An active arc extinguishing method for stator ground fault of multi-machine common ground generator system based on online calculation of ground capacitance parameters

Abstract

The application discloses a kind of active arc extinguishing methods of multi-machine common ground generator system stator grounding fault based on online calculation of ground capacitance parameter, comprising the following steps: S1.in the neutral point grounding transformer of generator parallel controllable current source in secondary side, inject current to neutral point;Extract the voltage component of the same frequency as injected current, and calculate the ground capacitance parameter of generator system by online voltage component and injected current value;S2.measure the three-phase voltage of generator and the phase value of generator terminal zero sequence current, obtain the fundamental wave potential of fault point based on measured value;Deduce the compensation current that needs to be injected in the generator terminal side of fault phase, and inject compensation current in generator terminal;S3.when arc extinguishing of fault point is realized by injecting compensation current in generator terminal, measure the phase of generator terminal zero sequence current again, carry out fault selective positioning, to determine the fault unit in multi-machine common ground system.The application can not only realize effective arc extinguishing, but also reliably determine fault unit.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system relay protection technology, in particular to a multi-machine common bus generator system stator ground fault active arc extinguishing method based on online calculation of ground capacitance parameters. BACKGROUND

[0002] Multi-machine common bus generator set is the core power supply unit of independent power systems such as offshore oil platforms. Due to the long-term vibration environment of waves and other impacts, the insulation of the generator stator winding is easily damaged, leading to frequent ground faults, often accompanied by arcs. Grounding arcs can cause serious burns to the stator core and damage the winding insulation. If it cannot be extinguished quickly, it may evolve into a phase-to-phase or turn-to-turn short circuit, threatening the safety of the equipment and system. Therefore, an effective arc extinguishing method is needed to suppress the fault current.

[0003] For a multi-machine parallel system, after a ground fault occurs, the fault unit needs to be quickly and accurately identified and isolated to avoid affecting the normal operation of non-fault units. The traditional protection method realizes zero sequence directional protection by increasing the fault current, but this method is not conducive to the safety of the generator equipment and has certain theoretical defects. Existing line selection methods rely on zero sequence fault characteristic quantities after the fault, but in complex operating environments such as offshore oil platforms, there is a lot of measurement noise, which can easily lead to misjudgment of the fault unit. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a multi-machine common bus generator system stator ground fault active arc extinguishing method based on online calculation of ground capacitance parameters, which not only realizes effective arc extinguishing, but also reliably judges the fault unit.

[0005] To solve the above technical problems, the technical solutions adopted by the present application are as follows.

[0006] A multi-machine common bus generator system stator ground fault active arc extinguishing method based on online calculation of ground capacitance parameters, comprising the following steps:

[0007] S1. A controllable current source is connected in parallel at the secondary side of the generator neutral point grounding transformer, and the controllable current source is used to inject a current into the neutral point; the measured neutral point voltage signal is subjected to Fourier transform, the voltage component with the same frequency as the injected current is extracted, and the voltage component and the injected current value are substituted into a preset formula to calculate the ground capacitance parameters of the generator system online;

[0008] S2. The three-phase phase voltage of the generator and the phase value of the generator terminal zero sequence current are measured, and the fault point fundamental potential is calculated based on the measured values; based on the ground capacitance parameters and the fault point fundamental potential, the compensation current to be injected at the generator terminal side of the fault phase is derived, and the compensation current is injected through the active current control device installed at the terminal;

[0009] S3. After the generator terminals are injected with compensation current to extinguish the arc at the fault point, the phase of the zero-sequence current at the generator terminals of each generator is measured again. By utilizing the fact that the phase change of the zero-sequence current at the generator terminals of the faulty unit before and after the arc is extinguished is greater than the phase change of the zero-sequence current at the generator terminals of the non-faulty units, selective fault location is performed, thereby identifying the faulty unit in the multi-generator common bus system.

[0010] Preferably, in step S1, the ground capacitance parameter C ∑ The online calculations are specifically as follows:

[0011] Injecting current into the neutral point using a controllable current source I And the neutral point voltage component at the corresponding specific frequency was measured. U 1;

[0012] According to the system admittance formula:

[0013]

[0014] in, Y For system admittance; R n The neutral point grounding impedance; C ∑ This is the sum of the generator's three-phase-to-ground capacitance and the direct-connected system's to-ground capacitance, i.e., the to-ground capacitance parameter; G ∑ This is the sum of the three-phase total grounding conductance of the generator; j The imaginary unit; ω Angular frequency;

[0015] Let the real part of the system admittance formula be S and the imaginary part be X, that is:

[0016]

[0017] According to the rule that the real and imaginary parts are equal, we can obtain:

[0018]

[0019] Thus, the capacitance parameters to ground are obtained. C ∑ The value is:

[0020] .

[0021] Preferably, the process of deriving the compensation current to be injected at the generator terminal side of the faulty phase in step S2 includes:

[0022] S21. Let the fault occur in phase A, and establish an equivalent structure diagram of the fault phase;

[0023] S22. Based on the equivalent structure diagram of the faulted phase, the Kirchhoff current equations for the faulted phase A winding are as follows:

[0024]

[0025] in, I An1 This refers to the fundamental frequency current to ground at the neutral point of phase A in case of fault. C a This is the total equivalent capacitance to ground of the faulty phase A winding; U Ai1 The fundamental voltage of the i-th turn of the faulty phase A coil relative to ground; C t This refers to the total capacitance to ground flowing through the machine terminal side; U At1 The fundamental voltage of camera A relative to ground; U f1 The voltage at the fault point; R f This refers to the grounding transition resistance at the fault point; I i1 The compensation current injected from the fault A phase of the generator is denoted as n; n is the total number of turns of the stator winding of the fault A phase.

[0026] Meanwhile, Kirchhoff's current equations for a healthy phase winding are as follows:

[0027]

[0028]

[0029] in, I Bn1 To ensure the stability of the fundamental wave to ground current at the neutral point of phase B; C b To improve the overall equivalent capacitance to ground of the B-phase winding; U Bi1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase B coil and ground; U Bt1 To ensure the fundamental voltage of camera B to ground; I Cn1 To ensure the stability of the fundamental current to ground at the C-phase neutral point; C c To improve the overall equivalent capacitance to ground of the C-phase winding; U Ci1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase C coil and ground; U Ct1 To ensure the fundamental voltage of the C-camera terminal to ground;

[0030] S23. Kirchhoff's current equations for the generator neutral point are as follows:

[0031]

[0032] in, I An1 This refers to the fundamental frequency current to ground at the neutral point of phase A in case of fault. I Bn1 To ensure the stability of the fundamental wave to ground current at the neutral point of phase B; I Cn1 To ensure the stability of the fundamental current to ground at the C-phase neutral point; I n1 The current flowing through the neutral point grounding impedance is calculated using the following formula:

[0033]

[0034] in, U n1 This is the fundamental voltage of the neutral point relative to ground;

[0035] S24. Define the voltage variable relationship as follows:

[0036]

[0037] in, E Ai1 The fundamental potential from the midpoint of the i-th turn of the coil in phase A of the fault to the neutral point; E Bi1 To ensure the fundamental potential from the midpoint of the i-th turn of phase B coil to the neutral point; E Ci1 To ensure the fundamental potential from the midpoint of the i-th turn of the C-phase coil to the neutral point;

[0038]

[0039] in, E A1 The fundamental potential of phase A in the fault; E B1 To improve the fundamental potential of phase B; E C1 To improve the fundamental potential of phase C;

[0040] S25. Assuming the effect of asymmetric three-phase winding capacitance to ground is ignored, then the generator's three-phase windings are symmetrical and the total equivalent capacitance to ground of the three-phase windings is equal, i.e. C a = C b = C c The three-phase phase potentials of the generator remain symmetrical, satisfying the following conditions. E A1 + E B1 +E C1 =0; the fundamental potential of the i-th turn of each phase of the generator coil also remains symmetrical with respect to the neutral point, satisfying... E Ai1 + E Bi1 + E Ci1 =0; Substitute the Kirchhoff current equations for the faulty phase winding and the healthy phase winding in step S22, as well as the voltage variable relationship in step S24, into the Kirchhoff current equation for the neutral point in S23 to obtain the compensation current. I i1 for:

[0041]

[0042] in, U t1 This refers to the voltage at the generator terminals relative to the ground.

[0043] S26. Establish the fundamental voltage of the system neutral point to ground. U n1 Generator terminal voltage to ground U t1 With the fundamental potential at the fault point E f1 The relationship between them satisfies the following voltage relationship:

[0044] ;

[0045] S27. The control objective of active arc suppression is to reduce the voltage at the fault point. U f1 Forced regulation is zero, even if... U f1 =0, and then the required terminal voltage regulation target is determined by the relationship in step S26:

[0046] ;

[0047] S28. Substitute the terminal voltage regulation target into the compensation current from step S25. I i1 The compensation current is derived from the calculation formula. I i1 for:

[0048]

[0049] Among them, the fundamental potential at the fault point E f1 The calculation formula is:

[0050]

[0051] in, α This represents the percentage of the number of coils from the fault point to the neutral point out of the total number of turns in the series-connected coils of the fault branch.

[0052] Preferably, in step S27, the active current control device regulates the injected compensation current. I i1 The amplitude and phase angle of the generator terminal voltage relative to the ground wave will determine the voltage at the generator terminals. U t1 Forced regulation to a specific value, so that the voltage at the fault point... U f1 It is suppressed to zero.

[0053] Preferably, in step S3, the zero-sequence current phase change of one generator is compared with the average phase change of all other generators in the system plus a safety margin to perform selective fault location. Specifically, the criteria for selective fault location are:

[0054] For the i-th generator in the system, it is determined to be a faulty unit if it satisfies the following formula:

[0055]

[0056] in, k =1,2,..., m , representing the k One generator; m This represents the total number of generators. I 0t_k The first before the arc was extinguished k Zero-sequence current at the generator terminals; I ′ 0t_k For the first time after the arc is extinguished k Zero-sequence current at the generator terminals; arg() indicates the phase; ε This is the preset threshold.

[0057] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0058] This invention achieves accurate calculation of the active arc suppression compensation current by connecting a controllable current source in parallel at the neutral point and injecting a current signal of a specific frequency, and extracting the voltage component by combining Fourier transform. This enables the online real-time and accurate calculation of the ground capacitance parameters of the generator system, overcoming the problem of arc suppression effect being affected by inaccurate parameters caused by changes in system operation mode or equipment aging.

[0059] This invention establishes a distributed parameter model of the faulty phase winding, writes Kirchhoff's current equation and voltage relationship, and derives an analytical expression for the compensation current based on the control objective of forcibly returning the fault point voltage to zero. This enables the rapid and reliable extinguishing of the arc at the ground fault point, effectively avoiding equipment damage.

[0060] This invention utilizes active arc extinguishing as an active disturbance to extract the phase characteristics of the change in zero-sequence current at the generator terminals before and after arc extinguishing of each unit, and constructs a selective location criterion based on phase comparison. This enables highly reliable identification of faulty units in complex electromagnetic environments and solves the problem of fault line selection in multi-unit common bus systems.

[0061] This invention organically integrates online parameter identification, active arc suppression, and fault location functions, suppressing fault arcs while maintaining short-term operation of faulty units and accurately locating faults, thus significantly improving the power supply continuity and safety of multi-unit shared bus systems.

[0062] This invention achieves active suppression of fault point voltage by precisely controlling the amplitude and phase angle of the compensation current and forcibly controlling the terminal voltage to the target value, demonstrating the advantages of the accuracy and controllability of the active arc suppression method. Attached Figure Description

[0063] Figure 1 This is a flowchart of the present invention;

[0064] Figure 2 This is the equivalent circuit diagram of the neutral point grounding system of the present invention;

[0065] Figure 3 This is the current signal flow loop of the current source in the neutral point grounded high-resistance system of the present invention;

[0066] Figure 4 This is a circuit diagram of the active arc suppression circuit based on terminal voltage regulation of the present invention;

[0067] Figure 5 This is a schematic diagram of the fault equivalent structure of the present invention;

[0068] Figure 6 This invention provides the zero-sequence equivalent network for a generator unit with a stator grounding fault before arc extinction.

[0069] Figure 7 This is the zero-sequence equivalent network of the stator grounding fault unit after arc extinction according to the present invention;

[0070] Figure 8 The figure shows the simulation results of the active arc suppression at the machine end of the present invention. Figure 8 (a) is R f =500Ω and α The simulation results of active arc suppression at the machine terminal are shown in the figure with a value of 0.25.Figure 8 (b) is R f =500Ω and α The simulation results of active arc suppression at the machine end are shown in the figure with a value of 0.50. Figure 8 (c) is R f =500Ω and α Simulation results of active arc suppression at the machine end with a value of 0.75;

[0071] Figure 9 The diagram shows the zero-sequence current phase results of the faulty and non-faulty units before and after arc suppression according to the present invention; wherein, Figure 9 (a) is R f =500Ω and α =0.25, zero-sequence current phase results of faulty and non-faulty units before and after arc suppression; Figure 9 (b) is R f =500Ω and α =0.50, zero-sequence current phase results of faulty and non-faulty units before and after arc suppression; Figure 9 (c) is R f =500Ω and α The zero-sequence current phase results of the faulty and non-faulty units before and after arc suppression are shown in the figure with a phase ratio of 0.75. Detailed Implementation

[0072] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0073] An active arc suppression method for stator grounding faults in a multi-machine common-bus generator system based on online calculation of ground capacitance parameters, combined with... Figure 1 As shown, it includes the following steps:

[0074] S1. Connect a controllable current source in parallel on the secondary side of the generator neutral point grounding transformer, and inject current into the neutral point using the controllable current source; perform Fourier transform on the measured neutral point voltage signal, extract the voltage component with the same frequency as the injected current, and substitute the voltage component and the injected current value into the preset formula to calculate the ground capacitance parameters of the generator system online.

[0075] like Figures 2 to 3 As shown, E A , E B , E C These are the voltages of phases A, B, and C, respectively. C a , C b ,C c These are the total equivalent capacitances to ground of the three-phase windings A, B, and C, respectively. G a , G b , G c The conductances of A, B, and C relative to ground are respectively; U 0 represents the neutral point voltage; R n The neutral point grounding impedance; I It represents the current quantity; U 1 represents the neutral point voltage component.

[0076] When the neutral point is grounded through a high-resistance circuit and the controllable current source is not connected, according to Kirchhoff's laws:

[0077]

[0078] In the formula, j The imaginary unit; ω Angular frequency; U A , U B , U C It is the sum of the power supply voltage of each phase and the neutral point voltage, that is:

[0079]

[0080] Using phase A as the reference phase, the neutral point voltage U 0 is:

[0081]

[0082] in, G ∑ This is the sum of the three-phase total grounding conductance of the generator; C ∑ This is the sum of the generator's three-phase-to-ground capacitance and the direct-connected system's to-ground capacitance, i.e., the to-ground capacitance parameter.

[0083] Ground capacitance parameters C ∑ The online calculations are specifically as follows:

[0084] Injecting current into the neutral point using a controllable current source I And the neutral point voltage component at the corresponding specific frequency was measured. U 1.

[0085] According to the system admittance formula:

[0086]

[0087] in, Y For system admittance;

[0088] Let the real part of the system admittance formula be S and the imaginary part be X, that is:

[0089]

[0090] According to the rule that the real and imaginary parts are equal, we can obtain:

[0091]

[0092] Thus, the capacitance parameters to ground are obtained. C ∑ The value is:

[0093] .

[0094] S2. Measure the three-phase phase voltage and the phase value of the zero-sequence current at the generator terminals, and calculate the fundamental potential at the fault point based on the measured values; derive the compensation current to be injected at the generator terminals of the fault phase based on the ground capacitance parameters and the fundamental potential at the fault point, and inject the compensation current through the active current control device installed at the generator terminals.

[0095] The process of deriving the compensation current that needs to be injected at the generator terminal of the faulty phase in this step includes:

[0096] S21. Let the fault occur in phase A, and establish the equivalent structure diagram of the fault phase.

[0097] Specifically, such as Figure 4 As shown, I i It is the current amplitude output by the active arc suppression device; θ i It is the phase of the current output by the active arc suppression device; K m It is a circuit breaker with an active arc suppression device connected to the busbar on the machine terminal side, specifically including K. mA K mB and K mC These are the three-phase circuit breakers connected to the active arc suppression device and the generator terminal busbar, respectively; G1, G2, G3, G4 and G5 are the names of each generator (taking 5 generators as an example); K1, K2, K3, K4 and K5 are the circuit breakers connected to each generator and the generator terminal busbar, respectively. R n1 , R n2 , R n3 , R n4 and R n5These are the neutral point grounding impedances of each generator.

[0098] Since the generator terminals of each generator in the generator system are connected to the active arc suppression device via a bus, when any generator in the generator system experiences a ground fault, the active current control device installed at the generator terminal bus can arbitrarily adjust the output current amplitude and phase angle to force and maintain the generator terminal voltage of each generator in the generator system, including the faulty generator, to the required voltage value, thereby suppressing the fault point voltage of the faulty generator to 0 and achieving reliable arc suppression.

[0099] When a stator ground fault occurs in a generator, and the active arc suppression compensation is injected from the faulty phase side of the generator, the stator winding diagram of the faulty generator is shown below. Figure 5 As shown (taking the fault occurring in phase A as an example), where, I An1 This refers to the fundamental frequency current to ground at the neutral point of phase A in case of fault. E Ai1 The fundamental potential from the midpoint of the i-th turn of the coil in phase A of the fault to the neutral point; N is the neutral point; C ai This is the equivalent capacitance to ground of a single-turn coil in phase A of the fault. U Ai1 The voltage between the midpoint of the i-th turn of the faulty phase A coil and ground. I i1 This is the compensation current injected from the generator fault A camera terminal; U N This refers to the voltage at the neutral point of the generator. C a1 This is the equivalent capacitance to ground of the first turn of the coil in phase A of the fault. C an This is the equivalent capacitance to ground of the nth turn of the coil in phase A of the fault. C t This refers to the total capacitance to ground flowing through the machine terminal side; U T This is the voltage at the generator terminal side.

[0100] S22. Based on the equivalent structure diagram of the fault phase, the Kirchhoff current equations for the faulty winding A are as follows:

[0101]

[0102] in, C a This is the total equivalent capacitance to ground of the faulty phase A winding; U Ai1 The fundamental voltage of the i-th turn of the faulty phase A coil relative to ground; U At1 The fundamental voltage of camera A relative to ground;U f1 The voltage at the fault point; R f This refers to the grounding transition resistance at the fault point; I i1 is the compensation current injected from the fault A phase of the generator; n is the total number of turns of the stator winding of the fault A phase.

[0103] Meanwhile, Kirchhoff's current equations are written for the healthy phase (phase B and phase C) windings as follows:

[0104]

[0105]

[0106] in, I Bn1 To ensure the stability of the fundamental wave to ground current at the neutral point of phase B; C b To improve the overall equivalent capacitance to ground of the B-phase winding; U Bi1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase B coil and ground; U Bt1 To ensure the fundamental voltage of camera B to ground; I Cn1 To ensure the stability of the fundamental current to ground at the C-phase neutral point; C c To improve the overall equivalent capacitance to ground of the C-phase winding; U Ci1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase C coil and ground; U Ct1 To improve the fundamental voltage of the C-camera terminal to ground.

[0107] S23. Kirchhoff's current equations for the generator neutral point are as follows:

[0108]

[0109] in, I Bn1 To ensure the stability of the fundamental wave to ground current at the neutral point of phase B; I Cn1 To ensure the stability of the fundamental current to ground at the C-phase neutral point; I n1 The current flowing through the neutral point grounding impedance is calculated using the following formula:

[0110]

[0111] in, U n1 This is the fundamental voltage of the neutral point relative to ground.

[0112] S24. Define the voltage variable relationship as follows:

[0113]

[0114] in, E Bi1 To ensure the fundamental potential from the midpoint of the i-th turn of phase B coil to the neutral point; E Ci1 To ensure the fundamental potential from the midpoint of the i-th turn of the C-phase coil to the neutral point;

[0115]

[0116] in, E A1 The fundamental potential of phase A in the fault; E B1 To improve the fundamental potential of phase B; E C1 To improve the fundamental potential of phase C.

[0117] S25. Assuming the effect of asymmetric three-phase winding capacitance to ground is ignored, then the generator's three-phase windings are symmetrical and the total equivalent capacitance to ground of the three-phase windings is equal, i.e. C a = C b = C c The three-phase phase potentials of the generator remain symmetrical, satisfying... E A1 + E B1 + E C1 =0. The fundamental potential of the i-th turn of each phase of the generator coil also remains symmetrical with respect to the neutral point, satisfying... E Ai1 + E Bi1 + E Ci1 =0. Substituting the Kirchhoff current equations for the faulty phase winding and the healthy phase winding from step S22, as well as the voltage variable relationship from step S24, into the Kirchhoff current equation for the neutral point in S23, we obtain the compensation current. I i1 for:

[0118]

[0119] in, U t1 This refers to the generator terminal voltage relative to the ground.

[0120] S26. Establish the fundamental voltage of the system neutral point to ground.U n1 Generator terminal voltage to ground U t1 With the fundamental potential at the fault point E f1 The relationship between them satisfies the following voltage relationship:

[0121] .

[0122] S27. The control objective of active arc suppression is to reduce the voltage at the fault point. U f1 Forced regulation is zero, even if... U f1 =0, and then the required terminal voltage regulation target is determined by the relationship in step S26:

[0123]

[0124] Specifically, the active current regulation device regulates the injected compensation current. I i1 The amplitude and phase angle of the generator terminal voltage relative to the ground wave will determine the voltage at the generator terminals. U t1 Forced regulation to a specific value, so that the voltage at the fault point... U f1 It is suppressed to zero.

[0125] S28. Substitute the terminal voltage regulation target into the compensation current from step S25. I i1 The compensation current is derived from the calculation formula. I i1 for:

[0126]

[0127] Among them, the fundamental potential at the fault point E f1 The calculation formula is:

[0128]

[0129] in, α This represents the percentage of the number of coils from the fault point to the neutral point out of the total number of turns in the series-connected coils of the fault branch.

[0130] S3. After the generator terminals are injected with compensation current to extinguish the arc at the fault point, the phase of the zero-sequence current at the generator terminals of each generator is measured again. By utilizing the fact that the phase change of the zero-sequence current at the generator terminals of the faulty unit before and after the arc is extinguished is greater than the phase change of the zero-sequence current at the generator terminals of the non-faulty units, selective fault location is performed, thereby identifying the faulty unit in the multi-generator common bus system.

[0131] During the arc suppression process, the fault current can be suppressed to zero, preventing damage to the generator equipment and allowing the faulty unit to continue supplying power to the offshore oil platform. However, in subsequent maintenance work, it is necessary to identify the faulty unit, thus requiring selective fault location.

[0132] Specifically, when a single-phase ground fault occurs in one generator in a multi-generator system operating in parallel with a common bus, its zero-sequence equivalent network is as follows: Figure 6 As shown, where, I 0t_1 This is the zero-sequence current at the generator terminals of generator 1 before arc extinction; I 0t_2 This is the zero-sequence current at the generator terminals of generator 2 before arc extinction; I 0t_3 This is the zero-sequence current at the generator terminal of generator 3 before arc extinction; I 0t_4 This is the zero-sequence current at the generator terminals of generator 4 before arc extinction; I 0t_5 This is the zero-sequence current at the generator terminal of generator 5 before arc extinction; I 0_o This refers to the zero-sequence current at the machine terminals of the external system before arc extinction. I 0n_1 This is the zero-sequence current on the neutral point side of generator 1 before arc extinction; I 0n_2 This is the zero-sequence current on the neutral point side of generator 2 before arc extinction; I 0n_3 This is the zero-sequence current on the neutral point side of generator 3 before arc extinction; I 0n_4 This is the zero-sequence current on the neutral point side of generator 4 before arc extinction; I 0n_5 This is the zero-sequence current on the neutral point side of generator 5 before arc extinction; C o The equivalent capacitance of the external system; C 1 represents the equivalent distributed capacitance of Unit 1; C 2 represents the equivalent distributed capacitance of Unit 2; C 3 represents the equivalent distributed capacitance of Unit 3; C 4 represents the equivalent distributed capacitance of Unit 4; C 5 represents the equivalent distributed capacitance of Unit 5; ρ For the stator winding ρ A single-phase ground fault occurred at the location; I f1 The fundamental current flowing out of the fault point.

[0133] Under fault conditions, the terminal current of each generator is:

[0134]

[0135] Depend on Figure 6 It can be seen that when a single-phase ground fault occurs in one generator in the generator system, the zero-sequence current amplitudes and phases of the terminals of all non-faulty units are equal; the amplitude of the zero-sequence current at the terminals of the faulty unit is greater than the sum of the amplitudes of the zero-sequence currents at the terminals of all non-faulty units, and its phase differs from that of the zero-sequence currents at the terminals of the non-faulty units by 180 degrees. For the faulty unit, the zero-sequence current at the terminals flows from the bus to the unit; for the non-faulty units, the zero-sequence current at the terminals flows from the unit to the bus.

[0136] like Figure 7 As shown, where, I ′ 0t_1 This is the zero-sequence current at the generator terminals of generator 1 after the arc is extinguished; I ′ 0t_2 This is the zero-sequence current at the generator terminals of generator 2 after the arc is extinguished; I ′ 0t_3 This is the zero-sequence current at the generator terminal of generator 3 after the arc is extinguished; I ′ 0t_4 This is the zero-sequence current at the generator terminals of generator 4 after the arc is extinguished; I ′ 0t_5 This is the zero-sequence current at the generator terminal of generator 5 after the arc is extinguished; I ′ 0n_1 This is the zero-sequence current on the neutral point side of generator 1 after the arc is extinguished; I ′ 0n_2 This is the zero-sequence current on the neutral point side of generator 2 after the arc is extinguished; I ′ 0n_3 This is the zero-sequence current on the neutral point side of generator 3 after the arc is extinguished; I ′ 0n_4 This is the zero-sequence current on the neutral point side of generator 4 after the arc is extinguished; I ′ 0n_5 This is the zero-sequence current on the neutral point side of generator 5 after the arc is extinguished; I ′ 0_o This refers to the terminal current of the external system after the arc is extinguished.

[0137] After the arc-extinguishing current is injected into the generator terminals to extinguish the fault arc, the voltage at the fault point of the faulty generator drops to 0, and the fault arc becomes approximately insulated. At this time, the zero-sequence current at each generator terminal is:

[0138]

[0139] Depend on Figure 7It can be seen that after the arc-extinguishing current is injected into the generator terminals to extinguish the fault, the terminal currents of all generators are equal. Furthermore, their direction is the same as that of the terminal currents of the non-faulty units when a ground fault occurs but no arc-extinguishing current is injected. Therefore, before and after arc extinguishing, the phase of the change in the zero-sequence current at the terminals of the faulty units is significantly greater than the phase of the change in the zero-sequence current at the terminals of the non-faulty units.

[0140] Based on the above fault characteristics, in this step, the phase change of the zero-sequence current at the terminal of the faulty unit before and after arc extinction is greater than that of the zero-sequence current at the terminal of the non-faulty unit to perform selective fault location, specifically as follows:

[0141] The zero-sequence current phase change of one generator is compared with the average phase change of all other generators in the system plus a safety margin to perform selective fault location. The specific criteria for selective fault location are as follows:

[0142] For the i-th generator in the system, it is determined to be a faulty unit if it satisfies the following formula:

[0143]

[0144] in, k =1,2,..., m , representing the k One generator; m This represents the total number of generators. I 0t_k The first before the arc was extinguished k Zero-sequence current at the generator terminals; I ′ 0t_k For the first time after the arc is extinguished k Zero-sequence current at the generator terminals; arg() indicates the phase; ε This is a preset threshold used to distinguish normal fluctuations, set according to the actual field conditions. For unit i, if the criteria for selective fault location are met, then unit i is determined to be a faulty unit.

[0145] Through the above steps, the present invention can achieve active arc suppression and selective fault location for multi-generator generators sharing a common mother. Example 1

[0146] A simulation model of a stator grounding fault in a multi-generator generator sharing a common bus was built in the PSCAD / EMTDC software platform. Five generators were included, all with identical parameters: rated voltage 10.5kV, rated capacity 10.5MW. The stator winding inductance per phase was 2.84μH, and the total system capacitance was 2.406μF.

[0147] A current with an amplitude of 0.5A and a frequency of 20Hz is injected through a current source. The result obtained after Fourier transform is...U The value of 1 is 1274.34∠-50.42°, from which the following can be calculated: C ∑ The value is 2.4607 μF, with a relative error of 0.03% compared to the actual value.

[0148] To verify the arc suppression effect of the active control method based on generator terminal voltage proposed in this invention, grounding transition resistances at different fault locations were set on phase A of generator No. 1 in the established simulation model at 0.2s. R f For a 500Ω stator single-phase ground fault, an active current control device installed at the generator terminal bus is activated in 0.3s. When the fault occurs at position 0.25, the fundamental wave injection is 6.78A∠-76.72° and the third harmonic injection is 8.01A∠-60.30°; when the fault occurs at position 0.50, the fundamental wave injection is 13.44A∠-69.22° and the third harmonic injection is 6.27A∠-26.82°; when the fault occurs at position 0.75, the fundamental wave injection is 19.86A∠-61.71° and the third harmonic injection is 4.02A∠17.94°. Simulation results are as follows. Figure 8 As shown, where, Figure 8 (a) is R f =500Ω and α The simulation results of active arc suppression at the machine terminal are shown in the figure with a value of 0.25. Figure 8 (b) is R f =500Ω and α The simulation results of active arc suppression at the machine end are shown in the figure with a value of 0.50. Figure 8 (c) is R f =500Ω and α The simulation results of active arc suppression at the machine end are shown in the figure with a value of 0.75.

[0149] from Figure 8 As can be seen, the proposed active arc suppression method based on terminal voltage regulation can reduce the fault current amplitude under different fault locations. I f The arc quenching efficiency was reduced from 4.55A, 7.24A, and 10.44A to near 0, respectively, achieving effective and reliable arc suppression and verifying the effectiveness of the method proposed in this invention.

[0150] To verify the selective location method proposed in this invention, at 0.2s, grounding transition resistances were set for phase A of generator 1 in the established simulation model under different fault locations. R fA 500Ω stator single-phase ground fault was simulated, and 20dB of white noise was added to the simulation to verify the noise immunity of the proposed method. An active current control device installed at the generator terminal bus was activated at 0.3s. The difference between the zero-sequence currents at the generator terminals of each unit before and after arc suppression was calculated. A Fourier transform was performed on the differential current, and its fundamental phase was extracted. The results are as follows: Figure 9 As shown. Figure 9 The time window is 0.1s, which is the zero-sequence current at the machine terminal between 0.2s and 0.3s minus the zero-sequence current between 0.1s and 0.2s. Figure 9 (a) is R f =500Ω and α =0.25, zero-sequence current phase results of faulty and non-faulty units before and after arc suppression; Figure 9 (b) is R f =500Ω and α =0.50, zero-sequence current phase results of faulty and non-faulty units before and after arc suppression; Figure 9 (c) is R f =500Ω and α The zero-sequence current phase results of the faulty and non-faulty units before and after arc suppression are shown in the figure with a phase ratio of 0.75.

[0151] from Figure 9 It can be seen that before and after the arc suppression injection, the phase of the zero-sequence differential current at the terminal of the faulty unit is significantly larger than the phase of the zero-sequence differential current at the terminal of the non-faulty unit. For example... Figure 9 As shown in (b), the fault occurred α At a value of 0.5, the zero-sequence differential current phase of the faulty unit is -95.15°, while that of the non-faulty unit is -50.86°. This satisfies the proposed selective fault location criterion, allowing for effective identification of the faulty unit.

Claims

1. An active arc suppression method for stator grounding faults in a multi-machine common-bus generator system based on online calculation of ground capacitance parameters, characterized in that: Includes the following steps: S1. Connect a controllable current source in parallel on the secondary side of the generator neutral point grounding transformer, and use the controllable current source to inject current into the neutral point; perform Fourier transform on the measured neutral point voltage signal, extract the voltage component with the same frequency as the injected current, substitute the voltage component and the injected current value into the preset formula, and calculate the ground capacitance parameters of the generator system online. S2. Measure the three-phase phase voltage and the phase value of the zero-sequence current at the generator terminals, and calculate the fundamental potential at the fault point based on the measured values; derive the compensation current to be injected at the generator terminals of the faulty phase based on the ground capacitance parameters and the fundamental potential at the fault point, and inject the compensation current through an active current control device installed at the generator terminals; the compensation current is: in, I i1 This is the compensation current injected from the generator fault A camera terminal; E f1 The fundamental potential at the fault point; j The imaginary unit; ω Angular frequency; C ∑ This is the sum of the generator's three-phase-to-ground capacitance and the direct-connected system's to-ground capacitance, i.e., the to-ground capacitance parameter; R n The neutral point grounding impedance; And the fundamental potential at the fault point E f1 The calculation formula is: in, E A1 The fundamental potential of phase A in the fault; α This represents the percentage of the number of coils from the fault point to the neutral point in the total number of turns of all series-connected coils in the fault branch. S3. After the generator terminal is injected with compensation current to extinguish the arc at the fault point, the phase of the zero-sequence current at the generator terminal of each generator is measured again. The phase change of the zero-sequence current at the generator terminal of the faulty unit before and after the arc is extinguished is greater than that of the phase change of the zero-sequence current at the generator terminal of the non-faulty unit. The faulty unit in the multi-generator common bus system is then identified. In step S3, the zero-sequence current phase change of one generator is compared with the average phase change of all other generators in the system plus a safety margin to perform selective fault location. The specific criteria for selective fault location are as follows: For the i-th generator in the system, it is determined to be a faulty unit if it satisfies the following formula: in, k =1,2,..., m , representing the k One generator; m This represents the total number of generators. I 0t_k The first before the arc was extinguished k Zero-sequence current at the generator terminals; I ′ 0t_k For the first time after the arc is extinguished k Zero-sequence current at the generator terminals; arg() indicates the phase; ε This is the preset threshold.

2. The active arc suppression method for stator grounding faults in a multi-machine common-bus generator system based on online calculation of ground capacitance parameters as described in claim 1, characterized in that: In step S1, the ground capacitance parameters C ∑ The online calculations are specifically as follows: Injecting current into the neutral point using a controllable current source I And the neutral point voltage component at the corresponding specific frequency was measured. U 1; According to the system admittance formula: in, Y For system admittance; G ∑ This is the sum of the three-phase total grounding conductance of the generator; Let the real part of the system admittance formula be S and the imaginary part be X, that is: According to the rule that the real and imaginary parts are equal, we can obtain: Thus, the capacitance parameters to ground are obtained. C ∑ The value is: 。 3. The active arc suppression method for stator grounding faults in a multi-machine common-bus generator system based on online calculation of ground capacitance parameters, as described in claim 2, is characterized in that: The process of deriving the compensation current to be injected at the generator terminal side of the faulty phase in step S2 includes: S21. Let the fault occur in phase A, and establish an equivalent structure diagram of the fault phase; S22. Based on the equivalent structure diagram of the faulted phase, the Kirchhoff current equations for the faulted phase A winding are as follows: in, I An1 This refers to the fundamental current to ground at the neutral point of phase A in case of fault. C a This is the total equivalent capacitance to ground of the faulty phase A winding; U Ai1 The fundamental voltage of the i-th turn of the faulty phase A coil relative to ground; C t This refers to the total capacitance to ground flowing through the machine terminal side; U At1 The fundamental voltage of camera A relative to ground; U f1 The voltage at the fault point; R f is the grounding transition resistance at the fault point; n is the total number of turns of the stator winding of phase A of the fault. Meanwhile, Kirchhoff's current equations for a healthy phase winding are as follows: in, I Bn1 To ensure the fundamental wave to ground current at the neutral point of phase B; C b To improve the overall equivalent capacitance to ground of the B-phase winding; U Bi1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase B coil and ground; U Bt1 To ensure the fundamental voltage of camera B to ground; I Cn1 To ensure the stability of the fundamental wave to ground current at the C-phase neutral point; C c To improve the overall equivalent capacitance to ground of the C-phase winding; U Ci1 To ensure the fundamental voltage between the midpoint of the i-th turn of phase C coil and ground; U Ct1 To ensure the fundamental voltage of the C-camera terminal to ground; S23. Kirchhoff's current equations for the generator neutral point are as follows: in, I n1 The current flowing through the neutral point grounding impedance is calculated using the following formula: in, U n1 This is the fundamental voltage of the neutral point relative to ground; S24. Define the voltage variable relationship as follows: in, E Ai1 The fundamental potential from the midpoint of the i-th turn of the coil in phase A of the fault to the neutral point; E Bi1 To ensure the fundamental potential from the midpoint of the i-th turn of phase B coil to the neutral point; E Ci1 To ensure the fundamental potential from the midpoint of the i-th turn of the C-phase coil to the neutral point; in, E B1 To improve the fundamental potential of phase B; E C1 To improve the fundamental potential of phase C; S25. Assuming the effect of asymmetric three-phase winding capacitance to ground is ignored, then the generator's three-phase windings are symmetrical and the total equivalent capacitance to ground of the three-phase windings is equal, i.e. C a = C b = C c The three-phase phase potentials of the generator remain symmetrical, satisfying the following conditions. E A1 + E B1 + E C1 =0; the fundamental potential of the i-th turn of each phase of the generator coil also remains symmetrical with respect to the neutral point, satisfying... E Ai1 + E Bi1 + E Ci1 =0; Substitute the Kirchhoff current equations for the faulty phase winding and the healthy phase winding in step S22, as well as the voltage variable relationship in step S24, into the Kirchhoff current equation for the neutral point in S23 to obtain the compensation current. I i1 for: in, U t1 This refers to the voltage at the generator terminals relative to the ground. S26. Establish the fundamental voltage of the system neutral point to ground. U n1 Generator terminal voltage to ground U t1 With the fundamental potential at the fault point E f1 The relationship between them satisfies the following voltage relationship: ； S27. The control objective of active arc suppression is to reduce the voltage at the fault point. U f1 Even if forced regulation is zero, it will be effective. U f1 =0, and then the required terminal voltage regulation target is determined by the relationship in step S26: ； S28. Substitute the terminal voltage regulation target into the compensation current from step S25. I i1 The compensation current is derived from the calculation formula. I i1 .

4. The active arc suppression method for stator grounding faults in a multi-machine common-bus generator system based on online calculation of ground capacitance parameters, as described in claim 3, is characterized in that: In step S27, the active current control device regulates the injected compensation current. I i1 The amplitude and phase angle of the generator terminal voltage relative to the ground wave will determine the voltage at the generator terminals. U t1 Forced regulation to a specific value, so that the voltage at the fault point... U f1 It is suppressed to zero.

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