A test method for networking and islanding of a hydroelectric generating set

Abstract

This invention discloses a test method for switching a hydro-generator unit from grid connection to islanded operation, relating to the field of hydropower control technology. The method includes: constructing a first overspeed protection mechanism based on the turbine generator unit's speed, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation; constructing a second overspeed protection mechanism based on the turbine generator unit's speed and the main and auxiliary displacement signals on the governor cabinet side; and further constructing a coordinated overspeed protection mechanism for the turbine generator unit; using the coordinated overspeed protection mechanism to perform overspeed protection on the turbine generator unit, thereby achieving the switch from grid connection to islanded operation; switching the turbine generator unit to islanded control mode, and using dynamically optimized PID parameters for frequency and voltage regulation. This invention, by improving the first overspeed protection mechanism, adding a second overspeed protection mechanism, and dynamically optimizing the PID parameters, solves the problem of protection maloperation during load shedding and ensures a smooth switch from grid connection to islanded operation.

Description

Technical Field

[0001] This invention relates to the field of hydropower control technology, specifically to a test method for switching a hydro-turbine generator unit from grid connection to islanded grid connection. Background Technology

[0002] In some regions, due to weak connections between local power grids and the main grid, when a local power grid is disconnected from the main grid, it is necessary for hydro-generator units to operate in isolated mode to ensure power supply and improve the reliability of the regional power grid. The smooth transition of hydro-generator units from grid-connected operation to isolated operation is crucial for ensuring the continuity of power supply from the local power grid.

[0003] Traditional methods for switching hydro-generator units from grid-connected to islanded operation employ a 115% overspeed emergency shutdown command logic. This logic requires three conditions to be met simultaneously: the hydro-generator unit exceeding 115% of its rated speed, main distribution failure, and guide vane opening greater than the no-load opening. This method has the following problems: the criterion for main distribution failure is based on the main distribution position signal from the governor cabinet side to determine whether the main distribution unit is in the neutral position and closed direction. However, during load shedding, the main distribution unit's displacement trajectory is a sawtooth waveform passing through the neutral position. Therefore, using the main distribution position signal from the governor cabinet side is prone to misjudgment, causing the three conditions to be simultaneously met during load shedding, triggering an emergency shutdown of the hydro-generator unit and preventing islanded operation.

[0004] In addition, after the hydro-generator unit is connected to the grid and then switched to islanded operation, the frequency and voltage stability during islanded operation are also critical issues. Therefore, reasonable PID parameter settings are required to ensure power supply quality. Summary of the Invention

[0005] To address the aforementioned shortcomings in the existing technology, this invention provides a test method for switching a hydro-generator unit from grid connection to islanded grid connection.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A test method for switching a hydro-generator unit from grid-connected to islanded grid includes the following steps: A first overspeed protection mechanism is constructed based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. A second overspeed protection mechanism is constructed based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side. The priority of the second overspeed protection mechanism is set to be higher than that of the first overspeed protection mechanism, so as to construct an overspeed collaborative protection mechanism for the hydro-generator unit. After the local power grid of the hydro-generator unit is disconnected from the main grid, the overspeed cooperative protection mechanism of the hydro-generator unit is used to protect the hydro-generator unit from overspeed, so as to realize the connection of the hydro-generator unit to the islanded grid. After the hydro-generator unit switches to isolated grid operation, it switches to isolated grid control mode and uses PID parameters optimized through dynamic testing for frequency and voltage regulation.

[0007] Furthermore, the guide vane opening deviation on the governor cabinet side is the difference between the guide vane opening command and the guide vane opening feedback value. Both the guide vane opening command and the guide vane opening feedback value are directly collected and generated by the governor cabinet side.

[0008] Furthermore, a first overspeed protection mechanism is constructed based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. The specific process is as follows: Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

[0009] Furthermore, the threshold is set to 5%, the preset duration is 800ms, and the median threshold is the median reference value of the main and auxiliary displacement signals on the speed controller cabinet side.

[0010] Furthermore, a second overspeed protection mechanism is constructed based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Based on the main and auxiliary displacement signals on the governor cabinet side, it is determined whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range. If so, it is determined that the governor adjustment of the hydro-generator unit is normal, and the emergency shutdown warning command of the second overspeed protection mechanism is locked. Otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered.

[0011] Furthermore, the second overspeed protection mechanism is set to have a higher priority than the first overspeed protection mechanism to construct a coordinated overspeed protection mechanism for the hydro-generator unit. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. The second overspeed protection mechanism is activated to monitor the main and auxiliary displacement signals on the governor cabinet side in real time, and simultaneously collect the main and auxiliary displacement signals and guide vane opening deviation on the governor cabinet side. Based on the main and auxiliary displacement signals on the governor cabinet side, determine whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range; if so, it is determined that the governor adjustment of the hydro-generator unit is normal, the emergency shutdown warning command of the second overspeed protection mechanism is locked and the subsequent steps are entered; otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered. Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

[0012] Furthermore, the specific process of dynamic experimental optimization is as follows: Frequency response data of the hydro-generator unit were collected during load shedding tests at 20% and 50% loads; Adjust the PID parameters based on the frequency response data of the hydro-generator unit until the frequency fluctuation range is stabilized within ±0.25Hz.

[0013] Furthermore, PID parameters include proportional gain, integral gain, derivative gain, and permanent slip coefficient.

[0014] The beneficial effects of this invention are as follows: (1) This invention constructs a first overspeed protection mechanism based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. It improves the main and auxiliary position switch signals used in the existing overspeed protection mechanism into a composite criterion of "the main and auxiliary displacement signals on the governor cabinet side and the guide vane opening deviation". This effectively filters out signal fluctuations during normal adjustment, avoids misjudging dynamic adjustment as failure to operate, and solves the pain point of the existing technology that "leads to emergency shutdown of the unit during load shedding, making it impossible to achieve isolated grid operation". In addition, the data required in the composite criterion are all from the analog signal acquisition of the governor cabinet, replacing the main and auxiliary position switch signals in the existing technology. This avoids the problems of easy wear, easy interference, and difficult installation and adjustment of mechanical limit switches, and improves the reliability of the signal source and the accuracy of the criterion. (2) This invention constructs a second overspeed protection mechanism based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side, and sets the priority of the second overspeed protection mechanism to be higher than that of the first overspeed protection mechanism, so as to construct a coordinated overspeed protection mechanism for the hydro-generator unit. The first overspeed protection mechanism pursues accuracy (preventing false tripping), while the second overspeed protection mechanism pursues reliability (preventing failure to tripping), and the two complement each other. In the 50% load shedding test, although the second overspeed protection mechanism tripped once, this invention adjusts it to only trigger the emergency shutdown warning command of the second overspeed protection mechanism and does not issue an emergency shutdown command. This not only preserves its redundant monitoring value, but also eliminates the risk of false tripping, which has high engineering value. (3) This invention dynamically optimizes the PID parameters of the isolated grid through load shedding tests at 20% and 50% load, effectively suppressing the guide vane oscillation caused by excessive derivative, making the adjustment process more stable, reducing mechanical wear and fatigue of the control system, and enabling zero-error frequency regulation in the isolated grid mode. No matter how the load changes, the frequency can eventually return to 50Hz, significantly improving the power supply quality of the isolated grid. Attached Figure Description

[0015] Figure 1 A schematic diagram of a test method for switching a hydro-generator unit from grid-connected to islanded grid; Figure 2 Waveform diagram of threshold verification for primary and secondary disengagement criteria; Figure 3 The waveform of the test when the frequency step is 0.4Hz during the frequency step anti-malfunction test; Figure 4 The waveform of the test when the frequency step is 0.6Hz during the frequency step anti-malfunction test; Figure 5 The waveform of the test when the frequency step is 8Hz during the frequency step anti-malfunction test; Figure 6 Test waveform diagram of limiting the main and auxiliary actions during the test of preventing false activation of the main and auxiliary action signals; Figure 7 This is a test waveform diagram showing the allowed main and auxiliary actions during the test to prevent malfunction of the main and auxiliary action signals. Detailed Implementation

[0016] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0017] like Figure 1As shown, a test method for switching a hydro-generator unit from grid-connected to islanded grid includes steps S1-S3, as detailed below: S1. Based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation, a first overspeed protection mechanism is constructed. Based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side, a second overspeed protection mechanism is constructed. The priority of the second overspeed protection mechanism is set to be higher than that of the first overspeed protection mechanism, so as to construct an overspeed collaborative protection mechanism for the hydro-generator unit.

[0018] In an optional embodiment of the present invention, the guide vane opening deviation on the speed controller cabinet side is the difference between the guide vane opening command and the guide vane opening feedback value, both of which are directly collected and generated by the speed controller cabinet side.

[0019] This invention constructs a first overspeed protection mechanism based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. The specific process is as follows: Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

[0020] The threshold is set to 5%, the preset duration is 800ms, and the median threshold is the median reference value of the main and auxiliary displacement signals on the speed controller cabinet side.

[0021] Specifically, the present invention sets the preset duration of the first set of protection logic to 800ms, which is based on the inherent response characteristics of the main pressure regulating valve and guide vane adjustment equipment. This duration is greater than the maximum normal response time of the speed controller, which is 500ms. This can effectively filter the sawtooth waveform signal fluctuations generated by the normal adjustment of the main and guide valves during the load shedding process and prevent false judgment and failure to operate. It can also ensure timely triggering of protection when there is actual jamming. It is an engineering choice that takes into account both preventing false operation and preventing failure to operate.

[0022] This invention constructs a second overspeed protection mechanism based on the rotational speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Based on the main and auxiliary displacement signals on the governor cabinet side, it is determined whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range. If so, it is determined that the governor adjustment of the hydro-generator unit is normal, and the emergency shutdown warning command of the second overspeed protection mechanism is locked. Otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered.

[0023] Specifically, this invention monitors whether a main control valve action signal has occurred on the governor cabinet side within the monitoring range. That is, it determines whether the main control valve core has left the neutral position based on the main control valve displacement signal on the governor cabinet side. If so, it indicates that a main control valve action signal has occurred; otherwise, it indicates that no main control valve action signal has occurred. In two 50% load shedding tests, this invention performed four verifications on each of the two overspeed protection mechanisms. The signal overspeed protection from the second overspeed protection mechanism malfunctioned once. Therefore, this invention modifies the second overspeed protection mechanism to only issue an emergency shutdown warning command, but does not issue an emergency shutdown command. This retains its monitoring function (to remind maintenance personnel) while avoiding unplanned shutdowns of the turbine generator unit due to malfunctions.

[0024] This invention sets the priority of the second overspeed protection mechanism higher than that of the first overspeed protection mechanism to construct a collaborative overspeed protection mechanism for hydro-generator units. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. The second overspeed protection mechanism is activated to monitor the main and auxiliary displacement signals on the governor cabinet side in real time, and simultaneously collect the main and auxiliary displacement signals and guide vane opening deviation on the governor cabinet side. Based on the main and auxiliary displacement signals on the governor cabinet side, determine whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range; if so, it is determined that the governor adjustment of the hydro-generator unit is normal, the emergency shutdown warning command of the second overspeed protection mechanism is locked and the subsequent steps are entered; otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered. Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

[0025] S2. After the local power grid of the hydro-generator unit is disconnected from the main grid, the overspeed cooperative protection mechanism of the hydro-generator unit is used to protect the hydro-generator unit from overspeed, so as to realize the connection of the hydro-generator unit to the islanded grid.

[0026] In an optional embodiment of the present invention, when the local power grid of the hydro-generator unit is disconnected from the main grid, causing the hydro-generator unit to shed load and its speed to increase sharply, the overspeed collaborative protection mechanism of the hydro-generator unit ensures the safe transfer of the hydro-generator unit to islanded operation by having two independent overspeed protection mechanisms with set priorities work in parallel. The first overspeed protection mechanism can accurately distinguish between actual failure to operate in the main grid and normal fluctuations during dynamic adjustment, preventing unplanned shutdowns due to misjudgment. Simultaneously, the second overspeed protection mechanism provides a final safety line for the first overspeed protection mechanism in case of missed judgments, delays, or cabinet failures. Through a collaborative mechanism of "time-sharing start-up, independent judgment, and priority arbitration," the two overspeed protection mechanisms ensure that the unit can successfully transfer to islanded operation under most operating conditions (preventing false operation) and prevent overspeed accidents caused by protection failure under extreme operating conditions (preventing failure to operate), ultimately achieving a balance between safety and reliability in the process of switching from grid connection to islanded operation.

[0027] S3. After the hydro-generator unit switches to isolated grid operation, the hydro-generator unit switches to isolated grid control mode and uses PID parameters optimized by dynamic testing for frequency and voltage regulation.

[0028] In an optional embodiment of the present invention, the specific process of dynamic test optimization is as follows: Frequency response data of the hydro-generator unit were collected during load shedding tests at 20% and 50% loads; Adjust the PID parameters based on the frequency response data of the hydro-generator unit until the frequency fluctuation range is stabilized within ±0.25Hz.

[0029] PID parameters include proportional gain, integral gain, derivative gain, and permanent slip coefficient.

[0030] The specific experimental process of this invention is as follows: 1. With the hydro-generator unit in a static state, the main and auxiliary power supply failure threshold verification, frequency step anti-maloperation test, and main and auxiliary power supply action signal anti-maloperation test are performed using the debugging software.

[0031] Main component misalignment test: In this invention, the main component is fixed (simulating jamming), the guide vane deviation is forced to 4.9%, and the simulated rotational speed exceeds 115%. For example... Figure 2As shown, when the guide vane deviation jumps from 0 to 4.9%, no main controller failure signal is issued. When the guide vane deviation jumps from 0 to 5.1%, the governor issues a main controller failure signal after 800ms. This proves the rationality of the 5% threshold set for guide vane opening deviation in the first overspeed protection mechanism, i.e., it does not falsely alarm when the deviation is below the threshold, and reliably issues a signal when the deviation is above the threshold after a delay of 800ms.

[0032] Frequency Step Anti-maloperation Test: This invention simulates grid connection of a hydro-generator unit, performing a frequency feedback step test to check whether the governor can switch to frequency mode normally and whether the main and distribution units will falsely report a failure to operate. The frequency deviation of the governor from grid-connected to islanded mode is 0.5Hz. Figure 3 As shown, the frequency fluctuation is 0.4Hz, and both the main actuator and guide vane deviations have outputs. Neither the main actuator failure nor the frequency switching mode signals are transmitted. Figure 4 As shown, the frequency step is 0.6Hz, and both the guide vane opening deviation and the main control outputs are active. The frequency mode switch operates, and the main control switch does not malfunction. (As shown) Figure 5 As shown, the frequency step is 8Hz, and both the guide vane opening deviation and the main and auxiliary switches have outputs. The frequency mode switch is activated, and the main and auxiliary switch does not malfunction. The frequency step anti-malfunction test verifies the anti-interference capability of the first overspeed protection mechanism, confirming that the main and auxiliary switch malfunction signal will not be malfunctioning during normal speed governor adjustment (including mode switching), proving that the 800ms delay and composite criteria effectively filter out dynamic interference.

[0033] Main and auxiliary action signal anti-malfunction test: such as Figure 6 As shown, the main and auxiliary actions are restricted, the speed is increased, and after reaching 115% speed, a speed failure signal is received, and an emergency stop order is issued. Figure 7 As shown, the main control system is allowed to operate, increasing the speed. A main control system operation signal is received in the 105%-115% range, but no emergency stop order is issued at 115%. The main control system operation signal anti-maloperation test proves that the first overspeed protection mechanism did not maloperate during the static test.

[0034] II. Dynamic test optimization of PID parameters, tuning the optimal control parameters in islanded network mode, including load shedding tests at 20% load and 50% load.

[0035] 20% load shedding test: Initially, the isolated grid PID controller had a proportional gain of 200, an integral gain of 20, a derivative gain of 30, and a permanent slip coefficient of 1. Test results: The turbine generator frequency peaked at 53.7Hz, reaching 49.8~50.2Hz within 40 seconds, and then stabilized with fluctuations ≤±0.25Hz; the terminal voltage peaked at 103%, stabilizing within 31 seconds; the governor and excitation regulator did not report any faults. The 20% load shedding test demonstrated that the initial parameters of "proportional gain 200, integral gain 20, derivative gain 30, and permanent slip coefficient 1" are basically usable, but there is still room for optimization in the adjustment process.

[0036] The 50% load shedding test (extreme condition optimization) includes the first test (proportional gain of 200, integral gain of 20, derivative gain of 30, and permanent slip coefficient of 1) and the second test (optimized parameters: proportional gain of 200, integral gain of 20, derivative gain of 20, and permanent slip coefficient of 0).

[0037] First test (proportional gain 200, integral gain 20, derivative gain 30, permanent slip coefficient 1): The highest frequency was 60.3Hz, with large fluctuations and a long duration. Analysis: The derivative gain of 30 resulted in excessively strong derivatives, exacerbating the sawtooth waveform of the master and slave displacements and causing guide vane oscillation. Parameter optimization: The derivative gain was reduced from 30 to 20 to suppress guide vane oscillation; the permanent slip coefficient was reduced from 1 to 0 to achieve zero-error frequency modulation on an isolated network and eliminate steady-state frequency error.

[0038] The second test (optimized parameters: proportional gain of 200, integral gain of 20, derivative gain of 20, and permanent slip coefficient of 0): the highest frequency was still 60.3Hz (determined by energy conservation), but it entered the 50.2Hz~49.8Hz range for the first time within 31 seconds, and the fluctuation stabilized within 50±0.2Hz after 44 seconds; the terminal voltage was 104% at its highest and 86% at its lowest, and stabilized within 28 seconds; the first and second overspeed protection mechanisms were verified 4 times. The first overspeed protection mechanism did not malfunction, while the second overspeed protection mechanism malfunctioned once. Therefore, this invention modifies the second overspeed protection mechanism to only issue an emergency shutdown warning command, but does not issue an emergency shutdown command. This retains its monitoring function (to remind maintenance personnel) and avoids unplanned shutdown of the turbine generator unit due to malfunction. The second test (optimized parameters: proportional gain of 200, integral gain of 20, derivative gain of 20, and permanent slip coefficient of 0) proved the effectiveness of parameter optimization under harsh operating conditions: it was confirmed that after reducing the derivative coefficient (anti-oscillation) and eliminating the permanent slip coefficient (achieving zero-difference frequency modulation), the stability of the island network was significantly improved (stabilized at ±0.2Hz for 44 seconds).

[0039] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A test method for switching a hydro-generator unit from grid-connected to islanded grid, characterized in that, Includes the following steps: A first overspeed protection mechanism is constructed based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. A second overspeed protection mechanism is constructed based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side. The priority of the second overspeed protection mechanism is set to be higher than that of the first overspeed protection mechanism, so as to construct an overspeed collaborative protection mechanism for the hydro-generator unit. After the local power grid of the hydro-generator unit is disconnected from the main grid, the overspeed cooperative protection mechanism of the hydro-generator unit is used to protect the hydro-generator unit from overspeed, so as to realize the connection of the hydro-generator unit to the islanded grid. After the hydro-generator unit switches to isolated grid operation, it switches to isolated grid control mode and uses PID parameters optimized through dynamic testing for frequency and voltage regulation.

2. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, The guide vane opening deviation on the speed controller cabinet side is the difference between the guide vane opening command and the guide vane opening feedback value. Both the guide vane opening command and the guide vane opening feedback value are directly collected and generated by the speed controller cabinet side.

3. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, The first overspeed protection mechanism is constructed based on the speed of the hydro-generator unit, the main and auxiliary displacement signals on the governor cabinet side, and the guide vane opening deviation. The specific process is as follows: Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

4. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, The threshold is set to 5%, the preset duration is 800ms, and the median threshold is the median reference value of the main and auxiliary displacement signals on the speed controller cabinet side.

5. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, A second overspeed protection mechanism is constructed based on the speed of the hydro-generator unit and the main and auxiliary displacement signals on the governor cabinet side. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if so, proceed to the next step; otherwise, return to the current step. Based on the main and auxiliary displacement signals on the governor cabinet side, it is determined whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range. If so, it is determined that the governor adjustment of the hydro-generator unit is normal, and the emergency shutdown warning command of the second overspeed protection mechanism is locked. Otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered.

6. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, The second overspeed protection mechanism is set to have a higher priority than the first overspeed protection mechanism to construct a coordinated overspeed protection mechanism for the hydro-generator unit. The specific process is as follows: Determine whether the speed of the hydro-generator unit has entered the monitoring range, which is 105%-115% of the rated speed; if so, proceed to the next step; otherwise, return to the current step. The second overspeed protection mechanism is activated to monitor the main and auxiliary displacement signals on the governor cabinet side in real time, and simultaneously collect the main and auxiliary displacement signals and guide vane opening deviation on the governor cabinet side. Based on the main and auxiliary displacement signals on the governor cabinet side, determine whether a main and auxiliary action signal has occurred on the governor cabinet side within the monitoring range; if so, it is determined that the governor adjustment of the hydro-generator unit is normal, the emergency shutdown warning command of the second overspeed protection mechanism is locked and the subsequent steps are entered; otherwise, when the speed of the hydro-generator unit reaches 115% of the rated speed, the emergency shutdown warning command of the second overspeed protection mechanism is triggered. Determine if the speed of the hydro-generator unit is greater than 115% of the rated speed; if yes, proceed to the next step; otherwise, return to the current step. Determine whether the guide vane opening deviation on the governor cabinet side is greater than the set threshold, and whether the main and auxiliary displacement signals on the governor cabinet side are continuously less than the median threshold within a preset time; if so, it is determined that the turbine generator set has experienced main and auxiliary failure to operate, and the shutdown command of the first overspeed protection mechanism is triggered.

7. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, The specific process of dynamic experiment optimization is as follows: Frequency response data of the hydro-generator unit were collected during load shedding tests at 20% and 50% loads; Adjust the PID parameters based on the frequency response data of the hydro-generator unit until the frequency fluctuation range is stabilized within ±0.25Hz.

8. The test method for switching hydro-generator units from grid connection to islanded grid as described in claim 1, characterized in that, PID parameters include proportional gain, integral gain, derivative gain, and permanent slip coefficient.

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