CN110297154B - Small current ground fault line selection method and device based on zero-mode current transient energy - Google Patents

Abstract

The invention discloses a small current ground fault line selection method and a small current ground fault line selection device based on zero-mode current transient energy, wherein the method adopts zero-mode voltage and zero-mode current OR gate starting in a starting link, and is not influenced by PT line breakage; zero-mode current transient energy calculation in a fault characteristic frequency band is provided, whether the bus is a bus grounding fault or a certain branch grounding fault is determined by adopting the zero-mode current transient energy of each branch and the amplitude magnitude relation between the zero-mode current transient energy and the current transient energy, a zero-mode voltage quantity is not needed in a line selection link, the influence of PT disconnection is avoided, and the influence of distribution difference on the time dimension of the zero-mode voltage transient quantity and the zero-mode current transient quantity caused by zero-mode voltage derivation on an energy acquisition effect is overcome; the problem that the line selection accuracy is influenced by the power frequency quantity of the arc suppression coil grounding system is solved, and meanwhile, the problem of insufficient sensitivity caused by high-resistance grounding faults is solved by adopting an integration algorithm of the square of the zero-mode current transient quantity in a time domain.

Description

Small current ground fault line selection method and device based on zero-mode current transient energy

Technical Field

The invention belongs to the technical field of power system relay protection, and particularly relates to a small current ground fault line selection method and device based on zero-mode current transient energy.

Background

Power systems can be divided into two broad categories depending on whether they are directly grounded: i.e. 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 a neutral point ungrounded system or a neutral point grounded via an arc suppression coil (resonance grounding), and when a single-phase ground fault occurs, a fault current flowing through the fault point is small, and therefore, the system is also called a low-current grounding system. When a low-current ground fault occurs in a neutral point ungrounded system, the problems of unobtrusive fault amount (the ground current is very small and is generally only a few amperes), uncertainty (the influence of arc 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) exist, and the low-current ground fault line selection technology is recognized as a difficult problem in a power system.

In order to solve the problem of fault line selection of a low-current grounding system, a great deal of research is carried out by many scholars, and line selection methods are divided into an active method and a passive method according to the source of a used signal. The active line selection method comprises an injection signal method, a medium resistance method, a residual current incremental method, a small disturbance method and the like; the passive line selection method can be divided into two types, namely a steady state characteristic quantity-based method and a transient state characteristic quantity-based method according to different used characteristic signals. The passive line selection method based on the steady-state information has the problem that the ground fault misjudgment exists under the working condition of the arc suppression coil grounding system, and the field requirement cannot be met. The line selection method based on the transient characteristic quantity comprises a first half-wave method, a transient zero-mode current amplitude and polarity comparison method, a transient zero-mode current direction method, a transient energy method and the like.

The zero-mode transient energy function is defined as the integral of the product of a zero-mode voltage derivative and zero-mode current in a time domain, the absolute value of the zero-mode transient energy function of a fault line is larger than that of a healthy line, the zero-mode transient energy function value of the fault line is a negative value, and the zero-mode transient energy function values of the healthy line are positive values, so that the judgment of the fault line is completed.

The existing small current ground fault line selection principle based on zero-mode transient energy adopts the integral of the product of a zero-mode voltage derivative (or zero-mode voltage phase shift) and zero-mode current in a time domain, the zero-mode voltage derivative or the zero-mode voltage phase shift can cause that the zero-mode voltage and the zero-mode current at the fault occurrence moment are not changed at the same moment, and the phase difference is 1/4 cycle waves, which brings disadvantages to the accumulation of the transient energy, especially when the high-resistance ground fault occurs, the transient energy is small, the time is only a few millisecond time window, the line selection sensitivity is poor, and the line selection accuracy is influenced; in addition, accumulation of energy in a characteristic frequency band is not considered before integration, and the line selection misjudgment rate is high when the power frequency component ratio of the system grounded through the arc suppression coil at the initial stage of the fault is high.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a small current grounding fault line selection method based on zero-mode current transient state energy, forms a complete line selection technical solution, is self-adaptive to a neutral point ungrounded system, an arc suppression coil grounding system and a high-resistance grounding system, and is not influenced by PT line breakage.

In order to solve the technical problem, the invention provides a small current ground fault line selection method based on zero mode current transient state energy, which is characterized by comprising the following steps of:

when a ground fault occurs, acquiring a zero-mode current sampling value of each branch circuit connected to a bus in a low-current grounding system;

filtering the zero-mode current or the variable quantity of the zero-mode current of each branch to obtain the zero-mode current transient quantity of each branch after filtering;

summing the transient state quantity of the zero-mode current of each branch circuit to obtain the transient state quantity of the zero-mode current and the transient state quantity of the current;

respectively carrying out T on the zero-mode current transient quantity and the zero-mode and current transient quantity of each branch₂Sampling value square integral in time is carried out, and zero mode current transient energy and zero mode sum current transient energy of each branch circuit are obtained;

t after Fault Start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; if the maximum transient energy of the zero-mode current is always larger than the transient energy of the zero-mode current and the current, the branch corresponding to the maximum transient energy of the zero-mode current is considered as the occurrenceA line with a ground fault.

Further, the criterion for judging the occurrence of the ground fault is as follows:

acquiring a zero-mode current sampling value and a variable quantity thereof, and a zero-mode voltage sampling value and a variable quantity thereof of each branch circuit connected to a bus in a low-current grounding system;

and when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the occurrence of the ground fault is considered.

Further, the variable quantity of the zero mode current sampling value and the variable quantity of the zero mode voltage sampling value of each branch circuit connected to the bus in the low current grounding system include:

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): a bus zero-mode voltage sampling value at the current time t;

u₀(T-NxDeltaT): a bus zero-mode voltage sampling value of a previous cycle at the current time t;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

Further, the filtering zero-mode current or the variation thereof of each branch specifically includes:

the filtering mode for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch is band-pass filtering or wavelet transformation.

Further, respectivelyCarrying out T on the transient state quantity of the zero-mode current and the transient state quantity of the zero-mode sum current of each branch₂The integration of the square of the sampled values over time includes:

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each branch

E_{sum_filter}(t): transient state energy corresponding to characteristic frequency bands of zero mode and current of all branches

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

Δi_{0k_filter}(t) is the transient zero-mode current transient, Δ i, of the kth branch_{0sum_filter}(t) is the zero mode and transient amount of current.

Correspondingly, the invention provides a small current ground fault line selection device based on zero-mode current transient energy, which is characterized by comprising a sampling value acquisition module, a zero-mode current transient quantity calculation module and a zero-mode and current transient quantity calculation module; the fault line selection module is used for selecting a fault line;

the sampling value acquisition module is used for acquiring zero-mode current sampling values of all branches connected to a bus in a low-current grounding system when a grounding fault occurs;

the zero-mode current transient state quantity calculation module is used for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch circuit to obtain the filtered zero-mode current transient state quantity of each branch circuit;

the zero-mode and current transient state quantity calculation module is used for summing the zero-mode current transient state quantity of each branch circuit to obtain the zero-mode and current transient state quantity;

a transient energy calculating module for performing T on the transient state quantity of the zero-mode current and the current of each branch circuit respectively₂Square product of sampled values over timeRespectively, acquiring zero-mode current transient energy and zero-mode and current transient energy of each branch circuit;

fault line selection module, T after fault start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; and if the maximum zero-mode current transient energy is always larger than the transient energy of the zero mode and the current, considering the branch circuit corresponding to the maximum zero-mode current transient energy as the circuit with the ground fault.

Furthermore, the sampling value acquisition module further comprises a ground fault judgment module, and the criterion for judging the occurrence of the ground fault in the ground fault judgment module is as follows:

acquiring a zero-mode current sampling value and a variable quantity thereof, and a zero-mode voltage sampling value and a variable quantity thereof of each branch circuit connected to a bus in a low-current grounding system;

and when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the ground fault is considered to occur.

Further, in the sampling value acquisition module, the variable quantity of the zero mode current sampling value of each branch circuit of connecting on the bus in the acquisition undercurrent grounding system, the variable quantity of zero mode voltage sampling value include:

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): bus zero at the current time tSampling values of the module voltage;

u₀(T-NxDeltaT): a bus zero-mode voltage sampling value of a previous cycle at the current time t;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

Further, in the zero-mode current transient state amount calculation module, the filtering of the zero-mode current or the variation thereof of each branch circuit specifically includes:

the filtering mode for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch is band-pass filtering or wavelet transformation.

Furthermore, in the transient energy calculation module, T is respectively performed on the transient quantity of the zero-mode current and the transient quantity of the current of each branch₂The integration of the square of the sampled values over time includes:

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each branch

E_{sum_filter}(t): transient state energy corresponding to characteristic frequency bands of zero mode and current of all branches

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

Δi_{0k_filter}(t) is the transient zero-mode current transient, Δ i, of the kth branch_{0sum_filter}(t) is the zero mode and transient amount of current.

Compared with the prior art, the invention has the following beneficial effects: the invention adopts the zero-mode voltage and zero-mode current OR gate start in the starting link, and is not influenced by PT disconnection; a zero-mode current transient energy calculation in a fault characteristic frequency band is provided in a fault line selection link, whether a bus grounding fault or a certain branch grounding fault is determined by adopting the zero-mode current transient energy of each branch and the amplitude magnitude relation between the zero-mode current transient energy and the transient energy of current, the problem that the line selection accuracy is influenced by the power frequency quantity of a grounding system through an arc suppression coil is solved, and meanwhile, the problem of insufficient sensitivity caused by high-resistance grounding fault is solved by adopting an integration algorithm of the square of the zero-mode current transient quantity in a time domain. The fault line selection does not need zero-mode voltage quantity, is not influenced by PT disconnection, and overcomes the influence of distribution difference on time dimensions of zero-mode voltage and zero-mode current transient quantity caused by zero-mode voltage derivation on energy acquisition effect.

Drawings

FIG. 1 is a flow chart of the method of the present invention.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

The invention provides a small current ground fault line selection method based on zero-mode current transient energy, namely, calculating the integral of the transient zero-mode current square of the maximum branch circuit in a time domain, calculating the integral of the transient zero-mode current squares of all branch circuits and the integral of the transient zero-mode current squares of all branch circuits in the time domain, and determining whether a fault point is positioned on a bus or a line according to the amplitude magnitude relation between the two.

The invention discloses a small current ground fault line selection method based on zero mode current transient state energy, which is shown in figure 1 and comprises the following processes:

the method comprises the following steps: calculating the variable quantity delta i of the zero-mode current sampling value of each branch circuit connected on the bus in the low-current grounding system_0k(t) variation Δ u of zero-mode voltage sampling value₀(t) to eliminate the effect of normal operating unbalance on subsequent criteria;

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): a bus zero-mode voltage sampling value at the current time t;

u₀(T-NxDeltaT): a bus zero-mode voltage sampling value of a previous cycle at the current time t;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

Step two: when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the ground fault is considered to occur, and the fault starting link is entered to start fault route selection;

(U₀＞U_0setor Delta U₀＞ΔU_0set)||(I_0k＞I_0setOr Δ I_0k＞ΔI_0set)

U₀: a bus zero mode voltage amplitude;

ΔU₀: calculating an amplitude value according to the variable quantity of the bus zero-mode voltage sampling value in the step one;

U_0setthe bus zero-mode voltage is fixed;

ΔU_0set: the bus zero-mode voltage variation is fixed;

I_0k: the amplitude of the zero mode current of the kth branch;

ΔI_0k: calculating an amplitude value according to the variation of the sampling value of the k-th branch zero-mode current in the step one;

I_0set: setting a zero-mode current;

ΔI_0set: and (4) determining the zero-mode electro-rheological variable.

In the method, the zero-mode voltage and zero-mode current OR gate starting is adopted in the fault starting link, and the influence of PT disconnection is avoided.

Step three: sampling or variation Δ i of the zero-mode current for each branch_0k(t) filtering to obtain zero-mode current transient state quantity delta i of each branch circuit after filtering_{0k_filter}(t)；

The filtering mode can be band-pass filtering or wavelet transformation, and the band-pass filtering mode is selected in the invention. The transient state quantity can be obtained by filtering the zero mode current sampling value or the variable quantity thereof, and the variable quantity is selected in the embodiment of the invention.

The transient zero-mode current of the fault branch circuit is opposite to the polarity of the sound branch circuit and is in a characteristic frequency band (SFB) (f)₀，f₁) And, if so, the characteristic band needs to be determined. Wherein the low-pass cut-off frequency f₀Can be selected as 3 times of power frequency, namely 150Hz, and high-pass cut-off frequency f₁The first resonant frequency of the impedance is measured for the line that is the longest outlet of the system.

Δi_{0k_filter}(t)＝filter(Δi_0k(t))

filter-band filtering processing function

Step four: transient zero-mode current transient quantity delta i for each branch_{0k_filter}(t) summing to obtain the transient quantity delta i of zero modulus sum current_{0sum_filter}(t)；

M is total number of lines

Step five: respectively carrying out T on the zero-mode current transient quantity and the zero-mode and current transient quantity of each branch₂Sampling value square integral in time is carried out, and zero mode current transient energy and zero mode sum current transient energy of each branch circuit are obtained;

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each line

E_{sum_filter}(t): transient state energy corresponding to all line zero mode and current characteristic frequency band

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

T₂Size 1/f ₀1/3 cycle time to ensure that the zero mode current transient energy calculates a transient for at least one complete cycle representing the high frequency component.

Step six: t after Fault Start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; and if the maximum zero-mode current transient energy is always larger than the transient energy of the zero mode and the current, considering the branch circuit corresponding to the maximum zero-mode current transient energy as the circuit with the ground fault.

The formula is expressed as:

at 0 to T₂All satisfy E_{sum_filter}(t)＞k₁×max(E_{k_filter}(t)), the bus bar is in ground fault

At 0 to T₂All satisfy E_{k_filter}(t)＞k₂E_{sum_filter}(t), and E_{k_filter}(t) is the branch with the maximum transient energy, the kth branch has ground fault

k₁、k₂Max (E) as a reliability factor_{k_filter}(t)) is the maximum zero-mode current transient energy function in all branches

Wherein k is₁、k₂Taking the value of 2.

From the above formula description, T after the fault start₂In time, the transient energy of the zero mode and the current is always larger than the maximum transient energy of the zero mode current (equivalently larger than the transient energy of the zero mode current of any branch circuit), and then the bus grounding fault is considered to occur; if the zero mode of a branchAnd if the current transient energy is greater than the zero-mode current transient energy of all other branches (equivalent to the maximum zero-mode current transient energy) and is also greater than the transient energy of the zero-mode current and the current all the time, the branch is considered to have a ground fault, and the branch is a line with the ground fault.

The invention provides zero-mode current transient energy calculation in a fault characteristic frequency band in a fault line selection link, determines whether the bus grounding fault or a certain branch grounding fault is the bus grounding fault by adopting the zero-mode current transient energy of each branch and the amplitude value relation between the zero-mode current transient energy and the transient energy of current, and overcomes the problem that the line selection accuracy is influenced by the power frequency quantity of a grounding system through an arc suppression coil. The fault line selection does not need zero-mode voltage quantity, is not influenced by PT disconnection, and overcomes the influence of distribution difference on time dimensions of zero-mode voltage and zero-mode current transient quantity caused by zero-mode voltage derivation on energy acquisition effect.

Correspondingly, the invention provides a small current ground fault line selection device based on zero-mode current transient energy, which is characterized by comprising a sampling value acquisition module, a zero-mode current transient quantity calculation module and a zero-mode and current transient quantity calculation module; the fault line selection module is used for selecting a fault line;

the sampling value acquisition module is used for acquiring zero-mode current sampling values of all branches connected to a bus in a low-current grounding system when a grounding fault occurs;

the zero-mode current transient state quantity calculation module is used for filtering the zero-mode current transient state quantity or the variable quantity of each branch circuit to obtain the zero-mode current transient state quantity of each branch circuit after filtering;

the zero-mode and current transient state quantity calculation module is used for summing the zero-mode current transient state quantity of each branch circuit to obtain the zero-mode and current transient state quantity;

a transient energy calculating module for performing T on the transient state quantity of the zero-mode current and the current of each branch circuit respectively₂The square integral of the sampling value in time is used for obtaining the zero-mode current transient energy and the zero mode of each branch circuitAnd the transient energy of the current;

fault line selection module, T after fault start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; and if the maximum zero-mode current transient energy is always larger than the transient energy of the zero mode and the current, considering the branch circuit corresponding to the maximum zero-mode current transient energy as the circuit with the ground fault.

Furthermore, the sampling value acquisition module further comprises a ground fault judgment module, and the criterion for judging the occurrence of the ground fault in the ground fault judgment module is as follows:

acquiring a zero-mode current sampling value and a variable quantity thereof, and a zero-mode voltage sampling value and a variable quantity thereof of each branch circuit connected to a bus in a low-current grounding system;

and when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the occurrence of the ground fault is considered.

Further, in the sampling value acquisition module, the variable quantity of the zero mode current sampling value of each branch circuit of connecting on the bus in the acquisition undercurrent grounding system, the variable quantity of zero mode voltage sampling value include:

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): a bus zero-mode voltage sampling value at the current time t;

u₀(T-NxDeltaT): a bus zero-mode voltage sampling value of a previous cycle at the current time t;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

Furthermore, in the zero-mode current transient state quantity calculation module, the filtering mode is band-pass filtering or wavelet transformation.

Furthermore, in the transient energy calculation module, T is respectively performed on the transient quantity of the zero-mode current and the transient quantity of the current of each branch₂The integration of the square of the sampled values over time includes:

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each branch

E_{sum_filter}(t): transient state energy corresponding to characteristic frequency bands of zero mode and current of all branches

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

Δi_{0k_filter}(t) is the transient zero-mode current transient, Δ i, of the kth branch_{0sum_filter}(t) is the zero mode and transient amount of current.

Compared with the prior art, the invention has the following beneficial effects:

the transient state quantity in the fault characteristic frequency band of zero-mode current and zero-mode current of all lines is adopted, theoretically approaches to 0 when the lines are in fault, and is the sum of the transient state quantities in the fault characteristic frequency band of the zero-mode current of all lines when a bus is in fault, the sum is always larger than the transient state quantity in the fault characteristic frequency band of the zero-mode current of the maximum line, and the discrimination is obvious;

a transient energy method in a zero-mode current fault characteristic frequency band is adopted, work frequency components are eliminated in the frequency band, and meanwhile, inductive current in an arc suppression coil grounding system in the frequency band is far smaller than branch circuit ground capacitance current, so that misjudgment caused by influence of steady-state power frequency signals in a distributed arc coil grounding system on energy accumulation is eliminated;

the starting link adopts the OR gate starting of zero-mode voltage and zero-mode current, the line selection link adopts the integral of the transient state quantity square of the zero-mode current on a time domain, the zero-mode voltage quantity is not needed, and the method is not influenced by PT disconnection;

the zero-mode voltage is not needed in the line selection link, and the influence of distribution difference on the time dimension of zero-mode voltage and zero-mode current transient state quantity caused by zero-mode voltage derivation on the energy acquisition effect is overcome;

the integral of the square of the zero-mode current in the characteristic frequency band on the time domain is adopted, so that the influence of insufficient sensitivity caused by high-resistance grounding fault is overcome;

the invention is not affected by the grounding system of the arc suppression coil in principle, is self-adaptive to a neutral point ungrounded system, a grounding system through the arc suppression coil and a high-resistance grounding system in method, has wide application range and does not have a line selection blind area.

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.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims (6)

1. A small current ground fault line selection method based on zero mode current transient state energy is characterized by comprising the following processes:

when a ground fault occurs, acquiring a zero-mode current sampling value of each branch circuit connected to a bus in a low-current grounding system;

filtering the zero-mode current or the variable quantity of the zero-mode current of each branch to obtain the zero-mode current transient quantity of each branch after filtering;

summing the transient state quantity of the zero-mode current of each branch circuit to obtain the transient state quantity of the zero-mode current and the transient state quantity of the current;

respectively carrying out zero mode current transient quantity and zero mode current and current on each branchIs measured by T₂Sampling value square integral in time is carried out, and zero mode current transient energy of each branch circuit and transient energy of zero mode sum current of all branch circuits are obtained;

t after Fault Start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; if the maximum zero-mode current transient energy is always larger than the transient energy of the zero mode and the current, the branch circuit corresponding to the maximum zero-mode current transient energy is considered as a circuit with a ground fault;

the filtering is performed on the zero-mode current or the variable quantity of each branch circuit, and specifically includes:

the filtering mode for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch is band-pass filtering or wavelet transformation; wherein the low-pass cut-off frequency f₀Selecting as 3 times power frequency, high pass cut-off frequency f₁Measuring the first resonant frequency of impedance for the line with the longest outgoing line of the system;

respectively carrying out T on the transient state quantity of the zero-mode current and the current of each branch₂The integration of the square of the sampled values over time includes:

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each branch

E_{sum_filter}(t): transient state energy corresponding to characteristic frequency bands of zero mode and current of all branches

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

Δi_{0k_filter}(t) is the zero mode current transient, Δ i, of the kth branch_{0sum_filter}(t) is the zero mode and transient amount of current;

T₂size 1/f₀1/3 cycle time to ensure that the zero mode current transient energy calculates a transient for at least one complete cycle representing the high frequency component.

2. The small-current ground fault line selection method based on zero-mode current transient energy as claimed in claim 1, wherein the ground fault criterion is as follows:

acquiring a zero-mode current sampling value and a variable quantity thereof, and a zero-mode voltage sampling value and a variable quantity thereof of each branch circuit connected to a bus in a low-current grounding system;

and when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the ground fault is considered to occur.

3. The small-current ground fault line selection method based on zero-mode current transient energy according to claim 1, wherein the variation of the zero-mode current sampling value and the variation of the zero-mode voltage sampling value of each branch connected to a bus in the small-current ground system comprise:

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): a bus zero-mode voltage sampling value at the current time t;

u₀(T-NxDeltaT): bus zero-mode voltage of previous cycle at current time tSampling values;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

4. A small current ground fault line selection device based on zero-mode current transient energy is characterized by comprising a sampling value acquisition module, a zero-mode current transient calculation module and a zero-mode and current transient calculation module; the fault line selection module is used for selecting a fault line;

the sampling value acquisition module is used for acquiring and calculating zero mode current sampling values of all branches connected to a bus in a small current grounding system when a grounding fault occurs;

the zero-mode current transient state quantity calculation module is used for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch circuit to obtain the filtered zero-mode current transient state quantity of each branch circuit;

the zero-mode and current transient state quantity calculation module is used for summing the zero-mode current transient state quantity of each branch circuit to obtain the zero-mode and current transient state quantity;

a transient energy calculating module for performing T on the transient state quantity of the zero-mode current and the current of each branch circuit respectively₂Sampling value square integral in time is carried out, and zero mode current transient energy and zero mode sum current transient energy of each branch circuit are obtained;

fault line selection module, T after fault start₂In time, if the transient energy of the zero mode and the current is always larger than the transient energy of the zero mode current of any branch circuit, the bus grounding fault is considered to occur; if the maximum zero-mode current transient energy is always larger than the transient energy of the zero mode and the current, the branch circuit corresponding to the maximum zero-mode current transient energy is considered as a circuit with a ground fault;

in the zero-mode current transient state quantity calculation module, the filtering is performed on the zero-mode current or the variable quantity thereof of each branch, specifically:

the filtering mode for filtering the zero-mode current or the variable quantity of the zero-mode current of each branch is band-pass filtering or wavelet transformation; wherein the low-pass cut-off frequency f₀Selecting as 3 times power frequency, high pass cut-off frequency f₁Head for measuring impedance of line with longest outgoing line of systemA resonant frequency;

in the transient energy calculating module, the T is respectively carried out on the transient quantity of the zero-mode current and the transient quantity of the current of each branch circuit₂The integration of the square of the sampled values over time includes:

E_{k_filter}(t): transient state energy corresponding to characteristic frequency band of zero mode current of each line

E_{sum_filter}(t): transient state energy corresponding to all line zero mode and current characteristic frequency band

T₂Upper limit of transient integral time in characteristic frequency band from fault starting time

Δi_{0k_filter}(t) is the transient zero-mode current transient, Δ i, of the kth branch_{0sum_filter}(t) is the zero mode and transient amount of current; t is₂Size 1/f₀1/3 cycle time to ensure that the zero mode current transient energy calculates a transient for at least one complete cycle representing the high frequency component.

5. The small-current ground fault line selection device based on zero-mode current transient energy as claimed in claim 4, wherein the sampling value acquisition module further comprises a ground fault judgment module, and the ground fault judgment module has the following criteria for the occurrence of ground fault:

acquiring a zero-mode current sampling value and a variable quantity thereof, and a zero-mode voltage sampling value and a variable quantity thereof of each branch circuit connected to a bus in a low-current grounding system;

and when the amplitude of the zero-mode voltage exceeds a fixed value or the amplitude of the zero-mode voltage variation exceeds a fixed value, or the amplitude of the zero-mode current of any branch circuit exceeds a fixed value or the amplitude of the zero-mode current variation exceeds a fixed value, the ground fault is considered to occur.

6. The small-current ground fault line selection device based on zero-mode current transient energy as claimed in claim 4, wherein in the sampling value acquisition module, the variation of the zero-mode current sampling value and the variation of the zero-mode voltage sampling value of each branch connected to the bus in the small-current ground system include:

Δi_0k(t)＝i_0k(t)-i_0k(t-N×ΔT)

Δu₀(t)＝u₀(t)-u₀(t-N×ΔT)

Δ T is the sampling interval time; n is the number of sampling points in a power frequency period; k is the kth branch

i_0k(t) sampling the zero-mode current of the kth branch at the current time t;

i_0k(T-NxDeltaT): sampling values of zero mode current of the kth branch of the previous cycle at the current time t;

Δi_0k(t): the variation of the zero-mode current sampling value of the kth branch at the current time t;

u₀(t): a bus zero-mode voltage sampling value at the current time t;

u₀(T-NxDeltaT): a bus zero-mode voltage sampling value of a previous cycle at the current time t;

Δu₀(t): and (4) the variation of the bus zero-mode voltage sampling value at the current t moment.

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