A method for determining the aging state of a power distribution cable based on resistance change

Abstract

The present application relates to the technical field of cable aging, in particular to a method for judging the aging state of distribution cable based on resistance change. The method comprises the following steps: S1, collecting the current value and temperature value of the distribution cable by the edge computing terminal; S2, collecting data by the edge computing terminal; S3, collecting data for at least one complete collection period in each statistical stage by the edge computing terminal; S4, calculating the current and temperature difference of each collection point, and calculating the mean value of the data in the collection period; S5, calculating the aging coefficient k0 of the initial data, and uploading it to the cloud platform by the edge computing terminal; S6, horizontal comparison and sending coordination notification. Compared with the prior art, the aging coefficient of the distribution cable is calculated by collecting the current value and temperature value of the distribution cable, and the parameters are continuously collected as the basis to correct the aging coefficient, which is uploaded to the cloud platform by the edge computing terminal to form a more accurate analysis and judgment.

Description

Technical Field

[0001] This invention relates to the field of cable aging technology, specifically a method for judging the aging status of power distribution cables based on resistance changes. Background Technology

[0002] Aging of power supply and distribution cables generally refers to the sustained increase in temperature caused by factors such as long-term current overload, abnormal ambient temperature, and abnormal ambient humidity, leading to damage to the insulation layer and increased cable resistance. Aging power supply and distribution cables increase energy loss and heat generation, making them more susceptible to igniting nearby flammable materials, and are a major cause of fires in modern cities. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, this invention provides a method for judging the aging status of power distribution cables based on resistance changes.

[0004] To achieve the above objectives, a method for determining the aging status of power distribution cables based on resistance changes is designed, characterized by the following steps:

[0005] S1, the edge computing terminal collects the current and temperature values ​​of the power distribution cables, and the data collection frequency for each power distribution cable is once per second;

[0006] S2, the edge computing terminal takes the current carrying capacity of the power supply and distribution cable as 0 and the current carrying capacity of the next collection period as exceeding 0 as the starting point of data collection, and takes the current carrying capacity of the power supply and distribution cable as 0, the cable temperature as equal to the ambient temperature, and the current carrying capacity of the power supply and distribution cable as 0 and the cable temperature as greater than the ambient temperature in the previous collection period as the ending point of data collection.

[0007] S3, the edge computing terminal collects data for at least one complete collection period in each statistical stage, and removes data whose collection period exceeds one hour;

[0008] S4, calculate the current and cable temperature difference at each collection point, and calculate the average value of the data during the collection period;

[0009] S5 calculates the aging coefficient k0 of the initial data and uploads it to the cloud platform from the edge computing terminal;

[0010] S6, the cloud platform performs a horizontal comparison of the aging coefficient k0. When the value of k0 is higher than 95% of the monitoring pool and / or higher than the default warning value J for three consecutive statistical periods, the cloud platform sends a notice for assistance, requiring system maintenance and relevant property electricians to conduct on-site tracking and inspection of the cable. If the cable with aging problem is confirmed, the person assisting in the investigation will mark the aging of the cable in the system.

[0011] The aging coefficient of the initial data in step S5 I1 represents the current carried by the power distribution cable during a certain data collection period, ΔT1 represents the temperature of the power distribution cable during a certain data collection period, I2 represents the current carried by the power distribution cable during the next data collection period, and ΔT2 represents the temperature of the power distribution cable during the next data collection period.

[0012] The statistical period is one month.

[0013] The monitoring pool in step S6 is to put the aging coefficient values ​​of all monitored cables in the same period into one pool to find the corresponding suspected problematic cables. The specific method is as follows: put the aging coefficient k0 of all cables in each period into an array, find the 5% with the largest k0 value through natural sorting, and record the cables that are found. When the same cable is in the range of the largest 5% of k0 value in three consecutive periods, it is determined that the cable needs to be manually inspected on site.

[0014] The default warning value J is determined as follows: When the cable is determined to be aged after manual inspection, the average value of the cable's aging coefficient k0 for three consecutive months is taken as the default warning value J.

[0015] Compared with existing technologies, this invention calculates the aging coefficient of power distribution cables by collecting current and temperature values, and continuously collects parameters to correct the aging coefficient. The data is then uploaded to the cloud platform from the edge computing terminal for more accurate analysis and judgment. Detailed Implementation

[0016] Example 1:

[0017] This embodiment describes a method for determining the aging status of power distribution cables based on resistance changes, including the following steps:

[0018] A method for determining the aging status of power distribution cables based on resistance changes, characterized by the following steps:

[0019] S1, the edge computing terminal collects the current and temperature values ​​of the power distribution cables, and the data collection frequency for each power distribution cable is once per second;

[0020] S2, the edge computing terminal takes the current carrying capacity of the power supply and distribution cable as 0 and the current carrying capacity of the next collection period as exceeding 0 as the starting point of data collection, and takes the current carrying capacity of the power supply and distribution cable as 0, the cable temperature as equal to the ambient temperature, and the current carrying capacity of the power supply and distribution cable as 0 and the cable temperature as greater than the ambient temperature in the previous collection period as the ending point of data collection.

[0021] S3, the edge computing terminal collects data for at least one complete collection period in each statistical stage, and removes data whose collection period exceeds one hour;

[0022] S4, calculate the current and cable temperature difference at each collection point, and calculate the average value of the data during the collection period;

[0023] S5 calculates the aging coefficient k0 of the initial data and uploads it to the cloud platform from the edge computing terminal;

[0024] S6, the cloud platform performs a horizontal comparison of the aging coefficient k0. When the value of k0 is higher than 95% of the monitoring pool and / or higher than the default warning value J for three consecutive statistical periods, the cloud platform sends a notice for assistance, requiring system maintenance and relevant property electricians to conduct on-site tracking and inspection of the cable. If the cable with aging problem is confirmed, the person assisting in the investigation will mark the aging of the cable in the system.

[0025] The aging coefficient of the initial data in step S5 I1 represents the current carried by the power distribution cable during a certain data collection period, ΔT1 represents the temperature of the power distribution cable during a certain data collection period, I2 represents the current carried by the power distribution cable during the next data collection period, and ΔT2 represents the temperature of the power distribution cable during the next data collection period.

[0026] The statistical period is one month.

[0027] The monitoring pool in step S6 is to put the aging coefficient values ​​of all monitored cables in the same period into one pool to find the corresponding suspected problematic cables. The specific method is as follows: put the aging coefficient k0 of all cables in each period into an array, find the 5% with the largest k0 value through natural sorting, and record the cables that are found. When the same cable is in the range of the largest 5% of k0 value in three consecutive periods, it is determined that the cable needs to be manually inspected on site.

[0028] The default warning value J is determined as follows: When the cable is determined to be aged after manual inspection, the average value of the cable's aging coefficient k0 for three consecutive months is taken as the default warning value J.

[0029] The derivation of the formula for calculating the aging coefficient k0 is as follows:

[0030] The self-heating of conductive cables is considered to be related to the current, resistance, and duration of energization. The calculation formula is as follows: Q=I 2 *R*t. Where Q is the heat generated by the conductor due to carrying current, I is the amount of current carried, R is the resistance of the conductor, and t is the duration of the conductor carrying current.

[0031] Under normal circumstances, the direct data collected to measure the self-heating degree of a conductor is temperature. Therefore, the amount of heat generated by the conductor's self-heating is also related to factors such as the conductor's specific heat capacity, conductor mass, and temperature rise. The calculation formula is as follows: Q = c * m * ΔT, where c is the specific heat capacity, m is the conductor mass, and ΔT is the temperature rise difference of the conductor.

[0032] Combining the two equations above, we get: c*m*△T = I 2 *R*t.

[0033] For the same power distribution cable under the same electrical load, the increased heat generation of the aged cable indicates that the resistance of the conductor may change after aging. This change coefficient can be represented by k. Therefore, the self-heating formula for conductor aging can be expressed as: c*m*△T = I 2 *R*(1+k)*t.

[0034] Where R is the resistance value measured when the power distribution cable is completed, k is the resistance change coefficient during the cable aging process, and c is the theoretical specific heat capacity of the conductor material. This k value gradually increases with the degree of aging, so this coefficient value is also one of the measurable bases that can reflect cable aging.

[0035] In the above formula, since the specific heat capacity c, conductor mass m, and initial measured resistance R of a power distribution cable are all constant, the data collected to calculate the k value needs to include: the current of the power distribution cable, the cable temperature, the ambient temperature, and the collection time. In actual use, the initial data is used for calculation, and the results are compared with the currently collected data. In historical data used for comparison, k1 = 0.

[0036] Based on the above reasoning, the calculation formula continues to evolve:

[0037] c*m / R = I1 2 *(1+0)*t1 / △T1 = I2 2 *(1+k2)*t2 / △T2

[0038] I1 2 *t1 / △T1 = I2 2 *t2 / △T2+ I2 2 *k2*t2 / △T2

[0039] k2 = (I1 2 *t1 / △T1 - I2 2 *t2 / △T2)*△T2 / I2 2

[0040] k2 = I1 2 *t1△T2 / (△T1*I2 2 ) - t2

[0041] When the data acquisition frequency is once per second, the formula is:

[0042] k2 = I1 2*△T2 / (△T1*I2 2 ) – 1.

[0043] The sampling point in step S3 refers to any point located within the power distribution cable. Typically, the metal conductors we use are also good thermal conductors, and the temperature difference between the two ends of the conductor is negligible. Therefore, in a complete power distribution cable, only one point needs to be selected for measurement. The difference between current and cable temperature rise refers to the difference in the measured self-temperature rise of the cable under different line-load current conditions. For example, at a room temperature of 20 degrees Celsius, with a current of 10 amps, the measured cable temperature is 22.5 degrees Celsius, which can be considered as a self-temperature rise of 2.5 degrees Celsius at 10 amps. At a room temperature of 20 degrees Celsius, with a current of 3 amps, the measured cable temperature is 20.8 degrees Celsius, which can be considered as a self-temperature rise of 0.8 degrees Celsius at 3 amps. If the above data are measured on the same cable, and the ambient temperature is consistent, then a 10-amp line-load current results in a 1.7-degree Celsius higher self-temperature rise in the cable compared to a 3-amp line-load current. In actual cable measurements, the influence of the cable's self-temperature rise in the previous period on the self-temperature rise in the next period must be considered. For example, the actual temperature of the cable will differ when the current rapidly increases from 0 amps to 10 amps and decreases from 20 amps to 10 amps. Therefore, this invention uses a time-period averaging method to reduce the impact of these time-period current differences by extending the sampling time.

[0044] In step S6, as the number of confirmed aging cable samples increases, the number of aging coefficient k0 data involved in determining the default warning value J also increases, and the resulting average value will be more representative, and the default warning value J will gradually become more accurate.

[0045] This invention is a method for judging the aging status of power distribution cables based on resistance changes. Based on the analysis of power distribution cable aging, a dedicated data acquisition, processing, and calculation process is designed. In an IoT system, through the collaboration of edge computing terminals and a cloud platform, continuous data acquisition and tracking of cable aging parameters are performed. Based on the horizontal comparison results of cloud platform data, aging cables are automatically screened. After manual on-site confirmation of the identified aging cables, not only is the aging of the cables reconfirmed, but the default warning value J can also be adjusted based on the aging coefficient of the aging cable, progressively iteratively improving the accuracy of cable aging identification.

Claims

1. A method for determining the aging status of power distribution cables based on resistance changes, characterized in that: Includes the following steps: S1, the edge computing terminal collects the current and temperature values ​​of the power distribution cables, and the data collection frequency for each power distribution cable is once per second; S2, the edge computing terminal takes the current carrying capacity of the power distribution cable as 0 and the current carrying capacity of the next collection period as exceeding 0 as the starting point of data collection, and takes the current carrying capacity of the power distribution cable as 0, the cable temperature as equal to the ambient temperature, and the current carrying capacity of the power distribution cable as 0 and the cable temperature as greater than the ambient temperature in the previous collection period as the ending point of data collection. S3, the edge computing terminal collects data for at least one complete collection period in each statistical period, and removes data whose collection period exceeds one hour; S4, calculate the current and cable temperature difference at each collection point, and calculate the average value of the data during the collection period; S5 calculates the aging coefficient k0 of the initial data and uploads it to the cloud platform from the edge computing terminal; S6, the cloud platform performs a horizontal comparison of the aging coefficient k0. When the value of k0 is higher than 95% of the monitoring pool and / or higher than the default warning value J for three consecutive statistical periods, the cloud platform sends a notice for assistance, requiring system maintenance and relevant property electricians to conduct on-site tracking and inspection of the cable. If the cable with aging problems is confirmed, the person assisting in the investigation will mark the aging of the cable in the system.

2. The method for determining the aging status of power distribution cables based on resistance changes according to claim 1, characterized in that: The statistical period is one month.

3. The method for determining the aging status of power distribution cables based on resistance changes according to claim 1, characterized in that: The monitoring pool in step S6 is to put the aging coefficient values ​​of all monitored cables in the same period into one pool to find the corresponding suspected problematic cables. The specific method is as follows: put the aging coefficient k0 of all cables in each period into an array, find the 5% with the largest k0 value through natural sorting, and record the cables that are found. When the same cable is in the range of the largest 5% of k0 value in three consecutive periods, it is determined that the cable needs to be manually inspected on site.

4. The method for determining the aging status of power distribution cables based on resistance changes according to claim 1, characterized in that: The default warning value J is determined as follows: When the cable is determined to be aged after manual inspection, the average value of the cable's aging coefficient k0 for three consecutive months is taken as the default warning value J.