CN114256813B - CT broken line quick locking method and system based on brake current and zero sequence current - Google Patents
CT broken line quick locking method and system based on brake current and zero sequence current 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
- H02H7/22—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 for distribution gear, e.g. bus-bar systems; for switching devices
- H02H7/226—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 for distribution gear, e.g. bus-bar systems; for switching devices for wires or cables, e.g. heating wires
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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
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/262—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 involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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Abstract
The invention discloses a CT broken line quick locking method and system based on brake current and zero sequence current in the technical field of bus differential protection. The method comprises the following steps: according to the current sampling value of each branch of the bus; outputting a first comparison result by comparing the magnitude of the large differential braking current value and the floating threshold value; comparing the sum of K times of the maximum value of the zero sequence mutation values of each branch of the bus and the absolute value of the zero sequence mutation value of each branch, and outputting a second comparison result; judging that the single-phase CT disconnection of the bus occurs according to a preset criterion, and locking the differential protection of the other bus; the problem of misoperation locking of bus differential protection when the conditions of single-phase high-resistance faults in the area, metallic faults outside the bus area, homonymous phase high-resistance faults in the back transfer bus area and the like occur in the brake current CT disconnection criterion under the condition of partial heavy load is solved; meanwhile, the problem of misoperation-locking bus differential protection under the conditions of loop shunt, unbalanced three-phase impedance and the like of zero-sequence current CT disconnection criterion in a three-half wiring mode is solved.
Description
Technical Field
The invention belongs to the technical field of bus differential protection, and particularly relates to a CT broken line quick locking method and system based on braking current and zero sequence current.
Background
The bus differential protection is finished by means of a Current Transformer (CT) and a secondary circuit thereof, and if the secondary circuit is abnormal to cause disconnection of the current transformer, differential current can be generated in bus protection, and bus protection misoperation is extremely easy to occur. The bus false tripping will cause the total station power failure, seriously threatening the stability of the power system.
Both CT disconnection and in-zone faults generate differential flows, and protection must judge whether the CT disconnection or in-zone faults exist in a short time. The influence of the conditions of single-phase high-resistance faults in an occurrence area and metallic faults outside a bus area firstly under the heavy load condition, homonymous phase high-resistance faults in a back-transfer bus area and the like on the CT wire breaking criterion based on the brake current is not fully considered by the current CT wire breaking criterion based on the brake current and the zero sequence current; and the influence of primary system loop shunt, three-phase impedance imbalance and the like under the three-half wiring mode on CT disconnection criteria for comparing the difference current with the zero sequence current of the branch.
Under the conditions of partial heavy load, single-phase high-resistance faults in the generation area and metallic faults outside the busbar area firstly occur, and then the same-name phase high-resistance faults in the busbar area are converted, and the busbar braking current is reduced, so that the criterion for judging CT disconnection by means of the rising of the braking current is invalid.
For bus protection of three-half wiring, due to primary system loop shunt and three-phase impedance imbalance, steady-state zero-sequence current with a certain level exists in normal operation, so that a CT wire breakage criterion by comparing a bus difference value with zero-sequence steady-state current values of all branches can fail.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a CT broken line quick locking method and a CT broken line quick locking system based on brake current and zero sequence current, which solve the technical problem of bus differential protection misoperation under partial heavy load and three-half wiring mode.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
in a first aspect, a method for fast locking a CT disconnection is provided, including: acquiring a current sampling value of each branch of a bus; calculating a large difference braking current value according to the current sampling value of each branch of the bus; calculating a floating threshold value; comparing the current large difference braking current value with a floating threshold value, and outputting a first comparison result; acquiring zero sequence mutation values of all branches except the contact branch; outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value; calculating the sum of absolute values of zero sequence mutation values of all branches of the bus except the contact branch as a second calculated value; comparing the second calculated value with the first calculated value which is K times, and outputting a second comparison result; and taking the first comparison result and the second comparison result as input of a preset criterion, judging that the bus single-phase CT disconnection occurs when the preset criterion is met, and locking the differential protection of the same bus.
Further, the preset criteria are specifically: if the first comparison result satisfies: the large difference braking current value is smaller than the floating threshold value; meanwhile, the second comparison result satisfies: the second calculated value is smaller than the first calculated value which is K times, and meanwhile, the busbar differential protection multiphase starting is not met; meanwhile, the busbar large difference current multiphase exceeds the CT broken line locking fixed value; meanwhile, only a certain phase difference flow is larger than a CT broken line locking fixed value; judging that the CT is broken, and locking the differential protection of the bus; otherwise, the differential protection of the same bus is opened.
Further, the value range of K is as follows: k is more than 1 and less than 2.
Further, the large differential flow is the sum of vectors of currents of all branches on the bus.
Further, the calculating the floating threshold value specifically includes: if the current interruption large difference braking current value is larger than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value plus A times the large difference braking current value and the previous interruption floating threshold value; if the current interruption large difference braking current value is smaller than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value minus B times and the previous interruption floating threshold value.
Further, the value range of A satisfies the following conditions: a is more than 0 and less than 0.3.
Further, the value range of B satisfies the following conditions: b is more than 0.1 and less than 1.
In a second aspect, a CT disconnection quick lock-up system is provided, comprising: the first data acquisition module is used for acquiring current sampling values of all branches of the bus; the first data processing module is used for calculating a large difference braking current value according to the current sampling value of each branch of the bus; the second data processing module is used for calculating a floating threshold value; the first comparison module is used for comparing the current large-difference braking current value with a floating threshold value and outputting a first comparison result; the second data acquisition module is used for acquiring zero sequence mutation values of all the branches of the bus except the contact branch; the third data processing module is used for outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value; the fourth data processing module is used for calculating the sum of absolute values of zero sequence mutation values of all the branches of the bus except the contact branch as a second calculated value; the second comparison module is used for comparing the second calculated value with the first calculated value which is K times and outputting a second comparison result; and the judging module is used for taking the first comparison result and the second comparison result as the input of a preset criterion, judging that the single-phase CT disconnection of the bus occurs when the preset criterion is met, and locking the differential protection of the same bus.
Compared with the prior art, the invention has the beneficial effects that: the method comprises the steps of acquiring a large difference braking current value and calculating a floating threshold value by acquiring the current value of each branch of a bus; acquiring the zero sequence mutation values of all the branches of the bus except the connecting branch, acquiring the maximum value and the sum of the absolute values of the maximum value, judging that the single-phase CT disconnection of the bus occurs according to a preset criterion, and locking the differential protection of the same bus; the problem of misoperation locking of bus differential protection when the conditions of single-phase high-resistance faults in the area, metallic faults outside the bus area, homonymous phase high-resistance faults in the back transfer bus area and the like occur in the brake current CT disconnection criterion under the condition of partial heavy load is solved; meanwhile, the problem of misoperation-locking bus differential protection under the conditions of loop shunt, unbalanced three-phase impedance and the like of zero-sequence current CT disconnection criterion in a three-half wiring mode is solved.
Drawings
Fig. 1 is a schematic diagram of a single-phase CT disconnection bus protection quick locking criterion of a CT disconnection quick locking method based on a braking current and a zero sequence current according to an embodiment of the present invention, where (a) is an a-phase single-phase CT disconnection bus protection quick locking criterion, (B) is a B-phase single-phase CT disconnection bus protection quick locking criterion, and (C) is a C-phase single-phase CT disconnection bus protection quick locking criterion.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
Embodiment one:
a CT broken line quick locking method based on brake current and zero sequence current comprises the following steps: acquiring a current sampling value of each branch of a bus; calculating a large difference braking current value according to the current sampling value of each branch of the bus; calculating a floating threshold value; comparing the current large difference braking current value with a floating threshold value, and outputting a first comparison result; acquiring zero sequence mutation values of all branches except the contact branch; outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value; calculating the sum of absolute values of zero sequence mutation values of all branches of the bus except the contact branch as a second calculated value; comparing the second calculated value with the first calculated value which is K times, and outputting a second comparison result; and taking the first comparison result and the second comparison result as input of a preset criterion, judging that the bus single-phase CT disconnection occurs when the preset criterion is met, and locking the differential protection of the same bus.
The specific steps of this embodiment are as follows:
1) Alternating current sampling: obtaining a current sampling value of each branch of a bus;
2) Calculating a large difference braking current: the sum of the absolute values of the currents of all the branches on the bus;
3) Calculating a current floating threshold value:
if the current interruption large difference braking current value is larger than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value multiplied by A and the previous interruption floating threshold value, and the value range of A meets the following conditions: a is more than 0 and less than 0.3; if the current interruption large difference braking current value is smaller than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value minus B times and the previous interruption floating threshold value, and the value range of B meets the following conditions: b is more than 0.1 and less than 1;
4) Comparing the currently interrupted large difference braking current value with a floating threshold value, and outputting a first comparison result;
5) Acquiring zero sequence mutation values of all branches (except the contact branch) of the bus; each branch circuit generates the amplitude difference between the current cycle and the previous cycle of the zero sequence current;
6) Finding the maximum value of zero sequence mutation values in each branch of the bus, and outputting the maximum value as a first calculated value;
7) Calculating the sum of absolute values of zero sequence mutation values of all branches (except the contact branch) of the bus as a second calculated value;
8) Comparing the second calculated value with the first calculated value which is K times, namely comparing the sum of absolute values of zero sequence mutation values of all branches (except a contact branch) of the bus with the magnitude of the two values which are K times of the maximum value of the zero sequence mutation values in all branches (except the contact branch) of the bus, wherein the value range of K is as follows: k is more than 1 and less than 2; outputting a second comparison result;
9) Calculating a large difference flow: vector sum of the currents of all branches on the bus;
10 The first comparison result and the second comparison result are used as the input of a preset criterion, and when the preset criterion is met, the single-phase CT disconnection of the bus is judged to occur, and the differential protection of the same bus is locked, as shown in fig. 1, the preset criterion is specifically:
if the first comparison result satisfies: the large difference braking current value is smaller than the floating threshold value; at the same time, the method comprises the steps of,
the second comparison result satisfies: the second calculated value is smaller than the first calculated value by a factor K, and at the same time,
the busbar differential protection multiphase start is not satisfied; at the same time, the method comprises the steps of,
the busbar large difference current is not satisfied, and the phases exceed CT broken line locking fixed values; at the same time, the method comprises the steps of,
only a certain phase difference flow is larger than a CT broken line locking fixed value;
judging that the CT is broken, and locking the differential protection of the bus; otherwise, the differential protection of the same bus is opened.
The present embodiment employs a brake current floating threshold, and the brake current at the present moment is no longer compared to the brake current at the previous moment, but rather to the floating threshold. When the braking current decreases, the floating threshold rapidly follows the decrease in braking current, and when the braking current increases, the floating threshold slowly follows the increase in braking current.
For the condition of the external large fault to the internal small fault, when the external large fault is converted into the internal small fault, the braking current is increased, the floating threshold is raised along with the external fault, but the raising speed is very slow, when the external large fault is converted into the internal small fault, the braking is reduced, the floating threshold is almost the same as the magnitude of the previous change, and at the moment, the braking current after the internal fault is compared with the floating threshold can be judged to be reduced.
When the single-phase CT of the bus single branch circuit is disconnected, the branch circuit current and the large-difference braking current necessarily contain zero sequence components, and the zero sequence component change of the braking current is completely concentrated in the disconnected branch circuit. When an asymmetric fault occurs in the bus area, the change of the zero sequence component is distributed on each branch of the bus except the condition of the fault in the no-load bus area of the single power supply, and the zero sequence component cannot be concentrated on one branch. Based on the principle, the bus single-phase CT disconnection and the faults in the area can be distinguished.
The criteria must use zero sequence current variation rather than zero sequence steady state. This is because for three-half wiring bus protection, there is a level of steady state zero sequence current during normal operation due to primary system loop splitting and three-phase impedance imbalance. The use of zero sequence delta current eliminates the interference of this factor.
The CT line breaking criterion and the zero sequence current distribution criterion based on the brake current floating threshold provided by the embodiment are combined with the conditions that the bus differential protection does not meet the conditions that the multiphase is started up, the bus large difference current does not meet the conditions that the multiphase exceeds the CT line breaking locking fixed value, only one phase large difference current is larger than the CT line breaking locking fixed value and the like, so that the bus protection can be quickly locked when CT line breaking occurs, and the bus protection is not locked by mistake when faults occur in a bus area. The logic diagram is shown in figure 1.
When the braking current criterion is met, the zero sequence current criterion is met, the busbar differential protection multiphase starting is not met, the busbar differential protection multiphase is not met, the busbar differential current exceeds the CT broken line locking fixed value, and only one phase differential current is larger than the CT broken line locking fixed value, the phase CT broken line is judged to be broken, and the phase busbar differential protection is locked; otherwise, opening the differential protection of the same bus; the problem of misoperation locking of bus differential protection when the conditions of single-phase high-resistance faults in the area, metallic faults outside the bus area, homonymous phase high-resistance faults in the back transfer bus area and the like occur in the brake current CT disconnection criterion under the condition of partial heavy load is solved; meanwhile, the problem of misoperation-locking bus differential protection under the conditions of loop shunt, unbalanced three-phase impedance and the like of zero-sequence current CT disconnection criterion in a three-half wiring mode is solved.
Embodiment two:
the embodiment provides a CT disconnection rapid locking method based on a braking current and a zero sequence current, which includes:
the first data acquisition module is used for acquiring current sampling values of all branches of the bus;
the first data processing module is used for calculating a large difference braking current value according to the current sampling value of each branch of the bus;
the second data processing module is used for calculating a floating threshold value;
the first comparison module is used for comparing the current large-difference braking current value with a floating threshold value and outputting a first comparison result;
the second data acquisition module is used for acquiring zero sequence mutation values of all the branches of the bus except the contact branch;
the third data processing module is used for outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value;
the fourth data processing module is used for calculating the sum of absolute values of zero sequence mutation values of all the branches of the bus except the contact branch as a second calculated value;
the second comparison module is used for comparing the second calculated value with the first calculated value which is K times and outputting a second comparison result;
and the judging module is used for taking the first comparison result and the second comparison result as the input of a preset criterion, judging that the single-phase CT disconnection of the bus occurs when the preset criterion is met, and locking the differential protection of the same bus.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Claims (7)
1. A CT broken line quick locking method is characterized by comprising the following steps:
acquiring a current sampling value of each branch of a bus;
calculating a large difference braking current value according to the current sampling value of each branch of the bus;
calculating a floating threshold value;
comparing the current large difference braking current value with a floating threshold value, and outputting a first comparison result;
acquiring zero sequence mutation values of all branches except the contact branch;
outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value;
calculating the sum of absolute values of zero sequence mutation values of all branches of the bus except the contact branch as a second calculated value;
comparing the second calculated value with the first calculated value which is K times, and outputting a second comparison result;
taking the first comparison result and the second comparison result as input of a preset criterion, judging that bus single-phase CT disconnection occurs when the preset criterion is met, and locking the differential protection of the same bus;
the preset criteria are specifically as follows:
if the first comparison result satisfies: the large difference braking current value is smaller than the floating threshold value; at the same time, the method comprises the steps of,
the second comparison result satisfies: the second calculated value is smaller than the first calculated value of K times; at the same time, the method comprises the steps of,
the busbar differential protection multiphase start is not satisfied; at the same time, the method comprises the steps of,
the busbar large difference current is not satisfied, and the phases exceed CT broken line locking fixed values; at the same time, the method comprises the steps of,
only a certain phase difference flow is larger than a CT broken line locking fixed value;
judging that the CT is broken, and locking the differential protection of the bus; otherwise, the differential protection of the same bus is opened.
2. The CT disconnection rapid locking method according to claim 1, wherein the range of values of K is: k is more than 1 and less than 2.
3. The CT disconnection fast locking method according to claim 1, wherein the large difference flow is a vector sum of currents of all branches on a bus.
4. The CT disconnection fast locking method according to claim 1, wherein the calculating the floating threshold value is specifically:
if the current interruption large difference braking current value is larger than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value plus A times the large difference braking current value and the previous interruption floating threshold value;
if the current interruption large difference braking current value is smaller than the previous interruption floating threshold value, the current interruption floating threshold value is equal to the difference value of the large difference braking current value minus B times and the previous interruption floating threshold value.
5. The method for quick locking of a CT disconnection according to claim 4, wherein the value range of A is as follows: a is more than 0 and less than 0.3.
6. The method for quick lock-up of a CT wire break of claim 4, wherein the value range of B is as follows: b is more than 0.1 and less than 1.
7. A CT disconnection quick lock-up system, comprising:
the first data acquisition module is used for acquiring current sampling values of all branches of the bus;
the first data processing module is used for calculating a large difference braking current value according to the current sampling value of each branch of the bus;
the second data processing module is used for calculating a floating threshold value;
the first comparison module is used for comparing the current large-difference braking current value with a floating threshold value and outputting a first comparison result;
the second data acquisition module is used for acquiring zero sequence mutation values of all the branches of the bus except the contact branch;
the third data processing module is used for outputting the maximum value in the zero sequence mutation values of all the branches except the contact branch as a first calculated value;
the fourth data processing module is used for calculating the sum of absolute values of zero sequence mutation values of all the branches of the bus except the contact branch as a second calculated value;
the second comparison module is used for comparing the second calculated value with the first calculated value which is K times and outputting a second comparison result;
the judging module is used for taking the first comparison result and the second comparison result as the input of a preset criterion, judging that the single-phase CT disconnection of the bus occurs when the preset criterion is met, and locking the differential protection of the same bus;
the preset criteria are specifically as follows:
if the first comparison result satisfies: the large difference braking current value is smaller than the floating threshold value; at the same time, the method comprises the steps of,
the second comparison result satisfies: the second calculated value is smaller than the first calculated value of K times; at the same time, the method comprises the steps of,
the busbar differential protection multiphase start is not satisfied; at the same time, the method comprises the steps of,
the busbar large difference current is not satisfied, and the phases exceed CT broken line locking fixed values; at the same time, the method comprises the steps of,
only a certain phase difference flow is larger than a CT broken line locking fixed value;
judging that the CT is broken, and locking the differential protection of the bus; otherwise, the differential protection of the same bus is opened.
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