Stator winding grounding fault arc extinction method and system based on grounding transition resistor

Abstract

The invention discloses a stator winding grounding fault arc extinction method and system based on grounding transition resistance. The method comprises the following steps: S1, acquiring fundamental voltage of a neutral point and a machine end after normal operation and a grounding fault in real time; s2, calculating a fault phase potential EA1, and calculating a phase angle delta between the fault phase potential EA1 and the neutral point ground voltage UN1; s3, constructing a generator stator winding grounding fundamental wave fault analysis positioning equation, and substituting the measurement and calculation amount to complete fundamental wave fault positioning; s4, if multiple solutions occur in fundamental wave fault positioning, introducing a low-frequency injection quantity check criterion, and screening out a unique correct transition resistance value; and S5, carrying out arc extinction on the fault point of the neutral point of the generator in a high-resistance grounding mode. According to the method, the accuracy and reliability of fault positioning are remarkably improved, the possibility of misjudgment is eliminated, and an accurate compensation basis is provided for arc extinction.

Description

Technical Field

[0001] The present invention relates to the technical field of arc extinguishing for stator winding grounding faults, and specifically relates to an arc extinguishing method and system for stator winding grounding faults based on a grounding transition resistance. Background Art

[0002] The generator of an ocean nuclear power platform is an integrated energy system that uses the thermal energy generated by a nuclear reactor to drive a steam turbine to generate electricity and provide continuous electrical energy for the ocean platform and surrounding facilities. The ocean nuclear power platform operates in a harsh ocean environment for a long time. Affected by the high-corrosion and high-wind-wave environment, single-phase grounding faults of the generator stator winding occur frequently. A relatively large grounding fault current will generate an arc, which will damage the winding insulation, burn the iron core, and sinter the iron core laminations. Moreover, the continuous arcing at the fault point is likely to trigger a destructive short-circuit fault, seriously threatening the safety of the equipment. In addition, the internal space of the platform is compact and contains nuclear reactor loads, and it is extremely sensitive to the arcing process. In order to reduce the damage of the grounding arc to the generator and avoid threatening the safety of the platform, it is urgent to propose a reliable grounding fault arc extinguishing method and be able to identify the nature of the fault after arc extinguishing, so as to take effective fault treatment measures.

[0003] When a single-phase grounding fault occurs in the generator stator winding, according to whether an external injection device is required, the existing fault arc extinguishing methods can be mainly divided into passive and active arc extinguishing methods. Among them, the passive method is mainly to ground the neutral point through an arc suppression coil to compensate for the fault current. However, the arc suppression coil can only basically compensate the fault components of a single frequency and cannot compensate the harmonic components in the fault current, resulting in a still relatively large residual current after compensation. Practical operation experience shows that the existing generator neutral point grounding methods cannot achieve reliable fault arc extinguishing in different fault scenarios. The active arc extinguishing method is to control the voltage at the fault point to be lower than the arc reignition voltage through an external injection source, and theoretically avoid arc reignition. However, the existing active arc extinguishing methods for generator stator grounding faults are prone to the problem of multiple solutions for fault location and there is a risk of secondary arcing. Patent CN113777526A discloses a stator grounding fault location method and system based on the distribution of third harmonic electromotive force, including: S1. Taking the third harmonic slot electromotive force as a unit, calculating the third harmonic slot electromotive force according to the third harmonic electromotive force measured at the neutral point and the machine terminal, and calculating the third harmonic electromotive force of the faulty part of the winding according to the winding connection sequence and the third harmonic slot electromotive force; S2. Based on the third harmonic equivalent circuit of the generator, constructing a fault evaluation index in combination with the third harmonic electromotive force; S3. Presetting multiple reference points in the faulty phase, calculating the fault evaluation index values of each reference point, and regarding the reference point with the smallest calculated value as the fault location to determine the slot number where the fault is located.

[0004] However, this patent only locates faults based on the third-harmonic relationship. Although it has a certain degree of accuracy in some scenarios, there are problems with multiple solutions in location. It is difficult to achieve a unique solution relying solely on the third-harmonic electromotive force, and improper operation is likely to cause secondary arcing problems. In addition, the location method of this patent cannot be used to solve the double-frequency fault electromotive force, and there are significant limitations in the actual application of arc suppression technology. At the same time, the location technology of this patent cannot achieve fault nature identification, which may lead to delays in fault handling and cause serious damage to the generator. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a stator winding grounding fault arc suppression method and system based on the grounding transition resistance to solve the problems of multiple solutions, easy secondary arcing, and inability to achieve fault nature identification existing in the existing location technology.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0007] The stator winding grounding fault arc suppression method based on the grounding transition resistance includes the following steps: S1. For the neutral point and the machine terminal of the generator, respectively obtain the fundamental wave voltages during normal operation and after the grounding fault in real time; S2. According to the terminal voltage during the fault U A and the neutral point-to-ground voltage U N1 , calculate the fault phase electromotive force E A1 by taking the difference, and calculate the phase angle E A1 between the fault phase electromotive force U N1 and the neutral point-to-ground voltage δ according to Fourier analysis; S3. According to the fundamental wave electromotive force phase distribution characteristics, construct a fundamental wave fault analysis and location equation of the generator stator winding grounding with the fault location as the independent variable, and substitute the above calculated quantities to complete the fundamental wave fault location; S4. If there are multiple solutions in the fundamental wave fault location, introduce a low-frequency injection quantity verification criterion to screen out the only correct transition resistance value, and the corresponding location result at this time is regarded as the true fault location; S5. Ground the neutral point of the generator with a high resistance to suppress the arc at the fault point; the high-resistance grounding method is: the neutral point is grounded through a high resistance, and a double-frequency current is injected into the neutral point through an externally added double-frequency active arc suppression device to keep the neutral point with a double-frequency reverse fault electromotive force.

[0008] Preferably, the fundamental wave fault analysis and location equation in step S3 is specifically:

[0009] In the formula, α represents the faulty turn ratio, that is, the ratio of the number of turns from the neutral point of the generator stator winding to the fault point to the number of turns of the complete fault branch; C ∑ is the three-phase capacitance to ground including the stator winding and the directly connected system; R N is a high resistance, and the neutral point is grounded through a high resistance R N high-resistance grounding.

[0010] Preferably, the unique correct positioning solution is screened out by the low-frequency injection quantity verification criterion in step S4. The specific method includes the following steps: T1. Inject a 20Hz low-frequency power supply at the neutral point of the generator, and the low-frequency power supply will not affect the normal operation of the generator; T2. Obtain the voltage and current at the neutral point of the generator at the first moment of normal operation and the second moment after the fault occurs until the arc extinction of the grounding fault respectively, and use Fourier transform to extract the low-frequency components of the voltage and current. The low-frequency components are consistent with the frequency of the low-frequency power supply; T3. Calculate the impedance to ground Z 1 during normal operation through the low-frequency components of the voltage and current at the neutral point at the first moment, and calculate the impedance to ground Z 2 during the grounding fault through the low-frequency components of the voltage and current at the neutral point at the second moment; comprehensively Z 1 and Z 2 to calculate the grounding transition resistance R f1 of the generator during the grounding fault; T4. Measure the actual value of the grounding transition resistance using the low-frequency injection quantity, compare it with the multiple transition resistance values calculated in the case of multiple solutions, and select the correct transition resistance value. The corresponding positioning result is regarded as the true fault location.

[0011] Preferably, the calculation formula of the impedance to ground Z in step T3 is as follows:

[0012] Wherein, U oc and I oc are the low-frequency components of the voltage and current at the neutral point respectively; The calculation formula of the grounding transition resistance in step T3 is as follows: .

[0013] Preferably, in the case of multiple solutions in step T4, the calculation formulas for calculating multiple transition resistances are as follows:

[0014] Wherein, R f ( α ) represents the ground transition resistance obtained through calculation.

[0015] Preferably, the dual-frequency currents injected in step S5 are respectively:

[0016]

[0017] Wherein, I in1 is the fundamental wave current injected; I in3 is the third harmonic current injected; represents the fundamental wave voltage from the neutral point to the fault point; represents the third harmonic voltage from the neutral point to the fault point; U N3 is the third harmonic voltage of the center point to the ground.

[0018] Preferably, the method further includes a fault identification method based on the measured value of the transition resistance. The fault identification method includes the following steps: M1. According to the ground transition resistance measurement method, continuously measure the value of the ground transition resistance, obtain the voltage and current of the generator neutral point at the third moment after the arc suppression is completed and stable, and use Fourier transform to extract the low-frequency components of the voltage and current, and calculate the impedance to the ground after the ground fault is stable Z 3 ; Comprehensively Z 2 and Z 3 Calculate the ground transition resistance of the generator after the ground fault occurs R f2 ; M2. Identify the nature of the fault through the following rules:

[0019] Wherein, R SET is the set threshold.

[0020] Preferably, in step M2, after the fault nature is determined, if it is a permanent fault, the neutral point voltage is maintained to be equal in amplitude and opposite in phase to the fault electromotive force to suppress the grounding fault current; at this time, if the generator does not have sufficient backup power, the arc suppression state is maintained and the operation continues. After sufficient backup power is available, the load is transferred, the protection operates, and the generator is smoothly tripped; if the generator has sufficient backup power, the protection is opened and the generator is quickly tripped. If it is a transient fault, the system continues to operate. Whether it is a transient grounding fault or a permanent grounding fault, the externally applied current injection finally stops.

[0021] An arc suppression system for stator winding grounding faults based on a grounding transition resistance, characterized in that: the arc suppression system executes the arc suppression method described above; the arc suppression system includes at least one memory for storing an arc suppression program; at least one processor for executing the arc suppression program stored in the memory. When the arc suppression program stored in the memory is entered, the processor is used to execute the arc suppression method described above.

[0022] Preferably, the memory is further used to store a fault identification program; the processor is used to execute the fault identification program stored in the memory. When the fault identification program stored in the memory is entered, the processor is used to execute the fault identification method described above.

[0023] Due to the adoption of the above technical solutions, the technical progress achieved by the present invention is as follows.

[0024] By obtaining the fundamental wave voltage phase distribution characteristics of the generator neutral point and the machine terminal, the present invention obtains an analytical positioning equation for generator stator winding grounding faults that may have multiple solutions. Further, through cooperation with the low-frequency injection quantity verification criterion, the unique positioning solution is screened out to determine the true fault location, realizing fault location at any position of the entire winding, breaking through the limitations of traditional methods, and significantly improving the accuracy of fault location. Compared with CN113777526A, the present invention comprehensively considers the fundamental wave and the low-frequency injection quantity, constructs a fundamental wave fault analytical positioning equation and a low-frequency injection quantity verification criterion with the fault location as the independent variable, screens out the unique positioning solution, significantly improves the accuracy and reliability of fault location, eliminates the possibility of misjudgment, and provides an accurate compensation basis for arc suppression; by injecting dual-frequency current through a dual-frequency active arc suppression device, the neutral point maintains a dual-frequency reverse fault potential, which can effectively suppress the fault current, achieve reliable arc suppression within the entire winding range, and prevent secondary arcing, significantly improving the reliability and effectiveness of arc suppression. Especially, the arc suppression effect at non-coil connection points is significantly better than traditional methods. Moreover, the present invention can adapt to various complex fault scenarios, including faults at coil connection points and non-coil connection points, enhancing the adaptability of the system in complex fault scenarios and improving the robustness of fault location.

[0025] According to the low-frequency components of the voltage and current at the neutral point of the generator, the present invention calculates the grounding transition resistance during the grounding fault and the stable grounding transition resistance after the arc suppression is completed respectively. By comparing the magnitudes of the transition resistances in different states with a threshold value, the nature of the fault can be judged, and the transient fault and the permanent fault can be accurately distinguished, and corresponding treatment measures can be taken. Moreover, by taking targeted treatment measures according to the nature of the fault, the risk brought by misjudgment is avoided, and the safety and reliability of the system are improved. At the same time, the present invention provides simple and effective fault identification rules, which are easy to implement in engineering, improve the practicability of fault identification and the convenience of engineering application, can quickly and accurately judge the nature of the fault, and provide strong support for the operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flowchart of the present invention; Figure 2 is a flowchart of screening out the only correct positioning solution by the low-frequency injection quantity verification criterion in step S4 of the present invention; Figure 3 is a flowchart of the fault identification method based on the measured value of the transition resistance of the present invention; Figure 4 is a schematic diagram of the positioning effect of the present invention, where Figure 4 (a) is a schematic diagram of the positioning effect of the fault positioning at α= 0.125 of the present invention, Figure 4 (b) is a schematic diagram of the positioning effect of the fault positioning at α= 0.250 of the present invention, Figure 4 (c) is a schematic diagram of the positioning effect of the fault positioning at α= 0.375 of the present invention, Figure 4 (d) is a schematic diagram of the positioning effect of the fault positioning at α= 0.50 of the present invention; Figure 5 is a schematic diagram of the arc suppression effect of the present invention, where Figure 5 (a) is a schematic diagram of the arc suppression effect of the arc suppression of the fault at α= 0.125 of the present invention, Figure 5 (b) is a schematic diagram of the arc suppression effect of the arc suppression of the fault at α= 0.250 of the present invention, Figure 5 (c) is a schematic diagram of the arc suppression effect of the arc suppression of the fault at α= 0.375 of the present invention, Figure 5 (d) is a schematic diagram of the arc suppression effect of the arc suppression of the fault at α= 0.50 of the present invention; Figure 6 is a graph of the change law of the transition resistance in the 300Ω constant resistance model corresponding to the transient grounding fault of the present invention; Figure 7 It is the variation law diagram of the transition resistance in the 300Ω constant resistance model corresponding to the permanent ground fault of the present invention. Specific embodiments

[0027] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0028] An arc suppression method for stator winding ground faults based on grounding transition resistance, combined with Figure 1 as shown, includes the following steps: S1. For the neutral point and the machine terminal of the generator, respectively, the fundamental voltages during normal operation and after the ground fault are obtained in real time.

[0029] The present invention is not limited to the judgment basis for whether a single-phase ground fault occurs. Generally, the phase with the lowest voltage is used as the fault phase.

[0030] S2. Based on the terminal voltage during the fault U A and the neutral point-to-ground voltage U N1 , calculate the fault phase electromotive force E A1 by taking the difference, and calculate the phase angle E A1 between the fault phase electromotive force U N1 and the neutral point-to-ground voltage δ according to Fourier analysis.

[0031] S3. Based on the phase distribution characteristics of the fundamental wave electromotive force, construct a fundamental wave fault analysis and positioning equation of the generator stator winding ground fault with the fault location as the independent variable, and substitute the above calculation quantities to complete the fundamental wave fault positioning.

[0032] Specifically, the fundamental wave fault analysis and positioning equation is as follows:

[0033] In the formula, α represents the fault turn ratio (that is, the ratio of the number of turns between the neutral point of the generator stator winding and the fault point to the number of turns of the complete fault branch. The present invention uses the fault turn ratio to represent the fault location); C ∑ is the three-phase capacitance to ground including the stator winding and the directly connected system; R N is a high resistance, and the neutral point is grounded through R N high resistance. Using the fundamental wave zero-sequence voltage and the fault phase electromotive force after the fault, find in the range of α ∈[0,1] such that f ( α) The solution closest to 0 can be calculated, and then α .

[0034] S4. If there are multiple solutions in the fundamental wave fault location, introduce the low-frequency injection quantity verification criterion to screen out the only correct transition resistance value. At this time, the corresponding location result can be regarded as the true fault location.

[0035] As Figure 2 shown, the low-frequency injection quantity verification criterion screens out the only correct location solution. The specific method includes the following steps: T1. Inject a 20Hz low-frequency power supply at the neutral point of the generator. The low-frequency power supply will not affect the normal operation of the generator.

[0036] T2. Obtain the voltage and current at the neutral point of the generator at the first moment of normal operation and the second moment after the fault occurs until the arc extinction of the ground fault respectively, and use Fourier transform to extract the low-frequency components of the voltage and current. The low-frequency components are consistent with the frequency of the low-frequency power supply.

[0037] T3. Calculate the impedance to the ground during normal operation through the low-frequency components of the voltage and current at the neutral point at the first moment Z 1 , and calculate the impedance to the ground during the ground fault through the low-frequency components of the voltage and current at the neutral point at the second moment Z 2 ; Combine Z 1 and Z 2 to calculate the grounding transition resistance of the generator during the ground fault R f1 .

[0038] T4. Use the low-frequency injection quantity to measure the actual value of the grounding transition resistance, compare it with the multiple transition resistance values calculated in the case of multiple solutions, and select the correct transition resistance value. The corresponding location result can be regarded as the true fault location.

[0039] Specifically, in step T3, the calculation formula for the impedance to the ground Z is as follows:

[0040] where U oc and I oc are the low-frequency components of the voltage and current at the neutral point respectively.

[0041] Specifically, in step T3, the calculation formula for the grounding transition resistance is as follows:

[0042] Specifically, in step T4, in the case of multiple solutions, the calculation formulas for multiple transition resistances are as follows:

[0043] where, R f ( α ) represents the grounding transition resistance obtained through calculation.

[0044] S5. The neutral point of the generator is grounded through a high resistance to extinguish the arc at the fault point; the high-resistance grounding method is: the neutral point is grounded through a high resistance, and a dual-frequency current is injected into the neutral point through an externally added dual-frequency active arc extinguishing device to keep the neutral point at a dual-frequency reverse fault potential.

[0045] Specifically, the injected dual-frequency currents are respectively:

[0046]

[0047] where, I in1 is the injected fundamental current; I in3 is the injected third-harmonic current; represents the fundamental voltage from the neutral point to the fault point; represents the third-harmonic voltage from the neutral point to the fault point.

[0048] As Figure 3 shown, this method also includes a fault identification method based on the measured value of the transition resistance. The fault identification method includes the following steps: M1. According to the grounding transition resistance measurement method in step S4, continuously measure the value of the grounding transition resistance, obtain the voltage and current at the neutral point of the generator at the third moment after the arc extinguishing is completed and stabilized, and use Fourier transform to extract the low-frequency components of the voltage and current, and calculate the impedance to the ground Z 3 ; comprehensively Z 2 and Z 3 calculate the grounding transition resistance R f2 of the generator after the grounding fault occurs; M2. Identify the nature of the fault through the following rules:

[0049] where, R SET is the set threshold value, and it is recommended to take a value of 8000 - 10000 Ω in engineering.

[0050] Specifically, after determining the nature of the fault, if it is a permanent fault, the neutral point voltage should be kept equal in magnitude and opposite in phase to the fault electromotive force to suppress the grounding fault current. At this time, if the generator does not have sufficient backup power, the arc suppression state should be maintained and the generator should continue to operate. After sufficient backup power is available, the load should be transferred, the protection should act, and the generator should be smoothly tripped; if the generator has sufficient backup power, the protection should be released and the generator should be quickly tripped.

[0051] If it is a transient fault, the system will continue to operate. Whether it is a transient grounding fault or a permanent grounding fault, the externally applied current injection will eventually stop.

[0052] The present invention can flexibly suppress the arc of the single-phase grounding fault of the generator stator and identify the nature of the fault, which is crucial for preventing equipment damage, avoiding accident power outages, ensuring power supply reliability, and protecting personal safety.

[0053] The effectiveness of the above method is verified by simulation below.

[0054] Each phase of the generator in this embodiment includes 2 branch windings, each branch is composed of 8 coils connected in series, the rated voltage is 10.5 kV, the stator winding resistance per phase: 1.528 mΩ, the stator winding leakage inductance per phase: 2.84 mH, the stator winding capacitance per phase: 0.397 μF, the number of pole pairs is 1, the total number of slots is 48, the corresponding slot pitch electrical angle is 7.5°, the neutral point grounding resistance is 2286 Ω, and the direct-connected system ground capacitance per phase: 0.405 μF. The analysis is carried out taking the first branch of phase A as an example.

[0055] To verify the arc suppression effect of the arc suppression unit based on the slot electromotive force analysis, a single-phase grounding fault with a transition resistance of 300 Ω is set at the connection of the A-phase coil of the generator at 0.2 s. α= 0.125, α= 0.250, α= 0.375, α= 0.50. The positioning results based on the method of the present invention are as Figure 4 shown, and the schematic diagrams of the positioning effects of the fault positioning at the above different a values are respectively as Figure 4 shown in (a), (b), (c), (d) in; the arc suppression results are as Figure 5 shown, and the schematic diagrams of the arc suppression effects of the fault arc suppression at the above different α values are respectively as Figure 5 shown in (a), (b), (c), (d) in. Figure 4 In, the horizontal axis represents time, with the unit of second, and the vertical axis α represents the fault location. It can be seen that in the method of the present invention, the problem of multi-solution in accurate positioning and elimination can be realized. Figure 5In it, the generators all adopt the high-resistance grounding method, and the active arc suppression device is put into operation at 0.3 s. The horizontal axis represents time, with the unit of second. The vertical axis I f represents the fault current, with the unit of A. U f represents the fault potential, with the unit of kV. In Figure 5 it can be seen that the arc suppression effect of the method of the present invention is very good, which can avoid secondary arc reignition and achieve accurate and reliable arc suppression.

[0056] In the simulation model, a 300-ohm constant resistance model is used to simulate the grounding fault resistance and verify the fault identification method proposed in this application.

[0057] Assume that the starting time of the single-phase grounding fault is the 0.2 s, the transient fault duration is 0.3 s, and the hybrid flexible grounding method is used to suppress the arc at the fault point at the 0.5 s. A 300Ω constant resistance model is used to simulate the grounding fault resistance. According to the method of the present invention, the waveform of the change of the transition resistance is calculated as Figure 6 shown. The measured transition resistance in the constant resistance model is about 300Ω at the time of fault occurrence. If the measured transition resistance value after arc suppression is greater than the set threshold of 10,000Ω, it is determined that the fault nature is a transient fault, verifying the effectiveness of the method.

[0058] Assume that the starting time of the single-phase grounding fault is the 0.2 s, a permanent fault is set, and the hybrid flexible grounding method is used to suppress the arc at the fault point at the 0.4 s. A 300Ω constant resistance model is used to simulate the grounding fault resistance. According to the method of the present invention, the waveform of the change of the transition resistance is calculated as Figure 7 shown. The measured transition resistance in the constant resistance model is about 300Ω at the time of fault occurrence. If the measured transition resistance value after arc suppression is less than 10,000Ω, it is determined that the fault nature is a permanent fault, verifying the effectiveness of the method.

[0059] An arc suppression system for stator winding grounding faults based on grounding transition resistance includes: a processor, a communications interface, a memory, and a communication bus. Among them, the processor, the communications interface, and the memory complete communication with each other through the communication bus. The processor can call the logical instructions in the memory to execute the above method. Specifically, the arc suppression system includes at least one memory for storing an arc suppression program; at least one processor for executing the arc suppression program stored in the memory. When the arc suppression program stored in the memory is entered, the processor is used to execute the arc suppression method in the present invention. The memory is also used to store a fault identification program; the processor is used to execute the fault identification program stored in the memory. When the fault identification program stored in the memory is entered, the processor is used to execute the fault identification method in the present invention.

[0060] In addition, when the logical instructions in the above memory can be implemented in the form of software functional units and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method of the present invention.

[0061] Based on the method in the present invention, the present invention provides a computer-readable storage medium. The computer-readable storage medium stores a computer program. When the computer program runs on the processor, it causes the processor to execute the method in the present invention.

[0062] Based on the method in the present invention, the present invention provides a computer program product. When the computer program product runs on the processor, it causes the processor to execute the method in the present invention.

[0063] It can be understood that the processor in the present invention can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor can be a microprocessor or any conventional processor.

[0064] The method steps in the present invention can be implemented in a hardware manner or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory (RAM), flash memory, read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), register, hard disk, removable hard disk, CD-ROM, or any other form of storage medium well-known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC.

[0065] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions according to the method of the present invention are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center in a wired manner (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or a wireless manner (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that the computer can access or a data storage device such as a server or data center that includes one or more integrated available media. The available medium can be a magnetic medium (such as a floppy disk, hard disk, magnetic tape), an optical medium (such as a DVD), or a semiconductor medium (such as a solid state disk (SSD)), etc.

Claims

1. A method for arc extinguishing of stator winding grounding fault based on grounding transition resistance, characterized in that: The following steps are involved: S1. Obtain the fundamental voltage of the generator at the neutral point and the generator end in real time during normal operation and after a ground fault; S2. Based on the terminal voltage at the time of fault U A and neutral point to ground voltage U N1 , calculate the fault phase potential by difference E A1 , according to Fourier analysis, calculate the fault phase potential E A1 Neutral point to ground voltage U N1 Phase angle δ ; S3. According to the phase distribution characteristics of the fundamental wave potential, an analytical positioning equation for the grounding fundamental wave fault of the generator stator winding is constructed with the fault position as the independent variable, and the above calculation amount is brought into play to complete the positioning of the fundamental wave fault; S4. If there are multiple solutions for fundamental wave fault location, the low-frequency injection amount verification criterion is introduced to screen out the only correct transition resistance value. At this time, the corresponding location result is regarded as the real fault location; S5. Use high-resistance grounding to extinguish arc at the fault point of the generator’s neutral point; the high-resistance grounding method is as follows: the neutral point is grounded through high resistance, and a dual-frequency current is injected into the neutral point through an external dual-frequency active arc extinguishing device, so that the neutral point maintains a dual-frequency reverse fault potential.

2. The arc extinguishing method for stator winding ground fault based on ground transition resistance according to claim 1 is characterized in that: The fundamental wave fault analytical location equation in step S3 is specifically: In the formula, α represents the fault turns ratio, which is the ratio of the number of turns between the neutral point and the fault point of the generator stator winding to the number of turns of the complete fault branch; C ∑ It is the three-phase capacitance to ground including the stator winding and the direct-connected system; R N The neutral point is connected to a high resistance R N High resistance ground.

3. The arc extinguishing method for stator winding grounding fault based on grounding transition resistance according to claim 2 is characterized in that: In step S4, the low-frequency injection amount verification criterion selects the only correct positioning solution, and the specific method includes the following steps: T1. Inject 20Hz low-frequency power into the neutral point of the generator, and the low-frequency power will not affect the normal operation of the generator; T2. Obtain the voltage and current of the generator neutral point at the first moment of normal operation and the second moment after the fault occurs and before the start of ground fault arc extinguishing, and use Fourier transform to extract the low-frequency components of the voltage and current, which are consistent with the frequency of the low-frequency power supply; T3. Calculate the impedance to ground during normal operation by using the voltage and current low-frequency components of the neutral point at the first moment. Z 1. Calculate the impedance to ground during ground fault by using the voltage and current low-frequency components of the neutral point at the second moment Z 2. Comprehensive Z 1 and Z 2 Calculate the ground transition resistance of the generator when a ground fault occurs R f1 ; T4. Use low-frequency injection to measure the actual ground transition resistance value, compare it with the multiple transition resistance values ​​calculated in the multiple solutions, select the correct transition resistance value, and the corresponding positioning result is regarded as the real fault location.

4. The arc extinguishing method for stator winding ground fault based on ground transition resistance according to claim 3 is characterized in that: The calculation formula of the ground impedance Z in step T3 is as follows: in, U oc and I oc They are the low-frequency components of the voltage and current at the neutral point respectively; The ground transition resistor in step T3 The calculation formula is as follows: 。 5. The arc extinguishing method for stator winding grounding fault based on grounding transition resistance according to claim 3 is characterized in that: The calculation formula for calculating multiple transition resistances in the case of multiple solutions in step T4 is as follows: in, R f ( α ) represents the ground transition resistance obtained by calculation.

6. The arc extinguishing method for stator winding ground fault based on ground transition resistance according to claim 3 is characterized in that: The dual-frequency currents injected in step S5 are respectively: ; in, I in1 is the injected fundamental current; I in3 is the injected third harmonic current; Represents the fundamental voltage from the neutral point to the fault point; Represents the third harmonic voltage from the neutral point to the fault point; U N3 It is the third harmonic voltage from the center point to the ground.

7. The arc extinguishing method for stator winding ground fault based on ground transition resistance according to claim 3 is characterized in that: The method also includes a fault identification method based on the transition resistance measurement value, the fault identification method comprising the following steps: M1. According to the grounding transition resistance measurement method as described in claim 3, the grounding transition resistance value is continuously measured, the voltage and current of the neutral point of the generator at the third moment after the arc extinguishing is completed and stabilized are obtained, and the low-frequency components of the voltage and current are extracted by Fourier transform to calculate the impedance to ground after the ground fault is stabilized Z 3. Comprehensive Z 2 and Z 3. Calculate the ground transition resistance of the generator after a ground fault occurs R f2 ; M2. Identify the nature of the fault by the following rules: in, R SET The threshold to set.

8. The arc extinguishing method for stator winding ground fault based on ground transition resistance according to claim 7, characterized in that: In the step M2, after the nature of the fault is determined, if it is a permanent fault, the neutral point voltage is kept equal to the fault electromotive force in amplitude and opposite in phase, and the ground fault current is suppressed; At this time, if the generator does not have sufficient backup power, it will maintain the arc extinguishing state and continue to run. When sufficient backup power is available, the load will be transferred, the protection will be activated, and the generator will be cut off smoothly. If the generator has sufficient backup power, the protection will be opened and the generator will be cut off quickly. If it is a transient fault, the system continues to operate, and the injection of external current will eventually stop regardless of whether it is a transient ground fault or a permanent ground fault.

9. The stator winding grounding fault arc extinguishing system based on grounding transition resistance is characterized by: The arc extinguishing system implements the arc extinguishing method according to any one of claims 7 to 8; the arc extinguishing system comprises At least one memory for storing an arc extinguishing program; At least one processor is used to execute the arc extinguishing program stored in the memory. When the arc extinguishing program stored in the memory is entered, the processor is used to execute the arc extinguishing method.

10. The stator winding grounding fault arc extinguishing system based on grounding transition resistance according to claim 9, characterized in that: The memory is also used to store a fault identification program; The processor is used to execute the fault identification program stored in the memory. When the fault identification program stored in the memory is entered, the processor is used to execute the fault identification method.

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