CN113267698A - Method, system and storage medium for distinguishing main transformer CT saturation - Google Patents
Method, system and storage medium for distinguishing main transformer CT saturation Download PDFInfo
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Abstract
The invention discloses a method, a system and a storage medium for judging the saturation of a main transformer CT, wherein the method is used for judging whether the main transformer CT is saturated or not based on the total cycle differential flow integral without judging the differential flow generation time and the fault time at the same time or judging the out-of-range fault through the time difference of the two times, is simple and practical, and provides beneficial technical supplement for the engineering practice of transformer differential protection.
Description
Technical Field
The invention relates to a method, a system and a storage medium for judging main transformer CT saturation, and belongs to the technical field of power system relay protection.
Background
With the high-speed development of power grids in China, particularly the appearance of ultra-high voltage and extra-high voltage power grids, the capacity of the power grids is increased sharply, high-voltage-level large-capacity transformers are more and more, and new requirements are provided for the selectivity of main transformer differential protection in order to ensure the safe operation of the transformers and the stability of a system. When a fault occurs in the ratio differential transformer, the fault can be quickly removed. However, the differential protection brings new problems besides improving the rapidity of the main transformer differential protection, and the main transformer differential protection is subjected to misoperation due to the CT saturation of the external fault on site.
The current mainstream CT saturation discrimination method is a synchronous discrimination method, but in the synchronous discrimination method, it is difficult to discriminate a difference stream generation time and a fault time at the same time, and it is also difficult to discriminate an out-of-range fault by the difference between the two times.
Disclosure of Invention
The invention provides a method, a system and a storage medium for judging main transformer CT saturation, which solve the problems disclosed in the background technology.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the method for judging the main transformer CT saturation comprises the following steps,
calculating the sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
calculating the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer according to the differential current of the current sampling point on the high-voltage side of the main transformer;
calculating the absolute value of the current sampling point differential current of the low-voltage side of the main transformer according to the current sampling point differential current of the low-voltage side of the main transformer;
obtaining braking current according to the absolute value of the current sampling point differential current at the high-voltage side of the main transformer, the absolute value of the current sampling point differential current at the low-voltage side of the main transformer and a preset obtaining rule;
calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
inputting the secondary harmonic amplitude value of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the main transformer at the current moment into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
and (4) carrying out main transformer CT saturation discrimination according to the total cycle difference flow integral and a preset discrimination rule.
The sampling point differential flow calculation formula of the main transformer at the current moment is as follows,
id(n)＝i1(n)-i2(n)*k
wherein id(n) is the difference stream value of the sampling point n at the current moment, i1(n) is the value of the sampling point n at the current moment of the secondary current at the high-voltage side of the main transformer, i2(n) is the value of a sampling point n at the current moment of the secondary current at the low-voltage side of the main transformer, and k is the turn ratio of the main transformer;
the sampling point differential flow calculation formula at the previous moment of the main transformer is as follows,
id(n-1)＝i1(n-1)-i2(n-1)*k
wherein id(n-1) is the difference stream value of the sampling point n-1 at the previous moment, i1(n-1) is the value of n-1 sampled at the previous moment of secondary current at the high-voltage side of the main transformer, i2And (n-1) is the value of a sampling point n-1 at the previous moment n-1 of the secondary current at the low-voltage side of the main transformer.
The differential flow calculation formula of the sampling point of the main transformer at the current moment is as follows,
i′d＝(id(n)-id(n-1))/Ts
wherein, i'dDifferential flow of sampling points at the current moment of the main transformerd(n) is a stream of n difference of sampling points at the current time, id(n-1) is the difference stream of the sampling point n-1 at the previous moment, TsIs the sampling interval time.
Calculating the absolute value of the differential current of the current sampling point at the high-voltage side of the main transformer by a specific formula,
wherein ir1Differential current i of the current sampling point at the high-voltage side of the main transformer1(n) is the value of the sampling point n at the current moment of the secondary current at the high-voltage side of the main transformer, i1(n-1) is the value of a sampling point n-1 at the previous moment of the secondary current at the high-voltage side of the main transformer, TsFor the sampling interval time, omega1Is the grid frequency;
calculating the absolute value of the differential current of the current sampling point at the low-voltage side of the main transformer by a specific formula,
wherein ir2Differential current i of the current sampling point at the low-voltage side of the main transformer2(n) is the value of the sampling point n at the current moment of the secondary current at the low-voltage side of the main transformer, i2And (n-1) is the value of a sampling point n-1 at the previous moment of the secondary current at the low-voltage side of the main transformer.
The preset obtaining rule is that the large value of the absolute value of the current sampling point differential current on the high-voltage side of the main transformer and the absolute value of the current sampling point differential current on the low-voltage side of the main transformer is selected as the braking current.
The calculation formula of the amplitude of the secondary harmonic on the high-voltage side of the main transformer is as follows,
i2max＝max(iah2，ibh2，ich2)
wherein i2maxThe amplitude of the secondary harmonic wave on the high-voltage side of the main transformer is iah2、ibh2、ich2The current amplitudes of the secondary harmonic waves of the phase A, the phase B and the phase C on the high-voltage side of the main transformer are respectively.
The preset total cycle difference flow integral function is,
wherein, IfIs the full cycle difference stream integral, i'dDifferential flow of sampling points at the current moment of the main transformerrFor braking current, i2maxThe amplitude of the secondary harmonic wave on the high-voltage side of the main transformer is TiIs a cycle, N is the number of cycle sampling points, omega1For the grid frequency, K is ANDrRelated segmentationAs a function, L is a constant.
The preset judgment rule is that,
if the total cycle difference flow integral is smaller than the threshold value, the main transformer CT is judged to be saturated, and differential motion is locked;
and if the total cycle difference flow integral is not less than the threshold value, judging that the main transformer CT is unsaturated.
A system for judging the main transformer CT saturation comprises,
a differential difference flow module: calculating the sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
high-side differential current module: calculating the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer according to the differential current of the current sampling point on the high-voltage side of the main transformer;
low-side differential current module: calculating the absolute value of the current sampling point differential current of the low-voltage side of the main transformer according to the current sampling point differential current of the low-voltage side of the main transformer;
a braking current module: obtaining braking current according to the absolute value of the current sampling point differential current at the high-voltage side of the main transformer, the absolute value of the current sampling point differential current at the low-voltage side of the main transformer and a preset obtaining rule;
a harmonic amplitude module: calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
a full cycle integration module: inputting the secondary harmonic amplitude value of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the main transformer at the current moment into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
a judging module: and (4) carrying out main transformer CT saturation discrimination according to the total cycle difference flow integral and a preset discrimination rule.
A computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by a computing device, cause the computing device to perform a method of discriminating main transform saturation.
The invention achieves the following beneficial effects: the method is used for judging whether the main transformer CT is saturated or not based on the full-cycle differential flow integral, the differential flow generation time and the fault time do not need to be judged at the same time, and the out-of-area fault is not needed to be judged through the time difference between the differential flow generation time and the fault time.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a logic diagram for latching the differential using a full cycle differential flow integral.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
As shown in fig. 1, the method for determining the main transformer CT saturation includes the following steps:
step 1, calculating a sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
step 2, calculating the absolute value of the differential current of the current sampling point of the high-voltage side of the main transformer according to the differential current of the current sampling point of the high-voltage side of the main transformer;
step 3, calculating the absolute value of the differential current of the current sampling point at the low-voltage side of the main transformer according to the differential current of the current sampling point at the low-voltage side of the main transformer;
step 4, obtaining the braking current according to the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer, the absolute value of the differential current of the current sampling point on the low-voltage side of the main transformer and a preset obtaining rule;
the preset acquisition rule is that the large value of the absolute value of the current sampling point differential current on the high-voltage side of the main transformer and the absolute value of the current sampling point differential current on the low-voltage side of the main transformer is selected as the braking current;
step 5, calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
step 6, inputting the secondary harmonic amplitude of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the current time of the main transformer into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
step 7, performing main transformer CT saturation judgment according to the total cycle difference flow integral and a preset judgment rule;
the preset discrimination rule is as follows: if the total cycle difference flow integral is smaller than the threshold value, the main transformer CT is judged to be saturated, and differential motion is locked; and if the total cycle difference flow integral is not less than the threshold value, judging that the main transformer CT is unsaturated.
The method judges whether the main transformer CT is saturated or not based on the total cycle differential flow integral, does not need to judge the differential flow generation time and the fault time at the same time, does not need to judge the out-of-area fault through the time difference of the two, is simple and practical, and provides beneficial technical supplement for the engineering practice of transformer differential protection.
As shown in FIG. 2, assume that the master becomes two volume change, i1(n) is the value of the sampling point n at the current moment of the secondary current at the high-voltage side of the main transformer, i2And (n) is a value of a sampling point n at the current moment of the secondary current at the low-voltage side of the main transformer, and a method for calculating the differential curve in the graph is the existing mature technical scheme and is not described herein again. Assuming that the CT transformation ratios of the main high voltage side and the low voltage side are consistent, the obtained sampling point differential current can be expressed as a difference obtained by multiplying the current of the high voltage side and the current of the low voltage side by the turn ratio according to the law of magnetic potential balance, as shown in the following formula:
the main transformer current time sampling point differential flow calculation formula is as follows:
id(n)＝i1(n)-i2(n)*k
wherein id(n) is a differential flow value of a sampling point n at the current moment, and k is a main transformer turn ratio;
the sampling point differential flow calculation formula at the previous moment of the main transformer is as follows,
id(n-1)＝i1(n-1)-i2(n-1)*k
wherein id(n-1) is the difference stream value of the sampling point n-1 at the previous moment, i1(n-1) is the value of n-1 sampled at the previous moment of secondary current at the high-voltage side of the main transformer, i2And (n-1) is the value of a sampling point n-1 at the previous moment n-1 of the secondary current at the low-voltage side of the main transformer.
According to id(n) and id(n-1) calculating the differential flow of the sampling points of the main transformer at the current moment, specifically as follows:
i′d＝(id(n)-id(n-1))/Ts
wherein, i'dFor the sampling point differential flow at the current moment of the main transformer, the direct current component in the differential flow can be effectively filtered by adopting the differential flow, and the interference to calculation is reduced; t issFor the sampling interval time, if the sampling is 48 points per cycle (20ms), T issIs 0.416 ms.
Respectively calculating the absolute value of the current sampling point differential current of the main transformer high-voltage side and the absolute value of the current sampling point differential current of the main transformer low-voltage side according to the current sampling point differential current of the main transformer high-voltage side and the current sampling point differential current of the main transformer low-voltage side, and taking the large values of the two as braking current irI.e. by
ir＝max(|ir1|，|ir2|)
Wherein ir1Is the differential current of the current sampling point at the high-voltage side of the main transformer and is the differential current i 'at the current sampling point at the high-voltage side of the main transformer'1Divided by frequency, ω1The grid frequency, typically 50 Hz; i.e. ir2The current sampling point differential current of the low-voltage side of the main transformer is the current sampling point differential current i'2Divided by the frequency.
The total cycle difference stream integral function is obtained as:
wherein, IfFor full cycle differential flow integration, TiIs a cycle (20ms), iopDividing the absolute value of the differential difference stream of the sampling points by the frequency, i.e.
K is a coefficient. By subtracting the full cycle integral of the braking current from the sampled point differential difference stream, the CT unsaturated time period can be included, adding to the effect of the constraint.
Will IfComparing with a threshold value H, if IfBelow the threshold H, it is assumed that the normal intra-zone fault does not cause a protective action, but may be caused by CT saturation, and a corresponding latch-up is performed.
To increase the sensitivity of the algorithm to braking, K is set to be AND irThe associated piece-wise function of the image data,
when i isrSmaller, the value of K follows irChange when i changesrAt larger, K is held constant, making irAnd iopA certain proportionality coefficient is maintained.
Considering that when the main transformer is in idle running, the excitation surge current can cause the high-voltage side current of the main transformer to generate larger second harmonic, possibly causing IfIs greater than the threshold H, so the second harmonic related content can be eliminated in the full cycle slip integral function, making the result more accurate, i.e.,
let i2max＝max(iah2，ibh2，ich2)
Wherein i2maxThe amplitude of the secondary harmonic wave on the high-voltage side of the main transformer is iah2、ibh2、ich2Respectively the secondary harmonic current amplitudes of the A phase, the B phase and the C phase at the high-voltage side of the main transformer, and taking the maximum value as i2max；
The total cycle difference flow integral function after eliminating the second harmonic content can be rewritten as:
wherein, L is a constant and can be 1-2.
In practical applications, discrete calculations may be used to represent the cycle integral of the difference stream,
wherein, N is a cycle sampling point number.
When the main transformer CT saturation is judged, the value of the threshold value H is important, and the condition convenient for analysis is considered, namely the internal fault of the main transformer high-voltage side single-side power supply, and the current i at the high-voltage side at the moment1Not equal to 0, low side current i2＝0。
Assume high side current i1Is a cosine waveform, i.e. i1＝-Acos(ω1t), then there is,
neglecting the second harmonic content, iopAnd irSubstituting the full-period integral function can obtain:
as described above, assuming that k is 0.3, If0.45A, high side current i when operating normally1Is about the rated current Ie at the high-voltage side, when the main transformer has an internal fault, the current i at the high-voltage side1Is generally much larger than the high-side rated current Ie, when IfWill be greater than 0.45Ie and so the threshold H may be set to 0.45Ie when IfWhen the current value is less than 0.45Ie, the protection action caused by normal internal fault is not considered, but caused by CT saturation, the differential protection is locked in time, and the protection misoperation is avoided.
On the basis of ferromagnetic characteristic analysis of CT, the characteristics of differential flow when the transformer CT is saturated are pointed out, namely, the differential flow is discontinuous under the full-cycle scale, the integral value of the differential flow is smaller than that of the fault in a region, and the method for judging the main transformer CT saturation based on the full-cycle differential flow integral is provided by using the characteristics, so that the problems that the existing CT saturation criterion needs to judge the fault time and the differential flow generation time at the same time, and the difference between the two is difficult to define when the fault is judged out of the region are solved. The method is simple and practical, and provides beneficial technical supplement for the engineering practice of transformer differential protection.
The system for distinguishing the main transformer CT saturation comprises:
a differential difference flow module: calculating the sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
high-side differential current module: calculating the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer according to the differential current of the current sampling point on the high-voltage side of the main transformer;
low-side differential current module: calculating the absolute value of the current sampling point differential current of the low-voltage side of the main transformer according to the current sampling point differential current of the low-voltage side of the main transformer;
a braking current module: obtaining braking current according to the absolute value of the current sampling point differential current at the high-voltage side of the main transformer, the absolute value of the current sampling point differential current at the low-voltage side of the main transformer and a preset obtaining rule;
a harmonic amplitude module: calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
a full cycle integration module: inputting the secondary harmonic amplitude value of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the main transformer at the current moment into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
a judging module: and (4) carrying out main transformer CT saturation discrimination according to the total cycle difference flow integral and a preset discrimination rule.
A computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by a computing device, cause the computing device to perform a method of discriminating main transform saturation.
A computing device comprising one or more processors, one or more memories, and one or more programs stored in the one or more memories and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing a method of discriminating primary transform CT saturation.
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 present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.
Claims (10)
1. The method for judging the main transformer CT saturation is characterized by comprising the following steps: comprises the steps of (a) preparing a mixture of a plurality of raw materials,
calculating the sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
calculating the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer according to the differential current of the current sampling point on the high-voltage side of the main transformer;
calculating the absolute value of the current sampling point differential current of the low-voltage side of the main transformer according to the current sampling point differential current of the low-voltage side of the main transformer;
obtaining braking current according to the absolute value of the current sampling point differential current at the high-voltage side of the main transformer, the absolute value of the current sampling point differential current at the low-voltage side of the main transformer and a preset obtaining rule;
calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
inputting the secondary harmonic amplitude value of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the main transformer at the current moment into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
and (4) carrying out main transformer CT saturation discrimination according to the total cycle difference flow integral and a preset discrimination rule.
2. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the sampling point differential flow calculation formula of the main transformer at the current moment is as follows,
id(n)＝i1(n)-i2(n)*k
wherein id(n) is the difference stream value of the sampling point n at the current moment, i1(n) is the value of the sampling point n at the current moment of the secondary current at the high-voltage side of the main transformer, i2(n) is the value of a sampling point n at the current moment of the secondary current at the low-voltage side of the main transformer, and k is the turn ratio of the main transformer;
the sampling point differential flow calculation formula at the previous moment of the main transformer is as follows,
id(n-1)＝i1(n-1)-i2(n-1)*k
wherein id(n-1) is the difference stream value of the sampling point n-1 at the previous moment, i1(n-1) is the value of n-1 sampled at the previous moment of secondary current at the high-voltage side of the main transformer, i2And (n-1) is the value of a sampling point n-1 at the previous moment n-1 of the secondary current at the low-voltage side of the main transformer.
3. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the differential flow calculation formula of the sampling point of the main transformer at the current moment is as follows,
i′d＝(id(n)-id(n-1))/Ts
wherein, i'dDifferential flow of sampling points at the current moment of the main transformerd(n) is the difference stream value of the sampling point n at the current moment, id(n-1) is the difference stream of the sampling point n-1 at the previous moment, TsIs the sampling interval time.
4. The method of distinguishing main transformer CT saturation according to claim 1, wherein: calculating the absolute value of the differential current of the current sampling point at the high-voltage side of the main transformer by a specific formula,
wherein ir1Differential current i of the current sampling point at the high-voltage side of the main transformer1(n) is the value of the sampling point n at the current moment of the secondary current at the high-voltage side of the main transformer, i1(n-1) is the value of a sampling point n-1 at the previous moment of the secondary current at the high-voltage side of the main transformer, TsFor the sampling interval time, omega1Is electricityA network frequency;
calculating the absolute value of the differential current of the current sampling point at the low-voltage side of the main transformer by a specific formula,
wherein ir2Differential current i of the current sampling point at the low-voltage side of the main transformer2(n) is the value of the sampling point n at the current moment of the secondary current at the low-voltage side of the main transformer, i2And (n-1) is the value of a sampling point n-1 at the previous moment of the secondary current at the low-voltage side of the main transformer.
5. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the preset obtaining rule is that the large value of the absolute value of the current sampling point differential current on the high-voltage side of the main transformer and the absolute value of the current sampling point differential current on the low-voltage side of the main transformer is selected as the braking current.
6. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the calculation formula of the amplitude of the secondary harmonic on the high-voltage side of the main transformer is as follows,
i2max＝max(iah2，ibh2，ich2)
wherein i2maxThe amplitude of the secondary harmonic wave on the high-voltage side of the main transformer is iah2、ibh2、ich2The current amplitudes of the secondary harmonic waves of the phase A, the phase B and the phase C on the high-voltage side of the main transformer are respectively.
7. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the preset total cycle difference flow integral function is,
wherein, IfIs the full cycle difference stream integral, i'dDifferential flow of sampling points at the current moment of the main transformerrFor braking current, i2maxThe amplitude of the secondary harmonic wave on the high-voltage side of the main transformer is TiIs a cycle, N is the number of cycle sampling points, omega1For the grid frequency, K is ANDrThe associated piecewise function, L, is a constant.
8. The method of distinguishing main transformer CT saturation according to claim 1, wherein: the preset judgment rule is that,
if the total cycle difference flow integral is smaller than the threshold value, the main transformer CT is judged to be saturated, and differential motion is locked;
and if the total cycle difference flow integral is not less than the threshold value, judging that the main transformer CT is unsaturated.
9. Differentiate the saturated system of main CT that becomes, its characterized in that: comprises the steps of (a) preparing a mixture of a plurality of raw materials,
a differential difference flow module: calculating the sampling point differential flow at the current moment of the main transformer according to the sampling point differential flow at the current moment of the main transformer and the sampling point differential flow at the previous moment of the main transformer;
high-side differential current module: calculating the absolute value of the differential current of the current sampling point on the high-voltage side of the main transformer according to the differential current of the current sampling point on the high-voltage side of the main transformer;
low-side differential current module: calculating the absolute value of the current sampling point differential current of the low-voltage side of the main transformer according to the current sampling point differential current of the low-voltage side of the main transformer;
a braking current module: obtaining braking current according to the absolute value of the current sampling point differential current at the high-voltage side of the main transformer, the absolute value of the current sampling point differential current at the low-voltage side of the main transformer and a preset obtaining rule;
a harmonic amplitude module: calculating the secondary harmonic amplitude of the high-voltage side of the main transformer according to the three-phase secondary harmonic current amplitude of the high-voltage side of the main transformer;
a full cycle integration module: inputting the secondary harmonic amplitude value of the high-voltage side of the main transformer, the braking current and the sampling point differential flow of the main transformer at the current moment into a preset full-cycle differential flow integral function to obtain a full-cycle differential flow integral;
a judging module: and (4) carrying out main transformer CT saturation discrimination according to the total cycle difference flow integral and a preset discrimination rule.
10. A computer readable storage medium storing one or more programs, characterized in that: the one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods of claims 1-8.
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