Method and system for analyzing insulation local aging of cable joint

Abstract

The invention discloses a method and a system for analyzing insulation local aging of a cable joint. The method comprises the following steps: S1, acquiring a thermal behavior of an insulation assembly through an infrared imager; and S2, according to the thermal behavior of the insulation assembly, distinguishing the difference of the temperature change rates of different areas based on the temperature rise change of the specific observation point in each time period so as to detect local insulation aging. According to the technical scheme, real-time monitoring and early detection are carried out on insulation aging of the T-shaped connector of the cable.

Description

Technical Field

[0001] The invention belongs to the technical field of cable T-type joints, and in particular relates to a method and a system for analyzing local aging of insulation of a cable joint. Background Art

[0002] As the cornerstone of modern society, the power system supports social and economic development, and its safe and stable operation is a key priority. Among its many components, cable T-joints are essential for maintaining reliable connections within the power network. However, the aging of insulation materials in these joints poses a major threat to system reliability, as the degradation of insulation performance can trigger abnormal temperature responses, compromising performance and safety. Cross-linked polyethylene (XLPE), as a common material for high-voltage cable insulation, plays a key role in ensuring the durability and reliability of power systems. Maintaining the integrity of XLPE insulation is extremely important to reduce the risks associated with insulation aging, thereby ensuring the stability, safety and efficiency of the entire power system.

[0003] Examples of insulation breakdown in cable joints highlight the risks posed by insulation aging. For example, at two wind farms in Hubei Province, the scale of the problem is clearly visible. At Wind Farm A, the T-connector of the box-type substation has experienced 11 insulation breakdown and explosion incidents since it was put into operation in October 2019. Similarly, Wind Farm B has experienced 8 such incidents since it was put into operation in March 2019. These failures often lead to emergency shutdown of the affected equipment, resulting in long-term outages, and in severe cases, threatening not only the wind turbines but also the safety and stability of the entire power grid. Such disturbances highlight the urgent need to study the failure mechanisms of cable joints, implement real-time monitoring systems, and provide early warnings to prevent failures. By addressing these issues, the safety and reliability of power transmission from wind farms can be ensured, ensuring uninterrupted operation of the power grid. Traditionally, monitoring insulation aging in T-joints relies on periodic offline inspections or post-failure analysis. Such methods include visual inspections for surface wear, insulation resistance measurements, or partial discharge (PD) tests to assess the overall condition of the insulation. While these techniques can identify obvious failures, they are inherently passive and have limited ability to predict early degradation or provide continuous monitoring.

[0004] Today, maintenance practices typically involve on-site inspections by operations and maintenance (O&M) personnel or real-time diagnostics using online monitoring systems. These systems are effective in responding quickly to incidents or predicting damage caused by abnormal operating conditions. However, they are often incapable of detecting progressive degradation under normal operating conditions, especially before damage reaches a critical threshold. This limitation makes preventive maintenance difficult and leaves systems vulnerable to sudden failures.

[0005] Although there are a variety of existing power cable monitoring technologies, existing methods have significant limitations. Many methods are unable to provide continuous, real-time monitoring, resulting in early aging being difficult to detect, especially in local areas prone to thermal degradation. The subtle temperature changes caused by local aging are usually difficult to detect, resulting in delayed identification of potential fault points and increasing the possibility of catastrophic failure.

[0006] Most research and maintenance work focuses on XLPE cable intermediate joints, with limited attention paid to T-joints. However, cable T-joints play an indispensable role in switchgear. As key incoming and outgoing line components, they have a significant impact on the safety and efficiency of power production systems. Despite their relatively low individual costs, failure of these joints can lead to serious economic and social consequences, including high downtime losses and risks to system reliability. The complex structure of T-joints often causes thermal stress to concentrate on the cable joints and the breaks between the insulation and shielding layers inside the joints, making them prone to performance degradation in long-term operation. However, research on the phenomenon of sudden and unexpected cracking of T-joints after years of normal operation is still scarce and needs further in-depth exploration. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method and system for analyzing local aging of cable joint insulation.

[0008] To achieve the above object, the present invention adopts the following technical solution:

[0009] A method for analyzing local aging of cable joint insulation, comprising:

[0010] Step S1, obtaining thermal behavior of an insulation component;

[0011] Step S2: according to the thermal behavior of the insulation component, the difference in the temperature change rate of different areas is identified based on the temperature rise change of a specific observation point in each time period.

[0012] Preferably, an infrared imager is used to perform infrared imaging of the insulating components of the cable T-joint at predetermined intervals to achieve continuous observation of the temperature behavior.

[0013] Preferably, the temperature rise change at a specific observation point is obtained according to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component based on the insulation aging threshold judgment.

[0014] As a preferred method, the insulating component is divided into multiple areas, and each area is equipped with an infrared imager, and each area S is calculated. i The temperature change rate is calculated as:

[0015]

[0016] ΔT i (t) = T i (t+△t)-T i (t)

[0017] Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval;

[0018] By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

[0019] The present invention also provides a system for analyzing local aging of cable joint insulation, comprising:

[0020] A collection device for acquiring thermal behavior of the insulation component;

[0021] The analyzing device is used to identify the difference in the rate of temperature change of different areas based on the change in temperature rise of a specific observation point in each time period according to the thermal behavior of the insulation component.

[0022] Preferably, the acquisition device uses an infrared imager to perform infrared imaging of the insulating components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

[0023] Preferably, the temperature rise change at a specific observation point is obtained according to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component based on the insulation aging threshold judgment.

[0024] As a preferred method, the insulating component is divided into multiple areas, and each area is equipped with an infrared imager, and each area S is calculated. i The temperature change rate is calculated as:

[0025]

[0026] ΔT i (t) = T i (t+△t)-T i (t)

[0027] Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval;

[0028] By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

[0029] The present invention provides real-time monitoring and early detection of cable T-joint insulation aging, focusing on the thermal behavior of insulation components, which will pave the way for more accurate prediction models and more intelligent maintenance practices, ultimately ensuring safe, reliable and efficient operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 A flow chart of a method for analyzing local aging of cable joint insulation according to an embodiment of the present invention;

[0032] Figure 2 Flow chart of thermal aging analysis experiment. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Embodiment 1:

[0036] like Figure 1 As shown, an embodiment of the present invention provides a method for analyzing local aging of cable joint insulation, comprising:

[0037] Step S1, obtaining the thermal behavior of the insulating component by an infrared imager; wherein the insulating component of the cable T-joint is subjected to infrared imaging by the infrared imager at predetermined intervals to achieve continuous observation of the temperature behavior;

[0038] Step S2, according to the thermal behavior of the insulation component, based on the temperature rise change of a specific observation point in each time period, the difference in the temperature change rate of different areas is identified to detect local insulation aging; wherein, according to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component, based on the insulation aging threshold judgment, the temperature rise change of the specific observation point is obtained; and the difference in the temperature change rate of different areas is identified according to differential thermal analysis.

[0039] As an implementation of an embodiment of the present invention, in step S1, an infrared imager is used as a temperature sensor to monitor critical insulation components prone to failure in the power system, such as cable T-joints. Infrared imaging is performed at regular intervals (usually several minutes to half an hour) to ensure continuous observation of temperature behavior. The temperature rise at a specific observation point in each time period is analyzed to distinguish subtle differences in the rate of temperature change in different areas. Subsequently, these changes are associated with the aging process of the insulating polymer based on the principle that the heat transfer rate decreases when the polymer degrades into smaller molecular structures.

[0040] Temperature differential analysis is essential to detect local insulation degradation by observing temperature differences that change rapidly over time. Continuous monitoring of temperature changes in the cable T-joint area can reveal abnormal heating, a key indicator of aging. Over long-term use, electrical and thermal stresses cause polymer degradation, changing its structure and slowing down heat transfer. According to heat conduction theory, well-insulated parts can transfer heat efficiently, while aged parts hinder heat transfer due to material changes. This behavior is consistent with the heat conduction equation, which describes the change in temperature within a material in space and time.

[0041]

[0042] Where T = T(x, y, z, t) represents the temperature as a function of position (x, y, z) and time t, and α is the thermal diffusion coefficient; it is defined as k is the thermal conductivity; ρ is the density of the insulator; c p is the specific heat capacity; is the Laplace operator, which describes the spatial variation of temperature in three-dimensional space, and its expression is:

[0043]

[0044] As an implementation method of an embodiment of the present invention, in step S2, by performing dynamic surface temperature detection on cable T-joints with different insulation thicknesses, the local and overall insulation aging conditions can be evaluated so that timely replacement can be performed when signs of aging appear. The thinner insulation layer in the T-joint responds more quickly to temperature changes, while the thicker insulation layer responds more slowly. The thinner cross-linked polyethylene (XLPE) insulation layer at the bottom of the T-joint conducts heat faster, and the initial temperature rises rapidly, but the heating rate gradually slows down over time. Conversely, the thicker insulation layer responds more slowly initially, but as heat accumulates in the T-joint cavity, its heating rate gradually accelerates. This method emphasizes the importance of insulation layer thickness in determining temperature response and insulation aging.

[0045] Insulation aging threshold judgment:

[0046] The outer surface layer of a cable T-junction usually maintains a stable temperature with minimal variations. As long as the temperature rise remains below a set threshold, the insulation is in good condition. Significant deviations from this pattern may indicate insulation degradation, as temperature variation is directly related to the severity of degradation. A temperature difference threshold derived from a well-insulated T-junction helps to assess this degradation. If the observed temperature difference exceeds this threshold, it indicates severe insulation degradation, as guided by the threshold equation.

[0047] Define temperature difference:

[0048] Determine the temperature T of the thick layer thick , determine the temperature T of the thin layer thin And the temperature difference change is;

[0049] ΔT=T thick -T thin

[0050] Initial reference value

[0051] During the well-insulated phase, the temperature difference between the thick and thin layers was measured and recorded:

[0052] ΔT ref =T thick,ref -T thin,ref

[0053] In subsequent monitoring, the current temperature difference ΔT is continuously recorded. current , and calculate the difference between it and the reference value. The relationship between the two is:

[0054] ΔT diff =ΔT current -ΔT ref

[0055] Set a temperature difference threshold ΔT threshold , if ΔTdiff Exceeding this threshold means that the insulation is seriously aged and is judged as:

[0056] |ΔT diff |>ΔT threshold

[0057] As an implementation method of an embodiment of the present invention, in step S2, the present invention monitors the temperature changes in different areas of the T-joint by dividing the insulating component into multiple areas (such as (S1, S2, S3, S4, S5)), obtaining infrared imaging of each area, and calculating each area S i The temperature change rate is calculated as:

[0058]

[0059] ΔT i (t) = T i (t+△t)-T i (t)

[0060] Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval;

[0061] By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

[0062] The differential analysis highlights the change in local heat transfer rate. The aged area dissipates heat more slowly, with a ΔT i The lower values ​​are a direct indication of insulation degradation. In particular, the response time of the aged area is significantly delayed compared to the new area.

[0063] like Figure 2 As shown, the method of the present invention is used to implement thermal aging analysis, including:

[0064] 1. Set the target temperature inside the T-joint. Use a programmable heating device to set the target temperature to simulate the working conditions of the T-joint or accelerate aging. Among them, the typical target temperature range is 40℃~90℃. This range is selected to represent normal operating conditions or for experimental purposes of accelerating the aging process.

[0065] 2. Determine the initial internal and external temperatures. Before heating begins, measure the initial temperature of the T-joint to establish a baseline for further analysis. Thermocouples are used to measure the internal temperature, while infrared imagers record the surface temperature. Separate measurements are taken for thick and thin insulation layers to assess their baseline thermal behavior.

[0066] 3. Continuous monitoring during heating. The temperature inside the T-joint and the temperature of the thick and thin insulation layers are continuously measured and recorded regularly. The measurements are taken at the same time intervals, for example, every 5 minutes during the experiment. These measurements are essential for analyzing how heat propagates through the T-joint over time.

[0067] 4. Cooling stage: After heating, the T-joint is allowed to cool naturally and the temperature is recorded during this stage. The heat dissipation characteristics of the insulation layer are evaluated by analyzing the cooling rate. The difference in cooling behavior between thick and thin insulation layers provides insights into local aging.

[0068] 5. Repeat the experiment under three different settings:

[0069] 1) Conduct multiple experiments under the following conditions:

[0070] The same T-junction with the same setup: The experiments were repeated to verify the repeatability and consistency of the results. Errors due to instrument noise and environmental factors were analyzed.

[0071] 2) Same T-joint, different settings: Change parameters such as target temperature and heating time to study their effects on thermal response. The systematic error caused by parameter changes is quantified.

[0072] 3) T-joints with different service life: Experiments were conducted on T-joints with different degrees of aging to compare their thermal responses.

[0073] 6. Error handling and data cleaning

[0074] The recorded temperature data is processed to remove anomalies or outliers caused by sensor inaccuracies or environmental noise. Data cleaning includes interpolation or smoothing techniques. Measurement errors are quantified using statistical metrics such as standard deviation and root mean square error (RMSE).

[0075] 7. Aging assessment

[0076] Based on the processed data, differential temperature analysis is used to evaluate the aging degree of the T-joint. The relationship between the thermal gradient (ΔT) and the insulation degradation state is analyzed. The threshold value (ΔT) is used to determine whether the insulation has reached a critical aging state.

[0077] 8. Warning signal or normal operation

[0078] If aging is found and the insulation is seriously degraded, a warning signal is issued. If the insulation temperature difference is within the acceptable range, normal operation continues.

[0079] Embodiment 2:

[0080] An embodiment of the present invention further provides a system for analyzing local aging of cable joint insulation, comprising:

[0081] A collection device for obtaining a thermal response of the insulation component;

[0082] The analyzing device is used to identify the difference in the rate of temperature change of different areas based on the change in temperature rise at a specific observation point within each time period according to the thermal response of the insulation component.

[0083] As an implementation mode of the embodiment of the present invention, the acquisition device uses an infrared imager to perform infrared imaging of the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

[0084] As an implementation mode of an embodiment of the present invention, according to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component, based on the insulation aging threshold judgment, the temperature increase change of a specific observation point is obtained.

[0085] As an implementation method of the present invention, the insulating component is divided into multiple areas, and each area is equipped with an infrared imager, and each area S is calculated. i The temperature change rate is calculated as:

[0086]

[0087] ΔT i (t) = T i (t+△t)-T i (t)

[0088] Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval;

[0089] By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

[0090] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for analyzing local aging of cable joint insulation, characterized in that: include: Step S1, obtaining thermal behavior of an insulation component; Step S2: according to the thermal behavior of the insulation component, the difference in the temperature change rate of different areas is identified based on the temperature rise change of a specific observation point in each time period.

2. The method for analyzing local aging of cable joint insulation according to claim 1, characterized in that: The infrared imaging device is used to perform infrared imaging of the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of the temperature behavior.

3. The method for analyzing local aging of cable joint insulation according to claim 2, characterized in that: According to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component, based on the insulation aging threshold judgment, the temperature rise change of a specific observation point is obtained.

4. The method for analyzing local aging of cable joint insulation according to claim 3, characterized in that: By dividing the insulation component into multiple areas, and each area is equipped with an infrared imager, the S i The temperature change rate is calculated as: ΔT i (t)=T i (t+Δt)-T i (t) Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval; By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

5. A system for analyzing local aging of cable joint insulation, characterized in that: include: A collection device for acquiring thermal behavior of the insulation component; The analyzing device is used to identify the difference in the rate of temperature change of different areas based on the change in temperature rise of a specific observation point in each time period according to the thermal behavior of the insulation component.

6. The system for analyzing local aging of cable joint insulation as claimed in claim 5, characterized in that: The acquisition device uses an infrared imager to perform infrared imaging of the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

7. The system for analyzing local aging of cable joint insulation according to claim 6, characterized in that: According to the temperature difference change between the thick layer temperature and the thin layer temperature of the insulation component, based on the insulation aging threshold judgment, the temperature rise change of a specific observation point is obtained.

8. The system for analyzing local aging of cable joint insulation according to claim 7, characterized in that: By dividing the insulation component into multiple areas, and each area is equipped with an infrared imager, the S i The temperature change rate is calculated as: ΔT i (t)=T i (t+Δt)-T i (t) Where, ΔT i For S i The change of temperature at a point with respect to time; ΔT i (t) represents the Sth i The temperature difference at different times of the point; Δt represents the time interval; By comparing the differences in different areas of the same thickness, anomalies in temperature changes can be identified.

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