A power fitting current overload early warning protection method and system

Abstract

The present application belongs to the technical field of current overload early warning, and particularly relates to a power fitting current overload early warning protection method and system, which comprises the following steps: obtaining the equivalent thermal sequence inside the power fitting and the temperature rise sequence on the surface; obtaining the main shaft deflection angle and dynamic ring area of the thermoelectric response trajectory according to the equivalent thermal sequence and the temperature rise sequence; obtaining the contact deterioration index based on the main shaft deflection angle, the dynamic ring area, the reference deflection angle data and the reference ring area data; obtaining multiple contact deterioration indexes within a preset aggregation period, and generating the current overload early warning protection signal of the power fitting according to the number of contact deterioration indexes with a value greater than the single-point deterioration threshold. The present application can trigger early warning before the contact resistance of the power fitting develops into a fuse overload by analyzing the state distortion of thermal conduction, and effectively overcomes the cooling interference under abnormal environment.

Description

Technical Field

[0001] This invention relates to the field of current overload early warning technology. More specifically, this invention relates to a method and system for early warning and protection of current overload in power fittings. Background Technology

[0002] Power monitoring plays a vital role in the operation and maintenance of power transmission and distribution networks. Outdoor power fittings often experience problems such as oxidation of internal contact surfaces or mechanical loosening during long-term operation, which can lead to a sharp increase in contact resistance and overheating. If overheating is not detected in time, it can cause serious accidents such as fitting meltdown. Therefore, high-precision power fitting current overload early warning protection is particularly important for the safe and stable operation of the power system.

[0003] In related technologies, a temperature threshold-based monitoring method is typically used to determine the status of power fittings. This method includes: continuously reading the surface temperature value through a temperature sensor deployed on the surface of the power fitting; directly comparing the collected surface temperature value with a preset safe overload temperature threshold; determining whether the surface temperature value is greater than the preset safe overload temperature threshold, and triggering an alarm or tripping action when the surface temperature value exceeds the threshold.

[0004] The existing technologies neglect the severe impact of complex outdoor natural environments on the heat dissipation process of power fittings. In actual operation scenarios of outdoor transmission lines, due to the large metal mass and heat capacity of power fittings, there is an inherent thermal inertia delay between the heat generated by internal current input and the surface temperature response, and the surface temperature is directly dominated by external wind speed dissipation. When facing strong winds and convective weather, intense convective heat transfer can cause the perceived surface temperature to remain within a low absolute value range even if the internal contact points of the power fittings have suffered severe heat accumulation and a surge in heat generation due to deterioration. Relying solely on the absolute surface temperature threshold cannot eliminate the illusion caused by the forced cooling conditions of strong external winds, and cannot penetrate the surface cooling phenomenon to perceive the true physical imbalance between internal heat generation and heat dissipation, which can easily lead to the risk of overload false alarms. Summary of the Invention

[0005] To address the technical problem that the current overload early warning detection of the aforementioned power fittings lacks resistance to interference from external strong winds and heat dissipation conditions, which easily leads to missed detections, the present invention provides solutions in the following aspects.

[0006] In a first aspect, the present invention provides a method for overload warning protection of power fittings, comprising: acquiring the induced voltage amplitude of a current transformer installed inside the power fitting and the resistance reading of a thermistor installed on the surface of the power fitting; acquiring an equivalent thermal sequence and a temperature rise sequence based on the induced voltage amplitude and the resistance reading; acquiring a thermoelectric response trajectory constructed with the values ​​in the equivalent thermal sequence as the abscissa and the values ​​in the temperature rise sequence corresponding to the same timestamp as the ordinate; acquiring the trajectory principal axis deflection angle and the dynamic loop area of ​​the thermoelectric response trajectory; acquiring a contact degradation index based on the difference between the trajectory principal axis deflection angle and the reference deflection angle data, as well as the dynamic loop area and the reference loop area data; acquiring each contact degradation index within a preset aggregation period; and generating an overload warning protection signal for the power fitting based on the number of contact degradation indices whose values ​​are greater than a single-point degradation threshold.

[0007] This invention maps a one-dimensional time-series signal to a two-dimensional plane, extracting spatial features that characterize changes in internal thermal conduction. By utilizing the temperature rise efficiency feature, which is unaffected by the absolute load amplitude, to constrain the internal thermal capacity buffering capacity feature, which is easily affected by the load, this invention effectively eliminates the interference of severe cooling dissipation caused by strong winds and convective weather on the surface temperature of power fittings. This avoids the serious underreporting caused by relying on the absolute surface temperature threshold for judgment, allowing the generated contact degradation index to truly reflect the imbalance between the heat generation rate and the heat dissipation rate caused by oxidation or loosening of the internal contact surface of the power fitting. Thus, it outputs early warning information in a timely manner before the power fitting develops into a fusible current overload, improving the reliability of power fitting current overload detection in complex outdoor natural environments.

[0008] Preferably, the step of obtaining the equivalent thermal sequence and temperature rise sequence based on the induced voltage amplitude and resistance reading includes: calculating the product of the induced voltage amplitude and the preset transformation ratio coefficient to obtain instantaneous effective current data; performing a square operation on each instantaneous effective current data within the time sliding window to map it to the physical heating power equivalent to obtain the equivalent thermal sequence; obtaining instantaneous power fitting surface temperature data based on the resistance reading; aligning the instantaneous power fitting surface temperature data within the time sliding window according to the timestamp to obtain the temperature rise sequence.

[0009] Preferably, obtaining the trajectory principal axis deflection angle and dynamic loop area of ​​the thermoelectric response trajectory includes: calculating a two-dimensional covariance matrix for all discrete points of the thermoelectric response trajectory, and extracting the eigenvector corresponding to the largest eigenvalue in the two-dimensional covariance matrix; obtaining the angle between the eigenvector and the horizontal axis as the trajectory principal axis deflection angle; extracting the outermost boundary points from all discrete points of the thermoelectric response trajectory using the convex hull algorithm; connecting the outermost boundary points in time stamp order to construct a closed polygon, and calculating the area enclosed by the closed polygon as the dynamic loop area.

[0010] This invention calculates the area enclosed by a closed polygon as the dynamic loop area, accurately defining the temperature response dominant efficiency axis that characterizes the direction of maximum variance in the two-dimensional scattered point distribution. It also transforms the buffering capacity exhibited by power fittings due to thermal inertia into the numerical value of the closed polygon area, overcoming the difficulty of directly measuring the drastic jumps in delay time during different periods in the time domain under non-periodic fluctuating loads in outdoor lines. This provides a basis for judging the changes in heat delay conduction of power fittings.

[0011] Preferably, the convex hull algorithm is the Graham Scan algorithm.

[0012] Preferably, the contact degradation index satisfies the following relationship: In the formula, To access the degradation index, The deflection angle of the principal axis of the trajectory. As the reference deflection angle data, For the dynamic ring area, Based on the area data of the reference ring, To prevent constants with a denominator of zero, It is an exponential function with the natural constant as its base. It is the tangent function. This is the sensitivity amplification factor.

[0013] This invention obtains a contact degradation index, combining data reflecting the deviation of unit heat dissipation power intensity with data reflecting the degree of heat accumulation in the metal structure. This makes the determination of the internal structural condition of power fittings unaffected by the direct interference of random load switching fluctuations on the user side, and reduces false alarms caused by the sharp drop in surface temperature due to strong external wind cooling conditions.

[0014] Preferably, generating a current overload warning protection signal for power fittings based on the number of contact degradation indices with values ​​greater than the single-point degradation threshold includes: counting the number of abnormal samples with values ​​greater than the single-point degradation threshold within a preset aggregation period; and generating and outputting a current overload warning protection signal for power fittings in response to the number of abnormal samples exceeding a preset quantity tolerance threshold.

[0015] Preferably, the single-point degradation threshold is the sum of the mean of the contact degradation index continuously collected under the reference operating conditions and three times the standard deviation.

[0016] Secondly, the present invention provides a power fitting current overload early warning and protection system, including a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, the above-mentioned power fitting current overload early warning and protection method is implemented.

[0017] By adopting the above technical solution, a computer program for the above-mentioned power fitting current overload early warning protection method is generated and stored in a memory so that it can be loaded and executed by a processor. A terminal device can then be made based on the memory and the processor for convenient use.

[0018] The beneficial effects of this invention are as follows: By simultaneously acquiring the equivalent thermal sequence inside the power fitting and the temperature rise sequence on its surface, and mapping the equivalent thermal sequence and temperature rise sequence onto a two-dimensional plane to construct a thermoelectric response trajectory, this invention effectively overcomes the lack of stable periodicity caused by the random switching of outdoor current loads by users. Furthermore, this invention extracts the trajectory principal axis deflection angle representing the intensity of the temperature rise response and the dynamic loop area representing the buffering capacity of the power fitting's thermal capacity for the temperature rise process. It then uses the trajectory principal axis deflection angle, which is insensitive to the absolute amplitude of the load, to adjust the dynamic loop area, which is sensitive to the load, thereby obtaining a contact degradation index. This allows the determination of power fitting contact degradation to be based on the physical imbalance between the internal heating rate and the heat dissipation rate. Thus, before the internal contact resistance degradation of the power fitting develops into a structural melting overload state, it triggers and outputs a current overload warning protection signal for the power fitting, improving the sensitivity to internal structural faults and the reliability of the warning protection. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart illustrating a current overload warning and protection method for power fittings according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] This invention discloses a method for overload warning and protection of power fittings, referring to... Figure 1 This includes steps S1-S4:

[0023] S1. Acquire the original electrothermal signal and, in conjunction with a preset sampling clock, construct an equivalent thermal sequence and a temperature rise sequence.

[0024] It should be noted that outdoor power fittings are exposed to the natural environment for extended periods, causing their surface temperature to be severely affected by solar radiation and wind dissipation. While absolute temperature thresholds are typically used to determine overload, this method is prone to missed detections during strong winds and convective weather, even when the internal contact resistance of the fittings has increased significantly. Therefore, this invention does not directly use absolute temperature thresholds to determine overload, but instead extracts the dynamic heat sources and the changing patterns of apparent response characteristics.

[0025] Specifically, the induced voltage amplitude of the current transformer installed inside the power fitting is read, and the product of the induced voltage amplitude and the preset transformation ratio coefficient is obtained to obtain the instantaneous effective current data. Simultaneously, the resistance reading of the thermistor installed on the surface of the power fitting is read, and the instantaneous surface temperature data of the power fitting is obtained based on the thermistor's resistance reading. Instantaneous effective current data and instantaneous surface temperature data are continuously captured within a time window according to a preset sampling clock.

[0026] Furthermore, the effective current data at each instant within the time sliding window is squared and mapped to the physical heating power equivalent to obtain the equivalent thermal sequence; the instantaneous surface temperature data within the time sliding window are aligned according to the timestamp to obtain the temperature rise sequence.

[0027] It should be added that the calculation of the product of the induced voltage amplitude and the preset transformation ratio coefficient is based on the electromagnetic induction principle of the current transformer: the primary current of the current transformer induces a voltage on the secondary side through the iron core, and its amplitude is proportional to the primary current. The ratio is determined by the turns ratio of the transformer, that is, the transformation ratio coefficient. Therefore, multiplying the induced voltage amplitude by this transformation ratio coefficient can restore the true value of the primary current. At the same time, according to Joule's law, the heating power of the conductor is proportional to the square of the current. The squaring operation converts the current sequence into the dimension of heating power, so that the horizontal axis of the subsequent phase space has the meaning of power.

[0028] In this embodiment, the sampling frequency is 1kHz. When the line harmonic content is high, the sampling frequency can be appropriately increased to fully capture transient details. When only power frequency equivalent information is needed, the sampling frequency can be appropriately reduced to reduce data throughput. The time window is 20 seconds. When the load fluctuation frequency is high, the time window can be appropriately shortened to obtain higher response sensitivity. When the load is stable, the time window can be appropriately extended to accumulate more scattered data and improve the statistical stability of the hysteresis loop pattern.

[0029] S2. Based on the temporal mapping relationship between the equivalent thermal sequence and the temperature rise sequence, extract the principal axis deflection angle and dynamic loop area of ​​the thermoelectric response trajectory.

[0030] It should be noted that power fittings typically possess significant metallic mass and heat capacity, resulting in a thermal inertia delay between current input and surface temperature response. This leads to inconsistent temperature behavior during the heating and cooling processes under the same current. Because the current load of outdoor lines is affected by random switching on the user side, its amplitude and waveform lack stable periodicity, causing drastic jumps in the delay time measurement results between different periods in the time domain. Therefore, directly extracting the delay time in the time domain presents certain difficulties. To measure this complex delay variation, this invention maps the one-dimensional time-series signal to a two-dimensional plane, utilizing the distortion characteristics of the graph to characterize the internal thermal conduction state.

[0031] Specifically, using the values ​​in the equivalent thermal sequence as the horizontal axis and the values ​​corresponding to the same timestamp in the temperature rise sequence as the vertical axis, discrete trajectory points are mapped in a two-dimensional coordinate system to construct the thermoelectric response trajectory.

[0032] Furthermore, a two-dimensional covariance matrix is ​​calculated for all discrete points of the thermoelectric response trajectory. The eigenvector corresponding to the largest eigenvalue of this covariance matrix is ​​extracted, and the angle between this eigenvector and the horizontal axis is obtained, marked as the trajectory principal axis deflection angle. This eigenvector represents the direction with the largest variance in the two-dimensional point distribution, corresponding to the dominant efficiency axis of the current-driven temperature response. Simultaneously, the outermost boundary points are extracted from all discrete points using the convex hull algorithm, and connected in timestamp order to construct a closed polygon. The area enclosed by this closed polygon is calculated and marked as the dynamic loop area.

[0033] Furthermore, under the baseline operating condition where the power fittings do not experience surface oxidation or mechanical loosening, instantaneous effective current data and instantaneous surface temperature data are continuously collected within a sliding window time period using a high-frequency current transformer and a thermistor. A thermoelectric response trajectory is then constructed, and the trajectory principal axis deflection angle and dynamic loop area are obtained. Instantaneous effective current data and instantaneous surface temperature data are collected multiple times for the length of the time sliding window, and the corresponding trajectory principal axis deflection angle and dynamic loop area are obtained. The mean values ​​of the trajectory principal axis deflection angle and dynamic loop area are calculated to obtain the baseline deflection angle data and baseline loop area data.

[0034] In one embodiment, the convex hull algorithm is the Graham Scan algorithm.

[0035] It should be added that, due to thermal inertia, the temperature always lags behind the change in current under normal conditions. At this time, the thermoelectric response trajectory is a full elliptical hysteresis loop. When the internal bolts of the fitting become loose or oxidized, causing a sharp increase in contact resistance, the Joule heat power rises rapidly. The heat capacity of the fitting cannot effectively buffer the temperature rise, and the temperature rises closely following the change in current. The thermoelectric response trajectory shows a significant contraction of the loop area and a significant deviation of the main axis of the trajectory from the longitudinal axis. Thus, by monitoring the changing trend of the dynamic loop area and the deflection angle of the main axis, an early warning can be triggered before the deterioration of the contact resistance develops into a fusible overload. This triggers the protection device to perform current reduction or tripping actions, thereby realizing the overload warning protection of the power fitting.

[0036] S3. Adjust the dynamic ring area using the spindle deflection angle to obtain the contact degradation index.

[0037] It should be noted that the dynamic ring area characterizes the fitting's ability to buffer temperature rise due to thermal inertia, while the spindle deflection angle characterizes the efficiency of driving temperature rise per unit current square. The spindle deflection angle is mainly determined by the fitting's own parameters such as contact resistance and thermal capacity, and is largely unaffected by the absolute load amplitude. Combining the two allows us to use the load-insensitive temperature rise efficiency characteristic to constrain the load-sensitive buffering capability characteristic, ensuring that the determination of contact degradation remains stable under load fluctuations.

[0038] Specifically, the contact degradation index is obtained by combining the currently extracted trajectory principal axis deflection angle and dynamic loop area, as well as the baseline deflection angle data and baseline loop area data.

[0039] Specifically, the contact degradation index satisfies the following relationship:

[0040] ;

[0041] In the formula, To access the degradation index, The deflection angle of the principal axis of the trajectory. As the reference deflection angle data, For the dynamic ring area, Based on the area data of the reference ring, To prevent constants with a denominator of zero, this embodiment... It is 0.001. It is an exponential function with the natural constant as its base. It is the tangent function. This is the sensitivity amplification factor. The empirical value range is [1.5, 3.5]. In this embodiment... The number is 2. The implementers can determine this based on the actual working conditions. When the fittings are in a high-wind area and heat dissipation is rapid, this parameter can be increased appropriately to improve the sensitivity to early heat accumulation. When the fittings are installed in a closed distribution box, this parameter can be decreased appropriately to prevent the overload index from being artificially high due to steady-state heat accumulation.

[0042] The essence of contact degradation in power fittings is the imbalance between the internal heat generation rate and the heat dissipation rate, due to the deflection angle of the main axis of the trajectory. Geometrically, the direction of the principal axis representing the scatter distribution of the phase space trajectory is given by the slope of this direction. This reflects the intensity of the temperature rise response under unit current square power injection, therefore... The degree of deviation of the internal heat conduction efficiency of the fitting is measured by the magnitude of the change relative to the reference deflection angle data. This represents the degree of deviation of the heating slope of the fitting from its healthy state. The larger the value, the greater the possibility that oxidation or loosening of the fitting contact surface will cause a sudden increase in contact resistance, resulting in an increase in local heat generation power. The smaller the value, the smoother and tighter the conductive contact surface of the fitting is, and the more likely the heating efficiency is to remain at the factory healthy level.

[0043] This represents the relative magnitude of the decline in the heat capacity buffering capacity of the fittings. The larger the value, the more drastic the shrinkage of the dynamic ring area, indicating that the heat capacity buffering capacity of the fittings has been damaged and heat cannot be conducted to the surrounding metal and is more likely to accumulate at the contact point. The closer the value is to 1, the more normal the heat capacity of the fittings is, and the heat dissipation and heat generation are maintained in a healthy dynamic balance.

[0044] It should be added that, The physical meaning of is the change in temperature caused by a unit square change in current. An infinitesimal change in current causes an infinitesimal temperature rise. This requires simultaneously satisfying two conditions: zero heat capacity and no heat dissipation. Since electrical fittings are metals, they possess both heat capacity and heat dissipation, making it impossible to meet these two conditions. Therefore, in actual operating conditions, the trajectory spindle deflection angle cannot reach 90°. Approaching 90° leads to When a value overflows, Truncate to the tangent value corresponding to 89.5° to avoid overflow and crash of the microcontroller's floating-point arithmetic unit.

[0045] S4. Based on the time series statistical characteristics of the contact deterioration index, generate an overload warning protection signal for the power fittings.

[0046] Specifically, all contact degradation indices within a preset aggregation period are extracted, and the number of abnormal samples whose values ​​exceed a preset single-point degradation threshold within the preset aggregation period is counted.

[0047] If the number of abnormal samples exceeds the preset quantity tolerance threshold, it is considered that irreversible structural degradation and severe current overload risk have indeed occurred inside the power fitting. At this time, a current overload warning protection signal for the power fitting is generated and output.

[0048] In this embodiment, the preset aggregation period is 10 minutes; the implementer can determine the length of the preset aggregation period according to the actual situation. The preset single-point degradation threshold is determined based on the contact degradation index collected during the benchmark calibration phase; specifically, the mean value is calculated from the continuously collected contact degradation index sequence under the benchmark operating condition. with standard deviation ,Pick As a single-point degradation threshold.

[0049] This invention also discloses an overload warning and protection system for power fittings, including a processor and a memory. The memory stores computer program instructions, which, when executed by the processor, implement an overload warning and protection method for power fittings according to the present invention.

[0050] The system also includes other components well known to those skilled in the art, such as communication buses and communication interfaces, the settings and functions of which are known in the art and will not be described in detail here.

Claims

1. A method for early warning and protection of current overload in power fittings, characterized in that, include: Obtain the induced voltage amplitude of the current transformer installed inside the power fitting and the resistance reading of the thermistor installed on the surface of the power fitting, and obtain the equivalent thermal sequence and temperature rise sequence based on the induced voltage amplitude and resistance reading; Obtain the thermoelectric response trajectory constructed with the values ​​in the equivalent thermal sequence as the x-axis and the values ​​in the temperature rise sequence corresponding to the same timestamp as the y-axis; obtain the trajectory principal axis deflection angle and dynamic loop area of ​​the thermoelectric response trajectory; The contact degradation index is obtained based on the difference between the trajectory principal axis deflection angle and the reference deflection angle data, as well as the dynamic ring area and reference ring area data. Obtain the contact degradation index within the preset aggregation period, and generate an overload warning protection signal for the power fittings based on the number of contact degradation indices whose values ​​are greater than the single-point degradation threshold.

2. The method for overload warning and protection of power fittings according to claim 1, characterized in that, The process of obtaining the equivalent thermal sequence and temperature rise sequence based on the induced voltage amplitude and resistance reading includes: The instantaneous effective current data is obtained by multiplying the induced voltage amplitude with the preset transformation ratio coefficient. The effective current data of each instantaneous moment within the time window is squared and mapped to the physical heating power equivalent to obtain the equivalent heat sequence. The instantaneous surface temperature data of the power fitting is obtained based on the resistance reading. The instantaneous surface temperature data of the power fitting within the time window is aligned according to the timestamp to obtain the temperature rise sequence.

3. The method for overload warning and protection of power fittings according to claim 1, characterized in that, The acquisition of the principal axis deflection angle and dynamic loop area of ​​the thermoelectric response trajectory includes: For all discrete points of the thermoelectric response trajectory, calculate the two-dimensional covariance matrix and extract the eigenvector corresponding to the largest eigenvalue in the two-dimensional covariance matrix; obtain the angle between the eigenvector and the horizontal axis as the trajectory principal axis deflection angle; use the convex hull algorithm to extract the outermost boundary points from all discrete points of the thermoelectric response trajectory; connect the outermost boundary points in the order of timestamps to construct a closed polygon, and calculate the area enclosed by the closed polygon as the dynamic loop area.

4. The method for overload warning and protection of power fittings according to claim 3, characterized in that, The convex hull algorithm is the Graham Scan algorithm.

5. The method for overload warning and protection of power fittings according to claim 1, characterized in that, The contact degradation index satisfies the following relationship: ； In the formula, To access the degradation index, The deflection angle of the principal axis of the trajectory. As the reference deflection angle data, For the dynamic ring area, Based on the area data of the reference ring, To prevent constants with a denominator of zero, It is an exponential function with the natural constant as its base. It is the tangent function. This is the sensitivity amplification factor.

6. The method for overload warning and protection of power fittings according to claim 1, characterized in that, The process of generating an overload warning protection signal for power fittings based on the number of contact degradation indices whose values ​​exceed the single-point degradation threshold includes: The system counts the number of abnormal samples whose values ​​exceed the single-point degradation threshold within a preset aggregation period; in response to the number of abnormal samples exceeding the preset quantity tolerance threshold, it generates and outputs a current overload warning protection signal for the power fittings.

7. A method for overload warning and protection of power fittings according to claim 6, characterized in that, The single-point degradation threshold is the sum of the mean of the contact degradation index continuously collected under the reference operating conditions and three times the standard deviation.

8. A current overload early warning and protection system for power fittings, characterized in that, include: A processor and a memory, wherein the memory stores computer program instructions that, when executed by the processor, implement a current overload warning and protection method for power fittings according to any one of claims 1-7.

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