Fault analysis method for single-circuit three-phase line breakage in four-circuit lines on the same pole

Abstract

The present invention relates to a single-circuit three-phase line break fault analysis method for four-circuit lines erected on the same pole, comprising: step 1, according to the boundary conditions of the line three-phase line break fault, under the condition of voltage constraint or current constraint only, the line three-phase line break composite fault sequence network diagram is deduced; step 2, according to the line three-phase line break composite fault sequence network diagram, an equation containing only one unknown sequence voltage component is deduced; step 3, based on the equation, according to the voltage and current constraint relationship, other sequence voltages and sequence currents are calculated, and then the voltage between two points of the line break and the normal phase current are calculated. The present invention fills the gap in line break fault analysis and provides a solid foundation for research on fault location, protection configuration, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission, and in particular relates to a method for analyzing a single-circuit three-phase line break fault of four-circuit lines erected on the same pole. Background Art

[0002] The four-circuit transmission technology on the same pole is widely used in developed countries with relatively developed economies and dense populations. However, there is relatively little research data published abroad on phase mode transformation methods, fault analysis methods, relay protection configuration, fault line selection methods and fault distance measurement principles. In China, the four-circuit transmission technology on the same pole is also a relatively new research topic.

[0003] There are 12 lines on the same pole with four circuits. The coupling is complex. The complex line mutual inductance greatly increases the difficulty of line decoupling. The original research method cannot be applied to the four circuits on the same pole. There are many types of faults on the four circuits on the same pole. In addition to single-circuit faults, cross-line faults may also occur, which brings difficulties to the line selection and setting of relay protection. The traditional symmetrical component method and six-sequence component method cannot eliminate the zero-sequence mutual inductance between lines. In order to eliminate the influence of line mutual inductance on fault analysis and fault distance measurement of the four circuits on the same pole, it is necessary to further study the decoupling method of line mutual inductance and phase mutual inductance.

[0004] At present, there is a 12-sequence component method for short-circuit fault analysis of four-circuit lines on the same pole, and this method has been promoted and applied in fault distance measurement, fault analysis and relay protection. The 12-sequence component method first solves the decoupling of mutual inductance between four-circuit lines on the same pole. The step-by-step matrix transformation can first eliminate the mutual inductance between each line, and then eliminate the mutual inductance between each phase, and obtain independent 12-sequence components. From the process of matrix transformation, the meaning and characteristics of each sequence component can be obtained, and the system impedance correction method can be deduced, so as to establish each sequence network during short-circuit fault, and jointly establish the fault boundary condition equations. By solving the equation group, the voltage and current of each sequence at the short-circuit point can be calculated, so that the short-circuit voltage and current at any point in the system can be obtained, and the short-circuit fault calculation of four-circuit lines on the same pole can be completed. However, the above method is only for short-circuit faults. For line break faults, the sequence network diagrams and the equations of each sequence fault component are different from those of short-circuit faults. It is necessary to conduct in-depth research on the drawing methods of each sequence network diagram for line break faults, the boundary condition equation group algorithm, the composite sequence network diagram method, etc., to fill the gap in line break fault analysis and provide a solid foundation for research on fault location, protection configuration, etc. Summary of the invention

[0005] The object of the present invention is to provide a method for analyzing a single-circuit three-phase line break fault of four-circuit lines erected on the same pole, comprising:

[0006] Step 1, according to the boundary conditions of the three-phase disconnection fault of the return line, under the condition of voltage constraint or current constraint only, the composite fault sequence network diagram of the three-phase disconnection of the return line is calculated;

[0007] Step 2: According to the three-phase disconnection composite fault sequence network diagram of the return line, it is inferred that only one unknown sequence voltage component is included. The equation is:

[0008]

[0009] In the formula, is the integrated electromotive force from the disconnection point into the system, E is the equivalent electromotive force on both sides of the line, δ is the phase angle between the electromotive forces on both sides of the line; Z e1 is the e1 sequence impedance; Z f1 is the f1 sequence impedance;

[0010] Step 3: Based on the equation and according to the voltage and current constraint relationship, other sequence voltages and sequence currents are calculated, and then the voltage between the two points of the broken line and the normal phase current are calculated.

[0011] By using the above scheme, through the single-circuit three-phase line break fault analysis method of four-circuit lines erected on the same pole, the voltage and current constraint relationship is obtained by simplifying the boundary condition equation group, and then the composite sequence network diagram is drawn. According to the sequence network diagram, it is possible to quickly deduce that only one unknown sequence voltage component is included. The equation According to the voltage and current constraint relationship, other sequence voltages and sequence currents can be quickly calculated, and then the voltage between the two points of the broken line and the normal phase current can be calculated, filling the gap in broken line fault analysis and providing a solid foundation for research such as fault location and protection configuration.

[0012] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the impedance structure diagram of four lines on the same pole;

[0014] Figure 2 It is the normal positive sequence network diagram and the e-sequence network diagram; Figure 2 Among them, a) is the positive sequence (012) network diagram; b) is the e-sequence network diagram;

[0015] Figure 3 It is a 12-sequence fault component sequence network diagram of the present invention; Figure 3 a) is the network diagram of e1 and e2; b) is the network diagram of e0; c) is the network diagram of f1, f2, g1, g2, h1, h2; d) is the network diagram of f0, g0, h0;

[0016] Figure 4 It is a composite sequence network diagram of an IABC line break fault in one embodiment of the present invention. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0018] This embodiment provides a method for analyzing a single-circuit three-phase line break fault of four-circuit lines installed on the same pole, comprising:

[0019] Step 1, according to the boundary conditions of the three-phase disconnection fault of the return line, under the condition of voltage constraint or current constraint only, the composite fault sequence network diagram of the three-phase disconnection of the return line is calculated;

[0020] Step 2: According to the three-phase disconnection composite fault sequence network diagram of the return line, it is inferred that only one unknown sequence voltage component is included. The equation is:

[0021]

[0022] In the formula, is the integrated electromotive force from the disconnection point into the system, E is the equivalent electromotive force on both sides of the line, δ is the phase angle between the electromotive forces on both sides of the line; Z e1 is the e1 sequence impedance; Z f1 is the f1 sequence impedance;

[0023] Step 3: Based on the equation and according to the voltage and current constraint relationship, other sequence voltages and sequence currents are calculated, and then the voltage between the two points of the broken line and the normal phase current are calculated.

[0024] The present invention is described in further detail below.

[0025] Ginseng Figure 1 The four-circuit line on the same pole shown in the figure, assuming the line self-impedance is z s , the mutual impedance between the phases of the line is equal to z m , the mutual impedance between different loops is also equal and is recorded as z x .

[0026] exist Figure 1 In the four-circuit lines on the same pole shown in the figure, the matrix equation (1-1) holds true between the phase voltages, phase currents and impedances of the four-circuit lines:

[0027]

[0028] Abbreviated as

[0029] is the voltage drop of four-circuit lines on the same pole, is the column vector of the phase current of the four-circuit line on the same pole, [Z] represents the impedance matrix of the four-circuit line, the elements on the diagonal represent the self-impedance of each phase, and the elements on the non-diagonal represent the phase-to-phase mutual impedance between the phases on the single-circuit line and the line-to-line mutual impedance between the loops. Because there is mutual inductance between the 12 electrical quantities of the three phases ABC of the four-circuit line on the same pole, to study the four-circuit line, it is necessary to first study the decoupling, that is, to eliminate the mutual inductance. The decoupling is carried out in two steps: first eliminate the line-to-line mutual inductance outside each loop, and then eliminate the phase-to-phase mutual inductance inside each loop. The impedance matrix is ​​transformed into a diagonal matrix, that is, all elements except the diagonal are zero, and the 12 electrical quantities are decoupled into 12 independent sequence components, and there is no mutual inductance.

[0030] The decoupling matrix is

[0031]

[0032] in The voltage and current matrix after decoupling is:

[0033]

[0034] The phase transformation of the double-circuit line is recorded as:

[0035]

[0036] According to formula (1-2), it can be deduced that

[0037]

[0038] Formula (1-3) is expanded to

[0039]

[0040] where z e0 =z s +2z m +9z x , z f0 =z g0 =z h0 =z s +2z m -3z x

[0041] z e1 =z f1 =z g1 =z h1 =z e2 =z f2 =z g2 =z h2 =z s -z m

[0042] From the inverse matrix of M, it can be seen that the e-sequence component reflects the amount of the same-direction flow in the four lines, while the f-sequence component, the g-sequence component and the h-sequence component reflect the circulation amount inside the four-circuit line on the same pole. Since the f-sequence component, the g-sequence component and the h-sequence component only circulate inside the four-circuit line on the same pole and do not flow out, the voltage of the sequence components f, g, and h on the busbars at both ends of the four-circuit line on the same pole is zero, and only the e-sequence voltage and current exist outside the line of the four-circuit line on the same pole.

[0043] The connection between the four-circuit line on the same pole and the external system is reflected by the e-sequence component, but the e-sequence component is not directly connected to the positive sequence network of the external system but needs to be processed accordingly. From the inverse matrix of M, we can see that:

[0044]

[0045] Among them, (i=0,1,2).

[0046] It can be seen from the equation that the e1 sequence voltage is equal to the positive sequence voltage of the four-circuit line divided by 4, that is, the average value. Figure 2 Positive sequence (012) network diagram, since the four lines are all connected to the bus M at the left end of the line, the positive sequence voltages of the four lines are equal. Therefore, at bus M, the e1 voltage is equal to the normal positive sequence voltage. For current, the e1 current flowing through the system impedance is equal to the sum of the positive sequence currents of the four lines divided by 4, and the positive sequence current flowing through the system impedance in the normal positive sequence network is the sum of the positive sequence currents of the four lines, so the e1 sequence current is 1 / 4 of the normal positive sequence current. According to Ohm's law, in the e1 sequence network diagram, the system impedance on the left should be corrected to 4 times the system impedance value of the normal positive sequence network. The same is true for e0 and e2. The system impedance correction method on the N side is the same as that on the M side. The normal positive sequence network diagram and e sequence network diagram of four lines on the same pole can be seen. Figure 2 .

[0047] Based on the sequence network diagrams of short-circuit faults, the sequence network diagrams of line break faults can be drawn. However, unlike short-circuit faults, in line break faults, the sequence impedances are in series when viewed from the break. Figure 3 shown.

[0048] From the 12-sequence component method, we know that only the e1 sequence is an active network, and the other sequence components are passive networks. The voltage and current equations of each sequence at the broken line are as follows:

[0049]

[0050] (i=0, 1, 2) are the sequence voltage components at the broken line, is the comprehensive electromotive force from the disconnection point into the system, where E is the equivalent electromotive force on both sides of the line, δ is the phase angle between the electromotive forces on both sides of the line, (i=0, 1, 2) are the sequence current components at the broken line, z kei 、z kfi 、z kgi 、z khi (i=0, 1, 2) are the sequence impedances seen from the disconnection point into the system.

[0051] Taking the three-phase disconnection fault of line I as an example, its boundary conditions are:

[0052]

[0053] Substituting formula (2-1) into formula (1-2), the relationship between the sequence components is as follows:

[0054]

[0055] After simplification, we can get

[0056]

[0057] According to the voltage constraint and current constraint conditions, the composite sequence network diagram for the three-phase disconnection fault of the I loop can be drawn, as shown in Figure 4 The specific analysis is as follows:

[0058] Except for the e1 sequence, the other 11 sequence components are passive networks. According to the current relationship The current of g0, g1, g2, h0, h1, and h2 sequences are 0, the current of e0 sequence and f0 sequence are connected in parallel, the current of e1 sequence and f1 sequence are connected in parallel, and the current of e2 sequence and f2 sequence are connected in parallel.

[0059] According to the voltage relationship The f0 sequence voltage is connected in parallel with the e0 sequence after passing through a transformer with a transformation ratio of (1:3), the f1 sequence voltage is connected in parallel with the e1 sequence after passing through a transformer with a transformation ratio of (1:3), and the f2 sequence voltage is connected in parallel with the e2 sequence after passing through a transformer with a transformation ratio of (1:3). Since only the e1 sequence is an active network, the e0, e2, f0, and f2 sequence currents are 0. In order to maintain the transformer secondary sequence current The f1 sequence impedance needs to be corrected. After passing through the transformer with a transformation ratio (1:3), the primary current becomes Maintain the sequence voltage on the sequence impedance That is, the primary voltage of the transformer remains unchanged, and the f1 sequence impedance is corrected to 3Z f1 .

[0060] according to Figure 4 , which can be quickly calculated Equation (2-4) can be used to calculate the other sequence voltages and currents through equation (2-3), and then through equation (1-2), the voltage between the two points of the broken line and the normal phase current can be calculated.

[0061]

[0062] The fault analysis method calculates the composite fault sequence network diagram of the three-phase disconnection of the I loop according to the voltage and current constraint relationship. The equation fills the gap in line break fault analysis and provides a solid foundation for research on fault location and protection configuration.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for analyzing single-circuit three-phase line break fault of four-circuit lines installed on the same pole, characterized in that: include: Step 1, according to the boundary conditions of the three-phase disconnection fault of the return line, under the condition of voltage constraint or current constraint only, the sequence network diagram of the three-phase disconnection composite fault of the return line is calculated, including: For the four-circuit line on the same pole, the self-impedance of the line is z s , the mutual impedance between the phases of the line is equal to z m , the mutual impedance between different loops is also equal and is recorded as z x ; The matrix equation (1-1) holds true between the four-circuit phase voltage, phase current and impedance: Decoupling is carried out in two steps: first, eliminate the line-to-line mutual inductance outside each loop, and then eliminate the phase-to-phase mutual inductance inside each loop; transform the impedance matrix into a diagonal matrix, that is, all elements except the diagonal are zero, and the 12 electrical quantities are decoupled into their own 12-sequence components, and there is no mutual inductance; The decoupling matrix is ​​recorded as: in The voltage and current matrix after decoupling is: The phase transformation of the double-circuit line is recorded as: According to formula (1-2), it can be deduced that Formula (1-3) is expanded to where z e0 = z s + 2z m + 9z x , z f0 = z g0 = z h0 = z s + 2z m - 3z x z e1 = z f1 = z g1 = z h1 = z e2 = z f2 = z g2 = z h2 = z s - z m ; From the inverse matrix of M, we can see that the e-sequence component reflects the amount of the same-direction flow in the four lines, while the f-sequence component, the g-sequence component and the h-sequence component reflect the circulation amount inside the four-circuit line on the same pole; the f-sequence component, the g-sequence component and the h-sequence component only circulate inside the four-circuit line on the same pole and do not flow out, so the voltage of the sequence components f, g, and h on the busbars at both ends of the four-circuit line on the same pole is zero, and only the e-sequence voltage and current exist outside the line of the four-circuit line on the same pole; The connection between the four-circuit line on the same pole and the external system is reflected by the e-sequence component, but the e-sequence component is not directly connected to the positive sequence network of the external system but needs to be processed accordingly; from the inverse matrix of M, it can be seen that: Where, i = 0, 1, 2; The e1 sequence voltage is equal to the positive sequence voltage of the four-circuit line divided by 4, that is, the average value. The four-circuit lines are all connected to the busbar M at the left end of the line. The positive sequence voltages of the four lines are equal. Therefore, at the busbar M, the e1 voltage is equal to the normal positive sequence voltage. For current, the e1 current flowing through the system impedance is equal to the sum of the positive sequence currents of the four-circuit lines divided by 4. The positive sequence current flowing through the system impedance in the normal positive sequence network is the sum of the positive sequence currents of the four-circuit lines, so the e1 sequence current is 1 / 4 of the normal positive sequence current. From the 12-sequence component method, it can be seen that only the e1 sequence is an active network, and the other sequence components are passive networks; the voltage and current equations of each sequence at the broken line are as follows: are the sequence voltage components at the broken line, is the comprehensive electromotive force from the disconnection point into the system, where E is the equivalent electromotive force on both sides of the line, δ is the phase angle between the electromotive forces on both sides of the line, are the sequence current components at the broken line, z kei 、z kfi 、z kgi 、z khi , i = 0, 1, 2, are the sequence impedances looking into the system from the disconnection point; Taking the three-phase disconnection fault of line I as an example, its boundary conditions are: Substituting formula (2-1) into formula (1-2), the relationship between the sequence components is as follows: After simplification, we can get According to the voltage constraint and current constraint conditions, the composite sequence network diagram can be drawn when the I loop three-phase line is disconnected; Except for the e1 sequence, the other 11 sequence components are passive networks. According to the current relationship The current of g0, g1, g2, h0, h1, and h2 sequences are 0, e0 sequence and f0 sequence are connected in parallel, e1 sequence and f1 sequence are connected in parallel, and e2 sequence and f2 sequence are connected in parallel; According to the voltage relationship The f0 sequence voltage is connected in parallel with the e0 sequence after passing through a transformer with a transformation ratio of 1:3, the f1 sequence voltage is connected in parallel with the e1 sequence after passing through a transformer with a transformation ratio of 1:3, and the f2 sequence voltage is connected in parallel with the e2 sequence after passing through a transformer with a transformation ratio of 1:3; since only the e1 sequence is an active network, the e0, e2, f0, and f2 sequence currents are 0; in order to maintain the transformer secondary sequence current unchanged, the f1 sequence impedance needs to be corrected; the secondary side of the transformer After passing through a transformer with a transformation ratio of 1:3, the primary current becomes Maintain the sequence voltage on the sequence impedance That is, the primary voltage of the transformer remains unchanged, and the f1 sequence impedance is corrected to 3Z f1 ; Step 2: According to the three-phase disconnection composite fault sequence network diagram of the return line, it is inferred that only one unknown sequence voltage component is included. The equation is: In the formula, is the integrated electromotive force from the disconnection point into the system, E is the equivalent electromotive force on both sides of the line, δ is the phase angle between the electromotive forces on both sides of the line; Z e1 is the e1 sequence impedance; Z f1 is the f1 sequence impedance; Step 3, calculate the other sequence voltages and currents through equation (2-3), and then calculate the voltage between the two points of the broken line and the normal phase current through equation (1-2).

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