CN108155625B - A kind of tranformer protection CT broken string method of discrimination, differential protecting method and device - Google Patents

A kind of tranformer protection CT broken string method of discrimination, differential protecting method and device Download PDF

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Publication number
CN108155625B
CN108155625B CN201711466009.1A CN201711466009A CN108155625B CN 108155625 B CN108155625 B CN 108155625B CN 201711466009 A CN201711466009 A CN 201711466009A CN 108155625 B CN108155625 B CN 108155625B
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current
breaker
phase
zero
given threshold
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CN108155625A (en
Inventor
陈继瑞
李宝伟
樊占峰
李旭
唐艳梅
姜自强
王东兴
吕利娟
汪花永
赵剑松
方正
董新涛
孟利平
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Xuji Group Co Ltd
XJ Electric Co Ltd
Xuchang XJ Software Technology Co Ltd
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Xuji Group Co Ltd
XJ Electric Co Ltd
Xuchang XJ Software Technology Co Ltd
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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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Protection Of Transformers (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The present invention relates to a kind of tranformer protection CT broken string method of discrimination, differential protecting method and devices; if the method for discrimination includes: that this side of transformer meets 3/2nds modes of connection; the three-phase phase current and three-phase difference current of this side of transformer, middle breaker are obtained, and calculates side, the corresponding zero-sequence current of middle breaker；Judge following criterion: 1) less than the first given threshold, the maximum value in three-phase phase current is greater than the second given threshold and is less than third given threshold the minimum value in the three-phase phase current of this side breaker or middle breaker；2) while breaker or middle breaker zero-sequence current and while, middle breaker zero-sequence current and be all larger than the 4th given threshold；3) maximum value in three-phase difference current is greater than the 5th given threshold；If condition above all meets, it is judged as that this side CT breaks.The present invention can quick and precisely judge whether transformer side CT breaks, and provide reliable basis for transformer differential protection precision maneuver.

Description

A kind of tranformer protection CT broken string method of discrimination, differential protecting method and device
Technical field
The present invention relates to a kind of tranformer protection CT broken string method of discrimination, differential protecting method and devices, belong to power train System technical field of relay protection.
Background technique
As electric system hair, the capital equipment of power transformation, the voltage that carry different voltages grade is of coupled connections transformer Relationship acts on particularly important.But it is smaller in load current for the transformer side of 3/2nds wiring, and side, middle breaker CT It is influenced by the passing through property electric current between two bus strings, it will lead to the side of 3/2nds connection side of transformer, middle breaker CT On the electric current that flows through occur uneven, cause device for transformer to be accidentally determined as CT broken string, Blocking Differential Protection causes differential protection Tripping；In addition, when smaller for 3/2nds side load of transformer, CT broken string occurs, while when load is slowly increased again, at this time The transformer CT broken string criterion of conventional differentiation difference stream Sudden Changing Rate, it is impossible to determine CT broken string, transformer differential will occur Malfunction will bring hidden danger to the electric power netting safe running of electric system, cause partial electric grid to paralyse when serious.
Therefore, in the protection equipment for transformer of 3/2nds modes of connection, when load current is smaller, fast and accurately Ground recognises that CT breaks, and correctly acts for transformer differential protection and provides reliable basis, to prevent transformer differential protection Malfunction or tripping become the major issue in electric system maintenance.
Summary of the invention
The object of the present invention is to provide a kind of tranformer protection CT broken string method of discrimination, differential protecting method and devices, use In solve load current it is smaller or occur CT broken string and load increase when, 3/2nds connection side transformer CT broken string differentiate not Accurate problem.
In order to solve the above technical problems, the present invention provides a kind of tranformer protection CT broken string method of discrimination, including it is following Scheme:
Method of discrimination scheme one: steps are as follows:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks.
Method of discrimination scheme two: further including carrying out after criterion all meets on the basis of method of discrimination scheme one Delay confirmation.
Method of discrimination scheme three: on the basis of method of discrimination scheme one or two, the condition 1) discrimination formula are as follows:
Or
Wherein, I1A、I1BAnd I1CThe respectively three-phase phase current of this side breaker, I2A、I2BAnd I2CRespectively in this side The three-phase phase current of breaker, k1∈ (0.03,0.04) is indicated without stream threshold coefficient, kp∈ (0.01,6) indicates this lateral balance system Number, Iset0=max (0.09Ie,0.06kpIn) indicate this side zero-sequence current threshold, Iset1=max (0.35Ie,0.2kpIn) indicate This side phase current threshold, InFor this side CT current rating, IeFor transformer reference current；
The condition 2) discrimination formula are as follows:
Or 3I02=| I2A+I2B+I2C| > Iset0
Wherein, 3I01、3I02Respectively side, middle breaker zero-sequence current, 3I0For side, middle breaker zero-sequence current it With；
The condition 3) discrimination formula are as follows:
max{IopA,IopB,IopC> Isetop
Wherein, IopA、IopBAnd IopCIndicate three-phase difference current, Isetop={ 0.15Ie,0.03kpInIt is difference current door Sill.
Method of discrimination scheme four: on the basis of method of discrimination scheme two, the time T ∈ (5s, 10s) of delay confirmation.
The present invention also provides a kind of tranformer protection CT broken string discriminating gears, including following scheme:
Discriminating gear scheme one: including processor and memory, the processor is stored in memory for handling Instruction is to realize following method:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks.
Discriminating gear scheme two: on the basis of discriminating gear scheme one, the processor is also used to handle and be stored in Instruction in reservoir is to realize: criterion all meets laggard line delay confirmation.
Discriminating gear scheme three: on the basis of discriminating gear scheme one or two, the condition 1) discrimination formula are as follows:
Or
Wherein, I1A、I1BAnd I1CThe respectively three-phase phase current of this side breaker, I2A、I2BAnd I2CRespectively in this side The three-phase phase current of breaker, k1∈ (0.03,0.04) is indicated without stream threshold coefficient, kp∈ (0.01,6) indicates this lateral balance system Number, Iset0=max (0.09Ie,0.06kpIn) indicate this side zero-sequence current threshold, Iset1=max (0.35Ie,0.2kpIn) indicate This side phase current threshold, InFor this side CT current rating, IeFor transformer reference current；
The condition 2) discrimination formula are as follows:
Or 3I02=| I2A+I2B+I2C| > Iset0
Wherein, 3I01、3I02Respectively side, middle breaker zero-sequence current, 3I0For side, middle breaker zero-sequence current it With；
The condition 3) discrimination formula are as follows:
max{IopA,IopB,IopC> Isetop
Wherein, IopA、IopBAnd IopCIndicate three-phase difference current, Isetop={ 0.15Ie,0.03kpInIt is difference current door Sill.
Discriminating gear scheme four: on the basis of discriminating gear scheme two, the time T ∈ (5s, 10s) of delay confirmation.
The present invention also provides a kind of differential protecting methods differentiated based on tranformer protection CT broken string, and steps are as follows:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks, Blocking Differential Protection.
The present invention also provides it is a kind of based on tranformer protection CT broken string differentiate differential protection, including processor and Memory, the processor is for handling instruction stored in memory to realize following method:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks, Blocking Differential Protection.
The beneficial effects of the present invention are:
For the transformer side of 3/2nds wiring, when load current is smaller, is influenced by passing through property electric current, Huo Zhefa In the case that generation load is slowly increased again after raw CT broken string, by the three-phase phase current and zero sequence electricity that judge side, middle breaker Whether stream and three-phase difference current meet corresponding condition, can fast and accurately judge whether transformer side CT breaks, It is not influenced by 3/2nds side out-of-balance currents, provides reliable basis for subsequent transformer differential protection precision maneuver, avoid difference Dynamic false protection or tripping, to improve transformer differential protection Reliability of Microprocessor.
Further, broken by delay confirmation CT and differentiated as a result, effectively increasing the accuracy for differentiating result.
Detailed description of the invention
Fig. 1 is 3/2nds wiring CT distribution map of 500kV transformer differential protection；
Fig. 2 is the flow chart of the differential protecting method differentiated based on tranformer protection CT broken string；
Voltage, curent change figure when Fig. 3 is high voltage side of transformer CT broken string during differential protection.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, below in conjunction with attached drawing and specific implementation The present invention will be described in further detail for example.
Fig. 1 gives the distribution map of 3/2nds wiring of 500kV transformer, includes six groups of Current Mutual Inductances in the distribution map Device, respectively TA1, TA2, TA3, TA4, TA5 and TA6；Including three groups of dc circuit breakers, respectively K11, K12 and K13, K22, K32.Wherein the breaker K11 and K13 in 3/2nds modes of connection are side breaker, and breaker K12 is intermediate breaker.
On the basis of above-mentioned 3/2nds wiring, the present invention provides a kind of tranformer protection CT break method of discrimination, Its corresponding flow chart as shown in Fig. 2, specifically includes the following steps:
(1) judge whether this side of transformer meets 3/2nds modes of connection.
(2) if meeting 3/2nds modes of connection, three-phase phase current, the middle breaker of this side breaker of transformer are obtained Three-phase phase current and three-phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker.
Certainly, if this side of transformer is unsatisfactory for 3/2nds modes of connection, without following corresponding judgment step.
(3) following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold, discrimination formula are as follows:
Or
Wherein, I1A、I1BAnd I1CThe respectively three-phase phase current of this side breaker, I2A、I2BAnd I2CRespectively in this side The three-phase phase current of breaker, k1∈ (0.03,0.04) is indicated without stream threshold coefficient, kp∈ (0.01,6) indicates this lateral balance system Number, Iset0=max (0.09Ie,0.06kpIn) indicate this side zero-sequence current threshold, Iset1=max (0.35Ie,0.2kpIn) indicate This side phase current threshold, InFor this side CT current rating, IeFor transformer reference current, min { I1A,I1B,I1CIt is I1A、I1B And I1CIn minimum value, max { I1A,I1B,I1CIt is I1A、I1BAnd I1CIn maximum value, min { I2A,I2B,I2CIt is I2A、I2BWith I2CIn minimum value, max { I2A,I2B,I2CIt is I2A、I2BAnd I2CIn maximum value.
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold, discrimination formula are as follows:
Or 3I02=| I2A+I2B+I2C| > Iset0
Wherein, 3I01、3I02Respectively side, middle breaker zero-sequence current, 3I0For side, middle breaker zero-sequence current it With Iset0For this side zero-sequence current threshold.
3) maximum value in three-phase difference current is greater than the 5th given threshold, discrimination formula are as follows:
max{IopA,IopB,IopC> Isetop
Wherein, IopA、IopBAnd IopCIndicate three-phase difference current, max { IopA,IopB,IopCIndicate IopA、IopBAnd IopCIn Maximum value, Isetop={ 0.15Ie,0.03kpInIt is differential current threshold.
Wherein, three-phase difference current respectively refers to 3/2nds side of high voltage side of transformer, middle breaker TA, medium voltage side breaker A, B, C phase current of TA and low-pressure side breaker TA are multiplied by the vector sum after respective side coefficient of balance.
(4) if criterion above all meets and pass through delay confirmation, it is judged as that this side CT breaks.
Wherein, the time T ∈ (5s, 10s) of delay confirmation adjusts input by device parameter and obtains in practical applications.
Fig. 3 gives the high voltage side of transformer i.e. side 500kV and the medium voltage side i.e. three-phase electricity of the side 220kV in the present embodiment Pressure, curent change figure, and three-phase difference current variation diagram is given, in high pressure side, event occurs for breaker A phase TA secondary circuit When barrier open circuit magnitude is 0, there is zero-sequence current in high pressure side breaker and each side A, C phase of transformer no longer balances and differential electricity occurs Stream can effectively determine high-pressure side using above CT broken string method of discrimination in conjunction with the characteristic of zero-sequence current and difference current CT broken string, while quick lock transformer differential protection outlet logic occur for side breaker A phase.By Fig. 3 field failure waveform, Differentiate it can be seen that the above CT broken string method of discrimination can carry out CT broken string fast and reliablely, improves differential protection reliable in action Property.
On the basis of above-mentioned tranformer protection CT breaks method of discrimination, the present invention also provides one kind to be protected based on transformer Protect the differential protecting method that CT broken string differentiates, i.e., in the case where judging transformer this side CT broken string, then Blocking Differential Protection, Prevent differential protection malfunction；In the case where judging that this side of transformer CT does not break, then differential protection is opened, differential guarantor is prevented Protect tripping.
The present invention also provides a kind of tranformer protection CT broken string discriminating gear, including processor and memory, the places Reason device is for handling instruction stored in memory to realize following method:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks.
The present invention also provides it is a kind of based on tranformer protection CT broken string differentiate differential protection, including processor and Memory, the processor is for handling instruction stored in memory to realize following method:
Judge whether this side of transformer meets 3/2nds modes of connection；
If satisfied, obtaining the three-phase phase current and three of the three-phase phase current of this side breaker of transformer, middle breaker Phase difference current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
Following criterion is judged, the criterion are as follows:
1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase Maximum value in electric current is greater than the second given threshold and is less than third given threshold；
2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th Given threshold；
3) maximum value in three-phase difference current is greater than the 5th given threshold；
If criterion above all meets, it is judged as that this side CT breaks, Blocking Differential Protection.
The core of CT broken string discriminating gear and differential protection is to realize above-mentioned CT broken string method of discrimination and difference respectively Dynamic guard method herein sentences CT broken string since CT broken string method of discrimination and differential protecting method being described in detail Other device and differential protection repeat no more.

Claims (10)

  1. The method of discrimination 1. a kind of tranformer protection CT breaks, which is characterized in that steps are as follows:
    Judge whether this side of transformer meets 3/2nds modes of connection；
    If satisfied, obtaining the three-phase phase current of this side breaker of transformer, the three-phase phase current of middle breaker and three differences Streaming current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
    Following criterion is judged, the criterion are as follows:
    1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase current In maximum value be greater than the second given threshold and be less than third given threshold；
    2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th setting Threshold value；
    3) maximum value in three-phase difference current is greater than the 5th given threshold；
    If criterion above all meets, it is judged as that this side CT breaks.
  2. The method of discrimination 2. tranformer protection CT according to claim 1 breaks, which is characterized in that further include that criterion is complete Portion meets laggard line delay confirmation.
  3. The method of discrimination 3. tranformer protection CT according to claim 1 or 2 breaks, which is characterized in that the condition 1) Discrimination formula are as follows:
    Or
    Wherein, I1A、I1BAnd I1CThe respectively three-phase phase current of this side breaker, I2A、I2BAnd I2CIt is breaking respectively in this side The three-phase phase current of device, k1∈ (0.03,0.04) is indicated without stream threshold coefficient, kp∈ (0.01,6) indicates this lateral balance coefficient, Iset0=max (0.09Ie,0.06kpIn) indicate this side zero-sequence current threshold, Iset1=max (0.35Ie,0.2kpIn) indicate this side Phase current threshold, InFor this side CT current rating, IeFor transformer reference current；
    The condition 2) discrimination formula are as follows:
    Wherein, 3I01、3I02Respectively side, middle breaker zero-sequence current, 3I0For the sum of side, the zero-sequence current of middle breaker；
    The condition 3) discrimination formula are as follows:
    max{IopA,IopB,IopC> Isetop
    Wherein, IopA、IopBAnd IopCIndicate three-phase difference current, Isetop={ 0.15Ie,0.03kpInIt is differential current threshold.
  4. The method of discrimination 4. tranformer protection CT according to claim 2 breaks, which is characterized in that the time T of delay confirmation ∈(5s,10s)。
  5. The discriminating gear 5. a kind of tranformer protection CT breaks, which is characterized in that including processor and memory, the processor is used In processing instruction stored in memory to realize following method:
    Judge whether this side of transformer meets 3/2nds modes of connection；
    If satisfied, obtaining the three-phase phase current of this side breaker of transformer, the three-phase phase current of middle breaker and three differences Streaming current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
    Following criterion is judged, the criterion are as follows:
    1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase current In maximum value be greater than the second given threshold and be less than third given threshold；
    2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th setting Threshold value；
    3) maximum value in three-phase difference current is greater than the 5th given threshold；
    If criterion above all meets, it is judged as that this side CT breaks.
  6. The discriminating gear 6. tranformer protection CT according to claim 5 breaks, which is characterized in that the processor is also used to Instruction stored in memory is handled to realize: criterion all meets laggard line delay confirmation.
  7. The discriminating gear 7. tranformer protection CT according to claim 5 or 6 breaks, which is characterized in that the condition 1) Discrimination formula are as follows:
    Or
    Wherein, I1A、I1BAnd I1CThe respectively three-phase phase current of this side breaker, I2A、I2BAnd I2CIt is breaking respectively in this side The three-phase phase current of device, k1∈ (0.03,0.04) is indicated without stream threshold coefficient, kp∈ (0.01,6) indicates this lateral balance coefficient, Iset0=max (0.09Ie,0.06kpIn) indicate this side zero-sequence current threshold, Iset1=max (0.35Ie,0.2kpIn) indicate this side Phase current threshold, InFor this side CT current rating, IeFor transformer reference current；
    The condition 2) discrimination formula are as follows:
    Wherein, 3I01、3I02Respectively side, middle breaker zero-sequence current, 3I0For the sum of side, the zero-sequence current of middle breaker；
    The condition 3) discrimination formula are as follows:
    max{IopA,IopB,IopC> Isetop
    Wherein, IopA、IopBAnd IopCIndicate three-phase difference current, Isetop={ 0.15Ie,0.03kpInIt is differential current threshold.
  8. The discriminating gear 8. tranformer protection CT according to claim 6 breaks, which is characterized in that the time T of delay confirmation ∈(5s,10s)。
  9. 9. a kind of differential protecting method differentiated based on tranformer protection CT broken string, which is characterized in that steps are as follows:
    Judge whether this side of transformer meets 3/2nds modes of connection；
    If satisfied, obtaining the three-phase phase current of this side breaker of transformer, the three-phase phase current of middle breaker and three differences Streaming current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
    Following criterion is judged, the criterion are as follows:
    1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase current In maximum value be greater than the second given threshold and be less than third given threshold；
    2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th setting Threshold value；
    3) maximum value in three-phase difference current is greater than the 5th given threshold；
    If criterion above all meets, it is judged as that this side CT breaks, Blocking Differential Protection.
  10. 10. a kind of differential protection differentiated based on tranformer protection CT broken string, which is characterized in that including processor and storage Device, the processor is for handling instruction stored in memory to realize following method:
    Judge whether this side of transformer meets 3/2nds modes of connection；
    If satisfied, obtaining the three-phase phase current of this side breaker of transformer, the three-phase phase current of middle breaker and three differences Streaming current, and calculate side breaker and the corresponding zero-sequence current of middle breaker；
    Following criterion is judged, the criterion are as follows:
    1) minimum value in the three-phase phase current of this side breaker or middle breaker is less than the first given threshold, three-phase phase current In maximum value be greater than the second given threshold and be less than third given threshold；
    2) while breaker or middle breaker zero-sequence current and while, the sum of the zero-sequence current of middle breaker be all larger than the 4th setting Threshold value；
    3) maximum value in three-phase difference current is greater than the 5th given threshold；
    If criterion above all meets, it is judged as that this side CT breaks, Blocking Differential Protection.
CN201711466009.1A 2017-12-28 2017-12-28 A kind of tranformer protection CT broken string method of discrimination, differential protecting method and device Active CN108155625B (en)

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