System for improving reliability of generator-transformer protection of AC excited variable-speed energy storage unit

Abstract

The application discloses a system and method for improving the reliability of generator-transformer protection of an AC excitation variable-speed energy storage unit, and belongs to the technical field of AC excitation variable-speed energy storage unit power generation. The technical problem to be solved is to solve the problem of phase sequence commutation and short-time exit required by main transformer main protection. The technical solution is as follows: the outgoing line end of the stator side of the generator motor is sequentially connected with the low-voltage side of the main transformer through a stator short-circuit switch, a commutation switch and a generator circuit breaker; the outgoing line end of the rotor side of the generator motor is sequentially connected with the low-voltage side of the main transformer through an AC excitation system, a current-limiting reactor and a disconnector; a station service power supply is sequentially connected with the disconnector through a station service branch circuit breaker and a current-limiting reactor; the main transformer main protection is configured in a large-difference dualization mode; and the main protection and small-difference protection of the generator motor are both configured in a dualization mode.

Description

Technical Field

[0001] This invention belongs to the field of AC excitation variable speed energy storage unit power generation technology, specifically relating to a system for improving the protection reliability of AC excitation variable speed energy storage unit generator-transformer unit. Background Technology

[0002] The generator-transformer protection system of AC-excited variable-speed energy storage units requires a dual configuration; it must ensure that the relay protection of energized equipment is always operational and cannot be deactivated; and the protection must not have any dead zones where it cannot be protected. Furthermore, during the operation of the AC-excited variable-speed energy storage unit, the main protection system of the generator-transformer unit may experience phase sequence commutation and short-term deactivation due to factors such as generator operation, pumping operation, the activation of electrical feedback braking during unit shutdown, and unit self-starting during pumping and pumping phase adjustment.

[0003] Therefore, existing pumped storage power stations adopt a design based on... Figure 1 The main wiring and the main protection of the main transformer 1 adopt a dual configuration for both the large differential and small differential protection. That is, the small differential protection of the main transformer 1 is dual configuration, including the main transformer small differential one 17-A and the main transformer small differential two 17-B. The large differential protection of the main transformer 1 is dual configuration, including the main transformer large differential one 16-A and the main transformer large differential two 16-B. Similarly, the main differential protection for generator motor 5 employs a dual configuration for both the large and small differential protections. Specifically, the small differential protection for generator motor 5 is configured with dual features, including generator motor small differential protection 1 (15-A) and generator motor small differential protection 2 (15-B). The large differential protection for generator motor 5 is configured with dual features, including generator motor large differential protection 1 (14-A) and generator motor large differential protection 2 (14-B). Figure 2 As shown.

[0004] The generator motor has two main differential protection systems: one large differential protection system 14-A and one large differential protection system 14-B. The generator motor 5 has a dual main differential protection configuration. The generator motor has two small differential protection systems: one small differential protection system 15-A and one small differential protection system 15-B. The generator motor has a dual main differential protection configuration. The main transformer has two large differential protection systems: one large differential protection system 16-A and one large differential protection system 16-B. The main transformer 1 has a dual main differential protection configuration. The main transformer has two small differential protection systems: one small differential protection system 17-A and one small differential protection system 17-B. The main transformer 1 has a dual main differential protection configuration.

[0005] Depend on Figure 2 It is known that when the unit is in operation, the main transformer 1 will always be energized, and the main protection configured on the main transformer 1 must always be operational and cannot be deactivated. During the selection operation of the unit in power generation or pumping mode, the main transformer differential pressure 16-A and main transformer differential pressure 26-B will perform phase sequence switching according to the unit's power generation or pumping mode, and there will be a short-term deactivation.

[0006] To prevent problems such as short-term tripping of the main protection due to phase sequence commutation of the main transformer 1's large differential protection 16-A and main transformer 16-B when the unit is operating in either power generation or pumping mode, main transformer 1 is also equipped with main transformer small differential protection 17-A and main transformer small differential protection 17-B. This ensures that the main protection is always online to protect main transformer 1, regardless of the unit's operating conditions.

[0007] During unit startup, the first step is to select between generator operation and pumping operation. During this operation, generator circuit breaker 3 is in the open state, meaning the unit is disconnected from the grid. Because current flows through the circuit between generator motor 5 and stator short-circuit switch 4 during self-starting in pumping mode or during electrical feedback braking during unit shutdown, generator motor differential protection 14-A and generator motor differential protection 214-B need to be deactivated. To prevent the generator motor from lacking main protection during self-starting and electrical feedback braking, generator motor 5 is equipped with generator motor differential protection 15-A and generator motor differential protection 215-B. These two differential protection devices ensure that protection is active under all operating conditions.

[0008] The above analysis shows that during the commissioning period, the main transformer 1 is always energized. When the unit selects between power generation and pumping modes, the main transformer differential switch 16-A and main transformer differential switch 16-B will perform phase sequence commutation and short-term deactivation while the main transformer 1 is energized. The protection phase sequence commutation and deactivation commands are controlled by the auxiliary contacts of the phase commutation switch 2. The reliability of the auxiliary contacts directly affects the reliability of the protection operation. Unreliable auxiliary contacts will cause the main protection of the main transformer 1 to malfunction, which in turn will lead to the circuit breakers on each side of the main transformer 1 tripping erroneously. Summary of the Invention

[0009] The purpose of this invention is to provide: A system and method for improving the reliability of the generator-transformer protection of AC-excited variable-speed energy storage units, in order to solve the technical problems of phase sequence switching and short-term shutdown of the main transformer protection.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: Firstly, This invention provides a system for improving the protection reliability of AC-excited variable speed energy storage unit. The AC-excited variable speed energy storage unit includes a main transformer 1, a phase switching switch 2, a generator circuit breaker 3, a stator short-circuit switch 4, a generator motor 5, an AC excitation system 10, a disconnecting switch 11, a current-limiting reactor 12, and a plant branch circuit breaker 13. The stator side output terminal of the generator motor is connected to the low-voltage side of the main transformer 1 after passing through the stator short-circuit switch 4, the phase-changing switch 2, and the generator circuit breaker 3 in sequence. The rotor output terminal of the generator motor 5 is connected to the low-voltage side of the main transformer 1 after passing through the AC excitation system 10 and the disconnecting switch 2 in sequence. The plant power supply is connected to the disconnecting switch 11 via the plant branch circuit breaker 13 and the current-limiting reactor 12 in sequence. Main transformer 1 has only a dual-configuration main protection differential; The generator motor 5 is equipped with main protection large differential and small differential protection, both of which adopt a dual configuration.

[0011] Furthermore, the AC excitation system 10 includes: an AC excitation input circuit breaker 6, an AC excitation input transformer 7, a frequency converter 8, and an overvoltage protection device 9 connected in series; wherein the overvoltage protection device 9 is connected to the rotor output terminal of the generator motor 5, and the AC excitation input circuit breaker 6 is connected to the disconnecting switch 11 via a current-limiting reactor 12.

[0012] Furthermore, the main protection differential of main transformer 1 is configured with main transformer differential protection 16-A and main transformer differential protection 16-B.

[0013] Furthermore, the two differential circuits of the main transformer 1 are connected: the current transformer (CT) at the end of the generator circuit breaker 3 near the phase-changing switch 2 is connected to the high-voltage side CT of the main transformer 1. CT: Current transformer.

[0014] Furthermore, the two sets of large differential circuit breakers of the main transformer 1 are also connected to the CT at the end of the plant branch circuit breaker 13 that is far away from the current limiting reactor 12 and the CT on the high voltage side of the main transformer 1.

[0015] Furthermore, the two large differential circuits of the main transformer 1 are also connected to: the CT at the end of the AC excitation input circuit breaker 6 near the AC excitation input transformer 7 and the CT on the high-voltage side of the main transformer 1.

[0016] Furthermore, the main protection for generator motor 5 is equipped with generator motor large differential protection 14-A, generator motor large differential protection 2 14-B, generator motor small differential protection 15-A, and generator motor small differential protection 2 15-B.

[0017] Furthermore, the two sets of large differential protection for the generator motor 5 are respectively connected to: the neutral point CT of the generator motor 5 and the CT at the end of the generator circuit breaker 3 closest to the main transformer 1.

[0018] Furthermore, the two sets of differential protection for the generator motor 5 are respectively connected to the neutral point CT and the stator side outgoing line CT of the generator motor 5.

[0019] Secondly, This invention provides a method for ensuring the reliability of protection for AC-excited variable-speed energy storage units, including: In pumping mode, the phase switch 2 switches to the pumping position, the generator motor 5 operates as a motor, absorbs electrical energy from the grid to drive the water pump, and the AC excitation system 10 adjusts the amplitude, frequency and phase of the excitation current to achieve variable speed pumping. In the power generation mode, the phase switching switch 2 is switched to the power generation position. The rotor winding of the generator motor 5 is provided with an adjustable excitation current in terms of amplitude, frequency and phase by the AC excitation system 10. The stator side is connected to the grid for power generation through the stator short-circuit switch 4, the phase switching switch 2, the generator circuit breaker 3 and the main transformer 1. At the same time, the low-voltage side of the main transformer 1 supplies power to the plant through the current limiting reactor 12 and the plant service branch circuit breaker 13. Under fault conditions, when an electrical fault occurs in the generator motor, the generator motor protection will trip, trip generator circuit breaker 3, and shut down the unit due to an electrical accident. The plant auxiliary branch circuit breaker 13 will remain closed, ensuring continuous operation of the plant auxiliary power supply. When an electrical fault occurs in the main transformer, the main transformer protection will trip generator circuit breaker 3, disconnect the high-voltage side circuit breaker of the main transformer, shut down the unit due to an electrical accident, trip plant auxiliary branch circuit breaker 13, and simultaneously switch to the backup plant auxiliary power supply to ensure continuous operation of the plant auxiliary power supply.

[0020] The present invention has at least the following beneficial effects: This invention, by swapping the positions of the reversing switch 2 and the generator circuit breaker 3 in the general main wiring of an AC-excited variable-speed energy storage unit, and reconfiguring the main protection of the generator-transformer unit based on the adjusted main wiring, not only eliminates the main transformer differential protection but also effectively eliminates the problems of phase sequence commutation and short-term shutdown of the main transformer protection. Simultaneously, while ensuring the selectivity and speed of the main transformer protection, it further improves the reliability of the main transformer protection. Specific analysis is as follows: Regarding the improvement of the reliability of the unit's operating condition switching protection, in the original main wiring, the phase-changing switch 2 is located between the generator circuit breaker 3 and the main transformer 1. When the unit switches between pumping and generating operating conditions, the phase sequence needs to be adjusted by operating the phase-changing switch 2. This phase-changing operation directly affects the sampling phase sequence of the main transformer 1's main protection (large differential), causing the main transformer 1's main protection (large differential) to need to perform phase sequence switching simultaneously. In order to avoid protection maloperation during the phase-changing and phase sequence adjustment process, the main transformer 1's main protection (large differential) needs to be temporarily deactivated. Therefore, the main transformer's main protection also needs to be configured with a main transformer small differential. Since the main transformer is always energized, if the phase sequence of the main transformer 1's main protection (large differential) is incorrect during the phase-changing process, it will cause the main transformer 1's main protection (large differential) to maloperate, seriously affecting the reliability of the main transformer 1's protection. By swapping the positions of the generator circuit breaker 3 and the phase-changing switch 2, the phase-changing switch 2 is placed between the stator side of the generator motor 5 and the generator circuit breaker 3. This achieves electrical isolation between the phase-changing switch 2 and the main circuit of the main transformer 1. When the unit's operating conditions change, the phase sequence adjustment of the phase-changing switch 2 only occurs from the reversing switch 4 inside the generator circuit breaker 3 to the generator motor bus and stator winding side. The phase sequence of the main circuit on the low-voltage side of the main transformer 1 remains unchanged. There is no need to perform phase sequence reversal operation on the main protection of the main transformer 1. Furthermore, the sampling circuit of the main protection of the main transformer 1 is not affected during the operation of the phase-changing switch 2, and there is no need to temporarily disconnect the main protection. This completely eliminates the protection vacuum during the operating condition change and ensures the continuous and effective operation of the main protection of the main transformer 1.

[0021] Based on meeting the requirements of protection dead zone, reliability, speed and selectivity of generator-transformer unit protection, the original small differential protection of the main transformer was eliminated, and only the large differential protection of the main transformer was retained, which simplified the differential protection of the main transformer. At the same time, it solved the problem that the main transformer 1 main protection needed to switch phase sequence and short-term disconnection when the unit changed operating conditions, which further improved the reliability of the generator-transformer unit protection of AC excitation variable speed energy storage unit.

[0022] This invention not only improves the reliability of the generator-transformer protection of AC-excited variable-speed energy storage units, but also simplifies the configuration of the main protection of the main transformer.

[0023] This invention interchanges the positions of the generator circuit breaker and the phase-changing switch. The phase-changing switch is isolated to the generator motor side section of the generator circuit breaker 3, and the phase sequence of the high-voltage power supply circuit from the low-voltage side of the main transformer to the outside of the generator circuit breaker 3 remains permanently fixed. During any operating condition switchover or phase-changing switch operation, the phase sequence characteristics of all sampling CT branches of the main transformer differential protection will not change. Therefore, the dual differential protection of the main transformer requires no phase sequence switching or short-term shutdown throughout the entire process. The main protection remains continuously and reliably operational throughout the energized operation of the main transformer, completely eliminating the systemic failure risk caused by protection vacuum and reliance on auxiliary contacts. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the main wiring structure of the AC excitation variable speed energy storage unit before the improvement.

[0025] Figure 2 This is a schematic diagram of the main protection configuration of the generator-transformer unit in the main wiring diagram of the AC excitation variable speed energy storage unit before the improvement. The main transformer 1 and the generator motor 5 are equipped with main protection.

[0026] Figure 3 This is a schematic diagram of the main protection configuration of the generator-transformer unit in the main wiring of the improved AC excitation variable speed energy storage unit. The main transformer 1 and the generator motor 5 are equipped with main protection.

[0027] 1. Main transformer; 2. Phase switching switch; 3. Generator circuit breaker; 4. Stator short-circuit switch; 5. Generator motor; 6. AC excitation input circuit breaker; 7. AC excitation input transformer; 8. Frequency converter; 9. Overvoltage protection device; 10. AC excitation system; 11. Disconnecting switch; 12. Current-limiting reactor; 13. Plant branch circuit breaker; 14-A, Generator motor large difference one; 14-B, Generator motor large difference two; 15-A, Generator motor small difference one; 15-B, Generator motor small difference two; 16-A, Main transformer major differential 1; 16-B, Main transformer major differential 2; 17-A, Main transformer minor differential 1; 17-B, Main transformer minor differential 2. Detailed Implementation

[0028] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0029] like Figure 1 As shown, the AC-excited variable speed energy storage unit consists of a main transformer 1, a phase switching switch 2, a generator circuit breaker 3, a stator short-circuit switch 4, a generator motor 5, an AC excitation system 10, a disconnecting switch 11, a current-limiting reactor 12, and a plant branch circuit breaker 13. The AC excitation system 10 includes an AC excitation input circuit breaker 6, an AC excitation input transformer 7, a frequency converter 8, and an overvoltage protection device 9.

[0030] When starting the pumping unit in pumping mode, the constant-speed pumped storage unit uses an external power source, which comes from the stationary frequency converter (SFC) and the other units' boiler tubes (BTB) in the power station. That is, there are two starting methods: SFC and BTB.

[0031] When starting the AC-excited variable speed energy storage unit in pumping operation, in addition to using SFC or BTB starting methods, some AC-excited variable speed energy storage units can also use the AC excitation system configured on the unit itself to achieve the starting method for pumping operation, i.e., self-starting. For AC-excited variable speed energy storage units with self-starting capability, starting the unit in pumping operation does not require an external power source for SFC or BTB starting methods; it only needs to be achieved through the AC excitation system 10.

[0032] The start-up and shutdown procedures for AC-excited variable-speed energy storage units with self-starting capability are as follows: 1. Pumping start-up procedure From standstill to pumping: First, the commutator switch 2 is switched to the pumping position. The turbine casing is purged and drained. After successful purging and draining, the stator short-circuit switch 4 is closed. The AC excitation system 10 provides power to drive the turbine to accelerate in the pumping direction. After the turbine accelerates from zero speed to the minimum speed required for grid connection, the AC excitation system 10 stops providing power and removes the magnetic flux of the generator motor 5. When the current flowing through the stator short-circuit switch 4 approaches zero, the stator short-circuit switch 4 is disconnected. After the stator short-circuit switch 4 is disconnected, the AC excitation system 10 is restarted, and the voltage, frequency, and phase of the generator motor 5 are controlled and adjusted. When the grid connection conditions are met, the generator circuit breaker 3 is closed. Then, the turbine is purged and filled with water. The guide vanes and inlet valve are opened, and the turbine absorbs active power from the grid. The turbine pumping operation is now complete. 2. Start-up procedure under power generation conditions From standstill to generating electricity: First, switch 2 to the generator position, open the inlet valve, engage the speed governor, and open the guide vanes. The potential energy of the water drives the generator to accelerate in the generator direction. After the generator reaches the minimum speed required for grid connection from zero speed, engage the AC excitation system 10 and control and adjust the terminal voltage, frequency, and phase of the generator motor 5. When the grid connection conditions are met, close the generator circuit breaker 3, and the generator's generator operation is started. 3. Shutdown Procedure During the shutdown process, a shutdown command is issued to the speed governor and AC excitation system. The unit reduces active and reactive power to no load, disconnects the generator circuit breaker 3, closes the stator short-circuit switch 4, and uses the energy feedback method of the AC excitation system 10 to achieve electrical feedback braking. The mechanical brake is then engaged, the unit speed is reduced to zero, the mechanical brake is disengaged, the stator short-circuit switch 4 is opened, and the unit shutdown process is completed.

[0033] The generator-transformer protection system of AC-excited variable-speed energy storage units requires a dual configuration; it must ensure that the relay protection of energized equipment is always operational and cannot be deactivated; and the protection must not have any dead zones where it cannot be protected. Furthermore, during the operation of AC-excited variable-speed energy storage units, the main protection system of the generator-transformer unit may experience phase sequence commutation and short-term deactivation due to factors such as generator operation, pumping operation, electrical feedback braking during unit shutdown, and unit self-starting during pumping operation. This creates a protection vacuum and seriously affects the reliability of the protection.

[0034] Therefore, based on Figure 1 The main wiring and the main protection of the main transformer 1 adopt a dual configuration for the large differential and small differential protection. That is, the small differential protection of the main transformer 1 is dual configuration, including the main transformer small differential one 17-A and the main transformer small differential two 17-B. The main differential protection of the main transformer 1 is dual configuration, including the main transformer large differential one 16-A and the main transformer large differential two 16-B. Similarly, the main differential protection for generator motor 5 adopts a dual configuration for both large and small differential protection. Specifically, the small differential protection for generator motor 5 is configured with dual features, including generator motor small differential protection 1 (15-A) and generator motor small differential protection 2 (15-B). The large differential protection for generator motor 5 is configured with dual features, including generator motor large differential protection 1 (14-A) and generator motor large differential protection 2 (14-B). Figure 2 As shown.

[0035] The generator motor has a large differential protection system 14-A and a large differential protection system 14-B, with dual configuration of the main differential protection for generator motor 5; the generator motor has a small differential protection system 15-A and a small differential protection system 15-B, with dual configuration of the main differential protection for generator motor 5. The main transformer has a large differential protection system 16-A and a large differential protection system 16-B, with the main transformer 1 having a dual large differential protection configuration; the main transformer has a small differential protection system 17-A and a small differential protection system 17-B, with the main transformer 1 having a dual small differential protection configuration.

[0036] Depend on Figure 2 It is known that when the unit is in operation, the main transformer 1 will always be energized, and the main protection configured on the main transformer 1 must always be operational and cannot be deactivated. During the selection operation of the unit in power generation or pumping mode, the main transformer differential pressure 16-A and main transformer differential pressure 26-B will perform phase sequence switching according to the unit's power generation or pumping mode, and there will be a short-term deactivation.

[0037] To prevent problems such as short-term tripping of the main protection due to phase sequence reversal in the main transformer's large differential protection 16-A and main transformer's large differential protection 16-B when the unit is operating in either power generation or pumping mode, main transformer 1 is also equipped with main transformer small differential protection 17-A and main transformer small differential protection 17-B. This ensures that the main protection is always online to protect main transformer 1, regardless of the unit's operating conditions.

[0038] During unit startup, the first step is to select between generator operation and pumping operation. During this operation, generator circuit breaker 3 is in the open state, meaning the unit is disconnected from the grid. Because current flows through the circuit between generator motor 5 and stator short-circuit switch 4 during self-starting in pumping mode or during electrical feedback braking during unit shutdown, generator motor differential protection devices 14-A and 14-B need to be deactivated. To prevent the generator motor 5 from lacking main protection during self-starting and electrical feedback braking, generator motor 5 is equipped with generator motor differential protection devices 15-A and 15-B. These devices ensure that the unit remains operational under all operating conditions without needing to be deactivated.

[0039] The above analysis shows that during commissioning, main transformer 1 is always energized. Before starting the unit, a mode selection operation is performed to choose between generating and pumping modes. During this selection, main transformer differential breaker 16-A and main transformer differential breaker 16-B will perform phase sequence commutation and short-term deactivation while main transformer 1 is energized. The protection phase sequence commutation and deactivation commands are controlled by the auxiliary contacts of phase commutation switch 2. Due to the frequent switching between generating and pumping modes of the AC-excited variable-speed energy storage unit, the reliability of the auxiliary contacts directly affects the reliability of the main transformer 1 protection operation. Unreliable auxiliary contacts will cause the main protection of main transformer 1 to malfunction, leading to false tripping of circuit breakers on each side of main transformer 1. Conversely, when the AC-excited variable-speed energy storage unit selects between generating and pumping modes before startup, generator circuit breaker 3 is in the disconnected position, disconnecting the unit from the grid, and the unit is in a stationary state (generator motor 5 is not energized). Figure 2 It can be seen that when the unit performs the operation selection operation in the power generation and pumping modes, the generator motor large differential 14-A, generator motor large differential 2 14-B, and generator motor small differential 15-A and generator motor small differential 2 15-B do not require phase sequence commutation. Even if the main protection of generator motor 5 has phase sequence commutation and short-term disconnection, because the generator circuit breaker 3 is in the disconnected position and the unit is in a stationary state (generator motor 5 is not energized), the phase sequence commutation error of the main protection of generator motor 5 will not affect the power grid.

[0040] Therefore, this invention provides a system for improving the reliability of protection for AC-excited variable-speed energy storage units, such as... Figure 3 As shown, the system achieves this by... Figure 1 The main wiring diagram is adjusted, specifically the positions of generator circuit breaker 3 and phase-changing switch 2 are swapped, and the main protection of the generator-transformer unit is reconfigured. The adjusted protection configuration not only ensures that the main protection of main transformer 1 will not experience phase-changing or short-term shutdown issues due to the unit's operation during power generation or pumping before startup, but also simplifies the main protection configuration of main transformer 1 and further improves the reliability of the generator-transformer unit's relay protection.

[0041] The system described in this invention includes an AC-excited variable-speed energy storage unit comprising a main transformer 1, a phase-switching switch 2, a generator circuit breaker 3, a stator short-circuit switch 4, a generator motor 5, an AC excitation system 10, a disconnecting switch 11, a current-limiting reactor 12, and a plant branch circuit breaker 13. The stator side output terminal of the generator motor is connected to the low-voltage side of the main transformer 1 after passing through the stator short-circuit switch 4, the phase-changing switch 2, and the generator circuit breaker 3 in sequence. The rotor-side output terminal of the generator motor 5 is connected to the low-voltage side of the main transformer 1 after passing through the AC excitation system 10 and the disconnecting switch 2 in sequence. The plant power supply is connected to the disconnecting switch 11 via the plant branch circuit breaker 13 and the current-limiting reactor 12 in sequence. The main transformer 1 is only equipped with dual main protection large differential protection, completely eliminating the main transformer small differential protection that must be set in the original technology, and greatly simplifying the protection architecture; The main protection for generator motor 5, both the large differential and small differential protection, adopts a dual configuration.

[0042] The AC excitation system 10 includes: an AC excitation input circuit breaker 6, an AC excitation input transformer 7, a frequency converter 8, and an overvoltage protection device 9 connected in series; wherein the overvoltage protection device 9 is connected to the rotor winding of the generator motor 5, and the AC excitation input circuit breaker 6 is connected to the disconnecting switch 11 via a current-limiting reactor 12.

[0043] The main protection differential circuit of main transformer 1 is equipped with main transformer differential circuit 1 (16-A) and main transformer differential circuit 2 (16-B). The two differential circuit circuits of main transformer 1 are respectively connected to: the CT at the end of generator circuit breaker 3 near the phase switching switch 2 and the CT on the high-voltage side of main transformer 1; the CT at the end of plant service branch circuit breaker 13 away from the current limiting reactor 12 and the CT on the high-voltage side of main transformer 1; and the CT at the end of AC excitation input circuit breaker 6 near AC excitation input transformer 7 and the CT on the high-voltage side of main transformer 1.

[0044] The main protection for generator motor 5 is equipped with generator motor large differential protection 14-A and generator motor large differential protection 2 14-B, as well as generator motor small differential protection 15-A and generator motor small differential protection 2 15-B. The two sets of large differential protection for generator motor 5 are respectively connected to: the neutral point CT of generator motor 5 and the CT at the end of generator circuit breaker 3 closest to main transformer 1.

[0045] The two sets of differential protection for generator motor 5 are respectively connected to the neutral point CT and the stator side outgoing line CT of generator motor 5.

[0046] The previous section introduced based on Figure 1 The main wiring diagram shows the unit's start-up and shutdown processes under power generation and pumping conditions. It also illustrates the... Figure 2 The main protection configuration of the generator-transformer unit shown was analyzed during the selection operation of the unit in power generation and pumping operation, the self-starting of the unit in pumping operation, and the electrical feedback braking process during the shutdown of the unit, as well as the phase switching and short-term shutdown of the main protection of the generator-transformer unit.

[0047] It can be seen that when the unit selects between power generation and pumping operation, the unit is in a static state, and the generator circuit breaker 3 is in the open position, disconnecting the unit from the grid. During this period, even if the generator motor differential 14-A and generator motor differential 24-B experience phase sequence commutation or short-term disconnection, any maloperation will not affect the grid. Conversely, the main transformer 1 will always be energized under unit operation conditions. During the selection between power generation and pumping operation, if the main transformer differential 16-A and main transformer differential 26-B maloperate during phase sequence commutation or short-term disconnection, it will cause the circuit breakers on each side of the main transformer 1 to trip erroneously.

[0048] Therefore, the improved technical solution of the present invention improves upon the following: Figure 1 The main wiring diagram shown is readjusted by swapping the positions of phase-changing switch 2 and generator circuit breaker 3, and reconfiguring the main protection of the generator-transformer unit, as follows: Figure 3 As shown.

[0049] It can be seen that, while meeting the requirements of no dead zone, reliability, speed, and selectivity for the generator-transformer unit protection, the main protection for main transformer 1 eliminates the main transformer minor differential protection 17-A and 17-B, retaining only the main transformer major differential protection, thus simplifying the main protection for main transformer 1. The configured main transformer major differential protection 16-A and 16-B will not cause phase sequence commutation or short-term shutdown issues due to various unit operating condition transitions, resolving the problem of maloperation of the main protection for main transformer 1 that may be caused by the unit's selection of power generation or pumping operation. The improved scheme of this invention not only simplifies the configuration of the main protection for main transformer 1 but also further improves the reliability of the main transformer 1 protection.

[0050] The main protection for generator motor 5 retains generator motor differential protection 14-A and 14-B, as well as generator motor differential protection 15-A and 15-B, which are always online and do not exit the protection. However, generator motor differential protection 14-A and 14-B need to exit during automatic start-up in pumping mode and during shutdown and power-on braking. In addition, they also need to add phase sequence reversing function when the unit selects between generating and pumping modes. However, the phase sequence reversing of generator motor differential protection 14-A and 14-B is performed when generator circuit breaker 3 disconnects the unit from the grid and the unit is in a stationary state (generator motor 5 is not energized). There will be no situation where generator motor differential protection 14-A and 14-B perform phase sequence reversing when generator motor 5 is energized, thus ensuring the reliability of the main protection for generator motor 5.

[0051] After adopting the system of the present invention for improving the reliability of the generator-transformer protection of AC excitation variable speed energy storage unit, the start-up and shutdown procedures of the AC excitation variable speed energy storage unit with self-starting capability are as follows: Under pumping conditions, First, the commutator switch 2 is switched to the pumping position. The turbine casing is purged and drained. After successful purging and draining, the stator short-circuit switch 4 is closed. The AC excitation system 10 provides power to drive the turbine to accelerate in the pumping direction. After the turbine accelerates from zero speed to the minimum speed required for grid connection, the AC excitation system 10 stops providing power and removes the magnetic flux of the generator motor 5. When the current flowing through the stator short-circuit switch 4 approaches zero, the stator short-circuit switch 4 is disconnected. After the stator short-circuit switch 4 is disconnected, the AC excitation system 10 is restarted, and the voltage, frequency, and phase of the generator motor 5 are controlled and adjusted. When the grid connection conditions are met, the generator circuit breaker 3 is closed. Then, the turbine is purged and filled with water. The guide vanes and inlet valve are opened, and the turbine absorbs active power from the grid. The turbine pumping operation is now complete. During the switching of phase switch 2 to the pumping phase sequence position, generator circuit breaker 3 remains in the open position, and main transformer 1 remains energized. The operation of phase switch 2 only changes the phase sequence from phase switch 2 to the stator windings of the generator motor (including the busbars connecting them). The low-voltage side of main transformer 1, generator circuit breaker 3, and the busbar phase sequence to phase switch 2 are completely unaffected. The main transformer differential 16-A and the main transformer differential 216-B remain in operation throughout the entire process, without the need for phase sequence commutation or short-term shutdown, thus completely avoiding the major hidden danger of vacuum protection during the energization of the main transformer in the original technology. During the startup process of the unit in pumping mode, the stator short-circuit switch 4 is closed, the generator motor large differential 14-A and generator motor large differential 2 14-B are disconnected, and the generator motor small differential 15-A and generator motor small differential 2 15-B are put into normal operation.

[0052] After grid connection, generator motors with large differential pressure 14-A and 14-B, generator motors with large differential pressure 2, generator motors with small differential pressure 15-A and 15-B all operated normally. Under power generation conditions, First, switch 2 to the generator position, open the inlet valve, engage the speed governor, and open the guide vanes. The potential energy of the water drives the generator to accelerate in the generator direction. After the generator reaches the minimum speed required for grid connection from zero speed, engage the AC excitation system 10 and control and adjust the terminal voltage, frequency, and phase of the generator motor 5. When the grid connection conditions are met, close the generator circuit breaker 3, and the generator's generator operation is started. When the phase-changing switch 2 is switched to the generating position, the rotor winding of the generator motor 5 is provided with an adjustable excitation current in terms of amplitude, frequency and phase by the AC excitation system 10. The stator side generates electricity through the stator short-circuit switch 4, the phase-changing switch 2, the generator circuit breaker 3 and the main transformer 1. At the same time, the low-voltage side of the main transformer 1 supplies power to the plant through the current-limiting reactor 12 and the plant branch circuit breaker 13. When the phase sequence switch 2 is switched to the generating phase sequence position, the generator circuit breaker 3 is tripped, and the main transformer 1 continues to operate under energized conditions. During the entire process of the unit starting up under generating conditions until the generator circuit breaker 3 closes and is connected to the grid for power generation, the phase sequence of the low-voltage side of the main transformer remains unchanged throughout the phase sequence switching process of the phase sequence switch 2. The two sets of differential protection of the main transformer 1 always maintain the original phase sequence and are engaged throughout the entire process, without any phase switching or protection deactivation operations. During the generator start-up process under power generation conditions until the generator circuit breaker 3 is closed and connected to the grid, the generator motors with large differential pressure 1 14-A, large differential pressure 2 14-B, small differential pressure 1 15-A, and small differential pressure 2 15-B are all in normal operation. Shutdown During the shutdown process, a shutdown command is issued to the speed governor and AC excitation system. The unit reduces active and reactive power to no load, disconnects the generator circuit breaker 3, closes the stator short-circuit switch 4, and uses the energy feedback method of the AC excitation system 10 to achieve electrical feedback braking. The mechanical brake is then engaged, the unit speed is reduced to zero, the mechanical brake is disengaged, the stator short-circuit switch 4 is opened, and the unit shutdown process is completed.

[0053] During the unit shutdown, the main transformer differential 16-A and the main transformer differential 26-B remain in operation throughout the entire process, without the need for phase sequence commutation or short-term shutdown. During unit shutdown, when stator short-circuit switch 4 is closed, generator motors 14-A (large differential) and 14-B (large differential) are disengaged and regenerative braking is engaged. After unit shutdown is completed, generator motors 14-A (large differential) and 14-B (large differential) and 15-A (small differential) and 15-B (small differential) are all put into normal operation. Under fault conditions, When an electrical fault occurs in the generator motor, the generator motor protection will trip, tripping generator circuit breaker 3, causing the unit to shut down due to an electrical accident. Plant auxiliary branch circuit breaker 13 will remain closed, ensuring continuous operation of plant auxiliary power. When an electrical fault occurs in the main transformer, the main transformer protection will trip generator circuit breaker 3, disconnect the high-voltage side circuit breaker of the main transformer, cause the unit to shut down due to an electrical accident, trip plant auxiliary branch circuit breaker 13, and simultaneously switch to the backup plant auxiliary power supply to ensure continuous operation of plant auxiliary power.

[0054] In this invention, the phase-changing switch 2 is always located on the generator circuit breaker 3 unit side. When switching between power generation and pumping operation, only the phase sequence of the phase sequence from the reversing switch 4 to the generator terminal bus and stator winding is changed. The phase sequence of the circuit from the low-voltage side of the main transformer and the generator circuit breaker 3 to the reversing switch 4 is completely constant. No matter how many times the operation is switched back and forth, the dual differential protection of the main transformer always operates continuously with the original phase sequence, without the need for phase switching and with zero exit throughout the entire process.

[0055] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A system for improving the protection reliability of AC-excited variable-speed energy storage units, characterized in that, The AC-excited variable speed energy storage unit includes a main transformer (1), a phase switching switch (2), a generator circuit breaker (3), a stator short-circuit switch (4), a generator motor (5), an AC excitation system (10), a disconnecting switch (11), a current-limiting reactor (12), and a plant branch circuit breaker (13). The stator side output terminal of the generator motor (5) is connected to the low-voltage side of the main transformer (1) after passing through the stator short-circuit switch (4), the phase switching switch (2), and the generator circuit breaker (3) in sequence. The rotor output terminal of the generator motor (5) is connected to the low-voltage side of the main transformer (1) after passing through the AC excitation system (10), the current-limiting reactor (12), and the disconnecting switch (11); The plant power supply is connected to the disconnecting switch (11) via the plant branch circuit breaker (13) and the current limiting reactor (12) in sequence; The main transformer (1) has only a dual-configuration main protection differential; The generator motor (5) is equipped with main protection large differential and small differential protection, both of which are dual-configuration.

2. The system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 1, characterized in that, The AC excitation system (10) includes: an AC excitation input circuit breaker (6), an AC excitation input transformer (7), a frequency converter (8), and an overvoltage protection device (9) connected in series; wherein the overvoltage protection device (9) is connected to the rotor output terminal of the generator motor (5), and the AC excitation input circuit breaker (6) is connected to the disconnecting switch (11) via a current-limiting reactor (12).

3. The system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 2, characterized in that, The main transformer (1) is equipped with main transformer differential protection system 1 (16-A) and main transformer differential protection system 2 (16-B).

4. The system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 3, characterized in that, The two sets of differential connections of the main transformer (1) are: the end of the generator circuit breaker (3) near the phase-changing switch (2) is connected to the high-voltage side of the main transformer (1).

5. The system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 4, characterized in that, The two sets of large differential circuits of the main transformer (1) are also connected to the high-voltage side of the main transformer (1): the end of the plant branch circuit breaker (13) that is far away from the current limiting reactor (12) is connected to the high-voltage side of the main transformer (1).

6. The system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 5, characterized in that, The two sets of large differential circuits of the main transformer (1) are also connected to the AC excitation input circuit breaker (6) at one end near the AC excitation input transformer (7) and the high voltage side of the main transformer (1).

7. The system for improving the reliability of protection of AC excitation variable speed energy storage unit generator-transformer unit according to claim 2, characterized in that, The main protection configuration of the generator motor (5) includes generator motor large differential protection 1 (14-A), generator motor large differential protection 2 (14-B), generator motor small differential protection 1 (15-A), and generator motor small differential protection 2 (15-B).

8. The system for improving the reliability of protection of AC excitation variable speed energy storage unit generator-transformer unit according to claim 7, characterized in that, The two sets of differential protection for the generator motor (5) are connected to the neutral point side of the generator motor (5) and the end of the generator circuit breaker (3) near the main transformer (1).

9. A system for improving the reliability of generator-transformer protection in an AC-excited variable-speed energy storage unit according to claim 7, characterized in that, The two sets of differential protection for the generator motor (5) are respectively connected to the neutral point side and the stator side output terminals of the generator motor (5).

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