CN111950125B - Method and system for judging fault type and position of direct-current cable - Google Patents

Abstract

The invention relates to a method and system for judging the fault type and position of a DC cable. The method comprises the following steps: respectively setting two isolation switches on the secondary side of the inverter and the primary side of the load DC/DC converter on the DC cable line. Magnetic ring; simulate the initial traveling wave of 1-mode fault voltage in a certain time window with different fault locations and different fault types according to the actual situation of the line, and obtain the fault simulation database, which is divided into internal fault and external fault simulation database; A traveling wave acquisition device is installed at one end of the line to record the initial traveling wave of the actual fault voltage; according to the initial traveling wave waveform of the actual fault voltage, the fault points are located inside and outside the area to distinguish; The initial traveling wave of the simulated voltage with the largest Pearson correlation coefficient of the wave is used to complete the judgment of the fault type and location. The invention can simultaneously complete the identification of the fault type and the location, and is convenient, quick, and high in accuracy.

Description

Method and system for judging type and location of DC cable faults

technical field

The invention relates to the technical field of electric power systems, in particular to a method and system for judging the fault type and position of a DC cable.

Background technique

In the event of a sudden fault in the DC distribution network, a step voltage drop will be caused. When the DC transmission cable fails (such as a two-pole short-circuit fault), the peak current in the capacitor discharge phase can reach 20-30 times the current during normal operation. With the continuous expansion of the DC distribution network, the load current increases rapidly, and even individual The regional short-circuit current has far exceeded the level of the circuit breakers currently used, causing more serious grid accidents. Therefore, how to quickly detect and determine the fault location and make further protection actions is of great significance for the safe operation of the DC distribution network. The voltage initial traveling wave method is a commonly used fault determination method for power grid lines at present. The double-ended method is to calculate the time difference between the partial discharge pulse signal and the two ends of the cable, and combine the length of the cable and the speed of the propagation wave to locate. Although the principle of the double-ended method is simpler and more reliable, it requires high-precision time synchronization at both ends of the cable to accurately obtain the absolute time when the partial discharge pulse reaches both ends of the cable. too high.

The single-ended method is to calculate the time difference between the time when the partial discharge pulse first arrives at the busbar on the local side and the arrival time of the reflected wave signal from the busbar at the opposite end of the cable. Relatively speaking, the single-ended method has lower hardware requirements. It only needs to install a signal detection device at the bus bar on one side of the line to extract and identify the initial traveling wave head of the voltage. There is no need for communication and signal synchronization with the opposite line, and the cost of distance measurement is greatly reduced. However, in single-ended traveling wave ranging, there are technical problems that the traveling wave refraction and reflection process is complex, and the traveling wave wave head identification is difficult. Further increase, the reliability is low.

The existing single-ended method also has the defect that the specific type and location of the fault cannot be accurately and quickly determined, and it can only confirm that a fault has occurred, but cannot determine whether the fault is a short-circuit fault, an open-circuit fault or an external impact fault; it is also difficult to be simple and fast. It can also accurately and reliably determine the specific location of the fault occurrence point, because the existing single-ended method uses the time difference to locate the fault point. The precise time information corresponding to the voltage signal has high requirements on the accuracy of the transient voltage measurement device.

More importantly, there is currently no method that can simultaneously determine the specific type and location of DC cable line faults efficiently and accurately.

SUMMARY OF THE INVENTION

Based on the above status quo, the main purpose of the present invention is to provide a method that can accurately and efficiently determine the specific type and location of DC cable line faults at the same time, and can overcome the difficulty of the voltage initial traveling wave head existing in the single-ended method in the prior art. Extraction and identification can only confirm that there is a fault, but cannot judge the type of fault, nor can it quickly and accurately locate the defect of the fault.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A method for judging the fault type and location of a DC cable, comprising the following steps:

S100: A magnetic ring is respectively set at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter on the DC cable line;

S200: Within the length of the DC cable line, from the beginning to the end of the line, take different positions at a certain interval distance, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit and external shock at each of the above-mentioned different positions. The initial traveling wave of the 1-mode fault voltage in a certain time window for three different fault types, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value, the fault simulation database is obtained, and the fault position is limited by the two magnetic rings. The fault simulation database is divided into the internal fault simulation database and the external fault simulation database, and the internal fault simulation database refers to the set of all simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings, The out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages where the fault point is located outside the area defined by the two magnetic rings;

S300: Set a traveling wave acquisition device at one end of the DC cable line to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and time window as S200 when the actual fault occurs. The abscissa of the traveling wave is the sampling point, and the ordinate is voltage value to obtain the initial traveling wave of the actual fault voltage;

S400: Judging whether the fault point is located within or outside the area defined by the two magnetic rings according to the waveform of the initial traveling wave of the actual fault voltage, wherein, if the waveform of the initial traveling wave of the actual fault voltage has an inflection point, the fault point corresponding to the waveform is located at In the area limited by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area limited by the two magnetic rings;

S500: According to the judgment result of S400, in the corresponding fault simulation database obtained in S200, search for the initial traveling wave of the simulated voltage with the largest Pearson correlation coefficient with the initial traveling wave of the actual fault voltage in step S300. The fault type corresponding to the wave is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault.

Preferably, the Pearson correlation coefficient in step S500 can be obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N].

Preferably, the method for judging the fault type and location of the DC cable further includes step S600: uploading the line fault type and location obtained in S500 to the fault processing center.

Preferably, in step S600, the uploading is implemented by using the LoRa wireless communication mode, with an external GPRS base station, and through the 5G public network.

Preferably, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable.

The present invention also provides a DC cable fault type and location judgment system, including:

The two magnetic rings are respectively arranged at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter on the DC transmission line;

The simulation unit is used to take different position points according to a certain interval distance from the beginning to the end of the DC cable line, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit, external The initial traveling wave of the 1-mode fault voltage in a certain time window when the three different fault types are impacted, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value. In the area limited by the ring, the fault simulation database is divided into an internal fault simulation database and an external fault simulation database. The internal fault simulation database refers to all the simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings. set, the out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages whose fault points are located outside the area defined by the two magnetic rings;

The traveling wave acquisition unit, set at one end of the DC cable line, is used to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and the same time window as described in the simulation unit when the actual fault occurs, and the abscissa of the traveling wave is the sampling point , the ordinate is the voltage value, and the initial traveling wave of the actual fault voltage is obtained;

The fault location area prediction unit judges whether the fault point is located in the area defined by the two magnetic rings or outside the area according to the waveform of the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit. If there is an inflection point, the fault point corresponding to the waveform is located in the area limited by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area limited by the two magnetic rings;

The fault type and location judgment unit searches for the Pearson correlation of the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit in the corresponding fault simulation database obtained by the simulation unit according to the judgment result of the fault location area prediction unit The initial traveling wave of the simulated voltage with the largest coefficient, the fault type corresponding to the initial traveling wave of the simulated voltage is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault.

Preferably, the Pearson correlation coefficient of the judgment unit can be obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N].

Preferably, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable.

Preferably, the DC cable fault type and location judging system further includes a transmission unit for uploading the line fault type and location obtained by the fault type and location judging unit to the fault processing center.

Preferably, the transmission unit includes a LoRa base station and a GPRS antenna.

Compared with the prior art, first of all, the present invention provides a method that can accurately and efficiently simultaneously determine the specific type and location of DC cable line faults. There is a single-ended method that can accurately locate the fault by obtaining the time difference between the fault traveling wave and the two ends of the line, and does not require a high-precision transient voltage measurement device, which significantly reduces the cost of cable fault monitoring and greatly improves the monitoring personnel. The work efficiency enables the monitoring personnel to quickly judge the fault location and reduce the power outage range when the fault occurs. At the same time, they can quickly arrange the troubleshooting personnel and corresponding troubleshooting measures according to the type of the fault, which significantly shortens the troubleshooting time and enables the cable line to recover quickly. In the normal state, the high-efficiency and stable operation of the power grid is ensured; at the same time, when the present invention is implemented, an internal fault simulation database and an external fault simulation database are established, and it is first identified whether the actual fault occurs in the area limited by the double magnetic ring or the area Then, the initial traveling wave of the actual fault voltage and the initial traveling wave of the simulated voltage in the corresponding simulation database are fitted to obtain the Pearson correlation coefficient. The technical means of fitting the simulated waveforms in the whole database with the simulated waveforms in the whole database greatly reduces the workload of the fitting calculation, further improves the judgment speed of the fault location and type, and enables the power grid to return to a normal state faster. The impact on the normal production and life of users is minimized.

In addition, the setting of the double magnetic ring can effectively slow down the traveling wave head, solve the problem of difficult and inaccurate identification of the wave head in the single-ended traveling wave method, and realize the application of the single-ended traveling wave method in the DC distribution network; On the one hand, the magnetic ring can affect the amplitude, steepness and peak time of the transient overvoltage (VFTO), so that the difference in the initial traveling wave waveform of the voltage at different positions becomes larger, and the faults at different positions can be clearly distinguished by the waveform. Furthermore, when the fault simulation database is established, the wave head brought by the double magnetic ring is easy to identify, and the external fault traveling wave waveforms at different positions are obviously different, which avoids the appearance of similar fault waveforms, and thus avoids the similarity of the positioning process. The confusion of waveforms makes fault location more accurate and reliable through simulation modeling; the Pearson correlation coefficient measures the waveform details of the initial traveling waves of the two voltages by calculating the covariance of the sampling points of the initial traveling waves of the two voltages, and then evaluates The similarity of the change trend of the two traveling waves is more rigorous than the similarity analysis by calculating the standard deviation of the sampling points of the two initial traveling waves of the voltage. accurate positioning of the location. In addition, the single-ended fault location method is adopted, which has low hardware requirements, low cost and easy implementation.

Other beneficial effects of the present invention will be illustrated in the specific embodiments through the introduction of specific technical features and technical solutions. Those skilled in the art should be able to understand the technical features and technical solutions through the introduction of these technical features and technical solutions. beneficial technical effects.

Description of drawings

Preferred embodiments of the method and system for judging the type and location of a DC cable fault according to the present invention will be described below with reference to the accompanying drawings. In the attached picture:

Fig. 1 is a flow chart of a method for judging fault types and locations of DC cables according to a preferred embodiment of the present invention;

2 is a schematic diagram of a magnetic ring frequency characteristic curve and an impedance equivalent circuit provided by the present invention;

Among them, (a) is the frequency characteristic curve of the magnetic ring; (b) is the equivalent circuit of the magnetic ring impedance after fitting (a) the frequency characteristic curve of the magnetic ring, and the left side is the equivalent circuit when the fitting result is a real number Schematic diagram, the right side is the equivalent circuit diagram when the fitting result is a complex number;

Fig. 3 is the waveform diagram of the initial traveling wave of the fault voltage at different positions of the DC line when the magnetic ring is not set;

Figure 4 is a waveform diagram of the initial traveling wave of the fault voltage at different positions of the DC line after the double magnetic ring is set;

5 is a schematic diagram of a fault monitoring model at different positions of a DC line with dual magnetic loops and a schematic diagram of the initial traveling wave of the obtained simulated voltage;

Among them, (a) is a schematic diagram of the fault monitoring model at different positions of the DC line with dual magnetic loops; (b) is the initial traveling wave of the fault voltage at different positions obtained by simulation.

Detailed ways

The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

Fig. 1 shows a method for judging the fault type and location of a DC cable according to a preferred embodiment of the present invention, which includes the following steps:

S100: A magnetic ring is respectively provided at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter on the DC cable line.

Specifically, the primary side and the secondary side are distinguished according to the direction of power transmission. The secondary side of the inverter refers to the side of the inverter close to the load; the primary side of the load DC/DC converter refers to the side close to the power supply. side. The impedance of the magnetic ring is related to the frequency of the signal flowing through the magnetic ring. The DC impedance of the magnetic ring itself is very small, and when the frequency is high, the DC impedance becomes larger. The frequency of the signal flowing through the magnetic ring includes the fundamental frequency and the harmonic frequency, and a transient high-frequency signal will appear in the event of a fault. When a fault occurs, the traveling wave boundary constructed by the double magnetic ring acts as the line boundary of the fault protection action, which can isolate the fault within the minimum range, and when the traveling wave reaches the magnetic ring, the wave is folded and reflected, which can quickly attenuate the fault The generated transient high-frequency signal makes the wave head significantly slower and improves the recognition degree. At the same time, it can affect the amplitude, steepness and peak time of the transient overvoltage (VFTO), so that the voltage of the fault at different positions can be initially The traveling wave difference becomes larger.

The influence of setting the dual magnetic rings on the initial traveling wave of the voltage can refer to the comparison between Figure 3 and Figure 4. The solid line in the figure is the initial voltage traveling wave of a fault within the area defined by the two magnetic rings, and the dotted line is outside the area. The voltage initial traveling wave of two faults.

Figure 3 is the waveform diagram of the initial traveling wave of the fault voltage at different positions of the DC line when the magnetic ring is not installed. It can be seen that the wave head interval time of the initial traveling wave of the voltage generated when an external fault located outside the limited area of the two magnetic rings occurs in the DC line It is short and difficult to identify; and the waveforms of the initial traveling waves of the faults at different positions have crosses, especially in the external faults, the fault voltage loses its high-frequency components due to the loss of its high-frequency components, mainly containing low-frequency components, the voltage initial changes gently, and the amplitude is small. The time-domain waveforms are highly similar and difficult to distinguish.

Figure 4 is the waveform diagram of the initial traveling wave of the fault voltage at different positions of the DC line after the double magnetic ring is set up. It can be seen that the core loss generated by the magnetic ring accelerates the attenuation of the fault voltage waveform, so that the ultra-fast transient overvoltage ( The amplitude, steepness and peak time of VFTO) have an effect, reduce the crossing of the initial traveling wave of the fault voltage at different positions, increase the amplitude change of the initial traveling wave of the external fault voltage, and slow down the wave head of the traveling wave. The waveform difference of the initial traveling wave of the fault voltage at different positions becomes larger, and it is easy to distinguish.

S200: Within the length of the DC cable line, from the beginning to the end of the line, take different positions at a certain interval distance, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit and external shock at each of the above-mentioned different positions. The initial traveling wave of 1-mode fault voltage in a certain time window for three different types of faults, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value, and the fault simulation database is obtained. The fault simulation database is divided into the internal fault simulation database and the external fault simulation database, and the internal fault simulation database refers to the set of all simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings, The out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages whose fault points are located outside the area defined by the two magnetic rings.

Specifically, the sampling point of the abscissa of the initial traveling wave of the voltage refers to the number of samples that can be collected within a certain time window under a certain sampling frequency. Different sampling points can also represent different time points within the time window. Suppose the sampling frequency is 2MHz, the sampling time corresponding to sampling point 1 is 0.5 μs, the sampling point 100 is corresponding to 50 μs, and the total sampling time of the abscissa is 50 μs. A point of 250 corresponds to a time of 125 μs, representing a time window of 125 μs.

Using the simulation software, according to the actual situation of the DC line, the effects of line impedance Z', admittance Y', surge impedance Z _C , the equivalent impedance of the magnetic ring set, the refraction coefficient _Ka and the attenuation coefficient γ of the DC distribution network are provided. The parameters of the fault voltage calculate the voltage value, where the line impedance Z' refers to the sum of the impedances of all components on the line, and the surge impedance Z _C refers to the fault current generated during the fault, which propagates at a certain speed in the line and is refracted. When , the resistance of the line to wave propagation is set, and a specific sampling frequency f and time window are set to simulate the initial traveling wave of the voltage when short-circuit, open-circuit and external impulse faults occur at different positions. Among them, the different positions of the fault can be taken from the beginning to the end of the line according to a certain interval distance.

When establishing the simulation model, in order to obtain the line impedance after setting the magnetic ring, it is necessary to obtain the equivalent circuit of the double magnetic ring first, and then connect it in series to the simulation model. The specific implementation process is as follows:

First, the impedance value Z of the magnetic ring can be calculated by the following formula:

Among them, A is the cross-sectional area of the magnetic ring, A=(r ₁ -r ₂ )×d, r ₁ is the outer radius of the magnetic ring, r ₂ is the inner radius; d is the thickness; l is the average circumference of the magnetic ring, l =π(r ₁ +r ₂ ); j is a complex symbol, μ′ and μ″ are the real and imaginary parts of the complex permeability, respectively. It can be seen that the impedance of the magnetic ring is related to the signal frequency f flowing through the magnetic ring.

Then, according to the frequency response curve of the impedance of the magnetic ring and the frequency of the signal flowing through the magnetic ring, perform vector fitting, divide the curve into N segments, and perform the fitting in sequence (refer to (a) in Figure 2 for the frequency response curve) ,Available:

Among them, N is the number of fitting segments, m, s, e, _{ri and p i are} all unknown parameters, which are calculated by the least squares method and iterative method according to the impedance curve, and the RLC equivalent circuit of the magnetic ring is obtained, as shown in the figure 2(b).

The terms m and se can be equal to the resistance R and the inductance L, respectively:

When _ri and _pi are real numbers, r/(sp) can be equivalent to the circuit on the left in (b) in Figure 2:

Among them, r is the zero point obtained by fitting, and p is the pole obtained by fitting.

When _ri and _pi are complex numbers, r/(sp) can be equivalent to the circuit on the right in (b) in Figure 2:

where r* and p* are the conjugates of zero r and pole p.

Finally, the equivalent circuit of the magnetic ring can be obtained by connecting all the equivalent circuits in series, and the simulation modeling process can be completed by adding the equivalent circuit string of the magnetic ring to the simulation model.

Other relevant parameters affecting the fault voltage can be calculated according to the following methods:

For HVDC transmission systems, the DC transmission lines generally use two identical pole lines arranged in parallel. There is an electrical coupling phenomenon between two-pole transmission lines. The following formula is used to decouple the decoupling matrix, and the 0-mode component and the 1-mode component of the line can be obtained.

Among them, S is the decoupling matrix, S ^-1 is the inverse matrix of the decoupling matrix, and S ^T is the transpose matrix of the decoupling matrix.

The two polar lines have symmetry, different polar lines have equal self-impedance and self-admittance, and there are mutual impedance and mutual admittance between the two polar lines. Let the unit self-impedance of each pole be Z ₀ =R ₀ +jωL ₀ , where R ₀ is the sum of all connected resistances of each pole, L ₀ is the sum of all connected inductances of each pole, which is the angular frequency; The mutual impedance is Z _m =R _m +jωL _m , where R _m is the sum of all the resistances between the two poles, and L _m is the sum of all the inductances between the two poles; the self-admittance of each pole is Y ₀ =G ₀ +jωC ₀ , where G ₀ is the sum of all the connected conductances of each pole, C ₀ is the sum of the reciprocals of the connected capacitances of each pole; the mutual admittance between poles is Y _m =G _m +jωC _m , where G _m is the connection between the two poles The sum of the conductances, C _m is the sum of the reciprocals of the capacitances connected between the two poles. Then the impedance matrix and admittance matrix of the DC cable are:

The diagonal impedance matrix and admittance matrix of the line are: Z'=S ^-1 ZS, Y'=S ^-1 YS (8).

According to the above formula, the surge impedance Z _C and the attenuation coefficient γ that affect the fault voltage can be calculated according to the actual situation of the line. Specifically, the following formula can be used to calculate:

Among them, R' is the resistance value of the whole circuit after setting the magnetic ring, L' is the inductance value of the whole circuit after setting the magnetic ring, G' is the conductance value of the whole circuit after setting the magnetic ring, C' is the whole circuit after setting the magnetic ring The capacitance value of , α is the real part after the attenuation coefficient is simplified.

The refraction coefficient k _α of the DC distribution network that affects the fault voltage can be calculated by the following formula:

Among them, Z _h is the equivalent impedance of the magnetic ring, and Z _c is the surge impedance.

Example: Based on the fault monitoring models at different positions of the DC line shown in (a) of FIG. 5 , the initial traveling wave waveform of the voltage is obtained by simulation. The parameters of the fault monitoring model are shown in Table 1:

Table 1 Parameters of the fault monitoring model at different positions of the DC line

It is assumed that the length of the faulted DC line L4 is L= _10km , and magnetic rings are respectively provided in H1 and H2, and it is assumed that the external fault f1 at the beginning of the line, the external fault f2 at the end of the line, and the internal fault point lx ₌ 6km at f3 A fault occurs; the harmonic current source is used to inject harmonics in the range of 0 to 1MHz, the frequency increment is 500Hz, and the initial traveling wave of the 1-mode voltage in the 2ms time window is recorded, and the sampling rate is 2MHz. The initial traveling wave waveform of the voltage obtained from the simulation is shown in (b) of Figure 5 .

It can be seen from (b) in Figure 5 that the waveforms of the voltage initial traveling wave at different positions are obviously different. There is an inflection point in the initial traveling wave of the internal fault voltage in the area defined by the two magnetic rings, and the external fault waveforms at the beginning and end of the DC cable line There is no inflection point, and the voltage initial traveling waves at different fault locations are easy to distinguish. No matter the fault type is short circuit, open circuit or external impact fault, there is an inflection point in the initial traveling wave waveform of the fault voltage located in the area defined by the two magnetic rings, but there is no inflection point in the initial traveling wave waveform of the voltage corresponding to the fault outside the area.

After acquiring the initial traveling wave fault database of the simulated voltage, the fault database can be further divided into an internal fault database and an external fault database according to whether the fault point is located in the area defined by the two magnetic rings.

S300: Set a traveling wave acquisition device at one end of the DC cable line to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and time window as S200 when the actual fault occurs. The abscissa of the traveling wave is the sampling point, and the ordinate is voltage value to obtain the initial traveling wave of the actual fault voltage.

Specifically, when a fault occurs, the traveling wave acquisition device is used to record the initial traveling wave of the 1-mode fault voltage with the same sampling frequency and time window as set in the simulation process of step S200 for subsequent analysis and judgment.

S400: Judging whether the fault point is located within or outside the area defined by the two magnetic rings according to the waveform of the initial traveling wave of the actual fault voltage, wherein, if the waveform of the initial traveling wave of the actual fault voltage has an inflection point, the fault point corresponding to the waveform is located at In the area defined by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area defined by the two magnetic rings.

Specifically, referring to FIG. 4 , it can be seen that when an internal fault occurs in the DC line, there is an inflection point in the initial voltage traveling wave, but when an external fault occurs in the DC line, there is no inflection point in the initial voltage traveling wave. Therefore, it can be quickly judged whether the fault point is located in the area defined by the two magnetic rings or outside the area according to whether the waveform of the initial traveling wave of the actual fault voltage has an inflection point.

The fault section can be quickly confirmed by the waveform. After the fault section is confirmed, the power outage range can be narrowed. At the same time, the fault simulation database corresponding to the subsequent specific positioning can be determined, which reduces the amount of calculation and improves the judgment of the fault type and fault location. The speed allows the investigators to deal with the fault in time, realize the rapid restoration of power supply, and ensure the efficient and stable operation of the power grid.

S500: According to the judgment result of S400, in the corresponding fault simulation database obtained in S200, search for the initial traveling wave of the simulated voltage with the largest Pearson correlation coefficient with the initial traveling wave of the actual fault voltage in step S300. The fault type corresponding to the wave is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault point.

Specifically, after it is determined whether the fault point is located in the area defined by the two magnetic rings or outside the area, in the corresponding fault simulation data obtained in step S200, the initial traveling wave of each simulated voltage and the initial traveling wave of the actual fault voltage are calculated within a certain time window The Pearson correlation coefficients of all sampling points of .

The similarity of the waveform details of the initial traveling wave of the voltage is measured by the Pearson correlation coefficient by calculating the covariance of the voltage at the sampling points of the initial traveling wave of the two voltages, and the similarity of the overall change trend of the initial traveling wave of the voltage is judged to accurately judge. Fault type, locate the fault point.

As a preferred embodiment, the Pearson correlation coefficient in step S500 can be obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N].

As a preferred embodiment, the method for judging the fault type and location of the DC cable further includes step S600: uploading the type and location of the line fault obtained in S500 to the fault processing center.

As a preferred implementation manner, the uploading in step S600 adopts LoRa wireless communication mode, an external GPRS base station is installed, and is realized through the 5G public network.

As a preferred embodiment, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable.

The split magnetic ring is easy to install at both ends of the DC distribution line, and the cost is low. In the actual project, the inner diameter of the magnetic ring is selected to be similar to the outer diameter of the cable, which is convenient for the installation and fixing of the magnetic ring.

In order to implement the above DC cable fault type and location determination method, the present invention also provides a DC cable fault type and location determination system, including:

The two magnetic rings are respectively arranged at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter in the range of the DC transmission line;

The simulation unit is used to take different position points according to a certain interval distance from the beginning to the end of the DC cable line, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit, external The initial traveling wave of the 1-mode fault voltage in a certain time window when the three different fault types are impacted, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value. In the area limited by the ring, the fault simulation database is divided into an internal fault simulation database and an external fault simulation database. The internal fault simulation database refers to all the simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings. set, the out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages whose fault points are located outside the area defined by the two magnetic rings;

The traveling wave acquisition unit, set at one end of the DC cable line, is used to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and the same time window as described in the simulation unit when the actual fault occurs, and the abscissa of the traveling wave is the sampling point , the ordinate is the voltage value, and the initial traveling wave of the actual fault voltage is obtained;

The fault location area prediction unit judges whether the fault point is located in the area defined by the two magnetic rings or outside the area according to the waveform of the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit. If there is an inflection point, the fault point corresponding to the waveform is located in the area limited by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area limited by the two magnetic rings;

The fault type and location judging unit, according to the judgment result of the fault location area judging unit, searches for the Pearson correlation coefficient with the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit in the corresponding fault simulation database obtained by the simulation unit The maximum simulated voltage initial traveling wave, the fault type corresponding to the simulated voltage initial traveling wave is the fault type of the actual fault, and the corresponding position point is the actual fault position point.

As a preferred embodiment, the Pearson correlation coefficient of the judgment unit can be obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N].

As a preferred embodiment, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable.

As a preferred embodiment, the DC cable fault type and location judging system further includes a transmission unit for uploading the line fault type and location obtained by the fault type and location judging unit to the fault processing center.

As a preferred embodiment, the transmission unit includes a LoRa base station and a GPRS antenna.

Compared with the prior art, first of all, the present invention provides a method that can accurately and efficiently simultaneously determine the specific type and location of DC cable line faults. There is a single-ended method that can accurately locate the fault by obtaining the time difference between the fault traveling wave and the two ends of the line, and does not require a high-precision transient voltage measurement device, which significantly reduces the cost of cable fault monitoring and greatly improves the monitoring personnel. The work efficiency enables the monitoring personnel to quickly judge the fault location and reduce the power outage range when the fault occurs. At the same time, they can quickly arrange the troubleshooting personnel and corresponding troubleshooting measures according to the type of the fault, which significantly shortens the troubleshooting time and enables the cable line to recover quickly. In the normal state, the high-efficiency and stable operation of the power grid is ensured; at the same time, when the present invention is implemented, an internal fault simulation database and an external fault simulation database are established, and it is first identified whether the actual fault occurs in the area limited by the double magnetic ring or the area Then, the initial traveling wave of the actual fault voltage and the initial traveling wave of the simulated voltage in the corresponding simulation database are fitted to obtain the Pearson correlation coefficient. The technical means of fitting the simulated waveforms in the whole database with the simulated waveforms in the whole database greatly reduces the workload of the fitting calculation, further improves the judgment speed of the fault location and type, and enables the power grid to return to a normal state faster. The impact on the normal production and life of users is minimized.

In addition, the setting of the double magnetic ring can effectively slow down the traveling wave head, solve the problem of difficult and inaccurate identification of the wave head in the single-ended traveling wave method, and realize the application of the single-ended traveling wave method in the DC distribution network; On the one hand, the magnetic ring can affect the amplitude, steepness and peak time of the transient overvoltage (VFTO), so that the difference in the initial traveling wave waveform of the voltage at different positions becomes larger, and the faults at different positions can be clearly distinguished by the waveform. Furthermore, when the fault simulation database is established, the wave head brought by the double magnetic ring is easy to identify, and the external fault traveling wave waveforms at different positions are obviously different, which avoids the appearance of similar fault waveforms, and thus avoids the similarity of the positioning process. The confusion of waveforms makes fault location more accurate and reliable through simulation modeling; the Pearson correlation coefficient measures the waveform details of the initial traveling waves of the two voltages by calculating the covariance of the sampling points of the initial traveling waves of the two voltages, and then evaluates The similarity of the change trend of the two traveling waves is more rigorous than the similarity analysis by calculating the standard deviation of the sampling points of the two initial traveling waves of the voltage. accurate positioning of the location. In addition, the single-ended fault location method is adopted, which has low hardware requirements, low cost and easy implementation.

It should be noted that, in the present invention, step numbers (letters or numbers) are used to refer to some specific method steps, which are only for the purpose of convenience and brevity of description, and are not intended to limit these method steps with letters or numbers. Order. Those skilled in the art can understand that the sequence of related method steps should be determined by the technology itself, and should not be unduly limited due to the existence of step numbers.

Those skilled in the art can understand that, under the premise of no conflict, the above preferred solutions can be freely combined and superimposed.

It should be understood that the above-mentioned embodiments are only exemplary rather than restrictive, and those skilled in the art can make various obvious or equivalent to the above-mentioned details without departing from the basic principles of the present invention. Modifications or substitutions will be included within the scope of the claims of the present invention.

Claims (10)

1. A method for judging fault type and position of a DC cable, characterized in that, comprising the following steps: S100: A magnetic ring is respectively set at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter on the DC cable line; S200: Within the length of the DC cable line, from the beginning to the end of the line, take different positions at a certain interval distance, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit and external shock at each of the above-mentioned different positions. The initial traveling wave of the 1-mode fault voltage in a certain time window for three different fault types, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value, the fault simulation database is obtained, and the fault position is limited by the two magnetic rings. The fault simulation database is divided into the internal fault simulation database and the external fault simulation database, and the internal fault simulation database refers to the set of all simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings, The out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages where the fault point is located outside the area defined by the two magnetic rings; S300: Set a traveling wave acquisition device at one end of the DC cable line to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and time window as S200 when the actual fault occurs. The abscissa of the traveling wave is the sampling point, and the ordinate is voltage value to obtain the initial traveling wave of the actual fault voltage; S400: Judging whether the fault point is located within or outside the area defined by the two magnetic rings according to the waveform of the initial traveling wave of the actual fault voltage, wherein, if the waveform of the initial traveling wave of the actual fault voltage has an inflection point, the fault point corresponding to the waveform is located at In the area limited by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area limited by the two magnetic rings; S500: According to the judgment result of S400, in the corresponding fault simulation database obtained in S200, search for the initial traveling wave of the simulated voltage with the largest Pearson correlation coefficient with the initial traveling wave of the actual fault voltage in step S300. The fault type corresponding to the wave is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault. 2. DC cable fault type and location judgment method according to claim 1, is characterized in that, the Pearson (Pearson) correlation coefficient in the step S500 is obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N]. 3. The method for judging the fault type and location of a DC cable according to claim 1 or 2, further comprising step S600: uploading the type and location of the line fault obtained in S500 to the fault processing center. 4. The method for judging the fault type and location of a DC cable according to claim 3, characterized in that, in step S600, the uploading adopts LoRa wireless communication mode, an external GPRS base station, and is realized through the 5G public network. 5 . The method for judging the fault type and position of a DC cable according to claim 1 or 2 , wherein the magnetic ring is a split magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable. 6 . 6. A DC cable fault type and location judgment system, characterized in that, comprising: The two magnetic rings are respectively arranged at the isolation switch of the secondary side of the inverter and the isolation switch of the primary side of the load DC/DC converter on the DC transmission line; The simulation unit is used to take different position points according to a certain interval distance from the beginning to the end of the DC cable line, and use a certain sampling frequency to simulate the occurrence of short-circuit, open-circuit, external The initial traveling wave of the 1-mode fault voltage in a certain time window when the three different fault types are impacted, the abscissa of the traveling wave is the sampling point, and the ordinate is the voltage value. In the area limited by the ring, the fault simulation database is divided into an internal fault simulation database and an external fault simulation database. The internal fault simulation database refers to all the simulated voltage initial traveling waves whose fault points are located in the area limited by the two magnetic rings. set, and the out-of-area fault simulation database refers to a set of initial traveling waves of all simulated voltages whose fault points are located outside the area defined by the two magnetic rings; The traveling wave acquisition unit, set at one end of the DC cable line, is used to record the initial traveling wave of the 1-mode fault voltage within the same sampling frequency and the same time window as the simulation unit when the actual fault occurs. The abscissa of the traveling wave is the sampling point, and the longitudinal The coordinate is the voltage value, and the initial traveling wave of the actual fault voltage is obtained; The fault location area prediction unit judges whether the fault point is located in the area defined by the two magnetic rings or outside the area according to the waveform of the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit. If there is an inflection point, the fault point corresponding to the waveform is located in the area limited by the two magnetic rings, otherwise, the fault point corresponding to the waveform is located outside the area limited by the two magnetic rings; The fault type and location judgment unit searches for the Pearson correlation of the initial traveling wave of the actual fault voltage obtained by the traveling wave acquisition unit in the corresponding fault simulation database obtained by the simulation unit according to the judgment result of the fault location area prediction unit The initial traveling wave of the simulated voltage with the largest coefficient, the fault type corresponding to the initial traveling wave of the simulated voltage is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault. 7. The DC cable fault type and position judgment system according to claim 6, wherein the Pearson (Pearson) correlation coefficient of the judgment unit is obtained by the following calculation method:

Among them, x _i and x _j are the voltage values corresponding to the i-th and j-th sampling points of an initial voltage traveling wave in the fault simulation database, and y _i and y _j are the i-th sum of the actual fault voltage initial traveling wave The voltage value corresponding to the jth sampling point, N is the number of sampling points in a certain time window, and the value range of i and j is [1, N]. 8 . The system for judging the fault type and position of a DC cable according to claim 6 or 7 , wherein the magnetic ring is a split magnetic ring, and the inner diameter of the magnetic ring is similar to the outer diameter of the cable. 9 . 9. The DC cable fault type and position judgment system according to claim 6 or 7, further comprising a transmission unit for uploading the line fault type and position obtained by the fault type and position judgment unit to the fault processing center . 10. The DC cable fault type and location judgment system according to claim 9, wherein the transmission unit comprises a LoRa base station and a GPRS antenna.

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