CN113655336B - Power distribution network single-pole ground fault detection method and system based on most value normalization - Google Patents
Power distribution network single-pole ground fault detection method and system based on most value normalization Download PDFInfo
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- CN113655336B CN113655336B CN202110832957.2A CN202110832957A CN113655336B CN 113655336 B CN113655336 B CN 113655336B CN 202110832957 A CN202110832957 A CN 202110832957A CN 113655336 B CN113655336 B CN 113655336B
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Abstract
The invention discloses a power distribution network single-pole ground fault detection method and system based on the most value normalization, which collects the positive pole current and the negative pole current of each feeder line before and after the fault of a power distribution network; based on the collected positive current and negative current of each feeder line before and after the fault, subtracting the current of the post fault from the current of the pre fault to obtain the sudden change of the current of the positive and negative of the feeder lines; normalizing the positive and negative current break variables of each feeder line by adopting a most-valued normalization method, wherein the normalized positive and negative current break variables of each feeder line are distributed between [0,1 ]; based on the distribution characteristics of the current mutation quantity of the positive pole and the negative pole of each feeder line after normalization processing, the size relation between each waveform data point and 1/2 after normalization is summed to construct a line selection and pole selection criterion, and the monopole grounding fault detection of the radial MMC-MVDC power distribution network is realized. The invention can accurately detect the single-pole grounding fault only by using a short data window of 1ms, and has small operand and excellent protection performance.
Description
Technical Field
The invention belongs to the technical field of ground fault detection, and particularly relates to a power distribution network monopole ground fault detection method and system based on most value normalization.
Background
The existing scheme for detecting the single-pole grounding fault of the direct-current power grid has the problems that the scheme is easily influenced by the transient current characteristic amplitude, the line selection and the pole selection cannot be realized at the same time, the bus voltage needs to be additionally introduced, and the conditions of large-resistance grounding and extremely short lines cannot be simultaneously solved. The normalization method can convert the original array into a dimensionless relative value without changing the concave-convex property of the original waveform, so that the normalization method has the advantage of being not influenced by the amplitude of the original numerical value.
Therefore, the difference of transient characteristics in the radial MMC-MVDC power distribution network is mined by applying a most-value normalization method, and the construction of the unipolar ground fault detection method with the transition resistance capability is worthy of deep research.
Disclosure of Invention
The invention aims to solve the technical problem of providing a power distribution network single-pole ground fault detection method and system based on the most value normalization aiming at the defects in the prior art, wherein the pole current mutation quantity is converted into a dimensionless relative value by adopting the normalization method, and a line selection and pole selection criterion which is not influenced by the size of original data is constructed, so that a foundation is laid for realizing line selection and pole selection of radial MMC-MVDC power distribution networks and bus faults by only utilizing current characteristics.
The invention adopts the following technical scheme:
a power distribution network single-pole ground fault detection method based on most value normalization comprises the following steps:
s1, collecting positive pole current and negative pole current of each feeder line before and after a power distribution network fault;
s2, based on the positive current and the negative current of each feeder line before and after the fault, which are acquired in the step S1, subtracting the current of the post fault from the current of the pre fault to obtain the sudden change of the current of the positive and negative of each feeder line;
s3, normalizing the positive and negative current break variables of each feeder line obtained in the step S2 by adopting a most-value normalization method, wherein the normalized positive and negative current break variables of each feeder line are distributed between [0,1 ];
and S4, based on the distribution characteristics of the current mutation quantity of the positive electrode and the negative electrode of each feeder line subjected to normalization processing in the step S3, summing the size relationship between each waveform data point and 1/2 to construct a line selection and pole selection criterion, and realizing the monopole grounding fault detection of the radial MMC-MVDC power distribution network.
Specifically, in step S1, when the power distribution network is in normal operation, the positive and negative currents i at the kth line protection installation position pk 、i nk Comprises the following steps:
wherein i Lk Is the load current.
Specifically, in step S1, after the power distribution network has a ground fault, the line-to-ground capacitors all discharge through the fault point, the fault electrode-to-ground capacitors of the fault line and the fault point form a loop, and the current i at the fault point f The sum of the whole network feeder line earth capacitance current and the polarity of the current is opposite to the line earth capacitance current, and the current flowing through the positive pole and the negative pole of a sound line after the power distribution network is in failure is i pk ′、i nk ' positive and negative currents i flowing through the fault line pK ′、i nK ′。
Further, the fault point current i f Comprises the following steps:
wherein, C k Is the equivalent capacitance of positive and negative poles to ground, K is the total feeder number, u pk Is the positive voltage of the feed line k, u nk Is the cathode voltage of the feed line k.
Further, the positive and negative current i flowing through the sound line pk ′、i nk ' is:
wherein u' pK 、u′ nK The voltages of the positive and negative poles of the line after the fault i pck ′、i nck ' is capacitance current of positive and negative electrodes to earth in fault, i Lk ' load current at fault, C k The equivalent capacitance is positive and negative electrodes to the ground.
Further, the positive and negative electrode currents i flowing through the fault line pK ′、i nK ' is:
wherein, u' pK 、u′ nK The voltages of the positive and negative poles of the line after the fault i pck ′、i nck ' is capacitance current of positive and negative electrodes to earth in fault, i Lk ' load Current at fault, C K The equivalent capacitance of the positive pole and the negative pole of the fault line to the ground.
Specifically, in step S2, the current mutation amount of each electrode is specifically:
wherein, Δ i pk For the positive current abrupt change of the feeder k, Δ i nk For the abrupt change of the cathode current of the feeder k, Δ i pK For the positive current abrupt change of the feeder K, Δ i nK For the change of the negative current of the feeder K, Δ u p 、Δu n Respectively, positive and negative bus voltage sudden change amount, C K The positive and negative electrodes of the fault line are equivalent capacitors to the ground, C k The equivalent capacitance of positive and negative poles to ground.
Specifically, in step S4, the line selection and the pole selection are as follows:
wherein d is nK Is a criterion value corresponding to the negative pole of the feeder line K, d pK Is a criterion value corresponding to the positive pole of the feeder line K, d jk For judgment of j pole correspondence of feeder line kAccording to the value.
Further, criterion d jk Comprises the following steps:
wherein M is the total data number in the data window,
and m is a relative value after the most value normalization, and the sequence number corresponding to the sampling point.
Another technical solution of the present invention is a power distribution network single-pole ground fault detection system based on the most value normalization, including:
the acquisition module acquires the positive pole current and the negative pole current of each feeder line before and after the power distribution network fault;
the mutation module is used for subtracting the current of the front pole of the fault from the current of the rear pole of the fault to obtain the current mutation quantity of the positive pole and the negative pole of the feeder line based on the current of the positive pole and the current of the negative pole of each feeder line before and after the fault, which are acquired by the acquisition module;
the normalization module is used for normalizing the positive and negative current break variables of each feeder line obtained by the break module by adopting a most-value normalization method, and the positive and negative current break variables of each feeder line after normalization are distributed between [0,1 ];
and the detection module is used for constructing a line selection and pole selection criterion by summing the size relation between each normalized waveform data point and 1/2 based on the positive and negative pole current mutation distribution characteristics of each feeder line subjected to normalization processing by the normalization module, so that the monopole grounding fault detection of the radial MMC-MVDC power distribution network is realized.
Compared with the prior art, the invention at least has the following beneficial effects:
the invention relates to a power distribution network single-pole ground fault detection method based on the most value normalization, when a radial MMC-MVDC power distribution network has a single-pole ground fault, the polarity of a current mutation quantity flowing through all non-fault poles is opposite to that of a current mutation quantity flowing through a fault pole, the current mutation quantities of a positive pole and a negative pole are converted into a dimensionless relative value by adopting the most value normalization method, the method has the advantages of being not influenced by the size of original data, not changing the original waveform concavity and convexity and the like, and the difference between a fault line and a sound line after normalization is utilized to construct a line selection and pole selection criterion. Theoretical analysis and PSCAD simulation show that the method can realize line selection and pole selection of line faults and bus faults only by using current characteristics, has strong transition resistance capability, and has certain adaptivity to load fluctuation, extremely short lines and low sampling rate.
Further, in step S1, when the power distribution network operates normally, the voltages of the positive and negative bus bars are almost unchanged, the line-to-ground capacitance is equivalent to an open circuit, and the positive and negative currents i at the k-th line protection installation position pk 、i nk The load current is equal in magnitude and opposite in polarity, namely the positive pole and the negative pole are only load current in normal operation, and the current amplitude is constant. .
Further, in step S1, after the power distribution network has a ground fault, the dynamic change of the positive and negative voltages causes the line to discharge through the fault point, the positive and negative currents of each feeder line are no longer constant load currents, and the positive and negative currents changing before and after the fault provide possibility for finding the difference between the faulty line and the healthy line.
Further, the fault point current i f The method provides theoretical basis for the sum of the earth capacitance current of all the feeder lines of the whole network and the polarity of the sum of the earth capacitance current of all the feeder lines of the whole network to be opposite to the earth capacitance current of all the feeder lines, and the theoretical basis for the fact that the current abrupt change quantity of the positive electrode and the current abrupt change quantity of the negative electrode of all the feeder lines obtained in the method in claim 7 are only the sum of the earth capacitance current of the line to the ground and the current abrupt change quantity of the fault electrode of the fault line to be the current abrupt change quantity of all the non-fault electrodes and the polarities of the current abrupt change quantities of all the non-fault electrodes are opposite.
Further, the positive and negative electrode currents i of the sound line pk ′、i nk The expressions are the same and are the sum of the local line capacitance-to-ground current and the load current. And (3) explaining that the positive and negative electrode currents of the healthy line after the fault are formed by the load current and the ground capacitance current of the line, and providing a theoretical basis for accurately solving the sudden change of the positive and negative electrode currents of the healthy line in the step S2.
Further, the positive and negative pole currents i of the fault line pK ′、i nK The expressions are different, the healthy pole current of the fault line is the earth capacitance current and the load current of the local line, and the fault pole current of the fault line is the sum of the earth capacitance current of the local line, the feed-in current of a fault point and the load current, and the polarities of the earth capacitance current, the feed-in current of the fault point and the load current are opposite. The pole current of the healthy pole of the fault line consists of load current and line-to-ground capacitance current, and the formation form of the pole current is the same as that of the healthy line; the fault pole current of the fault line consists of three parts, namely load current, line-to-ground capacitance current and fault point feed-in current, the forming form is different from that of a sound line and a sound pole of the fault line, and a theoretical basis is provided for accurately solving the sudden change of the positive and negative current of the fault line in the step S2.
Further, in step S2, the magnitude and polarity of the current transient of each pole represent the difference between the transient currents of the healthy line and the fault line.
Further, in step S4, the setting of the line selection and pole selection basis provides a theoretical basis for identifying different types of faults.
Further, criterion d jk And the normalized pole current break variable relative value is used for carrying out single-pole ground fault detection, so that the operation amount is small, and the fault line selection, pole selection and bus fault identification can be realized by only using current characteristics.
In conclusion, the single-pole grounding fault detection method can accurately detect the single-pole grounding fault only by using a short data window of 1ms, and has the advantages of small operand and excellent protection performance.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic diagram of a single-ended radial distribution network;
FIG. 2 is a schematic diagram showing a current waveform and a line selection result when the head end of L3 is in metallic grounding, wherein (a) is a pole current waveform, (b) is a pole current abrupt change waveform, (c) is normalization processing, and (d) is a line selection and pole selection result;
fig. 3 is a schematic diagram of a current waveform and a selection result when a bus is grounded, where (a) is a pole current waveform, (b) is a pole current abrupt change waveform, (c) is a normalization process, and (d) is a selection result;
FIG. 4 is a diagram illustrating the results of selecting lines and poles under different transition resistances;
FIG. 5 is a graphical comparison of load fluctuations for no fault and a fault, where (a) is no fault and (b) is fault;
FIG. 6 is a diagram showing the result of line selection under a very short line, wherein (a) is metallic ground and (b) is grounded via a 300 Ω resistor;
fig. 7 is a graph showing the results of line selection and pole selection at a sampling rate of 10kHZ, where (a) is normalization processing and (b) is the results of line selection and pole selection.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be understood that the terms "comprises" and/or "comprising" indicate the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of the various regions, layers and their relative sizes, positional relationships are shown in the drawings as examples only, and in practice deviations due to manufacturing tolerances or technical limitations are possible, and a person skilled in the art may additionally design regions/layers with different shapes, sizes, relative positions, according to the actual needs.
Referring to fig. 1, the method for detecting a single-pole ground fault of a power distribution network based on mode normalization of the present invention includes the following steps:
s1, calculating and collecting positive and negative currents of feeder lines before and after a fault of a single-ended radial distribution network;
please refer to fig. 1, i pk 、i nk Positive and negative electrode currents, i, at the place where the line protection is provided for the kth line Lk Is a load current, C k Is the equivalent capacitance of positive and negative poles to the ground i pck 、i nck Positive and negative electrode capacitance current to ground; c K Equivalent capacitance to earth for positive and negative poles of fault line, i pK 、i nK 、i LK 、i pcK 、i ncK Is the corresponding current; i all right angle f Is the fault point current; and adding "'" indicates corresponding voltage and current in fault.
a. When the circuit is in normal operation, the voltages of the positive and negative buses are almost unchanged, and the capacitance of the circuit to ground is equivalent to open circuit, namely i pck 、i nck =0 (K =1,.. K), the electrode currents being:
namely, when the feeder line normally runs, the positive pole and the negative pole of each feeder line can flow through the penetrating load current with equal magnitude and opposite polarity, and the current amplitude is constant.
b. After a ground fault occurs, the dynamic changes of the voltages of the positive and negative electrodes cause the discharge of the line-to-ground capacitance through a fault point.
Robust line positive capacitive dischargeThe path is indicated by white arrows in fig. 1, and the negative electrode capacitor discharge path is indicated by black arrows in fig. 1. The faulty line health pole capacitor discharge path is shown by the orange arrow in fig. 1; the fault electrode-to-ground capacitance and the fault point form a loop, and the discharge path is i in figure 1 nck As shown. I.e. fault point current i f The sum of the capacitance-to-ground currents of the whole network feeder line is opposite to the capacitance-to-ground current of the line in polarity, and the expression is
After the fault, the positive and negative currents i of the feeder lines of the sound line flow pk ′、i nk ' is:
positive and negative current i flowing through each feeder line of fault line pK ′、i nK ' is:
wherein, u' pK 、u′ nK The voltages of the positive pole and the negative pole of the line after the fault are respectively.
S2, subtracting the electric quantity in the fault state from the electric quantity in the normal running state before the fault to obtain the sudden change of the current of each electrode;
in the single-ended radial MMC-MVDC power distribution network, each feeder line is an outgoing line on the same bus, and the voltage change of the feeders lines is the same, so that the current mutation expression of each pole is
Wherein, Δ u p 、Δu n The voltage abrupt change of the positive and negative buses are respectively.
When the radial MMC-MVDC power distribution network has single-pole grounding fault, the sudden change of the current flowing through all the non-fault poles is only the capacitance current to the ground of the line, the sudden change of the current flowing through the fault pole is the sum of the capacitance currents of all the non-fault poles, and the polarities of the two currents are opposite.
S3, carrying out normalization processing on the original data by adopting a most-value normalization method;
the pole current abrupt change quantity normalization processing equation of the mth point of any pole line of the feeder line is
Wherein m is [1,M ]]J is p or n, min (Δ i) jk ) Is the minimum value of the index j, max (Δ i) jk ) Is the maximum value of the index j, and M is the total data number in the data window.
As is known from the formula (6),
namely, the irregularity of the current mutation quantity of each electrode can not be changed by normalization, and each feeder line still meets the original mutation characteristic; and compared with the original smaller data, the normalization can obviously increase the difference of the transient characteristics between the fault pole of the fault line and all non-fault poles.
And S4, comparing the normalized results, and constructing a radial MMC-MVDC monopole ground fault detection criterion.
And constructing a line selection and pole selection criterion by using the magnitude relation between each normalized waveform data point and 1/2 and summing, wherein the criterion form is as follows:
the line and pole selection is based as follows:
and the normalized pole current break variable relative value is used for carrying out single-pole ground fault detection, the calculation amount is small, and the fault line selection, pole selection and bus fault identification are realized by using the current characteristics.
In another embodiment of the present invention, a distribution network unipolar ground fault detection system based on the most value normalization is provided, where the system can be used to implement the distribution network unipolar ground fault detection method based on the most value normalization, and specifically, the distribution network unipolar ground fault detection system based on the most value normalization includes an acquisition module, a mutation module, a normalization module, and a detection module.
The acquisition module acquires the positive pole current and the negative pole current of each feeder line before and after the power distribution network fault;
the mutation module is used for subtracting the current of the front pole of the fault from the current of the rear pole of the fault to obtain the current mutation quantity of the positive pole and the negative pole of the feeder line based on the current of the positive pole and the current of the negative pole of each feeder line before and after the fault, which are acquired by the acquisition module;
the normalization module is used for normalizing the positive and negative current break variables of each feeder line obtained by the break module by adopting a most-value normalization method, and the positive and negative current break variables of each feeder line after normalization are distributed between [0,1 ];
and the detection module is used for constructing a line selection and pole selection criterion by summing the size relation between each normalized waveform data point and 1/2 based on the positive and negative pole current mutation distribution characteristics of each feeder line subjected to normalization processing by the normalization module, so that the monopole grounding fault detection of the radial MMC-MVDC power distribution network is realized.
In yet another embodiment of the present invention, a terminal device is provided that includes a processor and a memory for storing a computer program comprising program instructions, the processor being configured to execute the program instructions stored by the computer storage medium. The Processor may be a Central Processing Unit (CPU), or may be other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field-Programmable gate array (FPGA) or other Programmable logic device, discrete gate or transistor logic device, discrete hardware component, etc., which is a computing core and a control core of the terminal, and is specifically adapted to load and execute one or more instructions to implement a corresponding method flow or a corresponding function; the processor provided by the embodiment of the invention can be used for the operation of the distribution network single-pole ground fault detection method based on the most value normalization, and comprises the following steps:
collecting positive pole current and negative pole current of each feeder line before and after the power distribution network fault; based on the collected positive current and negative current of each feeder line before and after the fault, subtracting the current of the post fault from the current of the pre fault to obtain the sudden change of the current of the positive and negative of the feeder lines; normalizing the positive and negative current break variables of each feeder line by adopting a most-valued normalization method, wherein the normalized positive and negative current break variables of each feeder line are distributed between [0,1 ]; based on the distribution characteristics of the current mutation quantity of the positive pole and the negative pole of each feeder line after normalization processing, the size relation between each waveform data point and 1/2 after normalization is summed to construct a line selection and pole selection criterion, and the monopole grounding fault detection of the radial MMC-MVDC power distribution network is realized.
In still another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a Memory device in the terminal device and is used for storing programs and data. It is understood that the computer readable storage medium herein may include a built-in storage medium in the terminal device, and may also include an extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also, one or more instructions, which may be one or more computer programs (including program code), are stored in the memory space and are adapted to be loaded and executed by the processor. It should be noted that the computer readable storage medium may be a high-speed RAM memory, or a non-volatile memory (non-volatile memory), such as at least one disk memory.
The one or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the distribution network single-pole ground fault detection method based on the most-valued normalization in the above embodiments; one or more instructions in the computer-readable storage medium are loaded by the processor and perform the steps of:
collecting positive pole current and negative pole current of each feeder line before and after the power distribution network fault; based on the collected positive current and negative current of each feeder line before and after the fault, subtracting the current of the post fault from the current of the pre fault to obtain the sudden change of the current of the positive and negative of the feeder lines; normalizing the positive and negative current break variables of each feeder line by adopting a most-valued normalization method, wherein the normalized positive and negative current break variables of each feeder line are distributed between [0,1 ]; based on the distribution characteristics of the current mutation quantity of the positive pole and the negative pole of each feeder line after normalization processing, the size relation between each waveform data point and 1/2 of each waveform data point after normalization is summed to construct a line selection and pole selection criterion, and single-pole ground fault detection of the radial MMC-MVDC power distribution network is achieved.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Simulation verification
And (3) building a +/-7.5 kV medium-voltage direct-current distribution network model containing 3 feeders in the PSCAD for simulation verification. The sampling frequency is 20kHZ, the cut-off frequency of the low-pass filter is 600HZ, and the data window length is 1ms.
1) Action behavior analysis
Fig. 2 shows a current waveform and a line selection result when an N-pole metallic ground fault occurs at 0.4km from the head end of the line L3.
Fig. 3 shows the current waveform and the result of line selection when a metallic ground fault occurs in the N-pole of the bus.
D in FIGS. 2 and 3 jk The value is compared with the line selection and pole selection basis in the formula (4), so that a fault line and a fault pole can be easily selected.
2) Algorithm performance analysis
Fig. 4 shows the line selection result when the N pole at the midpoint of the feed line L3 is grounded through different transition resistors. As shown in fig. 4, when the transition resistance increases from 0 Ω to 20 Ω, the pole current suddenly decreases, but each feed line d is fed jk The absolute value of (a) is gradually increased, which shows that the normalization amplifies the characteristic difference between the fault electrode and the non-fault electrode; with the transition resistance of 300 omega, the cathode current abrupt change of the lines L1 and L2 gradually increases from a negative value to a positive value within 3.5-3.501 s, so that the normalized relative value is distributed on less points on the 1/2 central line relative to other fault-free feeder lines, and d is caused jk The value of (c) is decreased.
Fig. 5 is a comparison of waveforms for load reduction when line L3 is faultless and faulty. As can be seen from fig. 5, the load fluctuation does not affect the single-pole ground fault detection result.
Fig. 6 shows the line selection results when the length of the line L1 is 0.5km, the N pole in the L3 is grounded by metallic metal, and the N pole is grounded by a transition resistance of 300 Ω. As can be seen from fig. 6, the very short lines do not affect the line selection result under different transition resistances, i.e. the proposed method is not affected by the line length.
FIG. 7 shows the normalized waveform and the result of selecting line and pole when N-pole metal grounding fault occurs at the first 0.4km of L3 at the sampling rate of 10 kHz. As can be seen from a comparison of FIG. 7 (b) with FIG. 2 (d), although d is the former jk The numerical value is reduced, but the fault line and the fault pole can be accurately selected. Thus, the proposed method has some adaptivity to low sampling rates.
In summary, the power distribution network single-pole ground fault detection method and system based on the mode normalization of the invention realize the fault line selection and pole selection only by using the current characteristics, have strong transition resistance capability, have self-adaptability to load fluctuation, extremely short lines and low sampling rate, and have certain engineering practical value.
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 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 above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (8)
1. A power distribution network single-pole ground fault detection method based on most value normalization is characterized by comprising the following steps:
s1, collecting positive pole current and negative pole current of each feeder line before and after a power distribution network fault;
s2, based on the positive electrode current and the negative electrode current of each feeder line before and after the fault, which are acquired in the step S1, subtracting the current of the front electrode after the fault from the current of the rear electrode after the fault to obtain sudden change of the current of the positive electrode and the current of the negative electrode of each feeder line;
s3, normalizing the positive and negative current break variables of each feeder line obtained in the step S2 by adopting a most-value normalization method, wherein the normalized positive and negative current break variables of each feeder line are distributed between [0,1 ];
s4, based on the distribution characteristics of the current mutation quantity of the positive electrode and the negative electrode of each feeder line subjected to normalization processing in the step S3, summing the size relationship between each waveform data point and 1/2 to construct a line selection and pole selection criterion, and realizing the monopole grounding fault detection of the radial MMC-MVDC power distribution network, wherein the line selection and pole selection when K feeder lines are shared are based on the following steps:
wherein K =1 nK Is a criterion value corresponding to the negative pole when the feeder line K has a fault, d pK Is a criterion value, d, corresponding to the positive pole when the feeder line K fails jk A criterion value corresponding to j pole of any feeder line k, a criterion d jk Comprises the following steps:
wherein j is P or N, M is total data number in the data window,
and m is a relative value after the most value normalization, and the sequence number corresponding to the sampling point.
2. The method according to claim 1, wherein in step S1, when the distribution network is in normal operation, the positive and negative currents i at the k-th line protection installation place pk 、i nk Comprises the following steps:
wherein i Lk Is the load current.
3. The method according to claim 1, characterized in that in step S1, after the earth fault occurs in the distribution network, the line-to-ground capacitors are all discharged through the fault point, the fault electrode-to-ground capacitor of the fault line forms a loop with the fault point, and the current i at the fault point f The sum of the whole network feeder line earth capacitance current and the polarity of the current is opposite to the line earth capacitance current, and the current flowing through the positive pole and the negative pole of a sound line after the power distribution network is in failure is i pk ′、i nk ' positive and negative currents i flowing through the fault line pK ′、i nK ′。
4. Method according to claim 3, characterized in that the fault point current i f Comprises the following steps:
wherein, C k Is the equivalent capacitance of positive and negative poles to ground, K is the total feeder number, u pk Is the positive voltage of the feed line k, u nk Is the cathode voltage of the feed line k.
5. A method as claimed in claim 3, characterised by the positive and negative pole currents i flowing through the robust line pk ′、i nk ' is:
wherein u' pK 、u′ nK The voltages of the positive and negative poles of the line after the fault i pck ′、i nck ' is capacitance current of positive and negative electrodes to earth in fault, i Lk ' load current at fault, C k The equivalent capacitance is positive and negative electrodes to the ground.
6. A method according to claim 3, characterized in that the positive and negative currents i flowing through the faulty line pK ′、i nK ' is:
wherein u' pK 、u′ nK Positive and negative voltages, i, of the line after fault pck ′、i nck ' is capacitance current of positive and negative electrodes to earth in fault, i Lk ' load current at fault, C K The positive and negative electrodes of the fault line are equivalent capacitors to the ground.
7. The method according to claim 1, wherein in step S2, the current jump amount of each electrode is specifically:
wherein, Δ i pk For a robust line feeder k positive pole current abrupt change, Δ i nk For a robust line feeder k cathode current abrupt change, Δ i pK For positive pole current abrupt change, Δ i, of faulty line feeder K nK For the K-cathode current sudden change of the fault line feeder, deltau p 、Δu n Respectively, positive and negative bus voltage sudden change amount, C K The positive and negative electrodes of the fault line are equivalent capacitors to the ground, C k The equivalent capacitance of positive and negative poles to ground.
8. The utility model provides a distribution network unipolar ground fault detection system based on most value normalization which characterized in that includes:
the acquisition module acquires the positive pole current and the negative pole current of each feeder line before and after the power distribution network fault;
the mutation module is used for subtracting the current of the post fault electrode and the current of the pre fault electrode from the current of the post fault electrode to obtain the mutation quantity of the current of the positive electrode and the negative electrode of the feeder line on the basis of the current of the positive electrode and the current of the negative electrode of each feeder line before the fault and the current of the negative electrode of each feeder line after the fault, which are acquired by the acquisition module;
the normalization module is used for normalizing the positive and negative current mutation quantities of each feeder line obtained by the mutation module by adopting a most value normalization method, and the normalized positive and negative current mutation quantities of each feeder line are distributed between [0,1 ];
the detection module is used for constructing a line selection and pole selection criterion by summing the size relation between each normalized waveform data point and 1/2 based on the positive and negative pole current mutation distribution characteristics of each feeder line subjected to normalization processing by the normalization module, so that the monopole grounding fault detection of the radial MMC-MVDC power distribution network is realized, and the line selection and pole selection basis when K feeder lines are shared is as follows:
wherein K =1 nK Is a criterion value corresponding to the negative pole of the feeder line K, d pK Is a criterion value corresponding to the positive pole of the feeder line K, d jk Judging the criterion value corresponding to the j pole of the feeder line kAccording to d jk Comprises the following steps:
wherein j is P or N, M is the total data number in the data window,
is the relative value after the most value normalization, and m is the serial number corresponding to the sampling point.
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