10kV cable partial discharge test method based on temperature circulation
By applying temperature cycles to 10kV cables and establishing a temperature-discharge mapping model, the problem of insufficient consideration of temperature impact in the existing detection methods is solved, and accurate evaluation and early detection of cable defects are achieved to ensure the safety of the power system.
Patent Information
- Application Number
- CN202510527118.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-08-08
AI Technical Summary
The existing 10kV cable partial discharge detection method does not fully consider the temperature influence, which leads to the disconnection of the detection results from the actual operating conditions, making it difficult to detect early defects, and traditional detection methods may accelerate insulation aging.
By applying periodic temperature cycles to the 10kV cable sample, the local discharge signal and temperature field data are synchronized, the temperature-discharge mapping model based on the Arrhenius equation is established, the thermal activation energy and dielectric constant correction coefficient are calculated, and the classification standards are set for defect evaluation.
Simulate the actual operating temperature changes of the cable, quantify the relationship between temperature and local discharge, accurately evaluate the severity of defects, provide effective means for early detection of cable insulation defects, and ensure the safe and stable operation of the power system.
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Figure CN120446682A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of power system monitoring, and in particular to a 10kV cable partial discharge test method based on temperature cycling. Background Art
[0002] High-voltage cables are core equipment for power transmission, and their insulation condition is directly related to the safe and stable operation of the power grid. With the rapid growth of urban loads, cable load rates are climbing year by year. High loads increase core temperatures, accelerate insulation aging, and trigger partial discharge (PD) defects, which are a precursor to insulation breakdown. Therefore, accurate detection of PD defects is crucial to ensuring cable safety.
[0003] Existing partial discharge detection methods (such as pulse current method, ultrasonic method, and ultra-high frequency method) mainly rely on offline testing or online monitoring at a fixed voltage. The influence of temperature is not fully considered. Increased temperature will reduce the partial discharge starting voltage (for example, the starting voltage of a spike defect drops by about 40% at 80°C). However, the current standards (such as GB / T7354-2018) do not specify the temperature correction method, resulting in a disconnect between the detection results and the actual operating conditions. The partial discharge signal of tiny defects is weak at room temperature and easily drowned out by noise. The oscillation wave method has a partial discharge detection threshold of 500pC for joints over 5 years old at 1.7U0, making it difficult to detect early defects. The existing monitoring system independently collects temperature and partial discharge data, and no coupling relationship is established, making it impossible to quantify the accelerating effect of temperature on defect development. Although traditional voltage withstand tests (such as power frequency voltage withstand) can detect defects, they will accelerate insulation aging.
[0004] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.
[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the Invention
[0006] The purpose of the embodiments of the present disclosure is to provide a 10kV cable partial discharge test method based on temperature cycling, thereby overcoming one or more problems caused by the limitations and defects of the related art at least to a certain extent.
[0007] This application provides a 10kV cable partial discharge test method based on temperature cycling, including:
[0008] Based on the fact that the temperature of the cable body will change with the load current and ambient temperature, a periodic temperature cycle is applied to the 10kV cable sample;
[0009] During the temperature cycle, the partial discharge signal and temperature field data are collected synchronously, and the discharge amount and discharge phase are recorded;
[0010] The thermal activation energy and dielectric constant correction factor are calculated by using the partial discharge amount at different temperatures and the temperature-discharge amount mapping model based on the Arrhenius equation. The temperature sensitivity coefficient is then calculated based on the thermal activation energy and dielectric constant correction factor.
[0011] The grading standards were set based on the thermal activation energy and temperature sensitivity coefficient, and defect assessment was conducted on 10kV cable samples.
[0012] In one possible implementation, applying periodic temperature cycling to the 10 kV cable sample includes:
[0013] During the heating stage, the heating rate is 5-10℃ / min;
[0014] High temperature holding stage, the temperature is 80-120℃, and the heat preservation lasts for 1-2 hours;
[0015] In the cooling stage, the cooling rate is 5-10℃ / min;
[0016] Low temperature holding stage, the temperature is 20-40℃, and the insulation lasts for 0.5-1 hour;
[0017] Each stage is repeated in sequence to perform a periodic temperature cycle.
[0018] In a possible implementation, when synchronously collecting the partial discharge signal and the temperature field data, the partial discharge signal and the temperature data are synchronously collected during the high temperature holding stage and the low temperature holding stage.
[0019] In a possible implementation, the rates of the temperature increase stage and the temperature decrease stage are adjusted by a PID controller, and the temperature control accuracy is ±0.5°C.
[0020] In a possible implementation, the partial discharge signal is collected using an ultra-high frequency sensor.
[0021] In a possible implementation, the expression of the temperature-discharge amount mapping model established based on the Arrhenius equation is:
[0022]
[0023] Among them, Q(T) is the discharge capacity at temperature T, Q0 is a constant, E a is the thermal activation energy, k is the Boltzmann constant, T avg is the average temperature, ε r is the dielectric constant, and m is the dielectric constant correction factor.
[0024] In a possible implementation, the steps before calculating the thermal activation energy and the dielectric constant correction coefficient include:
[0025] Collect temperature data of 10kV cable samples at different locations and times;
[0026] Calculate the standard value of 10kV cable surface temperature distribution based on the collected data.
[0027] In a possible implementation manner, the calculation of the standard value of the surface temperature distribution of the 10kV cable based on the collected data includes: Calculate the average temperature of a 10kV cable, where T avg is the average temperature of the 10kV cable, L is the length of the 10kV cable, and T(x,t) represents the temperature of the cable surface position x at time t along the length direction of the 10kV cable.
[0028] In a possible implementation, the temperature sensitivity coefficient is calculated as follows:
[0029]
[0030] In one possible implementation, the steps of setting a grading standard based on thermal activation energy and temperature sensitivity coefficient and performing defect assessment on a 10 kV cable sample include:
[0031] If the thermal activation energy is greater than or equal to the first preset value and the temperature sensitivity coefficient is less than the second preset value, it is a mild defect;
[0032] A moderate defect occurs when the thermal activation energy is less than the first preset value and greater than or equal to the third preset value, and the temperature sensitivity coefficient is greater than the second preset value and less than or equal to the fourth preset value;
[0033] When the thermal activation energy is less than the third preset value and the temperature sensitivity coefficient is greater than the fourth preset value, it is a severe defect.
[0034] The technical solution provided by this application may have the following beneficial effects:
[0035] Through the 10kV cable partial discharge test method based on temperature cycle of this application, on the one hand, by actively controlling the temperature cycle, the temperature changes in the actual operation of the 10kV cable are simulated, the influence of temperature on partial discharge is fully considered, and the problem that the temperature influence is not fully considered in the existing detection method is solved, so that the detection results are closer to the actual operating conditions; on the other hand, by establishing a temperature-discharge mapping model, the relationship between temperature and partial discharge is quantified, which can more accurately evaluate the severity of cable defects, provide an effective technical means for the early detection of cable insulation defects, and help to ensure the safe and stable operation of the power system.
[0036] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification, are used to explain the principles of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort.
[0038] Figure 1 A schematic diagram showing steps of a 10kV cable partial discharge test method based on temperature cycling in an exemplary embodiment of the present disclosure is shown;
[0039] Figure 2 A schematic flow chart of a 10 kV cable partial discharge test method based on temperature cycling in an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION
[0040] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0041] In addition, the accompanying drawings are merely schematic illustrations of the present disclosure and are not necessarily drawn to scale. Identical reference numerals in the figures denote identical or similar parts, and thus repetitive descriptions thereof will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.
[0042] This example embodiment provides a 10kV cable partial discharge test method based on temperature cycling. Figure 1 As shown in , the method may include the following steps:
[0043] Step S101: Based on the fact that the temperature of the cable body changes with the load current and the ambient temperature, a periodic temperature cycle is applied to the 10 kV cable sample.
[0044] Step S102: During the temperature cycle, synchronously collect partial discharge signals and temperature field data, and record the discharge amount and discharge phase.
[0045] Step S103: Calculate the thermal activation energy and dielectric constant correction factor based on the partial discharge amount at different temperatures using a temperature-discharge amount mapping model established based on the Arrhenius equation, and calculate the temperature sensitivity coefficient based on the thermal activation energy and dielectric constant correction factor.
[0046] Step S104: setting a grading standard according to the thermal activation energy and the temperature sensitivity coefficient, and performing defect assessment on the 10 kV cable sample.
[0047] Through the above method, on the one hand, by actively controlling the temperature cycle, the temperature changes in the actual operation of the 10kV cable are simulated, and the influence of temperature on partial discharge is fully considered. This solves the problem that the temperature influence is not fully considered in the existing detection methods, and makes the detection results closer to the actual operating conditions; on the other hand, by establishing a temperature-discharge mapping model, the relationship between temperature and partial discharge is quantified, which can more accurately assess the severity of cable defects, provide an effective technical means for the early detection of cable insulation defects, and help ensure the safe and stable operation of the power system.
[0048] Below, we will refer to Figures 1 to 2 Each step of the above method in this exemplary embodiment is described in more detail.
[0049] Step S101: Based on the fact that the temperature of the cable body changes with the load current and the ambient temperature, a periodic temperature cycle is applied to the 10 kV cable sample.
[0050] Specifically, during the heating phase, the cable sample is wrapped in a thermostat or heating device (such as a resistance heating tape) and connected to a PID controller for real-time heating power adjustment. The temperature is increased at a rate of 5-10°C / min, with the PID controller maintaining a temperature control accuracy of ±0.5°C. For example, increasing the temperature from 30°C (the low-temperature hold phase) to the high-temperature target of 100°C takes approximately 7-14 minutes. The cable surface temperature is continuously monitored during the heating process, and temperature sensors are deployed to ensure that there is no local overheating.
[0051] During the high-temperature hold phase, the temperature is stabilized at any set point between 80°C and 120°C, depending on the cable type and operating standards. For example, the maximum operating temperature for cross-linked polyethylene insulated cables is typically 90°C, and can reach 120°C under overload conditions. This temperature is maintained for 1-2 hours, during which time temperature sensors are used to confirm that the overall cable temperature field has reached equilibrium, with temperature fluctuations of ≤±1°C at each measuring point.
[0052] During the cooling phase, the heating device is turned off and a cooling system, such as a water cooling loop, is activated. A PID controller is used to adjust the cooling rate to 5-10°C / min, with the same control accuracy as during the heating phase. Cooling from 100°C to the target low temperature of 30°C takes approximately 7-14 minutes.
[0053] During the low-temperature hold phase, set the temperature to any desired value between 20°C and 40°C, simulating a lightly loaded cable or normal temperature environment. Keep the temperature for 0.5-1 hour to ensure stable cable temperature and provide a baseline for subsequent data collection.
[0054] Repeat the above steps in the order of "heating → high temperature holding → cooling → low temperature holding". The number of cycles is determined according to the test requirements, such as 3-5 times, covering multiple temperature cycles.
[0055] Step S102: During the temperature cycle, synchronously collect partial discharge signals and temperature field data, and record the discharge amount and discharge phase.
[0056] Specifically, during the high-temperature holding stage and the low-temperature holding stage of the temperature cycle, the characteristic parameters of partial discharge and the surface temperature distribution of the cable are collected synchronously to ensure that the data is not affected by temperature fluctuations. An ultra-high frequency (UHF) sensor is used to capture the 300MHz-3GHz ultra-high frequency electromagnetic wave signal generated by partial discharge. It has the advantages of strong anti-electromagnetic interference ability and high sensitivity, and is suitable for weak signal detection in complex electromagnetic environments. The sensor is installed close to the surface of the weak insulation area of the cable sample (such as joints, terminals, and sections where defects may exist) to ensure that the sensor is tightly coupled with the outer sheath of the cable to maximize the signal reception efficiency. The discharge amount (Q, unit pC) and the discharge phase (the discharge angle within the power frequency cycle, unit °) are recorded in real time. The discharge phase reflects the position where the discharge occurs in the power frequency voltage cycle and is used for subsequent defect type identification (such as the phase distribution of air gap discharge and surface discharge has characteristic differences).
[0057] Use a partial discharge detection system (such as a digital oscilloscope or UHF acquisition instrument) and set the sampling frequency to ≥1GHz to ensure that the ultra-high frequency signal waveform is fully captured; the single acquisition time should be ≥2 minutes, covering a sufficient number of power frequency cycles (at least 60 cycles at a 50Hz power frequency). Evenly arrange thermocouples or infrared temperature sensors along the length of the cable, with the distance between measurement points ≤1 meter (for example, 11 measurement points are arranged for a 10-meter-long cable, covering the entire length L of the cable) to ensure that there are no blind spots in temperature measurement. Collect temperature data T(x,t) at different locations (x) and different times (t) on the cable surface, focusing on monitoring the temperature stability during the high / low temperature holding stage (for example, record the temperature of each measurement point every 10 minutes).
[0058] By formula Calculate the average temperature of a 10kV cable, where T avg is the average temperature of a 10kV cable, L is the length of the 10kV cable, and T(x,t) represents the temperature at position x on the cable surface at time t along the cable length. In actual operation, if N measuring points are evenly arranged, the arithmetic mean is used to approximate the average temperature, and the calculation formula is: Where N is the number of measurement points, T i (t) is the temperature of the i-th measuring point.
[0059] The local discharge signal at the same time is compared with the corresponding average temperature T avg A mapping relationship is established to form a "temperature-discharge amount-phase" data set (for example, the discharge amount and corresponding phase distribution at a high temperature of 100°C, and the discharge amount and corresponding phase distribution at a low temperature of 30°C), providing multi-dimensional input for subsequent modeling and analysis.
[0060] Step S103: Calculate the thermal activation energy and dielectric constant correction factor based on the partial discharge amount at different temperatures using a temperature-discharge amount mapping model established based on the Arrhenius equation, and calculate the temperature sensitivity coefficient based on the thermal activation energy and dielectric constant correction factor.
[0061] Specifically, the Arrhenius equation is used to describe the thermal activation acceleration effect of temperature on partial discharge. Combined with the temperature dependence of the dielectric constant of the insulating material, the temperature-discharge relationship is quantified through a mathematical model. The development of partial discharge is regarded as a thermal activation process, and the nonlinear effect of temperature on the discharge amount is reflected by the exponential term. At the same time, the dielectric constant correction term is introduced to consider the change of material properties. Finally, the model parameter E is used to calculate the temperature-discharge relationship. a and m.
[0062] The temperature-discharge mapping model based on the Arrhenius equation is:
[0063]
[0064] Among them, Q(T) is the discharge capacity at temperature T, Q0 is a constant, E a is the thermal activation energy, k is the Boltzmann constant, T avg is the average temperature, ε r is the dielectric constant, and m is the dielectric constant correction factor.
[0065] The discharge amount Q and the corresponding average temperature T in the high temperature / low temperature holding stage are obtained avg Then, a mathematical model was constructed based on the Arrhenius equation, and the thermal activation energy E was solved by nonlinear fitting. a and the dielectric constant correction factor m.
[0066] The temperature sensitivity coefficient is calculated based on the thermal activation energy and the dielectric constant correction coefficient. The calculation formula of the temperature sensitivity coefficient is:
[0067]
[0068] in, The rate of change of dielectric constant with average temperature. It can be obtained by measuring the dielectric constant-temperature curve of insulating materials or looking up the table (for example, the dielectric constant of polyethylene decreases slightly with increasing temperature, and the rate of change is about -0.001K -1 ).
[0069] Step S104: setting a grading standard according to the thermal activation energy and the temperature sensitivity coefficient, and performing defect assessment on the 10 kV cable sample.
[0070] Specifically, after obtaining the thermal activation energy and temperature sensitivity coefficient, a three-level defect classification standard was established based on their combined characteristics. By comparing the measured parameters with preset thresholds, the severity of defects in 10kV cable samples was determined. This overcomes the limitation of traditional testing, which relies solely on qualitative judgment of discharge volume to determine defect severity, and provides a scientific basis for cable operation and maintenance.
[0071] The first preset value is a critical value of thermal activation energy between a mild defect and a moderate defect.
[0072] The second preset value is a temperature sensitivity coefficient threshold value between a mild defect and a moderate defect.
[0073] The third preset value is a critical value of thermal activation energy between moderate defects and severe defects.
[0074] The fourth preset value is a temperature sensitivity coefficient threshold value between moderate defects and severe defects.
[0075] The first preset value is greater than the third preset value, and the second preset value is less than the fourth preset value.
[0076] The grading standards are set based on the thermal activation energy and temperature sensitivity coefficient, as shown in Table 1, and the steps for defect assessment of 10kV cable samples include:
[0077] If the thermal activation energy is greater than or equal to the first preset value and the temperature sensitivity coefficient is less than the second preset value, it is a mild defect;
[0078] A moderate defect occurs when the thermal activation energy is less than the first preset value and greater than or equal to the third preset value, and the temperature sensitivity coefficient is greater than the second preset value and less than or equal to the fourth preset value;
[0079] When the thermal activation energy is less than the third preset value and the temperature sensitivity coefficient is greater than the fourth preset value, it is a severe defect.
[0080] Table 1
[0081]
[0082] By setting a grading standard based on thermal activation energy and temperature sensitivity coefficient, the thermodynamic analysis results are converted into an operational defect assessment system. Through dual-parameter quantitative judgment, the "precise positioning of risk levels" and "intelligent matching of maintenance strategies" of cable insulation defects are achieved, significantly improving the engineering practical value of partial discharge testing.
[0083] It should be noted that those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the appended claims.
Claims
1. A 10kV cable partial discharge test method based on temperature cycling, characterized in that: The following steps are involved: Based on the fact that the temperature of the cable body will change with the load current and ambient temperature, a periodic temperature cycle is applied to the 10kV cable sample; During the temperature cycle, the partial discharge signal and temperature field data are collected synchronously, and the discharge amount and discharge phase are recorded; The thermal activation energy and dielectric constant correction factor are calculated by using the partial discharge amount at different temperatures and the temperature-discharge amount mapping model based on the Arrhenius equation. The temperature sensitivity coefficient is then calculated based on the thermal activation energy and dielectric constant correction factor. The grading standards were set based on the thermal activation energy and temperature sensitivity coefficient, and defect assessment was conducted on 10kV cable samples.
2. The 10kV cable partial discharge test method based on temperature cycling according to claim 1 is characterized in that: The step of applying a periodic temperature cycle to the 10 kV cable sample comprises: During the heating stage, the heating rate is 5-10℃ / min; High temperature holding stage, the temperature is 80-120℃, and the heat preservation lasts for 1-2 hours; In the cooling stage, the cooling rate is 5-10℃ / min; Low temperature holding stage, the temperature is 20-40℃, and the insulation lasts for 0.5-1 hour; Each stage is repeated in sequence to perform a periodic temperature cycle.
3. The 10kV cable partial discharge test method based on temperature cycling according to claim 2, characterized in that: When synchronously collecting the partial discharge signal and the temperature field data, the partial discharge signal and the temperature data are synchronously collected during the high temperature holding stage and the low temperature holding stage.
4. The 10kV cable partial discharge test method based on temperature cycling according to claim 2, characterized in that: The rates of the heating and cooling stages are adjusted by a PID controller, and the temperature control accuracy is ±0.5°C.
5. The 10kV cable partial discharge test method based on temperature cycling according to claim 3, characterized in that: The partial discharge signal is collected using an ultra-high frequency sensor.
6. The 10kV cable partial discharge test method based on temperature cycling according to claim 1, characterized in that: The expression of the temperature-discharge amount mapping model established based on the Arrhenius equation is: Among them, Q(T) is the discharge capacity at temperature T, Q0 is a constant, E a is the thermal activation energy, k is the Boltzmann constant, T avg is the average temperature, ε r is the dielectric constant, and m is the dielectric constant correction factor.
7. The 10kV cable partial discharge test method based on temperature cycling according to claim 1, characterized in that: The steps before calculating the thermal activation energy and the dielectric constant correction coefficient include: Collect temperature data of 10kV cable samples at different locations and times; Calculate the standard value of 10kV cable surface temperature distribution based on the collected data.
8. The 10kV cable partial discharge test method based on temperature cycling according to claim 7, characterized in that: The standard value of the surface temperature distribution of the 10kV cable is calculated based on the collected data, including: Calculate the average temperature of a 10kV cable, where T avg is the average temperature of the 10 kV cable, L is the length of the 10 kV cable, and T(x, t) represents the temperature of the cable surface at position x along the length of the cable at time t.
9. The 10kV cable partial discharge test method based on temperature cycling according to claim 8, characterized in that: The calculation formula of the temperature sensitivity coefficient is:
10. The 10kV cable partial discharge test method based on temperature cycling according to claim 1, characterized in that: The steps of setting the grading standard according to the thermal activation energy and the temperature sensitivity coefficient and performing defect assessment on the 10kV cable sample include: If the thermal activation energy is greater than or equal to the first preset value and the temperature sensitivity coefficient is less than the second preset value, it is a mild defect; A moderate defect occurs when the thermal activation energy is less than the first preset value and greater than or equal to the third preset value, and the temperature sensitivity coefficient is greater than the second preset value and less than or equal to the fourth preset value; When the thermal activation energy is less than the third preset value and the temperature sensitivity coefficient is greater than the fourth preset value, it is a severe defect.