;

[0086] When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

[0087] Preferably, the method determines the system-side negative sequence current phase angle in the following manner, including:

[0088]

[0089] in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

[0090] In step 103, the actual fault impedance is determined based on the additional impedance angle.

[0091] Preferably, determining the actual fault impedance based on the additional impedance angle comprises:

[0092]

[0093] Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

[0094] In step 104 , the fault location is determined based on the actual fault impedance.

[0095] Preferably, determining the fault location based on the actual fault impedance comprises:

[0096]

[0097] Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

[0098] In step 105, a protection action is performed based on the fault location.

[0099] Preferably, performing a protection action based on the fault location includes:

[0100] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated;

[0101] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time;

[0102] Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

[0103] Based on the establishment of an impedance analytical model for distance protection of transmission lines, the present invention proposes a distance protection method for renewable energy transmission lines by solving the additional impedance angles of different fault types and the phase of the negative sequence current on the system side.

[0104] In the present invention, the inverter-type new energy station involved sends the system topology diagram via the AC line as shown in the following figure: Figure 2 shown. Figure 2 M and N represent the station side and system side of the transmission line respectively. and are the measured currents on the new energy side and the system side respectively, These are the measured voltages on the renewable energy side and the system side, respectively. f1 (10%) represents a fault at the transmission line exit, f2 (50%) represents a fault at the midpoint of the transmission line, and f3 (70%) represents a fault at the end of protection section I of the transmission line. f4 (90%) represents a fault outside the transmission line area, and f5 (100%) represents a fault at the end of the transmission line. All inverter-type renewable energy sources, after passing through the collection line, are boosted by the step-up main transformer. The generated power is then transmitted to the AC grid via the AC transmission line.

[0105] exist Figure 2 In the new energy transmission system shown in the figure, if a transition resistance R gThe adaptability of distance protection is analyzed for asymmetric faults. The measured impedance of the impedance relay on the new energy side can be expressed as:

[0106]

[0107] Among them, Z MK is the positive sequence impedance of the line from the new energy side protection installation to the fault point, U M To measure the voltage at the transmission line station, and are the measured currents on the new energy side and the system side respectively, is the current flowing into the transition resistor, Z add is the additional impedance.

[0108] The following is a detailed description of the distance protection method for renewable energy transmission lines.

[0109] (A) Impedance analysis model

[0110] In the present invention, Figure 3 The establishment includes measuring the impedance Z M , real fault impedance Z MK and additional impedance Z add The impedance complex plane. Figure 3 In, φ L is the line positive sequence impedance angle, φ M is the measured impedance angle, that is, the phase angle difference between the measured voltage and the measured current, φ add is the additional impedance angle. Therefore, by Figure 2 The impedance triangle in the figure can be obtained as follows:

[0111]

[0112] In formula (2), φ1 is the real fault impedance Z MK and the measured impedance Z M The angle between the two, φ2 is the additional impedance Z add and the measured impedance Z M The angle between the two, φ3 is the additional impedance Z add and the true fault impedance Z MK That is, according to the sine theorem, the true fault impedance modulus and the measured impedance modulus have the following relationship:

[0113]

[0114] Substituting φ2 and φ3 in formula (2) into formula (3), we can get

[0115]

[0116] From formula (4), we can see that the real impedance Z MKThe modulus of is the quantity to be determined, and the impedance Z is measured. M , measure the impedance angle φ M It can be measured by the protection device, and the line positive sequence impedance angle φ L is a known quantity, then only the additional impedance angle φ add is an unknown quantity. Therefore, we only need to solve the additional impedance angle φ add The real fault impedance reflecting the fault distance can be calculated.

[0117] (B) Calculation of additional impedance angle under different types of faults

[0118] From formula (4), the calculation formula of the additional impedance angle can be obtained as follows:

[0119]

[0120] Among them, the measured current The phase angle can be measured by the measuring element at the protection installation. Solve for the phase angle.

[0121] The following are the currents of different fault types Solve for the phase angle.

[0122] B1) Single-phase ground fault

[0123] Take the A phase grounding fault as an example for analysis. The circuit diagram of the A phase grounding fault on the transmission line is as follows: Figure 4 shown.

[0124] from Figure 4 It can be concluded that when a phase A ground fault occurs, the current flowing into the transition resistor is Figure 4 middle, and The A-phase measured current on the new energy side and the system side, R g is the transition resistance, Z MK is the real fault impedance, Z L is the positive sequence impedance corresponding to the entire length of the transmission line. Figure 4 A composite sequence network diagram can be drawn, such as Figure 5 shown. Figure 5 In, Z M1 , Z M2 , Z M0 They are the positive sequence, negative sequence and zero sequence impedance from the protection installation to the fault point, Z L1 , Z L2 , Z L0 They are the positive sequence, negative sequence and zero sequence impedance of the entire line length, Z T0 is the zero-sequence impedance of the transformer, Z N1 , Z N2 , ZN0 They are the equivalent positive-sequence, negative-sequence, and zero-sequence internal impedances of the AC system respectively.

[0125] From the composite sequence network diagram of phase A ground fault, it can be concluded that:

[0126]

[0127] in, They are respectively the positive sequence, negative sequence and zero sequence components of the measured current of phase A on the new energy side, are the positive sequence, negative sequence and zero sequence components of the measured current of phase A on the system side, They are the positive sequence, negative sequence and zero sequence components of the current flowing into the transition resistor respectively.

[0128] Due to the negative sequence suppression control strategy, is 0, that is, the current flowing into the transition resistor can be simplified as follows:

[0129]

[0130] That is, after taking the phase angle, we can get:

[0131]

[0132] Similarly, for phase B grounding fault and phase C grounding fault, there are:

[0133]

[0134] From equations (8) and (9), it can be concluded that when a single-phase grounding fault occurs, the current flowing into the transition resistance is The phase angle can be equivalent to the negative sequence current phase angle on the system side.

[0135] B2) Two-phase fault

[0136] Take the BC two-phase fault as an example for analysis. The circuit diagram of the BC two-phase fault on the transmission line is as follows: Figure 6 As shown. Figure 6 It can be concluded that when a BC two-phase fault occurs, the current flowing into the transition resistor Rph is

[0137] Similarly, from the composite sequence network of BC two-phase fault Figure 7 It can be concluded that:

[0138]

[0139] Figure 7 Parameters in the composite sequence network of single-phase ground fault Figure 5 The parameters in have the same meaning.

[0140] That is, the current flowing into the transition resistor can be simplified as follows:

[0141]

[0142] Where α = 1∠120°.

[0143] Similar to the analysis of single-phase grounding, the negative sequence current of renewable energy is only provided by the system side. Then:

[0144]

[0145] Similarly, for AB two-phase fault and CA two-phase fault:

[0146]

[0147] From equations (12) and (13), we can see that when a two-phase fault occurs, the current flowing into the transition resistor is The phase angle can be equivalent to the negative sequence current phase angle on the system side plus 90°.

[0148] B3) Two-phase ground fault

[0149] Take the BC two-phase grounding fault as an example for analysis. The topology diagram of the two-phase grounding fault is as follows: Figure 8 The specific process is as follows:

[0150]

[0151]

[0152] Simplifying equations (14) and (15) yields:

[0153]

[0154] Where k = (Z0-Z1) / 3Z1 is the zero sequence compensation coefficient, It is the zero-sequence current measured at the protection installation on the new energy side.

[0155] According to formula (16), the phase angle of the current flowing into the transition resistor can be simplified as:

[0156]

[0157] The zero-sequence current at the protection installation location on the new energy side and the zero-sequence current at the fault point have the following relationship:

[0158]

[0159] Where C0 is the new energy zero-sequence current branch coefficient.

[0160] Since the zero-sequence current branching coefficient in the high-voltage system is approximately constant, the zero-sequence current at the new energy side protection installation and the zero-sequence current at the fault point can be considered to be in the same phase, then:

[0161]

[0162] Similarly, the same applies to the AB two-phase grounding fault and the CA two-phase grounding fault. From formula (19), it can be concluded that when a two-phase grounding fault occurs, the current flowing into the transition resistance is The phase angle can be equivalent to the zero-sequence current phase angle measured at the protection installation on the new energy side.

[0163] In summary, for single-phase and two-phase grounding faults, solving for the system-side negative-sequence current phase yields the current phase flowing into the transition resistor. For two-phase grounding faults, the zero-sequence current phase at the protection installation can be used to equate the current phase flowing into the transition resistor, taking advantage of the system's approximately constant zero-sequence current branching coefficient.

[0164] (C) Solution of negative sequence current phase on the system side

[0165] Depend on Figure 5 and Figure 7 The composite sequence network diagram can be further used to make a negative sequence network equivalent circuit as shown in the following example: Figure 9 shown.

[0166] Since the new energy adopts the control strategy of suppressing negative sequence current, the negative sequence current provided by the new energy is basically zero (e MA2 ≈0), so the negative sequence voltage measured at the protection installation is Equal to the negative sequence voltage at the fault location That is, according to Figure 9 , the negative sequence current on the system side can be calculated as follows:

[0167]

[0168] Taking the phase angle on both sides of the above equation, we can get:

[0169]

[0170] Since the impedance angle of the system's negative sequence impedance is similar to that of the line's negative sequence impedance, we can get ∠Z according to the above formula: L2 =∠Z L2 ≈∠Z N2 At this time, the phase angle of the negative sequence current on the system side can be simplified as:

[0171]

[0172] where ∠Z L2is the line negative-sequence impedance angle. It is worth noting that in the case of non-metallic faults or at different fault locations, differences in the equivalent circuits cause the line negative-sequence impedance angle to vary. This means that the error in the equivalent calculation also varies, leading to a certain error in the negative-sequence current phase solution on the system side.

[0173] (D) Distance protection setting criteria and protection calculation process

[0174] Since the fault distance is equal to the actual calculated impedance modulus |Z MK |Compared to the positive sequence impedance modulus corresponding to the full length of the transmission line, the distance protection setting criterion is:

[0175]

[0176]

[0177] Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

[0178] Combine Figure 10 As shown, the specific process of the distance protection method for renewable energy transmission lines of the present invention is as follows:

[0179] Step 1: When a fault occurs, after the protection is activated, determine the fault direction and type;

[0180] Step 2: If the fault is in the positive direction of the protection, the additional impedance angle is determined according to the fault type; if it is a single-phase grounding fault, the additional impedance angle is calculated according to formulas (8), (9), (22) and (5); if it is a two-phase fault, the additional impedance angle is calculated according to formulas (12), (13), (22) and (5); if it is a two-phase grounding fault, the additional impedance angle is calculated according to formulas (19), (22) and (5);

[0181] Step 3, based on the additional impedance angle, determine the actual fault impedance using formula (4);

[0182] Step 4: Based on the actual fault impedance, determine the fault location α using formula (23) act ;

[0183] Step 5: Perform protection action according to the fault location; if α act Continuously meet 50 points (5kHz sampling rate) are less than or equal to the I section setting value α Iset , α Iset Take 0.8 (80% of the protected line), then the line I section protection will be activated; at the same time, if α actContinuously meet 50 points (5kHz sampling rate) less than or equal to the setting value α of Section II Ⅱset , α Ⅱset If 1.2 (120% of the protected line) is used, the line II protection will be activated after a delay of 300ms. Iset <α Ⅱset , meaning the protection range of line section I is smaller than that of line section II. Therefore, when the fault location meets the criteria for section I, it also meets the criteria for section II. However, the delay for section II's operation is longer than that of section I, so generally section I operates first, and section II returns after section I's protection operates (i.e., section II protection does not operate). If the fault location is outside the protection range of section I but within the protection range of section II, section I protection does not operate, and section II protection operates to clear the fault.

[0184] In an embodiment of the present invention, the following is constructed in PSCAD: Figure 2 The simulation model of the transmission line of the new energy station shown in the figure verifies the effectiveness of the proposed protection principle. The power type is inverter power supply, the station capacity is 200MW, the transmission line voltage level is 220kV, the length of the transmission line is 40km, the model sampling rate is set to 5kHz, and the fault occurrence time is 2s. In this paper, a total of 5 fault points are set in the model, f1 (10%) represents the outlet of the transmission line side, f2 (50%) represents the fault at the midpoint of the transmission line, and f3 (70%) represents the fault at the end of the transmission line protection section I. f4 (90%) represents the fault outside the transmission line area, and f5 (100%) represents the fault at the end of the transmission line.

[0185] Single-phase ground faults (AG) are set at f1 (10%), f2 (50%), f3 (70%), f4 (90%) and f5 (100%) on the transmission line to verify the operation of the proposed protection under ground transition resistance fault. The specific simulation results are shown in the figure below. Figure 11 shown.

[0186] Figure 11 The horizontal axis is time t, and the vertical axis is the impedance per unit value. Figure 11 (a), (b), and (c) are the grounding transition resistance R g The distance protection stage I and stage II action conditions when the resistance is 1Ω, 20Ω, and 100Ω. Figure 11 It can be seen that when single-phase ground short circuit faults occur at different positions of the line, in the presence of transition resistance, Section I and Section II of the proposed protection principle can still operate correctly (when the line is 10%, 50%, and 70% of the total length, the fault position α act Less than the set value α of stage I Ⅰset =0.8, the fault is cleared by the distance protection stage I; when the line is 90% and 100% of the total length, the fault position αact Less than the set value α of stage II Ⅱset =1.2, the fault is removed by the distance protection stage II), and the actual fault distance can be accurately reflected. This is mainly because the proposed principle separates the transition resistance from the actual measured impedance through the sine theorem, eliminating the influence of the transition resistance, so that the actual impedance value measured by the protection is the fault loop impedance value between the measurement point and the fault point. In addition, Figure 11 The simulation results for the 100% fault in (a), (b), and (c) demonstrate that the protection section II covers the entire line length and is unaffected by transition resistance. Therefore, the simulation results show that the proposed protection principle operates correctly under single-phase-to-ground faults, verifying its effectiveness and reliability, and its strong resistance to transition resistance.

[0187] Assume that a BC two-phase fault occurs at f1 (10%), f2 (50%), f3 (70%), f4 (90%) and f5 (100%) on the transmission line, and verify the protection action by using different transition resistances. The specific simulation results are as follows Figure 12 shown. Figure 12 The horizontal axis is time t, and the vertical axis is the impedance per unit value. Figure 12 (a), (b), and (c) are the phase transition resistance R ph The distance protection stage I and stage II action conditions when the resistance is 1Ω, 20Ω, and 100Ω. Figure 12 It can be seen that when two-phase short circuit faults occur at different positions of the line, in the presence of transition resistance, Section I and Section II of the proposed protection principle can still operate correctly (when the line is 10%, 50%, and 70% of the total length, the fault position α act Less than the set value α of stage I Ⅰset =0.8, the fault is cleared by the distance protection stage I; when the line is 90% and 100% of the total length, the fault position α act Less than the set value α of stage II Ⅱset =1.2, the fault is cleared by the distance protection stage II), and can accurately reflect the actual fault distance. In addition, Figure 12 The simulation results for a 100% fault in (a), (b), and (c) demonstrate that the protection section II covers the entire line length and is unaffected by transition resistance. Therefore, the simulation results demonstrate that the proposed protection principle operates correctly under two-phase faults, verifying its effectiveness and reliability, and demonstrating its robustness against transition resistance.

[0188] Assume that a BC two-phase grounding fault occurs at f1 (10%), f2 (50%), f3 (70%), f4 (90%) and f5 (100%) on the transmission line, and verify the protection action by using different transition resistances. The specific simulation results are as follows Figure 13 shown. Figure 13 The horizontal axis is time t, and the vertical axis is the impedance per unit value. Figure 12 (a), (b), and (c) are transition resistances R ph =R pg The distance protection stage I and stage II action conditions when the resistance is 1Ω, 20Ω, and 100Ω. Figure 13 It can be seen that when two-phase grounding faults occur at different positions of the line, in the presence of transition resistance, Section I and Section II of the proposed protection principle can still operate correctly (when the line is 10%, 50%, and 70% of the total length, the fault position α act Less than the set value α of stage I Ⅰset =0.8, the fault is cleared by the distance protection stage I; when the line is 90% and 100% of the total length, the fault position α act Less than the set value α of stage II Ⅱset =1.2, the fault is cleared by the distance protection stage II), and can accurately reflect the actual fault distance. In addition, Figure 13 The simulation results for the 100% fault in (a), (b), and (c) demonstrate that the protection section II covers the entire line length and is unaffected by transition resistance. Therefore, the simulation results show that the proposed protection principle operates correctly under two-phase grounding faults, verifying its effectiveness and reliability, and its strong resistance to transition resistance.

[0189] The key point of the distance protection method for the renewable energy transmission line of the present invention is to first establish an impedance analytical model as the basis, combined with the boundary conditions of the post-sequence network of the asymmetric fault of the AC line, and then use the open circuit property of the renewable energy side in the negative-sequence network to solve the additional impedance phase based on the normalization of the negative-sequence network. On this basis, the sine theorem is used to calculate the fault distance. Finally, a distance protection method is constructed, which can effectively solve the problem that the distance protection in the scenario of renewable energy access to the AC power grid is seriously affected by the transition resistance due to the weak feedback characteristics of renewable energy.

[0190] Figure 14 FIG. 1 is a schematic structural diagram of a distance protection system 1400 for a new energy transmission line according to an embodiment of the present invention. Figure 14 As shown, the distance protection system 1400 for the new energy transmission line provided by the embodiment of the present invention includes: a fault direction and type determination unit 1401, an additional impedance angle determination unit 1402, a fault actual impedance determination unit 1403, a fault location determination unit 1404 and a protection action unit 1405.

[0191] Preferably, the fault direction and type determining unit 1401 is configured to determine the fault direction and fault type when protection is initiated.

[0192] Preferably, the additional impedance angle determining unit 1402 is configured to determine an additional impedance angle based on the fault type when the fault direction is a positive direction.

[0193] Preferably, the additional impedance angle determining unit 1402 determines the additional impedance angle based on the fault type, including:

[0194]

[0195] in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle;

[0196] Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistance is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase;

[0197] When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°;

[0198] When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

[0199] Preferably, the additional impedance angle determining unit 1402 determines the system-side negative sequence current phase angle in the following manner, including:

[0200]

[0201] in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

[0202] Preferably, the fault actual impedance determining unit 1403 is configured to determine the fault actual impedance based on the additional impedance angle.

[0203] Preferably, the fault actual impedance determining unit 1403 determines the fault actual impedance based on the additional impedance angle, including:

[0204]

[0205] Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

[0206] Preferably, the fault location determining unit 1404 is configured to determine the fault location based on the actual fault impedance.

[0207] Preferably, the fault location determining unit 1404 determines the fault location based on the actual fault impedance, including:

[0208]

[0209] Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

[0210] Preferably, the protection action unit 1405 is configured to perform a protection action based on the fault location.

[0211] Preferably, the protection action unit 1405 performs a protection action based on the fault location, including:

[0212] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated;

[0213] If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time;

[0214] Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

[0215] The distance protection system 1400 for a new energy transmission line according to an embodiment of the present invention corresponds to the distance protection method 100 for a new energy transmission line according to another embodiment of the present invention, and will not be described in detail here.

[0216] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, any step of a distance protection method for a new energy transmission line is implemented.

[0217] According to another aspect of the present invention, the present invention provides an electronic device, including:

[0218] The computer-readable storage medium described above; and

[0219] One or more processors are configured to execute the program in the computer-readable storage medium.

[0220] The present invention has been described with reference to a few embodiments. However, it is apparent to those skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the present invention.

[0221] Generally, all terms used in this disclosure are to be interpreted according to their ordinary meaning in the art, unless explicitly defined otherwise herein. All references to "a / the / the [device, component, etc.]" are to be interpreted openly as referring to at least one instance of the device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0222] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0223] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0224] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0225] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0226] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A distance protection method for a new energy transmission line, characterized in that: The method comprises: When protection is activated, determine the fault direction and fault type; When the fault direction is a positive direction, determining an additional impedance angle based on the fault type; determining the actual impedance of the fault based on the additional impedance angle; determining a fault location based on the actual fault impedance; A protection action is performed based on the fault location.

2. The method according to claim 1, characterized in that Determining an additional impedance angle based on the fault type includes: in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle; Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistor is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase; When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°; When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

3. The method according to claim 2, characterized in that The method determines the system-side negative sequence current phase angle in the following manner, including: in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

4. The method according to claim 1, wherein Determining the actual fault impedance based on the additional impedance angle includes: Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

5. The method according to claim 1, wherein Determining a fault location based on the actual fault impedance includes: Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

6. The method according to claim 1, characterized in that Performing a protection action based on the fault location includes: If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated; If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time; Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

7. A distance protection system for a new energy transmission line, characterized in that: The system comprises: A fault direction and type determination unit, used to determine the fault direction and fault type when the protection is activated; an additional impedance angle determining unit, configured to determine an additional impedance angle based on the fault type when the fault direction is a positive direction; a fault actual impedance determining unit, configured to determine the fault actual impedance based on the additional impedance angle; a fault location determining unit, configured to determine the fault location based on the actual fault impedance; A protection action unit is used to perform a protection action based on the fault location.

8. The system according to claim 7, characterized in that The additional impedance angle determining unit determines the additional impedance angle based on the fault type, including: in, is the additional impedance angle; is the current flowing into the transition resistor The phase angle; Current measured at the protection installation The phase angle; Among them, when the fault type is a single-phase grounding fault, the current flowing into the transition resistance is Phase angle Equal to the phase angle of the negative sequence current on the system side of the fault phase; When the fault type is a two-phase fault, the current flowing into the transition resistor Phase angle Equal to the system side negative sequence current phase angle of the non-fault phase plus 90°; When the fault type is a two-phase grounding fault, the current flowing into the transition resistor Phase angle Equal to the zero-sequence current phase angle measured at the protection installation on the new energy side.

9. The system according to claim 8, characterized in that The additional impedance angle determination unit determines the system-side negative sequence current phase angle in the following manner, including: in, Represents phase A, phase B or phase C, for The system side negative sequence current of the phase; Measured to protect the installation Negative sequence voltage of the phase; ∠Z L2 is the line negative sequence impedance angle.

10. The system according to claim 7, wherein: The fault actual impedance determining unit determines the fault actual impedance based on the additional impedance angle, including: Among them, Z MK is the actual fault impedance; is the additional impedance angle; Z M To measure impedance; To measure the impedance angle; is the line positive sequence impedance angle.

11. The system according to claim 7, wherein: The fault location determining unit determines the fault location based on the actual fault impedance, including: Among them, α act is the fault location; |Z MK | is the actual impedance modulus of the fault; |Z L | is the positive sequence impedance modulus corresponding to the entire length of the transmission line.

12. The system according to claim 7, wherein: The protection action unit performs a protection action based on the fault location, including: If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Iset , then the line I section protection is activated; If there are a number of consecutive sampling points corresponding to the fault location that satisfies 0<α act ≤α Ⅱset , then the line II section protection will be activated after the preset delay time; Among them, α act is the fault location; α Iset is the first setting value; α Ⅱset is the second set value.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

14. An electronic device, characterized in that: include: The computer-readable storage medium of claim 13; as well as One or more processors are configured to execute the program in the computer-readable storage medium.

Images