CN112379302A - Small current ground fault protection method, device and system integrating time-frequency domain information - Google Patents

Small current ground fault protection method, device and system integrating time-frequency domain information Download PDF

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Publication number
CN112379302A
CN112379302A CN202011116873.0A CN202011116873A CN112379302A CN 112379302 A CN112379302 A CN 112379302A CN 202011116873 A CN202011116873 A CN 202011116873A CN 112379302 A CN112379302 A CN 112379302A
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zero
mode
current
line
mode voltage
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CN112379302B (en
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郑玉平
潘书燕
余洪
吴通华
纪浩然
龙威
梁臣
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Nari Technology Co Ltd
NARI Nanjing Control System Co Ltd
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Nari Technology Co Ltd
NARI Nanjing Control System Co Ltd
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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
    • 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

Abstract

The invention discloses a method, a device and a system for protecting a single-phase earth fault of a small current earth system by integrating time-frequency domain information, wherein the method comprises the steps of responding to a signal with an earth fault; carrying out 90-degree forward phase shift on the acquired bus zero-mode voltage; extracting transient state quantity in a characteristic frequency band of the obtained line zero-mode current and the bus zero-mode voltage after phase shifting to obtain transient state zero-mode current and transient state zero-mode voltage; when the grounding is carried out through high resistance, the direction of the short window zero sequence power in the time domain information is utilized for judging; when the grounding is not high-resistance, the transient zero-mode power direction in the characteristic frequency band is used for judging; and judging the zero sequence power direction of the usable steady-state power frequency of the ungrounded system. The invention is adaptive to a system in which a neutral point is not grounded, the neutral point is grounded through an arc suppression coil and the neutral point is grounded through a small resistor.

Description

Small current ground fault protection method, device and system integrating time-frequency domain information
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a small current ground fault protection method, device and system integrating time-frequency domain information.
Background
The grounding mode of the neutral point of the power system is mainly divided into two categories: the neutral point is directly grounded (high current grounding system) and the neutral point is not directly grounded (low current grounding system). The neutral point is not directly grounded, including the neutral point is not grounded and the neutral point is grounded via an arc suppression coil (resonance grounding), and when a single-phase ground fault occurs in the system, the fault current flowing through the fault point is small, so that the system is also called a low-current grounding system. In China, a small-current grounding mode is mostly adopted for medium-voltage power distribution networks, but the small-current grounding fault positioning problem is not thoroughly and effectively solved until now because of unobtrusiveness (the grounding current is very small and is generally only a few amperes), uncertainty (the influence of arc coil compensating current in a resonance grounding system on power frequency current) and instability (the intermittent grounding and arc grounding occurrence rate is high) of the fault quantity.
At present, aiming at the problem of fault line selection of a small current grounding system, a centralized line selection mode is mostly adopted, namely, in a transformer substation, zero sequence currents and bus zero sequence voltages of all intervals on the grounding side of an ungrounded coil or an arc suppression coil are connected into an independent centralized line selection device for detecting and positioning a grounding fault, equipment is newly added in the centralized mode under the condition that the existing interval configuration protection or protection and detection device is necessary, and inconvenience is brought to the wiring and operation and maintenance of a secondary circuit on site; protection or protection measurement and control devices are arranged at intervals, single-phase earth fault judgment is carried out by accessing respective zero sequence current and bus voltage at intervals, the measured information is limited, the adopted judgment methods of zero sequence active power, reactive power, quintic harmonic zero sequence power direction and the like are influenced by transient state and steady state information aliasing, and the earth fault positioning misjudgment rate is high; under the condition of ground fault through protection of each interval unit, fault line judgment is carried out through a mode of protection trial jump and reclosing during ground fault, efficiency is low, and the problems that non-fault lines have power failure in short time, and equipment damage is possibly caused due to the fact that fault lines cannot be isolated in time exist.
Disclosure of Invention
Aiming at the problems, the invention provides a small current ground fault protection method, a device and a system for integrating time-frequency domain information, which adopt a time-domain and frequency-domain multi-information integrated judgment method and overcome the problem of high ground fault misjudgment rate of a distributed single-interval protection and protection device.
In a first aspect, a method for protecting a single-phase earth fault of a low-current earth system by integrating time-frequency domain information comprises the following steps
Responding to a signal that a ground fault has occurred;
acquiring bus zero-mode voltage, line zero-mode current and time-frequency domain information after response starting;
performing 90-degree phase advance on the obtained bus zero-mode voltage to obtain the bus zero-mode voltage after phase shift;
extracting transient state quantity in a characteristic frequency band from the zero-mode current of the line and the zero-mode voltage of the bus after phase shifting,
obtaining transient zero-mode current and transient zero-mode voltage after phase shifting;
calculating a zero-mode current offset direct-current component in the transient process based on the acquired zero-mode current of the line;
judging whether the line fault is present according to the zero-mode current offset direct-current component,
judging whether the line has a fault according to the angle formed by the zero-mode voltage and the steady-state power frequency of the zero-mode current,
judging whether the line is in fault according to the transient zero-mode current,
the judging whether the line fault is judged according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is larger than a threshold, if so, executing the step a, otherwise, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet the fault judgment condition, if so, judging that the line has a fault;
b, judging whether the product integral of the bus zero-mode voltage and the line zero-mode current short window meets the fault judgment condition, and if so, judging that the local line has a fault.
Further, the zero-mode current offset dc component calculation formula is:
Figure BDA0002730602340000021
in the formula ,IDCoffset(t) is the line zero-mode current direct current component (i.e. the line zero-mode current offset direct current component); t is power frequency cycle time; i.e. i0(t) is a zero-mode current sampling point;
when the zero-mode current offset direct-current component of the line is greater than a set threshold, the line has a single-phase earth fault;
IDCoffset＞IDCoffsetThr
in the formula ,IDCoffset(t) is the zero-mode current direct current quantity of the line; i isDCoffsetThrAnd (4) determining the direct current value of the zero-mode current of the line.
Further, the fault determination conditions in step a are as follows: and if the sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite in sign, the line has a single-phase earth fault.
Further, the determination method in step b is a short-window data integral value of zero-mode voltage and zero-mode current in the initial time domain information of the fault, and if the following formula is satisfied, a single-phase earth fault occurs in the line:
Figure BDA0002730602340000031
wherein ,u0(t) is a zero mode voltage sampling point; i.e. i0(t) is a zero-mode current sampling point; t is1Is the upper integration limit.
Further, the method for judging whether the line fault is the line fault according to the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency specifically comprises the step of judging whether the line fault is the line fault
If the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency satisfies the following formula, the line is considered to have a single-phase earth fault:
Figure BDA0002730602340000032
wherein ,
Figure BDA0002730602340000033
the steady state power frequency quantity of the bus zero-mode voltage is obtained;
Figure BDA0002730602340000034
the line zero mode current amplitude steady state power frequency quantity is obtained; theta1setA lower limit value for the angle; theta2setA value is defined for the angle.
Further, the steady-state power frequency of the bus zero-mode voltage
Figure BDA0002730602340000035
Zero-mode current amplitude steady-state power frequency quantity of line
Figure BDA0002730602340000036
The lower angle limit value theta is obtained by Fourier algorithm1set(ii) a Angular limit value theta2setAnd obtaining the zero sequence sensitive angle of the system.
Further, the 90-degree phase shifting method for the bus zero-mode voltage comprises the following steps:
u0_90(t)＝shift(u0(t))
in the formula ,u0(t) is a bus zero-mode voltage sampling point; u. of0_90(t) is the zero mode voltage after 90 degrees of phase shifting; shift is a 90 ° digital phase shifter.
Further, to the zero mould current of circuit that acquires to and the zero mould voltage of generating line after the phase shift, carry out the transient state quantity in the characteristic frequency band and extract, include:
performing band-pass filtering on the zero-mode current and the phase-shifted zero-mode voltage by adopting the following formula to obtain a transient zero-mode current and a transient zero-mode voltage;
i0_filter(t)＝filter(i0(t))
u0_filter(t)＝filter(u0_90(t))
wherein ,i0_filter(t) is the transient zero-mode current; i.e. i0(t) is a zero-mode current sampling point; u. of0_filter(t) is the transient zero mode voltage after phase shifting; u. of0_90(t) is a zero-mode voltage sampling point after phase shifting; the filter is a filter processing function.
Further, the ground fault is obtained by:
when the bus zero-mode voltage amplitude, the bus zero-mode voltage variation, the line zero-mode current amplitude and the line zero-mode current variation satisfy the following formulas, the occurrence of the ground fault is considered:
(U0＞U0set or ΔU0＞ΔU0set)||(I0＞I0set or ΔI0＞ΔI0set)
wherein ,U0Is the bus zero mode voltage amplitude; delta U0Is the bus zero-mode voltage variation, U0setSetting the bus zero-mode voltage; delta U0setSetting a constant value for the zero-mode voltage variation of the bus; i is0The amplitude of the zero mode current of the line is obtained; delta I0For zero mode current transformation of the line, I0setSetting the amplitude value of the zero-mode current of the line; delta I0setAnd (4) determining the zero-mode current transformation variable value of the line.
Further, the bus zero-mode voltage, the line zero-mode current and the time domain information are the bus zero-mode voltage, the line zero-mode current and the time domain information of the first half wave after response starting.
In a second aspect, the present invention further provides a protection device for a single-phase ground fault of a low-current grounding system, which integrates time-frequency domain information, and is characterized in that the protection device comprises:
a response unit for responding to a signal of occurrence of a ground fault;
the phase shifting unit is used for performing 90-degree forward phase shifting on the acquired bus zero-mode voltage;
the characteristic extraction unit is used for extracting the transient state quantity in a characteristic frequency band of the acquired line zero-mode current and the bus zero-mode voltage after phase shifting to obtain the transient state zero-mode current and the transient state zero-mode voltage after phase shifting;
the calculating unit is used for calculating a zero-mode current offset direct-current component in the transient process based on the acquired line zero-mode current;
and the judging unit judges whether the line fault exists according to the zero-mode current offset direct-current component and judges whether the line fault exists according to the transient zero-mode current.
In a third aspect, the present invention provides a single-phase earth fault protection system for a low-current grounding system, comprising: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of claims 1 to 10.
Compared with the prior art, the invention has the beneficial effects that:
the invention adopts a single-phase earth fault of a small current grounding system integrating time-frequency domain information, is not influenced by an arc suppression coil grounding system in principle, is self-adaptive to a neutral point ungrounded system, an arc suppression coil grounding system and a small resistance grounding system in method, has wide application range, does not have judgment blind areas, does not need to add additional primary equipment and does not need action coordination of other primary equipment.
The invention adopts the OR gate starting of the bus zero-mode voltage and the line zero-mode current in the starting link, and has high reliability and sensitivity. In the specific judgment process: the method comprises the following steps that a power direction element is formed by adopting a bus zero-mode voltage and a steady-state power frequency component of a line zero-mode current, and the method is adaptive to the ground fault judgment of an ungrounded system and a small-resistance grounded system; a power direction element of bus zero-mode voltage and line zero-mode current in a fault initial short window in a time domain is adopted, and the method is adaptive to a high-resistance ground fault application scene; the line zero-mode current in a characteristic frequency band and the bus zero-mode voltage after phase shifting are adopted to form a direction discrimination element, and the method is adaptive to the application scene of the non-high-resistance grounding fault.
The invention provides a 90-degree phase shifting algorithm for bus zero-mode voltage, which overcomes the defect that a differential algorithm can only perform 90-degree phase shifting on a certain specific frequency.
Drawings
Fig. 1 is a schematic flow chart of a single-phase earth fault protection method of a low-current earth system by integrating time-frequency domain information according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of the invention.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
Example 1
As shown in fig. 1, an embodiment of the present invention provides a method for protecting a single-phase ground fault of a low-current ground system by integrating time-frequency domain information, including:
responding to a signal that a ground fault has occurred;
acquiring bus zero-mode voltage, line zero-mode current and time domain information after starting, wherein the time domain information is time domain information of the bus zero-mode voltage and the line zero-mode current;
carrying out 90-degree forward phase shift on the acquired bus zero-mode voltage;
extracting transient state quantity in a characteristic frequency band of the obtained line zero-mode current and the bus zero-mode voltage after phase shifting to obtain transient state zero-mode current and transient state zero-mode voltage;
calculating a zero-mode current offset direct-current component in the transient process based on the acquired zero-mode current of the line;
based on the initial short-window time domain information of the fault of the zero-mode current and the zero-mode voltage of the line, the steady-state power frequency information of the zero-mode current and the zero-mode voltage, the transient information in the characteristic frequency band of the zero-mode current and the zero-mode voltage after phase shifting, and the zero-mode current offset direct current component of the transient process, whether the line has a single-phase earth fault or not is determined by comprehensive judgment, and the method specifically comprises the following steps:
judging whether the line fault is present according to the zero-mode current offset direct-current component,
judging whether the line has a fault according to the angle formed by the zero-mode voltage and the steady-state power frequency of the zero-mode current,
judging whether the line is in fault according to the transient zero-mode current,
the judging whether the line fault is judged according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is larger than a threshold, if so, executing the step a, otherwise, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet the fault judgment condition, if so, judging that the line has a fault;
b, judging whether the product integral of the bus zero-mode voltage and the line zero-mode current short window meets the fault judgment condition, and if so, judging that the local line has a fault.
In a specific implementation manner of the embodiment of the present invention, the ground fault is obtained by: when the bus zero-mode voltage amplitude, the bus zero-mode voltage variation, the line zero-mode current amplitude and the line zero-mode current change
If the quantity satisfies the following formula, then the occurrence of a ground fault is assumed:
(U0＞U0set or ΔU0＞ΔU0set)||(I0＞I0set or ΔI0＞ΔI0set)
wherein ,U0Is the bus zero mode voltage amplitude; delta U0Is the bus zero-mode voltage variation, U0setFor bus zero-mode voltage setting
A value; delta U0setSetting a constant value for the zero-mode voltage variation of the bus; i is0The amplitude of the zero mode current of the line is obtained; delta I0For zero mode current transformation of the line, I0setSetting the amplitude value of the zero-mode current of the line; delta I0setAnd (4) determining the zero-mode current transformation variable value of the line.
In a specific implementation manner of the embodiment of the present invention, the performing 90 ° forward phase shift on the acquired bus zero-mode voltage includes:
performing pre-phase shifting on the acquired bus zero-mode voltage based on the following formula:
u0_90(t)＝shift(u0(t))
in the formula ,u0(t) is a bus zero-mode voltage sampling point; u. of0_90(t) is the zero mode voltage after 90 degrees of phase shifting; shift is a 90 ° digital phase shifter.
In a specific implementation manner of the embodiment of the present invention, the extracting a transient component in a characteristic frequency band of the acquired line zero-mode current and the phase-shifted bus zero-mode voltage includes:
performing band-pass filtering on the zero-mode current and the phase-shifted zero-mode voltage by adopting the following formula to obtain a transient zero-mode current and a transient zero-mode voltage;
i0_filter(t)＝filter(i0(t))
u0_filter(t)＝filter(u0_90(t))
wherein ,i0_filter(t) is the transient zero-mode current; i.e. i0(t) is a zero-mode current sampling point; u. of0_filter(t) is the transient zero mode voltage; u. of0_90(t) is a zero-mode voltage sampling point after phase shifting; the filter is a filter processing function.
In a specific implementation manner of the embodiment of the present invention, the step of calculating the zero-mode current offset dc component in the transient process includes:
calculating a zero-mode current offset direct-current component in the transient process based on the acquired line zero-mode current by adopting the following formula:
Figure BDA0002730602340000071
in the formula ,IDCoffset(t) is the zero-mode current direct current quantity of the line; t is power frequency cycle time; i.e. i0And (t) is a zero-mode current sampling point.
And when the zero-mode current offset direct-current component of the line is greater than a set threshold, the line is considered to have a single-phase earth fault.
IDCoffset＞IDCoffsetThr
in the formula ,IDCoffset(t) is the zero-mode current direct current quantity of the line; i isDCoffsetThrAnd (4) determining the direct current value of the zero-mode current of the line.
In a specific implementation manner of the embodiment of the present invention, if an angle formed by the zero-mode voltage and the steady-state power frequency of the zero-mode current satisfies the following formula, it is determined that a single-phase ground fault occurs in the line:
Figure BDA0002730602340000072
wherein ,
Figure BDA0002730602340000073
the steady state power frequency quantity of the bus zero-mode voltage is obtained;
Figure BDA0002730602340000074
the line zero mode current amplitude steady state power frequency quantity is obtained; theta1setA lower limit value for the angle; theta2setA value is defined for the angle.
In a specific implementation manner of the embodiment of the present invention, the determination method in step a is: when the transient zero-mode current is large, and the sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite in sign, the line is considered to have a single-phase earth fault.
In some embodiments, the determination method of step b is
The short-window data integral value of the zero-mode voltage and the zero-mode current at the initial time domain information of the fault meets the following formula, and then the line has a single-phase earth fault:
Figure BDA0002730602340000081
wherein ,u0(t) is a zero mode voltage sampling point; i.e. i0(t) is a zero-mode current sampling point; t is1Is the upper integration limit.
The method of the invention uses the direction of the short window zero sequence power in the time domain information to judge when the grounding is carried out through high resistance; when the grounding is not high-resistance, the transient zero-mode power direction in the characteristic frequency band is used for judging; and judging the zero sequence power direction of the usable steady-state power frequency of the ungrounded system. The invention is adaptive to a system in which a neutral point is not grounded, the neutral point is grounded through an arc suppression coil and the neutral point is grounded through a small resistor.
Example 2
Based on the same inventive concept as embodiment 1, an embodiment of the present invention provides a single-phase ground fault protection device for a small current grounding system, which integrates time-frequency domain information, and includes:
a response unit for responding to a signal of occurrence of a ground fault;
the phase shifting unit is used for performing 90-degree forward phase shifting on the acquired bus zero-mode voltage;
a characteristic extraction unit for performing characteristics on the obtained line zero-mode current and the phase-shifted bus zero-mode voltage
Extracting transient state quantity in the frequency band to obtain transient state zero-mode current and transient state zero-mode voltage;
the calculating unit is used for calculating a zero-mode current offset direct-current component in the transient process based on the acquired line zero-mode current;
the angle is formed based on the zero-mode voltage and the steady-state power frequency quantity of the zero-mode current; the short-window data integration method is used for integrating short-window data in fault initial time domain information based on zero-mode voltage and zero-mode current;
a judging unit for judging angle, zero-mode voltage and zero-mode current based on the zero-mode current and the steady-state power frequency of the zero-mode voltage
And comprehensively judging and determining whether the line has a single-phase earth fault or not by using a short-window data integral value of the current in the initial time domain information of the fault and a zero-mode current offset direct-current component in the transient process.
The rest of the process was the same as in example 1.
Example 3
Based on the same inventive concept as embodiment 1, an embodiment of the present invention provides a single-phase ground fault protection system for a low-current grounding system, including: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any of embodiment 1.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (11)

1. A small current ground fault protection method of comprehensive time-frequency domain information is characterized in that: comprises the following steps
Responding to a signal that a ground fault has occurred;
acquiring bus zero-mode voltage, line zero-mode current and time-frequency domain information after response starting, wherein the time domain information is time domain information of the bus zero-mode voltage and the line zero-mode current;
performing 90-degree phase advance on the obtained bus zero-mode voltage to obtain the bus zero-mode voltage after phase shift;
transient state quantity extraction in a characteristic frequency band is carried out on the line zero-mode current and the bus zero-mode voltage after phase shifting, and the transient state zero-mode current and the transient state zero-mode voltage after phase shifting are obtained;
calculating a zero-mode current offset direct-current component in the transient process based on the acquired zero-mode current of the line;
judging whether the line fault is present according to the zero-mode current offset direct-current component,
judging whether the line has a fault according to the angle formed by the zero-mode voltage and the steady-state power frequency of the zero-mode current,
judging whether the line is in fault according to the transient zero-mode current,
the judging whether the line fault is judged according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is larger than a threshold, if so, executing the step a, otherwise, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet the fault judgment condition, if so, judging that the line has a fault;
b, judging whether the product integral of the bus zero-mode voltage and the line zero-mode current short window meets the fault judgment condition, and if so, judging that the local line has a fault.
2. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the zero-mode current offset direct current component calculation formula is as follows:
Figure FDA0002730602330000011
in the formula ,IDCoffset(t) is the zero mode current offset dc component of the line; t is power frequency cycle time; i.e. i0(t) is a zero-mode current sampling point;
when the zero-mode current offset direct-current component of the line is greater than a set threshold, the line has a single-phase earth fault;
IDCoffset＞IDCoffsetThr
in the formula ,IDCoffset(t) is the zero mode current offset dc component of the line; i isDCoffsetThrIs a line zeroThe modulus current is offset from the dc component constant.
3. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the fault determination conditions in the step a are as follows: and if the sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite in sign, the line has a single-phase earth fault.
4. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the judging method of the step b is that
The short-window data integral value of the zero-mode voltage and the zero-mode current at the initial time domain information of the fault meets the following formula, and then the line has a single-phase earth fault:
Figure FDA0002730602330000021
wherein ,u0(t) is a zero mode voltage sampling point; i.e. i0(t) is a zero-mode current sampling point; t is1Is the upper integration limit.
5. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the method for judging whether the line fault is the fault of the line or not according to the angle formed by the zero-mode voltage and the steady-state power frequency of the zero-mode current specifically comprises the following steps
If the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency satisfies the following formula, the line is considered to have a single-phase earth fault:
Figure FDA0002730602330000022
wherein ,
Figure FDA0002730602330000023
the steady state power frequency quantity of the bus zero-mode voltage is obtained;
Figure FDA0002730602330000024
the line zero mode current amplitude steady state power frequency quantity is obtained; theta1setA lower limit value for the angle; theta2setA value is defined for the angle.
6. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the 90-degree phase shifting method for the bus zero-mode voltage comprises the following steps:
u0_90(t)＝shift(u0(t))
in the formula ,u0(t) is a bus zero-mode voltage sampling point; u. of0_90(t) is the zero mode voltage after 90 degrees of phase shifting; shift is a 90 ° digital phase shifter.
7. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: extracting transient state quantity in a characteristic frequency band for the acquired line zero-mode current and the bus zero-mode voltage after phase shifting, wherein the extraction process comprises the following steps:
performing band-pass filtering on the zero-mode current and the phase-shifted zero-mode voltage by adopting the following formula to obtain a transient zero-mode current and a transient zero-mode voltage;
i0_filter(t)＝filter(i0(t))
u0_filter(t)＝filter(u0_90(t))
wherein ,i0_filter(t) is the transient zero-mode current; i.e. i0(t) is a zero-mode current sampling point; u. of0_filter(t) is the transient zero mode voltage after phase shifting; u. of0_90(t) is a zero-mode voltage sampling point after phase shifting; the filter is a filter processing function.
8. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the ground fault is obtained by the following steps:
when the bus zero-mode voltage amplitude, the bus zero-mode voltage variation, the line zero-mode current amplitude and the line zero-mode current variation satisfy the following formulas, the occurrence of the ground fault is considered:
(U0＞U0set or ΔU0＞ΔU0set)||(I0＞I0set or ΔI0＞ΔI0set)
wherein ,U0Is the bus zero mode voltage amplitude; delta U0Is the bus zero-mode voltage variation, U0setSetting the bus zero-mode voltage; delta U0setSetting a constant value for the zero-mode voltage variation of the bus; i is0The amplitude of the zero mode current of the line is obtained; delta I0For zero mode current transformation of the line, I0setSetting the amplitude value of the zero-mode current of the line; delta I0setAnd (4) determining the zero-mode current transformation variable value of the line.
9. The small-current ground fault protection method of integrated time-frequency domain information according to claim 1, characterized in that: the bus zero-mode voltage, the line zero-mode current and the time domain information are the bus zero-mode voltage, the line zero-mode current and the time domain information of the first half wave after response starting.
10. A low current ground fault protection device that synthesizes time-frequency domain information, comprising:
a response unit for responding to a signal of occurrence of a ground fault;
the phase shifting unit is used for performing 90-degree forward phase shifting on the acquired bus zero-mode voltage;
the characteristic extraction unit is used for extracting the transient state quantity in a characteristic frequency band of the acquired line zero-mode current and the bus zero-mode voltage after phase shifting to obtain the transient state zero-mode current and the transient state zero-mode voltage after phase shifting;
the calculating unit is used for calculating a zero-mode current offset direct-current component in the transient process based on the acquired line zero-mode current;
and the judging unit judges whether the line fault exists according to the zero-mode current offset direct-current component and judges whether the line fault exists according to the transient zero-mode current.
11. A single-phase ground fault protection system for a low current grounding system, comprising: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of claims 1 to 10.
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