CN111580020B - Three-phase split type transformer CT polarity verification method and system - Google Patents
Three-phase split type transformer CT polarity verification method and system Download PDFInfo
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Abstract
The invention belongs to the related field of CT polarity verification technology and discloses a CT polarity verification method of a three-phase split type transformer, which comprises the following steps: carrying out no-load switching-on operation on the three-phase split type transformer, and extracting each CT current secondary value corresponding to a low-voltage side, a high-voltage side and a neutral point under the working condition; based on the principle of waveform similarity, the CT polarity of the low-voltage side sleeve of the three-phase split type transformer is verified; and continuously checking the overall polarities of the two sides of the small-difference protection of the three-phase split type transformer. The invention also discloses a corresponding CT polarity checking system, a computer readable storage medium and a terminal. According to the invention, the polarity error condition of the three-phase split type transformer small-difference protection overall CT can be efficiently and accurately verified only through no-load switching-on operation under the condition of no load, and meanwhile, the corresponding polarity error type is identified, so that the protection reliability of the main transformer is correspondingly and obviously improved.
Description
Technical Field
The invention belongs to the related field of CT polarity verification technology, and particularly relates to a CT polarity verification method and system for a three-phase split type transformer.
Background
The polarity check of a Current Transformer (CT) is a work that must be performed during the starting and commissioning of power transmission and transformation equipment, and particularly for a protective CT, the correctness of the polarity of the protective CT affects the correctness of relay protection. In the starting and operation process of the transformer, the reliability of the whole protection is poor, generally, only simple zero-sequence overcurrent protection is used as main protection, and the transformer differential protection is not allowed to be put into use before the whole CT polarity is checked correctly.
At present, main transformers of 500kV and above in an electric power system are in a three-phase split type, main protection configuration requirements are doubled, two sets of differential protection CTs are required to be mutually independent and are divided according to the size of a protection range, and the two sets of differential protection are generally one large and one small in the existing system. The low-voltage side of the three-phase split transformer is generally in triangular connection, so a low-voltage side measuring point of small-difference protection is usually from a bushing CT of the three-phase split transformer.
However, further studies have shown that the above prior art still has the following drawbacks or disadvantages: in actual engineering, no-load polarity verification is difficult to carry out on the bushing CT, so that the small-difference protection of the transformer cannot be put into operation in time; the existing common solutions all need to carry out on-load test, and only can utilize load current to verify the polarity of the small-difference protection integral CT, so that specific polarity error types cannot be identified, and certain application limitation exists; in addition, in the process of starting and commissioning an actual transformer, there are cases that it is difficult to collect load current (for example, there is almost no load on the low-voltage side of a newly-built substation). Accordingly, how to develop a simple, reliable and easy-to-operate non-load polarity verification method is one of the technical problems to be solved in the art.
Disclosure of Invention
In view of the above defects or technical requirements of the prior art, an object of the present invention is to provide a CT polarity calibration method for a three-phase split transformer, wherein the whole calibration process is redesigned, and a plurality of aspects such as key operation steps and calibration mechanisms are improved in a targeted manner, so as to ensure that the overall CT polarity error state of the three-phase split transformer under the condition of no load can be accurately and quickly calibrated only through no-load switching-on operation, and meanwhile, the CT polarity calibration method has the advantages of noise interference resistance, no influence of the change of the switching-on angle of the idle charging, high responsivity, high reliability, and the like, and is particularly suitable for CT polarity calibration application occasions such as the three-phase split transformer in the power system.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a method for checking the polarity of a CT of a three-phase split type transformer, the method including:
s101, performing no-load switching-on operation on a high-voltage side of the three-phase split type transformer, correspondingly generating excitation inrush current and zero-mode inrush current on the high-voltage side and a neutral point, and simultaneously generating triangular winding circulation current on a low-voltage side;
s102, extracting secondary CT current values corresponding to a high-voltage side, a neutral point and a low-voltage side respectively, checking the CT polarities of the high-voltage side and the neutral point, and ensuring the CT polarities of the high-voltage side and the neutral point to be correct;
s103, respectively calculating S (i) based on the secondary CT current value corresponding to the low-voltage side extracted in S102a,ib)、S(ib,ic)、S(ic,ia) Wherein ia、ibAnd icRespectively representing the secondary values of CT currents of a-phase sleeve, a b-phase sleeve and a c-phase sleeve on the low-voltage side, and S (x, y) representing the solving calculation of cosine similarity between two groups of data x and y;
s104, obtaining S (i)a,ib)、S(ib,ic)、S(ic,ia) And judging whether the minimum value is larger than a preset first threshold value: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and entering a step S201; if not, the step S105 is executed;
s105, sequentially pairing ia、ibAnd icPerforming negation operation, and repeatedly executing the steps S103-S104 after each negation operation;
s201, solving and calculating i based on the secondary CT current values extracted in S102 and corresponding to the low-voltage side and the neutral pointDAnd i0nCosine similarity between the two sets of data, where iDRepresenting the second order of the circulating current of the low-voltage side delta winding and having a value equal to ia、ibAnd icAny one of (a); i.e. i0nA zero mode inrush current secondary value representing a neutral point;
s202, judging whether the calculation result of the step S201 is larger than a preset second threshold value: if yes, judging that the integral polarity of the small-difference protection of the three-phase split type transformer is correct; if not, go to step S203;
s203, circulating current quadratic value i of the low-voltage side triangular windingDAnd performing the negation operation, and then returning to repeatedly execute the steps S201 to S202.
Preferably, after step S105, the operations of recording and outputting the phase with the wrong polarity are further included.
Preferably, after step S203, an operation of identifying and outputting the type of the polarity error is further included.
Preferably, the value ranges of the first threshold and the second threshold are set to (-1, 1), and more preferably set to 0.9.
According to a second aspect of the present invention, there is provided a three-phase split type transformer CT polarity verification system, which is characterized in that the system includes:
the data acquisition module is used for acquiring secondary values of CT currents corresponding to a high-voltage side, a neutral point and a low-voltage side in real time after the high-voltage side of the three-phase split type transformer executes no-load switching-on operation;
the CT polarity checking module comprises a high-voltage side CT polarity checking module, a neutral point CT polarity checking module and a low-voltage side CT polarity checking module, and is respectively used for checking whether the CT polarities of the high-voltage side, the neutral point and the low-voltage side of the transformer are correct or not; and
the integral polarity checking module is used for checking whether the integral polarity of the small-difference protection of the transformer is correct or not;
wherein, the low pressure side CT polarity check module further comprises:
a first similarity calculation operator module for calculating S (i) according to the secondary value of the CT current corresponding to the low voltage sidea,ib)、S(ib,ic)、S(ic,ia) Then, the minimum value is obtained and stored; wherein ia、ibAnd icRespectively representing the secondary values of CT current of a-phase casing pipe, b-phase casing pipe and c-phase casing pipe on the low-voltage side, and S (x, y) representing the secondary values of CT current between x and y for two groups of dataSolving and calculating the cosine similarity;
the first judgment submodule judges whether the minimum value obtained by the first similarity calculation submodule is larger than a preset first threshold value or not according to the minimum value obtained by the first similarity calculation submodule: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and starting to enter an integral polarity check submodule; if not, starting to enter a first correction submodule;
a first correction submodule based on the CT current quadratic value ia、ib、icSequentially carrying out negation operations, substituting the obtained current secondary value data into the first similarity calculation submodule to carry out calculation again after each negation operation, and simultaneously continuing to carry out judgment operation through the first judgment submodule;
the first polarity error type identification submodule is used for recording the serial number of the last negation operation of the first correction submodule and outputting the phase corresponding to the serial number, namely the phase with the polarity error;
wherein the global polarity check module further comprises:
a data updating submodule for executing the corrected current secondary value i according to the low-voltage side CT polarity checking modulea、ib、icArbitrarily taking a second order value of the circulating current as the low-voltage side triangular winding and assigning the second order value as iD；
A second similarity calculation submodule which calculates a second-order value i according to the input low-voltage side triangular winding circulation currentDAnd a zero-modulus secondary inrush current value i of the neutral point0nCalculating the cosine similarity value S (i) between the twoD,i0n) Meanwhile, storing;
a second judgment submodule for calculating the cosine similarity value S (i) according to the second similarity calculation submoduleD,i0n) And judging whether the threshold value is larger than a preset second threshold value: if yes, judging the small difference protection unit of the three-phase split type transformerThe body polarities are all correct and the verification is finished; if not, starting to enter a second polarity error type identification submodule;
the second polarity error type identification submodule is used for outputting a small difference protection overall polarity error result and entering a second correction submodule;
a second correction submodule for correcting a second order value i of a circulating current of the low-voltage side triangular windingDAnd carrying out negation operation, and substituting the obtained current secondary value data into the second similarity calculation submodule to carry out calculation again after each negation operation.
According to the third aspect of the present invention, there is also provided a computer readable storage medium, wherein a computer program for implementing the method for checking the polarity of the three-phase split type transformer CT is stored in the computer readable storage medium.
According to a fourth aspect of the present invention, there is further provided a three-phase split type transformer CT polarity verification terminal, which is characterized by comprising a memory and a processor, wherein the memory stores a computer program for implementing the CT polarity verification method, and the processor is configured to call the computer program in the memory to implement a corresponding CT polarity verification process.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
(1) according to the invention, the whole calibration process is redesigned, and a plurality of aspects such as key operation steps, calibration mechanisms and the like are improved in a targeted manner, so that the CT polarity calibration process can be completed only through the high-voltage side no-load switching-on operation under the condition of no load, and especially, the accuracy and convenience of the low-voltage side bushing CT polarity calibration link can be obviously improved;
(2) the invention further improves and designs the integral CT polarity calibration process of the three-phase split type transformer small-difference protection, and accordingly, the specific polarity error type can be effectively identified, and the application range is expanded;
(3) according to the CT polarity verification method and the CT polarity verification system, noise interference to a certain degree can be resisted, the influence of the change of the idle charge closing angle is avoided, the small-difference protection of the transformer can be reliably put into operation along with the main transformer at the first time, the protection reliability in the starting and operation process of the main transformer is improved, and therefore the CT polarity verification method and the CT polarity verification system have important significance for reducing the safe and stable operation risk of a power grid caused by the starting and operation of the main transformer.
Drawings
FIG. 1 is an overall process flow diagram of a CT polarity calibration method for a three-phase split transformer constructed in accordance with the present invention;
fig. 2 is a schematic diagram of the small difference protection polarity of a three-phase split transformer according to the present invention;
FIG. 3 is a diagram (two-dimensional vector space) for exemplary explanation of the waveform similarity calculation principle of the present invention, in which for a current value sampled at n points per cycle, the n-dimensional vector space is expanded;
FIG. 4 is a diagram of the low-voltage side delta winding circulating current and neutral point zero-mode inrush current recording when a main transformer becomes empty and charged;
fig. 5 is a schematic structural diagram of a three-phase split type transformer differential protection polarity verification system constructed according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Taking the Ynd 11-shaped three-phase split transformer as an example, the longitudinal differential protection low voltage side test point can be taken from the bushing CT, and the longitudinal differential protection test point and the correct CT polarity are shown in fig. 2. When the transformer is empty charged at the Y side, the triangle winding generates a circulating current to flow through the bushing CT at the low-voltage side of the transformer.
Those skilled in the art can easily know that when the neutral point on the Y side of the transformer is grounded and the three-phase voltage of the system is assumed to be symmetrical, the low-voltage side delta winding circulating current and the Y side zero-mode inrush current are in a simple proportional relationship, so that one of the low-voltage side delta winding circulating current and the other can be obtained only by obtaining a proportionality coefficient.
However, for a three-phase split transformer, the delta winding circulating current can be measured directly from the bushing CT. In addition, only positive and negative needs to be judged for CT polarity check, so that the calculation of a proportionality coefficient can be omitted, and the triangular winding circulating current and the Y-side zero-mode inrush current are considered to be the same in phase theoretically and have similar waveform height.
More specifically, as shown in FIG. 2, a delta winding circulating current i is shownDThe following relationship exists between the three phase currents:
ia＝ib＝ic＝iD
therefore, the cosine similarity between any two low-voltage three-phase bushing CT currents should be very close to 1, and a threshold value (preferably, 0.9) can be set in consideration of errors and interferences, otherwise, a polarity error exists. Thus, the criterion whether the polarity between the low-voltage side three-phase bushings CT is correct can be expressed as:
min{S(ia,ib),S(ib,ic),S(ic,ia)}≥0.9
when the criterion is not satisfied, because the polarities of the same group of CT are opposite, the reversal of any two-phase CT is equivalent to the reversal of the remaining one-phase CT, so that only three polarity errors exist, namely, the polarities of the a \ b \ c three-phase CT are respectively and independently reversed. To further obtain a detailed polarity error type, a "hypothesis test" approach is applied herein for identification. The specific scheme is as follows: firstly, assuming that the polarity of the a-phase CT is reversed, and carrying out inversion operation on the current secondary value, and then recalculating: if yes, the polarity of the a-phase CT is wrong; otherwise, the operations are carried out on the b \ c phase CT in sequence, and finally the polarity error type can be obtained.
For example, based on the waveform similarity principle shown in fig. 3, the polarity verification scheme as described below can be obtained. The cosine similarity calculation formula is as follows:
after the polarity check between the low-voltage side three-phase bushing CTs is completed, it is very critical to determine whether the polarity of the overall CT on the low-voltage side and the Y side of the transformer is consistent with the polarity required by the small-difference protection device. On the basis of completing the polarity check of the Y-side homodyne protection CT by using zero-mode inrush current, only whether the relative polarity of the low-voltage side and the neutral point CT is correct or not needs to be checked. Based on the low-voltage side triangle winding circulating current iDZero-mode inrush current i from neutral point0nThe proportional relation between the two can use the polarity of the neutral point CT as a reference, and the relative polarity of the low-voltage side and the neutral point CT can be judged by utilizing the principle of waveform similarity, so that the check on the integral polarity of the small-difference protection is completed.
Specific criteria may be exemplarily shown as:
S(iD，i0n)≥0.9
the Y/delta shaped three-phase split transformer CT polarity verification scheme described above can be implemented by programming using MATLAB and can be represented as a flow chart shown in fig. 1, which can be explained in more detail as follows.
S101, performing no-load switching-on operation on a high-voltage side of the three-phase split type transformer, correspondingly generating excitation inrush current and zero-mode inrush current on the high-voltage side and a neutral point, and simultaneously generating triangular winding circulation current on a low-voltage side.
The method aims to generate excitation inrush current and low-voltage side triangular winding circulation current by using no-load closing operation and provide a data source for subsequent polarity verification.
S102, secondary CT current values corresponding to the high-voltage side, the neutral point and the low-voltage side are respectively extracted, CT polarities of the high-voltage side and the neutral point are verified, and the CT polarities of the high-voltage side and the neutral point are ensured to be correct.
S103, respectively calculating S (i) based on the secondary CT current value corresponding to the low-voltage side extracted in S102a,ib)、S(ib,ic)、S(ic,ia) Wherein ia、ibAnd icAnd the secondary values of the CT currents of the low-voltage side phase-a sleeve, the phase-b sleeve and the phase-c sleeve are respectively represented, and S (x, y) represents the solving calculation of the cosine similarity between the two groups of data x and y.
Among them, it should be noted that: all subscripts of the invention "a、b、cAll represent phases, iaThen, a secondary value of the current of the phase bushing CT at the low-voltage side of the transformer is represented, and so on, and S (x, y) represents calculating the cosine similarity between the two sets of data x and y, and the corresponding calculation formula in this embodiment is as follows:
s104: obtaining S (i)a,ib)、S(ib,ic)、S(ic,ia) And judging whether the minimum value is larger than a preset first threshold value: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and entering a step S201; if not, the process proceeds to step S105.
Among them, it should be noted that: the cosine similarity theoretical value of any two groups of data varies between (-1), and the threshold value can be arbitrarily selected between (-1), and is preferably 0.9.
S105: in sequence to ia、ibAnd icThe negation operation is performed, and steps S103 to S104 are repeatedly performed after each negation operation.
The step aims to make a hypothesis and a verification on three possible polarity error conditions one by one, and further identify which polarity error type is.
S201: solving and calculating i based on the secondary CT current values corresponding to the low-voltage side and the neutral point extracted in S102DAnd i0nCosine similarity between the two sets of data, where iDRepresenting the second order of the circulating current of the low-voltage side delta winding and having a value equal to ia、ibAnd icAny one of (a); i.e. i0nRepresenting a zero mode secondary inrush current value at the neutral point.
Based on the data shown in FIG. 4, the calculation results obtained are shown in the following table:
table 1 results of similarity calculation of waveforms shown in fig. 4
S202: judging whether the calculation result of the step S201 is greater than a preset second threshold value: if yes, judging that the integral polarity of the small-difference protection of the three-phase split type transformer is correct; if not, the process proceeds to step S203.
It should be noted that the threshold may still be any value between (-1 to 1), and is preferably 0.9 here.
S203: the second order of circulating current i to the low-voltage side triangular windingDAnd performing the negation operation, and then returning to repeatedly execute the steps S201 to S202.
This step is intended to verify whether the delta winding has an overall wrong polarity.
According to another aspect of the present invention, there is also provided a three-phase split type transformer CT polarity calibration system, specifically as shown in fig. 5, the system includes:
the data acquisition module is used for acquiring secondary values of CT currents corresponding to a high-voltage side, a neutral point and a low-voltage side in real time after the high-voltage side of the three-phase split type transformer executes no-load switching-on operation;
the CT polarity checking module comprises a high-voltage side CT polarity checking module, a neutral point CT polarity checking module and a low-voltage side CT polarity checking module, and is respectively used for checking whether the CT polarities of the high-voltage side, the neutral point and the low-voltage side of the transformer are correct or not; and
the integral polarity checking module is used for checking whether the integral polarity of the small-difference protection of the transformer is correct or not;
wherein, the low pressure side CT polarity check module further comprises:
a first similarity calculation operator module that performs secondary calculation according to the CT current corresponding to the low voltage sideValues, respectively calculate S (i)a,ib)、S(ib,ic)、S(ic,ia) Then, the minimum value is obtained and stored; wherein ia、ibAnd icRespectively representing the secondary values of CT currents of a-phase sleeve, a b-phase sleeve and a c-phase sleeve on the low-voltage side, and S (x, y) representing the solving calculation of cosine similarity between two groups of data x and y;
the first judgment submodule judges whether the minimum value obtained by the first similarity calculation submodule is larger than a preset first threshold value or not according to the minimum value obtained by the first similarity calculation submodule: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and starting to enter an integral polarity check submodule; if not, starting to enter a first correction submodule;
a first correction submodule based on the CT current quadratic value ia、ib、icSequentially carrying out negation operations, substituting the obtained current secondary value data into the first similarity calculation submodule to carry out calculation again after each negation operation, and simultaneously continuing to carry out judgment operation through the first judgment submodule;
the first polarity error type identification submodule is used for recording the serial number of the last negation operation of the first correction submodule and outputting the phase corresponding to the serial number, namely the phase with the polarity error;
wherein the global polarity check module further comprises:
a data updating submodule for executing the corrected current secondary value i according to the low-voltage side CT polarity checking modulea、ib、icArbitrarily taking a second order value of the circulating current as the low-voltage side triangular winding and assigning the second order value as iD；
A second similarity calculation submodule which calculates a second-order value i according to the input low-voltage side triangular winding circulation currentDAnd a zero-modulus secondary inrush current value i of the neutral point0nCalculating the cosine similarity value S (i) between the twoD,i0n) Meanwhile, storing;
a second judgment submodule for calculating the cosine similarity value S (i) according to the second similarity calculation submoduleD,i0n) And judging whether the threshold value is larger than a preset second threshold value: if yes, judging that the integral polarity of the small-difference protection of the three-phase split type transformer is correct and finishing the verification; if not, starting to enter a second polarity error type identification submodule;
the second polarity error type identification submodule is used for outputting a small difference protection overall polarity error result and entering a second correction submodule;
a second correction submodule for correcting a second order value i of a circulating current of the low-voltage side triangular windingDAnd carrying out negation operation, and substituting the obtained current secondary value data into the second similarity calculation submodule to carry out calculation again after each negation operation.
According to another aspect of the present invention, there is also provided a computer-readable storage medium having a computer program stored thereon, which when executed, can implement the steps provided by the above-described embodiments. More specifically, the storage medium may include: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
According to another aspect of the present invention, there is also provided a homodyne protection CT polarity check terminal, which may include a memory and a processor, where the memory stores a computer program, and when the processor calls the computer program in the memory, the steps provided in the foregoing embodiments may be implemented. Certainly, the homodyne protection CT polarity verification terminal may further include various network interfaces, power supplies, and other components.
It is to be noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A three-phase split type transformer CT polarity verification method is characterized by comprising the following steps:
s101, performing no-load switching-on operation on a high-voltage side of the three-phase split type transformer, correspondingly generating excitation inrush current and zero-mode inrush current on the high-voltage side and a neutral point, and simultaneously generating triangular winding circulation current on a low-voltage side;
s102, extracting secondary CT current values corresponding to a high-voltage side, a neutral point and a low-voltage side respectively, checking the CT polarities of the high-voltage side and the neutral point, and ensuring the CT polarities of the high-voltage side and the neutral point to be correct;
s103, respectively calculating S (i) based on the secondary CT current value corresponding to the low-voltage side extracted in S102a,ib)、S(ib,ic)、S(ic,ia) Wherein ia、ibAnd icRespectively representing the secondary values of CT currents of a-phase sleeve, a b-phase sleeve and a c-phase sleeve on the low-voltage side, and S (x, y) representing the solving calculation of cosine similarity between two groups of data x and y;
s104, obtaining S (i)a,ib)、S(ib,ic)、S(ic,ia) And judging whether the minimum value is larger than a preset first threshold value: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and entering a step S201; if not, the step S105 is executed;
s105, sequentially pairing ia、ibAnd icPerforming negation operation, and repeatedly executing the steps S103-S104 after each negation operation;
s201, solving and calculating i based on the secondary CT current values extracted in S102 and corresponding to the low-voltage side and the neutral pointDAnd i0nCosine similarity between the two sets of data, where iDRepresenting the second order of the circulating current of the low-voltage side delta winding and having a value equal to ia、ibAnd icAny one of (a); i.e. i0nA zero mode inrush current secondary value representing a neutral point;
s202, judging whether the calculation result of the step S201 is larger than a preset second threshold value: if yes, judging that the integral polarity of the small-difference protection of the three-phase split type transformer is correct; if not, go to step S203;
s203, circulating current quadratic value i of the low-voltage side triangular windingDAnd performing the negation operation, and then returning to repeatedly execute the steps S201 to S202.
2. The method for checking the polarity of the CT of the three-phase split transformer according to claim 1, further comprising the step of recording and outputting the phase with the wrong polarity after the step S105.
3. The method for checking the polarity of the CT of the three-phase split transformer according to claim 1 or 2, further comprising the operation of identifying and outputting the type of the polarity error after the step S203.
4. The method for checking the polarity of the CT of the three-phase split type transformer according to claim 1 or 2, wherein the value ranges of the first threshold and the second threshold are set to (-1, 1).
5. The method for checking the polarity of the CT of the three-phase split type transformer of claim 4, wherein the first threshold and the second threshold are set to 0.9.
6. The utility model provides a split type transformer CT polarity check-up system of three-phase which characterized in that, this system includes:
the data acquisition module is used for acquiring secondary values of CT currents corresponding to a high-voltage side, a neutral point and a low-voltage side in real time after the high-voltage side of the three-phase split type transformer executes no-load switching-on operation;
the CT polarity checking module comprises a high-voltage side CT polarity checking module, a neutral point CT polarity checking module and a low-voltage side CT polarity checking module, and is respectively used for checking whether the CT polarities of the high-voltage side, the neutral point and the low-voltage side of the transformer are correct or not; and
the integral polarity checking module is used for checking whether the integral polarity of the small-difference protection of the transformer is correct or not;
wherein, the low pressure side CT polarity check module further comprises:
a first similarity calculation operator module for calculating S (i) according to the secondary value of the CT current corresponding to the low voltage sidea,ib)、S(ib,ic)、S(ic,ia) Then, the minimum value is obtained and stored; wherein ia、ibAnd icRespectively representing the secondary values of CT currents of a-phase sleeve, a b-phase sleeve and a c-phase sleeve on the low-voltage side, and S (x, y) representing the solving calculation of cosine similarity between two groups of data x and y;
the first judgment submodule judges whether the minimum value obtained by the first similarity calculation submodule is larger than a preset first threshold value or not according to the minimum value obtained by the first similarity calculation submodule: if yes, judging that the polarities of the triangular windings CT on the low-voltage side are correct, and starting to enter an integral polarity check submodule; if not, starting to enter a first correction submodule;
a first correction submodule based on the CT currentSecond order value ia、ib、icSequentially carrying out negation operations, substituting the obtained current secondary value data into the first similarity calculation submodule to carry out calculation again after each negation operation, and simultaneously continuing to carry out judgment operation through the first judgment submodule;
the first polarity error type identification submodule is used for recording the serial number of the last negation operation of the first correction submodule and outputting the phase corresponding to the serial number, namely the phase with the polarity error;
wherein the global polarity check module further comprises:
a data updating submodule for executing the corrected current secondary value i according to the low-voltage side CT polarity checking modulea、ib、icArbitrarily taking a second order value of the circulating current as the low-voltage side triangular winding and assigning the second order value as iD；
A second similarity calculation submodule which calculates a second-order value i according to the input low-voltage side triangular winding circulation currentDAnd a zero-modulus secondary inrush current value i of the neutral point0nCalculating the cosine similarity value S (i) between the twoD,i0n) Meanwhile, storing;
a second judgment submodule for calculating the cosine similarity value S (i) according to the second similarity calculation submoduleD,i0n) And judging whether the threshold value is larger than a preset second threshold value: if yes, judging that the integral polarity of the small-difference protection of the three-phase split type transformer is correct and finishing the verification; if not, starting to enter a second polarity error type identification submodule;
the second polarity error type identification submodule is used for outputting a small difference protection overall polarity error result and entering a second correction submodule;
a second correction submodule for correcting a second order value i of a circulating current of the low-voltage side triangular windingDPerforming negation operation, and performing negation operation each timeAnd substituting the obtained current secondary value data into the second similarity calculation submodule for calculation again.
7. A computer-readable storage medium, wherein a computer program for implementing the method of polarity verification of three-phase split transformer CT as claimed in claim 5 is stored in the computer-readable storage medium.
8. A three-phase split transformer CT polarity check terminal, comprising a memory and a processor, wherein the memory stores a computer program for implementing the method of claim 7, and the processor is configured to call the computer program in the memory to implement the corresponding CT polarity check process.
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