A Method for Locating Stator Grounding Fault of Dual-Machine System of Rod Control Power Supply in Nuclear Power Plant

Abstract

The present invention relates to the technical fields of safety protection and fault location for dual-unit rod-controlled power systems in nuclear power plants. Specifically, a method for locating stator grounding faults in dual-unit rod-controlled power systems in nuclear power plants is disclosed. The method involves injecting a 20Hz low-frequency signal into the neutral point of the dual-unit system during a fault, acquiring multiple voltage and current parameters, and then calculating the zero-sequence current difference. The method then locates the faulty area and generator using a selective fault location criterion, calculates the grounding fault transition resistance, and calculates the winding fault point for faults within the area using a fault location function. The present invention effectively implements selective fault location and winding fault point location for dual-unit rod-controlled power systems, ensuring rapid repair and power restoration after a grounding fault in the nuclear power plant's rod-controlled power system.

Description

Technical Field

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

[0002] In large nuclear power plants, the reactor rod control system (RCS) drives the lifting and insertion of fuel rods to regulate reactor power generation. The Rotating Asynchronous Machine (RAM) (hereinafter referred to as the RCPS) is a dedicated electrical system that supplies power to the CRDM. Its core power generation unit consists of two generators operating in parallel. Engineering statistics indicate that single-phase ground faults in the stator winding are the most common fault type in generator systems. Sustained ground fault currents can easily generate arcs, potentially causing stator core burns and even developing into more serious inter-turn or inter-phase short circuits, posing a serious threat to the power supply security of the nuclear reactor.

[0003] The rod-controlled power supply dual-machine system operates in the form of two generator sets connected in parallel, such as Figure 2 As shown in Figure 2. Ground fault protection requires selectivity to accurately identify faulty units. However, current voltage criteria and injection methods lack the ability to correctly distinguish between normally operating units and faulty units, making accurate selective fault location impossible. Furthermore, because existing protection methods lack fault location capabilities, practical engineering often relies on sequential insulation measurements of winding coils to determine the fault location, which is time-consuming and labor-intensive. Therefore, after completing selective fault location and identifying the faulty unit, the fault point should be accurately located based on fault recording data to facilitate subsequent troubleshooting.

[0004] For the selective fault location of generators, Dang Xiaoqiang et al. proposed a protection method based on traveling wave signals in New Technology of Electrical Engineering and Power (2013, 32(1): 98-103) to expand the selective fault location of unit-connected units. This method uses the characteristics of the traveling wave zero-sequence power phase of the initial half-cycle time of the fault to distinguish between faulty units and non-faulty units. However, the traveling wave signal is greatly affected by the initial phase of the fault voltage and the transition resistance. In the case of a high-resistance grounding fault, the measurement of the traveling wave signal is more difficult. Mu Daqing and Yin Xianggen proposed a positioning method based on the power frequency variation characteristics of the differential current at the generator end and the neutral point side in Relay (2005, 33(22): 10-15). The method achieves selective fault location by distinguishing the amplitude and phase. However, this method has a certain dead zone. Since the voltage level of the generator in the rod-controlled power supply system is low and the neutral point adopts an ungrounded operation mode, the fault current characteristics are not obvious. Therefore, the above method is not completely applicable to the rod-controlled power supply dual-machine system of nuclear power plants.

[0005] For the location of generator stator grounding faults, Jia Wenchao and Huang Shaofeng proposed a location method based on the KVL equation between the fundamental zero-sequence voltage, fundamental fault potential and the fundamental voltage to ground at the fault point in Electric Power Automation Equipment (2017, 37(2): 134-139). The fault location was achieved by constructing a location equation. However, the fundamental potential of the stator winding of the steam turbine generator satisfies the 60° phase band distribution relationship, and the phase between the fault potential and the fault phase potential is not equal. This approximate treatment method will lead to certain theoretical errors. Wang Yuxue et al. proposed a location method based on injection equipment in the Proceedings of the Chinese Society for Electrical Engineering (2013, 33(31): 147-154+18). The fault coil is determined by measuring the transition resistance and combining the table lookup method. Huang Shaofeng and Jia Wenchao analyzed the potential distribution characteristics of large steam turbine generators in Power System Protection and Control (2017, 45(09): 35-40) and considered the phase difference of the fundamental potential. Yin Linpeng et al. proposed a stator ground fault location method based on winding potential distribution in Electric Power Automation Equipment (2019, 39(07): 141-146), and analyzed in detail the relationship between transition resistance and fundamental potential. These studies all considered the distribution characteristics of winding potential for fault location. However, since the nuclear power plant rod-controlled power supply dual-machine system adopts a special Zig-Zag winding connection method, its winding potential distribution is significantly different from that of conventional generators. Therefore, the above-mentioned location method is not fully applicable to the nuclear power plant rod-controlled power supply dual-machine system.

[0006] In summary, given the particularities of nuclear power plant dual-unit rod-controlled power systems and the limitations of existing methods, there is an urgent need to develop a fault location method specifically suited for this system. This includes a selective fault location method capable of identifying the faulty unit and a method for accurately locating the stator winding fault point, thereby improving the efficiency and reliability of fault diagnosis and treatment. Summary of the Invention

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

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

[0009] A method for locating a stator grounding fault in a dual-machine system of a rod-controlled power supply in a nuclear power plant comprises the following steps:

[0010] S101. Monitor the operating status of the rod-controlled power supply dual-machine system. When the operating status is a stator ground fault, inject a 20 Hz low-frequency signal into the neutral point of the dual-machine system. Obtain the 20 Hz voltage and current at the neutral point of the generator after the low-frequency signal is injected. 20 Hz currents at the neutral point and terminal sides of the two generators in the dual-machine system are obtained. Obtain the fundamental zero-sequence voltage at the neutral point and terminal sides.

[0011] S102. Calculate the zero-sequence current difference of the two generators in the dual-machine system based on the 20 Hz currents at the neutral point and terminal sides of the two generators in the dual-machine system after low-frequency injection;

[0012] S103. Based on the zero-sequence differential current of the two generators after the low-frequency injection, combined with the selective fault location criterion, locate the fault within or outside the zone. When the fault is an internal fault, locate the faulty generator;

[0013] S104. Calculate the ground fault transition resistance based on the 20 Hz voltage and current at the generator neutral point after injecting the low-frequency quantity;

[0014] S105. 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 generator terminal fundamental wave zero-sequence voltages and the ground transition resistance in combination with the fault location function.

[0015] Preferably, the step S102 specifically includes:

[0016] Based on the 20 Hz currents on the neutral point side and the terminal side of the two generators in the dual-machine system after the low-frequency input, 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:

[0017]

[0018] 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; The low-frequency current on the neutral point side of generator No. 1 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; 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.

[0019] Preferably, the step S103 specifically includes:

[0020] Based on the zero-sequence differential current of the two generators after the low-frequency signal 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-zone fault, the faulty generator is located. The second formula is:

[0021]

[0022] in, U in0n The low-frequency voltage at the neutral point of the dual-machine system; K set_in Set according to actual situation;

[0023] 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 generator meets the second formula, it is determined that an external fault has occurred.

[0024] Preferably, the step S104 specifically includes:

[0025] The ground fault transition resistance is calculated based on the 20 Hz voltage and current at the generator neutral point after low-frequency input, in combination with the third formula; the third formula is:

[0026]

[0027] in, R f is the calculated ground fault transition resistance.

[0028] Preferably, the step S105 specifically includes:

[0029] 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 generator terminal fundamental wave zero-sequence voltage and the ground transition resistance, combined with the fault location function of the fourth formula; the fourth formula is:

[0030]

[0031] 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 generator end and the fundamental voltage at the neutral point and performing Fourier transform to obtain the amplitude; C Σ The total ground capacitance of the dual-machine system of the rod-controlled power supply in a nuclear power plant; U 0 is the fundamental voltage of the generator neutral point;

[0032] 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.

[0033] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is as follows.

[0034] The present invention improves the accuracy of fault location:

[0035] Precise Selective Fault Location: This invention comprehensively considers factors such as the unique Zig-Zag winding connection scheme of the nuclear power plant's dual-unit rod-controlled power supply system and its ungrounded neutral point operation. Through a unique selective fault location criterion (combined with the selective fault location criterion of the second formula), it effectively distinguishes between internal and external faults. When an internal fault occurs, the faulty unit can be accurately identified, avoiding misjudgments caused by existing techniques such as the influence of the traveling wave signal on the initial phase of the fault voltage and transition resistance, and the presence of dead zones in methods based on current power frequency variation characteristics. This significantly improves the selectivity and accuracy of fault location.

[0036] Accurately locate winding fault points: For intra-zone faults, the winding fault point is calculated based on the fundamental zero-sequence voltage at the neutral point and the generator end, as well as the ground transition resistance, combined with an innovative fault location function (Formula 4). This method fully considers the winding potential distribution characteristics of the dual-unit system of the rod-controlled power supply. Compared with traditional methods, it can more accurately locate the actual fault location of the winding, providing precise fault point information for subsequent maintenance work.

[0037] The present invention improves maintenance efficiency and shortens power outage time:

[0038] Rapid fault identification: After detecting a stator ground fault, the system injects a 20Hz low-frequency signal into the neutral point and obtains a series of relevant parameters, enabling rapid initiation of various positioning calculation processes. Compared to the traditional method of determining the fault location by sequentially measuring the insulation of the winding coils, this method eliminates significant time-consuming and tedious measurements, rapidly identifies the faulty area and generator, and significantly shortens the troubleshooting cycle.

[0039] Reduced power outage duration: Accurate fault location allows maintenance personnel to directly target the fault point, avoiding potential delays caused by blind troubleshooting. This helps quickly restore power to the nuclear power plant, reduces the impact of power outages on the plant's overall operations and related facilities, and ensures the plant's safe and stable operation.

[0040] The present invention enhances the safety of nuclear power plant operation:

[0041] Timely fault response: Since stator grounding faults can be detected and located promptly and accurately, arc burns to the stator core caused by continuous grounding faults are avoided, thereby effectively preventing the fault from further developing into more serious situations such as inter-turn or inter-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 operations.

[0042] Adaptability to Special Operating Conditions: Taking into account the specificities of dual-unit rod-controlled power systems in nuclear power plants, the proposed method is effectively applicable under complex conditions such as low voltage, ungrounded operation, and unusual winding connections. Accurate fault location is achieved even under varying load conditions (such as no-load, 50% load, and full load, as verified by simulation and dynamic model testing), ensuring reliable fault location capabilities across all nuclear power plant operating states.

[0043] The present invention reduces maintenance costs:

[0044] Accurate positioning reduces troubleshooting workload: Accurate fault positioning reduces unnecessary maintenance links and inspections of a large number of normal equipment, avoiding waste of manpower and material resources, thereby reducing labor costs and equipment loss costs during troubleshooting and maintenance.

[0045] Preventing major failures and reducing maintenance costs: By promptly and accurately locating and handling early-stage failures, minor failures are prevented from becoming major failures, reducing the cost of large-scale repairs and equipment replacement. From a long-term perspective, this effectively reduces the maintenance cost of nuclear power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flow chart of the present invention;

[0047] Figure 2Schematic diagram of a dual-machine rod-controlled power supply system for a nuclear power plant according to an embodiment of the present invention;

[0048] Figure 3 20 Hz zero-sequence equivalent circuit diagram of the generator in an embodiment of the present invention;

[0049] Figure 4 This is a diagram showing the actual winding potential distribution of a rod-controlled power supply dual-machine system in an embodiment of the present invention;

[0050] Figure 5 Phase A and phase B of the actual winding potential distribution of the rod-controlled power supply dual-machine system in the embodiment of the present invention;

[0051] Figure 6 This is a diagram of the fault simulation results in an embodiment of the present invention, where: Figure 6 (a) is the simulation result of the phase angle difference of zero-sequence differential current and injection voltage under internal ground fault conditions. Figure 6 (b) is the simulation result of the phase angle difference of zero-sequence differential current and injection voltage under external ground fault conditions;

[0052] Figure 7 : is a diagram of fault location simulation results under different fault positions and different transition resistances in an embodiment of the present invention, wherein: Figure 7 (a) α =0.125 when the fault location simulation results are shown in the figure. Figure 7 (b) α =0.250 when the fault location simulation results are shown in the figure. Figure 7 (c) α =0.375 when the fault location simulation results are shown. Figure 7 (e) is α =0.625 when the fault location simulation results are shown in the figure. Figure 7 (f) is α =0.750 when the fault location simulation results are shown in the figure. Figure 7 (g) is α =0.875 when the fault location simulation results;

[0053] Figure 8 : is a graph showing the phase angle difference test results of the zero-sequence differential current and the injected voltage when a fault occurs under different load conditions in an embodiment of the present invention, wherein: Figure 8 (a) is the test result diagram of zero sequence differential current and phase angle difference of injected voltage under no-load condition. Figure 8 (b) is the test result diagram of the zero-sequence differential current and the phase angle difference of the injected voltage under 50% load condition. Figure 8 (c) is the test result diagram of zero-sequence differential current and phase angle difference of injected voltage when a fault occurs under full load;

[0054] Figure 9This is a diagram showing the results of a ground fault location calculation test in an embodiment of the present invention, wherein: Figure 9 (a) is the result of the ground fault location calculation test under no-load conditions. Figure 9 (b) is the result of the ground fault location calculation test under 50% load. Figure 9 (c) is the test result of ground fault location calculation under full load. DETAILED DESCRIPTION

[0055] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] A method for locating stator grounding faults in a dual-machine system of a nuclear power plant's rod-controlled power supply can be used to Figure 2 The selective fault location and winding fault point location of the rod-controlled power supply dual-machine system shown in the figure can ensure the rapid maintenance and power supply restoration after the grounding fault occurs in the rod-controlled power supply system of the nuclear power plant. Figure 1 As shown, the following steps are included:

[0057] S101. Monitor the operating status of the rod-controlled power supply dual-machine system. When the operating status is a stator ground fault, inject a 20 Hz low-frequency signal into the neutral point of the dual-machine system. Obtain the 20 Hz voltage and current at the neutral point of the generator after the low-frequency signal is injected. Also, obtain the 20 Hz current at the neutral point and the terminal side of the two generators in the dual-machine system. Obtain the fundamental zero-sequence voltage at the neutral point and the terminal.

[0058] S102. Calculate the zero-sequence differential current of the two generators in the dual-machine system based on the 20 Hz currents on the neutral point side and the machine terminal side of the two generators in the dual-machine system after the low-frequency quantity is injected.

[0059] Specifically include:

[0060] Based on the 20 Hz currents on the neutral point side and the terminal side of the two generators in the dual-machine system after the low-frequency quantity is injected, combined with the first formula, the zero-sequence differential current of the two generators in the dual-machine system is calculated.

[0061] The first formula is:

[0062]

[0063] 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; The low-frequency current on the neutral point side of generator No. 1 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; 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.

[0064] S103. Based on the zero-sequence differential current of the two generators after the low-frequency signal is injected, combined with the selective fault location criterion, locate the fault within or outside the zone. When the fault is an internal fault, locate the faulty generator.

[0065] Specifically include:

[0066] Based on the zero-sequence differential current of the two generators after the low-frequency signal 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-zone fault, the faulty generator is located.

[0067] The second formula is:

[0068]

[0069] in, U in0n The low-frequency voltage at the neutral point of the dual-machine system; K set_in Set it according to the actual situation.

[0070] 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 generator meets the second formula, it is determined that an external fault has occurred.

[0071] Specifically, when injecting U in After that, the 20Hz zero-sequence equivalent circuit of the generator is as follows Figure 3 shown.

[0072] Figure 3 middle U in represents the injected voltage; and They represent the generator stator winding admittance to ground, fault admittance, generator terminal admittance to ground and line admittance to ground respectively. It represents the zero sequence current, such as It represents the zero-sequence current on the neutral point side of the dual-machine system generator. For the zero-sequence current difference of the faulty unit, it satisfies the following relationship:

[0073]

[0074] Among them, the zero sequence differential current of the non-faulty unit No. 2 generator is The phase angle of the injection power supply is ahead of U in About 90 degrees. Due to the influence of fault admittance, the zero sequence differential current of the faulty unit No. 1 generator The phase angle should be ahead of the injection power Uin 0 to 90 degrees. Therefore, a selective fault location method suitable for a rod-controlled power supply dual-machine system can be constructed based on the fault characteristics of the zero-sequence differential current after the injection device is put into operation and the phase angle difference of the injection power supply.

[0075] Through the above analysis, an injection-type selective fault location criterion suitable for rod-controlled power supply systems is proposed, as shown in the second formula.

[0076] S104. Calculate the ground fault transition resistance based on the 20 Hz voltage and current at the generator neutral point after the low-frequency quantity is injected.

[0077] Specifically include:

[0078] The ground fault transition resistance is calculated based on the 20 Hz voltage and current at the generator neutral point after low-frequency input and the third formula.

[0079] The third formula is:

[0080]

[0081] in, R f is the calculated ground fault transition resistance.

[0082] S105. 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 generator terminal fundamental wave zero-sequence voltage and the ground transition resistance, combined with the fault location function.

[0083] Specifically include:

[0084] 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 generator terminal fundamental wave zero-sequence voltage and the ground transition resistance, combined with the fault location function of the fourth formula.

[0085] The fourth formula is:

[0086]

[0087] Among them, | E | is the amplitude of the fundamental phase potential of the generator, which can be obtained by taking the difference between the measured fundamental voltage at the generator end and the fundamental voltage at the neutral point and performing Fourier transform to obtain the amplitude; C Σ 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.

[0088] 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.

[0089] Specifically, in order to accurately locate the single-phase grounding fault in the rod-controlled power supply system, it is necessary to give an expression for the relationship between the fault potential and the fault turns ratio in combination with the winding distribution characteristics.

[0090] The nuclear power plant rod-controlled power supply dual-machine system generator adopts special Winding connection method. Figure 4 As shown in Figure 2, when the fault occurs in the front half of the winding, the fault potential is E f1 .from Figure 4 It can be seen that at this time, the winding potential distribution is the same as the conventional winding potential distribution.

[0091] When the fault occurs in the second half of the winding, the fault potential is E f2 .from Figure 4 As can be seen from the diagram, the second half of the winding is no longer the same as a conventional winding, but is instead the second half of the lagging phase connected in reverse. Therefore, the fault potential distribution cannot be directly calculated using the conventional winding potential distribution method, but must be recalculated based on its special winding distribution.

[0092] extract Figure 4 Phase A and its lagging phase B Figure 5 , combined with Figure 5 , the fault potential of the single-phase grounding fault in the second half of the winding is deduced as follows:

[0093] Figure 5 In the case of a single-phase grounding fault in the latter half of the actual winding, the fault potential is E f2 As can be seen from the figure, since the second half of the actual winding of phase A is equivalent to the second half of the conventional winding of phase B connected in reverse, when the fault occurs in the second half of phase A, α When the voltage is at 1.5V, it is equivalent to the second half of the conventional winding of phase B (1.5- α ) place. Figure 5 in E f20 shown.

[0094] E f20 The calculation results are shown as follows:

[0095]

[0096] The fault potential of the conventional winding of phase B is obtained E f20 Then, make the B phase normal winding potential E B0Subtract the obtained fault potential of the B phase normal winding E f20 ,have to E fB0 As shown in the following formula:

[0097]

[0098] Since the second half of the actual winding of phase A is equivalent to the second half of the conventional winding of phase B connected in reverse, based on the above deduction, the stator single-phase grounding fault occurring in the second half of the actual winding of phase A is E fB0 Reverse E fB , plus the potential of the midpoint of the A-phase conventional winding, as shown below:

[0099]

[0100] Therefore, the calculation method of the actual fault winding potential of phase A is as follows:

[0101]

[0102] The above formula is the potential distribution of the A-phase stator winding after taking into account the zigzag star connection form. From this, the fault location function of the nuclear power plant's rod-controlled power supply dual-machine system can be derived, as shown in the fourth formula.

[0103] The above-mentioned stator grounding fault location method of the rod-controlled power supply dual-machine system of a nuclear power plant realizes selective fault location and winding fault point location for the rod-controlled power supply dual-machine system, and can ensure rapid maintenance and power supply restoration after a grounding fault occurs in the rod-controlled power supply system of a nuclear power plant.

[0104] In order to verify the feasibility of the stator grounding fault location method of the nuclear power plant rod-controlled power dual-machine system described in the present invention, simulation tests and dynamic model tests are used for verification.

[0105] To verify the effectiveness of the proposed method, a quasi-distributed parameter model was used to construct an equivalent model of the generator stator winding based on PSCAD / EMTDC software for simulation verification. The nuclear power plant rod-controlled power supply dual-machine system adopts a 4-branch winding structure with 2 pole pairs and 96 total slots. Each branch consists of 8 turns of coils connected in series, and the corresponding slot pitch electrical angle is 7.5°. The generator stator winding meets the 60-degree phase belt distribution characteristics. In order to eliminate the constant magnetic field generated by the DC component, the stator winding adopts Wiring method.

[0106] 1) To verify the correctness and effectiveness of the proposed method, a simulation was conducted in the established rod-controlled power supply system. A stator single-phase grounding fault with a transition resistance of 1000Ω was set at 0.5 of the winding of generator No. 1, while generator No. 2 remained in normal operation. 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 1000Ω was set at the neutral point of the dual-machine system, while generators No. 1 and No. 2 remained in normal operation. The fault simulation results are shown in Figure 2. Figure 6 As shown, Figure 6 (a) is the simulation result of the phase angle difference of zero-sequence differential current and injection voltage under internal ground fault conditions; Figure 6 (b) is the simulation result of the phase angle difference of zero-sequence differential current and injection voltage under external ground fault conditions.

[0107] During the simulation, K set_in Set to 1.5. Figure 6 (a) Analysis shows that under normal operating conditions, the phase angle difference between the zero-sequence differential current of the two generators and the injection power supply is about 90 degrees. However, when a single stator ground fault occurs in generator No. 1, the phase angle difference will drop significantly to about 10 degrees. Therefore, the faulty units can be distinguished based on this feature. Figure 6 (b) Analysis shows that when an external ground fault occurs, the phase angle difference between the two generators remains at around 90 degrees. Therefore, this fault feature can also distinguish between internal and external faults.

[0108] In order 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.

[0109] Table 1 Verification of selectivity criteria for injection protection devices under different ground fault conditions

[0110]

[0111] Table 1 shows that when an internal fault occurs, the phase angle difference of the faulty unit meets the proposed injection-based selective fault location criteria for different fault locations and transition resistances. For example, when the fault occurs at a winding ratio of 0.5 and the transition resistance is 5000Ω, the phase angle difference is 53.36°, meeting the proposed selective fault criterion. However, when an external fault occurs, the phase angle difference is 86.91°, which does not meet the proposed selective fault criterion. Therefore, the faulty unit can be accurately identified under different fault scenarios. In the case of an external ground fault, the phase angle difference remains around 90 degrees in all fault scenarios, effectively distinguishing between internal and external faults. Simulation results demonstrate the correctness and effectiveness of the proposed method.

[0112] Using the proposed fault location method, fault location simulations were performed in the established single-machine rod-controlled power supply model under different fault locations and different transition resistances. The ground fault occurred at 0.1s. The ground fault location results are shown in Figure 2. Figure 7 As shown, Figure 7 (a) α =0.125 when the fault location simulation results are shown in the figure. Figure 7 (b) α =0.250 when the fault location simulation results are shown in the figure. Figure 7 (c) α =0.375 when the fault location simulation results are shown. Figure 7 (e) α =0.625 when the fault location simulation results are shown in the figure. Figure 7 (f) is α =0.750 when the fault location simulation results are shown in the figure. Figure 7 (g) is α Fault location simulation results when =0.875.

[0113] In order to effectively verify the accuracy of the proposed positioning method, the error analysis of the fault location results is performed, and the error analysis formula is defined as follows:

[0114]

[0115] in, α is the fault turns ratio set in the simulation analysis model; is the fault point location result calculated based on the ground fault location method; Indicates positioning error.

[0116] Table 2 shows the results of the fault location method proposed in the present invention and its location error under different fault scenarios consisting of different transition resistances and different fault locations.

[0117] Table 2 Fault location results and location errors

[0118]

[0119] 2) A dynamic model test model of a nuclear power plant rod-controlled power supply dual-machine system was established in the dynamic model test laboratory. The proposed method was analyzed by dynamic model tests under different load conditions. The dynamic model test parameters are shown in Table 3.

[0120] Table 3 Dynamic mold test unit parameters

[0121]

[0122] In order to verify the accuracy of the proposed selective fault location method based on low-frequency injection under different generator operating conditions, a programmable AC power supply is used to simulate a low-frequency injection device. Its capacity is 15kVA, and the single-phase output current effective value adjustment range is 0~10A, the phase adjustment range is -180°~+180°, and the frequency adjustment range is 15~1600Hz. It can output a low-frequency 20Hz voltage with any effective value and phase.

[0123] Taking the generators at no load, 50% load and full load as an example, a stator ground fault with a transition resistance of 100Ω is set on the No. 2 generator at 0.2s. At the same time, the No. 1 generator maintains normal operation. The test results are as follows Figure 8 As shown, Figure 8 (a) is the test result diagram of zero sequence differential current and phase angle difference of injected voltage under no-load condition. Figure 8 (b) is the test result diagram of the zero-sequence differential current and the phase angle difference of the injected voltage under 50% load condition. Figure 8 (c) is the test result diagram of the zero-sequence differential current and the phase angle difference of the injected voltage when a fault occurs under full load.

[0124] During the experiment, K set_in Set to 1.5. Figure 8 As can be seen from the data, when a ground fault occurs under different load conditions, the phase angle difference between the zero-sequence differential current and the injected voltage of generator 2 (the faulty unit) decreases from 90 degrees before the fault to approximately 0 degrees, while the phase angle difference of generator 1 (the non-faulty unit) remains unchanged at approximately 90 degrees. Combined with the selective fault location criteria proposed in this invention, the faulty unit can be accurately located. The proposed method is unaffected by the generator load operating conditions.

[0125] Taking the generator at no-load, 50% load and full load as an example, a stator grounding fault with a transition resistance of 100Ω is set at 0.5 of the generator stator winding at 0.2s.

[0126] For the above three load conditions, the positioning method proposed by the present invention is used, and the experimental results are as follows: Figure 9 As shown, Figure 9 (a) is the result of the ground fault location calculation test under no-load conditions. Figure 9 (b) is the result of the ground fault location calculation test under 50% load. Figure 9 (c) is the test result of ground fault location calculation under full load.

[0127] from Figure 9As can be seen from the results, the proposed fault location method can accurately locate faults under different load conditions, with a positioning error of less than 1%. This verifies that the proposed method can adapt to different load conditions and has strong engineering practicality.

Claims

1. A method for locating stator grounding faults in a dual-unit system of a rod-controlled power supply in a nuclear power plant, characterized by: The following steps are involved: S101. Monitor the operating status of the rod-controlled power supply dual-machine system. When the operating status is a stator ground fault, inject a 20 Hz low-frequency signal into the neutral point of the dual-machine system. Obtain the 20 Hz voltage and current at the neutral point of the generator after the low-frequency signal is injected. 20 Hz currents at the neutral point and terminal sides of the two generators in the dual-machine system are obtained. Obtain the fundamental zero-sequence voltage at the neutral point and terminal sides. S102. Calculate the zero-sequence current difference of the two generators in the dual-machine system based on the 20 Hz currents at the neutral point and terminal sides of the two generators in the dual-machine system after low-frequency injection; S103. Based on the zero-sequence differential current of the two generators after the low-frequency injection, combined with the selective fault location criterion, locate the fault within or outside the zone. When the fault is an internal fault, locate the faulty generator; S104. Calculate the ground fault transition resistance based on the 20 Hz voltage and current at the generator neutral point after injecting the low-frequency quantity; S105. 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 generator terminal fundamental wave zero-sequence voltages and the ground transition resistance in combination with the fault location function.

2. A method for locating stator grounding faults in a dual-machine system of a nuclear power plant's rod-controlled power supply according to claim 1, characterized in that: The step S102 specifically includes: Based on the 20 Hz currents on the neutral point side and the terminal side of the two generators in the dual-machine system after the low-frequency input, 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; The low-frequency current on the neutral point side of generator No. 1 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; 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. The method for locating a stator grounding fault in a dual-machine system of a nuclear power plant rod-controlled power supply according to claim 2, characterized in that: The step S103 specifically includes: Based on the zero-sequence differential current of the two generators after the low-frequency signal 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-zone fault, the faulty generator is located. The second formula is: in, The low-frequency voltage at the neutral point of the dual-machine system; Set according to 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 generator meets the second formula, it is determined that an external fault has occurred.

4. A method for locating stator grounding faults in a dual-unit system of a nuclear power plant's rod-controlled power supply according to claim 3, characterized in that: The step S104 specifically includes: The ground fault transition resistance is calculated based on the 20 Hz voltage and current at the generator neutral point after low-frequency input, in combination with the third formula; the third formula is: in, It represents the zero sequence current on the neutral point side of the generator in the dual-machine system; is the calculated ground fault transition resistance.

5. A method for locating stator grounding faults in a dual-machine system of a nuclear power plant's rod-controlled power supply according to claim 4, 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 generator terminal fundamental wave zero-sequence voltage and the ground transition resistance, combined with the fault location function of the fourth formula; the fourth formula is: in, The fundamental phase potential amplitude of the generator is obtained by taking the difference between the measured fundamental voltage at the generator end and the fundamental voltage at the neutral point and performing Fourier transform to obtain the amplitude. The total ground capacitance of the dual-machine system of the rod-controlled power supply in a nuclear power plant; is the fundamental voltage of the generator neutral point; The fault location Substitute them into the fourth formula respectively, where the fourth formula obtains the minimum value corresponding to This is the actual fault location.

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