CN116908622B - Direct-current distribution line fault offline positioning device and positioning method thereof - Google Patents
Direct-current distribution line fault offline positioning device and positioning method thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J2207/50—Charging of capacitors, supercapacitors, ultra-capacitors or double layer capacitors
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
The invention provides a direct current distribution line fault offline positioning device and a positioning method, wherein the device comprises the following steps: a capacitor bank and a discharge branch; one end of the discharging branch is connected with a first connecting point of the direct-current distribution line, the other end of the discharging branch is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded; when the capacitor bank is charged, a switch of the discharging branch is opened, and the capacitor bank discharges to a fault point through the discharging branch and a fault line; when the capacitor bank discharges the fault point, determining the equivalent reactance and the equivalent resistance of the discharge circuit, determining the unit reactance of the fault line according to the predetermined mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit, and finally determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branch circuit, and positioning the fault point. The invention overcomes the influence of frequency-dependent change of line parameters and has high positioning precision on fault points.
Description
Technical Field
The invention belongs to the field of power distribution network fault detection, and particularly relates to a direct current distribution line fault offline positioning device and a positioning method thereof.
Background
With the rapid development of economy, the air transmission corridor of a large and medium city has no development room, the underground alternating current cable has larger capacitive current, reactive compensation equipment is needed, and the transmission distance is limited. The direct current cable has no capacitance current, high transmission capacity and suitability for long-distance power transmission. With the rapid development of clean energy, the need to access various distributed power generation capacities with high intermittence, randomness and unpredictability is continuously increasing. The distributed power supply is connected to the direct-current distribution network or the direct-current micro-grid, so that some power supply conversion links can be omitted, the cost is reduced, the loss is reduced, and the distributed power supply is more suitable for being connected to the distributed power supply. The rapid development of power electronics promotes the change of the power consumption modes of users: the electric automobile, the semiconductor lighting, the communication equipment and part of household appliances all need direct current as a power supply, and the direct current distribution can improve the power supply conversion times and the efficiency. In addition, the line cost of direct current distribution is lower; the transmission capacity of the same voltage class is higher, and the loss of the lead wire is smaller under the same transmission capacity; and the reactive angle stability problem is limited, and the power supply reliability is high.
In order to accelerate fault recovery speed, reduce user power failure time and improve reliability of the power distribution network, accurate positioning of fault points and elimination of faults are required, switching operation and manual line inspection are reduced, and requirements of intelligent power distribution network development are met. Existing fault point locating methods can be generally classified into an online fault transient signal method and an offline injection signal method. After the direct current system fails on the line, the direct current breakers at the two ends of the line can quickly cut off the failed line, so that the data length for on-line fault positioning is limited, and the difficulty of fault positioning is increased. After fault is removed, a Probe Power Unit (PPU) is used for carrying out fault positioning, and a circuit is simplified into an R-L equivalent model, so that a fault loop forms an RLC second-order oscillation loop. The method comprises the steps of extracting the attenuation time constant, the attenuation frequency and the initial attenuation amplitude of the second-order oscillation loop through Prony, FFT and other algorithms, and calculating the fault distance through calculating the total inductance of the fault loop of the fault line. Because of the skin effect of the conductor, the line parameters are varied with frequency and there is a distribution characteristic of the line parameters. The centralized equivalent model of the line, such as the n-type equivalent model, the R-L equivalent model and the like, cannot completely equivalent the distribution characteristic and the frequency-dependent characteristic of the line parameters, and the accurate fault position is difficult to obtain in practical application.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a direct current distribution line fault offline positioning device and a positioning method thereof, which aim to solve the problems of inconvenient fault positioning operation and low positioning precision of the existing direct current distribution network.
To achieve the above object, in a first aspect, the present invention provides an offline fault locating device for a dc distribution line, including: a capacitor bank and a discharge branch;
one end of the discharging branch is connected with a first connection point of the direct-current distribution line, the other end of the discharging branch is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded; the first connecting point is close to a fault point of the direct-current distribution line and is arranged between a power supply of the direct-current distribution line on one side and the fault point;
when the capacitor bank is charged, a switch of the discharging branch is opened, and the capacitor bank discharges to a fault point through the discharging branch and a fault line to form a second-order oscillation discharging circuit; the discharge inductance of the discharge branch is larger than a preset value, so that the attenuation coefficient and the oscillation frequency of the second-order oscillation discharge circuit are not influenced by the fault distance; the fault line is a transmission line between the first connection point and the fault point; the fault distance refers to the distance between the fault point and the power supply;
when the capacitor bank discharges the fault point, determining the equivalent reactance and the equivalent resistance of the discharge circuit, determining the unit reactance of the fault line according to the predetermined mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit, and finally determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branch circuit, and positioning the fault point.
Optionally, the apparatus further comprises: a charging branch;
one end of the charging branch is connected with a second connection point of the direct-current distribution circuit, and the other end of the charging branch is connected with one end of the capacitor bank; the second connection point is disposed between the power source and the fault point, and the second connection point is closer to the power source than the first connection point;
when the switch of the charging branch is opened, the power supply charges the capacitor bank through the charging branch.
It should be noted that "close to" refers to that the distance is smaller than a predetermined value, for example, the first connection point is close to the fault point, and refers to that the first connection point is long from the fault point, that is, the distance is smaller than the predetermined value. Or "close" may also mean that the a object is at a smaller distance from the C object than the B object, i.e., the a object is at a smaller distance from the C object than the B object. It will be apparent from the above that the first connection point is closer to the fault point than the second connection point and, correspondingly, the second connection point is closer to the power source than the first connection point.
It will be appreciated that the first and second connection points are typically closely spaced, typically pure transmission lines between the two connection points.
In addition, when the invention only aims to solve the problem of low fault location precision, the problem of convenience in charging the capacitor bank can be solved, and the capacitor bank can be charged by other additional power supplies, then the charging branch circuit is not required to be connected through the second connection point. If the whole device is considered to be capable of completing the charge and discharge of the capacitor bank, the charging branch can be connected through the second connection point. The person skilled in the art can choose all or part of the above scheme of the invention to locate the fault point in real time according to the actual needs.
Optionally, the apparatus further comprises: a protection branch;
the protection branch is connected in parallel with two ends of the capacitor bank and is used for protecting the capacitor bank from energy leakage.
Optionally, the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit is determined by the following steps:
simulating faults of various transition resistances at preset positions of a direct-current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs;
the discharge inductance and discharge equation when various transition resistances fail are combined to obtain an overdetermined equation set;
solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit when each transition resistance fails;
subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, dividing the equivalent reactance of the fault line by the fault distance corresponding to the preset position to obtain the corresponding fault line unit reactance, and obtaining the fault line unit reactance when each transition resistance fails;
fitting the unit reactance of the fault line corresponding to the various transition resistances and the equivalent resistance of the discharge circuit to obtain the mapping relation between the unit reactance and the equivalent resistance.
Optionally, the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit is determined by the following steps:
simulating faults at different fault positions of the direct current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs;
the discharge inductance and discharge equation in multiple faults are combined to obtain an overdetermined equation set;
solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit in each fault;
subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, and dividing the equivalent impedance of the fault line by the corresponding fault distance to obtain the unit reactance of the fault line corresponding to different fault points;
fitting the unit reactance of the fault line and the equivalent resistance of the discharge circuit at a plurality of fault positions to obtain the mapping relation between the unit reactance and the equivalent resistance.
Optionally, according to the discharge at the fault pointThe equivalent reactance of the circuit, the unit reactance of the fault line and the discharge inductance of the discharge branch determine the fault distance of the fault pointxThe method specifically comprises the following steps:
wherein,L eq for the equivalent reactance of the discharge circuit,Lfor the discharge inductance of the discharge branch,the unit reactance of the fault line corresponding to the equivalent resistance of the discharge circuit,R eq is the equivalent resistance of the discharge circuit.
Optionally, the discharge inductance of the discharge branch is greater than a preset value, specifically:
the discharge inductance is larger than a preset multiple of the maximum equivalent reactance of the fault line; the preset multiple is between 5 times and 10 times.
Optionally, the fault of the fault point is a ground fault or a bipolar short circuit fault.
In a second aspect, the present invention provides a method for offline positioning of faults of a dc distribution line, including the following steps:
connecting the capacitor bank and the discharging branch circuit to a direct-current distribution circuit; one end of the discharging branch is connected with a first connection point of the direct-current distribution line, the other end of the discharging branch is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded; the first connecting point is close to a fault point of the direct-current distribution line and is arranged between a power supply of the direct-current distribution line on one side and the fault point;
when the capacitor bank is charged, a switch of the discharging branch is opened, and the capacitor bank discharges to a fault point through the discharging branch and a fault line to form a second-order oscillation discharging circuit; the discharge inductance of the discharge branch is larger than a preset value, so that the attenuation coefficient and the oscillation frequency of the second-order oscillation discharge circuit are not influenced by the fault distance; the fault line is a transmission line between the first connection point and the fault point; the fault distance refers to the distance between the fault point and the power supply;
when the capacitor bank discharges the fault point, determining the equivalent reactance and the equivalent resistance of the discharge circuit, determining the unit reactance of the fault line according to the predetermined mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit, and finally determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branch circuit, and positioning the fault point.
Optionally, determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branchxThe method specifically comprises the following steps:
wherein,L eq for the equivalent reactance of the discharge circuit,Lfor the discharge inductance of the discharge branch,the unit reactance of the fault line corresponding to the equivalent resistance of the discharge circuit,R eq is the equivalent resistance of the discharge circuit.
In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
the invention provides a direct-current distribution line fault offline positioning device and a positioning method thereof, which overcome the influence of direct-current line parameters on fault positioning precision according to frequency change characteristics, and a discharging loop forms a second-order oscillating circuit by switching in a capacitor bank which is pre-charged by a power grid direct-current power supply, so as to obtain a set of overdetermined equation set of the discharging loop. And solving an overdetermined equation set by a least square method to obtain the equivalent resistance and the equivalent reactance of the discharge loop. Because the equivalent impedance of the fault line is smaller, the relation between the unit reactance of the line and the equivalent resistance of the discharge loop can be established by a fitting method, thereby overcoming the influence of the frequency-dependent change of the line parameters. And finally, obtaining a relatively accurate fault point distance by utilizing the relation between the equivalent reactance and the line unit reactance obtained by fitting.
The invention provides a direct-current distribution line fault offline positioning device and a positioning method thereof, which utilize a power supply of a direct-current line to charge a parallel capacitor bank, do not need an additional independent power supply or a semiconductor device, have higher reliability and are simple and convenient to operate. The invention considers the influence of the direct current line parameter on the fault positioning result according to the frequency change characteristic, and has higher fault positioning precision. According to the method, the voltage at the two ends of the inductor is used for replacing current differential calculation, and the least square method is used for solving the overdetermined equation set, so that the fault positioning precision is improved, the anti-noise interference capability is high, and the practical application prospect is met.
Drawings
FIG. 1 is a schematic circuit diagram of an off-line fault location device for a DC distribution line according to an embodiment of the present invention;
FIG. 2 is a diagram of a fitting of an embodiment of the inventionL u (R eq ) A graph change curve schematic diagram;
fig. 3 is a flowchart of a method for offline fault location of a dc distribution line according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention discloses a direct-current distribution line fault offline positioning device, which comprises a parallel capacitor bank, wherein a second-order oscillating circuit is formed by a discharge loop formed by the parallel capacitor bank, a fault line and a fault point, and the second-order oscillating circuit is used for fault positioning; the parallel capacitor bank is connected with a charging branch, a discharging branch and a protection branch. The invention also discloses a direct-current distribution line fault offline positioning method, which comprises the steps of putting into a parallel capacitor bank charged in advance by a direct-current power supply of a power grid to enable a discharge loop to form a second-order oscillating circuit, measuring and establishing the change relation of the voltage and the current of the discharge loop along with time, and obtaining a set of overdetermined equation set. And solving an overdetermined equation set by a least square method to obtain the equivalent resistance and the equivalent reactance of the discharge loop. The invention overcomes the influence of the frequency-dependent characteristic of the line parameters on the fault positioning precision, and improves the reliability and the precision of the positioning of the fault point of the direct current line.
The parallel connection in the parallel capacitor bank means that the capacitor bank is connected in parallel with the dc distribution line.
The invention aims to provide a direct current distribution line fault offline positioning device and a positioning method thereof, which overcome the influence of line parameters on fault positioning precision according to frequency characteristics, and improve the reliability and the accuracy of direct current line fault point positioning so as to solve the defects or problems in the background technology.
The invention provides a direct-current distribution line fault offline positioning device, which comprises a parallel capacitor bank, wherein a second-order oscillating circuit is formed by a discharge loop formed by the parallel capacitor bank, a fault line and a fault point, and the second-order oscillating circuit is used for fault positioning; the parallel capacitor bank is connected with a charging branch, a discharging branch and a protection branch, the charging branch is formed by connecting a charging resistor and a charging switch in series, the discharging branch is formed by connecting a discharging reactor and a discharging switch in series, the protection branch is connected in parallel at two ends of the parallel capacitor, and the protection branch is formed by connecting a protection switch and a protection resistor in series.
Further, the charging switch and the discharging switch are arranged as one or a combination of a plurality of fast mechanical switches, anti-parallel transistor groups and controllable gap switches.
The embodiment 1 of the invention is a direct current distribution line fault offline positioning device, as shown in fig. 1, which is suitable for a direct current distribution network or a direct current micro-grid formed by overhead lines or cable lines, and can be applied to fault point positioning after monopole grounding and bipolar short-circuit faults. In the specific embodiment of the invention, the monopolar grounding fault is taken as an example, the bipolar short-circuit fault only needs to input the discharge switches on the positive electrode and the negative electrode at the same time, and the rest positioning process is similar to the monopolar grounding fault.
The discharging switch means S4; DCCB1 and DCCB2 are direct current circuit breakers at two ends of a direct current distribution line, and the off-line process refers to a process after the lines are isolated by the DCCB1 and the DCCB2 due to protection actions. Thus, by default, DCCB1 and DCCB2 are both disconnected when not mentioned.
As shown in fig. 1, the offline positioning method is based on a positioning method of a fault positioning device, the fault positioning device consists of a connection point g and a connection point j which are added to a line, the connection point j is close to a left power supply, the fault point is e, the fault point is close to a right power supply, and the connection point g is closer to the fault point than the connection point j; where, as corresponds to the claims, the connection point j is the second connection point and the connection point g is the first connection point. For feeding parallel capacitor banksCCharging switch S6 and charging resistor for chargingR c Is connected in series between connection point j and connection point i, forming a charging branch. For feeding capacitor banksCDischarge switch S4 and discharge reactor for dischargingLIs connected in series between the connection point g and the connection point i, forming a discharge branch. The parallel capacitor bank is connected between the connection point i and ground. Protective resistor for energy leakage protectionR p And a switch S5 connected in series across the capacitor bank, constituting a protection branch.
The fault locating method of the embodiment 1 of the invention has the following charging process: as shown in fig. 1, in the case of a parallel capacitor bankCIn the process of charging, firstly, the switches S3 and S6 are combined, the switches S4 and S1 are kept open, then the DCCB1 is combined, and the direct current power supply passes through the DCCB1, the switch S3, the switch S6 and the charging resistorR c To capacitor bankCCharging is carried out with a charging time constant ofτ=R c CTo be charged with currentI c Less than a thresholdI 0 After that, the switches S3 and S6 are turned off, and the charging ends.
The fault locating method of the embodiment 1 of the invention is based on the following principle: if at the distance axThe f position at the position has a ground fault, and the transition resistance isR f The equivalent impedance of the fault line between a and the fault point f isR 1 AndL 1 . After the charging is finished, the switch S4 and the switch S1 are put into, and the capacitor bankCWill pass through the discharge reactorLThe switch S4, the switch S1 and the fault line discharge to the fault point to form a second-order oscillation discharge circuit, which is expressed as follows:
wherein,L eq 、R eq is the equivalent reactance and equivalent resistance of the discharge circuit. When (when)When the equation satisfies the under-damping. Second order attenuation coefficient->Oscillation frequency->Wherein, the method comprises the steps of, wherein,L eq =L+L 1 ，R eq =R 1 +R f . Because the DC line parameters have strong frequency-dependent characteristics,R 1 andL 1 may be based on the fault locationxAnd a transition resistanceR f Therefore, the key of the fault locating method is how to eliminate the influence of the frequency-dependent change of the line parameters. In general, the equivalent impedance of a DC lineR 1 AndL 1 is small if the following conditions are met by parameter optimization:
in particular, becauseL 1 The actual size is small, which can be estimated according to the maximum length of the line, and then selectedL 1 Is 5-10 times as large asLAnd (3) obtaining the product.
Attenuation coefficient after satisfying the above conditionsσAnd oscillation frequencyωWill be hardly affected by the location of the line fault. Therefore, it can be deduced that the line unit reactance at this timeL u Hardly subject to failure locationxInfluenced only by the equivalent resistance of the discharge loopR eq Is a function of (a) and (b). Thus can be establishedL u AndR eq is a relationship of (3).
When the switch S4 and the switch S1 are put in, the equation of the fault loop can be obtained to satisfy:
for discharging reactorLBoth ends are available:
the above equation can be written in a discrete form, and increases as the sampling points increase, so as to obtain a set of overdetermined equation sets, and written in a matrix form to obtain:
wherein the matrixMatrix->。
Wherein,nfor the number of data points for fault localization, equation (5) is solved by using a least square method (Least square method), and the equivalent parameters of the fault loop are obtained as follows:
in one example, the fault line unit reactance is determined byEquivalent resistance with discharge circuit->Mapping relation between->：
Simulating multiple transition resistances at preset positions of direct-current distribution circuitR f And determining a discharge equation for the discharge inductance at each failure；
Multiple transition resistancesR f The discharge inductance and discharge equation during faults are combined to obtain an overdetermined equation set;
solving the overdetermined equation set to obtain the equivalent reactance of the discharge circuit when each transition resistance failsAnd equivalent resistance；
Equivalent reactance of the discharge circuitSubtracting the discharge inductanceLObtaining the equivalent reactance of the fault lineL 1 And equivalent reactance of the fault lineL 1 Dividing by the fault distance corresponding to the predetermined positionxObtain the corresponding unit reactance of the fault line>Obtaining each transition resistance faultR f Is +.>；
It should be noted that, the equivalent reactance of the line corresponding to the first connection point (connection point g in fig. 1) from the power supply is negligible with respect to the equivalent reactance of the line corresponding to the fault point from the first connection point.
For various transition resistancesR f Corresponding fault line unit reactanceAnd equivalent resistance of discharge circuit->Fitting to obtain the mapping relation between unit reactance and equivalent resistance>。
It will be appreciated that the above-mentioned predetermined positionsxIt can be the midpoint of the line, i.e. the line is in the middle position, the noise interference at the midpoint position is small, and the error of the fitted curve is relatively small.
In another example, the fault line unit reactance is determined byEquivalent resistance to discharge circuitMapping relation between->：
At different fault locations of a DC distribution linexSimulating faults and determining a discharge equation of the discharge inductance at each fault；
The discharge inductance and discharge equation in multiple faults are combined to obtain an overdetermined equation set;
solving the overdetermined equation system to obtain the equivalent reactance of the discharge circuit in each faultAnd equivalent resistance->；
Equivalent reactance of the discharge circuitSubtracting the discharge inductanceLObtaining the equivalent reactance of the fault lineL 1 And equivalent reactance of the fault lineL 1 Dividing by the fault distance corresponding to the predetermined positionxObtaining the unit reactance of the fault line corresponding to different fault points>；
For multiple fault locationsxIs a fault line unit reactance of (a)Fitting with equivalent resistance of discharge circuit->Obtaining the mapping relation between the unit reactance and the equivalent resistance ∈>。
Finally, according to the reactance of the line unitL u And obtaining the equivalent reactance of the fault lineL 1 Relationship between each other, find the fault distancexExpressed as:
in a specific embodiment, embodiment 1 of the present inventionL u (R eq ) The method for establishing the graph curve is as follows: the invention simulates various transition resistances at the midpoint of the circuit by experimental or simulation methodsR f Is a ground fault of (a). After each earth fault, a matrix is established by utilizing the principle of the fault positioning method provided by the inventionAAndBand obtaining the equivalent parameters of the fault lineL eq AndR eq . Due to the fact that at this timexIs a known parameter, so that the fault condition can be obtainedL u AndR eq is a relationship of (3). When (when)R f In the process from small to large, can be obtainedL u AndR eq discrete change relationships. Then establishing by numerical fitting methods such as cubic spline fitting, linear fitting function, polynomial fitting and the likeL u AndR eq numerical relation of (2) to obtainL u (R eq ) And the graph change curve is used for inquiring during offline fault positioning. To further describe, an electromagnetic transient simulation model is built in PSCAD/EMTDC, a 10 km-length direct current line sampling phase domain dependent frequency model is built, and simulation occurs at 5km positions in the line respectivelyR f = 0,0.5,1,2,3.5,5,7.5, 10 ohm ground fault, obtained by parametric fittingL u (R eq ) The graph change curve is shown in FIG. 2, in which a quadratic polynomial is used for fitting, and the result shows thatL u AndR eq the linear relation is approximately one time, specifically:. By passing throughL u (R eq ) The graph change curve can eliminate the influence of the frequency-dependent characteristic of the line parameters on the fault positioning precision, so that the fault positioning precision is improved.
A flowchart of the overall actions of an embodiment of the present invention is shown in FIG. 3, comprising the steps of:
s1, charging a capacitor bank through a charging switch and a charging resistor which are connected in parallel, and switching off the charging switch after the charging current is smaller than a threshold value;
s2, putting a parallel discharge switch into the capacitor bank, the discharge reactor, the fault line and the fault point to form a second-order oscillating discharge loop; obtaining the relation of the equivalent reactor and the equivalent resistance of the oscillating discharge circuit along with the discharge current, the voltage on the discharge reactor and the voltage on the capacitor along with the time, thereby obtaining a group of overdetermined equation sets; solving an overdetermined equation set through a least square method to obtain the equivalent resistance and the equivalent reactance of the discharge loop;
s3, because the equivalent impedance of the fault line is smaller, the fault line is formed by the direct current lineThe point positions simulate the grounding faults of various transition resistances to obtain experimental parameters, and then a fitting method is utilized to establish the relation between the unit reactance of the circuit and the equivalent resistance of the fault loop, namely, the relation is establishedL u (R eq ) A relationship curve;
and S4, finally, obtaining the fault distance by utilizing the relation between the obtained equivalent reactance of the fault loop and the unit reactance of the line obtained by fitting.
Specifically, first, before fault location is performed, the capacitor bank is charged by a charging resistor and a dc power supply. After the charging is completed, the switch S4 and the switch S1 are closed to form a second-order oscillating discharge loop. Measuring capacitor bankCVoltage acrossU C Discharging reactorLVoltage acrossU L And discharge currentI f 。U C 、U L 、I f The time-varying measurement can be written in discrete form to build and obtain a matrixASum matrixBObtaining the equivalent reactance of the discharge loop by using a least square methodL eq And equivalent resistanceR eq . By queryingL u (R eq ) Graph curve is obtainedR eq Corresponding unit reactance in caseL u Thereby finding the fault distance。
Detailed description of the preferred embodiments occurs at 3km of lineR f By way of example, a ground fault of =5 ohms, measuredU C 、U L 、I f Time-varying waveform diagram building matrixASum matrixBWherein the sampling rate is 10kHz,Ldata length setting =30mhn=200, i.e. 20ms data length, equivalent reactance is determined by least squaresL-L eq =2.180 mH and equivalent resistanceR eq =6.167 ohms. By querying curvesL u (R eq ) Obtain the correspondingR eq In the case ofL u = 0.7401mH/km to obtainkm, the range error was 54 meters.
In the traditional direct current power distribution network fault positioning method based on the probe power element, a centralized parameter equivalent model with a line of R-L or pi is assumed, and the fault distance is obtained by comparing the equivalent reactance or equivalent resistance of a fault loop with the unit reactance and unit resistance of a line which are known to be fixed. Fitting by the inventionL u (R eq ) The unit reactance of the line is found to be affected by the transition resistance, as shown in fig. 2. Taking the traditional method as an example, the equivalent reactance is obtainedL-L eq When=2.180 mH, if the line equivalent reactance at the time of smaller transition resistance is about 0.85mH/km, the calculated fault distance is 2.565km, and the error is 565 meters; the fault distance calculated with a line equivalent reactance of about 0.60mH/km at a larger transition resistance was 3.633km with an error of 1.6 km. Therefore, the method provided by the invention can greatly overcome the influence of the line parameters on the fault positioning precision according to the frequency change characteristic, and improve the fault positioning precision. The method adopts the least square method to solve the overdetermined equation set, improves the anti-noise interference capability and the influence of individual data point errors to a certain extent, and can meet the requirements of practical application.
In the direct-current distribution network and the direct-current micro-grid of various voltage level sequences, the invention can reliably position the fault point. In addition, the parameter discharge reactor can be controlled according to the length of the lineLAnd capacitor bankCIs optimized for the specific numerical value of (c).
In a word, the invention provides an off-line fault positioning device and method for a direct-current distribution line, which aim to overcome the influence of line parameters on fault positioning accuracy according to frequency characteristics and improve the reliability and accuracy of positioning fault points of the direct-current distribution line. The parallel capacitor bank is charged by the power supply of the direct current circuit, no additional independent power supply is needed, no semiconductor device is needed, and high reliability is achieved. The voltage at two ends of the inductor is used for replacing current differential calculation, and the least square method is used for solving an overdetermined equation set, so that the fault positioning precision is improved, the anti-noise interference capability is high, and the practical application prospect is met.
It is to be understood that the terms such as "comprises" and "comprising," which may be used in this invention, indicate the presence of the disclosed functions, operations or elements, and are not limited to one or more additional functions, operations or elements. In the present invention, terms such as "comprising" and/or "having" may be construed to mean a particular feature, number, operation, constituent element, component, or combination thereof, but may not be construed to exclude the presence or addition of one or more other features, numbers, operations, constituent elements, components, or combination thereof.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (7)
1. An off-line fault locating device for a direct current distribution line, comprising: a capacitor bank and a discharge branch;
one end of the discharging branch is connected with a first connection point of the direct-current distribution line, the other end of the discharging branch is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded; the first connecting point is close to a fault point of the direct-current distribution line and is arranged between a power supply of the direct-current distribution line on one side and the fault point;
when the capacitor bank is charged, a switch of the discharging branch is opened, and the capacitor bank discharges to a fault point through the discharging branch and a fault line to form a second-order oscillation discharging circuit; the discharge inductance of the discharge branch is larger than a preset value, so that the attenuation coefficient and the oscillation frequency of the second-order oscillation discharge circuit are not influenced by the fault distance; the fault line is a transmission line between the first connection point and the fault point; the fault distance refers to the distance between the fault point and the power supply; the discharge inductance is larger than a preset multiple of the maximum equivalent reactance of the fault line; the preset multiple is between 5 times and 10 times;
when the capacitor bank discharges the fault point, determining the equivalent reactance and the equivalent resistance of the discharge circuit, then determining the unit reactance of the fault line according to the predetermined mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit, and finally determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branch circuit, and positioning the fault point; the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit is determined by the following steps: simulating faults of various transition resistances at preset positions of a direct-current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs; the discharge inductance and discharge equation when various transition resistances fail are combined to obtain an overdetermined equation set; solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit when each transition resistance fails; subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, dividing the equivalent reactance of the fault line by the fault distance corresponding to the preset position to obtain the corresponding fault line unit reactance, and obtaining the fault line unit reactance when each transition resistance fails; fitting the unit reactance of the fault line corresponding to the various transition resistances with the equivalent resistance of the discharge circuit to obtain the mapping relation between the unit reactance and the equivalent resistance; or determining the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit by the following steps: simulating faults at different fault positions of the direct current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs; the discharge inductance and discharge equation in multiple faults are combined to obtain an overdetermined equation set; solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit in each fault; subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, and dividing the equivalent impedance of the fault line by the corresponding fault distance to obtain the unit reactance of the fault line corresponding to different fault points; fitting the unit reactance of the fault line and the equivalent resistance of the discharge circuit at a plurality of fault positions to obtain the mapping relation between the unit reactance and the equivalent resistance.
2. The apparatus as recited in claim 1, further comprising: a charging branch;
one end of the charging branch is connected with a second connection point of the direct-current distribution circuit, and the other end of the charging branch is connected with one end of the capacitor bank; the second connection point is disposed between the power source and the fault point, and the second connection point is closer to the power source than the first connection point;
when the switch of the charging branch is opened, the power supply charges the capacitor bank through the charging branch.
3. The apparatus as recited in claim 1, further comprising: a protection branch;
the protection branch is connected in parallel with two ends of the capacitor bank and is used for protecting the capacitor bank from energy leakage.
4. The apparatus of claim 1, wherein the fault distance of the fault point is determined based on the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line, and the discharge inductance of the discharge branchxThe method specifically comprises the following steps:
wherein,L eq for the equivalent reactance of the discharge circuit,Lfor the discharge inductance of the discharge branch,the unit reactance of the fault line corresponding to the equivalent resistance of the discharge circuit,R eq is the equivalent resistance of the discharge circuit.
5. The device of any one of claims 1 to 4, wherein the fault at the fault point is a ground fault or a bipolar short circuit fault.
6. The off-line fault locating method for the direct-current distribution line is characterized by comprising the following steps of:
connecting the capacitor bank and the discharging branch circuit to a direct-current distribution circuit; one end of the discharging branch is connected with a first connection point of the direct-current distribution line, the other end of the discharging branch is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded; the first connecting point is close to a fault point of the direct-current distribution line and is arranged between a power supply of the direct-current distribution line on one side and the fault point;
when the capacitor bank is charged, a switch of the discharging branch is opened, and the capacitor bank discharges to a fault point through the discharging branch and a fault line to form a second-order oscillation discharging circuit; the discharge inductance of the discharge branch is larger than a preset value, so that the attenuation coefficient and the oscillation frequency of the second-order oscillation discharge circuit are not influenced by the fault distance; the fault line is a transmission line between the first connection point and the fault point; the fault distance refers to the distance between the fault point and the power supply; the discharge inductance is larger than a preset multiple of the maximum equivalent reactance of the fault line; the preset multiple is between 5 times and 10 times;
when the capacitor bank discharges the fault point, determining the equivalent reactance and the equivalent resistance of the discharge circuit, then determining the unit reactance of the fault line according to the predetermined mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit, and finally determining the fault distance of the fault point according to the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line and the discharge inductance of the discharge branch circuit, and positioning the fault point; the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit is determined by the following steps: simulating faults of various transition resistances at preset positions of a direct-current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs; the discharge inductance and discharge equation when various transition resistances fail are combined to obtain an overdetermined equation set; solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit when each transition resistance fails; subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, dividing the equivalent reactance of the fault line by the fault distance corresponding to the preset position to obtain the corresponding fault line unit reactance, and obtaining the fault line unit reactance when each transition resistance fails; fitting the unit reactance of the fault line corresponding to the various transition resistances with the equivalent resistance of the discharge circuit to obtain the mapping relation between the unit reactance and the equivalent resistance; or determining the mapping relation between the unit reactance of the fault line and the equivalent resistance of the discharge circuit by the following steps: simulating faults at different fault positions of the direct current distribution line, and determining a discharge equation of a discharge inductor when each fault occurs; the discharge inductance and discharge equation in multiple faults are combined to obtain an overdetermined equation set; solving an overdetermined equation set to obtain the equivalent reactance and the equivalent resistance of the discharge circuit in each fault; subtracting the discharge inductance from the equivalent reactance of the discharge circuit to obtain the equivalent reactance of the fault line, and dividing the equivalent impedance of the fault line by the corresponding fault distance to obtain the unit reactance of the fault line corresponding to different fault points; fitting the unit reactance of the fault line and the equivalent resistance of the discharge circuit at a plurality of fault positions to obtain the mapping relation between the unit reactance and the equivalent resistance.
7. The method of claim 6, wherein the fault distance of the fault point is determined based on the equivalent reactance of the discharge circuit at the fault point, the unit reactance of the fault line, and the discharge inductance of the discharge branchxThe method specifically comprises the following steps:
wherein,L eq for the equivalent reactance of the discharge circuit,Lfor the discharge inductance of the discharge branch,the unit reactance of the fault line corresponding to the equivalent resistance of the discharge circuit,R eq is the equivalent resistance of the discharge circuit.
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