Single-phase ground fault protection method for new energy transmission line based on fault characteristics

Abstract

This application provides a single-phase grounding fault protection method for renewable energy transmission lines based on fault characteristics, belonging to the field of power technology. This application uses the ratio of the zero-sequence component to the negative-sequence component of the single-terminal three-phase current on the renewable energy transmission line system side as the protection discrimination factor. It presets the amplitude setting range of the discrimination factor and the phase angle setting range corresponding to each phase fault. Through real-time calculation of the discrimination factor, it completes the determination of single-phase grounding faults and identification of the faulty phase within the area, triggering the corresponding protection action. This application does not require a dual-end communication channel or additional voltage acquisition and is unaffected by fault transition resistance; therefore, the method is easy to implement, adaptable to renewable energy transmission scenarios, and possesses technical advantages such as fast action speed, excellent selectivity, and high sensitivity.

Description

Technical Field

[0001] This application relates to the field of power technology, specifically to a method for protecting a single-phase grounding fault in a new energy transmission line based on fault characteristics. Background Technology

[0002] With the advancement of the construction of new power systems, new energy sources such as wind power and photovoltaics have achieved large-scale and intensive development. A large amount of new energy power is transmitted over long distances via AC transmission lines. The operation status of these transmission lines directly affects the efficiency of new energy absorption and the overall power supply stability of the power grid.

[0003] Existing protection schemes for renewable energy transmission lines are still based on protection principles designed for the fault characteristics of traditional synchronous generators. However, renewable energy sources connected to the grid via power electronic converters exhibit weak feeder characteristics under fault conditions, with limited fault current amplitude and controlled phase angle. This leads to serious problems with traditional protection principles in fault detection and section identification for renewable energy transmission lines, resulting in safety issues such as protection failure to operate and false operation.

[0004] Existing improved protection schemes for new energy transmission lines partially rely on real-time interaction of electrical quantities at both ends of the line, which places high demands on the reliability and real-time performance of communication, and also result in high engineering deployment costs and significant operational risks. Some schemes have high computational complexity, insufficient anti-interference capabilities, and are difficult to adapt to complex field operating conditions. Other schemes require modifications to the control strategy on the new energy side, which significantly increases the complexity and stability risks of system operation.

[0005] In summary, existing single-phase grounding fault protection methods for new energy transmission lines cannot simultaneously ensure the reliability of protection actions, the ease of engineering application, and the adaptability to operating scenarios. They suffer from technical problems such as insufficient fault detection sensitivity, poor action reliability, and difficulty in engineering implementation. Summary of the Invention

[0006] This application addresses the problems existing in the prior art by providing a single-phase grounding fault protection method based on the fault characteristics of inverter power supplies and using the ratio of zero-sequence to negative-sequence components of the single-terminal current on the new energy transmission line system side as the discrimination factor, thereby solving the aforementioned problems.

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a method for protecting a single-phase ground fault in a new energy transmission line based on fault characteristics, which includes the following steps: The amplitude setting range of the preset protection discrimination factor and the phase angle setting range corresponding to each phase ground fault are set. The three-phase current values ​​of the new energy transmission line system are collected in real time, and the three-phase current values ​​are transformed by symmetrical component transformation to obtain the corresponding negative sequence current component and zero sequence current component. The ratio of the zero-sequence current component to the negative-sequence current component is calculated and denoted as the real-time protection discrimination factor. The amplitude of the real-time protection discrimination factor is compared with the amplitude setting range. If the amplitude of the real-time protection discrimination factor is within the amplitude setting range, it is determined to be a single-phase ground fault in the area. After determining that a single-phase ground fault is located within the area, the phase angle of the real-time protection discrimination factor is compared with each of the phase angle setting intervals, and the faulty phase is matched based on the comparison results to trigger the protection device of the faulty phase to perform protection actions.

[0008] Optionally, the amplitude setting range includes a first amplitude range and a second amplitude range; The first amplitude range corresponds to the near-end section of the new energy transmission line divided according to a first preset ratio; The second amplitude range corresponds to the terminal section of the new energy transmission line divided according to the second preset ratio.

[0009] Optionally, the setting value of the first amplitude range can be obtained based on the zero-sequence current distribution coefficient at 60%-90% of the length of the new energy transmission line; The setting value for the second amplitude range is obtained based on the zero-sequence current distribution coefficient at the end of the entire length of the new energy transmission line.

[0010] Optionally, the zero-sequence current distribution coefficient is calculated based on the inherent electrical parameters of the zero-sequence equivalent network on the new energy transmission line system side; The inherent electrical parameters include the line zero-sequence impedance and the grounding transformer zero-sequence impedance.

[0011] Optionally, if the amplitude of the real-time protection discrimination factor is within the second amplitude range, the protection device of the fault phase performs the protection action after a delay.

[0012] Optionally, the delay range for executing the protection action is 0.2s-1s.

[0013] Optionally, the method for obtaining each of the phase angle tuning intervals includes: Each phase angle is calculated as the phase angle of the protection discrimination factor under the corresponding single-phase ground fault, and a preset phase angle margin is superimposed.

[0014] Optionally, for each corresponding single-phase ground fault, the phase angle for calculating the protection discrimination factor includes: The calculated phase angle of phase A is the phase angle of the zero-sequence current distribution coefficient; The calculated phase angle of phase B is the phase angle of the zero-sequence current distribution coefficient plus 120°; The calculated phase angle of phase C is the phase angle of the zero-sequence current distribution coefficient minus 120°.

[0015] Optionally, the preset phase angle margin can be obtained based on the phase angle error caused by the capacitance to ground of the new energy transmission line.

[0016] Optionally, obtaining the corresponding negative-sequence current component and zero-sequence current component includes: The symmetrical component transformation is performed using the symmetrical component transformation matrix of the three-phase electrical quantities of the power system.

[0017] Compared with the prior art, this application has the following advantages: This application collects single-phase three-phase current from the new energy transmission line system side and extracts negative-sequence and zero-sequence current components through symmetrical component transformation. The ratio of zero-sequence to negative-sequence current components is used as the protection discrimination factor. The single-phase grounding fault determination and fault matching within the area can be completed solely based on the single-phase current, without relying on a dual-end communication channel and an additional voltage acquisition link. This reduces the operational difficulty and risk of the protection method, while solving the interference of the weak feeder fault characteristics of new energy on the protection action, effectively improving the operational reliability and adaptability of the single-phase grounding fault protection of new energy transmission lines. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the method in this application; Figure 2 This is a composite sequence network diagram for a single-phase ground fault. Figure 3 The zero-order equivalent network of the system; Figure 4 Create a diagram showing the system fault points; Figure 5 This is a diagram showing the protection action range of Embodiment 1. Figure 6 The simulation results are for different fault phases in Example 1. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] It should be noted that, for ease of understanding, the method steps in the specific embodiments of this application are described in a certain order, but those skilled in the art can change the order of the steps according to actual needs, so this should not be used as a limiting condition; further, in the description of the following specific embodiments, the superscripts and subscripts of each parameter should be understood as distinguishing marks of similar identifiers in accordance with common interpretations unless otherwise specified, representing the parameters of the related or corresponding devices, and should not be understood as specific models or special marks.

[0023] like Figure 1 As shown, this application provides a single-phase grounding fault protection method for renewable energy transmission lines based on fault characteristics. This method is applicable to AC transmission systems composed of full-power inverter-type renewable energy power sources. The renewable energy power sources include wind power, photovoltaic power, and other types. It is suitable for long-distance transmission scenarios where renewable energy power sources are directly connected to the grid or indirectly connected via a flexible DC transmission system, and particularly meets the protection requirements for extreme scenarios where 100% of renewable energy is transmitted via AC.

[0024] Furthermore, the method in this application is based on the fault characteristics of a single-phase ground fault in an inverter power supply. When a single-phase ground fault occurs, the inverter-type new energy power supply will suppress the negative sequence current output, making the new energy side in the negative sequence network exhibit open-circuit characteristics. Combining the composite sequence network of a single-phase ground fault with the boundary conditions of different fault phases, the ratio of the zero-sequence current component to the negative sequence current component at the protection installation point on the new energy transmission line system side can be derived. It is only related to the zero-sequence current distribution coefficient on the system side and is not affected by the fault location or transition resistance. Moreover, the phase angle of this ratio under different fault phases exhibits a fixed 120° offset characteristic. Based on this, protection criteria and phase selection logic are constructed.

[0025] like Figure 2 As shown, a composite sequence network diagram of the system is constructed when a single-phase ground fault occurs on the transmitting line. Among them, These are the positive-sequence, negative-sequence, and zero-sequence impedances from the new energy outlet to the fault point, respectively. These are the positive-sequence, negative-sequence, and zero-sequence impedances from the outlet of the flexible DC converter station to the fault point, respectively. This is the transition resistor at the fault point.

[0026] Therefore, the boundary conditions corresponding to different faults are as follows: ; In the formula, These represent ground faults in phases A, B, and C, respectively. , , These correspond to the three-phase voltages at fault points A, B, and C, respectively. , , These correspond to the phase currents at fault points A, B, and C, respectively.

[0027] After symmetric component transformation, the fault point sequence components satisfy the following relationship: ; In the formula, It is a general operator for the analysis of symmetric components in power systems; The positive sequence fault current phasor at the fault point; The negative sequence fault current phasor at the fault point; This is the zero-sequence fault current phasor at the fault point.

[0028] Based on the characteristics of the open-circuit negative-sequence network on the renewable energy side, the zero-sequence component of the current on the M-system side of line can be derived. With negative order components The formula for calculating the ratio is as follows: ; In the formula, The zero-sequence current distribution coefficient on the system side is the proportion of the zero-sequence current at the fault point distributed to the protection installation point on the system side. The calculation formula is: .

[0029] Furthermore, the ratio of the zero-sequence component to the negative-sequence component of the system-side current can be obtained. The expression is as follows: ; When a single-phase ground fault occurs on the line, without considering calculation and transmission errors, the amplitude of the ratio of the zero-sequence to the negative-sequence components of the system-side current is... Under phase A fault, the phase angle is Under phase B fault, the phase angle is Under a C-phase fault, the phase angle is The above ratio is the protection discrimination factor.

[0030] Therefore, it can be seen that when a single-phase ground fault occurs on a new energy transmission line, the correlation of the current sequence components on the system side under different fault phases varies significantly, which can constitute a protection criterion. Based on the aforementioned calculation results, the amplitude setting range of the protection discrimination factor and the phase angle setting range corresponding to each phase ground fault are first preset. The amplitude setting range includes a first amplitude range and a second amplitude range. The first amplitude range corresponds to the near-end section of the new energy transmission line divided according to a first preset ratio, and the second amplitude range corresponds to the end section of the new energy transmission line divided according to a second preset ratio, such as 10%-40%. The value range of the first preset ratio is 60%-90%, and in this application, the first preset ratio is 80%. That is, the setting value of the first amplitude range is obtained based on the zero-sequence current distribution coefficient at 80% of the length of the new energy transmission line; the setting value of the second amplitude range is obtained based on the zero-sequence current distribution coefficient at the end of the entire length of the new energy transmission line.

[0031] In this system, grounding transformers are used on both sides of the new energy transmission line, and the zero-sequence component is not constrained by the control strategy of the power electronic equipment. Therefore, combined with... Figure 3 The system zero-sequence equivalent network is shown, and the system-side zero-sequence current distribution coefficient is... It depends on the zero-sequence parameters of the electrical components, such as the zero-sequence impedance of the line. Transformer zero-sequence impedance Synchronous machine zero-sequence impedance Therefore, the zero-sequence current distribution coefficient is calculated based on the inherent electrical parameters of the zero-sequence equivalent network on the new energy transmission line system side. These inherent electrical parameters include the line zero-sequence impedance and the grounding transformer zero-sequence impedance. It should be noted that the typical range of the ground capacitance of conventional overhead transmission lines is usually between a few nanofarads and tens of nanofarads per kilometer, with a per-unit capacitance current of approximately 1% to 3%, corresponding to an amplitude error... The calculation formula is as follows: ; In the formula, This represents the capacitance current to ground per unit length of the line.

[0032] When a single-phase ground fault occurs on a new energy transmission line, a set value of the protection discrimination factor is used. Two-stage tuning value and the maximum value of the protection factor within the protection interval. The calculation formula is as follows: ; The corresponding first amplitude range is The second amplitude range is .

[0033] The purpose of this application's two-stage protection design is that the first stage quickly clears most of the faults in 80% of the line section, while the second stage clears dead zones and terminal faults through short delays to prevent cascading tripping.

[0034] The method for obtaining each phase angle setting interval is as follows: taking the calculated phase angle of the protection discrimination factor under the corresponding single-phase ground fault as the center, a preset phase angle margin is superimposed. The calculated phase angle of phase A is the phase angle of the zero-sequence current distribution coefficient, the calculated phase angle of phase B is the phase angle of the zero-sequence current distribution coefficient plus 120°, and the calculated phase angle of phase C is the phase angle of the zero-sequence current distribution coefficient minus 120°. The preset phase angle margin is obtained based on the phase angle error caused by the capacitance to ground of the new energy transmission line. The formula for setting the phase angle error is as follows: ; In the formula, The phase angle error is the protection discrimination factor caused by the line-to-ground capacitance. This represents the maximum offset of the phase angle error, calculated based on the line-to-ground capacitance parameters.

[0035] Therefore, after the preset of each setting interval is completed, the three-phase current value at the installation point of the protection device on the new energy transmission line system side is collected in real time. The collected three-phase current value is transformed by symmetrical components to obtain the corresponding negative sequence current component and zero sequence current component. The symmetrical component transformation is realized by the symmetrical component transformation matrix of the three-phase electrical quantities of the power system.

[0036] Calculate the ratio of the zero-sequence current component to the negative-sequence current component, and denote it as the real-time protection discrimination factor. Compare the amplitude of the real-time protection discrimination factor with the amplitude setting range, using the following comparison method: (1) If the amplitude of the real-time protection discrimination factor is within the amplitude setting range, it is determined to be a single-phase ground fault in the zone; (2) If the amplitude of the real-time protection discrimination factor does not fall within the amplitude setting range, it is determined to be a normal operating state or an external fault, and the protection will not operate.

[0037] After determining that it is a single-phase ground fault in the area, the phase angle of the real-time protection discrimination factor is compared with the phase angle setting interval of each phase angle, and the fault phase is matched based on the comparison result to trigger the protection device of the fault phase to perform protection action and complete the phase tripping and disconnection of the fault line.

[0038] If the amplitude of the real-time protection discrimination factor is within the first amplitude range, the protection operates instantaneously. The action response time can be understood as the inherent action time of the protection device, which is usually less than 0.1s. If the amplitude of the real-time protection discrimination factor is within the second amplitude range, the protection device of the fault phase performs the protection action after a delay. The delay range for performing the protection action is 0.2s-1s. In this application, the delay is taken as 0.5s, which serves as a supplement to the protection segment corresponding to the first amplitude range. This is used to clear the fault at the end of the line and to prevent incorrect protection action when there is a fault at the end of the line or a fault at the outlet of the lower-level line, thus preventing over-level tripping.

[0039] Example 1; This embodiment builds a simulation model of the new energy transmission line in the power system computer-aided design simulation software (PSCAD), such as... Figure 4 As shown, the effectiveness of the method protected in this application is verified.

[0040] In the simulation model, the power source is a full-power inverter type, represented by photovoltaic power, with a power station capacity of 200MW, a transmission line voltage level of 220kV, and a transmission line length of 100km. Multiple fault points are set in the simulation model, among which... and These are faults outside the reverse direction zone on the new energy side and the system side of the line, respectively. For faults within the zone, α represents the ratio of the distance from the fault point to the protection installation point on the line system side to the total length of the line.

[0041] Based on the system component parameters calculated in the simulation model, the protection's first operating range, i.e., the first amplitude range, is... The protection's second-stage action range, i.e., the second amplitude range, is... Simultaneously, the preset phase angle margin of the phase angle setting range is determined based on the line-to-ground capacitance parameters. The correspondence between the amplitude boundaries of the above protection operation range and the phase angle setting range is as follows: Figure 5 As shown, based on the fixed phase angle offset characteristics of the protection discrimination factor under three types of faults, the three types of faults include: AG fault (A-phase single-phase ground fault), and the discrimination factor phase angle is... BG fault (B-phase single-phase ground fault), the discrimination factor phase angle is: ;CG fault (C-phase single-phase ground fault), the discrimination factor phase angle is .

[0042] Multiple fault scenarios with different fault locations, fault phases, and transition resistances are set up in the simulation model to verify the protection performance, such as... Figure 6 The simulation statistics are shown below.

[0043] Simulation results show that as the fault location α increases, the ratio of zero-sequence to negative-sequence components gradually decreases, while the phase angle remains relatively stable within the fault operating range, ensuring accurate protection operation. Simultaneously, as the transition resistance increases, the ratio of zero-sequence to negative-sequence components remains almost unchanged, consistently falling within the fault operating range, also resulting in accurate protection operation. This demonstrates that the proposed protection is unaffected by the transition resistance. For faults within the fault zone, the proposed protection operates accurately and quickly selects and clears the fault phase; for faults outside the fault zone, it does not malfunction, exhibiting good selectivity and sensitivity.

[0044] In summary, this application addresses the significant decrease in sensitivity of longitudinal protection under the weak-feed controlled characteristics of high-proportion renewable energy transmission lines. Based on the control characteristics of suppressing negative-sequence current on the renewable energy side and combined with the boundary conditions of different fault phases of the renewable energy transmission line, it proposes a single-ended quantity protection method suitable for single-phase grounding faults by utilizing the open-circuit property of the renewable energy side in the negative-sequence network. This protection scheme is unaffected by transition resistance and can be applied to the application scenario of double-ended power electronic equipment in 100% renewable energy transmission lines. Furthermore, it requires no counterparty equipment or communication channel and has a fast response speed. Simulation results under various fault scenarios show that this scheme has high selectivity and sensitivity.

[0045] Finally, it should be noted that the above content is only used to illustrate the technical solution of this application, and is not intended to limit the scope of protection of this application. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this application shall not depart from the substance and scope of the technical solution of this application.

Claims

1. A method for protecting a single-phase ground fault in a new energy transmission line based on fault characteristics, characterized in that, include: The amplitude setting range of the preset protection discrimination factor and the phase angle setting range corresponding to each phase ground fault are set. The three-phase current values ​​of the new energy transmission line system are collected in real time, and the three-phase current values ​​are transformed by symmetrical component transformation to obtain the corresponding negative sequence current component and zero sequence current component. The ratio of the zero-sequence current component to the negative-sequence current component is calculated and denoted as the real-time protection discrimination factor. The amplitude of the real-time protection discrimination factor is compared with the amplitude setting range. If the amplitude of the real-time protection discrimination factor is within the amplitude setting range, it is determined to be a single-phase ground fault in the area. After determining that a single-phase ground fault is located within the area, the phase angle of the real-time protection discrimination factor is compared with each of the phase angle setting intervals, and the faulty phase is matched based on the comparison results to trigger the protection device of the faulty phase to perform protection actions.

2. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 1, characterized in that, The amplitude setting range includes a first amplitude range and a second amplitude range; The first amplitude range corresponds to the near-end section of the new energy transmission line divided according to a first preset ratio; The second amplitude range corresponds to the terminal section of the new energy transmission line divided according to the second preset ratio.

3. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 2, characterized in that, Based on the zero-sequence current distribution coefficient at 60%-90% of the length of the new energy transmission line, the setting value of the first amplitude range is obtained; The setting value for the second amplitude range is obtained based on the zero-sequence current distribution coefficient at the end of the entire length of the new energy transmission line.

4. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 3, characterized in that, The zero-sequence current distribution coefficient is calculated based on the inherent electrical parameters of the zero-sequence equivalent network on the new energy transmission line system side. The inherent electrical parameters include the line zero-sequence impedance and the grounding transformer zero-sequence impedance.

5. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 2, 3, or 4, characterized in that, If the amplitude of the real-time protection discrimination factor is within the second amplitude range, the protection device of the fault phase will perform a protection action after a delay.

6. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 5, characterized in that, The delay range for executing protection actions is 0.2s-1s.

7. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 1, characterized in that, The methods for obtaining each of the phase angle tuning intervals include: Each phase angle is calculated as the phase angle of the protection discrimination factor under the corresponding single-phase ground fault, and a preset phase angle margin is superimposed.

8. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 7, characterized in that, When a single-phase ground fault occurs in each phase, the phase angle for calculating the protection discrimination factor includes: The calculated phase angle of phase A is the phase angle of the zero-sequence current distribution coefficient; The calculated phase angle of phase B is the phase angle of the zero-sequence current distribution coefficient plus 120°; The calculated phase angle of phase C is the phase angle of the zero-sequence current distribution coefficient minus 120°.

9. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 7 or 8, characterized in that, The preset phase angle margin is obtained based on the phase angle error caused by the capacitance to ground of the new energy transmission line.

10. The method for single-phase grounding fault protection of new energy transmission lines based on fault characteristics according to claim 1, characterized in that, Obtaining the corresponding negative sequence current component and zero sequence current component includes: The symmetrical component transformation is performed using the symmetrical component transformation matrix of the three-phase electrical quantities of the power system.

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