CN113009282B - Medium-voltage power distribution network disconnection fault diagnosis method considering single PT - Google Patents
Medium-voltage power distribution network disconnection fault diagnosis method considering single PT Download PDFInfo
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- CN113009282B CN113009282B CN202110275397.5A CN202110275397A CN113009282B CN 113009282 B CN113009282 B CN 113009282B CN 202110275397 A CN202110275397 A CN 202110275397A CN 113009282 B CN113009282 B CN 113009282B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
Abstract
The invention discloses a medium-voltage distribution network disconnection fault diagnosis method considering single PT, which comprises the following steps of: step 1: analyzing the influence relationship of double PT (potential transformer) and single PT (potential transformer) power taking modes on the fault diagnosis of the single-phase disconnection of the medium-voltage distribution network from the perspective of feasibility of the single-phase disconnection fault diagnosis of the medium-voltage distribution network, and further establishing a PT power taking mode configuration principle; step 2: and optimizing a PT power-taking mode configuration principle from the angles of line diagnosable range maximization and positioning accuracy optimization. The method is characterized in that one double PT is equivalent to two single PTs, and an electricity taking mode configuration principle is established on the basis; from the angle of the maximum diagnosable range and the optimal positioning precision of the medium-voltage distribution network, the PT power-taking mode configuration principle is optimized in two scenes of a newly-built line and a newly-added user demarcation switch on the original line, and the quick and accurate diagnosis of the medium-voltage distribution network disconnection fault is realized.
Description
Technical Field
The invention relates to the field of power grid fault diagnosis, in particular to a single-phase broken line fault diagnosis method for a medium-voltage distribution network.
Background
The power distribution network disconnection fault is one of common faults of the power distribution network. After the distribution line has a disconnection fault, part of users are directly powered off, the disconnection and grounding can cause electric shock accidents, and meanwhile, the asymmetric voltage generated by long-time disconnection operation can damage electric equipment, so that the disconnection position can be timely positioned and the fault can be processed, which is an urgent requirement of power enterprises. At present, there are two aspects's problems in medium voltage distribution network disconnection fault diagnosis:
(1) the main station system of the power enterprise only concerns the measurement data at the outlet switch of the substation, and causes that: 1) if and only if the power supply side at the disconnection position is disconnected and grounded and grounding current is caused, the master station system can find out line faults; 2) the broken line position cannot be positioned only through the measurement data at the outlet switch of the substation. Therefore, at present, power enterprises mainly find disconnection faults in a manner of complaints of users, and fault positions are searched through manual line patrol, so that the fault diagnosis and processing efficiency is low.
(2) On the medium-voltage distribution line, two Potential Transformers (PT) are arranged at the section switch and the interconnection switch, and are marked as double PTs. Under the general condition, two PTs get electricity from switch both sides circuit respectively: one PT takes power from the AB phase on one side of the switch, and the other PT takes power from the BC phase on the other side of the switch. And only one voltage transformer is configured at the user demarcation switch, and is marked as single PT, and the power phase is not fixed. At present, part of documents research on the use of double PTs at a section switch and a tie switch for judging the line break fault of a power grid, but no research on a PT power taking mode under the condition of a single PT and how to use the PT power taking mode for diagnosing the line break fault of a power distribution line exists.
Disclosure of Invention
The invention aims to provide a medium-voltage distribution network disconnection fault diagnosis method considering single PT, aiming at realizing the medium-voltage distribution network disconnection fault diagnosis by utilizing the optimized configuration of the existing PT, particularly the single PT power-taking phase: by reasonably configuring the single PT power taking mode at the user demarcation switch, the method for diagnosing the disconnection fault of the medium-voltage distribution network is optimized, and the quick and accurate diagnosis of the disconnection fault of the medium-voltage distribution network is realized.
In order to solve the technical problem, the invention discloses a medium voltage distribution network disconnection fault diagnosis method considering single PT, which comprises the following steps of:
step 1: analyzing the influence relationship of double PT (potential transformer) and single PT (potential transformer) power taking modes on the fault diagnosis of the single-phase disconnection of the medium-voltage distribution network from the perspective of feasibility of the single-phase disconnection fault diagnosis of the medium-voltage distribution network, and further establishing a PT power taking mode configuration principle;
step 2: and optimizing a PT power-taking mode configuration principle from the angles of line diagnosable range maximization and positioning accuracy optimization.
The specific operation process of the step 1 is as follows:
step 1.1: analyzing the influence of the double PT power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network:
(1) taking power from the double PT in-phase, such as from AB phase, BC phase or CA phase; analysis was performed taking the double PT all from the AB phase as an example:
1) the A phase circuit on the upstream side of the double PT has a disconnection fault; when the A phase circuit on the upstream side of the double PTs has a disconnection fault, the double PTs take power from the AB phase, so that the measured line voltages are all 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
2) a B phase circuit on the upstream side of the double PT is broken; when a B phase line circuit on the upstream side of the double PTs breaks down, the double PTs take power from the AB phase, so that the measured line voltages are all 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
3) a C-phase circuit on the upstream side of the double PT is broken; when the C-phase line circuit on the upstream side of the double PTs has a disconnection fault, the double PTs take power from the AB phase, so that the measured line voltage is normal; only the normal operation of the upstream lines of the A phase and the B phase can be obtained from the measured value, but the operation condition of the C phase cannot be diagnosed;
(2) taking electricity from the double PT out of phase, such as taking electricity from the AB phase at one side and taking electricity from the BC phase at the other side, or taking electricity from the AB phase at one side and taking electricity from the CA phase at the other side; taking the example of taking electricity from AB phase at one side of double PT and electricity from BC phase at the other side as an example:
1) the A phase circuit on the upstream side of the double PT has a disconnection fault; when the A phase circuit on the upstream side of the double PT is broken, the line voltage obtained by measurement is obtained because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU AB=0，U BCThe value is normal; fromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BCThe normal value can obtain the normal operation of the upstream lines of the B phase and the C phase, so that the three-phase operation state can be deduced as follows: the phase A circuit has a disconnection fault, and the phase B circuit and the phase C circuit run normally;
2) a B phase circuit on the upstream side of the double PT is broken; when the B phase circuit on the upstream side of the double PT is broken, the line voltage obtained by measurement is obtained because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU AB=0，U BC= 0; fromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BC=0 available upstream line of B phase or C phase has a disconnection fault; from this measurement no accurate conclusions can be drawn, which may be as follows: a) the phase B circuit has a disconnection fault, and the phase A and phase C circuits normally operate; b) the line breakage fault occurs to the line of the phase A and the line of the phase B, and the line of the phase C runs normally; c) the circuit of the phase A and the phase C is broken, and the phase B operates normally; d) the circuit of the phase B and the phase C is broken, and the phase A operates normally; e) the phase A, the phase B and the phase C have disconnection faults;
3) a C-phase circuit on the upstream side of the double PT is broken; when the C phase circuit on the upstream side of the double PT is broken, because one side of the double PT takes power from the AB phase and the other side takes power from the BC phase,thus measured line voltageU ABThe value is normal and the value is normal,U BC= 0; fromU ABNormal value can obtain normal operation of A-phase and B-phase circuits, so thatU BC=0, the available B-phase or C-phase upstream line has a disconnection fault, so that the three-phase operation state can be inferred as follows: the phase A and phase B circuits normally operate, and the phase C circuit has a disconnection fault;
the above analysis can yield: no matter the double PT adopts in-phase power taking or out-of-phase power taking, the running state of the line cannot be accurately determined under any working condition; however, considering that the voltage information quantity and the corresponding judgment result obtained by the out-phase power taking mode are superior to those of the in-phase power taking mode, the power taking mode preferentially selects the out-phase power taking mode under the double PT working condition;
step 1.2: analyzing the influence of the single PT power taking mode on the line break fault diagnosis of the medium-voltage distribution network:
the single PT can take electricity from an AB phase, or from a BC phase, or from a CA phase; analysis was performed using single PT to take the electricity from the AB phase as an example:
(1) the A phase circuit on the upstream side of the single PT has a disconnection fault; when the A phase line on the upstream side of the single PT has a disconnection fault, the measured line voltageU AB= 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
(2) a B-phase circuit on the upstream side of the single PT has a disconnection fault; when the B phase line on the upstream side of the double PT has a disconnection fault, the measured line voltageU AB= 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
(3) a single PT upstream side C-phase circuit is broken; when the C-phase line circuit on the upstream side of the double PT is broken, the single PT takes power from the AB phase, so that the measured line voltage is normal; only the normal operation of the A-phase and B-phase upstream lines can be obtained from the measured value, but the C-phase operation state cannot be diagnosed;
according to the analysis, under any working condition, the line disconnection phase cannot be determined according to the measurement data of a single PT, but if the line disconnection fault occurs in the power taking phase, the fault alarm can still be sent;
step 1.3: analyzing the influence of the PT electricity taking mode at the interconnection switch on the disconnection fault diagnosis of the medium-voltage distribution network:
the double PTs are arranged at the interconnection switch and respectively get electricity from circuits at two sides of the interconnection switch; under a normal working condition, because the interconnection switch is in an off state, the two PTs respectively take power from two different medium-voltage lines, and for any medium-voltage line, only one PT measurement data in the double PTs at the interconnection switch is available, so that for any medium-voltage line, the double PTs can be regarded as a single PT, and the influence relationship of the power taking mode on the line breaking fault diagnosis of the medium-voltage power distribution network is the same as that of the single PT in the step 1.2;
step 1.4: under the condition that a double PT and a single PT are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
the double PT preferentially selects out-phase electricity taking, which can be obtained in the step 1.1; according to the analysis in the step 1.1, when double PTs respectively take electricity from the AB phase and the BC phase, and when an upstream line of the A phase or the C phase breaks down, the electricity taking method can accurately judge the fault condition of the upstream line; if and only if the upstream line of the B phase has a disconnection fault, an accurate diagnosis result cannot be obtained, and at the moment, the accurate diagnosis result cannot be obtainedU AB=0，U BC= 0; in order to accurately obtain a diagnosis result when a line break fault occurs in a B-phase upstream line, a single PT (potential transformer) and a double PT (potential transformer) can be combined to jointly judge the running state of the line;
the single PT has three electricity taking modes, namely taking electricity from an AB phase, taking electricity from a BC phase and taking electricity from a CA phase, and the line voltage values measured by the single PT and the double PT are respectively as follows:
single PT was taken from AB phase, single PT:U AB= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT gets electricity from BC phase, single PT:U BC= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT was taken from the CA phase, single PT:U CAthe value is normal; double PT:U AB=0，U BC=0, it can be determined that the phase a and phase C lines are operating normally, and the phase B upstream line is in a line break fault;
therefore, when a single PT and a double PT are combined, for judging whether the power grid has a disconnection fault under any working condition and can be specifically positioned to which phase disconnection, the power taking mode can be set as: the electricity taking mode of double PT out-phase electricity taking and single PT selection and double PT out-phase electricity taking is realized, thereby meeting the requirementU AB、U BC、U CAThree line voltages are measured;
step 1.5: under the condition that two single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
under the working condition of double PTs, because the breaker switch is in a closed state, the functions of two single PTs and one double PT can be approximately equivalent from the point of view of power taking mode and measurement value, and the two single PTs preferentially select out-of-phase power taking;
step 1.6: under the condition that three single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
from step 1.5, two single PTs can be approximately equivalent to one double PT, so three single PTs can be regarded as one single PT and one double PT; for judging whether the power grid has a broken line fault under any working condition and can be specifically positioned to which broken line, the power taking mode can be set as follows: three single PT satisfy the power taking out in different phases, thereby satisfyingU AB、U BC、U CAThree line voltages were measured.
3. The method for diagnosing the disconnection fault of the medium voltage distribution network considering the single PT as claimed in claim 2, wherein the specific operation process of the step 2 is as follows:
step 2.1: determining the diagnosable range of the distribution line according to the power taking mode:
(1) all single PT cases;
according to the analysis in the step 1, when one medium-voltage line is continuously connected with two or three single PTs, out-of-phase electricity taking is preferentially adopted; further, analyzing the line diagnosable range;
1) one single PT condition: according to the analysis in the step 1.2, the line disconnection phase can not be determined according to the measurement data of a single PT, but if the line disconnection fault occurs in the power taking phase, a fault alarm can still be sent;
2) two single PT conditions: if the downstream of the line only comprises a single PT, the broken line phase of the line L2 cannot be determined, but if the broken line fault occurs in the power-taking phase, a fault alarm can still be sent; if the line downstream comprises two single PTs and an out-of-phase power taking mode is adopted, taking power taking from an AB phase and a BC phase respectively as an example, according to the step 1.5, when a single-phase line break fault occurs to the A phase or the C phase, a fault phase can be accurately judged and can be positioned on the line; when the single-phase disconnection fault occurs in the phase B, the fault condition cannot be completely and accurately judged;
3) three single PT conditions: if the downstream of the line only comprises a single PT, the line breaking phase of the line cannot be determined, but if the line breaking fault occurs in the power taking phase, a fault alarm can still be sent; if the line downstream comprises two single PTs and an out-of-phase power taking mode is adopted, taking power taking from an AB phase and a BC phase as an example, according to the step 1.5, when a single-phase line break fault occurs in the A phase or the B phase, the fault phase can be accurately judged and can be positioned on the line; when the single-phase disconnection fault occurs in the phase C, the fault condition cannot be completely and accurately judged; if the line downstream comprises three single PTs and an out-of-phase power taking mode is adopted, according to the step 1.6, if any phase of the line has a disconnection fault, the fault phase can be accurately judged and can be positioned on the line;
4) four and more single PT conditions: for four single PT working conditions, three continuous single PTs can be regarded as a combination, and power is taken out of phase in the combination; the power taking mode can be analogized in sequence for the working condition of more than four single PTs, so that the following effects are achieved: a) the line state between the three PTs at the end of the line is unknown or partially known; b) the states of other lines are completely known;
(2) the case of single PT combined with double PT;
normally, the dual PTs exist only at the substation outlet switch, the section switch, the branch switch, and the tie switch; according to the analysis in step 1.3, the double PT at the tie switch can be regarded as single PT; therefore, only double PTs at the outgoing switch, the section switch, and the branch switch are considered; since one double PT can be regarded as two single PTs, the distribution line diagnosable range is the same as that of a plurality of single PTs for the case of the combination of the single PT and the double PTs;
step 2.2: determining a power taking mode of a medium-voltage line PT:
the analysis above yields that the double PT is equivalent to two single PTs, so only the single PT is considered in step 2.2;
(1) for the newly-built line: analysis according to step 2.1 gives:
1) for the trunk line: the power can be obtained from the PT at the switch of the substation to the last PT of the line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous three single PT combinations meet the requirement of out-phase power obtaining;
2) for a branch line: the power can be obtained from the PT at the switch of the substation to the branch switch and then to the last PT of the branch line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous combination of three single PTs meets the requirement of power obtaining in an out-phase manner;
(2) for a newly added user demarcation switch on an original line:
1) the newly-added user demarcation switch is positioned at the tail end of the line: according to the PT power taking mode at the upstream of the demarcation switch, if the two PT power taking modes at the upstream are different, the PT at the newly added demarcation switch is complementary with the two PT power taking modes at the upstream; if the two PT on the upstream have the same electricity taking mode, the third PT on the upstream is further considered until two PTs with different electricity taking modes are found, and the PT at the newly added demarcation switch is further different from the PTs with the two different electricity taking modes, so that the requirement of meeting the requirement that the PT at the newly added demarcation switch is different from the PTs with the two different electricity taking modesU AB、U BC、U CAThree line voltages are measured;
2) the downstream of the newly added user demarcation switch comprises a single PT: according to the principle of proximity, the latest PT different from the electricity taking modes of the PT at the downstream of the newly-added demarcation switch is searched at the upstream of the newly-added demarcation switch, and the PT at the newly-added demarcation switch is further different from the PTs different from the two electricity taking modes at the upstream of the newly-added demarcation switch, so that the requirement of meeting the requirement that the PT at the newly-added demarcation switch is different from the PT at the downstream of the newly-added demarcation switch in the two electricity taking modesU AB、U BC、U CAThree areLine voltages are all measured;
3) the downstream of the newly added user demarcation switch comprises two single PTs: if two single PT electricity taking modes at the downstream are different, the PT at the newly added demarcation switch is further different from the PT with the two different electricity taking modes, so as to meet the requirementU AB、U BC、U CAThree line voltages are measured; if two single-PT electricity taking modes at the downstream are different, the latest PT which is different from the electricity taking mode of the PT at the downstream of the newly-added demarcation switch is searched at the upstream of the newly-added demarcation switch according to the principle of proximity, and the PT at the newly-added demarcation switch is further different from the PTs which are different from the two electricity taking modes at the downstream of the newly-added demarcation switch, so that the requirement that the PT at the newly-added demarcation switch is different from the PT at the downstream of the newly-added demarcation switch is metU AB、U BC、U CAThree line voltages are measured;
4) the case where a plurality of PTs are included downstream of the newly added user demarcation switch is similar to the case where two single PTs are included.
Compared with the prior art, the invention has the beneficial effects that: according to the method, the influence relationship of double PT and single PT power taking modes on the fault diagnosis of the broken line of the medium-voltage distribution network is analyzed, one double PT is equivalent to two single PTs from the perspective of feasibility of single-phase broken line fault diagnosis of the medium-voltage distribution network, and a power taking mode configuration principle is established on the basis; furthermore, from the angle of the maximization of the diagnosable range of the medium-voltage distribution network and the optimization of the positioning precision, the PT power taking mode configuration principle is optimized in two scenes of a newly-built network and a newly-added user demarcation switch on the original network, and the quick and accurate diagnosis of the medium-voltage distribution network disconnection fault is realized.
The invention is further illustrated by the following figures and examples.
FIG. 1 is a schematic diagram of the dual PT in-phase power extraction in the present invention.
FIG. 2 is a schematic diagram of a double PT same-phase power taking and A-phase line disconnection fault in the present invention.
FIG. 3 is a schematic diagram of a double PT same-phase power taking and B-phase line disconnection fault in the present invention.
FIG. 4 is a schematic diagram of a double PT same-phase power taking and C-phase line circuit breaking fault in the present invention.
FIG. 5 is a schematic diagram of the double PT out-of-phase power extraction in the present invention.
FIG. 6 is a schematic diagram of the double PT out-of-phase power supply and A-phase line disconnection fault in the present invention.
FIG. 7 is a schematic diagram of the double PT power extraction out of phase and the B-phase line circuit breaking fault in the invention.
FIG. 8 is a schematic diagram of the double PT out-of-phase power supply and C-phase line circuit breaking fault in the present invention.
FIG. 9 is a schematic diagram of single PT power-taking in the present invention.
FIG. 10 is a schematic diagram of a single PT power supply and phase A line break fault in the present invention.
FIG. 11 is a schematic diagram of a single PT power supply and phase B line disconnection fault in the present invention.
FIG. 12 is a schematic diagram of a single PT power supply and C-phase line disconnection fault in the present invention.
FIG. 13 is a schematic diagram of the PT power supply at the interconnection switch of the present invention.
FIG. 14 is a schematic diagram of the current-taking when a single PT and a double PT are combined in the present invention.
FIG. 15 is a schematic diagram of two single PT power-taking operations in the present invention.
FIG. 16 is a schematic diagram of three single PT power-taking operations in the present invention.
FIG. 17 is a schematic diagram of four single PT power-taking operations in accordance with the present invention.
FIG. 18 is a schematic view of example 1 of the present invention.
FIG. 19 is a schematic view of example 2 of the present invention.
FIG. 20 is a schematic view of example 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.
A medium voltage distribution network disconnection fault diagnosis method considering single PT comprises the following steps:
step 1: analyzing the influence relationship of double PT (potential transformer) and single PT (potential transformer) power taking modes on the fault diagnosis of the single-phase disconnection of the medium-voltage distribution network from the perspective of feasibility of the single-phase disconnection fault diagnosis of the medium-voltage distribution network, and further establishing a PT power taking mode configuration principle;
step 2: and optimizing a PT power-taking mode configuration principle from the angles of line diagnosable range maximization and positioning accuracy optimization.
Further, the specific operation process of step 1 is as follows:
step 1.1: analyzing the influence of the double PT power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network:
(1) the double PT phase extraction can be performed by extracting from AB phase, BC phase or CA phase. Fig. 1 is a schematic diagram of taking electricity from the AB phase for both double PTs, and the analysis is performed by taking electricity from the AB phase for both double PTs as an example:
1) and the A-phase circuit on the upstream side of the double PT has a disconnection fault. As shown in fig. 2, when the line break fault occurs in the a-phase line on the upstream side of the dual PTs, the measured line voltages are all 0 because the dual PTs both take power from the AB phase. Only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c-phase information cannot be obtained.
2) And a B-phase circuit on the upstream side of the double PT has a disconnection fault. As shown in fig. 3, when a line break fault occurs in the B-phase line on the upstream side of the dual PTs, the dual PTs both take power from the AB phase, so the measured line voltages are all 0. Only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c-phase information cannot be obtained.
3) And the C-phase circuit on the upstream side of the double PT has a disconnection fault. As shown in fig. 4, when the line break fault occurs in the C-phase line on the upstream side of the dual PT, the dual PT takes power from the AB phase, so that the measured line voltage is normal. From the measured values, only normal operation of the upstream lines of the A phase and the B phase can be obtained, but the operation condition of the C phase cannot be diagnosed.
(2) Taking out electricity from the double PT phases, such as taking out electricity from the AB phase at one side and the BC phase at the other side, or taking out electricity from the AB phase at one side and the CA phase at the other side. FIG. 5 is a schematic diagram of taking electricity from AB phase at one side and BC phase at the other side of double PT, taking this as an example for analysis:
1) and the A-phase circuit on the upstream side of the double PT has a disconnection fault. When the double PT is on the upstream side, phase A, as shown in FIG. 6When the line is broken, the line voltage is measured because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU AB=0，U BCThe value was normal. FromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BCThe normal value can obtain the normal operation of the upstream lines of the B phase and the C phase, so that the three-phase operation state can be deduced as follows: and the phase A circuit has a disconnection fault, and the phase B and the phase C circuits normally operate.
2) And a B-phase circuit on the upstream side of the double PT has a disconnection fault. As shown in fig. 7, when the B-phase line on the upstream side of the dual PT is broken, the line voltage measured by the dual PT is taken from the AB phase and the BC phase, respectivelyU AB=0，U BCAnd = 0. FromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BC=0 available B-phase or C-phase upstream line disconnection fault. From this measurement no accurate conclusions can be drawn, which may be as follows: a) the phase B circuit has a disconnection fault, and the phase A and phase C circuits normally operate; b) the line breakage fault occurs to the line of the phase A and the line of the phase B, and the line of the phase C runs normally; c) the circuit of the phase A and the phase C is broken, and the phase B operates normally; d) the circuit of the phase B and the phase C is broken, and the phase A operates normally; e) and the phase A, the phase B and the phase C have disconnection faults.
3) And the C-phase circuit on the upstream side of the double PT has a disconnection fault. As shown in fig. 8, when the line break fault occurs in the C-phase line on the upstream side of the dual PT, the line voltage is measured because the power is taken from the AB phase on one side and from the BC phase on the other side of the dual PTU ABThe value is normal and the value is normal,U BCand = 0. FromU ABNormal value can obtain normal operation of A-phase and B-phase circuits, so thatU BC=0, the available B-phase or C-phase upstream line has a disconnection fault, so that the three-phase operation state can be inferred as follows: the phase A and the phase B are in normal operation, and the phase C is in disconnection fault.
The above analysis can yield: no matter the double PT adopts in-phase power taking or out-of-phase power taking, the running state of the line cannot be accurately determined under any working condition; however, considering that the voltage information quantity and the corresponding judgment result obtained by the out-phase power taking mode are superior to those of the in-phase power taking mode, the out-phase power taking mode is preferentially selected under the double PT working condition.
Step 1.2: analyzing the influence of the single PT power taking mode on the line break fault diagnosis of the medium-voltage distribution network:
the single PT can take electricity from AB phase, BC phase or CA phase. FIG. 9 is a schematic diagram of single PT extraction from the AB phase, and analysis is performed by taking single PT extraction from the AB phase as an example:
(1) and the A-phase circuit on the upstream side of the single PT has a disconnection fault. As shown in FIG. 10, when the line break failure occurs in the A-phase line on the upstream side of the single PT, the measured line voltage is obtainedU ABAnd = 0. Only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c-phase information cannot be obtained.
(2) And the B-phase circuit on the upstream side of the single PT has a disconnection fault. As shown in fig. 11, when a disconnection fault occurs in the B-phase line on the upstream side of the dual PT, the measured line voltage is measuredU ABAnd = 0. Only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c-phase information cannot be obtained.
(3) And the single PT upstream side C-phase circuit has a disconnection fault. As shown in fig. 12, when the line break fault occurs in the C-phase line on the upstream side of the dual PT, the single PT takes power from the AB phase, so that the measured line voltages are all normal. From the measured values, only normal operation of the upstream lines of the A-phase and the B-phase can be obtained, but the operation state of the C-phase cannot be diagnosed.
Through the analysis, the line disconnection phase can not be determined according to the measurement data of a single PT under any working condition, but the fault alarm can still be sent out if the line disconnection fault occurs in the power taking phase.
Step 1.3: analyzing the influence of the PT electricity taking mode at the interconnection switch on the disconnection fault diagnosis of the medium-voltage distribution network:
as shown in fig. 13, the interconnection switch is provided with dual PTs, and the dual PTs are respectively used for getting power from the two side circuits of the interconnection switch. Under normal operating conditions, because the interconnection switch is in the off state, therefore two PTs get the electricity from two different medium voltage lines respectively, to any one of them medium voltage line, only one PT measured data is available in the two PTs of interconnection switch department, consequently to any one medium voltage line, all can regard as single PT, and its way of getting the electricity is the same with the single PT in step 1.2 to the influence relation of line break fault diagnosis of medium voltage power grid.
Step 1.4: under the condition that a double PT and a single PT are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
fig. 14 is a schematic diagram of a combination of a dual PT and a single PT. From step 1.1, the double PTs are preferably selected to take out power out of phase, and in fig. 14, the double PTs take out power from the AB phase and the BC phase, respectively. Further, according to the analysis in the step 1.1, when the double PTs respectively take electricity from the AB phase and the BC phase, when the upstream line of the a phase or the C phase has a disconnection fault, the electricity taking method can accurately judge the fault condition of the upstream line; if and only if the upstream line of the B phase has a disconnection fault, an accurate diagnosis result cannot be obtained, and at the moment, the accurate diagnosis result cannot be obtainedU AB=0，U BCAnd = 0. In order to accurately obtain a diagnosis result when a disconnection fault occurs in a B-phase upstream line, a single PT and a double PT can be combined to jointly determine the line operation state.
The single PT has three electricity taking modes, namely taking electricity from an AB phase, taking electricity from a BC phase and taking electricity from a CA phase, and the line voltage values measured by the single PT and the double PT are respectively as follows:
single PT was taken from AB phase, single PT:U AB= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT gets electricity from BC phase, single PT:U BC= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT was taken from the CA phase, single PT:U CAthe value is normal; double PT:U AB=0，U BCand =0, the normal operation of the A-phase and C-phase lines can be judged, and the line break fault of the B-phase upstream line can be judged.
Therefore, when a single PT and a double PT are combined, in order to judge whether the power grid has line break fault under any working condition and specifically position which phase line break, the power supplier can be usedThe formula is set as follows: the electricity taking mode of double PT out-phase electricity taking and single PT selection and double PT out-phase electricity taking is realized, thereby meeting the requirementU AB、U BC、U CAThree line voltages were measured.
Step 1.5: under the condition that two single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
FIG. 15 is a schematic diagram of two single PTs. Comparing fig. 5 and fig. 15, it can be seen that, under the dual PT working condition, since the breaker switch is in the closed state, from the view of the power taking method and the measurement value, the functions of two single PTs and one dual PT can be approximately equivalent, and the two single PTs are preferentially selected to take power out in different phases.
Step 1.6: under the condition that three single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
fig. 16 is a schematic of three single PTs. From step 1.5, two single PTs can be approximately equivalent to one double PT, so three single PTs can be regarded as one single PT and one double PT. For judging whether the power grid has a broken line fault under any working condition and can be specifically positioned to which broken line, the power taking mode can be set as follows: three single PT satisfy the power taking out in different phases, thereby satisfyingU AB、U BC、U CAThree line voltages were measured.
Further, the specific operation process of step 2 is as follows:
step 2.1: determining the diagnosable range of the distribution line according to the power taking mode:
(1) all in the case of a single PT.
According to the analysis in step 1, when one medium voltage line is continuously connected with two or three single PTs, the power is taken out of phase preferentially. Further, the line diagnosable range is analyzed.
1) One single PT condition: according to the analysis in the step 1.2, the line open circuit phase can not be determined according to the measured data of a single PT, but if the line open circuit fault occurs in the power taking phase, the fault alarm can still be sent.
2) Two single PT conditions: as shown in fig. 15, the downstream of the line L2 only includes a single PT, and at this time, the open phase of the line L2 cannot be determined, but if the open phase fails, a fault alarm can still be sent. Two single PTs are arranged at the downstream of the line L1, and an out-of-phase power taking mode is adopted, so that according to the step 1.5, when a single-phase line break fault occurs in the phase A or the phase C, a fault phase can be accurately judged, and the fault phase can be positioned on the line L1; when a single-phase disconnection fault occurs in the B phase, the fault condition cannot be completely and accurately judged.
3) Three single PT conditions: as shown in fig. 16, the downstream of the line L3 only includes a single PT, and at this time, the open phase of the line L3 cannot be determined, but if the open phase fails, a fault alarm can still be sent. Two single PTs are arranged at the downstream of the line L2 and an out-of-phase power taking mode is adopted, according to the step 1.5, when a single-phase line break fault occurs in the phase A or the phase B, the fault phase can be accurately judged, and the fault phase can be positioned on the line L1; when the single-phase disconnection fault occurs in the C phase, the fault condition cannot be completely and accurately judged. The line L1 includes three single PTs downstream and adopts an out-of-phase power supply method, and according to step 1.6, if any phase of the line L1 has a disconnection fault, the faulty phase can be accurately determined and can be positioned on the line L1.
4) Four and more single PT conditions: for four single PT conditions, three continuous single PTs can be regarded as one combination to form a combination 1 and a combination 2 as shown in fig. 17, and power extraction is performed out of phase in each combination, at this time, the operating state of the line L4 cannot be determined, the operating state of the line L3 is partially known, and the operating states of the lines L1 and L2 are completely known. The power taking mode can be analogized in sequence for the working condition of more than four single PTs, so that the following effects are achieved: a) the line state between the three PTs at the end of the line is unknown or partially known; b) the state of the rest lines is completely known.
(2) Case of single PT combined with double PT.
Normally, the dual PTs exist only at the substation outlet switch, the section switch, the branch switch, and the tie switch. From the analysis of step 1.3, it can be seen that the dual PT at the tie switch can be considered a single PT. Therefore, only double PTs at the outgoing switch, the sectionalizing switch, and the branch switch are considered. Since one dual PT can be regarded as two single PTs, the distribution line can be diagnosed to the same extent as a plurality of single PTs for the case where the single PT and the dual PTs are combined.
Step 2.2: determining a power taking mode of a medium-voltage line PT:
the analysis above yields that the double PT is equivalent to two single PTs, so only single PTs are considered in step 2.2.
(1) For the newly-built line: analysis according to step 2.1 gives:
1) for the trunk line: the power can be obtained from the PT at the switch of the substation to the last PT of the line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous three single PT combinations meet the requirement of out-phase power obtaining;
2) for a branch line: the power can be obtained from the PT at the switch of the substation to the branch switch and then to the last PT of the branch line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous combination of three single PTs meets the requirement of out-phase power obtaining.
(2) For a newly added user demarcation switch on an original line:
1) the newly-added user demarcation switch is positioned at the tail end of the line: according to the PT power taking mode at the upstream of the demarcation switch, if the two PT power taking modes at the upstream are different, the PT at the newly added demarcation switch is complementary with the two PT power taking modes at the upstream; if the two PT on the upstream have the same electricity taking mode, the third PT on the upstream is further considered until two PTs with different electricity taking modes are found, and the PT at the newly added demarcation switch is further different from the PTs with the two different electricity taking modes, so that the requirement of meeting the requirement that the PT at the newly added demarcation switch is different from the PTs with the two different electricity taking modesU AB、U BC、U CAThree line voltages were measured.
2) The downstream of the newly added user demarcation switch comprises a single PT: according to the principle of proximity, the latest PT different from the electricity taking modes of the PT at the downstream of the newly-added demarcation switch is searched at the upstream of the newly-added demarcation switch, and the PT at the newly-added demarcation switch is further different from the PTs different from the two electricity taking modes at the upstream of the newly-added demarcation switch, so that the requirement of meeting the requirement that the PT at the newly-added demarcation switch is different from the PT at the downstream of the newly-added demarcation switch in the two electricity taking modesU AB、U BC、U CAThree line voltages were measured.
3) The downstream of the newly added user demarcation switch comprises two single PTs: if two single PT electricity taking modes at the downstream are different, the PT at the newly added demarcation switch is further different from the PT with the two different electricity taking modes, so as to meet the requirementU AB、U BC、U CAThree line voltages are measured; if two single-PT electricity taking modes at the downstream are different, the latest PT which is different from the electricity taking mode of the PT at the downstream of the newly-added demarcation switch is searched at the upstream of the newly-added demarcation switch according to the principle of proximity, and the PT at the newly-added demarcation switch is further different from the PTs which are different from the two electricity taking modes at the downstream of the newly-added demarcation switch, so that the requirement that the PT at the newly-added demarcation switch is different from the PT at the downstream of the newly-added demarcation switch is metU AB、U BC、U CAThree line voltages were measured.
4) The case where a plurality of PTs are included downstream of the newly added user demarcation switch is similar to the case where two single PTs are included.
Example 1
In this embodiment, a PT power-taking mode is configured on a newly-built 10kV medium-voltage distribution line, as shown in fig. 18. And in the newly-built line planning and designing stage, respectively configuring PT power taking modes of the trunk line and the branch line according to the configuration principle in the step 2.2 (1) of the invention. The dual PT is equivalent to two single PTs in the configuration process. The PT power receiving phases are arranged for the trunk line and the branch line in the order AB, BC, CA, AB, and BC … … as shown in fig. 18.
Example 2
This embodiment is the condition that newly-increased user demarcation switch and the different modes of getting of upstream and downstream PT on original circuit. Fig. 19 shows a power supply method in which a user T3 is added to an existing line and a single PTn is configured. According to the configuration principle of the power taking mode in the step 2.2 (2), firstly, only one PT4 is determined at the downstream of the newly added user demarcation switch, and power is taken from a BC phase; then, a PT3 phase which is different from the PT4 power taking mode and is nearest is searched at the upstream of the newly-added boundary switch according to the principle of proximity, and the PT3 phase is CA phase power taking; and finally determining the PTn as AB phase power taking according to the principle that PT3, PT4 and PTn power taking modes are different.
Example 3
This embodiment is the condition that newly-increased user demarcation switch and the same mode is got to the PT of going up low reaches on original circuit. Fig. 20 shows a power supply method in which a user T3 is added to an existing line and a single PTn is configured. According to the configuration principle of the power taking mode in the step 2.2 (2), firstly, only one PT4 is determined at the downstream of the newly added user demarcation switch, and power is taken from a BC phase; then, a PT which is different from the PT4 power taking mode and is the nearest is found at the upstream of the newly-added boundary switch according to the principle of the proximity: since PT3 and PT4 take electricity in the same way, it is excluded. Continuously searching PT2 upstream, wherein PT2 is used for taking electricity from AB phase, and the mode of taking electricity is different from that of PT4, so that the requirement is met; and finally determining the PTn as the CA phase power taking according to the principle that PT2, PT4 and PTn power taking modes are different.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (1)
1. The medium-voltage distribution network disconnection fault diagnosis method considering the single PT is characterized by comprising the following steps of:
step 1: analyzing the influence relationship of double PT (potential transformer) and single PT (potential transformer) power taking modes on the fault diagnosis of the single-phase disconnection of the medium-voltage distribution network from the perspective of feasibility of the single-phase disconnection fault diagnosis of the medium-voltage distribution network, and further establishing a PT power taking mode configuration principle;
step 2: optimizing a PT power-taking mode configuration principle from the angles of line diagnosable range maximization and positioning accuracy optimization;
the specific operation process of the step 1 is as follows:
step 1.1: analyzing the influence of the double PT power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network:
(1) taking power from the double PT in-phase, such as from AB phase, BC phase or CA phase; analysis was performed taking the double PT all from the AB phase as an example:
1) the A phase circuit on the upstream side of the double PT has a disconnection fault; when the A phase circuit on the upstream side of the double PTs has a disconnection fault, the double PTs take power from the AB phase, so that the measured line voltages are all 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
2) a B phase circuit on the upstream side of the double PT is broken; when a B phase line circuit on the upstream side of the double PTs breaks down, the double PTs take power from the AB phase, so that the measured line voltages are all 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
3) a C-phase circuit on the upstream side of the double PT is broken; when the C-phase line circuit on the upstream side of the double PTs has a disconnection fault, the double PTs take power from the AB phase, so that the measured line voltage is normal; only the normal operation of the upstream lines of the A phase and the B phase can be obtained from the measured value, but the operation condition of the C phase cannot be diagnosed;
(2) taking electricity from the double PT out of phase, such as taking electricity from the AB phase at one side and taking electricity from the BC phase at the other side, or taking electricity from the AB phase at one side and taking electricity from the CA phase at the other side; taking the example of taking electricity from AB phase at one side of double PT and electricity from BC phase at the other side as an example:
1) the A phase circuit on the upstream side of the double PT has a disconnection fault; when the A phase circuit on the upstream side of the double PT is broken, the line voltage obtained by measurement is obtained because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU AB=0，U BCThe value is normal; fromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BCThe normal value can obtain the normal operation of the upstream lines of the B phase and the C phase, so that the three-phase operation state can be deduced as follows: the phase A circuit has a disconnection fault, and the phase B circuit and the phase C circuit run normally;
2) a B phase circuit on the upstream side of the double PT is broken; when the B phase circuit on the upstream side of the double PT is broken, the line voltage obtained by measurement is obtained because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU AB=0，U BC= 0; fromU AB=0 available a-phase or B-phase upstream line has a disconnection fault, fromU BC=0 available upstream line of B phase or C phase has a disconnection fault; from this measurement no accurate conclusions can be drawn, which may be as follows: a) the phase B circuit has a disconnection fault, and the phase A and phase C circuits normally operate; b) the line breakage fault occurs to the line of the phase A and the line of the phase B, and the line of the phase C runs normally; c) the circuit of the phase A and the phase C is broken, and the phase B operates normally; d) the disconnection fault occurs to the B-phase circuit and the C-phase circuit,normal operation of phase A; e) the phase A, the phase B and the phase C have disconnection faults;
3) a C-phase circuit on the upstream side of the double PT is broken; when the C phase circuit on the upstream side of the double PT is broken, the line voltage obtained by measurement is obtained because one side of the double PT takes power from the AB phase and the other side takes power from the BC phaseU ABThe value is normal and the value is normal,U BC= 0; fromU ABNormal value can obtain normal operation of A-phase and B-phase circuits, so thatU BC=0, the available B-phase or C-phase upstream line has a disconnection fault, so that the three-phase operation state can be inferred as follows: the phase A and phase B circuits normally operate, and the phase C circuit has a disconnection fault;
the above analysis can yield: no matter the double PT adopts in-phase power taking or out-of-phase power taking, the running state of the line cannot be accurately determined under any working condition; however, considering that the voltage information quantity and the corresponding judgment result obtained by the out-phase power taking mode are superior to those of the in-phase power taking mode, the power taking mode preferentially selects the out-phase power taking mode under the double PT working condition;
step 1.2: analyzing the influence of the single PT power taking mode on the line break fault diagnosis of the medium-voltage distribution network:
the single PT can take electricity from an AB phase, or from a BC phase, or from a CA phase; analysis was performed using single PT to take the electricity from the AB phase as an example:
(1) the A phase circuit on the upstream side of the single PT has a disconnection fault; when the A phase line on the upstream side of the single PT has a disconnection fault, the measured line voltageU AB= 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
(2) a B-phase circuit on the upstream side of the single PT has a disconnection fault; when the B phase line on the upstream side of the double PT has a disconnection fault, the measured line voltageU AB= 0; only the upstream line of the A phase or the B phase is subjected to disconnection fault from the measured value, but the specific disconnection phase cannot be determined; c, information cannot be obtained;
(3) a single PT upstream side C-phase circuit is broken; when the C-phase line circuit on the upstream side of the double PT is broken, the single PT takes power from the AB phase, so that the measured line voltage is normal; only the normal operation of the A-phase and B-phase upstream lines can be obtained from the measured value, but the C-phase operation state cannot be diagnosed;
according to the analysis, under any working condition, the line disconnection phase cannot be determined according to the measurement data of a single PT, but if the line disconnection fault occurs in the power taking phase, the fault alarm can still be sent;
step 1.3: analyzing the influence of the PT electricity taking mode at the interconnection switch on the disconnection fault diagnosis of the medium-voltage distribution network:
the double PTs are arranged at the interconnection switch and respectively get electricity from circuits at two sides of the interconnection switch; under a normal working condition, because the interconnection switch is in an off state, the two PTs respectively take power from two different medium-voltage lines, and for any medium-voltage line, only one PT measurement data in the double PTs at the interconnection switch is available, so that for any medium-voltage line, the double PTs can be regarded as a single PT, and the influence relationship of the power taking mode on the line breaking fault diagnosis of the medium-voltage power distribution network is the same as that of the single PT in the step 1.2;
step 1.4: under the condition that a double PT and a single PT are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
the double PT preferentially selects out-phase electricity taking, which can be obtained in the step 1.1; according to the analysis in the step 1.1, when double PTs respectively take electricity from the AB phase and the BC phase, and when an upstream line of the A phase or the C phase breaks down, the electricity taking method can accurately judge the fault condition of the upstream line; if and only if the upstream line of the B phase has a disconnection fault, an accurate diagnosis result cannot be obtained, and at the moment, the accurate diagnosis result cannot be obtainedU AB=0，U BC= 0; in order to accurately obtain a diagnosis result when a line break fault occurs in a B-phase upstream line, a single PT (potential transformer) and a double PT (potential transformer) can be combined to jointly judge the running state of the line;
the single PT has three electricity taking modes, namely taking electricity from an AB phase, taking electricity from a BC phase and taking electricity from a CA phase, and the line voltage values measured by the single PT and the double PT are respectively as follows:
single PT was taken from AB phase, single PT:U AB= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT gets electricity from BC phase, single PT:U BC= 0; double PT:U AB=0，U BC=0, single PT measurement data redundancy;
single PT was taken from the CA phase, single PT:U CAthe value is normal; double PT:U AB=0，U BC=0, it can be determined that the phase a and phase C lines are operating normally, and the phase B upstream line is in a line break fault;
therefore, when a single PT and a double PT are combined, for judging whether the power grid has a disconnection fault under any working condition and can be specifically positioned to which phase disconnection, the power taking mode can be set as: the electricity taking mode of double PT out-phase electricity taking and single PT selection and double PT out-phase electricity taking is realized, thereby meeting the requirementU AB、U BC、U CAThree line voltages are measured;
step 1.5: under the condition that two single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
under the working condition of double PTs, because the breaker switch is in a closed state, the functions of two single PTs and one double PT can be approximately equivalent from the point of view of power taking mode and measurement value, and the two single PTs preferentially select out-of-phase power taking;
step 1.6: under the condition that three single PTs are combined, the influence of the power taking mode on the disconnection fault diagnosis of the medium-voltage distribution network is analyzed:
from step 1.5, two single PTs can be approximately equivalent to one double PT, so three single PTs can be regarded as one single PT and one double PT; for judging whether the power grid has a broken line fault under any working condition and can be specifically positioned to which broken line, the power taking mode can be set as follows: three single PT satisfy the power taking out in different phases, thereby satisfyingU AB、U BC、U CAThree line voltages are measured;
the specific operation process of the step 2 is as follows:
step 2.1: determining the diagnosable range of the distribution line according to the power taking mode:
(1) all single PT cases;
according to the analysis in the step 1, when one medium-voltage line is continuously connected with two or three single PTs, out-of-phase electricity taking is preferentially adopted; further, analyzing the line diagnosable range;
1) one single PT condition: according to the analysis in the step 1.2, the line disconnection phase can not be determined according to the measurement data of a single PT, but if the line disconnection fault occurs in the power taking phase, a fault alarm can still be sent;
2) two single PT conditions: if the downstream of the line only comprises a single PT, the broken line phase of the line L2 cannot be determined, but if the broken line fault occurs in the power-taking phase, a fault alarm can still be sent; if the line downstream comprises two single PTs and an out-of-phase power taking mode is adopted, taking power taking from an AB phase and a BC phase respectively as an example, according to the step 1.5, when a single-phase line break fault occurs to the A phase or the C phase, a fault phase can be accurately judged and can be positioned on the line; when the single-phase disconnection fault occurs in the phase B, the fault condition cannot be completely and accurately judged;
3) three single PT conditions: if the downstream of the line only comprises a single PT, the line breaking phase of the line cannot be determined, but if the line breaking fault occurs in the power taking phase, a fault alarm can still be sent; if the line downstream comprises two single PTs and an out-of-phase power taking mode is adopted, taking power taking from an AB phase and a BC phase as an example, according to the step 1.5, when a single-phase line break fault occurs in the A phase or the B phase, the fault phase can be accurately judged and can be positioned on the line; when the single-phase disconnection fault occurs in the phase C, the fault condition cannot be completely and accurately judged; if the line downstream comprises three single PTs and an out-of-phase power taking mode is adopted, according to the step 1.6, if any phase of the line has a disconnection fault, the fault phase can be accurately judged and can be positioned on the line;
4) four and more single PT conditions: for four single PT working conditions, three continuous single PTs can be regarded as a combination, and power is taken out of phase in the combination; the power taking mode can be analogized in sequence for the working condition of more than four single PTs, so that the following effects are achieved: a) the line state between the three PTs at the end of the line is unknown or partially known; b) the states of other lines are completely known;
(2) the case of single PT combined with double PT;
normally, the dual PTs exist only at the substation outlet switch, the section switch, the branch switch, and the tie switch; according to the analysis in step 1.3, the double PT at the tie switch can be regarded as single PT; therefore, only double PTs at the outgoing switch, the section switch, and the branch switch are considered; since one double PT can be regarded as two single PTs, the distribution line diagnosable range is the same as that of a plurality of single PTs for the case of the combination of the single PT and the double PTs;
step 2.2: determining a power taking mode of a medium-voltage line PT:
the analysis above yields that the double PT is equivalent to two single PTs, so only the single PT is considered in step 2.2;
(1) for the newly-built line: analysis according to step 2.1 gives:
1) for the trunk line: the power can be obtained from the PT at the switch of the substation to the last PT of the line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous three single PT combinations meet the requirement of out-phase power obtaining;
2) for a branch line: the power can be obtained from the PT at the switch of the substation to the branch switch and then to the last PT of the branch line according to the sequence of AB, BC, CA, AB and BC … …, thereby ensuring that any continuous combination of three single PTs meets the requirement of power obtaining in an out-phase manner;
(2) for a newly added user demarcation switch on an original line:
1) the newly-added user demarcation switch is positioned at the tail end of the line: according to the PT power taking mode at the upstream of the demarcation switch, if the two PT power taking modes at the upstream are different, the PT at the newly added demarcation switch is complementary with the two PT power taking modes at the upstream; if the two PT on the upstream have the same electricity taking mode, the third PT on the upstream is further considered until two PTs with different electricity taking modes are found, and the PT at the newly added demarcation switch is further different from the PTs with the two different electricity taking modes, so that the requirement of meeting the requirement that the PT at the newly added demarcation switch is different from the PTs with the two different electricity taking modesU AB、U BC、U CAThree line voltages are measured;
2) the downstream of the newly added user demarcation switch comprises a single PT: according to the principle of proximity, the latest PT which is different from the electricity taking mode of the PT at the downstream of the newly added demarcation switch is searched at the upstream of the newly added demarcation switch, at the moment, the PT at the newly added demarcation switch is further different from the PT which is different from the two electricity taking modes,satisfy the requirement ofU AB、U BC、U CAThree line voltages are measured;
3) the downstream of the newly added user demarcation switch comprises two single PTs: if two single PT electricity taking modes at the downstream are different, the PT at the newly added demarcation switch is further different from the PT with the two different electricity taking modes, so as to meet the requirementU AB、U BC、U CAThree line voltages are measured; if two single-PT electricity taking modes at the downstream are different, the latest PT which is different from the electricity taking mode of the PT at the downstream of the newly-added demarcation switch is searched at the upstream of the newly-added demarcation switch according to the principle of proximity, and the PT at the newly-added demarcation switch is further different from the PTs which are different from the two electricity taking modes at the downstream of the newly-added demarcation switch, so that the requirement that the PT at the newly-added demarcation switch is different from the PT at the downstream of the newly-added demarcation switch is metU AB、U BC、U CAThree line voltages are measured;
4) the case where a plurality of PTs are included downstream of the newly added user demarcation switch is similar to the case where two single PTs are included.
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