Distance protection method and device for phase-to-phase short-circuit fault of collection line in offshore wind farm

Abstract

The present application discloses a distance protection method and device for phase-to-phase short-circuit faults of a collection line in an offshore wind farm. The method includes: judging the fault type on the collection line of the offshore wind farm. If the fault type is a phase-to-phase short-circuit fault, calculating the original measured impedance and the phase angle of the additional impedance respectively by using the electrical quantity information measured at the protection installation location; correcting the original measured impedance according to a correction algorithm to obtain the corrected measured impedance; judging whether the calculated value of the corrected measured impedance satisfies the protection action criterion continuously for 5 ms. If it satisfies the protection action criterion continuously for 5 ms, sending a tripping signal to the circuit breaker. By utilizing the mechanism of the controlled negative sequence current on the fan side, the phase angle of the additional impedance is accurately obtained by using the local current on the flexible DC side of the collection line without relying on communication, and then the corrected measured impedance is obtained, excluding the influence of the transition resistance on the protection. The reliable detection of the phase-to-phase short-circuit fault of the collection line in the offshore wind farm is realized.

Description

Technical Field

[0001] The present application relates to the field of power grid control and protection, and particularly to a distance protection method and device for phase - to - phase short - circuit faults of the AC collection line in an offshore wind farm. Background Art

[0002] With the large - scale development of offshore wind power, the offshore distance of wind farms is gradually increasing, and long - distance offshore wind power will become a hot spot for future development. Due to its numerous advantages, the flexible DC transmission technology has become the preferred solution for grid connection of far - sea offshore wind power and an important boost to offshore wind power development. For the AC collection line connecting a far - sea wind farm to a flexible DC system, since both sides are power electronic devices, the controlled - power source characteristics presented by the power electronic devices after a fault will greatly affect the fault characteristics of the AC collection line, seriously affecting the performance of traditional protection and endangering the safe and stable operation of the system. Therefore, it is urgent to study a new protection principle for the AC collection line in the offshore wind power grid - connected system via flexible DC to improve the protection level of the AC collection line.

[0003] In the scenario where offshore wind turbines are connected to a 220 kV offshore booster station (transformer on the wind turbine side) through a 35 kV in - field collection system, and then connected to the flexible - DC - side transformer and offshore flexible DC converter station through a 220 kV submarine cable collection line, and connected to the receiving - end power grid through a flexible DC transmission line and subsequent converters. In this scenario, human and natural activities may cause damage to the outer sheath and steel armor of the submarine cable, resulting in faults in the collection line. Due to the relatively short phase - to - phase distance of the submarine cable and the harsh fault environment of the submarine cable, phase - to - phase short - circuit faults may occur. Distance protection does not rely on communication, and improving its ability to detect and remove phase - to - phase short - circuit faults is of great significance for ensuring the normal operation of other non - fault areas of the offshore wind farm and improving the safe and stable operation ability of the offshore wind farm.

[0004] Currently, traditional distance protection can correctly reflect the impedance and distance from the short - circuit fault point to the protection installation location during a metallic phase - to - phase short - circuit fault. However, during a phase - to - phase short - circuit fault through a transition resistance, affected by the transition resistance, limited current amplitude, and phase - controlled characteristics, the measured impedance calculated by the impedance relay of traditional distance protection will have a large error compared with the actual value, resulting in the inability of traditional distance protection to operate correctly. Therefore, how to reliably detect phase - to - phase short - circuit faults in the AC collection line of an offshore wind farm has become a technical problem that urgently needs to be solved. Summary of the Invention

[0005] In view of this, the present application provides a distance protection method and device for phase - to - phase short - circuit faults of a collection line in an offshore wind farm. The main purpose is to utilize the mechanism of controlled negative - sequence current on the fan side to accurately obtain the phase angle of the additional impedance by using the local current on the VSC side of the collection line without relying on communication, and then obtain the corrected measurement impedance, excluding the influence of the transition resistance on the protection, thereby realizing reliable detection of phase - to - phase short - circuit faults of the collection line in the offshore wind farm. It solves the problem that when a phase - to - phase short - circuit fault occurs through a transition resistance, due to the influence of the transition resistance, limited current amplitude, and controlled phase characteristics, the measurement impedance calculated by the impedance relay of the traditional distance protection will have a large error compared with the actual value, resulting in the inability of the traditional distance protection to operate correctly.

[0006] According to one aspect of the present application, there is provided a distance protection method for phase - to - phase short - circuit faults of a collection line in an offshore wind farm, the method comprising:

[0007] Judging the fault type on the collection line of the offshore wind farm. If the fault type is a phase - to - phase short - circuit fault, calculating the original measurement impedance and the phase angle of the additional impedance respectively by using the electrical quantity information measured at the protection installation location;

[0008] Correcting the original measurement impedance according to a correction algorithm to obtain the corrected measurement impedance;

[0009] Judging whether the calculated value of the corrected measurement impedance satisfies the protection action criterion continuously for 5 ms. If it satisfies the protection action criterion continuously for 5 ms, sending a tripping signal to the circuit breaker.

[0010] Optionally, the judging the fault type on the collection line of the offshore wind farm. If the fault type is a phase - to - phase short - circuit fault, calculating the original measurement impedance and the phase angle of the additional impedance respectively by using the electrical quantity information measured at the protection installation location includes:

[0011] In the case of a BC - phase metallic phase - to - phase short - circuit fault occurring at point f on the collection line of the offshore wind farm, obtaining the electrical quantity information at the protection installation location;

[0012] Based on the electrical quantity information, calculating the original measurement impedance Z by using a distance protection algorithm BC ;

[0013] According to the electrical quantity information, calculating the sound - phase current on the fan side, the fault - phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence. Among them, the formula for calculating the sound - phase current on the fan side is: I WD-A =-I MMC-A where I MMC-A represents the sound - phase A - phase current on the VSC side;

[0014] The formula for calculating the fault - phase current on the fan side is Among them, represents the phase difference between phase A and phase B currents;

[0015] The calculation formula for the additional impedance is: Among them, Z ADD represents the additional impedance, I f represents the short-circuit current of phase BC at point f, R a represents the transition resistance, I MMC-B represents the current of phase B on the VSC side, I MMC-C represents the current of phase C on the VSC side, I WD-B represents the current of phase B on the wind farm side;

[0016] The calculation formula for the phase angle of the additional impedance is:

[0017]

[0018] Among them, represents the phase angle of the additional impedance.

[0019] Optionally, correcting the original measured impedance according to the correction algorithm to obtain the corrected measured impedance includes:

[0020] Based on the original measured impedance and the phase angle of the additional impedance, correcting the original measured impedance using the sine theorem to obtain the corrected measured impedance, and the correction expression of the corrected measured impedance is:

[0021] Among them

[0022] Among them, Z′ BC represents the corrected measured impedance, |Z BC | represents the absolute value of the original measured impedance, represents the line impedance angle, represents the original measured impedance angle.

[0023] Optionally, determining whether the calculated value of the corrected measured impedance satisfies the protection action criterion continuously for 5 ms. If it satisfies the protection action criterion continuously for 5 ms, sending a trip signal to the circuit breaker includes:

[0024] Obtaining the protection setting value, where the protection setting value is set to 80% of the full-line impedance;

[0025] According to the corrected measured impedance and the protection setting value, determining the protection action judgment basis, and the expression of the protection action judgment basis is: 90° ≤ arg(Z′ BC , Z′ BC - Z set ) ≤ 270°, where Zset Indicates the set protection value;

[0026] Determine whether the calculated value of the corrected measured impedance satisfies 90° ≤ arg(Z′ BC , Z′ BC -Z set ) ≤ 270°. If it is satisfied, determine that the phase-to-phase short-circuit fault is a fault within the protection area, and send a trip signal to the circuit breaker.

[0027] Optionally, determining whether the calculated value of the corrected measured impedance satisfies 90° ≤ arg(Z′ BC , Z′ BC -Z set ) ≤ 270° includes:

[0028] If the calculated value of the corrected measured impedance does not satisfy 90° ≤ arg(Z′ BC , Z′ BC -Z set ) ≤ 270°, the protection determines that it is a fault outside the protection area and returns.

[0029] Optionally, before determining the fault type, if the fault type is a phase-to-phase short-circuit fault and before calculating the original measured impedance and the phase angle of the additional impedance using the electrical quantity information measured at the protection installation location, the method further includes:

[0030] Real-time collect and measure the voltage value and current value at the protection installation location on the flexible DC side;

[0031] Determine whether it meets the protection startup criterion. If it meets the protection startup criterion, the protection starts.

[0032] According to another aspect of the present application, a distance protection device for phase-to-phase short-circuit faults in a collection line of an offshore wind farm is provided. The device includes:

[0033] A judgment module for judging the fault type on the collection line of the offshore wind farm. If the fault type is a phase-to-phase short-circuit fault, calculate the original measured impedance and the phase angle of the additional impedance respectively using the electrical quantity information measured at the protection installation location;

[0034] A correction module for correcting the original measured impedance according to a correction algorithm to obtain a corrected measured impedance;

[0035] A sending module for judging whether the calculated value of the corrected measured impedance continuously satisfies the protection action criterion for 5 ms. If it continuously satisfies the protection action criterion for 5 ms, send a trip signal to the circuit breaker.

[0036] Optionally, the judgment module is further used for:

[0037] Under the condition of a BC-phase metallic interphase short-circuit fault occurring at point f on the collection line of an offshore wind farm, obtain the electrical quantity information at the protection installation location;

[0038] Based on the electrical quantity information, use the distance protection algorithm to calculate the original measured impedance Z BC ;

[0039] According to the electrical quantity information, calculate the healthy-phase current on the fan side, the fault-phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence. Among them, the calculation formula for the healthy-phase current on the fan side is: I WD-A =-I MMC-A , where I MMC-A represents the healthy-phase A-phase current on the VSC side;

[0040] The calculation formula for the fault-phase current on the fan side is Where, represents the phase difference between the A and B phase currents;

[0041] The calculation formula for the additional impedance is: Where, Z ADD represents the additional impedance, I f represents the BC-phase short-circuit current at point f, R a represents the transition resistance, I MMC-B represents the B-phase current on the VSC side, I MMC-C represents the C-phase current on the VSC side, I WD-B represents the B-phase current on the fan side;

[0042] The calculation formula for the phase angle of the additional impedance is:

[0043]

[0044] Where, represents the phase angle of the additional impedance.

[0045] Optionally, the judgment module is further configured to:

[0046] Based on the original measured impedance and the phase angle of the additional impedance, use the sine theorem to correct the original measured impedance to obtain the corrected measured impedance. The correction expression of the corrected measured impedance is:

[0047] Where

[0048] Where, Z′ BC represents the corrected measured impedance, |Z BC | represents the absolute value of the original measured impedance, represents the line impedance angle, Indicates the original measured impedance angle.

[0049] Optionally, the sending module is further configured to:

[0050] Obtain a protection setting value, where the protection setting value is set to 80% of the full-line impedance;

[0051] According to the corrected measured impedance and the protection setting value, determine the protection action judgment basis, and the expression of the protection action judgment basis is: 90° ≤ arg(Z′ BC ,Z′ BC -Z set ) ≤ 270°, where Z set represents the set protection setting value;

[0052] Judge whether the calculated value of the corrected measured impedance satisfies 90° ≤ arg(Z′ BC ,Z′ BC -Z set ) ≤ 270°. If it is satisfied, judge that the phase-to-phase short-circuit fault is a fault within the protection area, and send a trip signal to the circuit breaker.

[0053] Optionally, the sending module is further configured to:

[0054] If the calculated value of the corrected measured impedance does not satisfy 90° ≤ arg(Z′ BC ,Z′ BC -Z set ) ≤ 270°, then the protection determines that the fault is outside the protection area, and the protection returns.

[0055] Optionally, the device further includes:

[0056] An acquisition module, configured to acquire and measure the voltage value and current value at the installation location of the HVDC side protection in real time;

[0057] A start module, configured to judge whether it meets the protection start criterion. If it meets the protection start criterion, the protection starts.

[0058] According to another aspect of the present application, there is provided a storage medium on which a computer program is stored, and when the program is executed by a processor, the distance protection method for the phase-to-phase short-circuit fault of the offshore wind farm collection line is implemented.

[0059] According to still another aspect of the present application, there is provided a computer device, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the program, the distance protection method for the phase-to-phase short-circuit fault of the offshore wind farm collection line is implemented.

[0060] With the above technical solution, a distance protection method and device for phase-to-phase short-circuit faults of a collection line in an offshore wind farm provided by the present application first determines the fault type on the collection line of the offshore wind farm. If the fault type is a phase-to-phase short-circuit fault, the original measured impedance and the phase angle of the additional impedance are calculated respectively using the electrical quantity information measured at the protection installation location. Secondly, the original measured impedance is corrected according to the correction algorithm to obtain the corrected measured impedance; finally, it is judged whether the calculated value of the corrected measured impedance satisfies the protection action criterion continuously for 5 ms. If it satisfies the protection action criterion continuously for 5 ms, a tripping signal is sent to the circuit breaker. The present application utilizes the mechanism of the controlled negative-sequence current on the fan side to accurately obtain the phase angle of the additional impedance by using the local current on the flexible DC side of the collection line without relying on communication, and then obtain the corrected measured impedance, eliminating the influence of the transition resistance on the protection, thereby realizing the reliable detection of the phase-to-phase short-circuit faults of the collection line in the offshore wind farm. It solves the problem that when a phase-to-phase short-circuit fault occurs through a transition resistance, due to the influence of the transition resistance, the limited current amplitude, and the controlled phase characteristics, the measured impedance calculated by the impedance relay of the traditional distance protection will have a large error compared with the actual value, resulting in the inability of the traditional distance protection to operate correctly.

[0061] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the following specifically lists the specific embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0063] Figure 1 The flowchart showing a distance protection method for phase-to-phase short-circuit faults of a collection line in an offshore wind farm provided by an embodiment of the present application;

[0064] Figure 2 The flowchart showing another distance protection method for phase-to-phase short-circuit faults of a collection line in an offshore wind farm provided by an embodiment of the present application;

[0065] Figure 3 The structural diagram showing an offshore wind power transmission system via a flexible DC provided by an embodiment of the present application;

[0066] Figure 4 The diagram showing the protection impedance relationship provided by an embodiment of the present application;

[0067] Figure 5Shows a schematic diagram of the protection action results when a metallic phase-to-phase short-circuit fault occurs at different positions on the line provided by the embodiment of the present application;

[0068] Figure 6 Shows a schematic diagram of the protection action results when a phase-to-phase short-circuit fault with different transition resistances occurs at the far end (7 km) within the protection zone provided by the embodiment of the present application;

[0069] Figure 7 Shows a schematic diagram of the fault current distribution provided by the embodiment of the present application;

[0070] Figure 8 Shows a schematic structural diagram of a distance protection device for phase-to-phase short-circuit faults on the collection line of an offshore wind farm provided by the embodiment of the present application;

[0071] Figure 9 Shows a schematic structural diagram of a device of a computer device provided by the embodiment of the present application. Detailed implementation manners

[0072] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0073] In this embodiment, a distance protection method for phase-to-phase short-circuit faults on the collection line of an offshore wind farm is provided. As Figure 1 shown, the method includes:

[0074] Step 101: Judge the fault type on the collection line of the offshore wind farm. If the fault type is a phase-to-phase short-circuit fault, calculate the original measured impedance and the additional impedance phase angle respectively by using the electrical quantity information measured at the protection installation location.

[0075] Step 102: Correct the original measured impedance according to the correction algorithm to obtain the corrected measured impedance.

[0076] Step 103: Judge whether the calculated value of the corrected measured impedance satisfies the protection action criterion continuously for 5 ms. If it satisfies the protection action criterion continuously for 5 ms, send a tripping signal to the circuit breaker.

[0077] The distance protection method for phase-to-phase short-circuit faults on the collection line of the offshore wind farm provided by the embodiment of the present application can be applied to the scenario of phase-to-phase short-circuit faults on the collection line of the offshore wind farm. By studying the mechanism of limited fault amplitude and controlled phase, a protection theory that is not affected by the transition resistance is constructed at the principle level, and the influence of the size of the transition resistance on the protection is tested.

[0078] As Figure 3As shown in the figure, when a fault occurs at point f on the collection line of the offshore wind farm, first determine whether the fault at point f is an interphase short-circuit fault. If it is an interphase short-circuit fault, obtain the electrical quantity information measured at the protection installation point M, and use the electrical quantity information measured at the protection installation point M to calculate the original measured impedance and the phase angle of the additional impedance respectively. Secondly, after calculating the original measured impedance and the phase angle of the additional impedance, correct the original measured impedance according to the correction algorithm to obtain the corrected measured impedance. Finally, after obtaining the corrected measured impedance, determine whether the calculated value of the corrected measured impedance satisfies the protection operation criterion continuously for 5 ms. If it satisfies the protection operation criterion continuously for 5 ms, send a trip signal to the circuit breaker.

[0079] By applying the technical solution of this embodiment, the fault type on the collection line of the offshore wind farm is judged. If it is an interphase short-circuit fault, the original measured impedance and the phase angle of the additional impedance are calculated respectively by using the electrical quantity information measured at the protection installation point. And after calculating the original measured impedance and the phase angle of the additional impedance, correct the original measured impedance according to the correction algorithm to obtain the corrected measured impedance. After obtaining the corrected measured impedance, determine whether the calculated value of the corrected measured impedance satisfies the protection operation criterion continuously for 5 ms. If it satisfies the protection operation criterion continuously for 5 ms, send a trip signal to the circuit breaker. This application utilizes the mechanism that the negative-sequence current on the fan side is controlled, realizes accurately obtaining the phase angle of the additional impedance by using the local current on the flexible DC side of the collection line without relying on communication, and then obtains the corrected measured impedance, excluding the influence of the transition resistance on the protection, thereby realizing the reliable detection of the interphase short-circuit fault on the collection line of the offshore wind farm.

[0080] Further, as a refinement and extension of the specific implementation manner of the above embodiment, in order to fully illustrate the specific implementation process of this embodiment, another distance protection method for the interphase short-circuit fault on the collection line of the offshore wind farm is provided, as Figure 2 shown, the method includes:

[0081] Step 201, collect and measure the voltage value and current value at the protection installation point on the flexible DC side in real time.

[0082] In the embodiment of the present application, first as Figure 3 shown, the measuring device located at the protection installation point M on the flexible DC side collects and measures the voltage value and current value at this point. Among them, the measuring devices are a voltage transformer and a current transformer respectively.

[0083] Step 202, determine whether it meets the protection startup criterion. If it meets the protection startup criterion, the protection starts.

[0084] Next, based on the changes in the voltage value and current value at the installation point M of the VSC-HVDC side protection, it is determined whether the protection startup criterion is met. If the protection startup criterion is met, the protection starts; if not, return to step 201.

[0085] Step 203: Determine the fault type on the offshore wind farm collection line.

[0086] Step 204: Based on the electrical quantity information, calculate the original measured impedance Z using the distance protection algorithm. BC 。

[0087] Next, when the fault point on the offshore wind farm collection line is point f, determine the fault type at point f. If the fault type is an interphase short circuit fault, such as a BC interphase short circuit fault, obtain the electrical quantity information measured at the protection installation point M, and based on the electrical quantity information, calculate the original measured impedance Z using the distance protection algorithm. BC If the fault type is not an interphase short circuit fault, return to step 201.

[0088] Step 205: According to the electrical quantity information, calculate the sound-phase current on the fan side, the fault-phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence.

[0089] Next, according to the electrical quantity information at the protection installation point M, first calculate the sound-phase current on the fan side. The calculation formula for the sound-phase current on the fan side is I WD-A =-I MMC-A where I MMC-A represents the sound-phase current of phase A on the VSC-HVDC side. Then, according to the fact that after a fault occurs on the fan side of the collection line, only positive-sequence current is output under the influence of the converter negative-sequence current suppression control strategy, and the output current is three-phase symmetrical, calculate the fault-phase current on the fan side. The calculation formula for the fault-phase current on the fan side is where represents the phase difference between the A and B phase currents.

[0090] Then, calculate the additional impedance. The calculation formula for the additional impedance is:

[0091]

[0092] where Z ADD represents the additional impedance, I f represents the short-circuit current of the BC phase at point f, R a represents the transition resistance, I MMC-B represents the B-phase current on the VSC-HVDC side, I MMC-C represents the C-phase current on the VSC-HVDC side, I WD-B represents the B-phase current on the fan side. The relationship between the fault currents is as Figure 7 shown.

[0093] Next, calculate the additional impedance phase angle. The calculation formula for the additional impedance phase angle is as follows:

[0094]

[0095] where represents the additional impedance phase angle.

[0096] Therefore, based on the characteristic that the negative sequence current on the fan side is suppressed, the fault point current can be obtained by using the local current on the flexible DC side, and then the additional impedance phase angle can be calculated. Without double - end communication, it solves the problem of the decline in the performance of distance protection in the scenario where both ends of the line are inverter - type power supplies, the current amplitude is limited, and the phase is controlled.

[0097] Step 206: Correct the original measured impedance according to the correction algorithm to obtain the corrected measured impedance.

[0098] Next, after obtaining the original measured impedance and the additional impedance phase angle, correct the original measured impedance according to the correction algorithm. Among them, the relationship of each impedance is as Figure 4 shown. The line impedance angle in the figure is determined by the engineering cable selection, that is is a known value, Z L represents the impedance of the collection line. Therefore, applying the sine theorem in the impedance triangle in the figure can obtain the corrected measured impedance. The expression of the corrected measured impedance is:

[0099] where

[0100] where Z′ BC represents the corrected measured impedance, |Z BC | represents the absolute value of the original measured impedance, represents the line impedance angle, represents the original measured impedance angle.

[0101] Therefore, by correcting the influence of the transition resistance on the original measured impedance, the influence of the magnitude of the transition resistance on the protection is excluded in principle.

[0102] As shown in Table 1, when the transition resistance is of different magnitudes, the protection proposed in this application can still operate correctly, while the traditional distance protection scheme cannot operate well under the influence of the transition resistance. Therefore, the protection proposed in this application has good performance in the case of phase - to - phase short - circuit faults passing through the transition resistance.

[0103] Table 1

[0104]

[0105] Step 207: Determine whether the corrected calculated value of the measured impedance satisfies the protection operation criterion for 5 consecutive milliseconds. If it satisfies the protection operation criterion for 5 consecutive milliseconds, send a tripping signal to the circuit breaker.

[0106] Finally, determine whether the corrected calculated value of the measured impedance satisfies the protection operation criterion for 5 consecutive milliseconds. Here, the protection operation criterion means whether the corrected calculated value of the measured impedance is within the operation area for 5 consecutive milliseconds. Here, the adopted operation area is the Mho circle characteristic operation area, and the expression for the action judgment basis is: 90° ≤ arg(Z′ BC ,Z′ BC -Z set ) ≤ 270°, where Z set represents the set protection value, and the protection range is set to 80% of the full line length, that is, Z set = 0.8Z L , where 0.8 is the reliability coefficient.

[0107] It should be noted that the above reliability coefficient 0.8 can be specifically adjusted according to the actual situation.

[0108] If the corrected calculated value of the measured impedance is within the operation area for 5 consecutive milliseconds, it is determined that the BC-phase short-circuit fault is an in-zone fault, and the distance protection operates, that is, send a tripping signal to the circuit breaker to cut off the fault.

[0109] If the corrected calculated value of the measured impedance is not within the operation area for 5 consecutive milliseconds, that is, arg(Z′ BC ,Z′ BC -Z set ) < 90° or arg(Z′ BC ,Z′ BC -Z set ) > 270°, it is determined that the BC-phase short-circuit fault is an out-of-zone fault, and the protection returns, that is, return to Step 201.

[0110] As Figure 5 shown, within the protection area (the full length of the test line is 10 km, and the protection range is 8 km), when a metallic phase-to-phase short-circuit fault occurs at the near end (1 km) and the far end (7 km), the fault can be identified within 30 ms, which can meet the time requirement of the protection, and when there is a fault outside the protection area, the protection does not operate reliably, which can meet the reliability requirement.

[0111] As Figure 6As shown, within the protected area (the total length of the test line is 10 km and the protection range is 8 km), when phase-to-phase short-circuit faults occur through a small transition resistance at the near end (1 km) and the far end (7 km), the protection proposed in this application can identify the faults within 30 ms. In contrast, for traditional protection under the same fault conditions, protection refusal occurred during phase-to-phase faults through a transition resistance at the far end. The proposed protection effectively improves the reliability of the distance protection for offshore wind farms and verifies the reliability of the action criterion in the technical solution.

[0112] By applying the technical solution of this embodiment, the measuring device located at the protection installation point M on the flexible DC side continuously collects and measures the voltage value and current value at this point, and judges whether it meets the protection criterion based on the changes in the measured voltage value and current value. If it meets the protection start criterion, the protection starts and judges the fault type. If the fault type is a phase-to-phase short-circuit fault, the electrical quantity information measured at the protection installation point M is obtained, and the original measured impedance and the phase angle of the additional impedance are calculated respectively using the electrical quantity information measured at the protection installation point M. After obtaining the original measured impedance and the phase angle of the additional impedance, the original measured impedance is corrected using the sine theorem based on the original measured impedance and the phase angle of the additional impedance to obtain the corrected measured impedance. It is judged whether the calculated value of the corrected measured impedance meets the protection action criterion. If it meets, a tripping signal is sent to the circuit breaker; if not, the protection returns. This application utilizes the mechanism that the negative sequence current on the wind turbine side is controlled, and realizes accurately obtaining the phase angle of the additional impedance using the local current on the flexible DC side of the collection line without relying on communication, and then obtaining the corrected measured impedance, eliminating the influence of the transition resistance on the protection. Thus, reliable detection of phase-to-phase short-circuit faults in the collection line of offshore wind farms is achieved. It solves the problem that when a phase-to-phase short-circuit fault occurs through a transition resistance, due to the influence of the transition resistance, the limited current amplitude, and the controlled phase characteristics, the measured impedance calculated by the impedance relay of traditional distance protection will have a large error compared with the actual value, resulting in the inability of traditional distance protection to operate correctly.

[0113] Further, as Figure 1 a specific implementation of the method, the embodiment of this application provides a distance protection device for phase-to-phase short-circuit faults in the collection line of an offshore wind farm, as Figure 8 shown. The device includes:

[0114] A judgment module, used to judge the fault type on the collection line of the offshore wind farm. If the fault type is a phase-to-phase short-circuit fault, the original measured impedance and the phase angle of the additional impedance are calculated respectively using the electrical quantity information measured at the protection installation location;

[0115] A correction module, used to correct the original measured impedance according to the correction algorithm to obtain the corrected measured impedance;

[0116] A sending module, configured to determine whether the calculated value of the corrected measured impedance satisfies a protection operation criterion for 5 consecutive milliseconds. If the protection operation criterion is satisfied for 5 consecutive milliseconds, a tripping signal is sent to the circuit breaker.

[0117] Optionally, the determination module is further configured to:

[0118] In the case of a BC-phase metallic interphase short circuit fault at point f on the collection line of an offshore wind farm, obtain the electrical quantity information at the protection installation location;

[0119] Based on the electrical quantity information, use a distance protection algorithm to calculate the original measured impedance Z BC ;

[0120] According to the electrical quantity information, calculate the healthy-phase current on the fan side, the fault-phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence. Among them, the calculation formula for the healthy-phase current on the fan side is: I WD-A =-I MMC-A , where I MMC-A represents the healthy-phase current of phase A on the VSC side;

[0121] The calculation formula for the fault-phase current on the fan side is Among them, represents the phase difference between the A and B phase currents;

[0122] The calculation formula for the additional impedance is: Among them, Z ADD represents the additional impedance, I f represents the BC-phase short-circuit current at point f, R a represents the transition resistance, I MMC-B represents the B-phase current on the VSC side, I MMC-C represents the C-phase current on the VSC side, I WD-B represents the B-phase current on the fan side;

[0123] The calculation formula for the phase angle of the additional impedance is:

[0124]

[0125] Among them, represents the phase angle of the additional impedance.

[0126] Optionally, the determination module is further configured to:

[0127] Based on the original measured impedance and the phase angle of the additional impedance, use the sine theorem to correct the original measured impedance to obtain the corrected measured impedance. The correction expression of the corrected measured impedance is:

[0128]

[0129] Among them, Z′ BC represents the corrected measured impedance, and |Z BC | represents the absolute value of the original measured impedance. represents the line impedance angle, represents the original measured impedance angle.

[0130] Optionally, the sending module is further configured to:

[0131] Obtain a protection setting value, where the protection setting value is set to 80% of the full-line impedance;

[0132] According to the corrected measured impedance and the protection setting value, determine the protection action judgment basis. The expression of the protection action judgment basis is: 90° ≤ arg(Z′ BC , Z′ BC - Z set ) ≤ 270°, where Z set represents the set protection setting value;

[0133] Judge whether the calculated value of the corrected measured impedance satisfies 90° ≤ arg(Z′ BC , Z′ BC - Z set ) ≤ 270°. If it is satisfied, judge that the phase-to-phase short-circuit fault is a fault within the protection area, and send a trip signal to the circuit breaker.

[0134] Optionally, the sending module is further configured to:

[0135] If the calculated value of the corrected measured impedance does not satisfy 90° ≤ arg(Z′ BC , Z′ BC - Z set ) ≤ 270°, then the protection determines that the fault is outside the protection area, and the protection returns.

[0136] Optionally, the device further includes:

[0137] An acquisition module for real-time acquisition and measurement of the voltage value and current value at the installation location of the HVDC side protection; A startup module for judging whether the protection startup criterion is met. If the protection startup criterion is met, the protection starts.

[0138] It should be noted that for other corresponding descriptions of each functional unit involved in the distance protection device for phase-to-phase short-circuit faults in the collection line of an offshore wind farm provided in the embodiments of the present application, reference can be made to Figures 1 to 2 the corresponding description in the method, which will not be elaborated here.

[0139] The embodiments of the present application also provide a computer device, which may specifically be a personal computer, a server, a network device, etc. For example,Figure 9 As shown, the computer device includes a bus, a processor, a memory, and a communication interface, and may further include an input / output interface and a display device. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store location information. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, the steps in the method embodiments are implemented.

[0140] Those skilled in the art can understand that Figure 9 the structure shown in [the figure] is only a block diagram of some structures related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0141] In one embodiment, a computer-readable storage medium is provided. The computer-readable storage medium may be non-volatile or volatile, and stores a computer program. When the computer program is executed by the processor, the steps in the above method embodiments are implemented.

[0142] In one embodiment, a computer program product is provided, including a computer program. When the computer program is executed by the processor, the steps in the above method embodiments are implemented.

[0143] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or fully authorized by all parties.

[0144] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, data processing logics based on quantum computing, etc., without limitation.

[0145] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0146] The above-described embodiments only represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A distance protection method for phase-to-phase short-circuit faults of a collection line in an offshore wind farm, characterized in that, Including: Judge the fault type on the collection line of the offshore wind farm. If the fault type is an interphase short - circuit fault, calculate the original measured impedance and the phase angle of the additional impedance respectively using the electrical quantity information measured at the protection installation location, including: in the case of a metallic interphase short - circuit fault of phase BC occurring at point f on the collection line of the offshore wind farm, obtain the electrical quantity information at the protection installation location; based on the electrical quantity information, calculate the original measured impedance Z using the distance protection algorithm BC ; according to the electrical quantity information, calculate the healthy - phase current on the fan side, the fault - phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence; Calibrating the original measured impedance according to a calibration algorithm to obtain a calibrated measured impedance, including: calibrating the original measured impedance based on the original measured impedance and the additional impedance phase angle by using the sine theorem to obtain the calibrated measured impedance; Judging whether the calculated value of the calibrated measured impedance satisfies the protection operation criterion continuously for 5 ms. If it satisfies the protection operation criterion continuously for 5 ms, sending a tripping signal to the circuit breaker, including: obtaining a protection setting value, where the protection setting value is set to 80% of the full-line impedance; determining the protection operation criterion according to the calibrated measured impedance and the protection setting value; judging whether the calculated value of the calibrated measured impedance satisfies the protection operation criterion. If it satisfies, judging that the phase-to-phase short-circuit fault is a fault within the protection area, and then sending a tripping signal to the circuit breaker.

2. The method according to claim 1, wherein The formula for the sound-phase current on the fan side is: I WD-A =-I MMC-A , where I MMC-A represents the sound-phase current of phase A on the flexible DC side; The calculation formula for the faulty-phase current on the fan side is where represents the phase difference between the currents of phases A and B; The calculation formula for the additional impedance is as follows: where Z ADD represents the additional impedance, I f represents the short-circuit current of phases BC at point f, R a represents the transition resistance, I MMC-B table Show the flexible DC side B-phase current, I MMC-C Show the flexible DC side C-phase current, I WD-B Show the wind turbine side B-phase current; The calculation formula for the additional impedance phase angle is: Among them, represents the additional impedance phase angle.

3. The method according to claim 2, wherein The calibration expression for the calibrated measured impedance is: Among them Among them, Z′ BC represents the corrected measured impedance, |Z BC | represents the absolute value of the original measured impedance, represents the line impedance angle, represents the original measured impedance angle.

4. The method according to claim 1, wherein The protection operation criterion expression is: 90° ≤ arg(Z′ BC ,Z′ BC -Z set ) ≤ 270°, where Z set represents the set protection value, and Z′ BC represents the corrected measured impedance.

5. The method according to claim 4, wherein The judging whether the calculated value of the calibrated measured impedance satisfies the protection operation criterion includes: If the calculated value of the corrected measured impedance does not satisfy 90° ≤ arg(Z′ BC , Z′ BC - Z set ) ≤ 270°, the protection determines that the fault is outside the protection area and the protection returns.

6. The method according to claim 1, wherein Before judging the fault type on the offshore wind farm collection line, if the fault type is a phase-to-phase short-circuit fault, and before calculating the original measured impedance and the additional impedance phase angle respectively by using the electrical quantity information measured at the protection installation location, the method further includes: Real-time collecting and measuring the voltage value and current value at the flexible DC side protection installation location; Judging whether it meets the protection start criterion. If it meets the protection start criterion, the protection starts.

7. A distance protection device for phase-to-phase short-circuit faults of a collection line in an offshore wind farm, characterized in that, The device includes: A judgment module, which is used to judge the fault type on the collection line of the offshore wind farm. If the fault type is an interphase short-circuit fault, the original measured impedance and the phase angle of the additional impedance are calculated respectively by using the electrical quantity information measured at the protection installation location, including: obtaining the electrical quantity information at the protection installation location in the case of a metallic interphase short-circuit fault of phases BC occurring at point f on the collection line of the offshore wind farm; based on the electrical quantity information, calculating the original measured impedance Z by using the distance protection algorithm BC ; according to the electrical quantity information, calculating the sound-phase current on the fan side, the fault-phase current on the fan side, the additional impedance, and the phase angle of the additional impedance in sequence; A calibration module for calibrating the original measured impedance according to a calibration algorithm to obtain a calibrated measured impedance, including: calibrating the original measured impedance based on the original measured impedance and the additional impedance phase angle by using the sine theorem to obtain the calibrated measured impedance; A sending module for judging whether the calculated value of the calibrated measured impedance satisfies the protection operation criterion continuously for 5 ms. If it satisfies the protection operation criterion continuously for 5 ms, sending a tripping signal to the circuit breaker, including: obtaining a protection setting value, where the protection setting value is set to 80% of the full-line impedance; determining the protection operation criterion according to the calibrated measured impedance and the protection setting value; judging whether the calculated value of the calibrated measured impedance satisfies the protection operation criterion. If it satisfies, judging that the phase-to-phase short-circuit fault is a fault within the protection area, and then sending a tripping signal to the circuit breaker.

8. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, the method described in any one of claims 1 to 6 is implemented.

9. A computer device, comprising a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, characterized in that, When the processor executes the computer program, the method described in any one of claims 1 to 6 is implemented.

Images