Two-phase earth fault distance measurement method based on single-end power frequency quantity

Abstract

The invention relates to a two-phase earth fault distance measurement method based on a single-end power frequency quantity, which comprises the following steps of: 1, when a BC two-phase earth fault occurs in a single-power-supply power transmission line, obtaining a relational expression between a fault point voltage and a fault point current; 2, representing the quantity which cannot be directly measured through the quantity which can be directly measured, such as positive-sequence voltage, negative-sequence voltage, positive-sequence current, negative-sequence current, positive-sequence fault component current and negative-sequence fault component current, and obtaining a fault distance measurement formula at the moment by utilizing the property that the transition resistor is pure resistor; and step 3, fault distance measurement is carried out by utilizing the characteristic that the phase difference between the voltage and the current at the fault point is zero, a fault distance measurement function f (d) is obtained, a global one-dimensional search method is adopted, the voltage and current distribution of the whole line is estimated, and a search distance d capable of enabling the distance measurement function f (d) to take a minimum value is the solved fault distance. According to the invention, 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 two-phase grounding fault location method, especially a two-phase grounding fault location method based on single-end power frequency quantity. Background Technology

[0002] High-voltage transmission lines are a crucial component of power systems. With the ever-expanding scale of power systems, the number of long-distance high-voltage transmission lines is increasing, and their proper operation plays a vital role in the safety and stability of the power system. Transmission lines are widely distributed and have a high probability of failure; therefore, quickly and accurately locating the fault point after a line fault is not only essential for timely power restoration but also for the safe and stable operation of the power system. For a long time, scholars both domestically and internationally have conducted extensive research to find accurate and effective fault location methods, proposing various fault location principles and methods. Early fault location methods relied on knowing the line length and unit impedance parameters, measuring the line impedance using fault quantities, and then converting this to the measured line length; their accuracy was limited. With the rapid development of computer technology, instrument transformer technology, fault quantity acquisition technology, and time synchronization technology, fault location technology has also entered a period of rapid development, especially since the 1990s, when its achievements in practical applications in power systems have become increasingly prominent.

[0003] Fault location methods are further divided into single-ended and double-ended methods based on the source of the electrical quantities required for distance measurement. The double-ended method uses electrical quantity information from both ends of the line to derive circuit equations, which are then simplified to obtain the distance measurement equation, thus calculating the fault distance. However, the double-ended method requires a communication channel to exchange information at both ends, increasing hardware investment and limiting its application in practical engineering. The main idea of ​​the single-ended method is to use the relationship between voltage and current measured at one end of the transmission line to eliminate unknown variables, and then solve the resulting distance measurement equation to determine the fault distance. Due to its simple principle, economic efficiency, and lack of limitations imposed by communication technology, the single-ended method has long been a research hotspot for scholars both domestically and internationally.

[0004] Therefore, in order to solve the above problems, this invention proposes a two-phase ground fault location method based on single-ended power frequency.

[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 two-phase ground fault location method based on single-end power frequency quantities, which uses only the electrical quantities at one end of the transmission line and improves the accuracy of fault location.

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

[0008] A two-phase ground fault location method based on single-ended power frequency quantities includes the following steps:

[0009] Step 1: In a single-source transmission line, when a two-phase ground fault (B and C) occurs, the fault point voltage is obtained by applying the boundary conditions for the B and C two-phase ground 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 Negative sequence voltage Positive sequence current Negative sequence current Positive sequence fault component current Negative sequence fault component current We express this in terms of resistance, and then, by utilizing the property that the transition resistance is a pure resistance, we obtain the fault location formula at this point.

[0011] Step 3: Based on the fault location formula obtained in Step 2, fault location is performed using the feature that the phase difference between voltage and current at the fault point is zero, and the fault location function f(d) is obtained. A global one-dimensional search method is used to estimate the voltage and current distribution of the entire line. The search distance d that minimizes the location function f(d) is the required fault distance.

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

[0013] When a two-phase ground fault (B and C) occurs on the line, the following is obtained:

[0014]

[0015] In actual line faults, the interphase transition resistance R F It is usually a real number, so Compared to Since the phase is 0°, 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 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 Negative sequence voltage Positive sequence current Negative sequence current Positive sequence fault component current Negative sequence fault component current The specific method for representing this is as follows:

[0020] During a two-phase-to-ground fault (BC), the following relationship must be satisfied:

[0021]

[0022] in These are the positive-sequence voltage and negative-sequence voltage measured at terminal M, respectively. and are the positive sequence current and negative sequence current measured at terminal M, respectively. These represent the positive-sequence voltage and negative-sequence voltage at the fault point, respectively; C1 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... Negative sequence current of the faulty branch The positive sequence fault component current can be measured at the terminal. Negative sequence fault component current To indicate;

[0024] We can obtain:

[0025]

[0026] Where C M1 C M2 These are the positive-sequence and negative-sequence current distribution coefficients, respectively.

[0027] Furthermore, the fault location formula in step 2 is:

[0028] By combining equations (3), (4), and (5), the distance measurement formula for a two-phase ground fault can be obtained:

[0029]

[0030] Furthermore, the specific method for obtaining the fault location function f(d) based on the fault location formula obtained in step 2 in step 3, which utilizes the characteristic that the phase difference between voltage and current at the fault point is zero, is as follows:

[0031] 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 terminal M;

[0032] When satisfied When the search distance d is equal to the fault distance x, then the search distance d is equal to the fault distance x.

[0033] First, establish the functions of fault point voltage and fault current with respect to the search distance d:

[0034]

[0035] The ranging function for a two-phase ground fault is:

[0036]

[0037] 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;

[0038] Furthermore, the specific method for using a global one-dimensional search in step 3 to estimate the voltage and current distribution of the entire line, which allows the search distance d to minimize the ranging function f(d), thus determining the required fault distance, is as follows:

[0039] 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.

[0040] Advantages and beneficial effects of the present invention:

[0041] 1. This invention proposes a two-phase ground fault location method based on single-ended power frequency quantities. This invention uses only the electrical quantities at one end of the transmission line and constructs a corresponding location function based on the boundary conditions of the two-phase ground fault. This fault location method employs a lumped parameter model and considers the influence of distributed capacitance, thereby improving the accuracy of fault location.

[0042] 2. The two-phase ground fault location method 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] 3. The two-phase ground fault location method proposed in this invention is based on fault analysis. It establishes a location equation by combining the voltage and current at the location point after the fault occurs with various system-related characteristic parameters, 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, ease of implementation, low requirements for location equipment, and low cost, making it widely applicable.

[0044] 4. The two-phase ground fault location method proposed in this invention adopts a lumped parameter model and takes into account the influence of distributed capacitance, thereby improving the accuracy of fault location. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a single-power transmission line according to the present invention;

[0046] Figure 2 This is a schematic diagram of a two-phase grounding fault according to the present invention;

[0047] Figure 3 This is the positive sequence equivalent system diagram of a two-phase ground fault in a single power supply line according to the present invention;

[0048] Figure 4 This is a negative sequence equivalent system diagram of a two-phase ground fault in a single power supply line according to the present invention. Detailed Implementation

[0049] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:

[0050] A two-phase ground fault location method based on single-ended power frequency quantities includes the following steps:

[0051] Step 1, Single-power transmission line such as Figure 1 As shown, taking a two-phase ground fault (BC) as an example, through... Figure 2 The boundary conditions for a two-phase-to-ground fault (BC) can be determined, and the voltage at the fault point can be obtained. With fault point current The relational expression.

[0052] In this embodiment, Figure 1 This is a schematic diagram of a single-source power transmission line, where A, M, N, and D represent busbars.

[0053] Figure 2 This is a schematic diagram of a two-phase ground fault;

[0054] R F R G These are the grounding transition resistance and phase-to-phase transition resistance when a two-phase (BC) ground fault occurs on the line.

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

[0056]

[0057] In actual line faults, the interphase transition resistance R F It is usually a real number, so Compared to Since the phase is 0°, we can obtain:

[0058]

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

[0060]

[0061] Step 2, according to Figure 3 , Figure 4 The positive and negative sequence equivalent system diagram of a two-phase ground fault in a single-source Π-type equivalent transmission line can represent values ​​that cannot be directly measured. Through directly measurable quantities such as positive sequence voltage Negative sequence voltage Positive sequence current Negative sequence current Positive sequence fault component current Negative 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.

[0062] In this embodiment, Figure 3 This is a positive sequence equivalent system diagram of a two-phase ground fault in a single-power supply line;

[0063] Taking a two-phase (BC) ground fault as an example, converted to a fault with phase A as the reference phase. (See 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 represents the positive-sequence equivalent impedance on the system side of the M-end of the transmission line. LM1 Z represents the positive sequence equivalent impedance of the line from the fault point to terminal M. LM1 =xz1. The distance from the fault point to terminal M is x, and the total length of the line is l. Y LM1 Y is the positive-sequence equivalent admittance of the line from the fault point to terminal M. LM1 =jωC1x, 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.

[0064] Figure 4 This is a negative sequence equivalent system diagram of a two-phase ground fault in a single-power supply line.

[0065] The scenario of a two-phase (BC) ground fault is transformed into an example with phase A as the reference phase. (See diagram.) Z represents the negative sequence voltage and current phasors measured at the M-terminal protection point. M2 Z represents the negative sequence equivalent impedance on the system side of the M-end of the transmission line.LM2 Z is the negative sequence equivalent impedance of the line from the fault point to terminal M. LM2 =xz1, . Y LM2 Y is the negative-sequence equivalent admittance of the line from the fault point to terminal N. LM2 =jωC1x, This refers to the negative sequence fault voltage at fault point k. For the flow through the transition resistor R G The negative sequence current.

[0066] In step 2, by Figure 3 , Figure 4 It can be seen that, in the case of a two-phase ground fault, the following relationship is satisfied:

[0067]

[0068] in These are the positive-sequence voltage and negative-sequence voltage measured at terminal M, respectively. and are the positive sequence current and negative sequence current measured at terminal M, respectively. These represent the positive-sequence voltage and negative-sequence voltage at the fault point, respectively. C1 is the positive-sequence capacitance per unit length of the line.

[0069] According to the basic theory of fault components, the positive sequence current of the faulty branch... Negative sequence current of the faulty branch The positive sequence fault component current can be measured at the terminal. Negative sequence fault component current To represent this. We can obtain:

[0070]

[0071] Where C M1 C M2 These are the positive-sequence and negative-sequence current distribution coefficients, respectively.

[0072] By combining equations (3), (4), and (5), the distance measurement formula for a two-phase ground fault can be obtained:

[0073]

[0074] 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.

[0075] In step 3, a global one-dimensional search method can be used to estimate the voltage and current distribution of the entire line, 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 search distance d is equal to the fault distance x, the search distance d is equal to the fault distance x.

[0076] 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 is minimal at the fault point 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:

[0077]

[0078] The ranging function for a two-phase ground fault is:

[0079]

[0080] 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.

[0081] In this embodiment, to verify the two-phase ground fault location method based on single-ended power frequency quantity proposed in this invention, a single-power transmission system was built using PSCAD / EMTDC simulation software, and data processing was performed using MATLAB to obtain the location results and errors of the location method proposed in this invention under different fault distances and transition resistances when a two-phase ground fault occurs.

[0082] Table 1 Two-phase ground fault (R) F =0Ω)

[0083]

[0084] As can be seen from the simulation data in Table 1, the fault location method proposed in this invention has a fault location error of less than 1% as the transition resistance and fault distance change, which meets the needs of practical engineering.

[0085] 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 two-phase ground fault location method based on single-ended power frequency quantities, characterized in that: Includes the following steps: Step 1: In a single-source transmission line, when a two-phase ground fault (B and C) occurs, the fault point voltage is obtained by applying the boundary conditions for the B and C two-phase ground 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 Negative sequence voltage Positive sequence current Negative sequence current Positive sequence fault component current Negative sequence fault component current We express this in terms of resistance, and then, by utilizing the property that the transition resistance is a pure resistance, we obtain the fault location formula at this point. Step 3: Based on the fault location formula obtained in Step 2, fault location is performed using the feature that the phase difference between voltage and current at the fault point is zero, and the fault location function f(d) is obtained. A global one-dimensional search method is used to estimate the voltage and current distribution of the entire line. The search distance d that minimizes the location function f(d) is the required fault distance.

2. The two-phase ground fault location method based on single-ended power frequency quantity according to claim 1, characterized in that: The specific method for step 1 is as follows: When a two-phase ground fault (B and C) occurs on the line, the following is obtained: In actual line faults, the interphase transition resistance R F It is usually a real number, so Compared to Since the phase is 0°, we can obtain: Transforming equation (2) into an equation with phase A as the reference phase, we get:

3. The two-phase ground fault location method based on single-ended power frequency quantity according to claim 1, characterized in that: The fault point voltage obtained in step 2 is 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 Negative sequence voltage Positive sequence current Negative sequence current Positive sequence fault component current Negative sequence fault component current The specific method for representing this is as follows: During a two-phase-to-ground fault (BC), the following relationship must be satisfied: in These are the positive-sequence voltage and negative-sequence voltage measured at terminal M, respectively. and are the positive sequence current and negative sequence current measured at terminal M, respectively. These represent the positive-sequence voltage and negative-sequence voltage at the fault point, respectively; C1 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... Negative sequence current of the faulty branch The positive sequence fault component current can be measured at the terminal. Negative sequence fault component current To indicate; We can obtain: Where C M1 C M2 These are the positive-sequence and negative-sequence current distribution coefficients, respectively.

4. The two-phase ground fault location method based on single-ended power frequency quantity according to claim 1, characterized in that: The fault location formula in step 2 is: By combining equations (3), (4), and (5), the distance measurement formula for a two-phase ground fault can be obtained:

5. The two-phase ground fault location method based on single-ended power frequency quantity 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, which utilizes the characteristic that the phase difference between voltage and current at the fault point is zero, 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 terminal M; When satisfied When the search distance d is equal to the fault distance x, then the search distance d is equal to the fault distance x. First, establish the functions of fault point voltage and fault current with respect to the search distance d: The ranging function for a two-phase ground 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 two-phase ground fault location method based on single-ended power frequency quantity 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. The search distance d that minimizes the ranging function f(d) is the desired fault distance. The specific method for this 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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