Traveling wave protection method and system for high-voltage direct-current transmission line

Abstract

The invention relates to a traveling wave protection method and system for a high-voltage direct-current transmission line, and the method comprises the steps: judging whether an antipode line meets a pole wave criterion or not within a preset first time threshold value for judging whether the antipode line and the antipode line have faults at the same time or not when the pole wave criterion of the antipode line is met; if yes, when the local pole line meets the low voltage criterion and the current criterion within a preset second time threshold value used for waiting for the local pole line to carry out low voltage criterion and current criterion judgment, the traveling wave protection of the local pole line is triggered, and the purpose that the traveling wave protection of the local pole line is triggered when the double poles have faults at the same time is achieved. According to the pole line, the pole wave criterion, the low voltage criterion and the current criterion are judged, so that the traveling wave protection is triggered, the problem that the traveling wave protection cannot be triggered due to the fact that the ground wave criterion cannot be judged is effectively avoided, continuous calculation and comparison of data are not needed, the triggering time of line protection is shortened, and the stability of a power grid is effectively improved.

Description

Technical Field

[0001] The present invention relates to a method and system for traveling wave protection of a high - voltage direct - current (HVDC) transmission line, belonging to the field of HVDC lines. Background Art

[0002] Compared with traditional alternating - current (AC) transmission systems, HVDC transmission systems have the advantages of large transmission capacity, long transmission distance, and low loss, and are widely used in long - distance power transmission, large - area grid interconnection, and underground cable power transmission. The HVDC transmission line shoulders the important task of power transmission between the energy production area and the load center. High - performance protection for HVDC transmission lines is of great significance for improving the safety and stability of the entire power grid.

[0003] In the prior art, the protection of DC transmission lines is mainly carried out through traveling wave protection. Traveling wave protection refers to using the transient traveling waves generated during a fault to quickly determine the fault location, thereby performing fault detection, clearing, and protection of the line. Its triggering conditions are that the pole - wave criterion, ground - wave criterion, low - voltage criterion, and current criterion are all satisfied simultaneously. When a single - pole line fault or a successive fault of a bipolar line occurs in a DC transmission line, all four criteria can quickly respond and complete the judgment to trigger the traveling wave protection of the line. However, when a simultaneous fault of a bipolar line occurs in a DC transmission line, since the voltage polarities of the bipolar lines are opposite, the fault waveforms in the bipolar neutral - line area will be partially or completely cancelled out during a simultaneous fault, and the relevant analog quantity changes are not obvious. The ground - wave criterion uses the relevant analog quantity in the bipolar neutral - line area as the criterion, and it cannot be quickly determined during a simultaneous fault of a bipolar line, resulting in the inability to trigger the protection action of the traveling wave protection.

[0004] To solve the above technical problems, the published text of a Chinese invention patent application with the authorization announcement number CN109038515B discloses a traveling wave protection method and system for a hybrid HVDC transmission line based on dual-tree complex wavelet transform. Among them, the voltage difference modulus and voltage common modulus are calculated using the collected DC voltages of the positive and negative poles; then, the dual-tree complex wavelet transform is calculated for the calculated voltage difference modulus; the third preset threshold is used to judge with the dual-tree complex wavelet transform value of the voltage difference modulus to determine whether to start the criterion for judgment; when starting, the dual-tree complex wavelet transform is calculated for the voltage difference modulus again, and then comparisons of WSf(x)>k1WSf(x01), k2WSf(x02)<WSf(x)<k1WSf(x01), and k3WSf(x03)<WSf(x)<k2WSf(x02) are made. Although the problem that the bipolar simultaneous fault cannot be protected in the traveling wave protection mode is avoided, however, the fault judgment process includes multiple ratio coefficients (k1, k2, k3), multiple modulus extrema of the dual-tree complex wavelet transform, the products between the ratio coefficients and the modulus extrema of the dual-tree complex wavelet transform, and the comparisons between the foregoing data, which increases the data processing duration and complexity during fault judgment. And the instant occurrence of a line fault cannot support / wait for the continuous comparison and calculation process of data, which will lead to an extended processing time for the fault judgment process and even inaccurate fault troubleshooting due to data redundancy. Summary of the Invention

[0005] The object of the present invention is to provide a method and system for traveling wave protection of a high-voltage DC transmission line to solve the problem that the protection trigger process is complex and not fast when a bipolar simultaneous fault occurs in a bipolar DC transmission line.

[0006] To achieve the above object, on the one hand, the present invention proposes a method for traveling wave protection of a high-voltage DC transmission line, including:

[0007] When the pole wave criterion of the local line is satisfied, within a preset first time threshold for judging whether the local line and the opposite pole line have simultaneous faults, judge whether the opposite pole line satisfies the pole wave criterion;

[0008] If so, and when the local line satisfies the low-voltage criterion and the current criterion within a preset second time threshold for waiting for the local line to judge the low-voltage criterion and the current criterion, trigger the traveling wave protection of the local line.

[0009] Further, the first time threshold is set to 2ms - 4ms.

[0010] Further, the second time threshold is set to 10ms - 20ms.

[0011] Further, when judging whether the opposite pole line satisfies the pole wave criterion, it is also judged whether the opposite pole line satisfies the low-voltage criterion;

[0012] When the antipole line satisfies the pole wave criterion and the low voltage criterion, and within a preset second time threshold, this pole line satisfies the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered.

[0013] Furthermore, if the antipole line does not satisfy the pole wave criterion, but this pole line satisfies the ground wave criterion, the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered.

[0014] On the other hand, the present invention also proposes a system for traveling wave protection of a high voltage direct current transmission line, and the system is used to execute the following method: when the pole wave criterion of this pole line is satisfied, within a preset first time threshold for judging whether this pole line and the antipole line fail simultaneously, judge whether the antipole line satisfies the pole wave criterion;

[0015] If so, and within a preset second time threshold for waiting for this pole line to judge the low voltage criterion and the current criterion, when this pole line satisfies the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered.

[0016] Furthermore, the first time threshold is set to 2 ms - 4 ms.

[0017] Furthermore, the second time threshold is set to 10 ms - 20 ms.

[0018] Furthermore, when judging whether the antipole line satisfies the pole wave criterion, it is also judged whether the antipole line satisfies the low voltage criterion;

[0019] When the antipole line satisfies the pole wave criterion and the low voltage criterion, and within a preset second time threshold, this pole line satisfies the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered.

[0020] Furthermore, if the antipole line does not satisfy the pole wave criterion, but this pole line satisfies the ground wave criterion, the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered.

[0021] The beneficial effects of the present invention are as follows: When the pole wave criterion of the present pole line is satisfied, within a preset first time threshold for determining whether the present pole line and the opposite pole line fail simultaneously, it is determined whether the opposite pole line satisfies the pole wave criterion; if so, and when the present pole line satisfies the low voltage criterion and the current criterion within a preset second time threshold for waiting for the present pole line to perform the low voltage criterion and the current criterion judgment, the traveling wave protection of the present pole line is triggered, so that when a fault occurs simultaneously in both poles, the present pole line performs the judgment of the pole wave criterion, the low voltage criterion and the current criterion, and shields the judgment of the ground wave criterion, thereby realizing the triggering of the traveling wave protection, effectively avoiding the problem that the traveling wave protection cannot be triggered due to the inability to judge the ground wave criterion, and moreover, without continuously calculating and comparing data, shortening the triggering time of the line protection, and effectively improving the stability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic flow chart of a method for traveling wave protection of a high-voltage direct current transmission line proposed by the present invention;

[0023] Figure 2 is a schematic flow chart of the logical judgment of a method for traveling wave protection of a high-voltage direct current transmission line in an actual application scenario proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] The inventive concept of the present invention lies in: In order to avoid the technical problem that the traveling wave protection cannot be triggered due to the simultaneous failure of both poles, under the condition that the pole wave criterion of the present pole line is satisfied, a time window is opened. In response to the occurrence of a failure in the opposite pole line, the present pole line continues to perform the judgment of the low voltage criterion and the current criterion, that is, shields the judgment of the ground wave criterion in the present pole line, thereby triggering the traveling wave criterion, effectively performing the line protection of the bipolar lines with simultaneous failures, not only improving the line safety and the reliability of the traveling wave protection, but also effectively avoiding the risk of bipolar blocking caused by long-term line failures, and improving the stability of the power grid.

[0026] Method Embodiment 1:

[0027] As Figure 1 shown, it is a schematic flow chart of a method for traveling wave protection of a high-voltage direct current transmission line proposed by the present invention, which includes step S11 and step S12, specifically:

[0028] Step S11, when the pole wave criterion of the local pole line is satisfied, within a preset first time threshold for determining whether the local pole line and the opposite pole line fail simultaneously, determine whether the opposite pole line satisfies the pole wave criterion; it should be noted that when setting the first time threshold, it is necessary to ensure that the opposite pole line generates a fault waveform when responding to a fault, and also to ensure the quick operation of the line traveling wave protection. Therefore, considering comprehensively, the first time threshold is preferably set to 2 ms - 4 ms to achieve an appropriate judgment of whether a simultaneous fault occurs, and it will not affect the quick operation of the line traveling wave protection, and is based on the fault response time of the opposite pole line.

[0029] The pole wave criterion is used to detect line faults. In actual application scenarios, the current pole wave of the line can be calculated, and then the calculated current pole wave can be used to determine whether the line is faulty. Specifically, the pole wave can be calculated by the following formula:

[0030] P WA =(IDL + IZ) * Z p -UDL;

[0031] The pole wave criterion can be judged by the following formula:

[0032] P WA -P` wA >XU P ;

[0033] Where, P WA is the current pole wave; P` WA is the previous pole wave; IDL is the DC current; IZ is the current at the head of the DC filter; Zp is the differential mode wave impedance; UDL is the DC voltage; XU P is the pole wave setting value.

[0034] The previous pole wave is the pole wave value used to judge whether the current pole wave is abnormal. It can be the pole wave value under non-fault conditions of the line. In actual application scenarios, the pole wave values at 0.2 ms before, 0.6 ms before, 1 ms before, 2 ms before, etc. under other non-fault conditions can be selected.

[0035] Step S12, if so, and when the local pole line satisfies the low voltage criterion and the current criterion within a preset second time threshold for waiting for the local pole line to perform the low voltage criterion and the current criterion judgment, trigger the traveling wave protection of the local pole line; here, within the second time threshold, the local pole line performs the low voltage criterion and the current criterion judgment. Therefore, the setting of the second time threshold will cooperate with the local pole line to complete the criterion judgment, that is, the second time threshold will meet the judgment time requirements for the local pole line to complete the low voltage criterion and the current criterion judgment. Preferably, the second time threshold is set to 10 ms - 20 ms.

[0036] The low-voltage criterion is used to assist in detecting line faults. In actual application scenarios, when the DC voltage is less than a preset low-voltage setting value, it is determined that the line meets the low-voltage criterion. The preset low-voltage setting value is the voltage value when a fault occurs in the DC line, which is less than the normal voltage value. Preferably, the preset low-voltage setting value is 0.5 p.u. In actual application scenarios, the low-voltage criterion is judged through the following formula: UDL < U set ; where UDL is the DC voltage; U set is the voltage setting value.

[0037] The current criterion is used to assist in detecting line faults and distinguishing between internal and external faults in the zone. In actual application scenarios, the current criterion is judged through the following formula:

[0038] IDL - IDL` > I set ;

[0039] where IDL is the DC current; IDL` is the DC current when there is no fault; I set is the current setting value. Usually, preferably, IDL` is the DC current 1.4 ms ago.

[0040] Through the above step S11 and step S12, when a bipolar fault occurs, the execution of the ground wave criterion is shielded, and the effective triggering of the traveling wave protection is achieved.

[0041] Method Embodiment 2:

[0042] A method for traveling wave protection of a high-voltage DC transmission line proposed by the present invention also judges whether the opposite pole line meets the low-voltage criterion when judging whether the opposite pole line meets the pole wave criterion.

[0043] When the opposite pole line meets the pole wave criterion and the low-voltage criterion, and within a preset second time threshold, the present pole line meets the low-voltage criterion and the current criterion, the traveling wave protection of the present pole line is triggered, realizing the addition of the opposite pole wave criterion and the opposite pole low-voltage criterion to the judgment logic of the present pole criterion, and solving the problem that the traveling wave protection cannot operate correctly when a bipolar line fails simultaneously.

[0044] Such as Figure 2As shown in the figure, it is a schematic flowchart of the logical judgment of a method for traveling wave protection of a high-voltage DC transmission line proposed by the present invention in an actual application scenario. Among them, the DC protection system of this pole collects the UDL, IDL, and IZ of the opposite pole to open a 3-ms time window after judging whether the UDL, IDL, and IZ of this pole line meet the pole wave criterion of this pole line, and perform the determination of the pole wave criterion and the low-voltage criterion based on the UDL, IDL, and IZ of the opposite pole; when the pole wave criterion of the opposite pole is satisfied and the low-voltage criterion is also satisfied, it is determined that both poles fail, and the output of the ground wave criterion of this pole is set to 1 within 10 ms, that is, the ground wave criterion is satisfied (to achieve the shielding of the ground wave criterion. Of course, other methods of shielding the ground wave criterion such as directly setting the trigger traveling wave criterion logic to jump out of the ground wave judgment can also be used), and perform the judgment of the low-voltage criterion and the current criterion of this pole. Only when the low-voltage criterion and the current criterion of this pole are simultaneously satisfied, the traveling wave protection is triggered.

[0045] Method Embodiment 3:

[0046] For a method for traveling wave protection of a high-voltage DC transmission line proposed by the present invention, if the opposite pole line does not meet the pole wave criterion, but this pole line meets the ground wave criterion, the low-voltage criterion, and the current criterion, then the traveling wave protection of this pole line is triggered; here, the ground wave criterion is used to judge the faulty pole. In an actual application scenario, the current ground wave of the line can be calculated and then the current ground wave can be used to judge the line fault level. Specifically, the ground wave can be calculated by the following formula:

[0047] COM WA =(0.5*IDEL - ICN)*Z g -0.5UDN;

[0048] The ground wave criterion can be judged by the following formula:

[0049] COM WA -COM` WA >XU C ;

[0050] Among them, COM WA is the current ground wave; COM` WA is the previous ground wave; IDEL is the current of the grounding electrode line; ICN is the current of the neutral bus shock capacitor; Zg is the ground mode wave impedance; UDN is the neutral bus voltage; XU C is the ground wave setting value.

[0051] The previous ground wave is the ground wave value used to judge whether the current ground wave is abnormal. It can be the ground wave value under non-fault conditions of the line. In an actual application scenario, the ground wave value 1.6 ms ago or other ground wave values under non-fault conditions can be selected.

[0052] For example, within an open time window of 3 ms, based on the determination of the pole wave criterion for the opposite pole UDL, IDL, and IZ, if the opposite pole does not meet the pole wave criterion, the low voltage criterion is judged according to the UDL of this pole line, and the current criterion is judged according to the IDL. And when this pole line meets the low voltage criterion and the current criterion, the traveling wave protection is triggered.

[0053] System embodiment:

[0054] The present invention also proposes a system for traveling wave protection of a high - voltage direct - current transmission line. The system is used to execute the following method: when the pole wave criterion of this pole line is met, within a preset first time threshold for judging whether this pole line and the opposite pole line fail simultaneously, it is judged whether the opposite pole line meets the pole wave criterion; the first time threshold is set to 2 ms - 4 ms.

[0055] If so, and when this pole line meets the low voltage criterion and the current criterion within a preset second time threshold for waiting for this pole line to judge the low voltage criterion and the current criterion, the traveling wave protection of this pole line is triggered; the second time threshold is set to 10 ms - 20 ms.

[0056] Meanwhile, when judging whether the opposite pole line meets the pole wave criterion, it is also judged whether the opposite pole line meets the low voltage criterion; when the opposite pole line meets the pole wave criterion and the low voltage criterion, and this pole line meets the low voltage criterion and the current criterion within the preset second time threshold, the traveling wave protection of this pole line is triggered.

[0057] And if the opposite pole line does not meet the pole wave criterion, but this pole line meets the ground wave criterion, the low voltage criterion, and the current criterion, the traveling wave protection of this pole line is triggered.

[0058] Here, the introduction of the above - mentioned method has been described clearly enough in Method Embodiments 1 - 3, and will not be elaborated here.

[0059] In summary, aiming at the problem that the traveling wave protection cannot act correctly when both poles of the bipolar line fail simultaneously, the present invention enables the traveling wave protection to act correctly when both poles fail simultaneously by briefly shielding the ground wave criterion, improves the reliability of the traveling wave protection, avoids the risk of bipolar blocking of the DC transmission system caused by the incorrect action of the traveling wave protection when both poles fail simultaneously, and effectively improves the grid stability.

Claims

1. A method for traveling wave protection of a high voltage direct current transmission line, characterized in that: include: When the polar wave criterion of the local pole line is satisfied, within a preset first time threshold for determining whether the local pole line and the opposite pole line are simultaneously faulty, determining whether the opposite pole line satisfies the polar wave criterion; If so, and when the local pole line meets the low voltage criterion and the current criterion within the preset second time threshold for waiting for the local pole line to perform the low voltage criterion and the current criterion judgment, the traveling wave protection of the local pole line is triggered.

2. The method for traveling wave protection of a high voltage direct current transmission line according to claim 1, characterized in that: The first time threshold is set to 2ms-4ms.

3. The method for traveling wave protection of a high voltage direct current transmission line according to claim 1, characterized in that: The second time threshold is set to 10ms-20ms.

4. The method for traveling wave protection of a high voltage direct current transmission line according to claim 1, characterized in that: When judging whether the polar line meets the polar wave criterion, it is also judged whether the polar line meets the low voltage criterion; When the opposite pole line meets the pole wave criterion and the low voltage criterion, and the local pole line meets the low voltage criterion and the current criterion within the preset second time threshold, the traveling wave protection of the local pole line is triggered.

5. The method for traveling wave protection of a high voltage direct current transmission line according to claim 1, characterized in that: If the opposite pole line does not meet the pole wave criterion, but the local pole line meets the ground wave criterion, low voltage criterion and current criterion, the traveling wave protection of the local pole line will be triggered.

6. A system for travelling wave protection of high voltage direct current transmission lines, characterized in that: The system is used to perform the following method: when the polar wave criterion of the local polar line is satisfied, within a preset first time threshold for determining whether the local polar line and the opposite polar line are simultaneously faulty, determining whether the opposite polar line satisfies the polar wave criterion; If so, and when the local pole line meets the low voltage criterion and the current criterion within the preset second time threshold for waiting for the local pole line to perform the low voltage criterion and the current criterion judgment, the traveling wave protection of the local pole line is triggered.

7. The system for traveling wave protection of high voltage direct current transmission lines according to claim 6, characterized in that: The first time threshold is set to 2ms-4ms.

8. The system for traveling wave protection of high voltage direct current transmission lines according to claim 6, characterized in that: The second time threshold is set to 10ms-20ms.

9. The system for traveling wave protection of high voltage direct current transmission lines according to claim 6, characterized in that: When judging whether the polar line meets the polar wave criterion, it is also judged whether the polar line meets the low voltage criterion; When the opposite pole line meets the pole wave criterion and the low voltage criterion, and the local pole line meets the low voltage criterion and the current criterion within the preset second time threshold, the traveling wave protection of the local pole line is triggered.

10. The system for traveling wave protection of high voltage direct current transmission lines according to claim 6, characterized in that: If the opposite pole line does not meet the pole wave criterion, but the local pole line meets the ground wave criterion, low voltage criterion and current criterion, the traveling wave protection of the local pole line will be triggered.

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