Ground fault arc extinction and property identification method for multi-machine common-bus system based on machine terminal voltage regulation and control

Abstract

The invention discloses a multi-machine common-bus system grounding fault arc extinction and property identification method based on machine end voltage regulation and control. The method comprises the following steps: S1, machine end arc extinction; s2, low-frequency injection; s3, low-frequency component measurement; s4, grounding transition resistance calculation: through the low-frequency components of the terminal voltage and the current of each generator at the first moment, calculating the ground impedance Zi1 during a grounding fault; calculating the ground impedance Zi2 after the fault is stable through the low-frequency components of the terminal voltage and the current at the second moment; calculating the grounding transition resistance Rgi of each generator when any generator fails by integrating the Zi1 and the Zi2; s5, fault identification: if Rgi is greater than or equal to a set threshold value, identifying the fault as an instantaneous fault, and if Rgi is less than the set threshold value, identifying the fault as a permanent fault; if a generator is identified as a permanent fault, the generator can be identified as a fault unit. According to the method, the problem of poor economical efficiency of existing fault arc extinction and fault identification in a multi-machine common-mother system can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of generator safety protection of offshore oil platforms, and particularly relates to a multi-generator common ground fault arc extinguishing and property identification method based on machine terminal voltage regulation. BACKGROUND

[0002] Offshore oil platforms are operated in harsh marine environments for a long time, and are affected by high corrosion and stormy weather. As a result, single-phase ground faults of generator stator windings occur frequently. A large ground fault current can generate an arc, which can damage the winding insulation, burn the core, and sinter the core laminations. The continuous arc action of the fault point can also easily cause a destructive short-circuit fault, which seriously threatens the safety of the equipment. At the same time, the internal space of the platform is compact and very sensitive to the arc process. In order to avoid the harm of the arc to the safety of the platform, a reliable arc extinguishing method is urgently needed, and the fault property and the generator unit are identified after arc extinguishing to take effective fault handling measures.

[0003] When a single-phase ground fault occurs in the stator winding of a generator, the existing fault arc extinguishing methods can be mainly divided into passive and active arc extinguishing methods according to whether an external injection device is needed. Among them, the passive method is mainly to ground the neutral point through an arc extinguishing coil to compensate for the fault current. However, the arc extinguishing coil can only basically compensate for the single-frequency fault component and cannot compensate for the harmonic component in the fault current, and the residual current is still large after compensation. Practical operation experience shows that the existing generator neutral point grounding methods cannot achieve reliable fault arc extinguishing under different fault scenarios. The active arc extinguishing method controls the voltage at the fault point to be lower than the arc reignition voltage through an external injection source, which avoids arc reignition in principle. However, the existing active arc extinguishing method for generator stator ground faults has the problem of multiple solutions in fault positioning and has the risk of secondary arc.

[0004] Patent CN120073637A discloses a stator winding ground fault arc extinguishing method and system based on a grounding transition resistance, which specifically discloses a stator winding ground fault arc extinguishing method based on a grounding transition resistance and a fault identification method based on a transition resistance measurement value, including: S1. Real-time acquisition of the fundamental voltage of the neutral point and the machine terminal of the generator under normal operation and after ground fault; S2. According to the machine terminal voltage U A and the neutral point-to-ground voltage U N1 , the fault phase potential is calculated by difference E A1 According to Fourier analysis, the phase angle of the fault phase potential E A1 and the neutral point-to-ground voltage U N1 is calculated δ;S3. According to the phase distribution characteristics of the fundamental potential, a generator stator winding grounding fundamental fault analytical positioning equation with the fault position as the independent variable is constructed, the above calculation amount is substituted, and the fundamental fault positioning is completed; S4. If multiple solutions appear in the fundamental fault positioning, a low-frequency injection amount checking criterion is introduced to screen out a unique correct transition resistance value, and the positioning result corresponding to the transition resistance value is regarded as the real fault position; S5. The arc extinction of the fault point is performed by grounding the neutral point of the generator in a high-resistance grounding mode; the high-resistance grounding mode is that the neutral point is grounded through a high-resistance, and a double-frequency compensation current is injected into the neutral point through an external double-frequency active arc extinguishing device, so that the neutral point maintains a double-frequency reverse fault potential.

[0005] However, the patent only targets a single-machine system, and the arc extinction and fault identification are performed by injecting a current from the neutral point, so that if the multi-machine system is targeted, the same number of programmable alternating current sources as the number of generators is required, which reduces the economy. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a multi-machine common system grounding fault arc extinction and property identification method based on machine terminal voltage regulation, so as to solve the problem of poor economy of the existing fault arc extinction and fault identification in the multi-machine common system.

[0007] To solve the above technical problems, the technical solutions adopted by the present application are as follows.

[0008] The multi-machine common system grounding fault arc extinction and property identification method based on machine terminal voltage regulation comprises the following steps: S1. Machine terminal arc extinction: double-frequency injection current is calculated according to the fault positioning result, and then double-frequency compensation current is injected from the machine terminal bus through a double-frequency active arc extinguishing device, so that the machine terminal of the fault generator maintains a double-frequency reverse fault potential; S2. Low-frequency injection: 20Hz low-frequency current is continuously injected at the machine terminal bus, and the low-frequency current does not affect the normal operation of the generator; S3. Low-frequency component measurement: the voltage and current of each generator at a first time of normal operation and at a second time from the occurrence of the fault to the start of the grounding fault arc extinction are obtained respectively, and the low-frequency components are extracted by using Fourier transform, the low-frequency components being consistent with the frequency of the low-frequency power supply; S4. Grounding transition resistance calculation: the grounding impedance at the time of grounding fault is calculated by using the low-frequency components of the voltage and current of each generator at the first time Z i1 ; the grounding impedance after the fault is stabilized is calculated by using the low-frequency components of the voltage and current of each generator at the second time Z i2 ; and the transition resistance is calculated by comprehensively considering Z i1 and Z i2Calculate the grounding transition resistance of each generator in the event of a generator failure. R gi ; S5. Fault Identification: If R gi If the value is greater than or equal to the set threshold, it is identified as a transient fault. R gi If the value is less than the set threshold, it is identified as a permanent fault; if a generator is identified as a permanent fault, then the generator can be identified as a faulty unit.

[0009] Preferably, the calculation formula for the dual-frequency compensation current injected at the machine terminal in step S1 is as follows:

[0010] In the formula, I i1 and I i3 These are the fundamental compensation current and the third harmonic compensation current injected from the generator terminal side, respectively. E f1 and E f3 These are the ground wave and third harmonic voltage at the fault point, respectively. E Ai3 For the first i Third harmonic potential of the coil midpoint to the neutral point; E A3 is the third harmonic component of the phase voltage of the faulty phase; n is the total number of turns in the stator winding; C a This is the equivalent capacitance to ground of a single-turn coil; C ∑ This is the sum of the three-phase-to-ground capacitances, including the stator windings and the direct-connected system. R n1 For high resistance, the neutral point is via R n1 High-resistance grounding; j Indicates a 90° phase difference; Angular frequency; C t This is the equivalent capacitance to ground of the directly connected system terminal.

[0011] Preferably, step S2 specifically involves injecting a 20Hz low-frequency current into the generator terminal bus using a programmable AC power supply, and the low-frequency current will not affect the normal operation of the generator.

[0012] Preferably, the multi-generator shared-bus system includes 5 generators, namely generator units 1 to 5, with generator unit 1 being the faulty unit; in step S3, voltage and current are measured at the generator terminals of each generator using voltage and current transformers. Under fault conditions, the 20Hz low-frequency current at the generator terminals is:

[0013] In the formula, the 20Hz current measured on the secondary side of the current transformer at the generator terminal from Unit 1 to Unit 5 is used. I 20t_1 ~ I 20t_5 This indicates that the 20Hz current measured on the secondary side of the current transformer at the generator terminals at the neutral point between Unit 2 and Unit 5 is used for... I 20n_2 ~ I 20n_5 express; I 20_O It is the 20Hz current flowing to the equivalent capacitance of the external system; U f The voltage to ground at the fault point. C 2~ C 5 represents the equivalent distributed capacitance from Unit 2 to Unit 5; The calculation formula for injecting a 20Hz low-frequency current in step S2 is as follows:

[0014] The formula assumes that the ground capacitance parameters of each generator are the same, therefore the zero-sequence current at the terminals of non-faulty generators is equal. I 20t_1 To inject low-frequency current into the faulty generator; I i20 This refers to the continuous injection of a 20Hz low-frequency current at the machine terminal bus.

[0015] Preferably, step S4 specifically comprises:

[0016] in, U oc The terminal voltage is measured during normal operation. X c For the three-phase ground capacitive reactance of the generator;

[0017] in, U' oc Measure the terminal voltage after the fault has stabilized; The 20Hz current of Unit 1 was measured on the secondary side; R gFor the transition resistance at the fault point; Because at this time the generator's three-phase ground capacitance X c Given this information, the actual ground fault resistance can be calculated by substituting it into the given values:

[0018] and R gi = R g Therefore: .

[0019] Preferably, the threshold range set in step S5 is 8000 ohms to 10000 ohms.

[0020] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0021] This invention utilizes generator-end arc suppression to achieve dual-frequency current injection at the computer terminal based on fault location results. Then, a dual-frequency active arc suppression device injects dual-frequency compensation current from the generator-end bus, maintaining a dual-frequency reverse fault potential at the generator-end. Compared to the method mentioned in CN120073637A, this application only requires installing an AC converter at the generator-end bus to complete arc suppression for multiple generators, significantly improving economic efficiency and reducing maintenance costs. Simultaneously, it can adapt to various complex fault scenarios, including faults at coil connection points and non-coil connection points, enhancing the system's adaptability to complex fault scenarios and improving the robustness of fault location.

[0022] This invention identifies faults based on a grounding transition resistance threshold. It calculates the grounding transition resistance during a grounding fault and the grounding transition resistance after arc suppression by analyzing the low-frequency components of voltage and current at the generator terminals. By comparing the magnitude of the transition resistance in different states with the threshold, the nature of the fault is determined, accurately distinguishing between transient and permanent faults, and allowing for appropriate handling measures. For transient faults, the external voltage source is removed directly after successful arc suppression, restoring normal system operation. For permanent faults, the neutral point voltage and the fault electromotive force should be kept equal in amplitude but opposite in phase to suppress the grounding fault current. Simultaneously, the faulty generator unit can be identified, and targeted handling measures are taken based on fault identification, avoiding the risks of misjudgment and improving system safety and reliability. Compared to the method mentioned in CN120073637A, in a multi-generator shared-bus system, this method reduces the number of programmable AC power supplies while still identifying faulty generator units, offering more comprehensive functionality.

[0023] This invention provides simple and effective fault identification rules that are easy to implement in engineering, improving the practicality of fault identification and the convenience of engineering applications. It can quickly and accurately identify faults and provide strong support for system operation. Attached Figure Description

[0024] Figure 1 This is a flowchart of the present invention; Figure 2 This is a wiring diagram of the active arc suppression method based on terminal voltage regulation of the present invention; Figure 3 Wiring diagram for fault nature identification in this invention; Figure 4 This is the equivalent circuit diagram of the computer-side grounding transition resistor in step S4 of the present invention. Figure 5 This is a simulation diagram of the arc-suppression effect of the present invention, wherein, Figure 5 (a) is the present invention for α= A schematic diagram illustrating the arc extinguishing effect at fault extinguishing point 0.25. Figure 5 (b) For the present invention α= A schematic diagram illustrating the arc extinguishing effect at fault extinguishing point 0.50. Figure 5 (c) For the present invention α= A schematic diagram of the arc extinguishing effect at fault extinguishing point 0.75; Figure 6 The diagram shows the simulation results of fault nature identification under three different fault scenarios of the invention. Figure 6 (a) and Figure 6 (b) is α A single-phase ground fault at =0.125, with a ground transition resistance of 50Ω; Figure 6 (c) and Figure 6 (d) is α A single-phase ground fault at =0.625, with a ground transition resistance of 200Ω; Figure 6 (e) and Figure 6 (f) is α A single-phase ground fault at =0.5, with a grounding transition resistance of 500Ω; Figure 7 For the present invention in α A permanent fault with a grounding transition resistance of 500Ω was set at point =0.75. Simulation results were used to record the changes in grounding transition resistance for five generating units. Figure 7 (a) is a schematic diagram of the simulation results of the grounding transition resistance change of Unit 1; Figure 7 (b) is a schematic diagram of the simulation results of the grounding transition resistance change of Unit 2; Figure 7(c) is a schematic diagram of the simulation results of the grounding transition resistance change of Unit 3; Figure 7 (d) is a schematic diagram of the simulation results of the grounding transition resistance change of Unit 4; Figure 7 (e) is a schematic diagram of the simulation results of the grounding transition resistance change of Unit 5; Figure 8 Equivalent structure diagram of phase A fault in step S1 of the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] A method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation, combined with Figure 1 As shown, the process includes steps S1 to S5, where step S1 is used to extinguish the arc of the fault; steps S2 to S5 are used to identify the nature of the fault, as detailed below: S1. Generator Terminal Arc Suppression: Based on the fault location results, dual-frequency current is injected into the computer terminal, and then dual-frequency compensation current is injected from the generator terminal bus through the dual-frequency active arc suppression device to maintain the dual-frequency reverse fault potential at the generator terminal of the faulty generator.

[0027] This step is based on a generator terminal arc suppression method for a single-phase ground fault in any generator in a multi-generator shared bus system. The calculation of the dual-frequency compensation current injected into the generator terminal in this step is explained below with a specific example: When a stator ground fault occurs in a generator, and active arc suppression compensation is injected from the fault camera side of the generator, taking phase A as an example, each phase branch of the stator is composed of single-turn coils connected in series. The equivalent structure diagram of the faulty phase A is shown below. Figure 8 As shown.

[0028] Figure 8 The electrical quantities of phase A are explained as follows: E Ai(1,3) Let be the dual-frequency potential between the midpoint and neutral point of the i-th turn of the coil, where 1 represents the fundamental component and 3 represents the third harmonic component. I An1 This is the fundamental frequency current to ground at the neutral point; U Ai(1,3) It is the dual-frequency voltage between the midpoint of the i-th turn of the faulty winding and ground, where 1 represents the fundamental component and 3 represents the third harmonic component. I i(1,3) This refers to the dual-frequency compensation current injected from the generator terminal side, where 1 represents the fundamental component and 3 represents the third harmonic component. C ai This is the equivalent capacitance to ground of a single-turn coil; R g For the transition resistance at the fault point;E A(1,3) This refers to the dual-frequency phase voltage of phase A. U N(1,3) This is a neutral-to-ground dual-frequency voltage; C a1 This is the equivalent capacitance to ground value of the first single-turn coil; U f(1,3) The dual-frequency voltage to ground at the fault point; C an This is the equivalent capacitance to ground of the nth single-turn coil; C t This refers to the equivalent capacitance to ground at the directly connected system terminal. U T(1,3) This is the dual-frequency voltage at the generator terminals. Kirchhoff's current equation for phase A winding is as follows:

[0029] Where n is the total number of turns in the stator winding; U Ai1 The voltage between the midpoint of the i-th turn of the faulty winding and ground. U At1 The voltage of the faulty camera relative to ground wave; U f1 The voltage at the fault point relative to ground. I i1 This is the fundamental compensation current injected from the generator terminal side; j Indicates a 90° phase difference; Angular frequency; Assuming the generator's three-phase windings are symmetrical and the coil-to-ground capacitance parameters are equal, i.e. C ai = C bi = C ci ( C bi This is the equivalent capacitance to ground of a single-turn coil in phase B; C ci (Equivalent capacitance to ground of a single-turn coil in phase C). Fundamental compensation current injected from the generator terminal side: in, U t1 This is the fundamental voltage at the generator terminal to ground. E A1 This is the fundamental component of the phase voltage of the faulty phase; C Σ =3 C a +3 C t , which is the sum of the three-phase-to-ground capacitances, including the stator windings and the direct-connected system;R n1 For high resistance, the neutral point is via R n1 High-resistance grounding.

[0030] Similarly, the Kirchhoff current equation is calculated for the third harmonic compensation current injected from the generator terminal side:

[0031] in, I An3 This is the neutral point third harmonic to ground current; U Ai3 The third harmonic voltage between the midpoint of the i-th turn of the faulty winding and ground; U At3 This refers to the third harmonic voltage at the machine terminal. U f3 The third harmonic voltage at the fault point; R g For the transition resistance at the fault point; I i3 This refers to the third harmonic compensation current injected from the generator terminal side.

[0032] The required dual-frequency compensation current injected at the faulty camera side under the active voltage control method can be derived:

[0033] in, E f1 and E f3 These are the ground wave and third harmonic voltage at the fault point, respectively. E Ai3 For the first i Third harmonic potential of the coil midpoint to the neutral point; E A3 This represents the third harmonic component of the phase voltage of the faulty phase.

[0034] At this point, both the fundamental and third harmonic voltage and current at the fault point can be effectively suppressed. Furthermore, the actual output of the fundamental and third harmonic currents from the active arc suppression device installed on the bus side... I i1S = n × I i1 , I i3S = n × I i3 . n This refers to the number of generators in a multi-generator-shared-parent generator system.

[0035] like Figure 2 The diagram shown is a wiring diagram for an active arc suppression method based on generator terminal voltage regulation. It explains the system structure of a multi-generator common bus system for generator terminal arc suppression. The neutral points of generators 1 through 5 are respectively connected via… R n1 ~ R n5 High-resistance grounding. G1~G5 are five generators, and K1~K5 are the connection switches between the generator terminals and the busbar. I i(1,3) For the amplitude of dual-frequency current injection, θ i(1,3) Inject phase angle into dual-frequency current.

[0036] In this step, maintaining the dual-frequency reverse fault potential at the faulty generator terminals serves the following purpose: The dual-frequency active voltage regulator, utilizing advanced current control technology, enables flexible and precise adjustment of the output current amplitude and phase angle. Through this dynamic control mechanism, the device can forcibly adjust the terminal voltage to a preset target value and continuously maintain its voltage stability. According to KVL, the fault point voltage satisfies: (1) In the formula, α The fault turns ratio; E A(1- )(1,3) The fault potential contains the fundamental frequency and the third harmonic, which is the potential between the machine terminal and the fault point.

[0037] To achieve arc suppression during fault diagnosis, U f(1,3) The terminal voltage should be zero, based on equation (1), and should satisfy: (2) When a controllable current source is connected to the terminal, its flexible control characteristics allow for free and precise adjustment of the amplitude and phase angle of the terminal voltage. Through this control method, the neutral point voltage can be forcibly adjusted to a predetermined target value and maintained stably. In this state, both the fundamental and third harmonic voltages at the fault point are effectively suppressed to zero potential, thereby significantly suppressing the fundamental and third harmonic components in the fault current and greatly reducing the impact of the fault on the system.

[0038] S2. Low-frequency injection: Continuously inject 20Hz low-frequency current at the generator terminal bus. The low-frequency current will not affect the normal operation of the generator.

[0039] Specifically, a 20Hz low-frequency current is injected into the generator terminal bus using a programmable AC power supply, and this low-frequency current will not affect the normal operation of the generator. The purpose of injecting the low-frequency current is to measure the grounding transition resistance. The dual-frequency compensation current consists of 50Hz and 150Hz currents, and all three currents can be output simultaneously from a programmable AC power supply.

[0040] S3. Low-frequency component measurement: The voltage and current at the generator terminals of each generator are acquired at the first moment of normal operation and the second moment from the occurrence of the fault to the start of the ground fault arc suppression. The low-frequency component is extracted using Fourier transform. The low-frequency component has the same frequency as the low-frequency power supply.

[0041] This step is based on a low-frequency measurement method at the generator terminals. Taking a multi-generator system with five generators as an example, namely generator units 1 to 5, with generator unit 1 being the faulty unit; in step S3, the voltage and current at the generator terminals are measured using voltage and current transformers. Under fault conditions, the 20Hz low-frequency current at each generator terminal is:

[0042] In the formula, the 20Hz current measured on the secondary side of the current transformer at the generator terminal from Unit 1 to Unit 5 is used. I 20t_1 ~ I 20t_5 This indicates that the 20Hz current at the neutral point is used I 20n_1 ~ I 20n_5 express; I 20_O It is the 20Hz current flowing to the equivalent capacitance of the external system; U f The voltage to ground at the fault point. C 1~ C 5 represents the equivalent distributed capacitance from Unit 1 to Unit 5.

[0043] The calculation formula for injecting a 20Hz low-frequency current in step S2 is as follows:

[0044] The formula assumes that the ground capacitance parameters of each generator are the same, therefore the zero-sequence current at the terminals of non-faulty generators is equal. I 20t_1 To inject low-frequency current into the faulty generator.

[0045] S4. Grounding Transition Resistance Calculation: Calculate the ground impedance during a ground fault using the low-frequency components of the generator terminal voltage and current at the first moment for each generator. Z i1The impedance to ground after fault stabilization is calculated using the low-frequency components of the terminal voltage and current at the second moment. Z i2 ;comprehensive Z i1 and Z i2 Calculate the grounding transition resistance of each generator in the event of a generator failure. R gi .

[0046] This step is based on a method for calculating the grounding transition resistance based on low-frequency quantities at the generator terminal, as detailed below: During normal operation, calculate the impedance to ground during a ground fault:

[0047] in, U oc The terminal voltage is measured during normal operation. X c This represents the generator's three-phase-to-ground capacitive reactance. The generator's three-phase-to-ground capacitive reactance can then be calculated. X c .

[0048] After a ground fault occurs, calculate the impedance to ground after the fault stabilizes:

[0049] in, U' oc Measure the terminal voltage after the fault has stabilized; R g This is the transition resistor at the fault point.

[0050] Because at this time the generator's three-phase ground capacitance X c Given the information, the actual ground fault resistance can be calculated by substituting it into the equation:

[0051] and R gi = R g Therefore: .

[0052] S5. Fault Identification: If R gi If the value is greater than or equal to the set threshold, it is identified as a transient fault. R gi If the value is less than the set threshold, it is identified as a permanent fault; if a generator is identified as a permanent fault, then the generator can be identified as a faulty unit.

[0053] This step is based on an identification method based on a ground transition resistance threshold, with the threshold range set to 8000Ω-10000Ω. Example 1

[0054] Example 1 is a further elaboration of steps S3 to S4 based on the above technical solution.

[0055] like Figure 3 As shown, where, C 1~ C 5 represents the equivalent distributed capacitance from Unit 1 to Unit 5; C o The equivalent capacitance of the external system; on the stator winding α When a single-phase ground fault occurs at point A, the capacitances at both ends of the fault point are expressed as follows: αC 1 and (1- α ) C 1. αC 2 and (1- α ) C 2. αC 3 and (1- α ) C 3. αC 4 and (1- α ) C 4. αC 5 and (1- α ) C 5; Current transformers are designated A1~A5, and the 20Hz current measured on the secondary side from Unit 1 to Unit 5 is... I' 20t_1 ~ I' 20t_5 The voltage transformers are represented by V1 to V5. The 20Hz voltage measured on the secondary side from Unit 1 to Unit 5 is represented by... U' 20t_1 ~ U' 20t_5 express; I' 0_O This refers to the current flowing to the equivalent capacitance of the external system. R g For the transition resistance at the fault point; I i20 This refers to the amplitude of the injected 20Hz current. θ i20 The phase angle of the injected 20Hz current; R n1 ~ R n5 The neutral points of generators 1 through 5 are respectively... R n1 ~ R n5 High-resistance grounding.

[0056] like Figure 4 The figure shows the equivalent circuit diagram when the computer terminal is grounded with transition resistance, where Z is the total impedance; I 20t_1 Inject the equivalent current of the faulty generator into the injection source; I 20_O It is the 20Hz current flowing to the equivalent capacitance of the external system. Figure 4 This provides a theoretical basis for calculating the grounding transition resistance. The calculation process is as follows: use I' 20t_1 ~ I' 20t_5 , U' 20t_1 ~ U' 20t_5 We will calculate the transition resistance values ​​for the five generating units. The calculation method will be illustrated below using the faulty Unit 1 as an example; the calculations for the other units are similar.

[0057] The device measures voltage at a frequency of 20Hz. U oc Current I oc The actual current injected into the faulty generator I 20t_1 satisfy: in, I i20 The amplitude of the injected 20Hz current source. According to... Figure 3 Injected I i20 minus I 20_O The remaining current flows evenly to the terminals of the five generators.

[0058] During normal operation, calculate the impedance to ground during a ground fault:

[0059] At this point, the three-phase ground capacitance of the generator can be calculated. X c .

[0060] After a ground fault occurs, calculate the impedance to ground after the fault stabilizes:

[0061] because R gi = R g And at this time, the three-phase ground resistance X cGiven the information, the grounding transition resistance can be calculated by substituting it into the given information. .

[0062] This invention can flexibly extinguish single-phase grounding faults in generator stators and identify the nature of the fault, which is crucial for preventing equipment damage, avoiding power outages, ensuring power supply reliability, and protecting personal safety. Example 2

[0063] The effectiveness of the proposed method is verified through simulation below.

[0064] In this second embodiment, the generator has two branch windings per phase, each branch consisting of eight coils connected in series. The rated voltage is 10.5kV. The stator winding resistance / phase is 1.528mΩ, stator winding leakage inductance / phase is 2.84mH, stator winding capacitance / phase is 0.397μF, 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 2286Ω, and the direct-connected system capacitance to ground / phase is 0.405μF. The analysis will focus on the first branch of phase A.

[0065] To verify the arc suppression effect at the generator terminal, a time of 0.2s was taken at the connection point of the generator's A-phase coil. α= 0.25 α= 0.50 α= For a single-phase ground fault with a transition resistance of 500Ω set at 0.75, the arc suppression result is as follows: Figure 5 As shown, and the above differences α= The schematic diagrams of the arc extinguishing effect at the fault location are as follows: Figure 5 As shown in (a), (b), and (c) in the figure, and Figure 5 In this system, all generators use high-resistance grounding, and active arc suppression devices are activated at 0.2 seconds. (Horizontal axis) t Represents time, in seconds, vertical axis i f This represents the fault current, in amperes (A). u f This represents the fault potential, expressed in kV. Figure 5 As can be seen from the data, the arc suppression method for ground faults in multi-machine common bus systems based on terminal voltage regulation can achieve accurate and reliable arc suppression.

[0066] Figure 6 The simulation results for fault nature identification under three different fault scenarios are shown in the following diagram: Figure 6 In (a), it is assumed that αThe single-phase ground fault at point 0.125 started at 1 second, and the transient fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 50Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was approximately 50Ω at the time of the fault. After the arc was extinguished and stabilized, the calculated transition resistance value was greater than the set threshold of 8000Ω, thus determining the fault to be transient, verifying the effectiveness of the method.

[0067] Figure 6 In (b), it is assumed that α The single-phase ground fault at point 0.125 started at 1 second, and the permanent fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 50Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was approximately 50Ω at the time of the fault. After the arc was extinguished and stabilized, the calculated transition resistance value was less than 8000Ω, thus determining the fault to be permanent, verifying the effectiveness of the method.

[0068] Figure 6 In (c), it is assumed that α The single-phase ground fault at point 0.625 started at 1 second, and the transient fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 200Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was approximately 200Ω at the time of the fault. After the arc was extinguished and stabilized, the calculated transition resistance value was greater than the set threshold of 8000Ω, thus determining the fault to be transient, verifying the effectiveness of the method.

[0069] Figure 6 In (d), it is assumed that α The single-phase ground fault at point 0.625 started at 1 second, and the permanent fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 200Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was 200Ω at the time of the fault. After the arc was extinguished and stabilized, the calculated transition resistance value was less than 8000Ω, thus determining the fault to be permanent, verifying the effectiveness of the method.

[0070] Figure 6 In (e), it is assumed that αThe single-phase ground fault at point 0.5 started at 1 second, and the transient fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 500Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was approximately 500Ω at the time of the fault. After the arc extinguishing stabilized, the calculated transition resistance value was greater than the set threshold of 8000Ω, thus determining the fault to be transient, verifying the effectiveness of the method.

[0071] Figure 6 In (f), it is assumed that α The single-phase ground fault at point 0.5 started at 1 second, and the permanent fault lasted for 0.2 seconds. At 1.1 seconds, a high-resistance grounding method was used to extinguish the arc at the fault point. A 500Ω constant resistance model was used to simulate the ground fault resistance. The transition resistance calculated in the constant resistance model was 500Ω at the time of the fault. After the arc was extinguished and stabilized, the calculated transition resistance value was less than 8000Ω, thus determining the fault to be permanent, verifying the effectiveness of the method.

[0072] like Figure 7 The following is a simulation result for identifying the faulty unit: At 0.2s, in Unit 1 α A permanent fault with a grounding transition resistance of 500Ω was set at point =0.75. The changes in the grounding transition resistance of the five units were recorded. Only Unit 1 showed a significant change in grounding transition resistance after the fault, decreasing to 500Ω (the others maintained a very high resistance, greater than the threshold of 8000Ω, and were not faulty units, and were clearly different from Unit 1). Units with grounding transition resistance below the threshold of 8000Ω could be identified as faulty units.

[0073] Based on the methods in the above embodiments, this application provides an electronic device / image signal generator / network device / transmitter / terminal / base station / industrial control computer. This electronic device / image signal generator / network device / transmitter / terminal / base station / industrial control computer may include: a processor, a communication interface, a memory, and a communication bus. The processor, communication interface, and memory communicate with each other via the communication bus. The processor can call logical instructions in the memory to execute the methods in the above embodiments.

[0074] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the 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 to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application.

[0075] Based on the methods in the above embodiments, this application provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to execute the methods in the above embodiments. Example 3

[0076] Based on the above method, this embodiment provides a computer program product that, when run on a processor, causes the processor to execute the above method.

[0077] It is understood that the processor in this embodiment 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. A general-purpose processor can be a microprocessor or any conventional processor.

[0078] The method steps of this invention can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, enabling the processor to read information from 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 reside in an ASIC.

[0079] In the above methods, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the flow or function according to the present invention is generated, in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in 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 via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., a solid-state drive (SSD)).

Claims

1. A method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation, characterized in that: Includes the following steps: S1. Arc suppression at generator terminals: Based on the fault location results, dual-frequency current is injected into the computer terminal, and then dual-frequency compensation current is injected from the generator terminal bus through the dual-frequency active arc suppression device to maintain the dual-frequency reverse fault potential at the generator terminal of the faulty generator. S2. Low-frequency injection: Continuously inject a 20Hz low-frequency current at the generator terminal bus. The low-frequency current will not affect the normal operation of the generator. S3. Low-frequency component measurement: The voltage and current at the generator terminals of each generator are acquired at the first moment of normal operation and the second moment from the occurrence of the fault to the start of the ground fault arc suppression. The low-frequency component is extracted using Fourier transform. The low-frequency component has the same frequency as the low-frequency power supply. S4. Grounding Transition Resistance Calculation: Calculate the ground impedance during a ground fault using the low-frequency components of the generator terminal voltage and current at the first moment for each generator. Z i1 The impedance to ground after fault stabilization is calculated using the low-frequency components of the terminal voltage and current at the second moment. Z i2 ;comprehensive Z i1 and Z i2 Calculate the grounding transition resistance of each generator in the event of a generator failure. R gi ; S5. Fault Identification: If R gi If the value is greater than or equal to the set threshold, it is identified as a transient fault. R gi If the value is less than the set threshold, it is identified as a permanent fault; if a generator is identified as a permanent fault, then that generator can be identified as a faulty unit.

2. The method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation according to claim 1, characterized in that: The calculation formula for the dual-frequency compensation current injected at the machine terminal in step S1 is as follows: In the formula, I i1 and I i3 These are the fundamental compensation current and the third harmonic compensation current injected from the generator terminal side, respectively. E f1 and E f3 These are the ground wave and third harmonic voltage at the fault point, respectively. E Ai3 For the first i Third harmonic potential of the coil midpoint to the neutral point; E A3 is the third harmonic component of the phase voltage of the faulty phase; n is the total number of turns in the stator winding; C a This is the equivalent capacitance to ground of a single-turn coil; C ∑ This is the sum of the three-phase-to-ground capacitances, including the stator windings and the direct-connected system. R n1 For high resistance, the neutral point is via R n1 High-resistance grounding; j Indicates a 90° phase difference; Angular frequency; C t This is the equivalent capacitance to ground of the directly connected system terminal.

3. The method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation according to claim 2, characterized in that: Step S2 specifically involves injecting a 20Hz low-frequency current into the generator terminal bus using a programmable AC power supply, and ensuring that the low-frequency current does not affect the normal operation of the generator.

4. The method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation according to claim 3, characterized in that: The multi-generator shared-bus system includes 5 generators, designated as Unit 1 through Unit 5, with Unit 1 being the faulty unit. In step S3, voltage and current are measured at the generator terminals using voltage and current transformers. Under fault conditions, the 20Hz low-frequency current at each generator terminal is: In the formula, the 20Hz current measured on the secondary side of the current transformer at the generator terminal from Unit 1 to Unit 5 is used. I 20t_1 ~ I 20t_5 express; The 20Hz current measured on the secondary side of the current transformer at the generator terminal is used at the neutral point of units 2 to 5. I 20n_2 ~ I 20n_5 express; I 20_O It is the 20Hz current flowing to the equivalent capacitance of the external system; U f The voltage to ground at the fault point. C 2~ C 5 represents the equivalent distributed capacitance from Unit 2 to Unit 5; The calculation formula for injecting a 20Hz low-frequency current in step S2 is as follows: The formula assumes that the ground capacitance parameters of each generator are the same, therefore the zero-sequence current at the terminals of non-faulty generators is equal. I 20t_1 To inject low-frequency current into the faulty generator; I i20 This refers to the continuous injection of a 20Hz low-frequency current at the machine terminal bus.

5. The method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation according to claim 4, characterized in that: Step S4 specifically involves: in, U oc The terminal voltage is measured during normal operation. X c For the three-phase ground capacitive reactance of the generator; in, U' oc Measure the terminal voltage after the fault has stabilized; The 20Hz current of Unit 1 was measured on the secondary side; R g For the transition resistance at the fault point; Because at this time the generator's three-phase ground capacitance X c Given this information, the actual ground fault resistance can be calculated by substituting it into the given values: and R gi = R g Therefore: 。 6. The method for arc suppression and nature identification of grounding faults in a multi-machine common bus system based on terminal voltage regulation according to claim 5, characterized in that: The threshold range set in step S5 is 8000 ohms to 10000 ohms.

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