Injection direct current type rotor grounding protection method based on switching time dynamic adjustment

Abstract

The invention discloses an injection direct current type rotor grounding protection method based on switching time dynamic adjustment. The method comprises the following steps: acquiring a decay time constant of a leakage current transient component; setting an electronic switch switching time rule; determining an initial value of switching time of the electronic switch; during normal operation, if the sampling value of the leakage current is unstable, the switching time of the electronic switch is dynamically adjusted; if the grounding fault occurs, dynamically adjusting the switching time of the electronic switch to obtain the switching time of the electronic switch when the fault occurs; after the switching time of the electronic switch is dynamically adjusted, obtaining grounding resistance; and after the grounding fault is processed, the switching time of the electronic switch is adjusted to the switching time of the electronic switch during normal operation. The problem that the grounding resistance cannot be accurately measured under the condition that the equivalent distributed capacitance is relatively large is solved, and the time error of rotor grounding protection action delay is considered at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of generator rotor grounding protection, and in particular to an injection DC type rotor grounding protection method based on dynamic adjustment of switching time. Background Technique

[0002] The generator is a core device of the power system, and its stable operation is crucial for the reliability of power supply. One-point grounding of the generator excitation circuit is one of the common fault forms of the excitation winding. Although it does not cause harm to the generator, if a second point grounding occurs successively, the following impacts will be brought: a large fault current flows through the fault point, burning the rotor body; the excitation winding is burned due to overheating; the air-gap magnetic flux loses balance, causing vibration and leading to serious consequences.

[0003] When a rotor grounding fault occurs in the generator rotor winding, the rotor grounding protection accurately indicates the magnitude of the grounding resistance within the shortest possible time and the smallest possible range, and issues a signal to remind the operator to handle it or automatically stop the generator.

[0004] At present, the injection DC type rotor grounding protection is the most widely used. Compared with the bridge type and switching sampling type rotor grounding protection, it has higher sensitivity and can also monitor and protect the insulation of the rotor winding in the shutdown state; compared with the superimposed square wave voltage type rotor grounding protection, its injection power supply does not require additional power accessories and can be injected through the DC voltage of the protection device.

[0005] However, the existing injection DC type rotor grounding protection does not consider the influence of the ground capacitance of the excitation winding on the measurement and calculation of the grounding resistance, resulting in inaccurate measurement results. Therefore, the present invention proposes an injection DC type rotor grounding protection method based on dynamic adjustment of switching time. Summary of the Invention

[0006] To solve the current technical problems, the main purpose of the present invention is to provide an injection DC type rotor grounding protection method based on dynamic adjustment of switching time, aiming to propose the determination rule of the electronic switch switching time and the dynamic adjustment mechanism of the electronic switch switching time, while taking into account the action delay error of the rotor grounding protection, and solving the problem that the grounding resistance cannot be accurately measured under the condition of a large equivalent distributed capacitance.

[0007] To overcome the problems existing in the prior art, the technical solution adopted by the present invention is: an injection DC type rotor grounding protection method based on dynamic adjustment of switching time, including the following steps: S1. Obtain the decay time constant of the leakage current transient component; S2. Set the electronic switch switching time rule; S3. Determine the initial value of the electronic switch switching time ; S4. During normal operation, if the sampled value of the leakage current is unstable, dynamically adjust the switching time of the electronic switch. ; S5. If a ground fault occurs, dynamically adjust the switching time of the electronic switch to obtain the switching time of the electronic switch during the fault. ; S6. After the switching time of the electronic switch is dynamically adjusted, obtain the ground resistance. S7. After the ground fault is processed, adjust the switching time of the electronic switch to the switching time of the electronic switch during normal operation.

[0008] In S1, the calculation formula for the decay time constant is: ; In the formula: represents the decay time constant; represents the injection resistance parameter in the protection device; represents the ground resistance; represents the capacitance of the excitation winding to the ground.

[0009] In S2, the rule for the switching time of the electronic switch is: S21. Determine the value of the transient process time, and the value of the transient process time is equal to the decay time constant. S21. The initial moment for calculating the ground resistance is after the transient process ends and then after the first preset time period. S22. Calculate the ground resistance using the sampled value of the leakage current within the second preset time period after the first preset time period.

[0010] In S3, use the injection DC type rotor ground protection injection loop resistance, the maximum measured value of the ground resistance, and the maximum distributed capacitance of the excitation winding to obtain the decay time constant. According to the rule of the switching time of the electronic switch, obtain the time of the transient process and the start moment for calculating the ground resistance, and then determine the initial value of the switching time of the electronic switch. .

[0011] In S4, after the initial value of the switching time of the electronic switch is determined, if the sampled value of the leakage current is unstable, or the calculated value of the ground resistance fluctuates, then add the time step to the current switching time of the electronic switch ; If the measured value of the ground resistance is still unstable, then continue to add the time step to the current dynamically adjusted switching time as the new dynamically adjusted switching time , until If the calculated ground resistance is completely stable at the maximum value after several times, then this switching time is taken as the switching time of the electronic switch during normal operation, that is ; If there is no abnormality, .

[0012] In S5, if a single-point ground fault occurs in the excitation winding, the electronic switch switches by dynamically adjusting the switching time to obtain the steady-state values of the leakage current in the on and off states, and then calculate the ground resistance value at this time; calculate the time constant through the injected loop resistance, the current ground resistance value, and the maximum distributed capacitance of the excitation winding, and then obtain the switching time of the electronic switch during the fault .

[0013] In S6, after the switching time of the electronic switch is dynamically adjusted, the switching period is shortened, and the protection device calculates the ground resistance value. If the ground resistance value is less than the ground resistance setting value, the protection device issues a signal or trips. The calculation method of the ground resistance value is as follows: When the electronic switch S1 is conducting: ; When the electronic switch S1 is cut off: ; Combining the above two equations and solving, we get: ; When : ; Then the operating criterion for the rotor single-point ground protection is: ; In the formula: represents the excitation voltage at the grounding point; represents the voltage of the injection power supply; represents the injected high-power resistor; represents the measurement loop resistance; represents the leakage current when S1 is conducting; represents the leakage current when S1 is cut off; represents the ground resistance; is the setting value of the rotor ground protection resistance.

[0014] The formulas for calculating the steady-state value and transient amplitude of the leakage current in the on and off states are as follows: ; In the formula: A represents the steady-state value of the leakage current; B represents the transient amplitude of the leakage current; is the injection resistance parameter in the protection device, and E is the injection power supply voltage and the exciting voltage sum; represents the grounding resistance. In S7, after the ground fault is processed, due to the adjustment of the switching time, the obtained leakage current or grounding resistance is not a stable value. The protection device automatically adjusts the switching time of the electronic switch to the switching time of the electronic switch during normal operation. .

[0015] The present invention has the following beneficial effects: An injection DC type rotor grounding protection method based on dynamic adjustment of switching time is invented, aiming to propose a determination rule for the switching time of the electronic switch and a dynamic adjustment mechanism for the switching time of the electronic switch. While taking into account the action delay error of the rotor grounding protection, the problem of inaccurate measurement of the grounding resistance in the case of a large equivalent distributed capacitance is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 is the schematic diagram of the injection DC type single-point rotor grounding.

[0018] Figure 2 is the simulation diagram of the leakage current when the exciting winding is not connected in parallel with a capacitor.

[0019] Figure 3 is Figure 1 equivalent circuit diagram.

[0020] Figure 4 is the simulation diagram of the leakage current when the exciting winding is connected in parallel with a 1uF capacitor.

[0021] Figure 5 is the schematic diagram of the shaft voltage suppressor.

[0022] Figure 6 is the simulation diagram of the leakage current when the exciting winding is connected in parallel with a 10µF capacitor and the switching time of the electronic switch is 1s.

[0023] Figure 7 is the simulation diagram of the leakage current when the exciting winding is connected in parallel with a 10µF capacitor and the switching time of the electronic switch is 3s.

[0024] Figure 8 is the flow chart of the dynamic adjustment mechanism of the switching time of the electronic switch of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings of the specification.

[0026] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0027] Secondly, the so-called "this embodiment" or "embodiment" herein refers to specific features, structures or characteristics that may be included in at least one implementation manner of the present invention.

[0028] Furthermore, the present invention is described in detail with reference to schematic diagrams. When detailing the embodiments of the present invention, for the sake of convenience of explanation, the cross-sectional views showing the device structure will be enlarged locally out of the general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention herein. In addition, in actual production, three-dimensional spatial dimensions including length, width and depth should be included.

[0029] The DC injection type rotor grounding protection device generates an injected DC power supply. The output terminal of the power supply is connected to the negative pole of the rotor and the large shaft to form a DC loop for measuring the rotor-to-ground resistance. According to the rotor leakage current when the electronic switch S1 is in the on state and the off state, the insulation resistance value of the excitation winding to the ground is calculated to determine whether a single-point grounding fault occurs in the excitation winding. The on-site wiring schematic diagram is as Figure 1 shown.

[0030] As Figure 1 can be seen, the entire measurement process is divided into two parts: State 1: When the electronic switch S1 is on: (1); State 2: When the electronic switch S1 is off: (2); In the formula: is the excitation voltage at the grounding point; is the voltage of the injected power supply; represents the leakage current when S1 is on; represents the leakage current when S1 is off.

[0031] By solving the equations (1) and (2) simultaneously, we get: (3); When ; (4); Then the operating criterion for the rotor single-point grounding protection is: (5); In the formula: is the setting value of the rotor grounding protection resistance.

[0032] It can be seen from formula (3) that the grounding resistance has nothing to do with the excitation voltage, the injected power supply voltage and the fault point location. Moreover, when the measured currents and are both steady-state values, it also has nothing to do with the size of the capacitance between the excitation winding and the ground. However, in actual engineering, the capacitance has an impact on the leakage current in the on and off states of the electronic switch. Figure 2 is the simulation diagram of the leakage current of the circuit when the capacitance is not connected in parallel with the excitation winding. The leakage currents in both the open and closed states of the electronic switch are stable.

[0033] However, due to the existence of the distributed capacitance between the excitation winding and the ground, a large transient current will inevitably be generated in the measurement circuit when the electronic switch S1 is turned on and off. Assume that the excitation winding is grounded through the grounding resistance and the distributed capacitance between the excitation winding and the ground is represented by the lumped parameter , then the equivalent circuit of the measurement circuit is as shown in Figure 3 .

[0034] Figure 3 In is the injected resistance parameter in the protection device, E is the sum of the injected power supply voltage and the excitation voltage . The following will specifically analyze the influence of the distributed capacitance between the excitation winding and the ground on the measurement: According to Figure 3 , the loop equation of the equivalent circuit is (6); Among them: (7); In the formula, is the charge on the capacitor. Combining formula (6) and formula (7) gives: (8); Taking the indefinite integral of both sides of formula (7), assuming when, , we get: (9); In the formula, is the time constant: (10); It can be obtained from Equation (6): (11); where A is the steady-state part of the leakage current and B is the amplitude of the transient part of the leakage current: (12); As can be seen from Equation (11), due to the existence of the distributed capacitance of the excitation winding to the ground, when the electronic switch S1 is opened and closed, and the leakage current changes, the measurement circuit will charge and discharge the distributed capacitance. Only after the charge and discharge process ends can the measured steady-state leakage current be used for calculation.

[0035] Therefore, when the electronic switch S1 is conducting and cut off, the protection device cannot immediately measure the switching current 、 , but must wait until the transient process ends before measurement. Figure 4 Figure for simulation when a 1 μF capacitor is connected in parallel with the excitation winding and the switching time is 1 second. When the electronic switch is opened and closed, the change in the leakage current obviously has a transient component decay process.

[0036] Figure 4 In , is the transient process time, is the starting moment of the grounding resistance calculation, is the switching time of the electronic switch. Taking the switching moment of the electronic switch as the starting moment of timing, after time, the transient component decays completely. Therefore, to ensure that the leakage current obtained during the grounding resistance calculation is the steady-state value, the leakage current sampling value is obtained and calculated at

[0037] When the injected power supply voltage , the excitation voltage , the grounding resistance and the internal resistance of the protection device remain unchanged, taking the switching moment of the electronic switch as the starting moment of timing, the rule for determining the switching time of the electronic switch proposed in this patent is as follows: 1) Calculate the decay time constant of the transient component of the leakage current from Equation (10); 2) The value of the transient process time is equal to the decay time constant; 3) The initial moment of the grounding resistance calculation is 20 ms after the end of the transient process to ensure the stability and reliability of the grounding resistance, that is ; 4) The grounding resistance is calculated using the leakage current sampling values within 20 ms of the steady state; 5) The switching time of the electronic switch.

[0038] According to the simulation model, the decay time constant, steady-state current value, maximum transient current value and transient process time under different excitation winding-to-ground distributed capacitance are calculated, and the results are shown in Table 1. E = 500V, R g = 10kΩ, R op =40k Ω . Table 1: Time constants , steady-state current value, transient current maximum value and transient process time, ground resistance calculation start time and electronic switch switching time comparison table

[0039] It can be seen from Table 1 that, under the condition of a certain grounding resistance, the larger the distributed capacitance of the excitation winding to the ground, the larger the attenuation time constant, the longer the transient process time, the later the sampling start time, the longer the opening and closing time of the electronic switch needs to be set, and the larger the rotor grounding protection action delay error.

[0040] It can be seen from formula (10) and Table 1 that the distributed capacitance of the excitation winding has a great influence on the decay time of the transient part of the leakage current. In general, the capacitance of the excitation winding to ground in a thermal power plant is about 1 to 3 µF, while the capacitance of the excitation winding to ground in a hydropower unit is 4 to 8 µF. In recent years, the excitation system is generally equipped with a shaft voltage suppressor to suppress the shaft voltage, that is, the excitation winding is grounded through an R and C loop at both ends. The R value is generally small, and the capacitance value is generally 2 µF to 10 µF. Therefore, the equivalent distributed capacitance of the excitation winding to ground may reach about 10 µF, such as Figure 5 shown.

[0041] In order to analyze the influence of 10µF distributed capacitance on DC injection rotor grounding protection, MATLAB is used for simulation. The DC injection voltage is 50 V , the injection resistance is 30 kΩ , grounding resistance is 30 kΩ , electronic switch switching time is 1s, then the leakage current simulation is as follows Figure 6 shown.

[0042] Depend on Figure 6 It is known that within the 1s switching cycle, the leakage current does not reach the steady-state value, and the rotor protection cannot obtain a steady-state leakage current, so the grounding resistance cannot be calculated. To ensure that the rotor protection can obtain a stable leakage current, the switching time of the electronic switch is changed to 3s, and the leakage current simulation diagram is shown in the figure below. Figure 7 shown.

[0043] Depend on Figure 6 , Figure 7It can be seen that the opening and closing time of the electronic switch affects the measurement accuracy of the grounding resistance. Moreover, the longer the opening and closing time of the electronic switch, the closer the obtained leakage current approaches the steady-state value, and the higher the measurement accuracy of the grounding resistance.

[0044] In summary, the following conclusions can be obtained: ① As can be seen from Equation (10), and / or The larger, the longer the decay time constant, and the longer the decay time of the transient component of the leakage current. Under the same grounding capacitance, the theoretical grounding resistance during normal operation of the unit is infinite, and the time constant is the longest; during metallic grounding, the time constant is the smallest, and the transient component of the leakage current is theoretically 0; ② It can be seen from Equation (10) that the injection loop resistance The larger, the longer the time constant. The injection loop resistance in the open state of the electronic switch is greater than that in the closed state. Therefore, the determination of the switching time needs to be based on the injection loop resistance in the open state of the electronic switch; ③ The opening and closing time of the electronic switch can be adjusted according to the charging and discharging conditions of the loop for various types of unit rotors to ensure the accuracy during measurement; ④ In order to obtain a grounding resistance value with higher accuracy, it is necessary to ensure that the measured current is strictly the steady-state value. However, as can be seen from Equations (1) and (2), the prerequisite for obtaining Equation (3) is to ensure that the excitation voltage remains unchanged. Therefore, the opening and closing time of the electronic switch cannot be too long. In addition, if the opening and closing time of the electronic switch is too long, it will also affect the signal and the outlet time, and this factor should be comprehensively considered when adjusting the opening and closing time.

[0045] According to the above analysis, in order to ensure the measurement accuracy of the grounding resistance of the injected DC type rotor grounding protection, the switching time of the electronic switch needs to be long enough. However, too long a switching time will increase the error of the large rotor grounding protection action delay. To solve this contradiction, see Figure 8 This patent proposes a dynamic adjustment mechanism for the switching time of the electronic switch, specifically as follows: ① Determination of the initial value of the switching time of the electronic switch.

[0046] Using the injection loop resistance of the injected DC type rotor grounding protection, the maximum measured value of the grounding resistance (the maximum range of the protection grounding resistance), and the maximum distributed capacitance of the excitation winding (the distributed capacitance between the excitation winding and the ground + the capacitance between the shaft voltage suppressor and the ground), calculate the time constant according to Equation (10), and obtain the time of the transient process and the start time of the grounding resistance calculation according to the determination principle of the switching time of the electronic switch, and then determine the initial value of the switching time of the electronic switch; ② Dynamic adjustment of the initial switching time of the electronic switch during normal operation.

[0047] After the initial value of the switching time of the electronic switch is determined, if the sampled value of the leakage current is unstable or the calculated value of the grounding resistance fluctuates greatly, the current switching time is added with the time step As the new switching time of the electronic switch. If the measured value of the grounding resistance is still not stable enough, continue to add the current switching time with the time step as the new switching time of the electronic switch until After the grounding resistance calculation is completely stable at the maximum value for times, this switching time is used as the switching time of the electronic switch during normal operation, that is .

[0048] ③ Dynamic adjustment of the switching time of the electronic switch during ground fault.

[0049] When a single point ground fault occurs in the excitation winding, the electronic switch switches through to obtain the steady-state values of the leakage current in the open and closed states, and then calculate the grounding resistance value at this time. Using the injection loop resistance, the current grounding resistance value and the maximum distributed capacitance of the excitation winding, calculate the time constant using Equation (10), and then calculate the appropriate switching time of the electronic switch .

[0050] ④ Calculation of the grounding resistance at the new switching time of the electronic switch.

[0051] After the switching time of the electronic switch is updated, the switching period is shortened, and the protection device can correctly calculate the grounding resistance. If the grounding resistance is less than the grounding resistance setting value, the protection device sends a signal or trips after a set delay, and the time error of the action delay is obviously smaller than that before the switching time is updated.

[0052] ⑤ Dynamic adjustment of the switching time of the electronic switch after ground fault handling.

[0053] After the ground fault is handled, since the adjustment of the switching time results in the obtained leakage current or grounding resistance not being a stable value, the protection device automatically adjusts the switching of the electronic switch to the switching time of the electronic switch during normal operation .

[0054] In summary, the implementation process of the dynamic adjustment mechanism of the electronic switch switching time is as Figure 8 shown.

[0055] Beneficial effects brought by the technical solution of the present invention: The dynamic adjustment mechanism of the electronic switch switching time is programmed, actually verified on the protection device, and compared with the original scheme (the electronic switch switching time is 1 s). The verification results are shown in Table 2. During the test, a 10 µF capacitor is connected in parallel to the grounding resistance, and the maximum measured value of the grounding resistance of the rotor grounding protection is 120 , and the resistance action value is set to 10 The action delay is set to 5 s.

[0056] Table 2 Comparison of the measured values of the grounding resistance and the error of the protection action delay between the two schemes of fixed and dynamically adjusted switch switching times

[0057] From Table 2, by comparing the two protection schemes, it can be seen that: ① When operating normally (without grounding resistance) or when the grounding resistance is large, the decay time constant of the leakage current is also large. Comparing the two schemes horizontally, the former (fixed switching time of the electronic switch) is more affected by the grounding resistance measurement and cannot obtain a stable resistance calculation value; the grounding resistance value measured by the latter is relatively stable. ② Vertically, the stability and accuracy of the grounding resistance measurement of the former protection scheme increase with the decrease of the grounding resistance value. In the case of metallic grounding, the decay time constant of the leakage current is theoretically 0 and is not affected by transients. ③ Comparing the protection action delays of the two schemes, the latter (dynamically adjusted switching time) has a smaller delay error, basically remaining within 1 s.

[0058] In summary, compared with the existing DC injection type rotor grounding protection, a DC injection type rotor grounding protection method based on dynamically adjusted switching time invented in this patent solves the problem of inaccurate measurement of the grounding resistance in the case of a large equivalent distributed capacitance, and at the same time takes into account the time error of the rotor grounding protection action delay.

[0059] It should be understood that in the development process of any actual implementation, in any engineering or design project, a large number of specific implementation decisions can be made. Such development efforts may be complex and time-consuming, but for those ordinary technical personnel who benefit from this disclosure, without excessive experimentation, the development efforts will be a routine task of design, manufacturing and production.

[0060] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A DC injection rotor grounding protection method based on dynamic adjustment of switching time, characterized in that: The following steps are involved: S1. Obtain the decay time constant of the transient component of the leakage current; S2, setting the electronic switch switching time rule; S3. Determine the initial value of the electronic switch switching time ; S4. During normal operation, if the sampling value of the leakage current is unstable, the switching time of the electronic switch is dynamically adjusted. ; S5. If a ground fault occurs, dynamically adjust the switching time of the electronic switch to obtain the switching time of the electronic switch when the fault occurs. ; S6. After the electronic switch switching time is dynamically adjusted, the grounding resistance is obtained; S7. After the ground fault is handled, the switching time of the electronic switch is adjusted to the switching time of the electronic switch during normal operation.

2. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1 is characterized in that: In S1, the decay time constant is calculated as: ； Where: represents the decay time constant; Indicates the injection resistance parameter in the protection device; Indicates ground resistance; Represents the capacitance of the excitation winding to ground.

3. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1 is characterized in that: In S2, the electronic switch switching time rule is: S21, determining a value of a transient process time, wherein the value of the transient process time is equal to a decay time constant; S21, the initial moment of calculating the ground resistance is a first preset time period after the transient process ends; S22. The grounding resistance is calculated using the leakage current sampling value within a second preset time period after the first preset time period.

4. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1, characterized in that: In S3, the DC rotor grounding protection injection loop resistance, the maximum measured value of the grounding resistance and the maximum distributed capacitance of the excitation winding are used to obtain the attenuation time constant. According to the electronic switch switching time rule, the time of the transient process and the calculation start time of the grounding resistance are obtained, and then the initial value of the switching time of the electronic switch is determined. .

5. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1, characterized in that: In S4, the initial value of the switching time of the electronic switch After confirmation, if the sampling value of the leakage current is unstable, or the calculated value of the ground resistance fluctuates, the current switching time of the electronic switch is added with the time difference As a dynamically adjusted switching time of an electronic switch ; If the ground resistance measurement value is still unstable, continue to switch the time after the current dynamic adjustment Add time difference As the new dynamically adjusted switching time , until After the grounding resistance calculation is completely stable at the maximum value, this switching time is used as the switching time of the electronic switch during normal operation, that is, If there is no abnormality, .

6. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1 is characterized in that: In S5, if the field winding is grounded at one point, the electronic switch dynamically adjusts the switching time. Switching is performed to obtain the steady-state value of the leakage current in the open and closed states, and then the grounding resistance value at this time is calculated; by injecting the loop resistance, the grounding resistance value at this moment and the maximum distributed capacitance of the excitation winding, the time constant is calculated, and then the switching time of the electronic switch during the fault is obtained. .

7. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1 is characterized in that: In S6, after the switching time of the electronic switch is dynamically adjusted, the switching cycle is shortened, and the protection device calculates the grounding resistance value. If the grounding resistance value is less than the grounding resistance setting value, the protection device sends a signal or outputs.

8. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 7 is characterized in that: The calculation method of ground resistance value is: When the electronic switch S1 is turned on: ； When the electronic switch S1 is turned off: ； Combining the above two equations, we can get: ； when hour: ； The action criterion of the rotor single-point grounding protection is: ； Where: Indicates the excitation voltage at the grounding point; Indicates the voltage injected into the power supply; Indicates injection of high power resistance; Indicates the measurement loop resistance; Represents the leakage current when S1 is turned on; Represents the leakage current when S1 is turned off; Indicates ground resistance; It is the setting value of the rotor grounding protection resistance.

9. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 6, characterized in that: The formula for calculating the steady-state value and transient amplitude of the leakage current in the open and closed states is as follows: ； Where: A represents the steady-state value of the leakage current; B represents the transient amplitude of the leakage current; is the injection resistance parameter in the protection device, E is the injection power supply voltage and excitation voltage sum; Indicates the ground resistance.

10. The method for injecting direct current rotor grounding protection based on dynamic adjustment of switching time according to claim 1, characterized in that: In S7, after the ground fault is processed, the leakage current or ground resistance obtained is not a stable value due to the adjustment of the switching time. The protection device automatically adjusts the electronic switch switching time to the electronic switch switching time during normal operation. .

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