CN109119972B - Locking method and device for preventing differential misoperation caused by CT (current transformer) disconnection of balance winding - Google Patents
Locking method and device for preventing differential misoperation caused by CT (current transformer) disconnection of balance winding Download PDFInfo
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- CN109119972B CN109119972B CN201811093221.2A CN201811093221A CN109119972B CN 109119972 B CN109119972 B CN 109119972B CN 201811093221 A CN201811093221 A CN 201811093221A CN 109119972 B CN109119972 B CN 109119972B
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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
- H02H7/04—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 transformers
- H02H7/045—Differential protection of transformers
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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
- H02H3/02—Details
- H02H3/05—Details with means for increasing reliability, e.g. redundancy arrangements
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- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
Abstract
The invention provides a locking method and a device for preventing differential misoperation caused by CT (current transformer) disconnection of a balance winding, which have the working modes that: collecting each phase of winding current of a balance winding of a series transformer, calculating the amplitude or effective value of three-phase current in real time, comparing the amplitude or effective value of each phase of current with the amplitude or effective value of other phases of current respectively, and locking zero-sequence differential protection when the ratio is greater than a locking fixed value; locking the zero-sequence differential protection when the ratio of the zero-sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than the locking constant value; the invention can reliably prevent the protection from malfunction caused by the CT disconnection of the balance winding, and can be widely applied to the zero sequence differential protection of the series transformer.
Description
Technical Field
The invention relates to the field of relay protection of a power system, in particular to a locking method and a locking device for preventing differential misoperation caused by CT (current transformer) disconnection of a balance winding.
Background
The series transformer is one of the core components of a novel FACTS (Flexible AC Transmission Systems) device, and is in the core position where a direct current valve and an alternating current Transmission line are interchanged. When the series transformer has turn-to-turn faults, the zero-sequence current appears in the balance winding, and zero-sequence differential protection based on magnetic balance is configured, so that the faults can be sensitively reflected.
The balance winding has no load and three-phase symmetrical connection, so the current of the balance winding is very small when the transformer normally runs, and if the CT disconnection of the balance winding occurs in field application, the CT disconnection is difficult to find when the transformer normally runs. If the fault is out of balance, the zero sequence differential protection will generate differential current, resulting in the malfunction of the zero sequence differential protection.
The existing zero-sequence differential protection is generally winding zero-sequence differential protection based on electric balance, for the problem of line break, the prior art focuses on neutral point zero-sequence CT of a transformer, which is single-phase CT, and related methods cannot be applied to polarity judgment of three-phase CT of a balanced winding.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a locking method and a locking device for preventing differential misoperation caused by CT (current transformer) disconnection of a balance winding, so as to prevent zero-sequence differential protection misoperation caused by CT disconnection of the balance winding.
In order to achieve the above object, the present invention is achieved by the following means.
A locking method for preventing differential misoperation caused by CT wire breakage of a balance winding comprises the following steps:
(1) collecting three-phase current of a balance winding of a series transformer, and recording phase current A of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
(2) Respectively calculate Ia、Ib、IcThe ratio of the amplitude or effective value of any phase current to the amplitude or effective value of any phase current in other two-phase currents is less than the locking constant value Kset1And locking zero sequence differential protection.
In the above scheme, the locking constant value Kset1The value range is as follows: 0.5 to 0.8.
In the above scheme, the step 2 further includes: calculating the ratio of the zero-sequence differential protection differential flow to the longitudinal differential protection differential flowThe ratio of zero sequence differential protection differential flow to longitudinal differential protection differential flow is greater than locking constant value Kset2And locking zero sequence differential protection.
In the above scheme, the locking constant value Kset2The value range of (1) is 2-5.
In the scheme, the zero-sequence differential protection adopts a difference loop formed by a network side CT, a valve side CT and a balance winding CT; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop.
The invention also provides a protection device for preventing differential misoperation caused by CT wire breakage of the balance winding, which comprises a sampling unit and a locking judgment unit, wherein:
the sampling unit is used for acquiring three-phase current of a balance winding of the series transformer, and recording A-phase current of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
The locking decision unit is used for respectively calculating Ia、Ib、IcThe ratio of the amplitude or effective value of any phase current to the amplitude or effective value of any phase current in other two-phase currents is less than the locking constant value Kset1And locking zero sequence differential protection.
In the above scheme, the locking constant value Kset1The value range is as follows: 0.5 to 0.8.
In the above aspect, the locking determination unit further includes: calculating the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow, and when the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than a locking constant value Kset2And locking zero sequence differential protection.
In the above scheme, the locking constant value Kset2The value range of (1) is 2-5.
In the scheme, the zero-sequence differential protection adopts a difference loop formed by a network side CT, a valve side CT and a balance winding CT; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a locking method and a device for preventing differential misoperation caused by CT (current transformer) disconnection of a balance winding, which have the working modes that: collecting each phase of winding current of a balance winding of a series transformer, calculating the amplitude or effective value of three-phase current in real time, comparing the amplitude or effective value of each phase of current with the amplitude or effective value of other phases of current respectively, and locking zero-sequence differential protection when the ratio is greater than a locking fixed value; locking the zero-sequence differential protection when the ratio of the zero-sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than the locking constant value; the invention can reliably prevent the differential protection from malfunction caused by the disconnection of the balance winding CT, and can be widely applied to the zero sequence differential protection of the series transformer.
Drawings
FIG. 1 is a first flowchart of a zero-sequence differential protection equilibrium winding CT disconnection locking method;
FIG. 2 is a flow chart of a zero sequence differential protection equilibrium winding CT disconnection locking method;
FIG. 3 is a flow chart of a zero-sequence differential protection equilibrium winding CT line break locking method;
FIG. 4 is a flow chart of a zero-sequence differential protection equilibrium winding CT line break locking method
Fig. 5 is a schematic diagram of a transformer participating in longitudinal zero-sequence differential protection calculation of a series transformer.
Detailed Description
The invention discloses a locking method for preventing differential misoperation caused by CT disconnection of a balance winding, and the technical scheme of the invention is explained in detail below with reference to the accompanying drawings.
The first embodiment is as follows:
a locking method for preventing differential misoperation caused by CT wire breakage of a balance winding comprises the following steps:
(1) collecting three-phase current of a balance winding of a series transformer, and recording phase current A of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
As shown in fig. 5, the zero-sequence differential protection adopts a net-side CT, a valve-side CT and a balance winding CT to form a difference loop; longitudinal differential protection adopts net side CT and the valve side CT form a difference loop. When the series transformer operates normally, the balance winding has no load, and the three-phase current of the balance winding is very small, i.e. Ia、Ib、IcAre small. When the series transformer has turn-to-turn fault, a circular current I is generated in the triangular ring of the balance windinga、Ib、IcThe three-phase currents are equal in magnitude and same in direction;
(2) respectively calculate Ia、Ib、IcAnd the amplitude ratio of the other two-phase current, when the ratio of the amplitude of any phase current to the amplitude of any phase current in the other two-phase current is less than the locking fixed value Kset1Locking zero sequence differential protection and giving an alarm message, Kset1The value range is as follows: 0.5 to 0.8.
If there is a broken line in the three phases of the balanced winding A, B, C, for example, the a-phase is broken, in which case, when the system has a single-phase earth fault, the balanced winding a-phase will draw no current or only a small current, and the B, C-phase will draw equal current and the same direction. As shown in FIG. 1, when the ratio of the A-phase current to the B-phase or C-phase current is greater than the latch-up threshold Kset1And if so, judging that the balance winding three-phase CT is abnormal, locking zero-sequence differential protection and giving an alarm message. Latching constant value Kset1The value ranges of (a) are generally: 0.5 to 0.8.
Example two:
a locking method for preventing differential misoperation caused by CT wire breakage of a balance winding comprises the following steps:
(1) collecting three-phase current of a balance winding of a series transformer, and recording phase current A of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
As shown in fig. 5, the zero-sequence differential protection adopts a net-side CT, a valve-side CT and a balance winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop. When the series transformer operates normally, the balance winding has no load, and the three-phase current of the balance winding is very small, i.e. Ia、Ib、IcAre small. When turn-to-turn fault occurs in the series transformerIn time, a circulating current, I, will be generated in the triangular ring of the balance windinga、Ib、IcThe three-phase currents are equal in magnitude and same in direction;
(2) respectively calculate Ia、Ib、IcAnd the effective value ratio of the current of any phase to the effective value of the current of any phase in other two phases is less than the locking fixed value Kset1Locking zero sequence differential protection and giving an alarm message, Kset1The value range is as follows: 0.5 to 0.8.
If there is a broken line in the three phases of the balanced winding A, B, C, for example, the a-phase is broken, in which case, when the system has a single-phase earth fault, the balanced winding a-phase will draw no current or only a small current, and the B, C-phase will draw equal current and the same direction. As shown in FIG. 2, when the ratio of the effective value of the A-phase current to the B-phase or C-phase current is greater than the latch-up constant Kset1And if so, judging that the balance winding three-phase CT is abnormal, locking zero-sequence differential protection and giving an alarm message. Latching constant value Kset1The value ranges of (a) are generally: 0.5 to 0.8.
Example three:
a locking method for preventing differential misoperation caused by CT wire breakage of a balance winding comprises the following steps:
(1) collecting three-phase current of a balance winding of a series transformer, and recording phase current A of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
As shown in fig. 5, the zero-sequence differential protection adopts a net-side CT, a valve-side CT and a balance winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop. When the series transformer operates normally, the balance winding has no load, and the three-phase current of the balance winding is very small, i.e. Ia、Ib、IcAre small. When the series transformer has turn-to-turn fault, a circular current I is generated in the triangular ring of the balance windinga、Ib、IcThe three-phase currents are equal in magnitude and same in direction;
(2) respectively calculate Ia、Ib、IcAnd the amplitude ratio of the other two-phase current, when the ratio of the amplitude of any phase current to the amplitude of any phase current in the other two-phase current is less than the locking fixed value Kset1Locking zero sequence differential protection and giving an alarm message, Kset1The value range is as follows: 0.5 to 0.8. Calculating the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow, and when the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than a locking constant value Kset2And locking zero sequence differential protection. K isset2The value range of (1) is 2-5.
If there is a broken line in the three phases of the balanced winding A, B, C, for example, the a-phase is broken, in which case, when the system has a single-phase earth fault, the balanced winding a-phase will draw no current or only a small current, and the B, C-phase will draw equal current and the same direction. As shown in FIG. 3, when the ratio of the A-phase current to the B-phase or C-phase current is greater than the latch-up threshold Kset1And if so, judging that the balance winding three-phase CT is abnormal, locking zero-sequence differential protection and giving an alarm message. Latching constant value Kset1The value ranges of (a) are generally: 0.5 to 0.8.
If the three-phase CT of the balance winding A, B, C is broken, taking the single-phase earth fault outside the system occurrence area as an example, the differential current of the zero-sequence differential protection should be zero, but because the three-phase CT of the balance winding is broken, the zero-sequence differential protection will calculate a large differential current at this moment, and the value is close to 1 time of the adjustment current of the grid-side winding; the longitudinal differential protection does not adopt balance winding current, and the longitudinal differential protection differential current is very small when an external fault occurs; therefore, as shown in fig. 1, the ratio of the zero-sequence differential protection difference flow to the longitudinal differential protection difference flow can be used to determine whether there is an abnormality in the difference loop of the zero-sequence differential protection. Latching constant value Kset2The ranges of (A) are generally taken as: 2 to 5.
Example four:
a locking method for preventing differential misoperation caused by CT wire breakage of a balance winding comprises the following steps:
(1) collecting three-phase current of a balance winding of a series transformer, and recording phase current A of the balance winding as IaThe phase B current of the balance winding is recorded as IbMemory for recordingThe phase C current of the balance winding is Ic；
As shown in fig. 5, the zero-sequence differential protection adopts a net-side CT, a valve-side CT and a balance winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop. When the series transformer operates normally, the balance winding has no load, and the three-phase current of the balance winding is very small, i.e. Ia、Ib、IcAre small. When the series transformer has turn-to-turn fault, a circular current I is generated in the triangular ring of the balance windinga、Ib、IcThe three-phase currents are equal in magnitude and same in direction;
(2) respectively calculate Ia、Ib、IcAnd the effective value ratio of the current of any phase to the effective value of the current of any phase in other two phases is less than the locking fixed value Kset1Locking zero sequence differential protection and giving an alarm message, Kset1The value range is as follows: 0.5 to 0.8.
If there is a broken line in the three phases of the balanced winding A, B, C, for example, the a-phase is broken, in which case, when the system has a single-phase earth fault, the balanced winding a-phase will draw no current or only a small current, and the B, C-phase will draw equal current and the same direction. As shown in FIG. 4, when the ratio of the effective value of the A-phase current to the B-phase or C-phase current is greater than the latch-up constant Kset1And if so, judging that the balance winding three-phase CT is abnormal, locking zero-sequence differential protection and giving an alarm message. Latching constant value Kset1The value ranges of (a) are generally: 0.5 to 0.8.
If the three-phase CT of the balance winding A, B, C is broken, taking the single-phase earth fault outside the system occurrence area as an example, the differential current of the zero-sequence differential protection should be zero, but because the three-phase CT of the balance winding is broken, the zero-sequence differential protection will calculate a large differential current at this moment, and the value is close to 1 time of the adjustment current of the grid-side winding; the longitudinal differential protection does not adopt balance winding current, and the longitudinal differential protection differential current is very small when an external fault occurs; therefore, as shown in fig. 1, the ratio of the zero-sequence differential protection difference flow to the longitudinal differential protection difference flow can be used to determine whether there is an abnormality in the difference loop of the zero-sequence differential protection. Latching constant value Kset2The ranges of (A) are generally taken as: 2 to 5.
The invention also provides a protection device for preventing differential misoperation caused by CT wire breakage of the balance winding, which comprises a sampling unit and a locking judgment unit, wherein:
the sampling unit is used for acquiring three-phase current of a balance winding of the series transformer, and recording A-phase current of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
The locking decision unit is used for respectively calculating Ia、Ib、IcThe ratio of the amplitude or effective value of any phase current to the amplitude or effective value of any phase current in other two-phase currents is less than the locking constant value Kset1And locking zero sequence differential protection.
Wherein the latching constant value Kset1The value range is as follows: 0.5 to 0.8.
Wherein the lock determination unit further includes: calculating the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow, and when the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than a locking constant value Kset2And locking zero sequence differential protection.
Wherein the latching constant value Kset2The value range of (1) is 2-5.
The zero-sequence differential protection adopts a net side CT, a valve side CT and a balance winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (10)
1. A locking method for preventing differential misoperation caused by CT wire breakage of a balance winding is characterized by comprising the following steps:
(1) for collecting balanced windings of series transformersThe phase current of three phases, the phase current of A of the balance winding is recorded as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
(2) Respectively calculate Ia、Ib、IcWhen the ratio of the amplitude of any phase current to the amplitude of any phase current in other two-phase currents or the ratio of the effective value of any phase current to the effective value of any phase current in other two-phase currents is smaller than the locking constant value Kset1And locking zero sequence differential protection.
2. The latching method for preventing differential malfunction due to CT disconnection in balanced winding according to claim 1, wherein said latching constant K is set to be equal toset1The value range is as follows: 0.5 to 0.8.
3. A locking method for preventing differential malfunction caused by disconnection of the balanced winding CT according to any of the claims 1 or 2, wherein the step (2) further comprises: calculating the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow, and when the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than a locking constant value Kset2And locking zero sequence differential protection.
4. The latching method for preventing differential malfunction due to CT disconnection in balanced winding according to claim 3, wherein said latching constant K is set to be equal toset2The value range of (1) is 2-5.
5. The locking method for preventing the differential malfunction caused by the disconnection of the balanced winding CT as claimed in claim 3, wherein the zero sequence differential protection adopts a net side CT, a valve side CT and the balanced winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop.
6. A protection device for preventing differential misoperation caused by CT disconnection of a balance winding is characterized by comprising a sampling unit and a locking judgment unit, wherein:
the sampling unit is used for acquiring three-phase current of a balance winding of the series transformer, and recording A-phase current of the balance winding as IaThe phase B current of the balance winding is recorded as IbThe phase current of C phase of the balance winding is recorded as Ic；
The locking decision unit is used for respectively calculating Ia、Ib、IcWhen the ratio of the amplitude of any phase current to the amplitude of any phase current in other two-phase currents or the ratio of the effective value of any phase current to the effective value of any phase current in other two-phase currents is smaller than the locking constant value Kset1And locking zero sequence differential protection.
7. The apparatus of claim 6, wherein the latching constant K is set to prevent differential malfunction due to disconnection of the balanced winding CTset1The value range is as follows: 0.5 to 0.8.
8. The protection device for preventing the differential malfunction caused by the disconnection of the balanced winding CT according to any one of claims 6 or 7, wherein the latch determination unit further comprises: calculating the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow, and when the ratio of the zero sequence differential protection differential flow to the longitudinal differential protection differential flow is greater than a locking constant value Kset2And locking zero sequence differential protection.
9. The apparatus of claim 8, wherein the latching constant K is a constant value of Kset2The value range of (1) is 2-5.
10. The protection device for preventing the differential malfunction caused by the disconnection of the balanced winding CT as claimed in claim 8, wherein the zero sequence differential protection adopts a net side CT, a valve side CT and the balanced winding CT to form a difference loop; the longitudinal differential protection adopts a net side CT and a valve side CT to form a differential loop.
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| CN201811093221.2A CN109119972B (en) | 2018-09-19 | 2018-09-19 | Locking method and device for preventing differential misoperation caused by CT (current transformer) disconnection of balance winding |
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| CN111521951B (en) * | 2020-04-14 | 2023-03-28 | 南京国电南自电网自动化有限公司 | Method and device for preventing misjudgment of CT (current transformer) broken line caused by grounding fault of control winding side of valve-controlled reactor and storage medium |
| CN116365456B (en) * | 2023-04-03 | 2024-02-09 | 南京国电南自电网自动化有限公司 | Cross-interval protection data anomaly identification and intelligent processing method |
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| CN102004208B (en) * | 2011-01-05 | 2013-01-09 | 南京国电南自电网自动化有限公司 | Method for rapidly distinguishing CT wire break in bus protection |
| CN106771838B (en) * | 2016-12-29 | 2019-09-13 | 许继集团有限公司 | Transformer CT broken string method of discrimination, device and differential protecting method, device |
| CN107069673B (en) * | 2017-03-30 | 2019-01-01 | 南京南瑞继保电气有限公司 | A kind of method that quick identification branch CT breaks and is latched bus differential protection |
| CN108199349B (en) * | 2018-01-02 | 2024-05-31 | 中国电力科学研究院有限公司 | Series transformer valve side winding turn-to-turn zero sequence differential protection method and device |
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