CN112379302B - Small-current ground fault protection method, device and system for integrating time-frequency domain information - Google Patents
Small-current ground fault protection method, device and system for integrating time-frequency domain information Download PDFInfo
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- G—PHYSICS
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Abstract
The invention discloses a single-phase grounding fault protection method, a device and a system for a low-current grounding system, which integrate time-frequency domain information, wherein the method comprises the steps of responding to a signal of grounding fault; performing 90-degree front phase shifting on the obtained bus zero-mode voltage; the method comprises the steps of extracting transient state quantity in a characteristic frequency band to obtain transient state zero mode current and transient state zero mode voltage; when the high-resistance grounding is carried out, the short window zero sequence power direction in the time domain information is utilized for discrimination; when the non-high-resistance grounding is carried out, the transient zero mode power direction in the characteristic frequency band is utilized for judging; and the non-grounding system can be distinguished by utilizing the zero sequence power direction of the steady-state power frequency. The invention is self-adaptive to a system with neutral points not grounded, arc suppression coils grounded and small resistance grounded.
Description
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 for synthesizing time-frequency domain information.
Background
The neutral point grounding modes of the power system are mainly divided into two main types: 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, and the neutral point is grounded through an arc suppression coil (resonance grounding), so that when a single-phase grounding fault occurs in the system, the fault current flowing through the fault point is small, and therefore, the system is also called a small-current grounding mode. The medium-voltage distribution network in China mostly adopts a small-current grounding mode, but the problem of positioning the small-current grounding fault is not completely and effectively solved until now because of the fact that the fault quantity of the medium-voltage distribution network in China has unobtrusiveness (the grounding current is very small, generally only a few amperes), uncertainty (the influence of arc suppression coil compensation current in a resonant grounding system on power frequency current) and instability (the occurrence rate of intermittent grounding and arc grounding is high).
At present, aiming at the difficult problem of fault line selection of a low-current grounding system, a centralized line selection mode is adopted, namely, all the zero sequence currents and bus zero sequence voltages which are not grounded or pass through the grounding side of an arc suppression coil are connected into an independent centralized line selection device in a transformer substation, so that the detection and positioning of the grounding fault are carried out, equipment is newly added under the condition that the existing interval configuration protection or protection device is necessary, and inconvenience is brought to the wiring and operation maintenance of a secondary circuit on site; the protection or protection measurement and control device is configured at intervals, single-phase earth fault judgment is carried out by accessing the zero sequence current and the bus voltage at each interval, the measured information is limited, the adopted zero sequence active power, reactive power, five-order harmonic zero sequence power direction and other judgment methods are affected by transient state, steady state information aliasing and the like, and the earth fault positioning misjudgment rate is high; under the condition of the ground fault, the fault line is judged through the mode of protection test jump and reclosing during the ground fault under the protection of each interval unit, the efficiency is low, and the problems that the non-fault line is in short-time power failure, the fault line cannot be timely isolated, equipment damage is possibly caused and the like 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 comprehensive judgment method and solve the problems of single-interval protection and high ground fault misjudgment rate of a protection and measurement device.
In a first aspect, a single-phase ground fault protection method for a low-current grounding system integrating time-frequency domain information includes the steps of
Responding to a signal of the ground fault;
acquiring bus zero-mode voltage, line zero-mode current and time-frequency domain information after response starting;
performing 90-degree phase shifting on the obtained bus zero-mode voltage to obtain phase-shifted bus zero-mode voltage;
the transient state quantity in the characteristic frequency band is extracted for the line zero-mode current and the bus zero-mode voltage after phase shifting,
obtaining transient zero-mode current and transient zero-mode voltage after phase shifting;
calculating zero-mode current offset direct current component in transient process based on the obtained line zero-mode current;
judging whether the line fault exists according to the zero-mode current offset direct current component,
judging whether the line is in fault or not according to the angle formed by the steady-state power frequency of the zero-mode voltage and the zero-mode current,
judging whether the line fault is the line fault according to the transient zero-mode current,
the method for judging whether the line fault is the line fault according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is greater than a threshold, if so, executing the step a, and if not, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet fault judging conditions, and if so, the line is faulty;
and b, judging whether the product integral of the busbar zero mode voltage and the line zero mode current short window meets the fault judging condition, and if so, carrying out local line fault.
Further, the calculation formula of the zero-mode current offset direct current component is as follows:
in the formula ,IDCoffset (t) is line zero-mode current dc (i.e., line zero-mode current offset dc component); t is the power frequency cycle time; i.e 0 (t) is a zero-mode current sampling point;
when the zero-mode current offset direct current component of the line is larger than a set threshold, the line has single-phase grounding fault;
I DCoffset ＞I DCoffsetThr
in the formula ,IDCoffset (t) is the zero-mode current direct current of the line; i DCoffsetThr The DC value of the zero-mode current of the line is fixed.
Further, the fault determination condition in the step a is as follows: and if the signs of the sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite, the single-phase grounding fault of the circuit occurs.
Further, the judging method in the step b is that the zero mode voltage and the zero mode current are in the short window data integral value of the initial time domain information of the fault, and the single-phase grounding fault occurs to the line if the following formula is satisfied:
wherein ,u0 (t) is a zero-mode voltage sampling point; i.e 0 (t) is a zero-mode current sampling point; t (T) 1 Is the upper integral limit.
Further, the method is to judge 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
If the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency meets the following formula, the single-phase grounding fault of the line is considered to occur:
wherein ,
the power frequency is the steady-state power frequency of the zero-mode voltage of the bus; />
The steady-state power frequency quantity is the zero-mode current amplitude of the line; θ 1set Is the angle lower limit value; θ 2set Is at an angleAn upper limit value.
Further, the bus zero-mode voltage steady-state power frequency quantity
Line zero-mode current amplitude steady-state power frequency quantity +.>
Obtained by a Fourier algorithm, the angle lower limit value theta 1set The method comprises the steps of carrying out a first treatment on the surface of the Angle upper limit value theta 2set Obtained according to the zero sequence sensitivity angle of the system.
Further, the method for performing 90 DEG of forward phase shift on the zero-mode voltage of the bus comprises the following steps:
u 0_90 (t)＝shift(u 0 (t))
in the formula ,u0 (t) is a busbar zero-mode voltage sampling point; u (u) 0_90 (t) is zero mode voltage after 90 ° front phase shift; shift is a 90 ° digital phase shifter.
Further, the method for extracting the transient state quantity in the characteristic frequency band for the obtained line zero-mode current and the bus zero-mode voltage after phase shifting 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 transient zero-mode current and transient zero-mode voltage;
i 0_filter (t)＝filter(i 0 (t))
u 0_filter (t)＝filter(u 0_90 (t))
wherein ,i0_filter (t) is a transient zero-mode current; i.e 0 (t) is a zero-mode current sampling point; u (u) 0_filter (t) is the transient zero mode voltage after phase shifting; u (u) 0_90 (t) is the zero-mode voltage sampling point after phase shifting; 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 meet the following formulas, the ground fault is considered to occur:
(U 0 ＞U 0set or ΔU0 ＞ΔU 0set )||(I 0 ＞I 0set or ΔI0 ＞ΔI 0set )
wherein ,U0 The zero mode voltage amplitude of the bus is set; deltaU 0 U is the zero mode voltage variation of the bus 0set Setting the zero mode voltage of the bus; deltaU 0set The zero mode voltage variation of the bus is fixed; i 0 Zero mode current amplitude for the line; ΔI 0 I is the zero-mode current variation of the line 0set Setting the amplitude value of the zero-mode current of the line; ΔI 0set The zero-mode current variation of the line is fixed.
Further, the bus zero-mode voltage, the line zero-mode current and the time domain information are bus zero-mode voltage, line zero-mode current and time domain information of the first half wave after the response is started.
In a second aspect, the present invention further provides a single-phase earth fault protection device for a small-current grounding system that synthesizes time-frequency domain information, which is characterized by comprising:
a response unit for responding to a signal of the occurrence of the ground fault;
the phase shifting unit is used for carrying out 90-degree front phase shifting on the obtained bus zero-mode voltage;
the characteristic extraction unit is used for extracting the transient state quantity in the characteristic frequency band of the obtained 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 zero-mode current offset direct current components 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 earth system, comprising: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor being operative according to 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 grounding fault of a low-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 low-resistance grounding system in the method, has wide application range, does not have a judging blind area, does not need to add additional primary equipment and does not need to cooperate with other primary equipment.
The invention adopts the OR gate start of bus zero-mode voltage and line zero-mode current in the start link, and has high reliability and sensitivity. In the specific judging process: the steady-state power frequency components of the busbar zero-mode voltage and the line zero-mode current are adopted to form a power direction element, and the device is self-adaptive to the discrimination of the ground faults of a non-grounding system and a small-resistance grounding system; the power direction element of the busbar zero mode voltage and the line zero mode current in the fault initial short window in the time domain is adopted, so that the method is self-adaptive to the high-resistance grounding fault application scene; the line zero-mode current in the characteristic frequency band and the bus zero-mode voltage after phase shifting are adopted to form a direction judging element, so that the device is self-adaptive to the application scene of non-high-resistance ground faults.
The invention provides a 90-degree phase shifting algorithm for bus zero-mode voltage, which aims to overcome the defect that a differential algorithm can only carry out 90-degree phase shifting on a specific frequency.
Drawings
Fig. 1 is a flow chart of a single-phase earth fault protection method of a small-current grounding system integrating time-frequency domain information according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The principle of application of the invention is described in detail below with reference to the accompanying drawings.
Example 1
As shown in fig. 1, the embodiment of the invention provides a single-phase grounding fault protection method for a small-current grounding system, which integrates time-frequency domain information, and comprises the following steps:
responding to a signal of the ground fault;
acquiring the busbar zero mode voltage, the line zero mode current and time domain information after starting, wherein the time domain information is the time domain information of the busbar zero mode voltage and the line zero mode current;
performing 90-degree front phase shifting on the obtained bus zero-mode voltage;
the method comprises the steps of extracting transient state quantity in a characteristic frequency band to obtain transient state zero mode current and transient state zero mode voltage;
calculating zero-mode current offset direct current component in transient process based on the obtained line zero-mode current;
based on fault initial short window time domain information of the zero mode current and the busbar zero mode voltage of the circuit, steady-state power frequency information of the zero mode current and the zero mode voltage, transient information in characteristic frequency bands of the zero mode current and the zero mode voltage after phase shifting, and transient process zero mode current offset direct current components, comprehensively judging and determining whether single-phase grounding faults occur in the circuit, specifically:
judging whether the line fault exists according to the zero-mode current offset direct current component,
judging whether the line is in fault or not according to the angle formed by the steady-state power frequency of the zero-mode voltage and the zero-mode current,
judging whether the line fault is the line fault according to the transient zero-mode current,
the method for judging whether the line fault is the line fault according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is greater than a threshold, if so, executing the step a, and if not, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet fault judging conditions, and if so, the line is faulty;
and b, judging whether the product integral of the busbar zero mode voltage and the line zero mode current short window meets the fault judging condition, and if so, carrying out local line fault.
In a specific implementation manner of the embodiment of the present invention, the ground fault is obtained through 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 are performed
The amount satisfies the following equation, then a ground fault is considered to occur:
(U 0 ＞U 0set or ΔU0 ＞ΔU 0set )||(I 0 ＞I 0set or ΔI0 ＞ΔI 0set )
wherein ,U0 The zero mode voltage amplitude of the bus is set; deltaU 0 U is the zero mode voltage variation of the bus 0set Setting for bus zero mode voltage
A value; deltaU 0set The zero mode voltage variation of the bus is fixed; i 0 Zero mode current amplitude for the line; ΔI 0 I is the zero-mode current variation of the line 0set Setting the amplitude value of the zero-mode current of the line; ΔI 0set The zero-mode current variation of the line is fixed.
In a specific implementation manner of the embodiment of the present invention, the performing a 90 ° shift on the obtained bus zero mode voltage includes:
performing a pre-phase shift treatment on the obtained bus zero mode voltage based on the following formula:
u 0_90 (t)＝shift(u 0 (t))
in the formula ,u0 (t) is a busbar zero-mode voltage sampling point; u (u) 0_90 (t) is zero mode voltage after 90 ° front phase shift; shift is a 90 ° digital phase shifter.
In a specific implementation manner of the embodiment of the present invention, the extracting the transient state quantity in the characteristic frequency band for the obtained line zero-mode current and the bus zero-mode voltage after phase shifting includes:
performing band-pass filtering on the zero-mode current and the phase-shifted zero-mode voltage by adopting the following formula to obtain transient zero-mode current and transient zero-mode voltage;
i 0_filter (t)＝filter(i 0 (t))
u 0_filter (t)＝filter(u 0_90 (t))
wherein ,i0_filter (t) is a transient zero-mode current; i.e 0 (t) is a zero-mode current sampling point; u (u) 0_filter (t) is a transient zero mode voltage; u (u) 0_90 (t) is the zero-mode voltage sampling point after phase shifting; filter is a filter processing function.
In a specific implementation manner of the embodiment of the present invention, the step of calculating the transient zero-mode current offset dc component includes:
the transient zero-mode current offset direct current component is calculated based on the acquired line zero-mode current by adopting the following formula:
in the formula ,IDCoffset (t) is the zero-mode current direct current of the line; t is the power frequency cycle time; i.e 0 And (t) is a zero-mode current sampling point.
When the zero-mode current offset direct current component of the line is larger than a set threshold, the line is considered to have single-phase grounding fault.
I DCoffset ＞I DCoffsetThr
in the formula ,IDCoffset (t) is the zero-mode current direct current of the line; i DCoffsetThr The DC value of the zero-mode current of the line is fixed.
In a specific implementation manner of the embodiment of the present invention, the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency meets the following formula, and then the single-phase grounding fault of the line is considered to occur:
wherein ,
the power frequency is the steady-state power frequency of the zero-mode voltage of the bus; />
The steady-state power frequency quantity is the zero-mode current amplitude of the line; θ 1set Is the angle lower limit value; θ 2set Is an upper limit value of the angle.
In a specific implementation manner of the embodiment of the present invention, the determining method in step a is: when the transient zero-mode current is larger, when the sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite in sign, the single-phase grounding fault of the line is considered.
In some embodiments the determination method of step b is
Zero mode voltage and zero mode current are in fault initial time domain information short window data integral value, and the single-phase grounding fault occurs to the line:
wherein ,u0 (t) is a zero-mode voltage sampling point; i.e 0 (t) is a zero-mode current sampling point; t (T) 1 Is the upper integral limit.
The method of the invention uses the short window zero sequence power direction in the time domain information to judge when the high resistance grounding is carried out; when the non-high-resistance grounding is carried out, the transient zero mode power direction in the characteristic frequency band is utilized for judging; and the non-grounding system can be distinguished by utilizing the zero sequence power direction of the steady-state power frequency. The invention is self-adaptive to a system with neutral points not grounded, arc suppression coils grounded and small resistance grounded.
Example 2
Based on the same inventive concept as embodiment 1, the embodiment of the present invention provides a single-phase ground fault protection device of a small-current grounding system for synthesizing time-frequency domain information, which comprises:
a response unit for responding to a signal of the occurrence of the ground fault;
the phase shifting unit is used for carrying out 90-degree front phase shifting on the obtained bus zero-mode voltage;
the feature extraction unit is used for carrying out feature on the acquired line zero-mode current and the bus zero-mode voltage after phase shifting
Extracting transient state quantity in the frequency band to obtain transient zero-mode current and transient zero-mode voltage;
the calculating unit is used for calculating zero-mode current offset direct current components in the transient process based on the acquired line zero-mode current;
the angle is formed based on zero-mode voltage and zero-mode current steady-state power frequency quantity; the 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 zero mode voltage and zero mode electricity based on the angle formed by the zero mode current and the zero mode voltage steady-state power frequency quantity
And (3) short window data integral value of the current in the fault initial time domain information and zero-mode current offset direct current component in the transient process, and comprehensively judging and determining whether a single-phase grounding fault occurs to the line.
The remainder was the same as in example 1.
Example 3
Based on the same inventive concept as embodiment 1, in an embodiment of the present invention, there is provided a single-phase earth fault protection system of a low-current earth system, including: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is operative according to the instructions to perform the steps of the method according to any one of embodiment 1.
It will be appreciated by those skilled in the art that 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 flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations 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.
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the claims, which are all within the protection of the present invention.
The foregoing has shown and described the basic principles and main features of the present invention and the advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. A small current grounding fault protection method integrating time-frequency domain information is characterized in that: comprises the following steps
Responding to a signal of the ground fault;
acquiring bus zero-mode voltage, line zero-mode current and time domain information after response starting, wherein the time domain information is the time domain information of the bus zero-mode voltage and the line zero-mode current;
performing 90-degree phase shifting on the obtained bus zero-mode voltage to obtain phase-shifted bus zero-mode voltage;
extracting transient state quantity in a characteristic frequency band from the line zero-mode current and the phase-shifted bus zero-mode voltage to obtain transient state zero-mode current and phase-shifted transient state zero-mode voltage;
calculating zero-mode current offset direct current component in transient process based on the obtained line zero-mode current;
judging whether the line fault exists according to the zero-mode current offset direct current component,
judging whether the line is in fault or not according to the angle formed by the steady-state power frequency of the zero-mode voltage and the zero-mode current,
judging whether the line fault is the line fault according to the transient zero-mode current,
the method for judging whether the line fault is the line fault according to the transient zero-mode current comprises
Judging whether the transient zero-mode current is greater than a threshold, if so, executing the step a, and if not, executing the step b
a, judging whether the transient zero-mode current and the transient zero-mode voltage after phase shifting meet fault judging conditions, and if so, the line is faulty;
b, judging whether the product integral of the busbar zero mode voltage and the line zero mode current short window meets the fault judging condition, if so, the local line is faulty;
the zero-mode current offset direct current component calculation formula is as follows:
in the formula ,IDCoffset (t) is the line zero-mode current offset dc component; t is the power frequency cycle time; i.e 0 (t) is a zero-mode current sampling point;
when the zero-mode current offset direct current component of the line is larger than a set threshold, the line has single-phase grounding fault;
I DCoffset ＞I DCoffsetThr
in the formula ,IDCoffset (t) is the line zero-mode current offset dc component; i DCoffsetThr Setting a direct current component for zero-mode current offset of the line;
the fault judging conditions in the step a are as follows: the signs of sampling values of the transient zero-mode current and the transient zero-mode voltage are opposite, and if so, a single-phase grounding fault occurs to the line;
the judging method in the step b is as follows:
zero mode voltage and zero mode current are in fault initial time domain information short window data integral value, and the single-phase grounding fault occurs to the line:
wherein ,u0 (t) is a zero-mode voltage sampling point; i.e 0 (t) is a zero-mode current sampling point; t (T) 1 Is the upper integral limit;
the method is characterized in that whether the line fault is judged according to the angle formed by zero mode voltage and zero mode current steady-state power frequency, and specifically comprises the following steps:
if the angle formed by the zero-mode voltage and the zero-mode current steady-state power frequency meets the following formula, the single-phase grounding fault of the line is considered to occur:
wherein ,
the power frequency is the steady-state power frequency of the zero-mode voltage of the bus; />
The steady-state power frequency quantity is the zero-mode current amplitude of the line; θ 1set Is the angle lower limit value; θ 2set Is an upper limit value of the angle.
2. The method for protecting a small current ground fault integrating time-frequency domain information according to claim 1, wherein the method comprises the steps of: the method for performing 90 DEG of front phase shift on the zero-mode voltage of the bus comprises the following steps:
u 0_90 (t)＝shift(u 0 (t))
in the formula ,u0 (t) is a busbar zero-mode voltage sampling point; u (u) 0_90 (t) is zero mode voltage after 90 ° front phase shift; shift is a 90 ° digital phase shifter.
3. The method for protecting a small current ground fault integrating time-frequency domain information according to claim 1, wherein the method comprises the steps of: the method for extracting the transient state quantity in the characteristic frequency band of the obtained line zero-mode current and the bus zero-mode voltage after phase shifting 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 transient zero-mode current and transient zero-mode voltage;
i 0_filter (t)＝filter(i 0 (t))
u 0_filter (t)＝filter(u 0_90 (t))
wherein ,i0_filter (t) is a transient zero-mode current; i.e 0 (t) is a zero-mode current sampling point; u (u) 0_filter (t) is the transient zero mode voltage after phase shifting; u (u) 0_90 (t) is the zero-mode voltage sampling point after phase shifting; filter is a filter processing function.
4. The method for protecting a small current ground fault integrating time-frequency domain information according to claim 1, wherein the method comprises the steps of: 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 meet the following formulas, the ground fault is considered to occur:
(U 0 ＞U 0set or ΔU0 ＞ΔU 0set )||(I 0 ＞I 0set or ΔI0 ＞ΔI 0set )
wherein ,U0 The zero mode voltage amplitude of the bus is set; deltaU 0 U is the zero mode voltage variation of the bus 0set Setting the zero mode voltage of the bus; deltaU 0set The zero mode voltage variation of the bus is fixed; i 0 Zero mode current amplitude for the line; ΔI 0 I is the zero-mode current variation of the line 0set Setting the amplitude value of the zero-mode current of the line; ΔI 0set The zero-mode current variation of the line is fixed.
5. The method for protecting a small current ground fault integrating time-frequency domain information according to claim 1, wherein the method comprises the steps of: the bus zero-mode voltage, the line zero-mode current and the time domain information are bus zero-mode voltage, line zero-mode current and time domain information responding to the first half wave after starting.
6. A small current grounding fault protection device integrating time-frequency domain information is characterized in that,
the apparatus employing the method of any one of claims 1-5, the apparatus comprising:
a response unit for responding to a signal of the occurrence of the ground fault;
the phase shifting unit is used for carrying out 90-degree front phase shifting on the obtained bus zero-mode voltage;
the characteristic extraction unit is used for extracting the transient state quantity in the characteristic frequency band of the obtained 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 zero-mode current offset direct current components 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.
7. A low current grounding system single phase earth fault protection system comprising: a storage medium and a processor;
the storage medium is used for storing instructions;
the processor being operative according to the instructions to perform the steps of the method according to any one of claims 1 to 5.
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