CN114047402A - Phase current phase difference-based power distribution network single-phase earth fault line selection method - Google Patents

Phase current phase difference-based power distribution network single-phase earth fault line selection method Download PDF

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CN114047402A
CN114047402A CN202110772048.4A CN202110772048A CN114047402A CN 114047402 A CN114047402 A CN 114047402A CN 202110772048 A CN202110772048 A CN 202110772048A CN 114047402 A CN114047402 A CN 114047402A
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phase
fault
current
distribution network
power distribution
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朱承治
吴靖
郑伟彦
余天吟
李哲
刘兴业
姜建
钮伟樑
刘宏伟
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Innovation And Entrepreneurship Center Of State Grid Zhejiang Electric Power Co ltd
Hangzhou Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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State Grid Zhejiang Xinxing Technology Co ltd
Zhejiang Dayou Industrial Co ltd Hangzhou Science And Technology Development Branch
Innovation And Entrepreneurship Center Of State Grid Zhejiang Electric Power Co ltd
Hangzhou Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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    • 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
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Abstract

The invention discloses a phase current phase difference-based power distribution network single-phase earth fault line selection method, which comprises the following steps of: s01: judging whether a single-phase earth fault occurs or not, and further judging a fault phase if the single-phase earth fault occurs; s02: and calculating the sum of the first healthy phase current and the fault phase current and the sum of the second healthy phase current and the fault phase current according to the judgment result and the acquired electrical parameters, and judging the fault line according to the phase difference between the two sums. The substantial effects of the invention include: and realizing single-phase earth fault line selection of the power distribution network by using the phase current phase difference. The fault line is accurately judged after the single-phase earth fault occurs in the power distribution network, the fault is timely eliminated to avoid further development of phase-to-phase fault, and power supply is recovered as soon as possible to improve the power supply reliability of the power distribution network.

Description

Phase current phase difference-based power distribution network single-phase earth fault line selection method
Technical Field
The invention relates to the field of relay protection of a power system, in particular to a phase current phase difference-based single-phase earth fault line selection method for a power distribution network.
Background
The distribution network in China is mainly in the voltage class of 35kV and below, the indirect grounding mode that a neutral point is not grounded or is grounded through an arc suppression coil is mostly adopted, and after a single-phase grounding fault occurs, only a very small value of capacitance current to ground flows through a fault point, so that the distribution network belongs to a low-current grounding distribution network. The distribution line is easy to have various types of faults due to wide coverage range, complex working environment and numerous access devices, wherein the single-phase ground fault accounts for more than 80% of the total fault frequency of the distribution line. After the single-phase earth fault of the distribution line occurs, the line voltage still keeps symmetrical, and the power supply of the load is not influenced, so that the line with the fault is allowed to continue to operate for 1-2 hours, but the long-time operation with the fault easily causes phase-to-phase fault, so that the fault range is enlarged, and various problems which harm the safe operation of the system are caused, and therefore the line with the fault needs to be accurately judged in time after the single-phase earth fault occurs.
However, the fault characteristics of the single-phase earth fault of the distribution network line are not obvious, and the difficulty of fault line selection is increased. According to the selected fault information, the existing power distribution network single-phase earth fault line selection method can be divided into a steady-state signal method, a transient-state signal method and an injection signal method.
In the aspect of fault line selection by using steady-state signals, a fault line selection method [ J ] based on a zero-sequence current amplitude comparison method, university of North and Central university (Nature science edition), 2014,35(04), 473 and 478 proposes a power frequency zero-sequence current amplitude comparison method, and the fault line selection is realized by using the characteristic that the amplitude of the zero-sequence current of a fault line is larger than that of the zero-sequence current of a non-fault line. Another document proposes a power frequency zero-sequence current phase comparison method, and selects a line by using the characteristic that zero-sequence currents on a fault line and a non-fault line are opposite in direction. On the basis of amplitude comparison method and phase comparison method of zero sequence current, another document proposes a group amplitude comparison method, which includes selecting a plurality of lines with larger amplitude of zero sequence current as alternative lines, and then distinguishing fault lines according to phase. The three line selection methods are simple in principle and easy to implement, but accuracy is affected by a neutral point grounding mode, a transition resistor and a system operation mode, and universality is not achieved. In order to solve the problem that the accuracy of fault line selection is affected by the neutral point grounding mode, another document proposes that the fault line selection is performed by using the active component and the 5 th harmonic component of the zero-sequence current of the fault line, and the active current and the 5 th harmonic current cannot be compensated by the arc suppression coil, so that the method is not limited by the neutral point grounding mode, but the magnitudes of the two components in the fault current are closely related to system parameters, transition resistance and other factors, and the actual line selection effect is not ideal. In addition, another document proposes to use the difference of the amplitude and phase of the negative sequence current on the fault line and the non-fault line for fault line selection, but the asymmetry degree and load characteristics of the system can affect the negative sequence current, thereby interfering with the line selection result.
In the aspect of fault line selection by using transient signals, the prior art performs wavelet decomposition on zero sequence transient current of each line after a fault, and after a characteristic frequency band of each current is determined according to an energy maximum principle, the fault line is identified by using information such as amplitude, polarity and energy of the transient current in the characteristic frequency band. In other documents, similarity analysis is performed on the zero-sequence transient currents of all lines, and fault line selection is realized by using the characteristics that the similarity between the zero-sequence transient currents of non-fault lines is high and the similarity with the zero-sequence transient currents of fault lines is low. In other documents, line selection is performed by detecting fault traveling waves generated by fault points, and the method puts high requirements on accurate identification of fault wave heads.
In the aspect of utilizing an injection signal to perform fault line selection, the prior art proposes that a high-frequency signal is injected into a system from a grounding transformer, the signal forms a loop through a grounding point of a fault line, whether the line is the fault line is judged by detecting whether the injected high-frequency signal exists in the line, and the method has the main defect of causing impact on a primary system.
Therefore, the existing power distribution network single-phase earth fault line selection method is not complete, and the research on the single-phase earth fault line selection method has important theoretical value and practical value.
Disclosure of Invention
The invention provides a phase current phase difference-based power distribution network single-phase earth fault line selection method, aiming at the problem that the prior art lacks a proper power distribution network single-phase earth fault line selection method. The fault line is accurately judged after the single-phase earth fault occurs in the power distribution network, the fault is timely eliminated to avoid further development of phase-to-phase fault, and power supply is recovered as soon as possible to improve the power supply reliability of the power distribution network.
The technical scheme of the invention is as follows.
A phase current phase difference based power distribution network single-phase earth fault line selection method comprises the following steps:
s01: judging whether a single-phase earth fault occurs or not, and further judging a fault phase if the single-phase earth fault occurs;
s02: and calculating the sum of the first healthy phase current and the fault phase current and the sum of the second healthy phase current and the fault phase current according to the judgment result and the acquired electrical parameters, and judging the fault line according to the phase difference between the two sums.
The method is based on the electrical principle of phase current phase difference, and can accurately judge the fault phase and the fault line by calculating parameters such as voltage, current and the like.
Preferably, step S01 includes: the method comprises the steps of collecting voltage of a voltage transformer on a bus, calculating zero sequence voltage, judging that a single-phase earth fault occurs when the zero sequence voltage occurs, and judging that the phase with the minimum phase voltage is a fault phase.
Preferably, the determining a faulty line based on the phase difference between the two sums includes: when the phase difference between the two sums is 60 degrees, the line is a non-fault line, and when the phase difference between the two sums is less than 60 degrees, the line is a fault line.
Preferably, the error correction range is set when determining whether the phase difference is less than 60 degrees, and when the phase difference is greater than or equal to 54 degrees, the error correction range is determined to be equal to 60 degrees, otherwise, the error correction range is determined to be less than 60 degrees.
The phase difference judgment formula is as follows:
Figure RE-GDA0003439068920000031
wherein
Figure RE-GDA0003439068920000032
Is the sum of the healthy phase current and the fault phase current with relatively advanced phases on the ith line,
Figure RE-GDA0003439068920000033
is the sum of the healthy phase current and the fault phase current with relatively lagging phase on the ith line, thetasetIs a setting value of a criterion.
Preferably, the method is applied to a single-phase earth fault in a power distribution network indirect earth system in which a neutral point is not earthed or earthed through an arc suppression coil.
The substantial effects of the invention include: the principle is clear, and a fault line is judged based on the fact that the phase difference between the sum of two healthy phase currents and the fault phase current on the fault line after the fault is smaller than a setting value; the method is easy to realize, and can be realized by only utilizing the voltage of the installed voltage transformer and the current of the current transformer; the method is suitable for a distribution network with ungrounded neutral points and is also suitable for a distribution network with grounded arc suppression coils.
Drawings
FIG. 1 is a diagram of a capacitance current distribution during a single-phase earth fault of a distribution network with an ungrounded neutral point according to an embodiment of the present invention;
FIG. 2 is a phasor diagram of each phase-to-ground voltage and zero-sequence voltage when phase A is grounded according to the embodiment of the present invention;
FIG. 3 is a graph of the current phasors on a non-faulted line when phase A is grounded according to an embodiment of the present invention;
FIG. 4 is a current phasor diagram on a fault line with phase A grounded without a neutral point grounded in an embodiment of the invention;
FIG. 5 is a current distribution diagram for a single-phase ground fault in a power distribution network with a neutral point grounded via a crowbar coil in an embodiment of the present invention;
fig. 6 is a current phasor diagram on a fault line when phase a is grounded with the neutral point grounded through the arc suppression coil in the embodiment of the present invention.
Detailed Description
The technical solution of the present application will be described with reference to the following examples. In addition, numerous specific details are set forth below in order to provide a better understanding of the present invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some instances, methods, means, elements and circuits that are well known to those skilled in the art have not been described in detail so as not to obscure the present invention.
Example (b):
a phase current phase difference based power distribution network single-phase earth fault line selection method comprises the following steps:
s01: judging whether a single-phase earth fault occurs or not, and further judging a fault phase if the single-phase earth fault occurs; the method comprises the following steps: the method comprises the steps of collecting voltage of a voltage transformer on a bus, calculating zero sequence voltage, judging that a single-phase earth fault occurs when the zero sequence voltage occurs, and judging that the phase with the minimum phase voltage is a fault phase.
S02: calculating the sum of the first healthy phase current and the fault phase current and the sum of the second healthy phase current and the fault phase current according to the judgment result and the acquired electrical parameters, and judging a fault line according to the phase difference between the two sums; the method comprises the following steps: when the phase difference between the two sums is 60 degrees, the line is a non-fault line, and when the phase difference between the two sums is less than 60 degrees, the line is a fault line. And when the phase difference is judged to be less than 60 degrees, setting an error correction range, when the phase difference is more than or equal to 54 degrees, judging that the phase difference is equal to 60 degrees, otherwise, judging that the phase difference is less than 60 degrees.
The method is based on the electrical principle of phase current phase difference, and can accurately judge the fault phase and the fault line by calculating parameters such as voltage, current and the like.
The following explains the calculation principle of this embodiment by taking an ungrounded neutral point power distribution network and a power distribution network with a neutral point grounded by an arc suppression coil as examples, and proves the effectiveness of the method:
in the non-grounded neutral point power distribution network shown in the attached figure 1, a generator G is provided with two distribution lines, and the distributed capacitors to the ground of the generator G, the line I and the line II are respectively concentrated by a capacitor C0G、C0IAnd C0IIAnd (4) showing. After a single-phase ground fault occurs on the line II, if the influence of voltage drop of three-phase symmetrical load current and capacitance current on line impedance is not considered, the voltage to ground of the fault phase of the whole system is equal to zero, so that the capacitance current of each element fault to ground is also equal to 0, and the capacitance current flowing through the non-fault phase is analyzed below.
Taking phase a ground fault as an example, the distribution of capacitance current to ground in the post-fault system is shown in fig. 1, and "→" indicates the direction of the capacitance current. After the phase A is grounded, the voltage of each phase to ground and the zero sequence voltage are as follows:
Figure RE-GDA0003439068920000041
Figure RE-GDA0003439068920000042
and
Figure RE-GDA0003439068920000043
is the three-phase potential of the generator. The relationship between the various voltage phasors is shown in fig. 2.
On the non-fault line I, the phase A current is zero, and the phase B and the phase C have capacitance current flowing to the fault point
Figure RE-GDA0003439068920000044
And
Figure RE-GDA0003439068920000045
the expression of the capacitance current flowing through each phase is:
Figure RE-GDA0003439068920000046
omega is the power frequency angular frequency. The individual current phasors on the non-faulted line i are also plotted in fig. 2, from which it can be seen that the sum of the currents between healthy phases B and C and faulted phase a is the own current of each healthy phase, i.e.:
Figure RE-GDA0003439068920000051
two current phasors in equation (3)
Figure RE-GDA0003439068920000052
And
Figure RE-GDA0003439068920000053
shown in fig. 3, the phase difference between them is:
Figure RE-GDA0003439068920000054
i.e. the sum of two healthy phase currents and a fault phase current on a non-fault line I
Figure RE-GDA0003439068920000055
And
Figure RE-GDA0003439068920000056
the phase difference therebetween was 60 °.
On the fault line II, the grounding point needs to flow back to the sum of the B phase and C phase capacitance currents of the whole system, namely:
Figure RE-GDA0003439068920000057
C0Σ＝C0I+C0II+C0Gthe sum of the capacitances is distributed for each phase of the whole system. The current flows back to the generator through phase A, so that the current flowing out of phase A is
Figure RE-GDA0003439068920000058
. The phase B and the phase C flow own capacitance current. The expression for the current flowing through each phase is:
Figure RE-GDA0003439068920000059
the corresponding valid values are:
Figure RE-GDA00034390689200000510
thus, the sum of the currents of healthy phases B and C and fault phase a is:
Figure RE-GDA00034390689200000511
the individual current phasors on the fault line ii are plotted in fig. 4. Because:
Figure RE-GDA00034390689200000512
according to the cosine theorem, it can be known that:
Figure RE-GDA0003439068920000061
according to the sine theorem, it can be known that:
Figure RE-GDA0003439068920000062
thus, the number of the first and second electrodes,
Figure RE-GDA0003439068920000063
i.e. the sum of two healthy phase currents and the fault phase current on the fault line II
Figure RE-GDA0003439068920000064
And
Figure RE-GDA0003439068920000065
the phase difference therebetween is less than 60 °.
The following conclusion is drawn in conclusion: in a distribution network with ungrounded neutral points, the phase difference between the two healthy phase currents and the sum of the fault phase currents on a non-fault line is 60 degrees, and the phase difference between the two healthy phase currents and the sum of the fault phase currents on a fault line is less than 60 degrees.
When the neutral point of the distribution network is grounded by the arc suppression coil, the distribution of the capacitance current to the ground and the current of the arc suppression coil is marked in the attached figure 5. Sum of two healthy phase currents and fault phase current on non-fault line I
Figure RE-GDA0003439068920000066
And
Figure RE-GDA0003439068920000067
the phase difference between them is the same as in a neutral ungrounded system, i.e.
Figure RE-GDA0003439068920000068
On the fault line II, the earth point is connected to the sum of the capacitive currents of the phases B and C of the total system, and an inductive compensation current flows through the crowbar coil, and the inductive compensation current flows back to the generator through the phase A. When the power grid adopts the arc suppression coil to compensate, an overcompensation mode is adopted, and the overcompensation degree is generally selected to be 5% -10%. The current flowing from the A phase is
Figure RE-GDA0003439068920000069
The phase B and phase C flow have their own capacitance currents, and the current expressions thereof are the same as those in equation (6). The sum of the currents of healthy phases B and C and fault phase A is expressed as
Figure RE-GDA00034390689200000610
The two current phasors in equation (14) are plotted in fig. 6, as can be seen from the external angle theorem of the triangle,
Figure RE-GDA00034390689200000611
and
Figure RE-GDA00034390689200000612
phase difference between them is satisfied
Figure RE-GDA0003439068920000071
In the distribution network with the neutral point grounded through the arc suppression coil, the phase difference between the sum of two healthy phase currents and the sum of fault phase currents on a non-fault line is also 60 degrees, and the phase difference between the sum of two healthy phase currents and the sum of fault phase currents on a fault line is also smaller than 60 degrees. These characteristics are the same as in a grid with no neutral grounding.
Based on the above conclusion, it can be proved that when the zero sequence voltage occurs in the system, the phase with the minimum phase voltage is judged as the fault phase; for each line, a faulty line can be determined based on the phase difference between the sum of the healthy phase current and the faulty phase current. The judgment basis of the fault line is as follows:
Figure RE-GDA0003439068920000072
wherein the content of the first and second substances,
Figure RE-GDA0003439068920000073
is the sum of the healthy phase current and the fault phase current with relatively advanced phases on the ith line,
Figure RE-GDA0003439068920000074
is the sum of the healthy phase current and the fault phase current with relatively lagging phase on the ith line, thetasetIs a setting value of a criterion.
Through the description of the foregoing embodiments, those skilled in the art will understand that the embodiments of the present application may be implemented in the form of hardware, and may also be implemented in the form of software functional units. If implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application may be essentially or partially contributed to by the prior art, or all or part of the technical solutions may be embodied in the form of a software product, where the software product is stored in a storage medium and includes several instructions to enable a device (which may be a single chip, a chip, or the like) or a processor (processor) to execute all or part of the steps of the methods of the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (6)

1. A power distribution network single-phase earth fault line selection method based on phase current phase difference is characterized by comprising the following steps:
s01: judging whether a single-phase earth fault occurs or not, and further judging a fault phase if the single-phase earth fault occurs;
s02: and calculating the sum of the first healthy phase current and the fault phase current and the sum of the second healthy phase current and the fault phase current according to the judgment result and the acquired electrical parameters, and judging the fault line according to the phase difference between the two sums.
2. The phase-current phase-difference-based single-phase ground fault line selection method for the power distribution network according to claim 1, wherein the step S01 comprises: the method comprises the steps of collecting voltage of a voltage transformer on a bus, calculating zero sequence voltage, judging that a single-phase earth fault occurs when the zero sequence voltage occurs, and judging that the phase with the minimum phase voltage is a fault phase.
3. The method for selecting the single-phase earth fault line of the power distribution network based on the phase difference of the phase currents as claimed in claim 1, wherein the determining the fault line according to the phase difference between the two sums comprises: when the phase difference between the two sums is 60 degrees, the line is a non-fault line, and when the phase difference between the two sums is less than 60 degrees, the line is a fault line.
4. The phase-current phase difference based power distribution network single-phase ground fault line selection method according to claim 3, wherein an error correction range is set when judging whether the phase difference is less than 60 degrees, and when the phase difference is greater than or equal to 54 degrees, the phase difference is judged to be equal to 60 degrees, otherwise, the phase difference is judged to be less than 60 degrees.
5. The phase-current phase difference-based power distribution network single-phase earth fault line selection method according to claim 4, wherein the phase difference judgment formula is as follows:
Figure RE-FDA0003439068910000011
wherein
Figure RE-FDA0003439068910000012
Is the sum of the healthy phase current and the fault phase current with relatively advanced phases on the ith line,
Figure RE-FDA0003439068910000013
is the sum of the healthy phase current and the fault phase current with relatively lagging phase on the ith line, thetasetIs a setting value of a criterion.
6. The phase-current phase-difference-based single-phase earth fault line selection method for the power distribution network according to claim 1 or 2, wherein the method is applied to single-phase earth faults in a mode that a neutral point is not grounded or a power distribution network is not directly grounded through an arc suppression coil.
CN202110772048.4A 2021-07-08 2021-07-08 Phase current phase difference-based power distribution network single-phase earth fault line selection method Pending CN114047402A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115598564A (en) * 2022-10-12 2023-01-13 国网山东省电力公司电力科学研究院（Cn） Small resistance system high-resistance grounding positioning method and device based on voltage and current variation

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115598564A (en) * 2022-10-12 2023-01-13 国网山东省电力公司电力科学研究院（Cn） Small resistance system high-resistance grounding positioning method and device based on voltage and current variation
CN115598564B (en) * 2022-10-12 2023-07-25 国网山东省电力公司电力科学研究院 Small-resistance system high-resistance grounding positioning method and device based on voltage and current variation

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