CN115097253A - MMC-HVDC direct current transmission line fault distance measurement method and system - Google Patents

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

A method and system for fault location of MMC-HVDC direct current transmission line

technical field

The invention relates to a fault location method and system for an MMC-HVDC direct current transmission line, belonging to the technical field of power system relay protection.

Background technique

At present, with the depletion of fossil energy and the increasing destruction of water resources by hydropower, renewable energy power generation has been put into operation in the western and northern regions of my country. Development of transmission systems. The DC transmission technology based on the traditional commutating converter (LCC) is prone to problems such as commutation failure. -HVDC) DC transmission has gradually gained attention in the field of DC transmission and distribution. Compared with traditional AC transmission, flexible DC transmission has obvious advantages in new energy grid connection and island power supply. It has the advantages of large power supply capacity, small line loss, and high power quality. At the same time, the shortcomings of the flexible DC transmission system are also obvious. Since the DC transmission system is generally used for long-distance power transmission, the transmission line is long, and it is affected by environmental factors such as lightning strikes and tree branches all the year round, which is prone to failures, and the damping of the DC system itself is not enough It is smaller than the AC system, which leads to an increase in the failure rate. Due to the long distance, the cost of manual line inspection is high when a fault occurs. Therefore, in order to ensure the stable operation of the flexible DC transmission system, it is necessary to ensure that the transmission line can quickly identify the fault and locate the fault location as accurately as possible when a fault occurs, shorten the distance of manual line inspection, and gain time for the subsequent line repair work. To achieve faster restoration of power supply, improve the economic efficiency of the power sector.

In recent years, with the development of relay protection technology, the speed of fault removal is getting faster and faster when a fault occurs, resulting in no obvious damage marks on the surface of the line. It is difficult to rely on manual line inspection to find the fault point. Therefore, it is urgent to A reliable fault location device is developed. According to some distance measuring methods currently used, for the traveling wave method, the fault distance is calculated by using the time difference of the initial traveling wave arrival time of the fault and combined with the long line of the line. The advantages of the double-ended traveling wave method are obvious and high reliability. , the measurement accuracy is high, there is no ranging dead zone, but the communication synchronization of the acquisition devices at both ends is required, which depends on the GPS device to provide reliable synchronous communication, especially in long-distance transmission lines, small time errors will be It leads to a large ranging error; for the single-ended traveling wave method, it only relies on the fault traveling wave data on one side, and does not need to consider the communication synchronization problem. question. In short, the traditional traveling wave ranging is mostly based on the time domain characteristics of traveling waves and observes, characterizes, calibrates and discriminates traveling waves on the time axis to achieve the calculation of fault distance. If the traveling wave head is not calibrated accurately, it will make the measurement The distance error is extremely large, which increases the cost of manual line inspection.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a fault location method and a system for MMC-HVDC direct current transmission lines, which can effectively solve the problem that the traditional traveling wave method or fault analysis method is affected by the attenuation of fault information for long-distance transmission lines, resulting in the measurement of The problem of ranging failure and ranging blind spot occurs.

The technical scheme of the present invention is: a fault location method and system of MMC-HVDC direct current transmission line, and a novel single-ended traveling wave location principle based on the distribution characteristics of the sudden change of traveling wave energy along the line. The traveling wave will reflect and refract when it encounters discontinuous points of wave impedance, which are manifested as discontinuous points of voltage and current traveling wave energy distribution along the line in the line. The superposition point of the positive polarity with the largest amplitude corresponds to the distance from the hard fault point to the observation end, and the negative polarity point with the largest amplitude corresponds to the dual fault distance. In the flexible DC transmission system, the voltage levels are relatively high. Generally, the voltage and current are calculated at intervals of a certain distance step to describe the voltage and current distribution of each point on the whole line, and the combination of time dimension and distance dimension is obtained. Forward current traveling wave and reverse current traveling wave, and then construct the analytic expression of the current traveling wave mutation detection function in forward and reverse directions, and use the product of the two analytic expressions to construct the integral function. Measure the distance of the terminal to realize fault location.

The specific steps are:

Step1: When the line is faulty, collect the fault electrical signal of the line. In the MMC-HVDC DC transmission system, the current traveling wave cannot be directly measured at the measuring end, and the high-frequency voltage traveling wave cannot be directly obtained through the voltage transformer. Usually, the voltage traveling wave is obtained by passing the traveling wave coupling box. popular wave, and then indirectly measure the voltage signal through the current transformer.

Step2: According to the data collected by the measurement terminal, calculate the voltage and current every certain distance step, and obtain the voltage and current distribution of each point on the whole line. The specific steps are as follows:

Step2.1: In the MMC-HVDC direct current transmission system of the actual project, the transmission distance is long, and there is electromagnetic coupling between the positive and negative lines that are parallel to each other. Therefore, it is necessary to change the phase mode to eliminate the line coupling between different wires. , after the phase mode transformation, the line mode component and the zero mode component independent of each other are obtained. Since the propagation path of the zero-mode component is between the wire and the ground, environmental factors will cause a large amount of attenuation of the zero-mode component, while the wave velocity of the linear-mode component is relatively stable, and there will not be a lot of attenuation. Therefore, we choose to extract the linear-mode component. Characteristics. The positive and negative voltages of the transmission line are decoupled by using the Karen Bell transform, and the line mode traveling wave is obtained. Calculated as follows:

In the formula, U _M and U _N represent the positive and negative voltages, respectively, I _M and I _N represent the positive and negative currents, U ₁ and U ₀ represent the line-mode voltage and zero-mode voltage, respectively, and I ₁ and I ₀ line-mode currents and the zero-mode current, A is the Karen Bell phase mode change matrix.

Step2.2: Since the MMC-HVDC DC transmission is long-distance transmission, the distributed capacitance will have a greater impact on the current distribution of the line. The Bergeron transmission line equivalent model is used to equivalence the line. According to the voltage and current data collected at the measuring end, the voltage and current are calculated every 1 km step, and the voltage and current distribution of each point on the whole line are obtained. 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 is the current measured by the high-speed acquisition device at a certain time on the transmission line, u _M,s is a certain time on the transmission line The voltage measured by the high-speed acquisition device, _rs is the line mode resistance per unit length, and v _s is the line mode wave velocity.

Step3: According to the voltage and current of each point of the transmission line, calculate the current direction traveling wave series combining the time dimension and the distance dimension, where i ⁺ _{x, s} is the forward current traveling wave, which is defined as the propagation from the sending end to the receiving end, that is From the M terminal to the N terminal, i ^- _{x, s} is the reverse current traveling wave, which is defined as propagating from the receiving end to the sending end, that is, from the N terminal to the M terminal. The calculation formula is as follows:

Step4: Perform differential calculation on the traveling wave series in the current direction to obtain the current gradient distributed along the line, and calculate the third power of the current gradient distributed along the line, specifically:

和

计算公式如下：Step4.1: In order to increase the reliability of the ranging device, amplify the sudden change of traveling wave energy. Differential calculation of traveling wave series in current direction to obtain current gradient along the line

and

Calculated as follows:

和

分别表示沿线分布的正向电流梯度和沿线分布的反向电流梯度。In the formula, k represents the kth sampling point, i ⁺ (k) and i ^- (k) represent the value of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, respectively,

and

represent the forward current gradient along the line and the reverse current gradient along the line, respectively.

和

的3次幂。Step4.2: Due to the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate its influence on the fault location, further highlight the mutation point amplitude that reflects the fault location information, and ensure the original pole of the mutation point. The property does not change, calculate the current gradient along the line

and

power of 3.

和反向电流梯度

的3次幂的第k个采样值开始，每5个电流梯度的3次幂的采样值求一次叠加值。可构造出正向行波和反向行波的突变检测函数解析表达式，计算公式如下：Step5: In order to suppress the effect of Gaussian noise, the forward current gradient distributed along the line is respectively

and the reverse current gradient

Starting from the k-th sampling value of the power of 3, the superposition value is calculated for every 5 sampling values of the power of 3 of the current gradient. The analytical expression of the mutation detection function of forward traveling wave and reverse traveling wave can be constructed, and the calculation formula is as follows:

In equations (9) and (10), k is the kth sampling point, E ⁺ is the analytical expression of the forward current traveling wave mutation detection function, and E ^- is the analytical expression of the reverse current traveling wave mutation detection function.

Step 6: In order to ensure the completeness of the information reflecting the fault location, and at the same time minimize the influence of other interference mutation points. Multiply the analytical expressions of the two mutation detection functions of the directional traveling wave as a product, and integrate the product in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ]. The calculation formula is as follows:

In the formula, t ₀ and t ₁ are the upper and lower limits of the first half time window of traveling wave observation, and t ₁ and t ₂ are the upper and lower limits of the lower half time window of traveling wave observation.

Step7: Since the discontinuous point in the energy distribution of the current traveling wave along the line can be regarded as caused by the superposition of the forward current traveling wave and the reverse current traveling wave, the integral in the two time windows is used as the two ranging functions, Pairing the extreme points in the two ranging functions, using the relationship between the extreme points and combining the distances corresponding to the extreme points and their amplitudes, the fault location can be achieved, specifically:

Step7.1: Take the integral of the two time windows as two ranging functions, and measure the distance from each extreme point of the integral function to the sending end in the time window [t ₀ , t ₁ ], as the solution set g _1—i =[x ₁₁ , x ₁₂ ,...,x _1n ], measure the distance from each extreme point of the integral function to the sending end in the time window [t ₁ , t ₂ ], as the solution set g _2—i =[ x ₂₁ ,x ₂₂ ,...,x _2n ], and use each element in the solution set g _1-i as a reference value to match each element in the solution set g _2-i , and the matched elements must satisfy A set of extreme points whose amplitude is greater than 0 and the other whose amplitude is less than 0 satisfy the summation equal to or approximately equal to the full length of the line is the extreme point A(x) of the response fault position and the extreme point of the response dual fault position B(x);

Step7.2: Determine whether the amplitude of the extreme point in the solution set g _1-i that satisfies the condition is greater than 0;

If yes, then this point is the extreme point A(x) reflecting the fault location, and the fault distance x _f is the line length x _m1 corresponding to this point;

If not, the point is the extreme point B(x) of the dual fault location, and the fault distance x _f is the full length of the line l minus the length x _m2 corresponding to this point.

An MMC-HVDC direct current transmission line fault location system, which mainly includes:

The electrical signal acquisition module is used to collect and store fault voltage data, and is installed and operated in the high-speed data acquisition device at the sending end or/and the receiving end of the transmission line;

The numerical calculation module is used to perform differential calculation on the current direction traveling wave series and obtain its high power. Secondly, use the current direction traveling wave differential high power to construct the mutation detection function analysis of the forward traveling wave and the reverse traveling wave respectively. expression;

The fault location module is used to construct an integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows respectively, and use the maximum value point of the integral function to perform the fault location measurement. distance results.

The electrical signal acquisition module specifically includes:

The data acquisition unit is used to collect the analog signal output by the secondary side of the transformer;

The analog-to-digital conversion unit is used to convert the input signal from analog to digital;

The protection starting unit is used to compare the magnitude of the digital signal with the preset protection starting threshold. If the digital signal is greater than the preset starting threshold, read the starting time and store the relevant fault voltage value.

The numerical calculation module specifically includes:

The line-mode conversion unit is used to decouple the positive and negative voltages of the transmission line to obtain the line-mode traveling wave;

The numerical calculation unit is used to calculate the product of the analytical expressions of traveling waves in two directions, and integrate the product within the time windows of [t ₀ , t ₁ ] and [t ₁ , t ₂ ].

The fault location module specifically includes:

The integral function construction unit integrates the product of the analytical expressions of the traveling waves in two directions in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ] respectively to obtain the integral function;

The distance measurement unit is used to measure the distance corresponding to each maximum point of the integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows.

The maximum point matching unit is used to perform pairwise matching of the maximum points in the two time windows, and filter out a pair of maximum points that meet the conditions.

The maximum value judgment unit is used to judge whether the maximum value of the integral function in the [t ₀ , t ₁ ] time window is greater than zero.

The beneficial effects of the present invention are:

1. The present invention performs fault location for MMC-HVDC direct current transmission lines, adopts single-ended traveling wave for fault location, only needs to collect single-ended fault traveling wave data, and does not need to consider the problem of weak communication synchronization.

2. The present invention performs differential, exponentiated, superimposed and other calculations on traveling waves, so that the amplitude of the interference extreme point is small and easy to be eliminated, and the influence of the interference extreme point on the fault distance judgment can be effectively eliminated.

3. Compared with the traditional single-ended traveling wave ranging method, the present invention is less affected by the line length, and can still ensure higher measurement accuracy when a fault occurs at the far end of a long-distance transmission line.

4. The invention does not need to calibrate the wave head, avoids the influence of inaccurate wave head calibration on fault location, and has high reliability and high precision.

Description of drawings

Fig. 1 is a simulation model topology diagram of the present invention;

2 is a system block diagram of Embodiment 1 of the present invention;

Fig. 3 is the first half time window integral function result diagram of the embodiment 1 of the present invention;

Fig. 4 is the second half time window integral function result diagram of the embodiment 1 of the present invention;

Fig. 5 is the first half time window integral function result diagram of the embodiment 2 of the present invention;

FIG. 6 is a result diagram of the second half time window integral function of the second embodiment of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Example 1: Example 1: MMC-HVDC simulation model system As shown in Figure 1, the entire line is 400km long and the voltage level is ±800kV. Set the fault to occur at 145km of the line, set the fault type to positive grounding permanent fault, set the transition resistance to 0.01Ω, and set the sampling rate to 1MHz. The specific steps to be implemented are:

In the MMC-HVDC DC transmission system, the current traveling wave cannot be directly measured at the measuring end, and the high-frequency voltage traveling wave cannot be directly obtained through the voltage transformer. Usually, the voltage traveling wave is obtained by passing the traveling wave coupling box. popular wave, and then indirectly measure the voltage signal through the current transformer. When the line is faulty, the high-speed acquisition device is used to collect the fault voltage signal of the line.

In the MMC-HVDC direct current transmission system of the actual project, the transmission distance is long, and there is electromagnetic coupling between the positive and negative lines that are parallel to each other. Therefore, it is necessary to change the phase mode to eliminate the line coupling between different wires. After the phase mode transformation Obtain the line mode component and zero mode component independent of each other. Since the propagation path of the zero-mode component is between the wire and the ground, environmental factors will cause a large amount of attenuation of the zero-mode component, while the wave velocity of the linear-mode component is relatively stable, and there will not be a lot of attenuation. Therefore, we choose to extract the linear-mode component. Characteristics. The positive and negative voltages of the transmission line are decoupled by using the Karen Bell transform, and the line mode traveling wave is obtained. Calculated as follows:

In the formula, U _M and U _N represent the positive and negative voltages, respectively, I _M and I _N represent the positive and negative currents, U ₁ and U ₀ represent the line-mode voltage and zero-mode voltage, respectively, and I ₁ and I ₀ line-mode currents and the zero-mode current, A is the Karen Bell phase mode change matrix.

Since the MMC-HVDC DC transmission is long-distance transmission, the distributed capacitance will have a greater impact on the current distribution of the line. The Bergeron transmission line equivalent model is used to equivalence the line.

Specific steps are as follows:

Calculate the voltage and current every 1 km step, and obtain the voltage and current distribution of each point on the whole line. 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 is the current measured by the high-speed acquisition device at a certain time on the transmission line, u _M,s is a certain time on the transmission line The voltage measured by the high-speed acquisition device, _rs is the line mode resistance per unit length, and v _s is the line mode wave velocity.

According to the voltage and current at each point of the transmission line, calculate the current direction traveling wave series combining the time dimension and the distance dimension, where i ⁺ _{x, s} is the forward current traveling wave, which is defined as the propagation from the sending end to the receiving end, that is, from M From the end to the N end, i ^- _{x, s} is the reverse current traveling wave, which is defined as the propagation from the receiving end to the sending end, that is, from the N end to the M end. The calculation formula is as follows:

和

计算公式如下：In order to increase the reliability of the ranging device, the sudden change of traveling wave energy is amplified. Differential calculation of traveling wave series in current direction to obtain current gradient along the line

and

Calculated as follows:

和

分别表示沿线分布的正向电流梯度和沿线分布的反向电流梯度。In the formula, k represents the kth sampling point, i ⁺ (k) and i ^- (k) represent the value of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, respectively,

and

represent the forward current gradient along the line and the reverse current gradient along the line, respectively.

和

的3次幂。Due to the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate its influence on the fault location, the amplitude of the mutation point that reflects the fault location information is further highlighted, and the original polarity of the mutation point is not changed. , calculates the current gradient distributed along the line

and

power of 3.

和反向电流梯度

的3次幂的第k个采样值开始，每5个电流梯度的3次幂的采样值求一次叠加值。可构造出正向行波和反向行波的突变检测函数解析表达式，计算公式如下：In order to flatten the effect of suppressing Gaussian noise, the forward current gradients distributed along the line are respectively

and the reverse current gradient

Starting from the k-th sampling value of the power of 3, the superposition value is calculated for every 5 sampling values of the power of 3 of the current gradient. The analytical expression of the mutation detection function of forward traveling wave and reverse traveling wave can be constructed, and the calculation formula is as follows:

In the formula, k is the kth sampling point, E ⁺ is the analytical expression of the forward current traveling wave mutation detection function, and E ^- is the analytical expression of the reverse current traveling wave mutation detection function.

In order to ensure the completeness of reflecting the fault location information, and at the same time minimize the influence of other interference mutation points. Multiply the analytical expressions of the two mutation detection functions of the directional traveling wave as a product, and integrate the product in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ]. The calculation formula is as follows:

In the formula, t ₀ and t ₁ are the upper and lower limits of the first half time window of traveling wave observation, and t ₁ and t ₂ are the upper and lower limits of the lower half time window of traveling wave observation. In this embodiment, two consecutive time windows [t ₀ , t ₀ +l/(2v)] and [t ₀ +l/(2v), t ₀ +l/v] are taken.

Since the discontinuous point in the energy distribution of the current traveling wave along the line can be regarded as caused by the superposition of the forward current traveling wave and the reverse current traveling wave, the integrals in the two time windows are used as two ranging functions. From Figure 3 and Figure 4, Figure 3 is the distribution result of the integral function in the [t ₀ ,t ₀ +l/(2v)] time window. It can be seen that the distance from each extreme point of the integral function to the sending end is obtained by measuring Constitute the solution set g _1—i =[145,146]km; Figure 4 is the distribution result of the integral function in the [t ₀ +l/(2v), t ₀ +l/v] time window, it can be seen that the integral function is obtained by measuring The distance from each extreme point to the sending end constitutes a solution set g _2—i =[255,256]km. Use each element in the solution set g _1-i as the reference value to match with each element in the solution set g _2-i , because 145+255=400km, that is, the addition is equal to the full length of the line, which satisfies the condition, and corresponds to 145km The amplitude of the maximum point is greater than zero, and at the same time 146+256≠400km, the condition is not met, that is, the sum is not equal to the full length of the line, so the extreme point with a distance of 145km to the sending end is the extreme point A ( x), the extreme point with a distance of 255km to the sending end is the extreme point B(x) of the response dual fault location, so the fault distance x _f is 145km.

2 is a functional block diagram of the MMC-HVDC direct current transmission line fault location system provided by the present invention, which specifically includes:

The electrical signal acquisition module is used to collect and store fault voltage data, and is installed and operated in the high-speed data acquisition device at the sending end or/and the receiving end of the transmission line;

The numerical calculation module is used to perform differential calculation on the current direction traveling wave series and obtain its high power. Secondly, use the current direction traveling wave differential high power to construct the mutation detection function analysis of the forward traveling wave and the reverse traveling wave respectively. expression;

The fault location module is used to construct an integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows respectively, and use the maximum value point of the integral function to perform the fault location measurement. distance results.

The electrical signal acquisition module specifically includes:

The data acquisition unit is used to collect the analog signal output by the secondary side of the transformer;

The analog-to-digital conversion unit is used to convert the input signal from analog to digital;

The protection starting unit is used to compare the magnitude of the digital signal with the preset protection starting threshold. If the digital signal is greater than the preset starting threshold, read the starting time and store the relevant fault voltage value.

The numerical calculation module specifically includes:

The line-mode conversion unit is used to decouple the positive and negative voltages of the transmission line to obtain the line-mode traveling wave;

The numerical calculation unit is used to calculate the product of the analytical expressions of traveling waves in two directions, and integrate the product within the time windows of [t ₀ , t ₁ ] and [t ₁ , t ₂ ].

The fault location module specifically includes:

The integral function construction unit is used to integrate the product of the analytical expressions of traveling waves in two directions in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ] respectively to obtain the integral function;

The distance measurement unit is used to measure the distance corresponding to each maximum point of the integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows.

The maximum point matching unit is used to perform pairwise matching of the maximum points in the two time windows, and filter out a pair of maximum points that meet the conditions.

The maximum value judgment unit is used to judge whether the maximum value of the integral function in the [t ₀ , t ₁ ] time window is greater than zero.

Therefore, it is concluded that the fault distance x _f is 145km.

Embodiment 2: MMC-HVDC simulation model system As shown in Figure 1, the entire line is 400km long, and the voltage level is ±800kV. Set the fault to occur at 260km of the line, set the fault type to positive grounding permanent fault, set the transition resistance to 0.01Ω, and set the sampling rate to 1MHz. The specific steps to be implemented are:

In the MMC-HVDC DC transmission system, the current traveling wave cannot be directly measured at the measuring end, and the high-frequency voltage traveling wave cannot be directly obtained through the voltage transformer. Usually, the voltage traveling wave is obtained by passing the traveling wave coupling box. popular wave, and then indirectly measure the voltage signal through the current transformer. When the line is faulty, the high-speed acquisition device is used to collect the fault voltage signal of the line.

In the MMC-HVDC direct current transmission system of the actual project, the transmission distance is long, and there is electromagnetic coupling between the positive and negative lines that are parallel to each other. Therefore, it is necessary to change the phase mode to eliminate the line coupling between different wires. After the phase mode transformation Obtain the line mode component and zero mode component independent of each other. Since the propagation path of the zero-mode component is between the wire and the ground, environmental factors will cause a large amount of attenuation of the zero-mode component, while the wave velocity of the linear-mode component is relatively stable, and there will not be a lot of attenuation. Therefore, we choose to extract the linear-mode component. Characteristics. The positive and negative voltages of the transmission line are decoupled by using the Karen Bell transform, and the line mode traveling wave is obtained. Calculated as follows:

In the formula, U _M and U _N represent the positive and negative voltages, respectively, I _M and I _N represent the positive and negative currents, U ₁ and U ₀ represent the line-mode voltage and zero-mode voltage, respectively, and I ₁ and I ₀ line-mode currents and the zero-mode current, A is the Karen Bell phase mode change matrix.

Since the MMC-HVDC DC transmission is long-distance transmission, the distributed capacitance will have a greater impact on the current distribution of the line. The Bergeron transmission line equivalent model is used to equivalence the line.

Specific steps are as follows:

Calculate the voltage and current every 1 km step, and obtain the voltage and current distribution of each point on the whole line. 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 is the current measured by the high-speed acquisition device at a certain time on the transmission line, u _M,s is a certain time on the transmission line The voltage measured by the high-speed acquisition device, _rs is the line mode resistance per unit length, and v _s is the line mode wave velocity.

According to the voltage and current at each point of the transmission line, calculate the current direction traveling wave series combining the time dimension and the distance dimension, where i ⁺ _{x, s} is the forward current traveling wave, which is defined as the propagation from the sending end to the receiving end, that is, from M From the end to the N end, i ^- _{x, s} is the reverse current traveling wave, which is defined as the propagation from the receiving end to the sending end, that is, from the N end to the M end. The calculation formula is as follows:

和

计算公式如下：In order to increase the reliability of the ranging device, the sudden change of traveling wave energy is amplified. Differential calculation of traveling wave series in current direction to obtain current gradient along the line

and

Calculated as follows:

和

分别表示沿线分布的正向电流梯度和沿线分布的反向电流梯度。In the formula, k represents the kth sampling point, i ⁺ (k) and i ^- (k) represent the value of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, respectively,

and

represent the forward current gradient along the line and the reverse current gradient along the line, respectively.

和

的3次幂。Due to the existence of the interference mutation point, in order to further reduce the amplitude of the interference mutation point to eliminate its influence on the fault location, the amplitude of the mutation point that reflects the fault location information is further highlighted, and the original polarity of the mutation point is not changed. , calculates the current gradient distributed along the line

and

power of 3.

和反向电流梯度

的3次幂的第k个采样值开始，每5个电流梯度的3次幂的采样值求一次叠加值。可构造出正向行波和反向行波的突变检测函数解析表达式，计算公式如下：In order to flatten the effect of suppressing Gaussian noise, the forward current gradients distributed along the line are respectively

and the reverse current gradient

Starting from the k-th sampling value of the power of 3, the superposition value is calculated for every 5 sampling values of the power of 3 of the current gradient. The analytical expression of the mutation detection function of forward traveling wave and reverse traveling wave can be constructed, and the calculation formula is as follows:

In the formula, k is the kth sampling point, E ⁺ is the analytical expression of the forward current traveling wave mutation detection function, and E ^- is the analytical expression of the reverse current traveling wave mutation detection function.

In order to ensure the completeness of reflecting the fault location information, and at the same time minimize the influence of other interference mutation points. Multiply the analytical expressions of the two mutation detection functions of the directional traveling wave as a product, and integrate the product in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ]. The calculation formula is as follows:

In the formula, t ₀ and t ₁ are the upper and lower limits of the first half time window of traveling wave observation, and t ₁ and t ₂ are the upper and lower limits of the lower half time window of traveling wave observation. In this embodiment, two consecutive time windows [t ₀ , t ₀ +l/(2v)] and [t ₀ +l/(2v), t ₀ +l/v] are taken.

Since the discontinuous point in the energy distribution of the current traveling wave along the line can be regarded as caused by the superposition of the forward current traveling wave and the reverse current traveling wave, the integrals in the two time windows are used as two ranging functions. From Figure 5 and Figure 6, Figure 5 is the distribution result of the integral function in the [t ₀ , t ₀ +l/(2v)] time window. It can be seen that the distance from each extreme point of the integral function to the sending end is obtained by measuring Constitute the solution set g _1—i =[140,141]km; Figure 6 is the distribution result of the integral function in the [t ₀ +l/(2v), t ₀ +l/v] time window, it can be seen that the integral function is obtained by measuring The distance from each extreme point to the sending end constitutes a solution set g _2—i =[260,261]km. Use each element in the solution set g _1-i as the reference value to match with each element in the solution set g _2-i , because 140+260=400km, that is, the addition is equal to the full length of the line, which satisfies the condition, and corresponds to 140km The amplitude of the maximum point is less than zero, and at the same time 141+261≠400km, the condition is not met, that is, the sum is not equal to the full length of the line, so the extreme point with a distance of 260km to the sending end is the extreme point A ( x), the extreme point with a distance of 140km to the sending end is the extreme point B(x) of the dual fault position, so the fault distance x _f is the total length l of the transmission line minus the length corresponding to this point, that is 400-140=260km, the fault distance is 260km.

The MMC-HVDC direct current transmission line fault location system of this embodiment includes:

The electrical signal acquisition module is used to collect and store fault voltage data, and is installed and operated in the high-speed data acquisition device at the sending end or/and the receiving end of the transmission line;

The numerical calculation module is used to perform differential calculation on the current direction traveling wave series and obtain its high power. Secondly, use the current direction traveling wave differential high power to construct the mutation detection function analysis of the forward traveling wave and the reverse traveling wave respectively. expression;

The fault location module is used to construct an integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows respectively, and use the maximum value point of the integral function to perform the fault location measurement. distance results.

The electrical signal acquisition module specifically includes:

The data acquisition unit is used to collect the analog signal output by the secondary side of the transformer;

The analog-to-digital conversion unit is used to convert the input signal from analog to digital;

The protection starting unit is used to compare the magnitude of the digital signal with the preset protection starting threshold. If the digital signal is greater than the preset starting threshold, read the starting time and store the relevant fault voltage value.

The numerical calculation module specifically includes:

The line-mode conversion unit is used to decouple the positive and negative voltages of the transmission line to obtain the line-mode traveling wave;

The numerical calculation unit is used to calculate the product of the analytical expressions of traveling waves in two directions, and integrate the product within the time windows of [t ₀ , t ₁ ] and [t ₁ , t ₂ ].

The fault location module specifically includes:

The integral function construction unit is used to integrate the product of the analytical expressions of traveling waves in two directions in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ] respectively to obtain the integral function;

The distance measurement unit is used to measure the distance corresponding to each maximum point of the integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows.

The maximum point matching unit is used to perform pairwise matching of the maximum points in the two time windows, and filter out a pair of maximum points that meet the conditions.

The maximum value judgment unit is used to judge whether the maximum value of the integral function in the [t ₀ , t ₁ ] time window is greater than zero.

Therefore, it is concluded that the fault distance x _f is 260km.

The simulation verification of the MMC-HVDC direct current transmission line with a line length of 400km occurs in half-line faults and half-line external faults, indicating that the method and system for fault location of MMC-HVDC direct current transmission lines disclosed in the present invention are highly reliable. ,High precision.

The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and can also be made within the scope of knowledge possessed by those of ordinary skill in the art without departing from the spirit of the present invention. Various changes.

Claims (12)

1. a MMC-HVDC direct current transmission line fault location method is characterized in that: Step1: When the line is faulty, collect the fault electrical signal of the line; Step2: According to the data collected by the measurement terminal, calculate the voltage and current every certain distance step, and obtain the voltage and current distribution of each point on the whole line; Step3: According to the voltage and current of each point of the transmission line, calculate the current direction traveling wave series combining the time dimension and the distance dimension; Step4: Perform differential calculation on the traveling wave series in the current direction, and obtain its high power; Step5: Construct the analytical expression of the mutation detection function of the forward traveling wave and the reverse traveling wave by using the high power of the current direction traveling wave difference; Step6: Take the product of the two analytical expressions of the directional traveling wave, and integrate the product in two consecutive time windows; Step7: Use the integrals in two consecutive time windows as two ranging functions, pair the extreme points in the two ranging functions, use the relationship between the extreme points and combine the distances corresponding to the extreme points with their corresponding distances. Amplitude can realize fault location. 2. The MMC-HVDC direct current transmission line fault location method according to claim 1, wherein the fault electrical signal in the Step 1 is acquired by a high-speed acquisition device installed on the MMC-HVDC direct current transmission line bus. 3. MMC-HVDC direct current transmission line fault location method according to claim 1, is characterized in that, described Step2 is specifically: Step2.1: Use the Karen Bell transform to decouple the positive and negative voltages of the transmission line to obtain the line mode traveling wave:

In the formula, U _M and U _N represent the positive and negative voltages, respectively, I _M and I _N represent the positive and negative currents, U ₁ and U ₀ represent the line-mode voltage and zero-mode voltage, respectively, and I ₁ and I ₀ line-mode currents and the zero-mode current, A is the Karen Bell phase mode change matrix; Step2.2: According to the voltage and current data collected by the measuring terminal, calculate the voltage and current every 1 km step, and obtain the voltage and current distribution of each point on 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 is the current measured by the high-speed acquisition device at a certain time on the transmission line, u _M,s is a certain time on the transmission line The voltage measured by the high-speed acquisition device, _rs is the line mode resistance per unit length, and v _s is the line mode wave velocity. 4. The method for locating faults in MMC-HVDC direct current transmission lines according to claim 1, wherein in the Step 3, the current direction traveling wave series comprises a forward current traveling wave i ⁺ _{x, s} and a reverse current traveling wave Current traveling wave i ^- _x,s ;

The forward current traveling wave is defined as propagating from the sending end to the receiving end, and the reverse current traveling wave is defined as propagating from the receiving end to the sending end. 5. MMC-HVDC direct current transmission line fault location method according to claim 1, is characterized in that, described Step4 is specifically: Step4.1: Perform differential calculation on the traveling wave series in the current direction to obtain the current gradient distributed along the line

and

In the formula, k represents the kth sampling point, i ⁺ (k) and i ^- (k) represent the value of the kth sampling point of the current forward traveling wave and the current reverse traveling wave, respectively,

and

represent the forward current gradient along the line and the reverse current gradient along the line, respectively; Step4.2: Calculate the current gradient distributed along the line

and

power of 3. 6. MMC-HVDC direct current transmission line fault location method according to claim 1, is characterized in that: described Step5 forward traveling wave and reverse traveling wave mutation detection function analytical expression is specifically:

In the formula, k is the kth sampling point, E ⁺ is the analytical expression of the forward current traveling wave mutation detection function, and E ^- is the analytical expression of the reverse current traveling wave mutation detection function. 7. MMC-HVDC direct current transmission line fault location method according to claim 1, is characterized in that: described Step6 is specifically: Multiply the analytic expression of the forward current traveling wave mutation detection function obtained in Step 5 and the analytical expression of the reverse current traveling wave mutation detection function, respectively, in [t ₀ , t ₁ ] and [t ₁ , t ₂ ] Integrate in successive time windows;

In the formula, t ₀ and t ₁ are the upper and lower limits of the first half time window of traveling wave observation, and t ₁ and t ₂ are the upper and lower limits of the lower half time window of traveling wave observation. 8. MMC-HVDC direct current transmission line fault location method according to claim 1, is characterized in that: described Step7 is specifically: Step7.1: Take the integral of the two time windows as two ranging functions, and measure the distance from each extreme point of the integral function to the sending end in the time window [t ₀ , t ₁ ], as the solution set g _1—i =[x ₁₁ , x ₁₂ ,...,x _1n ], measure the distance from each extreme point of the integral function to the sending end in the time window [t ₁ , t ₂ ], as the solution set g _2—i =[ x ₂₁ ,x ₂₂ ,...,x _2n ], and use each element in the solution set g _1-i as a reference value to match with each element in the solution set g _2-i , satisfying the addition equal to or approximate A set of extreme points equal to the full length of the line is the extreme point A(x) that reflects the fault location and the extreme point B(x) that responds to the dual fault location; Step7.2: Determine whether the amplitude of the extreme point in the solution set g _1-i that satisfies the condition is greater than 0; If yes, then this point is the extreme point A(x) reflecting the fault location, and the fault distance x _f is the line length x _m1 corresponding to this point; If not, the point is the extreme point B(x) of the dual fault location, and the fault distance x _f is the full length of the line l minus the length x _m2 corresponding to this point. 9. An MMC-HVDC direct current transmission line fault location system, characterized in that, comprising: The electrical signal acquisition module is used to collect and store fault voltage data, and is installed and operated in the high-speed data acquisition device at the sending end or/and the receiving end of the transmission line; The numerical calculation module is used to perform differential calculation on the current direction traveling wave series and obtain its high power. Secondly, use the current direction traveling wave differential high power to construct the mutation detection function analysis of the forward traveling wave and the reverse traveling wave respectively. expression; The fault location module is used to construct an integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows respectively, and use the maximum value point of the integral function to perform the fault location measurement. distance results. 10. The MMC-HVDC direct current transmission line fault location system according to claim 9, wherein the electrical signal acquisition module comprises: The data acquisition unit is used to collect the analog signal output by the secondary side of the transformer; The analog-to-digital conversion unit is used to convert the input signal from analog to digital; The protection starting unit is used to compare the magnitude of the digital signal with the preset protection starting threshold. If the digital signal is greater than the preset starting threshold, read the starting time and store the relevant fault voltage value. 11. The MMC-HVDC direct current transmission line fault location system according to claim 9, wherein the numerical calculation module specifically comprises: The line-mode conversion unit is used to decouple the positive and negative voltages of the transmission line to obtain the line-mode traveling wave; The numerical calculation unit is used to calculate the product of the analytical expressions of traveling waves in two directions. 12. The MMC-HVDC direct current transmission line fault location system according to claim 9, wherein the fault location module specifically comprises: The integral function construction unit integrates the product of the analytical expressions of the traveling waves in two directions in two successive time windows [t ₀ , t ₁ ] and [t ₁ , t ₂ ] respectively to obtain the integral function; A distance measurement unit, used to measure the distance corresponding to each maximum point of the integral function in the [t ₀ , t ₁ ] and [t ₁ , t ₂ ] time windows; The maximum point matching unit is used to match the maximum points in the two time windows in pairs, and filter out a pair of maximum points that meet the conditions; The maximum value judgment unit is used to judge whether the maximum value of the integral function in the [t ₀ , t ₁ ] time window is greater than zero.

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