CN107918079B - Power distribution network single-phase earth fault positioning method and system based on sweep frequency injection - Google Patents

Power distribution network single-phase earth fault positioning method and system based on sweep frequency injection Download PDF

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CN107918079B
CN107918079B CN201711144938.0A CN201711144938A CN107918079B CN 107918079 B CN107918079 B CN 107918079B CN 201711144938 A CN201711144938 A CN 201711144938A CN 107918079 B CN107918079 B CN 107918079B
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fault
phase
current
frequency
voltage
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CN107918079A (en
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于辉
李富云
王洪林
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/081Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/088Aspects of digital computing
    • YGENERAL 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
    • Y04INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04SSYSTEMS 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
    • Y04S10/00Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52Outage or fault management, e.g. fault detection or location

Abstract

The invention provides a power distribution network single-phase earth fault positioning method and system based on sweep frequency injection, which comprises a plurality of lines to be positioned, wherein the input ends of the lines to be positioned are respectively connected with the output end of a three-phase bus, and the output ends of the lines to be positioned are sequentially and electrically connected with a three-phase voltage transformer and three high-voltage switches; the device also comprises a controllable power supply electrically connected with the three high-voltage switches and a plurality of fault indicators which are dispersedly arranged on the plurality of lines to be positioned and are positioned behind the three high-voltage switches. The controllable power supply is used for injecting current with wide frequency and adjustable amplitude into the three-phase bus, the injection process utilizes a frequency sweeping method, the injection current can be set according to different power grid architecture parameters, the optimal injection characteristic current is selected from the injection current, the fault area is accurately positioned according to the real-time characteristic current value generated by the fault indicator in each phase of the three-phase bus aiming at the optimal injection characteristic current, and compared with the existing positioning mode, the accuracy is higher.

Description

Power distribution network single-phase earth fault positioning method and system based on sweep frequency injection
Technical Field
The invention belongs to the field of single-phase earth fault positioning of a power distribution network line of a three-phase neutral point ungrounded system, and particularly relates to a power distribution network single-phase earth fault positioning method and system based on sweep frequency injection.
Background
The medium-voltage distribution network at home and abroad widely adopts a neutral point ungrounded mode or a mode of grounding through an arc suppression coil, and compared with a high-voltage transmission network, the medium-voltage distribution network has high probability of faults, wherein single-phase grounding faults occur frequently. When a single-phase fault is grounded, a non-fault phase-to-ground voltage rises, and overvoltage can cause the ground fault to be converted into an interphase short-circuit fault, so that system insulation and equipment safety are seriously damaged, and tripping and power supply interruption are caused. For the safe operation of the system, the fault line and the fault point position need to be determined quickly after the single-phase earth fault, so as to take fault treatment measures further.
Currently, the single-phase earth fault positioning method is mainly divided into an active positioning method and a passive positioning method. The passive fault locating method is mainly used for locating and calculating by utilizing the characteristics of voltage and current signals generated by faults. However, the positioning result of this method is not accurate because the signal is susceptible to interference. The active fault positioning method mainly utilizes an alternating current signal injection method, and mainly utilizes a signal injection device to inject an alternating current signal with specific frequency into a system through a bus voltage transformer, and realizes fault positioning by detecting the position distribution of the signal on a fault line. However, this method has the influence of the capacity limitation of the voltage transformer and the shunt of the distribution capacitance to the injection signal on the injection signal, and the fault location is easy to fail for the power distribution network line architecture with different parameter distributions.
In summary, it is a problem to be solved to further improve the accuracy of locating a single-phase earth fault of a power distribution network line of a three-phase neutral point ungrounded system.
Disclosure of Invention
The invention provides a power distribution network single-phase earth fault positioning system and method based on sweep frequency injection, which aim to improve the positioning accuracy of a single-phase earth fault of a power distribution network line of a three-phase neutral point ungrounded system.
According to the first aspect of the invention, the power distribution network single-phase earth fault positioning system based on sweep frequency injection comprises a plurality of lines to be positioned, wherein the input ends of the lines to be positioned are respectively connected with the output end of a three-phase bus of a power distribution network, and the output ends of the lines to be positioned are sequentially and electrically connected with a three-phase voltage transformer and three high-voltage switches. The three-phase voltage transformer is characterized by further comprising a centralized processor electrically connected with the three-phase voltage transformer and the three high-voltage switches, and a controllable power supply electrically connected with the three high-voltage switches, wherein the other end of the controllable power supply is grounded. The fault indicator is arranged on the lines to be positioned in a scattered manner and is positioned behind the three high-voltage switches; all fault indicators are communicatively coupled to the centralized processor.
Preferably, in the system for locating a single-phase ground fault of a power distribution network based on sweep frequency injection, the controllable power supply is a cascaded H-bridge.
Preferably, in the system for locating a single-phase ground fault of a power distribution network based on swept-frequency injection, a return current detection device electrically connected to the centralized processor is disposed near a ground end of the controllable power supply.
Preferably, in the system for positioning a single-phase earth fault of a power distribution network based on sweep frequency injection, the centralized processor includes a three-phase bus line-to-earth real-time voltage receiving module, a single-phase fault judging module, a controllable power access fault phase control module, a sweep frequency injection command sending module, a real-time characteristic current receiving module and a single-phase earth fault positioning module, which are electrically connected in sequence; the device comprises a three-phase bus ground real-time voltage receiving module, a controllable power supply access fault phase control module, a sweep frequency injection command sending module, a three-phase voltage transformer, a three-phase bus ground real-time voltage receiving module, a three-phase bus ground real-time voltage transformer, a controllable power supply access fault phase control module, a high-voltage switch, a sweep frequency injection command sending module, a real-time characteristic current receiving module and a fault indicator, wherein the three-phase bus ground.
Preferably, in the system for locating a single-phase ground fault of a power distribution network based on sweep frequency injection, the fault indicator includes a characteristic current sending module, and the characteristic current sending module is in communication connection with the real-time characteristic current receiving module.
In combination with the first aspect, a second aspect of the present invention provides a method for locating a single-phase ground fault of a power distribution network based on frequency sweep injection, which is applied to a centralized processor, and the method includes,
receiving real-time ground voltage of a three-phase bus of the power distribution network sent by a three-phase voltage transformer;
judging whether a single-phase fault occurs according to the voltage of the three-phase bus line to the ground, and if so, continuously judging a fault phase;
controlling a high-voltage switch corresponding to the fault to be closed so that a controllable power supply is connected to the fault phase;
sending a fault point positioning command to the controllable power supply so that the controllable power supply injects voltage or current with adjustable frequency and amplitude into a fault phase by using a sweep frequency normal and generates the characteristic current on a line upstream of the fault phase fault point;
receiving real-time characteristic current groups sent by each fault indicator on a fault phase, wherein each real-time characteristic current group comprises three characteristic currents corresponding to the same position of a three-phase bus, and the real-time characteristic currents carry position information of corresponding fault indicator detectors;
and determining the position behind the fault indicator farthest from the output end of the three-phase bus among the fault indicators corresponding to the real-time characteristic current groups with unequal amplitudes of the three characteristic currents as a fault position.
Preferably, the method further comprises detecting the grounding current of the controllable power supply in real time.
Preferably, the sending of the fault point positioning command to the controllable power supply so as to inject a voltage or a current with adjustable frequency and amplitude into the fault phase by using a sweep normal method, and the generating of the characteristic current on the line upstream of the fault phase fault point specifically includes:
determining an initial frequency value, a frequency step and a termination frequency value of the injection frequency;
determining an initial current/voltage amplitude, a current/voltage step and a final current/voltage amplitude;
the controllable power supply changes the output frequency from the initial frequency value to the final frequency value according to the frequency step length to finish one frequency sweep, changes the output current/voltage amplitude from the initial current/voltage amplitude to the final current/voltage amplitude according to the current/voltage step length, and repeats the frequency sweep; ending the sweep injection process until the central processor determines a fault point location or reaches a termination current/voltage amplitude such that the signature current is generated on the line upstream of the fault phase fault point.
Preferably, the injection frequency fcomSatisfies the following range intervals:
wherein, R is the grounding resistance value of the fault point, C0 is the grounding capacitance value of the single-phase line of the normal operation system, omega is the power angular frequency,for the voltage amplitude on the phase of the earth fault, | UNGL is the amplitude of the neutral point to the ground voltage; the injection current amplitude range is less than or equal to one twentieth of the grounding current.
Preferably, the injection current is a direct current or an alternating current.
The invention adopts an active positioning mode to position the single-phase earth fault. The controllable power supply is used for injecting current into the three-phase bus, and the current is injected into the controllable power supply, so that the controllable power supply has the advantages of wide frequency, adjustable amplitude and capability of realizing voltage or current output. The injection process utilizes a frequency sweeping method, the injection current can set a range according to different power grid architecture parameters, the optimal injection characteristic current is selected from the range, the fault area is accurately positioned according to the real-time characteristic current value generated by the optimal injection characteristic current in each phase of the three-phase bus returned by the fault indicator, and compared with the existing positioning mode, the accuracy is higher.
Drawings
Fig. 1 is a schematic structural diagram of a power distribution network single-phase earth fault positioning system based on sweep frequency injection according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the characteristic voltage injection circuit of FIG. 1;
FIG. 3 is a block diagram of the central processor of FIG. 1;
the system comprises a 1-centralized processor, a 101-three-phase bus ground real-time voltage receiving module, a 102-single-phase fault judging module, a 103-controllable power supply access fault phase control module, a 104-sweep frequency injection command sending module, a 105-real-time characteristic current receiving module, a 106-single-phase ground fault positioning module, a 2-three-phase voltage transformer, a 3-high voltage switch, a 4-controllable power supply, a 5-fault indicator, a 501-characteristic current sending module and a 6-return current detection device.
Detailed Description
The invention provides a power distribution network single-phase earth fault positioning system and method based on sweep frequency injection, which aim to improve the positioning accuracy of a single-phase earth fault of a power distribution network line of a three-phase neutral point ungrounded system. The following description is given by way of example.
The power distribution network single-phase earth fault positioning system based on sweep frequency injection comprises a plurality of lines to be positioned, wherein the input ends of the lines to be positioned are respectively connected with the output end of a three-phase bus of a power distribution network. And the output ends of the lines to be positioned are sequentially and electrically connected with the three-phase voltage transformer and the three high-voltage switches. The three-phase voltage transformer is characterized by further comprising a centralized processor electrically connected with the three-phase voltage transformer and the three high-voltage switches, and a controllable power supply electrically connected with the three high-voltage switches, wherein the other end of the controllable power supply is grounded. The fault indicator is arranged on the lines to be positioned in a scattered manner and is positioned behind the three high-voltage switches; all fault indicators are communicatively coupled to the centralized processor.
According to the positioning system provided by the invention, the number of the lines to be positioned connected by the three-phase bus can be multiple, and the number of the lines is not limited by the positioning system provided by the invention. In the implementation, the bus is only required to be divided into a plurality of branches, and each line to be positioned is connected to the plurality of branches, so that all the lines to be positioned are connected to the three-phase bus. Referring to fig. 1, a diagram illustrates a structure of a single-phase ground fault location system of a power distribution network based on sweep frequency injection according to an embodiment of the present invention. This embodiment will be described by taking an example in which three lines to be positioned are connected to the output end of a three-phase bus. As shown in the figure, the positioning system comprises three lines to be positioned, the input ends of the three lines to be positioned are respectively connected with the output end of a three-phase bus of the power distribution network, and the output ends of the three lines to be positioned are respectively and electrically connected with a three-phase voltage transformer 2 and three high-voltage switches 3 in sequence. Three high-voltage switches are K1、K2And K3And the three-phase bus is respectively connected with the phase A, the phase B and the phase C in the three-phase bus. The three-phase voltage transformer is characterized by further comprising a centralized processor 1 electrically connected with a three-phase voltage transformer 2 and three high-voltage switches 3, and a controllable power supply 4 electrically connected with the three high-voltage switches 3, wherein the controllable power supply 4 is controllableThe other end of the power supply 4 is grounded.
The fault indicator is characterized by also comprising a plurality of fault indicators 5 which are dispersedly arranged on the plurality of lines to be positioned and are positioned behind the three high-voltage switches 3; all fault indicators are in communication with the central processor 1. As shown in fig. 1, the fault indicators are labeled a through F. All fault indicators are in communication with the central processor 1. The fault indicator is a fault indicator and has the functions of current detection, fault alarm and the like. The injected specific frequency current can be identified, and the characteristic current amplitude information can be read. A to F all include and connect the three fault indicator that corresponds in the same position of three-phase generating line. A and D are accessed in a line 1 to be positioned, B and F are accessed in a line 2 to be positioned, and C and E are accessed in a line 3 to be positioned.
The working process of the system is divided into three stages. The first stage is to judge whether a single-phase fault occurs; the second stage is to inject characteristic current into the fault phase by using a sweep frequency normal method, the injected characteristic current is adjusted to be optimal injected characteristic current before injection begins, and the third stage is to locate the single-phase grounding position of the fault phase when the injected current is the optimal injected characteristic current. The operation of the system is described below in the sequence of these three phases of operation.
In the first stage, the three-phase voltage transformer 2 detects the real-time voltage of the three-phase bus of the power distribution network to the ground and sends the real-time voltage to the centralized processor. With reference to fig. 1, three real-time voltages U to ground are obtainedA、UBAnd UCWhen there is no single-phase earth fault, UA、UBAnd UCShould be equal or approximately equal, and if U isA、UBOr UCIf one of the two phases suddenly becomes low and the other two phases rise but are smaller than the line voltage, the single-phase earth fault is judged to occur, and UA、UBOr UCThe phase with the medium real-time voltage reduced is the fault phase, and the fault needs to be located immediately. In connection with fig. 1, assume a single-phase earth fault point IgThe failure phase is the C phase. Before positioning, the central processor 1 controls the high-voltage switch K corresponding to C3Closed, so that the controllable power source 4 is switched into the C phase. ThenClosing phase C causes the fault indicators C and E to be connected to the controllable power source 4.
The characteristic voltage injection circuit adopted by the method is shown in figure 2, the controllable power supply 4 adopts a cascade H-bridge topology, the direct current side of each cascade H-bridge adopts a direct current power supply for supplying power, and the cascade H-bridge can inject characteristic voltage with certain frequency and amplitude between a C-phase bus and the ground through a PWM (pulse width modulation) technology. The controllable power supply may be a cascaded H-bridge. The current is injected using a cascaded H-bridge for two reasons: firstly, the cascaded H bridge is a common structural form of the direct-hanging device, can meet the output voltage requirement when directly hanging a network, and can be matched with different cascaded H bridges for power networks with different architectures. Secondly, when the cascade H bridge outputs the current with the specific frequency, the harmonic waves are less, and the coupling link of the transformer is removed, so that the amplitude of the current which can be injected is increased, and the positioning accuracy is facilitated.
The injection current of the controllable power supply of the cascade H bridge can be a direct current injection mode or an alternating current injection mode, and the two injection modes can be selected and used in combination according to specific situations without stipulation.
In the second phase, the central processor 1 sends a fault point positioning command to the controllable power supply 4, so that it injects a voltage or a current with adjustable frequency and amplitude to the C-phase by using the sweep normal, and so that a fault point I is formed at the C-phasegGenerates a characteristic current on the line upstream of (c). When a certain amount of characteristic voltage to ground is injected into the C-phase bus, characteristic current with the same frequency is generated in the C-phase line, and the characteristic current can be subjected to capacitance to ground C from the line1And a ground point IgFlows through and flows back to the cascade H-bridge. The C and E fault indicators on the C line can measure the amplitude information of the characteristic current, and the real-time characteristic currents carry corresponding position information, wherein the position information refers to geographical position information. The real-time characteristic current is transmitted back to the centralized processing system through wireless communication, so that the specific interval of the grounding point can be judged. A return current detection device electrically connected with the centralized processor is arranged at the position close to the ground end of the controllable power supply and used for detecting the injection current flowing out of the controllable power supply in real time, generating characteristic current through a fault phase and flowing back to the return current when the characteristic current flows back to the cascade H-bridgeA flow value. The reflux current value is combined with a real-time characteristic current value which is transmitted back to the centralized processor by the fault indicator, and can be used as a basis for feeding back and adjusting the real-time injection current of the controllable power supply. The injection current of the controllable power supply can be adjusted to the optimal injection characteristic current which is matched with the power grid architecture parameters most. The adjustment process is realized by using a sweep frequency injection method.
In the second stage, the sweep frequency injection method specifically includes: after determining an initial frequency value, a frequency step and a termination frequency value of the injection frequency, and determining an initial current/voltage amplitude value, a current/voltage step and a termination current/voltage amplitude value, the controllable power supply changes the output frequency from the initial frequency value to the termination frequency value according to the frequency step to finish one frequency sweep, changes the output current/voltage amplitude from the initial current/voltage amplitude to the termination current/voltage amplitude according to the current/voltage step, and repeats the frequency sweep; ending the sweep injection process until the central processor determines a fault point location or reaches a termination current/voltage amplitude such that the signature current is generated on the line upstream of the fault phase fault point.
Wherein the selection of the optimal injection characteristic current is specifically operated as follows: first according to neutral point to ground voltage UA、UBAnd a fault phase voltage UCAnd calculating the grounding resistance value. In order to reduce the shunt influence of the distributed capacitance of the fault phase circuit on the characteristic current of the circuit, the range of the frequency of the injection current can be obtained according to the relation between the impedance of the grounding resistance and the impedance of the distributed capacitance. Again, the ground current of the controllable power supply is detected in real time by a return current detection means 6 arranged close to the ground of the controllable power supply 4 as shown in fig. 1. And considering the influence of the injection current on the system, and determining the amplitude range of the injection current according to the detection precision of the fault indicator and the size of the grounding current. Experiments show that when the amplitude range of the injection current is less than or equal to one twentieth of the grounding current, the current has small influence on a system and is easy to detect. The grounding current is sent to the centralized processor 1, and the centralized processor controls the amplitude of the output current of the controllable power supply to be less than or equal to one twentieth of the grounding current according to the grounding current.
Injection frequency fcomSatisfies the following range intervals:
wherein R is the grounding resistance value of the fault point, C0For normal operation of the system, the capacitance value of the single-phase line to the ground, omega is the angular frequency of the power supply,for the voltage amplitude on the phase of the earth fault, | UNGAnd | is the amplitude of the neutral point to the ground voltage. For the same grid circuit, | UCGI and I UNGAnd | is a constant.
After the frequency range and the amplitude range of the current injection are determined, the controllable power supply output voltage injection or the current injection is determined. If the current is injected, the initial current is selected as the minimum value, in the frequency sweeping process, the frequency is gradually adjusted to 0Hz according to the frequency step from the maximum value of the calculated selectable range to finish one frequency sweeping, and the injection current is increased according to the current step until the centralized processing system can receive the signal sent by the fault indicator. If the voltage is injected, the initial voltage is started from 0v, in the process of frequency sweep, the frequency is gradually adjusted to 0Hz according to the frequency step from the maximum value of the calculated selectable range to finish one frequency sweep, and the injection voltage is increased according to the voltage step until the centralized processing system can receive the signal sent by the fault indicator.
The following illustrates the process of the swept frequency implantation method with specific values. Firstly, the ground capacitance C of the power distribution network is obtained0And a ground resistance R. The initial frequency is set as the maximum value of the calculated injection characteristic frequency, the injection characteristic frequency is reduced in sequence by 5Hz frequency steps, and the termination frequency is 0 Hz. Under current injection, in order to facilitate the detection of the characteristic current by the fault indicator, the initial current amplitude is set to be 50mA, the current is increased by 10mA in steps, and the final current amplitude is set to be 5% of the grounding current (generally 20-30A) according to the size of the grounding current. Under voltage injection, the initial voltage amplitude is set to be 0V, the voltage step length is set to be 30V, and the final voltage amplitudeThe setting is 5% of the dc voltage, determined by the dc voltage of the device, thus ensuring that the device is always within the available capacity. According to the parameter setting, changing the output frequency from the initial frequency value to the end frequency value to finish one frequency sweep, changing the output current/voltage amplitude from the initial current/voltage amplitude to the end current/voltage amplitude according to the current/voltage step length, and repeatedly carrying out frequency sweep; the sweep injection process is terminated until the central processor determines the fault point location or the termination current/voltage amplitude is reached.
In the third stage, after the optimal injection characteristic current is determined through the process, the fault area is accurately positioned according to the optimal characteristic current value. The specific positioning process comprises the following steps: and determining the position behind the fault indicator farthest from the output end of the three-phase bus among the fault indicators corresponding to the real-time characteristic current groups with unequal amplitudes of the three characteristic currents as a fault position. With reference to fig. 1, the specific process is as follows: the three of the C and E fault indicators, which are mounted in the same location, transmit the detected characteristic current magnitude back to the centralized processor. When a single-phase earth fault occurs, a condition that one characteristic quantity is obviously increased to the other two currents in three characteristic currents of the fault indicator at the same position before a fault point occurs, and the current values of the three characteristic currents of the fault indicator at the position after the fault point are basically consistent. Therefore, the fault phase with larger characteristic current amount in the same position can be judged by comparing all the returned characteristic currents in the centralized processor, and the position behind the fault indicator which is farthest from the output end of the three-phase bus in the fault indicators corresponding to the real-time characteristic current groups with unequal amplitude of the three characteristic currents is determined as the fault position according to the position information carried in the characteristic currents. Referring to fig. 1, the fault phase is a C-phase, the fault location is Ig, and when the characteristic current is injected into the C-phase, the characteristic current amount detected by the C-fault indicator and the characteristic current amount not detected by the E-fault indicator, the centralized processing system can determine that the single-phase ground fault point is located on the distribution line between the C-fault indicator and the E-fault indicator according to the return signal.
Although only C and E are shown in FIG. 1 as fault indicators on the faulted phase, and fault point IgThe previous fault indicator shows only C. However, fig. 1 is only exemplary, and the density of the arrangement of the fault indicators may be increased if the distribution network is long and the fault rate is high, for example, five fault indicators C are arranged in sequence between C and E in fig. 11-C5To find the grounding point I more accuratelygIs located at C1-C5May be determined by injecting a plurality of current signals of different frequencies and amplitudes. Central processor gets multiple times C1-C5Three sets of real-time signature currents are returned. The injection current with one frequency and amplitude corresponds to the real-time characteristic current returned once. E.g. after the first pass, at C1-C5In the three characteristic currents, one characteristic quantity is obviously increased by the other two currents, and after the Nth return transmission, the characteristic quantity is transmitted to the current C1-C5Of the three characteristic currents, only C1-C3A significant increase of one characteristic quantity to the other two currents, C4-C5This does not happen, and it can be seen that the fault point Ig of the single phase can be determined more accurately according to the multiple feedback information until the precise position of the fault point Ig is locked. Wherein the frequency range of the characteristic current of different frequencies satisfies the above fcomThe range of (1).
In summary, the single-phase ground fault is located by the active locating method. The controllable power supply is used for injecting current into the three-phase bus, and the current is injected into the controllable power supply, so that the controllable power supply has the advantages of wide frequency, adjustable amplitude and capability of realizing voltage or current output. The injection process utilizes a frequency sweeping method, the injection current can set a range according to different power grid architecture parameters, the optimal injection characteristic current is selected from the range, the fault area is accurately positioned according to the real-time characteristic current value generated by the optimal injection characteristic current in each phase of the three-phase bus returned by the fault indicator, and compared with the existing positioning mode, the accuracy is higher.
To implement the three phases of operation described above, reference is made to fig. 3, which shows the architecture of the centralized processor. The centralized processor comprises a three-phase bus ground-to-ground real-time voltage receiving module 101, a single-phase fault judging module 102, a controllable power access fault phase control module 103, a sweep frequency injection command sending module 104, a real-time characteristic current receiving module 105 and a single-phase ground fault positioning module 106 which are electrically connected in sequence; the three-phase bus ground real-time voltage receiving module 101 is electrically connected with the three-phase voltage transformer 2, the controllable power access fault phase control module 103 is electrically connected with the high-voltage switch 3, the sweep frequency injection command sending module 104 is electrically connected with the controllable power supply 4, and the real-time characteristic current receiving module 105 is connected with the fault indicator in a communication mode 501. The communication connection may preferably be a wireless communication. The fault indicator 5 comprises a characteristic current sending module, and the characteristic current sending module 501 is connected with the real-time characteristic current receiving module 105 in a communication mode. The working process of the centralized processor is as follows: the real-time voltage receiving module 101 of the three-phase bus line to ground receives the real-time three-phase voltage to ground transmitted by the three-phase voltage transformer 2, the single-phase fault judging module 102 judges whether a single-phase fault occurs according to the voltage to ground of the three-phase bus line, and if so, the fault phase is continuously judged. When the fault phase is determined, the controllable power access fault phase control module 103 controls the high-voltage switch corresponding to the fault to be closed, so that the controllable power is accessed to the fault phase. The sweep injection command sending module 104 sends a fault point location command to the controllable power supply so that it injects a voltage or current with adjustable frequency and amplitude to the fault phase using the sweep normal and so that the characteristic current is generated on the line upstream of the fault phase fault point. The real-time signature current receiving module 105 receives the real-time signature current sets sent by the fault indicator communication 501 in each fault indicator on the fault phase. The single-phase ground fault location module 106 determines that the position behind the fault indicator farthest from the output end of the three-phase bus among the fault indicators corresponding to the real-time characteristic current groups with unequal amplitudes of the three characteristic currents is the fault position. For detailed processes, reference may be made to the above description of the three-phase operation process of the power distribution network single-phase ground fault location system based on sweep frequency injection, which is not described in detail herein.
It should be noted that the fault indicators in fig. 1 are some of the fault indicators in fig. 3, and are labeled a-E. In practice, the installation distance of the fault indicators is not specified, and can be determined according to the actual operation line, and usually, in the fault-prone line, one fault indicator is arranged every 5 km. The distance can be properly increased due to the non-fault line which is easy to send. In order to quickly eliminate the earth fault after the single-phase earth fault occurs, the inspection personnel can conveniently and sparsely install the inspection area, and the inspection-inconvenient area needs intensive installation. The geographical accuracy of the single-phase earth fault point positioning method is related to the actual installation distance of the current detector, and the more dense the installation is, the more accurate the geographical positioning information is.
In summary, the method for positioning the single-phase earth fault of the power distribution network based on the frequency sweep injection provided by the invention is applied to the system for positioning the single-phase earth fault of the power distribution network based on the frequency sweep injection according to the working processes of the three stages, and the accuracy for positioning the single-phase earth fault of the power distribution network line of the three-phase neutral point ungrounded system can be improved.
The foregoing is directed to embodiments of the present invention, and it is understood that various modifications and improvements can be made by those skilled in the art without departing from the spirit of the invention.

Claims (8)

1. The power distribution network single-phase earth fault positioning system based on sweep frequency injection is characterized by comprising a plurality of lines to be positioned, wherein the input ends of the lines to be positioned are respectively connected with the output end of a three-phase bus of a power distribution network, and the output ends of the lines to be positioned are sequentially and electrically connected with a three-phase voltage transformer (2) and three high-voltage switches (3);
the three-phase voltage transformer is characterized by further comprising a centralized processor (1) electrically connected with the three-phase voltage transformer (2) and the three high-voltage switches (3), and a controllable power supply (4) electrically connected with the three high-voltage switches (3), wherein the controllable power supply (4) is a cascade H-bridge, and the other end of the controllable power supply (4) is grounded;
the fault indicator is characterized by also comprising a plurality of fault indicators (5) which are dispersedly arranged on the plurality of lines to be positioned and are positioned behind the three high-voltage switches (3); all fault indicators are in communication connection with the central processor (1);
the centralized processor (1) is used for receiving the real-time ground voltage of the three-phase bus of the power distribution network sent by the three-phase voltage transformer (2);
judging whether a single-phase fault occurs according to the real-time ground voltage of the three-phase bus, and if so, continuously judging a fault phase;
controlling the high-voltage switch (3) corresponding to the fault to be closed so that the controllable power supply (4) is connected to the fault phase;
sending a fault point positioning command to the controllable power supply (4) so that the controllable power supply injects a voltage or a current with adjustable frequency and amplitude into a fault phase by using a sweep frequency normal and generates a characteristic current on a line upstream of the fault phase fault point;
the injection frequency satisfies the following range interval:
wherein f iscomFor the injection frequency, R is the fault point grounding resistance value, C0For normal operation of the system, the capacitance value of the single-phase line to the ground, omega is the angular frequency of the power supply,for the magnitude of the voltage on the ground fault phase,a neutral-to-ground voltage amplitude; the range of the current amplitude with adjustable injection frequency and amplitude is less than or equal to one twentieth of the grounding current;
receiving real-time characteristic current groups sent by each fault indicator (5) on a fault phase, wherein each real-time characteristic current group comprises three characteristic currents corresponding to the same position of a three-phase bus, and the real-time characteristic currents carry position information of the corresponding fault indicator (5);
and determining the position behind the fault indicator (5) farthest from the output end of the three-phase bus in the fault indicators (5) corresponding to the real-time characteristic current groups with unequal amplitudes of the three characteristic currents as a fault position.
2. A swept frequency injection based single-phase earth fault location system for a power distribution network according to claim 1, characterized in that a return current detection device (6) electrically connected to the centralized processor (1) is provided near the earth end of the controllable power source (4).
3. A frequency sweep injection based single-phase earth fault location system of a power distribution network according to claim 1, characterized in that the centralized processor comprises a three-phase bus earth real-time voltage receiving module (101), a single-phase fault judging module (102), a controllable power access fault phase control module (103), a frequency sweep injection command sending module (104), a real-time characteristic current receiving module (105) and a single-phase earth fault location module (106) which are electrically connected in sequence; the three-phase bus ground-to-ground real-time voltage receiving module (101) is electrically connected with the three-phase voltage transformer (2), the controllable power supply is connected to the fault phase control module (103) and is electrically connected with the high-voltage switch (3), the sweep frequency injection command sending module (104) is electrically connected with the controllable power supply (4), and the real-time characteristic current receiving module (105) is in communication connection with the fault indicator (5).
4. A swept frequency injection based power distribution network single-phase ground fault location system according to claim 3, characterized in that the fault indicator (5) comprises a characteristic current sending module (501), and the characteristic current sending module (501) is in communication connection with the real-time characteristic current receiving module (105).
5. A power distribution network single-phase earth fault positioning method based on sweep frequency injection is applied to a centralized processor and is characterized by comprising the following steps:
receiving real-time ground voltage of a three-phase bus of the power distribution network sent by a three-phase voltage transformer;
judging whether a single-phase fault occurs according to the real-time ground voltage of the three-phase bus, and if so, continuously judging a fault phase;
controlling a high-voltage switch corresponding to the fault to be closed so that a controllable power supply is connected to the fault phase;
sending a fault point positioning command to the controllable power supply so that the controllable power supply injects voltage or current with adjustable frequency and amplitude into a fault phase by using a sweep frequency normal and generates characteristic current on a line upstream of a fault point of the fault phase;
the injection frequency satisfies the following range interval:
wherein f iscomFor the injection frequency, R is the fault point grounding resistance value, C0For normal operation of the system, the capacitance value of the single-phase line to the ground, omega is the angular frequency of the power supply,for the magnitude of the voltage on the ground fault phase,a neutral-to-ground voltage amplitude; the range of the current amplitude with adjustable injection frequency and amplitude is less than or equal to one twentieth of the grounding current;
receiving a real-time characteristic current group sent by each fault indicator on a fault phase, wherein each real-time characteristic current group comprises three characteristic currents corresponding to the same position of a three-phase bus, and the real-time characteristic currents carry position information of the corresponding fault indicators;
and determining the position behind the fault indicator farthest from the output end of the three-phase bus among the fault indicators corresponding to the real-time characteristic current groups with unequal amplitudes of the three characteristic currents as a fault position.
6. A swept frequency injection-based power distribution network single-phase ground fault location method according to claim 5, further comprising detecting ground current of a controllable power source in real time.
7. A swept frequency injection-based single-phase ground fault location method for a power distribution network according to claim 6, wherein the sending of a fault point location command to the controllable power supply enables the controllable power supply to inject a voltage or a current with adjustable frequency and amplitude by using a swept frequency normal, and the generating of the characteristic current on a line upstream of the fault phase fault point specifically means:
determining an initial frequency value, a frequency step and a termination frequency value of the injection frequency;
determining an initial current/voltage amplitude, a current/voltage step and a final current/voltage amplitude;
the controllable power supply changes the output frequency from the initial frequency value to the final frequency value according to the frequency step length to finish one frequency sweep, changes the output current/voltage amplitude from the initial current/voltage amplitude to the final current/voltage amplitude according to the current/voltage step length, and repeats the frequency sweep; ending the sweep injection process until the central processor determines a fault point location or reaches a termination current/voltage amplitude such that the signature current is generated on the line upstream of the fault phase fault point.
8. A swept frequency injection-based power distribution network single-phase ground fault location method according to claim 7, wherein the current with adjustable injection frequency and amplitude is direct current or alternating current.
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