CN115201716A - Sheath protector fault online diagnosis method based on sheath current difference amplitude-frequency characteristic - Google Patents

Sheath protector fault online diagnosis method based on sheath current difference amplitude-frequency characteristic Download PDF

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CN115201716A
CN115201716A CN202210832175.3A CN202210832175A CN115201716A CN 115201716 A CN115201716 A CN 115201716A CN 202210832175 A CN202210832175 A CN 202210832175A CN 115201716 A CN115201716 A CN 115201716A
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sheath
fault
protector
cable
current
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王航
刘福源
周莎莎
夏湛然
杨斌
周灏
杨乐之
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Hubei University of Technology
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Hubei University of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—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
    • G01R31/08—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
    • G01R31/088—Aspects of digital computing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
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  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)

Abstract

The invention provides a sheath current difference amplitude-frequency characteristic-based sheath protector fault online diagnosis method, which comprises the following steps of: judging whether the current difference between the tail end and the head end of the cable is equal to the sum of leakage currents flowing into each segmented cable in the cable, and if so, judging that the cable loop has no ground short circuit fault; otherwise, judging whether the abnormal current difference contains harmonic waves, if not, not generating other types of grounding short circuit faults in the cable loop; if the fault is contained, a short-circuit grounding fault occurs in the cable loop. The invention provides a method for calculating current difference under power frequency and leakage current of a fault sheath protector, establishes an equivalent circuit model of harmonic component after the sheath protector fails, designs a sheath protector fault diagnosis method based on amplitude-frequency characteristics of the current difference of the cable sheath, and improves the maintenance efficiency of the sheath protector at the present stage.

Description

Sheath protector fault online diagnosis method based on sheath current difference amplitude-frequency characteristic
Technical Field
The invention relates to the technical field of high-voltage cable lines, in particular to a sheath protector fault online diagnosis method based on sheath current difference amplitude frequency characteristics.
Background
The existing fault monitoring method of the sheath protector mainly depends on manual inspection, the current change of the power frequency sheath caused by the faults of the sheath protector, the damage of the outer sheath of a cable and the like is similar, and the current amplitude, the relative value of the sheath current, the phase angle of the difference between the sheath current and the like are used for difficultly distinguishing the sheath protector and the cable. Aiming at the nonlinear resistance characteristic of a zinc oxide valve plate in the protective layer protector, the invention improves the accuracy of fault diagnosis of the protective layer protector by using the amplitude-frequency characteristic of the current difference of the protective layer.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a calculation method of current difference under power frequency and leakage current of the fault sheath protector, establishes an equivalent circuit model of harmonic component after the fault of the sheath protector, designs a fault diagnosis method of the sheath protector based on the amplitude-frequency characteristic of the current difference of the cable sheath, and improves the maintenance efficiency of the sheath protector at the present stage.
The invention provides a sheath protector fault on-line diagnosis method based on sheath current difference amplitude-frequency characteristics, which comprises the following steps:
acquiring the current difference between the tail end and the head end of the cable, judging whether the current difference is equal to the sum of leakage currents flowing into each segmented cable in the cable, and if so, judging that the ground short circuit fault does not occur in a cable loop; otherwise, the line has a short-circuit fault.
On the basis of the technical scheme, the invention can be improved as follows.
Preferably, after the line has a short-circuit to ground fault, the method further comprises: judging whether the current difference contains harmonic waves, if not, not generating other types of grounding short circuit faults in the cable loop; if yes, fault diagnosis and positioning of the protective layer protector are carried out according to preset criteria and diagnosis results.
Preferably, the diagnosing and locating the fault of the sheath protector according to the preset criterion and the diagnosis result comprises establishing a fault diagnosis criterion according to the amplitude-frequency characteristic of the sheath current caused by the fault of the sheath protector and judging a loop where the fault of the sheath protector is located through the established current difference of the sheath circuit after the fault of the sheath protector and the established equivalent circuit model of the harmonic component after the fault of the sheath protector under the power frequency.
Preferably, the step of formulating the fault diagnosis criterion according to the amplitude-frequency characteristic of the sheath current caused by the sheath protector fault comprises the following steps: the harmonic content in the sheath current at the first and the last ends of the cable is changed due to the fault position of the sheath protector under the filtering action of the cable sheath, and the harmonic content graph of the leakage current in the fault sheath protector is made as the fault diagnosis criterion.
Preferably, said obtaining a current difference between the cable end and the head end comprises the steps of:
installing 6 power frequency current transformers in grounding boxes at two ends of a cross-connection high-voltage cable line, and synchronously acquiring sheath current signals at two ends of the cable;
grouping the collected sheath current signals according to sheath loops, and respectively calculating corresponding grouped sheath current differences;
and performing Fourier transform on the sheath current difference waveform to obtain the content of harmonic waves in the leakage current.
Preferably, the determining whether the current difference is equal to the sum of the leakage currents flowing into the segmented cables inside the cable comprises:
obtaining equivalent impedance of the sheath protector;
respectively establishing equivalent circuits of the capacitive coupling component and the inductive coupling component, and obtaining a sheath current phase difference caused by the fault of the sheath fault protector according to the equivalent circuits;
and calculating leakage current containing harmonic components of the fault sheath protector according to the sheath current phase difference, and obtaining current difference containing harmonic components of a fundamental current difference phase angle according to the leakage current.
Preferably, the obtaining the equivalent impedance of the sheath protector includes the following steps:
acquiring a parallel equivalent resistance and a parallel equivalent capacitance of the sheath protector;
establishing an equivalent impedance calculation model;
and substituting the parallel equivalent resistance and the parallel equivalent capacitance into an equivalent impedance calculation model to obtain equivalent impedance.
Preferably, the equivalent impedance calculation model is represented as:
Figure BDA0003745931960000031
in the formula, Z L Representing equivalent impedance, j representing an imaginary factor, and omega representing a power frequency angular velocity; rsvl represents the parallel equivalent resistance, and Csvl represents the parallel equivalent capacitance.
Preferably, the obtaining of the current difference including the harmonic component in the fundamental current difference phase angle according to the leakage current includes:
in the simulation of a cable line with the protective layer protector after the fault, protective layer circuit models under power frequency and harmonic frequency are respectively established, in an equivalent circuit model of harmonic component after the fault of the protective layer protector, the fault protective layer protector is regarded as a harmonic source, the cable protective layer circuit is equivalent to a series R-L circuit, and in the line with the total length of the loop being L, the transfer function of the protective layer current difference to the harmonic component of leakage current of the fault protective layer protector is defined as the ratio of the two in the assumption that the ground impedances of the head end and the tail end of the cable are equal.
The invention has the technical effects and advantages that:
according to the nonlinear resistance characteristic of a zinc oxide valve plate in the internal structure of the protective layer protector, the fault of the protective layer protector is monitored according to the current difference harmonic content; the method comprises the steps of establishing an equivalent circuit model of the cross-connection high-voltage cable, providing a detection method taking current difference harmonic content as fault characteristic quantity of the sheath protector, providing a calculation method of current difference during fault, formulating a fault diagnosis process of the sheath protector in a three-phase nine-section cross-connection high-voltage cable system, and improving the maintenance efficiency of the sheath protector at the present stage.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
FIG. 1 is a flow chart of a fault diagnosis method of the present invention;
FIG. 2 is a flow chart of the fault criterion establishment for the sheath protector of the present invention;
FIG. 3 is a graph of leakage current subharmonic content in a fault sheath protector of the present invention;
FIG. 4 is a schematic diagram of a three-phase nine-segment cross-connected high-voltage sheath protector according to the present invention;
FIG. 5 is a schematic diagram of the loop 1 sheath current of the present invention;
FIG. 6 is an equivalent circuit diagram of capacitive coupling component of the loop 1 sheath circuit of the present invention;
FIG. 7 is an equivalent circuit diagram of the inductive coupling component of the loop 1 sheath circuit according to the present invention;
FIG. 8 is an equivalent circuit model of harmonic components after a fault in the circuit 1 sheath protector of the present invention;
fig. 9 is a graph of the current content of the harmonic component after a loop 1 sheath protector fault in accordance with the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
When the protective layer protector is broken down, a carbonization channel from the upper electrode to the lower electrode through the zinc oxide valve plate appears, and physical properties such as equivalent impedance of the protective layer protector are changed. When the fault of the protective layer protector occurs, the difference amplitude frequency characteristic change of the protective layer current is utilized to realize the fault on-line diagnosis and positioning of the protective layer protector.
In order to solve the defects of the prior art, the invention provides an on-line fault diagnosis method for a sheath protector based on a sheath current difference amplitude-frequency characteristic, which comprises the following steps of:
installing 6 power frequency current transformers in grounding boxes at two ends of a cross-connection high-voltage cable line, and synchronously acquiring sheath current signals at two ends of the cable;
specifically, after the current difference between the tail end and the head end of the cable is obtained, whether the current difference between the tail end and the head end of the cable is equal to the sum of leakage currents flowing into three sections of cables or not is judged, if yes, the ground short circuit fault does not occur in a cable loop, and otherwise, the ground short circuit fault occurs in a line.
Grouping the acquired current signals according to the sheath loops, and respectively calculating corresponding sheath current differences;
specifically, the step of calculating the corresponding sheath current difference comprises measuring the sheath protector parameters, establishing a cable line model, diagnosing the sheath protector fault, calculating the leakage current and current difference of the fault sheath protector, and classifying and detecting the fault. The step of calculating the corresponding sheath current difference will be described in detail later, and will not be described again. Fig. 2 is a flow chart for formulating a fault criterion of the sheath protector, wherein after it is determined that a line has an earth short fault, it is further determined whether a current difference contains a harmonic, and if not, no other types of earth short faults occur in a cable loop; if the fault is contained, a short-circuit grounding fault occurs in the cable loop.
And performing fast Fourier transform on the sheath current difference waveform to obtain the content of 3, 5, 7 and 9 subharmonics.
Specifically, the obtained contents of the 3 rd, 5 th, 7 th and 9 th harmonics are used as the diagnosis result of fault diagnosis.
And diagnosing and positioning the faults of the protective layer protector according to preset criteria and diagnosis results.
Specifically, fault diagnosis and location of the sheath protector are carried out according to preset criteria and diagnosis results, namely, the fault diagnosis criteria are formulated according to the amplitude-frequency characteristic of sheath current caused by the sheath protector fault and the equivalent circuit model of the current difference of the sheath circuit after the sheath protector fault and the harmonic component after the sheath protector fault under the power frequency, and the loop where the sheath protector fault is located is judged.
The method comprises the steps of establishing a fault diagnosis criterion according to the amplitude-frequency characteristic of sheath current caused by a fault of a sheath protector, namely enabling each sub-component of leakage current in the fault sheath protector to be equivalent to a harmonic source, injecting the harmonic source into a metal sheath loop from the position of the fault sheath protector, changing the harmonic content in the sheath current at the first end and the tail end of a cable due to the fault position of the sheath protector under the filtering action of a cable sheath, and establishing a diagram of each sub-harmonic content of the leakage current in the fault sheath protector as a preset criterion for fault diagnosis.
In this embodiment, the content of each harmonic of the leakage current in the fault sheath protector is tested according to experiments, and when a ground short circuit fault occurs in a circuit, the zinc oxide valve sheet inside the sheath protector has harmonics of mainly 3, 5, 7, and 9 times in the leakage current at a power frequency of 100V, as shown in fig. 3, the content of each harmonic of the leakage current in the fault sheath protector is 65.4%, 27.5%, 5.9%, and 3.4% respectively, with the fundamental current as a reference. The invention establishes the fault diagnosis standard of the protective layer protector in three loops, and the fault current difference amplitude-frequency characteristic of the protective layer protector is shown in the following table 1:
loop 1 Loop 2 Loop 3
Current difference 3 th harmonic content (%) 1.88～21.31 1.30～23.71 1.53～16.15
Current difference 5 th harmonic content (%) 0.79～8.98 0.55～9.99 0.65～6.81
Current difference 7 th harmonic content (%) 0.17～1.94 0.12～2.16 0.14～1.47
Current difference 9 th harmonic content (%) 0.11～1.10 0.07～1.22 0.08～0.83
It should be noted that, the present invention diagnoses and locates the fault of the sheath protector by detecting the current of the sheath of the high voltage cable and calculating the current phase difference. By applying the technical scheme of the invention, the detection current data can be effectively utilized in the current inspection of the high-voltage cable sheath, and the fault of the sheath protector can be found and positioned in time so as to be convenient for the subsequent replacement of the fault protector, thereby effectively protecting the safety of the high-voltage cable sheath and the insulation and ensuring the safe operation of a cable line.
Meanwhile, the calculation of the corresponding sheath current difference includes the following steps:
01 Measurement of sheath protector parameters
In this embodiment, the cable includes the outer jacket from outside to inside in proper order, the metal sheath, insulating layer and cable core, wherein, the sheath protector is installed in the cross interconnection grounding box between two metal sheath subsections in the cross interconnection cable run, 35kV large cross section power cable and 66kV usually, the power cable of 110kV and above voltage class is a single core cable, one end of the cable metal sheath is connected in parallel and grounded, the other end is ungrounded, when lightning wave or internal overvoltage flows along the cable core, the cable metal sheath does not have the grounding end and can have higher surge overvoltage, or when the system short circuit accident current flows through the cable core, the sheath does not have the grounding end and can also have very high power frequency induced overvoltage. The overvoltage can break down the insulation of the outer protective layer of the cable, so that multipoint grounding faults of the metal protective layer of the cable are caused, the normal operation of the power cable is seriously influenced, and the service life of the cable is even greatly reduced. Therefore, to limit the induced voltage and fault overvoltage on the metal sheath of the power cable and to avoid the formation of circulating currents in the sheath, one end of the sheath is directly grounded and the other end is grounded through the sheath protector. If the circuit is longer, the cable sheath can be divided into three sections or multiple sections of three sections to be insulated with each other, and the sheaths at the sections are connected with each other in a cross mode and then grounded through the sheath protectors. The protective layer protector adopts ZnO piezoresistor or ZnO valve plate as protective element, the ZnO valve plate has no series gap, and has excellent voltage-current characteristic curve. The protective layer protector uses the insulating material as external insulation, and has more excellent volt-ampere characteristics compared with the traditional discharge gap protection, silicon carbide resistor sheet with gap protection and other modes.
In practical application, if the sheath protector is punctured, a carbonization channel from the upper electrode to the lower electrode through the zinc oxide valve plate will appear, physical characteristics such as equivalent impedance of the sheath protector will change at this moment, and an equivalent circuit model of the sheath protector is established according to the characteristics of the zinc oxide valve plate which is the main component of the oxygen sheath protector, wherein the equivalent circuit model of the sheath protector is established, and the method comprises the following steps: obtaining parallel equivalent resistance R of fault protection layer protector svl And parallel equivalent capacitanceC svl (ii) a Establishing an equivalent impedance calculation model, and connecting equivalent resistors R in parallel svl And a parallel equivalent capacitor C svl Substituting into the equivalent impedance calculation model to obtain the equivalent impedance Z L . In this embodiment, the parallel equivalent resistance R of the fault sheath protector can be measured by using an AC bridge svl And a parallel equivalent capacitor C svl Equivalent resistance R svl And an equivalent capacitance C svl Are connected in parallel, and the equivalent impedance Z is calculated L Includes connecting equivalent resistors R in parallel svl And a parallel equivalent capacitor C svl Substituting the equivalent impedance into the equivalent impedance calculation model of the following formula 1 to obtain the equivalent impedance Z L ，
Figure BDA0003745931960000071
In the formula, j represents an imaginary factor, and omega represents a power frequency angular velocity; r svl Represents the equivalent resistance in parallel, C svl Representing the equivalent capacitance in parallel.
02 To build a cable route model
The invention adopts a three-phase nine-section type cross-interconnected high-voltage sheath protector, and particularly as shown in figure 4, the cable sheath is divided into three sections which are mutually insulated, and in figure 4, 9 metal sheath sections of the cable sheath consist of a first section of metal sheath S1, a second section of metal sheath S2, a third section of metal sheath S3, a fourth section of metal sheath S4, a fifth section of metal sheath S5, a sixth section of metal sheath S6, a seventh section of metal sheath S7, an eighth section of metal sheath S8 and a ninth section of metal sheath S9. The first section of metal sheath S1, the fifth section of metal sheath S5 and the ninth section of metal sheath S9 form a sheath loop 1; the fourth section of metal sheath S4, the eighth section of metal sheath S8 and the third section of metal sheath S3 form a sheath loop 2; the seventh section of metal sheath S7, the second section of metal sheath S2 and the sixth section of metal sheath S6 form a sheath loop 3. First protective layer protector Z SVL1 Second protective layer protector Z SVL2 The third protective layer protector Z SVL3 The fourth protective layer protector Z SVL4 The fifth protective layer protector Z SVL5 The sixth protective layer protector Z SVL6 Are respectively arranged at the head of the cable lineTerminal first current sensor cs 1 A second current sensor cs 2 And a third current sensor cs 3 And a fourth current sensor cs installed at the end of the cable line 4 And a fifth current sensor cs 5 Sixth current sensor cs 6 The above. Wherein, the first and the second end of the pipe are connected with each other,
Figure BDA0003745931960000081
the core current of the three phases of the cable.
3) Sheath protector fault diagnosis
The invention is mainly explained by taking the loop 1 as an example, and the loop 2 and the loop 3 are similar to the loop 1 and are not described herein again. Specifically, as shown in fig. 5, a schematic diagram of the current of the sheath of the loop 1 is shown, wherein the first metal sheath S1, the fifth metal sheath S5 and the ninth metal sheath S9 are connected in series, I cs1 、I cs5 The current sensors cs1 and cs5 respectively measure the ground current of the protective layer; I.C. A LS1 、I LS5 And I LS9 Respectively representing the leakage current flowing into the first section of metal sheath S1, the fifth section of metal sheath S5 and the ninth section of metal sheath S9 from the cable core, wherein under the normal fault-free condition, the current difference in the metal sheath is equal to the leakage current flowing into the first section of metal sheath S1 according to kirchhoff' S current law:
Figure BDA0003745931960000082
under the condition that the mutual layer protector breaks down, physical characteristics such as equivalent impedance of the protective layer protector are changed at the moment, and the characteristics of zinc oxide valve plates which are main components of the oxygen protective layer protector are used. When the fault of the protective layer protector occurs, the difference amplitude frequency characteristic change of the protective layer current is utilized to realize the fault on-line diagnosis and positioning of the protective layer protector. The invention considers the nonlinear resistance characteristic of the fault protective layer protector, and distinguishes the protective layer protector fault and other types of ground short circuit faults by judging whether the abnormal current difference contains harmonic waves; and establishing a fault diagnosis criterion according to the amplitude-frequency characteristic of the sheath current caused by the sheath fault through the established equivalent circuit model of the current difference of the sheath circuit after the sheath fault under the power frequency and the harmonic component after the sheath fault, and judging the loop where the sheath fault exists.
3) Calculation of leakage current and current difference of fault sheath protector
In order to analyze the relation between the fault impedance and the detected sheath current, the invention provides a method for calculating the current difference under the power frequency and the leakage current of the fault sheath protector. Since the sheath protector has negligible impedance to ground, compared to the insulation impedance, it is assumed that the leakage current is equal to that in normal operation when the sheath protector has a ground fault. Another normal sheath protector in the same loop has a large impedance compared to the point of failure, and is considered open to ground. For the sake of calculation, it is assumed that the impedances of the cable line end and head end are approximately equal, i.e. R e1 ＝R e2 ＝R。
Judging whether the current difference is equal to the sum of the leakage currents flowing into each segmented cable in the cable or not, including calculating the leakage current and the current difference of the sheath protector, wherein the current difference is specifically that equivalent circuits of capacitive coupling components and inductive coupling components are respectively established, and the sheath current phase difference caused by the fault of the sheath fault protector is obtained according to the equivalent circuits; and calculating leakage current containing harmonic components of the fault sheath protector according to the sheath current phase difference, and obtaining current difference containing harmonic components of a fundamental current difference phase angle according to the leakage current. In this embodiment, the cross-connected high-voltage cable sheath current is a superposition of a capacitive coupling current component and an inductive coupling current component, so that equivalent circuit models of the capacitive coupling component and the inductive coupling component need to be established respectively.
(1) Capacitively coupled current component calculation
FIG. 6 is an equivalent circuit diagram of capacitive coupling component of the loop 1 sheath circuit, in which EA1 is the induced voltage at the first section of the metal sheath S1, and E B2 Is the induced voltage at the fifth section of the metal sheath S5, E C3 The induced voltage at the ninth section of metal sheath S9; z is a linear or branched member SA1 Is the sheath impedance, Z, at the first section of the metal sheath S1 SB2 Is the sheath impedance, Z, at the fifth metal sheath S5 SC3 Is the sheath impedance at the ninth segment S9 of the metal sheath. I is cs1m And I cs2m The inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1, respectively.
Impedance Z of cable metal sheath S The calculation process is shown in the formula (3),
Figure BDA0003745931960000091
wherein l is the cable length; r S Resistance per unit length of the metal sheath; d S Is the sheath average diameter; f is the power frequency of the system operation, and omega represents the power frequency angular velocity.
M X,Sn Mutual inductance between the x-phase cable core and the Sn section of the cable is as follows:
Figure BDA0003745931960000092
in the formula, d x,Sy Is the average geometric distance mu between the core of the x-phase cable and the sheath of the Sn-section cable 0 Is a vacuum permeability of n The length of each short cable.
The calculation formulas of the induced voltages of the upper protective layers of the first section of metal sheath S1, the fifth section of metal sheath S5 and the ninth section of metal sheath S9 of the protective layers are as follows:
Figure BDA0003745931960000101
in the formula, E S1 、E S5 、E S9 Induced voltages of the protective layer generated on the sections S1, S5 and S9 of the protective sleeve respectively; m A,S1 、M B,S1 、M C,S1 Mutual inductance of the A, B and C three-phase cables to the first section of the metal sheath S1 is respectively realized; m A,S5 、M B,S5 、M C,S5 Mutual inductance of the A, B and C three-phase cables to the first section of the metal sheath S5 is respectively realized; m A,S9 、M B,S9 、M C,S9 Mutual inductance of the A, B and C three-phase cables to the first section of metal sheath S9 is respectively realized; i is A 、I B 、I C Is respectively the negative of the A, B and C phases of the cableCarrying current.
(2) Inductively coupled current component calculation
FIG. 7 is an equivalent circuit diagram of the inductive coupling component of the loop 1 sheath circuit, in which ES1 is the induced voltage at the first section of the metal sheath S1, ES5 is the induced voltage at the fifth section of the metal sheath S5, and E S9 The induced voltage at the ninth section of metal sheath S9; z S1 Is the sheath impedance, Z, at the first section of the metal sheath S1 S5 Is the sheath impedance, Z, at the fifth metal sheath S5 S9 Is the sheath impedance at the ninth segment S9 of the metal sheath. I is cs1m And I cs2m The inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1, respectively.
(3) Computation of the interbed current vector difference
Specifically, obtaining the difference of the sheath current phasor caused by the fault of the sheath fault protector according to the equivalent circuit comprises: at power frequency f 1 Analyzing a circuit S1-S2-S3 of the faults of the protective layer protector of the loop 1 under the frequency of =50 Hz;
calculating cable insulation capacitance C i ：
Figure BDA0003745931960000102
Wherein epsilon is the relative dielectric constant of the insulating layer; epsilon 0 Dielectric constant in vacuum; d C Is the core conductor diameter; d S Is the average geometric diameter of the metal sheath of the cable.
In the first circuit, I LS1 Is a capacitively coupled component current, I, at the first section of the metal sheath S1 LS5 Is a capacitive coupling component current, I, at the fifth section of the metal sheath S5 LS9 Is a capacitively coupled component current at the ninth segment of the metal sheath S9, where ω 1 And the angular speed is corresponding to the power frequency.
Figure BDA0003745931960000111
The working voltage vector in the first loop is U loop1 Wherein U is A 、U B 、U C Respectively working voltages of A phase, B phase and C phase; the load current vector is I loop1 In which I A 、I B 、I C Load currents of A, B and C phases respectively; the equivalent capacitance vector of the cable insulating layer is C i In which C is S1 、C S5 、C S9 Equivalent capacitances of a first section of metal sheath S1, a fifth section of metal sheath S5 and a ninth section of metal sheath S9 are respectively set; m loop1 Is a mutual inductance matrix of the cable sheath and the cable core in the loop 1, wherein the mutual impedance of the x phase cable core and the Sn section of the sheath is defined as Z x,Sn ：
U loop1 ＝[U A U B U C ] (8)
I loop1 ＝[I A I B I C ] T (9)
C i ＝[C S1 C S5 C S9 ] (10)
Figure BDA0003745931960000112
Sheath current phase difference I caused by sheath protector svl1 fault in loop 1 loop1,svl1 Comprises the following steps:
Figure BDA0003745931960000113
in the same way, the sheath current phase difference I caused by the fault of the sheath protector svl5 can be obtained loop1,svl5 Comprises the following steps:
Figure BDA0003745931960000114
(4) calculation of leakage current containing harmonic component of fault sheath protector
According to the sheath current phase difference I loop1,svl5 Calculating the leakage current of the fault sheath protector containing harmonic components comprises the following steps:
the leakage current calculation formula of the protective layer protectors through the fault after the protective layer protectors svl1 and svl5 respectively have faults under the power frequency is as follows:
Figure BDA0003745931960000121
Figure BDA0003745931960000122
due to the randomness of harmonic phase angle, the phase angle of each harmonic current is equal to the phase angle phi of the fundamental current svl(1) The harmonic frequency is h, the fault of the sheath protector svl1 is taken as an example, and the leakage current of the fault sheath protector containing the harmonic component is as follows:
Figure BDA0003745931960000123
in the simulation of the cable line after the fault of the sheath protector, sheath circuit models under power frequency and harmonic frequency are respectively established. Regarding the fault sheath protector as a harmonic source, the cable sheath circuit is equivalent to a series R-L circuit, and an equivalent circuit model of harmonic component after the fault of the sheath protector is shown in FIG. 8, wherein R is S1 、L s1 、R S5 、L s5 、R S9 、L s9 Are connected in series between I cs1m And I cs2m The inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1 respectively; in a series R-L circuit, the inductance L per unit length S (unit is H/m), resistance per unit length R S (in Ω/m) and the impedance to ground at the head and tail ends of the cable are assumed to be equal. In a line with a total length l of the loop 1, the transfer function of the sheath current difference to the harmonic component of the leakage current of the fault sheath protector is defined as the ratio G (ω) of the two.
Figure BDA0003745931960000124
(5) Calculating the current difference of the harmonic component contained in the fundamental current difference phase angle;
obtaining a current difference including a harmonic component in a fundamental current difference phase angle according to the leakage current includes:
when the protective layer protector svl1 has a fault, the fundamental current difference phase angle phi (1) The current difference calculation formula containing harmonic components is as follows:
Figure BDA0003745931960000125
5) Fault classification and detection
Equivalent resistance R taking collected fault sheath protector as an example svl =216 Ω, and fig. 9 shows amplitude-frequency characteristics of current differences in the sheath circuit when the sheath protectors svl1 to svl6 fail, respectively. In this example, the cable parameters are shown in table 2 below,
parameter/unit Numerical value Parameter/unit Numerical value
AB phase spacing/m 0.27 Operating voltage/kV 110
BC phase spacing/m 0.27 Resistance per unit length of sheath/omega m -1 4.26×10 -5
AC phase spacing/m 0.54 Volume resistivity/omega m of insulating layer 10 15
Ground resistance/omega 0.50 Length of the first section/m 425
Outer diameter/mm of metal conductor 35.90 Second length/m 477
Thickness/mm of insulating layer 17.30 Length of third segment/m 536
Thickness/mm of metal passivation layer 2 Dielectric constant in free space 8.85×10 -12
frequency/Hz 50 Relative dielectric constant 2.30
With the known line parameters table 2 and the fault impedance of the sheath protector, the current difference of the sheath loop where the fault exists can be calculated by the method. Judging whether the current difference is equal to the sum of leakage currents flowing into each segmented cable in the cable, and if so, judging that the cable loop has no ground short circuit fault; otherwise, the line has a ground short-circuit fault, when the line has the ground short-circuit fault, whether the current difference contains harmonic waves is also judged, and if the current difference does not contain the harmonic waves, other types of ground short-circuit faults do not occur in the cable loop; if the harmonic wave is contained, the grounding short circuit fault occurs in the cable loop, and the harmonic wave is compared with the harmonic wave in the leakage current in the figure 9, and the loop where the fault of the sheath protector is located is judged.
In this embodiment, the influence of the field cable parameters, the cable core current, the three small cable lengths, the ground impedance, the core voltage and other influencing factors needs to be considered when the criterion is determined.
In conclusion, the invention establishes the equivalent model of the three-phase nine-section type cross-connection high-voltage cable and provides a method for calculating the leakage current and the current difference in the sheath protector under the power frequency when the sheath protector fails. And (3) enabling each harmonic current equivalently generated by the fault sheath protector to be equivalent as a harmonic source to be injected into the cable sheath circuit, and establishing a corresponding harmonic circuit model. The invention uses the current difference harmonic content as the characteristic quantity to judge whether the fault in the line is the fault of the protective layer protector and determine the loop of the fault of the protective layer protector.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.

Claims (9)

1. The sheath protector fault on-line diagnosis method based on the sheath current difference amplitude-frequency characteristic is characterized by comprising the following steps of:
acquiring current difference between the tail end and the head end of the cable, judging whether the current difference is equal to the sum of leakage currents flowing into each segmented cable in the cable, and if the current difference is equal to the sum, not generating a ground short circuit fault in a cable loop; otherwise, the circuit has a short-circuit fault.
2. The method of claim 1, wherein: after the line has a short-circuit to ground fault, the method further comprises the following steps: judging whether the current difference contains harmonic waves, if not, not generating other types of grounding short circuit faults in the cable loop; if the fault is contained, fault diagnosis and positioning of the protective layer protector are carried out according to preset criteria and diagnosis results.
3. The method of claim 2, wherein: the step of diagnosing and positioning the faults of the protective layer protector according to the preset criterion and the diagnosis result comprises the steps of,
establishing an equivalent circuit model of current difference of a protective layer circuit after the protective layer protector fails and harmonic component after the protective layer protector fails under power frequency, formulating a fault diagnosis criterion according to amplitude-frequency characteristics of the protective layer current caused by the protective layer protector failure, and judging a loop where the protective layer protector fails.
4. The method of claim 3, wherein: the fault diagnosis criterion is formulated according to the amplitude-frequency characteristic of the sheath current caused by the sheath protector fault, and comprises the following steps:
the harmonic content in the sheath current at the first and the last ends of the cable is changed due to the fault position of the sheath protector under the filtering action of the cable sheath, and the harmonic content in the leakage current in the fault sheath protector is used as a fault diagnosis criterion.
5. The method of claim 1, wherein: said obtaining a current difference between the cable end and the head end comprises the steps of:
installing 6 power frequency current transformers in grounding boxes at two ends of a cross-connection high-voltage cable line, and synchronously acquiring sheath current signals at two ends of the cable;
grouping the collected sheath current signals according to sheath loops, and respectively calculating corresponding grouped sheath current differences;
and performing Fourier transform on the sheath current difference waveform to obtain the content of harmonic waves in the leakage current.
6. The method of claim 1, wherein: the judging whether the current difference is equal to the sum of the leakage currents flowing into each segmented cable in the cable comprises the following steps:
obtaining equivalent impedance of the protective layer protector;
respectively establishing equivalent circuits of the capacitive coupling component and the inductive coupling component, and obtaining a sheath current phase difference caused by the fault of the sheath fault protector according to the equivalent circuits;
and calculating leakage current containing harmonic components of the fault sheath protector according to the sheath current phase difference, and obtaining current difference containing harmonic components of a fundamental current difference phase angle according to the leakage current.
7. The method of claim 6, wherein: the method for acquiring the equivalent impedance of the sheath protector comprises the following steps:
acquiring a parallel equivalent resistance and a parallel equivalent capacitance of the sheath protector;
establishing an equivalent impedance calculation model;
and substituting the parallel equivalent resistance and the parallel equivalent capacitance into an equivalent impedance calculation model to obtain equivalent impedance.
8. The method of claim 7, wherein: the equivalent impedance calculation model is expressed as:
Figure FDA0003745931950000021
in the formula, Z L Representing the equivalent impedance, j represents the imaginary factor,omega represents the power frequency angular velocity; rsvl represents the parallel equivalent resistance, and Csvl represents the parallel equivalent capacitance.
9. The method of claim 6, wherein: the obtaining of the current difference including the harmonic component of the fundamental current difference phase angle according to the leakage current includes:
in the simulation of a cable line with the protective layer protector after the fault, protective layer circuit models under power frequency and harmonic frequency are respectively established, in an equivalent circuit model of harmonic component after the fault of the protective layer protector, the fault protective layer protector is regarded as a harmonic source, the cable protective layer circuit is equivalent to a series R-L circuit, and in the line with the total length of the loop being L, the transfer function of the protective layer current difference to the harmonic component of leakage current of the fault protective layer protector is defined as the ratio of the two in the assumption that the ground impedances of the head end and the tail end of the cable are equal.
CN202210832175.3A 2022-07-14 2022-07-14 Sheath protector fault online diagnosis method based on sheath current difference amplitude-frequency characteristic Pending CN115201716A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115656719A (en) * 2022-10-26 2023-01-31 徐忠林 High-voltage cable sheath defect online diagnosis method based on sheath current abnormal motion
CN116544895A (en) * 2023-07-06 2023-08-04 广东电网有限责任公司汕尾供电局 Pumped storage power station cable sheath fault grading protection method based on induced parameters

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115656719A (en) * 2022-10-26 2023-01-31 徐忠林 High-voltage cable sheath defect online diagnosis method based on sheath current abnormal motion
CN115656719B (en) * 2022-10-26 2023-04-07 徐忠林 High-voltage cable sheath defect online diagnosis method based on sheath current transaction
CN116544895A (en) * 2023-07-06 2023-08-04 广东电网有限责任公司汕尾供电局 Pumped storage power station cable sheath fault grading protection method based on induced parameters
CN116544895B (en) * 2023-07-06 2023-10-20 广东电网有限责任公司汕尾供电局 Pumped storage power station cable sheath fault grading protection method based on induced parameters

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