A Double-Ended Fault Location Method and System for Four-Terminal Transmission Lines

Abstract

The present invention discloses a double - end fault location method and system for a four - terminal line. The method includes identifying all intersection points of the four - terminal line and calculating the line distance lengths between adjacent intersection points; in response to a line protection tripping signal, calculating the virtual voltage and virtual current of each intersection point respectively; calculating the virtual voltage converted to the corresponding intersection point based on the analog quantity information and branch parameter information at each line protection installation location, and locating the area where the fault point is located; and using a double - end ranging algorithm to locate the fault point based on the line distance lengths of each area. The present invention does not require additional setting of line parameters, is easy to implement in existing line protections, and can accurately measure the distance in various fault conditions.

Description

Technical Field

[0001] The present invention belongs to the field of relay protection of power systems, and particularly relates to a double - end fault location method and system for four - terminal lines. Background Art

[0002] At present, the fault location algorithms applied to transmission lines mainly include two categories: single - end fault location algorithms and double - end fault location algorithms. For single - end fault location algorithms, for general metallic faults, only one - end line can accurately locate the fault. For the other two ends, due to the existence of shunt branches, the fault location results are inaccurate. And in the case of high - resistance grounding faults, multi - end lines cannot accurately locate the fault or even cannot locate the fault. Traditional double - end fault location algorithms are only applicable to double - end systems. For T - connected lines (three - end systems), the double - end fault location algorithm based on the virtual voltage at the T - point is only applicable to three - end systems with only one intersection point. When the number of intersection points is greater than one, the existing double - end fault location methods for T - connected lines are not applicable; for four - terminal lines, since there is more than one intersection point (such as Figure 1 ), the existing double - end fault location methods for T - connected lines are not applicable. Therefore, four - terminal line fault location algorithms are proposed, mainly including the traveling - wave method and the wave - impedance method, which have problems such as large computational complexity or complex principles, resulting in difficulties in engineering implementation. Summary of the Invention

[0003] In view of the above problems, the present invention proposes a double - end fault location method and system for four - terminal lines. First, automatically identify the intersection points in different regions and calculate the line distance lengths between the intersection points; divide the four - terminal system lines into at most five regions, and calculate the virtual voltages and virtual currents of two intersection points respectively; locate the region where the fault point is located and use the double - end fault location algorithm to locate the fault point, which can achieve accurate fault location under various fault conditions.

[0004] To achieve the above technical objectives and technical effects, the present invention is realized through the following technical solutions:

[0005] In a first aspect, the present invention provides a double - end fault location method for four - terminal lines, including:

[0006] Identify all intersection points of the four - terminal line and calculate the line distance lengths between adjacent intersection points;

[0007] In response to the line protection tripping signal, calculate the virtual voltages and virtual currents of each intersection point respectively;

[0008] Based on the analog quantity information and branch parameter information at each line protection installation location, calculate the virtual voltage converted to the corresponding intersection point, and locate the region where the fault point is located;

[0009] Based on the line distance lengths of each region, use the double - end fault location algorithm to locate the fault point.

[0010] Optionally, the method for identifying the intersection points includes:

[0011] Divide the four-terminal line into 5 regions, with the number of intersection points being 2, denoted as the first intersection point T 1 and the second intersection point T 2 ;

[0012] In response to the signal that the four-terminal line has no fault and the load current of any intersection point meets the preset requirements, calculate the virtual compensation voltage of each branch converted to the same intersection point;

[0013] Select the branch with the smallest absolute value of the difference between the virtual compensation voltages corresponding to the branch where the host is located, and determine that the two share the first intersection point T 1 , and the other two branches share the second intersection point T 2 .

[0014] Optionally, the calculation formula for the virtual compensation voltage is:

[0015]

[0016] where is the positive-sequence virtual compensation voltage of branch n converted to the same intersection point, n = 1, 2, 3, 4, is the positive-sequence voltage at the protection installation location of branch n, is the positive-sequence current at the protection installation location of branch n, Z 1_n is the positive-sequence impedance of the full length of branch n.

[0017] Optionally, when branch 1 and branch 2 share the first intersection point T 1 , and branch 3 and branch 4 share the second intersection point T 2 , the calculation method for the line distance length between the two intersection points is:

[0018] Calculate the current 1 of the first intersection point T and the current 2 of the second intersection point T

[0019] Calculate the ratio of the positive-sequence impedance of the line between the two intersection points to the positive-sequence impedance of branch 1

[0020] Based on the ratio and the line distance length of branch 1, calculate the line distance length between the two intersection points.

[0021] Optionally, the method for locating the region where the fault point is located includes:

[0022] In response to the line protection tripping signal, calculate the virtual compensation voltage of each branch converted to the corresponding intersection point;

[0023] Calculate separately Compare the calculation result with a preset threshold value, and determine the fault area according to the comparison result, where Correspond to phase A, phase B, and phase C of the line respectively For the virtual compensation voltage of each phase of branch 1 converted to the first intersection point T 1 The virtual compensation voltage of each phase For the virtual compensation voltage of each phase of branch 2 converted to the first intersection point T 1 The virtual compensation voltage of each phase For the virtual compensation voltage of each phase of branch 3 converted to the second intersection point T 2 The virtual compensation voltage of each phase For the virtual compensation voltage of each phase of branch 4 converted to the second intersection point T 2 The virtual compensation voltage of each phase

[0024] Optionally, the determination of the fault area according to the judgment result specifically includes:

[0025] When And The fault is located between the two intersection points

[0026] When And The fault point is in branch 1 or branch 2

[0027] When And The fault point is in branch 3 or branch 4

[0028] When And The fault point is in branch 1 or branch 2

[0029] When And The fault point is in branch 3 or branch 4

[0030] Optionally, if the fault is located in branch 1 or branch 2

[0031] First, use the compensated virtual voltage at the second intersection point T 2 To calculate the compensated virtual voltage at the first intersection point T 1 Of Where Is the fault phase current at the second intersection point T 2 Point, And Are the fault phase currents measured at the protection installation locations of branch 3 and branch 4 respectively Is the zero-sequence current at the second intersection point T 2 Point Z 1_1, Z 0_1 are the positive sequence impedance and zero sequence impedance of the total length of branch 1 respectively;

[0032] If then the fault point is in Zone 1;

[0033] If then the fault point is in Zone 2.

[0034] Optionally, if the fault is located in branch 3 or branch 4;

[0035] First, calculate the compensated virtual voltage at the second junction point T 1 using the compensated virtual voltage at the first junction point T 2 where is the fault phase current at the first junction point T and 1 are the fault phase currents measured at the protection installation points of branch 1 and branch 2 respectively; and is the zero sequence current at the first junction point T 1 Z 1_1 Z 0_1 are the positive sequence impedance and zero sequence impedance of the total length of branch 1 respectively;

[0036] Ifthen the fault point is in branch 3;

[0037] If

[0038] then the fault point is in branch 4.

[0039] Optionally, when branch 1 and branch 2 share the first junction point T 1 , and branch 3 and branch 4 share the second junction point T 2 ; the area between the first junction point T 1 and the second junction point T 2 is line 5;

[0039] When a fault occurs in branch n and it is an asymmetric fault, the following formula is used to calculate the per-unit value of fault location:

[0040]

[0041] Where: is the negative sequence current at the head of branch n, is the negative sequence current at the end of branch n, is the negative sequence voltage at the head of branch n, is the negative sequence voltage at the end of branch n, Z 2_n is the negative sequence impedance of branch n.

[0042] When a fault occurs in branch n and it is a symmetrical fault, the following formula is used to calculate the per-unit value of fault location:

[0043]

[0044] Where: is the positive-sequence current at the head of branch n, is the positive-sequence current at the end of branch n, is the positive-sequence voltage at the head of branch n, is the positive-sequence voltage at the end of branch n, Z 1_n is the positive-sequence impedance of branch n;

[0045] Based on L f = k*l n Calculate the fault location point, l n is the total length of the line of branch n.

[0046] In the second aspect, the present invention provides a four-terminal line fault double-end ranging system, including a storage medium and a processor;

[0047] The storage medium is used to store instructions;

[0048] The processor is used to operate according to the instructions to execute the steps of the method according to any one of the first aspects.

[0049] Compared with the prior art, the beneficial effects of the present invention:

[0050] The present invention proposes a four-terminal line fault double-end ranging method and system, which first automatically identifies the intersection points in different regions and calculates the line distance length between the intersection points; divides the four-terminal system line into at most five regions, calculates the virtual voltage and virtual current of two intersection points respectively; locates which region the fault point is in, and uses the double-end ranging algorithm to locate the fault point, which can achieve accurate ranging under various fault conditions, and does not require additional line parameter setting, and is easy to implement in the existing line protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to make the content of the present invention be more clearly understood, the following further details the present invention according to specific embodiments in conjunction with the drawings, where:

[0052] Figure 1 is the structural schematic diagram of the four-terminal line partition;

[0053] Figure 2 is the flowchart of intersection point identification of an embodiment of the present invention;

[0054] Figure 3 is the flowchart of fault area selection of an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the protection scope of the present invention.

[0056] The application principle of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] Embodiment 1

[0058] A double - end fault location method for a four - terminal line is provided in an embodiment of the present invention, including:

[0059] Identifying all intersection points of the four - terminal line and calculating the line distance lengths between adjacent intersection points;

[0060] In response to a line protection tripping signal, calculating the virtual voltage and virtual current of each intersection point respectively;

[0061] Calculating the virtual voltage converted to the corresponding intersection point based on the analog quantity information and branch parameter information at each line protection installation location, and locating the area where the fault point is located;

[0062] Based on the line distance lengths of each area, using a double - end ranging algorithm to locate the fault point.

[0063] In a specific implementation manner of the embodiment of the present invention, as Figure 2 shown, the method for identifying the intersection point includes:

[0064] As Figure 1 shown, the four - terminal line is divided into 5 areas, the number of intersection points is 2, which are respectively denoted as the first intersection point T 1 and the second intersection point T 2 ; the area corresponding to branch 1 is M - T 1 , called area 1; the area corresponding to branch 2 is P - T 1 , called area 2; the area corresponding to branch 3 is N - T 2 , called area 3; the area corresponding to branch 4 is Q - T 2 , called area 4; the area between T 1 and T 2 is called area 5;

[0065] In response to a signal that there is no fault in the four - terminal line (M, P, Q, N) and the load of any intersection point meets the preset requirements, such as the load current at any end is greater than 0.1I n , I n is the rated current), calculating the conversion of each branch to the same intersection point T (the first intersection point T 1 or the second intersection point T2 ) virtual compensation voltage;

[0066] Select the branch with the smallest absolute value of the difference in virtual compensation voltage corresponding to the branch where the host is located, and determine that the two share the first intersection point T 1 , and the other two branches share the second intersection point T 2 .

[0067] In the specific implementation process of the embodiment of the present invention, the calculation formula of the virtual compensation voltage is:

[0068]

[0069] Among them, is the positive-sequence virtual compensation voltage of branch n converted to the same intersection point, n = 1, 2, 3, 4, is the positive-sequence voltage at the protection installation location of branch n, is the positive-sequence current at the protection installation location of branch n, Z 1_n is the positive-sequence impedance of the full length of branch n.

[0070] By default, the line protection installed on branch 1 is the host, and the line protections installed on branches 2, 3, and 4 are slaves. The intersection point closest to branch 1 is defaulted to the first intersection point T 1 , and calculate Using the principle of selecting the smallest value among the three, identify the line sharing the first intersection point T 1 (such as: is the smallest among the three, then branch 2 and branch 1 share the first intersection point T 1 ), and the areas where the other two ends of the system are located share T 2 point.

[0071] In a specific implementation manner of the embodiment of the present invention, when branch 1 and branch 2 share the first intersection point T 1 , and branch 3 and branch 4 share the second intersection point T 2 , the calculation method for the line distance length between the two intersection points is:

[0072] Calculate the current 1 of the first intersection point T and the current 2 of the second intersection point T

[0073] Calculate the ratio of the positive-sequence impedance of the line between the two intersection points to the positive-sequence impedance of branch 1

[0074] Based on the ratio and the line distance length of branch 1, calculate the line distance length between the two intersection points.

[0075] In a specific implementation manner of the embodiment of the present invention, as Figure 3 shown, the positioning method for the area where the fault point is located includes:

[0076] In response to the line protection tripping signal, that is, after the line protection trips, enter the fault selection logic, and calculate the virtual compensation voltage of each line converted to its corresponding intersection point;

[0077] Calculate respectively Compare the calculation result with a preset threshold, and determine the fault area according to the comparison result, where correspond to phase A, phase B, and phase C of the line respectively, is the virtual compensation voltage of each phase of branch 1 converted to the first intersection point T 1 of each phase, is the virtual compensation voltage of each phase of branch 2 converted to the first intersection point T 1 of each phase, is the virtual compensation voltage of each phase of branch 3 converted to the second intersection point T 2 of each phase, is the virtual compensation voltage of each phase of branch 4 converted to the second intersection point T 2 of each phase.

[0078] Among them, the determination of the fault area according to the judgment result specifically includes:

[0079] When and at the same time, the fault is located between the two intersection points (i.e., area 5);

[0080] When and at the same time, then the fault point is in branch 1 (i.e., area 1) or branch 2 (i.e., area 2);

[0081] When and then the fault point is in branch 3 (i.e., area 3) or branch 4 (i.e., area 4);

[0082] When and then the fault point is in branch 1 or branch 2;

[0083] When and then the fault point is in branch 3 or branch 4.

[0084] If the fault is located in branch 1 or branch 2;

[0085] First, use the compensated virtual voltage at the second intersection point T 2 to calculate the compensated virtual voltage at the first intersection point T 1 ​ wherein is the second intersection point T 2 phase current of the fault point and are the phase currents of the fault measured at the protection installation points of branch 3 and branch 4 respectively; is the second intersection point T 2 zero-sequence current Z 1_1 、Z 0_1 are the positive-sequence impedance and zero-sequence impedance of the full length of the line of branch 1 respectively;

[0086] If then the fault point is in area 1;

[0087] If then the fault point is in area 2.

[0088] If the fault is located in branch 3 or branch 4;

[0089] First, use the compensated virtual voltage of the first intersection point T 1 to calculate the compensated virtual voltage of the second intersection point T 2 point wherein is the phase current of the fault of the first intersection point T 1 phase current of the fault point and are the phase currents of the fault measured at the protection installation points of branch 1 and branch 2 respectively; is the zero-sequence current of the first intersection point T 1 zero-sequence current Z 1_1 、Z 0_1 are the positive-sequence impedance and zero-sequence impedance of the full length of the line of branch 1 respectively;

[0090] If then the fault point is in branch 3;

[0091] If then the fault point is in branch 4.

[0092] In a specific implementation manner of the embodiment of the present invention, the method for locating the fault point by using the double-ended ranging algorithm specifically includes the following steps:

[0093] Taking the fault occurring in branch n as an example, and when it is an asymmetric fault, the following formula is used to calculate the per-unit value of the fault ranging:

[0094]

[0095] Wherein: is the negative-sequence current at the head of branch n is the negative sequence current at the end of branch n, is the negative sequence voltage at the beginning of branch n, is the negative sequence voltage at the end of branch n, Z 2_n is the negative sequence impedance of branch n.

[0096] Taking the fault occurring in branch n as an example, and when it is a symmetrical fault, the per-unit value of fault location measurement is calculated using the following formula:

[0097]

[0098] Where: is the positive sequence current at the beginning of branch n, is the positive sequence current at the end of branch n, is the positive sequence voltage at the beginning of branch n, is the positive sequence voltage at the end of branch n, Z 1_n is the positive sequence impedance of branch n.

[0099] Based on L f = k * l n The fault location point is calculated to complete the double-ended fault location measurement.

[0100] Embodiment 2

[0101] Based on the same inventive concept as Embodiment 1, an embodiment of the present invention provides a four-terminal line fault double-ended location measurement system, including a storage medium and a processor;

[0102] The storage medium is used to store instructions;

[0103] The processor is used to operate according to the instructions to execute the steps of the method according to any one of Embodiment 1.

[0104] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A double - ended fault location method for a four - terminal line, characterized in that, it includes: Identify all the intersection points of the four - terminal line and calculate the line distance lengths between adjacent intersection points; In response to the line protection tripping signal, calculate the virtual compensation voltage and virtual current of each intersection point respectively; Based on the analog quantity information and branch parameter information at each line protection installation location, calculate the virtual compensation voltage converted to the corresponding intersection point, and locate the area where the fault point is located; Based on the line distance lengths of each area, use the double - ended ranging algorithm to locate the fault point; The method for locating the area where the fault point is located includes: In response to the line protection tripping signal, calculate the virtual compensation voltage of each branch converted to the corresponding intersection point; Calculate separately Compare the calculation result with a preset threshold value, and determine the fault area according to the comparison result, where respectively correspond to phase A, phase B, and phase C of the line is the virtual compensation voltage of each phase of branch 1 converted to the first intersection point T 1 for each phase of the virtual compensation voltage is the virtual compensation voltage of each phase of branch 2 converted to the first intersection point T 1 for each phase of the virtual compensation voltage is the virtual compensation voltage of each phase of branch 3 converted to the second intersection point T 2 for each phase of the virtual compensation voltage is the virtual compensation voltage of each phase of branch 4 converted to the second intersection point T 2 for each phase of the virtual compensation voltage 2. The double - ended fault location method for a four - terminal line according to claim 1, characterized in that, The method for identifying the intersection point includes: The four-terminal line is divided into five regions, and the number of intersection points is 2, which are respectively denoted as the first intersection point T 1 and the second intersection point T 2 ; in response to the signal that the four-terminal line has no fault and the load current of any intersection point meets the preset requirements, calculate the virtual compensation voltage of each branch converted to the same intersection point; Select the branch with the smallest absolute value of the difference between the virtual compensation voltages corresponding to the branch where the host is located, and determine that the two share the first intersection point T 1 , and the other two branches share the second intersection point T 2 .

3. The double - ended fault location method for a four - terminal line according to claim 2, characterized in that: The calculation formula for the virtual compensation voltage is: Among them, is the positive-sequence virtual compensation voltage of branch n converted to the same intersection point, where n = 1, 2, 3, 4, is the positive-sequence voltage at the protection installation location of branch n, is the positive-sequence current at the protection installation location of branch n, and Z 1_n is the positive-sequence impedance of the full length of branch n line.

4. The double - ended fault location method for a four - terminal line according to claim 2, characterized in that: When branch 1 and branch 2 share the first intersection point T 1 , and branch 3 and branch 4 share the second intersection point T 2 , the calculation method for the line distance length between the two intersection points is as follows: Calculate the first intersection point T 1 The current of And the current of the second intersection point T 2 The current of Calculate the ratio of the positive sequence impedance of the line between the two intersection points to the positive sequence impedance of branch 1 Based on the ratio and the line distance length of branch 1, calculate the line distance length between the two intersection points.

5. The double - ended fault location method for a four - terminal line according to claim 1, characterized in that: Judging the fault area according to the comparison result specifically includes: When and the fault location is between the two intersection points; When and then the fault point is in branch 1 or branch 2; When and then the fault point is in branch 3 or branch 4; When and then the fault point is in branch 1 or branch 2; When and then the fault point is in branch 3 or branch 4.

6. The double - ended fault location method for a four - terminal line according to claim 5, characterized in that: If the located fault is in branch 1 or branch 2; First, use the virtual compensation voltage at the second intersection point T 2 to calculate the virtual compensation voltage at the first intersection point T 1 wherein is the fault phase current at the second intersection point T point, 2 and and are the fault phase currents measured at the protection installation points of branch 3 and branch 4 respectively; is the second intersection point T 2 zero-sequence current Z 1_1 and Z 0_1 are the positive-sequence impedance and zero-sequence impedance of the full length of the line of branch 1 respectively; If then the fault point is in Area 1; If then the fault point is in Zone 2.

7. The double - ended fault location method for a four - terminal line according to claim 5, characterized in that: If the located fault is in branch 3 or branch 4; First, use the virtual compensation voltage at the first intersection point T 1 to calculate the virtual compensation voltage at the second intersection point T 2 point where is the faulty-phase current at the first intersection point T 1 ​ and are the fault phase currents measured at the protection installation points of branch 1 and branch 2 respectively; is the first intersection point T 1 zero-sequence current Z 1_1 and Z 0_1 are the positive-sequence impedance and zero-sequence impedance of the full length of the line of branch 1 respectively; If then the fault point is in branch 3; If then the fault point is in branch 4.

8. The double - ended fault location method for a four - terminal line according to claim 5, characterized in that: When branch 1 and branch 2 share the first intersection point T 1 , branch 3 and branch 4 share the second intersection point T 2 ; The area between the first intersection point T 1 and the second intersection point T 2 is line 5; When a fault occurs in branch n and it is an asymmetrical fault, the following formula is used to calculate the per - unit value of fault location: Wherein: is the negative sequence current at the head of branch n, is the negative sequence current at the end of branch n, is the negative sequence voltage at the head of branch n, is the negative sequence voltage at the end of branch n, Z 2_n is the negative sequence impedance of branch n; When a fault occurs in branch n and it is a symmetrical fault, the following formula is used to calculate the per - unit value of fault location: Wherein: is the positive-sequence current at the head end of branch n, is the positive-sequence current at the tail end of branch n, is the positive-sequence voltage at the head end of branch n, is the positive-sequence voltage at the tail end of branch n, Z 1_n is the positive-sequence impedance of branch n; Based on L f = k * l n Calculate the fault location point, l n is the total length of branch n line.

9. A double - ended fault location system for a four - terminal line, characterized in that, it includes a storage medium and a processor; The storage medium is used to store instructions; The processor is used to operate according to the instructions to execute the steps of the method according to any one of claims 1 - 8.

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