AC power system fault traveling wave analysis method and system

Abstract

The invention relates to the technical field of traveling wave analysis, in particular to an alternating-current power system fault traveling wave analysis method and system, and the method comprises the steps: constructing a fault component network at an alternating-current line fault point according to a fault current component and a fault voltage component at the fault point of an alternating-current power system; according to the fault component network, analyzing current and voltage changes at a fault point by using a Kirchhoff's law, and determining a boundary condition of the fault point; based on the boundary condition of the fault point, solving a mode fault component analytical expression at the fault point of the alternating current line by using phase-mode transformation and an Ohm law; and according to the physical propagation characteristics of the alternating current line and the mode fault component analytical expression, obtaining a fault traveling wave wavefront analytical component at the traveling wave protection installation position by using a Laplace transformation algorithm. According to the method, the wavefront information of the fault traveling wave at the fault point is accurately analyzed by combining the fault component network and the circuit theory, a more reliable basis is provided for fault detection, and the safety and stability of a power system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of traveling wave analysis, and in particular to a method and system for analyzing traveling wave faults in an alternating current power system. Background Art

[0002] In modern power systems, fault detection and isolation are important links to ensure the safe and stable operation of the system. Although traditional fault detection methods such as overcurrent protection and distance protection can meet the basic needs of power system protection to a certain extent, with the continuous expansion of the scale of the power grid and the increasing complexity of the power grid structure, these traditional fault detection methods still have limitations in response speed and fault location accuracy, and cannot meet the requirements of modern power systems for high reliability and rapid response, especially in high-voltage and ultra-high-voltage AC power systems. The traveling wave phenomenon caused by faults is becoming more and more obvious. These traveling waves contain rich fault information, which is of great significance for the rapid detection and location of faults.

[0003] In response to these problems, traveling wave protection technology has gradually demonstrated its unique advantages. It is based on traveling wave theory and can quickly and accurately locate faults by monitoring the propagation characteristics of traveling waves on power lines. When a fault occurs, traveling wave signals will be generated on the power lines. These signals propagate at the speed of light. Traveling wave protection can detect faults within milliseconds and calculate the fault location in real time. However, in the existing technology, the transmission of traveling waves in the power grid is affected by many factors, such as the impedance characteristics of the line, the initial fault angle, and the response speed of the transformer. As a result, when a fault occurs, the changes in the traveling wave waveform are often difficult to accurately analyze. Especially in complex power systems, the propagation characteristics of the lines and the types of faults are diverse. How to accurately obtain and analyze the characteristics of the fault traveling wave front to achieve accurate positioning and rapid response to power system faults has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method and system for analyzing fault traveling waves in an AC power system.

[0005] In a first aspect, the present invention provides a method for analyzing fault traveling waves in an AC power system, the method comprising the following steps:

[0006] According to the fault current component and the fault voltage component at the fault point of the AC power system, a fault component network at the fault point of the AC line is constructed;

[0007] According to the fault component network, Kirchhoff's law is used to analyze the current and voltage changes at the fault point to determine the boundary conditions of the fault point;

[0008] Based on the fault point boundary conditions, the analytical expression of the mode fault component at the AC line fault point is solved by using phase mode transformation and Ohm's law;

[0009] According to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component, the analytical component of the fault traveling wave front at the traveling wave protection installation location is obtained by using the Laplace transform algorithm.

[0010] In a further embodiment, when a phase-to-ground fault occurs in the AC line, the fault point boundary conditions include:

[0011] The fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault moment is equal to the difference between the normal working voltage at the fault point at the fault moment and the voltage drop caused by the fault component of the fault phase current passing through the transition resistor.

[0012] In a further embodiment, the step of solving the analytical expression of the mode fault component at the fault point by using phase mode transformation and Ohm's law based on the fault point boundary condition includes:

[0013] Performing phase-mode transformation on the three-phase voltage components and the three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component;

[0014] Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails;

[0015] Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters;

[0016] According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

[0017] In a further embodiment, the mode component boundary conditions include:

[0018] The sum of the zero-mode current fault component and the second-mode current fault component at the fault point of the AC line is equal to twice the first-mode current fault component;

[0019] The sum of the zero-mode current fault component and the first-mode current fault component at the fault point of the AC line is equal to twice the second-mode current fault component;

[0020] When an AC line fault occurs, the normal operating voltage at the fault point minus the weighted sum of the transition resistance and the fault components of each mode current is equal to the sum of the fault components of each mode voltage at the fault point.

[0021] In a further embodiment, the step of obtaining the fault traveling wave front analytical component at the traveling wave protection installation location using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component comprises:

[0022] According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed;

[0023] The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed;

[0024] The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function;

[0025] The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point;

[0026] The frequency domain characteristic component of the fault traveling wave is subjected to an inverse Laplace transform to obtain a wavefront analytical component of the fault traveling wave at the traveling wave protection installation location.

[0027] In a further embodiment, the mathematical expression of the analytical component of the fault traveling wave front is:

[0028]

[0029] in,

[0030]

[0031] λ=tan -1 (w0τ a x f )

[0032] In the formula, Δu P (s) is the fault traveling wave front analytical component; K1 is the fault traveling wave amplitude adjustment coefficient measured at the traveling wave protection installation location; w0 is the angular frequency; t is the time; θ is the fault traveling wave phase angle at the traveling wave protection installation location; τ a is the dispersion coefficient; x f is the traveling wave propagation distance; A f is the amplitude of the fault component of the mode voltage at the fault point; Ka is the traveling wave amplitude attenuation coefficient of the AC line; is the initial voltage phase when the fault point is operating normally; T f is the absolute moment when the fault occurs; λ is the phase deviation angle caused by the dispersion effect.

[0033] In a second aspect, the present invention provides an AC power system fault traveling wave analysis system, the system comprising:

[0034] A fault network construction module, used to construct a fault component network at the fault point of the AC line according to the fault current component and the fault voltage component at the fault point of the AC power system;

[0035] A fault network analysis module is used to analyze the current and voltage changes at the fault point according to the fault component network using Kirchhoff's law to determine the boundary conditions of the fault point;

[0036] A fault analysis module is used to solve the fault component analytical expression at the fault point of the AC line by using phase mode transformation and Ohm's law based on the boundary conditions of the fault point;

[0037] The fault traveling wave analysis module is used to obtain the fault traveling wave front analytical component at the traveling wave protection installation location using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component.

[0038] In a further embodiment, when a phase-to-ground fault occurs in the AC line, the fault point boundary conditions include:

[0039] The fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault moment is equal to the difference between the normal working voltage at the fault point at the fault moment and the voltage drop caused by the fault component of the fault phase current passing through the transition resistor.

[0040] In a further embodiment, the fault resolution analysis module is specifically used to:

[0041] Performing phase-mode transformation on the three-phase voltage components or three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component;

[0042] Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails;

[0043] Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters;

[0044] According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

[0045] In a further embodiment, the fault traveling wave analysis module is specifically used for:

[0046] According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed;

[0047] The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed;

[0048] The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function;

[0049] The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point;

[0050] The frequency domain characteristic component of the fault traveling wave is subjected to inverse Laplace transformation to obtain the wavefront analytical component of the fault traveling wave at the protection installation location.

[0051] The present invention provides a method and system for analyzing fault traveling waves in an AC power system. The method constructs a fault component network at the fault point of an AC line according to the fault current component and the fault voltage component at the fault point of the AC power system; according to the fault component network, Kirchhoff's law is used to analyze the current and voltage changes at the fault point to determine the boundary conditions of the fault point; based on the boundary conditions of the fault point, the analytical expression of the mode fault component at the fault point of the AC line is solved by using phase mode transformation and Ohm's law; according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component, the Laplace transform algorithm is used to obtain the analytical component of the fault traveling wave front at the installation of the traveling wave protection. Compared with the prior art, the method can accurately and quickly analyze the fault traveling wave front component data generated when the AC system fails by constructing a fault component network and Kirchhoff's law and other technologies, providing a more reliable basis for the rapid detection and precise positioning of power system faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1It is a schematic diagram of the flow chart of the method for analyzing traveling waves of AC power system faults provided by an embodiment of the present invention;

[0053] Figure 2 is a schematic diagram of a line fault provided by an embodiment of the present invention;

[0054] Figure 3 is a schematic diagram of a fault component network under a phase a grounding fault provided by an embodiment of the present invention;

[0055] Figure 4 is a schematic diagram of the topological structure of an AC simulation system provided by an embodiment of the present invention;

[0056] Figure 5 It is a schematic diagram of simulation results of a mode voltage fault component under a 0Ω transition resistance and a 100km fault distance provided by an embodiment of the present invention;

[0057] Figure 6 It is a schematic diagram of simulation results of a mode voltage fault component under a 0Ω transition resistance and a 200km fault distance provided by an embodiment of the present invention;

[0058] Figure 7 It is a schematic diagram of simulation results of a mode voltage fault component under a 50Ω transition resistance and a 100km fault distance provided by an embodiment of the present invention;

[0059] Figure 8 It is a schematic diagram of simulation results of a mode voltage fault component under a 50Ω transition resistance and a 200km fault distance provided by an embodiment of the present invention;

[0060] Fig. 9 It is a block diagram of an AC power system fault traveling wave analysis system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0062] refer to Figure 1 , the embodiment of the present invention provides a method for analyzing fault traveling waves in an AC power system, such as Figure 1 As shown, the method comprises the following steps:

[0063] S1. Construct a fault component network at the fault point of the AC line according to the fault current component and the fault voltage component at the fault point of the AC power system.

[0064] Figure 2 This is a schematic diagram of a line fault in an AC power system. Figure 2 In the figure, G1 and G2 both represent AC power supply, L b is the equivalent inductance of the AC power supply, F represents the location of the fault point, the measuring point represents the location of the traveling wave protection installation, and the transmission line is an AC line. For ease of understanding, the following will take the a phase fault as an example for detailed description. Figure 2 When a phase fault occurs at the fault point F in the example, phase a is the fault phase. This embodiment constructs a fault component network at the fault point of the AC line according to the fault current component and the fault voltage component at the fault point of the AC power system, so as to more accurately simulate the situation of the actual system fault point, such as Figure 3 As shown in the figure, in the fault component network under phase a ground fault, u fa (t f ) indicates that at the time of AC line fault t = t f When the normal working voltage of phase a at the fault point is fa represents the phase-to-ground current fault component at the AC line fault point, Δu fa represents the voltage fault component of phase a at the fault point of the AC line, R f It is the transition resistance of the fault point. The transition resistance is mainly the resistance formed between the fault point and the ground when a fault occurs.

[0065] S2. According to the fault component network, Kirchhoff's law is used to analyze the current and voltage changes at the fault point to determine the boundary conditions of the fault point.

[0066] Figure 3 The fault component network shows the relationship between the voltage and current at the fault point. This embodiment analyzes the fault component network and analyzes the phase a-to-ground fault branch and phase b and phase c respectively in combination with Kirchhoff's law, lists the boundary conditions at the fault point, and forms the fault point boundary conditions, wherein phase a is the fault phase, and phase b and phase c are the non-fault phases. In this embodiment, when a fault phase to ground fault occurs in the AC line, the fault point boundary conditions include: the fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault time is equal to the difference between the normal working voltage at the fault point at the fault time and the voltage drop generated by the fault phase current fault component through the transition resistor. In this embodiment, the fault point boundary conditions are expressed by the following formula:

[0067]

[0068] In the formula, Δi fb Indicates the fault component of the b-phase (non-fault phase) to ground current at the fault point of the AC line; Δi fc It represents the fault component of the c-phase (non-fault phase) to ground current at the fault point of the AC line.

[0069] S3. Based on the fault point boundary conditions, use phase mode transformation and Ohm's law to solve the analytical expression of the mode fault component at the AC line fault point.

[0070] In this embodiment, the step of solving the analytical expression of the mode fault component at the fault point by using phase mode transformation and Ohm's law based on the fault point boundary condition includes:

[0071] Performing phase-mode transformation on the three-phase voltage components and the three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component;

[0072] Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails;

[0073] Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters;

[0074] According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

[0075] Specifically, when solving the mode voltage fault component and the mode current fault component at the fault point, the present embodiment uses phase-mode transformation to convert the three-phase voltage component and the three-phase current component of the three-phase system into corresponding mode components to obtain the mode voltage fault component and the mode current fault component. Then, the present embodiment substitutes these mode voltage fault components and the mode current fault components into the fault point boundary conditions to obtain the mode component boundary conditions at the fault point when the AC line fails. In the present embodiment, the mode component boundary conditions include:

[0076] The sum of the zero-mode current fault component and the second-mode current fault component at the fault point of the AC line is equal to twice the first-mode current fault component;

[0077] The sum of the zero-mode current fault component and the first-mode current fault component at the fault point of the AC line is equal to twice the second-mode current fault component;

[0078] When an AC line fault occurs, the normal operating voltage at the fault point minus the weighted sum of the transition resistance and the fault components of each mode current is equal to the sum of the fault components of each mode voltage at the fault point.

[0079] In this embodiment, the modulus component boundary condition is expressed by the following formula:

[0080]

[0081] In the formula, Δu f0 , Δu f1 and Δu f2 are the zero-mode voltage fault component, the first-mode voltage fault component and the second-mode voltage fault component at the fault point of the AC line respectively; Δi f0 , Δi f1 and Δi f2 They are respectively the zero-mode current fault component to ground, the first-mode current fault component, and the second-mode current fault component at the fault point of the AC line.

[0082] It should be noted that, since the zero-mode component is zero when the three-phase AC line is operating normally, the zero-mode fault component is equal to the zero-mode fault full amount. Therefore, this embodiment adopts u f0 and i f0 Instead of Δu f0 and Δi f0 In this embodiment, the positive direction of voltage is defined as the line pointing to the earth, and the positive direction of current is defined as the busbar pointing to the line. Based on the positive direction of voltage and current, Ohm's law and AC line wave impedance parameters are used to analyze the relationship between the voltage fault component and the current fault component at the fault point, and a fault voltage-current relationship model between the mode voltage fault component and the mode current fault component at the AC line fault point is established. The fault voltage-current relationship model is specifically:

[0083] Δu f0 =Z c0 Δi f0

[0084] Δu f1 =Z c1 Δi f1

[0085] Δu f2 =Z c2 Δi f2

[0086] In the formula, Z c0 , Z c1 and Z c2 are the zero-mode wave impedance, first-mode wave impedance and second-mode wave impedance of the AC line respectively, and satisfy Z c1 =Z c2 .

[0087] Finally, the above fault voltage-current relationship model is substituted into the equation group of the mode component boundary conditions, and the analytical expression of the mode fault component at the fault point when the a-phase grounding fault occurs in the AC line is solved. In this embodiment, the analytical expression of the mode fault component includes analytical expressions of each mode voltage fault component and analytical expressions of each mode current fault component, wherein the analytical expression of each mode voltage fault component includes an analytical expression of a zero-mode voltage fault component at the fault point, an analytical expression of a one-mode voltage fault component and an analytical expression of a two-mode voltage fault component, wherein the analytical expression of the zero-mode voltage fault component at the fault point is the product of the normal working voltage at the fault point when the AC line fails and the zero-mode wave impedance of the AC line divided by the sum of the zero-mode wave impedance, twice the one-mode wave impedance and six times the transition resistance; the one-mode voltage at the fault point The fault component analytical expression and the two-mode voltage fault component analytical expression are both the product of the normal working voltage at the fault point when the AC line fails and the first-mode wave impedance of the AC line divided by the sum of the zero-mode wave impedance, twice the first-mode wave impedance and six times the transition resistance; the analytical expression of each mode current fault component includes the zero-mode current fault component analytical expression at the fault point, the first-mode current fault component analytical expression and the two-mode current fault component analytical expression. The zero-mode current fault component analytical expression at the fault point, the first-mode current fault component analytical expression and the two-mode current fault component analytical expression are all equal to the normal working voltage at the fault point when the AC line fails divided by the sum of the zero-mode wave impedance, twice the first-mode wave impedance and six times the transition resistance. In this embodiment, the analytical expression of the mode fault component is expressed by the following formula:

[0088]

[0089] S4. According to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component, the Laplace transform algorithm is used to obtain the analytical component of the fault traveling wave front at the traveling wave protection installation.

[0090] In this embodiment, the step of obtaining the fault traveling wave front analytical component at the traveling wave protection installation location by using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component includes:

[0091] According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed;

[0092] The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed;

[0093] The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function;

[0094] The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point;

[0095] The fault traveling wave frequency domain characteristic component is subjected to inverse Laplace transformation to obtain the fault traveling wave wavefront analytical component at the traveling wave protection installation location; in this embodiment, the mathematical expression of the fault traveling wave front analytical component is:

[0096]

[0097] in,

[0098]

[0099] λ=tan -1 (w0τ a x f )

[0100] In the formula, Δu P (s) is the fault traveling wave front analytical component; K1 is the fault traveling wave amplitude adjustment coefficient measured at the traveling wave protection installation location; w0 is the angular frequency; t is the time; θ is the fault traveling wave phase angle at the traveling wave protection installation location, which takes into account the influence of the original phase, fault time and dispersion effect; τ a is the dispersion coefficient; x f is the traveling wave propagation distance; A f is the amplitude of the fault component of the mode voltage at the fault point; K a is the traveling wave amplitude attenuation coefficient of the AC line; is the initial voltage phase when the fault point is operating normally; T f is the absolute moment when the fault occurs; λ is the phase deviation angle caused by the dispersion effect.

[0101] Specifically, for the sake of convenience, this embodiment takes a single-mode voltage as an example to illustrate step S4. It is assumed that under normal working conditions, the normal working voltage at the fault point at the time of the fault can be expressed as the voltage amplitude A0 of the fault point when it is operating normally multiplied by a cosine function. The cosine function is constructed according to the system angular frequency multiplied by the time t plus the initial phase of the voltage when the fault point is operating normally. That is, the normal working voltage expression at the fault point at the time of the fault is:

[0102]

[0103] Where A0 is the voltage amplitude when the fault point is operating normally.

[0104] In this embodiment, based on the analytical expression of the mode fault component at the fault point when the AC line fails and the normal working voltage expression at the fault point at the time of the fault, a time domain formula of the first mode (similarly, the zero mode and the second mode) voltage fault component at the fault point is constructed to form a time domain fault point traveling wave expression at the fault point. The time domain fault point traveling wave expression at the fault point is specifically:

[0105]

[0106] in,

[0107]

[0108] In the formula, Δu f1 is the first-mode voltage fault component at the fault point of the AC line; ε(*) is a step function, which is used to represent the fault traveling wave at t = T f Sudden change of moment.

[0109] Next, the Laplace transform algorithm is used to perform Laplace transform on the time domain fault point traveling wave expression to obtain the frequency domain representation of the fault point traveling wave at the traveling wave protection installation location. The frequency domain representation of the fault point traveling wave is used to describe the characteristics of the fault point traveling wave in the frequency domain. The mathematical expression of the frequency domain representation of the fault point traveling wave is:

[0110]

[0111] In the formula, ΔU f1 (s) is the frequency domain representation of the traveling wave at the fault point; s is the complex variable of the Laplace transform.

[0112] Then, according to the physical propagation characteristics of the AC line, the frequency domain transmission characteristics of the AC line are modeled in the first order approximation to obtain the frequency domain transfer function, which describes the attenuation and dispersion phenomenon of the traveling wave during the transmission process. The specific frequency domain transfer function is:

[0113]

[0114] Where T(s) is the frequency domain transfer function, which can be used to describe the propagation characteristics of fault traveling waves on the transmission line; s is the complex variable of Laplace transform; τ a1 is the dispersion coefficient corresponding to the single-mode voltage fault component, which characterizes the degree of traveling wave dispersion.

[0115] In this embodiment, the time when the fault occurs is taken as the time t=0, and the frequency domain representation of the fault point traveling wave is taken as the input signal, which is input into the frequency domain transfer function. The delay property of Laplace transform is used to simulate the traveling wave propagation process from the fault point to the protection installation. The frequency domain characteristic component of the fault traveling wave at the protection installation is obtained by calculation. The output is the first traveling wave at the fault point, that is, the original traveling wave fault without the reflected wave. The delay theorem can consider the propagation delay of the signal in the complex frequency domain. The mathematical expression of the fault traveling wave frequency domain characteristic component is:

[0116] ΔU P1 (s)=T(s)*ΔU f1 (s)

[0117] therefore,

[0118]

[0119] In the formula, ΔU P1 (s) is the frequency domain characteristic component of the fault traveling wave measured at the protection installation.

[0120] Finally, the fault traveling wave frequency domain characteristic component at the protection installation is subjected to an inverse Laplace transform, and the complex frequency domain signal is converted back to the time domain to obtain the fault traveling wave wavefront analytical component at the traveling wave protection installation. In this embodiment, the expression of the fault traveling wavefront analytical component corresponding to the single-mode voltage fault component is:

[0121]

[0122] in,

[0123]

[0124] λ=tan -1 (w0τ a1 x f )

[0125] In the formula, Δu P1 (s) is the analytical component of the fault traveling wave front measured at the traveling wave protection installation location; τ a1 is the dispersion coefficient corresponding to the single-mode voltage fault component.

[0126] It should be noted that accurate analysis of the traveling wave front generated when an AC system fails is crucial for power system fault detection and location based on traveling wave protection. The fault traveling wave time domain analysis component at the traveling wave protection installation calculated in this embodiment describes the change pattern of the fault traveling wave measured at the protection installation over time, which contains rich fault information, such as the time when the fault occurred, the waveform characteristics of the fault traveling wave, etc. This information is an important basis for subsequent fault type identification, fault location and fault severity assessment. Compared with the frequency domain representation, the fault traveling wave time domain analysis component more intuitively reflects the actual changes of the fault traveling wave, which helps to improve the accuracy and reliability of fault handling. In the prior art, the transmission of traveling waves in the power grid is affected by many factors, which makes it difficult to accurately analyze the changes in the traveling wave waveform. This embodiment constructs a fault component network at the actual system fault point and uses circuit theory to analyze it, accurately analyzing the fault traveling wave front analysis component at the fault point, and uses it as the fault traveling wave front feature information to achieve subsequent precise positioning and rapid response to power system faults. This embodiment can quickly determine the nature and location of the fault by analyzing the time domain analysis component of the fault traveling wave at the protection installation, thereby triggering corresponding protection actions, such as tripping, isolating the fault area, etc., reducing the impact of the fault on the power system and ensuring the safe and stable operation of the power system.

[0127] In order to verify the accuracy of the traveling wavefront analysis results, this embodiment constructs a simplified AC system model in PSCAD (electromagnetic transient simulation software), and its topology is as follows: Figure 4 As shown in Figure 1, in this AC system model, the sine wave amplitudes of the two power sources are set to 230 kV, the total length of the system AC line is 400 km, and fault points F1, F2, and F3 are set at different locations (100 km, 200 km, and 300 km) from the measuring point. For each fault point, two fault transition resistances of 0 ohm (Ω) and 50 ohm are simulated. The first wave simulation waveforms at the measuring point are as follows: Figure 5 , Figure 6 , Figure 7 and Figure 8 As shown, it should be noted that Figure 5 , Figure 6 , Figure 7 and Figure 8The first-wave simulation result curve in is the first-wave waveform obtained by simulating the actual AC system fault (including the set fault location, fault transition resistance and other conditions) directly in the PSCAD simulation software. It reflects the actual situation of the traveling wave signal received at the measuring point under the specific fault condition; and the first-wave analytical numerical result curve is calculated by substituting the transmission line parameters (such as zero-mode wave impedance, one-mode wave impedance, etc.) derived from PSCAD and other related parameters (such as the amplitude of the normal working voltage at the fault point, the absolute time of the fault, the initial phase of the voltage at the fault point, etc.) into the analytical component expression of the fault traveling wave front proposed in this embodiment. This embodiment uses The transmission line parameters exported by PSCAD software were used to calculate the zero-mode wave impedance and the first-mode wave impedance, which were 580.198Ω and 383.0531Ω respectively. These parameters and other related parameters were then substituted into the calculation formula of the analytical component of the fault traveling wave front, and the numerical result of the analytical formula was obtained. Through the analysis of the simulation results, it can be seen that the expression of the analytical component of the fault traveling wave front can accurately characterize the dispersion characteristics of the traveling wave. In summary, the expression of the analytical component of the fault traveling wave front proposed in this embodiment is not only correct, but also has practical application potential for relay protection, and provides strong technical support for the design and implementation of the traveling wave protection principle.

[0128] The embodiment of the present invention provides a method for analyzing fault traveling waves in an AC power system. The method constructs a fault component network at the fault point of an AC line according to the fault current component and the fault voltage component at the fault point of the AC power system; according to the fault component network, Kirchhoff's law is used to analyze the current and voltage changes at the fault point to determine the boundary conditions of the fault point; based on the boundary conditions of the fault point, the analytical expression of the mode fault component at the fault point of the AC line is solved by using phase mode transformation and Ohm's law; according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component, the Laplace transform algorithm is used to obtain the analytical component of the fault traveling wave front at the installation of the traveling wave protection. Compared with the prior art, the method proposed in this embodiment combines the fault component network and circuit theory to accurately analyze the fault traveling wave front characteristic information at the fault point, providing a more reliable basis for fault detection, so as to achieve accurate positioning and rapid response to power system faults, which is helpful to improve the safety and stability of the power system and meet the requirements of modern power systems for high reliability and rapid response.

[0129] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0130] In one embodiment, Fig. 9 As shown, an embodiment of the present invention provides an AC power system fault traveling wave analysis system, the system comprising:

[0131] A fault network construction module 101 is used to construct a fault component network at the fault point of the AC line according to the fault current component and the fault voltage component at the fault point of the AC power system;

[0132] A fault network analysis module 102 is used to analyze the current and voltage changes at the fault point according to the fault component network using Kirchhoff's law to determine the boundary conditions of the fault point;

[0133] A fault analysis module 103 is used to solve the analytical expression of the mode fault component at the fault point of the AC line by using phase mode transformation and Ohm's law based on the boundary conditions of the fault point;

[0134] The fault traveling wave analysis module 104 is used to obtain the fault traveling wave front analytical component at the traveling wave protection installation location by using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component.

[0135] In this embodiment, when a phase-to-ground fault occurs in the AC line, the fault point boundary conditions include:

[0136] The fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault moment is equal to the difference between the normal working voltage at the fault point at the fault moment and the voltage drop caused by the fault component of the fault phase current passing through the transition resistor.

[0137] In this embodiment, the fault analysis module is specifically used to:

[0138] Performing phase-mode transformation on the three-phase voltage components or three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component;

[0139] Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails;

[0140] Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters;

[0141] According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

[0142] In this embodiment, the fault traveling wave analysis module is specifically used for:

[0143] According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed;

[0144] The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed;

[0145] The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function;

[0146] The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point;

[0147] The frequency domain characteristic component of the fault traveling wave is subjected to inverse Laplace transformation to obtain the wavefront analytical component of the fault traveling wave at the protection installation location.

[0148] For the specific limitations of a traveling wave analysis system for faults in an AC power system, please refer to the above-mentioned limitations on a traveling wave analysis method for faults in an AC power system, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0149] The embodiment of the present invention provides an AC power system fault traveling wave analysis system, the system constructs a fault component network at the fault point of the AC line through a fault network construction module; the fault network analysis module analyzes the current and voltage changes at the fault point based on the fault component network using Kirchhoff's law to determine the boundary conditions of the fault point; the fault analysis module solves the model fault component analytical expression at the AC line fault point based on the boundary conditions of the fault point using phase model transformation and Ohm's law; the fault traveling wave analysis module obtains the fault traveling wave front analytical component at the traveling wave protection installation location using the Laplace transform algorithm based on the physical propagation characteristics of the AC line and the model fault component analytical expression. Compared with the prior art, the system proposed in this embodiment combines the fault component network and circuit theory to accurately analyze the fault traveling wave front characteristic information at the fault point, providing a more reliable basis for fault detection, so as to achieve accurate positioning and rapid response to power system faults, which is helpful to improve the safety and stability of the power system and meet the requirements of modern power systems for high reliability and rapid response.

[0150] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A method for analyzing traveling waves of AC power system faults, characterized in that: The following steps are involved: According to the fault current component and the fault voltage component at the fault point of the AC power system, a fault component network at the fault point of the AC line is constructed; According to the fault component network, Kirchhoff's law is used to analyze the current and voltage changes at the fault point to determine the boundary conditions of the fault point; Based on the fault point boundary conditions, the analytical expression of the mode fault component at the AC line fault point is solved by using phase mode transformation and Ohm's law; According to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component, the analytical component of the fault traveling wave front at the traveling wave protection installation location is obtained by using the Laplace transform algorithm.

2. A method for analyzing fault traveling waves in an AC power system according to claim 1, characterized in that: When a phase-to-ground fault occurs in the AC line, the fault point boundary conditions include: The fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault moment is equal to the difference between the normal working voltage at the fault point at the fault moment and the voltage drop caused by the fault component of the fault phase current passing through the transition resistor.

3. The method for analyzing fault traveling waves in an AC power system according to claim 1, characterized in that: The step of solving the analytical expression of the mode fault component at the fault point by using phase mode transformation and Ohm's law based on the fault point boundary condition comprises: Performing phase-mode transformation on the three-phase voltage components and the three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component; Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails; Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters; According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

4. A method for analyzing fault traveling waves in an AC power system according to claim 3, characterized in that: The modulus component boundary conditions include: The sum of the zero-mode current fault component and the second-mode current fault component at the fault point of the AC line is equal to twice the first-mode current fault component; The sum of the zero-mode current fault component and the first-mode current fault component at the fault point of the AC line is equal to twice the second-mode current fault component; When an AC line fault occurs, the normal operating voltage at the fault point minus the weighted sum of the transition resistance and the fault components of each mode current is equal to the sum of the fault components of each mode voltage at the fault point.

5. The method for analyzing fault traveling waves in an AC power system according to claim 1, characterized in that: The step of obtaining the fault traveling wave front analytical component at the traveling wave protection installation location by using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component comprises: According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed; The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed; The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function; The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point; The frequency domain characteristic component of the fault traveling wave is subjected to an inverse Laplace transform to obtain a wavefront analytical component of the fault traveling wave at the traveling wave protection installation location.

6. A method for analyzing fault traveling waves in an AC power system according to claim 5, characterized in that: The mathematical expression of the analytical component of the fault traveling wave front is: in, λ=tan -1 (w0t a x f ) In the formula, Δu P (s) is the fault traveling wave front analytical component; K1 is the fault traveling wave amplitude adjustment coefficient measured at the traveling wave protection installation location; w0 is the angular frequency; t is the time; θ is the fault traveling wave phase angle at the traveling wave protection installation location; τ a is the dispersion coefficient; x f is the traveling wave propagation distance; A f is the amplitude of the fault component of the mode voltage at the fault point; K a is the traveling wave amplitude attenuation coefficient of the AC line; is the initial voltage phase when the fault point is operating normally; T f is the absolute moment when the fault occurs; λ is the phase deviation angle caused by the dispersion effect.

7. An AC power system fault traveling wave analysis system, characterized in that: The system comprises: A fault network construction module, used to construct a fault component network at the fault point of the AC line according to the fault current component and the fault voltage component at the fault point of the AC power system; A fault network analysis module is used to analyze the current and voltage changes at the fault point according to the fault component network using Kirchhoff's law to determine the boundary conditions of the fault point; A fault analysis module is used to solve the fault component analytical expression at the fault point of the AC line by using phase mode transformation and Ohm's law based on the boundary conditions of the fault point; The fault traveling wave analysis module is used to obtain the fault traveling wave front analytical component at the traveling wave protection installation location using the Laplace transform algorithm according to the physical propagation characteristics of the AC line and the analytical expression of the mode fault component.

8. The AC power system fault traveling wave analysis system according to claim 7, characterized in that: When a phase-to-ground fault occurs in the AC line, the fault point boundary conditions include: The fault components of the ground current of the non-fault phase at the fault point are all zero, and the voltage fault component of the fault phase at the fault moment is equal to the difference between the normal working voltage at the fault point at the fault moment and the voltage drop caused by the fault component of the fault phase current passing through the transition resistor.

9. The AC power system fault traveling wave analysis system according to claim 7, characterized in that: The fault analysis module is specifically used for: Performing phase-mode transformation on the three-phase voltage components or three-phase current components at the fault point to obtain a mode voltage fault component and a mode current fault component; the mode voltage fault component includes a zero mode voltage fault component, a one mode voltage fault component and a two mode voltage fault component, and the mode current fault component includes a zero mode current fault component, a one mode current fault component and a two mode current fault component; Substituting the mode voltage fault component and the mode current fault component into the fault point boundary condition to obtain the mode component boundary condition at the fault point when the AC line fails; Determine the positive direction of voltage and current, and based on the positive direction of voltage and current, establish a fault voltage-current relationship model between a mode voltage fault component and a mode current fault component at a fault point of the AC line using Ohm's law and AC line wave impedance parameters; According to the fault voltage-current relationship model and the mode component boundary conditions, an analytical expression of the mode fault component at the fault point when a fault occurs in the AC line is obtained.

10. The AC power system fault traveling wave analysis system according to claim 7, characterized in that: The fault traveling wave analysis module is specifically used for: According to the analytical expression of the mode fault component at the fault point when the AC line fails, the time domain fault point traveling wave expression at the fault point is constructed; The traveling wave expression of the time-domain fault point is converted into a frequency-domain expression by using a Laplace transform algorithm, so as to obtain a frequency-domain expression of the traveling wave of the fault point where the traveling wave protection is installed; The frequency domain transmission characteristics of the AC line are modeled in a first-order approximate manner according to the physical propagation characteristics of the AC line to obtain the frequency domain transmission function; The frequency domain representation of the traveling wave at the fault point is used as the input signal of the frequency domain transfer function, and the Laplace transform delay theorem is used to simulate the traveling wave propagation process from the fault point to the traveling wave protection installation point, so as to obtain the fault traveling wave frequency domain characteristic component at the traveling wave protection installation point; The frequency domain characteristic component of the fault traveling wave is subjected to inverse Laplace transformation to obtain the wavefront analytical component of the fault traveling wave at the protection installation location.

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