Standardized fault line mode voltage single-ended traveling wave protection method for DC transmission lines

Abstract

This invention discloses a single-ended traveling wave protection method for DC transmission lines based on standardized fault line-mode voltage, belonging to the field of DC transmission system relay protection technology. The method first acquires the positive and negative voltage signals at the beginning of the line and decouples them to obtain the fault line-mode voltage, extracting the minimum voltage value within the fault window. By calculating waveform difference or standardization coefficients, the fault line-mode voltage is standardized to eliminate the influence of transition resistance. Protection criteria are constructed based on the amplitude integral, concavity / convexity integral, or relative convexity characteristic quantity of the waveform difference or standardized fault line-mode voltage, achieving rapid and accurate identification of faults inside and outside the protection zone. This invention effectively overcomes the fault characteristic attenuation problem caused by transition resistance, significantly improves protection sensitivity and reliability, and is unaffected by grid structure, ground capacitance, and system oscillations, making it suitable for single-ended quantity protection of high-voltage DC transmission lines.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology for DC transmission systems, and particularly relates to a single-ended traveling wave protection method for DC transmission lines based on standardized fault line mode voltage. Background Technology

[0002] As grid voltage levels continue to rise, high-voltage direct current (HVDC) transmission systems offer advantages over traditional AC transmission systems, including larger transmission capacity, longer transmission distances, and lower losses. Simultaneously, the demands on grid protection performance are also increasing. Existing HVDC transmission system line protection can be categorized into two main types: unit protection and non-unit protection. Unit protection identifies faults by exchanging electrical quantities at both ends of the line, exhibiting absolute selectivity. However, this method relies on precise and synchronized measurement data between multiple relay terminals. In long-distance transmission lines or communication systems, data synchronization issues may lead to false tripping or failure to trip. Non-unit protection primarily relies on single-end electrical quantity information for fault identification. For example, by utilizing the characteristic quantities of the fault traveling wavefront, it can distinguish between faults within and outside the fault zone in a relatively short time. However, the characteristic quantities such as the rate of change, polarity, and amplitude upon which the traveling wavefront depends have low sensitivity. When a high-resistance fault occurs at the end of the line, insufficient sensitivity can easily lead to failure to trip. Furthermore, it is susceptible to the effects of transition resistance and noise.

[0003] After a fault occurs, rapid and accurate identification of the fault location is crucial for improving the transient stability of the power system and enhancing the transmission capacity of transmission lines. However, traditional traveling wave protection is susceptible to interference from noise and transition resistance. When the transition resistance is large, the fault transient signal attenuates significantly, leading to blurred fault characteristics, severely impacting protection performance, and making it difficult to meet sensitivity requirements. Therefore, there is an urgent need to develop a novel detection method capable of reliably identifying fault areas to achieve rapid and accurate isolation of flexible DC transmission lines after a fault occurs, ensuring the safe and stable operation of the system. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology, apply the linear attenuation effect of the transition resistance on the fault signal, and consider the influence of the transition resistance on the fault characteristics, so as to provide a single-ended traveling wave protection method for DC transmission lines based on standardized fault line mode voltage.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: Standardized fault line mode voltage single-ended traveling wave protection method for DC transmission lines includes: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Fault quantity window Integrate to obtain the voltage integral value. ; Step 7: Based on the standardized coefficients and voltage integral value Determine the internal and external faults of a DC transmission circuit.

[0006] Furthermore, the formula for calculating the voltage integral value in step 6 is as follows: ;

[0007] In the formula This is the start-up time of the starting element.

[0008] Furthermore, the specific method for determining internal and external faults in step 7 is as follows: If the standardization coefficient is satisfied And voltage integral value If so, it indicates a fault within the zone; If the standardization coefficient is satisfied And voltage integral value This indicates an out-of-area fault; among which, and This is the set value for the fault criterion.

[0009] Standardized fault line mode voltage single-ended traveling wave protection method for DC transmission lines includes: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Take two points above and The voltage connecting the line segments is ; Step 7: Voltage of the line segment and standardized fault line mode voltage In the fault quantity time window respectively Integrating within the range yields the voltage integral value. and voltage integral value ; Step 8: Calculate the integral value of concavity / convexity. ; Step 9: Determine the internal and external faults of the DC transmission circuit based on the standardization coefficient and the integral value of concavity / convexity.

[0010] Furthermore, the voltage integral value in step 7 and voltage integral value The calculation formula is: ; ; In the formula This is the start-up time of the starting element.

[0011] Furthermore, if the standardization coefficient is satisfied... And the integral value of concavity / convexity If so, it indicates a fault within the zone; If the standardization coefficient is satisfied And the integral value of concavity / convexity This indicates an external fault; among which and This is the set value for the fault criterion.

[0012] Standardized fault line mode voltage single-ended traveling wave protection method for DC transmission lines includes: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Take two points above and The voltage connecting the line segments is ; Step 7: Take the line segment voltage and standardized fault line mode voltage Upper Midpoint Time voltage value and voltage value ; Step 8: Calculate relative convexity ; Step 9: Determine the internal and external faults of the DC transmission circuit based on the standardized coefficient and relative convexity.

[0013] Standardized fault line mode voltage single-ended traveling wave protection method for DC transmission lines includes: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage The waveform; Step 4: Calculate the waveform similarity between the fault line mode voltage waveform and the reference waveform. The formula is: ; in Indicates the relevant parameters of the reference waveform. Relevant parameters representing the fault line-mode voltage waveform; Step 5: Based on waveform similarity Criteria for determining faults inside and outside the DC transmission line; if similarity This indicates an out-of-area fault; if the similarity... This indicates a fault within the zone.

[0014] Furthermore, the standardized coefficients in step 4 The calculation formula is: ; In the formula, To extract the fault line mode voltage under special fault conditions in DC lines Fault quantity window The minimum value within.

[0015] Furthermore, the formula for calculating the standardized fault line mode voltage in step 5 is as follows: .

[0016] The beneficial effects of this invention are as follows: (1) The technical solution of this application eliminates the influence of the transition resistance during a fault by using the linear relationship between the fault line mode voltage and the transition resistance. This solves the problem of insufficient reliability of traveling wave protection when a high-resistance fault occurs in a DC transmission line.

[0017] (2) The technical solution of this application standardizes the fault line mode voltage to offset the influence of the transition resistance on the transient fault characteristic quantity, and is not affected by the power grid structure and noise, which greatly improves the sensitivity and reliability of the traveling wave protection when a high resistance fault occurs in a DC transmission line. Attached Figure Description

[0018] Figure 1 This is a wiring diagram of a high-voltage direct current power system. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] The application principle of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1: Refer to the instruction manual. Figure 1 In a four-terminal flexible DC transmission system, to protect the lines Taking this as an example, we will explain the traveling wave protection method for DC transmission lines. Figure 1 As shown, the single-ended traveling wave protection method for DC lines based on the amplitude integration of standardized fault line mode voltage includes the following steps:

[0022] Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window In this embodiment, 0.06ms is used. Fault quantity extraction time window. Internal fault line mode voltage minimum value ;

[0023] Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient The calculation formula is: In the formula, To extract the fault line mode voltage under special fault conditions in DC lines Fault quantity window The minimum value within the range is taken as -545.1383kV in this embodiment; Step 5: Check the voltage of the faulty line mode. Standardization is performed to obtain the offsetting transition resistance. Standardized fault line mode voltage after impact Calculation formula ; Step 6: Standardize the fault line mode voltage Fault quantity window Integrating The formula is In the formula This refers to the start-up time of the starting element; Step 7: Determine the internal and external fault zones of the DC transmission circuit based on the standardized coefficients and voltage integral values. If the standardized coefficients are satisfied... And voltage integral value If the standardized coefficient is satisfied, then it is a fault within the area; And voltage integral value This indicates an external fault; where, and This is the set value for the fault criterion. Set to -0.012515. Set to 12V·s.

[0024] This method eliminates fault signal attenuation caused by transition resistance by standardizing the fault line-mode voltage. It then uses the amplitude integral of the standardized voltage within a time window as a criterion to distinguish between faults within and outside the fault zone. Furthermore, the standardization process linearly decouples the fault line-mode voltage from the transition resistance, addressing the insufficient sensitivity of traditional traveling wave protection for high-resistance faults. This is achieved through standardization coefficients. and voltage integral value The dual threshold judgment means that the integral value is significantly higher than the set value when the fault is within the zone, and significantly lower than the set value when the fault is outside the zone, which has high discrimination.

[0025] As shown in Table 1, it is clear that when an in-zone fault occurs, the integral result is significantly greater than the set value of 12V·s; when an out-of-zone fault occurs, the integral result is significantly less than the set value of 12V·s. Therefore, this method can effectively identify faults inside and outside the zone.

[0026] Table 1 Simulation results of DC lines based on the integral of standardized fault line mode voltage amplitude. ; Note: The total length of the DC transmission line is 207km. In the table, f1-10km indicates the location 10km from the beginning of the line; f2-103.5km indicates the location 103.5km from the beginning of the line; f3-197km indicates the location 197km from the beginning of the line; f4-outside the forward zone indicates the outside of the smoothing reactor at the beginning of the line (busbar side); f5-outside the reverse zone indicates the outside of the smoothing reactor at the end of the line (busbar side).

[0027] Example 2: Refer to the instruction manual. Figure 1 To protect the line Taking an example, this paper illustrates a method for traveling wave protection of DC transmission lines. It incorporates the implementation details of Embodiment 1 described above. For specific implementation methods of the above embodiments, please refer to the above description; the embodiments described here will not be repeated in detail. However, the difference between this embodiment and the above embodiments lies in the following:

[0028] like Figure 1 As shown, the single-ended traveling wave protection method for DC lines based on the concavity / convexity integral of the standardized fault line mode voltage includes the following steps: Step 6: Standardize the fault line mode voltage Take two points above ( , )and( , The voltage across the line segment connecting the two points is... Voltage on line segment Fault quantity window Integrating within the range The formula is In the formula This refers to the start-up time of the starting element; Step 7: Standardize the fault line mode voltage Fault quantity window Integrating The formula is ; Step 8: Perform integration on the results. and The integral value of concavity and convexity is obtained by subtraction. The formula is ; Step 9: Determine the internal and external fault zones of the DC transmission circuit based on the normalized coefficients and the integral value of concavity / convexity. If the normalized coefficients are satisfied... And the integral value of concavity / convexity If the standardized coefficient is satisfied, then it is a fault within the area; And the integral value of concavity / convexity This indicates an external fault; where, and This is the set value for the fault criterion. Set to -0.012515. Set to 1.6V·s.

[0029] In this embodiment, based on the standardized fault line mode voltage, the concavity / convexity integral between the standardized voltage waveform and the connection is calculated by constructing an endpoint connection, serving as the criterion for distinguishing between faults inside and outside the fault zone. The concavity / convexity integral reflects the curvature of the standardized voltage waveform; faults inside the fault zone exhibit a convex shape with a positive and large integral value, while faults outside the fault zone exhibit a concave shape with a negative integral value. In a four-terminal flexible DC system, the traditional concavity / convexity integral method cannot effectively distinguish between faults inside and outside the fault zone (as shown in Table 3). However, this method, through standardization, makes the criterion stable under different fault locations and transition resistances (as shown in Table 2), significantly improving its adaptability.

[0030] As shown in Table 2, the integral result is significantly greater than 1.6 V·s when an in-zone fault occurs; and significantly less than 1.6 V·s when an out-of-zone fault occurs. Therefore, the method in this embodiment can effectively identify faults inside and outside the zone.

[0031] The single-ended protection method for DC lines based on the convexity / concavity integral of the standardized fault line mode voltage used in this embodiment is compared with existing single-ended protection methods for DC lines based on the convexity / concavity integral (refer to existing literature: Single-ended protection scheme for flexible DC transmission lines based on the convexity / concavity of current-limiting reactor voltage integration, mainly used for double-ended flexible DC transmission systems). When applied to the four-terminal flexible DC transmission system of this application, Table 3 shows that the integral result is less than 0 regardless of whether the fault occurs within or outside the fault zone. Furthermore, when the fault location is at the beginning or end of the line, the integral result is greater than that for faults outside the fault zone. This indicates that when the single-ended protection method for DC lines based on the convexity / concavity integral is applied to the four-terminal flexible DC transmission system of this application, its results cannot effectively identify faults within or outside the fault zone of the DC line.

[0032] Table 2 Simulation results of DC lines based on the concavity / convexity integral of standardized fault line mode voltage. ; Table 3 Test results of concavity-convexity integrals in a four-terminal flexible DC transmission system ; Note: In Table 3, D represents the integral calculation value of the concave-convex arc property.

[0033] Example 3: Refer to the instruction manual. Figure 1 To protect the line Taking an example, this paper illustrates a method for traveling wave protection of DC transmission lines. It incorporates the implementation details of Embodiment 1 described above. For specific implementation methods of the above embodiments, please refer to the above description; the embodiments described here will not be repeated in detail. However, the difference between this embodiment and the above embodiments lies in the following:

[0034] like Figure 1 As shown, the single-ended traveling wave protection method for DC lines based on the relative convexity of the standardized fault line mode voltage includes the following steps: Step 6: Standardize the fault line mode voltage Take two points above ( , )and( , The voltage across the line segment formed by connecting two points is... Take the line segment voltage Upper Midpoint Time The voltage value is ,in This refers to the start-up time of the starting element; Step 7: Take the standardized fault line mode voltage Upper Midpoint Time The voltage value is ; Step 8: Analyze the results and The relative convexity is obtained by performing the difference operation. The formula is ; Step 9: Determine the internal and external fault zones of the DC transmission circuit based on the normalized coefficient and relative convexity. If the normalized coefficient is satisfied... and relative convexity If the standardized coefficient is satisfied, then it is a fault within the area; and relative convexity This indicates an external fault; where, and This is the set value for the fault criterion. Set to -0.012515. Set to 0.2.

[0035] In this embodiment, based on the standardized fault line mode voltage, the relative convexity of the actual voltage at the midpoint of the time window and the voltage of the terminal connection is extracted as a fault discrimination feature. Compared with integral calculation, relative convexity only requires the voltage difference at the midpoint, resulting in less computation and making it suitable for engineering implementation. The relative convexity is greater than 0.2 for faults within the fault zone and much less than 0.2 for faults outside the fault zone. The criterion is simple, stable, and consistent under different transition resistances.

[0036] As shown in Table 4, even with a 500Ω transition resistance, the relative convexity of faults within the fault zone is still much greater than the set value, demonstrating good resistance to transition resistance. Table 4 also clearly shows that when a fault occurs within the fault zone, the relative convexity is significantly greater than the set value of 0.2; when a fault occurs outside the fault zone, the relative convexity is significantly less than the set value of 0.2. Therefore, the method in this embodiment can effectively identify faults within and outside the fault zone.

[0037] Table 4 Simulation results of DC lines based on the relative convexity of standardized fault line mode voltages ; Example 4: Refer to the instruction manual. Figure 1 To protect the line Taking an example, this paper illustrates a method for traveling wave protection of DC transmission lines. It incorporates the implementation details of Embodiment 1 described above. For specific implementation methods of the above embodiments, please refer to the above description; the embodiments described here will not be repeated in detail. However, the difference between this embodiment and the above embodiments lies in the following:

[0038] like Figure 1 As shown, the single-ended traveling wave protection method for DC lines based on the similarity of fault line mode voltage waveforms includes the following steps: Step 3: Select the fault quantity window In this embodiment, 0.06ms is used. Fault quantity extraction time window. Internal fault line mode voltage The waveform;

[0039] Step 4: Calculate the waveform similarity between the fault line voltage waveform and the preset reference waveform. The formula is: ; in Indicates the relevant parameters of the reference waveform. The relevant parameters represent the fault line-mode voltage waveform. The average value of all sampling points of the reference waveform. The average value of all sampling points of the fault line mode voltage waveform is given by n, where n is the total number of waveform data points involved in the calculation, and i represents the nth point in the waveform. Step 5: Based on waveform similarity Criteria for determining whether a DC transmission circuit is faulty inside or outside the designated area. If similarity... This indicates an out-of-area fault; if the similarity... This indicates a fault within the zone.

[0040] Without standardization, this method directly calculates the similarity between the fault line voltage waveform and the reference waveform, using waveform shape differences to identify faults inside and outside the fault zone. This method is suitable for scenarios with a fixed system structure and a well-defined reference waveform, avoiding the calculation of standardization coefficients.

[0041] Based on standardized methods, this embodiment provides an auxiliary discrimination method based on waveform morphology, which enhances the diversity and adaptability of protection schemes.

[0042] According to the results in Tables 1-4 of the application examples, the single-ended traveling wave protection method for DC transmission lines based on the standardized fault line mode voltage, with the smoothing reactors at both ends of the DC transmission line as the boundary, has good resistance to transition resistance and is not affected by the fault distance. It can quickly and accurately identify faults inside and outside the DC transmission line.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for single-ended traveling wave protection of DC transmission lines with standardized fault line mode voltage, characterized in that, include: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Fault quantity window Integrate to obtain the voltage integral value. ; Step 7: Based on the standardized coefficients and voltage integral value Determine the internal and external faults of a DC transmission circuit.

2. The method according to claim 1, characterized in that the formula for calculating the voltage integral value in step 6 is: In the formula This is the start-up time of the starting element.

3. The method according to claim 1, characterized in that the internal and external fault judgment method in step 7 specifically comprises: If the standardization coefficient is satisfied And voltage integral value If so, it indicates a fault within the zone; If the standardization coefficient is satisfied And voltage integral value This indicates an out-of-area fault; among which, and This is the set value for the fault criterion.

4. A method for single-ended traveling wave protection of DC transmission lines with standardized fault line mode voltage, characterized in that, include: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Take two points above and The voltage connecting the line segments is ; Step 7: Voltage of the line segment and standardized fault line mode voltage In the fault quantity time window respectively Integrating within the range yields the voltage integral value. and voltage integral value ; Step 8: Calculate the integral value of concavity / convexity. ; Step 9: Determine the internal and external faults of the DC transmission circuit based on the standardization coefficient and the integral value of concavity / convexity.

5. The method according to claim 4, characterized in that the voltage integral value in step 7... and voltage integral value The calculation formula is: In the formula This is the start-up time of the starting element.

6. The method according to claim 4, characterized in that the fault judgment method for internal and external zones in step 9 is as follows: If the standardization coefficient is satisfied And the integral value of concavity / convexity If so, it indicates a fault within the zone; If the standardization coefficient is satisfied And the integral value of concavity / convexity This indicates an external fault; among which and This is the set value for the fault criterion.

7. A method for single-ended traveling wave protection of DC transmission lines with standardized fault line mode voltage, characterized in that, include: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage minimum value ; Step 4: Based on the fault line mode voltage minimum value Calculate the standardized coefficient ; Step 5: Check the voltage of the faulty line mode. Standardization processing is performed to obtain standardized fault line mode voltages. ; Step 6: Standardize the fault line mode voltage Take two points above and The voltage connecting the line segments is ; Step 7: Take the line segment voltage and standardized fault line mode voltage Upper Midpoint Time voltage value and voltage value ; Step 8: Calculate relative convexity ; Step 9: Determine the internal and external faults of the DC transmission circuit based on the standardized coefficient and relative convexity.

8. A method for single-ended traveling wave protection of DC transmission lines with standardized fault line mode voltage, characterized in that, include: Step 1: Collect the positive voltage at the beginning of the protected circuit. and negative voltage ; Step 2: Decouple the acquired positive and negative voltage signals to obtain the fault line mode voltage. ; Step 3: Select the fault quantity window Extracting fault quantities during window Internal fault line mode voltage The waveform; Step 4: Calculate the waveform similarity between the fault line mode voltage waveform and the reference waveform. The formula is: in Indicates the relevant parameters of the reference waveform. Relevant parameters representing the fault line-mode voltage waveform; Step 5: Based on waveform similarity Criteria for determining faults inside and outside the DC transmission line; if similarity This indicates an out-of-area fault; if the similarity... This indicates a fault within the zone.

9. The method according to any one of claims 1, 4, and 7, characterized in that the standardization coefficient in step 4... The calculation formula is: In the formula, To extract the fault line mode voltage under special fault conditions in DC lines Fault quantity window The minimum value within.

10. The method according to any one of claims 1, 4, and 7, characterized in that the formula for calculating the standardized fault line mode voltage in step 5 is: 。

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