CN112531641B - Active power distribution network differential protection method and system based on direct axis current - Google Patents
Active power distribution network differential protection method and system based on direct axis current Download PDFInfo
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- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
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Abstract
The invention belongs to the technical field of active power distribution network fault section positioning, and provides a direct-axis current-based active power distribution network differential protection method and system. The active power distribution network differential protection method based on the direct axis current comprises the steps of obtaining three-phase currents at two ends of a protected section; after detecting that the protected section breaks down, respectively calculating the direct-axis current of each sampling point after the faults at the two ends of the protected section occur, and exchanging the information of each sampling point at the two ends of the protected section; calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient; and solving the differential quantity average value and the braking quantity average value of all sampling points in a period, and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
Description
Technical Field
The invention belongs to the technical field of active power distribution network fault section positioning, and particularly relates to a direct-axis current-based active power distribution network differential protection method and system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The access of a Distributed Generation (DG) changes the grid structure of the traditional power distribution network, the traditional power distribution network is changed from a radial network powered by a single-side power supply into a radial network powered by a multi-terminal power supply, and the load current and the short-circuit current after the fault during normal operation are changed into bidirectional flow. Uncertainty of the current magnitude and direction influences the action characteristics of the traditional power distribution network protection scheme.
According to whether DG is grid-connected through an inverter or not, the method can be divided into the following steps: rotary distributed generation (RTDG) and inverter distributed generation (IIDG). The fault characteristics of an RTDG are similar to those of a rotating electrical machine, compared to an IIDG which is more complex. For IIDG, when the voltage of the power grid drops, IIDG is affected by internal power electronic devices, and an inrush current may be generated to damage devices, resulting in the disconnection of DG from the power grid. However, as the capacity of the DG connected to the distribution network increases, if the DG is still treated in a manner of splitting after a fault, a series of chain influences are caused on the power grid. Therefore, the existing grid connection regulation requires that the IIDG has a certain low voltage ride through capability, when a power grid fails, the grid connection operation state is maintained, a reactive current is preferentially output to provide voltage support, and the magnitude of the output reactive current is related to the voltage drop degree. The uncertainty affects the setting of the current protection based on the traditional power distribution network, so that the reliability and the sensitivity of the protection scheme are reduced. Therefore, it is of great significance to provide an active power distribution network protection scheme widely applicable to various DG accesses.
In order to better adapt to the protection requirement of an active power distribution network, on one hand, students actively improve the traditional current protection and distance protection and put forward a self-adaptive protection scheme; on the other hand, a brand-new protection scheme aiming at the active power distribution network is provided aiming at the fault characteristic of the active power distribution network.
The prior art provides a self-adaptive protection scheme based on real-time detection of an operation mode and a fault type of an electric power system. Under different operation modes, the setting value is calculated in real time according to the short-circuit current when the short circuit at the tail end of the line is avoided, and the setting result is related to the fault type, the system impedance and the equivalent potential of the line impedance system. The principle of the protection mode is simple, but because the DG still has current output under the fault condition, two-phase short-circuit current and three-phase short-circuit current are not
If the protection system is still set according to the scheme, the protection sensitivity is reduced, and even the phenomenon of operation failure or misoperation occurs.
The prior art provides a self-adaptive positive sequence current quick-break protection scheme. The characteristic that the DG only outputs positive sequence current is utilized, the solution of the impedance at the back side of the system is improved according to the voltage and the current of the negative sequence network, the influence of the DG on the setting value of the protection scheme of the power distribution network is eliminated, and then the positive sequence voltage and the positive sequence current at the protection installation position are utilized to obtain the protection setting value. The protection scheme has the self-adaptive characteristic, the problem of reduction of the protection range caused by DG access is improved to a certain extent, but the influence of the transition resistance is not considered in theory, and the protection sensitivity is reduced under the influence of the transition resistance in the actual situation.
The prior art proposes a self-adaptive directional protection scheme. The concept of a power distribution network tree structure is introduced, and the reference direction rule is redefined: in the distribution network tree structure, the reference direction of the directional element is the direction from the leaf node to the root node. Based on the direction locking principle, the full-line quick-action removal of line faults is realized by using the impedance relay, but voltage information needs to be acquired during application, and the current configuration condition of a power distribution network is difficult to realize.
The prior art provides an active power distribution network protection scheme based on current phase change. And judging a fault section by comparing whether the current change directions detected by the protection of the two ends of the feeder line before and after the fault occurs are the same as the fault judgment basis. This protection scheme has low communication requirements, but does not take into account the difference between RTDG and IIDG, and the protection scheme may fail after a large number of accesses to the IIDG.
The prior art proposes a differential protection scheme based on current amplitudes at two ends of a feeder line. The protection scheme only utilizes the current amplitude information at the two ends of the protection to construct the fault section positioning criterion, has simple protection principle, is easy to realize, and has higher sensitivity when the DG permeability is lower and the provided fault current is smaller. However, the reliable implementation of such protection schemes limits the DG capacity to some extent, against the original intention of distributed power generation technology.
The prior art proposes a "quasi-differential" protection scheme based on region classification and information interaction sharing. According to the protection scheme, the regions are classified, information sharing in the regions is achieved based on global information interaction, and the power grid operation mode is judged in real time through communication coordination of a plurality of agent systems. This protection scheme is fully adaptive, but has high requirements on the reliability and speed of communication.
Therefore, the inventor finds that the existing active power distribution network protection scheme does not consider the difference between the RTDG and the IIDG, is easily influenced by the type and the capacity of the DG, and cannot meet the requirements on the reliability and the high speed of communication.
Disclosure of Invention
In order to solve at least one technical problem in the background technology, the invention provides a direct-axis current-based active power distribution network differential protection method and system.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides an active power distribution network differential protection method based on direct-axis current.
A differential protection method for an active power distribution network based on direct-axis current comprises the following steps:
acquiring three-phase currents at two ends of a protected section;
after detecting that the protected section breaks down, respectively calculating the direct-axis current of each sampling point after the faults at the two ends of the protected section occur, and exchanging the information of each sampling point at the two ends of the protected section;
calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient;
and solving the differential quantity average value and the braking quantity average value of all sampling points in a period, and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
A second aspect of the present invention provides a direct-axis current-based differential protection system for an active power distribution network.
A direct-axis current-based active power distribution network differential protection system comprises:
the current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the direct-axis current calculation module is used for respectively calculating the direct-axis current of each sampling point after the fault of the two ends of the protected section is detected after the fault of the protected section is detected, and exchanging information of each sampling point of the two ends of the protected section;
The differential momentum and braking quantity calculation module is used for calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient;
and the fault judgment module is used for solving the differential quantity average value and the braking quantity average value of all sampling points in a period and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
A third aspect of the invention provides a computer-readable storage medium.
A computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, carries out the steps of the direct-axis current based differential protection method for an active power distribution network as described above.
A fourth aspect of the invention provides a computer apparatus.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the direct current based active power distribution network differential protection method as described above when executing the program.
Compared with the prior art, the invention has the beneficial effects that:
the invention collects three-phase current values at two ends of a feeder line, and converts three-phase alternating current under a static coordinate system into direct current under a rotating coordinate system through park transformation. Constructing a difference momentum by using the absolute value of the sum of the direct-axis currents of the sampling points at the two ends, constructing a braking momentum by multiplying the absolute value of the difference of the direct-axis currents of the sampling points at the two ends by a braking coefficient, and comparing the accumulated difference momentum of a time window with the average value of the braking momentum to judge a fault section; compared with other differential protection methods of an active power distribution network: the method only needs one communication line to exchange information, can reflect all types of faults, and greatly relieves the communication burden; only current information is utilized, and a voltage transformer is not required to be installed, so that the method is more economical; the method is suitable for RTDG access and IIDG access at the same time, and has good reliability and sensitivity under the condition of high DG permeability; after the three-phase current is subjected to park conversion to obtain direct-axis current, the frequency is changed to be 2 times of the original frequency, the time for protecting utilized information is short, and the action speed is improved; the identification method has the advantages of simple and clear principle, accurate identification and easy engineering realization.
Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
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The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1(a) shows the relative positions of the AC-DC axis, the three-phase current axis and the reference axis;
FIG. 1(b) the relative position relationship between the AC-DC axis and the three-phase current axis inside the synchronous motor;
FIG. 2 is a schematic diagram of a simple active power distribution network;
FIG. 3 is a schematic diagram of a simulation model of an active power distribution network;
FIG. 4(a) is a change curve of difference momentum between two ends of MN and braking quantity when a three-phase short circuit occurs at point f 1;
fig. 4(b) is a change curve of the difference between the two ends of MN and the braking amount when the point f1 has a two-phase short circuit;
fig. 4(c) is a change curve of the difference momentum between the two ends of MN and the braking amount when the point f1 has a two-phase ground short circuit;
fig. 4(d) is a change curve of the difference momentum between the two ends of MN and the braking amount when a two-phase ground short circuit occurs at point f1 and includes a 10 Ω transition resistance;
fig. 5 is a flowchart of an active power distribution network differential protection method based on direct axis current according to an embodiment of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example one
Referring to fig. 5, the active power distribution network differential protection method based on direct axis current of the present embodiment includes the following steps:
s101: and acquiring three-phase currents at two ends of the protected section.
S102: and after detecting that the protected section breaks down, respectively calculating the direct-axis current of each sampling point after the faults at the two ends of the protected section break down, and exchanging the information of each sampling point at the two ends of the protected section.
In the specific implementation, the park transformation is used for respectively calculating the direct-axis current of each sampling point after the faults at the two ends of the feeder line.
The number and transmission quantity of communication lines are reduced by the park transformation without phase splitting differential and phase information; the direct axis current obtained by park transformation has the frequency doubling characteristic, the information of the whole period can be obtained only by half the time of the previous period, and the speed is greatly improved. And the required fault judgment information is obtained by utilizing the three-phase current information through park transformation, a voltage transformer is not required to be installed, and the method is more economical.
In this embodiment, the two ends of the protected section exchange the direct axis current information and the sampling time information of each sampling point based on optical fiber communication.
The method of the embodiment does not need split-phase differential, only communicates through one line, and reduces the requirement on communication.
In this embodiment, exchanging information of each sampling point at both ends of the protected zone includes: and exchanging the direct-axis current information and the sampling time information of each sampling point at two ends of the protected section.
Wherein, the direct axis current i of the kth sampling point collected at the protective installation position d (k) Sampling value i from three-phase current abc (k) And a time-varying phase phi, as calculated by the following equation:
where phi is 2 pi fk delta t + theta 0 F is the fundamental frequency of the three-phase current, delta t is the sampling interval, theta 0 The included angle between the straight axis and the reference axis is shown in fig. 1(a) and 1 (b).
S103: calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct currents at the two ends of the protected zone and the braking coefficient.
Wherein the value of the braking coefficient is greater than 0 and less than 1.
The principle of calculating the protection differential quantity and the braking quantity based on the direct axis current at two ends of the line is as follows:
Taking the active power distribution network shown in fig. 2 as an example, when a fault occurs inside the feeder MN, it is noted that the direct-axis currents flowing through the ends M, N are I respectively dm (k)、I dn (k) And the reference positive directions at the two ends of the MN point to the line for the bus. And analyzing the reliability of the protection scheme after the RTDG and the IIDG are accessed. Differential C of kth sampling point diff Comprises the following steps:
C diff (k)＝|I dm (k)+I dn (k)|
braking quantity C of k-th sampling point res Comprises the following steps:
C res (k)＝K res ·|I dm (k)-I dn (k)|
wherein, K res Is the braking coefficient.
Under the normal operation condition, according to kirchhoff's current law, the currents flowing through the two ends of the MN are equal in magnitude and opposite in direction. That is, the calculated direct axis currents at the two ends of the MN are opposite numbers to each other. At this time, the absolute value of the sum of the direct-axis currents, i.e. the differential quantity, is approximately 0, the absolute value of the difference of the direct-axis currents is approximately 2 times of the current flowing through the feeder line, and the reliability of the protection scheme can be ensured by reasonably selecting the braking coefficient.
The RTDG has the fault characteristic similar to that of the motor, when the RTDG is connected into the power distribution network and faults occur in the MN section, currents at two ends of the MN are increased, correspondingly, the calculated direct-axis current is also increased, and the directions are positive directions. At this time, the differential quantity is approximately 2 times of the current on the feeder line, the braking quantity is approximately 0, and the protection scheme can be ensured to judge the fault correctly.
The IIDG is limited by the inverter, and the output short-circuit current is generally 1.2-2 times of the rated current. When the IIDG is connected into the power distribution network, the interior of the MN section breaks down, the current supplied by the system is increased at the M end, and the power supplied by the IIDG is supplied at the N end, so that the supplied current is smaller. At this time, the braking coefficient is activated, and the value of the braking amount is adjusted so that the differential amount is still larger than the braking amount and sufficient sensitivity is ensured at the time of the in-zone failure.
In conclusion, no matter the type of the distributed power supply, under the condition of a fault, the difference between the braking quantity and the differential quantity of the fault section and the non-fault section has obvious difference, and a theoretical basis is established for the scheme based on the direct-axis current differential protection.
S104: and solving the differential quantity average value and the braking quantity average value of all sampling points in a period, and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
In step S104, the principle of respectively calculating the difference momentum and the braking quantity average value of n sampling points in one period as the final criterion for determining the fault section is as follows:
when sampling point differential is adopted, the method is easily influenced by the transient state after the fault, and the initial process of the fault is different at different fault starting angles. Further, since the sensitivity and reliability of the initial fault protection are affected, a smooth response can be obtained by calculating the average value of the differential amount and the braking amount by periodically taking the time window.
As shown in FIG. 2, I dm (k)、I dn (k) Respectively is the direct axis current of the kth sampling point at the two ends of MN.
The mean value of the difference momentum of n sampling points in one period is as follows:
the average braking amount of n sampling points in one period is as follows:
when the differential quantity average value of all sampling points in a period is larger than the brake quantity average value of all sampling points in the period, judging that the inside of the protected section breaks down; otherwise, the fault is judged to occur outside the protected section.
The method comprises the following steps of (1) constructing a power distribution network simulation model containing DGs of different types by utilizing PSCAD, and carrying out simulation verification on a differential protection method:
1) modeling
The structure of the simulation model is shown in FIG. 3. The system reference voltage is 10.5kV, and the equivalent internal resistance Z of the system s J0.14 Ω, line parameter r 1 ＝0.13Ω/km，x 1 The length of the line is 0.402 omega/km and 2 km; the bus P is connected with the IIDG, the capacity is 2MW, the bus Q is connected with the RTDG, and the capacity is 5 MW; the rated power of each load on the feeder is 5MVA, and the power factor is 0.9. Corresponding protection is provided at the circuit breaker Sij. Fault point f 1 、f 2 、f 3 Respectively located in the feeders MN, NP, NQ.
2) Exemplary Fault simulation
At f 1 When a three-phase short circuit, a two-phase ground short circuit and a two-phase ground short circuit passing through a 10 Ω transition resistor are set at a point 0.3s, the fault occurrence position is in the middle of the line, and time window transition calculation of one period length is taken before and after the fault occurrence, as shown in fig. 4(a), 4(b), 4(c) and 4(d), respectively.
As can be seen from the analysis of fig. 4(a) to (d), no matter what kind of failure occurs, the differential amount rapidly exceeds the braking amount in a very short time after the occurrence of the failure in the failure section. Under different fault types, the differential quantity and the braking quantity are changed, but the braking device can rapidly and reliably act under various conditions and has strong transient resistance tolerance.
Are respectively at f 1 、f 2 、f 3 Respectively setting various types of faults, wherein 1 、f 2 Point faults take into account both the case where the fault is at the head end and the tail end of the line. The simulation results are shown in tables 1 to 3, in whichThe data of (2) are all taken from 10ms after the fault.
TABLE 1 points of failure f 1 Simulation result of time
TABLE 2 points of failure f 2 Simulation result of time
TABLE 3 points of failure f 3 Simulation result of time
As can be seen from the simulation results in tables 1, 2, and 3, on the feeder line connected to the distributed power supplies of different types, regardless of the fault occurrence position or the fault type, the differential amount is greater than the braking amount in the fault section, and the differential amount is less than the braking amount in the non-fault section. Although the sensitivity of the protection criterion is different for different fault types and different fault positions according to different values of the current difference and the braking amount calculated by the direct current, the correct judgment of the fault section can be always ensured, and the sensitivity is ensured to be more than 2. Therefore, for a power distribution network containing different types of distributed power supplies, the differential protection scheme based on direct-axis current provided by the embodiment can correctly judge the fault section.
From the simulation results, the differential protection method based on the direct-axis current provided by the embodiment is suitable for power distribution networks containing DGs of different types, can reflect faults of different positions and different types, ensures correct judgment of fault sections, and has high sensitivity.
In the embodiment, the difference and the braking amount are calculated according to the relationship of the direct-axis currents of the sampling points by utilizing the characteristics of the direct-axis currents at two ends of the feeder line, the average value of the difference and the braking amount of one period is taken to eliminate the influence of fault transient states caused by different fault initial angles, and the fault section is determined by comparing the average values of the difference and the braking amount in one period.
According to the simulation result of PSCAD, the embodiment can correctly position the fault section within 10ms under different fault conditions, and can still ensure the correct judgment of the protection scheme under the condition of larger transition resistance. In addition, the embodiment converts three-phase current into direct-axis current, and only one communication line needs to be installed. In addition, the embodiment only utilizes the three-phase current information to calculate the direct-axis current, and does not need to install a voltage transformer, thereby greatly reducing the equipment cost
Example two
The active power distribution network differential protection system based on direct-axis current provided by the embodiment comprises:
The current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the direct-axis current calculation module is used for respectively calculating the direct-axis current of each sampling point after the fault of the two ends of the protected section is detected after the fault of the protected section is detected, and exchanging information of each sampling point of the two ends of the protected section;
the differential momentum and braking quantity calculation module is used for calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient;
and the fault judgment module is used for solving the differential quantity average value and the braking quantity average value of all sampling points in a period and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
The active power distribution network differential protection system based on direct-axis current in this embodiment corresponds to the steps in the active power distribution network differential protection method based on direct-axis current in the first embodiment one to one, and the specific implementation process is the same, and will not be described here again.
EXAMPLE III
The present embodiment provides a computer-readable storage medium, on which a computer program is stored, and the program, when executed by a processor, implements the steps in the direct-axis current based differential protection method for an active distribution network.
Example four
The embodiment provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, the processor implements the steps in the direct-axis current-based differential protection method for an active power distribution network according to the first embodiment.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention 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, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. 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.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above may be implemented by a computer program, which may be stored in a computer readable storage medium and executed by a computer to implement the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A differential protection method for an active power distribution network based on direct-axis current is characterized by comprising the following steps:
acquiring three-phase currents at two ends of a protected section;
after detecting that the protected section breaks down, respectively calculating the direct-axis current of each sampling point after the faults at the two ends of the protected section occur, and exchanging the information of each sampling point at the two ends of the protected section;
calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient;
and solving the differential quantity average value and the braking quantity average value of all sampling points in a period, and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
2. The active power distribution network differential protection method based on direct-axis current as claimed in claim 1, characterized in that when the average value of the differential quantities of all sampling points in a period is larger than the average value of the braking quantities of all sampling points in the period, it is determined that a fault occurs inside the protected section; otherwise, the fault is judged to occur outside the protected section.
3. The direct current based differential protection method for an active distribution network, according to claim 1, wherein the value of the braking coefficient is greater than 0 and less than 1.
4. The direct-axis current-based differential protection method for the active power distribution network according to claim 1, wherein the direct-axis current of each sampling point after the fault at the two ends of the feeder line is respectively calculated by park transformation.
5. The direct-axis current-based differential protection method for the active power distribution network, according to claim 1, wherein the two ends of the protected section exchange information of each sampling point based on optical fiber communication.
6. The direct-axis current-based differential protection method for an active power distribution network according to claim 1 or 5, wherein exchanging information of each sampling point at two ends of a protected section comprises: the direct axis current information and the sampling time information of each sampling point.
7. An active power distribution network differential protection system based on direct-axis current is characterized by comprising:
The current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the direct-axis current calculation module is used for respectively calculating the direct-axis current of each sampling point after the fault of the two ends of the protected section is detected after the fault of the protected section is detected, and exchanging information of each sampling point of the two ends of the protected section;
the differential momentum and braking quantity calculation module is used for calculating the differential momentum and braking quantity of each corresponding sampling point at the two ends of the protected section; wherein the differential quantity is the absolute value of the sum of direct-axis currents at two ends of the protected section; the braking amount is the product of the absolute value of the difference between the direct-axis currents at the two ends of the protected section and the braking coefficient;
and the fault judgment module is used for solving the differential quantity average value and the braking quantity average value of all sampling points in a period and judging the fault section according to the comparison result of the differential quantity average value and the braking quantity average value.
8. The active power distribution network differential protection system based on direct-axis current as claimed in claim 7, wherein in the fault judgment module, when the average value of the differential quantities of all sampling points in a period is greater than the average value of the braking quantities of all sampling points in the period, it is judged that a fault occurs inside the protected section; otherwise, the fault is judged to occur outside the protected section.
9. A computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, carries out the steps of the direct-axis current based differential protection method for an active power distribution network according to any one of claims 1 to 6.
10. Computer arrangement comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor when executing the program performs the steps in the direct current based active power distribution network differential protection method according to any of the claims 1-6.
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