CN110794355B - Bus current transformer disconnection identification method, differential protection method and device - Google Patents
Bus current transformer disconnection identification method, differential protection method and device Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/02—Testing or calibrating of apparatus covered by the other groups of this subclass of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
- H02H3/093—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current with timing means
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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
Abstract
The invention relates to a bus current transformer disconnection identification method, a differential protection method and a device, comprising the following steps: judging whether the judgment of the disconnection starting of the current transformer is met; if the judgment result meets the judgment of the disconnection starting of the current transformer, judging whether the disconnection judgment condition is met: (a) the broken branch of the current transformer has zero-sequence current, and any phase current is suddenly changed and the current is reduced; (b) before the line break starting of the current transformer, the three-phase current of the branch has current and no zero sequence current, and after the line break starting of the current transformer, the other phase current of the branch has no change; (c) when the current transformer is started in a broken line state, other branches have no zero-sequence current and the phase current is not changed; (d) when the current transformer is started in a broken line state, the bus at the current side has no zero sequence voltage or negative sequence voltage, and the zero sequence voltage is not changed; and if all the conditions in the wire breakage judging conditions are met, judging that the current transformer is broken. The invention can quickly and accurately judge whether the current transformer is broken, and avoid bus differential protection misoperation.
Description
Technical Field
The invention relates to a bus current transformer disconnection identification method, a differential protection method and a differential protection device, and belongs to the technical field of relay protection of power systems.
Background
The safety work regulations of the electric industry stipulate that the secondary circuit of the electrified current transformer is strictly forbidden to be opened when working. The secondary winding of the current transformer used for protecting the high-voltage bus has many turns and high open-circuit voltage, so that the high secondary voltage can not only cause the insulation of the secondary winding and secondary equipment to be damaged, but also cause an iron core to be burnt due to overheating, and even threaten the personal safety. Therefore, the current regulations and countermeasures require locking differential protection when the bus protection current transformer is disconnected, but the disconnection judgment time of the bus protection current transformer is usually long, and bus differential protection misoperation can be caused when the load current of a disconnection branch is large. This is due to: the existing current transformer disconnection judgment is simple, a current transformer disconnection alarm signal is generated after a time delay of 7s after a differential current is larger than a locking fixed value, and differential protection is locked, the simple differential current judgment cannot distinguish the current transformer disconnection and bus faults, so that the time delay is usually needed for judgment, the differential current returns after normal fault differential protection action tripping, the current transformer disconnection alarm signal cannot be generated by mistake, and the current transformer disconnection alarm signal is generated and the differential protection is locked only when the differential current exists for a long time. When the differential current is larger than the locking fixed value, the differential protection is not locked within 7s, and when the load current of the disconnection branch is large, the bus differential protection misoperation can be caused.
Therefore, how to quickly and accurately judge whether the bus protection current transformer is broken and how to avoid bus differential protection malfunction becomes an urgent problem to be solved under the condition that the current transformer is broken.
Disclosure of Invention
The invention aims to provide a method and a device for identifying the disconnection of a bus current transformer, which are used for solving the problem of long time for judging the disconnection of the bus differential protection current transformer; the invention also provides a bus differential protection method and a bus differential protection device, which are used for solving the problem of bus differential protection misoperation caused by disconnection of the bus protection current transformer.
In order to solve the problem of long time for judging the disconnection of the bus differential protection current transformer, the invention provides a method for identifying the disconnection of the bus current transformer, which comprises the following steps:
judging whether the judgment of the disconnection starting of the current transformer is met;
if the judgment of the disconnection starting of the current transformer is met, judging whether the disconnection judgment condition is met, wherein the disconnection judgment condition is as follows:
(a) the broken branch of the current transformer has zero-sequence current, and any phase current is suddenly changed and the current is reduced;
(b) before the line break starting of the current transformer, the three-phase current of the branch has current and no zero sequence current, and after the line break starting of the current transformer, the other phase current of the branch has no change;
(c) when the current transformer is started in a broken line state, other branches have no zero-sequence current and the phase current is not changed;
(d) when the current transformer is started in a broken line state, the bus at the current side has no zero sequence voltage or negative sequence voltage, and the zero sequence voltage is not changed;
and if all the conditions in the disconnection judging conditions are met, judging that the current transformer is disconnected.
The invention has the beneficial effects that: when any branch of the bus is disconnected with a single-phase or two-phase current transformer, whether the current transformer is disconnected or not can be judged quickly and accurately according to the current and voltage variation under the condition that the disconnection starting judgment of the current transformer is met, and the bus protection can be controlled correspondingly according to the disconnection condition of the current transformer.
Further, in order to judge whether the current transformer is started or not by judging the disconnection of the current transformer, the calculation formula for judging the disconnection and the starting of the current transformer is as follows:
Iop＞Iop.SET1
wherein, IopFor bus differential protection of the amplitude of the differential current, Iop.SET1And setting a disconnection warning value for the bus differential protection current transformer.
Further, in order to reliably determine whether the current transformer is disconnected, the criterion formula of the condition (a) is as follows:
wherein, IΦ1(t) is A, B, C phase current amplitude value of the branch when the current transformer is started in a disconnection mode, IΦ1(t-nT) is the amplitude of A, B, C phase current before n cycles of the branch when the current transformer is started to be disconnected; k is a radical of1The value is constant and ranges from 0.04 to 0.06; i isNFor secondary rating of bus-protecting current transformers, 3I01(t) the three-phase self-generating zero sequence current amplitude of the branch when the current transformer is started in a broken line state;
the discrimination formula of the condition (b) is:
wherein k is2The value is constant and ranges from 1.1 to 1.3; i isΦ1.min(t-nT) is the minimum phase current amplitude in three-phase current before n cycles of the branch when the current transformer is started in a disconnection mode, and 3I01(t-nT) is the three-phase self-generating zero-sequence current amplitude value before n cycles of the branch when the current transformer is started in a broken line mode;
the discrimination formula of the condition (c) is:
wherein, IΦ2(t) A, B, C phase current amplitude values of other branches when the current transformer is disconnected and started, IΦ2(t-nT) is A, B, C phase current amplitude before n cycles of other branches when the current transformer is started to be disconnected, and 3I0(t) zero sequence current amplitude values of other branches when the current transformer is started in a broken line state; k is a radical of3The value is constant and ranges from 0.6 to 0.85;
the discrimination formula of the condition (d) is:
wherein, U2(t) is the negative sequence voltage amplitude of the bus when the current transformer is started in case of disconnection, namely 3U0(t) is the bus zero sequence voltage amplitude value when the current transformer is started in case of wire break, 3U0(t-nT) is zero sequence voltage amplitude value before n cycles of bus when current transformer is started in case of disconnection, UNIs a secondary rated value of a bus PT; k is a radical of4、k5、k6Are all constants, k4The value range is 0.06-0.10, k5The value range is 0.08-0.15, k6The value range is 0.01-0.03.
In order to solve the problem of long time for judging the disconnection of the bus differential protection current transformer, the invention also provides a disconnection identifying device of the bus current transformer, which comprises a processor and a memory, wherein the processor is used for processing the instruction stored in the memory so as to realize the disconnection identifying method of the bus current transformer.
In order to solve the problem of bus differential protection misoperation caused by disconnection of a bus protection current transformer, the invention provides a bus differential protection method, which comprises the following steps:
judging whether the judgment of the disconnection starting of the current transformer is met;
if the judgment of the disconnection starting of the current transformer is met, judging whether the disconnection judgment condition is met, wherein the disconnection judgment condition is as follows:
(a) the broken branch of the current transformer has zero-sequence current, and any phase current is suddenly changed and the current is reduced;
(b) before the line break starting of the current transformer, the three-phase current of the branch has current and no zero sequence current, and after the line break starting of the current transformer, the other phase current of the branch has no change;
(c) when the current transformer is started in a broken line state, other branches have no zero-sequence current and the phase current is not changed;
(d) when the current transformer is started in a broken line state, the bus at the current side has no zero sequence voltage or negative sequence voltage, and the zero sequence voltage is not changed;
if all the conditions in the disconnection judging conditions are met, judging that the current transformer is disconnected;
and judging whether the load current of the open circuit branch of the bus current transformer is greater than a set load current value, if so, delaying a first time set value to generate a disconnection warning signal of the current transformer and locking the bus differential protection.
The invention has the beneficial effects that: when any branch of the bus is disconnected with a single-phase or two-phase current transformer, whether the current transformer is disconnected or not can be judged quickly and accurately according to the current voltage variation under the condition of meeting the judgment of the disconnection start of the current transformer, and under the condition of the disconnection of the current transformer, when the load current of the disconnection branch of the bus current transformer is larger, the bus differential protection is locked, so that the bus differential protection misoperation caused by the disconnection of the current transformer is avoided.
Further, in order to realize reliable protection and avoid the bus differential protection from not acting under the condition of failure, the method further comprises the following steps: and if the load current of the open circuit branch of the bus current transformer is not greater than the set load current value, delaying a second time set value to generate a disconnection warning signal of the current transformer and opening the bus differential protection.
Further, in order to judge whether the current transformer is started or not by judging the disconnection of the current transformer, the calculation formula for judging the disconnection and the starting of the current transformer is as follows:
Iop＞Iop.SET1
wherein, IopFor bus differential protection of the amplitude of the differential current, Iop.SET1And setting a disconnection warning value for the bus differential protection current transformer.
Further, in order to reliably determine whether the current transformer is disconnected, the criterion formula of the condition (a) is as follows:
wherein, IΦ1(t) is A, B, C phase current amplitude value of the branch when the current transformer is started in a disconnection mode, IΦ1(t-nT) is a current transformerA, B, C phase current amplitude before n cycles of the branch when the line is broken and started; k is a radical of1The value is constant and ranges from 0.04 to 0.06; i isNFor secondary rating of bus-protecting current transformers, 3I01(t) the three-phase self-generating zero sequence current amplitude of the branch when the current transformer is started in a broken line state;
the discrimination formula of the condition (b) is:
wherein k is2The value is constant and ranges from 1.1 to 1.3; i isΦ1.min(t-nT) is the minimum phase current amplitude in three-phase current before n cycles of the branch when the current transformer is started in a disconnection mode, and 3I01(t-nT) is the three-phase self-generating zero-sequence current amplitude value before n cycles of the branch when the current transformer is started in a broken line mode;
the discrimination formula of the condition (c) is:
wherein, IΦ2(t) A, B, C phase current amplitude values of other branches when the current transformer is disconnected and started, IΦ2(t-nT) is A, B, C phase current amplitude before n cycles of other branches when the current transformer is started to be disconnected, and 3I0(t) zero sequence current amplitude values of other branches when the current transformer is started in a broken line state; k is a radical of3The value is constant and ranges from 0.6 to 0.85;
the discrimination formula of the condition (d) is:
wherein, U2(t) is the negative sequence voltage amplitude of the bus when the current transformer is started in case of disconnection, namely 3U0(t) is the bus zero sequence voltage amplitude value when the current transformer is started in case of wire break, 3U0(t-nT) is zero sequence voltage amplitude value before n cycles of bus when current transformer is started in case of disconnection, UNIs a busPT secondary rated value; k is a radical of4、k5、k6Are all constants, k4The value range is 0.06-0.10, k5The value range is 0.08-0.15, k6The value range is 0.01-0.03.
Further, for reliable protection, the first time setting is 5ms and the second time setting is 7 s.
In order to solve the problem of bus differential protection misoperation caused by disconnection of the bus protection current transformer, the invention also provides a bus differential protection device which comprises a processor and a memory, wherein the processor is used for processing instructions stored in the memory so as to realize the bus differential protection method.
Drawings
FIG. 1 is a main wiring diagram of the double bus bar connection of the present invention;
FIG. 2 is a flow chart of a bus differential protection method of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The embodiment of the bus current transformer disconnection identification method comprises the following steps:
the main wiring diagram of the double-bus wiring mode is shown in FIG. 1, the bus large-difference specific-rate differential protection is composed of six-side currents of TA2, TA3, TA4, TA5, TA6 and TA7, and the bus voltage is the voltage of TV1 and TV 2; the I bus differential ratio differential protection is composed of currents on four sides of TA1, TA2, TA3 and TA4, and the bus voltage is the voltage of TV 1; the II bus small difference specific value differential protection is composed of currents on four sides of TA1, TA5, TA6 and TA7, and the bus voltage is the voltage of TV 2.
Based on the main wiring diagram of the dual bus wiring manner in fig. 1, but not limited to the main wiring diagram, the present embodiment provides a method for identifying a bus current transformer disconnection, which identifies a current transformer (also referred to as CT) disconnection by performing auxiliary discrimination using bus voltage according to characteristics of the current transformer disconnection and a system fault, and effectively improves reliability of the bus current transformer disconnection identification.
Specifically, a flow chart corresponding to the bus current transformer disconnection identification method is shown in fig. 2, and includes the following steps:
(1) judging whether the judgment of the disconnection starting judgment of the current transformer is met, wherein the calculation formula of the disconnection starting judgment of the current transformer is as follows:
Iop＞Iop.SET1
wherein, IopFor bus differential protection of the amplitude of the differential current, Iop.SET1For bus differential protection current transformer disconnection warning constant value, Iop.SET1Usually the setting is 0.06IN～0.1IN，INAnd protecting the secondary rated value of the current transformer for the bus.
It should be noted that the judgment of the disconnection start of the current transformer is not limited to the above given calculation formula, and other judgment formulas in the prior art may also be adopted to judge whether to start the disconnection judgment of the current transformer.
(2) If the judgment result meets the judgment of the disconnection starting of the current transformer, judging whether the disconnection judgment condition is met, wherein the disconnection judgment condition is as follows:
(a) and (3) judging the broken line branch of the bus: the broken line branch of the current transformer has zero sequence current, any phase current is suddenly changed and the current is reduced, and the corresponding discrimination formula is as follows:
wherein, IΦ1(t) is A, B, C phase current amplitude value of the branch when the current transformer is started in a disconnection mode, IΦ1(T-2T) is A, B, C phase current amplitude before 2 weeks of the current branch when the current transformer is started to be disconnected; k is a radical of1The value is constant and ranges from 0.04 to 0.06; i isNFor secondary rating of bus-protecting current transformers, INTaking 1A or 5A, 3I01And (t) is the three-phase self-generating zero sequence current amplitude of the branch when the current transformer is started in a broken line mode.
(b) The three-phase current of the branch circuit is provided with current and has no zero sequence current before the current transformer is disconnected and started, the other phase currents of the branch circuit are not changed after the current transformer is disconnected and started, and the corresponding discrimination formula is as follows:
wherein k is2The value is constant and ranges from 1.1 to 1.3; i isΦ1.min(T-2T) is the minimum phase current amplitude in three-phase current before 2 cycles of the branch when the current transformer is started in a disconnection mode, and 3I01And (T-2T) is the three-phase self-generating zero-sequence current amplitude value 2 weeks before the current branch when the current transformer is started in a broken line mode.
(c) When the current transformer is started in a broken line state, other branches have no zero sequence current and the phase current is not changed, and the corresponding discrimination formula is as follows:
wherein, IΦ2(t) A, B, C phase current amplitude values of other branches when the current transformer is disconnected and started, IΦ2(T-2T) is A, B, C phase current amplitude before 2 weeks of other branches when the current transformer is started to be disconnected, and 3I0(t) zero sequence current amplitude values of other branches when the current transformer is started in a broken line state; k is a radical of3Is constant and has a value range of 0.6-0.85.
(d) When the current transformer is started in a broken line state, the bus on the current side has no zero sequence voltage and negative sequence voltage, and the zero sequence voltage has no change, and the corresponding discrimination formula is as follows:
wherein, U2(t) is the negative sequence voltage amplitude of the bus when the current transformer is started in case of disconnection, namely 3U0(t) is the bus zero sequence voltage amplitude value when the current transformer is started in case of wire break, 3U0(T-2T) is zero sequence voltage amplitude value of 2 cycles before bus when current transformer is started in case of disconnection, UNFor secondary rating of bus PT (see FIG. 1, U)NIndicating a secondary of a PT to which TV1 or TV2 is connectedRated value) of 57.7V; k is a radical of4、k5、k6Are all constants, k4The value range is 0.06-0.10, k5The value range is 0.08-0.15, k6The value range is 0.01-0.03.
In addition, in the disconnection determination condition in the step (2), the current and voltage data corresponding to 2 weeks before the disconnection start of the current transformer are taken as an example, and as another embodiment, the current and voltage data corresponding to n weeks before the disconnection start of the current transformer may be taken as the disconnection determination condition determination, and n is a positive integer such as 1, 3, or 4, for example.
(3) And if all the conditions in the wire breakage judging conditions are met, judging that the current transformer is broken.
As shown in fig. 2, when either one of the conditions in step (1) and step (2) is not satisfied, the current transformer disconnection determination is exited.
It should be noted that the method for identifying the disconnection of the bus current transformer is based on the disconnection identification of the current transformer of any branch circuit when the bus normally runs, does not include the phenomenon that two or more branch circuits are disconnected simultaneously, can reliably identify whether the single-phase or two-phase current transformer of any branch circuit of the bus is disconnected, and effectively solves the problem that the disconnection identification time of the bus differential protection current transformer is long. During implementation, the bus current transformer disconnection identification method can be used as an independent functional module to be placed in a bus protection device and put into use all the time.
The embodiment of the bus differential protection method comprises the following steps:
based on the above method for identifying the disconnection of the bus current transformer, the present embodiment provides a bus differential protection method to solve the problem that the bus differential protection may malfunction after the disconnection of the current transformer, and a corresponding flowchart is shown in fig. 2. Under the condition of judging that the current transformer is broken, the instantaneous discrimination or the delay discrimination can be automatically selected according to the magnitude of the differential current, and the specific process is as follows: judging whether the load current of the open circuit branch of the current transformer of the bus is larger or not, wherein the corresponding discrimination formula is as follows:
Iop＞Iop.SET2
wherein, Iop.SET2For the disconnection locking constant value of the bus differential protection current transformer, Iop.SET2Usually set to 0.15IN～0.3IN。
If it satisfies Iop＞Iop.SET2If the current is greater than the set value, the differential protection is locked, and the bus differential protection is prevented from being operated by mistake. If not satisfy Iop＞Iop.SET2If the load current of the open circuit branch of the bus current transformer is not large, delaying the second time set value to generate the disconnection warning signal of the current transformer and opening the bus differential protection, namely, delaying the second time set value to generate the disconnection warning signal of the current transformer but not locking the bus differential protection.
In this embodiment, the first time setting value is 5ms, which indicates that the current transformer is generating the disconnection warning signal instantaneously and the bus differential protection is locked, and the second time setting value is 7s, which indicates that the current transformer is generating the disconnection warning signal in a delayed manner and the bus differential protection is opened. As another embodiment, the first time setting value and the second time setting value may be adaptively adjusted when the requirement is satisfied.
The embodiment of the bus current transformer disconnection identification device comprises:
the embodiment provides a bus current transformer disconnection identification device which comprises a processor and a memory, wherein the processor is used for processing instructions stored in the memory so as to realize the bus current transformer disconnection identification method. Since the bus current transformer disconnection identification method has been described in detail in the above embodiments of the bus current transformer disconnection identification method, it is not described herein again.
Bus differential protection device embodiment:
the embodiment provides a bus differential protection device, which comprises a processor and a memory, wherein the processor is used for processing instructions stored in the memory so as to realize the bus differential protection method. Since the bus differential protection method has been described in detail in the above embodiments of the bus differential protection method, it is not described herein again.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope thereof, and although the present application is described in detail with reference to the above embodiments, those skilled in the art should understand that after reading the present application, various changes, modifications or equivalents of the embodiments of the present application can be made, and these changes, modifications or equivalents are within the protection scope of the claims of the present invention.
Claims (5)
1. A bus current transformer disconnection identification method is characterized by comprising the following steps:
judging whether the judgment of the disconnection starting of the current transformer is met;
if the judgment of the disconnection starting of the current transformer is met, judging whether the disconnection judgment condition is met, wherein the disconnection judgment condition is as follows:
(a) the broken branch of the current transformer has zero-sequence current, and any phase current is suddenly changed and the current is reduced;
(b) before the line break starting of the current transformer, the three-phase current of the branch has current and no zero sequence current, and after the line break starting of the current transformer, the other phase current of the branch has no change;
(c) when the current transformer is started in a broken line state, other branches have no zero-sequence current and the phase current is not changed;
(d) when the current transformer is started in a broken line state, the bus at the current side has no zero sequence voltage or negative sequence voltage, and the zero sequence voltage is not changed;
if all the conditions in the disconnection judging conditions are met, judging that the current transformer is disconnected;
the calculation formula for judging the disconnection start of the current transformer is as follows:
Iop＞Iop.SET1
wherein, IopFor bus differential protection of the amplitude of the differential current, Iop.SET1Differential protection current transformer for busSetting a disconnection alarm value;
the discrimination formula of the condition (a) is as follows:
wherein, IΦ1(t) is A, B, C phase current amplitude value of the branch when the current transformer is started in a disconnection mode, IΦ1(t-nT) is the amplitude of A, B, C phase current before n cycles of the branch when the current transformer is started to be disconnected; k is a radical of1The value is constant and ranges from 0.04 to 0.06; i isNFor secondary rating of bus-protecting current transformers, 3I01(t) the three-phase self-generating zero sequence current amplitude of the branch when the current transformer is started in a broken line state;
the discrimination formula of the condition (b) is:
wherein k is2The value is constant and ranges from 1.1 to 1.3; i isΦ1.min(t-nT) is the minimum phase current amplitude in three-phase current before n cycles of the branch when the current transformer is started in a disconnection mode, and 3I01(t-nT) is the three-phase self-generating zero-sequence current amplitude value before n cycles of the branch when the current transformer is started in a broken line mode;
the discrimination formula of the condition (c) is:
wherein, IΦ2(t) A, B, C phase current amplitude values of other branches when the current transformer is disconnected and started, IΦ2(t-nT) is A, B, C phase current amplitude before n cycles of other branches when the current transformer is started to be disconnected, and 3I0(t) zero sequence current amplitude values of other branches when the current transformer is started in a broken line state; k is a radical of3The value is constant and ranges from 0.6 to 0.85;
the discrimination formula of the condition (d) is:
wherein, U2(t) is the negative sequence voltage amplitude of the bus when the current transformer is started in case of disconnection, namely 3U0(t) is the bus zero sequence voltage amplitude value when the current transformer is started in case of wire break, 3U0(t-nT) is zero sequence voltage amplitude value before n cycles of bus when current transformer is started in case of disconnection, UNIs a secondary rated value of a bus PT; k is a radical of4、k5、k6Are all constants, k4The value range is 0.06-0.10, k5The value range is 0.08-0.15, k6The value range is 0.01-0.03.
2. A bus differential protection method is characterized by comprising the following steps:
judging whether the judgment of the disconnection starting of the current transformer is met;
if the judgment of the disconnection starting of the current transformer is met, judging whether the disconnection judgment condition is met, wherein the disconnection judgment condition is as follows:
(a) the broken branch of the current transformer has zero-sequence current, and any phase current is suddenly changed and the current is reduced;
(b) before the line break starting of the current transformer, the three-phase current of the branch has current and no zero sequence current, and after the line break starting of the current transformer, the other phase current of the branch has no change;
(c) when the current transformer is started in a broken line state, other branches have no zero-sequence current and the phase current is not changed;
(d) when the current transformer is started in a broken line state, the bus at the current side has no zero sequence voltage or negative sequence voltage, and the zero sequence voltage is not changed;
if all the conditions in the disconnection judging conditions are met, judging that the current transformer is disconnected;
judging whether the load current of the open circuit branch of the bus current transformer is greater than a set load current value, if so, delaying a first time set value to generate a current transformer disconnection warning signal and locking bus differential protection;
if the load current of the open circuit branch of the bus current transformer is not greater than the set load current value, delaying a second time set value to generate a current transformer disconnection warning signal and opening the bus differential protection;
the calculation formula for judging the disconnection start of the current transformer is as follows:
Iop＞Iop.SET1
wherein, IopFor bus differential protection of the amplitude of the differential current, Iop.SET1Setting a disconnection warning value for the bus differential protection current transformer;
the discrimination formula of the condition (a) is as follows:
wherein, IΦ1(t) is A, B, C phase current amplitude value of the branch when the current transformer is started in a disconnection mode, IΦ1(t-nT) is the amplitude of A, B, C phase current before n cycles of the branch when the current transformer is started to be disconnected; k is a radical of1The value is constant and ranges from 0.04 to 0.06; i isNFor secondary rating of bus-protecting current transformers, 3I01(t) the three-phase self-generating zero sequence current amplitude of the branch when the current transformer is started in a broken line state;
the discrimination formula of the condition (b) is:
wherein k is2The value is constant and ranges from 1.1 to 1.3; i isΦ1.min(t-nT) is the minimum phase current amplitude in three-phase current before n cycles of the branch when the current transformer is started in a disconnection mode, and 3I01(t-nT) is the three-phase self-generating zero-sequence current amplitude value before n cycles of the branch when the current transformer is started in a broken line mode;
the discrimination formula of the condition (c) is:
wherein, IΦ2(t) A, B, C phase current amplitude values of other branches when the current transformer is disconnected and started, IΦ2(t-nT) is A, B, C phase current amplitude before n cycles of other branches when the current transformer is started to be disconnected, and 3I0(t) zero sequence current amplitude values of other branches when the current transformer is started in a broken line state; k is a radical of3The value is constant and ranges from 0.6 to 0.85;
the discrimination formula of the condition (d) is:
wherein, U2(t) is the negative sequence voltage amplitude of the bus when the current transformer is started in case of disconnection, namely 3U0(t) is the bus zero sequence voltage amplitude value when the current transformer is started in case of wire break, 3U0(t-nT) is zero sequence voltage amplitude value before n cycles of bus when current transformer is started in case of disconnection, UNIs a secondary rated value of a bus PT; k is a radical of4、k5、k6Are all constants, k4The value range is 0.06-0.10, k5The value range is 0.08-0.15, k6The value range is 0.01-0.03.
3. The bus differential protection method of claim 2, wherein the first time setpoint is 5ms and the second time setpoint is 7 s.
4. A bus current transformer disconnection identifying device, comprising a processor and a memory, wherein the processor is used for processing instructions stored in the memory to implement the bus current transformer disconnection identifying method of claim 1.
5. A bus differential protection device, comprising a processor and a memory, wherein the processor is configured to process instructions stored in the memory to implement the bus differential protection method of claim 2.
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| CN111999678B (en) * | 2020-07-24 | 2023-06-16 | 南京国电南自电网自动化有限公司 | Three-phase PT secondary circuit neutral point N line disconnection judging method and system |
| CN112736867B (en) * | 2020-12-16 | 2023-12-01 | 北京四方继保工程技术有限公司 | Method and system for rapidly judging CT disconnection of line protection device |
| CN112904265B (en) * | 2021-03-18 | 2022-05-13 | 浙江聚创智能科技有限公司 | Second winding open circuit detection circuit of zero sequence current transformer |
| CN113534011B (en) * | 2021-06-25 | 2024-02-13 | 许继电气股份有限公司 | Intelligent substation current transformer broken line identification method and device |
| CN113625189B (en) * | 2021-08-02 | 2022-09-02 | 国网江苏省电力有限公司镇江供电分公司 | 110kV line disconnection protection method for measuring low-voltage side phase voltage of transformer |
| CN113625190B (en) * | 2021-08-02 | 2022-09-02 | 国网江苏省电力有限公司镇江供电分公司 | Adaptive identification and protection method for 110kV line disconnection fault |
| CN115166603B (en) * | 2022-06-24 | 2023-02-28 | 北京天能继保电力科技有限公司 | Virtual connection judgment method and device for secondary circuit wiring terminal of power grid voltage transformer |
| CN117388759B (en) * | 2023-12-07 | 2024-02-23 | 国网辽宁省电力有限公司 | Bus disconnection discriminating method and device utilizing transformer substation monitoring data |
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