Nuclear power station rod-controlled power supply dual-machine system stator grounding fault positioning method

Abstract

The invention relates to the technical field of safety protection and fault positioning of a nuclear power station rod-controlled power supply dual-computer system, and particularly discloses a nuclear power station rod-controlled power supply dual-computer system stator grounding fault positioning method, which comprises the following steps of: injecting a 20Hz low frequency quantity into a neutral point of a dual-computer system when a fault occurs, acquiring various voltage and current parameters, and further calculating zero sequence differential current; and a fault area and a generator are positioned by combining a selective fault positioning criterion, grounding fault transition resistance is calculated, and a winding fault point is calculated by using a fault positioning function for the fault in the area. According to the method, selective fault positioning and winding fault point positioning of the rod control power supply dual-unit system can be effectively realized, and rapid maintenance and power supply recovery after the nuclear power station rod control power supply system has a grounding fault can be guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of safety protection and fault location of the dual-machine system of the rod control power supply in a nuclear power plant, and particularly relates to a method for locating the stator grounding fault of the dual-machine system of the rod control power supply in a nuclear power plant. Background Art

[0002] In a large nuclear power plant, a nuclear reactor rod control system is used to drive the lifting or insertion of fuel rods to achieve the regulation of the reactor power generation. The power supply system of the control rod drive mechanism (Rotating Asynchronous Machine, abbreviated as RAM, hereinafter simply referred to as the rod control power supply) is a dedicated electrical system for supplying power to the control rod drive mechanism (CRDM), and its core power generation device is two generators operating in parallel. Engineering statistical data shows that the single-phase grounding fault of the stator winding is the most common fault type in the generator system. The continuous grounding fault current is likely to generate an arc, which may cause the stator core to be burned, and even develop into a more serious inter-turn or phase-to-phase short-circuit fault, seriously threatening the power supply safety of the nuclear reactor.

[0003] The dual-machine system of the rod control power supply operates in the form of two columns of generator sets connected in parallel, as Figure 2 shown. The grounding fault protection needs to consider its selectivity requirements to accurately identify the faulty unit. However, the current voltage criterion and injection method do not have the ability to correctly distinguish between the normally operating unit and the faulty unit, and cannot achieve accurate selective fault location. In addition, since the existing protection method does not have the function of fault location, in actual engineering, the insulation condition of the winding coils is often measured successively to determine the fault location, which is time-consuming and laborious. Therefore, after completing the selective fault location and determining the faulty unit, the fault point should be accurately located based on the fault recording data to facilitate the subsequent fault repair work.

[0004] For the selective fault location of generators, authors such as Dang Xiaoqiang proposed a protection method based on traveling wave signals in "Advanced Technology of Electrical Engineering and Energy" (2013, 32(1): 98-103) to expand the selective fault location of unit-connected generator sets. This method uses the characteristics of the traveling wave zero-sequence power phase in the initial half-cycle time of the fault to distinguish between faulty and non-faulty generator sets. However, the traveling wave signal is greatly affected by the initial phase of the fault voltage and the transition resistance, and it is difficult to measure the traveling wave signal in the case of high-resistance grounding faults. Mu Daqing and Yin Xianggen proposed a location method based on the characteristics of the power frequency variation of differential current at the generator terminal and neutral point side in "Relay" (2005, 33(22): 10-15), and achieved selective fault location through the difference in its amplitude and phase, but this method has a certain dead zone. Since the voltage level of the generator in the rod control power supply system is relatively low and the neutral point operates in an ungrounded manner, the fault current characteristics are not obvious. Therefore, the above methods are not fully applicable to the dual-generator system of nuclear power plant rod control power supply.

[0005] For the stator grounding fault location of generators, Jia Wenchao and Huang Shaofeng proposed a location method based on the KVL equation between the fundamental zero-sequence voltage, fundamental fault potential, and fundamental voltage to ground at the fault point in "Electric Power Automation Equipment" (2017, 37(2): 134-139), and achieved fault location by constructing a location equation. However, the fundamental potential of the stator winding of a turbo-generator satisfies a 60° phase belt distribution relationship, and the phase between the fault potential and the fault phase potential is not equal. This approximate treatment method will cause a certain theoretical error. Authors such as Wang Yuxue proposed a location method based on an injection device in "Proceedings of the CSEE" (2013, 33(31): 147-154+18), and determined the faulty coil by measuring the transition resistance and combining the look-up table method. Huang Shaofeng and Jia Wenchao analyzed the potential distribution characteristics of large turbo-generators in "Power System Protection and Control" (2017, 45(09): 35-40) and considered the phase difference of the fundamental potential. Authors such as Yin Linpeng proposed a stator grounding fault location method based on the potential distribution of the winding in "Electric Power Automation Equipment" (2019, 39(07): 141-146), and analyzed the relationship between the transition resistance and the fundamental potential in detail. These studies all considered the distribution characteristics of the winding potential for fault location. However, since the dual-generator system of nuclear power plant rod control power supply adopts a special Zig-Zag winding connection method, its winding potential distribution is significantly different from that of conventional generators. Therefore, the above location methods are not fully applicable to the dual-generator system of nuclear power plant rod control power supply.

[0006] In summary, considering the particularity of the dual-machine system of the rod control power supply in nuclear power plants and the limitations of existing methods, there is an urgent need to propose a fault location method specifically applicable to this system. This includes a selective fault location method that can identify the faulty unit and an accurate fault location method for the stator winding fault point, so as to improve the efficiency and reliability of fault diagnosis and handling. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a stator grounding fault location method for the dual-machine system of the rod control power supply in nuclear power plants, which can achieve selective fault location and winding fault point location for the dual-machine system of the rod control power supply, and can ensure the rapid maintenance and power supply restoration after a grounding fault occurs in the rod control power supply system of nuclear power plants.

[0008] To solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0009] A stator grounding fault location method for the dual-machine system of the rod control power supply in nuclear power plants includes the following steps: S101. Monitor the working state of the dual-machine system of the rod control power supply. When the working state is a stator grounding fault, inject a 20 Hz low-frequency quantity into the neutral point of the dual-machine system, obtain the 20 Hz voltage and current at the neutral point of the generator after injecting the low-frequency quantity, the 20 Hz currents at the neutral point side and the machine terminal side of the two generators in the dual-machine system, and obtain the fundamental wave zero-sequence voltages at the neutral point and the machine terminal. S102. Calculate the zero-sequence differential currents of the two generators in the dual-machine system based on the 20 Hz currents at the neutral point side and the machine terminal side of the two generators in the dual-machine system after injecting the low-frequency quantity. S103. Based on the zero-sequence differential currents of the two generators after injecting the low-frequency quantity, combined with the selective fault location criterion, locate the in-zone or out-of-zone fault. When the fault is an in-zone fault, locate the faulty generator. S104. Calculate the grounding fault transition resistance based on the 20 Hz voltage and current at the neutral point of the generator after injecting the low-frequency quantity. S105. When the grounding fault is an in-zone fault, calculate the winding fault point of the located faulty generator based on the fundamental wave zero-sequence voltages at the neutral point and the machine terminal and the grounding transition resistance, combined with the fault location function.

[0010] Preferably, the step S102 specifically includes: Calculate the zero-sequence differential currents of the two generators in the dual-machine system based on the 20 Hz currents at the neutral point side and the machine terminal side of the two generators in the dual-machine system after injecting the low-frequency quantity, combined with the first formula; the first formula is:

[0011] Wherein, is the zero-sequence differential current of the No. 1 generator in the dual-machine system; is the zero-sequence differential current of Generator No. 2 in the dual-generator system; is the low-frequency current on the neutral side of Generator No. 1 in the dual-generator system; is the low-frequency current on the neutral side of Generator No. 2 in the dual-generator system; is the low-frequency current at the machine terminal of Generator No. 1 in the dual-generator system; is the low-frequency current at the machine terminal of Generator No. 2 in the dual-generator system.

[0012] Preferably, the step S103 specifically includes: Based on the zero-sequence differential current of the two generators after injecting the low-frequency quantity, combined with the selective fault location criterion of the second formula, locate the in-zone or out-of-zone fault. When the fault is an in-zone fault, locate the faulty generator; the second formula is:

[0013] Wherein, U in0n is the low-frequency voltage of the neutral point of the dual-generator system; K set_in is set according to the actual situation; Ensure that there is no misoperation when an external ground fault occurs, and accurately judge the faulty unit when an in-zone fault occurs; when one of the two generators meets the second formula, it is determined that the generator meeting the second formula is the faulty generator; when neither of the two generators meets the formula, it is determined that an out-of-zone fault has occurred.

[0014] Preferably, the step S104 specifically includes: Based on the 20Hz voltage and current of the generator neutral point after injecting the low-frequency quantity, combined with the third formula, calculate the grounding fault transition resistance; the third formula is:

[0015] Wherein, R f is the calculated grounding fault transition resistance.

[0016] Preferably, the step S105 specifically includes: When the grounding fault is an in-zone fault, based on the fundamental zero-sequence voltage and grounding transition resistance of the neutral point and machine terminal, combined with the fault location function of the fourth formula, calculate the winding fault point of the located faulty generator; the fourth formula is:

[0017] Wherein, | E | is the amplitude of the fundamental wave phase electromotive force of the generator, obtained by taking the amplitude after Fourier transform of the difference between the measured fundamental wave voltage at the machine terminal and the fundamental wave voltage at the neutral point; C Σis the total ground capacitance of the dual - machine system for the rod control power supply of the nuclear power plant; U 0 is the fundamental voltage of the generator neutral point; the fault location α Substitute = 0~1 into the fourth formula respectively, and the one corresponding to the minimum value obtained by the fourth formula α is the true fault location.

[0018] Due to the adoption of the above - mentioned technical solution, the technical progress achieved by the present invention is as follows.

[0019] The present invention improves the accuracy of fault location: Accurate selective fault location: The present invention comprehensively considers factors such as the special Zig - Zag winding connection mode of the dual - machine system for the rod control power supply of the nuclear power plant and the ungrounded neutral operation mode. Through a unique selective fault location criterion (the selective fault location criterion combined with the second formula), it can effectively distinguish between internal and external faults. When an internal fault occurs, it can accurately determine the faulty unit, avoiding misjudgment situations caused by problems such as traveling wave signals being affected by the initial phase of the fault voltage and transition resistance, and the dead zone existing in the method based on the characteristics of the power - frequency change of current in the prior art, greatly improving the selectivity and accuracy of fault location.

[0020] Accurate location of the winding fault point: For internal faults, based on obtaining the fundamental zero - sequence voltages at the neutral point and machine terminal and the grounding transition resistance, combined with an innovative fault location function (the fourth formula) to calculate the winding fault point. This method fully considers the winding potential distribution characteristics of the dual - machine system for the rod control power supply. Compared with traditional methods, it can more accurately locate the actual fault position of the winding, providing accurate fault point information for subsequent maintenance work.

[0021] The present invention improves the maintenance efficiency and shortens the power outage time: Quickly discriminate faults: After detecting a stator ground fault, by injecting a 20Hz low - frequency quantity at the neutral point and obtaining a series of relevant parameters, it can quickly start various location calculation processes. Compared with the traditional method of successively measuring the insulation of the winding coils to determine the fault location, it saves a large amount of cumbersome measurement time, realizes quickly discriminating the fault area and the faulty generator, and significantly shortens the fault troubleshooting period.

[0022] Reduce the power outage duration: Accurate fault location allows maintenance personnel to directly repair the fault point, avoiding time delays that may be caused by blind troubleshooting. This helps to quickly restore the power supply of the nuclear power plant, reduce the impact on the overall operation of the nuclear power plant and related facilities caused by power outages, and ensure the safe and stable operation of the nuclear power plant.

[0023] The present invention enhances the safety of the nuclear power plant operation: Timely fault response: Since it can detect and locate stator ground faults in a timely and accurate manner, it avoids the burning of the stator core by the arc generated by the continuous ground fault, thereby effectively preventing the further development of the fault into more serious situations such as turn-to-turn or phase-to-phase short circuit faults, reducing the risk of major safety accidents in nuclear power plants, and enhancing the safety and reliability of nuclear power plant operation.

[0024] Adapt to special working conditions: Fully considering the various particularities of the dual-machine system of the rod control power supply in nuclear power plants, the proposed method can be effectively applied under complex conditions such as low voltage, ungrounded operation, and special winding connection methods. Even under different load conditions (such as no-load, 50% load, and full load verified by simulation and dynamic simulation tests), it can accurately locate faults, ensuring reliable fault location capabilities in various operating states of nuclear power plants.

[0025] The present invention reduces maintenance costs: Precise positioning reduces troubleshooting workload: Precise fault location reduces unnecessary maintenance procedures and inspections of a large number of normal equipment, avoiding waste of human and material resources, thereby reducing the labor cost and equipment loss cost during fault troubleshooting and maintenance.

[0026] Prevent major faults and reduce maintenance costs: By timely and accurately locating and handling early faults, it avoids small faults evolving into major faults, reducing the costs of large-scale maintenance and equipment replacement. In the long run, it effectively reduces the maintenance costs of nuclear power plants. Brief description of the drawings

[0027] Figure 1 is a flow chart of the present invention; Figure 2 is a schematic diagram of the dual-machine system of the rod control power supply in a nuclear power plant in an embodiment of the present invention; Figure 3 is a 20Hz zero-sequence equivalent circuit diagram of the generator in an embodiment of the present invention; Figure 4 is the actual winding potential distribution diagram of the dual-machine system of the rod control power supply in an embodiment of the present invention; Figure 5 is the A-phase and B-phase of the actual winding potential distribution of the dual-machine system of the rod control power supply in an embodiment of the present invention; Figure 6 is the fault simulation result diagram in an embodiment of the present invention, where Figure 6 (a) is the simulation result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage under the internal ground fault condition, Figure 6 (b) is the simulation result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage under the external ground fault condition; Figure 7This is the fault location simulation result diagram for different fault positions and different transition resistances in the embodiments of the present invention. Among them, Figure 7 (a) is the α fault location simulation result diagram when Figure 7 = 0.125, α = 0.250, Figure 7 = 0.375, α = 0.625, Figure 7 = 0.750, α = 0.875; Figure 7 = 0.625, α = 0.750, Figure 7 = 0.875; α = 0.875; Figure 8 This is the test result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage during a fault under different load conditions in the embodiments of the present invention. Among them, Figure 8 (a) is the test result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage during a fault under no-load conditions, Figure 8 = 50% load, Figure 8 = full load; Figure 9 This is the test result diagram of the ground fault location calculation in the embodiments of the present invention. Among them, Figure 9 = no-load, Figure 9 = 50% load, Figure 9 = full load; Detailed implementation manners

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0029] A method for locating the stator ground fault of a dual-machine system for rod control power supply in a nuclear power plant can achieve selective fault location and winding fault point location for the rod control power supply dual-machine system as shown in Figure 2 , and can ensure the rapid repair and power supply restoration after a ground fault occurs in the rod control power supply system of the nuclear power plant. As shown in Figure 1 , the method includes the following steps: S101. Monitor the working status of the dual - machine system of the rod control power supply. When the working status is stator grounding fault, inject a 20 - Hz low - frequency quantity into the neutral point of the dual - machine system, obtain the 20 - Hz voltage and current at the neutral point of the generator after injecting the low - frequency quantity, the 20 - Hz currents at the neutral - point side and machine - end side of the two generators in the dual - machine system, and obtain the fundamental - wave zero - sequence voltages at the neutral point and machine end.

[0030] S102. Based on the 20 - Hz currents at the neutral - point side and machine - end side of the two generators in the dual - machine system after injecting the low - frequency quantity, calculate the zero - sequence differential currents of the two generators in the dual - machine system.

[0031] Specifically include: Based on the 20 - Hz currents at the neutral - point side and machine - end side of the two generators in the dual - machine system after injecting the low - frequency quantity, combined with the first formula, calculate the zero - sequence differential currents of the two generators in the dual - machine system.

[0032] The first formula is:

[0033] Among them, is the zero - sequence differential current of Generator No. 1 in the dual - machine system; is the zero - sequence differential current of Generator No. 2 in the dual - machine system; is the low - frequency current at the neutral - point side of Generator No. 1 in the dual - machine system; is the low - frequency current at the neutral - point side of Generator No. 2 in the dual - machine system; is the low - frequency current at the machine end of Generator No. 1 in the dual - machine system; is the low - frequency current at the machine end of Generator No. 2 in the dual - machine system.

[0034] S103. Based on the zero - sequence differential currents of the two generators after injecting the low - frequency quantity, combined with the selective fault - location criterion, locate the in - zone or out - of - zone fault. When the fault is an in - zone fault, locate the faulty generator.

[0035] Specifically include: Based on the zero - sequence differential currents of the two generators after injecting the low - frequency quantity, combined with the selective fault - location criterion of the second formula, locate the in - zone or out - of - zone fault. When the fault is an in - zone fault, locate the faulty generator.

[0036] The second formula is:

[0037] Among them, U in0n is the low - frequency voltage at the neutral point of the dual - machine system; K set_in Set according to the actual situation.

[0038] When an external ground fault occurs, ensure that there is no misoperation, and accurately judge the faulty generator when an internal fault occurs; when one of the two generators satisfies the second formula, the generator that satisfies the second formula is determined to be the faulty generator; when neither of the two generators satisfies it, it is determined that an external fault has occurred.

[0039] Specifically, after injecting U in the 20Hz zero-sequence equivalent circuit of the generator is as Figure 3 shown.

[0040] Figure 3 in U in represents the injected voltage; and respectively represent the admittance of the generator stator winding to the ground, the fault admittance, the admittance of the generator terminal to the ground, and the admittance of the line to the ground. represents the zero-sequence current, as represents the zero-sequence current on the neutral point side of the generator in the double-generator system. For the faulty generator, the zero-sequence current differential current satisfies the following relationship:

[0041] Among them, the zero-sequence differential current of the non-faulty generator No. 2 leads the injected power supply U in by about 90 degrees. Due to the influence of the fault admittance, the zero-sequence differential current of the faulty generator No. 1 should lead the injected power supply U in by 0 to 90 degrees. Therefore, based on the fault characteristics of the zero-sequence differential current and the phase angle difference of the injected power supply after the injection device is put into operation, a selective fault location method applicable to the double-generator system of the rod control power supply can be constituted.

[0042] Through the above analysis, an injection-type selective fault location criterion applicable to the rod control power supply system is proposed, as shown in the second formula.

[0043] S104. Calculate the grounding fault transition resistance based on the 20Hz voltage and current at the neutral point of the generator after injecting low-frequency quantities.

[0044] Specifically, it includes: Based on the 20Hz voltage and current at the neutral point of the generator after injecting low-frequency quantities, combined with the third formula, calculate the grounding fault transition resistance.

[0045] The third formula is:

[0046] Among them, R fis the calculated ground fault transition resistance.

[0047] S105. When the ground fault is an in-zone fault, based on the fundamental zero-sequence voltages at the neutral point and the machine terminal and the ground transition resistance, combined with the fault location function, calculate the winding fault point of the located faulty generator.

[0048] Specifically, it includes: When the ground fault is an in-zone fault, based on the fundamental zero-sequence voltages at the neutral point and the machine terminal and the ground transition resistance, combined with the fault location function of the fourth formula, calculate the winding fault point of the located faulty generator.

[0049] The fourth formula is:

[0050] where, | E | is the amplitude of the fundamental phase electromotive force of the generator, which can be obtained by taking the difference between the measured fundamental voltage at the machine terminal and the fundamental voltage at the neutral point and then taking the amplitude through Fourier transform; C Σ is the total capacitance to ground of the dual-machine system of the nuclear power plant rod control power supply; U 0 is the fundamental voltage at the generator neutral point.

[0051] Substitute the fault location α = 0~1 into the fourth formula respectively, and the α corresponding to the minimum value of the fourth formula is the true fault location.

[0052] Specifically, in order to accurately locate the stator single-phase ground fault of the rod control power supply system, it is necessary to give the relationship expression between the fault electromotive force and the fault turn ratio in combination with its winding distribution characteristics.

[0053] The generator of the dual-machine system of the nuclear power plant rod control power supply adopts a special winding connection method. As Figure 4 shown, when the fault occurs in the first half of the winding, the fault electromotive force at this time is E f1 . It can be seen from Figure 4 that at this time, its winding electromotive force distribution is the same as that of the conventional winding.

[0054] When the fault occurs in the second half of the winding, the fault electromotive force at this time is E f2 . It can be seen from Figure 4 that at this time, the second half of the winding is no longer the same as the conventional winding, but is formed by the reverse connection of the second half of the lagging phase. Therefore, its fault electromotive force distribution cannot be directly calculated by the conventional winding electromotive force distribution method, but should be recalculated according to its special winding distribution form.

[0055] Extract Figure 4 the A-phase and its lagging B-phase of Figure 5 and combine with Figure 5 to deduce the fault potential of single-phase ground fault in the second half of the winding as follows: Figure 5 In E f2 . It can be seen from the figure that since the second half of the actual winding of the A-phase is equivalent to the reverse connection of the second half of the conventional winding of the B-phase. Therefore, when the fault occurs in the second half of the A-phase α at the position of α ), it is equivalent to occurring at the position of (1.5 - Figure 5 ) in the second half of the conventional winding of the B-phase. As shown in E f20 .

[0056] E f20 The calculation result of

[0057] After obtaining the fault potential E f20 of the conventional winding of the B-phase, subtract the obtained fault potential E B0 of the conventional winding of the B-phase from the potential E f20 of the conventional winding of the B-phase, and get E fB0 as shown in the following formula:

[0058] Since the second half of the actual winding of the A-phase is equivalent to the reverse connection of the second half of the conventional winding of the B-phase, so based on the above derivation, the single-phase ground fault of the stator occurring in the second half of the actual winding of the A-phase is E fB0 in the reverse direction of E fB , plus the potential at the midpoint of the conventional winding of the A-phase, as shown in the following formula:

[0059] Therefore, the calculation method of the actual fault winding potential of the A-phase is shown in the following formula:

[0060] The above formula is the potential distribution form of the A-phase stator winding after considering the zigzag star connection form, from which the fault location function of the dual-machine system of the nuclear power plant rod control power supply can be deduced, as shown in the fourth formula.

[0061] The above-mentioned method for locating the stator grounding fault of the dual-machine system of the nuclear power plant rod control power supply realizes the selective fault location and the location of the winding fault point of the dual-machine system of the rod control power supply, and can ensure the rapid maintenance and power supply restoration after the grounding fault occurs in the rod control power supply system of the nuclear power plant.

[0062] To verify the feasibility of a method for locating the stator grounding fault of the dual-machine system of the nuclear power plant rod control power supply described in the present invention, simulation tests and dynamic simulation tests are used for verification.

[0063] To verify the effectiveness of the proposed method, based on the PSCAD / EMTDC software, a quasi-distributed parameter model is used to construct an equivalent model of the generator stator winding for simulation verification. The dual-machine system of the nuclear power plant rod control power supply adopts a 4-branch winding structure, with a pole-pair number of 2, a total number of slots of 96, each branch consisting of 8 turns of coils connected in series, and the corresponding slot pitch electrical angle is 7.5°. The generator stator winding satisfies the 60-degree phase belt distribution characteristic. To eliminate the constant magnetic field generated by the DC component, the stator winding adopts a wiring method.

[0064] 1) To verify the correctness and effectiveness of the proposed method, simulations are carried out in the established rod control power supply system. A single-phase grounding fault of the stator with a transition resistance of 1000 Ω is set at the 0.5 position of the 1st generator winding, while the 2nd generator remains in the normal operating state; at the same time, to verify whether the proposed location method can distinguish between internal and external faults, a single-phase grounding fault with a transition resistance of 1000 Ω is set at the neutral point of the dual-machine system, and the 1st generator and the 2nd generator remain in the normal operating state. The fault simulation results are as Figure 6 shown, where Figure 6 (a) is the simulation result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage under the internal grounding fault condition; Figure 6 (b) is the simulation result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage under the external grounding fault condition.

[0065] During the simulation process, K set_in is set to 1.5. Through the analysis of Figure 6 (a), it can be seen that under the normal operating state, the phase angle difference between the zero-sequence differential current of the two generators and the injected power supply is about 90 degrees, while when a single-phase grounding fault of the stator occurs in the 1st generator, its phase angle difference will drop significantly, to about 10 degrees. Therefore, the faulty generator can be distinguished according to this characteristic. And according to the analysis of Figure 6 (b), it can be seen that when an external grounding fault occurs, the phase angle differences of the two generators both remain at about 90 degrees. Therefore, this fault characteristic can also distinguish between internal and external faults.

[0066] To further illustrate the effectiveness of the proposed criterion, simulations are carried out under different fault locations and different transition resistances. The simulation results are shown in Table 1.

[0067] Table 1 Verification of the selectivity criterion of the injection protection device under different ground fault conditions

[0068] As can be seen from Table 1, when a fault occurs in the zone, under different fault locations and different transition resistances, the phase angle differences of the faulty generator sets all meet the proposed injection-type selective fault location criterion. For example, when the fault occurs at the winding ratio of 0.5 and the transition resistance is 5000 Ω, the phase angle difference is 53.36°, meeting the proposed selective fault criterion. When an external fault occurs, the phase difference is 86.91°, not meeting the proposed selective fault criterion. Therefore, the faulty generator set can be accurately discriminated under different fault scenarios. When an external ground fault occurs, the phase angle difference remains around 90° under different fault scenarios. Thus, the distinction between in-zone faults and out-of-zone faults can be well achieved. The simulation results prove the correctness and effectiveness of the proposed method.

[0069] Using the proposed fault location method, fault location simulations are carried out in the established single-machine rod control power supply model under different fault locations and different transition resistances. The grounding fault occurs at 0.1 s, and the grounding fault location results are as Figure 7 shown, where Figure 7 (a) is the fault location simulation result diagram when α = 0.125, Figure 7 (b) is the fault location simulation result diagram when α = 0.250, Figure 7 (c) is the fault location simulation result diagram when α = 0.375, Figure 7 (e) is the fault location simulation result diagram when α = 0.625, Figure 7 (f) is the fault location simulation result diagram when α = 0.750, Figure 7 (g) is the fault location simulation result diagram when α = 0.875.

[0070] To effectively verify the accuracy of the proposed location method, an error analysis is carried out on the obtained fault location results, and the error analysis formula is defined as shown in the following formula:

[0071] where α is the fault turn ratio set in the simulation analysis model; is the fault location result calculated based on the grounding fault location method; represents the positioning error.

[0072] Under different fault scenarios formed by different transition resistances and different fault positions, the results of the fault location method proposed by the present invention and its positioning error are shown in Table 2.

[0073] Table 2 Fault Location Results and Positioning Errors

[0074] 2) A dynamic simulation test model of the dual-machine system of the nuclear power plant rod control power supply was established in the dynamic simulation laboratory, and the proposed method was analyzed through dynamic simulation tests under different load conditions. The parameters of the dynamic simulation test are shown in Table 3.

[0075] Table 3 Parameters of the Dynamic Simulation Test Unit

[0076] To verify the accuracy of the proposed selective fault location method based on the low-frequency injection amount under different operating conditions of the generator, a programmable AC power supply was used to simulate the low-frequency injection device, with a capacity of 15 kVA, a single-phase output current effective value adjustment range of 0 - 10 A, a phase adjustment range of -180° to +180°, and a frequency adjustment range of 15 - 1600 Hz. It can output a low-frequency 20 Hz voltage with any effective value and phase.

[0077] Taking the cases where the generator is respectively in no-load, 50% load, and full-load conditions as examples, a stator grounding fault with a transition resistance of 100 Ω was set at the No. 2 generator at 0.2 s. Meanwhile, the No. 1 generator remained in the normal operating state. The test results are as Figure 8 shown, where Figure 8 (a) is the test result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage when a fault occurs under no-load conditions, Figure 8 (b) is the test result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage when a fault occurs under 50% load conditions, Figure 8 (c) is the test result diagram of the phase angle difference between the zero-sequence differential current and the injected voltage when a fault occurs under full-load conditions.

[0078] During the experiment, K set_in is set to 1.5. As can be seen from Figure 8 , when a grounding fault occurs under different load conditions, the phase angle difference between the zero-sequence differential current and the injected voltage of the No. 2 generator with the set fault decreases from 90 degrees before the fault to about 0 degrees, while the phase angle difference of the non-faulty No. 1 generator remains unchanged at about 90 degrees. Combining the selective fault location criterion proposed by the present invention, the faulty generator can be accurately located. The proposed method is not affected by the load operating conditions of the generator.

[0079] Taking the cases where the generator is under no-load, 50% load, and full-load conditions as examples, a stator ground fault with a transition resistance of 100 Ω is set at 0.5 of the generator stator winding at 0.2 s.

[0080] For the above three load conditions, the proposed location method of the present invention is adopted, and the experimental results are as Figure 9 shown, where Figure 9 (a) is the calculation test result diagram of the ground fault location under no-load condition, Figure 9 (b) is the calculation test result diagram of the ground fault location under 50% load condition, Figure 9 (c) is the calculation test result diagram of the ground fault location under full-load condition.

[0081] It can be seen from Figure 9 that the proposed fault location method can achieve accurate fault location under different load conditions, and the location error is less than 1%. It is verified that the method proposed in the present invention can adapt to different load conditions and has strong engineering practicability.

Claims

1. A method for locating stator grounding faults in a dual-machine system of a rod-controlled power supply in a nuclear power plant, characterized in that: The following steps are involved: S101. Monitor the working state of the rod-controlled power supply dual-machine system. When the working state is a stator grounding fault, inject a 20Hz low-frequency quantity into the neutral point of the dual-machine system, obtain the 20Hz voltage and current of the neutral point of the generator after the low-frequency quantity is injected, and the 20Hz current of the neutral point side and the machine end side of the two generators of the dual-machine system, and obtain the fundamental zero-sequence voltage of the neutral point and the machine end; S102. Calculate the zero-sequence differential current of the two generators in the dual-machine system based on the 20 Hz currents at the neutral point side and the machine end side of the two generators in the dual-machine system after the low-frequency quantity is injected; S103. Based on the zero-sequence differential current of the two generators after the low-frequency quantity is injected, combined with the selective fault location criterion, locate the fault inside or outside the zone, and when the fault is an inside fault, locate the faulty generator; S104. Calculate the ground fault transition resistance based on the 20 Hz voltage and current of the generator neutral point after the low frequency quantity is injected; S105. When the ground fault is an intra-zone fault, based on the neutral point and machine end fundamental wave zero-sequence voltage and ground transition resistance, combined with the fault location function, the winding fault point of the located faulty generator is calculated.

2. A method for locating stator grounding faults in a dual-machine system of a rod-controlled power supply in a nuclear power plant according to claim 1, characterized in that: The step S102 specifically includes: Based on the 20Hz current on the neutral point side and the machine end side of the two generators in the dual-machine system after the low-frequency quantity is injected, the zero-sequence differential current of the two generators in the dual-machine system is calculated in combination with the first formula; the first formula is: in, is the zero-sequence differential current of generator No. 1 in the dual-machine system; is the zero-sequence differential current of generator No. 2 in the dual-machine system; It is the low-frequency current on the neutral point side of No. 1 generator in the dual-machine system; It is the low-frequency current on the neutral point side of No. 2 generator in the dual-machine system; It is the low-frequency current at the generator end of No. 1 in the dual-machine system; It is the low-frequency current at the generator end of No. 2 in the dual-machine system.

3. A method for locating stator grounding faults in a dual-machine system of a rod-controlled power supply in a nuclear power plant according to claim 1, characterized in that: The step S103 specifically includes: Based on the zero-sequence differential current of the two generators after the low-frequency quantity is injected, combined with the selective fault location criterion of the second formula, the fault inside or outside the zone is located. When the fault is an inside fault, the faulty generator is located; the second formula is: in, It is the low-frequency voltage of the neutral point of the dual-machine system; Set according to the actual situation; It ensures that there will be no false operation when an external grounding fault occurs, and accurately determines the faulty unit when an internal fault occurs; when one of the two generators meets the second formula, the generator that meets the second formula is determined to be the faulty generator; when neither of the two generators meets the second formula, it is determined that an external fault has occurred.

4. A method for locating stator grounding faults in a dual-machine system of a rod-controlled power supply in a nuclear power plant according to claim 1, characterized in that: The step S104 specifically includes: Based on the 20 Hz voltage and current at the neutral point of the generator after the low-frequency quantity is injected, the ground fault transition resistance is calculated in combination with the third formula; the third formula is: in, is the calculated ground fault transition resistance.

5. A method for locating stator grounding faults in a dual-machine system of a rod-controlled power supply in a nuclear power plant according to claim 1, characterized in that: The step S105 specifically includes: When the ground fault is an intra-zone fault, the winding fault point of the located faulty generator is calculated based on the neutral point and machine end fundamental wave zero-sequence voltage and grounding transition resistance, combined with the fault location function of the fourth formula; the fourth formula is: Among them, | E | is the amplitude of the fundamental phase potential of the generator, which is obtained by taking the difference between the measured fundamental voltage at the machine end and the fundamental voltage at the neutral point and performing Fourier transform to obtain the amplitude; C Σ It is the total ground capacitance of the dual-machine system of the nuclear power plant's rod-controlled power supply; U 0 is the fundamental voltage of the generator neutral point; The fault location α =0~1 are substituted into the fourth formula respectively, where the fourth formula obtains the minimum value corresponding to α This is the actual fault location.

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