Method for reducing neutral displacement voltage in large generator

Abstract

The application provides a large generator neutral point displacement voltage reduction optimization method, and belongs to the technical field of generator relay protection. The application relies on the existing relay protection of the unit, a fault recorder collects the three-phase voltage at the unit end and the open delta waveform under the no-load / grid-connected condition, and calculates the fundamental phase voltage and the neutral point displacement voltage. According to Kirchhoff's law, the three-phase unbalanced current is calculated. With only a single-phase unit end external capacitor as a constraint, the displacement voltage minimization objective function is established by traversing the three phases, and the optimal compensation phase and matching capacitor capacity are determined by extreme value solution to be put into operation. The application does not need to build a fine distribution capacitor model of the stator and does not need to carry out a grounding fault simulation test, and only a single compensation capacitor can realize optimization, which reduces the equipment investment and operation and maintenance amount compared with the traditional two-phase compensation scheme. After verification of the hydroelectric unit, the stator grounding protection dead zone is greatly reduced, and the application is suitable for various large-capacity generator units such as arc extinction coils and high-resistance grounding, and has strong engineering practicability.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology for main equipment in power systems, and specifically to an optimization method for reducing neutral point displacement voltage in large generators. Background Technology

[0002] Single-phase grounding faults in the generator stator windings are among the most common generator faults. These faults can develop into phase-to-phase or turn-to-turn short circuits, exacerbating stator core burnout and causing significant economic losses. Therefore, generator fundamental zero-sequence voltage stator grounding protection is widely used. Excessive displacement voltage increases the dead zone of single-phase grounding protection in the generator stator windings, threatening the safe and stable operation of the generator. With economic development and increasing electricity demand, generator unit capacity has increased. To compensate for capacitor current, some generators operate using a neutral point grounding method via an arc suppression coil, amplifying the problem of excessive displacement voltage. Asymmetrical generator branch potentials and uneven distributed capacitance can also lead to excessive displacement voltage. In recent years, several large hydropower units have exhibited excessive displacement voltage, which has become a common problem.

[0003] In early engineering, the three-phase-to-ground capacitance was often measured while the generator was stationary, with the phase with the largest capacitance serving as the benchmark, and compensation capacitors added to the other two phases or one phase. This method is prone to failure under conditions of asymmetrical stator winding fundamental potential because static capacitance parameters cannot reflect the actual distributed current during operation. The subsequently developed dynamic measurement method, which involves running the generator at rated speed and indirectly calculating parameters by simulating a single-phase ground fault, avoids the shortcomings of the static method, but the difficulty and safety of experimental implementation limit its widespread adoption. Another approach is to establish a complex quasi-distributed capacitance parameter model for simulation calculations, but this modeling process is cumbersome, highly dependent on the generator's internal structural parameters, has poor versatility, and is computationally complex.

[0004] To address the shortcomings of the aforementioned methods, an effective improvement is to determine, through conventional measurement and calculation, the appropriate values ​​of capacitors to be connected to two phases at the generator terminals to balance the ground capacitance current and thus reduce the displacement voltage. Theoretically, this approach can reduce the neutral point displacement voltage to zero. However, its practical application in engineering still faces challenges: firstly, installing capacitors on two phases increases equipment investment costs and reduces safety; secondly, the long-term monitoring and maintenance of the two capacitor banks requires significantly more work. Therefore, the core issue currently being addressed is how to simplify the capacitor configuration structure and improve engineering practicality while ensuring a significant reduction in neutral point displacement voltage. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide an optimized method for reducing neutral point displacement voltage in large generators. This method aims to address the shortcomings of existing two-phase external capacitor compensation schemes, such as high equipment cost, large maintenance workload, high safety risks, failure of static compensation methods, difficulty in implementing dynamic testing methods, and poor versatility of detailed modeling methods. The new method only requires a single-phase external compensation capacitor at the generator terminal, relying on the unit's existing relay protection and fault recording equipment to complete data acquisition and parameter calculation. It eliminates the need for shutdown, simulated grounding faults, and complex stator winding modeling. While significantly reducing neutral point displacement voltage, it simplifies primary equipment configuration, reduces investment and maintenance costs, and improves the engineering practicality of the solution.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An optimization method for reducing neutral point displacement voltage in large generators includes the following steps: S1. Data acquisition steps: When the generator is in no-load operation or normal grid-connected operation, the three-phase voltage waveform and the open delta zero-sequence voltage waveform of the voltage transformer output by the generator terminal voltage transformer are acquired through the relay protection device and / or fault recorder to obtain complete voltage waveform data. S2. Fundamental electrical quantity calculation steps: Based on the voltage waveform data, calculate the fundamental phase voltage of generator A phase and the fundamental displacement voltage of generator neutral point, and use the phase of the fundamental phase voltage of generator A phase as the global phase reference. S3. Three-phase unbalanced current calculation steps: Input the equivalent series inductance L, equivalent series resistance R of the generator neutral point grounding equipment, the total static capacitance C of the generator stator three phases to ground, and the fundamental angular frequency ω. Combine the generator equivalent circuit model with Kirchhoff's current law to calculate the three-phase unbalanced current characterizing the asymmetry of the stator three-phase-to-ground capacitance. And extract the magnitude of the unbalanced current. Phase angle ; S4. Steps for solving single-phase external capacitor parameters: With the constraint that only a single-phase external compensation capacitor is connected at the generator terminal, phases A, B, and C are considered as candidate phases x for the external capacitor. For each candidate phase x, a neutral point displacement voltage minimization objective function is established. The optimal external phase x and its corresponding optimal capacitor value are determined through extreme value calculations. ; S5. Capacitor commissioning optimization steps: The optimal single-phase installed capacity at the generator terminal determined in step S4 is... The ground compensation capacitor offsets the unbalanced capacitor current caused by the uneven distribution of the three-phase ground capacitance of the stator and the asymmetry of the generator potential, thereby reducing the neutral point displacement voltage of the generator.

[0007] In step S1 above, the voltage transformer is a three-phase voltage transformer built into the generator terminal. There is no need to add a special capacitor measurement and ground fault simulation test device. Waveform acquisition is completed by relying only on the original relay protection and fault recording hardware of the unit.

[0008] In step S2 above, the neutral point displacement voltage is directly calculated from the open delta output voltage of the voltage transformer. The phases of the three-phase symmetrical voltages A, B, and C are set to 0°, 240°, and 120° respectively with phase A as the reference, and the magnitudes of the three-phase voltages are equal under normal operating conditions.

[0009] The three-phase unbalanced current in step S3 above The calculation formula is based on the equivalent circuit of the neutral grounding equipment RL series and the equivalent model of the stator-to-ground concentrated capacitance. The calculation process does not require the establishment of a fine simulation model of the quasi-distributed capacitance of the generator stator winding.

[0010] The constraint of step S4 above is that only a single phase of the generator terminal is connected to the external compensation capacitor, excluding the configuration of two-phase or three-phase simultaneous external capacitor connection, and neutral point displacement voltage suppression is achieved through a single capacitor device.

[0011] The objective function for step S4 above is constructed as follows: An expression for the neutral point displacement voltage vector is established after adding an external single-phase capacitor. Minimizing the displacement voltage amplitude is transformed into solving a problem of finding the minimum value of a univariate continuous function. The unique optimal external capacitor capacity is obtained by taking the extreme value through differentiation. .

[0012] The above-mentioned generator neutral point grounding equipment is either an arc suppression coil grounding device or a high-resistance grounding device, which can be equivalent to an RL grounding circuit with a series resistor R and a series inductor L, and is suitable for large-capacity models of hydro-generator sets and steam-generator sets.

[0013] The aforementioned stator three-phase static total capacitance C is calculated by measuring the independent capacitances to ground of each phase A, B, and C when the generator is stationary and stopped. The summation yields a result that can be reused long-term with only one static offline measurement.

[0014] In this method, there is no need to conduct dynamic tests to simulate single-phase ground faults at the generator's rated speed. All parameters are calculated solely based on the steady-state waveform data of the unit's normal no-load / grid-connected operation. There are no test safety risks and the normal power generation of the unit is not affected.

[0015] In this method, the calculations obtained under the optimal single-phase input... After compensation capacitor, the generator neutral point displacement voltage is reduced by no less than 45% compared to before optimization, significantly reducing the dead zone of single-phase grounding protection of stator winding.

[0016] In this method, only a single compensation capacitor is used to complete the unbalanced current correction. Compared with the two-phase external capacitor scheme, it reduces the investment in capacitor equipment, simplifies the layout of primary equipment on site, and reduces the workload of long-term operation and maintenance and online monitoring of capacitor equipment.

[0017] In this method, when the target unit is a 350MW hydro-generator, the neutral point equivalent R=604.83Ω, L=0.946H, and the stator-to-ground capacitance is... =1.93μF =1.92μF When the voltage is 1.92μF, the optimal external phase is calculated as phase B after step S4, and the optimal compensation capacitor capacity is 256nF. After commissioning, the neutral point displacement voltage drops to 279.03V.

[0018] The computer-readable storage medium using the above-described optimization method for reducing neutral point displacement voltage of a large generator stores a computer program that, when executed by a processor, implements all the steps of the optimization method for reducing neutral point displacement voltage of a generator.

[0019] The neutral point displacement voltage optimization and adjustment device using the above-mentioned large generator neutral point displacement voltage reduction optimization method includes an acquisition module, a data calculation module, a parameter storage module, a capacitance calculation and output module, and a single-phase capacitor switching execution module. The acquisition module is used to perform waveform acquisition in step S1; the data calculation module is used to perform electrical quantity and unbalanced current calculations in steps S2 and S3; the parameter storage module stores the neutral point grounding R and L parameters and the stator three-phase ground static capacitance; the capacitance calculation and output module performs step S4 to solve for the optimal external phase and capacitor capacity; the single-phase capacitor switching execution module only connects the corresponding compensation capacitor to a single generator terminal phase.

[0020] The method for optimizing the reduction of neutral point displacement voltage in a large generator mentioned in this invention has the following beneficial effects: (1) Low equipment investment and low operation and maintenance costs: Unlike the existing two-phase external capacitor scheme, this invention only requires a compensation capacitor to be configured on a single phase at the generator end, which greatly reduces the procurement costs of high voltage capacitors, matching transformers and protection devices; with only one set of capacitor equipment, the workload of inspection, monitoring and maintenance is halved, the primary wiring circuit is simplified, and the safety risk of insulation failure is reduced.

[0021] (2) Convenient implementation and no need for shutdown testing: All data acquisition is completed by relying on the original relay protection, fault recorder and generator terminal PT of the unit, without the need for additional special measurement equipment; the whole process only collects the no-load / grid-connected steady-state operation waveform of the unit, without the need to speed up to simulate single-phase grounding fault, avoids the risk of test insulation damage, and does not affect the unit's power generation output.

[0022] (3) Simple modeling and strong versatility: There is no need to build a complex stator winding quasi-distributed capacitance fine simulation model. The calculation is completed by using the equivalent circuit of concentrated capacitance and the equivalent circuit of RL neutral point grounding combined with Kirchhoff's law. Only one shutdown is needed to measure the three-phase ground capacitance for long-term reuse. It is compatible with various large-capacity generators such as water turbines and steam turbines, and is compatible with two mainstream grounding methods: neutral point arc suppression coil grounding and high resistance grounding.

[0023] (4) Significant compensation effect, improving unit protection performance: According to on-site measurements, the neutral point displacement voltage drop can reach 49% after the optimal single-phase compensation capacitor is put into operation, which greatly reduces the dead zone of stator single-phase grounding protection, improves the sensitivity of grounding fault identification, and avoids stator winding burnout accidents.

[0024] (5) The solution can be implemented in software and hardware: This method can be packaged into a computer program and stored in a readable medium, or it can be integrated with a dedicated optimization and adjustment device to form a dual protection system of "algorithm software + dedicated hardware", with comprehensive patent protection scope. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the generator main wiring in this invention; Figure 2 This is a simplified equivalent circuit diagram for calculating the generator displacement voltage in this invention; Figure 3 This is a flowchart illustrating the optimization method for reducing neutral point displacement voltage in a large generator according to the present invention. Figure 4 This refers to the actual waveform data of the target generator in this embodiment of the invention; Figure 5 This is a comparison diagram of the neutral point displacement voltage after different phases of the target generator are connected to external capacitors in an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] A method for reducing neutral point displacement voltage in a generator is disclosed. This method, under conditions of normal generator operation with displacement voltage, determines an appropriate capacitor value for connecting to a specific phase at the generator terminals through conventional measurement and simple calculation, thereby significantly reducing the displacement voltage. This method is implemented under normal no-load or grid-connected operating conditions of the generator, and the main steps are as follows: Step 1: Read the voltage waveform data using a relay protection device or fault recorder.

[0028] Step 2: Calculate the fundamental phase voltage of generator phase A using voltage waveform data. and neutral point displacement voltage ; Step 3: Combining the relevant parameters of the generator and its neutral grounding equipment with the voltage waveform data recorded by the relay protection device and fault recorder, and applying the generator equivalent circuit and Kirchhoff's current law, calculate the three-phase unbalanced current. : (1) in, It is the fundamental angular frequency. L and R These are the equivalent series inductance and series resistance of the generator neutral point grounding equipment, respectively. It is the sum of the three-phase-to-ground capacitances of the stator windings measured under static conditions of the generator; Step 4: Obtained from the preceding steps , , Further calculations yielded the phase and value of the external capacitor connected to the generator terminals. C x+ ; Furthermore, in the aforementioned second step, the three-phase voltage of the generator terminal voltage transformer and the open delta voltage of the transformer are measured by a relay protection device or a fault recorder to obtain the fundamental phase voltage of generator phase A. and neutral point displacement voltage ,by The phase is used as a reference.

[0029] Furthermore, in the aforementioned fourth step, the phase and value of the external capacitor are obtained by solving the following formula. C x+ ; (2) in, The three-phase unbalanced current defined by the method of this invention, This represents the magnitude of the three-phase unbalanced current. For current The phase angle, let the phase of the external capacitor be... x , x Choose a, b, or c to represent phases A, B, or C. The size of the external capacitor connected to the machine terminal. This refers to the phase voltage of the external capacitor phase. This represents the magnitude of the phase voltage of the external capacitor phase. for The phase angle, with Based on the phase, , , The three-phase voltages of a normally operating generator are symmetrical at 0°, 240°, and 120° respectively. .

[0030] like Figure 1 As shown, the generator sends power to the grid via a step-up transformer, and the generator neutral point is grounded through a grounding device, which can typically be equivalent to an inductor. L With a resistor R It is series grounded and equipped with a voltage transformer at the generator terminal, which can measure the three-phase phase-to-ground voltage and the open delta zero-sequence voltage at the generator terminal.

[0031] Secondly, to clearly illustrate the method of the present invention, an equivalent circuit diagram is used. Figure 2 Explanation is provided. In the diagram, , and These are the phase voltages of generator phases A, B, and C, respectively. The measured capacitances to ground of the stator windings of phases A, B, and C under static conditions are as follows: , and For simplicity, the equivalent is that the lumped capacitor parameters are placed at the machine terminal, and the neutral point grounding device can be equivalent to a series circuit of a resistor and an inductor. R It is the equivalent series resistance of the neutral point grounding device. L This is the equivalent series inductance of the neutral point grounding device. Let the three-phase unbalanced current be... : (3) in C This is the sum of the three-phase capacitance to ground, i.e. .

[0032] Assume that an external capacitor is connected to only one phase of the generator, and let the phase of the external capacitor be... x , x Choose a, b, or c to represent phases A, B, or C. The size of the external capacitor connected to the machine terminal. Let the phase voltage of the external capacitor be denoted as... ,by Based on the phase, , , The three-phase voltages of a normally operating generator are symmetrical at 0°, 240°, and 120° respectively. Neutral point displacement voltage after generator external capacitor connection. as follows: (4) remember To minimize the displacement voltage after the external capacitor, it is necessary to make The minimum value is found, and the problem then changes from solving the equation to finding the minimum value.

[0033] (5) Substituting equation (3) into equation (5), we get: (6) set up , y If it is always greater than 0, let: (7) Normally operating generator Equation (9) can be simplified as follows, where It is about y Functions: (8) Finding the minimum value of the displacement voltage is equivalent to finding... Minimum value.

[0034] (9) According to equation (12), when Right now At that time, the displacement voltage has a minimum value, and The smaller, The smaller the minimum value, the more it determines which phase of the generator terminal should have an external capacitor connected. exist There is only one solution, therefore the solution is... The size of the external capacitor at the machine end can be obtained, thereby reducing the displacement voltage.

[0035] Example 1: like Figure 3 As shown, the specific steps of the method of the present invention are as follows: The main steps are as follows: Step 1: Read the voltage waveform data using a relay protection device or fault recorder.

[0036] Step 2: Calculate the fundamental phase voltage of generator phase A using voltage waveform data. and neutral point displacement voltage ; Step 3: Combining the relevant parameters of the generator and its neutral grounding equipment with the voltage waveform data recorded by the relay protection device and fault recorder, and applying the generator equivalent circuit and Kirchhoff's current law, calculate the three-phase unbalanced current. : (1) in, It is the fundamental angular frequency. L and R These are the equivalent series inductance and series resistance of the generator neutral point grounding equipment, respectively. It is the sum of the three-phase-to-ground capacitances of the stator windings measured under static conditions of the generator; Step 4: Obtained from the preceding steps , , Further calculations yielded the phase and value of the external capacitor connected to the generator terminals. C x+ ; Furthermore, in the aforementioned second step, the three-phase voltage of the generator terminal voltage transformer and the open delta voltage of the transformer are measured by a relay protection device or a fault recorder to obtain the fundamental phase voltage of generator phase A. and neutral point displacement voltage ,by The phase is used as a reference.

[0037] Furthermore, in the aforementioned fourth step, the phase and value of the external capacitor are obtained by solving the following formula. C x+ ; (2) in, The three-phase unbalanced current defined by the method of this invention, This represents the magnitude of the three-phase unbalanced current. For current The phase angle, let the phase of the external capacitor be... x , x Choose a, b, or c to represent phases A, B, or C. The size of the external capacitor connected to the machine terminal. This refers to the phase voltage of the external capacitor phase. This represents the magnitude of the phase voltage of the external capacitor phase. for The phase angle, with Based on the phase, , , The three-phase voltages of a normally operating generator are symmetrical at 0°, 240°, and 120° respectively. .

[0038] Example 2: To more clearly illustrate the technical solution of this invention, we take a generator from a hydropower station as an example. The main parameters of this generator are as follows: Table 2. Parameters of a Generator Nameplate

[0039] The generator's neutral point is grounded via a high-resistance connection. The neutral point can be equivalent to an inductance of 0.946H connected in series with a resistor of 604.83Ω. The stator winding single-phase-to-ground capacitance... C a 1.93μF, C b 1.92μF, C c It is 1.92 μF.

[0040] Step 1: Read the voltage waveform data using a relay protection device or fault recorder.

[0041] Step 2: Calculate the fundamental phase voltage of generator phase A using voltage waveform data. V and neutral point displacement voltage V; Step 3: Combining the relevant parameters of the generator and its neutral grounding equipment with the voltage waveform data recorded by the relay protection device and fault recorder, and applying the generator equivalent circuit and Kirchhoff's current law, calculate the three-phase unbalanced current. : A; (1) in, It is the fundamental angular frequency. L and R These are the equivalent series inductance and series resistance of the generator neutral point grounding equipment, respectively. It is the sum of the three-phase-to-ground capacitances of the stator windings measured under static conditions of the generator; Step 4: Obtained from the preceding steps , , Further calculations yielded the phase and value of the external capacitor connected to the generator terminals. C x+ ; Furthermore, in the aforementioned second step, the three-phase voltage of the generator terminal voltage transformer and the open delta voltage of the transformer are measured by a relay protection device or a fault recorder to obtain the fundamental phase voltage of generator phase A. and neutral point displacement voltage ,by The phase is used as a reference.

[0042] Furthermore, in the aforementioned fourth step, the phase and value of the external capacitor are calculated using the following formula. C x+ Solving for x For b, Cb+ Since the value is 256nF, it can be concluded that adding an external capacitor of 256nF to phase B can minimize the displacement voltage. At this time, the displacement voltage is 279.03V, which is 49% lower than before adding the external capacitor.

[0043] (2) in, The three-phase unbalanced current defined by the method of this invention, This represents the magnitude of the three-phase unbalanced current. For current The phase angle, let the phase of the external capacitor be... x , x Choose a, b, or c to represent phases A, B, or C. The size of the external capacitor connected to the machine terminal. This refers to the phase voltage of the external capacitor phase. This represents the magnitude of the phase voltage of the external capacitor phase. for The phase angle, with Based on the phase, , , The three-phase voltages of a normally operating generator are symmetrical at 0°, 240°, and 120° respectively. .like Figure 4 The figures shown are the actual waveform data of the target generator. Figure a shows that the amplitudes of phase B are inconsistent with those of phases A and C. Figure b provides a clearer view of the neutral point displacement voltage value. Figure 5 The figure shown is a comparison of the neutral point displacement voltage after different phases are connected to external capacitors.

Claims

1. An optimization method for reducing neutral point displacement voltage in large generators, characterized in that, Includes the following steps: S1. Data acquisition steps: When the generator is in no-load operation or normal grid-connected operation, the three-phase voltage waveform and the open delta zero-sequence voltage waveform of the voltage transformer output by the generator terminal voltage transformer are acquired through the relay protection device and / or fault recorder to obtain complete voltage waveform data. S2. Fundamental electrical quantity calculation steps: Based on the voltage waveform data, calculate the fundamental phase voltage of generator A phase and the fundamental displacement voltage of generator neutral point, and use the phase of the fundamental phase voltage of A phase as the global phase reference. S3. Three-phase unbalanced current calculation steps: Input the equivalent series inductance L, equivalent series resistance R of the generator neutral point grounding equipment, the total static capacitance C of the generator stator three phases to ground, and the fundamental angular frequency ω. Combine the generator equivalent circuit model with Kirchhoff's current law to calculate the three-phase unbalanced current characterizing the asymmetry of the stator three-phase-to-ground capacitance. And extract the magnitude of the unbalanced current. Phase angle ; S4. Steps for solving single-phase external capacitor parameters: With the constraint that only a single-phase external compensation capacitor is connected at the generator terminal, phases A, B, and C are considered as candidate phases x for the external capacitor. For each candidate phase x, a neutral point displacement voltage minimization objective function is established. The optimal external phase x and its corresponding optimal capacitor value are determined through extreme value calculations. ; S5. Capacitor commissioning optimization steps: The optimal single-phase installed capacity at the generator terminal determined in step S4 is... The ground compensation capacitor offsets the unbalanced capacitor current caused by the uneven distribution of the three-phase ground capacitance of the stator and the asymmetry of the generator potential, thereby reducing the neutral point displacement voltage of the generator.

2. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, In step S1, the voltage transformer is a three-phase voltage transformer built into the generator terminal. There is no need to add a special capacitor measurement and ground fault simulation test device. Waveform acquisition is completed by relying only on the original relay protection and fault recording hardware of the unit.

3. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, In step S2, the neutral point displacement voltage is directly calculated from the open delta output voltage of the voltage transformer. The phases of the three-phase symmetrical voltages A, B, and C are set to 0°, 240°, and 120° respectively with phase A as the reference, and the magnitudes of the three-phase voltages are equal under normal operating conditions.

4. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The three-phase unbalanced current in step S3 The calculation formula is based on the equivalent circuit of the neutral grounding equipment RL series and the equivalent model of the stator-to-ground concentrated capacitance. The calculation process does not require the establishment of a fine simulation model of the quasi-distributed capacitance of the generator stator winding.

5. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The constraint of step S4 is that only a single-phase external compensation capacitor is connected to the generator terminal, excluding the configuration of two-phase or three-phase external capacitors at the same time, and neutral point displacement voltage suppression is achieved by a single capacitor device.

6. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The objective function construction method for step S4 is as follows: Establish the neutral point displacement voltage vector expression after adding an external single-phase capacitor; transform the minimization of the displacement voltage amplitude into a problem of finding the minimum value of a univariate continuous function; and obtain the unique optimal external capacitor capacity by taking the extreme value through differentiation. .

7. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The generator neutral point grounding device is either an arc suppression coil grounding device or a high-resistance grounding device, both of which can be equivalent to an RL grounding circuit with a series resistor R and a series inductor L, and are suitable for large-capacity models of hydro-generator sets and steam-generator sets.

8. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The stator three-phase static total capacitance C is the measured capacitance to ground of each of phases A, B, and C when the generator is stationary and stopped. The summation yields a result that can be reused long-term with only one static offline measurement.

9. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, The entire process does not require simulating a single-phase ground fault for dynamic testing at the generator's rated speed. All parameter calculations are completed solely based on the steady-state waveform data of the unit's normal no-load / grid-connected operation. There are no test safety risks and the normal power generation of the unit is not affected.

10. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, Calculated based on optimal single-phase input After compensation capacitor, the generator neutral point displacement voltage is reduced by no less than 45% compared to before optimization, significantly reducing the dead zone of single-phase grounding protection of stator winding.

11. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 5, characterized in that, Using only a single compensation capacitor to correct unbalanced current reduces investment in capacitor equipment, simplifies the layout of primary equipment on site, and reduces the workload of long-term operation and maintenance and online monitoring of capacitor equipment compared to the two-phase external capacitor scheme.

12. The method for optimizing the reduction of neutral point displacement voltage in a large generator according to claim 1, characterized in that, When the target unit is a 350MW hydro-generator, with an equivalent neutral point R=604.83Ω and L=0.946H, the stator-to-ground capacitance is... =1.93μF =1.92μF When the voltage is 1.92μF, the optimal external phase is calculated as phase B after step S4, and the optimal compensation capacitor capacity is 256nF. After commissioning, the neutral point displacement voltage drops to 279.03V.

13. A computer-readable storage medium for using the optimization method for reducing neutral point displacement voltage of a large generator according to any one of claims 1-12, wherein a computer program is stored thereon, characterized in that, When the computer program is executed by the processor, it implements all the steps of the generator neutral point displacement voltage reduction optimization method.

14. A neutral point displacement voltage optimization and adjustment device using the neutral point displacement voltage reduction optimization method for any one of claims 1-12, characterized in that, It includes an acquisition module, a data calculation module, a parameter storage module, a capacitance calculation output module, and a single-phase capacitor switching execution module. The acquisition module is used to perform waveform acquisition in step S1. The data calculation module is used to perform electrical quantity and unbalanced current calculations in steps S2 and S3. The parameter storage module stores the neutral point grounding R and L parameters and the stator three-phase ground static capacitance. The capacitance calculation output module performs step S4 to solve for the optimal external phase and capacitor capacity. The single-phase capacitor switching execution module only connects the corresponding compensation capacitor to a single terminal phase.

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