A Method for Identifying and Protecting Single-Phase Ground Fault Types in Wind Farm Collector Lines Based on Dynamic Increment of Injected Current

Abstract

This invention discloses a method for identifying and protecting single-phase grounding faults in wind farm collector lines based on dynamic increments of injected current. When a single-phase grounding fault occurs in a collector line of a wind farm, a suppressing current is injected into the neutral point led out by the grounding transformer to continuously suppress the voltage at the fault point to zero. After a preset time, a fixed component of the injected suppressing current is continuously used to compensate for the zero-sequence unbalanced current, while gradually reducing the changing component of the suppressing current, and simultaneously monitoring the changes in zero-sequence voltage. The type of single-phase grounding fault is determined based on the changes in zero-sequence voltage. If it is determined to be a transient single-phase grounding fault, the injection of suppressing current is stopped. If it is determined to be a permanent single-phase grounding fault, the faulty collector line is then identified and isolated based on the changes in zero-sequence current of each collector line. This invention, by continuously compensating for the zero-sequence unbalanced current, avoids interference from unbalanced voltage on fault type identification, and can effectively achieve sensitive detection and protection against grounding faults.

Description

Technical Field

[0001] This invention relates to the field of single-phase grounding fault identification technology for wind farm collector lines, and particularly to a method for identifying and protecting against single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current. Background Technology

[0002] Wind farms are often built in areas with high wind speeds, such as mountain passes, canyons, and plateaus, resulting in harsh operating environments and frequent single-phase grounding faults. Single-phase grounding faults are diverse. Transient single-phase grounding faults, such as those caused by lightning strikes or bird damage, can generally be extinguished spontaneously by injecting zero-sequence compensation current. However, with the expansion of wind farms and the increase in the proportion of cables in the collector lines, the capacitive current of the collector system increases dramatically, making it difficult for intermittent fault arcs to extinguish naturally. For transient grounding faults, the injection of zero-sequence compensation current should be stopped, and the collector system should be restored to normal operation. For permanent single-phase grounding faults, the faulty line should be quickly isolated to restore the wind farm's collector lines to normal operation.

[0003] Previous ground fault detection methods generally relied on passive detection, that is, after the arc suppression coil is compensated, the fault identification and protection are based on the zero-sequence voltage of the neutral point and the zero-sequence current of the line after compensation. However, the influence of system asymmetry (i.e., system unbalanced current), the degree of compensation of the arc suppression coil, and the transition resistance is not considered, which has certain limitations. It also has the problem of low sensitivity for detecting high-resistance grounding and intermittent grounding faults.

[0004] If the existing technology assumes that the system does not consider the influence of unbalanced current, its fault type determination principle is as follows: If the fault is a transient ground fault and the arc is extinguished, the transient ground fault is eliminated, and the controllable current source is the only excitation. As the injected current decreases, according to the homogeneity theorem, the zero-sequence voltage changes linearly. However, if the fault is a permanent ground fault and the arc is extinguished, the fault has not disappeared. There are two zero-sequence excitation sources: the zero-sequence ground fault branch power source and the controllable current source. When one of these excitation sources, i.e., the controllable current source, is adjusted, according to the homogeneity theorem, the zero-sequence voltage changes non-linearly, which can be used to determine the fault type.

[0005] However, in reality, unbalanced currents due to imbalances in ground parameters exist in both wind farm collector lines and distribution network feeders. Considering the unbalanced current, if the fault is a transient ground fault that is then extinguished, the transient ground fault is eliminated, and the zero-sequence circuit has two excitations: a controllable current source and the unbalanced current. Therefore, by adjusting the injected current, according to the homogeneity theorem, the zero-sequence voltage cannot achieve a linear change, causing the method based on the above fault type judgment principle to fail. Summary of the Invention

[0006] To address the low sensitivity of current single-phase grounding fault identification and protection methods in wind farm collector lines, this invention proposes a method for identifying and protecting single-phase grounding faults in wind farm collector lines based on dynamic increments of zero-sequence current. This method transforms the existing passive identification and protection of grounding faults into an active one, effectively identifying different types of grounding faults, unaffected by system asymmetry, and providing highly reliable and sensitive protection against grounding faults.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] A method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current includes:

[0009] Step 1: When a single-phase ground fault occurs in the collector line of the wind farm, a suppressing current is injected into the neutral point led out by the grounding transformer to continuously suppress the voltage at the fault point to zero.

[0010] Step 2: After injecting the suppression current for a preset time, the zero-sequence unbalanced current is continuously compensated by a fixed component in the injected current, the changing component in the suppression current is gradually reduced, and the change in the zero-sequence voltage is monitored simultaneously.

[0011] Step 3: Based on the monitored changes in zero-sequence voltage, determine whether the single-phase grounding fault is a transient single-phase grounding fault or a permanent single-phase grounding fault;

[0012] Step 4: If the fault is determined to be a transient single-phase ground fault, stop injecting the suppression current; if the fault is determined to be a permanent single-phase ground fault, determine the faulty collector line based on the change in zero-sequence current of each collector line, and isolate the faulty collector line.

[0013] Furthermore, the suppression current injected in step 1 for:

[0014]

[0015] in, To suppress the changing components in the current, To suppress the fixed component in the current, which is also the inherent unbalanced current of the wind farm's power collection system.

[0016] Furthermore, the changing component in the suppression current injected in step 1 for:

[0017]

[0018] in, Y is the positive-sequence circuit equivalent potential of the wind farm, and Y0 is the zero-sequence admittance to ground of the wind farm's collector system.

[0019] Furthermore, the positive sequence circuit equivalent potential of the wind farm The calculation method is as follows: When a single-phase ground fault occurs in the wind farm's collector line, a measurement current signal is pre-injected into the neutral point led out from the wind farm's grounding transformer. Then, the positive sequence circuit equivalent potential of the wind farm is calculated:

[0020]

[0021] in, This refers to the natural offset of the zero-sequence voltage after a fault. This refers to the zero-sequence voltage offset monitored after the injection of the measurement current signal.

[0022] Furthermore, the pre-injected measurement current signal for:

[0023]

[0024] Where α is a proportionality coefficient not greater than 0.15, Take the potential of a certain phase in the primary winding of the grounding transformer. This phase refers to the phase with the lowest collector bus voltage after a single-phase grounding fault occurs.

[0025] Furthermore, the method for determining the type of single-phase ground fault is as follows:

[0026] Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases linearly with the decrease of the variable component in the suppression current, and its slope is equal to the zero-sequence impedance of the wind farm, then it is judged as a transient single-phase grounding fault.

[0027] Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases in a non-linear proportional relationship with the decrease of the variable component in the suppression current, it is judged as a permanent single-phase ground fault.

[0028] Furthermore, the method for determining whether a single-phase grounding fault has occurred in the collector line of a wind farm is as follows: real-time monitoring of the zero-sequence voltage and the change in zero-sequence voltage of the wind farm; when the zero-sequence voltage or the change in zero-sequence voltage exceeds its respective preset threshold, it is determined that a single-phase grounding fault has occurred in the collector line.

[0029] Furthermore, the method for determining the faulty collector line is as follows: if the change in zero-sequence current of a certain collector line is greater than the change in zero-sequence current of the other collector lines, then the collector line is determined to be the faulty collector line.

[0030] Furthermore, zero-sequence current is injected into the neutral point through an electronically controllable current source, the amplitude and phase of which are both controllable.

[0031] Beneficial effects

[0032] To address the failure of existing fault type determination methods when considering system unbalanced current, this invention determines the ground fault type by continuously suppressing the unbalanced current with a fixed component in the compensation current and adjusting the changing component of the suppression current. When the fault is a transient ground fault, the transient ground fault is eliminated. At this time, the zero-sequence circuit has two excitations: a controllable current source and the unbalanced current. After suppressing the unbalanced current with the fixed component in the compensation current, the zero-sequence circuit has only one excitation, namely the changing component of the suppression current. Adjusting the changing component at this time, according to the homogeneity theorem, the zero-sequence voltage changes linearly. When the fault is a permanent ground fault, the unbalanced current is compensated by the fixed component in the suppression current. At this time, the zero-sequence excitation source in the zero-sequence circuit is the controllable current source and the power supply of the ground fault branch. The zero-sequence voltage changes nonlinearly.

[0033] This invention, based on continuously suppressing the unbalanced voltage of the wind farm's power collection system, analyzes the changes in line zero-sequence current and system zero-sequence voltage with injected current, transforming ground fault identification and protection from passive to active identification and protection. It can effectively identify different types of ground faults, is unaffected by system asymmetry, and effectively provide sensitive protection against ground faults. This significantly enhances the fault resistance of large wind farms, reliably ensures the stable transmission of new energy power, and has a very promising future. Attached Figure Description

[0034] Figure 1 This is a diagram of the wind farm topology.

[0035] Figure 2 The positive sequence equivalent circuit of a wind farm

[0036] Figure 3 This is the negative sequence equivalent circuit for a wind farm.

[0037] Figure 4 For the composite sequence network of grounding faults in the collector lines of flexible grounded wind farms;

[0038] Figure 5 Zero-sequence equivalent circuit for multi-collector line systems in wind farms;

[0039] Figure 6 This is a schematic diagram of the fault identification method described in an embodiment of the present invention;

[0040] Figure 7 A topology diagram of a flexible grounded wind farm grounding fault constructed for experimental simulation;

[0041] Figure 8 The present invention simulates the change trend of neutral point voltage in the wind farm collector system under different operating conditions.

[0042] Figure 9 The zero-sequence current of each collector line varies with the injected current under different fault conditions; where (a) is R f Ground fault resistance R f =100Ω, (b) is R f Ground fault resistance R f =500Ω;

[0043] Figure 10 The present invention simulates the voltage variation trend of the neutral point of the distribution network under different operating conditions. Detailed Implementation

[0044] The embodiments of the present invention will be described in detail below. These embodiments are based on the technical solutions of the present invention and provide detailed implementation methods and specific operation processes to further explain the technical solutions of the present invention.

[0045] The basic working principle of this embodiment is as follows: Addressing the technical problem of low sensitivity in the identification and protection of single-phase grounding faults in wind farm collector lines, this invention proposes a method for identifying and protecting single-phase grounding faults in wind farm collector lines based on dynamic increments of injected current. This method involves injecting a suppressing current into the neutral point to continuously suppress the fault voltage to zero. After a certain delay, a fixed component of the injected current continuously compensates for the zero-sequence unbalanced current, gradually reducing the changing component in the suppressing current. The type of single-phase grounding fault is determined based on the change in the system's zero-sequence voltage with the injected current. If it is determined to be a transient single-phase grounding fault, the injection of the suppressing current is stopped. If it is determined to be a permanent single-phase grounding fault, the faulty collector line is identified based on the change in the line's zero-sequence current, and the faulty line is quickly isolated at the protection outlet. This method transforms grounding fault identification and protection from a passive to an active approach. It can effectively identify different types of grounding faults, is unaffected by system asymmetry, and can effectively provide sensitive protection against grounding faults. It is highly reliable and has a promising future.

[0046] (I) Fault Arc Extinction

[0047] The wind farm topology diagram in this embodiment is as follows: Figure 1 As shown in the figure, c0 and g0 are the phase-to-ground capacitance and leakage conductance to ground of each collector line; r L x L R represents the resistance and reactance of each phase of the collector line; α is the ratio of the distance from the collector bus to the fault point to the total length of the line; f For ground fault resistance; Y N This refers to the neutral-to-ground admittance of the wind farm. A controllable current source injects a zero-sequence current with adjustable amplitude and phase into the system through the neutral point N led out by the wind farm's grounding transformer. To achieve flexible control of the zero-sequence voltage of the system.

[0048] according to Figure 1 The wind farm topology diagram shown is used to derive the positive-sequence and negative-sequence equivalent circuits of the wind farm by combining the stator and rotor voltage and flux linkage equations of the DFIG in the dq-axis rotating coordinate system and the rotor-side converter control structure. Figure 2 , Figure 3 As shown in the figure: Z D(1) This represents the positive sequence equivalent impedance of a doubly-fed induction generator (DFIG). Z is a positive-sequence DFIG current source. D(2) The equivalent impedance for the negative sequence of the DFIG is given. Based on the boundary conditions for a single-phase ground fault, the positive and negative sequence equivalent impedances of the wind farm are connected in series with the zero-sequence ground-to-ground branch to obtain the composite sequence network for ground faults in the collector lines of a neutral-point flexible-grounded wind farm, as shown below. Figure 4 As shown in the figure. Z represents the equivalent potential of the positive sequence circuit of the wind farm as seen from the fault point. (1) The equivalent impedance of the positive sequence circuit of the wind farm as seen from the fault point. Given the zero-sequence current at the fault point, the system's zero-sequence admittance to ground is Y0 = Y N +Y 0A +Y 0B +Y 0C The system's inherent zero-sequence current Kirchhoff's current equations were applied to the composite sequence network of grounding faults in a flexible grounded wind farm, and the relationship between the three sequence functions of the wind farm was obtained as shown in equation (1).

[0049]

[0050] Let's assume that the natural offset of the neutral point voltage after the fault is... By injecting zero-sequence current into the neutral point for the first time The change in neutral point voltage offset is By combining the three-sequence function relationships of the wind farm under the two states, the equivalent potential of the positive-sequence circuit can be obtained. The expression:

[0051]

[0052] The neutral point voltage can be further obtained from equation (1). With injected current The relationship is:

[0053]

[0054] The ground fault current is obtained by applying Kirchhoff's voltage equation to the composite sequence network. voltage at the fault point neutral point voltage and the equivalent potential of the positive sequence circuit The relationship is:

[0055]

[0056] From equations (3) and (4), it can be seen that when the injected current... At that time, the neutral point zero-sequence voltage This can make the fault current By injecting current to control the neutral point zero-sequence voltage to equal the equivalent potential of the wind farm's positive-sequence circuit, full compensation of single-phase ground fault current is achieved, reliably eliminating single-phase ground fault arc.

[0057] Therefore, when a single-phase ground fault occurs in a wind farm, a current with adjustable amplitude and phase can be injected into the system through a controllable current source via the neutral point N led out from the wind farm grounding transformer. The fault point voltage is suppressed to zero by the fault point voltage complete suppression method, thereby achieving fault voltage arc extinguishing.

[0058] (II) Fault Type Identification

[0059] Injection suppression current After a certain delay, dynamic identification of the single-phase ground fault type is performed. Assuming the fault has been completely eliminated, the zero-sequence voltage at the neutral point of the system at this time is:

[0060]

[0061] From equation (4), it can be seen that at this time, there exists a zero-sequence loop. and Two zero-sequence excitation sources. Let but That is, by continuously compensating for the zero-sequence unbalanced current with a fixed component in the injected current, the variation component of the injected current can be considered as... This is the only zero-sequence excitation in the circuit. According to the homogeneity theorem, the injected current can be controlled... Make the amplitude of the change component I it The neutral point voltage U gradually decreases. N If the slope decreases linearly and is equal to the zero-sequence impedance of the wind farm, then the fault is identified as a transient grounding fault.

[0062] If the fault arc reignites, the ground fault branch still exists in the zero-sequence equivalent loop. At this time, the zero-sequence loop contains... With two zero-sequence excitations from the fault zero-sequence voltage source, the line zero-sequence current is the sum of the single-phase ground fault ground current and the leakage current to ground. When regulating... make I it When U decreases linearly, N The fault will exhibit a non-linear trend, thus indicating that it is a permanent single-phase ground fault.

[0063] (III) Faulty Circuit Identification

[0064] Zero-sequence equivalent circuit of multi-collector line system in wind farm, such as Figure 5 As shown, there are n collector lines. Let the j-th collector line be the faulty line, and let the negative value of the voltage at the fault point before the fault be...

[0065] Adjusting the injection current Change the neutral point voltage of the system For a faulty collector line, the zero-sequence current... for:

[0066]

[0067] By comparing the natural zero-sequence current of the system after the fault, the change in zero-sequence current of the fault collector line before and after voltage regulation is obtained. for:

[0068]

[0069] Similarly, the zero-sequence current of the non-faulted collector line under the action of the injected current is calculated. With zero-sequence current change expression:

[0070]

[0071]

[0072] Since the zero-sequence impedance to ground of a collector line characterizes the insulation performance of the line, and the value of the zero-sequence impedance to ground is usually much larger than the transition resistance value at the fault point, by comparing equation (6) and equation (8), we have: This means that the change in zero-sequence current in the faulty collector line is much greater than that in the non-faulty collector line. Based on this, by adjusting the amplitude of the injected zero-sequence compensation current, the collector line with the largest change in zero-sequence current is identified as having a single-phase ground fault, and the faulty line should be quickly isolated by the protection outlet.

[0073] (iv) Implementation Method

[0074] Based on the aforementioned principles of flexible arc suppression, fault type judgment, and fault collector line identification, this embodiment provides a method for identifying and protecting single-phase grounding faults in wind farm collector lines based on dynamic increments of zero-sequence current. (Refer to...) Figure 6 Includes the following steps:

[0075] Step 1: When a single-phase ground fault occurs in the collector line of the wind farm, inject zero-sequence compensation current into the neutral point led out by the grounding transformer to continuously suppress the voltage at the fault point to zero.

[0076] In this embodiment, the zero-sequence voltage of the wind farm is first obtained by measuring the neutral point voltage in real time using a voltage transformer. Then, the zero-sequence voltage and its change in real time are monitored. When the zero-sequence voltage or its change in value exceeds its respective preset threshold, it is determined that a single-phase ground fault has occurred in the collector line. The change in zero-sequence voltage refers to the change in the zero-sequence voltage of the previous cycle relative to the zero-sequence voltage of the next cycle.

[0077] When a single-phase ground fault occurs in a collector line of a wind farm, a measurement current signal is injected into the neutral point led out by the wind farm's grounding transformer. In this embodiment, a zero-sequence current can be injected into the neutral point using an electronically controllable current source, the amplitude and phase of which are controllable. The initial injected measurement current signal... for: Take the potential of a certain phase in the primary winding of the grounding transformer. This phase refers to the phase with the lowest collector bus voltage after a single-phase grounding fault occurs.

[0078] After injecting the measurement current signal, the equivalent potential of the positive sequence circuit of the wind farm is calculated, and then the suppression current value that can make the fault point voltage zero is calculated. The formula for calculating the equivalent potential of the positive sequence circuit of the wind farm is as follows:

[0079]

[0080] in, This represents the equivalent potential of the positive sequence circuit of the wind farm. This refers to the inherent zero-sequence current of the wind farm's collector system. This refers to the natural offset of the zero-sequence voltage after a fault. To inject measurement current signal The zero-sequence voltage offset, Y0, is the zero-sequence admittance to ground of the wind farm's collector system. Since the influence of the neutral point unbalanced voltage caused by the asymmetry of the three-phase ground parameters is considered, the equivalent potential of the positive-sequence circuit can be accurately calculated.

[0081] After obtaining the equivalent potential of the positive-sequence circuit, it can be used to calculate the zero-sequence current that makes the fault current zero.

[0082]

[0083] Step 2: Inject zero-sequence current into the neutral point The preset duration is then used to gradually reduce the changing component in the injected zero-sequence compensation current, while simultaneously monitoring the changes in the zero-sequence voltage.

[0084] Injected current In This is the inherent unbalanced current of the wind farm's collector system, which is a fixed component; the rest... This refers to the changing component in the injected current.

[0085] Step 3: Based on the monitored zero-sequence voltage changes, determine the type of single-phase ground fault:

[0086] Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases linearly with the decrease of the variable component in the suppression current, and its slope is equal to the zero-sequence impedance of the wind farm, then it is judged as a transient single-phase grounding fault.

[0087] Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases in a non-linear proportional relationship with the decrease of the variable component in the suppression current, it is judged as a permanent single-phase ground fault.

[0088] Step 4: If the fault is determined to be a transient single-phase ground fault, stop injecting the suppression current; if the fault is determined to be a permanent single-phase ground fault, determine the faulty collector line based on the change in zero-sequence current of each collector line, and isolate the faulty collector line.

[0089] The method for determining the faulty collector line is as follows: if the change in zero-sequence current of a certain collector line is greater than the change in zero-sequence current of the other collector lines, then the collector line is determined to be the faulty collector line.

[0090] (V) Simulation Verification:

[0091] Build such a simulation environment in PSCAD / EMTDC Figure 7 As shown, the wind farm comprises three collector lines, each connecting to a wind turbine cluster containing 10 turbines. Each turbine in clusters 1 and 2 has a capacity of 2MW, while each turbine in cluster 3 has a capacity of 1.5MW. The overcompensation of the neutral point arc suppression coil in the wind farm is set to 9%. To characterize the three-phase imbalance phenomenon commonly found in actual medium-voltage systems, a certain degree of asymmetry is set in the collector line-to-ground parameters.

[0092] After the fault point voltage is completely suppressed for a certain delay, the variable component in the injected current is gradually reduced while continuously compensating for the unbalanced current and suppressing the unbalanced voltage. The amplitude was measured, and the effective value of the neutral point voltage and the zero-sequence current value of each collector line were also measured. The relationship between the neutral point voltage and the injected compensation current under different operating conditions is shown in Table 1. Figure 8 As shown.

[0093] From Table 1 and Figure 8It can be seen that when a transient single-phase ground fault has been reliably eliminated by the fault point voltage suppression technology, as the variable component of the injected current decreases linearly, the neutral point voltage of the system exhibits a linear decreasing trend. The slope of this change is the zero-sequence impedance of the wind farm's collector system to ground. At this point, the injection of suppression current into the system's neutral point can be stopped, and the wind farm can resume normal operation. For permanent single-phase ground faults, when the injected compensation current decreases, the fault arc will reignite. The fault zero-sequence voltage source and the injected current source in the system act together on the neutral point voltage, thus the neutral point voltage exhibits a nonlinear changing trend.

[0094] During the zero-sequence compensation current injection and regulation process, the changes in the zero-sequence current of each collector line were measured and listed in Table 2, and plotted. Figure 9 The table shows the variation trend of zero-sequence current in each collector circuit. (From Table 2 and...) Figure 9 Under the passive compensation effect of the arc suppression coil (i.e. When the zero-sequence current of a faulty collector line is not the maximum value among all lines, it can easily lead to misjudgment by line protection. A dynamic incremental zero-sequence current protection method is adopted to examine the variation of the zero-sequence current of each line with the injected current. The injected compensation current causes a change in the system's zero-sequence voltage, which in turn causes a change in the zero-sequence current of each collector line. Because the impedance to ground of non-faulty collector lines is relatively large, the variation of the zero-sequence current with the zero-sequence voltage is smaller. Compared with non-faulty collector lines, the impedance to ground of the faulty line is significantly reduced under the action of the transition resistance. Therefore, when the system's zero-sequence voltage changes, the decrease in the zero-sequence current of the faulty collector line is the largest, much higher than that of the non-faulty lines. Based on this, collector line L1 can be identified as the faulty line, and the faulty collector line can be tripped and isolated to restore normal operation of the wind farm.

[0095] Table 1. Relationship between neutral point voltage and variable component of injected current under different fault conditions.

[0096]

[0097] Table 2. Relationship between zero-sequence current and injection current of each collector line under different fault conditions.

[0098]

[0099]

[0100] Furthermore, this method is also applicable to ground fault type identification in distribution networks with unbalanced ground parameters. A 10kV distribution network model was built in the PSCAD / EMTDC simulation environment. Under the premise of suppressing unbalanced current, as the variable component of the injected current decreases linearly, when the fault is a transient ground fault, the neutral point voltage exhibits a linear decreasing trend, with the slope of the change being the zero-sequence impedance of the distribution network to ground; when the fault is a permanent ground fault, the neutral point voltage exhibits a non-linear decreasing trend, such as... Figure 10 As shown.

[0101] The above embodiments are preferred embodiments of this application. Those skilled in the art can make various changes or improvements based on them. Without departing from the overall concept of this application, these changes or improvements should fall within the scope of protection claimed in this application.

Claims

1. A method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, characterized in that, include: Step 1: When a single-phase ground fault occurs in the collector line of the wind farm, a suppressing current is injected into the neutral point led out by the grounding transformer to continuously suppress the voltage at the fault point to zero. Step 2: After injecting the suppression current for a preset time, the zero-sequence unbalanced current is continuously compensated by a fixed component in the injected current, the changing component in the suppression current is gradually reduced, and the change in the zero-sequence voltage is monitored simultaneously. Step 3: Based on the monitored changes in zero-sequence voltage, determine whether the single-phase ground fault is a transient single-phase ground fault or a permanent single-phase ground fault; Step 4: If the fault is determined to be a transient single-phase ground fault, stop injecting the suppression current; if the fault is determined to be a permanent single-phase ground fault, determine the faulty collector line based on the change in zero-sequence current of each collector line, and isolate the faulty collector line.

2. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 1, is characterized in that... Suppression current injected in step 1 for: in, To suppress the changing components in the current, To suppress the fixed component in the current, which is also the inherent unbalanced current of the wind farm's power collection system.

3. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 2, is characterized in that... The changing component in the suppression current injected in step 1 for: in, Y is the positive-sequence circuit equivalent potential of the wind farm, and Y0 is the zero-sequence admittance to ground of the wind farm's collector system.

4. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 3, is characterized in that... Positive sequence circuit equivalent potential of a wind farm The calculation method is as follows: When a single-phase ground fault occurs in the wind farm's collector line, a measurement current signal is pre-injected into the neutral point led out from the wind farm's grounding transformer. Then, the positive sequence circuit equivalent potential of the wind farm is calculated: in, This refers to the natural offset of the zero-sequence voltage after a fault. This refers to the zero-sequence voltage offset monitored after the injection of the measurement current signal.

5. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 4, is characterized in that... Pre-injected measurement current signal for: Where α is a proportionality coefficient not greater than 0.15, Take the potential of a certain phase in the primary winding of the grounding transformer. This phase refers to the phase with the lowest collector bus voltage after a single-phase grounding fault occurs.

6. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 1, is characterized in that... The method for determining the type of single-phase ground fault is as follows: Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases linearly with the decrease of the variable component in the suppression current, and its slope is equal to the zero-sequence impedance of the wind farm, then it is judged as a transient single-phase grounding fault. Based on the compensation of the zero-sequence unbalanced current by the fixed component of the continuously injected suppression current, if the zero-sequence voltage decreases in a non-linear proportional relationship with the decrease of the variable component in the suppression current, it is judged as a permanent single-phase ground fault.

7. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 1, is characterized in that... The method for determining whether a single-phase grounding fault has occurred in the collector line of a wind farm is as follows: monitor the zero-sequence voltage and the change in zero-sequence voltage in real time. When the zero-sequence voltage or the change in zero-sequence voltage exceeds its respective preset threshold, it is determined that a single-phase grounding fault has occurred in the collector line.

8. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 1, is characterized in that... The method for determining the faulty collector line is as follows: if the change in zero-sequence current of a certain collector line is greater than the change in zero-sequence current of the other collector lines, then the collector line is determined to be the faulty collector line.

9. The method for identifying and protecting single-phase grounding fault types in wind farm collector lines based on dynamic increments of injected current, as described in claim 1, is characterized in that... Zero-sequence current is injected into the neutral point through an electronically controllable current source, the amplitude and phase of which are both controllable.

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