CN115015687A - Four-end annular flexible direct-current power grid fault location method and system - Google Patents
Four-end annular flexible direct-current power grid fault location method and system Download PDFInfo
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Abstract
The invention relates to a four-end annular flexible direct-current power grid fault location method and system, and belongs to the technical field of relay protection of power systems. The invention adopts single-ended traveling waves to carry out fault location, changes the sudden change of the wave head of time-domain transient traveling waves into the sudden change distribution of traveling wave energy of a transmission path along the line, applies a Bergeron transmission equation to start from the initial end of the line, calculates voltage traveling waves and current traveling waves along the line, carries out directional traveling wave decomposition on the voltage traveling waves and the current traveling waves to obtain forward current traveling waves and reverse current traveling waves distributed along the line, constructs and extracts a forward traveling wave sudden change function and a reverse traveling wave sudden change function, integrates the product of the forward traveling wave sudden change function and the reverse traveling wave sudden change function in an observation time window to form a location function, and realizes fault location by combining the polarity of a sudden change point in the location function with the distance from the sudden change point to a measurement end. According to the invention, only single-ended fault voltage traveling wave data need to be acquired, so that the influence of asynchronous communication at two ends of a line on a ranging result is effectively avoided; the problems of wave head distortion and oscillation are not needed to be considered, and correct catastrophe points can be accurately distinguished.
Description
Technical Field
The invention relates to a four-end annular flexible direct-current power grid fault location method and system, and belongs to the technical field of relay protection of power systems.
Background
With the implementation of global energy internet strategy, the utilization rate of renewable energy sources such as wind power, photovoltaic and the like in the power generation field is gradually improved in China, a large number of new energy generating sets are connected to a grid, the construction of a direct current power grid is not made public, and meanwhile, the development of a flexible direct current power transmission technology is promoted. At present, a multi-terminal direct-current power grid system mainly has two connection modes of a series connection mode and a parallel connection mode. The voltages of all converter stations of the parallel direct current network system are the same, and power distribution can be realized by changing the current in the loop; and the current flowing through each converter station of the series direct current network system is the same, and the distribution of power is realized by changing the voltage of each converter station. Compared with a series system, a direct-current power grid adopting a parallel connection mode has a larger power regulation range, smaller line loss and more convenient system expansion, so that a parallel topology is mostly adopted in engineering application. The parallel topology can be divided into a tree connection mode and a ring connection mode according to different connection modes. For a four-end annular flexible direct-current power grid, the number of line branches is large, the span is far, the complexity of the terrain where an overhead line passes is large, manual line inspection is difficult after a fault occurs, and the line emergency repair work is affected. The rapid development of relay protection nowadays greatly shortens the time of trouble excision, and the trouble is all less to transmission line's destruction degree, hardly relies on artifical observation to find the fault point. Therefore, it is necessary to quickly and accurately locate the fault point, reduce the cost of manual line patrol, quickly recover power supply and improve the economic benefit of the power department.
For the fault location method, the traditional traveling wave method mainly calculates the fault distance according to the refraction and reflection time of the traveling wave between the bus and the fault point and the traveling wave speed, and the accuracy of location is ensured by accurately identifying the traveling wave head and calibrating the arrival time of the traveling wave. The natural frequency method utilizes the frequency characteristic presented by the refraction and reflection of the traveling wave between the line bus and the fault point to realize fault location, and when a far-end fault occurs, the traveling wave refraction and reflection period is short, and a location dead zone exists. The fault analysis method is to calculate the fault distance by utilizing the time domain voltage and the electrical quantity of the observation end, and if the calculation of the electrical quantity along the line is not accurate, higher distance measurement precision cannot be ensured.
Disclosure of Invention
The invention aims to solve the technical problem of providing a four-end annular flexible direct-current power grid fault location method and a system thereof, which convert sudden change of a time-domain transient traveling wave head when the wave impedance meets discontinuous points into traveling wave energy sudden change distribution of a transmission path along a line, and effectively solve the problem of large location error caused by inaccurate identification of the traveling wave head.
The technical scheme of the invention is as follows: a four-end annular flexible direct-current power grid fault location method adopts single-end traveling waves to perform fault location. The method is characterized in that the forward traveling wave and the directional traveling wave are superposed at a fault point, and the position of the mutation point is directly related to the fault position. The method comprises the steps of calculating voltage traveling waves and current traveling waves along the line by applying a Bergeron transmission equation from the initial end of the line, carrying out directional traveling wave decomposition on the voltage traveling waves and the current traveling waves to obtain forward current traveling waves and reverse current traveling waves distributed along the line, constructing and extracting forward traveling wave mutation and reverse traveling wave mutation, integrating the product of the forward traveling waves and the reverse traveling waves in an observation time window to form a ranging function, and realizing fault location by combining the polarity of a mutation point in the ranging function with the distance from the mutation point to a measuring end.
The method comprises the following specific steps:
step 1: collecting fault voltage traveling wave data of a fault line, obtaining current traveling waves after the voltage traveling waves pass through a traveling wave coupling box, and obtaining voltage signals through a current transformer.
Step 2: according to the obtained fault voltage traveling wave data, calculating the voltage traveling wave and the current traveling wave along the line by applying a Bergeron transmission equation from the initial end of the line, and the method specifically comprises the following steps:
step 2.1: due to mutual inductance and distributed capacitance, complex electromagnetic coupling phenomena exist between positive and negative electrode lines of a direct-current transmission line, the electromagnetic coupling phenomena are solved by applying Kernel's variation suitable for transient time domain analysis, a line mode component and a zero mode component are obtained after phase mode variation, and as the zero mode component is transmitted between a lead and the ground, loop parameters are greatly influenced by external factors such as grounding conditions, soil resistivity and the like, the characteristics of the line mode component are generally selected and extracted. And decoupling the fault positive and negative voltages acquired by the measuring end by using Kernel transformation to obtain the line mode traveling wave. The calculation formula is as follows:
in the formula of U M And U N Respectively represent positive and negative voltages, I M And I N Respectively representing the positive and negative electrode currents, U 1 And U 0 Respectively representing line mode voltage and zero mode voltage, I 1 And I 0 Line mode current and zero mode current, C is the Kerenbel phase mode change matrix.
Step2.2: the Bergeron transmission equation can play the role of a high-pass filter along the line, divides a section of uniform lossy transmission line into 2 sections of uniform lossless lines, and can accurately approximate the transmission line in actual engineering. And calculating voltage traveling waves and current traveling waves along the line from the starting end of the line by applying a Bergeron transmission equation according to the voltage and current data acquired by the measuring end. The calculation formula is as follows:
in the formula, Z c,s Is the line mode wave impedance, x is the distance from the point to the sending end, i M,s The current u measured by a high-speed acquisition device at a certain moment on the power transmission line M,s The voltage r measured by a high-speed acquisition device at a certain moment on the power transmission line s Line mode resistance per unit length, v s Is the linear mode wave velocity.
Step 3: combining wave impedance to carry out directional traveling wave decomposition on the voltage traveling wave and the current traveling wave along the line so as to obtain the forward current traveling wave i distributed along the line + x,s The direction from the measuring end to the other end of the line is specified to be positive, and a reverse current traveling wave i is obtained - x,s The direction from one end of the line to the measuring end is specified to be reverse:
in the formula i x,s For calculating the current travelling wave u along the line by applying Bergeron transmission equation x,s The method is applied to the voltage traveling wave along the line obtained by calculation of the Bergeron transmission equation.
Step 4: in order to highlight the variation of the signal and stabilize the effect of Gaussian noise. And differentiating the forward differential 5 th power of the current direction traveling wave series, and then performing integral operation to construct and extract forward current traveling wave mutation functions and reverse current traveling wave mutation functions along the line.
In order to ensure that the original polarity of the mutation point is not changed, odd power is selected, and influence of interference on the mutation point can be reduced to a greater extent by selecting 5 power:
wherein k represents the kth sample point, i + (k) And i - (k) Respectively representing the values of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, S + For sudden forward current wave change, S - The traveling wave is suddenly changed for reverse current.
Step 5: in order to improve the characterization and ranging effects based on the abrupt change energy distribution abrupt change points of the traveling waves along the line, ensure the completeness of the reflected fault position information and further reduce the influence of the interference abrupt change points. Multiplying forward current traveling wave mutation functions distributed along the line by reverse current traveling wave mutation functions respectively at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integration is performed in two successive time windows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of the upper half time window for travelling wave observation 1 ，t 2 The upper limit and the lower limit of the lower half-time window are observed by the traveling wave.
Step 6: in order to utilize redundant information of fault positions and improve the distance measurement reliability, a single-ended traveling wave distance measurement function based on the abrupt change along the traveling wave is constructed, one of the abrupt change points A (x) reflecting the fault positions and the abrupt change points B (x) reflecting the dual fault positions is used in each time window, the amplitude values of the interference abrupt change points are far smaller than the amplitude values of the abrupt change points A (x) and B (x) to remove the interference abrupt change points, and then the polarity of the correct abrupt change points is combined for further judgment, so that the fault distance measurement can be realized. The method comprises the following specific steps:
step6.1: and constructing a single-ended traveling wave ranging function based on abrupt change along the traveling wave. In the travelling wave observation time window t 0 ,t 1 ]Internally calculating the range function at [0, l/2]A distribution of mutations within a range that is integral to both points of mutation a (x) that reflect fault locations and points of mutation b (x) that reflect dual fault locations; at observation time window [ t ] 1 ,t 2 ]Internally calculating the distance measuring function at [ l/2, l]Distribution of mutations within a range that must be either one of a mutation point a (x) that reflects a fault location and a mutation point b (x) that reflects a dual fault location.
Step6.2: for traveling wave observation time window t 0 ,t 1 ]Internally calculating the range function at [0, l/2 ]]And after the distribution of the mutation points obtained in the range is removed, the polarity of the correct mutation points is judged.
If the polarity is positive, the mutation point is a mutation point A (x) reflecting the fault position, and the fault distance x f Line length x corresponding to the point m1 ；
If the polarity is not positive, the mutation point is a mutation point B (x) reflecting the dual fault position, and the fault distance x f The corresponding length x is subtracted from the total length l of the line m2 。
A four-terminal annular flexible direct current power grid fault location system, comprising:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in the high-speed data acquisition device at the M ends of the positive and negative circuits;
the numerical value calculation module is used for constructing and extracting the forward current traveling wave mutation function and the reverse current traveling wave mutation function along the line and solving the product of the forward current traveling wave mutation function and the reverse current traveling wave mutation function;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And respectively constructing an integral function in the time window, and performing fault distance measurement by using the catastrophe points of the integral function to obtain a fault distance measurement result at the outlet.
The electrical signal acquisition module comprises:
the data acquisition unit is used for acquiring analog signals output by the secondary side of the mutual inductor;
the analog-to-digital conversion unit is used for converting an input signal into a digital quantity from an analog quantity;
and the protection starting unit is used for comparing the digital signal with a preset protection starting threshold value, and reading the starting time and storing a related fault voltage value if the digital signal is greater than the preset starting threshold value.
The electrical signal acquisition module comprises:
the line-mode conversion unit is used for decoupling the positive and negative voltages of the fault line to obtain line-mode traveling waves;
the numerical calculation unit calculates voltage traveling waves and current traveling waves along the line by applying a Bergeron transmission equation from the initial end of the line, and carries out directional traveling wave decomposition to obtain forward current traveling waves and reverse current traveling waves distributed along the line; secondly, calculating the forward differential power of the current direction traveling wave series by 5, differentiating the forward differential power and then performing integral operation to obtain a forward current traveling wave mutation function and a reverse current traveling wave mutation function along the line; and finally, calculating the product of the two directional traveling wave mutation functions.
The fault location module includes:
an integral function constructing unit for respectively setting the product of the traveling wave sudden change functions in two directions at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integrating in two successive time windows to obtain an integral function;
a distance measuring unit for measuring an integral function at t 0 ,t 1 ]And [ t 1 ,t 2 ]The distance corresponding to each mutation point in the time window;
a polarity judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the polarity of the mutation point within the time window is positive.
The invention has the beneficial effects that:
1. the fault location method is used for fault location of the four-end annular flexible direct-current power grid, only a fault voltage signal of the M end of the line needs to be acquired, and the influence of asynchronous communication of the two ends of the line on a location result is effectively avoided;
2. the invention converts the time domain transient state traveling wave head mutation into traveling wave energy mutation distribution along the transmission path, does not need to identify the traveling wave head, does not need to consider the problems of wave head distortion and oscillation, and can accurately distinguish correct mutation points.
3. Through a large number of simulation analyses, the invention has extremely high transition resistance capability, can obtain accurate ranging result when high-resistance ground fault occurs at the far end of the line, and has no ranging dead zone.
4. Compared with other distance measurement methods, the method has the advantages that the influence of the line model precision on the distance measurement result is small, the cost of manual line patrol is effectively reduced due to the high distance measurement precision, and the economic benefit of the power department is improved.
Drawings
FIG. 1 is a simulation model topology of the present invention;
FIG. 2 is a system block diagram of embodiment 1 of the present invention;
FIG. 3 is a graph showing the results of the first half time window integration function in example 1 of the present invention;
FIG. 4 is a graph showing the integration function result of the second half time window in example 1 of the present invention;
FIG. 5 is a graph of the first half time window integration function results of example 2 of the present invention;
FIG. 6 is a graph of the integration function result of the second half time window in example 2 of the present invention.
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
Example 1: the four-terminal annular flexible direct-current power grid simulation model system is shown in figure 1, the total length of a line 1 is 210km, the total length of a line 2 is 50.9km, the total length of a line 3 is 215km, the total length of a line 4 is 190km, and the voltage level is +/-500 kV. The set fault occurs at 63km in the half-line length of the line 1, the fault type is set as the anode grounding permanent fault, the transition resistance is set as 0.01 omega, and the sampling rate is 1 MHz. The method comprises the following specific steps:
and collecting fault voltage traveling wave data of the fault line. And the voltage traveling wave passes through the traveling wave coupling box to obtain a current traveling wave, and then a voltage signal is obtained through the current transformer.
According to the obtained fault voltage traveling wave data, calculating the voltage traveling wave and the current traveling wave along the line by applying a Bergeron transmission equation from the initial end of the line, and the method specifically comprises the following steps:
due to mutual inductance and distributed capacitance, complex electromagnetic coupling phenomena exist between positive and negative electrode lines of a direct-current transmission line, the electromagnetic coupling phenomena are solved by applying Kernel's variation suitable for transient time domain analysis, a line mode component and a zero mode component are obtained after phase mode variation, and as the zero mode component is transmitted between a lead and the ground, loop parameters are greatly influenced by external factors such as grounding conditions, soil resistivity and the like, the characteristics of the line mode component are generally selected and extracted. And decoupling the fault positive and negative voltages acquired by the measuring end by using Kernel transformation to obtain the line mode traveling wave. The calculation formula is as follows:
in the formula of U M And U N Respectively represent positive and negative voltages, I M And I N Respectively representing the positive and negative electrode currents, U 1 And U 0 Respectively representing line mode voltage and zero mode voltage, I 1 And I 0 A line mode current and a zero mode current,and C is a Kelenebel phase mode change matrix.
The Bergeron transmission equation can play the role of a high-pass filter along the line, divides a section of uniform lossy transmission line into 2 sections of uniform lossless lines, and can accurately approximate the transmission line in the actual engineering. And calculating voltage traveling waves and current traveling waves along the line from the starting end of the line by applying a Bergeron transmission equation according to the voltage and current data acquired by the measuring end. The calculation formula is as follows:
in the formula, Z c,s Is the line mode wave impedance, x is the distance from the point to the sending end, i M,s The current u measured by a high-speed acquisition device at a certain moment on the power transmission line M,s The voltage r measured by a high-speed acquisition device at a certain moment on the power transmission line s Line mode resistance per unit length, v s Is the linear mode wave velocity.
Combining wave impedance to carry out directional traveling wave decomposition on the voltage traveling wave and the current traveling wave along the line so as to obtain the forward current traveling wave i distributed along the line + x,s The direction from the measuring end to the other end of the line is specified to be positive, and a reverse current traveling wave i is obtained - x,s The direction from one end of the line to the measuring end is specified to be reverse:
in the formula i x,s For calculating the current travelling wave u along the line by applying Bergeron transmission equation x,s For application of shellfishAnd calculating the voltage traveling wave along the line by using the Geilon transmission equation.
In order to highlight the variation of the signal and stabilize the effect of Gaussian noise. And differentiating the forward differential 5 th power of the current direction traveling wave series, and then performing integral operation to construct and extract forward current traveling wave mutation functions and reverse current traveling wave mutation functions along the line.
In order to ensure that the original polarity of the mutation point is not changed, odd power is selected, and 5 power is selected to reduce the influence of the interference mutation point to a greater extent:
where k denotes the kth sample point, i + (k) And i - (k) Respectively representing the values of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, S + For sudden change of forward current traveling wave, S - The wave is suddenly changed for reverse current.
In order to improve the characterization and ranging effects based on the abrupt change energy distribution abrupt change points of the traveling waves along the line, ensure the completeness of the reflected fault position information and further reduce the influence of the interference abrupt change points. Multiplying forward current traveling wave mutation functions distributed along the line by reverse current traveling wave mutation functions respectively at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integration is performed in two successive time windows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of the upper half time window for travelling wave observation 1 ，t 2 The upper limit and the lower limit of the lower half-time window are observed by the traveling wave. In this example, [ t ] is taken 0 ,t 0 +l/(2v)]And [ t 0 +l/(2v)，t 0 +l/v]When two are in successionAnd a window.
In order to utilize redundant information of fault positions and improve the ranging reliability, a single-ended traveling wave ranging function based on abrupt change along the traveling wave is constructed. In the travelling wave observation time window t 0 ,t 0 +l/(2v)]Internally calculating the range function at [0, l/2]The distribution of mutations within the range is shown in FIG. 3, which reflects both the mutation points A (x) of the fault location and the mutation points B (x) of the dual fault location; at observation time window [ t ] 1 ,t 2 ]Internally calculating the distance function at t 0 +l/(2v)，t 0 +l/v]The distribution of mutations within the range is shown in fig. 4, which reflects both the mutation point a (x) of the fault location and the mutation point b (x) of the dual fault location. As can be seen from FIG. 3, after the interference mutation points are eliminated by using the amplitude values of the interference mutation points which are far smaller than the amplitude values of the mutation points A (x) and B (x), the distance from the position where the correct mutation point reacts to the M end is 63km, and the polarity of the mutation points is positive, so that the mutation points A (x) reflecting the fault positions are obtained, and therefore, the fault distance x is obtained f Was 63 km.
Fig. 2 is a functional block diagram of a four-terminal annular flexible direct-current power grid fault location system provided by the present invention, which specifically includes:
the electric signal acquisition module is mainly used for acquiring and storing fault voltage data, and is installed and operated in the high-speed data acquisition device at the M ends of the positive and negative circuits;
the numerical value calculation module is used for constructing and extracting the forward current traveling wave mutation function and the reverse current traveling wave mutation function along the line and solving the product of the forward current traveling wave mutation function and the reverse current traveling wave mutation function;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And respectively constructing an integral function in the time window, and performing fault distance measurement by using the catastrophe points of the integral function to obtain a fault distance measurement result at the outlet.
The electrical signal acquisition module specifically includes:
the data acquisition unit is used for acquiring analog signals output by the secondary side of the mutual inductor;
the analog-to-digital conversion unit is used for converting an input signal into a digital quantity from an analog quantity;
and the protection starting unit is used for comparing the digital signal with a preset protection starting threshold value, and reading the starting time and storing a related fault voltage value if the digital signal is greater than the preset starting threshold value.
The numerical calculation module specifically comprises:
the line-mode conversion unit is used for carrying out Kerenbel phase-mode conversion on the positive and negative voltages of the fault line to obtain a line-mode traveling wave;
the numerical calculation unit calculates voltage traveling waves and current traveling waves along the line by applying a Bergeron transmission equation from the initial end of the line, and carries out directional traveling wave decomposition to obtain forward current traveling waves and reverse current traveling waves distributed along the line; secondly, calculating the forward difference power of 5 of the current direction traveling wave series, differentiating the forward difference power firstly and then carrying out integral operation to obtain a forward current traveling wave mutation function and a reverse current traveling wave mutation function along the line; finally, the product of the two directional traveling wave mutation functions is calculated
The fault location module specifically comprises:
an integral function constructing unit for respectively setting the product of the traveling wave mutation functions in two directions at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integrating in two successive time windows to obtain an integral function;
a distance measuring unit for measuring an integral function at t 0 ,t 1 ]And [ t 1 ,t 2 ]The distance corresponding to each mutation point in the time window.
A polarity judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the polarity of the mutation point within the time window is positive.
Thus, the fault distance x is obtained f Was 63 km.
Example 2: the four-end annular flexible direct current power grid simulation model system is shown in figure 1, the total length of a line 1 is 210km, the total length of a line 2 is 50.9km, the total length of a line 3 is 215km, the total length of a line 4 is 190km, and the voltage level is +/-500 kV. The fault is set to be 198km out of the half line length of the line 1, the fault type is set to be a positive electrode grounding permanent fault, the transition resistance is set to be 200 omega, and the sampling rate is 1 MHz. The method comprises the following specific steps:
and collecting fault voltage traveling wave data of the fault line. And the voltage traveling wave passes through the traveling wave coupling box to obtain a current traveling wave, and then a voltage signal is obtained through the current transformer.
According to the obtained fault voltage traveling wave data, calculating the voltage traveling wave and the current traveling wave along the line by applying a Bergeron transmission equation from the initial end of the line, and the method specifically comprises the following steps:
due to mutual inductance and distributed capacitance, complex electromagnetic coupling phenomena exist between positive and negative electrode lines of a direct current transmission line, the electromagnetic coupling phenomena are solved by using Kelenebel change suitable for transient time domain analysis, a line mode component and a zero mode component are obtained after phase mode change, and the characteristics of the line mode component are usually selected to be extracted because the zero mode component is transmitted between a lead and the ground, loop parameters are greatly influenced by external factors such as grounding conditions, soil resistivity and the like. And decoupling the fault positive and negative voltages acquired by the measuring end by using Kernel transformation to obtain the line mode traveling wave. The calculation formula is as follows:
in the formula of U M And U N Respectively represent positive and negative voltages, I M And I N Respectively representing the positive and negative electrode currents, U 1 And U 0 Respectively representing line mode voltage and zero mode voltage, I 1 And I 0 Line mode current and zero mode current, C is the Kerenbel phase mode change matrix.
The Bergeron transmission equation can play the role of a high-pass filter along the line, divides a section of uniform lossy transmission line into 2 sections of uniform lossless lines, and can accurately approximate the transmission line in the actual engineering. And calculating voltage traveling waves and current traveling waves along the line from the starting end of the line by applying a Bergeron transmission equation according to the voltage and current data acquired by the measuring end. The calculation formula is as follows:
in the formula, Z c,s Is the line mode wave impedance, x is the distance from the point to the sending end, i M,s The current u measured by a high-speed acquisition device at a certain moment on the power transmission line M,s The voltage r measured by a high-speed acquisition device at a certain moment on the power transmission line s Line mode resistance per unit length, v s Is the linear mode wave velocity.
Combining wave impedance to carry out directional traveling wave decomposition on the voltage traveling wave and the current traveling wave along the line so as to obtain the forward current traveling wave i distributed along the line + x,s The direction from the measuring end to the other end of the line is specified to be positive, and a reverse current traveling wave i is obtained - x,s The direction from one end of the line to the measuring end is specified to be reverse:
in the formula i x,s For calculating the current travelling wave u along the line by applying Bergeron transmission equation x,s The method is applied to the voltage traveling wave along the line obtained by calculation of the Bergeron transmission equation.
In order to highlight the variation of the signal and stabilize the effect of Gaussian noise. And differentiating the forward differential 5 th power of the current direction traveling wave series, and then performing integral operation to construct and extract forward current traveling wave mutation functions and reverse current traveling wave mutation functions along the line.
In order to ensure that the original polarity of the mutation point is not changed, odd power is selected, and influence of interference on the mutation point can be reduced to a greater extent by selecting 5 power:
where k denotes the kth sample point, i - (k) And i - (k) Respectively representing the values of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, S + For sudden change of forward current traveling wave, S - The traveling wave is suddenly changed for reverse current.
In order to improve the characterization and ranging effect based on the traveling wave sudden change energy distribution along the line, the completeness of the reflected fault position information is ensured, and the influence of interference on the sudden change points is further reduced. Multiplying forward current traveling wave mutation functions distributed along the line by reverse current traveling wave mutation functions respectively at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integration is performed in two successive time windows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of the upper half-time window for travelling wave observation 1 ，t 2 The upper limit and the lower limit of the lower half-time window are observed by the traveling wave. In this example, [ t ] is taken 0 ,t 0 +l/(2v)]And [ t 0 +l/(2v)，t 0 +l/v]Two successive time windows.
In order to utilize redundant information of fault positions and improve the ranging reliability, a single-ended traveling wave ranging function based on abrupt change along the traveling wave is constructed. In the travelling-wave observation window [ t ] 0 ,t 0 +l/(2v)]The intra-computation distance measurement function is calculated at 0,l/2]the distribution of mutations within the range is shown in FIG. 5, which reflects the mutation points A (x) of the fault positions and the mutation points B (x) of the dual fault positions, which are bound to each other, within the observation time window [ t [ ([ t ]) ] 1 ,t 2 ]Internally calculating the distance function at t 0 +l/(2v)，t 0 +l/v]The distribution of mutations within the range is shown in FIG. 6, which reflects both the mutation points A (x) at the fault sites and the mutation points B (x) at the dual fault sites. As can be seen from FIG. 5, after the interference mutation points are eliminated by using the amplitude values of the interference mutation points which are far smaller than the amplitude values of the mutation points A (x) and B (x), the distance from the position where the correct mutation point reacts to the M end is 12km, and the polarity of the mutation point is negative, so that the mutation point is the mutation point B (x) which reacts to the dual fault position, and therefore the fault distance x is obtained f The length corresponding to the point is subtracted from the total length l of the transmission line, namely 210-12 to 198km, and the fault distance is 198 km.
Fig. 2 is a functional block diagram of a four-terminal annular flexible direct-current power grid fault location system provided by the present invention, which specifically includes:
the electric signal acquisition module is mainly used for acquiring and storing fault voltage data, and is installed and operated in the high-speed data acquisition device at the M ends of the positive and negative circuits;
the numerical value calculation module is used for constructing and extracting the forward current traveling wave mutation function and the reverse current traveling wave mutation function along the line and solving the product of the forward current traveling wave mutation function and the reverse current traveling wave mutation function;
fault location module for locating at t 0 ,t 1 ]And [ t 1 ,t 2 ]And respectively constructing an integral function in the time window, and performing fault distance measurement by using the catastrophe points of the integral function to obtain a fault distance measurement result at the outlet.
The electrical signal acquisition module specifically includes:
the data acquisition unit is used for acquiring analog signals output by the secondary side of the mutual inductor;
the analog-to-digital conversion unit is used for converting an input signal into a digital quantity from an analog quantity;
and the protection starting unit is used for comparing the digital signal with a preset protection starting threshold value, and reading the starting time and storing a related fault electrical signal if the digital signal is greater than the preset starting threshold value.
The numerical calculation module specifically includes:
the line-mode conversion unit is used for carrying out Kerenbel phase-mode conversion on the positive and negative voltages of the fault line to obtain a line-mode traveling wave;
the numerical calculation unit calculates voltage traveling waves and current traveling waves along the line by applying a Bergeron transmission equation from the initial end of the line, and carries out directional traveling wave decomposition to obtain forward current traveling waves and reverse current traveling waves distributed along the line; secondly, calculating the forward difference power of 5 of the current direction traveling wave series, differentiating the forward difference power firstly and then carrying out integral operation to obtain a forward current traveling wave mutation function and a reverse current traveling wave mutation function along the line; finally, the product of the two directional traveling wave mutation functions is calculated
The fault location module specifically comprises:
an integral function constructing unit for respectively setting the product of the traveling wave mutation functions in two directions at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integrating in two successive time windows to obtain an integral function;
a distance measuring unit for measuring an integral function at t 0 ,t 1 ]And [ t 1 ,t 2 ]The distance corresponding to each mutation point in the time window.
A polarity judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the polarity of the mutation point within the time window is positive.
Thus, the fault distance x is obtained f And was 198 km.
Simulation verification of faults that the four-terminal annular flexible direct-current power grid line 1 has an internal half-line length fault and a fault that the half-line length is external and the transition resistance is 200 ohms shows that the four-terminal annular flexible direct-current power grid fault location method and the system are high in reliability, high in precision and extremely high in transition resistance.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit and scope of the present invention.
Claims (11)
1. A four-end annular flexible direct current power grid fault location method is characterized by comprising the following steps:
step 1: collecting fault voltage traveling wave data of a fault line;
step 2: according to the obtained fault voltage traveling wave data, acquiring a voltage traveling wave and a current traveling wave along the line from the initial end of the line by applying a Bergeron transmission equation;
step 3: combining wave impedance to carry out directional traveling wave decomposition on the voltage traveling wave and the current traveling wave along the line so as to obtain a forward current traveling wave and a reverse current traveling wave which are distributed along the line;
step 4: constructing and extracting forward current traveling wave mutation functions and reverse current traveling wave mutation functions along the line;
step 5: multiplying the forward current traveling wave mutation function distributed along the line by the reverse current traveling wave mutation function, and then integrating in an observation time window;
step 6: and (3) constructing a single-ended traveling wave ranging function based on the abrupt change along the traveling wave, and eliminating the interference abrupt change point by using one of the abrupt change point A (x) reflecting the fault position and the abrupt change point B (x) reflecting the dual fault position in each time window, and then further judging by combining the polarity of the correct abrupt change point, so that the fault ranging can be realized.
2. The four-terminal ring-shaped flexible direct-current power grid fault location method according to claim 1, characterized in that: in Step1, fault voltage signals are acquired and stored through a high-speed data acquisition device arranged at the end M of the positive and negative electrode lines.
3. The quadripole ring-shaped flexible direct current power grid fault location method according to claim 1, wherein Step2 is specifically:
step2.1: decoupling the fault positive and negative voltages obtained by the measuring end by using Kerenbel transformation to obtain a line mode traveling wave:
in the formula of U M And U N Respectively represent positive and negative voltages, I M And I N Respectively representing the positive and negative electrode currents, U 1 And U 0 Respectively representing line mode voltage and zero mode voltage, I 1 And I 0 Line mode current and zero mode current;
step2.2: according to the voltage and current data collected by the measuring end, calculating the voltage traveling wave and the current traveling wave along the line by applying a Bergeron transmission equation from the starting end of the line:
in the formula, Z c,s Is the line mode wave impedance, x is the distance from the point to the sending end, i M,s The current u measured by a high-speed acquisition device at a certain moment on the power transmission line M,s The voltage r measured by a high-speed acquisition device at a certain moment on the power transmission line s Line mode resistance per unit length, v s Is the linear mode wave velocity.
4. The four-terminal ring-shaped flexible direct current power grid fault location method according to claim 1, wherein Step3 is specifically:
combining wave impedance to carry out directional traveling wave decomposition on the voltage traveling wave and the current traveling wave along the line to obtain a forward current traveling wave i distributed along the line + x,s The direction of the measuring end is specified to be the forward direction from the other end of the measuring end to the circuit; obtaining reverse current traveling wave i - x,s The direction from one end of the line to the measuring end is specified to be reverse:
in the formula i x,s For calculating the current travelling wave u along the line by using Bergeron transmission equation x,s The method is applied to the voltage traveling wave along the line obtained by calculation of the Bergeron transmission equation.
5. The four-terminal ring-shaped flexible direct current power grid fault location method according to claim 1, wherein Step4 is specifically:
differentiating the forward differential 5 th power of the current direction traveling wave series, and then performing integral operation to construct and extract a forward current traveling wave mutation function and a reverse current traveling wave mutation function along the line;
where k denotes the kth sample point, i + (k) And i - (k) Respectively representing the values of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, S + As a function of sudden change in forward current traveling wave, S - Is a reverse current traveling wave abrupt function.
6. The four-terminal ring-shaped flexible direct current power grid fault location method according to claim 1, wherein Step5 is specifically:
multiplying forward current traveling wave mutation functions distributed along the line by reverse current traveling wave mutation functions, and respectively setting the functions at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integration is performed in two successive time windows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of the upper half-time window for travelling wave observation 1 ，t 2 The upper limit and the lower limit of the lower half-time window are observed by the traveling wave.
7. The quadripole ring-shaped flexible direct current power grid fault location method according to claim 1, wherein Step6 is specifically:
step6.1: constructing a single-ended traveling wave ranging function based on abrupt change along the traveling wave line, and observing a time window [ t ] in the traveling wave 0 ,t 1 ]Internally calculating the range function at [0, l/2 ]]A distribution of mutations within a range that is integral to both points of mutation a (x) that reflect fault locations and points of mutation b (x) that reflect dual fault locations;
at observation time window [ t ] 1 ,t 2 ]Internally calculating the distance measuring function at [ l/2, l]A distribution of mutations within a range that reflects either mutational points a (x) of fault locations and mutational points b (x) of dual fault locations;
step6.2: for traveling wave observation time window t 0 ,t 1 ]Internally calculating the range function at [0, l/2]Polarity judgment is carried out on the obtained mutation distribution in the range;
if the polarity is positive, the mutation point is a mutation point A (x) reflecting the fault position, and the fault distance x f Line length x corresponding to the point m1 ；
If the polarity is not positive, the mutation point is a mutation point B (x) reflecting the dual fault position, and the fault distance x f The corresponding length x is subtracted from the total length l of the line m2 。
8. The utility model provides a flexible direct current electric wire netting fault location system of four end ring-types which characterized in that includes:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in the high-speed data acquisition device at the M ends of the positive and negative circuits;
the numerical value calculation module is used for constructing and extracting the forward current traveling wave mutation function and the reverse current traveling wave mutation function along the line and solving the product of the forward current traveling wave mutation function and the reverse current traveling wave mutation function;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And respectively constructing an integral function in the time window, and performing fault distance measurement by using the catastrophe points of the integral function to obtain a fault distance measurement result at the outlet.
9. The four-terminal ring-shaped flexible direct current power grid fault ranging system of claim 8, wherein the electrical signal acquisition module comprises:
the data acquisition unit is used for acquiring analog signals output by the secondary side of the mutual inductor;
the analog-to-digital conversion unit is used for converting an input signal into a digital quantity from an analog quantity;
and the protection starting unit is used for comparing the digital signal with a preset protection starting threshold value, and reading the starting time and storing a related fault voltage value if the digital signal is greater than the preset starting threshold value.
10. The four-terminal ring-shaped flexible direct current power grid fault ranging system of claim 8, wherein the electrical signal acquisition module comprises:
the line-mode conversion unit is used for decoupling the positive and negative voltages of the fault line to obtain line-mode traveling waves;
and the numerical value calculation unit is used for calculating the product of the traveling wave mutation functions in the two directions.
11. The four-pole ring-like flexible direct current power grid fault ranging system of claim 8, wherein the fault ranging module comprises:
an integral function constructing unit for constructing twoThe products of the abrupt change functions of the directional traveling wave are respectively in [ t ] 0 ,t 1 ]And [ t 1 ,t 2 ]Integrating in two successive time windows to obtain an integral function;
a distance measuring unit for measuring an integral function at t 0 ,t 1 ]And [ t 1 ,t 2 ]The distance corresponding to each mutation point in the time window;
a polarity judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the polarity of the mutation point within the time window is positive.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115963358A (en) * | 2023-03-13 | 2023-04-14 | 昆明理工大学 | Fault location method and system for hybrid three-terminal flexible direct-current transmission line |
| CN117805555A (en) * | 2024-02-28 | 2024-04-02 | 昆明理工大学 | Two-way deduction four-terminal flexible direct current transmission line fault location method and system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115963358A (en) * | 2023-03-13 | 2023-04-14 | 昆明理工大学 | Fault location method and system for hybrid three-terminal flexible direct-current transmission line |
| CN115963358B (en) * | 2023-03-13 | 2023-08-04 | 昆明理工大学 | Mixed three-terminal flexible direct current transmission line fault location method and system |
| CN117805555A (en) * | 2024-02-28 | 2024-04-02 | 昆明理工大学 | Two-way deduction four-terminal flexible direct current transmission line fault location method and system |
| CN117805555B (en) * | 2024-02-28 | 2024-05-03 | 昆明理工大学 | Two-way deduction four-terminal flexible direct current transmission line fault location method and system |
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