CN115097253A - MMC-HVDC direct current transmission line fault distance measurement method and system - Google Patents
MMC-HVDC direct current transmission line fault distance measurement method and system Download PDFInfo
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Abstract
The invention relates to a fault location method and a fault location system for an MMC-HVDC direct current transmission line, and belongs to the technical field of relay protection of power systems. The invention utilizes single-end traveling waves to carry out fault location, decouples the obtained fault voltage traveling waves to obtain line mode traveling waves, calculates the voltage and the current at intervals of a certain distance step length to obtain the voltage and current distribution condition of each point of the whole line, and calculates the forward current traveling waves and the reverse current traveling waves combining the time dimension and the distance dimension, thereby constructing the current traveling wave mutation detection function analytical expression in the forward and reverse directions, and making the product for constructing the integral function, and carrying out fault location through the distance from the extreme point of the integral function to the measuring end. The method carries out fault location on the flexible direct current transmission line, adopts single-ended traveling waves to carry out fault location, only needs to collect single-ended fault traveling wave data, and does not need to consider the problem of weak synchronization of communication; the influence of the interference extreme point on the fault distance judgment can be effectively eliminated.
Description
Technical Field
The invention relates to a fault location method and a fault location system for an MMC-HVDC direct current transmission line, and belongs to the technical field of relay protection of power systems.
Background
At present, with the exhaustion of fossil energy and the increasing damage of hydroelectric power generation to water resources, renewable energy power generation is put into operation in western and northern areas of China in large quantity, and a large quantity of renewable energy power generation such as wind power and solar energy is connected into a power grid, so that the development of a direct current power transmission system is promoted. The problem of commutation failure easily appears in the direct current transmission technique based on traditional commutation transverter (LCC), nevertheless with the power electronics technology development mature day by day, adopts voltage source type transverter (VSC) to gain attention in the direct current power transmission and distribution field gradually as flexible (MMC-HVDC) direct current transmission of core component. Compared with the traditional alternating current transmission, the flexible direct current transmission has obvious advantages in new energy grid connection and island power supply, and has the advantages of large power supply capacity, low line loss, high electric energy quality and the like. Meanwhile, the flexible direct current transmission system has obvious defects, because the direct current transmission system is generally applied to long-distance transmission, the transmission line of the direct current transmission system is longer, and is influenced by environmental factors such as lightning stroke, branches and the like all the year round, so that faults are easy to occur, the damping of the direct current system is smaller than that of the alternating current system, so that the fault rate is increased, and the manual line patrol cost is higher when the faults occur due to the longer distance. Therefore, in order to ensure that the flexible direct current transmission system can operate stably, the fault can be rapidly identified and the fault position can be accurately positioned as much as possible when the transmission line breaks down, the distance of manual line patrol is shortened, time is won for subsequent line repair work, power supply can be recovered more quickly, and the economic benefit of an electric power department is improved.
In recent years, with the development of relay protection technology, the fault removing speed is faster and faster when a fault occurs, so that a relatively obvious damage trace cannot appear on the surface of a circuit, and a fault point is difficult to find by means of manual line patrol, so that a reliable fault distance measuring device is urgently needed to be researched. According to some distance measurement methods adopted at present, for a travelling wave method, the fault distance is obtained by utilizing the time difference of the arrival time of the initial fault travelling wave and combining with the long path of the line through calculation, the double-end travelling wave method has obvious advantages of distance measurement, high reliability and high measurement precision, and has no distance measurement dead zone, but the acquisition devices at two ends need to be in communication synchronization, so that reliable synchronous communication is provided for the double-end travelling wave method depending on a GPS device, and particularly in a long-distance power transmission line, a small time error can cause a large distance measurement error; for the single-ended traveling wave method, only one side of fault traveling wave data is relied on, the problem of communication synchronization does not need to be considered, the device is simple, but the problem of failure in distance measurement can occur when the far end of the power transmission line breaks down. In a word, the traditional traveling wave distance measurement is mostly based on traveling wave time domain characteristics and is used for observing, depicting, calibrating and discriminating traveling waves on a time axis so as to achieve the calculation of fault distance, and if the traveling wave head calibration is not accurate, the distance measurement error is extremely large, and the cost of manual line inspection is increased.
Disclosure of Invention
The invention aims to solve the technical problem of providing a fault location method and a fault location system for an MMC-HVDC direct-current transmission line, which can effectively solve the problem that the traditional traveling wave method or fault analysis method has the influence on the attenuation of fault information of a long-distance transmission line, so that the location fails and a location blind area occurs.
The technical scheme of the invention is as follows: a fault location method and a system for an MMC-HVDC direct current transmission line are based on a novel single-end method traveling wave location principle of traveling wave energy abrupt change along-line distribution characteristics. The traveling wave can be reflected and refracted when meeting the point of wave impedance discontinuity, the traveling wave is represented as the discontinuity point of voltage and current traveling wave energy distribution along the line, the discontinuity points can be regarded as the result of meeting and overlapping of forward current traveling wave and reverse current traveling wave, the positive polarity overlapping point with the maximum amplitude value corresponds to the distance from the hard fault point to the observation end, and the negative polarity point with the maximum amplitude value corresponds to the dual fault distance. In a flexible direct current transmission system, the voltage grade is high, the voltage and the current are generally calculated once at certain distance step length to describe the voltage and current distribution condition of each point of the whole line, forward current traveling waves and reverse current traveling waves combining time dimension and distance dimension are solved, further forward and reverse current traveling wave mutation detection function analytical expressions are constructed, the product of the two analytical expressions is used for constructing an integral function, and fault positioning is realized through the distance from an extreme point of the integral function to a measurement end.
The method comprises the following specific steps:
step 1: when the line is in fault, a fault electrical signal of the line is collected. In an MMC-HVDC direct-current transmission system, current traveling waves cannot be directly measured at a measuring end, high-frequency voltage traveling waves cannot be directly obtained through a voltage transformer, and generally, voltage traveling waves are obtained after passing through a traveling wave coupling box and then are indirectly measured through the current transformer to obtain voltage signals.
Step 2: according to the data collected by the measuring end, voltage and current are calculated once at intervals of a certain distance step length, so that the voltage and current distribution condition of each point of the whole line is obtained, and the method specifically comprises the following steps:
step 2.1: in an MMC-HVDC direct-current power transmission system of practical engineering, the power transmission distance is long, electromagnetic coupling action exists between positive and negative electrode circuits which are parallel to each other, so that phase-mode change is needed to eliminate the line coupling action between different conducting wires, and line-mode components and zero-mode components which are independent of each other are obtained after the phase-mode change. Because the propagation path of the zero-mode component is between a conducting wire and the ground, a large amount of attenuation of the zero-mode component can be caused by environmental factors, the wave velocity of the line-mode component is stable, and a large amount of attenuation can not occur, so that the characteristic of the line-mode component is selected and extracted. Decoupling the positive and negative voltages of the power transmission line by using Kerenbel transformation to obtain line mode traveling waves. 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, A is a Kerenbel phase mode change matrix.
Step2.2: as MMC-HVDC direct current transmission is long-distance transmission, distributed capacitance can generate larger influence on current distribution of a line, and a Bergeron transmission line equivalent model is adopted to carry out equivalence on the line. According to the voltage and current data collected by measuring end, calculating voltage and current every 1 km step length to obtain voltage and current distribution condition of every point of whole line, and its 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 a 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: according to the voltage and the current of each point of the transmission line, calculating a current direction traveling wave series combining a time dimension and a distance dimension, wherein i + x,s Is a forward current traveling wave and is defined as propagating from a sending end to a receiving end, i.e. from an M end to an N end, i - x,s For a reverse current traveling wave, defined as propagating from the receiving end to the sending end, i.e. from the N end to the M end, the calculation formula is as follows:
step 4: carrying out differential calculation on the current direction traveling wave series to obtain a current gradient distributed along the line, and calculating the power of 3 of the current gradient distributed along the line, wherein the specific steps are as follows:
step4.1: in order to increase the reliability of the distance measuring device, the sudden change of the traveling wave energy is amplified. Carrying out differential calculation on the current direction traveling wave series to obtain current gradient distributed along the line
And
the calculation formula is as follows:
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,
and
respectively representing the forward current gradient and the reverse current gradient along the line.
Step4.2: because of the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate the influence of the interference mutation point on fault positioning, further highlight the mutation point amplitude reflecting fault position information and ensure that the original polarity of the mutation point is not changed, and calculate the current gradient distributed along the line
And
to the power of 3.
Step 5: in order to suppress the effect of Gaussian noise, the forward current gradients are respectively distributed along the line
And reverse current gradient
Beginning with the kth sample value raised to the power of 3, a superposition value is obtained for each sample value raised to the power of 3 of 5 current gradients. The mutation detection function analytical expression of the forward traveling wave and the reverse traveling wave can be constructed, and the calculation formula is as follows:
in the equations (9) and (10), k is the kth sampling point, E + Analytical expression of function for forward current traveling wave mutation detection, E - And analyzing an expression for the reverse current traveling wave mutation detection function.
Step 6: in order to ensure the completeness of the information of reflecting the fault position and simultaneously reduce the influence of other interference catastrophe points to the maximum extent. The analytical expressions of the two sudden change detection functions of the directional traveling wave are multiplied, and the product is set at t 0 ,t 1 ]And [ t 1 ,t 2 ]The integration is performed in two successive time windows, and the calculation formula is as follows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of 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 7: because the discontinuity of current travelling wave energy distribution along the line can be regarded as meeting the stack by forward current travelling wave and reverse current travelling wave and cause, consequently regard as two range finding functions with the integral in two time windows, with two liang of extreme points in two range finding functions pairs, utilize the relation between the extreme point and combine the distance that the extreme point corresponds to and its amplitude can realize fault location, specifically do:
step7.1: taking the integral of two time windows as two distance measuring functions in the time window t 0 ,t 1 ]The distance from each extreme point of the integral function to the sending end is obtained through internal measurement and is used as a solution set g 1—i ＝[x 11 ,x 12 ,...,x 1n ]In the time window [ t ] 1 ,t 2 ]Obtaining integral function poles by internal measurementThe distance from the value point to the sending end is used as a solution set g 2—i ＝[x 21 ,x 22 ,...,x 2n ]And will collect solution g 1—i Each element in (1) is respectively used as a reference value and a solution set g 2—i The matched elements need to satisfy that one amplitude is larger than 0 and the other amplitude is smaller than 0, and a group of extreme points which are equal to or approximately equal to the total length of the line are added, namely an extreme point A (x) of a reaction fault position and an extreme point B (x) of a reaction dual fault position;
step7.2: judging the solution set g satisfying the condition 1—i Whether the amplitude of the extreme point in (1) is greater than 0;
if yes, the point is an extreme point A (x) reflecting the fault position, and the fault distance x f Line length x corresponding to the point m1 ；
If not, the point is an extreme 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 MMC-HVDC direct current transmission line fault distance measuring system mainly comprises:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in a high-speed data acquisition device at a transmission end or/and a receiving end of the power transmission line;
the numerical calculation module is used for carrying out differential calculation on the current direction traveling wave series, solving the high power of the current direction traveling wave series, and then respectively constructing mutation detection function analytical expressions of the forward traveling wave and the reverse traveling wave by utilizing the current direction traveling wave differential high power;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And (4) respectively constructing integral functions in the time windows, and performing fault distance measurement by using the maximum point of the integral functions 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 includes:
the line-mode conversion unit is used for decoupling the positive and negative voltages of the power transmission line to obtain line-mode traveling waves;
a numerical calculation unit for calculating the product of the traveling wave analytic expressions in two directions and setting the product at [ t ] 0 ,t 1 ]And [ t 1 ,t 2 ]Integration within a time window.
The fault location module specifically comprises:
an integral function construction unit for respectively setting the product of the traveling wave analytic expressions 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 ]And the distance corresponding to each maximum point in the time window.
And the most point matching unit is used for matching every two most points in the two time windows and screening out a pair of most points meeting the conditions.
A maximum judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the most significant value in the time window is greater than zero.
The invention has the beneficial effects that:
1. the method and the device aim at fault location of the MMC-HVDC direct-current transmission line, adopt single-ended traveling waves to carry out fault location, only need to collect single-ended fault traveling wave data, and do not need to consider the problem of weak synchronization of communication.
2. According to the method, the traveling wave is subjected to calculation such as difference, exponentiation and superposition, so that the amplitude of the interference extreme point is small and easy to remove, and the influence of the interference extreme point on fault distance judgment can be effectively eliminated.
3. Compared with the traditional single-ended traveling wave distance measurement method, the method has the advantages that the influence of the line length is small, and the high measurement precision can be still ensured when the far end of the long-distance transmission line fails.
4. The invention does not need to calibrate the wave head, avoids the influence of inaccurate wave head calibration on fault positioning, and has high reliability and high precision.
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 of integration function results for the second half time window of 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: example 1: the MMC-HVDC simulation model system is shown in figure 1, wherein the whole line length of the line is 400km, and the voltage level is +/-800 kV. The fault is set to occur at 145km of the line, the fault type is set to be a positive grounding permanent fault, the transition resistance is set to be 0.01 omega, and the sampling rate is 1 MHz. The method comprises the following specific steps:
in an MMC-HVDC direct-current transmission system, current traveling waves cannot be directly measured at a measuring end, high-frequency voltage traveling waves cannot be directly obtained through a voltage transformer, and generally, the voltage traveling waves are subjected to traveling wave coupling box to obtain the current traveling waves, and then are indirectly measured through the current transformer to obtain voltage signals. When the line is in fault, a high-speed acquisition device is used for acquiring fault voltage signals of the line.
In an MMC-HVDC direct-current power transmission system of practical engineering, the power transmission distance is long, electromagnetic coupling action exists between positive and negative electrode circuits which are parallel to each other, so that phase-mode change is needed to eliminate the line coupling action between different conducting wires, and line-mode components and zero-mode components which are independent of each other are obtained after the phase-mode change. Because the propagation path of the zero-mode component is between a conducting wire and the ground, a large amount of attenuation of the zero-mode component can be caused by environmental factors, the wave velocity of the line-mode component is stable, and a large amount of attenuation can not occur, so that the characteristic of the line-mode component is selected and extracted. Decoupling the positive and negative voltages of the power transmission line by using Kerenbel transformation to obtain line mode traveling waves. 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 represent 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, A is a Kerenbel phase mode change matrix.
As MMC-HVDC direct current transmission is long-distance transmission, distributed capacitance can generate larger influence on current distribution of a line, and a Bergeron transmission line equivalent model is adopted to carry out equivalence on the line.
The method comprises the following specific steps:
the voltage and the current are calculated every 1 kilometer step length to obtain the voltage and current distribution condition of each point of the whole line, and 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 For a high-speed collection system of a moment on power transmission lineMeasured current u 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.
According to the voltage and the current of each point of the transmission line, calculating a current direction traveling wave series combining a time dimension and a distance dimension, wherein i + x,s Is a forward current traveling wave and is defined as propagating from a sending end to a receiving end, i.e. from an M end to an N end - x,s For a reverse current traveling wave, defined as propagating from the receiving end to the sending end, i.e. from the N end to the M end, the calculation formula is as follows:
in order to increase the reliability of the distance measuring device, the sudden change of the traveling wave energy is amplified. Carrying out differential calculation on the current direction traveling wave series to obtain current gradient distributed along the line
And
the calculation formula is as follows:
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,
and
respectively representing the forward current gradient and the reverse current gradient along the line.
Because of the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate the influence of the interference mutation point on fault positioning, further highlight the mutation point amplitude reflecting fault position information and ensure that the original polarity of the mutation point is not changed, and calculate the current gradient distributed along the line
And
to the 3 rd power.
To suppress the effect of Gaussian noise, the forward current gradients are respectively distributed along the line
And reverse current gradient
Beginning with the kth sample value raised to the power of 3, a superposition value is obtained for each sample value raised to the power of 3 of 5 current gradients. The mutation detection function analytical expression of the forward traveling wave and the reverse traveling wave can be constructed, and the calculation formula is as follows:
where k is the kth sample point, E + Analytical expression for forward current traveling wave mutation detection function, E - Analytical expression for reverse current traveling wave mutation detection functionFormula (II) is shown.
In order to ensure the completeness of the information of reflecting the fault position and simultaneously reduce the influence of other interference catastrophe points to the maximum extent. The analytical expressions of the two sudden change detection functions of the directional traveling wave are multiplied, and the product is set at t 0 ,t 1 ]And [ t 1 ,t 2 ]The integration is performed in two successive time windows, and the calculation formula is as follows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of 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.
Because the discontinuous point of the energy distribution of the current traveling wave along the line can be regarded as the result of the meeting and superposition of the forward current traveling wave and the reverse current traveling wave, the integral in the two time windows is used as two ranging functions. FIG. 3 and FIG. 4 show that 0 ,t 0 +l/(2v)]The distribution result graph of the integral function in the time window can be known that the distance from each extreme point of the integral function to the sending end obtained by measurement forms a solution set g 1—i ＝[145,146]km; FIG. 4 is a graph showing that 0 +l/(2v)，t 0 +l/v]The distribution result graph of the integral function in the time window can be known that the distance from each extreme point of the integral function to the sending end obtained by measurement forms a solution set g 2—i ＝[255,256]And km. Will solve and collect g 1—i Taking each element in the solution as a reference value and a solution set g 2—i The maximum value point amplitude of the corresponding maximum value point at 145km is larger than zero, and the maximum value point amplitude of the corresponding maximum value point at 146+256 ≠ 400km, the maximum value point at 145km to the sending end is inverse to the maximum value point amplitude of the corresponding maximum value point at 145km, namely the sum equals to the total length of the line, and the maximum value point is matchedThe extreme point A (x) corresponding to the fault position and the extreme point with the distance of 255km to the sending end are the extreme points B (x) reflecting the dual fault position, so the fault distance x is obtained f Was 145 km.
Fig. 2 is a functional block diagram of a fault location system for an MMC-HVDC direct current transmission line provided in the present invention, which specifically includes:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in a high-speed data acquisition device at a transmission end or/and a receiving end of the power transmission line;
the numerical value calculation module is used for carrying out differential calculation on the current direction traveling wave series, solving the high power of the current direction traveling wave series, and then respectively constructing mutation detection function analytical expressions of the forward traveling wave and the reverse traveling wave by utilizing the current direction traveling wave differential high power;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And (4) respectively constructing integral functions in the time windows, and performing fault distance measurement by using the maximum point of the integral functions 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 decoupling the positive and negative voltages of the power transmission line to obtain line-mode traveling waves;
a numerical value calculation unit for calculating the product of the two directional traveling wave analytic expressions and setting the product at [ t ] 0 ,t 1 ]And [ t 1 ,t 2 ]Integration within a time window.
The fault location module specifically comprises:
an integral function construction unit for respectively setting the product of the analytic expressions of the traveling waves 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 ]And the distance corresponding to each maximum point in the time window.
And the maximum point matching unit is used for matching every two maximum points in the two time windows to screen out a pair of maximum points meeting the conditions.
A maximum judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the most significant value in the time window is greater than zero.
Thus, the fault distance x is obtained f Was 145 km.
Example 2: the MMC-HVDC simulation model system is shown in figure 1, wherein the whole line length of the line is 400km, and the voltage level is +/-800 kV. The fault is set to occur at 260km of the line, the fault type is set to be a positive grounding permanent fault, the transition resistance is set to be 0.01 omega, and the sampling rate is 1 MHz. The method comprises the following specific steps:
in an MMC-HVDC direct-current transmission system, current traveling waves cannot be directly measured at a measuring end, high-frequency voltage traveling waves cannot be directly obtained through a voltage transformer, and generally, voltage traveling waves are obtained after passing through a traveling wave coupling box and then are indirectly measured through the current transformer to obtain voltage signals. When the line is in fault, a high-speed acquisition device is used for acquiring fault voltage signals of the line.
In an MMC-HVDC direct-current power transmission system of practical engineering, the power transmission distance is long, electromagnetic coupling action exists between positive and negative electrode circuits which are parallel to each other, so that phase-mode change is needed to eliminate the line coupling action between different conducting wires, and line-mode components and zero-mode components which are independent of each other are obtained after the phase-mode change. Because the propagation path of the zero-mode component is between a conducting wire and the ground, a large amount of attenuation of the zero-mode component can be caused by environmental factors, the wave velocity of the line-mode component is stable, and a large amount of attenuation can not occur, so that the characteristic of the line-mode component is selected and extracted. And decoupling the positive and negative voltages of the power transmission line by using the Kerenbel 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, A is a Kerenbel phase mode change matrix.
As MMC-HVDC direct current transmission is long-distance transmission, distributed capacitance can generate larger influence on current distribution of a line, and a Bergeron transmission line equivalent model is adopted to carry out equivalence on the line.
The method comprises the following specific steps:
calculating the voltage and the current every 1 kilometer step length to obtain the voltage and current distribution condition of each point of the whole line, wherein 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 a transmission line M,s For high-speed mining at a certain moment on the transmission lineThe voltage, r, measured by the collecting means s Line mode resistance per unit length, v s Is the linear mode wave velocity.
According to the voltage and the current of each point of the transmission line, calculating a current direction traveling wave series combining a time dimension and a distance dimension, wherein i + x,s Is a forward current traveling wave and is defined as propagating from a sending end to a receiving end, i.e. from an M end to an N end - x,s For a reverse current traveling wave, defined as propagating from the receiving end to the sending end, i.e. from the N end to the M end, the calculation formula is as follows:
in order to increase the reliability of the distance measuring device, the sudden change of the traveling wave energy is amplified. Carrying out differential calculation on the current direction traveling wave series to obtain current gradient distributed along the line
And
the calculation formula is as follows:
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,
and
respectively representing the forward current gradient and the reverse current gradient along the line.
Because of the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate the influence of the interference mutation point on fault positioning, further highlight the mutation point amplitude reflecting fault position information and ensure that the original polarity of the mutation point is not changed, and calculate the current gradient distributed along the line
And
to the power of 3.
To suppress the effect of Gaussian noise, the forward current gradients are respectively distributed along the line
And reverse current gradient
Beginning with the kth sample value raised to the power of 3, a superposition value is obtained for each sample value raised to the power of 3 of 5 current gradients. The mutation detection function analytical expression of the forward traveling wave and the reverse traveling wave can be constructed, and the calculation formula is as follows:
where k is the kth sample point, E + Analytical expression of function for forward current traveling wave mutation detection, E - And analyzing an expression for the reverse current traveling wave mutation detection function.
To ensure the reliability of reflecting fault positionThe completeness of the information and the influence of other interference mutation points can be reduced to the maximum extent. The analytical expressions of the two sudden change detection functions of the directional traveling wave are multiplied, and the product is set at t 0 ,t 1 ]And [ t 1 ,t 2 ]The integration is performed in two successive time windows, and the calculation formula is as follows:
in the formula, t 0 ，t 1 Upper and lower limits, t, of 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.
Because the discontinuous point of the energy distribution of the current traveling wave along the line can be regarded as the result of the superposition of the meeting of the forward current traveling wave and the reverse current traveling wave, the integrals in the two time windows are used as two distance measuring functions. FIG. 5 and FIG. 6 show that 0 ,t 0 +l/(2v)]The distribution result graph of the integral function in the time window can be known that the distance from each extreme point of the integral function to the sending end obtained by measurement forms a solution set g 1—i ＝[140,141]km; FIG. 6 is a graph showing that 0 +l/(2v)，t 0 +l/v]The distribution result graph of the integral function in the time window can be known that the distance from each extreme point of the integral function to the sending end obtained by measurement forms a solution set g 2—i ＝[260,261]And km. Will solve and collect g 1—i Each element in (1) is used as a reference value and a solution set g 2—i The matching is performed on each element in (1), because 140+260 is 400km, namely the sum equals to the total length of the line, the condition is satisfied, the amplitude of the corresponding maximum point at 140km is less than zero, and 141+261 is not equal to 400km, the condition is not satisfied, namely the sum does not equal to the total length of the line, the extreme point with the distance to the sending end of 260km is the extreme point A (x) of the reaction fault position, and the extreme point with the distance to the sending end of 140km is the extreme point A (x) of the reaction fault positionReflecting extreme points B (x) of dual fault positions, thereby obtaining a fault distance x f The length corresponding to the point is subtracted from the total length l of the transmission line, namely 400-140-260 km, and the fault distance is 260 km.
The MMC-HVDC direct current transmission line fault distance measuring system of this embodiment includes:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in a high-speed data acquisition device at a transmission end or/and a receiving end of the power transmission line;
the numerical value calculation module is used for carrying out differential calculation on the current direction traveling wave series, solving the high power of the current direction traveling wave series, and then respectively constructing mutation detection function analytical expressions of the forward traveling wave and the reverse traveling wave by utilizing the current direction traveling wave differential high power;
fault location module for locating at t 0 ,t 1 ]And [ t 1 ,t 2 ]And (4) respectively constructing integral functions in the time windows, and performing fault distance measurement by using the maximum point of the integral functions 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 includes:
the line-mode conversion unit is used for decoupling the positive and negative voltages of the power transmission line to obtain line-mode traveling waves;
a numerical value calculation unit for calculating the product of the two directional traveling wave analytic expressions and setting the product at [ t ] 0 ,t 1 ]And [ t 1 ,t 2 ]Integration over a time window.
The fault location module specifically comprises:
an integral function construction unit for respectively setting the product of the traveling wave analytic expressions 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 ]And the distance corresponding to each maximum point in the time window.
And the maximum point matching unit is used for matching every two maximum points in the two time windows to screen out a pair of maximum points meeting the conditions.
A maximum judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the most significant value within the time window is greater than zero.
Thus, the fault distance x is obtained f Is 260 km.
Simulation verification of half-line-length internal faults and half-line-length external faults of the MMC-HVDC direct-current transmission line with the line length of 400km shows that the MMC-HVDC direct-current transmission line fault distance measuring method and system disclosed by the invention are high in reliability and high in precision.
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 of the present invention within the knowledge of those skilled in the art.
Claims (12)
1. A fault location method for an MMC-HVDC direct current transmission line is characterized by comprising the following steps:
step 1: when the line is in fault, collecting a fault electrical signal of the line;
step 2: according to the data collected by the measuring end, calculating the voltage and the current at regular intervals to obtain the voltage and current distribution condition of each point of the whole line;
step 3: calculating a current direction traveling wave series combining a time dimension and a distance dimension according to the voltage and the current of each point of the power transmission line;
step 4: carrying out differential calculation on the current direction traveling wave series, and solving the high power of the current direction traveling wave series;
step 5: respectively constructing mutation detection function analytical expressions of the forward traveling wave and the reverse traveling wave by utilizing the current direction traveling wave differential high power;
step 6: taking the two analytical expressions of the directional traveling wave as a product, and integrating the product in two successive time windows;
step 7: and taking the integrals in two successive time windows as two ranging functions, pairing extreme points in the two ranging functions pairwise, and realizing fault ranging by utilizing the relationship between the extreme points and combining the distance corresponding to the extreme point and the amplitude value thereof.
2. The MMC-HVDC direct current transmission line fault location method of claim 1, characterized in that: and the fault electrical signal in Step1 is acquired by a high-speed acquisition device arranged on an MMC-HVDC direct current transmission line bus.
3. The MMC-HVDC direct current transmission line fault location method of claim 1, wherein Step2 specifically is:
step2.1: decoupling the positive and negative voltages of the power transmission line by using Kerenbel transformation to obtain line mode traveling waves:
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, A is a Kerenbel phase mode change matrix;
step2.2: according to the voltage and current data collected by the measuring end, calculating the voltage and current at intervals of 1 kilometer step length to obtain the voltage and current distribution conditions of all points of the whole 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 a transmission line M,s The voltage r measured by a high-speed acquisition device at a certain moment on a power transmission line s Line mode resistance per unit length, v s Is the linear mode wave velocity.
4. The MMC-HVDC direct current transmission line fault location method of claim 1, characterized in that: in Step3, the current direction traveling wave series comprises a forward current traveling wave i + x,s And reverse current traveling wave i - x,s ；
The forward current traveling wave is defined as propagating from the transmitting end to the receiving end, and the reverse current traveling wave is defined as propagating from the receiving end to the transmitting end.
5. The MMC-HVDC direct current transmission line fault location method of claim 1, wherein Step4 specifically is:
step4.1: carrying out differential calculation on the current direction traveling wave series to obtain the current gradient distributed along the line
And
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,
and
respectively representing a forward current gradient distributed along the line and a reverse current gradient distributed along the line;
step4.2: calculating the current gradient distributed along the line
And
to the power of 3.
6. The MMC-HVDC direct current transmission line fault location method of claim 1, characterized in that: the Step5 forward traveling wave and reverse traveling wave mutation detection function analytical expression specifically comprises the following steps:
where k is the kth sample point, E + Analytical expression of function for forward current traveling wave mutation detection, E - And analyzing an expression for the reverse current traveling wave mutation detection function.
7. The MMC-HVDC direct current transmission line fault location method of claim 1, characterized in that: the Step6 is specifically as follows:
multiplying the forward current traveling wave mutation detection function analytical expression and the reverse current traveling wave mutation detection function analytical expression obtained in Step5 respectively at t 0 ,t 1 ]And [ t 1 ,t 2 ]Integrating in two successive time windows;
in the formula, t 0 ，t 1 Upper and lower limits, t, of 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.
8. The MMC-HVDC direct current transmission line fault location method of claim 1, characterized in that: the Step7 is specifically as follows:
step7.1: taking the integral of two time windows as two distance measuring functions in the time window t 0 ,t 1 ]The distance from each extreme point of the integral function to the sending end is obtained by internal measurement and is used as a solution set g 1—i ＝[x 11 ,x 12 ,...,x 1n ]In the time window [ t ] 1 ,t 2 ]The distance from each extreme point of the integral function to the sending end is obtained through internal measurement and is used as a solution set g 2—i ＝[x 21 ,x 22 ,...,x 2n ]And will solveCollection g 1—i The elements in (1) are respectively used as reference values and solution sets g 2—i The elements in the system are matched, and a group of extreme points which are equal to or approximately equal to the total length of the line are added to form an extreme point A (x) of a reaction fault position and an extreme point B (x) of a reaction dual fault position;
step7.2: judging the solution set g satisfying the condition 1—i Whether the amplitude of the extreme point in (1) is greater than 0;
if yes, the point is an extreme point A (x) reflecting the fault position, and the fault distance x f Line length x corresponding to the point m1 ；
If not, the point is an extreme point B (x) reflecting the dual fault position, and the fault distance x f Subtracting the corresponding length x from the total length l of the line m2 。
9. A MMC-HVDC direct current transmission line fault distance measuring system is characterized by comprising:
the electric signal acquisition module is used for acquiring and storing fault voltage data, and is installed and operated in a high-speed data acquisition device at a transmission end or/and a receiving end of the power transmission line;
the numerical value calculation module is used for carrying out differential calculation on the current direction traveling wave series, solving the high power of the current direction traveling wave series, and then respectively constructing mutation detection function analytical expressions of the forward traveling wave and the reverse traveling wave by utilizing the current direction traveling wave differential high power;
fault location module for locating at [ t 0 ,t 1 ]And [ t 1 ,t 2 ]And (4) respectively constructing integral functions in the time windows, and performing fault distance measurement by using the maximum point of the integral functions to obtain a fault distance measurement result at the outlet.
10. The MMC-HVDC direct current transmission line fault location system of claim 9, 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.
11. The MMC-HVDC direct current transmission line fault location system of claim 9, wherein the numerical calculation module specifically comprises:
the line-mode conversion unit is used for decoupling the positive and negative voltages of the power transmission line to obtain line-mode traveling waves;
and the numerical value calculation unit is used for calculating the product of the two directional traveling wave analytic expressions.
12. The MMC-HVDC direct current transmission line fault location system of claim 9, wherein the fault location module specifically comprises:
an integral function construction unit for respectively setting the product of the analytic expressions of the traveling waves 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 maximum point in the time window;
the maximum point matching unit is used for matching every two maximum points in the two time windows and screening out a pair of maximum points meeting the conditions;
a maximum judgment unit for judging whether the integral function is at [ t ] 0 ,t 1 ]Whether the most significant value within the time window is greater than zero.
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Cited By (3)
| 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 |
| CN116087693A (en) * | 2023-04-13 | 2023-05-09 | 昆明理工大学 | LCC-HVDC power transmission line single-ended distance measurement method and system |
| CN117517876A (en) * | 2024-01-04 | 2024-02-06 | 昆明理工大学 | Fault positioning method, fault positioning equipment and storage medium for direct current transmission line |
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Cited By (6)
| 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 |
| 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 |
| CN116087693A (en) * | 2023-04-13 | 2023-05-09 | 昆明理工大学 | LCC-HVDC power transmission line single-ended distance measurement method and system |
| CN116087693B (en) * | 2023-04-13 | 2023-08-04 | 昆明理工大学 | LCC-HVDC power transmission line single-ended distance measurement method and system |
| CN117517876A (en) * | 2024-01-04 | 2024-02-06 | 昆明理工大学 | Fault positioning method, fault positioning equipment and storage medium for direct current transmission line |
| CN117517876B (en) * | 2024-01-04 | 2024-05-03 | 昆明理工大学 | Fault positioning method, fault positioning equipment and storage medium for direct current transmission line |
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