Rotor grounding protection method and device for doubly-fed variable-speed pumped storage unit

Abstract

The invention discloses a doubly-fed variable-speed pumped storage unit rotor grounding protection method and device, and the method comprises the steps: setting protection points at two different positions of a three-phase winding at the rotor side of a variable-speed unit, obtaining the three-phase voltage of the rotor winding at each protection point, and calculating a zero-sequence voltage component and a zero-sequence voltage amplitude; if the amplitude of the zero-sequence voltage exceeds a starting threshold, a protection action allowing signal and the three-phase voltage of the rotor winding of the protection point are sent to another protection point; and comparing the three-phase voltage of the rotor winding of the protection point with the three-phase voltage of the rotor winding of another protection point, judging whether the amplitude of the zero-sequence voltage exceeds an action threshold or not, carrying out zero-sequence voltage protection action according to a result, and sending out an alarm signal and the like. According to the technical scheme, the zero-sequence voltage protection principle is utilized to realize the rotor grounding protection of the variable speed unit, and maloperation caused by abnormity of a voltage transformer or a secondary circuit can be prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of relay protection of main equipment of an electric power system, and in particular relates to a rotor grounding protection method and device for a double-fed variable-speed pumped-storage unit. Background Art

[0002] Damage to the insulation of the rotor winding to the ground (iron core) causes a single-phase grounding fault, which is a common electrical fault on the rotor side. There is capacitance between the rotor winding and the ground (large shaft). When single-phase grounding occurs, the current flowing through the fault point is the sum of the capacitance currents of the entire AC excitation system (rotor winding, AC excitation output terminal connection components, etc.). If this current is large, it may cause damage to the winding insulation and even burn the iron core.

[0003] In order to respond to the single-phase grounding fault of the rotor winding, the commonly used zero-sequence voltage protection principle can be used for reference. Since the frequency range of the AC excitation on the rotor side when the unit is connected to the grid is -5Hz to 5Hz, the electromagnetic voltage transformer cannot measure the low-frequency voltage. The electronic voltage transformer is often used to measure the three-phase voltage separately, and then the three-phase voltage measurement values ​​are summed to obtain the zero-sequence voltage (3U0). This protection scheme has the following difficulties: when the electronic voltage transformer fails or its secondary circuit is abnormal, it will cause a false self-generated zero-sequence voltage to be calculated. This feature is similar to the electrical feature of the zero-sequence voltage when the rotor grounds a fault. It is necessary to study the appropriate voltage transformer abnormality judgment criteria and rotor grounding protection scheme to distinguish between voltage abnormalities and real grounding faults to prevent protection malfunctions caused by transformer failures.

[0004] The only power station in China with variable speed units under construction is the Fengning Phase II Pumped Storage Power Station, which has two 300MW variable speed pumped storage units and does not use the zero sequence voltage protection grounding protection technology. Therefore, there is no mature zero sequence voltage protection principle for variable speed unit rotor grounding protection. Summary of the invention

[0005] The purpose of the present invention is to provide a doubly-fed variable-speed pumped storage unit rotor grounding protection method and device, which utilizes the zero-sequence voltage protection principle to achieve variable-speed unit rotor grounding protection and can prevent false operation caused by abnormalities in the voltage transformer or secondary circuit.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A method for protecting a rotor from grounding of a double-fed variable-speed pumped storage unit is provided. Protection points are respectively set at two different positions of a three-phase winding on the rotor side of the variable-speed unit. The following steps are adopted for each protection point:

[0008] Step 1, obtaining the three-phase voltage of the rotor winding at the protection point, calculating the zero-sequence voltage component in the three-phase voltage of the rotor winding, and calculating the zero-sequence voltage amplitude;

[0009] Step 2, judging whether the zero-sequence voltage amplitude exceeds the starting threshold, if so, sending a protection action permission signal and the rotor winding three-phase voltage of the protection point to another protection point; otherwise, disconnecting the signal or setting it to 0;

[0010] Step 3, when receiving the protection action permission signal sent by another protection point and the three-phase voltage of the rotor winding of another protection point, compare the three-phase voltage of the rotor winding of this protection point with the three-phase voltage of the rotor winding of another protection point. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormality alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of this protection point is locked; at the same time, it is determined whether the zero-sequence voltage amplitude of this protection point exceeds the action threshold. If it exceeds the action threshold and a protection action permission signal is received from another protection point, the zero-sequence voltage protection is activated after a certain confirmation delay; if it exceeds the action threshold and no protection action permission signal is received from another protection point, a zero-sequence voltage alarm signal is issued after a certain delay confirmation.

[0011] In the above step 1, the three-phase voltage of the rotor winding is obtained, the zero-sequence voltage component in the three-phase voltage of the rotor winding is calculated, and the zero-sequence voltage amplitude is calculated, including monitoring and obtaining the three-phase voltage u of the rotor winding. a (k),u b (k),u c (k), using u0(k)=[u a (k)+u b (k)+u c (k)] / 3 calculate the zero-sequence voltage component u0(k) in the three-phase voltage of the rotor winding, and then obtain the zero-sequence voltage amplitude U0 through the phasor algorithm.

[0012] In the above step 2, it is determined whether the zero-sequence voltage amplitude exceeds the starting threshold, including that the starting threshold is U 0set1 = k·U h , k is 0.1~0.2, U n is the rated phase voltage of the rotor.

[0013] In the above step 2, a protection action permission signal is sent to another protection point, including using an optical fiber or Ethernet communication method, the communication protocol is IEC60044-8 or 103, or using a hard contact method.

[0014] In the above step 2, the three-phase voltage of the rotor winding of the current protection point is sent to another protection point, including using optical fiber or Ethernet communication, and the communication protocol is IEC60044-8 or 103.

[0015] In the above step 3, the three-phase voltage of the rotor winding of the current protection point is compared with the three-phase voltage of the rotor winding of another protection point, including determining UA -U a >U dset , U B -U b >U dset or U C -U c >U dset , where U A , U B , U C is the three-phase voltage amplitude of the rotor winding at this protection point, U a , U b , U c is the three-phase voltage amplitude of the rotor winding at another protection point, U dset is the rotor voltage phasor difference threshold, which is 5~10V.

[0016] In the above step 3, after a certain delay confirmation, a voltage transformer abnormality alarm signal is issued, including a delay value of 2 to 3 seconds.

[0017] In the above step 3, it is determined whether the zero-sequence voltage amplitude of the protection point exceeds the action threshold, including setting the action threshold to U 0set2 = k2·U n , k2 takes 0.1~0.3, U n is the rated phase voltage of the rotor.

[0018] In the above step 3, after a certain confirmation delay, the zero-sequence voltage protection is activated, including a delay value of 2 to 5 seconds.

[0019] In the above step 3, after a certain delay confirmation, a zero-sequence voltage alarm signal is issued, including a delay value of 5 to 10 seconds.

[0020] A doubly-fed variable speed pumped storage unit rotor grounding protection device is arranged at a protection point on a three-phase winding on the rotor side of the variable speed unit and communicates with another protection device arranged at another protection point on the three-phase winding on the rotor side of the variable speed unit; comprising:

[0021] The rotor voltage sampling and calculation module is configured to obtain the three-phase voltage of the rotor winding of this protection point, calculate the zero-sequence voltage component in the three-phase voltage of the rotor winding, and calculate the zero-sequence voltage amplitude.

[0022] The data sending module is configured to send the three-phase voltage of the rotor winding of the protection point to another protection device, and determine whether the zero-sequence voltage amplitude exceeds the starting threshold. If so, a protection action permission signal is sent to the other protection device; otherwise, the signal is disconnected or set to 0;

[0023] A data receiving module is configured to receive a protection action permission signal and three-phase voltage sampling data sent by another set of protection devices;

[0024] The voltage transformer abnormal alarm discrimination module is configured to compare the rotor winding three-phase voltage of the current protection point with the rotor winding three-phase voltage of another set of protection points received. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormal alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of the current protection point is locked; and,

[0025] The grounding protection logic judgment module is configured to determine whether the zero-sequence voltage amplitude of the protection point exceeds the action threshold. If it exceeds the action threshold and a protection action permission signal is received from another protection device, the zero-sequence voltage protection will be activated after a certain confirmation delay; if it exceeds the action threshold and a protection action permission signal is not received from another protection device, a zero-sequence voltage alarm signal will be issued after a certain delay confirmation.

[0026] The method for calculating the zero-sequence voltage amplitude by the rotor voltage sampling calculation module is: using u0(k)=[u a (k)+u b (k)+u c (k)] / 3 calculate the zero-sequence voltage component u0(k) in the three-phase voltage of the rotor winding, and then obtain the zero-sequence voltage amplitude U0 through the phasor algorithm; where u a (k),u b (k),u c (k) are the three-phase voltages of the rotor winding respectively.

[0027] The data transmission module determines that the starting threshold of the zero-sequence voltage amplitude used is U 0set1 = k·U n , k is 0.1~0.2, U n is the rated phase voltage of the rotor.

[0028] The data transmission module transmits the protection action permission signal to another protection device by optical fiber or Ethernet communication, the communication protocol is IEC60044-8 or 103, or hard contact method.

[0029] The data transmission module transmits the three-phase voltage of the rotor winding of the protection point to another protection device by optical fiber or Ethernet communication, and the communication protocol is IEC60044-8 or 103.

[0030] The above voltage transformer abnormal alarm compares the rotor winding three-phase voltage of the protection point with the rotor winding three-phase voltage of another protection point, including judging U A -U a >U dset , U B -U b >U dset or UC -U c >U dset , where U A , U B , U C is the three-phase voltage amplitude of the rotor winding at this protection point, U a , U b , U c is the three-phase voltage amplitude of the rotor winding at another protection point, U dset is the rotor voltage phasor difference threshold, which is 5~10V.

[0031] The delay value of the voltage transformer abnormal alarm discrimination module sending out the voltage transformer abnormal alarm signal is 2 to 3 seconds.

[0032] The zero-sequence voltage amplitude action threshold of the ground protection logic judgment module is U 0set2 = k2·U n , k2 takes 0.1~0.3, U n is the rated phase voltage of the rotor.

[0033] The action delay value of the zero-sequence voltage protection of the above-mentioned grounding protection logic judgment module is 2 to 5s.

[0034] The alarm delay value of the zero-sequence voltage protection of the above-mentioned grounding protection logic judgment module is 5 to 10s.

[0035] After adopting the above scheme, the beneficial effect of the present invention is: providing a rotor grounding protection method and device for a doubly-fed variable-speed unit based on the zero-sequence overvoltage principle, which can operate correctly when the rotor winding is grounded and send an alarm signal when the voltage transformer or the secondary circuit is abnormal. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic diagram of the device architecture of the present invention;

[0037] Figure 2 This is the main wiring diagram of the double-fed variable speed unit;

[0038] Among them, K1 indicates a single-phase grounding fault inside the rotor winding, and K2 indicates a single-phase grounding fault at the end of the rotor winding;

[0039] Figure 3 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0040] The present invention provides a method for protecting the rotor of a double-fed variable-speed pumped storage unit from grounding. Figure 3 As shown, including the following:

[0041] (1) Two identical protection devices receive the secondary signals of a set of independent rotor winding voltage transformers and monitor the three-phase voltage of the rotor winding; both protection devices calculate the zero-sequence voltage component in the three-phase voltage of the rotor winding and calculate the zero-sequence voltage amplitude. Each protection device performs the following operations:

[0042] ① Send the rotor winding three-phase voltage sampling data to another set of protection devices.

[0043] ② If the zero-sequence voltage amplitude calculated by this set of protection devices exceeds the starting threshold, a protection action permission signal is sent to another set of protection devices; otherwise, the signal is disconnected or set to 0.

[0044] (2) Each set of protection devices receives the protection action permission signal and three-phase voltage sampling data sent by another set of protection devices, and performs the following operations and judgments;

[0045] ① Compare the rotor winding three-phase voltage of this protection device with the rotor winding three-phase voltage data received from another protection device. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormality alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of this protection device is locked;

[0046] ② When the zero-sequence voltage amplitude of this protection device exceeds the action threshold, if a protection action permission signal is received from another protection device, the zero-sequence voltage protection will be activated after a certain confirmation delay; otherwise, if a protection action permission signal is not received from another protection device, a zero-sequence voltage alarm signal will be issued after a certain confirmation delay.

[0047] The protection device provided by the present invention comprises a rotor voltage sampling and calculation module, a data sending module, a data receiving module, a voltage transformer abnormal alarm judgment module and a grounding protection logic judgment module, which are respectively introduced below.

[0048] The rotor voltage sampling and calculation module is used to monitor the three-phase voltage of the rotor winding, calculate the zero-sequence voltage component in the three-phase voltage of the rotor winding, and calculate the zero-sequence voltage amplitude;

[0049] The data sending module is used to send the rotor winding three-phase voltage sampling data to another set of protection devices; determine whether the zero-sequence voltage amplitude exceeds the starting threshold, and if so, send a protection action permission signal to the other set of protection devices; otherwise, disconnect or set the signal to 0;

[0050] The data receiving module is used to enable the protection device to receive the protection action permission signal and three-phase voltage sampling data sent by another protection device;

[0051] The voltage transformer abnormal alarm discrimination module is used to compare the rotor winding three-phase voltage of this set of protection device with the rotor winding three-phase voltage data received from another set of protection device. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormal alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of this set of protection device is locked;

[0052] The grounding protection logic judgment module is used to determine whether the zero-sequence voltage amplitude of this set of protection devices exceeds the action threshold. When the conditions are met, if a protection action permission signal is received from another set of protection devices, the zero-sequence voltage protection will be activated after a certain confirmation delay; otherwise, if a protection action permission signal is not received from another set of protection devices, a zero-sequence voltage alarm signal will be issued after a certain delay confirmation.

[0053] The technical solutions and beneficial effects of the present invention will be described in detail below in conjunction with specific embodiments.

[0054] A method and device for protecting a rotor of a double-fed variable-speed pumped storage unit from grounding faults is provided in an embodiment of the present invention and is applicable to Figure 1 The variable speed unit shown in the figure has a three-phase AC excitation winding on the rotor side. Two sets of electronic voltage transformers are installed on the three-phase windings. The rotor winding grounding fault point is located at any phase of the rotor winding (such as Figure 2 The fault point K1 shown in the figure) or at the end of the rotor winding (such as Figure 2 K2 fault point shown in the figure).

[0055] The protection device provided by the present invention is installed on Figure 1 As shown in the figure, the two sets of protection devices have exactly the same hardware and software logic. The following implementation process is only described for one set of protection devices, and the implementation method of the other set of protection is the same.

[0056] (1) The protection device introduces the secondary voltage of the electronic voltage transformer on the rotor side of the variable speed pumped storage unit to calculate the zero-sequence voltage component in the three-phase voltage of the rotor winding and the zero-sequence voltage amplitude. The method for calculating the zero-sequence voltage component is: if the collected three-phase voltages are u a (k),u v (k),u c (k), then the zero-sequence voltage component is u0(k)=[u a (k)+u b (k)+u c (k)] / 3, and then the zero-sequence voltage amplitude U0 is obtained by the phasor algorithm. The phasor algorithm used can be any of the following two methods:

[0057] The first method is to adjust the sampling frequency of the hardware according to the change of the frequency of the electrical quantity, so that at any current frequency, each electrical quantity cycle has a fixed number of sampling points, for example, 24 sampling points are fixed for each cycle; then the fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor value;

[0058] The second method uses a fixed sampling frequency to discretely sample the three-phase voltage to obtain a sequence of sampling values; according to the current electrical quantity frequency, the data window (number of sampling value points) of the Fourier algorithm is dynamically adjusted. For example, at the rated frequency, the data window takes 24 sampling points. When the actual frequency is half of the rated frequency, the data window becomes 48 sampling points; then the Fourier algorithm is used to measure and calculate the real and imaginary parts of the current and voltage, thereby obtaining the voltage phasor value.

[0059] The second method is used as an example to illustrate the specific calculation process: the variable data window Fourier algorithm is used to calculate the three-phase voltage phasor value from the three-phase voltage of the rotor winding. First, the current frequency is obtained using the frequency measurement algorithm (see "Li Yiquan, He Benteng. A high-precision frequency measurement method based on Fourier algorithm [J]. Proceedings of the CSEE. 2006 26(2).78-81"). According to the current sampling frequency f s and the current frequency f of the terminal voltage e , calculate the number of sampling points N per cycle, that is, the length of the real-time data window.

[0060]

[0061] [] indicates rounding down or up.

[0062] Assuming the sampling frequency is 1200 Hz and the current voltage and current frequency is 48.8 Hz, N is 24 or 25.

[0063] When the data window length N of the Fourier algorithm is determined, the sine and cosine coefficient tables of the Fourier algorithm are calculated.

[0064]

[0065] Ksin(k) is the sine coefficient of the kth point, and Kcos(k) is the cosine coefficient of the kth point.

[0066] The variable data window Fourier algorithm is used to calculate the zero-sequence voltage phasor value from the zero-sequence voltage sampling value. 0r and the imaginary part U 0i , the matching Fourier algorithm calculation formula is:

[0067]

[0068] Wherein, u0(n) represents the zero-sequence voltage sampling value data sequence.

[0069] Thus, the electrical quantity phasor is obtained as follows:

[0070]

[0071]

[0072] Among them, U 0r is the real part of the zero-sequence voltage, U 0i is the imaginary part of the zero-sequence voltage, and U0 is the amplitude of the zero-sequence voltage.

[0073] (2) This set of protection devices sends the rotor winding three-phase voltage sampling data collected by this set of protection to another set of protection devices respectively. The data is sent by optical fiber or Ethernet communication, and the communication protocol is IEC60044-8 or 103.

[0074] (3) If the zero-sequence voltage amplitude U0 ≥ U 0set1 , U 0set1 As the starting threshold, take 0.15U n , U n If it is the rated phase voltage of the rotor, a protection action permission signal is sent to another set of protection devices; the signal sending method can be optical fiber or Ethernet communication method, the communication protocol is IEC60044-8 or 103, or it can be a hard contact method.

[0075] (4) The method for comparing the rotor winding three-phase voltage of the present protection device with the rotor winding three-phase voltage data received from another protection device is: A -U a >5V or U B -U b >5V or U C -U c >5V, where U A , U B , U C is the three-phase voltage amplitude of the rotor winding of this protection device, U a , U b , U c It is the three-phase voltage amplitude of the rotor winding of another protection device received by this protection device. If the phasor difference of any phase voltage exceeds 5V, a voltage transformer abnormality alarm signal will be issued after 2s confirmation, and the zero-sequence voltage protection of this protection device will be locked.

[0076] (5) Determine whether the zero-sequence voltage amplitude of this protection device exceeds the action threshold U 0set2 =0.25U n , U nis the rated phase voltage of the rotor. If yes, and a protection action permission signal is received from another set of protection devices, it will act after 5 seconds; otherwise, if no protection action permission signal is received from another set of protection devices, a zero-sequence voltage alarm signal will be issued after 10 seconds of confirmation.

[0077] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0078] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0079] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0080] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0081] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0082] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0083] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for protecting a rotor from grounding of a double-fed variable-speed pumped storage unit, characterized in that: Protection points are set at two different positions of the three-phase winding on the rotor side of the variable speed unit. The following steps are adopted for each protection point: Step 1, obtaining the three-phase voltage of the rotor winding at the protection point, calculating the zero-sequence voltage component in the three-phase voltage of the rotor winding, and calculating the zero-sequence voltage amplitude; Step 2, judging whether the zero-sequence voltage amplitude exceeds the starting threshold, if so, sending a protection action permission signal and the rotor winding three-phase voltage of the protection point to another protection point; otherwise, disconnecting the signal or setting it to 0; Step 3, when receiving the protection action permission signal sent by another protection point and the three-phase voltage of the rotor winding of another protection point, compare the three-phase voltage of the rotor winding of this protection point with the three-phase voltage of the rotor winding of another protection point. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormality alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of this protection point is locked; at the same time, it is determined whether the zero-sequence voltage amplitude of this protection point exceeds the action threshold. If it exceeds the action threshold and a protection action permission signal is received from another protection point, the zero-sequence voltage protection is activated after a certain confirmation delay; if it exceeds the action threshold and no protection action permission signal is received from another protection point, a zero-sequence voltage alarm signal is issued after a certain delay confirmation.

2. The method according to claim 1, characterized in that: In the step 1, the three-phase voltage of the rotor winding is obtained, the zero-sequence voltage component in the three-phase voltage of the rotor winding is calculated, and the zero-sequence voltage amplitude is calculated, including monitoring and obtaining the three-phase voltage u of the rotor winding. a (k),u b (k),u c (k), using u0(k)=[u a (k)+u b (k)+u c (k)] / 3 calculate the zero-sequence voltage component u0(k) in the three-phase voltage of the rotor winding, and then obtain the zero-sequence voltage amplitude U0 through the phasor algorithm.

3. The method according to claim 1, characterized in that: In step 2, judging whether the zero-sequence voltage amplitude exceeds the starting threshold includes: the starting threshold is U 0set1 = k·U n , k is 0.1~0.2, U n is the rated phase voltage of the rotor.

4. The method according to claim 1, characterized in that: In the step 2, a protection action permission signal is sent to another protection point, including using an optical fiber or Ethernet communication method, the communication protocol is IEC60044-8 or 103, or using a hard connection method.

5. The method according to claim 1, characterized in that: In the step 2, the three-phase voltage of the rotor winding of the protection point is sent to another protection point, including using optical fiber or Ethernet communication, and the communication protocol is IEC60044-8 or 103.

6. The method according to claim 1, characterized in that: In step 3, the three-phase voltage of the rotor winding of the current protection point is compared with the three-phase voltage of the rotor winding of another protection point, including determining U A -U a >U dset , U B -U b >U dset or U C -U c >U dset , where U A , U B , U C is the three-phase voltage amplitude of the rotor winding at this protection point, U a , U b , U c is the three-phase voltage amplitude of the rotor winding at another protection point, U dset is the rotor voltage phasor difference threshold, which is 5~10V.

7. The method according to claim 1, characterized in that: In step 3, after a certain delay, a voltage transformer abnormality alarm signal is issued. Including, the delay value is 2 to 3s.

8. The method according to claim 1, characterized in that: In step 3, it is determined whether the zero-sequence voltage amplitude of the protection point exceeds the action threshold, including setting the action threshold to U 0set2 = k2·U n , k2 takes 0.1~0.3, U n is the rated phase voltage of the rotor.

9. The method according to claim 1, characterized in that: In step 3, after a certain confirmation delay, the zero-sequence voltage protection is activated, including a delay value of 2 to 5 seconds.

10. The method according to claim 1, characterized in that: In step 3, after a certain delay confirmation, a zero-sequence voltage alarm signal is issued. Including, the delay value is 5 to 10s.

11. A doubly-fed variable-speed pumped storage unit rotor grounding protection device, characterized in that: A protection point is arranged on the three-phase winding on the rotor side of the variable speed unit, and communicates with another protection device arranged on another protection point on the three-phase winding on the rotor side of the variable speed unit; include, The rotor voltage sampling and calculation module is configured to obtain the three-phase voltage of the rotor winding of this protection point, calculate the zero-sequence voltage component in the three-phase voltage of the rotor winding, and calculate the zero-sequence voltage amplitude. The data sending module is configured to send the three-phase voltage of the rotor winding of the protection point to another protection device, and determine whether the zero-sequence voltage amplitude exceeds the starting threshold. If so, a protection action permission signal is sent to the other protection device; otherwise, the signal is disconnected or set to 0; A data receiving module is configured to receive a protection action permission signal and three-phase voltage sampling data sent by another set of protection devices; The voltage transformer abnormal alarm discrimination module is configured to compare the rotor winding three-phase voltage of the current protection point with the rotor winding three-phase voltage of another set of protection points received. If the phasor difference of at least one phase voltage exceeds the threshold, a voltage transformer abnormal alarm signal is issued after a certain delay confirmation, and the zero-sequence voltage protection of the current protection point is locked; and, The grounding protection logic judgment module is configured to determine whether the zero-sequence voltage amplitude of this protection point exceeds the action threshold. If it exceeds the action threshold and a protection action permission signal is received from another protection device, the zero-sequence voltage protection will be activated after a certain confirmation delay; if it exceeds the action threshold and a protection action permission signal is not received from another protection device, a zero-sequence voltage alarm signal will be issued after a certain delay confirmation.

12. The device according to claim 11, characterized in that: The method for calculating the zero-sequence voltage amplitude by the rotor voltage sampling and calculation module is: using u0(k)=[u a (k)+u b (k)+u c (k)] / 3 calculate the zero-sequence voltage component u0(k) in the three-phase voltage of the rotor winding, and then obtain the zero-sequence voltage amplitude U0 through the phasor algorithm; Among them, u a (k),u b (k),u c (k) are the three-phase voltages of the rotor winding respectively.

13. The device according to claim 11, characterized in that: The data sending module determines that the starting threshold of the zero-sequence voltage amplitude adopted is U 0set1 = k·U n , k is 0.1~0.2, U n is the rated phase voltage of the rotor.

14. The device according to claim 11, characterized in that: The data transmission module sends the protection action permission signal to another protection device by optical fiber or Ethernet communication, the communication protocol is IEC60044-8 or 103, or a hard contact method.

15. The device according to claim 11, characterized in that: The data transmission module transmits the three-phase voltage of the rotor winding of the protection point to another protection device by optical fiber or Ethernet communication, and the communication protocol is IEC60044-8 or 103.

16. The device according to claim 11, characterized in that: The voltage transformer abnormal alarm compares the rotor winding three-phase voltage of the protection point with the rotor winding three-phase voltage of another protection point, including judging U A -U a >U dset , U B -U b >U dset or U C -U c >U dset , where U A , U B , U C is the three-phase voltage amplitude of the rotor winding at this protection point, U a , U b , U c is the three-phase voltage amplitude of the rotor winding at another protection point, U dset is the rotor voltage phasor difference threshold, which is 5~10V.

17. The device according to claim 11, characterized in that: The delay value of the voltage transformer abnormal alarm discrimination module sending out the voltage transformer abnormal alarm signal is 2 to 3 seconds.

18. The device according to claim 11, characterized in that: The action threshold of the zero-sequence voltage amplitude of the ground protection logic judgment module is U 0set2 = k2·U n , k2 takes 0.1~0.3, U n is the rated phase voltage of the rotor.

19. The device according to claim 11, characterized in that: The action delay value of the zero-sequence voltage protection of the grounding protection logic judgment module is 2 to 5 seconds.

20. The device according to claim 11, characterized in that: The alarm delay value of the zero-sequence voltage protection of the grounding protection logic judgment module is 5 to 10 seconds.

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