CN113541111B - Power transmission line disconnection fault judgment method based on disconnection fault criterion - Google Patents

Power transmission line disconnection fault judgment method based on disconnection fault criterion Download PDF

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CN113541111B
CN113541111B CN202110779462.8A CN202110779462A CN113541111B CN 113541111 B CN113541111 B CN 113541111B CN 202110779462 A CN202110779462 A CN 202110779462A CN 113541111 B CN113541111 B CN 113541111B
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fault
transmission line
power transmission
disconnection
current
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CN113541111A (en
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易建波
黄琦
井实
李坚
张真源
胡维昊
隋佳闽
范树威
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University of Electronic Science and Technology of China
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/54—Testing for continuity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/28—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for meshed systems

Abstract

The invention discloses a method for judging a disconnection fault of a power transmission line based on disconnection fault criteria, which comprises the steps of constructing the disconnection fault criteria of the power transmission line by utilizing the change characteristics of voltage and current on two sides of the line when the disconnection occurs and then the grounding fault occurs; the disconnection fault on the power transmission line is distinguished through the established disconnection fault criterion at night, and the disconnection-earthing fault identification criterion is established on the basis of the disconnection fault criterion, so that the protection logics of the disconnection fault and the disconnection-earthing fault are added in the existing protection of the power transmission line, powerful support is provided for timely identifying the disconnection fault on the power transmission line, and the safe and stable operation of the power transmission line is better ensured.

Description

Power transmission line disconnection fault judgment method based on disconnection fault criterion
Technical Field
The invention belongs to the technical field of electric power, and particularly relates to a method for judging a disconnection fault of a power transmission line based on a disconnection fault criterion.
Background
The transmission line is an important carrier for transmitting energy of the power system, and because the operation environment of the transmission line is complex, the transmission line is easily affected by factors such as insulation aging, environmental erosion, complex weather, artificial damage and the like, which leads to the increasing occurrence proportion of the disconnection fault of the transmission line in recent years. The disconnection fault can cause the power transmission and transformation system to be in a non-full-phase operation state, and the dropped electric wires can cause electric shock accidents, and if the electric shock accidents are not handled in time, the damage to associated equipment and major safety accidents are easily caused. However, the existing relay protection device for the power transmission line is mainly used for short-circuit faults and grounding faults on the line, and is difficult to quickly respond to disconnection faults on the line, so that the problems of diagnosis and protection setting of the disconnection faults of the power transmission line are very troublesome at present.
The document "analysis and countermeasure of protection behavior during single-phase disconnection of power transmission line" discusses in detail the reaction situation of main protection and backup protection after the disconnection fault occurs in the power transmission line, and indicates that the existing protection device cannot timely deal with the disconnection fault. The document 'identification and isolation of power distribution network line breakage based on zero sequence voltage amplitude difference' is used for researching the characteristics of zero sequence voltage at each position of a line after line breakage fault, and provides a protection method based on zero sequence voltage amplitude difference; a line break fault distance measuring method based on the change characteristic of positive sequence voltage after line break is provided in the literature of Location of single phase disconnection fault with non-grouping in distribution group on positive sequence voltage. The method switches the line break fault into a symmetric component method for judging, but symmetric phase sequence parameters are greatly influenced by the actual working condition of the line, the threshold aliasing condition for establishing the judgment is serious, the probability of erroneous judgment and missing judgment is high, and the method is not beneficial to popularization.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a power transmission line disconnection fault judgment method based on disconnection fault judgment, which realizes the fault identification of the disconnection or disconnection and reconnection of a power transmission line by utilizing the change characteristics of voltage and current on two sides of the line during disconnection and reconnection of a ground fault and combining the disconnection fault identification judgment.
In order to achieve the above object, the present invention provides a method for determining a disconnection fault of a power transmission line based on a disconnection fault criterion, comprising the steps of:
(1) setting action protection after the transmission line is in fault;
defining a power transmission line MN, wherein the fault phase of the power transmission line MN is recorded as
Figure GDA0003224576180000027
Recording the non-fault phase as phi;
the method comprises the following steps that the power transmission line MN is additionally provided with line break fault criterion protection on the basis of traditional distance protection and zero sequence current protection, wherein the line break fault criterion conditions are as follows:
Figure GDA0003224576180000021
wherein the content of the first and second substances,
Figure GDA0003224576180000022
are measured values of the phase currents of faults on the M and N sides of the transmission line, IMφ、INφA measured current representative of a non-faulted phase; delta U is the variable quantity of each phase voltage of the power transmission line MN; kdMAnd KdNRepresenting the action condition of distance protection devices at two sides of a power transmission line MN by 1; i isset、IactAnd UsetThe current-free setting value, the over-current setting value and the voltage change setting value respectively meet the following requirements: i isset＝5％IE、Iact＝120％IE、Uset＝5％UEWherein, IE、UERated current and rated voltage of the transmission line during normal operation;
(2) measuring current and voltage at two sides of a fault phase of the power transmission line, and calculating zero sequence current after fault;
(2.1) measuring the current and the voltage of two sides of a fault phase of the power transmission line MN after the fault occurs, wherein the current is recorded as
Figure GDA0003224576180000023
And voltage is noted
Figure GDA0003224576180000024
The measured impedances on both sides of the faulted phase are then calculated:
Figure GDA0003224576180000025
(2.2) calculating the zero sequence current of the fault phase after the fault of the power transmission line MN according to a symmetric component method and a fault boundary condition;
Figure GDA0003224576180000026
wherein, IloadBefore the line break fault of the transmission line occurs
Figure GDA0003224576180000031
Load current on phase, Z00、Z22、Z11Zero sequence, negative sequence and positive sequence impedances seen from the fracture are respectively measured;
(3) starting the action protection after the transmission line fault;
(3.1) if ZMA、ZNAAre all greater than Zact，ZactSetting a distance protection action value; judging that the power transmission line disconnection fault does not meet the distance protection action condition, and the distance protection on the two sides of the line does not act, and then jumping to the step (3.3);
(3.2) if 3I0＜I0act，I0actSetting a zero-sequence overcurrent protection action value; judging that the line break fault of the power transmission line does not meet the zero sequence current protection action condition, and the zero sequence current protection on the two sides of the line does not act, and then jumping to the step (3.3);
and (3.3) starting a disconnection fault criterion, entering disconnection fault judgment, and if the formula (1) is met, directly judging that the disconnection fault is the disconnection fault.
Furthermore, the invention also provides a method for judging disconnection and earthing of the transmission line, which comprises the following judgment conditions:
when t is0The disconnection fault happens at any moment, but the protection is not operated, namely:
Figure GDA0003224576180000032
when t is1The time meets the following conditions:
Figure GDA0003224576180000033
judging whether the power transmission line is broken and then grounded, and starting a protection action; wherein, Delta UMφAnd Δ UNφThe voltage variations of the faulty phases on the M-side and N-side of the line, respectively.
The invention aims to realize the following steps:
the invention relates to a power transmission line disconnection fault judgment method based on disconnection fault judgment, which constructs the disconnection fault judgment of a power transmission line by using the change characteristics of voltage and current at two sides of the line when the disconnection occurs and then the grounding fault occurs; the disconnection fault on the power transmission line is distinguished through the established disconnection fault criterion at night, and the disconnection-earthing fault identification criterion is established on the basis of the disconnection fault criterion, so that the protection logics of the disconnection fault and the disconnection-earthing fault are added in the existing protection of the power transmission line, powerful support is provided for timely identifying the disconnection fault on the power transmission line, and the safe and stable operation of the power transmission line is better ensured.
Meanwhile, the method for judging the disconnection fault of the power transmission line based on the disconnection fault criterion also has the following beneficial effects:
(1) the disconnection fault identification criterion does not need to measure the sequence components of voltage and current, does not need to increase extra relay protection equipment, can identify the disconnection fault on the power transmission line through the voltage variation and the current obtained by measuring the protection installation positions on the two sides of the power transmission line, and is suitable for application and popularization.
(2) The identification criterion of the broken line fault of the power transmission line can not be confused with the grounding protection criterion, and the normal work of the existing distance protection and zero-sequence current protection can not be influenced after the identification criterion of the broken line fault and the protection logic are added in the existing protection.
(3) And the influence of the transition resistance on the distance protection can be reduced to a certain extent by adding a disconnection fault identification criterion in the protection.
Drawings
FIG. 1 is a flow chart of a method for judging a disconnection fault of a power transmission line based on a disconnection fault criterion according to the present invention;
FIG. 2 is a power system transmission line model topology;
FIG. 3 is a graph showing the simulation of the currents of the respective phases on the line L16-19M side when the transition resistance is 5. omega.;
FIG. 4 is a graph showing the simulation of the currents of the N-side phases of the lines L16-19 when the transition resistance is 5. omega.;
FIG. 5 is a graph showing the simulation of the currents of the respective phases on the line L16-19M side when the transition resistance is 50 Ω;
fig. 6 is a simulation diagram of the currents of the respective phases on the N side of the lines L16-19 when the transition resistance is 50 Ω.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
Fig. 1 is a flow chart of a method for judging a disconnection fault of a power transmission line based on a disconnection fault criterion.
In this embodiment, the fault is described as: when t is 0.3s, the power transmission line has an A-phase single-phase disconnection fault, when t is 0.9s, one side of the disconnection phase is grounded, the simulation time length is set to be 1.5s, and the simulation step length is set to be 0.0001 s.
In this embodiment, the condition that both sides of the line break phase are grounded after the line break of the power transmission line is not considered, in this embodiment, the power transmission line L16-19 with the voltage class of 220kV is selected to perform the simulation analysis of the line break fault, and one side of the bus 16 is defined as the M side of the line, and one side of the bus 19 is defined as the N side of the line.
The method for judging the disconnection fault of the power transmission line based on the disconnection fault criterion of the invention is described in detail with reference to fig. 1, and specifically comprises the following steps:
s1, constructing a power transmission line model of the power system;
in the process of establishing a power transmission line model of a power system in PSCAD simulation software, as shown in figure 2, both sides of each power transmission line are provided with distance protection and zero-sequence current protection, wherein a setting value Z of the distance protectionactSetting value I of 40 omega zero sequence overcurrent protection0actAnd 300A, carrying out simulation experiments on disconnection faults, disconnection and earthing faults in the power transmission line model.
S2, measuring the current and voltage of two sides of the fault phase of the power transmission line, and calculating the zero sequence current after the fault;
s2.1, setting a single-phase disconnection ungrounded fault on the transmission line L16-19 (two ends are marked as MN), and recording the action conditions of voltage, current and distance protection at two sides of the transmission line;
in the embodiment, the PSCAD software is used for simulation analysis of the action conditions of the protection at two sides of the line after the single-phase simple disconnection fault occurs in the power transmission lines L16-19, and the action conditions, the voltage and the current of the distance protection at two sides of the power transmission lines L16-19 are shown in Table 1.
Table 1 shows the voltage, current, and distance protection behavior of the two sides of the transmission line after a simple phase-a disconnection fault occurs in the line L16-19.
Figure GDA0003224576180000051
TABLE 1
Through the table 1, it can be determined that the measured impedances of the fault phase and the normal phase are both greater than 40 Ω after the power transmission line is disconnected, and the distance protection on both sides of the line is refused.
S2.2, repeating the step S2.1, recording the zero sequence current at two sides of the power transmission line and the action condition of zero sequence current protection, wherein the action condition and the magnitude of the zero sequence current protection at two sides of the power transmission line L16-19 are shown in a table 2.
Table 2 shows the magnitude of the zero sequence current on both sides of the transmission line and the action condition of the zero sequence current protection after the a-phase simple line break fault occurs in the line L16-19.
Figure GDA0003224576180000061
TABLE 2
Through the table 2, it can be determined that zero sequence currents on both sides of the power transmission line do not exceed 300A and zero sequence current protection on both sides fails after the power transmission line is subjected to a line break fault.
S3, adding a simple disconnection fault identification criterion of the transmission line in the relay protection device of the transmission line L16-19;
Figure GDA0003224576180000062
wherein the content of the first and second substances,
Figure GDA0003224576180000063
are measured values of the phase currents of faults on the M and N sides of the transmission line, IMφ、INφA measured current representative of a non-faulted phase; delta U is the variable quantity of each phase voltage of the power transmission line MN; kdMAnd KdNThe method comprises the following steps that 1 represents protection action and 0 represents protection non-action for action conditions of distance protection devices at two sides of a power transmission line MN; i isset、IactAnd UsetRespectively a no-current setting value, an over-current setting value and a voltage change setting value;
in this embodiment, a voltage and current standard of a 220kV transmission line is used to set a voltage change setting value, a no-current setting value and an over-current setting value in a criterion, and the setting result is shown in table 3:
table 3 is the parameter values for the no-flow setting, the over-current setting and the voltage change setting.
Setting value of current and voltage Parameter value
Iset 17.58A
Iact 425.12A
Uset 11kV
TABLE 3
S4, verifying the correctness of the identification criterion of the simple disconnection fault of the power transmission line;
in this embodiment, the voltage and current at the two sides of the power transmission line L16-19 after the simple disconnection fault occurs in the power transmission line L16-19 are analyzed through the PSCAD software simulation, and the voltage variation and current at the two sides of the power transmission line L16-19 are shown in table 4.
Table 4 shows the amount of change in the phase voltage of each line and the phase current of each line after a simple disconnection fault occurs in the line L16-19.
Figure GDA0003224576180000071
TABLE 4
The fact that the identification criterion of the simple disconnection fault of the power transmission line is correct and effective can be determined through the table 4.
S5, adding a disconnection and grounding fault identification criterion in the relay protection device of the power transmission line L16-19;
Figure GDA0003224576180000072
the no-flow setting value, the over-current setting value and the voltage change setting value in the disconnection and earthing fault identification criterion are the same as those in table 2.
S6, verifying feasibility of a fault identification criterion and protection logic of the broken line and the earthing of the transmission line;
the method comprises the steps of respectively setting single-phase disconnection earthing faults with transition resistances of 5 omega and 50 omega on transmission lines L16-19, setting the M side of a line as an earthing side, adding disconnection earthing fault identification criteria and protection logic in a relay protection device of the line L16-19, and recording the variation of each phase voltage on two sides of the line and the variation of current.
In the embodiment, the change conditions of the voltage and the current at two sides of the line after the line disconnection and reconnection failure of the power transmission line L16-19 are analyzed through PSCAD software simulation. The additional protection logic and the judgment method for the disconnection fault of the power transmission line can quickly identify and timely remove the disconnection and then grounding fault on the power transmission line, and are less affected by the transition resistance. When the transition resistance is 5 Ω, the simulation result of the current change of the L16-19M side of the power transmission line is shown in FIG. 3, and the simulation result of the current change of the N side is shown in FIG. 4; when the transition resistance is 50 Ω, the simulation result of the current change on the L16-19M side of the transmission line is shown in fig. 5, and the simulation result of the current change on the N side is shown in fig. 6.
The voltage changes on both sides of the line after the line break and the earth fault occur in the transmission lines L16-19 are shown in table 5.
Table 5 shows the variation of the phase voltages after disconnection and reconnection to ground of the transmission lines L16-19.
Figure GDA0003224576180000081
TABLE 5
After the transmission line has a single-phase disconnection and earth fault with the transition resistance of 5 omega, according to the table 5, only the variation of the A-phase voltage on the M side of the transmission line exceeds the voltage variation set value, and all the phase voltages on the N side have no obvious variation; according to the graphs in fig. 3 and 4, the phase-a currents of the M side and the N side of the line both decrease and are lower than the no-current setting value in 0.3s, the phase-a current of the M side increases and exceeds the over-current setting value in 0.9s, and the other two-phase currents of the M side and the phase-a currents of the N side do not change, which indicates that the fault is removed when the M-side grounding fault occurs in 0.9s and the protection is not reached in 0.1s, and proves that the disconnection-and-grounding fault identification criterion and the protection logic of the power transmission line can timely remove the disconnection-and-grounding fault with small transition resistance. Similarly, according to fig. 5, fig. 6 and table 5, the disconnection-to-earth fault identification criterion and the protection logic of the power transmission line can also remove disconnection-to-earth faults with large transition resistance.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.

Claims (3)

1. A power transmission line disconnection fault judgment method based on disconnection fault criteria is characterized by comprising the following steps:
(1) setting action protection after the transmission line is in fault;
defining a power transmission line MN, wherein the fault phase of the power transmission line MN is recorded as
Figure FDA0003503689190000011
Recording the non-fault phase as phi;
the method comprises the following steps that the power transmission line MN is additionally provided with line break fault criterion protection on the basis of traditional distance protection and zero sequence current protection, wherein the line break fault criterion conditions are as follows:
Figure FDA0003503689190000012
wherein the content of the first and second substances,
Figure FDA0003503689190000013
are measured values of the phase currents of faults on the M and N sides of the transmission line, IMφ、INφA measured current representative of a non-faulted phase; the | Δ U | is the variation of each phase voltage of the power transmission line MN; kdMAnd KdNRepresenting the action condition of distance protection devices at two sides of a power transmission line MN by 1; i isset、IactAnd UsetRespectively a no-current setting value, an over-current setting value and a voltage change setting value;
(2) measuring current and voltage at two sides of a fault phase of the power transmission line, and calculating zero sequence current after fault;
(2.1) measuring the current and the voltage of two sides of a fault phase of the power transmission line MN after the fault occurs, wherein the current is recorded as
Figure FDA0003503689190000014
And voltage is noted
Figure FDA0003503689190000015
The measured impedances on both sides of the faulted phase are then calculated:
Figure FDA0003503689190000016
(2.2) calculating the zero sequence current of the fault phase after the fault of the power transmission line MN according to a symmetric component method and a fault boundary condition;
Figure FDA0003503689190000017
wherein, IloadBefore the line break fault of the transmission line occurs
Figure FDA0003503689190000021
Load current on phase, Z00、Z22、Z11Zero sequence, negative sequence and positive sequence impedances seen from the fracture are respectively measured;
(3) starting the action protection after the transmission line fault;
(3.1) if
Figure FDA0003503689190000022
Are all greater than Zact，ZactSetting a distance protection action value; judging that the power transmission line disconnection fault does not meet the distance protection action condition, and the distance protection on the two sides of the line does not act, and then jumping to the step (3.3);
(3.2) if 3I0＜I0act，I0actSetting a zero-sequence overcurrent protection action value; determining a power transmission lineThe line break fault does not meet the zero sequence current protection action condition, the zero sequence current protection on both sides of the line does not act, and then the step (3.3) is skipped;
and (3.3) starting a disconnection fault criterion, entering disconnection fault judgment, and if the formula (1) is met, directly judging that the disconnection fault is the disconnection fault.
2. The method for judging the disconnection fault of the power transmission line based on the disconnection fault criterion of claim 1, wherein the no-flow setting value IsetOver-current setting value IactSum voltage change set value UsetSatisfies the following conditions:
Iset＝5％IE
Iact＝120％IE
Uset＝5％UE
wherein, IE、UEThe rated current and the rated voltage of the power transmission line during normal operation.
3. The method for judging the disconnection fault of the power transmission line based on the disconnection fault criterion of claim 1, wherein the disconnection fault is judged and then whether the power transmission line is disconnected and then grounded is further judged, and the judgment conditions are as follows:
when t is0The disconnection fault happens at any moment, but the protection is not operated, namely:
Figure FDA0003503689190000023
when t is1The time meets the following conditions:
Figure FDA0003503689190000031
judging whether the power transmission line is broken and then grounded, and starting a protection action; wherein, Delta UMφAnd Δ UNφThe voltage variations of the faulty phases on the M-side and N-side of the line, respectively.
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