Fault distance measurement method and system for direct current transmission line

Abstract

The invention discloses a fault distance measurement method and system for a direct-current transmission line, and the method comprises the steps: obtaining the initial fault traveling wave arrival time and the fault point reflection wave arrival time of measurement points at two ends of the direct-current transmission line when the direct-current transmission line triggers fault distance measurement; according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time, calculating the arrival time difference between the initial fault traveling wave and the fault point reflected wave of the measurement points at the two ends, and calculating the distance between the measurement points at the two ends and the fault point based on the time difference between the measurement points at the two ends; the time difference of the measuring points is calculated according to the distance between the measuring points at the two ends and the fault point, strict clock synchronization of the measuring points at the two ends is not needed, calculation does not need to depend on the wave speed, and therefore the fault distance measurement accuracy of the direct-current power transmission line is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fault location, in particular to a fault location method and system for a DC transmission line. BACKGROUND

[0002] Power lines are the lifelines of power systems, and bear the important responsibility of transmitting electric energy. Therefore, the operation reliability of power lines affects the power supply reliability of power systems. The working environment of power lines is extremely harsh, and it is the place where faults occur most frequently in power systems, and the fault location is usually extremely difficult to find.

[0003] The DC transmission line transmits a large amount of power, and if the fault point cannot be quickly found and subsequent measures are taken, the consequences will be more serious. Therefore, after a fault occurs in the line, quickly and accurately finding the fault point, i.e. fault location, is not only very important for timely repairing the line and quickly restoring power supply, but also has important significance for the safe and stable operation and economic operation of the power system.

[0004] At present, there are mainly two types of fault location algorithms for transmission line distance measurement devices. One is impedance method, which directly calculates the fault impedance or its percentage algorithm. The other is traveling wave method, which uses high-frequency fault transient current, voltage traveling wave, etc. to determine the distance of the fault point from the measurement point. The impedance method is suitable for AC systems, and is easily affected by fault location, fault type and transition resistance, resulting in large measurement error, and is not suitable for fault location of DC transmission lines. For the traveling wave method, the widely used single-ended traveling wave distance measurement method and double-ended traveling wave distance measurement method have their own advantages and disadvantages. The single-ended traveling wave distance measurement method only needs one end of the line measurement point, relies on the time difference between the initial fault traveling wave and the fault point reflection wave for distance measurement, and does not need to communicate with the measurement point on the other side of the line, but the reflection wave from the fault point is difficult to distinguish from the reflection wave of the opposite bus and the reflection wave of the adjacent line. The double-ended traveling wave distance measurement method measures the time difference between the arrival of the initial fault traveling wave at the two ends of the line measurement point, but this method requires strict clock synchronization, and if strict clock synchronization cannot be guaranteed, the accuracy of the distance measurement result will be reduced. Moreover, whether it is single-ended traveling wave distance measurement method or double-ended traveling wave distance measurement method, the distance measurement result depends on the wave speed, and the wave speed needs to be set in advance. The accuracy of the wave speed setting will directly affect the accuracy of the distance measurement result, and it is impossible to set an accurate wave speed in reality.

[0005] Therefore, for DC transmission lines, there is an urgent need for a fault location method with higher accuracy. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a fault location method and system for a DC transmission line, which can effectively improve the fault location accuracy of the DC transmission line.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is: A fault location method of a DC transmission line, comprising the steps of: determining whether the DC transmission line triggers fault location, if yes, obtaining initial fault traveling wave arrival time and fault point reflected wave arrival time of two end measurement points of the DC transmission line; calculating time difference of initial fault traveling wave and fault point reflected wave arrival of the two end measurement points according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time; calculating distance of the two end measurement points and the fault point based on the time difference of the two end measurement points.

[0008] To solve the above technical problems, another technical scheme adopted by the present application is: A fault location system of a DC transmission line, comprising a memory, a processor and a computer program stored in the memory and running on the processor, the processor implements the following steps when executing the computer program: determining whether the DC transmission line triggers fault location, if yes, obtaining initial fault traveling wave arrival time and fault point reflected wave arrival time of two end measurement points of the DC transmission line; calculating time difference of initial fault traveling wave and fault point reflected wave arrival of the two end measurement points according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time; calculating distance of the two end measurement points and the fault point based on the time difference of the two end measurement points.

[0009] The present application has the beneficial effects that when the DC transmission line triggers fault location, the initial fault traveling wave arrival time and the fault point reflected wave arrival time of the two end measurement points of the DC transmission line are obtained, the time difference of initial fault traveling wave and fault point reflected wave arrival of the two end measurement points is calculated according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time, and the distance of the two end measurement points and the fault point is calculated based on the time difference of the two end measurement points, so that the time difference of each measurement point is used for calculating the distance of the two end measurement points and the fault point, strict clock synchronization of the two end measurement points is not required, and the calculation does not need to rely on wave speed, thereby effectively improving the fault location accuracy of the DC transmission line. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 A flow chart of a fault location method of a DC transmission line according to an embodiment of the present application; Figure 2 A schematic diagram of a fault location system of a DC transmission line according to an embodiment of the present application; Figure 3A topology diagram of a fault DC transmission line in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 4 A diagram of a fault branch and a transmission line being parallel in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 5 A flow chart of a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 6 A line mode voltage waveform diagram of M side and N side in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 7 A maximum value waveform diagram of M side mode in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 8 A maximum value waveform diagram of N side mode in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 9 A diagram of an initial fault traveling wave arrival time and a fault point reflection wave arrival time of M side in a fault distance measurement method of a DC transmission line according to an embodiment of the present application; Figure 10 A diagram of an initial fault traveling wave arrival time and a fault point reflection wave arrival time of N side in a fault distance measurement method of a DC transmission line according to an embodiment of the present application. DETAILED DESCRIPTION

[0011] To make the technical content, the purposes and effects of the present application clear, the embodiments are described below in conjunction with the accompanying drawings.

[0012] Before the embodiments of the present application are described in detail, some related concepts are explained first: Initial fault traveling wave: the first traveling wave propagating from the fault point to the measurement point; Fault point reflection wave: the traveling wave propagating to the fault point after the initial fault traveling wave is totally reflected at the measurement point, and then propagating to the measurement point after being reflected at the fault point; Opposite end bus reflection wave: the traveling wave propagating to the measurement point after the initial fault traveling wave is totally reflected at the opposite end measurement point; Pole mode transformation: a decoupling method in a metal return bipolar DC system, which is derived from the transformation condition of matrix diagonalization and used to eliminate the pole coupling problem; Wavelet transformation: a new transformation analysis method, which inherits and develops the localization idea of short-time Fourier transformation, and overcomes the shortcomings that the window size does not change with frequency, and can provide a "time-frequency" window changing with frequency, and is an ideal tool for time-frequency analysis and processing of signals.

[0013] In the prior art, the principle of single-ended traveling wave distance measurement method is to identify the time when the initial fault traveling wave reaches the measuring point and the time when the reflected wave from the fault point to the measuring point, and the time difference and wave velocity are used for distance measurement. The principle of double-ended traveling wave distance measurement method is to identify the time when the initial fault traveling wave reaches the two measuring points, and the time difference and wave velocity are used for distance measurement. The principle of single-ended traveling wave distance measurement method is simple and does not require communication, but it is difficult to identify the reflected wave from the fault point because the initial fault traveling wave will be reflected at each discontinuous point on the line after reaching the measuring point, and the reflected wave from the fault point is mixed with the reflected wave, which is not easy to identify. The double-ended traveling wave distance measurement method only uses the initial fault traveling wave and does not have other interference, but since the time when the wave head reaches is recorded, strict communication synchronization of the two measuring points is required. The common point of the two methods is that the wave velocity is used to calculate the fault distance, and the wave velocity is regarded as a known constant in the current application, but in fact the wave velocity is closely related to the line environment, line material and line geometric size, and it is difficult to preset and set to an accurate value, resulting in low fault distance measurement accuracy.

[0014] To at least solve the above problems, please refer to Figure 1 The embodiment of the present application provides a fault distance measurement method of a DC transmission line, comprising the steps of: determining whether the DC transmission line triggers fault distance measurement, if yes, obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time of the two measuring points of the DC transmission line; calculating the time difference of the initial fault traveling wave and the fault point reflected wave arrival time of the two measuring points according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time; calculating the distance between the two measuring points and the fault point based on the time difference of the two measuring points.

[0015] From the above description, the beneficial effects of the present application are that when the DC transmission line triggers fault distance measurement, the initial fault traveling wave arrival time and the fault point reflected wave arrival time of the two measuring points of the DC transmission line are obtained, the time difference of the initial fault traveling wave and the fault point reflected wave arrival time of the two measuring points is calculated according to the initial fault traveling wave arrival time and the fault point reflected wave arrival time, and the distance between the two measuring points and the fault point is calculated based on the time difference of the two measuring points. The distance calculation between the two measuring points and the fault point is the time difference of each measuring point, which does not require strict clock synchronization of the two measuring points, and does not need to rely on wave velocity during calculation, thereby effectively improving the fault distance measurement accuracy of the DC transmission line.

[0016] Further, before obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time of the two measuring points of the DC transmission line, the method further comprises: Obtain the positive and negative voltages at both ends of the DC transmission line within a preset time window before and after fault location is triggered; The positive and negative voltages are subjected to pole mode transformation and wavelet transform to obtain the modulus maxima waveforms at the two measurement points.

[0017] As described above, before obtaining the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave, the positive and negative voltages of the two measuring points within a preset time window before and after the fault location of the DC transmission line are subjected to pole mode transformation and wavelet transformation to obtain the modulus maxima waveforms of the two measuring points. Subsequently, the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave can be obtained simply and efficiently using the modulus maxima waveforms.

[0018] Furthermore, obtaining the arrival time of the fault point reflected wave at both ends of the DC transmission line includes: Determine whether the polarity of the second wavefront in the modulus maxima waveform at both measurement points is negative. If not, take the time corresponding to the second wavefront with positive polarity as the arrival time of the reflected wave from the fault point. If yes, determine whether there is a first wavefront with a sudden increase in amplitude after the amplitude of the wavefront decreases in the modulus maxima waveform. If not, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point. If yes, determine whether the polarity of the first wavefront with a sudden increase in amplitude is positive. If positive, take the time corresponding to the first wavefront with a sudden increase in amplitude and positive polarity as the arrival time of the reflected wave from the fault point. If not positive, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point.

[0019] As described above, considering the special characteristics of DC engineering structures, the smoothing reactors installed at both ends of DC transmission lines can totally reflect traveling waves. The arrival time of the reflected wave at the fault point is taken as the time when the second wavefront with positive polarity in the modulus maximum waveform arrives. If the polarity of the second wavefront is negative, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront decreases and then suddenly increases with positive polarity. If no such wavefront exists, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront with the largest positive polarity arrives. By comparing the trend of modulus maximum change and wavefront polarity, the arrival time of the reflected wave at the fault point can be accurately determined, which is beneficial for achieving accurate distance measurement.

[0020] Furthermore, obtaining the arrival time of the initial fault traveling wave at the two measuring points at both ends of the DC transmission line includes: The time corresponding to the first wavefront in the modulus maxima waveform at both measurement points is taken as the arrival time of the initial fault traveling wave.

[0021] As described above, since the initial fault traveling wave is the first arriving traveling wave detected by the measurement point and there is no other interference, the time corresponding to the first wavefront in the modulus maximum waveform at both measurement points is directly taken as the arrival time of the initial fault traveling wave, thus quickly determining the arrival time of the initial fault traveling wave.

[0022] Furthermore, the distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points, specifically as follows: ; ; In the formula, Indicates measurement point M and the point of failure F distance, Indicates measurement point N and the point of failure F distance, L Indicates the total length of a DC transmission line. Indicates measurement point M The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point N The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point.

[0023] As described above, when calculating the distance between the two measurement points and the fault point, only the total line length and the time difference between the arrival of the initial fault traveling wave and the reflected wave at each measurement point are needed. There is no need to use the traveling wave velocity, which reduces time synchronization error and wave velocity error, thereby accurately locating the fault point, shortening the fault repair time, and reducing power outage losses.

[0024] Please refer to Figure 2 Another embodiment of the present invention provides a fault location system for a DC transmission line, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it performs the following steps: Determine whether the DC transmission line has triggered fault location; if so, obtain the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave at the two ends of the DC transmission line. Calculate the time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two measurement points based on the arrival times of the initial fault traveling wave and the arrival times of the fault point reflected wave. The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points.

[0025] Determine whether the DC transmission line has triggered fault location; if so, obtain the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave at the two ends of the DC transmission line. Calculate the time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two measurement points based on the arrival times of the initial fault traveling wave and the arrival times of the fault point reflected wave. The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points.

[0026] As can be seen from the above description, the beneficial effects of the present invention are as follows: when a DC transmission line triggers fault location, the arrival times of the initial fault traveling wave and the arrival times of the fault point reflected wave at the two ends of the DC transmission line are obtained. The time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two ends of the measurement point is calculated based on the arrival times of the initial fault traveling wave and the fault point reflected wave. The distance between the two ends of the measurement point and the fault point is calculated based on the time difference between the two ends of the measurement point. The time difference between the two ends of the measurement point and the fault point is used in the calculation of the distance between the two ends of the measurement point and the fault point. It does not require the two ends of the measurement point to ensure strict clock synchronization, and the calculation does not depend on the wave velocity, thereby effectively improving the fault location accuracy of DC transmission lines.

[0027] Furthermore, before obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time at the two end measurement points of the DC transmission line, the process further includes: Obtain the positive and negative voltages at both ends of the DC transmission line within a preset time window before and after fault location is triggered; The positive and negative voltages are subjected to pole mode transformation and wavelet transform to obtain the modulus maxima waveforms at the two measurement points.

[0028] As described above, before obtaining the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave, the positive and negative voltages of the two measuring points within a preset time window before and after the fault location of the DC transmission line are subjected to pole mode transformation and wavelet transformation to obtain the modulus maxima waveforms of the two measuring points. Subsequently, the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave can be obtained simply and efficiently using the modulus maxima waveforms.

[0029] Furthermore, obtaining the arrival time of the fault point reflected wave at both ends of the DC transmission line includes: Determine whether the polarity of the second wavefront in the modulus maxima waveform at both measurement points is negative. If not, take the time corresponding to the second wavefront with positive polarity as the arrival time of the reflected wave from the fault point. If yes, determine whether there is a first wavefront with a sudden increase in amplitude after the amplitude of the wavefront decreases in the modulus maxima waveform. If not, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point. If yes, determine whether the polarity of the first wavefront with a sudden increase in amplitude is positive. If positive, take the time corresponding to the first wavefront with a sudden increase in amplitude and positive polarity as the arrival time of the reflected wave from the fault point. If not positive, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point.

[0030] As described above, considering the special characteristics of DC engineering structures, the smoothing reactors installed at both ends of DC transmission lines can totally reflect traveling waves. The arrival time of the reflected wave at the fault point is taken as the time when the second wavefront with positive polarity in the modulus maximum waveform arrives. If the polarity of the second wavefront is negative, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront decreases and then suddenly increases with positive polarity. If no such wavefront exists, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront with the largest positive polarity arrives. By comparing the trend of modulus maximum change and wavefront polarity, the arrival time of the reflected wave at the fault point can be accurately determined, which is beneficial for achieving accurate distance measurement.

[0031] Furthermore, obtaining the arrival time of the initial fault traveling wave at the two measuring points at both ends of the DC transmission line includes: The time corresponding to the first wavefront in the modulus maxima waveform at both measurement points is taken as the arrival time of the initial fault traveling wave.

[0032] As described above, since the initial fault traveling wave is the first arriving traveling wave detected by the measurement point and there is no other interference, the time corresponding to the first wavefront in the modulus maximum waveform at both measurement points is directly taken as the arrival time of the initial fault traveling wave, thus quickly determining the arrival time of the initial fault traveling wave.

[0033] Furthermore, the distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points, specifically as follows: ; ; In the formula, Indicates measurement point M and the point of failure F distance, Indicates measurement point N and the point of failure F distance,L Indicates the total length of a DC transmission line. Indicates measurement point M The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point N The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point.

[0034] As described above, when calculating the distance between the two measurement points and the fault point, only the total line length and the time difference between the arrival of the initial fault traveling wave and the reflected wave at each measurement point are needed. There is no need to use the traveling wave velocity, which reduces time synchronization error and wave velocity error, thereby accurately locating the fault point, shortening the fault repair time, and reducing power outage losses.

[0035] The fault location method and system for DC transmission lines described above are applicable to fault location scenarios for all flexible DC transmission lines, including cables and overhead lines. The specific implementation methods are described below: Please refer to Figure 1 One embodiment of the present invention is as follows: A fault location method for DC transmission lines includes the following steps: S1. Determine whether fault location has been triggered on the DC transmission line. If so, obtain the initial arrival time of the traveling wave and the arrival time of the reflected wave at both ends of the DC transmission line. Figure 5 As shown.

[0036] Smoothing reactors are installed at both ends of the DC transmission line.

[0037] In one optional implementation, determining whether a DC transmission line has triggered fault location includes: Determine the voltage of a DC transmission line U Is it lower than the preset value? U set If yes, then fault ranging is triggered; otherwise, fault ranging is not triggered.

[0038] In one alternative implementation, such as Figure 5 As shown, before obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time at the two end measurement points of the DC transmission line, the following steps are also included: Obtain the positive and negative voltages at both ends of the DC transmission line within a preset time window before and after fault location is triggered; The positive and negative voltages are subjected to pole mode transformation and wavelet transform to obtain the modulus maxima waveforms at the two measurement points.

[0039] In addition to polar mode transform and wavelet transform, one alternative implementation for determining the arrival time of a traveling wave is to use the time corresponding to the point where the absolute value of the slope of the entire traveling wave is the maximum as the arrival time of the traveling wave.

[0040] In one alternative implementation, such as Figure 5 As shown, obtaining the arrival time of the initial fault traveling wave at the two measuring points at both ends of the DC transmission line includes: The time corresponding to the first wavefront in the modulus maxima waveform at both measurement points is taken as the arrival time of the initial fault traveling wave.

[0041] Since the initial fault traveling wave is the first arriving traveling wave detected at the measurement point and there are no other interferences, it is relatively easy to obtain the arrival time of the initial fault traveling wave, which is also the basis for the traditional two-end traveling wave ranging method.

[0042] When the initial fault traveling wave reaches the measurement point, because the measurement point is connected to the line side of the smoothing reactor, the traveling wave will undergo total reflection at the smoothing reactor and will not penetrate into other lines. This means that after the initial fault traveling wave is identified, only the reflected wave from the fault point and the reflected wave from the smoothing reactor on the opposite side exist.

[0043] like Figure 3 The diagram illustrates a DC transmission line topology, showing the positive and negative outlets on the DC side of the converter ( Figure 3 (middle elliptical frame) and smoothing reactor ( Figure 3 (The Chinese frame) is connected, with a total length of L Measurement points are set at both ends of the line. M and N The measurement point is located on the line side of the smoothing reactor, and the fault point is... F Measurement points M and the point of failure F The distance is Measurement points N and the point of failure F The distance is .

[0044] when F After a fault occurs, the traveling wave propagates as follows: Figure 3 As shown, due to the blocking effect of the smoothing reactor, the traveling wave propagates to... M Point and N At this point, total internal reflection will occur. Additionally, at the fault point... F At that point, due to the disruption of the line's continuity, the traveling wave will undergo refraction and reflection.

[0045] Initial fault traveling wave arrival M The time of the point is The initial fault traveling wave arrived. N The time of the point is Initial fault traveling wave arrives N Total internal reflection occurs after the point, and then the light propagates to... M A traveling wave at a point is called N The reflected wave from the point busbar; since the reflected wave from the opposite busbar will continue to exist, this specifically refers to the first arriving wave. N A wave that is reflected at a point. N Point bus reflected wave arrives M The time of the point is Similarly, M Point bus reflected wave arrives N The time of the point is Initial fault traveling wave arrives M Total internal reflection occurs after the point, towards F Point propagation, and in F After reflection at a point, it propagates to... M The traveling wave at a point is called the fault point reflected wave. Since the fault point reflected wave will continue to exist, it specifically refers to the first wave formed by the fault point reflected wave. M Point propagation to F Point, and in F The wave reflected from the fault point reaches the fault point. M The time of the point is Similarly, the reflected wave from the fault point arrives N The time of the point is .

[0046] After a certain time, at the measurement point M place, and The arrival of the traveling wave will be measured at specific times. Due to the existence of the smoothing reactor boundary, there are no reflected waves from other lines. The subsequent traveling waves recorded at the measurement point will definitely be the reflected wave from the opposite bus and the reflected wave from the fault point. For the acquisition of the fault point reflected wave, there is interference from the reflected wave from the opposite bus; therefore, it is necessary to distinguish between the two, i.e., to correctly differentiate them. and Correctly distinguish and . Measured points M For example: A short circuit occurs at the fault point. Let the short-circuit resistance be... The line impedance is When a traveling wave propagates to the fault point, according to Peterson's law, if... Figure 4 As shown, the faulty branch and the transmission line are considered to be connected in parallel. When the incident wave The refracted wave continues to propagate along the line when it reaches the fault point. Specifically: ; Reflected wave Specifically: ; because The reflection coefficient is <0, and the absolute value of the reflection coefficient is <1. Therefore, we know... and The polarity is opposite, and the amplitude of the traveling wave decreases after reflection at the fault point. Because smoothing reactors are installed at both ends of the line, the incident traveling wave undergoes total reflection at the end of the line, without changing the polarity of the incident wave. This means that whenever a traveling wave propagates to the fault point, the polarity of the reflected wave is opposite to that of the incident wave.

[0047] Propagation path of the reflected wave from the opposite bus: the fault point propagates to... N Point, at N The point undergoes total internal reflection, propagates to the fault point, and is refracted at the fault point to reach... M point.

[0048] The propagation path of the reflected wave from the fault point: the wave propagates from the fault point to... M Point, at M Total internal reflection occurs at the point, propagating to the fault point, and then reflected back to the point where the virus reaches its destination. M point.

[0049] The comparison shows that the reflected wave from the opposite bus has one less fault-point reflection than the reflected wave from the fault point. Therefore, the polarity of the reflected wave from the opposite bus is the same as that of the initial fault traveling wave, while the polarity of the reflected wave from the fault point is opposite to that of the initial fault traveling wave. The initial fault traveling wave has a negative polarity. If a second traveling wave with a positive polarity is detected, then that traveling wave is the fault-point reflected wave, and the time corresponding to that point is... If the second traveling wave has a negative polarity, it indicates that the reflected wave from the opposite bus arrived first. Subsequent traveling waves with positive polarity are not necessarily fault-point reflected waves; they could be the initial fault traveling wave reaching the opposite bus, reflecting once at the fault point, and then reaching the local measurement point. Here, the reflected wave whose first reflection occurs at the opposite bus and propagates to the local measurement point (regardless of how many reflections occur afterward) is called the opposite bus reflected wave. Because the reflection of traveling waves causes energy attenuation, the amplitude of the same series of opposite bus reflected waves decreases over time. Similarly, the reflected wave that first propagates to the local measurement point, then to the fault point, reflects at the fault point, and continues propagating back to the local point (regardless of how many reflections occur afterward) is called the fault-point reflected wave. The amplitude of the same series of fault-point reflected waves also decreases over time. When a series of opposite bus reflected waves propagate to the measurement point sequentially, a series of fault-point reflected waves will also arrive at different times.

[0050] Therefore, for the measurement point, the absolute value of the modulus maxima of the detected wavefront exhibits a local decreasing trend. If, within a preset time window, the absolute value of the modulus maxima first decreases and then increases, the wavefront corresponding to the point where the increase first occurs, if its polarity is positive, is the reflected wavefront from the fault point. The corresponding time is... When a fault occurs at the midpoint of the line, the reflected wave from the opposite bus and the reflected wave from the fault point arrive simultaneously. However, the reflected wave from the opposite bus is refracted at the fault point, resulting in a reduced amplitude and a longer propagation path. The polarity of the resulting traveling wave is determined by the reflected wave from the fault point.

[0051] In summary, by comparing the changing trend of the modulus maxima and the polarity of the wavefront, the arrival time of the reflected wave at the fault point can be accurately determined. and The details are as follows: In one alternative implementation, such as Figure 5 As shown, obtaining the arrival time of the fault point reflected wave at both ends of the DC transmission line includes: Determine whether the polarity of the second wavefront in the modulus maxima waveform at both measurement points is negative. If not, take the time corresponding to the second wavefront with positive polarity as the arrival time of the reflected wave from the fault point. If yes, determine whether there is a first wavefront with a sudden increase in amplitude after the amplitude of the wavefront decreases in the modulus maxima waveform. If not, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point. If yes, determine whether the polarity of the first wavefront with a sudden increase in amplitude is positive. If positive, take the time corresponding to the first wavefront with a sudden increase in amplitude and positive polarity as the arrival time of the reflected wave from the fault point. If not positive, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point.

[0052] S2. Calculate the time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two measurement points based on the arrival times of the initial fault traveling wave and the fault point reflected wave. Figure 5 As shown, specifically: ; ; In the formula, Indicates measurement point M The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point N The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point M The arrival time of the reflected wave at the fault point Indicates measurement point MThe arrival time of the initial fault traveling wave, Indicates measurement point N The arrival time of the reflected wave at the fault point Indicates measurement point N The arrival time of the initial fault traveling wave.

[0053] Assuming the traveling wave velocity is The following relationship exists: ; ; And because ; so: ; Therefore, by using the information from the two measurement points, the wave velocity can be eliminated, resulting in the following distance measurement formula: S3. Calculate the distance between the two measuring points and the fault point based on the time difference between the two measuring points, such as... Figure 5 As shown, specifically: ; ; In the formula, Indicates measurement point M and the point of failure F distance, Indicates measurement point N and the point of failure F distance, L This indicates the total length of a DC transmission line.

[0054] The above-described method of the present invention will be described in detail using simulation methods: First, a DC transmission line model was established in PSCAD (electromagnetic transient simulation software) based on the cable parameters. The line is 15km long, and measurement points M (starting point) and N (ending point) were set at both ends of the line to measure the voltage at the positive and negative poles, respectively. A positive ground fault was assumed to occur on the line in 0.01s, and the fault transition resistance was set to 0.01... 1 5 10 20 The distance from the fault to the beginning of the fault was randomly set to 0.35 km, 2.4 km, 6 km, 8.31 km, 9.25 km, 13.7 km, and 14.6 km.

[0055] Secondly, considering the line length of 15km, in order to ensure that the reflected wave from the fault point can be recorded, the time window length is set. : ; Cable wave velocity in this model Generally between 1.8 and 1.9 (10 8 Approximately (m / s), take 1.8. Therefore, Capture 250 seconds before ranging starts And 250 after startup The data.

[0056] Next, the simulation was set up so that the positive ground fault occurred 2.4 km away from the measurement point M, with a transition resistance of 20 Ω. The positive and negative voltages at both measurement points are transformed by polarity conversion to obtain the line-mode voltage waveforms on the M and N sides of the measurement points, as shown below. Figure 6 As shown.

[0057] Perform wavelet transform on the line-mode voltage to obtain its modulus maxima. Record the amplitude, polarity, and corresponding time of each extreme point of the modulus maxima to obtain the modulus maxima waveforms on the M and N sides of the measurement point, such as... Figure 7 and Figure 8 As shown.

[0058] Record the time corresponding to the first wavefront in the modulus maxima waveform at measurement point M. This time is the arrival time of the initial fault traveling wave at measurement point M. Similarly, the arrival time of the initial fault traveling wave at measurement point N can be obtained. ,like Figure 9 and Figure 10 As shown.

[0059] like Figure 9 and Figure 10 As shown, determine the polarity of the second wavefront in the modulus maxima waveform at the measurement point. If it is positive, the time corresponding to this wavefront is the arrival time of the reflected wave from the fault point. If it is negative, find the wavefront where the absolute value first decreases and then increases among all wavefronts. If the polarity of the wavefront corresponding to the first point of increase is positive, this wavefront corresponds to the reflected wave from the fault point. If its polarity is negative, the wavefront with the largest amplitude among the positive polarity wavefronts is taken as the reflected wave from the fault point. This is how the arrival times of the reflected waves from the fault points at both measurement points are obtained. and .

[0060] Calculate according to the formula and : ; ; The cable wave velocity is set to 1.8 × 10⁻⁶. 8 The accuracy of the traditional two-end traveling wave ranging method and the method of the present invention is compared in Table 1.

[0061] Table 1. Accuracy Comparison between Traditional Two-End Traveling Wave Ranging Method and the Method of this Invention

[0062] In Table 1, the calculated distance v is obtained using the traditional two-end traveling wave ranging method, the calculated distance plus is obtained using the method of this invention, the error v is the error between the calculated distance v and the actual distance, and the error plus is the error between the calculated distance plus and the actual distance. It can be seen that, compared with the traditional two-end traveling wave ranging method, the method of this invention does not require strict time synchronization between the two measuring points and does not rely on wave velocity to calculate the fault distance, thus having higher ranging accuracy.

[0063] In summary, the fault location method for DC transmission lines described above, when fault location is triggered on the DC transmission line, acquires the arrival times of the initial fault traveling wave and the arrival times of the reflected wave at both ends of the DC transmission line. Based on these arrival times, the time difference between the initial fault traveling wave and the reflected wave at both ends of the measurement line is calculated. The distance between the two ends of the measurement line and the fault point is then calculated based on this time difference. Since the distance calculation between the two ends of the measurement line and the fault point uses the time difference between the individual measurement points, strict clock synchronization at both ends is not required, and the calculation does not rely on wave velocity. This effectively improves the fault location accuracy of DC transmission lines. The accuracy of distance measurement is improved. Furthermore, considering the special characteristics of DC engineering structures, the smoothing reactors installed at both ends of DC transmission lines are used to fully reflect traveling waves. The arrival time of the reflected wave at the fault point is taken as the time when the second wavefront with positive polarity in the modulus maximum waveform arrives. If the polarity of the second wavefront is negative, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront decreases and then suddenly increases with positive polarity. If no such wavefront exists, the arrival time of the reflected wave at the fault point is taken as the time when the amplitude of the wavefront with the largest positive polarity arrives. By comparing the trend of modulus maximum change and wavefront polarity, the arrival time of the reflected wave at the fault point can be accurately determined, which is beneficial for achieving accurate distance measurement.

[0064] According to another aspect of the invention, Figure 2 This is a schematic diagram illustrating a fault location system for a DC transmission line according to an embodiment of the present invention. The system includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the various steps of the fault location method for DC transmission lines as described above.

[0065] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A fault location method for DC transmission lines, characterized in that, Including the following steps: Determine whether the DC transmission line has triggered fault location; if so, obtain the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave at the two ends of the DC transmission line. Calculate the time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two measurement points based on the arrival times of the initial fault traveling wave and the arrival times of the fault point reflected wave. The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points.

2. The fault location method for DC transmission lines according to claim 1, characterized in that, Before obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time at the two ends of the DC transmission line, the method further includes: Obtain the positive and negative voltages at both ends of the DC transmission line within a preset time window before and after fault location is triggered; The positive and negative voltages are subjected to pole mode transformation and wavelet transform to obtain the modulus maxima waveforms at the two measurement points.

3. The fault location method for DC transmission lines according to claim 2, characterized in that, Obtaining the arrival time of the fault point reflected wave at both ends of the DC transmission line includes: Determine whether the polarity of the second wavefront in the modulus maxima waveform at both measurement points is negative. If not, take the time corresponding to the second wavefront with positive polarity as the arrival time of the reflected wave from the fault point. If yes, determine whether there is a first wavefront with a sudden increase in amplitude after the amplitude of the wavefront decreases in the modulus maxima waveform. If not, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point. If yes, determine whether the polarity of the first wavefront with a sudden increase in amplitude is positive. If positive, take the time corresponding to the first wavefront with a sudden increase in amplitude and positive polarity as the arrival time of the reflected wave from the fault point. If not positive, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point.

4. The fault location method for a DC transmission line according to claim 2, characterized in that, Obtaining the arrival time of the initial fault traveling wave at the two measuring points at both ends of the DC transmission line includes: The time corresponding to the first wavefront in the modulus maxima waveform at both measurement points is taken as the arrival time of the initial fault traveling wave.

5. The fault location method for a DC transmission line according to claim 1, characterized in that, The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points, specifically as follows: ； ； In the formula, Indicates measurement point M and the point of failure F distance, Indicates measurement point N and the point of failure F distance, L Indicates the total length of a DC transmission line. Indicates measurement point M The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point N The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point.

6. A fault location system for a DC transmission line, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it performs the following steps: Determine whether the DC transmission line has triggered fault location; if so, obtain the arrival time of the initial fault traveling wave and the arrival time of the fault point reflected wave at the two ends of the DC transmission line. Calculate the time difference between the arrival times of the initial fault traveling wave and the fault point reflected wave at the two measurement points based on the arrival times of the initial fault traveling wave and the arrival times of the fault point reflected wave. The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points.

7. The fault location system for a DC transmission line according to claim 6, characterized in that, Before obtaining the initial fault traveling wave arrival time and the fault point reflected wave arrival time at the two ends of the DC transmission line, the method further includes: Obtain the positive and negative voltages at both ends of the DC transmission line within a preset time window before and after fault location is triggered; The positive and negative voltages are subjected to pole mode transformation and wavelet transform to obtain the modulus maxima waveforms at the two measurement points.

8. The fault location system for a DC transmission line according to claim 7, characterized in that, Obtaining the arrival time of the fault point reflected wave at both ends of the DC transmission line includes: Determine whether the polarity of the second wavefront in the modulus maxima waveform at both measurement points is negative. If not, take the time corresponding to the second wavefront with positive polarity as the arrival time of the reflected wave from the fault point. If yes, determine whether there is a first wavefront with a sudden increase in amplitude after the amplitude of the wavefront decreases in the modulus maxima waveform. If not, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point. If yes, determine whether the polarity of the first wavefront with a sudden increase in amplitude is positive. If positive, take the time corresponding to the first wavefront with a sudden increase in amplitude and positive polarity as the arrival time of the reflected wave from the fault point. If not positive, take the time corresponding to the wavefront with the largest amplitude and positive polarity in the modulus maxima waveform as the arrival time of the reflected wave from the fault point.

9. A fault location system for a DC transmission line according to claim 7, characterized in that, Obtaining the arrival time of the initial fault traveling wave at the two measuring points at both ends of the DC transmission line includes: The time corresponding to the first wavefront in the modulus maxima waveform at both measurement points is taken as the arrival time of the initial fault traveling wave.

10. A fault location system for a DC transmission line according to claim 6, characterized in that, The distance between the two measuring points and the fault point is calculated based on the time difference between the two measuring points, specifically as follows: ； ； In the formula, Indicates measurement point M and the point of failure F distance, Indicates measurement point N and the point of failure F distance, L Indicates the total length of a DC transmission line. Indicates measurement point M The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point. Indicates measurement point N The time difference between the arrival of the initial fault traveling wave and the reflected wave at the fault point.

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