CN109449894A - A kind of active power distribution network current differential protection method and device - Google Patents
A kind of active power distribution network current differential protection method and device Download PDFInfo
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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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Abstract
The present invention relates to a kind of active power distribution network current differential protection method and devices, the described method includes: determining the attribute-bit of the protection section before and after failure according to the positive-sequence component of protection section both ends electric current before and after active power distribution network failure, and then differential protection is carried out to the protection section according to the attribute-bit of protection section described before and after the failure, determine whether that carrying out differential protection and different attribute identifies the corresponding specific adjusting threshold for carrying out differential protection according to the positive-sequence component of protection section both ends electric current before and after active power distribution network failure respectively using technical solution of the present invention, improve the sensitivity of that differential protection of active power distribution network, the timeliness of isolated fault is effectively ensured simultaneously.
Description
Technical Field
The invention relates to the technical field of power distribution network protection, in particular to a current differential protection method and device for an active power distribution network.
Background
After the concept of the smart grid is proposed, Distributed Generation (DG) obtains wider application, in recent years, the Distributed Generation close to the load side is greatly supported to be developed, the access of a small-capacity Distributed power supply in a power distribution network is promoted, the permeability of the DG in the power distribution network is gradually increased and the Distributed Generation develops towards active power distribution networks with multiple sources, multiple ends and the like, and based on the characteristic of bidirectional flow of tide and fault current, the transition of a power supply mode of the active power distribution network from large-scale centralized power supply to centralized Distributed power supply is realized, the combined power supply of the large power grid and the DG has the advantages of low energy consumption, low investment, high reliability, high flexibility and the like, but the power Generation characteristics of the DG are different from those of the traditional power Generation, when the DG is accessed into the power distribution network, a simple network with a single radial power supply of the power supply is changed into a complex network with multiple power supplies, finally, the selectivity, sensitivity, speed and reliability of the relay protection device are influenced. Therefore, in order to ensure the power supply reliability of the power distribution network and to play the role of the DG as much as possible, a solution suitable for the current power grid development environment needs to be considered.
At present, the conventional current differential protection in an active power distribution network mainly aims at conventional lines, adopts a technology of setting a protection criterion starting current to be a fixed high threshold value, and aims at the problems that the line fault conditions except the conventional lines in the power grid cannot be protected, the protection coverage is incomplete, the sensitivity is insufficient and the like.
Disclosure of Invention
The invention provides a current differential protection method and a current differential protection device for an active power distribution network, and aims to determine attribute identifications of protection sections before and after a fault according to positive sequence components of currents at two ends of the protection sections before and after the fault of the active power distribution network, and further perform differential protection on the protection sections according to the attribute identifications of different protection sections before and after the fault, solve the problem of insufficient differential protection sensitivity in the prior art, improve the timeliness of isolating the fault of the active power distribution network and reduce loss caused by the fault of the power distribution network.
The purpose of the invention is realized by adopting the following technical scheme:
in an active power distribution network current differential protection method, the improvement comprising:
determining attribute identifications of the protection sections before and after the fault according to positive sequence components of currents at two ends of the protection sections before and after the fault of the active power distribution network;
and carrying out differential protection on the protection sections according to the attribute identifications of the protection sections before and after the fault.
Preferably, the process of determining the attribute identification of the protection section before and after the fault according to the positive sequence component of the current at two ends of the protection section before the fault of the active power distribution network comprises the following steps:
if the sum I of positive sequence components of the current at two ends of the protection section before the fault of the active power distribution networkun.mLess than or equal to attribute setting threshold I of undetected branchset.unIf not, the attribute of the protection section is identified as existing as a detection branch.
Preferably, the process of determining the attribute identifications of the protection sections before and after the fault according to the positive sequence component of the current at two ends of the protection section after the fault of the active power distribution network comprises the following steps:
if the sum of the positive sequence components of the currents at the two ends of the protection section after the active power distribution network fails is not zero, identifying the attribute of the protection section after the failure as an intra-area failure, otherwise, identifying the attribute of the protection section after the failure as an extra-area failure;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preTo failPositive sequence component of front guard section end current, Iset.unSetting a threshold for the attributes of the undetected branches.
Preferably, the differentially protecting the protection zones according to the attribute identifications of the protection zones before and after the fault includes:
if the attribute identification of the protection section after the fault is the in-zone fault and the attribute identification of the protection section before the fault is that no branch which is not detected exists, when the positive sequence component of the current at the two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the undetected branch does not have a voltage signal, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and a voltage signal exists on the undetected branch, when a positive sequence component of current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein,Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)， Krel3＝Krel2∈[0.35,0.45]，ΔIm1for the positive-sequence component of the head-end current of the protection section after a fault, Δ In1For protecting the positive-sequence component of the section-end current after a fault, Iset1For a pre-fault attribute label that is a starting current threshold, K, corresponding to a protection zone where no undetected branch existsmFor reliable coefficients corresponding to protection zones for which the pre-fault attribute label is absent of undetected branches, INRated current for the feed line, Krel1For braking coefficients corresponding to protection zones with pre-fault attribute labels absent of undetected branches, Iset2For the pre-fault attribute label, the starting current threshold, K, corresponding to the protection section with the undetected branch and no voltage signal in the undetected branchrel2A braking coefficient, K, corresponding to a protection zone with an attribute label before failure being that an undetected branch exists and no voltage signal exists in the undetected branchunFor the reliability factor corresponding to the protection zone with the pre-fault attribute label as the presence of undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3Starting current threshold, K, corresponding to protection section with attribute label before fault being undetected branch and voltage signal existing in undetected branchrel3A braking coefficient, U, corresponding to a protection zone with an attribute label of existence of an undetected branch and a voltage signal of the undetected branch before a faultφφIs any two-phase voltage difference, U, among three-phase voltagessetAnd setting a threshold for the voltage of the active power distribution network after the fault.
In an active power distribution network current differential protection device, the improvement comprising:
the determining module is used for determining the attribute identification of the protection sections before and after the fault according to the positive sequence components of the currents at the two ends of the protection sections before and after the fault of the active power distribution network;
and the protection module is used for carrying out differential protection on the protection section according to the attribute identification of the protection section before and after the fault.
Preferably, the determining module includes:
a first determination unit for protecting the sum I of the positive sequence components of the current across the section if the active distribution network failsun.mAttribute setting threshold I less than or equal to undetected branchset.unIf not, the attribute of the protection section is identified as the existence of the detection branch.
The second determining unit is used for identifying the attribute of the protection section as an intra-area fault if the sum of positive sequence components of currents at two ends of the protection section is not zero after the active power distribution network fails, and otherwise, identifying the attribute of the protection section as an extra-area fault;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preFor the positive sequence component of the end current of the protection section before fault, Iset.unSetting a threshold for the attributes of the undetected branches.
Preferably, the protection module is configured to:
if the attribute identification of the protection section after the fault is the in-zone fault and the attribute identification of the protection section before the fault is that no branch which is not detected exists, when the positive sequence component of the current at the two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the undetected branch does not have a voltage signal, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and a voltage signal exists on the undetected branch, when a positive sequence component of current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein, Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)， Krel3＝Krel2∈[0.35,0.45]，ΔIm1For the positive-sequence component of the head-end current of the protection section after a fault, Δ In1For protecting the positive-sequence component of the section-end current after a fault, Iset1For a pre-fault attribute label that is a starting current threshold, K, corresponding to a protection zone where no undetected branch existsmFor reliable coefficients corresponding to protection zones for which the pre-fault attribute label is absent of undetected branches, INRated current for the feed line, Krel1For braking coefficients corresponding to protection zones with pre-fault attribute labels absent of undetected branches, Iset2For the pre-fault attribute label, the starting current threshold, K, corresponding to the protection section with the undetected branch and no voltage signal in the undetected branchrel2A braking coefficient, K, corresponding to a protection zone with an attribute label before failure being that an undetected branch exists and no voltage signal exists in the undetected branchunTo belong to before failureThe characteristic label is a reliable coefficient corresponding to a protection section with undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3Starting current threshold, K, corresponding to protection section with attribute label before fault being undetected branch and voltage signal existing in undetected branchrel3A braking coefficient, U, corresponding to a protection zone with an attribute label of existence of an undetected branch and a voltage signal of the undetected branch before a faultφφIs any two-phase voltage difference, U, among three-phase voltagessetAnd setting a threshold for the voltage of the active power distribution network after the fault.
Compared with the prior art, the invention has the following beneficial effects:
by adopting the technical scheme of the invention, the attribute identifications of the protection sections before and after the fault are determined according to the positive sequence components of the currents at the two ends of the protection sections before and after the fault of the active power distribution network, the attribute identifications corresponding to the protection sections are obtained according to the positive sequence components of the currents before and after the clapping of the protection sections, the reliability of criterion source data is ensured, a foundation is laid for the sensitivity of differential protection, and the protection sections are subjected to differential protection according to the attribute identifications of the protection sections before and after the fault.
Drawings
Fig. 1 is a flowchart of an active power distribution network current differential protection method according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an active power distribution network according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a feeder structure without undetected branches in an active power distribution network current differential protection method according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a feeder structure with an undetected branch in the active power distribution network current differential protection method according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of an active power distribution network current differential protection device according to an embodiment of the present invention.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
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 accompanying 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.
The invention provides a current differential protection method and a current differential protection device for an active power distribution network, which are explained below.
The technical scheme provided by the invention determines protection criteria corresponding to different conditions by using current amplitude and phase information in the protection sections before and after the fault so as to implement differential protection, and for an active power distribution network, undetected branches may exist in the protection sections to cause insufficient sensitivity of part of conditions.
The first embodiment is as follows:
fig. 1 shows a flowchart of a current differential protection method for an active power distribution network in an embodiment of the present invention, and as shown in fig. 1, the method may include:
101. determining attribute identifications of the protection sections before and after the fault according to positive sequence components of currents at two ends of the protection sections before and after the fault of the active power distribution network;
102. and carrying out differential protection on the protection sections according to the attribute identifications of the protection sections before and after the fault.
Recording data of a period of time before a fault by a protection device, acquiring phase currents or positive sequence components of currents at two ends of a protection section before the fault, carrying out phasor operation on the data before the fault at the two ends by using a kirchhoff current law, comparing the phasors of the data before the fault of the two sections of currents with a setting threshold according to a detection branch criterion, and judging whether a protection section has an undetected branch or not;
fig. 2 is a schematic diagram of an active power distribution network structure of the active power distribution network current differential protection method according to the embodiment of the present invention, and as shown in fig. 2, a protection section is set between a node M and a node N of a feeder line, Load1 is an intra-area Load, DG is an undetected branch, and f is1Point is an intra-area fault, f2Point sum f3The point is an out-of-range fault.
The process of determining the attribute identification of the protection section before and after the fault according to the positive sequence component of the current at two ends of the protection section before the fault of the active power distribution network may include:
if the sum I of positive sequence components of the current at two ends of the protection section before the fault of the active power distribution networkun.mLess than or equal to attribute setting threshold I of undetected branchset.unIf the attribute identification of the protection section before the fault is that no undetected branch exists, otherwise, the attribute identification of the protection section before the fault is that the detected branch exists, wherein the undetected branch attribute setting threshold is set according to the maximum unbalanced current at the two ends of the protection section, and the detection error of TA is mainly detected in the power distribution network.
And identifying internal faults through the action criterion of the self-adaptive current differential protection scheme, comparing the side current of the distributed power supply with the protection starting current, and judging whether to execute a tripping command to isolate the faults.
Specifically, the process of determining the attribute identifications of the protection sections before and after the fault according to the positive sequence component of the current at two ends of the protection section after the fault of the active power distribution network may include:
if the sum of the positive sequence components of the currents at the two ends of the protection section after the active power distribution network fails is not zero, identifying the attribute of the protection section after the failure as an intra-area failure, otherwise, identifying the attribute of the protection section after the failure as an extra-area failure;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preFor the positive sequence component of the end current of the protection section before fault, Iset.unSetting a threshold for the attributes of the undetected branches.
The performing differential protection on the protection zone according to the attribute identifier of the protection zone before and after the fault may include:
fig. 3 is a schematic diagram of a feeder structure without an undetected branch in the active power distribution network current differential protection method according to the embodiment of the present invention, and as shown in fig. 3, no undetected branch exists between protection sections MN, and it can be found from data before a fault that the Load current amplitude on Load1 is about 260A, and then I isset1Has an amplitude of about 312A and a braking coefficient Krel1Taking 0.4;
if the attribute identification of the protection section after the fault is an intra-area fault and the attribute identification of the protection section before the fault is that no branch which is not detected exists, namely the protection section has no branch power supply or load, designing an active power distribution network current differential protection criterion based on a current positive sequence component after the fault, and setting a starting current threshold and a current differential protection braking coefficient, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection, and executes a tripping command to realize remote tripping:
fig. 4 shows a feeder structure diagram with undetected branches in the active power distribution network current differential protection method according to an embodiment of the present invention, where as shown in fig. 4, the protection section is an MN section, the MN section contains undetected load branches, DG is an undetected branch, the protection section has undetected branches, when no voltage signal is introduced, the feeder power fluctuation of the undetected branch is considered, a current differential protection criterion is determined, and a protection scheme is determined by setting a criterion to complete fault isolation; if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists and no voltage signal exists on the undetected branch, designing an active power distribution network current differential protection criterion based on a current positive sequence component after the fault, and setting a starting current threshold and a current differential protection braking coefficient, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection, and executes a trip command to realize remote trip:
introducing a voltage quantity signal to deal with the self-starting process of the motor, and adopting current differential protection locking to prevent current differential protection misoperation by detecting the voltage fluctuation condition during fault; if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the voltage signal exists on the undetected branch, namely the protection section has a large number of motors, the voltage fluctuation is obvious during the fault, the voltage quantity is introduced as a current differential protection locking condition, the maximum fluctuation setting voltage is set, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection, and executes a trip command to realize remote trip:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein, Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)， Krel3＝Krel2∈[0.35,0.45]，ΔIm1For the positive-sequence component of the head-end (M-terminal) current of the protection section after a fault, Δ In1For the positive sequence component of the post-fault protection segment end (N-terminal) current, Iset1For setting the starting current threshold, the maximum unbalanced current of a differential protection area is considered, setting is carried out according to TA detection error, the influence of load (distributed power supply) transfer is considered, the current of an undetected branch feeder line is considered not to be overlarge, setting is carried out according to the condition that the rated capacity of the transferred load is 10% of the rated current of the feeder line, K is carried outmFor pre-fault attribute labels as reliable coefficients corresponding to protection zones where no undetected branch exists, INFor rated current of the feeder, Krel1Considering the TA saturation maximum braking angle and the phase difference of the current positive sequence fault components at two ends of the protection section after the fault, Iset2Considering the power fluctuation of the undetected branch feeder and the condition of the power fluctuation of the undetected branch feeder under normal conditions, Krel2For the braking coefficient corresponding to the protection section with the attribute label before the fault being that the undetected branch exists and the undetected branch does not have the voltage signal, the influence of the TA saturation current outside the area needs to be considered, and the upper division of the undetected branch with the fault outside the area needs to be consideredInfluence of power fluctuations on the stream and undetected branch feeders on the protection, KunFor the reliability factor corresponding to the protection zone with the pre-fault attribute label as the presence of undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3The method is characterized in that a pre-fault attribute label is a starting current threshold corresponding to a protection section with an undetected branch and a voltage signal in the undetected branch, is usually the maximum unbalanced current caused by a detection error of a current Transformer (TA) in the protection section, does not need to consider the influence of load fluctuation, and is set only according to the maximum unbalanced current caused by the detection error of the TA in the protection section, Krel3For the braking coefficient, U, corresponding to the protection zone with the attribute tag of existence of the undetected branch and the voltage signal of the undetected branch before the faultφφIs any two-phase voltage difference in the three-phase voltage, namely any two-phase voltage difference of A, B, C three-phase, UsetAnd setting a voltage setting threshold of the active power distribution network after the fault according to the maximum fluctuation range under the condition of avoiding normal operation.
If the attribute label of the MN in the protection section after the fault is identified as an intra-area fault and the N-side protection cannot be started due to too small current, the tripping of the N-end switch is realized by a tripping command from the M end to the N end through a special logic design, and finally the isolation of the fault is completed.
Compared with the conventional current differential protection technology, the self-adaptive current differential protection provided by the invention is used as one of important protection technologies of an active power distribution network, and has the following advantages: the cost is low, the realization is easy, and the distribution network protection containing DG can be better realized only by additionally arranging a small number of direction elements on the basis of the original protection configuration and adjusting the setting scheme of the original protection; the action speed is fast, and the method can adapt to network change and DG operation mode change to a certain extent. The key to the adaptive protection scheme is to automatically identify the operating conditions of the protected section, i.e., the presence or absence of an undetected branch.
The current differential protection utilizes amplitude and phase information in a protection section, and for an active power distribution network, undetected branches may exist in the protection section, so that the sensitivity of partial conditions is insufficient, and the self-adaptive current differential protection scheme of the active power distribution network is provided by combining the distribution characteristics of current positive sequence fault components at two ends of the protection section of the power distribution network. The self-adaptability of the self-adaptive current differential protection scheme provided by the invention is mainly embodied in that the self-adaptive setting scheme can be selected in combination with the self running condition (whether an undetected branch exists or not and whether the voltage quantity is introduced) of the protection section, and the self-adaptive current differential protection scheme can adapt to the conditions of feeder line structure change, power fluctuation and the like of the protection section of the power distribution network.
Example two:
fig. 5 is a schematic structural diagram of an active power distribution network current differential protection device according to an embodiment of the present invention, and as shown in fig. 5, the device may include:
the determining module is used for determining the attribute identification of the protection sections before and after the fault according to the positive sequence components of the currents at the two ends of the protection sections before and after the fault of the active power distribution network;
and the protection module is used for carrying out differential protection on the protection section according to the attribute identification of the protection section before and after the fault.
Specifically, the determining module may include:
a first determination unit for protecting the sum I of the positive sequence components of the current across the section if the active distribution network failsun.mAttribute setting threshold I less than or equal to undetected branchset.unIf the attribute of the protection section before the fault is marked as that no undetected branch exists, otherwise, the attribute of the protection section before the fault is marked as that the detected branch exists;
the second determining unit is used for identifying the attribute of the protection section as an intra-area fault if the sum of positive sequence components of currents at two ends of the protection section is not zero after the active power distribution network fails, and otherwise, identifying the attribute of the protection section as an extra-area fault;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preFor the positive sequence component of the end current of the protection section before fault, Iset.unSetting a threshold for the attributes of the undetected branches.
The protection module is used for: if the attribute identifier of the protection section after the fault is an intra-area fault and the attribute identifier of the protection section before the fault is that no branch which is not detected exists, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the undetected branch does not have a voltage signal, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and a voltage signal exists on the undetected branch, when a positive sequence component of current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein，Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)， Krel3＝Krel2∈[0.35,0.45]，ΔIm1For the positive-sequence component of the head-end current of the protection section after a fault, Δ In1For protecting the positive-sequence component of the section-end current after a fault, Iset1For a pre-fault attribute label that is a starting current threshold, K, corresponding to a protection zone where no undetected branch existsmFor reliable coefficients corresponding to protection zones for which the pre-fault attribute label is absent of undetected branches, INRated current for the feed line, Krel1For braking coefficients corresponding to protection zones with pre-fault attribute labels absent of undetected branches, Iset2For the pre-fault attribute label, the starting current threshold, K, corresponding to the protection section with the undetected branch and no voltage signal in the undetected branchrel2A braking coefficient, K, corresponding to a protection zone with an attribute label before failure being that an undetected branch exists and no voltage signal exists in the undetected branchunFor the reliability factor corresponding to the protection zone with the pre-fault attribute label as the presence of undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3Starting current threshold, K, corresponding to protection section with attribute label before fault being undetected branch and voltage signal existing in undetected branchrel3A braking coefficient, U, corresponding to a protection zone with an attribute label of existence of an undetected branch and a voltage signal of the undetected branch before a faultφφIs any two-phase voltage difference, U, among three-phase voltagessetAnd setting a threshold for the voltage of the active power distribution network after the fault.
Example three:
the simulation verification result after the scheme is adopted is as follows:
(1) effect of undetected branch load on out-of-range faults
The protection section is an MN section, and the MN areaThe segment contains an undetected load branch, and Table 1 below is used to verify an out-of-range fault (fault occurs at f)2Point sum f3Point), the rated capacity of undetected branch Load1 is adjusted to 3.6MW in accordance with the adaptive current differential protection method operating conditions and the effect of the undetected Load branch on the out-of-range fault.
TABLE 1 simulation data table for undetected load branches
The data in the table 1 can show that when a fault point is generated at the downstream of a protection section, the shunt on the undetected branch load is small, the amplitudes of the current positive sequence fault components at the two ends are basically consistent, the phase difference is approximately equal to 182 degrees, the action current is far less than the brake current, and the protection is reliable and does not act; when a fault occurs upstream of the protection zone, the shunting of undetected branch load current is large, but the protection may still be reliably inactive.
(2) Influence of undetected branch power supply on out-of-range fault
Table 2 below is used to verify an out-of-range fault (fault occurred at f)2Point sum f3Point), the adaptive current differential protection method described above operates and the effect of undetected load branches on an out-of-range fault. And adjusting the DG in the simulation model to the MN protection section, wherein the distance between the access point and the bus is 4 km. If the amplitude of the power supply current is about 117A according to the data before the fault, the protection starting criterion starting current threshold Iset2About 140A, coefficient of braking Krel2Take 0.4.
TABLE 2 simulation data table for undetected power branches
The data in table 2 can be used to draw a conclusion similar to the corresponding result in table 1, the undetected branch power supply has no influence on the action reliability of the out-of-area fault protection, and the protection is reliable and does not act.
(3) Impact of normal load switching on protection
The protection segment is an MN segment, and the MN segment includes an undetected power branch. Table 3 is used to verify the behavior of the adaptive current differential protection scheme during normal load switching and motor self-starting. The rated current of the switching load in the section is considered according to 10% of the rated current of the feeder line, the rated current is assumed to be 60A, and the starting current threshold of the protection starting criterion is 72A. The simulation data for load switching is shown in table 3.
Table 3 load switching simulation data table
As can be seen from the data in table 3, the load switching process is identified as an intra-area fault by using the action criterion of the adaptive current differential protection scheme, but for the RL load, the phasor sum of the positive sequence fault components of the currents at the two ends is less than the starting current threshold, so that the protection is reliable and cannot be started; for the self-starting process of the motor, the protection starting criterion can be effectively started, the assistance of a voltage signal is needed, and otherwise, the misoperation can be caused.
In summary, the adaptive current differential protection scheme can be combined with the operation conditions (whether there is an undetected branch or not, and whether there is introduction of a voltage amount) of the protection section itself to adaptively select a reasonable setting scheme, and can adapt to the conditions of feeder line structure change, power fluctuation and the like of the protection section of the power distribution network.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (7)
1. A current differential protection method for an active power distribution network is characterized by comprising the following steps:
determining attribute identifications of the protection sections before and after the fault according to positive sequence components of currents at two ends of the protection sections before and after the fault of the active power distribution network;
and carrying out differential protection on the protection sections according to the attribute identifications of the protection sections before and after the fault.
2. The method of claim 1, wherein determining the identity of the attributes of the protection segment before and after the fault based on the positive sequence component of the current across the protection segment before the fault in the active power distribution network comprises:
if the sum I of positive sequence components of the current at two ends of the protection section before the fault of the active power distribution networkun.mLess than or equal to undetected branch attribute setting threshold Iset.unIf not, the attribute of the protection section is identified as the existence of the detection branch.
3. The method of claim 1, wherein determining the identity of the attributes of the protection segment before and after the fault based on the positive sequence component of the current across the protection segment after the fault in the active power distribution network comprises:
if the sum of the positive sequence components of the currents at the two ends of the protection section after the active power distribution network fails is not zero, identifying the attribute of the protection section after the failure as an intra-area failure, otherwise, identifying the attribute of the protection section after the failure as an extra-area failure;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preFor the positive sequence component of the end current of the protection section before fault, Iset.unSetting a threshold for the attributes of the undetected branches.
4. The method of claim 1, wherein said differentially protecting the protection segments based on the identification of the attributes of the protection segments before and after the fault comprises:
if the attribute identification of the protection section after the fault is the in-zone fault and the attribute identification of the protection section before the fault is that no branch which is not detected exists, when the positive sequence component of the current at the two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the undetected branch does not have a voltage signal, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and a voltage signal exists on the undetected branch, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein, Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)，Krel3＝Krel2∈[0.35,0.45]，ΔIm1For the positive-sequence component of the head-end current of the protection section after a fault, Δ In1For protecting the positive-sequence component of the section-end current after a fault, Iset1For the pre-fault attribute label being the starting current threshold, K, corresponding to the protection zone without the undetected branchmFor reliable coefficients corresponding to protection zones for which the pre-fault attribute label is absent of undetected branches, INFor rated current of the feeder, Krel1For braking coefficients corresponding to protection zones with pre-fault attribute labels absent of undetected branches, Iset2A starting current threshold, K, corresponding to a protection section with an attribute label before a fault being that an undetected branch exists and no voltage signal exists in the undetected branchrel2Tagging attributes before failureBraking coefficients corresponding to protection zones in which no branch is detected and no voltage signal is present in the branch, KunFor the reliability factor corresponding to the protection zone with the pre-fault attribute label as the presence of undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3Starting current threshold, K, corresponding to protection section with attribute label before fault being undetected branch and voltage signal existing in undetected branchrel3A braking coefficient, U, corresponding to a protection zone with an attribute label of existence of an undetected branch and a voltage signal of the undetected branch before a faultφφIs any two-phase voltage difference, U, in three-phase voltagesetAnd setting a threshold for the voltage of the active power distribution network after the fault.
5. An active power distribution network current differential protection device, the device comprising:
the determining module is used for determining the attribute identification of the protection section before and after the fault according to the positive sequence component of the current at the two ends of the protection section before and after the fault of the active power distribution network;
and the protection module is used for carrying out differential protection on the protection section according to the attribute identification of the protection section before and after the fault.
6. The apparatus of claim 5, wherein the determining module comprises:
a first determination unit for protecting the sum I of the positive sequence components of the current across the section if the active distribution network failsun.mLess than or equal to undetected branch attribute setting threshold Iset.unIf the attribute of the protection section before the fault is marked as that no undetected branch exists, otherwise, the attribute of the protection section before the fault is marked as that the detected branch exists;
the second determining unit is used for identifying the attribute of the protection section as an intra-area fault if the sum of positive sequence components of currents at two ends of the protection section is not zero after the active power distribution network fails, and otherwise, identifying the attribute of the protection section as an extra-area fault;
wherein, Iun.m＝|Im.pre+In.pre|，Im.preFor positive sequence components of head-end currents of protection sections before faults, In.preFor the positive sequence component of the end current of the protection section before fault, Iset.unSetting a threshold for the attributes of the undetected branches.
7. The apparatus of claim 5, wherein the protection module is to:
if the attribute identification of the protection section after the fault is the in-zone fault and the attribute identification of the protection section before the fault is that no branch which is not detected exists, when the positive sequence component of the current at the two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and the undetected branch does not have a voltage signal, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute identification of the protection section after the fault is an intra-area fault, the attribute identification of the protection section before the fault is that an undetected branch exists, and a voltage signal exists on the undetected branch, when the positive sequence component of the current at two ends of the protection section after the fault meets the following formula, the protection section performs differential protection:
if the attribute mark of the protection section before the fault is an out-of-area fault, the protection section does not carry out differential protection;
wherein, Iset1＝0.1KmIN，Krel1∈[0.275,0.45]，Iset2＝max(KunIun.m,0.1KmIN)，Krel3＝Krel2∈[0.35,0.45]，ΔIm1For the positive-sequence component of the head-end current of the protection section after a fault, Δ In1For protecting the positive-sequence component of the section-end current after a fault, Iset1For the pre-fault attribute label being the starting current threshold, K, corresponding to the protection zone without the undetected branchmFor reliable coefficients corresponding to protection zones for which the pre-fault attribute label is absent of undetected branches, INFor rated current of the feeder, Krel1For braking coefficients corresponding to protection zones with pre-fault attribute labels absent of undetected branches, Iset2A starting current threshold, K, corresponding to a protection section with an attribute label before a fault being that an undetected branch exists and no voltage signal exists in the undetected branchrel2A braking coefficient, K, corresponding to a protection zone with an attribute label before failure being that an undetected branch exists and no voltage signal exists in the undetected branchunFor the reliability factor corresponding to the protection zone with the pre-fault attribute label as the presence of undetected branches, Iun.mIs the sum of the positive sequence components of the current across the protection section before fault, Iset3Starting current threshold, K, corresponding to protection section with attribute label before fault being undetected branch and voltage signal existing in undetected branchrel3A braking coefficient, U, corresponding to a protection zone with an attribute label of existence of an undetected branch and a voltage signal of the undetected branch before a faultφφIs any two-phase voltage difference, U, in three-phase voltagesetAnd setting a threshold for the voltage of the active power distribution network after the fault.
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| CN112531657A (en) * | 2020-12-04 | 2021-03-19 | 东莞理工学院 | Braking coefficient self-adaptive distribution network differential protection method based on transient direction |
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| CN113708352A (en) * | 2021-08-23 | 2021-11-26 | 广东电网有限责任公司 | Relay protection method and device |
| CN114221307A (en) * | 2021-12-09 | 2022-03-22 | 南京南瑞继保电气有限公司 | Line differential protection braking coefficient adjusting method and device and electronic equipment |
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