CN110535104B - Direct-current line rapid protection method and system - Google Patents
Direct-current line rapid protection method and system Download PDFInfo
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- CN110535104B CN110535104B CN201910666471.9A CN201910666471A CN110535104B CN 110535104 B CN110535104 B CN 110535104B CN 201910666471 A CN201910666471 A CN 201910666471A CN 110535104 B CN110535104 B CN 110535104B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0092—Details of emergency protective circuit arrangements concerning the data processing means, e.g. expert systems, neural networks
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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
- H02H7/268—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 for dc systems
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Abstract
The invention discloses a method and a system for quickly protecting a direct current line, wherein the method comprises the following steps: starting high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired direct-current voltage meets a preset high-sensitivity protection starting criterion; if the current direct-current voltage meets a preset abnormal majority locking criterion, locking protection is carried out; and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the preset fault criterion, protecting an action outlet. After the high-sensitivity protection is started, if the bipolar fault sub criterion is met, the bipolar protection directly acts without the fault pole selection sub criterion; if the fault pole selection sub criterion is met, after the fault pole is determined, the fault pole is protected; if the abnormal large number is judged, directly locking and protecting; the invention can quickly and reliably identify the faults inside and outside the area, has higher sensitivity to the high-resistance grounding fault, is suitable for LCC and VSC systems, and meets various requirements.
Description
Technical Field
The invention relates to the technical field of relay protection, in particular to a method and a system for rapidly protecting a direct-current line.
Background
The protection equipped in the current direct current transmission engineering mainly takes traveling wave protection and under-voltage differential protection as main protection, takes current differential protection as backup protection, and part of the engineering is also equipped with low-voltage protection.
In the aspects of traveling wave protection and under-voltage differential protection, the ABB traveling wave protection criterion can protect the whole length of a line, but the anti-interference capability and the transition resistance tolerance capability are weaker. The SIEMENS improves the anti-interference capability of the criterion in an integral mode, but the action time delay is longer than that of ABB traveling wave protection. Under-voltage differential protection takes voltage differential and under-voltage criteria as main criteria, and takes current variation and current break criterion as assistance to remove back-side faults, and generally the under-voltage differential protection is used as main protection of a direct current circuit and backup protection of traveling wave protection. According to the traveling wave protection principle based on polar waves adopted by ABB and SIEMENS, reverse traveling waves in voltage traveling waves are extracted through the polar waves, fault judgment is carried out through modes such as differential and the like, and under-voltage differential protection directly carries out fault judgment according to the voltage change rate, so that the problems of low action speed and low sensitivity exist in the current engineering application.
Disclosure of Invention
The invention provides a method and a system for rapidly protecting a direct current line, which aim to solve the problem of how to identify faults inside and outside a region with high sensitivity so as to protect the region.
In order to solve the above problem, according to an aspect of the present invention, there is provided a method for fast protection of a dc line, the method including:
when the dual-tree complex wavelet transform decomposition amount corresponding to the obtained direct-current voltage meets a preset high-sensitivity protection starting criterion, starting high-sensitivity protection;
if the current direct-current voltage meets a preset abnormal majority locking criterion, locking protection is carried out;
and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the preset fault criterion, protecting an action outlet.
Preferably, the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is straightThe decomposition amount of the dual-tree complex wavelet transform corresponding to the current voltage U; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold.
Preferably, the preset abnormal majority locking criterion comprises:
when using voltage comparison method, if U > lambda2If true; or
When the voltage difference integral method is adopted, if ^ f' (n) > λ ^ f3If yes, determining the number is an abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda [ alpha ]3A second preset lockout threshold; f' (n) is a difference value of the dc voltage.
Preferably, the preset fault criteria include: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criterion is: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If yes, determining that the cathode is in fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If yes, determining that the positive electrode is in fault;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
Preferably, the protecting the action exit if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current dc voltage meets a preset fault criterion includes:
if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported;
and if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the fault pole selection sub criterion, the fault pole protection action is exported.
According to another aspect of the present invention, there is provided a dc line fast protection system, the system comprising:
the high-sensitivity protection starting unit is used for starting high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired direct-current voltage meets the preset high-sensitivity protection starting criterion;
the locking protection unit is used for locking protection if the current direct-current voltage meets a preset abnormal majority locking criterion;
and the protection action outlet unit is used for protecting an action outlet if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets a preset fault criterion.
Preferably, the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is the decomposition quantity of the dual-tree complex wavelet transform corresponding to the direct-current voltage U; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold.
Preferably, the preset abnormal majority locking criterion comprises:
when using voltage comparison method, if U > lambda2If true; or
When a voltage differential integral system is used, if ^ f' (n) > λ3If yes, determining the number is an abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda [ alpha ]3A second preset lockout threshold; f' (n) is a difference value of the dc voltage.
Preferably, the preset fault criteria include: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criterion is: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If yes, determining that the cathode is in fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If yes, determining that the positive electrode is in fault;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
Preferably, the protection action exit unit, if the dual-tree complex wavelet transform decomposition amount corresponding to the current dc voltage meets a preset fault criterion, protects the action exit, and includes:
if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported;
and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the fault pole selection sub-criterion, the fault pole is protected to act as an outlet.
The invention provides a method and a system for rapidly protecting a direct current line, which comprise the following steps: starting high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired direct-current voltage meets a preset high-sensitivity protection starting criterion; if the current direct-current voltage meets a preset abnormal majority locking criterion, locking protection is carried out; and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the preset fault criterion, protecting an action outlet. After the high-sensitivity protection is started, if the bipolar fault sub criterion is met, the bipolar protection directly acts without the fault pole selection sub criterion; if the fault pole selection sub criterion is met, after the fault pole is determined, the fault pole is protected; if the abnormal large number is judged, directly locking and protecting; the invention can quickly and reliably identify the faults inside and outside the area, has higher sensitivity to the high-resistance grounding fault, is suitable for LCC and VSC systems, and meets various requirements.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a flow chart of a method 100 for fast protection of a dc link according to an embodiment of the present invention;
FIG. 2 is a diagram of protection logic according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a window-shifting method according to an embodiment of the present invention; and
fig. 4 is a schematic structural diagram of a dc line fast protection system 400 according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including 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. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Fig. 1 is a flowchart of a dc line fast protection method 100 according to an embodiment of the present invention. As shown in fig. 1, after the high-sensitivity protection is started, if the bipolar fault sub-criterion is satisfied, the bipolar protection directly acts without passing through the fault pole-selecting sub-criterion; if the fault pole selection sub criterion is met, after the fault pole is determined, the fault pole is protected; if the abnormal large number is judged, directly locking and protecting; the invention can quickly and reliably identify the faults inside and outside the area, has higher sensitivity to the high-resistance grounding fault, is suitable for LCC and VSC systems, and meets various requirements. The method 100 for fast protecting a dc line provided by the embodiment of the present invention starts from step 101, and starts high sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired dc voltage meets a preset high sensitivity protection start criterion in step 101.
Preferably, the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is the decomposition quantity of the dual-tree complex wavelet transform corresponding to the direct-current voltage U; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold.
In step 102, if the current dc voltage meets a predetermined abnormal majority blocking criterion, blocking protection.
Preferably, the preset abnormal majority locking criterion comprises:
when using voltage comparison method, if U > lambda2If true; or
When the voltage difference integral method is adopted, if ^ f' (n) > λ ^ f3If yes, determining the number is an abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda [ alpha ]3A second preset lockout threshold; f' (n) is a difference value of the dc voltage.
In step 103, if the dual-tree complex wavelet transform decomposition amount corresponding to the current dc voltage meets a preset fault criterion, the action exit is protected.
Preferably, the preset fault criteria include: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criterion is: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If yes, determining that the cathode is in fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If true, it is determined as positiveA barrier;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
Preferably, the protecting the action exit if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current dc voltage meets a preset fault criterion includes:
if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported;
and if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the fault pole selection sub criterion, the fault pole protection action is exported.
Fig. 2 is a diagram of protection logic according to an embodiment of the present invention. As shown in fig. 2, in the embodiment of the present invention, the fault pole selector criterion includes: monopole pole selection criterion and monopole criterion; the bipolar fault sub criterion and the fault pole selection sub criterion are in an OR relationship, and when protection is carried out, after high-sensitivity protection is started, if the bipolar fault sub criterion is met, the bipolar protection directly acts without passing through the fault pole selection sub criterion; if the fault pole selection sub criterion is met, after the fault pole is determined, the fault pole is protected; and if the abnormal majority of locking criteria are met, directly locking protection.
In the embodiment of the invention, the direct current rapid protection method is completed based on dual-tree complex wavelet transform. When all sampling points are decomposed based on dual-tree complex wavelet transform, the frequency is reduced to one half of the original frequency by one layer of decomposition, the frequency is reduced to one fourth of the original frequency by two layers of decomposition, and the like. In order to apply the dual-tree complex wavelet transform to protection, the requirement of point-by-point sampling calculation of protection needs to be satisfied, and a window-shifting algorithm suitable for the dual-tree complex wavelet transform is studied, as shown in fig. 3.
When the discrete signal and the wavelet basis are subjected to convolution operation, the effective boundary data often cannot be subjected to effective operation due to the fact that the effective boundary data is not as long as the wavelet basis, and the effective lengths of the high-frequency component and the low-frequency component after transformation are correspondingly changed due to the fact that the wavelet basis lengths are different. In the embodiment of the invention, the base length of the wavelet is 19 points, and the length of the data window is 20 points in order to effectively reflect the fault characteristics. The 20 sampling points are taken as 1 window, and the calculation is carried out by moving one sampling interval each time, then the integration interval is an area formed by the current point and the previous 19 points, and since the 20 sampling data can obtain 5 data after being subjected to two-layer decomposition and frequency reduction twice, a data column of 5x1 can be calculated for the protection criterion by moving the data window once.
When high-sensitivity protection starting criterion judgment is carried out, WSU is the two-layer decomposition quantity of the dual-tree complex wavelet transform of the DC voltage, lambda1For a starting value, the single pole outside the area can be sensitively started and set through 1 sampling point of 300 omega transition resistance ground fault.
When the abnormal majority locking criterion is judged, if a voltage comparison method is adopted, after protection is started, the abnormal majority locking criterion logic is entered, and if the condition that U is more than lambda is met2Then locked-out protection, λ2The action is fixed. For example, the terminal in the region is set through the reliable action of 500 Ω transition resistance protection, the reliability coefficient is selected to be 1.2, and when the voltage is lower than 300kV, a fault is considered to occur, and the judgment of fault criterion logic is carried out. Otherwise, after the protection is started, if the voltage is higher than 300kV, the data is considered to be abnormal data, and the protection is locked.
When the abnormal large number locking criterion is judged, if a voltage differential integration method is adopted, after protection is started, voltage is firstly differentiated and then integrated, the difference calculation formula is f ' (n) ═ f (n) — f (n-1), and if the integral value satisfies ^ f ' (n) > lambda in 0.6ms, ^ f ' (n) > lambda3Judging the data to be abnormal data; otherwise, the fault is determined, wherein lambda is set3Is-150. The method can prevent abnormal large numbers of continuous 4 points in 0.6 ms.
When fault criterion judgment is carried out, two-layer decomposition is carried out on the voltage difference value after protection starting, and if the two-layer decomposition meets the requirement of WSU＞λ5Judging the fault as a bipolar fault; if it satisfiesλ5＞WSU＞λ4And Δ Ucom＞λ6If the positive voltage and the negative voltage are simultaneously established, determining that the negative electrode is in fault; if λ is satisfied5＞WSU＞λ4And Δ Ucom＜λ7And if the positive pole fault is established, the positive pole fault is determined. Wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a). Lambda [ alpha ]4And setting the action constant value according to reliably avoiding the out-of-area fault.
Fig. 4 is a schematic structural diagram of a dc line fast protection system 400 according to an embodiment of the present invention. As shown in fig. 4, the embodiment of the present invention provides a dc line fast protection system 400, which includes: a high-sensitivity protection starting unit 401, a lockout protection unit 402 and a protection action exit unit 403.
Preferably, the high-sensitivity protection starting unit 401 is configured to start the high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired dc voltage meets a preset high-sensitivity protection starting criterion.
Preferably, the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is the decomposition quantity of the dual-tree complex wavelet transform corresponding to the direct-current voltage U; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold.
Preferably, the latch-up protection unit 402 is configured to latch-up protection if the current dc voltage meets a preset abnormal majority latch-up criterion.
Preferably, the preset exceptional majority locking criterion comprises:
when using voltage comparison method, if U > lambda2If true; or
When a voltage differential integration system is employed, if ^ f' (n) > λ3If true, then it is confirmedDetermining the abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda [ alpha ]3A second preset lockout threshold; f' (n) is a difference value of the dc voltage.
Preferably, the protection action exit unit 403 is configured to protect an action exit if the dual-tree complex wavelet transform decomposition amount corresponding to the current dc voltage meets a preset fault criterion.
Preferably, the preset fault criteria include: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criteria are: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If yes, determining that the cathode is in fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If yes, determining that the positive electrode is in fault;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
Preferably, the protection action exit unit 403, if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current dc voltage meets a preset fault criterion, performs a protection action exit, including: if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported; and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the fault pole selection sub-criterion, the fault pole is protected to act as an outlet.
The dc line fast protection system 400 according to the embodiment of the present invention corresponds to the dc line fast protection method 100 according to another embodiment of the present invention, and is not described herein again.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
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 (4)
1. A fast protection method for a direct current line is characterized by comprising the following steps:
starting high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired direct-current voltage meets a preset high-sensitivity protection starting criterion;
if the current direct-current voltage meets a preset abnormal majority locking criterion, locking protection is carried out;
if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets a preset fault criterion, protecting an action outlet;
wherein the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is the double tree corresponding to the direct voltage UA complex wavelet transform decomposition amount; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold;
the preset abnormal majority locking criterion comprises the following steps:
when using voltage comparison method, if U > lambda2If true; or
When the voltage difference integral method is adopted, if ^ f' (n) > λ ^ f3If yes, determining the number is an abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda [ alpha ]3A second preset lockout threshold; f' (n) is a difference value of the direct-current voltage;
the preset fault criteria comprise: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criterion is: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If yes, determining that the cathode is in fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If yes, determining that the positive electrode is in fault;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
2. The method according to claim 1, wherein if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current dc voltage meets a preset fault criterion, protecting the action exit comprises:
if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported;
and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the fault pole selection sub-criterion, the fault pole is protected to act as an outlet.
3. A dc link fast protection system, the system comprising:
the high-sensitivity protection starting unit is used for starting high-sensitivity protection when the decomposition amount of the dual-tree complex wavelet transform corresponding to the acquired direct-current voltage meets the preset high-sensitivity protection starting criterion;
the locking protection unit is used for locking protection if the current direct-current voltage meets a preset abnormal majority locking criterion;
the protection action outlet unit is used for protecting an action outlet if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets a preset fault criterion;
wherein the preset high-sensitivity protection starting criterion is as follows:
if WSU＞λ1If yes, starting high-sensitivity protection;
wherein, WSU is the decomposition quantity of the dual-tree complex wavelet transform corresponding to the direct-current voltage U; s is a scale function; lambda [ alpha ]1Is a preset sensitivity threshold;
the preset abnormal majority locking criterion comprises the following steps:
when using voltage comparison method, if U > lambda2If true; or
When a voltage differential integration system is employed, if ^ f' (n) > λ3If yes, determining the number is an abnormal large number, and locking and protecting;
wherein λ is2A first preset lockout threshold; lambda3A second preset lockout threshold; f' (n) is a difference value of the direct-current voltage;
the preset fault criteria comprise: bipolar fault sub-criteria and fault-select sub-criteria,
the bipolar fault sub-criterion is: if WSU＞λ5If yes, determining the double-pole fault;
the fault pole selection sub-criterion is as follows: if λ5＞WSU＞λ4And Δ Ucom＞λ6If true, then determine as negativeAn extreme fault; if λ5＞WSU＞λ4And Δ Ucom＜λ7If yes, determining that the positive pole is in fault;
wherein λ is4A first preset fault threshold value; lambda [ alpha ]5A second preset fault threshold; lambda [ alpha ]6Is a preset negative fault threshold; lambda [ alpha ]7Is a preset positive fault threshold; delta UcomCommon mode quantity U being a direct voltage UcomThe difference operation value of (a).
4. The system according to claim 3, wherein the protection action exit unit, if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current dc voltage meets a preset fault criterion, protects the action exit, and includes:
if the dual-tree complex wavelet transform decomposition amount corresponding to the current direct-current voltage meets the bipolar fault sub criterion, the bipolar protection action is exported;
and if the decomposition amount of the dual-tree complex wavelet transform corresponding to the current direct-current voltage meets the fault pole selection sub-criterion, the fault pole is protected to act as an outlet.
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| WO2018094862A1 (en) * | 2016-11-25 | 2018-05-31 | 许继集团有限公司 | Method for identifying single pole ground fault in vsc-dc power distribution network, and single pole ground fault protection method for vsc-dc power distribution network |
| CN109038515A (en) * | 2018-07-09 | 2018-12-18 | 中国电力科学研究院有限公司 | A kind of Hybrid HVDC route traveling-wave protection method and system based on Dual Tree Complex Wavelet variation |
| CN109119977A (en) * | 2018-09-20 | 2019-01-01 | 山东大学 | Multiterminal flexible direct current power grid DC line fast protection method and system based on single ended voltage |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018094862A1 (en) * | 2016-11-25 | 2018-05-31 | 许继集团有限公司 | Method for identifying single pole ground fault in vsc-dc power distribution network, and single pole ground fault protection method for vsc-dc power distribution network |
| CN109038515A (en) * | 2018-07-09 | 2018-12-18 | 中国电力科学研究院有限公司 | A kind of Hybrid HVDC route traveling-wave protection method and system based on Dual Tree Complex Wavelet variation |
| CN109119977A (en) * | 2018-09-20 | 2019-01-01 | 山东大学 | Multiterminal flexible direct current power grid DC line fast protection method and system based on single ended voltage |
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