1. A method for monitoring the mechanical state of an on-load tap-changer based on waveform trend information is characterized by comprising the following steps:

step S1, collecting vibration signal x (t) in the process of switching on-load tap-changer of transformer, wherein the length is N₀Sampling frequency of f_s；

Step S2, calculating the time domain envelope e of the vibration signal x (t) of the transformer on-load tap-changer by adopting optimized continuous wavelet transformation;

step S3, carrying out segmentation and in-segment fitting on the time domain envelope of the vibration signal X (t) of the on-load tap-changer to obtain a coefficient set matrix X consisting of a plurality of groups of fitting coefficients;

step S4, calculating an inner product matrix Y of the coefficient set matrix X;

step S5, calculating eigenvalue lambda of inner product matrix Y₁,λ₂,…,λ_MObtaining an eigenvalue diagonal matrix Z consisting of M eigenvalues;

step S6, constructing a statistic gamma of the eigenvalue diagonal matrix Z, and determining a control limit psi of the statistic gamma by using a 3 sigma criterion;

and step S7, accurately judging the mechanical state of the on-load tap-changer according to the statistic gamma of the eigenvalue diagonal matrix Z and the control limit psi.

2. The on-load tap-changer mechanical state monitoring method based on waveform trend information as claimed in claim 1, wherein said specific process of calculating time domain envelope e of transformer on-load tap-changer vibration signal x (t) by using optimized continuous wavelet transform comprises:

s201, performing continuous Morlet wavelet transformation on the vibration signal x (t) of the on-load tap-changer to obtain a wavelet transformation coefficient matrix W, wherein the Morlet wavelet can be expressed as:

wherein: f. of_cIs the center frequency; f. of_bIs a bandwidth parameter; a is a transformation scale;

s202, constructing a Hankel matrix according to a wavelet transformation coefficient matrix W line by line, wherein the wavelet coefficients of the ith line in the wavelet transformation coefficient matrix WThe Hankel matrix of (a) can be expressed as:

wherein: 1<n<N₀；

Let m be N₀N +1, the Hankel matrix of the wavelet coefficient of the ith row is an m multiplied by n real matrix;

s203, carrying out singular value decomposition on the Hankel matrix of the ith row of wavelet coefficients, and calculating the singular value energy E of the ith row of wavelet coefficients_iSaid singular value energy E_iCan be expressed as:

wherein: p is a singular value sigma obtained by singular value decomposition₁,σ₂,…,σ_pAnd p ═ min (m, n).

S204, according to the singular value energy of wavelet coefficients of each row in the wavelet transform coefficient matrix W, selecting the scale parameter corresponding to the wavelet line number corresponding to the maximum extreme point of the singular value energy as the optimal transform scale alpha of the Morlet wavelet₁；

S205, transforming the scale alpha through the optimal transformation₁Carrying out continuous Morlet wavelet transformation on vibration signals x (t) of the on-load tap-changer to obtain a real part s of the Morlet wavelet transformation_RAnd imaginary part s_IDemodulating to obtain a time domain envelope e of the on-load tap-changer vibration signal x (t), wherein the time domain envelope e is calculated by the following formula:

3. the on-load tap-changer mechanical state monitoring method based on waveform trend information according to claim 1, wherein the specific process of performing segmentation and in-segment fitting on the time-domain envelope of the on-load tap-changer vibration signal X (t) to obtain a coefficient set matrix X composed of multiple sets of fitting coefficients comprises:

s301, starting from the head end of the time domain envelope of the vibration signal of the on-load tap-changer, sliding m data backwards each time by adopting a sliding time window with the length of l;

s302, establishing a quadratic fit function for each sliding time window, wherein the quadratic fit function of the ith time window can be expressed as:

Pr_i＝a_it²+b_it+c_i

wherein: a is_i、b_iAnd c_iThree coefficients of a quadratic fitting function are respectively;

s303, mixingThe coefficients of the fitting function for each sliding time window are represented in the form of a set of coefficients, said set of coefficients for the first time window being represented as { a }_i,b_i,c_i}；

S304, writing the coefficient set of all time windows into a matrix form, where the coefficient set matrix X may be represented as:

wherein: w is the number of coefficient sets.

4. The on-load tap-changer mechanical state monitoring method based on the waveform trend information as claimed in claim 1, wherein the principle of distinguishing the mechanical state of the on-load tap-changer according to the statistic Γ of the eigenvalue diagonal matrix Z and the control limit Ψ is as follows: when the statistic gamma does not belong to the control limit psi, judging that the mechanical state of the on-load tap-changer changes; when the statistic Γ belongs to the control limit Ψ, it indicates that the mechanical state of the on-load tap-changer is normal.

5. The on-load tap-changer mechanical state monitoring method based on waveform trend information as claimed in claim 1, wherein the process of segmenting and fit within the segment of the time domain envelope of the on-load tap-changer vibration signal obtains the fluctuation mode of the time domain envelope of the vibration signal and the transfer process of information between adjacent time domain envelopes.

6. The on-load tap changer mechanical condition monitoring method based on waveform trend information of claim 1, wherein said characteristic value comprises a zero characteristic value.

Background

The on-load tap changer is the only movable component of the on-load tap changer, mainly comprises a selector switch, a change-over switch, an electric mechanism, a quick mechanism and the like, can change the voltage transformation ratio under the condition of load, realizes the regulation of system voltage under the condition of no power failure, and realizes the important functions of compensating voltage fluctuation, regulating power, improving system performance, improving power quality and the like.

However, as the service life of the on-load tap-changer increases and the number of times of voltage regulation increases, the failure rate also increases. According to statistics, the fault types of the on-load tap-changer mainly include electrical faults and mechanical faults, and the mechanical faults are main fault types and are also main causes of partial electrical faults. However, the existing methods for acquiring the running state information of the on-load tap-changer mainly depend on switching times, electrical tests and the like, and the methods are not suitable for scientific requirements of state maintenance and state evaluation of power equipment.

In the gear shifting process of the on-load tap-changer, mechanical vibration can be caused by collision or friction between mechanical parts such as moving contacts and static contacts in the switch, and the mechanical vibration is transmitted to the wall of a transformer oil tank through insulating oil or structural members of the tap-changer to form a mechanical vibration signal. Obviously, the mechanical vibration signals contain abundant on-load tap-changer mechanical state information, so that the on-load tap-changer mechanical state monitoring method through a vibration analysis method attracts increasing attention of researchers at home and abroad. However, the mechanical structure of the on-load tap-changer is complicated, and the mechanical vibration signal generated by collision or friction between the moving and static contacts and other mechanism parts in the diverter switch presents strong time-varying and non-stationary characteristics, and how to obtain the evaluation index of the vibration signal for monitoring the mechanical state of the on-load tap-changer is always a difficult point of research due to the existence of interference components in the mechanical vibration signal of the on-load tap-changer obtained through the wall of the transformer tank.

Disclosure of Invention

The invention aims to provide a method for monitoring the mechanical state of an on-load tap-changer based on waveform trend information, which can solve the problem that the judgment index of a vibration signal for monitoring the mechanical state of the on-load tap-changer is difficult to obtain in the prior art.

The purpose of the invention is realized by the following technical scheme:

the invention provides a method for monitoring the mechanical state of an on-load tap-changer based on waveform trend information, which comprises the following steps:

step S1, collecting vibration signal x (t) in the process of switching on-load tap-changer of transformer, wherein the length is N₀Sampling frequency of f_s；

Step S2, calculating the time domain envelope e of the vibration signal x (t) of the transformer on-load tap-changer by adopting optimized continuous wavelet transformation;

step S3, carrying out segmentation and in-segment fitting on the time domain envelope of the vibration signal X (t) of the on-load tap-changer to obtain a coefficient set matrix X consisting of a plurality of groups of fitting coefficients;

step S4, calculating an inner product matrix Y of the coefficient set matrix X;

step S5, calculating eigenvalue lambda of inner product matrix Y₁,λ₂,…,λ_MObtaining an eigenvalue diagonal matrix Z consisting of M eigenvalues;

step S6, constructing a statistic gamma of the eigenvalue diagonal matrix Z, and determining a control limit psi of the statistic gamma by using a 3 sigma criterion;

and step S7, accurately judging the mechanical state of the on-load tap-changer according to the statistic gamma of the eigenvalue diagonal matrix Z and the control limit psi.

Further, the specific process for calculating the time domain envelope e of the transformer on-load tap-changer vibration signal x (t) by using the optimized continuous wavelet transform includes:

s201, performing continuous Morlet wavelet transformation on the vibration signal x (t) of the on-load tap-changer to obtain a wavelet transformation coefficient matrix W, wherein the Morlet wavelet can be expressed as:

wherein: f. of_cIs the center frequency; f. of_bIs a bandwidth parameter; a is a transformation scale;

s202, constructing a Hankel matrix according to a wavelet transformation coefficient matrix W line by line, wherein the wavelet coefficients of the ith line in the wavelet transformation coefficient matrix WThe Hankel matrix of (a) can be expressed as:

wherein: 1<n<N₀；

Let m be N₀N +1, the Hankel matrix of the wavelet coefficients of the ith row is an m × n real matrix.

S203, carrying out singular value decomposition on the Hankel matrix of the ith row of wavelet coefficients, and calculating the singular value energy E of the ith row of wavelet coefficients_iSaid singular value energy E_iCan be expressed as:

wherein: p is a singular value sigma obtained by singular value decomposition₁,σ₂,…,σ_pAnd p ═ min (m, n).

S204, selecting a ruler corresponding to the wavelet line number corresponding to the maximum extreme point of the singular value energy according to the singular value energy of the wavelet coefficients of each line in the wavelet transform coefficient matrix WDegree parameter as optimal transformation scale alpha of Morlet wavelet₁；

S205, transforming the scale alpha through the optimal transformation₁Carrying out continuous Morlet wavelet transformation on vibration signals x (t) of the on-load tap-changer to obtain a real part s of the Morlet wavelet transformation_RAnd imaginary part s_IDemodulating to obtain a time domain envelope e of the on-load tap-changer vibration signal x (t), wherein the time domain envelope e is calculated by the following formula:

further, the specific process of performing segmentation and in-segment fitting on the time domain envelope of the on-load tap-changer vibration signal to obtain a coefficient set matrix X composed of multiple groups of fitting coefficients includes:

s301, starting from the head end of the time domain envelope of the vibration signal of the on-load tap-changer, sliding m data backwards each time by adopting a sliding time window with the length of l;

s302, establishing a quadratic fit function for each sliding time window, wherein the quadratic fit function of the ith time window can be expressed as:

Pr_i＝a_it²+b_it+c_i

wherein: a is_i、b_iAnd c_iThree coefficients of a quadratic fitting function are respectively;

s303, representing the coefficient of the fitting function of each sliding time window into a form of a coefficient set, wherein the coefficient set of the first time window can be represented as { a_i,b_i,c_i}；

S304, writing the coefficient set of all time windows into a matrix form, where the coefficient set matrix X may be represented as:

wherein: w is the number of coefficient sets.

Further, the principle of distinguishing the mechanical state of the on-load tap-changer according to the statistic Γ of the eigenvalue diagonal matrix Z and the control limit Ψ is as follows: when the statistic gamma does not belong to the control limit psi, judging that the mechanical state of the on-load tap-changer changes; when the statistic Γ belongs to the control limit Ψ, it indicates that the mechanical state of the on-load tap-changer is normal.

Further, the process of segmenting and in-segment fitting the time domain envelope of the on-load tap-changer vibration signal obtains the fluctuation mode of the time domain envelope of the vibration signal and the transmission process of information between adjacent time domain envelopes.

Further, the eigenvalue comprises a zero eigenvalue.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of an embodiment of a method for monitoring a mechanical state of an on-load tap-changer based on waveform trend information according to the present application;

fig. 2 is a vibration signal for mechanical condition monitoring of an on-load tap changer according to an embodiment of the present application;

fig. 3 is a frequency spectrum distribution of a vibration signal fluctuation term for on-load tap-changer mechanical condition monitoring in an embodiment of the present application.

Detailed Description

The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

The embodiments of the present disclosure are described below with specific examples, and other advantages and effects of the present disclosure will be readily apparent to those skilled in the art from the disclosure in the specification. It is to be understood that the described embodiments are merely illustrative of some, and not restrictive, of the embodiments of the disclosure. The disclosure may be embodied or carried out in various other specific embodiments, and various modifications and changes may be made in the details within the description without departing from the spirit of the disclosure. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

Referring to fig. 1 to fig. 3, in the embodiment of the present application, a 110kV transformer on-load tap-changer is used as a test object, and a vibration signal in a switching process of the on-load tap-changer is tested, and the embodiment of the method for monitoring a mechanical state of an on-load tap-changer based on waveform trend information includes:

step S1, collecting a vibration signal x (t) during the on-load tap-changer switching process of the transformer, where the length N of the vibration signal in this embodiment is₀9000, sampling frequency f_s51200 kHz;

it should be noted that, in a substation site, a vibration sensor is installed on a transformer on-load tap changer, and a vibration signal collected by the vibration sensor is collected by a mobile phone in a collection system.

Step S2, calculating the time domain envelope e of the vibration signal x (t) of the transformer on-load tap-changer by adopting optimized continuous wavelet transformation; the specific process of calculating the time-domain envelope e in the implementation of the present application is as follows:

s201, performing continuous Morlet wavelet transformation on the vibration signal x (t) of the on-load tap-changer to obtain a wavelet transformation coefficient matrix W, wherein the Morlet wavelet can be expressed as:

wherein: f. of_cIs the center frequency; f. of_bIs a bandwidth parameter; a is a transformation scale;

s202, constructing a Hankel matrix according to a wavelet transformation coefficient matrix W line by line, wherein the wavelet coefficients of the ith line in the wavelet transformation coefficient matrix WThe Hankel matrix of (a) can be expressed as:

wherein: 1<n<N₀；

Let m be N₀N +1, the Hankel matrix of the wavelet coefficient of the ith row is an m multiplied by n real matrix;

s203, carrying out singular value decomposition on the Hankel matrix of the ith row of wavelet coefficients, and calculating the singular value energy E of the ith row of wavelet coefficients_iSaid singular value energy E_iCan be expressed as:

wherein: p is a singular value sigma obtained by singular value decomposition₁,σ₂,…,σ_pAnd p ═ min (m, n);

wherein matrix singular value decomposition is a matrix transformation familiar to those skilled in the art and is not described herein again;

s204, according to the singular value energy of wavelet coefficients of each row in the wavelet transform coefficient matrix W, selecting the scale parameter corresponding to the wavelet line number corresponding to the maximum extreme point of the singular value energy as the optimal transform scale alpha of the Morlet wavelet₁；

S205, transforming the scale alpha through the optimal transformation₁Carrying out continuous Morlet wavelet transformation on vibration signals x (t) of the on-load tap-changer to obtain a real part s of the Morlet wavelet transformation_RAnd imaginary part s_IDemodulating to obtain a time domain envelope e of the on-load tap-changer vibration signal x (t), wherein the time domain envelope e is calculated by the following formula:

whereinBy optimally transforming the scale alpha₁The change trend of the vibration signal time sequence is accurately reflected to the maximum extent by the time domain envelope of the vibration signal of the on-load tap-changer, which carries out continuous Morlet wavelet transformation on the vibration signal x (t) of the on-load tap-changer.

Step S3, carrying out segmentation and in-segment fitting on the time domain envelope of the vibration signal X (t) of the on-load tap-changer to obtain a coefficient set matrix X consisting of a plurality of groups of fitting coefficients;

in addition, the time domain envelope of the vibration signal of the on-load tap-changer is subjected to fine processing by adopting segmentation and in-segment fitting, so that the fluctuation mode of the time domain envelope of the vibration signal can be effectively obtained, and the information transmission process between adjacent time domain envelopes can be accurately described.

The specific process of calculating the coefficient set matrix X in the implementation of the present application includes:

s301, starting from the head end of the time domain envelope of the vibration signal of the on-load tap-changer, sliding m data backwards each time by adopting a sliding time window with the length of l; in this embodiment, l is 3, m is 5;

s302, establishing a quadratic fit function for each sliding time window, wherein the quadratic fit function of the ith time window can be expressed as:

Pr_i＝a_it²+b_it+c_i

wherein: a is_i、b_iAnd c_iThree coefficients of a quadratic fitting function are respectively;

s303, representing the coefficient of the fitting function of each sliding time window into a form of a coefficient set, wherein the coefficient set of the ith time window can be represented as { a_i,b_i,c_i}；

S304, writing the coefficient set of all time windows into a matrix form, where the coefficient set matrix X may be represented as:

wherein: w is the number of coefficient sets.

Step S4, calculating an inner product matrix Y of the coefficient set matrix, wherein the calculation formula of the inner product matrix Y is as follows:

Y＝X^TX

wherein: t denotes a matrix transposition.

Step S5, calculating eigenvalue lambda of inner product matrix Y₁,λ₂,…,λ_MObtaining an eigenvalue diagonal matrix Z composed of M eigenvalues, where the eigenvalue diagonal matrix Z can be expressed as:

Z＝diag(λ₁,λ₂,…,λ_M)

in the application, the characteristic value diagonal matrix of the inner product matrix is constructed in the preferred implementation, and the calculation precision is improved while the calculation is simple and convenient.

Step S6, constructing a statistic Γ of the eigenvalue diagonal matrix Z, and determining a control limit Ψ of the statistic Γ by using a 3 σ criterion, where the statistic Γ may be represented as:

wherein: l is the number of zero elements in the eigenvalue diagonal matrix Z;

in the application, the important characteristic information of the zero characteristic value is considered in the statistical measurement in the preferred implementation, and the monitoring accuracy of the mechanical state of the on-load tap-changer is effectively improved.

And step S7, judging the mechanical state of the on-load tap-changer according to the statistic gamma of the eigenvalue diagonal matrix Z and the control limit psi. In a specific implementation process, when the statistic gamma does not belong to the control limit psi, judging that the mechanical state of the on-load tap-changer changes; when the statistic Γ belongs to the control limit Ψ, it indicates that the mechanical state of the on-load tap-changer is normal.

The working principle of the invention is as follows: the method comprises the steps of obtaining a vibration signal in the switching process of the on-load tap-changer of the transformer, obtaining a time domain envelope of the on-load tap-changer of the transformer by using the vibration signal, carrying out segmentation and in-segment fitting on the time domain envelope to obtain a coefficient set matrix consisting of a plurality of groups of fitting coefficients, solving an inner product matrix, constructing by using the inner product matrix to obtain a characteristic value diagonal matrix, obtaining statistics and a control limit of the characteristic value diagonal matrix, and finally distinguishing the mechanical state of the on-load tap-changer according to the statistics and the control limit of the characteristic value diagonal matrix. When the statistic does not belong to the control limit, judging that the mechanical state of the on-load tap-changer changes; when the statistic belongs to the control limit, the mechanical state of the on-load tap-changer is normal.

It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a read-only memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and the like.