CN112653102A - Active power distribution network differential protection method and system based on quadrature axis current - Google Patents
Active power distribution network differential protection method and system based on quadrature axis current Download PDFInfo
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- CN112653102A CN112653102A CN202011358901.XA CN202011358901A CN112653102A CN 112653102 A CN112653102 A CN 112653102A CN 202011358901 A CN202011358901 A CN 202011358901A CN 112653102 A CN112653102 A CN 112653102A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—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
- H02H3/006—Calibration or setting of parameters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—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
- 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 quadrature axis current-based active power distribution network differential protection method and system. The method 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 quadrature 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 starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1; and comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of action thresholds of all sampling points in one cycle, and judging that the inside of the protected section has a fault when the sum is larger than the action threshold of all sampling points in one cycle.
Description
Technical Field
The invention belongs to the technical field of active power distribution network fault section positioning, and particularly relates to an active power distribution network differential protection method and system based on quadrature axis current.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The definition of Distributed Generator (DG) is: the distributed power supply is arranged on the load side, and not only needs to provide electric energy, but also needs to assist the power distribution network in carrying out balance adjustment. DG is divided into two classes: rotary distributed generation (RTDG) and inverter distributed generation (IIDG). The RTDG has similar fault characteristics to conventional generators. The IIDG is connected with a power grid through an inverter and is influenced by a control mode and current limiting of a power electronic device, the fault characteristic of the IIDG is more complex, the fault current is generally 1.2-2 times of rated current, and the composition of the output current is influenced by the voltage of a grid-connected point. DG detects different voltage drop degrees of the grid-connected point, and the output currents are different. The existing grid connection regulation requires that the operation is not stopped when the voltage of a DG grid connection point drops, and reactive current, namely cross-axis current, is preferentially provided to provide voltage support.
With the access of the DG, the conventional distribution network becomes an active distribution network. The relative position relationship between the DG and the protected feeder line section is uncertain, so that the boosting action or the pumping action of the DG has uncertainty. In addition, the access of the DG enables the distribution network to be changed into a network with bidirectional tidal current flow, so that the setting of the traditional protection is difficult to determine, the selectivity and the sensitivity of the traditional protection are influenced, and the phenomenon of operation rejection or misoperation can occur. Therefore, the research on the protection scheme of the active power distribution network is of great significance.
The protection scheme of the existing active power distribution network can be divided into three directions: the first is to limit the access capacity of the DG; the second type is an adaptive protection scheme with a protection device; the third category is communication-based protection schemes for power distribution networks.
The prior art proposes a DG access scheme that takes into account the reliable operation and current distribution characteristics of the protection device. On the basis of slightly changing the existing power distribution network protection, the selectivity, sensitivity and reliability of the existing protection under the conditions of different fault points and different DG positions are comprehensively analyzed, and a DG access scheme is provided. The performance of the protection scheme can be improved only by slightly changing the original protection scheme. But only suitable for a specific power distribution network, and has no universality, thereby limiting the development of the DG to a certain extent. In addition, the protection scheme does not analyze the protection action characteristics after different types of DGs are accessed, and whether effective protection can be provided for the active power distribution network needs to be further researched.
The prior art provides an adaptive distance protection scheme for an active power distribution network. The scheme divides the protected feeder line into different areas, fully analyzes the boosting and external sucking functions of DG access on protection of two ends of the feeder line, records the voltage and current of the protected feeder line, and calculates the distance protection setting value under the current operating condition so as to achieve the self-adaption purpose. This protection scheme does not require communication and has a high sensitivity. However, the requirement for voltage information requires that a voltage transformer is installed on the power distribution network, which increases the construction cost of the power grid.
The prior art proposes a self-adaptive current outage protection scheme. And adjusting the setting value of the protection scheme according to whether the DG is accessed on the protection back side. When two-phase short circuit fault occurs, the system impedance is calculated in real time by using the negative sequence current, and the current setting scheme is maintained unchanged when three-phase short circuit occurs. The protection scheme is an improvement of the original protection scheme and has economical efficiency. However, the inventor finds that the method is only suitable for the power distribution network with low DG permeability, does not consider the fault characteristic under the condition of large DG capacity, and reduces the protection range.
The prior art proposes an adaptive protection scheme based on branch contribution factors. And constructing a branch contribution factor matrix according to the operation mode of the system and the DG output condition so as to eliminate the influence of the DG on the feeder line flowing on the system side. The protection scheme is simple to calculate and easy to set. However, the inventors have found that the influence of the transition resistance is not considered in the protection scheme analysis process, and that a protection failure phenomenon may occur in the case where the transition resistance is large.
The prior art proposes a protection scheme based on positive sequence current and phase angle. The protection scheme calculates the difference amount according to the amplitude of the positive sequence current, constructs the braking amount according to the phase of the positive sequence current, can reflect all fault types, is hardly influenced by transition resistance, and has high sensitivity. The inventors have found that this protection scheme only considers the bi-directional flow of current in the active distribution network, neglects the fault characteristics of the IIDG itself, and has high requirements for communication.
The prior art proposes a differential protection scheme based on negative sequence current. The direction from the bus to the line is specified to be positive, when a fault occurs in the protection section, the phase difference of negative sequence currents flowing through the protection devices at the two ends is close to 0 degrees, and the phase difference of negative sequence currents at the two ends of the non-fault section is close to 180 degrees. The inventors have found that this protection scheme is not affected by load currents, but when a more harmful three-phase short-circuit fault occurs in the distribution network, there is theoretically no negative-sequence current in the line, so this protection scheme can only reflect asymmetric faults.
Therefore, the inventor finds that the existing active power distribution network protection scheme has the following problems: the fault characteristic when the DG capacity is large is not considered, the influence of the DG type and capacity is easily caused, the fault characteristic of the IIDG is ignored, and the requirement on communication is high.
Disclosure of Invention
In order to solve at least one technical problem in the background art, the invention provides an active power distribution network differential protection method and system based on quadrature axis current.
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 quadrature axis current.
A differential protection method for an active power distribution network based on quadrature 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 quadrature 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 starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1;
and comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of action thresholds of all sampling points in one cycle, and judging that the inside of the protected section has a fault when the sum is larger than the action threshold of all sampling points in one cycle.
A second aspect of the present invention provides a quadrature axis current based differential protection system for an active power distribution network.
An active power distribution network differential protection system based on quadrature axis current, comprising:
the current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the quadrature axis current calculation module is used for respectively calculating the quadrature 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 starting amount and action threshold value calculation module is used for calculating the starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1;
and the fault judgment module is used for comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of the action thresholds of all sampling points in one cycle, and when the sum is greater than the action threshold of all sampling points in one cycle, judging that the inside of the protected section has a fault.
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 quadrature 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 quadrature axis 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:
(1) the invention does not need split-phase differential, only communicates through a line, reduces the requirement for communication; the required fault judgment information is obtained only 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; the quadrature axis current obtained by park transformation has the double frequency characteristic, phase-splitting differential motion is not needed, phase information is not needed, the number and transmission quantity of communication lines are reduced, the information of the whole period can be obtained only in half of the previous period, and the speed is greatly improved.
(2) The method fully considers the control strategy of the distributed power supply, is suitable for the power distribution networks accessed by various types of DGs, has higher sensitivity particularly when the IIDGs with special fault characteristics are accessed, is not influenced by the types and the capacities of the DGs, and has higher sensitivity when the inverter type distributed power supply with special fault characteristics is accessed.
(3) The method only utilizes the three-phase current information to obtain the required fault information through park transformation, does not need to install a voltage transformer, and has economical efficiency; 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.
Drawings
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 position relationship between 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 variation curve of the starting amount and the motion threshold value at two ends of the section MN when a three-phase short circuit occurs at point f 1;
fig. 4(b) is a variation curve of the starting amount and the action threshold amount at both ends of the section MN when the point f1 has a two-phase short circuit;
fig. 4(c) is a variation curve of the starting amount and the motion threshold value at both ends of the section MN when the point f1 has a two-phase ground short circuit;
FIG. 4(d) is a variation curve of the starting amount and the threshold value of the two ends of the section MN when a two-phase ground short circuit with a transition resistance of 10 Ω occurs at point f 1;
fig. 5 is a flowchart of a method for locating a fault section 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 quadrature 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, calculating the quadrature axis current of each sampling point after the faults at the two ends of the protected section respectively, and exchanging the information of each sampling point at the two ends of the protected section.
In the specific implementation, quadrature axis currents of sampling points after faults at two ends of a feeder line are calculated through park transformation.
Three-phase current value i from k-th sampling point by park transformationabc(k) Converted into quadrature axis current i of the kth sampling pointq(k) The values are specifically:
where phi is 2 pi fk delta t + theta0F is the fundamental frequency of the three-phase alternating current, delta t is the sampling interval, theta0The included angle between the intersecting axis and the reference axis is shown in fig. 1(a) and 1 (b).
The quadrature axis current signals are advanced through park transformation, so that split-phase differential and phase information are not needed, and the quantity and the transmission quantity of communication lines are reduced; the quadrature 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 cross-axis current information and 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: exchanging the quadrature axis current information and the sampling time information of each sampling point at two ends of the protected section.
S103: calculating the starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold is the absolute value of the difference between the quadrature axis currents at the two ends of the protected section, and is multiplied by a reliability coefficient smaller than 1.
The principle of calculating the protection starting amount and the action threshold value based on the quadrature axis current at two ends of the line is as follows:
taking the active power distribution network shown in fig. 2 as an example, the reference positive directions at the two ends of the MN are defined as bus pointing lines. Calculating the starting amount and the action threshold value of each corresponding sampling point at two ends, specifically:
the action quantity of the kth sampling point is as follows:
the action threshold for the kth sample point is:
wherein
The k-th sampling point quadrature axis current values at two ends of the protected section respectively, and the Kset is a reliability coefficient which is larger than 0 and smaller than 1.
RTDG's fault characteristic is similar with traditional motor, and when the inside trouble that breaks down in district section, the electric current that flows through the district section both ends increases rapidly, and the direction is by the generating line directional circuit, is the positive direction, can make the volume of starting increase rapidly, and the action threshold value reduces rapidly.
The IIDG adopts a double closed-loop control mode, namely outer loop power control and inner loop current control. The inner ring adopts quadrature-direct axis current control in order to simplify the control mode. The IIDG is connected with a power grid through the inverter, and in order to avoid damage to power electronic equipment caused by overlarge short-circuit current, the maximum short-circuit current generated by the IIDG is limited within 1.2-2 times of rated current after a fault occurs. The IIDG coupled to the medium and high voltage power distribution systems must have low voltage ride through capability, as dictated by the grid tie regulations. That is, when the system voltage drops, the inverter-type distributed power supply is required to maintain grid-connected operation, and preferentially output reactive current (cross-axis current) to support the voltage. Considering the characteristic that the output power factor of the inverter type distributed power supply is 1 under the normal operation condition, namely only the direct-axis current is output, and the priority reactive current under the fault condition is the quadrature-axis current, although the IIDG short-circuit current is small, the IIDG short-circuit current is almost the quadrature-axis current, so that the starting quantity of two ends in the area can be rapidly increased, and the reliability of the fault section positioning method is ensured.
In addition, the quadrature axis current output condition of the IIDG is related to the drop degree of the voltage of the grid-connected point. Extreme conditions such as a fault position far away from the IIDG access point or a large transition resistor short circuit are considered, and a reliability coefficient smaller than 1 is introduced to ensure that the differential protection method of the embodiment can be widely applied.
In summary, no matter the type of DG, under the fault condition, there is a significant difference between the activation amount and the action threshold value in the fault section and the non-fault section, which establishes a theoretical basis for the scheme based on the quadrature axis current differential protection.
S104: and comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of action thresholds of all sampling points in one cycle, and judging that the inside of the protected section has a fault when the sum is larger than the action threshold of all sampling points in one cycle.
In the specific implementation, the starting amount and the action threshold value of n sampling points in one period are accumulated to be used as the criterion of a fault section, and the principle is as follows:
the current of one cycle can reflect all fault information, but the current value of the first cycle is different because of the different initial states of the faults. In order to eliminate the uncertainty of the current change of the first period caused by different fault starting states, the action amount and the action threshold value are calculated in an accumulated mode, and a more stable response can be obtained.
Accumulating the starting amount and the action threshold value of n sampling points in one period, specifically as follows:
sum of the start quantities of n sampling points in one period:
sum of action thresholds of n sampling points in one period:
the method comprises the following steps of (1) constructing a power distribution network simulation model containing DGs of different types by utilizing PSCAD, and performing simulation verification on a fault section positioning 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 systemsJ0.14 Ω, line parameter r1＝0.13Ω/km，x1The length of the line is 0.402 omega/km and 2 km; the bus P is connected with the inverter type distributed power supply, the capacity is 2MW, the bus Q is connected with the rotary type distributed power supply, and the capacity is 5 MW; the rated power of each load on the feeder is 5MVA, and the power factor is 0.9. At the circuit breaker SijAnd configures corresponding protection. The fault points f1, f2 and f3 are respectively positioned on the feeders MN, NP and NIn Q.
2) Exemplary Fault simulation
When a three-phase short circuit, a two-phase ground short circuit, and a two-phase ground short circuit via a 10 Ω transition resistance are set at 0.3s at point f1, a time window lapse calculation of one cycle length is taken after a fault occurs in the middle of the fault occurrence position re-route, 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) - (d), no matter what kind of failure occurs, the start amount of the failure section rapidly exceeds the action threshold value in a very short time after the failure occurs. The starting amount and the action threshold value are changed under different fault types, but the fault types can be correctly judged under the set different fault types.
Different types of faults are set at f1, f2, f3, respectively, and both cases where the fault is located at the head end and the tail end of the line are considered. The simulation results are shown in tables 1-3, wherein each item of data is taken from the 10 th ms after the fault.
TABLE 1 simulation results for a failure point of f1
TABLE 2 simulation results for failure point f2
TABLE 3 simulation results for failure point f3
As can be seen from the simulation results in tables 1, 2 and 3, on the feeders connected to different types of DGs, the obtained simulation result is consistent with the theoretical analysis result regardless of the fault type or the distance between the fault location and the DG. The protection principle of the invention can ensure that the starting amount in the fault section is rapidly larger than the action threshold value, and the starting amount in the non-fault section is always smaller than the action threshold value. In different fault types, the obtained starting amount and the action threshold have obvious numerical difference, but the magnitude relation between the starting amount and the action threshold always conforms to the theoretical result.
As can be seen from the simulation results, the fault section positioning method based on quadrature axis current provided in this embodiment is widely applicable to distribution networks to which various DGs are connected, can reflect all fault types, and ensures high sensitivity.
In this embodiment, three-phase currents at two ends of the protected feeder line need to be collected to calculate quadrature axis currents, the starting amount and the action threshold value at two ends of the protected feeder line are calculated according to the characteristics of the quadrature axis currents of the sampling points, and the sum of the starting amount and the action threshold value of each sampling point in one period is taken to reduce the influence caused by different initial states of faults so as to obtain smooth and stable response.
According to the simulation result of PSCAD, the embodiment can correctly position the fault section within 10ms under different fault conditions, and ensure that the fault section is judged with high sensitivity under the condition of relatively large transition resistance. In addition, the three-phase current is converted into the quadrature-axis current, and the required fault information can be exchanged only by one communication line, so that the communication burden is reduced. In addition, the protection method of the embodiment only utilizes three-phase current information to calculate quadrature axis current, and a voltage transformer is not required to be installed, so that the equipment cost is greatly reduced, and the method is more suitable for complex power distribution networks.
Example two
The embodiment provides an active power distribution network differential protection system based on quadrature axis current, it includes:
the current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the quadrature axis current calculation module is used for respectively calculating the quadrature 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 starting amount and action threshold value calculation module is used for calculating the starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1;
and the fault judgment module is used for comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of the action thresholds of all sampling points in one cycle, and when the sum is greater than the action threshold of all sampling points in one cycle, judging that the inside of the protected section has a fault.
Each module in the active power distribution network differential protection system based on quadrature axis current in this embodiment corresponds to each step in the active power distribution network differential protection method based on quadrature axis current in the first embodiment one by 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, which when executed by a processor implements the steps in the differential protection method for an active power distribution network based on quadrature axis current as described in the first embodiment.
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 program, the processor implements the steps in the quadrature 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 can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include 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 quadrature 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 quadrature 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 starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1;
and comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of action thresholds of all sampling points in one cycle, and judging that the inside of the protected section has a fault when the sum is larger than the action threshold of all sampling points in one cycle.
2. The quadrature axis current based differential protection method for an active power distribution network of claim 1, wherein the quadrature axis current of each sampling point after a fault at two ends of the feeder line is calculated by park transformation.
3. The quadrature axis current based differential protection method for an active power distribution network as claimed in claim 1, wherein sampling point information is exchanged between two ends of the protected section based on optical fiber communication.
4. A quadrature axis current based differential protection method for an active power distribution network as claimed in claim 1 or 3, wherein exchanging information of sampling points at both ends of a protected section comprises: and quadrature axis current information and sampling time information of each sampling point.
5. An active power distribution network differential protection system based on quadrature axis current, comprising:
the current acquisition module is used for acquiring three-phase currents at two ends of the protected section;
the quadrature axis current calculation module is used for respectively calculating the quadrature 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 starting amount and action threshold value calculation module is used for calculating the starting amount and the action threshold value of each corresponding sampling point at the two ends of the protected section; wherein, the starting quantity is the absolute value of the sum of quadrature axis currents at two ends of the protected section; the action threshold value is the absolute value of the difference of quadrature axis currents at two ends of the protected section, and then is multiplied by a reliability coefficient smaller than 1;
and the fault judgment module is used for comparing the sum of the quadrature axis current starting quantities of all sampling points in one cycle with the sum of the action thresholds of all sampling points in one cycle, and when the sum is greater than the action threshold of all sampling points in one cycle, judging that the inside of the protected section has a fault.
6. The quadrature axis current based active power distribution network differential protection system of claim 5, wherein in said quadrature axis current calculation module, the quadrature axis current of each sampling point after a fault at both ends of the feeder line is calculated by park transformation.
7. A quadrature axis current based active power distribution network differential protection system as claimed in claim 5, wherein in said quadrature axis current calculation module, the two ends of the protected section exchange sampling point information based on optical fiber communication.
8. A quadrature axis current based active power distribution network differential protection system as claimed in claim 5 or 7, wherein exchanging information at sample points across a protected section comprises: and quadrature axis current information and sampling time information of each sampling point.
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 quadrature axis current based differential protection method for an active power distribution network according to any of claims 1-4.
10. Computer device 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 implements the steps in the quadrature axis current based active power distribution network differential protection method according to any of claims 1-4.
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