A method for identifying and repairing errors of active arc extinguishing result of generator stator ground fault based on phase leakage current change

Abstract

This invention discloses a method for identifying and correcting errors in active arc suppression of generator stator grounding faults based on changes in phase leakage current. Belonging to the field of large generator safety protection technology, the method includes the following steps: real-time monitoring of the generator status, and initiation of active arc suppression after a fault occurs. By recording the phase neutral point current and terminal current of the faulty phase before and after the fault, and before and after arc suppression, the changes in phase leakage current before and after the fault, as well as before and after arc suppression, are calculated. Based on these changes, identification criteria are constructed to determine in real time whether arc suppression is successful. If successful, subsequent processes are executed; if unsuccessful, the arc suppression error is calculated using an error correction algorithm, the arc suppression injection amount is corrected accordingly, and arc suppression and identification are repeated, forming a closed-loop iteration until arc suppression is successful. This invention achieves online identification and closed-loop correction of arc suppression effects, significantly improving the reliability, accuracy, and adaptability of the arc suppression system.

Description

Technical Field

[0001] This invention relates to the field of safety protection technology for large generators, specifically to a method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on changes in phase leakage current. Background Technology

[0002] Single-phase ground faults in the stator windings are among the most common faults in large generators, occurring in several large generators such as the Three Gorges and Wudongde generators in recent years. The ground fault current is mainly composed of the ground capacitance current, which currently exceeds 20A in most large generators, reaching 55.27A in some large-capacity units. The arc generated by this current can damage the winding insulation, burn the core and sintered core laminations, and prolonged arcing can also trigger more serious short-circuit faults, posing a direct threat to generator safety.

[0003] Arc suppression methods for generator stator grounding faults can be divided into passive and active categories. Passive methods primarily rely on grounding the neutral point through an arc suppression coil, but they can only compensate for the power frequency component, cannot suppress harmonic currents, and are difficult to dynamically adapt to different fault conditions, resulting in limited actual arc suppression effectiveness. Active arc suppression methods, on the other hand, actively regulate the fault point voltage through an external injection source, simultaneously compensating for both the fundamental and third harmonic components, achieving more precise arc suppression. However, this method depends on accurate calculation and injection of compensation amounts; errors can lead to incomplete arc suppression, and excessive errors may even amplify the fault.

[0004] Current research on active arc suppression has not systematically solved the problems of arc suppression result identification and error correction. Existing research mainly focuses on arc suppression method construction, fault calculation, and device control, without fully considering the compensation deviations caused by measurement and calculation errors. Although the theory of arc suppression in distribution networks is relatively mature, it also lacks effective methods for arc suppression result identification and error correction. Therefore, it is necessary to reliably identify the arc suppression effect after implementing active arc suppression, and to perform error correction and closed-loop control when failure is identified, to further improve the theoretical system and engineering practicality of existing generator active arc suppression methods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on changes in phase leakage current, so as to solve the problems of existing active arc suppression technology lacking effective online identification means for arc suppression results and being unable to close the loop when there are errors in the calculated or injected compensation amount, thereby improving the reliability, accuracy and adaptability of the arc suppression system.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0007] A method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on changes in phase leakage current includes the following steps:

[0008] S1. Monitor the generator's operating status in real time, and activate active arc suppression measures after detecting a single-phase ground fault in the stator winding;

[0009] S2. Record the phase neutral point current and terminal current of the generator fault phase before and after the ground fault occurs, and calculate the change in phase leakage current before and after the fault occurs accordingly.

[0010] S3. After implementing active arc suppression measures, record the phase neutral point current and terminal current of the faulty phase of the generator before and after applying arc suppression, and calculate the change in phase leakage current before and after applying arc suppression; identify whether the arc suppression was successful based on the arc suppression result identification method based on the change in phase leakage current.

[0011] S4. If the arc suppression is identified as successful, continue with subsequent work; if the arc suppression is identified as unsuccessful, calculate the arc suppression error based on the error repair method based on injection volume fine-tuning.

[0012] S5. Based on the calculated arc suppression error, correct the injection amount of the current active arc suppression measure, and return to step S3 until the arc suppression is identified as successful.

[0013] Preferably, the active arc suppression measure in step S1 is:

[0014] A controllable fundamental frequency voltage and third harmonic voltage are injected into the neutral point of the generator through a dual-frequency active voltage regulation device.

[0015] The dual-frequency active voltage regulation device independently adjusts the amplitude and phase of its output fundamental frequency voltage and third harmonic voltage, thereby forcing and maintaining the neutral point voltage at a preset value.

[0016] Assuming a ground fault occurs in phase A of the generator, when the base frequency voltage output by the dual-frequency active voltage regulation device is... U i1 At that time, the injected fundamental frequency current I i1 The following relationship must be satisfied:

[0017]

[0018] in, U n1 is the fundamental voltage at the neutral point of the generator after a ground fault occurs; j is the imaginary unit. ω Angular frequency; This is the sum of the generator stator winding capacitance to ground; E f1 The fundamental potential at the fault point;R g For grounding transition resistance;

[0019] When the third harmonic voltage output by the dual-frequency active voltage regulation device is U i3 At that time, the injected third harmonic current I i3 The following relationship must be satisfied:

[0020]

[0021] in, U n3 This refers to the third harmonic voltage at the neutral point of the generator after a ground fault occurs. E Ai3 For phase A, number 1 i The third harmonic potential of the coil midpoint to the neutral point; n This represents the total number of turns in the stator winding of phase A. C a This is the equivalent capacitance to ground of phase A; C t This represents the equivalent capacitance to ground for each phase at the machine end of the directly connected system. E A3 The third harmonic potential at camera A; E f3 The third harmonic potential at the fault point.

[0022] Preferably, step S2 specifically includes:

[0023] For large generators with an ungrounded neutral point, the state change caused by the fault is obtained by calculating the change in phase leakage current of the faulted phase before and after the ground fault occurs; specifically:

[0024] Record the phase neutral point current and generator terminal current of generator phase A during normal operation and after a single-phase ground fault.

[0025] During normal operation, the fundamental leakage current of phase A of the generator I (1) A_leak_1 With third harmonic leakage current I (1) A_leak_3 Calculated using the following formulas respectively:

[0026] I (1) A_leak_1 = I (1) An1 - I (1) At1

[0027] I (1) A_leak_3 = I (1) An3 - I (1) At3

[0028] in, I (1) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point during normal operation. I (1) An3 This refers to the third harmonic current flowing through the A-phase winding at the neutral point during normal operation. I (1) At1 This refers to the fundamental current flowing through the A-phase winding at the terminal measurement point during normal operation. I (1) At3 This refers to the third harmonic current flowing through the A-phase winding at the terminal measurement point during normal operation.

[0029] After a single-phase ground fault occurs, the fundamental leakage current of phase A of the generator becomes I (2) A_leak_1 The third harmonic leakage current becomes I (2) A_leak_3 Calculated by the following formulas respectively:

[0030] I (2) A_leak_1 = I (2) An1 - I (2) At1

[0031] I (2) A_leak_3 = I (2) An3 - I (2) At3

[0032] in, I (2) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) An3This refers to the third harmonic current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) At1 This refers to the fundamental current flowing through the A-phase winding at the generator terminal after a ground fault occurs in phase A of the generator. I (2) At3 This refers to the third harmonic current flowing through the A-phase winding at the generator terminal measurement point after a ground fault occurs in phase A of the generator.

[0033] When the generator changes from normal operation to a ground fault state, the measured value Δ of the fundamental change in phase leakage current is... I (2)-(1) A_leak_1_meas Measured value of third harmonic variation Δ I (2)-(1) A_leak_3_meas Calculated by the following formula:

[0034] Δ I (2)-(1) A_leak_1_meas = I (2) A_leak_1 - I (1) A_leak_1

[0035] Δ I (2)-(1) A_leak_3_meas = I (2) A_leak_3 - I (1) A_leak_3 .

[0036] Preferably, step S3 specifically includes:

[0037] S31. Calculate the measured changes in phase leakage current before and after arc suppression, specifically:

[0038] After arc suppression is applied, the fundamental leakage current of phase A of the generator... I (3) A_leak_1 With third harmonic leakage current I (3) A_leak_3 Calculated using the following formulas respectively:

[0039] I (3) A_leak_1 = I (3) An1 - I (3)At1

[0040] I (3) A_leak_3 = I (3) An3 - I (3) At3

[0041] in, I (3) An1 The fundamental current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) An3 The third harmonic current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) At1 The fundamental current flowing through the A-phase winding at the machine terminal measurement point after applying active arc suppression measures; I (3) At3 The third harmonic current flowing through the A-phase winding at the machine terminal measurement point after applying active arc suppression measures;

[0042] When the generator changes from a ground fault state to an arc suppression state, the measured value Δ of the fundamental change in phase leakage current is... I (3 )-(2) A_leak_1_meas Measured value of third harmonic variation Δ I (3)-(2) A_leak_3_meas Calculated by the following formula:

[0043] Δ I (3)-(2) A_leak_1_meas = I (3) A_leak_1 - I (2) A_leak_1

[0044] Δ I (3)-(2) A_leak_3_meas = I (3) A_leak_3 - I (2) A_leak_3 ;

[0045] S32. The success of arc suppression is determined based on the arc suppression result identification method based on the change in phase leakage current, specifically as follows:

[0046] The sum of the measured fundamental frequency changes A1 and the sum of the third harmonic frequency changes A3 after arc suppression are calculated using the following formula:

[0047] A1=Δ I (2)-(1) A_leak_1_meas +Δ I (3)-(2) A_leak_1_meas

[0048] A3=Δ I (2)-(1) A_leak_3_meas +Δ I (3)-(2) A_leak_3_meas

[0049] If the amplitude and phase error of the sum of A1 and the preset fundamental frequency variation theoretical value B1 are both less than a set of preset thresholds, and the amplitude and phase error of the sum of A3 and the preset third harmonic frequency variation theoretical value B3 are both less than the set of preset thresholds, then the arc suppression is deemed successful; otherwise, the arc suppression is deemed unsuccessful.

[0050] Preferably, step S4 specifically comprises:

[0051] Once the arc suppression is confirmed to be successful, continue with the subsequent load transfer and demagnetization shutdown procedures.

[0052] When arc suppression failure is identified, the arc suppression error is calculated based on the error repair method based on injection volume fine-tuning, specifically:

[0053] When a single-phase ground fault occurs in phase A of the generator, the actual injection quantity satisfies:

[0054]

[0055] in, U' i1 The fundamental compensation voltage actually injected into the dual-frequency active voltage regulation device; U' n1 To apply the actual arc-suppression voltage U' i1 Then, the actual fundamental voltage at the neutral point when the system reaches steady state; Δ E f1 This is the fundamental wave arc suppression error;

[0056] Calculate Δ I (2)-(1) A_leak_1 and Δ I (4)-(2) A_leak_1 The theoretical value of the sum A1 ' With Δ I (2)-(1)A_leak_3 and Δ I (4)-(2) A_leak_3 The theoretical value of the sum A3 ' :

[0057]

[0058] in, U' i3 The actual third harmonic compensation voltage injected into the dual-frequency active voltage regulation device; Δ E f3 This is the arc suppression error due to the third harmonic;

[0059] Solving the above three equations simultaneously, we can obtain the fundamental wave arc suppression error Δ. E f1 And the third harmonic arc suppression error Δ E f3 The specific value.

[0060] Preferably, step S5 specifically comprises:

[0061] Based on the arc suppression error calculated in step S4, the injection amount of the current active arc suppression measure is corrected.

[0062] The specific correction method is as follows: Let the first... m The arc-extinguishing injection amount in the next iteration is and The calculated arc suppression error is and Then the first m The new arc-extinguishing amount in +1 iteration and Determined by the following formula:

[0063]

[0064] After adopting the new arc suppression amount, return to step S3 to recalculate the change in phase leakage current before and after applying the arc suppression and identify the arc suppression result;

[0065] If the identification result is still unsuccessful, repeat steps S4 and S5 to continue iteratively correcting the arc-extinguishing injection amount until the identification result of step S3 is successful, thus achieving accurate arc extinguishing.

[0066] The technological advancements achieved by this invention are as follows, thanks to the adoption of the above technical solutions.

[0067] This invention achieves reliable online real-time identification of arc suppression effectiveness. It innovatively proposes a criterion based on the sum of changes in phase leakage current during two stages: "before and after the fault occurs" and "before and after arc suppression is applied." This criterion utilizes the superposition principle to effectively offset the interference from load current and unbalanced current during normal operation by calculating the changes, resulting in a pure and highly sensitive criterion signal. This method solves the problem of existing technologies being unable to determine the success of arc suppression online, providing a reliable basis for subsequent operational decisions.

[0068] This invention establishes closed-loop error correction and adaptive arc suppression capabilities: For identified arc suppression failures, this invention proposes an error repair method based on fine-tuning of the injection amount. By establishing and solving a mathematical model incorporating the arc suppression error, the deviation between the current injection amount and the actual requirement can be accurately calculated. This deviation is then used to instantly correct the arc suppression command, upgrading the traditional "open-loop" one-time arc suppression to adaptive arc suppression using "closed-loop feedback control," significantly improving the robustness of the arc suppression system against parameter uncertainties and measurement errors.

[0069] This invention constructs a complete intelligent arc suppression control process: it organically integrates multiple stages, including fault detection, active arc suppression, result identification, and error correction, forming a complete and intelligent closed-loop control strategy. This process can automatically address compensation deviations caused by fault location, changes in transition resistance, and measurement calculation errors, ensuring the final effectiveness and accuracy of arc suppression under different fault conditions, and greatly improving the overall reliability and automation level of large generator stator grounding protection.

[0070] This invention possesses excellent engineering applicability and compatibility: the electrical quantities upon which this invention relies (phase neutral point current and generator terminal current) are easily measured in existing generator protection systems, and the criterion calculation is based on mature circuit theory, making it easy to implement in digital protection devices or monitoring systems. This method can be seamlessly integrated with existing dual-frequency active voltage regulation devices without adding expensive hardware; the performance of existing systems can be significantly improved through algorithm upgrades. Attached Figure Description

[0071] Figure 1 This is a flowchart of the present invention;

[0072] Figure 2 To simulate and verify the relevant current quantities when arc suppression is successful, the present invention includes... Figure 2 (a) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.25. Figure 2 (b) is R g =200Ω andα Simulation results of fundamental leakage current, third harmonic leakage current and fault current at a value of 0.50. Figure 2 (c) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current and fault current when ω = 0.75.

[0073] Figure 3 To simulate and verify the relevant current quantities when arc suppression fails, the present invention includes... Figure 3 (a) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.25. Figure 3 (b) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current and fault current at a value of 0.50. Figure 3 (c) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current and fault current when ω = 0.75.

[0074] Figure 4 To simulate and verify the fault current waveform for arc suppression error repair in this invention, wherein, Figure 4 (a) is R g =200Ω and α Simulation results of the waveforms before and after fault current error repair when the fault current error is 0.25. Figure 4 (b) is R g =200Ω and α Simulation results of the waveforms before and after fault current error repair when the fault current error is 0.50. Figure 4 (c) is R g =200Ω and α Simulation results of the waveforms before and after fault current error repair when the fault current error is 0.75. Detailed Implementation

[0075] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0076] A method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on changes in phase leakage current, combined with... Figure 1 As shown, it includes the following steps:

[0077] S1. Monitor the generator's operating status in real time, and activate active arc suppression measures after detecting a single-phase ground fault in the stator winding.

[0078] By injecting controllable fundamental frequency voltage and third harmonic voltage into the generator neutral point through a dual-frequency active voltage regulation device, the voltage at the fault point is forced to decrease.

[0079] The dual-frequency active voltage regulator independently adjusts the amplitude and phase of its output fundamental frequency voltage and third harmonic voltage to force and maintain the neutral point voltage at a preset value, i.e., the desired voltage value. According to Kirchhoff's voltage law, when the fault point voltage is forced to 0, the neutral point voltage should satisfy the relationship of being equal in magnitude and 180° out of phase with the fault potential, i.e.:

[0080]

[0081] in, U n(1，3) The voltage at the neutral point; E f(1，3) The potential at the fault point is denoted as .

[0082] Assuming a ground fault occurs in phase A of the generator, when the base frequency voltage output by the dual-frequency active voltage regulator is... U i1 At that time, the KCL equation for the neutral point is established, and the fundamental frequency current injected by the dual-frequency active voltage regulation device is... I i1 The following relationship must be satisfied:

[0083]

[0084] in, U n1 is the fundamental voltage at the neutral point of the generator after a ground fault occurs; j is the imaginary unit. ω Angular frequency; This is the sum of the generator stator winding capacitance to ground; E f1 The fundamental potential at the fault point; R g This is the grounding transition resistor.

[0085] When the third harmonic voltage output by the dual-frequency active voltage regulator is U i3 At this time, an equivalent model of the stator winding of the faulty phase (phase A) is established. Since the third harmonic voltage exhibits zero-sequence characteristics and the parameters of the three-phase stator windings are symmetrical, the third harmonic current injected by the dual-frequency active voltage control device is... I i3 The following relationship must be satisfied:

[0086]

[0087] in, U n3 This refers to the third harmonic voltage at the neutral point of the generator after a ground fault occurs. E Ai3 For phase A, number 1 i The third harmonic potential of the coil midpoint to the neutral point; n This represents the total number of turns in the stator winding of phase A. C a This is the equivalent capacitance to ground of phase A; C t This represents the equivalent capacitance to ground for each phase at the machine end of the directly connected system. E A3 The third harmonic potential at camera A; E f3 The third harmonic potential at the fault point.

[0088] S2. Record the phase neutral point current and generator terminal current of the faulty phase of the generator before and after the ground fault occurs, and calculate the change in phase leakage current before and after the fault occurs.

[0089] For large generators with an ungrounded neutral point, the state change caused by the fault is obtained by calculating the change in phase leakage current of the faulted phase before and after the ground fault occurs; specifically:

[0090] Record the phase neutral point current and generator terminal current of generator phase A during normal operation and after a single-phase ground fault.

[0091] During normal operation, the fundamental leakage current of phase A of the generator I (1) A_leak_1 Equal to the generator fundamental frequency capacitance current to ground and the third harmonic leakage current of generator phase A. I (1) A_leak_3 This is equal to the generator's third harmonic capacitor current. And the fundamental leakage current of phase A... I (1) A_leak_1 With third harmonic leakage current I (1) A_leak_3 Calculated using the following formulas respectively:

[0092] I (1) A_leak_1 = I (1) An1 - I (1) At1

[0093] I (1) A_leak_3 = I (1) An3 - I (1) At3

[0094] in, I (1) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point during normal operation. I (1) An3 This refers to the third harmonic current flowing through the A-phase winding at the neutral point during normal operation. I (1) At1 This refers to the fundamental current flowing through the A-phase winding at the terminal measurement point during normal operation. I (1) At3 This refers to the third harmonic current flowing through the A-phase winding at the terminal measurement point during normal operation.

[0095] After a single-phase ground fault occurs, the fundamental leakage current of phase A of the generator becomes I (2) A_leak_1 The third harmonic leakage current becomes I (2) A_leak_3 Calculated by the following formulas respectively:

[0096] I (2) A_leak_1 = I (2) An1 - I (2) At1

[0097] I (2) A_leak_3 = I (2) An3 - I (2) At3

[0098] in, I (2) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) An3This refers to the third harmonic current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) At1 This refers to the fundamental current flowing through the A-phase winding at the generator terminal after a ground fault occurs in phase A of the generator. I (2) At3 This refers to the third harmonic current flowing through the A-phase winding at the generator terminal after a ground fault occurs in phase A of the generator.

[0099] When the generator changes from normal operation to a ground fault state, the measured value Δ of the fundamental change in phase leakage current is... I (2)-(1) A_leak_1_meas Measured value of third harmonic variation Δ I (2)-(1) A_leak_3_meas Calculated by the following formula:

[0100] Δ I (2)-(1) A_leak_1_meas = I (2) A_leak_1 - I (1) A_leak_1

[0101] Δ I (2)-(1) A_leak_3_meas = I (2) A_leak_3 - I (1) A_leak_3 .

[0102] S3. After implementing active arc suppression measures, record the phase neutral point current and terminal current of the faulty phase of the generator before and after applying arc suppression, and calculate the change in phase leakage current before and after applying arc suppression; identify whether the arc suppression was successful based on the arc suppression result identification method based on the change in phase leakage current.

[0103] When performing active arc suppression, a dual-frequency reverse fault potential needs to be injected into the generator neutral point. If there is an error in the injection amount during this process, a significant arc suppression error will occur, potentially even exacerbating the fault. Therefore, it is necessary to identify successful arc suppression and implement appropriate handling methods for unsuccessful cases.

[0104] S31. Calculate the measured changes in phase leakage current before and after arc suppression, specifically:

[0105] After arc suppression is applied, the fundamental leakage current of phase A of the generator... I(3) A_leak_1 With third harmonic leakage current I (3) A_leak_3 Calculated using the following formulas respectively:

[0106] I (3) A_leak_1 = I (3) An1 - I (3) At1

[0107] I (3) A_leak_3 = I (3) An3 - I (3) At3

[0108] in, I (3) An1 The fundamental current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) An3 The third harmonic current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) At1 The fundamental current flowing through the A-phase winding at the machine terminal measurement point after applying active arc suppression measures; I (3) At3 The third harmonic current flowing through the A-phase winding at the machine terminal is measured after active arc suppression measures are applied.

[0109] When the generator changes from a ground fault state to an arc suppression state, the measured value Δ of the fundamental change in phase leakage current is... I (3 )-(2) A_leak_1_meas Measured value of third harmonic variation Δ I (3)-(2) A_leak_3_meas Calculated by the following formula:

[0110] Δ I (3)-(2) A_leak_1_meas = I (3) A_leak_1 - I (2) A_leak_1

[0111] Δ I (3)-(2) A_leak_3_meas = I (3) A_leak_3 - I (2) A_leak_3 .

[0112] S32. The success of arc suppression is determined based on the arc suppression result identification method based on the change in phase leakage current, specifically as follows:

[0113] When the generator changes from normal operation to a ground fault state, the theoretical value of the change in the fundamental frequency of the phase leakage current Δ I (2)-(1) A_leak_1 Theoretical value of third harmonic variation Δ I (2)-(1) A_leak_3 They are respectively:

[0114]

[0115] in, U f1 The fundamental voltage at the fault point; U f3 The voltage at the fault point is the third harmonic voltage.

[0116] Assuming the ideal injection volume is U i1 =- E f1 , U i3 =- E f3 The actual injection volume is U' i1 =- E f1 +Δ E f1 , U' i3 =- E f3 +Δ E f3 ,in, U' i1 The fundamental compensation voltage actually injected into the dual-frequency active voltage regulation device; U' i3 The actual third harmonic compensation voltage injected into the dual-frequency active voltage regulation device; Δ E f1 For fundamental wave arc suppression error; Δ E f3 This is the arc suppression error of the third harmonic.

[0117] During actual generator operation, the phase leakage current measurement includes a significant amount of load current and unbalanced current. Directly using the measured phase leakage current as the criterion for arc suppression result identification can easily lead to substantial errors. To address this issue, it is proposed to use the change in phase leakage current as the criterion for arc suppression result identification. Based on the superposition principle, the post-fault system state can be considered as a superposition of the normal load state and a pure fault state excited by the voltage source at the fault point.

[0118] When arc suppression is successful, the generator changes from a ground fault state to a successfully suppressed state, and the change in the fundamental frequency of the phase leakage current Δ I (3)-(2) A_leak_1 Theoretical value of third harmonic variation Δ I (3)-(2) A_leak_3 They are respectively:

[0119]

[0120] In a pure fault-prone network, all power sources are short-circuited, leaving only passive components such as line-to-ground capacitance. The current response in this state completely excludes interference components such as load current. Therefore, a criterion for identification can be constructed based on the change in phase leakage current. In the calculation of current change, load components with large amplitudes but continuous operation during the fault are canceled out. The calculated change is the change in phase leakage current. Similarly, unbalanced current is also canceled out in this process and will not affect the calculation results of the proposed criterion.

[0121] exist E f1 If the calculation is accurate and the arc suppression is successful, Δ I (2)-(1) A_leak_1 and Δ I (3)-(2) A_leak_1 The theoretical value of the sum B1 = In the case of successful arc suppression, E f1 The quantity is known; therefore, it can be determined based on Δ after arc extinguishing. I (2 )-(1) A_leak_1_meas and Δ I (3)-(2) A_leak_1_meas Whether the sum A1 equals the theoretical value B1 is used to determine whether arc suppression was successful.

[0122] Similarly, in E f3 If the calculation is accurate and the arc suppression is successful, Δ I (2)-(1)A_leak_3 and Δ I (3)-(2) A_leak_3 The theoretical value of the sum B3 = In the case of successful arc suppression, E f3 The quantity is known; therefore, it can be determined based on Δ after arc extinguishing. I (2)-(1) A_leak_3_meas and Δ I (3)-(2) A_leak_3_meas Whether the sum of A3 equals the theoretical value B3 is used to determine whether arc suppression was successful.

[0123] When arc suppression fails, the generator changes from a ground fault state to an arc suppression failure state, and the theoretical value of the change in the fundamental frequency of the phase leakage current Δ I (4)-(2) A_leak_1 Theoretical value of third harmonic variation Δ I (4)-(2) A_leak_3 They are respectively:

[0124]

[0125] Compared to the case where arc suppression is successful, Δ at this time I (2)-(1) A_leak_1 and Δ I (4)-(2) A_leak_1 The theoretical value of the sum A1 ' = There are errors in the calculation. Similarly, Δ I (2)-(1) A_leak_3 and Δ I (4)-(2) A_leak_3 The theoretical value of the sum A3 ' There are also calculation errors. .

[0126] Based on the above theoretical relationships, the criteria for judging successful arc extinguishing are:

[0127] The sum of the measured fundamental frequency changes A1 and the sum of the third harmonic frequency changes A3 after arc suppression are calculated using the following formula:

[0128] A1=Δ I (2)-(1) A_leak_1_meas +Δ I (3)-(2) A_leak_1_meas

[0129] A3=Δ I(2)-(1) A_leak_3_meas +Δ I (3)-(2) A_leak_3_meas

[0130] If the amplitude and phase errors of A1 and B1 are both less than a set of preset thresholds, and the amplitude and phase errors of A3 and B3 are both less than the same set of preset thresholds, then the arc suppression is considered successful; otherwise, the arc suppression is considered unsuccessful.

[0131] Specifically, a set of preset thresholds can be: amplitude error less than 5% and phase error less than 5°.

[0132] S4. If the arc suppression is identified as successful, continue with subsequent work; if the arc suppression is identified as unsuccessful, calculate the arc suppression error based on the error repair method based on injection amount fine-tuning.

[0133] Once the arc suppression is confirmed to be successful, proceed with subsequent load transfer and demagnetization shutdown procedures.

[0134] When arc suppression failure is identified, the arc suppression error is calculated based on the error repair method based on injection volume fine-tuning, specifically:

[0135] At the ideal injection volume U i1 =- E f1 , U i3 =- E f3 The actual injection volume is U' i1 =- E f1 +Δ E f1 , U' i3 =- E f3 +Δ E f3 In the case of arc suppression error Δ, solve for the arc suppression error. E f1 Δ E f3 This allows for control over the actual amount of arc extinguishing injected. U' i1 , U' i3 Fine-tuning to correct errors:

[0136] When a single-phase ground fault occurs in phase A of the generator, we can obtain:

[0137]

[0138] in, U'n1 To apply the actual arc-suppression voltage U' i1 Then, the actual fundamental voltage of the neutral point when the system reaches steady state;

[0139] Due to errors in arc suppression, the actual injection volume satisfies: U' i1 =- E f1 +Δ E f1 .

[0140] After sorting, we can obtain:

[0141]

[0142] Calculate Δ I (2)-(1) A_leak_1 and Δ I (4)-(2) A_leak_1 The theoretical value of the sum A1 ' With Δ I (2)-(1) A_leak_3 and Δ I (4)-(2) A_leak_3 The theoretical value of the sum A3 ' :

[0143]

[0144] Among them, the fundamental wave arc suppression error Δ E f1 Grounding transition resistance R g And the third harmonic arc suppression error Δ E f3 It is an unknown quantity.

[0145] By solving the three equations simultaneously, we obtain the three unknowns and thus the fundamental wave arc suppression error Δ. E f1 And the third harmonic arc suppression error Δ E f3 The specific value is used to adjust the amount of arc-extinguishing injection for error correction.

[0146] S5. Based on the calculated arc suppression error, correct the injection amount of the current active arc suppression measure, and return to step S3 until the arc suppression is identified as successful.

[0147] Based on the arc suppression error calculated in step S4, the injection amount of the current active arc suppression measure is corrected.

[0148] The specific correction method is as follows: Let the first... mThe arc-extinguishing injection amount in the next iteration is and The calculated arc suppression error is and Then the first m The new arc-extinguishing amount in +1 iteration and Determined by the following formula:

[0149]

[0150] After adopting the new arc suppression amount, return to step S3 to recalculate the change in phase leakage current before and after applying the arc suppression and identify the arc suppression result;

[0151] If the identification result is still unsuccessful, repeat steps S4 and S5 to continue iteratively correcting the arc-extinguishing injection amount until the identification result of step S3 is successful, thus achieving accurate arc extinguishing.

[0152] The effectiveness of the proposed method is verified through simulation below.

[0153] This embodiment uses a nuclear power unit as a prototype and employs PSCAD / EMTDC software to establish a quasi-distributed parameter model for simulation analysis. The generator has a capacity of 30kVA, a rated voltage of 10.5kV, and a rated current of 2.86A. Each branch consists of 8 coils connected in series, with 1 pole pair and a total of 48 slots. The corresponding slot pitch electrical angle is 7.5°. The stator winding capacitance to ground per phase is 0.397μF, and the equivalent capacitance to ground per phase for directly connected equipment at the generator terminals is 0.405μF. Taking the first branch of phase A as an example, the amplitude and phase angle of the fundamental and third harmonic fault potentials when a ground fault occurs at the connection point of each coil are shown in Table 1.

[0154] Table 1. Fault Potential Parameters of Example Generator Simulation Model

[0155]

[0156] (1) Verification of the criteria for successful arc suppression

[0157] To verify the effectiveness of the proposed arc suppression success criterion, the fault turns ratio at time 0.2s in phase A of the generator was measured. αSingle-phase ground faults were set at points 0.75, 0.50, and 0.25, with a ground transition resistance of 200Ω. At 0.3s, a dual-frequency active voltage regulator installed at the generator neutral point was activated to actively regulate the dual-frequency voltage at the generator neutral point. The following simulations verify the proposed arc suppression result identification criteria for successful and unsuccessful arc suppression after the injection of arc suppression quantity. Based on the pre-simulation data, arc suppression is considered successful when the amplitude error of Ai / Bi (i=1,3) is less than 5% and the phase error is less than 5°; otherwise, it is considered unsuccessful.

[0158] Scenario 1: When the controlled generator neutral point dual-frequency voltage is completely accurate, achieving accurate and reliable arc suppression, the fundamental leakage current, third harmonic leakage current, and fault current are as follows: Figure 2 As shown, where, Figure 2 (a) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.25. Figure 2 (b) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current and fault current at a value of 0.50. Figure 2 (c) is R g =200Ω and α The simulation results of the fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.75 are shown in Table 2. Detailed results of arc suppression identification are shown in Table 2.

[0159] Table 2. Arc suppression identification results under different fault scenarios - successful arc suppression

[0160]

[0161] Based on the calculation results in Table 2 and Figure 2 The fault current waveform shows that the proposed arc suppression result identification method is accurate when the arc suppression is successful.

[0162] Scenario 2: When the controlled neutral point dual-frequency voltage of the generator is inaccurate, arc suppression fails. Assume there is a 5% error in the controlled neutral point dual-frequency voltage at this time. The fundamental leakage current, third harmonic leakage current, and fault current are as follows: Figure 3 As shown, where, Figure 3 (a) is R g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.25. Figure 3 (b) isR g =200Ω and α Simulation results of fundamental leakage current, third harmonic leakage current and fault current at a value of 0.50. Figure 3 (c) is R g =200Ω and α The simulation results of the fundamental leakage current, third harmonic leakage current, and fault current at a value of 0.75 are shown in Table 3. Detailed results of arc suppression identification are shown in Table 3.

[0163] Table 3. Arc suppression identification results under different fault scenarios - Arc suppression failure

[0164]

[0165] Based on the calculation results in Table 3 and Figure 3 The fault current waveform shows that the proposed arc suppression result identification method is accurate even when there is an error in arc suppression.

[0166] To further verify the effectiveness of the proposed arc suppression result identification method, simulation verification was performed under different fault scenarios. Detailed simulation results for successful arc suppression are shown in Table 2, and detailed simulation results for failed arc suppression are shown in Table 3.

[0167] The simulation results in Tables 2 and 3 show that the proposed method can accurately determine the arc extinguishing result under different fault scenarios. For example, in... α The fault location is 0.75, with a transition resistance of 200Ω. When arc suppression is successful, the amplitude error of A1 and B1 is 0%, and the phase error is 0.35°; the amplitude error of A3 and B3 is 0%, and the phase error is 2.72°. This indicates that the fundamental and third harmonic compensations are accurate, and arc suppression is successful. When arc suppression is unsuccessful, the amplitude error of A1 and B1 is 274.36%, and the phase error is 10.91°; the amplitude error of A3 and B3 is 1362.52%, and the phase error is 30.84°. This indicates that the fundamental and third harmonic compensations have significant errors, and arc suppression is unsuccessful. This proves that the method proposed in this paper is not affected by the grounding transition resistance or the fault location, and has strong engineering applicability.

[0168] (2) Verification of error repair methods

[0169] To verify the effectiveness of the error repair method proposed in this paper, we took the case of unsuccessful arc suppression under a 200Ω grounding transition resistance in Table 3 as an example and used the method proposed in this paper to repair the error.

[0170] After the arc suppression result is determined to be unsuccessful, the arc suppression error is calculated according to the method proposed in this paper, and the injection amount is adjusted at 0.4s. The fault current waveform is as follows. Figure 4As shown, where, Figure 4 (a) is R g =200Ω and α Simulation results of the waveforms before and after fault current error repair when the fault current error is 0.25. Figure 4 (b) is R g =200Ω and α Simulation results of the waveforms before and after fault current error repair when the fault current error is 0.50. Figure 4 (c) is R g =200Ω and α The simulation results of the waveforms before and after fault current error repair at a value of 0.75 are shown in Table 4. Detailed calculation results are shown in Table 4.

[0171] Table 4. Arc suppression repair results under different fault scenarios

[0172]

[0173] according to Figure 4 As can be seen from Table 4, the Δ calculated by the proposed method E f1 and Δ E f3 With an error of less than 0.4%, it can accurately correct arc suppression errors and achieve accurate and reliable arc suppression.

Claims

1. A method for identifying and repairing errors in active arc extinction results of a generator stator ground fault based on phase leakage current change, characterized in that: Includes the following steps: S1. Monitor the generator's operating status in real time, and activate active arc suppression measures after detecting a single-phase ground fault in the stator winding; S2. Record the phase neutral point current and terminal current of the generator fault phase before and after the ground fault occurs, and calculate the change in phase leakage current before and after the fault occurs accordingly. S3. After implementing active arc suppression measures, record the phase neutral point current and terminal current of the faulty phase of the generator before and after applying arc suppression, and calculate the change in phase leakage current before and after applying arc suppression. The success of arc suppression is determined by the arc suppression result identification method based on the change in phase leakage current. Step S3 specifically includes: S31. Calculate the measured changes in phase leakage current before and after arc suppression, specifically: After arc suppression is applied, the fundamental leakage current of phase A of the generator... I (3) A_leak_1 With third harmonic leakage current I (3) A_leak_3 Calculated using the following formulas respectively: I (3) A_leak_1 = I (3) An1 - I (3) At1 （1） I (3) A_leak_3 = I (3) An3 - I (3) At3 （2） in, I (3) An1 The fundamental current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) An3 The third harmonic current flowing through the A-phase winding at the neutral point after the active arc suppression measures are applied; I (3) At1 The fundamental current flowing through the A-phase winding at the machine terminal measurement point after applying active arc suppression measures; I (3) At3 The third harmonic current flowing through the A-phase winding at the machine terminal measurement point after applying active arc suppression measures; When the generator changes from a ground fault state to an arc suppression state, the measured value Δ of the fundamental change in phase leakage current is... I (3 )-(2) A_leak_1_meas Measured value of third harmonic variation Δ I (3)-(2) A_leak_3_meas Calculated by the following formula: D I (3)-(2) A_leak_1_meas = I (3) A_leak_1 - I (2) A_leak_1 (3) D I (3)-(2) A_leak_3_meas = I (3) A_leak_3 - I (2) A_leak_3 (4); S32. The success of arc suppression is determined based on the arc suppression result identification method based on the change in phase leakage current, specifically as follows: The sum of the measured fundamental frequency changes A1 and the sum of the third harmonic frequency changes A3 after arc suppression are calculated using the following formula: A1=D I (2)-(1) A_leak_1_meas +D I (3)-(2) A_leak_1_meas (5) A3=D I (2)-(1) A_leak_3_meas +D I (3)-(2) A_leak_3_meas (6) If the amplitude and phase error of the sum of A1 and the preset fundamental frequency variation theoretical value B1 are both less than a set of preset thresholds, and the amplitude and phase error of the sum of A3 and the preset third harmonic frequency variation theoretical value B3 are both less than the set of preset thresholds, then the arc suppression is determined to be successful; otherwise, the arc suppression is determined to be unsuccessful. S4. If the arc suppression is identified as successful, continue with subsequent work; if the arc suppression is identified as unsuccessful, calculate the arc suppression error based on the error repair method based on injection volume fine-tuning. Step S4 is as follows: Once the arc suppression is confirmed to be successful, continue with the subsequent load transfer and demagnetization shutdown procedures. When arc suppression failure is identified, the arc suppression error is calculated based on the error repair method based on injection volume fine-tuning, specifically: When a single-phase ground fault occurs in phase A of the generator, the actual injection quantity satisfies: （7） in, U' i1 The fundamental compensation voltage actually injected into the dual-frequency active voltage regulation device; U' n1 To apply the actual arc-suppression voltage U' i1 Then, the actual fundamental voltage at the neutral point when the system reaches steady state; Δ E f1 This is the fundamental wave arc suppression error; Calculate Δ I (2)-(1) A_leak_1 and Δ I (4)-(2) A_leak_1 The theoretical value of the sum A1 ' With Δ I (2)-(1) A_leak_3 and Δ I (4 )-(2) A_leak_3 The theoretical value of the sum A3 ' : in, U' i3 The actual third harmonic compensation voltage injected into the dual-frequency active voltage regulation device; Δ E f3 This is the arc suppression error due to the third harmonic; Solving equations (7), (8), and (9) simultaneously yields the fundamental wave arc suppression error Δ. E f1 And the third harmonic arc suppression error Δ E f3 The specific value; S5. Based on the calculated arc suppression error, correct the injection amount of the current active arc suppression measure, and return to step S3 until the arc suppression is identified as successful.

2. The method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on phase leakage current variation, as described in claim 1, is characterized in that: The active arc suppression measure in step S1 is as follows: A controllable fundamental frequency voltage and third harmonic voltage are injected into the neutral point of the generator through a dual-frequency active voltage regulation device. The dual-frequency active voltage regulation device independently adjusts the amplitude and phase of its output fundamental frequency voltage and third harmonic voltage, thereby forcing and maintaining the neutral point voltage at a preset value. Assuming a ground fault occurs in phase A of the generator, when the base frequency voltage output by the dual-frequency active voltage regulation device is... U i1 At that time, the injected fundamental frequency current I i1 The following relationship must be satisfied: （10） in, U n1 is the fundamental voltage at the neutral point of the generator after a ground fault occurs; j is the imaginary unit. ω Angular frequency; This is the sum of the generator stator winding capacitance to ground; E f1 The fundamental potential at the fault point; R g For grounding transition resistance; When the third harmonic voltage output by the dual-frequency active voltage regulation device is U i3 At that time, the injected third harmonic current I i3 The following relationship must be satisfied: （11） in, U n3 This refers to the third harmonic voltage at the neutral point of the generator after a ground fault occurs. E Ai3 For phase A, number 1 i The third harmonic potential of the coil midpoint to the neutral point; n This represents the total number of turns in the stator winding of phase A. C a This is the equivalent capacitance to ground of phase A; C t This represents the equivalent capacitance to ground for each phase at the machine end of the directly connected system. E A3 The third harmonic potential at camera A; E f3 The third harmonic potential at the fault point.

3. The method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on phase leakage current changes, as described in claim 2, is characterized in that: Step S2 specifically includes: For large generators with an ungrounded neutral point, the state change caused by the fault is obtained by calculating the change in phase leakage current of the faulted phase before and after the ground fault occurs; specifically: Record the phase neutral point current and generator terminal current of generator phase A during normal operation and after a single-phase ground fault. During normal operation, the fundamental leakage current of phase A of the generator I (1) A_leak_1 With third harmonic leakage current I (1) A_leak_3 Calculated using the following formulas respectively: I (1) A_leak_1 = I (1) An1 - I (1) At1 （12） I (1) A_leak_3 = I (1) An3 - I (1) At3 （13） in, I (1) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point during normal operation. I (1) An3 This refers to the third harmonic current flowing through the A-phase winding at the neutral point during normal operation. I (1) At1 This refers to the fundamental current flowing through the A-phase winding at the terminal measurement point during normal operation. I (1) At3 This refers to the third harmonic current flowing through the A-phase winding at the terminal measurement point during normal operation. After a single-phase ground fault occurs, the fundamental leakage current of phase A of the generator becomes I (2) A_leak_1 The third harmonic leakage current becomes I (2) A_leak_3 Calculated by the following formulas respectively: I (2) A_leak_1 = I (2) An1 - I (2) At1 （14） I (2) A_leak_3 = I (2) An3 - I (2) At3 （15） in, I (2) An1 This refers to the fundamental current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) An3 This refers to the third harmonic current flowing through the A-phase winding at the neutral point after a ground fault occurs in the generator; I (2) At1 This refers to the fundamental current flowing through the A-phase winding at the generator terminal after a ground fault occurs in phase A of the generator. I (2) At3 This refers to the third harmonic current flowing through the A-phase winding at the generator terminal measurement point after a ground fault occurs in phase A of the generator. When the generator changes from normal operation to a ground fault state, the measured value Δ of the fundamental change in phase leakage current is... I (2)-(1) A_leak_1_meas Measured value of third harmonic variation Δ I (2)-(1) A_leak_3_meas Calculated by the following formula: D I (2)-(1) A_leak_1_meas = I (2) A_leak_1 - I (1) A_leak_1 (16) D I (2)-(1) A_leak_3_meas = I (2) A_leak_3 - I (1) A_leak_3 (17).

4. The method for identifying and correcting errors in active arc suppression results of generator stator grounding faults based on phase leakage current variation, as described in claim 3, is characterized in that: Step S5 specifically involves: Based on the arc suppression error calculated in step S4, the injection amount of the current active arc suppression measure is corrected. The specific correction method is as follows: Let the first... m The arc-extinguishing injection amount in the next iteration is and The calculated arc suppression error is and Then the first m The new arc-extinguishing amount in +1 iteration and Determined by the following formula: After adopting the new arc suppression amount, return to step S3 to recalculate the change in phase leakage current before and after applying the arc suppression and identify the arc suppression result; If the identification result is still unsuccessful, repeat steps S4 and S5 to continue iteratively correcting the arc-extinguishing injection amount until the identification result of step S3 is successful, thus achieving accurate arc extinguishing.

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