CN113625111B - Distribution network fault location system and method based on additional power supply - Google Patents

Distribution network fault location system and method based on additional power supply Download PDF

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Publication number
CN113625111B
CN113625111B CN202110914103.9A CN202110914103A CN113625111B CN 113625111 B CN113625111 B CN 113625111B CN 202110914103 A CN202110914103 A CN 202110914103A CN 113625111 B CN113625111 B CN 113625111B
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fault
phase
power supply
line
switching tube
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CN113625111A (en
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张超
王怀宇
王建东
刘宇
徐明燕
王涛
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Shandong University of Science and Technology
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Shandong University of Science and Technology
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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
    • 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
    • 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
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • 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
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • 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

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Locating Faults (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The disclosure provides a distribution network fault location system and method based on an additional power supply, comprising the following steps: the control module, the trigger module and the power electronic power supply comprise an alternating current power supply and a switching circuit connected with the alternating current power supply; the switching circuit comprises a plurality of connected switching tubes, the output ends of the switching tubes are connected with each phase line to be detected, and the control module is connected with each switching tube through the triggering module; the control module acquires the operation data of the circuit to be detected in real time, and when the circuit to be detected is detected to be powered off, the switching-on and switching-off of the switching tube of the power electronic power supply are controlled through the trigger module, and a fault distance measurement result is obtained according to the feedback quantity of the detection signal of the circuit to be detected; according to the power electronic power supply, the power electronic power supply is used as an additional power supply, so that fault detection and distance measurement after the three-phase power transmission line is powered off are realized, accurate fault positioning can be performed after the fault type is rapidly determined, the power failure time is shortened, and the power supply stability is improved.

Description

Distribution network fault location system and method based on additional power supply
Technical Field
The disclosure relates to the technical field of fault location, in particular to a power distribution network fault location system and method based on an additional power supply.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
With the increasing demand of electricity, the power system in high-speed development enters a large power grid era with large units, high voltage and cross regions as basic characteristics. The distribution network is at the end of the power system and acts as a bridge between the power system and the power consumers. Since the distribution network is directly connected to the power load, its impact on the power consumer is also greatest. Therefore, the operation stability of the power distribution network is important to the production of enterprises and the life of residents.
Compared with a transmission network, the power distribution network has the advantages that the power distribution network has a plurality of devices, the connection relationship of lines is complex, the lines are staggered and overlapped, the environment is relatively complex, and the power distribution network is easily influenced by various external environments and self problems.
The inventor discovers that for a long time, the research on the fault location of the power system is more biased to the power transmission network, the fault location result is inaccurate when the fault location method of the power transmission network is directly applied to the fault location of the power distribution network, and meanwhile, the fault location cannot be performed according to the response signal of the power system by the existing fault location strategy of the power transmission network.
Disclosure of Invention
In order to solve the defects of the prior art, the present disclosure provides a power distribution network fault distance measurement system and method based on an additional power supply, by setting a power electronic power supply as the additional power supply, fault detection and distance measurement after the three-phase power transmission line is powered off are realized, accurate fault positioning can be performed after the fault type is rapidly determined, power failure time is reduced, and power supply stability is improved.
In order to achieve the above purpose, the present disclosure adopts the following technical scheme:
The first aspect of the disclosure provides a distribution network fault location system based on an additional power supply.
A distribution network fault location system based on an additional power source, comprising: the control module, the trigger module and the power electronic power supply comprise an alternating current power supply and a switching circuit connected with the alternating current power supply;
the switching circuit comprises a plurality of connected switching tubes, the output ends of the switching tubes are connected with each phase line to be detected, and the control module is connected with each switching tube through the triggering module;
the control module acquires the operation data of the circuit to be detected in real time, and when the circuit to be detected is detected to be powered off, the switching-on and switching-off of the switching tube of the power electronic power supply are controlled through the trigger module, and a fault distance measurement result is obtained according to the feedback quantity of the detection signal of the circuit to be detected.
Further, the switching circuit comprises three branches, the first branch comprises a first switching tube and a second switching tube which are connected in series, the middle point of the first branch is connected with the A, the first switching tube is connected with the output end of the alternating current power supply, and the second switching tube is grounded;
The second branch comprises a third switching tube and a fourth switching tube which are connected in series, the middle point of the second branch is connected with the B, the third switching tube is connected with the output end of the alternating current power supply, and the fourth switching tube is grounded;
The third branch circuit comprises a fifth switching tube and a sixth switching tube which are connected in series, the middle point of the third branch circuit is connected with C, the fifth switching tube is connected with the output end of the alternating current power supply, and the sixth switching tube is grounded.
Furthermore, a current transformer and/or a voltage transformer connected with the control module are arranged on the connecting line of the output end of the alternating current power supply and each switch tube.
A second aspect of the present disclosure provides a power distribution network fault location method based on an additional power source.
An additional power supply-based power distribution network fault location method, using the additional power supply-based power distribution network fault location system according to the first aspect of the present disclosure, includes the following processes:
The control module acquires the operation data of the circuit to be detected in real time, and when the circuit to be detected is detected to be powered off, the switching tube of the power electronic power supply is controlled to be turned on and off through the trigger module, so that the power electronic power supply injects detection signals into the circuit to be detected;
in one period of the sine detection signal, fault distance measurement is performed according to the following stages:
The first stage: applying a trigger pulse to the first switching tube, the third switching tube and the fifth switching tube once in each signal period, and turning off the rest switching tubes, wherein the trigger at the stage is used for detecting the ground fault;
And a second stage: triggering pulses are applied to the first switching tube and the fourth switching tube, and the rest switching tubes are turned off and used for detecting AB interphase faults;
And a third stage: triggering pulses are applied to the first switching tube and the sixth switching tube, and the rest switching tubes are turned off and used for detecting AC phase-to-phase faults;
Fourth stage: triggering pulses are applied to the third switching tube and the sixth switching tube, and the rest switching tubes are turned off and used for detecting BC interphase faults;
fifth stage: and judging according to the fault types carried out in the first four stages, and carrying out fault distance measurement.
Further, in the first stage, the ground fault is judged to be a single-phase ground fault or a double-phase ground fault or a three-phase ground fault according to the response currents of A, B, C three phases.
Further, when the response current of the C phase is greater than that of the A phase and the B phase, the C phase is judged to be failed;
When a two-phase short-circuit ground fault occurs, the response current of the fault phase is larger than the response current of the non-fault phase;
when the distribution line has three-phase ground faults, the three-phase response currents are the same;
When the line has no ground fault, the three phases have no response current;
and injecting an excitation voltage signal to the determined grounding fault phase, obtaining a fault loop inductance according to the excitation voltage signal and the response current signal, and obtaining a ranging result according to the fault loop inductance.
Further, in the second stage, the third stage and the fourth stage, inter-phase fault location is performed, including:
the response current between the two failed phases is greater than the response current between the failed phase and the non-failed phase;
And injecting excitation voltage signals to the two phases of the determined interphase faults, obtaining fault loop inductance according to the excitation voltage signals and response current signals, and obtaining a ranging result according to the fault loop inductance.
Further, the fault location of the three-phase short-circuit fault includes:
injecting an excitation voltage signal containing harmonic waves into the line, collecting a response current signal of the line, and measuring harmonic wave impedance of the line in fault and non-fault states through the excitation voltage signal and the response current signal;
The two curves can be expressed by a first-order function, the value of the variable coefficient changes along with the change of the line parameter in the line fault state, the threshold value of the variable coefficient is set according to the line parameter, and whether the line has a three-phase short circuit fault or not is judged according to the value of the variable coefficient;
And injecting excitation voltage signals into the three phases of the determined interphase faults, obtaining fault loop inductance according to the excitation voltage signals and response current signals, and obtaining a ranging result according to the fault loop inductance.
Further, a voltage pulse signal with harmonic content is applied to the head end of the line to obtain a response current signal of the line, the excitation voltage signal and the response current signal are subjected to fast Fourier transformation, and the harmonic impedance of the line is obtained through the excitation voltage signal and the response current signal of the fast Fourier transformation.
Further, the fault ranging result is: the ratio of the fault loop inductance to the inductance of the line per unit length.
Compared with the prior art, the beneficial effects of the present disclosure are:
1. the power electronic switching circuit is used as a controllable disturbance source, the power electronic switching device is converted into an independent controllable signal source from a traditional energy conversion role, the power electronic switching device is high in voltage resistance, high in switching speed, small in driving power and flexible and controllable in conducting state, a detection signal is injected into a system, and fault distance detection can be achieved through analysis of a system response signal.
2. After the power distribution network fails due to faults, an additional power supply is arranged to inject signals into the line, and detection signals injected into the power loss line can form different detection loops by controlling the conduction of different IGBTs in the additional power electronic power supply, so that the fault type detection and the distance measurement of the power loss line can be realized by analyzing the detection signals; the method can detect the fault distance of the power distribution network in a short time, accurately locate the fault and greatly reduce the power failure time of the power distribution network.
Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the exemplary embodiments of the disclosure and together with the description serve to explain the disclosure, and do not constitute an undue limitation on the disclosure.
Fig. 1 is a schematic structural diagram of a detection system according to embodiment 1 of the present disclosure.
Fig. 2 is a schematic diagram of a distance measurement principle of a ground fault according to embodiment 2 of the present disclosure.
Fig. 3 is a circuit diagram of a circuit C phase ground fault equivalent circuit according to embodiment 2 of the present disclosure.
Fig. 4 is a simplified circuit model of a line C ground fault as described in embodiment 2 of the present disclosure.
Fig. 5 is a simulation diagram of a detected current waveform when a C-phase earth fault exists in a line according to embodiment 2 of the present disclosure.
Fig. 6 is a simplified model of a line C ground fault location circuit according to embodiment 2 of the present disclosure.
Fig. 7 is an equivalent circuit diagram of an AB interphase fault in a line according to embodiment 2 of the present disclosure.
Fig. 8 is a simplified model of a ranging circuit in the presence of an AB phase-to-phase fault on a line according to embodiment 2 of the present disclosure.
Fig. 9 is a simulation diagram of a detected current waveform when an AB interphase fault exists in a line according to embodiment 2 of the present disclosure.
Fig. 10 is a response current wave line when a three-phase short-circuit fault exists in a line according to example 2 of the present disclosure.
Fig. 11 is a plot of harmonic impedance in a fault versus non-fault condition for a line with a three-phase short circuit fault as described in example 2 of the present disclosure.
Fig. 12 is a signal spectrum and harmonic impedance for a line with an a-phase ground fault as described in example 3 of the present disclosure.
Fig. 13 is a fault location result when a line has an a-phase ground fault according to example 3 of the present disclosure.
Fig. 14 is a signal spectrum and harmonic impedance of a line with an AB interphase fault as described in example 3 of the present disclosure.
Fig. 15 is a fault location result when an AB interphase fault exists in a line according to example 3 of the present disclosure.
Detailed Description
The disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Embodiments of the present disclosure and features of embodiments may be combined with each other without conflict.
Example 1:
As shown in fig. 1, embodiment 1 of the present disclosure provides a power distribution network fault location system based on an additional power source, which includes a control module, a trigger module and a power electronic power source, wherein output ends of the power electronic power source are respectively connected with each phase line to be detected, the control module respectively controls and connects with the output ends of the power electronic power source through the trigger module, and analyzes detection signals injected into corresponding phase lines to obtain fault distances of the fault lines.
And the control module is used for: the control instruction is used for generating a control instruction of the power electronic switching power supply, and fault distance calculation is carried out after the fault type is obtained through analysis;
The triggering module is used for: the power electronic device is used for generating a trigger signal according to a control instruction of the control module and triggering the power electronic device of the power electronic switching power supply to work;
In this embodiment, the power electronic power supply includes an ac power supply and a switching circuit, the switching circuit includes a plurality of connected switching tubes, the output end of the switching tube is connected to each phase line to be detected, and the trigger end of the switching tube is connected to the trigger module.
The power electronic power supply comprises an alternating current power supply and a switching circuit connected to two ends of the alternating current power supply, the switching circuit comprises six IGBTs, wherein two IGBTs are connected in parallel after being connected in series to form three IGBT branches, the middle point of each branch is an output end and is respectively connected to an A phase, a B phase and a C phase of a three-phase circuit, two IGBTs on each branch are respectively connected, one IGBT is a signal injection IGBT and is used for being connected with the output end of the alternating current power supply, and the other IGBT is a grounding IGBT and is used for being connected with the grounding end.
Specifically, in this embodiment, the IGBT leg connected to the a phase includes a first injection IGBT Q1 and a first ground IGBT Q2 connected in series, the IGBT leg connected to the B phase includes a second injection IGBT Q3 and a second ground IGBT Q4 connected in series, and the IGBT leg connected to the C phase includes a third injection IGBT Q5 and a third ground IGBT Q6 connected in series.
The detection signal provided by the alternating current power supply is injected into the power-losing circuit through the IGBT unit, then passes through the insulation resistance and the grounding capacitance of the cable, and finally flows into the grounding point of the alternating current power supply to form a loop.
Further, the system also comprises a current transformer and a voltage transformer which are arranged on the line, wherein the current transformer is connected with the voltage transformer control module and is used for detecting the injected current detection signal and the voltage detection signal.
The embodiment adopts the power electronic switch circuit as a controllable disturbance source, converts the power electronic switch device from the traditional energy conversion role into an independent controllable signal source, has high voltage resistance, large capacity and flexible and controllable conduction state, injects detection signals into a system, and can analyze the response of the system to realize fault distance measurement.
According to the system, after the power distribution network is powered off due to failure, an additional power supply is arranged to inject signals into the line, different detection loops are formed by detecting signals injected into the power loss line by controlling the conduction of different IGBTs in the additional power electronic power supply, and the detection signals are analyzed to realize the failure type detection and distance measurement of the power loss line. The method can detect the fault distance of the power distribution network in a short time, and greatly reduces the power failure time of the power distribution network.
Example 2:
Based on the system of embodiment 1, embodiment 2 of the present disclosure provides a power distribution network fault location method based on an additional power source, which may be implemented in a control module, including the following steps;
Step 1, acquiring operation data of a circuit to be detected in real time, identifying whether the circuit to be detected is powered off, and executing the next step if the circuit to be detected is powered off;
Step 2, detecting the ground fault, outputting a control signal to control the injection of an IGBT (insulated gate bipolar transistor) triggering a switch unit of the power electronic power supply so that the power electronic power supply injects a detection signal into a line to be detected, analyzing the detection signal to obtain a fault type, and performing distance calculation to obtain a fault distance detection result;
For interphase fault detection, a control signal is output to control injection IGBT of a switching unit connected with one phase line, so that a power electronic power supply injects detection signals into a phase line to be detected, ground IGBT of switching units connected with other phase lines is controlled to trigger, the detection signals are analyzed to obtain fault types, and distance calculation is carried out to obtain a fault distance detection result.
Different IGBT turn-on strategies are needed for fault location of different line faults, and accordingly an IGBT turn-on scheme is formulated.
Step 2 is an IGBT turn-on scheme, and the trigger module turns on the IGBT of the switch unit by outputting a control signal of the control module to the trigger module. As shown in table 1, the conduction condition table of each IGBT during different types of fault detection, specifically, the embodiment adopts the following trigger control method, which includes:
because the detection signal is a sine signal, and the conduction of the IGBT is required to be within the positive half cycle of the signal, a signal cycle is specified for convenience of description, namely, a cycle of the sine detection signal;
the first stage: the duration is 1 signal period, a trigger pulse is applied to the IGBT Q 1,Q3,Q5 at each signal period at this stage, the rest of the IGBTs are turned off, and the trigger at this stage is used for detecting the ground fault.
And a second stage: the duration is 1 signal period, trigger pulse is applied to the IGBT Q 1,Q4 at this stage, and other IGBTs are turned off and used for detecting AB phase-to-phase faults.
And a third stage: the duration is 1 signal period, trigger pulse is applied to the IGBT Q 1,Q6 at this stage, and the rest of the IGBTs are turned off for detecting AC phase-to-phase faults.
Fourth stage: the duration is 1 signal period, trigger pulse is applied to IGBT Q 3,Q6 at this stage, and other IGBTs are turned off for detecting BC interphase faults.
Fifth stage: and judging according to the fault types carried out in the first four stages, and carrying out fault distance measurement.
Table 1:
in step 2, various faults are identified, and the following description is given according to the fault type.
Step 2.1: ground fault ranging
In step 2, the output control signal controls the injection of the switch unit triggering the power electronic power supply into the IGBT, the type of the ground fault is mainly judged according to the current of A, B, C three phases, and if one phase of current is far greater than the other two phases of current, the phase is in the ground fault. After the fault type is determined, fault location is performed according to the detection signal.
The principle of ground fault ranging is described below with specific examples, and as shown in fig. 2, the turn-on condition of the IGBT and the flow direction of the detection current are included.
The control module controls the trigger module to conduct the IGBTs Q 1,Q3,Q5 simultaneously, and the Q 2,Q4,Q6 is closed. The current signal is injected into the three-phase line through the IGBT Q 1,Q3,Q5, a current loop is formed, the fault type is judged by analyzing the detected current signal, and fault distance measurement is carried out.
Taking the C-phase earth fault as an example, the fault phase and non-fault equivalent circuit is drawn according to the fault loop as shown in figure 3. In the drawing of figure 3 of the drawings,For bus-to-load line impedance,/>For load impedance, the ratio of the distance from the fault point to the head end of the line to the total length of the line is represented by R f, the fault resistance is represented by E, and when the conduction angle of the IGBT is delta:
In phases 1,2,3 and 4, different loops are formed by controlling the on-combinations of IGBTs. When the distribution line fails, the response current will be different from the unbalanced current that occurs when the load is unbalanced, and the fault type can be determined according to the unbalanced current. Assuming that the three-phase line parameters are the same, the three-phase loads are balanced and the parameters are the same. In order to study the effect of the line shunt capacitance, a PI model of the transmission line is considered, and the simplified network is shown in fig. 4 (a). The line parameters are represented by impedance, and the AB two phases are combined because the a phase and B phase parameters are identical, and the combined network is as in (B) of fig. 4.
Z5＝kZlineC
Z6＝(1-k)ZlineA
As can be seen from fig. 4 (b), the connection between the impedances Z 1,Z2 and Z 4 is Y-shaped, and the connection between the impedances Z 6,Z7 and Z 8 is also Y-shaped. The impedance is converted into delta connection to further simplify the circuit, and an equivalent circuit shown in (c) of fig. 4 is obtained, and the impedance parameters after conversion are as follows:
The whole of the impedances Z 9,Z14 and Z 11+13+15 has a delta connection characteristic, and in order to simplify the circuit, the delta connection impedance can be converted into a Y connection, so as to obtain an equivalent circuit shown in (d) of fig. 4, and the impedance parameters after conversion are as follows:
Z23＝Z11+Z13+Z15
Assuming that the three-phase line parameters are uniform and the three-phase loads are balanced, the impedance parameters Z lineA、ZlineB、ZlineC and the three-phase load parameters Z loadA、ZloadB、ZloadC of the above lines are the same, and for convenience of comparison, the three-phase line and the three-phase load parameters are represented by a-phase parameters, and further simplified fault loop parameters are as follows
The fault phase current is:
fault-free phase current:
as can be derived from the above formula, the current I b flowing through the non-faulted phase is the same as the current I a flowing through the non-faulted phase, because the denominator in the faulted phase is much smaller than the denominator in the non-faulted phase, the current I c flowing through the faulted phase is much greater than the current I a、Ib flowing through the non-faulted phase. The simulated waveforms of the sensed current are shown in fig. 5.
In phase 1, when the response current of the C phase is greater than that of the a phase and the B phase, it can be judged that the C phase is failed. Similarly, when a two-phase short-circuit ground fault occurs, the response current of the fault phase is greater than the response current of the non-fault phase under the same excitation voltage signal because the equivalent impedance of the fault phase is less than the equivalent impedance of the non-fault phase. When the distribution line has three-phase ground faults, the three-phase response currents are the same due to the symmetry of the faults. When the circuit has no ground fault, the IGBT converter in the step 1 and the circuit do not form a loop, and three phases have no obvious response current.
In stage 5, a voltage pulse signal with rich harmonic content is applied to the head end of the line to obtain a response current signal of the line, and FFT (Fast Fourier Transform) is performed on the excitation voltage signal and the response current signal to obtain fundamental wave and harmonic components in the excitation voltage signal and the response current signal. When the conduction angle is 0 °, the excitation voltage signal contains only the fundamental frequency voltage (original signal) having the same amplitude as the excitation voltage signal, and does not contain the higher harmonic voltage. When the conduction angle is 90 degrees, the excitation voltage signal contains rich harmonic voltage signals, and the harmonic impedance of the line can be obtained through the excitation voltage signal and the response current signal.
By the fault type detection method, the fault type of the line can be obtained, taking a C-phase grounding fault as an example, when the power distribution network fault distance measuring device detects that the C-phase grounding fault exists in the line, the IGBT 5 is selected to be conducted in the stage 1 to inject an excitation voltage signal into the fault line, and as the IGBT corresponding to the fault phase is only controlled to be conducted, the effect on a distance measuring result when the auxiliary current of the non-fault phase flows through a fault resistor is avoided, and an equivalent circuit of the fault loop is shown in the figure 6.
The ranging circuit after determining the fault type is more specific than the fault type identification, so the fault circuit is simpler and clearer, and as can be seen from (b) in fig. 6, the simplified ranging circuit has only line impedance, fault resistance and capacitance to ground, and the influence on the ground resistance is very small and can be almost ignored.
From the foregoing, it can be seen that when the acquisition period is fixed, the frequency variation of the power supply has little influence on the experimental result, the acquisition period does not need to vary along with the period variation of the power supply signal, the acquisition point number is N, the sampling time interval is T, and the acquisition period is T
T＝N*t
Let the sampling frequency be f
Let the angular velocity be ω 0
In the harmonic impedance calculated by the excitation voltage signal and the response current signal, the magnitude of the 0 th harmonic impedance is
Zeq0＝Rf+kRCL
The magnitude of the n-order harmonic impedance is
The harmonic impedance of the distribution line at different frequencies can be expressed as
The fundamental frequency reactance X 1 of the line is
According to the harmonic impedance, the reactance is calculated, and further according to the angular velocity information, the inductance of the line is calculated
The fault distance is s=l/L 0,l0 is the inductance of the line per unit length. The inductance of the fault loop is calculated through the steps, the fault is measured, and the influence of the fault resistance on the measuring result can be avoided by measuring the fault by using the inductance.
Step 2.2: interphase fault distance measurement
The inter-phase fault detection and ranging method specifically controls trigger signals to trigger IGBTs of any two-phase lines, wherein a switching unit connected with one phase line triggers injection of the IGBTs, a switching unit connected with the other phase line triggers a grounding IGBT, fault types are judged according to the magnitude and the polarity of inter-phase current, and fault ranging is conducted according to detection information.
The interphase fault detection method, see fig. 7, includes the turn-on condition of the IGBT and the flow direction of the detection current.
Taking the detection of AB interphase faults as an example, the IGBT Q 1,Q4 is turned on, the rest is turned off, and a fault ranging equivalent circuit diagram is shown in the figure 8.
Assuming the three-phase line parameters are the same, the three-phase loads are balanced. In order to study the effect of the line shunt capacitance, PI models of the transmission line are considered. The simplified network is shown in fig. 8 (a), the positions of the elements in fig. 8 (a) are adjusted and rearranged, the simplified network is shown in fig. 8 (b), and the parallel devices Z 4 and Z 3 are combined to obtain Z 6.
The simplified circuit is shown in fig. 8 (c), the circuit is further simplified, and Z 6、Rf and Z 2 are combined, resulting in a simplified equivalent element Z 7 as shown in fig. 8 (d):
Further combining the impedances in FIG. 8 (d) to obtain Z eq as in FIG. 8 (e)
In the case of a non-fault:
Zeq＝2(ZlineB+ZloadB)
As can be seen from the above equation, when the line phase fault loop and the normal loop have a large difference in impedance, the current will be significantly different when the voltage signal is injected into the fault loop and the non-fault loop. The simulated waveform of A, B phase detection current at the time of failure is shown in fig. 9.
When the IGBT combination for detecting interphase faults is conducted, current flows through the fault phase and the fault point, current Ia approximately equal to Ib flowing through the fault phase, and non-fault phase current ic=0, and it can be judged that the fault phase current is larger than the non-fault phase current. Similarly, when the line is shorted in BC two phases or AC two phases, the response current of the two failed phases will be greater than the response current of the failed and non-failed phases. The fault type may be determined based on the above features.
After the AB interphase fault is obtained through the fault type detection method, the IGBT Q 1 and the IGBT Q 4 are selected to be conducted in the stage 2 to inject the excitation voltage signal into the fault line, and as the IGBT corresponding to the fault phase is only controlled to be conducted, the auxiliary current generated by the non-fault phase at the fault point is prevented from influencing the distance measurement result when the auxiliary current of the non-fault phase flows through the fault resistor.
The same distance measurement mode as that in the case of the ground fault is adopted
T＝N*t
The harmonic impedance of the distribution line at different frequencies can be expressed as
The fundamental frequency reactance X 1 of the line is
The inductance of the circuit is
The fault distance can be calculated by s=l/L 0, and L 0 is the inductance of the line per unit length.
Step 2.3: three-phase short circuit fault distance measurement
When a three-phase short-circuit fault occurs on a line, neither a ground current can be detected nor a three-phase short-circuit fault can be judged by unbalanced response currents, and the response currents in the fault and non-fault conditions are shown in fig. 10.
Although the three-phase short-circuit fault current is larger than the short-circuit current under the non-fault condition, the fault type is difficult to accurately judge by taking the current size as a standard, the change of the load and the distance of a fault point can influence the current size, and the current judgment threshold value of the three-phase short circuit is difficult to define, so that the judgment result is influenced. In order to accurately judge the fault type under the condition of three-phase short circuit, the harmonic impedance of the line can be detected at the moment, and whether the three-phase line has permanent faults or not is judged through the harmonic impedance. The harmonic impedance is represented by Z (n), and the expression of the harmonic impedance is:
where n is the harmonic order, and the harmonic impedance is the impedance characteristic of the system at different frequency harmonics.
An excitation voltage signal containing harmonic waves is injected into the line, a response current signal of the line is acquired, and the harmonic wave impedance of the line in fault and non-fault states is measured through the excitation voltage signal and the response current signal, and the measurement result is shown in fig. 11.
When the line is fault-free, the harmonic impedance in the non-fault state increases with the increase of the frequency, so that the harmonic impedance of the system in the non-fault state presents a larger slope. When a three-phase short circuit fault occurs, the change amplitude of the harmonic impedance in the fault state along with the increase of the frequency is smaller, so that the harmonic impedance of the system in the fault state presents a smaller slope. Both curves can be represented by y=a+bx, the value of b in the line fault state changes along with the change of the line parameter, the threshold value of b is set according to the line parameter, and whether the line has a three-phase short circuit fault or not can be judged according to the value of b.
After the fault type is determined by the method, fault location can be performed. The distance measurement principle is the same as that of the method, inductance data is obtained through harmonic impedance data, and the fault is measured.
Example 3:
based on the system of embodiment 1 and the method of embodiment 2, a fault is set on a distribution line, an excitation voltage signal is injected, an excitation voltage signal and a response current signal are detected, the signals are decomposed to obtain harmonic information, impedance information is further obtained through the harmonic information, and then the fault is located, and specific examples are as follows:
(1) Ground fault ranging
Taking an A-phase grounding fault at 4km of a line as an example, injecting an excitation voltage signal, detecting an excitation signal and a response signal, decomposing the signals to obtain harmonic components of the voltage and current signals, positioning the fault through the voltage and current harmonic components, and decomposing harmonic impedance data of a third column of a first line to obtain position information of the line fault by using each signal and harmonic component under single-phase grounding fault as shown in figure 12, wherein each line represents voltage spectrum, current spectrum and harmonic impedance information of each phase.
The ground fault is measured by harmonic impedance, the fault is measured by 9 times by 0 to 9 times of harmonic impedance, the measured result is shown in figure 13, the measured result is very close to the actual fault position, the error is less than or equal to 0.1%, the error of taking the median as the experimental result is 0.05%, and the average value error is 0.0417%.
To verify the influence of the change in the distance of the fault point on the ranging result, the distance of the fault point was adjusted a plurality of times, ranging was sequentially performed from the setting of the fault distance to 0.5km until the fault distance reached 5.5km, and the ranging result is shown in table 2.
TABLE 2
Further, in order to determine the influence of the fault resistance on the ranging result, the size of the fault resistance was changed with the line length unchanged, the fault distance was set to 2km, and the test result is shown in table 3.
Table 3:
(2) Interphase fault distance measurement
An AB two-phase short circuit fault is arranged at a position 4km away from the head end of the line, corresponding IGBT conduction combinations are arranged according to fault types, excitation voltage signals are injected into the fault line, and the excitation voltage and response current signals are decomposed to obtain harmonic components of the signals, as shown in figure 14.
The inter-phase faults are measured through harmonic components, 0 to 9 harmonics are taken for measuring the faults for 9 times, and the measuring result is shown in figure 15. As shown by the ranging results, most of the ranging results have higher accuracy except that the deviation of the individual ranging results is larger, two ranging data with larger errors are removed, the error is 0.65%, the ranging error is 0.125% when the median 4.005 is adopted as the experimental result, and the average value error is 0.63%.
To verify the influence of the change in the distance of the fault point on the ranging result, the distance of the fault point was adjusted a plurality of times, ranging was sequentially performed from the setting of the fault distance to 0.5km until the fault distance reached 5.5km, and the ranging result is shown in table 4.
TABLE 4 Table 4
Further, in order to determine the influence of the fault resistance on the ranging result, the magnitude of the fault resistance was changed with the line length unchanged, the fault distance was set to 2km, and the test result is shown in table 5.
TABLE 5
The foregoing description of the preferred embodiments of the present disclosure is provided only and not intended to limit the disclosure so that various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims (5)

1. A power distribution network fault location method based on an additional power supply is characterized by comprising the following steps of: the method comprises the following steps:
The control module acquires the operation data of the circuit to be detected in real time, and when the circuit to be detected is detected to be powered off, the switching tube of the power electronic power supply is controlled to be turned on and off through the trigger module, so that the power electronic power supply injects detection signals into the circuit to be detected;
in one period of the sine detection signal, fault distance measurement is performed according to the following stages:
The first stage: applying a trigger pulse to the first switching tube, the third switching tube and the fifth switching tube once in each signal period, and turning off the rest switching tubes, wherein the trigger at the stage is used for detecting the ground fault;
And a second stage: triggering pulses are applied to the first switching tube and the fourth switching tube, and the rest switching tubes are turned off and used for detecting AB interphase faults;
And a third stage: triggering pulses are applied to the first switching tube and the sixth switching tube, and the rest switching tubes are turned off and used for detecting AC phase-to-phase faults;
Fourth stage: triggering pulses are applied to the third switching tube and the sixth switching tube, and the rest switching tubes are turned off and used for detecting BC interphase faults;
fifth stage: judging according to the fault types carried out in the first four stages, and carrying out fault distance measurement;
In the first stage, according to the response current of A, B, C three phases, judging that the ground fault is a single-phase ground fault or a double-phase ground fault or a three-phase ground fault;
when the response current of the C phase is larger than that of the A phase and the B phase, judging that the C phase is in fault;
When a two-phase short-circuit ground fault occurs, the response current of the fault phase is larger than the response current of the non-fault phase;
when the distribution line has three-phase ground faults, the three-phase response currents are the same;
When the line has no ground fault, the three phases have no response current;
injecting excitation voltage signals to the determined grounding fault phases, obtaining fault loop inductance according to the excitation voltage signals and response current signals, and obtaining a ranging result according to the fault loop inductance;
Applying a voltage pulse signal with harmonic content to the head end of the line to obtain a response current signal of the line, performing fast Fourier transform on the excitation voltage signal and the response current signal, and obtaining the harmonic impedance of the line through the excitation voltage signal and the response current signal of the fast Fourier transform; and calculating according to harmonic impedance to obtain reactance, and further calculating according to angular velocity information to obtain inductance of the line.
2. The additional power source-based power distribution network fault location method as claimed in claim 1, wherein:
And in the second stage, the third stage and the fourth stage, inter-phase fault distance measurement is performed, including:
the response current between the two failed phases is greater than the response current between the failed phase and the non-failed phase;
And injecting excitation voltage signals to the two phases of the determined interphase faults, obtaining fault loop inductance according to the excitation voltage signals and response current signals, and obtaining a ranging result according to the fault loop inductance.
3. The additional power source-based power distribution network fault location method as claimed in claim 1, wherein:
Fault location for a three-phase short circuit fault, comprising:
injecting an excitation voltage signal containing harmonic waves into the line, collecting a response current signal of the line, and measuring harmonic wave impedance of the line in fault and non-fault states through the excitation voltage signal and the response current signal;
The two curves can be expressed by a first-order function, the value of the variable coefficient changes along with the change of the line parameter in the line fault state, the threshold value of the variable coefficient is set according to the line parameter, and whether the line has a three-phase short circuit fault or not is judged according to the value of the variable coefficient;
And injecting excitation voltage signals into the three phases of the determined interphase faults, obtaining fault loop inductance according to the excitation voltage signals and response current signals, and obtaining a ranging result according to the fault loop inductance.
4. An additional power source based power distribution network fault location method as claimed in claim 1 or 2 or 3, wherein:
The fault ranging result is as follows: the ratio of the fault loop inductance to the inductance of the line per unit length.
5. A distribution network fault location system based on additional power supply, its characterized in that: with the additional power source based distribution network fault location method as claimed in any one of claims 1-4,
Comprising the following steps: the control module, the trigger module and the power electronic power supply comprise an alternating current power supply and a switching circuit connected with the alternating current power supply;
the switching circuit comprises a plurality of connected switching tubes, the output ends of the switching tubes are connected with each phase line to be detected, and the control module is connected with each switching tube through the triggering module;
the control module acquires the operation data of the circuit to be detected in real time, and when the circuit to be detected is detected to be powered off, the switching-on and switching-off of the switching tube of the power electronic power supply are controlled through the trigger module, and a fault distance measurement result is obtained according to the feedback quantity of the detection signal of the circuit to be detected;
the switching circuit comprises three branches, wherein the first branch comprises a first switching tube and a second switching tube which are connected in series, the midpoint of the first branch is connected with A, the first switching tube is connected with the output end of an alternating current power supply, and the second switching tube is grounded;
The second branch comprises a third switching tube and a fourth switching tube which are connected in series, the middle point of the second branch is connected with the B, the third switching tube is connected with the output end of the alternating current power supply, and the fourth switching tube is grounded;
The third branch comprises a fifth switching tube and a sixth switching tube which are connected in series, the midpoint of the third branch is connected with C, the fifth switching tube is connected with the output end of the alternating current power supply, and the sixth switching tube is grounded;
And a current transformer and/or a voltage transformer connected with the control module are arranged on the connecting line of the output end of the alternating current power supply and each switch tube.
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