Generator combined grounding transformer optimization design method considering grounding fault location accuracy

Abstract

The application provides a generator combined grounding transformer optimization design method considering grounding fault positioning accuracy, and the method comprises the following steps: calculating inherent capacitance current according to various parameters of a generator, and determining single-phase grounding fault safety current; calculating resistance current and inductance current based on a design principle that resistance current is equal to a preset multiple of compensated capacitance current; determining various design parameters of the generator combined grounding transformer based on the resistance current and the inductance current; checking transfer overvoltage, neutral point displacement voltage and heavy arc transient overvoltage of the generator, and judging the number of intersection points of a straight line where a vector determined by a positioning indication angle in a graphic method is located and branch potential based on the various design parameters, and adjusting the various design parameters so that the number of intersection points is one. The method improves the positioning accuracy of stator grounding faults through optimization design of a neutral point grounding transformer of a large generator.

Description

Technical Field

[0001] This application relates to the field of design and manufacturing technology of neutral point grounding transformers for large generators, and in particular to an optimized design method for generator combined grounding transformers that takes into account the accuracy of grounding fault location. Background Technology

[0002] With the construction and commissioning of giant hydropower units, the ground capacitance current of the stator winding of the hydropower generator has increased dramatically. In order to reduce the single-phase ground fault current and avoid burning the stator core, combined grounding methods (such as "distribution transformer + load resistor / parallel inductor" or "distribution transformer + load resistor / series inductor") have been gradually promoted and applied.

[0003] Among them, single-phase grounding faults in the stator are the most common type of fault causing insulation damage in the stator windings of large generators. The decrease in grounding fault current and the change in transition resistance inevitably increase the difficulty of on-site fault diagnosis. In related technologies, stator grounding fault location generally adopts the "graphical method." The "graphical method" can improve the location accuracy down to the faulty conductor, thus gaining time for generator fault repair and power restoration.

[0004] In the "graphical method," ground fault location is abstracted into finding a vector. The potential of the line and the branch The intersection problem. That is, the fundamental zero-sequence voltage after the fault. First, the ground potential point was identified. sum vector ( (for generator neutral point), while fault location indicator angle It is a vector with vector The phase angle difference can be used to determine the vector. Based on the characteristics of the branch potential of different types of stator windings, if there is only one intersection point, then it is not necessary to know the grounding transition resistance value to accurately locate it.

[0005] Considering the positioning indicator angle It is unrelated to the grounding transition resistance, and only related to the parameters of the generator and the grounding transformer itself. Therefore, by optimizing the design of the grounding transformer to adjust the positioning indicator angle, the vector... The potential of the line and the branch Having only one intersection point can improve the positioning accuracy to the faulty line bar, thus pointing the way for the optimized design of generator-combined grounding transformers.

[0006] Therefore, how to optimize the design of generator-combined grounding transformers while ensuring the accuracy of grounding fault location has become an urgent problem to be solved. Summary of the Invention

[0007] This application aims to at least partially address one of the technical problems in the related art.

[0008] Therefore, the first objective of this application is to propose an optimized design method for generator-combined grounding transformers that takes into account the accuracy of grounding fault location. Based on the optimized design of the parameters of the neutral point grounding transformer of a large generator, the method improves the location accuracy of stator grounding faults.

[0009] The second objective of this application is to propose an optimized design system for generator-combined grounding transformers that takes into account the accuracy of grounding fault location.

[0010] The third objective of this application is to propose an electronic device.

[0011] The fourth objective of this application is to provide a computer-readable storage medium.

[0012] To achieve the above objectives, the first aspect of this application is to propose an optimized design method for generator-combined grounding transformers that takes into account the accuracy of grounding fault location, comprising the following steps: The inherent capacitance current of the generator is calculated based on various parameters of the generator to be optimized, and the safe current for a single-phase ground fault in the generator stator is determined. Inductor current is introduced to compensate for the inherent capacitor current. Based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitor current, the resistance current and inductor current are calculated using the inherent capacitor current and the safety current. Based on the resistive current and the inductor current, various design parameters of the generator-combined grounding transformer are determined. These various design parameters are used to ensure that the single-phase ground fault current is within the safe current range. The various design parameters include the inductance and resistance values ​​of the combined grounding transformer. The overvoltage transmitted by the generator, the neutral point displacement voltage, and the reignition arc transient overvoltage are checked. Based on the various design parameters, the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential is determined. The various design parameters are adjusted so that the number of intersection points is one.

[0013] Optionally, the step of calculating the inherent capacitance current of the generator based on multiple parameters of the generator to be optimized includes: The generator phase potential is calculated based on the generator's rated voltage. Combining this phase potential, the generator stator winding-to-ground capacitance, and the capacitances on both sides of the generator terminal circuit breaker (GCB), the inherent capacitance current is calculated. Based on the design principle that the resistance current equals a preset multiple of the compensated capacitance current, the resistance current and inductance current are calculated using the inherent capacitance current and the safety current. This includes: calculating the compensated capacitance current based on the safety current; calculating the resistance current based on the compensated capacitance current and the preset multiple; and calculating the inductance current based on the compensated capacitance current and the inherent capacitance current.

[0014] Optionally, determining various design parameters of the generator-combined grounding transformer based on the resistive current and the inductor current includes: calculating the overall impedance of the neutral point grounding device based on the resistive current and the inductor current; detecting the load loss and impedance voltage percentage through load tests and short-circuit tests, and calculating the leakage resistance and leakage reactance of the combined grounding transformer based on the load loss and impedance voltage percentage; and calculating the parallel resistance and inductance values ​​of the secondary side of the grounding transformer by combining the overall impedance, the leakage resistance, the leakage reactance, and the secondary side impedance of the grounding transformer.

[0015] Optionally, the overvoltage transmitted by the generator is checked, including: calculating the overvoltage transmitted by the generator using an equivalent circuit of the overvoltage transmitted by the generator system; converting the overvoltage transmitted to a secondary value and determining whether the converted overvoltage transmitted to a secondary value is lower than the set value for the fundamental zero-sequence stator grounding protection to operate; and checking the neutral point displacement voltage of the generator, including: calculating the neutral point displacement voltage of the generator using a circuit of asymmetrical three-phase ground capacitance and a preset single-phase capacitance change rule; converting the neutral point displacement voltage to a secondary value and determining whether the converted neutral point displacement voltage is within the allowable range.

[0016] Optionally, the re-ignition transient overvoltage of the generator is verified, including: constructing a large generator circuit model in a circuit simulation application for analyzing the transient overvoltage of a single-phase ground fault in a combined grounding transformer; setting a single-phase ground fault in any phase of the circuit model to obtain the re-ignition transient voltage waveform during the arc change process; and analyzing whether the peak value of the re-ignition transient overvoltage affects the insulation of the generator windings based on the re-ignition transient voltage waveform.

[0017] Optionally, determining the number of intersections between the line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential based on the various design parameters includes: converting the leakage resistance, leakage reactance, and parallel resistance value of the secondary side of the combined grounding transformer to the primary side, and calculating the equivalent impedance and equivalent capacitive reactance in the improved fundamental zero-sequence equivalent circuit of the graphical method based on the leakage impedance and grounding resistance of the combined grounding transformer on the primary side; calculating the positioning indicator angle based on the equivalent impedance and the equivalent capacitive reactance; and determining the number of intersections between the line containing the vector determined by the positioning indicator angle and the branch potential based on the simulation calculation results of the fundamental zero-sequence equivalent circuit or the historical waveform data of the stator grounding fault site using the graphical method.

[0018] Optionally, after determining the number of intersections between the straight line containing the vector determined by the positioning indicator angle and the branch potential using the graphical method, the method further includes: calculating the ground fault location and transition resistance value, and determining the fault bar corresponding to the ground fault location by combining the generator stator winding connection diagram.

[0019] To achieve the above objectives, a second aspect of this application also proposes a generator-combined grounding transformer optimization design system that takes into account the accuracy of grounding fault location, comprising the following modules: The first calculation module is used to calculate the inherent capacitance current of the generator based on various parameters of the generator to be optimized, and to determine the safe current for a single-phase ground fault in the generator stator. The second calculation module is used to introduce inductor current to compensate for the inherent capacitor current. Based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitor current, the resistance current and inductor current are calculated using the inherent capacitor current and the safety current. The determination module is used to determine multiple design parameters of the generator-combined grounding transformer based on the resistive current and the inductor current. The multiple design parameters are used to ensure that the single-phase ground fault current is within the safe current range. The multiple design parameters include the inductance value and resistance value of the combined grounding transformer. The verification and adjustment module is used to verify the overvoltage transmitted by the generator, the neutral point displacement voltage, and the restart arc transient overvoltage. Based on the various design parameters, it determines the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential, and adjusts the various design parameters to make the number of intersection points one.

[0020] To achieve the above objectives, a third aspect of this application also provides an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to execute the generator-combined grounding transformer optimization design method that takes into account grounding fault location accuracy as described in any one of the first aspects above.

[0021] To achieve the above objectives, the fourth aspect of this application also proposes a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the generator-combined grounding transformer optimization design method described in any one of the first aspects above, which takes into account the accuracy of grounding fault location.

[0022] The technical solution provided by the embodiments of this application brings at least the following beneficial effects: Based on the introduction of an inductive component to compensate for the inherent capacitance current of the generator to meet the safe current value for ground faults, this application optimizes the design of the grounding transformer parameters so that the straight line containing the vector determined by the fault location indicator angle intersects the branch potential at only one point. Therefore, based on the optimized design of the parameters of the neutral point grounding transformer of a large generator, this application improves the location accuracy of stator ground faults, reduces location errors, significantly shortens fault troubleshooting time, improves the stability of fault location, and is conducive to improving generator maintenance efficiency. Furthermore, the combined grounding transformer designed in this application can meet the fault current safety limit, effectively suppressing various overvoltage risks and ensuring the safe and stable operation of the generator.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart illustrating an optimized design method for a generator-combined grounding transformer that takes into account the accuracy of grounding fault location, as proposed in an embodiment of this application. Figure 2 This is a schematic diagram of an equivalent circuit for transmitting overvoltage in a generator system according to an embodiment of this application; Figure 3 This is a schematic diagram illustrating the neutral point displacement voltage generated by the asymmetry of the three-phase ground capacitance of a generator according to an embodiment of this application. Figure 4 This is a schematic diagram of a PSpice circuit model for analyzing transient overvoltages in a single-phase ground fault, as proposed in an embodiment of this application. Figure 5 This is a schematic diagram of a waveform for simulation analysis of a reignition arc transient overvoltage proposed in an embodiment of this application; Figure 6 This is a schematic diagram of an improved fundamental zero-sequence equivalent circuit based on a graphical method proposed in an embodiment of this application; Figure 7 This is a schematic diagram of waveform data from a field grounding fault case according to an embodiment of this application; Figure 8 This is a schematic diagram illustrating the implementation principle of a graphical method proposed in an embodiment of this application; Figure 9 This is a schematic diagram of a generator stator winding connection according to an embodiment of this application; Figure 10 This is a schematic diagram of the structure of a generator-combined grounding transformer optimization design system that takes into account the accuracy of grounding fault location, as proposed in an embodiment of this application. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The following description, with reference to the accompanying drawings, describes an optimized design method and system for a generator-combined grounding transformer that balances grounding fault location accuracy, as proposed in an embodiment of this application.

[0027] Figure 1 This is a flowchart illustrating an optimized design method for a generator-combined grounding transformer that balances grounding fault location accuracy, as proposed in an embodiment of this application. Figure 1 As shown, the method includes the following steps: Step S101: Calculate the inherent capacitance current of the generator based on various parameters of the generator to be optimized, and determine the safe current for a single-phase ground fault in the generator stator.

[0028] Specifically, this application first estimates the capacitor current of the generator system. Then set the safe current for a single-phase ground fault in the generator stator. I F0 The set safe current for single-phase ground fault of generator stator must comply with the range of safe current values ​​for ground fault of large generator stator as specified in the national standard (15A to 20A).

[0029] It should be noted that, in order to more clearly and intuitively illustrate the implementation principle and process of the generator-combined grounding transformer optimization design method that takes into account the accuracy of grounding fault location in this application, the following explanation will be based on a generator of a hydropower station in a specific embodiment.

[0030] In this example, we first obtain several known parameters of the generator. The nameplate parameters of the generator are shown in Table 1 below: Table 1. Parameters of a Generator Nameplate

[0031] Furthermore, the single-phase grounding capacitance value on the main transformer side of the generator outlet circuit breaker was obtained as 0.26 μF, and the single-phase grounding capacitance value on the generator side was obtained as 0.13 μF. The coupling capacitance of the high and low voltage windings of the main transformer was also obtained. When calculating the transmitted overvoltage, the fundamental zero-sequence voltage on the high-voltage side of the main transformer is set to... When calculating the neutral point displacement voltage, it is assumed that the phase B capacitance increases by 5% and the phase C capacitance decreases by 5%; the neutral point grounding transformer ratio is... .

[0032] Based on the various parameters of the generator described above, in one embodiment of this application, the inherent capacitance current of the generator is calculated according to the various parameters of the generator to be optimized, including: calculating the generator phase potential based on the generator rated voltage, and calculating the inherent capacitance current by combining the generator phase potential, the generator stator winding to ground capacitance and the capacitances on both sides of the generator terminal circuit breaker (GCB).

[0033] Referring to the example above, the generator phase potential is first calculated using the following formula:

[0034] in, U gn It is the generator's rated voltage. U gn The values ​​can be obtained from Table 1 above. It is the phase potential of the generator.

[0035] Then, the magnitude of the generator's inherent capacitance current is calculated using the following formula: Where Cg is the generator stator winding capacitance to ground, C GCB These are small capacitors on both sides of the terminal circuit breaker (GCB) to suppress operating overvoltages.

[0036] Furthermore, when selecting the safe current for a single-phase ground fault in the generator stator, the already calculated magnitude of the inherent capacitance current can be considered, and the safe current for a single-phase ground fault in the generator stator can be set accordingly. I F0 It is 25A.

[0037] Step S102: Inductor current is introduced to compensate for the inherent capacitor current. Based on the design principle that the resistor current is equal to a preset multiple of the compensated capacitor current, the resistor current and inductor current are calculated using the inherent capacitor current and the safety current.

[0038] Specifically, using the inherent capacitance current and safety current calculated in the previous step, the resistance current is determined. I R and inductor current I L The design principle for these two design parameters is that the resistance current equals the compensated capacitor current. The preset multiple (for example, it can be 1.1 times).

[0039] In one embodiment of this application, based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitance current, the resistance current and inductance current are calculated using the inherent capacitance current and the safety current, including: calculating the compensated capacitance current based on the safety current; calculating the resistance current based on the compensated capacitance current and the preset multiple; and calculating the inductance current based on the compensated capacitance current and the inherent capacitance current.

[0040] Continuing with the example above, based on the fact that the resistor current equals the compensated capacitor current ( The design principle of 1.1 times the resistance current can be calculated using the following formula: ; The compensated capacitor current can be calculated using the following formula: ; Furthermore, the inductive component of the neutral point current I L That is, 40.1 - 16.82 = 23.28A.

[0041] Step S103: Based on the resistance current and inductance current, determine various design parameters of the generator-combined grounding transformer. These various design parameters are used to ensure that the single-phase ground fault current is within the range of the safe current. The various design parameters include the inductance value and resistance value of the combined grounding transformer.

[0042] Specifically, by using the resistance current and inductance current determined in the previous step, we can further determine the inductance value and other design parameters that the combined grounding transformer needs to be connected in series or in parallel. Thus, by reasonably configuring the resistance and inductance connected in parallel on the secondary side of the neutral point grounding transformer, this application can limit the fault current to within the above-mentioned set safe current (25A).

[0043] In one embodiment of this application, various design parameters of the generator-combined grounding transformer are determined based on the resistance current and the inductance current, including: calculating the overall impedance of the neutral point grounding device based on the resistance current and the inductance current; detecting the load loss and impedance voltage percentage through load tests and short-circuit tests, and calculating the leakage resistance and leakage reactance of the combined grounding transformer based on the load loss and impedance voltage percentage; and calculating the parallel resistance and inductance values ​​of the secondary side of the grounding transformer by combining the overall impedance, leakage resistance, leakage reactance and the secondary side impedance of the grounding transformer.

[0044] Continuing with the example above, based on the neutral point resistive current component and inductive current component calculated above, the overall impedance of the neutral point grounding device (including the resistance and inductance of the secondary side) can be obtained using the following formula:

[0045] in, I N This refers to the safe current for a single-phase ground fault in the generator stator, i.e. I N For the above settings I F0 .

[0046] Furthermore, by combining the relevant parameters of the grounding transformer, the resistance and inductance that need to be connected in series on the secondary side of the actual grounding transformer can be calculated. The detailed calculation process is as follows: First, load loss is measured through load tests and short-circuit tests. P k and impedance voltage percentage U d After that, the leakage resistance of the grounding transformer can be calculated using the following formula. and leakage reactance (All are single values):

[0047]

[0048] .

[0049] Furthermore, since the total impedance of the neutral point grounding device has been determined... Then, by using the secondary impedance of the grounding transformer... The resistance of parallel circuits can be calculated using the following formula. and parallel inductors The possible values ​​of:

[0050]

[0051]

[0052]

[0053] Therefore, the grounding device parameter configuration obtained through the above design method can ensure that the single-phase ground fault current is within the safe current range.

[0054] Step S104: Verify the overvoltage transmitted by the generator, the neutral point displacement voltage, and the transient overvoltage of the reignition arc. Based on multiple design parameters, determine the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential. Adjust multiple design parameters to make the number of intersection points one.

[0055] Specifically, after the device parameter design is completed, this application also verifies the transmitted overvoltage and neutral point displacement voltage, and uses simulation analysis to verify whether the reignition arc overvoltage will threaten the insulation of the stator bars, so as to determine whether the designed device parameters meet the requirements.

[0056] In one embodiment of this application, the overvoltage transmitted by the generator is checked by: using the equivalent circuit of the overvoltage transmitted by the generator system to calculate the overvoltage transmitted by the generator; converting the overvoltage transmitted by the generator into a secondary value, and determining whether the converted overvoltage transmitted by the generator is lower than the set value for the fundamental zero-sequence stator grounding protection to operate.

[0057] Specifically, the transmission of overvoltage can be based on Figure 2 The equivalent circuit shown is used for verification, based on Figure 2 The equivalent circuit shown can be used to calculate the transmitted overvoltage of the generator using the following formula:

[0058] Continuing with the example above, X C and X M The following formulas can be used to calculate them respectively:

[0059]

[0060] Therefore, substituting into the above formula X C and X M Grounding device parameters and The transferred overvoltage U0 can be calculated to be 41.8V, which translates to a secondary value of 0.33V. Therefore, this transferred overvoltage is far below the operating setting of 5V for the fundamental zero-sequence stator grounding protection. Thus, the transferred overvoltage under these design parameters will not cause the protection to malfunction, meeting the requirements.

[0061] In one embodiment of this application, the neutral point displacement voltage of the generator is checked, including: calculating the neutral point displacement voltage of the generator using the three-phase ground capacitance asymmetry circuit of the generator and the preset single-phase capacitance change rule; converting the neutral point displacement voltage into a secondary value, and determining whether the converted neutral point displacement voltage is within the allowable range.

[0062] Specifically, the neutral point displacement voltage U N According to Figure 3 The circuit shown was verified based on Figure 3 The neutral point displacement voltage of the circuit shown can be calculated using the following formula:

[0063] Continuing with the example above, assuming that the phase B capacitance increases by 5% and the phase C capacitance decreases by 5%, substituting these values ​​into the above formula yields the neutral point displacement voltage U. N =334.6V, which translates to a secondary value of 2.63V, indicating that the neutral point displacement voltage under this parameter selection is within the allowable range.

[0064] Then, simulation analysis was used to calculate the reignition transient overvoltage under intermittent grounding faults to ensure that adding inductance to the secondary side of the neutral grounding transformer would not introduce excessively high reignition transient overvoltages.

[0065] In one embodiment of this application, the verification of the reignition arc transient overvoltage of the generator includes: constructing a large generator circuit model in a circuit simulation application for analyzing the transient overvoltage of a single-phase ground fault in a combined grounding transformer; setting a single-phase ground fault in any phase of the circuit model to obtain the reignition arc transient process voltage waveform during the arc change process; and analyzing whether the peak value of the reignition arc transient overvoltage affects the insulation of the generator windings based on the reignition arc transient process voltage waveform.

[0066] Specifically, this embodiment uses PSpice simulation software for simulation analysis. First, a simulation model is built in PSpice as follows: Figure 4 The circuit model shown.

[0067] In this circuit model, the electromotive force amplitude is calculated using the following formula:

[0068] The resistance value is: The inductance value (using an ultra-transient inductor) is calculated using the following formula: ; The capacitance value is: .

[0069] In this embodiment, it is assumed that an intermittent single-phase ground fault occurs at the generator terminal in phase A. The three-phase voltage waveforms at the generator terminal during the arc ignition-extinguishing-reignition process are as follows: Figure 5 As shown, where, Figure 5 The voltage waveforms during the reignition arc transient process shown represent phases A, B, and C from top to bottom. Figure 5 It can be seen that the first arc extinction time is selected when the fault phase current crosses zero three cycles after the first arc ignition, while the re-arcing time is selected when the fault phase voltage rises to its maximum value. Transient peak overvoltages appeared in both phases B and C during the first and re-arcing. The peak value of the transient overvoltage during the re-arcing was approximately equal to that during the first arc ignition, at about 48.30 kV (2.69 pu). Therefore, the risk of excessively high transient overvoltages during the re-arcing due to the use of a combined grounding method is very small and will not threaten the generator winding insulation.

[0070] Furthermore, assuming that the reignition arc transient overvoltage, transmitted overvoltage, and neutral point displacement voltage all meet the requirements, the ground fault location indication angle is calculated based on the parameters of the relevant generator and grounding transformer determined in the above embodiments. Based on the simulation calculation results of the generator fundamental zero-sequence equivalent circuit or the waveform recording data of the stator grounding fault case in the field, the positioning indicator angle in the "graphical method" is determined. The determined vector The potential of the line and the branch The number of intersection points. Finally, by adjusting the parameters of the grounding transformer, the positioning indicator angle in the "graphical method" is ensured. The determined vector The potential of the line and the branch There is only one intersection point, so as to complete the optimized design of the generator combined grounding transformer and improve the positioning accuracy to the fault line bar.

[0071] In one embodiment of this application, determining the number of intersections between the line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential, based on multiple design parameters, includes: converting the leakage resistance, leakage reactance, and parallel resistance values ​​of the secondary side of the combined grounding transformer to the primary side, and calculating the equivalent impedance and equivalent capacitive reactance in the improved fundamental zero-sequence equivalent circuit of the graphical method based on the leakage impedance and grounding resistance of the combined grounding transformer on the primary side; calculating the positioning indicator angle based on the equivalent impedance and equivalent capacitive reactance; and determining the number of intersections between the line containing the vector determined by the positioning indicator angle and the branch potential using the graphical method based on the simulation calculation results of the fundamental zero-sequence equivalent circuit or historical waveform data of the stator grounding fault site.

[0072] Continuing with the example above, based on the transformation ratio of the grounding transformer, by referring the leakage impedance and grounding resistance of the grounding transformer to the primary side, the following parameters can be calculated: , , , .

[0073] Furthermore, using the aforementioned parameters of the primary side, the following formula can be used to deduce... Figure 6 The equivalent impedance and equivalent capacitive reactance in the improved fundamental zero-sequence equivalent circuit shown are as follows: ; ; Then calculate the ground fault location indicator angle using the following formula. : .

[0074] Then, to Figure 7 The recorded waveform data of the on-site grounding fault case shown was analyzed according to... Figure 7 The stator ground fault three-phase voltage recording data shown indicates that after the ground fault occurred, the voltage of phase B to ground decreased, while the voltages of phases A and C to ground increased, thus identifying the faulty phase as phase B. Based on the generator stator winding connection method, the potential distribution of phase B can be obtained. Using the phase B potential as the reference vector, i.e., Then we can obtain: .

[0075] Finally, according to Figure 8 The graphical method shown determines the vector. The potential of the line and the branch There is only one intersection point, and the location of the ground fault can be determined: 72.4%. Further calculation of the transition resistance value is then performed. The following formula can be used in this calculation process:

[0076] .

[0077] Furthermore, more precise fault location can be achieved based on the above embodiments. In one embodiment of this application, after determining the number of intersections between the straight line containing the vector determined by the location indicator angle and the branch potential using a graphical method, the method further includes: calculating the ground fault location and transition resistance value, and determining the fault bar corresponding to the ground fault location by combining the generator stator winding connection diagram.

[0078] Continuing with the example above, based on the ground fault location already determined in the above embodiments to be 72.4%, etc., combined with... Figure 9 The generator stator winding connection diagram shown below indicates that the specific fault location is from the upper layer bar of slot 178 to the lower layer bar of slot 154, resulting in the fault location results shown in Table 2 below: Table 2 Fault Location Results

[0079] Therefore, based on the quantitative calculations and verifications in the above embodiments, the design of this combined grounding transformer can effectively limit the single-phase ground fault current within the safe current range, while ensuring that the transmitted overvoltage, neutral point displacement voltage, and reignition arc overvoltage during intermittent ground faults are all within the allowable range. Furthermore, the appropriate positioning indicator angle value is beneficial for improving the stator ground fault location accuracy. In other embodiments, if the conditions are not met, it is necessary to adjust the parameters of the grounding transformer to change the positioning indicator angle. Ensure vector The potential of the line and the branch There is one and only one intersection point.

[0080] In summary, the generator-combined grounding transformer optimization design method of this application, which balances ground fault location accuracy, introduces an inductive component to compensate for the generator's inherent capacitance current to meet the safe ground fault current value. Through optimized design of the grounding transformer parameters, it ensures that the straight line containing the vector determined by the fault location indicator angle intersects the branch potential at exactly one point. Therefore, this method, based on optimized design of the neutral point grounding transformer parameters of a large generator, improves the location accuracy of stator ground faults, reduces location errors, significantly shortens fault investigation time, and improves the stability of fault location, thus enhancing generator maintenance efficiency. Furthermore, the combined grounding transformer designed by this method can meet the fault current safety limit, effectively suppressing various overvoltage risks and ensuring the safe and stable operation of the generator.

[0081] To achieve the above embodiments, this application also proposes a generator-combined grounding transformer optimization design system that takes into account the accuracy of grounding fault location. Figure 10 This is a schematic diagram of the structure of an optimized design for a generator-combined grounding transformer that takes into account the accuracy of grounding fault location, as proposed in an embodiment of this application. Figure 10 As shown, the system includes: The first calculation module 100 is used to calculate the inherent capacitance current of the generator based on various parameters of the generator to be optimized, and to determine the safe current for a single-phase ground fault in the generator stator.

[0082] The second calculation module 200 is used to introduce inductor current to compensate for the inherent capacitor current. Based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitor current, the resistance current and the inductor current are calculated using the inherent capacitor current and the safety current.

[0083] The determination module 300 is used to determine various design parameters of the generator-combined grounding transformer based on the resistance current and the inductance current. These various design parameters are used to ensure that the single-phase ground fault current is within the safe current range. The various design parameters include the inductance value and resistance value of the combined grounding transformer.

[0084] The verification and adjustment module 400 is used to verify the overvoltage transmitted by the generator, the neutral point displacement voltage, and the transient overvoltage of the reignition arc. Based on multiple design parameters, it determines the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential, and adjusts multiple design parameters to make the number of intersection points one.

[0085] It should be noted that the explanation of the aforementioned embodiment of the generator-combined grounding transformer optimization design method that takes into account the accuracy of grounding fault location also applies to the system of this embodiment, and will not be repeated here.

[0086] In summary, the generator-combined grounding transformer optimization design method system of this application, which takes into account the accuracy of grounding fault location, improves the location accuracy of stator grounding faults by optimizing the parameters of the neutral point grounding transformer of a large generator.

[0087] To implement the above embodiments, this application also proposes an electronic device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to execute the generator-combined grounding transformer optimization design method that takes into account the grounding fault location accuracy as described in any of the first aspect embodiments above.

[0088] To implement the above embodiments, this application also proposes a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the generator-combined grounding transformer optimization design method that takes into account the grounding fault location accuracy as described in any of the first aspect embodiments above.

[0089] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0090] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0091] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0092] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0093] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0094] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it includes one or a combination of the steps of the method embodiments.

[0095] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0096] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A generator-combined grounding transformer optimization design method that takes into account grounding fault location accuracy, characterized in that, Includes the following steps: The inherent capacitance current of the generator is calculated based on various parameters of the generator to be optimized, and the safe current for a single-phase ground fault in the generator stator is determined. Inductor current is introduced to compensate for the inherent capacitor current. Based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitor current, the resistance current and inductor current are calculated using the inherent capacitor current and the safety current. Based on the resistive current and the inductor current, various design parameters of the generator-combined grounding transformer are determined. These various design parameters are used to ensure that the single-phase ground fault current is within the safe current range. The various design parameters include the inductance and resistance values ​​of the combined grounding transformer. The overvoltage transmitted by the generator, the neutral point displacement voltage, and the reignition arc transient overvoltage are checked. Based on the various design parameters, the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential is determined. The various design parameters are adjusted so that the number of intersection points is one.

2. The method according to claim 1, characterized in that, The calculation of the inherent capacitance current of the generator based on multiple parameters of the generator to be optimized includes: Calculate the generator phase potential based on the generator rated voltage, and calculate the inherent capacitance current by combining the generator phase potential, the generator stator winding to ground capacitance, and the capacitances on both sides of the generator terminal circuit breaker GCB. The design principle, based on the fact that the resistive current equals a preset multiple of the compensated capacitive current, calculates the resistive current and inductor current using the inherent capacitive current and the safety current, including: Calculate the compensated capacitor current based on the safety current; The resistance current is calculated based on the compensated capacitor current and the preset multiple; The inductor current is calculated based on the compensated capacitor current and the inherent capacitor current.

3. The method according to claim 1, characterized in that, The determination of various design parameters for the generator-combined grounding transformer based on the resistive current and the inductor current includes: Calculate the overall impedance of the neutral point grounding device based on the resistor current and the inductor current; Load loss and impedance voltage percentage are detected through load test and short-circuit test, and leakage resistance and leakage reactance of the combined grounding transformer are calculated based on the load loss and impedance voltage percentage. Based on the overall impedance, leakage resistance, leakage reactance, and secondary impedance of the grounding transformer, calculate the parallel resistance and inductance values ​​of the secondary side of the grounding transformer.

4. The method according to claim 1, characterized in that, The overvoltage transmitted by the generator is checked, including: The transmitted overvoltage of the generator is calculated using the equivalent circuit of the generator system transmitting overvoltage. The transmitted overvoltage is converted into a secondary value, and it is determined whether the converted transmitted overvoltage is lower than the set value for the fundamental zero-sequence stator grounding protection to operate. The neutral point displacement voltage of the generator is checked, including: The neutral point displacement voltage of the generator is calculated using the asymmetrical circuit of the generator's three-phase ground capacitance and the preset single-phase capacitance variation rule. The neutral point displacement voltage is converted into a secondary value, and it is determined whether the converted neutral point displacement voltage is within the allowable range.

5. The method according to claim 1, characterized in that, The re-ignition transient overvoltage of the generator is checked, including: In circuit simulation applications, a large generator circuit model is constructed for analyzing transient overvoltages in single-phase grounding faults of combined grounding transformers. By assuming a single-phase ground fault occurs in any phase of the circuit model, the voltage waveform of the reignition transient process during the arc change process is obtained; Based on the transient voltage waveform of the reignition arc, analyze whether the peak value of the transient overvoltage of the reignition arc affects the insulation of the generator winding.

6. The method according to claim 3, characterized in that, The determination of the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential, based on the aforementioned multiple design parameters, includes: The leakage resistance, leakage reactance, and parallel resistance value of the secondary side of the combined grounding transformer are converted to the primary side, and the equivalent impedance and equivalent capacitive reactance in the improved fundamental zero-sequence equivalent circuit of the graphical method are calculated based on the leakage impedance and grounding resistance of the combined grounding transformer on the primary side. The positioning indicator angle is calculated based on the equivalent impedance and the equivalent capacitive reactance. Based on the simulation results of the fundamental zero-sequence equivalent circuit or the historical waveform data of the stator grounding fault site, the number of intersection points between the straight line containing the vector determined by the positioning indicator angle and the branch potential is determined using a graphical method.

7. The method according to claim 6, characterized in that, After determining the number of intersection points between the straight line containing the vector determined by the positioning indicator angle and the branch potential using a graphical method, the method further includes: Calculate the location of the ground fault and the transition resistance value, and determine the faulty conductor corresponding to the location of the ground fault by referring to the generator stator winding connection diagram.

8. A generator-combined grounding transformer optimization design system that takes into account the accuracy of grounding fault location, characterized in that, Includes the following modules: The first calculation module is used to calculate the inherent capacitance current of the generator based on various parameters of the generator to be optimized, and to determine the safe current for a single-phase ground fault in the generator stator. The second calculation module is used to introduce inductor current to compensate for the inherent capacitor current. Based on the design principle that the resistance current is equal to a preset multiple of the compensated capacitor current, the resistance current and inductor current are calculated using the inherent capacitor current and the safety current. The determination module is used to determine multiple design parameters of the generator-combined grounding transformer based on the resistive current and the inductor current. The multiple design parameters are used to ensure that the single-phase ground fault current is within the safe current range. The multiple design parameters include the inductance value and resistance value of the combined grounding transformer. The verification and adjustment module is used to verify the overvoltage transmitted by the generator, the neutral point displacement voltage, and the restart arc transient overvoltage. Based on the various design parameters, it determines the number of intersection points between the straight line containing the vector determined by the positioning indicator angle in the graphical method and the branch potential, and adjusts the various design parameters to make the number of intersection points one.

9. An electronic device, comprising: At least one processor; as well as A memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor, which, when executed by the at least one processor, enables the at least one processor to perform the generator-combined grounding transformer optimization design method that takes into account the grounding fault location accuracy as described in any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the generator-combined grounding transformer optimization design method that takes into account the grounding fault location accuracy as described in any one of claims 1-7.

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