Same-tower double-circuit direct current transmission line multi-pole fault identification method based on interelectrode differential mode voltage variation combination

Abstract

The invention discloses a same-tower double-circuit direct-current transmission line multi-pole fault identification method based on interelectrode differential mode voltage variation combination. The method comprises the following steps: firstly, acquiring single-end voltage of a double-circuit common quadrupole line of a same-tower double-circuit direct-current transmission system; then, according to the obtained line quadrupole voltage, calculating six differential mode components between each two poles of the quadrupole line of the same-tower double-circuit direct current power transmission system, and further calculating the interelectrode differential mode voltage variation integral after the fault; and finally, according to the polarities of the six differential mode voltage variable quantity integrals under the inter-pole fault, identifying fault poles under the bipolar, tripolar and even quadrupole faults. According to the method, the complex multi-pole fault in the same-tower double-circuit direct-current power transmission system can be quickly and reliably judged. Meanwhile, according to the scheme, the influence of electromagnetic coupling between poles under the condition that the direct-current power transmission system is erected on the same tower on fault pole selection is effectively avoided, and the method has important significance in guaranteeing safe and stable operation of a power system.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology of power systems, and specifically relates to a method for identifying multi-pole faults in double-circuit DC transmission lines on the same tower based on the combination of inter-pole differential mode voltage changes. Background Technology

[0002] With technological advancements, high-voltage direct current (HVDC) transmission lines are increasingly widely used in global power systems. Facing the global challenge of uneven distribution of energy resources and load centers, HVDC transmission, with its advantages of large transmission capacity, flexible control, and no synchronization stability issues, has become an ideal choice for long-distance, high-capacity power transmission, grid interconnection, and renewable energy integration. At the same time, issues such as limited land for transmission corridors and rising construction costs make the adoption of compact transmission technologies, such as multi-circuit lines on the same tower, particularly important. These technologies not only significantly improve corridor utilization but also meet the higher requirements of modern power systems for transmission capacity and power supply reliability.

[0003] However, in a double-circuit DC transmission system on the same tower, the conductors of different circuits are close together, resulting in mutual inductance not only between lines within the same circuit but also between lines of different circuits. Therefore, a single fault in a double-circuit DC transmission line can induce fault currents on multiple lines, making its fault characteristics far more complex than those in a single-circuit DC transmission line, thus placing higher demands on existing protection technologies.

[0004] Existing research mainly focuses on single-circuit bipolar DC transmission lines, while research on double-circuit DC transmission lines on the same tower is relatively limited. Existing DC transmission line protection technologies primarily rely on the electrical quantities of the protected line's own circuit, neglecting the influence of inter-circuit mutual inductance. Therefore, they cannot distinguish between faults within the same circuit and non-fault situations affected by faults in other circuits. Thus, research on fault polarity selection methods for double-circuit DC transmission lines on the same tower has significant theoretical and engineering value. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention aims to provide a multi-pole fault identification method for double-circuit DC transmission lines on the same tower based on the combination of inter-pole differential mode voltage changes. This invention constructs a criterion based on the proposed combination of inter-pole differential mode voltage changes to achieve pole selection for inter-pole faults in double-circuit DC transmission systems on the same tower. Compared with traditional DC line protection, this invention can effectively avoid the influence of electromagnetic coupling on protection judgment in double-circuit DC transmission lines on the same tower, thus improving the accuracy of fault line identification in double-circuit DC transmission systems on the same tower.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for identifying multi-pole faults in a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes includes the following steps:

[0008] Step 1: Obtain the voltage u1 to u4 of the positive and negative poles of the double-circuit DC transmission system on this side of the tower, and set the positive pole of the first circuit to pole 1 and the negative pole to pole 2; set the positive pole of the second circuit to pole 3 and the negative pole to pole 4.

[0009] Step 2: In the event of an inter-pole fault in a dual-circuit DC transmission system on the same tower, calculate the inter-pole differential mode voltage combination after the pole selection fault is initiated, based on the signal obtained in Step 1: differential mode voltage u between pole 1 and pole 2. 12 Differential mode voltage u between poles 2 and 3 23 Differential mode voltage u between poles 3 and 4 34 Differential mode voltage u between pole 1 and pole 4 14 Differential mode voltage u between pole 1 and pole 3 13 Differential mode voltage u between poles 2 and 4 24 ;

[0010] Step 3: Using the inter-electrode differential mode voltage combination calculated in Step 2, calculate the combination of inter-electrode differential mode voltage changes after the start of the polarity selection fault: Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 ;

[0011] Step 4: Using the combination of inter-electrode differential mode voltage changes calculated in Step 3, calculate the integral combination of the inter-electrode differential mode voltage changes within 1 ms after the pole selection fault starts:

[0012] Step 5: Determine the specific fault pole of the line inter-pole fault based on the integral combination of the inter-pole differential voltage change. According to the polarity law of the integral change of the inter-pole differential voltage change under different multi-pole faults shown in Table 1, select a set of differential voltage change integrals with the fewest number for each fault type and construct the fault pole selection criterion as shown in Table 2.

[0013] Table 1. Integral polarity law of inter-electrode differential mode voltage variation under different multi-electrode faults.

[0014]

[0015] Table 2 Fault Polarity Selection Criteria

[0016]

[0017] In Table 2, TH1 is the integral threshold for the inter-electrode differential voltage change.

[0018] In step 2, the specific calculation method for the inter-electrode differential mode voltage combination is as follows:

[0019]

[0020] In equation (1), u1 to u4 are the voltage values ​​of the four poles of the double-circuit DC transmission line, respectively. 12 u 23 u 34 ,

[0021] u 14 u 13 u 24 These are the differential mode voltages between each pair of the four poles of a double-circuit DC transmission line;

[0022] In step 3, the specific calculation method for the combination of inter-electrode differential mode voltage changes is as follows:

[0023]

[0024] In equation (2), Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 These represent the differential-mode voltage changes between each pair of poles in a double-circuit DC transmission line, u. 12,pre u 23,pre u 34,pre u 14,pre u 13,pre u 24,pre These are the differential mode voltages between each pair of the four poles of the double-circuit DC transmission line before the fault.

[0025] In step 4, the specific calculation method for the integral combination of the inter-electrode differential mode voltage change is as follows:

[0026]

[0027] In equation (3), k represents the sampling point at different times, k0 represents the sampling point at the start time of the polarity selection function, N represents the number of data points calculated by integrating the differential mode voltage change, and ΔT represents the time interval between two sampling points corresponding to the system protection sampling rate. These are the integrals of the differential mode voltage changes between each pair of the four poles of a double-circuit DC transmission line.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] Compared with traditional DC line protection that only utilizes fault information from the current circuit, this invention utilizes four-pole line voltage information to construct protection criteria. Therefore, it can effectively avoid the influence of electromagnetic coupling between lines on the fault pole selection judgment under multi-pole faults when they are erected on the same tower. It also avoids the possibility that a fault in one circuit may cause another protection circuit to malfunction, which is a problem in traditional protection methods based on single-circuit fault information. It can achieve accurate judgment of complex multi-pole fault types across circuits and has important significance in fault pole identification in DC transmission systems erected on the same tower. Attached Figure Description

[0030] Figure 1 This is a flowchart of the method of the present invention.

[0031] Figure 2 This is a power transmission system model diagram applicable to the method of the present invention.

[0032] Figure 3 This is a diagram showing the location distribution parameters of a double-circuit DC transmission system on the same tower. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0034] like Figure 1 As shown, this invention is a method for identifying multi-pole faults in a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes, comprising the following steps:

[0035] Step 1: Obtain the voltage u1 to u4 of the positive and negative poles of the double-circuit DC transmission system on this side of the tower, and set the positive pole of the first circuit to pole 1 and the negative pole to pole 2; set the positive pole of the second circuit to pole 3 and the negative pole to pole 4.

[0036] Step 2: In the event of an inter-pole fault in a dual-circuit DC transmission system on the same tower, calculate the inter-pole differential mode voltage combination after the pole selection fault is initiated, based on the signal obtained in Step 1: differential mode voltage u between pole 1 and pole 2. 12 Differential mode voltage u between poles 2 and 3 23 Differential mode voltage u between poles 3 and 4 34 Differential mode voltage u between pole 1 and pole 4 14 Differential mode voltage u between pole 1 and pole 3 13 Differential mode voltage u between poles 2 and 4 24 The specific calculation method is as follows:

[0037]

[0038] In equation (1), u1 to u4 are the voltage values ​​of the four poles of the double-circuit DC transmission line, respectively. 12 u 23 u 34 ,

[0039] u 14 u 13 u 24 These are the differential mode voltages between each pair of the four poles of a double-circuit DC transmission line;

[0040] Step 3: Using the inter-electrode differential mode voltage combination calculated in Step 2, calculate the combination of inter-electrode differential mode voltage changes after the start of the polarity selection fault: Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 The specific calculation method is as follows:

[0041]

[0042] In equation (2), Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 These represent the differential-mode voltage changes between each pair of poles in a double-circuit DC transmission line, u. 12,pre u 23,pre u 34,pre u 14,pre u 13,pre u 24,pre These are the differential mode voltages between each pair of the four poles of the double-circuit DC transmission line before the fault;

[0043] Step 4: Using the combination of inter-electrode differential mode voltage changes calculated in Step 3, calculate the integral combination of the inter-electrode differential mode voltage changes within 1 ms after the pole selection fault starts: The specific calculation method is as follows:

[0044]

[0045] In equation (3), k represents the sampling point at different times, k0 represents the sampling point at the start time of the polarity selection function, N represents the number of data points calculated by integrating the differential mode voltage change, and ΔT represents the time interval between two sampling points corresponding to the system protection sampling rate. These are the integrals of the differential mode voltage changes between each pair of the four poles of a double-circuit DC transmission line.

[0046] Step 5: Determine the specific fault pole of the line inter-pole fault based on the integral combination of the inter-pole differential voltage change. According to the polarity law of the integral change of the inter-pole differential voltage under different multi-pole faults shown in Table 1, select a set of differential voltage change integrals with the fewest number for each fault type and construct the fault pole selection criterion as shown in Table 2.

[0047] Table 1. Integral polarity law of inter-electrode differential mode voltage variation under different multi-electrode faults.

[0048]

[0049]

[0050] Table 2 Fault Polarity Selection Criteria

[0051]

[0052] Example:

[0053] The method of this invention is aimed at solving the problems of electromagnetic coupling affecting pole selection for inter-pole faults in double-circuit DC transmission lines on the same tower, as well as the complex fault types in double-circuit transmission lines on the same tower.

[0054] To verify the correctness of the above analysis, a simulation system was built on the simulation software. Figure 2 The model of a double-circuit DC transmission line on the same tower shown below illustrates the spatial relationship between the two lines. Figure 3 As shown, pole 1 is the positive terminal of the first loop, pole 2 is the negative terminal of the first loop, pole 3 is the positive terminal of the second loop, and pole 4 is the negative terminal of the second loop. Simulation verification was performed with the following parameters:

[0055] The voltage of the dual-circuit DC transmission system on the same tower is ±500kV, and the length of each circuit is 1000km.

[0056] In this embodiment, the protection sampling frequency is set to 20kHz, and the time interval ΔT between two sampling points is set to 0.05 seconds. The threshold value TH1 for the integration of the differential mode voltage change is set to 0.15, and the number of data points N for the integration calculation of the differential mode voltage change is set to 20.

[0057] Assuming that different inter-pole faults occur at a distance of 1000km from the line protection installation location (i.e., the end of the line) within 3 seconds, the method provided by this invention can accurately and quickly detect the specific faulty pole. When different types of inter-pole faults occur at the end of the line, the integral values ​​of the differential mode voltage change between each pole are shown in Table 3, which basically satisfy the law of the combination integral values ​​of the differential mode change between poles under different fault types shown in Table 1.

[0058] Table 3. Combined integral values ​​of differential mode changes for different fault types

[0059]

[0060] The absolute values ​​of the differential mode components that are zero in Table 3 are basically close to zero relative to the other differential mode components.

[0061] As shown in Table 4, the specific criteria for different types of inter-pole short-circuit faults occurring at the end of the line are shown in the right column of the table.

[0062] Table 4. Threshold judgment results for different fault types

[0063]

[0064]

[0065] As shown in Table 4, the identification method of the present invention can accurately determine the fault type when different types of inter-pole short-circuit faults occur.

Claims

1. A method for identifying multi-pole faults in a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes, characterized in that: Includes the following steps: Step 1: Obtain the voltage u1 to u4 of the positive and negative poles of the double-circuit DC transmission system on this side of the tower, and set the positive pole of the first circuit to pole 1 and the negative pole to pole 2; set the positive pole of the second circuit to pole 3 and the negative pole to pole 4. Step 2: In the event of an inter-pole fault in a dual-circuit DC transmission system on the same tower, calculate the inter-pole differential mode voltage combination after the pole selection fault is initiated, based on the signal obtained in Step 1: differential mode voltage u between pole 1 and pole 2. 12 Differential mode voltage u between poles 2 and 3 23 Differential mode voltage u between poles 3 and 4 34 Differential mode voltage u between pole 1 and pole 4 14 Differential mode voltage u between pole 1 and pole 3 13 Differential mode voltage u between poles 2 and 4 24 ; Step 3: Using the inter-electrode differential mode voltage combination calculated in Step 2, calculate the combination of inter-electrode differential mode voltage changes after the start of the polarity selection fault: Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 ; Step 4: Using the combination of inter-electrode differential mode voltage changes calculated in Step 3, calculate the integral combination of the inter-electrode differential mode voltage changes within 1 ms after the pole selection fault starts: Step 5: Determine the specific fault pole of the line inter-pole fault based on the integral combination of the inter-pole differential voltage change. According to the polarity law of the integral change of the inter-pole differential voltage change under different multi-pole faults shown in Table 1, select a set of differential voltage change integrals with the fewest number for each fault type and construct the fault pole selection criterion as shown in Table 2. Table 1. Integral polarity law of inter-electrode differential mode voltage variation under different multi-electrode faults. Table 2 Fault Polarity Selection Criteria In Table 2, TH1 is the integral threshold for the inter-electrode differential voltage change.

2. The method for multi-pole fault identification of a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes as described in claim 1, characterized in that: In step 2, the specific calculation method for the inter-electrode differential mode voltage combination is as follows: In equation (1), u1 to u4 are the voltage values ​​of the four poles of the double-circuit DC transmission line, respectively. 12 u 23 u 34 , u 14 u 13 u 24 These are the differential mode voltages between each pair of the four poles of a double-circuit DC transmission line.

3. The method for identifying multi-pole faults in a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes as described in claim 1, characterized in that: In step 3, the specific calculation method for the combination of inter-electrode differential mode voltage changes is as follows: In equation (2), Δu 12 , Δu 23 , Δu 34 , Δu 14 , Δu 13 , Δu 24 These represent the differential-mode voltage changes between each pair of poles in a double-circuit DC transmission line, u 12,pre u 23,pre u 34,pre u 14,pre u 13,pre u 24,pre These are the differential mode voltages between each pair of the four poles of the double-circuit DC transmission line before the fault.

4. The method for identifying multi-pole faults in a double-circuit DC transmission line on the same tower based on the combination of inter-pole differential mode voltage changes as described in claim 1, characterized in that: In step 4, the specific calculation method for the integral combination of the inter-electrode differential mode voltage change is as follows: In equation (3), k represents the sampling point at different times, k0 represents the sampling point at the start time of the polarity selection function, N represents the number of data points calculated by integrating the differential mode voltage change, and ΔT represents the time interval between two sampling points corresponding to the system protection sampling rate. These are the integrals of the differential mode voltage changes between each pair of the four poles of a double-circuit DC transmission line.

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