Method and device for accurately positioning ground fault of stator winding of large hydro-generator

Abstract

The invention discloses a large-scale hydro-generator stator winding grounding fault accurate positioning method and device, and relates to the technical field of hydro-generator fault diagnosis, and the method comprises the steps: obtaining the neutral point zero-sequence current of a hydro-generator; according to the neutral point zero-sequence current of the hydro-generator, judging whether winding grounding has a fault or not; determining a fault phase according to the asymmetric current of the three-phase winding of the hydro-generator when the grounding fault of the winding occurs; determining a fault branch according to the parallel branch current difference of the fault phase; determining a fault bar on the fault branch based on a direct current voltage division method; obtaining the corresponding slot number of the fault bar according to the winding wiring mode of the hydro-generator, and dividing the corresponding slot number of the fault bar and the slot numbers on the two sides of the fault bar into suspicious fault slots; and screening the suspicious fault slots based on the direct-current magnetic field direction to obtain fault slots. According to the invention, the problem of accurate positioning of the fault slot when the stator winding grounding fault occurs in the large-scale hydro-generator is solved.

Description

Technical Field

[0001] This invention relates to a method and device for accurately locating grounding faults in the stator windings of a large hydro-generator, belonging to the field of hydro-generator fault diagnosis technology. Background Technology

[0002] The safe operation of generator units plays a decisive role in the stability of power system operation. Generator units have complex structures and high value. If a failure is not promptly investigated and repaired, it will not only severely damage the lifespan of the generator unit, but also cause incalculable losses to the power system and the national economy.

[0003] Once a ground fault occurs in a large hydro-generator, the corresponding single-phase grounding current increases sharply, seriously threatening the safety of the stator core. Furthermore, the large ground fault current can cause an electric arc, and the heat generated by the arc can damage the winding insulation, burn the core, and sinter the core laminations. Continued arcing can also easily trigger destructive short-circuit faults, seriously threatening the safety of the generator equipment. For large-capacity generators, the high rated voltage level and large inherent ground capacitance mean that the current and voltage values ​​of the fault arc are large during a single-phase ground fault, resulting in a large fault arc power. Within a certain period, the accumulated energy of the fault arc can easily lead to severe damage to the generator. If a single-phase ground fault in the stator is not eliminated in time, it will damage the stator core and may even cause more serious accidents. Because large hydro-generators have many stator slots, it is difficult to locate the fault once a ground fault occurs, requiring a large amount of manpower and time for repair, resulting in huge maintenance costs and downtime losses.

[0004] Therefore, in-depth research on the precise location technology of grounding faults in the stator windings of large hydro-generators is of great significance for reducing the maintenance costs of power generation enterprises and improving economic efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and device for accurately locating ground faults in the stator windings of large hydro-generators, so as to solve the problem of accurately locating the fault slot when a ground fault occurs in the stator windings of a large hydro-generator.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: On one hand, the present invention provides a method for accurately locating ground faults in the stator windings of a large hydro-generator, comprising: Obtain the zero-sequence current at the neutral point of the hydro-generator; Determine whether a winding grounding fault has occurred based on the zero-sequence current at the neutral point of the hydro generator. When a winding ground fault is detected: The faulty phase is determined based on the asymmetrical current in the three-phase windings of the hydro-generator. The faulty branch is determined based on the difference in current between the parallel branches of the faulty phase. The initial location of the fault is determined on the faulty branch based on the DC voltage divider method; Based on the winding connection method of the hydro-generator, suspected fault slots are identified by the initial location of the fault; Faulty slots are identified by filtering from suspected faulty slots based on the direction of the DC magnetic field.

[0007] Furthermore, obtaining the zero-sequence current at the neutral point of the hydro-generator includes: A zero-sequence current transformer is installed on the grounding wire extending from the neutral point of the hydro-generator. The zero-sequence current at the neutral point of the hydro-generator is obtained in real time through the zero-sequence current transformer during the operation of the hydro-generator.

[0008] Furthermore, the step of determining whether a winding grounding fault has occurred based on the zero-sequence current at the neutral point of the hydro-generator includes: If the zero-sequence current at the neutral point of the hydro-generator suddenly increases and persists, it is determined that a winding grounding fault has occurred; otherwise, no winding grounding fault has occurred.

[0009] Furthermore, the determination of the fault phase based on the asymmetrical current of the three-phase windings of the hydro-generator includes: Connect the neutral point terminals of the three-phase windings of the hydro generator; Apply a three-phase symmetrical voltage to the output terminals of each phase so that the current amplitude of the three-phase windings of the hydro-generator does not exceed 5A. By comparing the currents of each phase winding, the phase with the largest increase in current is the faulty phase.

[0010] Furthermore, before determining the faulty branch based on the current difference in the parallel branches of the faulty phase, the following steps are also included: Determine whether the faulty phase is a low-resistance grounding fault; If the faulty phase is a high-resistance ground fault, connect the positive terminal of the high-voltage DC pulse power supply to the output terminal of the faulty phase winding, and ground the negative terminal. By using a high-voltage DC pulse power supply to output a high-voltage DC pulse current, a high-resistance ground fault can be transformed into a low-resistance ground fault. The output voltage range of the high-voltage DC pulse power supply is 1~32kV, and the pulse duration is 0~4s.

[0011] Furthermore, determining the faulty branch based on the current difference of the parallel branches of the faulty phase includes: Apply an AC voltage between the outgoing terminal of the faulty phase and the grounding wire of the hydro-generator, so that the current in each branch of the faulty phase does not exceed 5A. Monitor the current in each branch; the branch with the highest current is the faulty branch.

[0012] Furthermore, determining the initial location of the fault on the faulty branch based on the DC voltage divider method includes: Apply a DC voltage between the output terminal of the faulty phase and the neutral point terminal; Monitor the potential values ​​of the outgoing terminals and neutral point terminals of the faulty branch relative to ground; The initial location of the fault can be determined based on the potential values ​​of the outgoing and neutral terminals of the faulty branch relative to ground. The determination formula is as follows: ; in, This indicates the potential value of the outgoing terminal of the faulty branch relative to ground. This indicates the potential value of the neutral point terminal relative to ground in the faulty branch. This indicates the winding resistance from the initial location of the fault in the faulty branch to the outgoing terminal. This indicates the winding resistance from the initial location of the fault in the faulty branch to the center point terminal. This indicates the number of conductors connected in series between the initial location of the fault and the outgoing terminal in the faulty branch. This indicates the number of conductors connected in series between the initial location of the fault and the neutral point terminal in the faulty branch. This indicates the fault location error correction parameter.

[0013] Furthermore, the step of dividing suspected fault slots based on the winding connection method of the hydro-generator and the initial location of the fault includes: The winding connection method of the hydro-generator is obtained from the winding connection diagram of the hydro-generator; By checking the winding connection method of the hydro-generator, the slot number of the bar corresponding to the initial location of the fault and the bars connected in series on both sides is classified as the slot with suspected fault.

[0014] Furthermore, the step of selecting faulty slots from suspected faulty slots based on the direction of the DC magnetic field includes: Apply a DC voltage between the outgoing terminal of the faulty phase and the stator core, and ensure that the current in each branch of the faulty phase does not exceed 5A. Measure the magnetic field direction on both the top and bottom sides of the wire bar inside each suspected faulty slot; If the magnetic field directions on the upper and lower sides of the bar are the same, the suspected faulty slot is excluded; if the magnetic field directions on the upper and lower sides of the bar are opposite, the suspected faulty slot is determined to be a faulty slot.

[0015] On the other hand, the present invention also provides a device for accurately locating ground faults in the stator windings of a large hydro-generator, comprising: The neutral point zero-sequence current acquisition module is configured to acquire the neutral point zero-sequence current. The winding grounding fault detection module is configured to determine whether a winding grounding fault has occurred based on the zero-sequence current of the neutral point of the hydro generator. The fault phase determination module is configured to determine the fault phase based on the asymmetrical current of the three-phase windings of the hydro generator; The fault branch determination module is configured to determine the fault branch based on the current difference between the parallel branches of the faulty phase. The fault line identification module is configured to determine the initial location of the fault on the faulty branch based on the DC voltage divider method; The suspected fault slot division module is configured to divide suspected fault slots based on the winding connection method of the hydro generator and the initial location of the fault. The fault slot screening module is configured to screen out fault slots from suspected fault slots based on the direction of the DC magnetic field.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention employs a non-invasive detection method that can accurately determine whether a winding grounding fault has occurred, the faulty phase, the faulty branch, and the faulty conductor in sequence. Finally, it uses a magnetic field to determine the final faulty slot, achieving precise location of the faulty slot without damaging the conductors inside the slot that are not faulty. The operation is simple and can significantly improve the efficiency of stator grounding fault repair. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for accurately locating grounding faults in the stator windings of a large hydro-generator according to one embodiment of the present invention. Figure 2 This is a wiring diagram illustrating how a high-resistance grounding fault can be transformed into a low-resistance grounding fault using a high-voltage DC pulse in one embodiment of the present invention. Figure 3 This is a wiring diagram illustrating the determination of the fault branch based on the current difference in the parallel branches of the faulty phase in one embodiment of the present invention. Figure 4 This is a wiring diagram illustrating the determination of the faulty conductor on a faulty branch based on the DC voltage divider method in one embodiment of the present invention. Figure 5 This is a wiring diagram illustrating the process of selecting faulty slots from suspected faulty slots based on the direction of a DC magnetic field in one embodiment of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention. Example 1

[0019] This embodiment uses a large hydroelectric generator to study the precise location of a ground fault in the A-phase winding. The basic parameters of the generator are shown in Table 1. Table 1: Basic Parameters of Large Hydro Generators

[0020] like Figure 1 As shown, this embodiment of the invention provides a method for accurately locating ground faults in the stator windings of a large hydro-generator, applicable to hydro-generator neutral point grounded through a high-impedance grounding system, comprising the following steps: Step S1: Determine whether a winding grounding fault has occurred based on the zero-sequence current at the neutral point of the hydro-generator. In this embodiment, a zero-sequence current transformer is installed on the grounding wire extending from the neutral point of the hydro generator. The zero-sequence current transformer continuously monitors and records the zero-sequence current at the neutral point during the operation of the hydro generator.

[0021] When a zero-sequence current transformer detects a sudden increase in a continuous zero-sequence current, the value of which is much greater than the ground capacitance current during normal operation, it is determined that a winding grounding fault has occurred; otherwise, no winding grounding fault has occurred.

[0022] Step S2: Determine the fault phase based on the asymmetrical current of the three-phase windings under the fault condition of the hydro-generator. Connect the neutral point terminals of the three-phase windings of the hydro generator.

[0023] A low-amplitude three-phase symmetrical voltage is applied to the output terminals of each phase. In this embodiment, low amplitude means that the current amplitude of the three-phase windings of the hydro generator does not exceed 5A.

[0024] By comparing the currents of each phase winding, the phase with the largest increase in current is the faulty phase.

[0025] Step S3: Use a high-voltage DC pulse to transform a high-resistance ground fault into a low-resistance ground fault. The faulty phase can be determined to be either a low-resistance grounding fault or a high-resistance grounding fault.

[0026] If the faulty phase is a high-resistance ground fault, a suitable high-voltage DC pulse power supply should be selected. Its output voltage, pulse width, and energy must be set according to the fault resistance and motor insulation characteristics. In this embodiment, the output voltage range of the high-voltage DC pulse power supply is 1~32kV, and the pulse duration is 0~4s.

[0027] Connect the positive terminal of the high-voltage DC pulse power supply to the output terminal of the faulty phase winding, and ground the negative terminal. Then start the high-voltage DC pulse power supply and apply a high-voltage DC pulse current to the faulty phase. The energy of the pulse current will instantly break down the high-resistance faulty phase, turning it into a low-resistance grounded phase. The connection circuit between the high-voltage DC power supply and the faulty phase is as follows: Figure 2As shown in the figure, the resistance of a single wire bar is R. Each branch is composed of multiple wire bars connected in series, and the faulty phase winding is composed of multiple branches connected in parallel.

[0028] Step S4: Determine the faulty branch based on the difference in current between the parallel branches of the faulty phase. First, such as Figure 3 As shown, a low-voltage AC voltage is applied between the outgoing terminal of the faulty phase and the grounding wire of the hydro-generator, so that the current of each branch is much smaller than the rated current of the hydro-generator. In this embodiment, the current of each branch of the faulty phase does not exceed 5A.

[0029] Measure and record the current magnitude of each branch. Because a circulating current forms between the faulty and non-faulty branches, the currents of the faulty and non-faulty branches differ. The currents of non-faulty branches are the same in magnitude but smaller, while the currents of the faulty branches are much larger than those of other non-faulty branches. This characteristic can be used to identify the faulty branch.

[0030] Step S5: Preliminary location of the fault based on the DC voltage divider method. like Figure 4 As shown, a DC voltage with a current less than 5A is applied to the outgoing terminal and the neutral point terminal of the faulty phase.

[0031] Monitor the potential values ​​of the outgoing terminals and neutral terminals of the faulty branch relative to ground. The initial location of the fault can be determined based on the potential values ​​of the outgoing and neutral terminals of the faulty branch relative to ground. The determination formula is as follows: ; in, This indicates the potential value of the outgoing terminal of the faulty branch relative to ground. This indicates the potential value of the neutral point terminal relative to ground in the faulty branch. This indicates the winding resistance from the initial location of the fault in the faulty branch to the outgoing terminal. This indicates the winding resistance from the initial location of the fault in the faulty branch to the center point terminal. This indicates the number of conductors connected in series between the initial location of the fault and the outgoing terminal in the faulty branch. This indicates the number of conductors connected in series between the initial location of the fault and the neutral point terminal in the faulty branch. , All are integers. This represents the fault location error correction parameter, which is the error caused by the different positions of the grounding points on the conductor. Its value is a decimal.

[0032] The following example will illustrate this step in detail. For instance, for a winding with 10 bars connected in series, if the fault location is set at the middle of the 4th bar, then the ratio of V1 / V2 might be 3.5:6.5. Since... , Since all values ​​are integers, a fault location error correction parameter is needed to correct them, i.e., k=0.5 should be chosen so that... , .

[0033] The initial location of the fault is The position of each bar.

[0034] It should be noted that, in reality, due to the resistance deviation of each bar and measurement error, the bar corresponding to the preliminary fault location obtained in this step may not be the actual fault point.

[0035] Step S6: Identify suspected faulty slots based on the winding connection method. By querying the winding connection method of the hydro-generator, the slot number of the bar corresponding to the preliminary fault location calculated in step S5 is determined. However, due to the resistance deviation of each bar and measurement error, the calculated N1 has an error of about 3 slots. Therefore, the slot number corresponding to the faulty bar and the slot numbers on both sides are classified as suspected fault slots. In this embodiment, 2 slot numbers are taken on each side, that is, the total number of suspected fault slots is 5.

[0036] Step S7: Accurately locate the fault slot based on the direction of the DC magnetic field. Apply a DC voltage between the outgoing terminal of the faulty phase and the stator core. The DC voltage must ensure that the current in each branch of the faulty phase does not exceed 5A.

[0037] The magnetic field direction on the upper and lower sides of the conductor bar in each suspected fault slot is measured. If the magnetic field direction on the upper and lower sides of the conductor bar is the same, the suspected fault slot is excluded. If the magnetic field direction on the upper and lower sides of the conductor bar is opposite, the suspected fault slot is determined to be a fault slot, thus realizing the accurate location of the grounding fault slot. Example 2

[0038] Based on Example 1, this example also provides a device for accurately locating ground faults in the stator windings of a large hydro-generator, comprising: The neutral point zero-sequence current acquisition module is configured to acquire the neutral point zero-sequence current. The winding grounding fault detection module is configured to determine whether a winding grounding fault has occurred based on the zero-sequence current of the neutral point of the hydro generator. The fault phase determination module is configured to determine the fault phase based on the asymmetrical current of the three-phase windings of the hydro generator; The fault branch determination module is configured to determine the fault branch based on the current difference between the parallel branches of the faulty phase. The fault line identification module is configured to determine the initial location of the fault on the faulty branch based on the DC voltage divider method; The suspected fault slot identification module is configured to identify suspected fault slots based on the winding connection method of the hydro generator and the initial location of the fault. The fault slot screening module is configured to screen out fault slots from suspected fault slots based on the direction of the DC magnetic field.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for accurately locating grounding faults in the stator windings of a large hydro-generator, characterized in that, include: Obtain the zero-sequence current at the neutral point of the hydro-generator; Determine whether a winding grounding fault has occurred based on the zero-sequence current at the neutral point of the hydro generator. When a winding ground fault is detected: The faulty phase is determined based on the asymmetrical current in the three-phase windings of the hydro-generator. The faulty branch is determined based on the difference in current between the parallel branches of the faulty phase. The initial location of the fault is determined on the faulty branch based on the DC voltage divider method; Based on the winding connection method of the hydro-generator, the suspected fault slot is determined by the preliminary location of the fault; Faulty slots are identified by filtering from suspected faulty slots based on the direction of the DC magnetic field.

2. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The acquisition of the neutral point zero-sequence current of the hydro-generator includes: A zero-sequence current transformer is installed on the grounding wire extending from the neutral point of the hydro-generator. The zero-sequence current at the neutral point of the hydro-generator is obtained in real time through the zero-sequence current transformer during the operation of the hydro-generator.

3. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The method of determining whether a winding grounding fault has occurred based on the zero-sequence current of the neutral point of the hydro-generator includes: If the zero-sequence current at the neutral point of the hydro-generator suddenly increases and persists, it is determined that a winding grounding fault has occurred; otherwise, no winding grounding fault has occurred.

4. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The method of determining the faulty phase based on the asymmetrical current of the three-phase windings of the hydro-generator includes: Connect the neutral point terminals of the three-phase windings of the hydro generator; Apply a three-phase symmetrical voltage to the output terminals of each phase so that the current amplitude of the three-phase windings of the hydro-generator does not exceed 5A. By comparing the currents of each phase winding, the phase with the largest increase in current is the faulty phase.

5. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, Before determining the faulty branch based on the current difference between the parallel branches of the faulty phase, the following steps are also included: Determine whether the faulty phase is a low-resistance grounding fault; If the faulty phase is a high-resistance ground fault, connect the positive terminal of the high-voltage DC pulse power supply to the output terminal of the faulty phase winding, and ground the negative terminal. By using a high-voltage DC pulse power supply to output a high-voltage DC pulse current, a high-resistance ground fault can be transformed into a low-resistance ground fault. The output voltage range of the high-voltage DC pulse power supply is 1~32kV, and the pulse duration is 0~4s.

6. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The step of determining the faulty branch based on the current difference of the parallel branches of the faulty phase includes: Apply an AC voltage between the outgoing terminal of the faulty phase and the grounding wire of the hydro-generator, so that the current in each branch of the faulty phase does not exceed 5A. Monitor the current in each branch; the branch with the highest current is the faulty branch.

7. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The method of determining the initial location of the fault on the faulty branch based on the DC voltage divider method includes: Apply a DC voltage between the output terminal of the faulty phase and the neutral point terminal; Monitor the potential values ​​of the outgoing terminals and neutral point terminals of the faulty branch relative to ground; The preliminary location of the fault is calculated based on the potential values ​​of the outgoing terminal and neutral point terminal of the faulty branch relative to ground. The calculation expression is as follows: ； in, This indicates the potential value of the outgoing terminal of the faulty branch relative to ground. This indicates the potential value of the neutral point terminal relative to ground in the faulty branch. This indicates the winding resistance from the initial location of the fault in the faulty branch to the outgoing terminal. This indicates the winding resistance from the initial location of the fault in the faulty branch to the center point terminal. This indicates the number of conductors connected in series between the initial location of the fault and the outgoing terminal in the faulty branch. This indicates the number of conductors connected in series between the initial location of the fault and the neutral point terminal in the faulty branch. This indicates the fault location error correction parameter.

8. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The process of dividing suspected fault slots based on the winding connection method of the hydro-generator and the initial location of the fault includes: The winding connection method of the hydro-generator is obtained from the winding connection diagram of the hydro-generator; By checking the winding connection method of the hydro-generator, the slot number of the bar corresponding to the initial location of the fault and the bars connected in series on both sides is classified as the slot with suspected fault.

9. The method for accurately locating grounding faults in the stator windings of a large hydro-generator according to claim 1, characterized in that, The process of identifying faulty slots from suspected faulty slots based on the direction of the DC magnetic field includes: Apply a DC voltage between the outgoing terminal of the faulty phase and the stator core, and ensure that the current in each branch of the faulty phase does not exceed 5A. Measure the magnetic field direction on both the top and bottom sides of the wire bar inside each suspected faulty slot; If the magnetic field directions on the upper and lower sides of the bar are the same, the suspected faulty slot is excluded; if the magnetic field directions on the upper and lower sides of the bar are opposite, the suspected faulty slot is determined to be a faulty slot.

10. A device for accurately locating grounding faults in the stator winding of a large hydro-generator, characterized in that, include: The neutral point zero-sequence current acquisition module is configured to acquire the neutral point zero-sequence current. The winding grounding fault detection module is configured to determine whether a winding grounding fault has occurred based on the zero-sequence current of the neutral point of the hydro generator. The fault phase determination module is configured to determine the fault phase based on the asymmetrical current of the three-phase windings of the hydro generator; The fault branch determination module is configured to determine the fault branch based on the current difference between the parallel branches of the faulty phase. The fault line identification module is configured to determine the initial location of the fault on the faulty branch based on the DC voltage divider method; The suspected fault slot division module is configured to divide suspected fault slots based on the winding connection method of the hydro generator and the initial location of the fault. The fault slot screening module is configured to screen out fault slots from suspected fault slots based on the direction of the DC magnetic field.

Images