A hexagonal diagram vector synthesis algorithm and detection device for main transformer differential protection based on differential current calculation

Abstract

The present invention provides a main transformer differential protection hexagonal diagram vector synthesis algorithm and detection device based on differential current calculation, which relates to the technical field of secondary vector detection of substations, and includes the following steps: S1, collecting current and voltage phasors on each side of the transformer, S2, double-branch current vector synthesis, S3, horizontal vector synthesis calculation of whether the secondary three-phase current of the CT on one side of the main transformer is balanced, and S4, longitudinal vector synthesis calculation of whether the differential current is qualified. The present invention adopts a multi-threaded detection and acquisition mode, fast docking, and one-time wiring can complete the test of the current hexagonal diagram on each side of the transformer, improve the test efficiency, realize fast data collection, dynamically display the vector synthesis process, and automatically draw the hexagonal diagram, intelligently analyze and judge the test results, provide decision-making basis for production front-line protection personnel, realize the most optimized man-machine operation mode and the intuitive display of the hexagonal diagram, greatly shorten the test time during testing, improve work efficiency, and save 50% of manpower.

Description

Technical Field

[0001] The invention relates to the technical field of substation secondary vector detection, in particular to a main transformer differential protection hexagonal diagram vector synthesis algorithm and a detection device based on differential current calculation. Background Art

[0002] At present, the hexagonal diagram tester on the market only displays the current vector test results on each side of the main transformer, and cannot draw conclusions on whether the differential current is qualified through vector synthesis and differential current calculation. After investigation, it was found that most power workers use phase meters to measure the amplitude and phase of the current on each side of the main transformer based on the single-phase voltage phase when performing the secondary "hexagonal diagram" test of the main transformer. This traditional test method has the following disadvantages: First, during the measurement process, the test line needs to be changed many times, which increases the risk of accidentally touching the live circuit, which is not conducive to personal and equipment safety; second, there is no unified and standardized test process to constrain the test steps of the operators, which is very easy to miss items, and the amplitude and phase of each measurement need to be manually recorded, which is time-consuming, labor-intensive and error-prone; third, after the test is completed, the differential current needs to be manually calculated to determine whether the test result is correct, which is very easy to misjudge; fourth, the time is tight and the task is heavy at the site of the substation technical transformation and overhaul project. The traditional test method is cumbersome to operate, the workload is large, and the test efficiency is low, which affects the progress of the transformation project.

[0003] Therefore, it is an inevitable choice to develop a device that can complete wiring in one go, automatically collect current and voltage phases with one click, and use phase synthesis mathematical algorithms, with the help of computers for efficient and accurate calculations and data storage, and human-computer interaction functions to solidify standardized operating procedures and improve the accuracy and work efficiency of the transformer "hexagonal diagram" test. Summary of the invention

[0004] The present invention provides a hexagonal diagram vector synthesis algorithm and detection device for main transformer differential protection based on differential current calculation. The present invention adopts a multi-threaded detection and acquisition mode, fast docking, and one-time wiring to complete the test of the current hexagonal diagram on each side of the transformer, thereby improving the test efficiency. It realizes fast data collection, dynamic display of the vector synthesis process, and automatic drawing of the hexagonal diagram, intelligent analysis and judgment of the test results, providing a decision-making basis for the front-line protection personnel of the production line, realizing the most optimized man-machine operation mode and the intuitive display of the hexagonal diagram, and the test time is directly shortened from the original 2 hours to 10 minutes, which greatly shortens the test time. The number of testers is reduced from the original 4 to 2, which improves the work efficiency and can save 50% of manpower. The device is highly professional and there is no substitute for it in the domestic market.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a main transformer differential protection hexagonal diagram vector synthesis algorithm based on differential current calculation, comprising the following steps:

[0006] S1. Collect current and voltage phasors on each side of the transformer: measure the magnitude of the secondary three-phase current of the CT on each side of the transformer and the phase angle relative to the A-phase voltage on this side;

[0007] S2, dual-branch current vector synthesis;

[0008] S3, transverse vector synthesis calculation of the transformer single-side CT secondary three-phase current is balanced;

[0009] S4. The longitudinal vector synthesis calculates whether the differential flow is qualified.

[0010] The present invention is further configured as follows: in the S1 operation step, the current and voltage phasors on each side of the transformer are collected: the secondary three-phase current of the CT on each side of the transformer and the phase angle relative to the A-phase voltage on the local side are measured, including the following steps:

[0011] S101, high voltage side: high voltage side A phase voltage The phase angle θ UHA As the benchmark, θ UHA =0°, measure the A phase current I HA Vector The amplitude and angle θ HA , measure the B phase current vector The amplitude I HB and angle θ HB , measure the C phase current vector The amplitude I HC and angle θ HC ;

[0012] S102, medium voltage side: the phase angle θ of the medium voltage side A phase voltage UMA As the benchmark, θ UMA =0°, measure the current vector of phase A The amplitude I MA and angle θ MA , measure the B phase current vector The amplitude I MB and angle θ MB , measure the C phase current vector The amplitude I MC and angle θ MC ;

[0013] S103, low voltage side: the phase angle θ of the voltage of phase A on the low voltage side ULA As the benchmark, θ ULA =0°, measure the current vector of phase A The amplitude I LA and angle θ LA , measure the B phase current vector The amplitude I LB and angle θ LB, measure the C phase current vector The amplitude I LC and angle θ LB .

[0014] The present invention is further configured as follows: in the S2 operation step, the dual-branch current vector synthesis includes the following steps: (if one side of the transformer is powered by dual branches, it is necessary to perform vector synthesis on the two current phasors measured in the branch. The dual-branch current vector synthesis calculation may be used on the high, medium and low sides of the transformer. Therefore, the subscript symbols of each value in the following calculation steps do not distinguish between the high, medium and low sides, and the H, M and L in the symbol subscripts are cancelled)

[0015] S201, with the phase angle θ of the voltage of phase A on the high voltage side UHA As the benchmark, θ UHA = 0°, measure the 1A phase current I A1 and angle θ A1 , measure the branch 1B phase current I B1 and angle θ B1 , measure the branch 1C phase current I C1 and angle θ C1 , measure the branch 2A phase current I A2 and angle θ A2 , measure the branch 2B phase current I B2 and angle θ B2 , measure the branch 2C phase current I C2 and angle θ C2 ;

[0016] S202, with the phase angle θ of the A phase voltage on the high voltage side UHA As the benchmark, θ UHA =0°, is the current vector measured in branch 1, and the angle between it and the phase A voltage on the high voltage side is θ A1 , is the current vector measured in branch 2, which is related to the high-voltage side A phase voltage The angle between them is θ A2 , the current vectors of the two branches A phase and The angle between them is θ A1 -θ A2 According to the cosine theorem, the current vector after the two branches are combined is The size is

[0017] S203, according to the cosine theorem, the current vector The angle θ A ,

[0018] S204, use the same method as S202 and S203 to obtain the current vector of phases B and C Size and angle θ B ,θ C ,in, is the current vector after the synthesis of phase B, is the current vector after synthesis of phase C.

[0019] The present invention is further configured as follows: in the S3 operation step, the lateral vector synthesis calculation of whether the secondary three-phase current of the transformer single-side CT is balanced refers to the B and C phase current vectors Current vector Hewei like and If the phases are opposite and the magnitudes are equal, the three-phase currents on this side are balanced;

[0020] The method of lateral vector synthesis is: draw an extension line in the reverse direction of the A phase current vector, and the B and C phase current vectors The sum of the projections on this extension line is equal to the A phase current vector The current vectors of phases B and C are equal in magnitude. The projected length on the extended line of the phase A current vector is calculated as: in is the A phase current vector, and are the projections of B and C on the reverse extension line of the A phase current vector, θ A is the A phase angle, θ B and θ C These are the angles of phase B and phase C respectively.

[0021] The present invention is further configured as follows: in the S4 operation step, the longitudinal vector synthesis calculation of whether the differential flow is qualified includes the following steps:

[0022] S401, triangle to star 30° angle compensation vector synthesis;

[0023] S402, differential current calculation;

[0024] S403, determine whether the differential current is qualified.

[0025] The present invention is further configured as follows: in the operation step S401, the triangle-to-star 30° angle compensation vector synthesis includes the following steps:

[0026] S4011, calculate the final value of the current vector synthesis of phase A and the angle θ′ LA , It is the final quantity involved in the synthesis of the A-phase current vector of the three sides, high, medium and low. and The angle between them is θ AC =θ LC -θ LA , and The angle between them is θ1, The angle θ′ LA for minus 180° plus θ1, which is θ′ LA =θ LC -180°+θ1+30°;

[0027] S4012, calculate the final value of the current vector synthesis of phase B and the angle θ′ LB , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ BA =θ LB -θ LA , and The angle between them is θ2, The angle θ′ LB for minus 180° plus θ2, which is θ′ LB =θ LA -180°+θ2+30°;

[0028] S4013, calculate the final value of the current vector synthesis of phase C and the angle θ′ LC , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ CB θ LC -θ LB , and The angle between them is θ3, The angle θ′ LC for minus 180° plus θ3, which is θ′ LC =θ LB -180°+θ3+30°.

[0029] The present invention is further configured as follows: in the operation step S402, the differential current calculation includes the following steps:

[0030] S4021. Calculate the rated current of the three sides. In the formula, S e is the rated capacity of the transformer, U He , U Me and U Le Respectively, the rated voltages of the high, medium and low voltage sides; n H 、n M and n L They are the CT transformation ratios at the high, medium and low voltage sides respectively;

[0031] S4022, use the normalized secondary vector to calculate the differential current, and the current phasor obtained on the high voltage side Compared with the reference current on the high voltage side, the normalized current phasor is obtained. The current phasor obtained on the medium voltage side is Compared with the reference current on the medium voltage side, the normalized current phasor is obtained. Compared with the low-voltage side reference current, the normalized current phasor is obtained. The normalized three-phase differential current is: In the formula, I cdA is the A phase differential current, I cdB is the B phase differential current, I cdC is the C phase differential current, It has been measured in step S1. If a dual-branch power supply is involved, the current vector Represents the final current vector obtained in step S2.

[0032] The present invention is further configured as follows: in the operation step S403, judging whether the differential current is qualified includes the following steps:

[0033] S4031, introduce braking current, A coordinate system is established with the braking current as the horizontal axis and the differential current as the vertical axis;

[0034] S4032, the criterion for the qualified ratio characteristic differential current is: I cd ≤K bl ×I zd +I cs , where I cd The phase difference current corresponding to the criterion for judging the qualified ratio braking differential current of the three-phase differential current of A, B, and C, among which, the phase difference current I cdA 、B phase difference flow I cdB 、C phase difference flow I cdC All have been measured in step S4022, K bl is the ratio braking coefficient, Izd The braking current corresponding to the qualified criterion of the braking differential current of the three-phase braking current of A, B, and C is as follows: zdA , Braking current I zdB , Braking current I zdC All have been measured in step S4031. cd and I zd It is the general term for the three-phase differential current of A, B, and C and the braking current. cs is the initial allowable differential current value. If the three-phase differential current and braking current of A, B, and C all meet the criteria for qualified ratio braking differential current, the device determines that the hexagonal diagram measurement is correct and the differential current is qualified.

[0035] The present invention also provides a main transformer differential protection hexagonal diagram vector detection device based on differential current calculation, which is used to implement the above-mentioned main transformer differential protection hexagonal diagram vector synthesis algorithm based on differential current calculation, including a detection box body, a touch screen is installed on the top of the detection box body, and three current vector data acquisition units and three voltage vector data acquisition units are arranged inside the detection box body.

[0036] The present invention is further configured as follows: a Bluetooth printer is installed on one side of the detection box body.

[0037] The present invention provides a main transformer differential protection hexagonal diagram vector synthesis algorithm and detection device based on differential current calculation. It has the following beneficial effects:

[0038] The present invention adopts a multi-threaded detection and acquisition mode, fast docking, and one-time wiring to complete the test of the current hexagonal diagram on each side of the transformer, thereby improving the test efficiency. It realizes fast data acquisition, dynamic display of the vector synthesis process, and automatic drawing of the hexagonal diagram, intelligent analysis and judgment of the test results, and provides a decision-making basis for the production front-line protection personnel, realizing the most optimized man-machine operation mode and the intuitive display of the hexagonal diagram. The test time is directly shortened from the original 2 hours to 10 minutes, which greatly shortens the test time. The number of testers is reduced from the original 4 to 2, which improves work efficiency and can save 50% of manpower. The device is highly professional and has no substitute in the domestic market. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of a hexagonal diagram vector synthesis algorithm for main transformer differential protection based on differential current calculation;

[0040] Figure 2 It is a schematic diagram of two-branch vector synthesis in a hexagonal diagram vector synthesis algorithm for main transformer differential protection based on differential current calculation;

[0041] Figure 3It is a schematic diagram of compensating the 30° angle of the triangle winding on the low voltage side in a hexagonal diagram vector synthesis algorithm of the main transformer differential protection based on differential current calculation;

[0042] Figure 4 It is a schematic diagram of longitudinal vector synthesis in a hexagonal diagram vector synthesis algorithm for main transformer differential protection based on differential current calculation;

[0043] Figure 5 It is a coordinate diagram of the braking current and the differential current in a hexagonal diagram vector synthesis algorithm for the main transformer differential protection based on differential current calculation;

[0044] Figure 6 The figure is a schematic diagram of a hexagonal diagram vector detection device for main transformer differential protection based on differential current calculation.

[0045] Description of the numbers in the figure:

[0046] 100. Testing box body; 110. Touch screen; 200. Bluetooth printer. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0048] Example:

[0049] Please refer to Figure 1-6 As shown, a hexagonal diagram vector synthesis algorithm for main transformer differential protection based on differential current calculation includes the following steps:

[0050] Step 1: Collect current and voltage phase quantities on each side of the transformer: Measure the magnitude of the CT secondary three-phase current on each side of the transformer and its phase angle relative to the A-phase voltage on this side.

[0051] Collect current and voltage phase quantities on each side of the transformer: Measure the magnitude of the secondary three-phase current of the CT on each side of the transformer and the phase angle relative to the A-phase voltage on this side, including the following steps:

[0052] S101, high voltage side: the voltage of phase A on this side θ UHA As the benchmark, θ UHA =0°, measure the A phase current I HA and angle θ HA , measure the B phase current I HB and angle θ HB , measure the C phase current I HC and angle θ HC ;

[0053] S102, medium voltage side: the A phase voltage θ UHA As the benchmark, θ UHA =0°, measure the A phase current I MA and angle θMA , measure the B phase current I MB and angle θ MB , measure the C phase current I MC and angle θ MC ;

[0054] S103, low voltage side: the A phase voltage θ UHA As the benchmark, θ UHA =0°, measure the A phase current I LA and angle θ LA , measure the B phase current I LB and angle θ LB , measure the C phase current I LC and angle θ LB .

[0055] Step 2: Double-branch current vector synthesis.

[0056] The dual-branch current vector synthesis includes the following steps:

[0057] S201, taking the A phase voltage ∠Ua on this side as the reference, ∠Ua=0°, measure the A phase current I of branch 1 A1 and angle θ A1 , measure the branch 1B phase current I B1 and angle θ B1 , measure the branch 1C phase current I C1 and angle θ C1 , measure the branch 2A phase current I A2 and angle θ A2 , measure the branch 2B phase current I B2 and angle θ B2 , measure the branch 2C phase current I C2 and angle θ C2 ;

[0058] S202, with the A phase voltage on this side As a benchmark, The angle is 0°, is the current vector measured in branch 1, which is The angle between them is θ A1 , is the current vector measured in branch 2, which is related to the phase A voltage on this side. The angle between them is θ A2 , the current vectors of the two branches A phase and The angle between them is θ A1 -θ A2 According to the cosine theorem, the combined current of the two branches is for

[0059] S203, according to the cosine theorem, the current vector The angle θ A ,

[0060] S204, seek The size and angle θ B ,θ C ,in, is the current vector after the synthesis of phase B, is the current vector after synthesis of phase C.

[0061] Step 3: Calculate the balance of the three-phase secondary current of the transformer CT on one side by transverse vector synthesis.

[0062] The calculation of the horizontal vector synthesis is whether the three-phase current of the secondary CT on one side of the transformer is balanced. It refers to the current vector of the B and C phases. Current vector Hewei like and If the phases are opposite and the magnitudes are equal, the three-phase currents on this side are balanced;

[0063] The method of lateral vector synthesis is: draw an extension line in the reverse direction of the A phase current vector, and the B and C phase current vectors The sum of the projections on this extension line is equal to the A phase current vector The current vectors of phases B and C are equal in magnitude. The projected length on the extended line of the phase A current vector is calculated as: in is the magnitude of the A phase current vector, and are the projections of B and C on the reverse extension line of the A phase current vector, θ A is the A phase angle, θ B and θ C These are the angles of phase B and phase C respectively.

[0064] If the quantities and obtained from the above formula are equal in magnitude, it is judged that the three-phase is in equilibrium.

[0065] Use the same method to calculate the lateral vector synthesis on the medium voltage side. If the three phases are balanced, the test is qualified.

[0066] Use the same method to calculate the lateral vector synthesis on the low-voltage side. If the three phases are balanced, the test is qualified.

[0067] Step 4: Calculate the difference flow by longitudinal vector synthesis to see if it is qualified.

[0068] The balance of three-phase current on the high, medium and low sides is only one of the criteria for judging whether the hexagonal diagram test is qualified. It is also necessary to longitudinally synthesize the current of each phase on the high, medium and low sides to see whether it conforms to Kirchhoff's current law, that is, to judge whether the differential current is qualified. Taking phase A as an example, take out the phase A current on the high, medium and low sides and synthesize them vectorially to see whether the vector sum is 0. If it is close to 0, it is qualified, otherwise it is unqualified. The method for phase B\C is the same as that for phase A.

[0069] However, the longitudinal vector synthesis must first overcome a difficulty, that is, the low-voltage side winding of the transformer is connected in a triangle, and the high and medium voltage sides are connected in a star. The current vectors on the high and medium voltage sides and the current vector on the low voltage side are not on the same straight line, and there is a 30° angle difference. Therefore, it is necessary to compensate the 30° angle so that they are on a straight line before vector synthesis can be performed to obtain the true differential current.

[0070] The longitudinal vector synthesis calculation of the differential flow is qualified, including the following steps:

[0071] S401, triangle to star 30° angle compensation vector synthesis.

[0072] S402: Calculate differential current.

[0073] S403, determine whether the differential current is qualified.

[0074] Since the connection group of the transformer was selected in step 1, if the low-voltage side is connected in a triangle, there is a 30° angle between the high-voltage and low-voltage side voltages. When calculating the differential current, the 30° angle between the high-voltage and low-voltage side currents must be compensated so that the high-voltage and low-voltage side current vectors are on the same straight line before the differential current calculation can be performed.

[0075] Low voltage side: The voltage of phase A on this side is θ UHA As the benchmark, θ UHA =0°.

[0076] Measure the A phase current I LA and angle θ LA .

[0077] Measure the B phase current I LB and angle θ LB .

[0078] Measure the C phase current I LC and angle θ CB .

[0079] Since the voltage on the low voltage side of the transformer leads the voltage on the high voltage side by 30°, θ UHA The three-phase current measured as the reference 30° should be added so that its phase angle can be under the same voltage reference as the current vector on the high and medium voltage sides.

[0080] In order to compensate for 30° and make the low voltage side current and the high and medium voltage side current vector synthesis on the same straight line, the following vector operation must be performed first:

[0081] The 30° angle compensation vector synthesis of the triangle to star includes the following steps:

[0082] S4011, calculate the final value of the current vector synthesis of phase A and the angle θ′ LA , It is the final quantity involved in the synthesis of the A-phase current vector of the three sides, high, medium and low. and The angle between them is θ AC =θ LC -θ LA , and The angle between them is θ1, The angle θ′ LA for minus 180° plus θ1, which is θ′ LA =θ LC -180°+θ1+30°;

[0083] S4012, calculate the final value of the current vector synthesis of phase B and the angle θ′ LB , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ BA =θ LB -θ LA , and The angle between them is θ2, The angle θ′ LB for minus 180° plus θ2, which is θ′ LB =θ LA -180°+θ2+30°;

[0084] S4013, calculate the final value of the current vector synthesis of phase C and the angle θ′ LC , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ CB =θ LC -θLB , and The angle between them is θ3, The angle θ′ LC for minus 180° plus θ3, which is θ′ LC =θ LB -180°+θ3+30°.

[0085] The above vector Angle: θ′ LA ,θ′ LB ,θ′ LC The angle is measured based on the low-voltage side voltage. If the longitudinal vector is synthesized with the high- and medium-voltage side currents, a 30° angle is added.

[0086] This device can dynamically display the synthesis process based on the above-mentioned triangle-to-star 30° angle compensation vector synthesis mathematical model, overcoming the difficulty of the longitudinal vector synthesis of the 30° angle difference between the low-voltage side and the high and medium voltage side current vectors. The work of longitudinal vector synthesis differential current calculation is now carried out, that is, the step of calculating whether the differential current is qualified.

[0087] In summary, the vector values ​​of high, medium and low pressure sides are as follows:

[0088] High voltage side A phase current I HA and angle θ HA .

[0089] High voltage side B phase current I HB and angle θ HB .

[0090] High voltage side C phase current I HC and angle θ HC .

[0091] Medium voltage side phase current I MA and angle θ MA .

[0092] Phase current I on the medium voltage side MB and angle θ MB .

[0093] Phase current I on the medium voltage side MC and angle θ MC .

[0094] Low voltage side phase current I′ LA and angle θ′ LA .

[0095] Low voltage side phase current I′ LB and angle θ′ LB.

[0096] Low voltage side phase current I′ LC and angle θ′ LC .

[0097] After vector calculation, the in-phase current vectors on each side have been placed on a straight line.

[0098] The differential current calculation includes the following steps:

[0099] S4021. Calculate the rated current of the three sides. In the formula, S e is the rated capacity of the transformer, U He , U Me and U Le Respectively, the rated voltages of the high, medium and low voltage sides; n H 、n M and n L They are the CT transformation ratios at the high, medium and low voltage sides respectively;

[0100] S4022, use the normalized secondary vector to calculate the differential current, and the current phasor obtained on the high voltage side Compared with the reference current on the high voltage side, the normalized current phasor is obtained. The current phasor obtained on the medium voltage side is Compared with the reference current on the medium voltage side, the normalized current phasor is obtained. Compared with the low-voltage side reference current, the normalized current phasor is obtained. The normalized three-phase differential current is: In the formula, I cdA is the A phase differential current, I cdB is the B phase differential current, I cdC It is the C phase difference flow.

[0101] Taking phase A as an example, first calculate the medium and low voltage and current vectors

[0102] According to the cosine theorem, the angles of medium and low voltage and current are: Then the medium and low voltage and current vector With high voltage side current Synthesize to get the A phase longitudinal vector synthesis result

[0103] We only need to get the amplitude of the synthesis result, and the angle does not need to be considered.

[0104] Similarly, the calculation formula for the difference current between phases B and C is as follows:

[0105] Phase B:

[0106]

[0107]

[0108] Phase C:

[0109]

[0110] Judging whether the differential current is qualified includes the following steps:

[0111] S4031, introduce braking current, A coordinate system is established with the braking current as the horizontal axis and the differential current as the vertical axis;

[0112] S4032, the criterion for the qualified ratio characteristic differential current is: I cd ≤K bl ×I zd +I cs , where I cd The phase difference current corresponding to the criterion for judging the qualified ratio braking differential current of the three-phase differential current of A, B, and C, among which, the phase difference current I cdA 、B phase difference flow I cdB 、C phase difference flow I cdC All have been measured in step S4022, K bl is the ratio braking coefficient, I zd The braking current corresponding to the qualified criterion of the braking differential current of the three-phase braking current of A, B, and C is as follows: zdA , Braking current I zdB , Braking current I zdC All have been measured in step S4031. cd and I zd It is the general term for the three-phase differential current of A, B, and C and the braking current. cs is the initial allowable differential current value. If the three-phase differential current and braking current of A, B, and C all meet the criteria for qualified ratio braking differential current, the device determines that the hexagonal diagram measurement is correct and the differential current is qualified.

[0113] The device can dynamically display the synthesis process according to the above longitudinal vector synthesis method mathematical model.

[0114] The present invention also provides a main transformer differential protection hexagonal diagram vector detection device based on differential current calculation, including a detection box body 100, a touch screen 110 is installed on the top of the detection box body 100, and three current vector data acquisition units and three voltage vector data acquisition units are arranged inside the detection box body 100.

[0115] A Bluetooth printer 200 is installed on one side of the detection box body 100 .

[0116] The above are only preferred embodiments of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A hexagonal diagram vector synthesis algorithm for main transformer differential protection based on differential current calculation, characterized in that: The following steps are involved: S1. Collect current and voltage phasors on each side of the transformer: measure the magnitude of the secondary three-phase current of the CT on each side of the transformer and the phase angle relative to the A-phase voltage on this side; The following steps are involved: S101, high voltage side: high voltage side A phase voltage The phase angle θ UHA As the benchmark, θ UHA =0°, measure the current vector of phase A The amplitude I HA and angle θ HA , measure the B phase current vector The amplitude I HB and angle θ HB , measure the C phase current vector The amplitude I HC and angle θ HC ; S102, medium voltage side: the phase angle θ of the medium voltage side A phase voltage UMA As the benchmark, θ UMA =0°, measure the current vector of phase A The amplitude I MA and angle θ MA , measure the B phase current vector The amplitude I MB and angle θ MB , measure the C phase current vector The amplitude I MC and angle θ MC ; S103, low voltage side: the phase angle θ of the voltage of phase A on the low voltage side ULA As the benchmark, θ ULA =0°, measure the current vector of phase A The amplitude I LA and angle θ LA , measure the B phase current vector The amplitude I LB and angle θ LB , measure the C phase current vector The amplitude I LC and angle θ LB ; S2, dual-branch current vector synthesis; The following steps are involved: S201, with the phase angle θ of the voltage of phase A on the high voltage side UHA As the benchmark, θ UHA = 0°, measure the 1A phase current I A1 and angle θ A1 , measure the branch 1B phase current I B1 and angle θ B1 , measure the branch 1C phase current I C1 and angle θ C1 , measure the branch 2A phase current I A2 and angle θ A2 , measure the branch 2B phase current I B2 and angle θ B2 , measure the branch 2C phase current I C2 and angle θ C2 ; S202, with the phase angle θ of the A phase voltage on the high voltage side UHA As the benchmark, θ UHA =0°, is the current vector measured in branch 1, and the angle between it and the phase A voltage on the high voltage side is θ A1 , is the current vector measured in branch 2, and the angle between it and the phase A voltage on the high voltage side is θ A2 , the current vectors of the two branches A phase and The angle between them is θ A1 -θ A2 According to the cosine theorem, the current vector after the two branches are combined is The size is S203, according to the cosine theorem, the current vector The angle θ A , S204, use the same method as S202 and S203 to obtain the current vector of phases B and C Size and angle θ B ,θ C ,in, is the current vector after the synthesis of phase B, is the current vector after synthesis of phase C; S3, transverse vector synthesis calculation of the transformer single-side CT secondary three-phase current is balanced; The calculation of the horizontal vector synthesis is whether the three-phase current of the secondary CT on one side of the transformer is balanced. It refers to the current vector of the B and C phases. Current vector Hewei like and If the phases are opposite and the magnitudes are equal, the three-phase currents on this side are balanced; The method of lateral vector synthesis is: draw an extension line in the reverse direction of the A phase current vector, and the B and C phase current vectors The sum of the projections on this extension line is equal to the A phase current vector The current vectors of phases B and C are equal in magnitude. The projected length on the extended line of the phase A current vector is calculated as: in is the magnitude of the A phase current vector, and are the projections of B and C on the reverse extension line of the A phase current vector, θ A is the A phase angle, θ B and θ C are the angles of phase B and phase C respectively; S4. Whether the longitudinal vector synthesis calculation difference flow is qualified; The following steps are involved: S401, triangle to star 30° angle compensation vector synthesis; S402, differential current calculation; S403, judging whether the differential current is qualified; The 30° angle compensation vector synthesis of the triangle to star includes the following steps: S4011, calculate the final value of the current vector synthesis of phase A and the angle θ L ' A , It is the final quantity involved in the synthesis of the A-phase current vector of the three sides, high, medium and low. and The angle between them is θ AC =θ LC -θ LA , and The angle between them is θ1, The angle θ′ LA for minus 180° plus θ1, which is θ′ LA =θ LC -180°+θ1+30°; S4012, calculate the final value of the current vector synthesis of phase B and the angle θ′ LB , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ BA =θ LB -θ LA , and The angle between them is θ2, The angle θ L ' B for minus 180° plus θ2, which is θ′ LB =θ LA -180°+θ2+30°; S4013, calculate the final value of the current vector synthesis of phase C and the angle θ′ LC , It is the final quantity involved in the synthesis of the B-phase current vector on the high, medium and low sides. and The angle between them is θ CB =θ LC -θ LB , and The angle between them is θ3, The angle θ L ' C for minus 180° plus θ3, which is θ′ LC =θ LB -180°+θ3+30°; The differential current calculation includes the following steps: S4021. Calculate the rated current of the three sides. In the formula, S e is the rated capacity of the transformer, U He , U Me and U Le Respectively, the rated voltages of the high, medium and low voltage sides; n H 、n M and n L They are the CT transformation ratios at the high, medium and low voltage sides respectively; S4022, use the normalized secondary vector to calculate the differential current, and the current phasor obtained on the high voltage side Compared with the reference current on the high voltage side, the normalized current phasor is obtained. The current phasor obtained on the medium voltage side is Compared with the reference current on the medium voltage side, the normalized current phasor is obtained. Compared with the low-voltage side reference current, the normalized current phasor is obtained. The normalized three-phase differential current is: In the formula, I cdA is the A phase differential current, I cdB is the B phase differential current, I cdC is the C phase differential current, It has been measured in step S1. If a dual-branch power supply is involved, the current vector represents the final current vector obtained in step S2; Judging whether the differential current is qualified includes the following steps: S4031, introduce braking current, A coordinate system is established with the braking current as the horizontal axis and the differential current as the vertical axis; S4032, the criterion for the qualified ratio characteristic differential current is: I cd ≤K bl ×I zd +I cs , where I cd The phase difference current corresponding to the criterion for judging the qualified ratio braking differential current of the three-phase differential current of A, B, and C, among which, the phase difference current I cdA 、B phase difference flow I cdB 、C phase difference flow I cdC All have been measured in step S4022, K bl is the ratio braking coefficient, I zd The braking current corresponding to the qualified criterion of the braking differential current of the three-phase braking current of A, B, and C is as follows: zdA , Braking current I zdB , Braking current I zdC All have been measured in step S4031. cd and I zd It is the general term for the three-phase differential current of A, B, and C and the braking current. cs is the initial allowable differential current value. If the three-phase differential current and braking current of A, B, and C all meet the criteria for qualified ratio braking differential current, the device determines that the hexagonal diagram measurement is correct and the differential current is qualified.

2. A main transformer differential protection hexagonal diagram vector detection device based on differential current calculation, used to implement a main transformer differential protection hexagonal diagram vector synthesis algorithm based on differential current calculation as claimed in claim 1, comprising a detection box body, characterized in that: A touch screen is installed on the top of the detection box body, and a three-way current vector data acquisition unit and a three-way voltage vector data acquisition unit are arranged inside the detection box body.

3. The main transformer differential protection hexagonal diagram vector detection device based on differential current calculation according to claim 2 is characterized in that: A Bluetooth printer is installed on one side of the detection box body.

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