Three-phase fault distance measurement method based on chained series supply type line

Abstract

The invention relates to a three-phase fault distance measurement method based on a chained series supply type line, and the method comprises the following specific steps: 1, obtaining a relation between the voltage of a fault point and the current of the fault point based on a boundary condition when a three-phase fault occurs in a chained series supply type power transmission line; 2, representing quantities which cannot be directly measured, such as positive-sequence voltage, positive-sequence current and positive-sequence fault component current, through quantities which can be directly measured, and obtaining a fault distance measurement formula at the moment by utilizing the property that a transition resistor is a pure resistor; and step 3, obtaining a fault distance measurement function f (d), estimating the voltage and current distribution of the whole line by adopting a global one-dimensional search method, and enabling the distance measurement function f (d) to obtain a search distance d of a minimum value, namely the solved fault distance. According to the invention, errors caused by line distributed capacitance are eliminated, and the accuracy of fault distance measurement is improved.

Description

Technical Field

[0001] This invention belongs to the field of power system distribution network fault location technology, and relates to a three-phase fault location method, especially a three-phase fault location method based on a chain-type series power supply line. Background Technology

[0002] Economic development begins with electricity. With the continuous improvement of the national economy and people's living standards, the demand for electricity for residential and industrial use is increasing year by year, and the power industry has gradually become a pillar industry of the national economy. Electricity, as a crucial component of energy, is an important material foundation for the survival and development of human society today, and a vital technical indicator reflecting national material production and people's living standards. It holds extremely important strategic significance in national economic and social production. While long-distance chain-type transmission lines bring economic and social benefits, they also place higher demands on fault location methods.

[0003] The accuracy of fault location algorithms depends on whether the line model used matches the actual line. Currently, commonly used fault location algorithms based on single-ended power frequency quantities include: the linear equation method, the quadratic equation method, and the iterative method. Generally, when the transmission line length is less than 100km, fault location algorithms using an RL-type equivalent line model can obtain relatively accurate results. However, for chain-type transmission lines with lengths ranging from 100km to 300km, the distributed capacitance on the transmission line cannot be ignored, and its presence significantly impacts the accuracy of fault location.

[0004] Therefore, in order to solve the above problems, this invention proposes a three-phase fault location method based on a chain-type series power supply line.

[0005] A search revealed no publicly available literature of the same or similar prior art as this invention. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a three-phase fault location method based on a chain-type series power transmission line, which is unaffected by the distributed capacitance of the line.

[0007] The present invention solves its practical problem by adopting the following technical solution:

[0008] A three-phase fault location method based on a chain-type series power supply line includes the following specific steps:

[0009] Step 1: When a three-phase fault occurs in a chain-type transmission line, the fault point voltage is obtained based on the boundary conditions at the time of the three-phase fault. With fault point current Relationship;

[0010] Step 2: Based on the fault point voltage obtained in Step 1 With fault point current The relational expression will be something that cannot be directly measured. Through quantities that can be directly measured, such as positive sequence voltage Positive sequence current Positive sequence fault component current We express this in terms of resistance, and then use the property that the transition resistance is a pure resistance to obtain the fault location formula at this time.

[0011] Step 3: Based on the fault location formula obtained in Step 2, the fault location function f(d) is obtained. Using a global one-dimensional search method, the voltage and current distribution of the entire line is estimated. The search distance d that minimizes the location function f(d) is the required fault distance.

[0012] Furthermore, the specific method for step 1 is as follows:

[0013] When a three-phase fault occurs in a chain-type transmission line, the following is obtained:

[0014]

[0015] Among them, R G For grounding transition resistance, R is usually considered to be present in actual line faults. G It exhibits pure resistivity, therefore Compared to The phase is 0°. Therefore, we can obtain:

[0016]

[0017] Transforming equation (2) into an equation with phase A as the reference phase, we get:

[0018]

[0019] Furthermore, the fault point voltage obtained in step 1 is used in step 2. With fault point current The relational expression will be something that cannot be directly measured. Through quantities that can be directly measured, such as positive sequence voltage Positive sequence current Positive sequence fault component current The specific method for representing this is as follows:

[0020] During a three-phase fault, the following relationship must be satisfied:

[0021]

[0022] in This is the positive sequence voltage measured at terminal M. This is the positive sequence current measured at terminal M. C1 is the positive sequence voltage at the fault point. C2 is the positive sequence capacitance per unit length of the line.

[0023] According to the basic theory of fault components, the positive sequence current of the faulty branch... Use the positive sequence fault component current at the measuring terminal Let's represent this. We can then obtain:

[0024]

[0025] Where C M1 This is the positive sequence current distribution coefficient.

[0026] Furthermore, the fault location formula in step 2 is:

[0027] By combining equations (3), (4), and (5), we can obtain the distance measurement formula for a three-phase fault:

[0028]

[0029] Furthermore, the specific method for obtaining the fault location function f(d) in step 3 based on the fault location formula obtained in step 2 is as follows:

[0030] A global one-dimensional search method is used to estimate the voltage and current distribution of the entire line;

[0031] Let: where d is the distance from any point on the line to end M; when satisfying When the search distance d is equal to the fault distance x, the search distance d is equal to the fault distance x.

[0032] Fault location is performed by utilizing the characteristic that the phase difference between voltage and current is minimal at the fault point. First, a function of the fault point voltage and fault current with respect to the search distance d is established:

[0033]

[0034] The ranging function for a three-phase fault is:

[0035]

[0036] The ranging function f(d) represents the voltage of the faulty branch corresponding to the search distance d. and current The absolute value of the phase difference;

[0037] Furthermore, the specific method for step 3, which employs a global one-dimensional search to estimate the voltage and current distribution of the entire line and minimizes the distance d of the ranging function f(d), is as follows:

[0038] The search distance d is searched in the interval [0,l] with a certain step size. The search distance d that makes the ranging function f(d) take the minimum value is the fault distance to be found.

[0039] Advantages and beneficial effects of the present invention:

[0040] 1. The three-phase fault location algorithm based on chain-type series power supply line proposed in this invention adopts the Π-type equivalent line model, considers the influence of line distributed capacitance on fault location, eliminates the error caused by line distributed capacitance, and improves the accuracy of fault location.

[0041] 2. The three-phase fault location algorithm based on a chain-type series power supply line proposed in this invention is based on the fault analysis method. It establishes a location equation by combining the voltage and current at the location point after a fault occurs with various characteristic parameters related to the system, and then analyzes and calculates the distance from the fault location to the location point. The fault analysis method has advantages such as simple and reliable principle, easy implementation, low requirements for location equipment, and low cost, and is widely used.

[0042] 3. The three-phase fault location algorithm based on chain-type series power supply line proposed in this invention only requires electrical quantities at one end, is not limited by communication technology conditions, has low cost, and is widely used.

[0043] 4. This invention proposes a three-phase fault location method based on a chain-type series power supply line. To eliminate errors caused by line distributed capacitance, this invention utilizes the property that the transition resistance is purely resistive and constructs a fault location algorithm based on the boundary conditions of different short-circuit types and the characteristic that the voltage and current at the fault point are in phase. This invention reduces the influence of line distributed capacitance, improves the accuracy of fault location, and has certain engineering application value. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a single-power chain-type series power transmission line according to the present invention;

[0045] Figure 2 This is a schematic diagram of a three-phase fault according to the present invention;

[0046] Figure 3 A positive-sequence equivalent system diagram of a three-phase fault in a transmission line for a lumped parameter model considering distributed capacitance for a single power source, as presented in this invention. Detailed Implementation

[0047] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:

[0048] A three-phase fault location method based on a chain-type series power supply line includes the following specific steps:

[0049] Step 1, chain-type series power supply transmission lines, such as Figure 1 As shown, taking a three-phase fault as an example, through... Figure 2 The boundary conditions for a three-phase fault can be determined, and the voltage at the fault point can be obtained. With fault point current The relational expression.

[0050] In this embodiment, Figure 1 This is a schematic diagram of a single-source chain-type series power transmission line. In the diagram, A, M, N, and D represent busbars;

[0051] Figure 2 This is a schematic diagram of a three-phase fault. R G This is the transition resistance when a three-phase fault occurs in phase A of the line.

[0052] Step 2, according to Figure 3 The positive-sequence equivalent system diagram of a three-phase fault in a transmission line with a single power source considering distributed capacitance, based on a lumped-parameter model, can represent the values ​​that cannot be directly measured. Through directly measurable quantities such as positive sequence voltage Positive sequence current Positive sequence fault component current This can be expressed as follows. Then, utilizing the property that the transition resistance is purely resistive, the fault location formula can be obtained at this point.

[0053] In this embodiment, Figure 3 This is a positive-sequence equivalent system diagram of a three-phase fault in a transmission line with a single power source and considering distributed capacitance, using a lumped-parameter model. The example shown is a three-phase fault occurring in phase A. In the diagram, These are the positive sequence voltage and current phasors measured at the M-terminal protection point. Z represents the system power supply potential. M1 Z is the positive-sequence equivalent impedance on the system side of the M-end of the transmission line. N1 Z is the positive-sequence equivalent impedance on the N-terminal load side. LM1 and Z LN1 Z represents the positive sequence equivalent impedance of the line from the fault point to terminals M and N, respectively. LM1 =xz1,Z LN1 = z1(lx). The distance from the fault point to terminal M is x, and the total length of the line is l. Y LM1 and Y LN1 Y represents the positive sequence equivalent admittance of the line from the fault point to terminals M and N, respectively. LM1 =jωC1x,Y LN1 =jωC1(lx), z1 is the positive sequence impedance per unit length of the line, and C1 is the positive sequence capacitance per unit length of the line. This represents the positive-sequence fault voltage at fault point k. For the flow through the transition resistor R G The positive sequence current.

[0054] Step 3: Since the transition resistance at the fault point is purely resistive, the characteristic that the phase difference between the voltage and current at the fault point is zero can be used to determine the fault location, thereby obtaining the fault location function f(d). A global one-dimensional search method is used to estimate the voltage and current distribution of the entire line. When applying the global one-dimensional search method in the calculation, the phase difference between the voltage and current at the fault point is not strictly zero. Therefore, the search distance d that minimizes the location function f(d) is the fault distance.

[0055] In step 1, when a three-phase fault occurs on the line, the fault diagram is as follows: Figure 2 As shown, we can obtain:

[0056]

[0057] Where R G For grounding transition resistance, R is usually considered to be present in actual line faults. G It exhibits pure resistivity, therefore Compared to The phase is 0°. Therefore, we can obtain:

[0058]

[0059] Transforming equation (2) into an equation with phase A as the reference phase, we get:

[0060]

[0061] In step 2, by Figure 3 It can be seen that, under a three-phase fault, the following relationship is satisfied:

[0062]

[0063] in This is the positive sequence voltage measured at terminal M. This is the positive sequence current measured at terminal M. C1 is the positive sequence voltage at the fault point. C2 is the positive sequence capacitance per unit length of the line.

[0064] According to the basic theory of fault components, the positive sequence current of the faulty branch... The positive sequence fault component current can be measured at the terminal. Let's represent this. We can then obtain:

[0065]

[0066] Where C M1 This is the positive sequence current distribution coefficient.

[0067] By combining equations (3), (4), and (5), we can obtain the distance measurement formula for a three-phase fault:

[0068]

[0069] In step 3, a global one-dimensional search method can be used to estimate the voltage and current distribution of the entire line, let: where d is the distance from any point on the line to terminal M. Since the transition resistance at the fault point is purely resistive, when the following conditions are met... When the fault location is determined, the corresponding search distance d is the fault distance x. However, when applying the global one-dimensional search method in the calculation, the phase difference between the voltage and current at the fault point is not strictly zero. The characteristic that the phase difference between the voltage and current at the fault point is minimal can be used for fault location. First, a function of the fault point voltage and fault current with respect to the search distance d can be established:

[0070]

[0071] The ranging function for a three-phase fault is:

[0072]

[0073] The ranging function f(d) represents the voltage of the faulty branch corresponding to the search distance d. and current The absolute value of the phase difference. The search distance d is searched in the interval [0,l] with a certain step size. The search distance d that makes the ranging function f(d) take the minimum value is the fault distance to be found.

[0074] To verify the fault location algorithm proposed in this invention, a simulation system was built using PSCAD / EMTDC software. Figure 1 The single-power chain-type series power transmission system shown in Table 1 presents the ranging results and errors of the ranging algorithm based on the RL-type equivalent line and the ranging algorithm proposed in this invention when a three-phase fault occurs in the single-power chain-type series power transmission line, under different fault distances and transition resistances.

[0075] Table 1 Three-phase faults

[0076]

[0077] As can be seen from the simulation data in Table 1, the fault location algorithm proposed in this invention has a fault location error of less than 1% throughout, which meets the needs of practical engineering.

[0078] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A three-phase fault location method based on a chain-type series power supply line, characterized in that: The specific steps include the following: Step 1: When a three-phase fault occurs in a chain-type transmission line, the fault point voltage is obtained based on the boundary conditions at the time of the three-phase fault. With fault point current Relationship; Step 2: Based on the fault point voltage obtained in Step 1 With fault point current The relational expression will be something that cannot be directly measured. Through quantities that can be directly measured, such as positive sequence voltage Positive sequence current Positive sequence fault component current We express this in terms of resistance, and then use the property that the transition resistance is a pure resistance to obtain the fault location formula at this time. Step 3: Based on the fault location formula obtained in Step 2, the fault location function f(d) is obtained. Using a global one-dimensional search method, the voltage and current distribution of the entire line is estimated. The search distance d that minimizes the location function f(d) is the required fault distance.

2. The three-phase fault location method based on a chain-type series power supply line according to claim 1, characterized in that: The specific method for step 1 is as follows: When a three-phase fault occurs in a chain-type transmission line, the following is obtained: Among them, R G For grounding transition resistance, R is usually considered to be present in actual line faults. G It exhibits pure resistivity, therefore Compared to The phase is 0°; therefore, we can obtain: Transforming equation (2) into an equation with phase A as the reference phase, we get:

3. The three-phase fault location method based on a chain-type series power supply line according to claim 1, characterized in that: The fault point voltage obtained in step 2 is based on the voltage obtained in step 1. With fault point current The relational expression will be something that cannot be directly measured. Through quantities that can be directly measured, such as positive sequence voltage Positive sequence current Positive sequence fault component current The specific method for representing this is as follows: During a three-phase fault, the following relationship must be satisfied: in The positive sequence voltage measured at terminal M; where The positive sequence current measured at terminal M; C1 is the positive sequence voltage at the fault point; C2 is the positive sequence capacitance per unit length of the line. According to the basic theory of fault components, the positive sequence current of the faulty branch... Use the positive sequence fault component current at the measuring terminal To represent; we can obtain: Where C M1 This is the positive sequence current distribution coefficient.

4. The three-phase fault location method based on a chain-type series power supply line according to claim 1, characterized in that: The fault location formula in step 2 is: By combining equations (3), (4), and (5), we can obtain the distance measurement formula for a three-phase fault:

5. A three-phase fault location method based on a chain-type series power supply line according to claim 1, characterized in that: The specific method for obtaining the fault location function f(d) based on the fault location formula obtained in step 2 in step 3 is as follows: A global one-dimensional search method is used to estimate the voltage and current distribution of the entire line; Let: where d is the distance from any point on the line to end M; when satisfying When the search distance d is equal to the fault distance x, then the search distance d is equal to the fault distance x. Fault location is performed by utilizing the characteristic that the phase difference between voltage and current is minimal at the fault point. First, a function of the fault point voltage and fault current with respect to the search distance d is established: The ranging function for a three-phase fault is: The ranging function f(d) represents the voltage of the faulty branch corresponding to the search distance d. and current The absolute value of the phase difference.

6. The three-phase fault location method based on a chain-type series power supply line according to claim 1, characterized in that: Step 3 employs a global one-dimensional search method to estimate the voltage and current distribution of the entire line, and the search distance d that minimizes the ranging function f(d) is the desired fault distance. The specific method is as follows: The search distance d is searched in the interval [0,l] with a certain step size. The search distance d that makes the ranging function f(d) take the minimum value is the fault distance to be found.

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