CN113725816A - Transformer differential protection method and system based on current phasor difference 2 norm - Google Patents

Transformer differential protection method and system based on current phasor difference 2 norm Download PDF

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CN113725816A
CN113725816A CN202111049817.4A CN202111049817A CN113725816A CN 113725816 A CN113725816 A CN 113725816A CN 202111049817 A CN202111049817 A CN 202111049817A CN 113725816 A CN113725816 A CN 113725816A
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current
braking
fault
norm
phasor
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CN113725816B (en
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廖小君
王晓茹
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Sichuan Electric Vocational & Technical College
Technology & Skill Training Center Of Sichuan Electric Power Corp
Southwest Jiaotong University
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Sichuan Electric Vocational & Technical College
Technology & Skill Training Center Of Sichuan Electric Power Corp
Southwest Jiaotong University
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation

Abstract

The invention discloses a transformer differential protection method and a system based on a current phasor difference 2 norm, which relate to the technical field of relay protection and have the technical scheme key points that: collecting a periodic wave data of each side current signal; extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain a calculated current phasor; calculating to obtain differential current according to the calculated current phasor of each side node; carrying out phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude at each side and the calculated current phasor at each side node to obtain braking current; judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking. The invention improves the fault sensitivity when the multiple sides are short-circuited in the area, the braking capability and the TA saturation resistance when the ratio braking differential protection area is out of fault, and the safety of the out-of-area fault.

Description

Transformer differential protection method and system based on current phasor difference 2 norm
Technical Field
The invention relates to the technical field of relay protection, in particular to a transformer differential protection method and system based on current phase difference 2 norm.
Background
The transformer differential protection is an important protection for power grid elements, and is widely applied to power systems due to the simple principle. In practical engineering application, the differential protection of the transformer still mainly takes the differential protection with the ratio braking characteristic, and the main braking modes include modular sum braking, sum-difference braking, maximum braking, scalar braking and the like. The braking current of the ratio braking differential protection is selected to be as large as possible in case of an external fault, and to be as small as possible in case of an internal fault, preferably without braking.
At present, the differential current protection at two sides mostly adopts a sum-difference braking mode, because the mode adopts two-phase current difference under two outgoing lines, the characteristics of the out-of-area ride-through fault can be better reflected, and the braking current is smaller when the internal fault occurs. However, when the differential motion is performed on multiple sides, the braking modes such as the module value and the maximum value are generally selected, or the multiple sides are converted into two sides, although the braking modes have a good braking effect when the fault is out of the area, the braking currents are also large when the fault is in the area, and the main reason is that the braking currents for braking the module value and the maximum value are not obviously changed when the fault is out of the area, and the characteristic of the through fault current when the fault is out of the area cannot be reflected. For multi-side differential protection, when the maximum current is out of the zone, because the fault branch is the maximum current, the maximum current is greatly influenced by TA error, the capacity of allowing out-of-zone unbalance is weak, the application is less, and the mode value and the braking mode are most widely applied.
However, although the principle of the transformer differential protection is simple, the difference of the TA characteristics of the voltage levels on the sides is larger, the unbalanced current is larger, and the problems of magnetizing inrush current, TA saturation of an out-of-range fault and the like exist. Because the differential protection of the transformer needs to carry out the balance of the current amplitude and the phase, the differential unbalanced current is larger than that of a generator and a line, the TA saturation influence of the transformer is also large, and the differential protection malfunction is caused by the TA saturation of the transformer when the site has external faults for many times. Therefore, the differential protection of the modulus and the braking ratio braking has the problems of insufficient anti-saturation capacity in case of an out-of-area fault, no more than 2 sensitivities in case of more than two power supplies in an area, insufficient sensitivity and the like.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide a transformer differential protection method and a transformer differential protection system based on a current phase difference 2 norm.
The technical purpose of the invention is realized by the following technical scheme:
in a first aspect, a method for differential protection of a transformer based on current phasor difference 2 norm is provided, which includes the following steps:
collecting a periodic wave data of current signals of all sides when a transformer fault occurs;
extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node;
calculating to obtain differential current according to the calculated current phasor of each side node;
screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and carrying out phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasor of the nodes of each side to obtain braking current;
judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
Further, the differential current is calculated by the following formula:
Figure BDA0003252327790000021
wherein, IdRepresents a differential current;
Figure BDA0003252327790000022
representing the calculated current phasor at each side node of the transformer.
Further, the calculation formula of the braking current is specifically as follows:
Figure BDA0003252327790000023
wherein, Ir2m,jRepresents the braking current;
Figure BDA0003252327790000024
representing the current phasor with the maximum current amplitude on each side;
Figure BDA0003252327790000025
representing the calculated current phasor at each side node of the transformer.
Further, the method also comprises the step of optimizing the braking current through the regulating factor to obtain the optimized braking current;
the calculation formula for optimizing the braking current is specifically as follows:
Figure BDA0003252327790000026
wherein, Irpm,jRepresents an optimized braking current; ε represents a regulatory factor; i isr2m,jRepresenting the braking current.
Further, the adjusting factor is calculated by a boundary constraint relation between a 1 norm and an infinite norm of the current signal of each side.
Further, the calculation formula of the adjustment factor is specifically as follows:
ε＝||Is||1/2||Is||∞
Figure BDA0003252327790000027
Figure BDA0003252327790000028
wherein the content of the first and second substances,
Figure BDA0003252327790000029
representing the respective side current signal vector.
Further, the value range of the preset ratio brake parameter is [0.6, 0.7 ].
In a second aspect, a transformer differential protection system based on current phasor difference 2 norm is provided, comprising:
the data acquisition module is used for acquiring one cycle wave data of each side current signal when the transformer fault occurs;
the data extraction module is used for extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node;
the differential calculation module is used for calculating to obtain differential current according to the calculated current phasor of each side node;
the braking calculation module is used for screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and performing phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasors of the nodes of each side to obtain braking current;
the protection control module is used for judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
In a third aspect, a computer terminal is provided, which includes a memory, a processor and a computer program stored in the memory and executable on the processor, and when the processor executes the program, the method for transformer differential protection based on current phasor difference 2 norm as described in any one of the first aspect is implemented.
In a fourth aspect, a computer-readable medium is provided, on which a computer program is stored, the computer program being executed by a processor to implement the method for transformer differential protection based on current phase difference 2 norm as described in any one of the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with the current modular value and the braking mode of the transformer differential protection widely adopted in the current engineering, the multi-power supply has higher sensitivity under the condition that a single power supply ensures enough sensitivity, the braking capability and the TA saturation resistance of the out-of-range fault are obviously improved, the new criterion principle is simple to form, and the norm theory strictly proves that the reliability is high and the engineering practicability is strong; specifically, the braking capacity of an external fault is improved by 1.5 times, the sensitivity is improved when power is provided to two sides and three sides outside the area, the sensitivity is improved by 1.4 times when power is provided to two sides, and the sensitivity is improved by more than 2 times when power is provided to three sides;
2. after the adjusting factor epsilon is introduced, the braking capability of the external fault is further improved, compared with the modulus and the braking, the modulus and the braking are improved by more than 2 times, meanwhile, the sensitivity of the internal fault is still more than 2 times when the power is supplied to multiple sides, the sensitivity of a single power supply is also ensured, and the comprehensive performance is further improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a flow chart in the present invention;
FIG. 2 is a graph showing current waveforms on respective sides in the inventive example 1;
FIG. 3 is a graph showing the differential current waveform in the embodiment 1 of the present invention;
FIG. 4 is a comparison graph of the differential phase and braking amount of the fault in the calculation example 1 of the present invention;
FIG. 5 is a graph showing the waveforms of the side currents in the embodiment 2 of the present invention;
FIG. 6 is a graph showing the differential current waveform in the embodiment 2 of the present invention;
FIG. 7 is a comparison graph of the differential phase and the braking amount in the embodiment 2 of the present invention;
FIG. 8 is a diagram showing current waveforms on each side of a three-phase short circuit outside the area in the embodiment 3 of the present invention;
FIG. 9 is a diagram showing differential current waveforms of three-phase short circuits outside the area in the embodiment 3 of the present invention;
FIG. 10 is a comparison graph of the differential and braking amounts of the three-phase short circuit in the area outside the area in the calculation example 3 of the present invention;
FIG. 11 is a diagram showing current waveforms on each side of a three-phase short circuit in a region in the embodiment 3 of the present invention;
FIG. 12 is a graph showing the differential current waveform of the three-phase short circuit in the area in the embodiment 3 of the present invention;
FIG. 13 is a comparison graph of the differential and braking amounts of the three-phase short circuit in the area of the invention in the calculation example 3;
FIG. 14 is a waveform diagram of the main transformer side current in the inventive example 4;
FIG. 15 is a graph showing the differential current waveform in the embodiment 4 of the present invention;
fig. 16 is a graph comparing the differential and braking amounts of the most saturated failure phase C in the invention example 4.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1: transformer differential protection method based on current phasor difference 2 norm
Analysis of internal and external fault performance of transformer area in traditional modulus and braking mode
The mode value and the braking mode adopted in the engineering are most widely applied at present.
The modulus and braking current of the brake are:
Figure BDA0003252327790000041
wherein
Figure BDA0003252327790000042
And calculating current phasor for each side node of the transformer.
(1) Transformer out-of-zone fault braking capability calculation
When out-of-zone fault occurs
Figure BDA0003252327790000043
Wherein
Figure BDA0003252327790000044
For fault side current, assume
Figure BDA0003252327790000045
A medium maximum current of
Figure BDA0003252327790000046
Normalized maximum value of
Figure BDA0003252327790000047
Order to
Figure BDA0003252327790000048
Is α ejθAlpha is more than or equal to 0 and less than or equal to 1, theta is more than or equal to 0 and less than or equal to pi, and alpha is
Figure BDA0003252327790000049
And
Figure BDA00032523277900000410
is a ratio of the amplitudes of theta
Figure BDA00032523277900000411
And
Figure BDA00032523277900000412
the phase difference of (1). When out-of-range fault occurs
Figure BDA00032523277900000413
Thus Is＝[1,αejθ,-(1+αejθ)]T. Due to the fact that
Figure BDA00032523277900000414
Amplitude and
Figure BDA00032523277900000415
and
Figure BDA00032523277900000416
is related to the phase angle of (1), so
Figure BDA0003252327790000051
Need to consider
Figure BDA0003252327790000052
And
Figure BDA0003252327790000053
the phase relationship between them. Calculation of Ir1.jThe braking currents in each case are shown in table 1.
TABLE 1 model of out-of-zone fault and braking conditions
Figure BDA0003252327790000054
(2) Calculation of fault braking capability in transformer area
When the transformer area is in fault, the current on three sides can be taken as any value theoretically, so that only the current amplitude relation of each side can be considered. To pair
Figure BDA0003252327790000055
Is provided with
Figure BDA0003252327790000056
The maximum current in three sides is 1, order
Figure BDA0003252327790000057
Order to
Figure BDA0003252327790000058
Thus, it is possible to provide
Figure BDA00032523277900000510
Figure BDA00032523277900000511
The in-zone fault modulus and braking conditions for the braking current are shown in table 2.
TABLE 2 in-zone Fault modulus and brake conditions
Figure BDA0003252327790000059
(3) Performance analysis
Through analysis of the module value of the fault inside and outside the area and the braking current, the braking amount outside the area is 1-2, the braking amount is not high, the braking capacity outside the area is not strong, the sensitivity is not high when the fault inside the area is more than or equal to 0 and less than or equal to 1, beta is 0 and more than or equal to 0 and less than or equal to 1, and the maximum is not more than 2.
The invention provides a current phase difference 2 norm-based transformer differential protection method, which improves the braking capacity outside a region and improves the sensitivity of faults inside the region to power supplies on two sides and three sides.
As shown in fig. 1, the method comprises the following steps:
s1: collecting a periodic wave data of current signals of all sides when a transformer fault occurs;
s2: extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node;
s3: calculating to obtain differential current according to the calculated current phasor of each side node;
s4: screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and carrying out phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasor of the nodes of each side to obtain braking current;
s5: judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
(1) Differential protection braking current criterion of current phase difference 2 norm
When the transformer has an external fault, the current on each side has the following characteristics except that the difference current is 0 theoretically: the absolute value of the current of the branch at the fault point is generally greater than or equal to the absolute value of the current of other branches at non-fault points, because the current of the fault branch is the sum of the currents of all other branches at non-fault points. The phase difference between the current of the fault branch and the current of the non-fault branch is about 180 degrees when the phase difference of each power supply is not considered. The phase difference of each normal power supply is not large, and the absolute value of the phase difference between the fault branch current and the non-fault branch current is larger than that of the fault branch current.
When the fault occurs in the area, the fault point is positioned in the transformer, all the branches are fault branches, the phases are close, and the phasor difference absolute value of each branch is small. The phasor difference between the maximum value in each branch current of the transformer and other branch currents is obviously larger than that of an internal fault outside the area, so that the characteristic of the through current during the external fault can be reflected, and the through current can be used as the braking current of the differential protection of the transformer to better identify the internal and external faults inside the area.
(2) For three-side differential protection, the structure is based on the current phasor difference l of each side branch2In the form of a norm.
The differential current calculation formula is specifically as follows:
Figure BDA0003252327790000061
the current phasor with the maximum absolute value in the currents of all sides is
Figure BDA0003252327790000062
Memory vector
Figure BDA0003252327790000063
It and vector
Figure BDA0003252327790000064
Vector difference of (I)sm-IsAlso form apNorm whose phasors differ by 2 norm lr2mComprises the following steps:
Figure BDA0003252327790000065
in engineering, the brake current is formed as follows:
Ir2m,j＝lr2m/1.41
wherein, Ir2m,jRepresents the braking current;
Figure BDA0003252327790000066
representing the current phasor with the maximum current amplitude on each side;
Figure BDA0003252327790000067
representing the calculated current phasor at each side node of the transformer.
(3) For I in case of out-of-area faults＝[1,αejθ,-(1+αejθ)]TCalculating lr2m.jComparison Ir1.jAs shown in table 3.
TABLE 3 comparison of out-of-zone fault modulus values and braking conditions
Figure BDA0003252327790000068
As can be seen from Table 3, when there is an out-of-range fault,/r2m.jBi | (R) |r1.jThe brake capacity and the anti-saturation capacity are obviously improved by about 1.5 times.
(4) In case of a zone fault
Figure BDA0003252327790000078
Calculating lr2m.jComparison Ir1.jAs shown in table 4.
TABLE 4 comparison of fault modulus and braking conditions in zone
Figure BDA0003252327790000071
As can be seen from Table 4, when there is an intra-zone fault,/r2m.jRatio Ir1.jIn dual power supply and multipleIn the case of power supplies, the sensitivity is better than the modulus and the braking mode, and can be from 2 to infinity. Since in the case of a single power supply, lr2m.jThe reduction is large, so that the out-of-region fault braking capability is further improved by introducing a boundary constraint relation between norms, and the sensitivity of the in-region single power supply is improved.
(5) The calculation formula for optimizing the braking current is specifically as follows:
Figure BDA0003252327790000072
wherein, Irpm,jRepresents an optimized braking current; ε represents a regulatory factor; i isr2m,jRepresenting the braking current.
The adjusting factor is calculated by the boundary constraint relation of the 1 norm and the infinite norm of the current signals of all sides.
The calculation formula of the adjusting factor is specifically as follows:
ε＝||Is||1/2||Is||∞
Figure BDA0003252327790000073
Figure BDA0003252327790000074
wherein the content of the first and second substances,
Figure BDA0003252327790000075
representing the respective side current signal vector.
(6) The optimized differential protection action criterion is as follows:
Figure BDA0003252327790000076
wherein the braking parameter K is presetresHas a value range of [0.6, 0.7]]。
(7) In case of out-of-range faultI of (A)s＝[1,αejθ,-(1+αejθ)]TCalculating lrpm.jComparison Ir1.jAs shown in table 5.
TABLE 5 comparison of out-of-zone fault modulus values and braking conditions
Figure BDA0003252327790000077
As can be seen from Table 5, when there is an out-of-range fault, irpm.jBi | (R) |r1m.jThe brake capacity and the anti-saturation capacity are further improved by more than 2 times.
(8) In case of a zone fault
Figure BDA0003252327790000083
Calculating lrpm.jComparison Ir1.jAs shown in table 6.
TABLE 6 comparison of fault modulus and braking conditions in zone
Figure BDA0003252327790000081
As can be seen from Table 6, when there is an intra-zone fault,/rpm.jSensitivity is better than modulus and braking mode, can be from 2 to infinity, and sensitivity ratio l of single power failure in a zoner2m.jThe comprehensive performance is improved by 1.4 times.
Example 2: the transformer differential protection system based on the current phasor difference 2 norm comprises a data acquisition module, a data extraction module, a differential calculation module, a brake calculation module and a protection control module.
The data acquisition module is used for acquiring one cycle wave data of each side current signal when the transformer fault occurs. And the data extraction module is used for extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node. And the differential calculation module is used for calculating to obtain differential current according to the calculated current phasor of each side node. And the braking calculation module is used for screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and performing phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasor of the nodes of each side to obtain braking current. The protection control module is used for judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
Example 3: transformer differential protection test based on current vector 2 norm
The protection algorithm adopts a universal y-side corner, the high-voltage side is a reference side mode, and the full-wave Fourier algorithm calculates the differential current and the braking current.
First, example 1
Out-of-zone fault to in-zone fault testing
The fault is ab fault in the out-of-area C phase transition area, the current waveform of each side is tested and shown in figure 2, and the differential current waveform is shown in figure 3. Fig. 4 is a comparison graph of the differential phase and braking amount of the failure in the example 1. The differential current is hereinafter referred to as the differential current.
The transformer parameters were as follows:
Figure BDA0003252327790000082
the per unit values of the currents at the respective stages at the time of the fault steady state are shown in table 7.
TABLE 7 EXAMPLE 1 Fault differential flow and brake Current conditions
Figure BDA0003252327790000091
An out-of-range fault occurs when t is 140ms, with 2-norm braking (l)r2m.j) Is obviously higher than the sum of modulus values (l)r1m.j) And maximum, while the braking (l) is optimized with a 2 normrpm.j) The braking capacity is further improved, and the braking capacity is more than 2 times of the sum of the modulus values. When the fault is converted into the zone-in fault, the sum of the 2 norm braking quantity and the modulus is approximate, the 2 norm optimal braking mode is slightly larger in braking quantity, and at the moment, the k value isThe sensitivity is 1.25, the setting is carried out according to 0.6, the sensitivity is more than 2, and the sensitivity meets the requirement. And when t is 260ms, after the out-of-area fault is removed, the in-area fault still exists, the module value and the braking quantity slightly decrease at this time, the k value is close to the self critical action value of 2, the optimized braking quantity adopting the 2 norm and the 2 norm has more than 1 time of decrease amplitude, and the corresponding k value is close to 3 and is higher than the module value and the k value by 1.5 times. Therefore, the 2 norm and the optimized braking mode thereof can be used for more accurately identifying the faults inside and outside the area, and the comprehensive performance is better.
Second, EXAMPLE 2
Out-of-band fault TA saturation fault test
The fault is an out-of-range high-voltage side a-phase ab fault, and the current waveform and the differential current waveform of each side are tested along with TA saturation, as shown in fig. 5 and 6. Fig. 7 is a comparison graph of the phase difference and the braking amount of the failure in the example 2.
The per unit value of current when the corresponding fault saturation is the most severe is shown in table 8.
TABLE 8 EXAMPLE 2 Fault differential flow and brake Current conditions
Figure BDA0003252327790000092
When t is 100ms, an out-of-range fault occurs, and TA transient saturation is severe, especially the first cycle, as can be seen from the difference flow. At the moment, the modulus, the maximum value and the k value are both larger than 0.8, the 2 norm and the optimized braking mode are respectively 0.6 and 0.48, and particularly, the out-of-area fault anti-saturation capacity of the 2 norm optimized braking mode is 1 time stronger than that of the modulus and the braking. The 2-norm optimized brake not only has stronger anti-saturation capacity, but also has steeper fault rise outside a visible region according to waveforms, so that the k value is greater than 0.4 and the duration is not more than 4ms when the transient state of the embodiment is saturated, and the modulus value and the brake k value are greater than 0.6 and the duration is greater than 6 ms.
Third, EXAMPLE 3
In-zone and out-of-zone fault testing
The fault is a three-phase short-circuit fault in a 3# main transformer area of a certain 110kV transformer substation, and the 2# main transformer and the 3# main transformer run in parallel, so that the fault is an out-of-area fault for the 2# main transformer.
The main transformer parameters of 2# and 3# are the same, and the transformer parameter table is as follows:
Figure BDA0003252327790000101
1. out-of-zone three-phase short circuit
The test current waveform and the differential current waveform are shown in fig. 8 and 9, respectively. Fig. 10 is a differential current waveform diagram of a failed a-phase of an out-of-range three-phase short circuit.
The per unit value of current at steady state for the corresponding out-of-band fault is shown in table 9.
TABLE 9 COMPARATIVE EXAMPLE 3.1 Fault Difference flow and brake Current conditions
Figure BDA0003252327790000102
When t is 20ms, an out-of-range fault occurs, differential current is unbalanced current, and the per unit value is 1.26, and the vehicle enters a braking region. The braking capacity outside the 2 norm and optimized braking mode area is obviously higher than that of a mode value and maximum braking mode.
2. Three phase short circuit in zone
Fig. 11 and 12 show the 3# main transformation log wave and the differential current waveform of the in-zone fault, and fig. 13 is a differential current waveform diagram of the fault a phase with three short-circuited phases in the zone.
The per unit value of the steady-state current at the time of the fault in the corresponding zone is shown in table 10.
TABLE 10 EXAMPLE 3.2 Fault differential flow and brake Current conditions
Figure BDA0003252327790000103
When the three-phase short circuit serious fault occurs in the region when t is 20ms, the 2-norm optimal braking quantity and the module value are basically the same as the braking, the 2-norm braking quantity is lower, and the k value is close to 3. The 2 norm optimization is about 2.6 in k value at the early stage of the fault and 2.11 in stable state, and is superior to the mode value, braking mode and the maximum braking mode.
Fourth, EXAMPLE 4
Out-of-band fault TA severe saturation
The fault is A, C phase short circuit fault outside a main transformer area of a certain 110kV transformer substation, and TA is seriously saturated. Fig. 14 and 15 show main transformer recording and differential current waveforms, respectively, and fig. 16 is a differential current waveform diagram of a fault phase C with the most severe saturation.
Transformer parameter table:
Figure BDA0003252327790000111
the per unit value of the current at the time of the corresponding fault is shown in table 11.
TABLE 11 EXAMPLE 4 Fault differential flow and brake Current conditions
Figure BDA0003252327790000112
When t is 60ms, an out-of-range fault occurs, and the first cycle TA and the second cycle TA after the fault are seriously saturated in transient state according to the difference flow. At the moment, the modulus and the maximum k value are both larger than 0.8, the modulus and the brake are close to 1, and other anti-saturation measures are needed to avoid false operation. The 2 norm optimal braking mode is 0.55, and false action cannot be caused even if other anti-saturation measures are not adopted.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. The transformer differential protection method based on the current phasor difference 2 norm is characterized by comprising the following steps of:
collecting a periodic wave data of current signals of all sides when a transformer fault occurs;
extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node;
calculating to obtain differential current according to the calculated current phasor of each side node;
screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and carrying out phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasor of the nodes of each side to obtain braking current;
judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
2. The transformer differential protection method based on current phasor difference 2 norm as claimed in claim 1, wherein the differential current is calculated by the following formula:
Figure FDA0003252327780000011
wherein, IdRepresents a differential current;
Figure FDA0003252327780000012
representing the calculated current phasor at each side node of the transformer.
3. The current phasor difference 2 norm-based transformer differential protection method according to claim 1, wherein the braking current is calculated by the following formula:
Figure FDA0003252327780000013
wherein, Ir2m,jRepresents the braking current;
Figure FDA0003252327780000014
indicating each side of electricityThe current phasor with the largest current amplitude;
Figure FDA0003252327780000015
representing the calculated current phasor at each side node of the transformer.
4. The differential protection method of the transformer based on the current phasor difference 2 norm as claimed in any one of claims 1 to 3, characterized in that the method further comprises optimizing the braking current by a regulating factor to obtain an optimized braking current;
the calculation formula for optimizing the braking current is specifically as follows:
Figure FDA0003252327780000016
wherein, Irpm,jRepresents an optimized braking current; ε represents a regulatory factor; i isr2m,jRepresenting the braking current.
5. The method as claimed in claim 4, wherein the adjustment factor is calculated by a boundary constraint relationship between a 1 norm and an infinite norm of the current signal of each side.
6. The current phasor difference 2 norm-based transformer differential protection method according to claim 5, wherein the formula for calculating the adjustment factor is specifically as follows:
ε＝||Is||1/2||Is||∞
Figure FDA0003252327780000021
Figure FDA0003252327780000022
wherein the content of the first and second substances,
Figure FDA0003252327780000023
representing the respective side current signal vector.
7. The current phasor difference 2 norm based transformer differential protection method according to claim 1, wherein said predetermined ratiometric braking parameter is taken from the range of [0.6, 0.7 ].
8. Transformer differential protection system based on current phasor difference 2 norm, characterized by includes:
the data acquisition module is used for acquiring one cycle wave data of each side current signal when the transformer fault occurs;
the data extraction module is used for extracting the amplitude and the phase of each current in the periodic wave data by utilizing a full-wave Fourier algorithm to obtain the calculated current phasor of each side node;
the differential calculation module is used for calculating to obtain differential current according to the calculated current phasor of each side node;
the braking calculation module is used for screening out the current phasor with the maximum current amplitude of each side from the calculated current phasors of the nodes of each side, and performing phasor difference 2 norm calculation according to the current phasor with the maximum current amplitude of each side and the calculated current phasors of the nodes of each side to obtain braking current;
the protection control module is used for judging whether the ratio of the differential current to the braking current is greater than or equal to a preset ratio braking parameter or not; if yes, judging the fault in the area, and starting a protection action; if not, judging the fault is an out-of-area fault, and starting protection locking.
9. A computer terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method for differential protection of a transformer based on current phasor difference 2 norm as claimed in any one of claims 1 to 7.
10. A computer-readable medium, on which a computer program is stored, the computer program being executable by a processor to implement the method for current-phasor difference 2 norm based differential protection of a transformer according to any of claims 1-7.
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