CN111950125B - Method and system for judging fault type and position of direct-current cable - Google Patents
Method and system for judging fault type and position of direct-current cable Download PDFInfo
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Abstract
The invention relates to a method and a system for judging the fault type and the position of a direct current cable, wherein the method comprises the following steps: two magnetic rings are respectively arranged on the secondary side of the inverter and the primary side of the load DC/DC converter on the direct current cable circuit; simulating 1-mode fault voltage initial traveling waves of a certain time window at different fault positions and different fault types according to the actual condition of a line to obtain a fault simulation database, and dividing the fault simulation database into an intra-area fault simulation database and an extra-area fault simulation database; arranging a traveling wave acquisition device at one end of the line, and recording the initial traveling wave of the actual fault voltage; distinguishing the fault points inside and outside the area according to the initial traveling wave waveform of the actual fault voltage; and searching the simulated voltage initial traveling wave with the maximum correlation coefficient with Pearson of the actual fault voltage initial traveling wave in the corresponding fault simulation database according to the judgment result, and finishing the judgment of the fault type and the fault position. The invention can simultaneously complete the identification of the fault type and the fault position, and has the advantages of convenience, rapidness and high accuracy.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a method and a system for judging the fault type and the position of a direct-current cable.
Background
When a sudden fault occurs in a direct current distribution network, a step voltage drop is caused. When a direct current transmission cable has a fault (such as a two-pole short circuit fault), the peak current of a capacitor discharge stage can reach 20-30 times of the current in normal operation, along with the continuous expansion of the scale of a direct current distribution network, the load current is rapidly increased, even the short circuit current of a certain region is far beyond the level of a current breaker, and more serious grid accidents are caused. Therefore, how to quickly detect and judge the fault position and make further protection actions has very important significance for the safe operation of the direct-current power distribution network. The voltage initial traveling wave method is a commonly used fault determination method for the power grid line at present, and most of the existing voltage initial traveling wave methods are mainly a double-end method and are assisted by a single-end method. The double-end method is to calculate the time difference of the partial discharge pulse signal reaching the two ends of the cable and combine the length of the cable, the propagation wave speed and the like to perform positioning. Although the principle of the double-end method is simpler and more reliable, high-precision time synchronization at two ends of the cable is needed, the absolute time of the partial discharge pulse reaching the two ends of the cable is accurately obtained, a large amount of implementation difficulty is high in the current direct-current line construction, and the cost of additional detection equipment is too high.
The single-end method is to position by calculating the time difference between the initial arrival of the partial discharge pulse at the local side bus and the arrival time of the reflected wave signal of the bus at the opposite end of the cable, and combining the propagation wave speed. Relatively speaking, the single-ended method has lower requirements on hardware, only needs to install a signal detection device at a bus on one side of a line, extracts and identifies the initial traveling wave head of the voltage, does not need to carry out communication and signal synchronization with the bus on the other side, and greatly reduces the distance measurement cost.
The existing single-end method has the defect that the specific type and position of the fault cannot be accurately and quickly judged, only the occurrence of the fault can be confirmed, and whether the fault is a short-circuit fault, a broken-circuit fault or an external impact fault cannot be judged; the specific position of the fault occurrence point is difficult to judge simply, quickly, accurately and reliably, and the existing single-end method adopts the time difference to position the core of the fault point, so as to determine the time difference of the fault traveling wave propagating to the two ends of the line, further realize the accurate positioning of the fault, require to obtain accurate time information corresponding to the transient voltage signal, and have high precision requirements on the transient voltage measuring device.
More importantly, no method exists at present, and the specific type and the occurrence position of the direct-current cable line fault can be judged efficiently and accurately at the same time.
Disclosure of Invention
Based on the above situation, the main objective of the present invention is to provide a means for accurately and efficiently determining the specific type and occurrence position of the dc cable line fault at the same time, and overcome the defects that the single-ended method in the prior art is difficult to extract and identify the initial traveling wave head of the voltage, can only confirm that the fault occurs but cannot determine the fault type, and cannot quickly and accurately locate the fault.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for judging the fault type and position of a direct current cable comprises the following steps:
s100: respectively arranging a magnetic ring at an isolating switch at the secondary side of the inverter and an isolating switch at the primary side of the load DC/DC converter on a direct-current cable circuit;
s200: taking different position points from the initial end to the tail end of the direct current cable line within the length range of the direct current cable line according to a certain interval distance, adopting a certain sampling frequency, simulating 1-mode fault voltage initial traveling wave of a certain time window when three different fault types of short circuit, open circuit and external impact respectively occur at each point of the different position points, wherein the abscissa of the traveling wave is a sampling point, the ordinate is a voltage value, and obtaining a fault simulation database, and dividing the fault simulation database into an in-region fault simulation database and an out-region fault simulation database according to whether the fault position is in the region limited by the two magnetic rings, the in-zone fault simulation database refers to all simulated voltage initial traveling wave sets of which fault points are located in a zone defined by the two magnetic rings, the outside-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located outside a zone limited by the two magnetic rings;
s300: arranging a traveling wave collecting device at one end of the direct current cable line to record a 1-mode fault voltage initial traveling wave with the same sampling frequency and time window as S200 when an actual fault occurs, wherein the abscissa of the traveling wave is a sampling point, and the ordinate is a voltage value to obtain the actual fault voltage initial traveling wave;
s400: judging whether a fault point is located in an area defined by the two magnetic rings or outside the area according to the waveform of the actual fault voltage initial traveling wave, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is located 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;
s500: according to the judgment result of S400, a simulated voltage initial traveling wave having the largest correlation coefficient with Pearson of the actual fault voltage initial traveling wave in step S300 is searched in the corresponding fault simulation database obtained in S200, 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 position point of the actual fault.
Preferably, the Pearson correlation coefficient in step S500 may be obtained by the following calculation:
wherein x is i And x j Corresponding voltage values y for the ith and jth sampling points of a voltage initial traveling wave in a fault simulation database i And y j Corresponding voltage values of the ith and jth sampling points of the initial traveling wave of the actual fault voltage, wherein N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N ]]。
Preferably, the method for determining the fault type and the fault position of the dc cable further includes step S600: and uploading the type and the position of the line fault obtained in the step S500 to a fault processing center.
Preferably, in step S600, the uploading is implemented by using an LoRa wireless communication mode and an external GPRS base station through a 5G public network.
Preferably, the magnetic ring is an open type magnetic ring, and the inner diameter of the magnetic ring is close to the outer diameter of the cable.
The invention also provides a system for judging the fault type and position of the direct current cable, which comprises:
the two magnetic rings are respectively arranged at an isolating switch at the secondary side of the inverter and an isolating switch at the primary side of the load DC/DC converter on the direct-current transmission line;
the simulation unit is used for taking different position points from the initial end to the tail end of the direct-current cable line within the length range of the direct-current cable line according to a certain interval distance, simulating 1-mode fault voltage initial traveling waves of a certain time window when three different fault types of short circuit, open circuit and external impact occur at each point of the different position points by adopting a certain sampling frequency, obtaining a fault simulation database by taking the abscissa of the traveling waves as a sampling point and the ordinate as a voltage value, and dividing the fault simulation database into an in-region fault simulation database and an out-region fault simulation database according to whether the fault position is in the region limited by the two magnetic rings, the in-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located in the zone defined by the two magnetic rings, the outside-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located outside a zone limited by the two magnetic rings;
the traveling wave acquisition unit is arranged at one end of the direct current cable line and used for recording a 1-mode fault voltage initial traveling wave which has the same sampling frequency and the same time window as the simulation unit when an actual fault occurs, the abscissa of the traveling wave is a sampling point, and the ordinate of the traveling wave is a voltage value, so that the actual fault voltage initial traveling wave is obtained;
the fault position area pre-judging unit is used for judging whether a fault point is positioned in an area limited by the two magnetic rings or not according to the waveform of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is positioned in the area limited by the two magnetic rings, and otherwise, the fault point corresponding to the waveform is positioned outside the area limited by the two magnetic rings;
and the fault type and position judging unit is used for searching the simulation voltage initial traveling wave with the maximum correlation coefficient with Pearson of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit in a corresponding fault simulation database obtained by the simulation unit according to the judgment result of the fault position region pre-judging unit, wherein the fault type corresponding to the simulation voltage initial traveling 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 of the determination unit may be calculated as follows:
wherein x is i And x j Corresponding voltage values y for the ith and jth sampling points of a voltage initial traveling wave in a fault simulation database i And y j The voltage values corresponding to the ith and jth sampling points of the initial traveling wave of the actual fault voltage are obtained, N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N]。
Preferably, the magnetic ring is an open type magnetic ring, and the inner diameter of the magnetic ring is close to the outer diameter of the cable.
Preferably, the system for judging the fault type and the position of the direct current cable further comprises a transmission unit, and the transmission unit is used for uploading the fault type and the position of the line obtained by the fault type and position judging unit to the fault processing center.
Preferably, the transmission unit includes an LoRa base station and a GPRS antenna.
Compared with the prior art, firstly, the invention provides a means for accurately and efficiently judging the specific type and the occurrence position of the direct current cable line fault at the same time, only the similarity comparison is carried out on the voltage initial traveling wave, the method of obtaining the time difference of the fault traveling wave propagating to the two ends of the line and further realizing the accurate positioning of the fault by the existing single-end method is abandoned, a high-precision transient voltage measuring device is not required, the cable fault monitoring cost is obviously reduced, and the working efficiency of monitoring personnel is greatly improved, so that monitoring personnel can quickly judge the fault position and reduce the power failure range when the fault occurs, meanwhile, troubleshooting personnel and corresponding troubleshooting measures can be quickly arranged immediately according to the fault types, so that the fault troubleshooting time is obviously shortened, the cable line can be quickly recovered to a normal state, and the efficient and stable operation of a power grid is ensured; meanwhile, when the method is implemented, an intra-area fault simulation database and an extra-area fault simulation database are established, whether the actual fault occurs in the area limited by the double magnetic rings or outside the area is identified, then the actual fault voltage initial traveling wave and the simulation voltage initial traveling wave in the corresponding simulation database are fitted to obtain the Pearson correlation coefficient, compared with the technical means that the faults in and outside the areas are not distinguished, and the waveform of the actual fault voltage initial traveling wave and the simulation waveform in the whole database are fitted, the working amount of fitting calculation is greatly reduced, the judgment speed of the fault position and type is further improved, the power grid can be quickly restored to a normal state, and the influence on the normal production and life of a power grid user is reduced to the minimum.
In addition, due to the arrangement of the double magnetic rings, on one hand, a traveling wave head can be effectively slowed down, the problems that the wave head is difficult to identify and not accurate enough in a single-ended traveling wave method are solved, and the application of the single-ended traveling wave method in a direct-current power distribution network is realized; on the other hand, the magnetic ring can affect the amplitude, the gradient and the peak time of the transient overvoltage (VFTO), so that the waveform difference of the initial voltage traveling waves at different positions is increased, and the faults at different positions can be clearly distinguished through the waveform; moreover, when a fault simulation database is established, wave heads caused by the double magnetic rings are easy to identify, the difference of external fault traveling wave waveforms at different positions is obvious, and similar fault waveforms are avoided, so that the confusion of similar waveforms in the positioning process is avoided, and the fault positioning through simulation modeling is more accurate and reliable; the Pearson correlation coefficient measures waveform details of the two voltage initial traveling waves by calculating covariance of sampling points of the two voltage initial traveling waves, further evaluates similarity of variation trends of the two traveling waves, is more rigorous than similarity analysis by calculating standard deviation of the sampling points of the two voltage initial traveling waves, and realizes accurate positioning of a fault position by carrying out similarity analysis and evaluation on the details and the variation trends of the voltage initial traveling waves. And a single-end fault positioning method is adopted, so that the requirement on hardware is low, the cost is low, and the implementation is easy.
Other advantages of the present invention will be described in the detailed description, which is provided by the technical features and technical solutions.
Drawings
Preferred embodiments of a dc cable fault type and location determination method and system according to the present invention will be described below with reference to the accompanying drawings. In the drawings:
fig. 1 is a flow chart of a method for determining the type and location of a dc cable fault according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of a frequency characteristic curve and an impedance equivalent circuit of a magnetic ring according to the present invention;
wherein, (a) is a magnetic ring frequency characteristic curve; (b) the method comprises the steps that (a) a magnetic ring impedance equivalent circuit after fitting of a magnetic ring frequency characteristic curve is achieved, wherein the left side is an equivalent circuit schematic diagram when a fitting result is a real number, and the right side is an equivalent circuit schematic diagram when the fitting result is a complex number;
FIG. 3 is a waveform diagram of initial traveling waves of fault voltages at different positions of a DC line when no magnetic ring is arranged;
FIG. 4 is a waveform diagram of initial traveling waves of fault voltages at different positions of a DC line after a double-magnetic-ring arrangement;
FIG. 5 is a schematic diagram of a fault monitoring model at different positions of a DC line with double magnetic rings and an obtained simulation voltage initial traveling wave;
wherein, (a) is a schematic diagram of a fault monitoring model at different positions of a direct current line provided with double magnetic rings; (b) and obtaining initial traveling waves of fault voltages at different positions for simulation.
Detailed Description
Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
Fig. 1 shows a method for determining the type and location of a dc cable fault according to a preferred embodiment of the present invention, which includes the following steps:
s100: and the isolation switch at the secondary side of the inverter and the isolation switch at the primary side of the load DC/DC converter on the direct-current cable circuit are respectively provided with a magnetic ring.
Specifically, the primary side and the secondary side are distinguished according to the direction of power transmission, and the secondary side of the inverter refers to the side of the inverter close to the load; the load DC/DC converter primary side is the side close to the power supply. 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 is small, and when the frequency is higher, the DC impedance is increased. The signal frequency flowing through the magnetic ring comprises fundamental wave frequency and harmonic frequency, and transient high-frequency signals can appear in the fault. When a fault occurs, the traveling wave boundary constructed by the double magnetic rings is used as the line boundary of fault protection action, so that the fault can be isolated in the minimum range, and when the traveling wave reaches the magnetic rings, the wave is folded and reflected, so that a transient high-frequency signal generated by the fault can be quickly attenuated, the wave head is obviously slowed down, the identification degree is improved, meanwhile, the amplitude, the gradient and the peak time of transient overvoltage (VFTO) can be influenced, and the voltage initial traveling wave difference of the faults at different positions is increased.
The effect of the double magnetic rings on the initial traveling wave of the voltage can be compared with fig. 3 and 4, wherein the solid line in the figure is the initial traveling wave of the voltage of one fault in the region defined by the two magnetic rings, and the dotted line is the initial traveling wave of the voltage of two faults outside the region.
Fig. 3 is a waveform diagram of the initial traveling wave of the fault voltage at different positions of the dc line when no magnetic ring is provided, and it can be seen that the interval time of the wave heads of the initial traveling wave of the voltage generated when an external fault occurs in the dc line outside the limited area of the two magnetic rings is short, and the identification is difficult; and the waveforms of the initial voltage traveling waves of the faults at different positions are crossed, especially the fault voltage mainly contains low-frequency components due to the loss of high-frequency components of the fault voltage under the external fault, the initial voltage change is smooth, the amplitude is small, the similarity between the time-domain waveforms is high, and the fault voltage is not easy to distinguish.
Fig. 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 rings are arranged, it can be seen that the magnetic core loss generated by the magnetic rings accelerates the attenuation of the fault voltage waveform, thereby affecting the amplitude, the gradient and the peak time of the Very Fast Transient Overvoltage (VFTO), reducing the crossing of the initial traveling wave of the fault voltage at different positions, increasing the amplitude change of the initial traveling wave of the external fault voltage, slowing down the wave head of the traveling wave, making the waveform difference of the initial traveling wave of the fault voltage at different positions larger, and easily distinguishing.
S200: taking different position points from the initial end to the tail end of the direct current cable line within the length range of the direct current cable line according to a certain interval distance, adopting a certain sampling frequency, simulating 1-mode fault voltage initial traveling waves of a certain time window when three different types of faults of short circuit, open circuit and external impact respectively occur at each point of the different position points, wherein the abscissa of the traveling waves is a sampling point, the ordinate is a voltage value, and obtaining a fault simulation database, and dividing the fault simulation database into an intra-area fault simulation database and an extra-area fault simulation database according to whether the fault position is in the area limited by the double magnetic rings, the in-zone fault simulation database refers to all simulated voltage initial traveling wave sets of which fault points are located in a zone defined by the two magnetic rings, the out-of-area fault simulation database refers to a set of all simulated voltage initial traveling waves of which fault points are located outside an area limited by the two magnetic rings.
Specifically, the sampling points of the abscissa of the initial voltage traveling wave refer to the number of samples that can be collected within a certain time window at a specific sampling frequency. The sampling frequency is 2MHz, the sampling time corresponding to the sampling point 1 is 0.5 μ s, the sampling time corresponding to the sampling point 100 is 50 μ s, the time corresponding to the abscissa total sampling point 250 is 125 μ s, and the representative time window is 125 μ s.
Providing line impedance Z ', admittance Y' and surge impedance Z according to the actual condition of the direct current line by using simulation software C Equivalent impedance of the magnetic ring and refractive index K of the direct-current power distribution network a And attenuation coefficient gammaCalculating voltage value according to parameters of fault voltage, wherein line impedance Z' refers to the sum of impedances of all components on the line, and surge impedance Z C The method is characterized in that when fault current generated during fault is transmitted at a certain speed in a line and is refracted and reflected, the resistance of the line to wave transmission is set, a specific sampling frequency f and a time window are set, and voltage initial traveling waves generated when short circuit, open circuit and external impact fault occur at different positions are simulated. Wherein, different position points of the fault can be taken from the initial end to the tail end of the line according to a certain interval distance.
When the simulation model is established, in order to obtain the line impedance after the magnetic rings are arranged, the equivalent circuit of the double magnetic rings is firstly obtained and then is connected in series into the simulation model. The specific implementation process is as follows:
firstly, the impedance value Z of the magnetic ring can be calculated by the following formula:
wherein, A is the cross-sectional area of the magnetic ring, and A ═ r (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 ═ pi (r) 1 +r 2 ) (ii) a j is the complex symbol and μ' and μ "are the real and imaginary parts of the complex permeability, respectively, it can be seen that the impedance of the magnetic loop is related to the frequency f of the signal flowing through the magnetic loop.
Then, vector fitting is performed based on a frequency response curve of the magnetic loop impedance and the frequency of the signal flowing through the magnetic loop, the curve is divided equally into N segments, and fitting is performed in sequence (the frequency response curve can refer to fig. 2 (a)), so that:
where N is the number of fitting segments, m, s, e, r i And p i All unknown parameters are obtained by calculation with least square method and iterative method according to impedance curve, and RLC equivalent circuit of magnetic ring is obtained, as shown in (b) of figure 2)。
The terms m and se may be equal to the resistance R and inductance L, respectively:
when r is i And p i When real, r/(s-p) can be equivalent to the left circuit in (b) of FIG. 2:
wherein r is a zero obtained by fitting, and p is a pole obtained by fitting.
When r is i And p i In the case of complex numbers, r/(s-p) may be equivalent to the right circuit in (b) of FIG. 2:
where r and p are the conjugates of the zero r and the pole p.
And finally, all the equivalent circuits are connected in series to obtain the equivalent circuit of the magnetic ring, and the equivalent circuit of the magnetic ring is connected in a simulation model in series to complete the simulation modeling process.
Other relevant parameters affecting the fault voltage can be calculated according to the following method:
for high voltage direct current transmission systems, the direct current transmission lines are generally arranged in parallel with two identical polar lines. An electrical coupling phenomenon exists between two poles of power transmission lines, decoupling is carried out by adopting a decoupling matrix with the following formula, and a 0-mode component and a 1-mode component of the line can be obtained.
Wherein S is a decoupling matrix, S -1 To decouple the inverse of the matrix, S T Is the transpose of the decoupling matrix.
The two polar lines have symmetry, the different polar lines have equal self-impedance and self-admittance, and there is mutual impedance and mutual admittance between the two polar lines. Let the unit self-impedance per pole be Z 0 ＝R 0 +jωL 0 Wherein R is 0 Is the sum of all connected resistances per pole, L 0 The sum of all connected inductors of each pole is angular frequency; the mutual impedance between poles is Z m ＝R m +jωL m Wherein R is m Is the sum of all resistances between the two poles, L m Is the sum of all inductances between the two poles; the self-admittance of each pole being Y 0 ＝G 0 +jωC 0 Wherein, G 0 Is the sum of all connected conductances per pole, C 0 Is the sum of the reciprocal of the capacitance connected with each pole; interpolar transadmittance of Y m ＝G m +jωC m Wherein G is m Is the sum of the electrical conductances connected between the two poles, C m Is the sum of the reciprocal of the capacitance connected between the two electrodes. The impedance matrix and the 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 formula, the surge impedance Z influencing the fault voltage can be calculated according to the actual condition of the line C And an attenuation coefficient γ, which is calculated by the following formula:
wherein, R 'is the resistance value of the whole circuit after the magnetic ring is arranged, L' is the inductance value of the whole circuit after the magnetic ring is arranged, G 'is the conductance value of the whole circuit after the magnetic ring is arranged, C' is the capacitance value of the whole circuit after the magnetic ring is arranged, and alpha is the real part after the attenuation coefficient is simplified.
DC distribution network refractive index k influencing fault voltage α The calculation can be obtained by the following formula:
wherein, Z h Is a magnetic ring equivalent impedance, Z c Is the surge impedance.
Example (b): based on the fault monitoring models at different positions of the direct current line shown in (a) in fig. 5, the voltage initial traveling wave waveform is obtained through simulation. The fault monitoring model parameters are shown in table 1:
TABLE 1 DC LINE FAULT MONITORING MODEL PARAMETERS AT DIFFERENT POSITIONS
Suppose a faulty dc line L 4 Is 10km, H1 and H2 are respectively provided with magnetic rings, respectively assuming a line start external fault f1, a line end external fault f2 and an internal fault point L x Failure at f3 of 6 km; injecting a harmonic wave with the range of 0-1 MHz by using a harmonic current source, recording a 1-mode voltage initial traveling wave of a 2ms time window with the frequency increment of 500Hz, and obtaining the sampling rate of 2 MHz. The simulated voltage initial traveling waveform is shown in fig. 5 (b).
As can be seen from (b) in fig. 5, the voltage initial traveling waves at different positions have obvious difference, there is an inflection point in the internal fault voltage initial traveling wave in the region defined by the two magnetic rings, there is no inflection point in the external fault waveforms at the beginning and the end of the dc cable line, and the voltage initial traveling waves at different fault positions are easily distinguished. No matter the fault type is short circuit, open circuit or external impact fault, the inflection point exists in the fault voltage initial traveling wave waveform in the area limited by the two magnetic rings, and the inflection point does not exist in the voltage initial traveling wave waveform corresponding to the external fault in the area.
After the initial traveling wave fault database of the simulation voltage is obtained, the fault database can be further divided into an intra-area fault database and an extra-area fault database according to whether the position of the fault point is located in the area defined by the two magnetic rings.
S300: and arranging a traveling wave collecting device at one end of the direct current cable line to record the 1-mode fault voltage initial traveling wave with the same sampling frequency and time window as the sampling frequency of S200 when the actual fault occurs, wherein the abscissa of the traveling wave is a sampling point, and the ordinate is a voltage value, so as to obtain the actual fault voltage initial traveling wave.
Specifically, when a fault occurs, a traveling wave collecting device is used to record a 1-mode fault voltage initial traveling wave with the same sampling frequency and time window as those set in the simulation process of step S200 for subsequent analysis and judgment.
S400: and judging whether the fault point is positioned in the area defined by the two magnetic rings or outside the area according to the waveform of the actual fault voltage initial traveling wave, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is positioned in the area defined by the two magnetic rings, and otherwise, the fault point corresponding to the waveform is positioned 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, and when an external fault occurs in the dc line, there is no inflection point in the initial voltage traveling wave. Therefore, whether the fault point is located in the area defined by the two magnetic rings or not can be quickly judged according to whether the waveform of the initial traveling wave of the actual fault voltage has the inflection point or not.
The fault section is confirmed quickly through the waveform, the power failure range can be reduced after the fault section is confirmed, meanwhile, a fault simulation database corresponding to subsequent specific positioning can be determined, the calculated amount is reduced, the judgment speed of the fault type and the fault position is increased, troubleshooting personnel can process the fault in time, the power supply can be recovered quickly, and the efficient and stable operation of a power grid is ensured.
S500: according to the judgment result of S400, a simulated voltage initial traveling wave having the largest Pearson correlation coefficient with the actual fault voltage initial traveling wave in step S300 is searched in the corresponding fault simulation database obtained in S200, 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 position point of the actual fault point.
Specifically, after it is determined whether the fault point is located in the region defined by the two magnetic rings or outside the region, the Pearson correlation coefficients of all sampling points in a certain time window of the initial traveling wave of each simulation voltage and the initial traveling wave of the actual fault voltage are calculated in the corresponding fault simulation data obtained in step S200, where the fault type of the initial traveling wave of the simulation voltage with the largest Pearson correlation coefficient is the fault type of the actual fault, and the location of the fault is the location of the actual fault point.
And measuring the similarity of waveform details of the initial voltage traveling wave by calculating the covariance of the voltages of the sampling points of the two initial voltage traveling waves through Pearson correlation coefficients, and judging the similarity of the overall variation trend of the initial voltage traveling wave so as to accurately judge the fault type and position the fault point.
As a preferred embodiment, the Pearson correlation coefficient in step S500 can be calculated as follows:
wherein x is i And x j Corresponding voltage values y for ith and jth sampling points of a voltage initial traveling wave in a fault simulation database i And y j The voltage values corresponding to the ith and jth sampling points of the initial traveling wave of the actual fault voltage are obtained, N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N]。
As a preferred embodiment, the method for determining the type and location of the dc cable fault further includes step S600: and uploading the type and the position of the line fault obtained in the step S500 to a fault processing center.
As a preferred embodiment, in step S600, the uploading is implemented by using an LoRa wireless communication mode and an external GPRS base station through a 5G public network.
In a preferred embodiment, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is close to the outer diameter of the cable.
The open type magnetic rings are convenient to install at two ends of the direct current distribution line and low in cost. In practical engineering, the inner diameter of the magnetic ring is close to the outer diameter of the cable, so that the magnetic ring is convenient to mount and fix.
In order to implement the method for judging the type and position of the direct current cable fault, the invention also provides a system for judging the type and position of the direct current cable fault, which comprises the following steps:
the two magnetic rings are respectively arranged at an isolating switch at the secondary side of the inverter and an isolating switch at the primary side of the load DC/DC converter in the range of the direct-current transmission line;
the simulation unit is used for taking different position points from the initial end to the tail end of the direct-current cable line within the length range of the direct-current cable line according to a certain interval distance, simulating 1-mode fault voltage initial traveling waves of a certain time window when three different fault types of short circuit, open circuit and external impact occur at each point of the different position points by adopting a certain sampling frequency, obtaining a fault simulation database by taking the abscissa of the traveling waves as a sampling point and the ordinate as a voltage value, and dividing the fault simulation database into an in-region fault simulation database and an out-region fault simulation database according to whether the fault position is in the region limited by the two magnetic rings, the in-zone fault simulation database refers to all simulated voltage initial traveling wave sets of which fault points are located in a zone defined by the two magnetic rings, the outside-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located outside a zone limited by the two magnetic rings;
the traveling wave acquisition unit is arranged at one end of the direct current cable line and used for recording a 1-mode fault voltage initial traveling wave which has the same sampling frequency and the same time window as the simulation unit when an actual fault occurs, the abscissa of the traveling wave is a sampling point, and the ordinate of the traveling wave is a voltage value, so that the actual fault voltage initial traveling wave is obtained;
the fault position area pre-judging unit is used for judging whether a fault point is positioned in an area limited by the two magnetic rings or not according to the waveform of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is positioned in the area limited by the two magnetic rings, and otherwise, the fault point corresponding to the waveform is positioned outside the area limited by the two magnetic rings;
and the fault type and position judging unit is used for searching the simulated voltage initial traveling wave with the maximum correlation coefficient with Pearson of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit in a corresponding fault simulation database obtained by the simulation unit according to the judgment result of the fault position area judging unit, wherein 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 position point of the actual fault.
As a preferred embodiment, the Pearson correlation coefficient of the judging unit can be obtained by the following calculation method:
wherein x is i And x j Corresponding voltage values y for the ith and jth sampling points of a voltage initial traveling wave in a fault simulation database i And y j The voltage values corresponding to the ith and jth sampling points of the initial traveling wave of the actual fault voltage are obtained, N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N]。
In a preferred embodiment, the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is close to the outer diameter of the cable.
As a preferred embodiment, the system for determining the fault type and location of the dc cable further includes a transmission unit, configured to upload the fault type and location of the line obtained by the fault type and location determination unit to a fault processing center.
As a preferred embodiment, the transmission unit includes an LoRa base station and a GPRS antenna.
Compared with the prior art, firstly, the invention provides a means which can accurately and efficiently judge the specific type and the occurrence position of the direct current cable line fault at the same time, only needs to compare the similarity of the initial voltage traveling wave, abandons the mode that the prior single-end method realizes the accurate positioning of the fault by obtaining the time difference of the fault traveling wave propagating to the two ends of the line, does not require a high-precision transient voltage measuring device, obviously reduces the cable fault monitoring cost and greatly improves the working efficiency of monitoring personnel, so that monitoring personnel can quickly judge the fault position and reduce the power failure range when the fault occurs, meanwhile, troubleshooting personnel and corresponding troubleshooting measures can be quickly arranged immediately according to the fault types, so that the fault troubleshooting time is obviously shortened, the cable line can be quickly recovered to a normal state, and the efficient and stable operation of a power grid is ensured; meanwhile, when the method is implemented, an intra-area fault simulation database and an extra-area fault simulation database are established, whether the actual fault occurs in the area limited by the double magnetic rings or outside the area is identified, then the actual fault voltage initial traveling wave and the simulation voltage initial traveling wave in the corresponding simulation database are fitted to obtain the Pearson correlation coefficient, compared with the technical means that the faults in and outside the areas are not distinguished, and the waveform of the actual fault voltage initial traveling wave and the simulation waveform in the whole database are fitted, the working amount of fitting calculation is greatly reduced, the judgment speed of the fault position and type is further improved, the power grid can be quickly restored to a normal state, and the influence on the normal production and life of a power grid user is reduced to the minimum.
In addition, due to the arrangement of the double magnetic rings, on one hand, a traveling wave head can be effectively slowed down, the problems that the wave head is difficult to identify and not accurate enough in a single-ended traveling wave method are solved, and the application of the single-ended traveling wave method in a direct-current power distribution network is realized; on the other hand, the magnetic ring can influence the amplitude, the gradient and the peak time of transient overvoltage (VFTO), so that the waveform difference of initial voltage traveling waves at different positions is increased, and faults at different positions are clearly distinguished through waveforms; moreover, when a fault simulation database is established, wave heads brought by the double magnetic rings are easy to identify, the difference of external fault traveling wave waveforms at different positions is obvious, and similar fault waveforms are avoided, so that the confusion of similar waveforms in a positioning process is avoided, and the fault positioning through simulation modeling is more accurate and reliable; the Pearson correlation coefficient measures waveform details of the two voltage initial traveling waves by calculating covariance of sampling points of the two voltage initial traveling waves, further evaluates similarity of variation trends of the two traveling waves, is more rigorous than similarity analysis by calculating standard deviation of the sampling points of the two voltage initial traveling waves, and realizes accurate positioning of a fault position by carrying out similarity analysis and evaluation on the details and the variation trends of the voltage initial traveling waves. And a single-end fault positioning method is adopted, so that the requirement on hardware is low, the cost is low, and the implementation is easy.
It should be noted that step numbers (letter or number numbers) are used to refer to some specific method steps in the present invention only for the purpose of convenience and brevity of description, and the order of the method steps is not limited by letters or numbers in any way. It will be clear to a person skilled in the art that the order of the steps of the method concerned, as determined by the technology itself, should not be unduly limited by the presence of step numbers.
It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.
It will be understood that the embodiments described above are illustrative only and not restrictive, and that various obvious and equivalent modifications and substitutions for details described herein may be made by those skilled in the art without departing from the basic principles of the invention.
Claims (10)
1. A method for judging the fault type and the fault position of a direct current cable is characterized by comprising the following steps:
s100: respectively arranging a magnetic ring at an isolating switch at the secondary side of the inverter and an isolating switch at the primary side of the load DC/DC converter on a direct-current cable circuit;
s200: taking different position points from the initial end to the tail end of the direct current cable line within the length range of the direct current cable line according to a certain interval distance, adopting a certain sampling frequency, simulating 1-mode fault voltage initial traveling wave of a certain time window when three different fault types of short circuit, open circuit and external impact respectively occur at each point of the different position points, wherein the abscissa of the traveling wave is a sampling point, the ordinate is a voltage value, and obtaining a fault simulation database, and dividing the fault simulation database into an intra-area fault simulation database and an extra-area fault simulation database according to whether the fault position is in the area limited by the two magnetic rings, the in-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located in the zone defined by the two magnetic rings, the outside-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located outside a zone limited by the two magnetic rings;
s300: arranging a traveling wave collecting device at one end of the direct current cable line to record a 1-mode fault voltage initial traveling wave with the same sampling frequency and time window as S200 when an actual fault occurs, wherein the abscissa of the traveling wave is a sampling point, and the ordinate is a voltage value to obtain the actual fault voltage initial traveling wave;
s400: judging whether a fault point is located in an area defined by the two magnetic rings or outside the area according to the waveform of the actual fault voltage initial traveling wave, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is located 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;
s500: according to the judgment result of S400, a simulated voltage initial traveling wave having the largest correlation coefficient with Pearson of the actual fault voltage initial traveling wave in step S300 is searched in the corresponding fault simulation database obtained in S200, 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 position point of the actual fault.
2. The method for determining the type and location of a dc cable fault according to claim 1, wherein the Pearson correlation coefficient in step S500 is obtained by the following calculation:
wherein x is i And x j For simulating faultsThe voltage value y corresponding to the ith and jth sampling points of a voltage initial traveling wave in the database i And y j Corresponding voltage values of the ith and jth sampling points of the initial traveling wave of the actual fault voltage, wherein N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N ]]。
3. The method for determining the type and location of the direct current cable fault according to claim 1 or 2, further comprising step S600: and uploading the type and the position of the line fault obtained in the step S500 to a fault processing center.
4. The method for judging the fault type and the fault position of the direct current cable according to claim 3, wherein in the step S600, the uploading is realized through a 5G public network by adopting a LoRa wireless communication mode and an external GPRS base station.
5. The method as claimed in claim 1 or 2, wherein the magnetic ring is an open magnetic ring, and the inner diameter of the magnetic ring is close to the outer diameter of the cable.
6. A system for judging the fault type and the fault position of a direct current cable is characterized by comprising:
the two magnetic rings are respectively arranged at the isolating switch at the secondary side of the inverter and the isolating switch at the primary side of the load DC/DC converter on the direct-current transmission line;
the simulation unit is used for taking different position points from the initial end to the tail end of the direct-current cable line within the length range of the direct-current cable line according to a certain interval distance, simulating 1-mode fault voltage initial traveling waves of a certain time window when three different fault types of short circuit, open circuit and external impact occur at each point of the different position points by adopting a certain sampling frequency, obtaining a fault simulation database by taking the abscissa of the traveling waves as a sampling point and the ordinate as a voltage value, and dividing the fault simulation database into an in-region fault simulation database and an out-region fault simulation database according to whether the fault position is in the region limited by the two magnetic rings, the in-zone fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are located in the zone defined by the two magnetic rings, the out-of-area fault simulation database refers to all simulation voltage initial traveling wave sets of which fault points are positioned outside an area limited by the two magnetic rings;
the traveling wave acquisition unit is arranged at one end of the direct current cable line and used for recording a 1-mode fault voltage initial traveling wave which has the same sampling frequency and the same time window as the simulation unit when an actual fault occurs, the abscissa of the traveling wave is a sampling point, and the ordinate of the traveling wave is a voltage value, so that the actual fault voltage initial traveling wave is obtained;
the fault position area pre-judging unit is used for judging whether a fault point is positioned in an area limited by the two magnetic rings or not according to the waveform of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit, wherein if the waveform of the actual fault voltage initial traveling wave has an inflection point, the fault point corresponding to the waveform is positioned in the area limited by the two magnetic rings, and otherwise, the fault point corresponding to the waveform is positioned outside the area limited by the two magnetic rings;
and the fault type and position judging unit is used for searching the simulation voltage initial traveling wave with the maximum correlation coefficient with Pearson of the actual fault voltage initial traveling wave obtained by the traveling wave collecting unit in a corresponding fault simulation database obtained by the simulation unit according to the judgment result of the fault position region pre-judging unit, wherein the fault type corresponding to the simulation voltage initial traveling wave is the fault type of the actual fault, and the corresponding position point is the position point of the actual fault.
7. The system according to claim 6, wherein the Pearson correlation coefficient of the determination unit is calculated as follows:
wherein x is i And x j For the ith and jth samples of a voltage initial traveling wave in a fault simulation databaseCorresponding voltage value, y i And y j The voltage values corresponding to the ith and jth sampling points of the initial traveling wave of the actual fault voltage are obtained, N is the number of sampling points of a certain time window, and the value ranges of i and j are [1, N]。
8. The system for determining the type and location of a fault in a dc cable according to claim 6 or 7, wherein 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.
9. The system for determining the type and location of a dc cable fault according to claim 6 or 7, further comprising a transmission unit for uploading the type and location of the line fault obtained by the fault type and location determination unit to a fault processing center.
10. The system according to claim 9, wherein the transmission unit comprises an LoRa base station and a GPRS antenna.
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