阅读说明：本技术 一种基于多变量状态估计的高压隧道电缆过热预警方法 (High-voltage tunnel cable overheating early warning method based on multivariate state estimation ) 是由 周贺 林梓圻 周海鹏 孙秋芹 牛林华 刘耀中 谢枫 张家倩 孟宪乔 邵松涛 吴睿 于 2020-08-31 设计创作，主要内容包括：本发明涉及一种基于多变量状态估计的高压隧道电缆过热预警方法,包括：采集正常历史数据,进行数据预处理；进行数据标准化；构建记忆矩阵D；输入当前运行数据,形成观测向量；预估估计向量；计算残差和置信区间并预警。本发明可以在不额外增加监测设备的前提下,实现高压隧道电缆过热预警的目的；本发明实现了在潜在故障点影响系统运行之前就触发报警,提醒运维检修人员进行维修,避免出现事故,提高了高压电缆输电系统的运行安全性和经济性。(The invention relates to a high-voltage tunnel cable overheating early warning method based on multivariate state estimation, which comprises the following steps: collecting normal historical data, and performing data preprocessing; carrying out data standardization; constructing a memory matrix D; inputting current operation data to form an observation vector; estimating an estimation vector; and calculating residual errors and confidence intervals and carrying out early warning. The invention can realize the purpose of early warning the overheating of the high-voltage tunnel cable on the premise of not additionally increasing monitoring equipment; the invention realizes that the alarm is triggered before the potential fault point affects the operation of the system, and the operation and maintenance maintainers are reminded to maintain, thereby avoiding accidents and improving the operation safety and the economical efficiency of the high-voltage cable power transmission system.)

1. A high-voltage tunnel cable overheating early warning method based on multivariate state estimation is characterized by comprising the following steps: the method comprises the following steps in sequence:

(1) collecting normal historical data, and performing data preprocessing;

(2) carrying out data standardization;

(3) constructing a memory matrix D;

(4) inputting current operation data to form an observation vector;

(5) estimating an estimation vector;

(6) and calculating residual errors and confidence intervals and carrying out early warning.

2. The multivariable state estimation-based high-voltage tunnel cable overheating early warning method according to claim 1, wherein: the step (1) specifically comprises the following steps: obtaining data monitored and stored by a high-voltage cable on-line monitoring system, and screening the data: if the data fluctuate in the established normal range, the running state is normal, the data are extracted as normal historical data, and if the data exceed the normal range, the data are rejected; forming a history observation vector set M by the screened history data;

the column vector represents the state of the high-voltage cable at a certain normal operation moment, and then the column vector at a certain moment i is:

X(i)＝[x₁ x₂ … x_n]^T

after collecting the normal operation data of M normal state values of the high-voltage cable, a historical observation vector set M is expressed as:

wherein n represents n related measuring point parameters of the high-voltage cable; m represents that a certain measuring point parameter of the high-voltage cable has m normal state values.

3. The multivariable state estimation-based high-voltage tunnel cable overheating early warning method according to claim 1, wherein: the step (2) specifically comprises the following steps:

the run data was normalized using the z-score method:

wherein μ is the mean of the overall data; δ is the standard deviation of the overall data; x is an observed value of an individual.

4. The multivariable state estimation-based high-voltage tunnel cable overheating early warning method according to claim 1, wherein: the step (3) specifically comprises the following steps: firstly, extracting special points from a historical observation vector set M, wherein the special points comprise the maximum value and the minimum value of each variable of the system, and then selecting data except the special points from the historical observation vector set M in an equal step length manner to construct a memory matrix D.

5. The multivariable state estimation-based high-voltage tunnel cable overheating early warning method according to claim 1, wherein: the step (5) specifically comprises the following steps: performing state estimation by using a multivariate state estimation method MSET (minimum likelihood estimation) and setting an observation vector of a time point as X_obsEstimate vector as X_estThere is a corresponding weight vector W:

W＝[ω₁ ω₂ … ω_m]^T

estimate vector X_estThe vector is output after the historical observation vectors of m time points in the memory matrix D are linearly combined with the weight vector W;

estimate vector X_estThe following relationships exist with the memory matrix D and the weight vector W:

X_est＝D·W＝ω₁·X(1)+ω₂·X(2)+...ω_m·X(m)

the weight vector W is determined as follows:

W＝(D^T·D)^-1·(D^-1·X_obs)

by non-linear operatorsThe method replaces the dot product operation in the common matrix operation, and the expression of the obtained weight vector is as follows:

wherein the non-linear operatorRepresenting the Euclidean distance;

the estimated vector calculation expression is:

6. the multivariable state estimation-based high-voltage tunnel cable overheating early warning method according to claim 1, wherein: the step (6) specifically comprises the following steps: the fault warning threshold is determined by the following formula:

E＝k×E_max

wherein E is_maxThe absolute value of the residual mean value is the maximum value, and k is an early warning threshold coefficient;

the residual between the observed vector and the estimated vector is:

ε＝X_obs-X_est

the residual error follows normal distribution with unknown mean and standard deviation, the confidence coefficient is 1-alpha, and then the confidence interval of the mean value is:

confidence intervals for standard deviation were:

wherein N is the window width,is the mean of the residuals, S_sIs the standard deviation of the residual error,distributed as tThe position of the branch point is divided into two parts,is x²Distributed byDividing the site;

and when one of the two confidence intervals exceeds a set threshold range, triggering an early warning signal.

Technical Field

The invention relates to the technical field of overheating early warning of high-voltage cables, in particular to a high-voltage tunnel cable overheating early warning method based on multivariate state estimation.

Background

Compared with an overhead transmission line, the high-voltage cable has the advantages of high power supply reliability, small floor area, small external interference and the like, and is widely applied to a power transmission system. Potential fault points of the high-voltage cable caused by mechanical damage, overload operation, cable joint faults and the like usually appear on an insulating layer or a metal sheath layer, and are difficult to find by maintainers. In addition, currently there is no established monitoring index to determine the operating state of the fault point, so that the reference standard is lacking for the service personnel. The appearance of high tension cable latent fault point can lead to the operating current unusual to the thermal effect aggravates, if not in time maintenance, fault point and conductor and the insulating long-term operation around the fault point lead to insulating ageing and conductor damage easily, and then the thermal effect is more obvious, so circulation is reciprocal, finally leads to cable fault, thereby causes the high tension apparatus of cable or connection around influenced, has enlarged the accident scope.

High-voltage cable on-line monitoring systems based on infrared temperature measurement, thermoelectric temperature measurement and distributed optical fiber temperature measurement principles are widely applied, the system can monitor the temperature of each point on a cable in real time, and if the temperature exceeds a given threshold value, an alarm can be triggered to inform maintenance personnel. However, the function of the existing online monitoring system can trigger an alarm only when the temperature exceeds a certain threshold value, namely, a potential fault point appears at the moment, and the occurrence of the potential fault point cannot be stopped in time before the fault point appears.

Disclosure of Invention

The invention aims to provide a multivariable state estimation-based high-voltage tunnel cable overheating early warning method which can estimate the occurrence of fault points in advance, trigger alarm to inform operation and maintenance staff, avoid damages such as insulation aging and conductor damage caused by the occurrence of potential fault points, facilitate prolonging of the service life of a cable, reduce the occurrence rate of faults and improve the operation safety and economy of a high-voltage cable power transmission system.

In order to achieve the purpose, the invention adopts the following technical scheme: a high-voltage tunnel cable overheating early warning method based on multivariate state estimation comprises the following sequential steps:

(1) collecting normal historical data, and performing data preprocessing;

(2) carrying out data standardization;

(3) constructing a memory matrix D;

(4) inputting current operation data to form an observation vector;

(5) estimating an estimation vector;

(6) and calculating residual errors and confidence intervals and carrying out early warning.

The step (1) specifically comprises the following steps: obtaining data monitored and stored by a high-voltage cable on-line monitoring system, and screening the data: if the data fluctuate in the established normal range, the running state is normal, the data are extracted as normal historical data, and if the data exceed the normal range, the data are rejected; forming a history observation vector set M by the screened history data;

the column vector represents the state of the high-voltage cable at a certain normal operation moment, and then the column vector at a certain moment i is:

X(i)＝[x₁ x₂ … x_n]^T

after collecting the normal operation data of M normal state values of the high-voltage cable, a historical observation vector set M is expressed as:

wherein n represents n related measuring point parameters of the high-voltage cable; m represents that a certain measuring point parameter of the high-voltage cable has m normal state values.

The step (2) specifically comprises the following steps:

the run data was normalized using the z-score method:

wherein μ is the mean of the overall data; δ is the standard deviation of the overall data; x is an observed value of an individual.

The step (3) specifically comprises the following steps: firstly, extracting special points from a historical observation vector set M, wherein the special points comprise the maximum value and the minimum value of each variable of the system, and then selecting data except the special points from the historical observation vector set M in an equal step length manner to construct a memory matrix D.

The step (5) specifically comprises the following steps: performing state estimation by using a multivariate state estimation method MSET (minimum likelihood estimation) and setting an observation vector of a time point as X_obsEstimate vector as X_estThere is a corresponding weight vector W:

W＝[ω₁ ω₂ … ω_m]^T

estimate vector X_estThe vector is output after the historical observation vectors of m time points in the memory matrix D are linearly combined with the weight vector W;

estimate vector X_estThe following relationships exist with the memory matrix D and the weight vector W:

X_est＝D·W＝ω₁·X(1)+ω₂·X(2)+...ω_m·X(m)

the weight vector W is determined as follows:

W＝(D^T·D)^-1·(D^-1·X_obs)

by non-linear operatorsThe method replaces the dot product operation in the common matrix operation, and the expression of the obtained weight vector is as follows:

wherein the non-linear operatorRepresenting the Euclidean distance;

the estimated vector calculation expression is:

the step (6) specifically comprises the following steps: the fault warning threshold is determined by the following formula:

E＝k×E_max

wherein E is_maxThe absolute value of the residual mean value is the maximum value, and k is an early warning threshold coefficient;

the residual between the observed vector and the estimated vector is:

ε＝X_obs-X_est

the residual error follows normal distribution with unknown mean and standard deviation, the confidence coefficient is 1-alpha, and then the confidence interval of the mean value is:

confidence intervals for standard deviation were:

wherein N is the window width,is the mean of the residuals, S_sIs the standard deviation of the residual error,distributed as tThe position of the branch point is divided into two parts,is x²Distributed byDividing the site;

and when one of the two confidence intervals exceeds a set threshold range, triggering an early warning signal.

According to the technical scheme, the beneficial effects of the invention are as follows: firstly, the invention can realize the purpose of overheating early warning of the high-voltage tunnel cable on the premise of not additionally increasing monitoring equipment; secondly, the alarm is triggered before the potential fault point affects the operation of the system, operation and maintenance staff are reminded to maintain, accidents are avoided, and the operation safety and the economical efficiency of the high-voltage cable transmission system are improved.

Drawings

FIG. 1 is a flow chart of a method of the present invention;

FIG. 2 is a schematic view of a No. 1 cable joint and cable segment;

FIG. 3 is a diagram of a data culling step;

FIG. 4 is a flow chart of a method for screening memory matrices.

Detailed Description

As shown in fig. 1, a method for early warning of overheating of a high voltage tunnel cable based on multivariate state estimation comprises the following steps in sequence:

(1) collecting normal historical data, and performing data preprocessing;

(2) carrying out data standardization;

(3) constructing a memory matrix D;

(4) inputting current operation data to form an observation vector;

(5) estimating an estimation vector;

(6) and calculating residual errors and confidence intervals and carrying out early warning.

The step (1) specifically comprises the following steps: obtaining data monitored and stored by a high-voltage cable on-line monitoring system, and screening the data: if the data fluctuate in the established normal range, the running state is normal, the data are extracted as normal historical data, and if the data exceed the normal range, the data are rejected; and forming a historical observation vector set M by the screened historical data.

According to the important indexes of the cable state detected by the high-voltage cable on-line monitoring system, the grounding current of the cable sheath, the temperature of the cable intermediate joint, the surface temperature of the three-phase cable and the core current are selected as important indexes of fault early warning. The research object takes a section of high-voltage cable 1# cable joint and cable as an example, as shown in fig. 2. The state monitoring is realized through a high-voltage cable on-line monitoring system, and the monitoring parameters are shown in table 1.

TABLE 1

As can be seen from Table 1, the No. 1 cable connector and the cable have 16 monitoring variables, respectively denoted as x₁、x₂、…、x₁₆2017 data with 10min intervals in a certain half month are selected for analysis and processing. As shown in fig. 3, if the data fluctuates within a predetermined range, the operation state is normal, and the data is extracted as normal history data; if the data are out of the normal range, the data are rejected. Forming a historical observation vector set M by the screened historical data, and screeningThere are a total of m normal state values after the selection.

The column vector represents the state of the high-voltage cable at a certain normal operation moment, and then the column vector at a certain moment i is:

X(i)＝[x₁ x₂ … x_n]^T

after collecting the normal operation data of M normal state values of the high-voltage cable, a historical observation vector set M is expressed as:

wherein n represents n related measuring point parameters of the high-voltage cable; m represents that a certain measuring point parameter of the high-voltage cable has m normal state values.

The step (2) specifically comprises the following steps:

the run data was normalized using the z-score method:

wherein μ is the mean of the overall data; δ is the standard deviation of the overall data; x is an observed value of an individual. Therefore, data with different dimensions can be converted to the same magnitude, and standardization is achieved.

The step (3) specifically comprises the following steps: firstly, extracting special points from a historical observation vector set M, wherein the special points comprise the maximum value and the minimum value of each variable of the system, and then selecting data except the special points from the historical observation vector set M in an equal step length manner to construct a memory matrix D.

The essence of the process is a learning and memorizing process of the characteristics of the high-voltage cable in normal operation, and the memory matrix covers the normal operation space of the high-voltage cable. When constructing the memory matrix D from the set of historical observation vectors M, first, special points including the maximum value and the minimum value of each variable of the system should be extracted from the set of historical observation vectors M, because the variables represent the special state of the system during normal operationState. Then, selecting other data in equal step length, wherein the specific steps are shown in fig. 4, wherein δ is a small positive number, and is generally 0.001; l is the step size and is generally 0.01. i represents the ith row in the historical observation vector set M, t represents the tth column in the historical observation vector set M, and x_minIs the minimum value of the row variable, x_maxIs the maximum value of the row variable, and A is the intermediate variable. Step one, i is made to be 1; in the second step, calculate A ═ l × (i-1) + x_minLet t equal to 1. Thirdly, judging whether the value of | x (t) -A | is less than the set delta, if so, adding the corresponding x (t) into a memory matrix D, and proceeding to the fifth step; and if so, entering the next step. Step four, judging whether t is larger than m, if so, entering the next step; if not, t is added with 1 to the original value and then returns to the third step. The fifth step is to judge i > (x)_max-x_min) Whether the equation is established or not is judged, and if yes, the memory matrix D is constructed; if not, i returns to the second step after 1 in the original value. The memory matrix D finally formed is:

the memory matrix constructed and screened by the method can enable the preprocessed data to fully cover the historical running state, and the states are not repeated, so that the subsequent operation is simplified.

The step (4) specifically comprises the following steps: inputting the grounding current of the cable sheath, the temperature of the middle joint of the cable, the surface temperature of the three-phase cable and the temperature of the fiber core detected by the current high-voltage cable monitoring system at a certain time point to form an observation vector which is expressed as X_obs＝[x₁，x₂，...，x₁₆]^T。

The step (5) specifically comprises the following steps: performing state estimation by using a multivariate state estimation method MSET (minimum likelihood estimation) and setting an observation vector of a time point as X_obsEstimate vector as X_estThere is a corresponding weight vector W:

W＝[ω₁ ω₂ … ω_m]^T

estimate vector X_estThe vector is output after the historical observation vectors of m time points in the memory matrix D are linearly combined with the weight vector W;

estimate vector X_estThe following relationships exist with the memory matrix D and the weight vector W:

X_est＝D·W＝ω₁·X(1)+ω₂·X(2)+...ω_m·X(m)

the weight vector W is determined as follows:

W＝(D^T·D)^-1·(D^-1·X_obs)

by non-linear operatorsThe method replaces the dot product operation in the common matrix operation, and the expression of the obtained weight vector is as follows:

wherein the non-linear operatorRepresenting the Euclidean distance;

the estimated vector calculation expression is:

therefore, when the system normally operates, the input current observation vector belongs to the operation space of the memory matrix, the Euclidean distance between the observation vector and a certain historical observation vector is extremely close, and the precision of the estimation vector obtained through operation is extremely high. When a system has a fault or a potential fault point exists, the characteristics of system parameters change, an observation vector deviates from the normal space of a memory matrix, the Euclidean distance between the observation vector and a historical observation vector is increased, the precision of an estimated vector obtained through operation is greatly reduced, and the residual error between the observation vector and the estimated vector is increased.

The step (6) specifically comprises the following steps: the fault warning threshold is determined by the following formula:

E＝k×E_max

wherein E is_maxThe absolute value of the residual mean value is the maximum value, and k is an early warning threshold coefficient;

the residual between the observed vector and the estimated vector is:

ε＝X_obs-X_est

the residual error follows normal distribution with unknown mean and standard deviation, the confidence coefficient is 1-alpha, and then the confidence interval of the mean value is:

confidence intervals for standard deviation were:

wherein N is the window width,is the mean of the residuals, S_sIs the standard deviation of the residual error,distributed as tThe position of the branch point is divided into two parts,is x²Distributed byDividing the site;

and when one of the two confidence intervals exceeds a set threshold range, triggering an early warning signal.

When the system normally operates, the mean value of the residual errors is close to zero, and the standard deviation is small. When a system fails or potential failure points exist, the mean value and the standard deviation of residual errors can occur in the following three cases

1. The mean of the residuals is close to zero and the standard deviation of the residuals increases.

2. The mean of the residuals deviate from zero and the standard deviation of the residuals does not vary much.

3. A combination of the two above.

In summary, the method comprises the steps of firstly collecting the grounding current of the cable sheath, the temperature of the cable middle joint, the surface temperature of the three-phase cable and the temperature of the fiber core when the high-voltage cable normally runs, eliminating abnormal data, and then standardizing by adopting a z-score method to obtain normal historical data with the same dimension to form a historical observation set; then, a memory matrix is constructed, rows of the matrix represent the number of monitoring points, columns represent different normal operation states, and a method of selecting special points and selecting other data in equal step length is adopted when data are extracted from a historical observation set to form the memory matrix, so that the states are ensured not to be repeated; and finally, inputting current operation data, estimating an estimation vector, calculating a residual error and a confidence interval between the observation vector and the estimation vector, and triggering an overheating early warning signal when the confidence interval corresponding to the mean value or standard deviation of the residual error exceeds a set threshold value, so that the problem of inaccurate early warning when the input observation vector is just in an area with weak coverage of a memory matrix is solved, the early warning accuracy is improved, and the early warning is realized.