A method and system for ground protection and area identification of variable speed pumping and storage units

Abstract

A variable-speed pumped storage unit grounding protection and area identification method, comprising: setting a grounding circuit on the DC link of the rotor-side converter of the variable-speed pumped storage unit, the grounding circuit comprising a grounding resistor; collecting a voltage signal across the grounding resistor in real time; when the amplitude of the voltage signal is greater than a preset protection threshold, determining that a grounding fault of the variable-speed pumped storage unit occurs, and triggering a protection start; after the protection start, continuously recording the recording wave data of the voltage signal, and starting timing; when the timing time reaches a preset delay duration, issuing a trip shutdown instruction to the variable-speed pumped storage unit, and stopping timing; extracting the recording wave data during timing, and performing frequency domain transformation to obtain a plurality of characteristic components, and determining the physical area of the grounding fault based on the amplitude size comparison of the plurality of characteristic components.

Description

Technical Field

[0001] This invention relates to the field of relay protection and safe operation technology for pumped storage units, and more specifically, to a grounding protection and area identification method and system for variable speed pumped storage units. Background Technology

[0002] Variable-speed pumped-storage units (hereinafter referred to as "variable-speed pumped-storage units") are key equipment in power system construction, possessing high flexibility. Variable-speed pumped-storage units can inject variable-frequency current into the rotor windings to regulate the unit's speed, allowing the motor to operate at the desired operating point. In this case, the pulse-width modulation voltage injected into the rotor will significantly stress the unit's insulation resistance, shortening its service life. With the degradation of insulation materials, the risk of electrical faults also increases. Grounding faults are among the most common and extremely dangerous electrical faults in generator sets. Once a single-phase grounding fault occurs, if it cannot be cleared in time, it can easily lead to inter-turn short circuits or phase-to-phase short circuits, or even burn out the iron core, causing huge economic losses. Depending on the grounding type of the grounding system, various different scenarios can be identified. Their common characteristic is that if a single-phase grounding fault is not cleared in time, it may lead to a two-phase grounding fault, or even a three-phase grounding fault, causing more serious damage. In variable-speed pumped-storage units, due to the presence of AC-DC-AC converters, when a ground fault occurs at any point on the stator side, DC link, or rotor side, the fault signal will be coupled to the entire electrical circuit through the distributed capacitance or power devices inside the converter. This results in maintenance personnel having to blindly and time-consumingly troubleshoot the entire large unit system after a fault occurs.

[0003] In existing technologies, rotor grounding faults are typically detected by artificially constructing a neutral point and connecting an external injection device. The physical location of the rotor fault is identified by analyzing the frequency and phase difference of the current signal and using the voltage or voltage difference between the stator-to-ground voltage and the grounding resistance. This method requires a large additional signal generator, injection transformer, and frequency-selective receiver. This adds extra structure to the original system topology, increasing hardware costs and wiring complexity. Furthermore, the injection device itself constitutes a new potential fault location, reducing the overall reliability of the system and making this method impractical.

[0004] To address the aforementioned technical issues, this application proposes a method based on DC grounding resistance voltage analysis, which can reliably monitor and protect against grounding faults in variable-speed pumped-storage units, and accurately identify the physical area where the fault is located without adding additional injection equipment. Summary of the Invention

[0005] The first aspect of this application provides a method for grounding protection and area identification of a variable-speed pumped-storage unit, characterized by comprising the following steps: A grounding circuit is installed on the DC link of the rotor-side converter of the variable speed pumped storage unit. The grounding circuit includes a grounding resistor. The voltage signal across the grounding resistor is collected in real time. When the amplitude of the voltage signal is greater than the preset protection threshold, it is determined that a grounding fault has occurred in the variable speed pumped storage unit, and the protection is triggered. After the protection is activated, the waveform data of the voltage signal of the grounding resistance is continuously recorded, and timing begins. Once the preset delay time is reached, a trip shutdown command is sent to the variable speed pumped storage unit, and the timing is stopped. The waveform data recorded during the timing period is extracted and frequency domain transformation is performed to obtain multiple characteristic components. Based on the comparison of the amplitude of multiple characteristic components, the physical area of ​​the grounding fault is determined.

[0006] Optionally, the grounding circuit includes two voltage-dividing resistors connected in series between the positive and negative buses of the DC link; One end of the grounding resistor is connected to the middle node of the two voltage divider resistors, and the other end of the grounding resistor is grounded. The resistance of the grounding resistor is on the same order of magnitude as the resistance of the voltage divider resistor.

[0007] Optionally, the resistance of the voltage divider resistor is in the tens or thousands of ohms.

[0008] Optionally, the protection threshold is set to be greater than the maximum unbalanced voltage value measured across the grounding resistance under normal operating conditions of the variable speed pumped storage unit.

[0009] Optionally, the delay duration is set as follows:

[0010] in, T To extend the duration, f r This refers to the rotor-side operating frequency of the variable-speed pumped storage unit.

[0011] Optionally, based on a comparison of the amplitudes of multiple characteristic frequency components, the physical region of the ground fault can be determined as follows: Extract the component characteristic values ​​of the waveform recording data in the preset DC frequency band, power frequency band, and rotor-side operating frequency band; The physical area of ​​a grounding fault is determined based on the magnitude of multiple component characteristic values.

[0012] Optionally, determining the physical region of a ground fault based on the magnitude of multiple component characteristic values ​​includes: By comparing the magnitudes of multiple component characteristic values, when one component characteristic value is greater than the other component characteristic values, it is determined that the ground fault is located in the physical area corresponding to that component characteristic value.

[0013] Optionally, if the component characteristic value of the DC frequency band is the largest, then the ground fault is determined to be located at the DC link of the variable speed pumped storage unit. If the component characteristic value of the power frequency band is the largest, then the ground fault is determined to be located on the stator side of the variable speed pumped storage unit. If the component characteristic value of the rotor-side operating frequency band is the largest, then the ground fault is determined to be located on the rotor side of the variable speed pumped storage unit.

[0014] The second aspect of this application provides a grounding protection and area identification system for a variable-speed pumped-storage unit, characterized in that it includes: at least one processor; and a readable storage medium communicatively connected to the at least one processor; wherein the readable storage medium stores a computer program executable by the at least one processor; when the computer program is executed by the processor, it implements the grounding protection and area identification method for the variable-speed pumped-storage unit as described above.

[0015] According to the grounding protection and area identification method and system for pumped storage units of this application, by setting a grounding circuit on the DC link, the physical area where the fault is located can be accurately identified without adding additional injection equipment.

[0016] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the background art, the accompanying drawings used in the embodiments of this application or the background art will be described below.

[0018] Figure 1 This is a flowchart illustrating the implementation of the grounding protection and area identification method for variable-speed pumped-storage units according to embodiments of this application; Figure 2 The circuit topology of a variable-speed pumped-storage unit in one embodiment of this application is shown; Figure 3 The following is an embodiment of the present application showing the grounding resistance voltage waveform during a stator-side grounding fault; Figure 4 The grounding resistance voltage waveform during a rotor-side grounding fault in the above embodiment is shown. Figure 5 The grounding resistance voltage waveform during a DC link grounding fault in the above embodiment is shown. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will now be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of this disclosure and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] The rotor side of a variable-speed pumped-storage unit is connected to the power grid via an AC-DC-AC converter, which includes a grid-side converter, a rotor-side converter, and a DC link between them. In the physical topology of a variable-speed pumped-storage unit, there is electrical coupling between the stator side, the DC link, and the rotor side.

[0023] This application provides a grounding protection and area identification method for variable-speed pumped-storage units based on DC grounding resistance voltage analysis, including the following steps: A grounding circuit is installed on the DC link of the rotor-side converter of the variable-speed pumped-storage unit. For example... Figure 2 As shown, two voltage divider resistors are connected in series between the positive and negative terminals of the DC link. R x and in the voltage divider resistor R x Connect the grounding resistor between R gnd Grounding resistance R gnd One end is connected to the voltage divider resistor R x The middle node is connected to the protective ground at the other end. Voltage divider resistor. R x With grounding resistance R gndThe resistor. In an optional embodiment, a voltage divider resistor. R x It is a large-value resistor in the tens or thousands of ohms range. In the embodiments of this application, the grounding circuit loop adopts a pure resistive voltage divider structure, and the grounding resistor... R gnd The voltage acquisition device is connected in parallel at both ends. Compared with the traditional protection scheme that uses an injection device, the technical solution of this application does not require an external low-frequency AC or DC signal generator, which greatly simplifies the hardware structure.

[0024] During system operation, the grounding resistance is collected in real time through voltage acquisition equipment. R gnd voltage signals at both ends U gnd Due to the electrical coupling between the internal and external networks of the converter, this voltage signal actually comprehensively reflects the ground insulation status of the stator side, DC side, and rotor side of the unit. The collected voltage signal... U gnd With the preset protection threshold U set The amplitude is compared in real time.

[0025] Under normal operating conditions, due to the non-ideal characteristics of the internal switching devices and the presence of stray capacitance in the AC-DC-AC converter, an inherent unbalanced voltage exists between the DC link and ground. By measuring the unit's normal operating conditions, the maximum unbalanced voltage value of the variable-speed pumped-storage unit during normal operation can be obtained. U 0 .

[0026] In the embodiments of this application, the protection threshold U set The set voltage value is greater than the measured maximum unbalanced voltage value. U 0 In an optional embodiment, a preset protection threshold is set. U set It can be set as follows:

[0027] in K rel The reliability factor is introduced. K rel This provides the necessary safety margin for protection activation, avoiding sudden transient interference in the power grid environment, preventing protection malfunctions, and avoiding unnecessary downtime. In the embodiments of this application, the reliability coefficient... K relIt can be set within the range of 1.2 to 1.5. When the reliability coefficient is larger, it helps to prevent false tripping caused by sudden external surges or asymmetrical loads. When the reliability coefficient is smaller, the protection sensitivity is higher, which helps to avoid missing minor faults.

[0028] The criteria for initiating protection are:

[0029] When the collected voltage signal U gnd The amplitude is greater than the preset protection threshold. U set When the variable-speed pumped-storage unit is detected to have a ground fault, the protection system is immediately triggered. After the protection system is activated, the voltage signal waveform data is continuously recorded, and a timer begins.

[0030] To locate the fault area, frequency domain analysis of the fault waveform is required. The accuracy of the frequency domain analysis depends on the window length of the acquired signal. In the embodiments of this application, a protection action delay time is preset, and the duration of the delay time is set as follows:

[0031] in, T To extend the duration, f r The operating frequency of the variable-speed pumped-storage unit's rotor side is used. This delay time is set to be greater than or equal to the reciprocal of the actual rotor operating frequency, ensuring that the voltage signal recording time is no less than one complete rotor operating cycle. During this delay period, a trip command is not issued to the variable-speed pumped-storage unit; instead, the voltage signal waveform after the fault occurs is continuously recorded to obtain a data window containing the complete cycle, providing a reliable data foundation for subsequent feature component extraction.

[0032] Frequency domain analysis algorithms, such as Fast Fourier Transform (FFT), are used to analyze the voltage signal waveform recorded during the delay time. A frequency domain transformation is performed on the waveform data recorded during the timing period to obtain multiple characteristic components. Further comparison of the amplitudes of these characteristic components allows for the determination of the physical area where a ground fault has occurred. When a ground fault occurs in different areas, the voltage at the fault point will be coupled to the DC-side grounding resistance through the converter. R gnd However, their frequency characteristics differ significantly. If the fault occurs on the DC side, it manifests as a DC voltage deviation; if the fault occurs on the stator side, the power frequency zero-sequence voltage on the stator side will be coupled to the grounding resistance through the grid-side converter. R gnd If the fault occurs on the rotor side, the zero-sequence voltage at the slip frequency corresponding to the current speed on the rotor side will be coupled to the grounding resistor through the rotor-side converter. Rgnd Therefore, in the embodiments of this application, the component characteristic values ​​of the waveform recording data are extracted within a preset DC frequency band, power frequency band, and rotor-side operating frequency band. After extracting the amplitudes of the above three characteristic frequencies, these three amplitudes are compared laterally.

[0033] In an optional embodiment, the component with the largest amplitude is determined as the dominant characteristic component, and the fault location result is output accordingly. The voltage signal... U gnd After performing a Fast Fourier Transform (FFT), the DC component is obtained. U gnd (f 0 ) Power frequency component U gnd (f s ) and rotor-side operating frequency components U gnd (f r ) .

[0034] Comparison of DC components U gnd (f 0 ) Power frequency component U gnd (f s ) and rotor-side operating frequency components U gnd (f r ) The magnitude of the amplitude. If the comparison result shows a DC component. U gnd (f 0 ) The amplitude is at its maximum value, indicating that the ground fault occurred in the DC link of the variable-speed pumped-storage unit. If the comparison result shows the power frequency component... U gnd (f s ) The amplitude is at its maximum value, indicating that the ground fault occurred on the stator side of the variable-speed pumped-storage unit. If the comparison result shows the rotor frequency component... U gnd (f r ) The amplitude is at its maximum value, indicating that the ground fault occurred on the rotor side of the variable speed pumped storage unit.

[0035] The following uses a simulation model of a 300MW variable-speed pumped-storage unit as an example to illustrate the execution process of the protection and area identification method in this application. Figure 2 As shown, ground faults are set on the stator side, rotor side, and DC link respectively, and are denoted as follows: F 1 , F 2 and F 3 The ground fault resistance is set to 100Ω, and the ground fault is set to occur in the 4th second.

[0036] When a stator-side ground fault occurs F 1 At that time, grounding resistance R gnd voltage signal U gnd Waveform as Figure 3 As shown in the figure. It can be seen that the voltage after a ground fault... U gnd The amplitude of increases significantly, and an FFT transformation of it reveals that... U gnd ( f s The frequency component is significantly larger than other frequency components, which can identify the ground fault area on the stator side.

[0037] When a rotor-side ground fault occurs F 2 At that time, grounding resistance R gnd voltage signal U gnd Waveform as Figure 4 As shown in the figure. It can be seen that the voltage after a ground fault... U gnd The amplitude of increases significantly, and an FFT transformation of it reveals that... U gnd ( f r The frequency component is significantly larger than other frequency components, which can identify the ground fault area on the rotor side.

[0038] When a DC link ground fault occurs F 3 At that time, grounding resistance R gnd voltage signal U gnd Waveform as Figure 5 As shown in the figure. It can be seen that the voltage after a ground fault... U gnd The amplitude of increases significantly, and an FFT transformation of it reveals that...U gnd ( f The 0) component is significantly larger than other frequency components, which can identify the ground fault area in the DC link.

[0039] Through the above embodiments, this application achieves reliable detection and protection against grounding faults, and can determine the specific physical area where the fault occurs while providing shutdown protection.

[0040] This application also provides a grounding protection and area identification system for a variable-speed pumped-storage unit, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements all the steps of the aforementioned grounding protection and area identification method for the variable-speed pumped-storage unit. This system can be integrated into the unit's microprocessor-based relay protection device or measurement and control terminal. Furthermore, this invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, similarly implements the aforementioned method steps.

[0041] The variable-speed pumped-storage unit grounding protection and area identification method and system provided in this application embodiment, by setting a grounding circuit on the DC link, collecting the voltage across the resistor of the grounding circuit and performing frequency domain transformation, and determining the area where a grounding fault has occurred based on the comparison of the amplitudes of the multiple characteristic components, can accurately identify the physical area where the fault occurs while performing shutdown protection.

[0042] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions of technical solutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for grounding protection and area identification of a variable-speed pumped-storage unit, characterized in that, Includes the following steps: A grounding circuit is installed on the DC link of the rotor-side converter of the variable speed pumped storage unit, and the grounding circuit includes a grounding resistor; The voltage signal across the grounding resistor is collected in real time. When the amplitude of the voltage signal is greater than the preset protection threshold, it is determined that the variable speed pumped storage unit has a grounding fault and the protection is triggered. After the protection is activated, the waveform data of the voltage signal is continuously recorded, and timing begins. When the timing reaches the preset delay time, a trip shutdown command is sent to the variable speed pumped storage unit, and the timing is stopped; The waveform data recorded during the timing period is extracted and frequency domain transformation is performed to obtain multiple feature components. Based on the comparison of the amplitude of the multiple feature components, the physical area of ​​the grounding fault is determined.

2. The method according to claim 1, characterized in that, The grounding circuit includes two voltage-dividing resistors connected in series between the positive bus and the negative bus of the DC link; One end of the grounding resistor is connected to the middle node of the two voltage divider resistors, and the other end of the grounding resistor is grounded. The resistance value of the grounding resistor is on the same order of magnitude as the resistance value of the voltage divider resistor.

3. The method according to claim 2, characterized in that, The resistance of the voltage divider resistor is in the tens of thousands of ohms.

4. The method according to claim 1, characterized in that, The protection threshold is set to be greater than the maximum unbalanced voltage value measured across the grounding resistor under normal operating conditions of the variable-speed pumped storage unit.

5. The method according to claim 1, characterized in that, The delay duration is set to: in, T The delay duration is... f r The operating frequency of the variable-speed pumped storage unit on the rotor side is denoted as .

6. The method according to claim 1, characterized in that, The determination of the physical region of the ground fault based on the comparison of the amplitudes of the multiple characteristic frequency components includes: Extract the component characteristic values ​​of the recorded waveform data in the preset DC frequency band, power frequency band, and rotor-side operating frequency band; The physical region of the grounding fault is determined based on the magnitude of multiple component characteristic values.

7. The method according to claim 6, characterized in that, The determination of the physical region of the ground fault based on the magnitude of multiple component characteristic values ​​includes: By comparing the magnitudes of multiple component characteristic values, when one component characteristic value is greater than the other component characteristic values, it is determined that the grounding fault is located in the physical area corresponding to that component characteristic value.

8. The method according to claim 7, characterized in that, If the component characteristic value of the DC frequency band is the largest, then the ground fault is determined to be located at the DC link of the variable speed pumped storage unit; If the component characteristic value of the power frequency band is the largest, then the ground fault is determined to be located on the stator side of the variable speed pumped storage unit. If the component characteristic value of the rotor-side operating frequency band is the largest, then the grounding fault is determined to be located on the rotor side of the variable speed pumped storage unit.

9. A grounding protection and area identification system for a variable-speed pumped-storage unit, characterized in that, include: At least one processor; and a readable storage medium communicatively connected to the at least one processor; The readable storage medium stores a computer program that can be executed by the at least one processor; When the computer program is executed by the processor, it implements the method for grounding protection and area identification of variable speed pumped storage units as described in any one of claims 1 to 8.

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