A method and system for fault location measurement of LCC-VSC hybrid high voltage direct current transmission line

Abstract

The present invention relates to a fault distance measurement method and system for an LCC-VSC hybrid high-voltage direct current transmission line, and belongs to the technical field of relay protection of electric power systems. The initial fault voltage signal and current signal are obtained at the measuring end; the voltage and current at any point along the line are calculated according to the fault voltage signal and current signal at the measuring end; the voltage forward traveling wave and the voltage reverse traveling wave at any point are calculated according to the above voltage and current; the fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount are calculated respectively; the superposition value of the fifth power of the voltage forward traveling wave change amount and the fifth power of the voltage reverse traveling wave change amount are calculated respectively by sliding integral with a window length of 3, and the two sets of values ​​are multiplied; the above products are integrated in the observation time window respectively; the fault distance is measured according to the polarity of the integral value mutation point in the two observation time windows. The present invention does not need to calibrate the fault traveling wave head, and overcomes the problem of inaccurate distance measurement using head information in the traditional single-ended distance measurement method.

Description

Technical Field

[0001] The invention relates to a LCC-VSC hybrid high-voltage direct current transmission line fault distance measurement method and system, belonging to the technical field of power system relay protection. Background Art

[0002] After a high-voltage direct current transmission line fails, if the fault can be quickly and accurately eliminated, it can not only improve the reliability of the power system operation, but also reduce the huge losses caused by power outages. Therefore, when a line fails, if different fault characteristics can be analyzed and mastered, the fault distance can be quickly and accurately predicted, insulation hidden dangers can be discovered in time, and the inconvenience caused by the line fault can be eliminated, it can not only repair the faulty line in the first time, ensure the safe and stable operation of the power grid system, and reduce the economic losses caused by the line fault, but also reduce the physical labor of the line patrol personnel, reduce costs, and generate huge economic benefits. In the high-voltage direct current transmission system, the transmission distance is long, and the use of the double-end measurement method requires a communication channel, and requires data synchronization at both ends, and the action speed is slow; therefore, the single-end measurement method can be used for fault distance measurement, and there is no need to synchronize the double-end data. In the previous distance measurement methods for calculating the fault distance, basically the traveling wave head is observed, calibrated and identified on the time axis. If the wave head calibration is not accurate, the distance measurement fails. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a LCC-VSC hybrid high-voltage direct current transmission line fault location method and system to solve the above technical problems.

[0004] The technical solution of the present invention is: a fault ranging method for LCC-VSC hybrid high-voltage direct current transmission lines, based on the single-ended traveling wave ranging principle, when there is no point of discontinuous wave impedance (such as a hard fault point, a point where forward and reverse traveling waves are superimposed), the voltage traveling wave mutation obtained based on the Berylon line transmission equation changes continuously. When a line fault occurs, the traveling wave will be refracted and reflected when it encounters a point of discontinuous wave impedance, then the voltage traveling wave distributed over the entire line length will change discontinuously, and when a hard fault point is encountered, the forward voltage traveling wave and the reverse voltage traveling wave are superimposed with opposite polarities, and the amplitude of the voltage traveling wave at the fault point is less than the amplitude of the voltage traveling wave at other positions before and after the fault location, that is, the amplitude of the voltage traveling wave at the fault point undergoes a negative polarity mutation; for a dual fault point, the forward voltage traveling wave and the reverse voltage traveling wave are superimposed with the same polarity, so that the voltage at the dual fault point The amplitude of the traveling wave is greater than the amplitude of the voltage traveling wave before and after the dual fault point, that is, the amplitude of the voltage traveling wave undergoes a positive polarity mutation at the fault point; and the sum of the distances corresponding to the hard fault point and the dual fault point is equal to the total length of the line. Therefore, the fault current traveling wave data obtained at a single end is used to apply the Berylon line transmission line equation to infer the voltage and current traveling waves at any time and any position within the entire line length, and directional traveling wave decomposition is performed. The directional traveling wave is used to construct an integral function, and the position of the fault point is determined according to the mutation point of the integral function.

[0005] The specific steps are:

[0006] Step 1: The protection method based on single-ended traveling wave ranging requires the construction of a protection boundary. When the system frequency is high, the boundary will present a relatively large impedance characteristic, which is equivalent to an open circuit, so the current traveling wave cannot be measured. A traveling wave coupling box and a current transformer can be installed at the measurement point. After the fault, the voltage traveling wave generates a current signal after passing through the traveling wave coupling box. The current transformer is used to measure the current signal and indirectly measure the voltage signal. The initial fault voltage signal and current signal are obtained at the measurement end.

[0007] Step 2: The Berelon line model is a very accurate transmission line model. It fully considers the influence of distributed capacitance of high-voltage DC long-distance transmission. Therefore, the Berelon line model is used to analyze transient characteristics. The voltage and current at any point along the line are calculated based on the fault voltage signal and current signal at the measuring end. The calculation formula is:

[0008]

[0009]

[0010] Among them, Z c,s is the line mode wave impedance, x is the distance from the sending end, v s is the linear mode wave velocity, r s is the line resistance per unit length, Z1 = r sx / 4, Z2=Z c,s +Z1,Z3=Z c,s -Z1, Z4 = Z c,s -4Z1,u M,s It represents the voltage measured at the sending end at a certain moment, i M,s Indicates the current measured at the sending end at a certain moment.

[0011] Step 3: For the starting end, the wave from the end of the transmission line to the beginning of the transmission line is defined as the forward wave, and the wave from the beginning of the transmission line to the end of the transmission line is defined as the reverse wave. The forward voltage wave and the reverse voltage wave at any point are calculated based on the above voltage and current. The calculation formula is as follows.

[0012]

[0013]

[0014] Step 4: Calculate the fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount respectively.

[0015]

[0016]

[0017] Step 5: Use the sliding integral with a window length of 3 to calculate the superposition value of the fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount.

[0018] Step 5.1: To suppress the influence of Gaussian noise on the fault signal, the voltage positive wave change is 5 times the power h. + Starting from the kth sampling value, every N h + The sampling value of is calculated once as the voltage forward traveling wave mutation energy E + The kth value of can be used to obtain the superposition value of the fifth power of the voltage positive traveling wave change at any time and any position within the entire line length. The calculation formula is as follows.

[0019]

[0020]

[0021] In the formula, k is the kth sampling point, N is the number of h at each time + The number of superimposed sampling values ​​can be selected according to needs.

[0022] Step 5.2: Reverse the voltage wave to the 5th power h - Starting from the kth sampling value, every n h - The sampling value of is calculated once, which is used as the voltage reverse traveling wave mutation energy E- The kth value of can be used to obtain the superposition value of the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length. The calculation formula is as follows.

[0023]

[0024]

[0025] In the formula, k is the kth sampling point, N is the number of h at each time - The number of superimposed sampling values ​​can be selected according to needs.

[0026] Step 6: Multiply the two sets of values ​​in Step 5. After multiplication, integrate them in the observation time windows [t1, t1+l / (2v)] and [t1+l / (2v), l / v] respectively.

[0027] The calculation formula is as follows.

[0028]

[0029]

[0030] Where, t1, t1+l / 2v. t1+l / 2v, t1+l / v are the upper and lower limits of the two sets of traveling wave observation time windows respectively.

[0031] Step 7: Equations (8) and (9) show that when there are no discontinuous points (such as hard fault points, superposition points of positive and reverse traveling waves), the voltage traveling wave mutation calculated based on the Berelon line transmission equation is a continuous change. When a hard fault point or a dual fault point is encountered, it is presented as a discontinuous distribution of the superposition value of the fifth power of the traveling wave change at any time within the entire line length, and a negative polarity mutation point appears. The integral of any time in the two intervals [t1, t1+l / (2v)] and [t1+l / (2v), l / v] is used as a function. When a fault occurs at a certain time and place, first, measure the distance corresponding to the first mutation point of the integral function. Secondly, determine the polarity of the first mutation point of the integral function. If it is negative, the fault distance x f is the line length x corresponding to this point m1 If it is positive, the fault distance x f The total length of the transmission line l minus the length x corresponding to the point m1 .

[0032] A LCC-VSC hybrid high-voltage direct current transmission line fault location system, characterized by comprising:

[0033] The electrical signal acquisition module is used to collect and store data information. A traveling wave coupling box and a current transformer are installed at the measuring end to obtain the initial fault voltage signal and current signal.

[0034] The numerical calculation module is used to calculate the superposition value of the h-power of the forward traveling wave mutation amount and the superposition value of the h-power of the reverse traveling wave mutation amount at any time and any position within the entire line length.

[0035] The fault distance measurement module is used to construct an integral function, multiply the two superposition values ​​calculated by the numerical calculation module and then integrate them, and use the integral function mutation point to perform fault distance measurement to obtain the fault distance and the final exit distance measurement result.

[0036] The electrical signal acquisition module comprises:

[0037] The data acquisition unit is used to collect the analog signal output from the secondary side of the transformer installed at the measuring end.

[0038] The analog-to-digital conversion unit is used to convert the analog signal collected by the data acquisition unit into a digital signal.

[0039] The protection startup unit is used to determine whether the digital signal is greater than the set startup threshold. If so, the startup time is read and the data is stored.

[0040] The numerical calculation module includes:

[0041] The line mode conversion unit is used to calculate the line mode component of the voltage traveling wave at the measuring end.

[0042] The numerical calculation unit is used to perform fault distance measurement according to the polarity of the integral value mutation point within two observation time windows.

[0043] The fault distance measurement module comprises:

[0044] The integral function construction unit is used to obtain the product of the superposition value of the fifth power of the voltage positive wave change amount and the superposition value of the fifth power of the voltage reverse wave change amount at any time and any position within the entire line length, and integrate the product within a certain time window to obtain the integral function.

[0045] The distance measurement unit is used to measure the distance of the first mutation point of the integral function relative to the beginning of the line.

[0046] The polarity judgment unit is used to judge whether the polarity of the first mutation point of the integral function is positive or negative.

[0047] The beneficial effects of the present invention are:

[0048] 1. Compared with the distance measurement method based on the principle of fault analysis method, the distance measurement method based on the traveling wave method has higher distance measurement accuracy.

[0049] 2. The present invention performs fault distance measurement on high-voltage direct current transmission lines, adopts single-ended traveling wave distance measurement, and does not have data synchronization problems.

[0050] 3. The distance measurement error of the present invention is small, which can greatly reduce the cost of manual line inspection and has good economic benefits.

[0051] 4. The present invention does not require calibration of the fault traveling wave head, thus overcoming the problem of inaccurate ranging using wave head information in the traditional single-ended ranging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a topological diagram of the simulation model of the present invention;

[0053] Figure 2 It is a schematic diagram of an equivalent model of the Berylon circuit of the present invention;

[0054] Figure 3 is a system block diagram of Embodiment 1 of the present invention;

[0055] Figure 4 1 is a graph showing the result of the first half time window integral function of Embodiment 1 of the present invention;

[0056] Figure 5 is a graph showing the result of the second half time window integral function of Embodiment 1 of the present invention;

[0057] Figure 6 This is the result of the first half time window integral function of Example 2 of the present invention.

[0058] Figure 7 This is a graph of the result of the second half time window integral function of Example 2 of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0060] Embodiment 1: LCC-VSC simulation model system as shown in the attached Figure 1 As shown in the figure, the line is 1500km long and the voltage level is ±800kV. The fault is set to occur at 600km of the line, the fault type is set to a permanent positive ground fault, the transition resistance is set to 0.01Ω, and the sampling rate is 1MHz.

[0061] The specific steps for implementation are:

[0062] Step 1: Obtain the initial fault voltage signal and current signal at the measuring end;

[0063] Step 2: The distributed parameter characteristics in the high-voltage DC long-distance transmission system are obvious. The charging current generated by the distributed capacitance in the line cannot be ignored. The Berelon line model is a very accurate transmission line model that fully considers the influence of distributed capacitance. Therefore, the Berelon line model is used to analyze transient characteristics. The transmission line is equivalent to the Berelon line model. The equivalent diagram is shown in the attached figure. Figure 2 shown.

[0064] The specific steps of the distance measurement process of the high-voltage direct current transmission line fault distance measurement method provided by the present invention are described as follows: the voltage and current at any position at any time within the entire line length are calculated, and the calculation formula is:

[0065]

[0066]

[0067] Among them, Z c,s is the line mode wave impedance, x is the distance from the sending end, v s is the linear mode wave velocity, r s is the line resistance per unit length, Z1 = r s x / 4, Z2=Z c,s +Z1,Z3=Z c,s -Z1, Z4 = Z c,s -4Z1,u M,s It represents the voltage measured at the sending end at a certain moment, i M,s Indicates the current measured at the sending end at a certain moment.

[0068] Step 3: For the starting end, the traveling wave from the end of the transmission line to the starting end of the transmission line is defined as the forward traveling wave, and the traveling wave from the starting end of the transmission line to the end of the transmission line is defined as the reverse traveling wave. Based on the above voltage and current, the forward voltage traveling wave and the reverse voltage traveling wave at any point are calculated using the following formulas:

[0069]

[0070]

[0071] Step 4: In order to amplify the fault characteristics of the voltage forward wave and the voltage reverse wave and highlight the mutation amount of the fault point, the first-order linear differential equation is used to calculate the change amount of the voltage forward wave and the voltage reverse wave respectively. In order to further highlight the change amount of the fault signal, suppress the points with smaller changes and eliminate the influence of small mutation points, the fifth power of the voltage forward wave change amount and the fifth power of the voltage reverse wave change amount are calculated. The odd power is taken to make the calculated voltage forward wave and voltage reverse wave mutation points retain the original polarity.

[0072]

[0073]

[0074] Step 5: To suppress the influence of Gaussian noise on the fault signal, the voltage positive wave change is 5 times the power h. + Starting from the kth sampling value, every N h +The sampling value of is calculated once as the voltage forward traveling wave mutation energy E + The kth value of can be used to obtain the superposition value of the fifth power of the voltage positive traveling wave variation at any time and any position within the entire line length. The calculation formula is as follows;

[0075]

[0076]

[0077] In the formula, k is the kth sampling point, N is the number of h at each time + The number of superimposed sampling values ​​can be selected according to needs.

[0078] From the voltage reverse wave change to the 5th power h - Starting from the kth sampling value, every n h - The sampling value of is calculated once, which is used as the voltage reverse traveling wave mutation energy E - The kth value of can be used to obtain the superposition value of the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length. The calculation formula is as follows:

[0079]

[0080]

[0081] In the formula, k is the kth sampling point, N is the number of h at each time - The number of superimposed sampling values ​​can be selected according to needs.

[0082] Step 6: Calculate the product of the fifth power superposition value of the voltage positive wave variation and the fifth power superposition value of the voltage reverse wave variation at any time and any position within the entire line length, and integrate the product within a certain time window. The calculation formula is as follows;

[0083]

[0084]

[0085] Wherein, t1, t1+l / 2v; t1+l / 2v, t1+l / v are the upper and lower limits of the two groups of traveling wave observation time windows respectively. In this embodiment, t1 is the moment when the initial traveling wave of the fault arrives at the measurement end, and t1+l / v is the moment corresponding to the l / v time window length after the initial traveling wave of the fault arrives at the measurement end.

[0086] Step 7: Since the voltage traveling wave mutation calculated by the Berylon line transmission equation is continuously changing, when encountering a hard fault point or a dual fault point, the superposition value of the traveling wave change at any time within the entire line length is discontinuous, that is, a mutation point appears. The integral at any time in the two integral intervals [t1, t1+l / (2v)] and [t1+l / (2v, l / v] is taken as a function, and the integral function distribution result is as follows: Figure 4 , Figure 5 , as shown. First, the distance corresponding to the first mutation point of the integral function is measured to be 600km; second, determine whether the polarity of the first mutation point of the integral function is negative. If so, the fault distance x f is the line length x corresponding to this point m1 ; If not, then the fault distance x f The total length of the transmission line l minus the length x corresponding to the point m1 In this embodiment, the polarity of the first mutation point is negative, and the fault distance x f The line length corresponding to this point is 600km.

[0087] Figure 3 The functional block diagram of the LCC-VSC hybrid high-voltage direct current transmission line fault location system provided by the present invention includes:

[0088] The electrical signal acquisition module is used to collect and store data information. A traveling wave coupling box and a current transformer are installed at the measuring end to obtain the initial fault voltage signal and current signal.

[0089] A numerical calculation module is used to calculate the superposition value of the h-th power of the forward traveling wave mutation amount and the superposition value of the h-th power of the reverse traveling wave mutation amount at any time and any position within the entire line length;

[0090] The fault distance measurement module is used to construct an integral function, multiply the two superposition values ​​calculated by the numerical calculation module and then integrate them, and use the integral function mutation point to perform fault distance measurement to obtain the fault distance and the final exit distance measurement result.

[0091] The electrical signal acquisition module specifically includes:

[0092] A data acquisition unit, used to collect analog signals output from the secondary side of the transformer installed at the measuring end;

[0093] An analog-to-digital conversion unit, used to convert the analog signal collected by the data collection unit into a digital signal;

[0094] The protection startup unit is used to determine whether the digital signal is greater than the set startup threshold. If so, the startup time is read and the data is stored.

[0095] The numerical calculation module specifically includes:

[0096] A line mode conversion unit, used for calculating the line mode component of the voltage traveling wave at the measuring end;

[0097] The numerical calculation unit first obtains the initial fault voltage signal and current signal at the measuring end, and calculates the voltage and current at any point along the line according to the fault voltage signal and current signal at the measuring end; secondly, calculates the voltage forward wave and voltage reverse wave at any point according to the above voltage and current; thirdly, respectively calculates the fifth power of the voltage forward wave mutation amount and the fifth power of the voltage reverse wave mutation amount; finally, respectively calculates the fifth power of the voltage forward wave change amount and the fifth power of the voltage reverse wave change amount using a sliding integral with a window length of 3, and multiplies the two sets of values; integrates the above products in the observation time windows [t1, t1+l / (2v)] and [t1+l / (2v), l / v] respectively; and performs fault distance measurement according to the polarity of the integral value mutation point in the two observation time windows.

[0098] The fault distance measurement module specifically includes:

[0099] The integral function construction unit is used to obtain the product of the superposition value of the fifth power of the voltage positive traveling wave variation and the superposition value of the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length, and integrate the product within a certain time window to obtain an integral function;

[0100] The distance measurement unit is used to measure the distance between the first mutation point of the integral function and the beginning of the line. The distance is 600km.

[0101] The polarity judgment unit is used to judge the polarity of the first mutation point of the integral function, and the polarity is negative.

[0102] So the fault distance x f It is 600km.

[0103] Embodiment 2: LCC-VSC simulation model system as shown in the attached Figure 1 As shown in the figure, the line is 1500km long and the voltage level is ±800kV. The fault is set to occur at 100km of the line, the fault type is set to a permanent positive ground fault, the transition resistance is set to 0.01Ω, and the sampling rate is 1MHz. The specific steps for implementation are:

[0104] Step 1: In the sending and receiving ends of the high-voltage DC transmission system, there are generally boundaries formed by smoothing reactors and DC filters. When the system frequency is high, the boundary will show a relatively large impedance characteristic, which is equivalent to an open circuit, and the current traveling wave cannot be measured. For high-frequency signals, the transmission capability of the voltage transformer is poor, and the voltage transformer is generally not used to measure the voltage signal. Therefore, a traveling wave coupling box is installed at the measurement point. The fault voltage traveling wave will generate a current traveling wave after passing through the traveling coupling box, and then the current transformer is used to measure the current signal to indirectly measure the voltage signal. The initial fault voltage signal and current signal are obtained at the measurement end.

[0105] Step 2: In the HVDC transmission system, the transmission line is long, and there is electromagnetic coupling between the positive and negative poles of the transmission line. Therefore, it is necessary to decouple the fault voltage traveling wave and decouple the positive and negative voltages into independent line mode components and zero mode components. Since the zero mode electrical quantity is severely attenuated during the propagation process, and the zero mode electrical quantity only exists in the case of ground fault, while the line mode electrical quantity exists not only in the ground fault but also in the inter-pole fault, the use of line mode quantity is more suitable for the analysis of different fault types. Decouple the fault voltage traveling wave to obtain the line mode voltage traveling waves at the sending and receiving ends.

[0106] The distributed parameter characteristics in the high-voltage DC long-distance transmission system are obvious, and the charging current generated by the distributed capacitance in the line cannot be ignored. The Berelon line model is a very accurate transmission line model that fully considers the influence of distributed capacitance. Therefore, the Berelon line model is used to analyze transient characteristics. The transmission line is equivalent to the Berelon line model, and the equivalent diagram is shown in the attached figure. Figure 2 As shown. The voltage and current at any position at any time within the entire line length are calculated using the following formula:

[0107]

[0108]

[0109] Among them, Z c,s is the line mode wave impedance, x is the distance from the sending end, v s is the linear mode wave velocity, r s is the line resistance per unit length, Z1 = r s x / 4, Z2=Z c,s +Z1,Z3=Z c,s -Z1, Z4 = Z c,s -4Z1,u M,s It represents the voltage measured at the sending end at a certain moment, i M,s Indicates the current measured at the sending end at a certain moment.

[0110] Step 3: For the starting end, the traveling wave from the end of the transmission line to the starting end of the transmission line is defined as the forward traveling wave, and the traveling wave from the starting end of the transmission line to the end of the transmission line is defined as the reverse traveling wave. Based on the above voltage and current, the forward voltage traveling wave and the reverse voltage traveling wave at any point are calculated using the following formulas:

[0111]

[0112]

[0113] Step 4: In order to amplify the fault characteristics of the voltage forward wave and the voltage reverse wave and highlight the mutation amount of the fault point, the first-order linear differential equation is used to calculate the change amount of the voltage forward wave and the voltage reverse wave respectively. In order to further highlight the change amount of the fault signal, suppress the points with smaller changes and eliminate the influence of small mutation points, the fifth power of the voltage forward wave change amount and the fifth power of the voltage reverse wave change amount are calculated. The odd power is taken to make the calculated voltage forward wave and voltage reverse wave mutation points retain the original polarity.

[0114]

[0115]

[0116] Step 5: To suppress the influence of Gaussian noise on the fault signal, the voltage positive wave change is 5 times the power h. + Starting from the kth sampling value, every N h + The sampling value of is calculated once as the voltage forward traveling wave mutation energy E + The kth value of can be used to obtain the superposition value of the fifth power of the voltage positive traveling wave variation at any time and any position within the entire line length. The calculation formula is as follows;

[0117]

[0118]

[0119] In the formula, k is the kth sampling point, N is the number of h at each time + The number of superimposed sampling values ​​can be selected according to needs.

[0120] From the voltage reverse wave change to the 5th power h - Starting from the kth sampling value, every n h - The sampling value of is calculated once, which is used as the voltage reverse traveling wave mutation energy E - The kth value of can be used to obtain the superposition value of the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length. The calculation formula is as follows:

[0121]

[0122]

[0123] In the formula, k is the kth sampling point, N is the number of h at each time - The number of superimposed sampling values ​​can be selected according to needs.

[0124] Step 6: Calculate the product of the fifth power superposition value of the voltage positive wave variation and the fifth power superposition value of the voltage reverse wave variation at any time and any position within the entire line length, and integrate the product within a certain time window. The calculation formula is as follows;

[0125]

[0126]

[0127] Wherein, t1, t1+l / 2v; t1+l / 2v, t1+l / v are the upper and lower limits of the two groups of traveling wave observation time windows respectively. In this embodiment, t1 is the moment when the initial traveling wave of the fault arrives at the measurement end, and t1+l / v is the moment corresponding to the l / v time window length after the initial traveling wave of the fault arrives at the measurement end.

[0128] Step 7: Since the voltage traveling wave mutation calculated by the Berylon line transmission equation is continuously changing, when encountering a hard fault point or a dual fault point, the superposition value of the traveling wave change at any time within the entire line length is discontinuous, that is, a mutation point appears. The integral at any time and any position within the entire line length is taken as a function, and the integral function distribution result is as follows: Figure 6 , Figure 7 As shown, first, the distance corresponding to the first mutation point of the integral function is measured to be 100 km; secondly, it is determined whether the polarity of the first mutation point of the integral function is negative. If so, the fault distance x f is the line length x corresponding to this point m1 ; If not, then the fault distance x f The total length of the transmission line l minus the length x corresponding to the point m1 In this embodiment, the polarity of the first mutation point is negative, so the fault distance x f is the line length corresponding to this point, i.e. 100km, and the fault distance is 100km.

[0129] The LCC-VSC hybrid high-voltage direct current transmission line fault location system of this embodiment includes:

[0130] The electrical signal acquisition module is used to collect and store data information. A traveling wave coupling box and a current transformer are installed at the measuring end to obtain the initial fault voltage signal and current signal.

[0131] A numerical calculation module is used to calculate the superposition value of the h-th power of the forward traveling wave mutation amount and the superposition value of the h-th power of the reverse traveling wave mutation amount at any time and any position within the entire line length;

[0132] The fault distance measurement module is used to construct an integral function, multiply the two superposition values ​​calculated by the numerical calculation module and then integrate them, and use the integral function mutation point to perform fault distance measurement to obtain the fault distance and the final exit distance measurement result.

[0133] The electrical signal acquisition module specifically includes:

[0134] A data acquisition unit, used to collect analog signals output from the secondary side of the transformer installed at the measuring end;

[0135] An analog-to-digital conversion unit, used to convert the analog signal collected by the data collection unit into a digital signal;

[0136] The protection startup unit is used to determine whether the digital signal is greater than the set startup threshold. If so, the startup time is read and the data is stored.

[0137] The numerical calculation module specifically includes:

[0138] A line mode conversion unit, used for calculating the line mode component of the voltage traveling wave at the measuring end;

[0139] The numerical calculation unit is used to perform fault distance measurement according to the polarity of the integral value mutation point within two observation time windows.

[0140] The fault distance measurement module specifically includes:

[0141] The integral function construction unit is used to obtain the product of the superposition value of the fifth power of the voltage positive traveling wave variation and the superposition value of the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length, and integrate the product within a certain time window to obtain an integral function;

[0142] The distance measurement unit is used to measure the distance of the first mutation point of the integral function relative to the beginning of the line, and the distance is 100 km.

[0143] The polarity judgment unit is used to judge the polarity of the first mutation point of the integral function, and the polarity is negative.

[0144] So the fault distance x f is the line length corresponding to this point, i.e. 100km, and the fault distance is 100km.

[0145] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for fault location of a LCC-VSC hybrid high voltage direct current transmission line, characterized in that: Step 1: Obtain the initial fault voltage signal and current signal at the measuring end; Step 2: Calculate the voltage and current at any point along the line based on the fault voltage signal and current signal at the measuring end; Step 3: Calculate the voltage forward traveling wave and the voltage reverse traveling wave at any point according to the voltage and current; Step 4: Calculate the fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount respectively; Step 5: Use the sliding integral with a window length of 3 to calculate the superposition value of the fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount; Step 6: Multiply the two sets of values ​​in Step 5 and integrate them in the observation time windows [t1, t1+l / (2v)] and [t1+l / (2v), l / v] respectively. Step 7: Fault location is performed based on the polarity of the integral value mutation point within the two observation time windows; The fifth power of the voltage forward traveling wave mutation amount and the fifth power of the voltage reverse traveling wave mutation amount in Step 4 are: The Step 5 is specifically as follows: Step 5.1: From the voltage positive wave change to the 5th power h + Starting from the kth sampling value, every N h + The sampling value of is calculated once, which is used as the voltage forward traveling wave mutation energy E + The kth value of can be obtained by superposing the fifth power of the voltage positive traveling wave variation at any time and any position within the entire line length: In the formula, k is the kth sampling point, N is the number of h at each time + The number of superposition of sampling values; Step 5.2: Reverse the voltage wave to the 5th power h - Starting from the kth sampling value, every N h - The sampling value of is calculated once as the voltage reverse traveling wave mutation energy E - The kth value of can be obtained by superposing the fifth power of the voltage reverse traveling wave variation at any time and any position within the entire line length: In the formula, k is the kth sampling point, N is the number of h at each time - The number of sample values ​​superimposed.

2. The LCC-VSC hybrid high voltage direct current transmission line fault location method according to claim 1, characterized in that: The voltage forward wave and the voltage reverse wave in Step 3 are: In the formula, Z c,s is the line mode wave impedance, u x,s is the voltage measured at the sending end at a certain moment, i x,s It is the current measured at the sending end at a certain moment.

3. The LCC-VSC hybrid high voltage direct current transmission line fault location method according to claim 1, characterized in that: The Step 6 is specifically as follows: Wherein, t1, t1+l / 2v; t1+l / 2v, t1+l / v are the upper and lower limits of the two sets of traveling wave observation time windows respectively.

4. The LCC-VSC hybrid high voltage direct current transmission line fault location method according to claim 1, characterized in that: The Step 7 is specifically as follows: taking the integral of any time in the two intervals [t1, t1+l / (2v)] and [t1+l / (2v), l / v] as a function, when a fault occurs at a certain time and a certain location, firstly, measuring the distance corresponding to the first mutation point of the integral function; secondly, determining the polarity of the first mutation point of the integral function; If negative, the fault distance x f is the line length x corresponding to this point m1 ; If positive, the fault distance x f The total length of the transmission line l minus the length x corresponding to the point m1 .

5. A system for implementing the LCC-VSC hybrid high voltage direct current transmission line fault location method according to claim 1, characterized in that: include: The electrical signal acquisition module is used to collect and store data information. A traveling wave coupling box and a current transformer are installed at the measuring end to obtain the initial fault voltage signal and current signal. A numerical calculation module is used to calculate the superposition value of the h-th power of the forward traveling wave mutation amount and the superposition value of the h-th power of the reverse traveling wave mutation amount at any time and any position within the entire line length; The fault distance measurement module is used to construct an integral function, multiply the two superposition values ​​calculated by the numerical calculation module and then integrate them, and use the integral function mutation point to perform fault distance measurement to obtain the fault distance and the final exit distance measurement result.

6. The system according to claim 5, characterized in that The electrical signal acquisition module comprises: A data acquisition unit, used to collect analog signals output from the secondary side of the transformer installed at the measuring end; An analog-to-digital conversion unit, used to convert the analog signal collected by the data collection unit into a digital signal; The protection startup unit is used to determine whether the digital signal is greater than the set startup threshold. If so, the startup time is read and the data is stored.

7. The system according to claim 5, characterized in that The numerical calculation module includes: A line mode conversion unit, used for calculating the line mode component of the voltage traveling wave at the measuring end; The numerical calculation unit is used to perform fault distance measurement according to the polarity of the integral value mutation point within two observation time windows.

8. The system according to claim 5, characterized in that The fault distance measurement module comprises: An integral function construction unit is used to obtain the product of the superposition value of the fifth power of the voltage positive wave variation and the superposition value of the fifth power of the voltage reverse wave variation at any time and any position within the entire line length, and integrate the product within a certain time window to obtain an integral function; A distance measurement unit, used to measure the distance of the first mutation point of the integral function relative to the beginning of the line; The polarity judgment unit is used to judge whether the polarity of the first mutation point of the integral function is positive or negative.

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