Method and system for evaluating dynamic and thermal stability of power supply cable

Abstract

The invention relates to the technical field, in particular to an evaluation system and evaluation method for dynamic thermal stability of a power supply cable, and the method comprises the steps: determining a short-circuit detection point of the power supply cable based on the state of the power supply cable; determining the maximum loss point of the buried power supply cable based on the soil thermal conductivity of the buried power supply cable in a preset time period and the buried depth change rate of the power supply cable in the preset time period, and determining the maximum loss point of the buried power supply cable based on the dust accumulation thickness of the exposed power supply cable and whether the completely exposed power supply cable has cracks or not. Determining a maximum loss point of the exposed laid power supply cable; and performing a short circuit stability verification test on the short circuit detection point of the power supply cable, and determining whether the dynamic thermal stability of the power supply cable is qualified based on whether the short circuit detection point of the power supply cable is damaged or deformed after the test. According to the invention, the accuracy of short-circuit detection point analysis is improved, so that the energy waste is reduced, and the energy utilization efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field, and in particular to an evaluation method and an evaluation system for dynamic thermal stability of a power supply cable. Background Art

[0002] In modern society, power supply cables are key infrastructure for power transmission. Whether it is industrial production, commercial activities or daily life, they are inseparable from a stable and reliable power supply. The performance of power supply cables is directly related to the safe operation of the power system and the efficient transmission of electric energy. Power supply cables may suffer from short-circuit faults during operation. Short-circuit currents will generate huge heat and mechanical stress, which poses a severe challenge to the dynamic thermal stability of power supply cables. Good dynamic thermal stability can ensure that power supply cables can maintain stable performance in normal operation and fault conditions, reduce energy loss, and improve power transmission efficiency. Traditional evaluation methods only consider the physical parameters of the power supply cable itself, but ignore the influence of its environment. They are not accurate enough in determining the short-circuit detection point, resulting in low reliability of the evaluation results and energy loss.

[0003] The prior art discloses a method and device for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable. The method comprises the following steps: obtaining the environmental thermal resistance under air laying and / or the environmental thermal resistance under soil laying according to the thermal circuit model of the three-core cable; obtaining the core temperature of the three-core cable according to the thermal circuit model of the three-core cable; if the three-core cable is air laid, determining the sensitivity of the core temperature to the environmental thermal resistance under air laying according to the relationship between the environmental thermal resistance and the ambient temperature under air laying; if the three-core cable is soil laid, determining the sensitivity of the core temperature to the environmental thermal resistance under soil laying. The present invention can accurately analyze the influence of environmental thermal resistance on the core temperature of the three-core cable; according to the sensitivity when air laying or soil laying, when the three-core cable is loaded with a large current, especially when the three-core cable is laid for air radiation, the monitoring of the ambient temperature is increased, thereby ensuring the safe and stable operation of the power cable; it can be seen that the prior art has the problem of low accuracy in the analysis of short-circuit detection points, resulting in energy waste and thus reducing energy utilization efficiency. Summary of the invention

[0004] To this end, the present invention provides an evaluation method and an evaluation system for the dynamic thermal stability of a power supply cable, so as to overcome the problem in the prior art that the low accuracy of short circuit detection point analysis leads to energy waste and thus reduces energy utilization efficiency.

[0005] To achieve the above object, on the one hand, the present invention provides a method for evaluating the dynamic thermal stability of a power supply cable, comprising:

[0006] Obtain the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environmental data;

[0007] Based on the state of the power supply cable being in a laid and used state, or being unlaid and waiting to be used state, determining a point with a maximum short-circuit current of the power supply cable, or a point with a maximum loss of the power supply cable, as a short-circuit detection point for dynamic thermal stability of the power supply cable;

[0008] Based on the soil thermal conductivity of the power cable buried underground within a preset time and the rate of change of the buried depth of the power cable within the preset time, the maximum loss point of the buried power cable is determined, and based on the dust accumulation thickness of the exposed power cable and whether there are cracks in the completely exposed power cable, the maximum loss point of the exposed power cable is determined;

[0009] When determining the dust accumulation thickness of the exposed power supply cable, the dust accumulation thickness of the exposed power supply cable is directly determined based on the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period, or the dust accumulation thickness is determined after flushing the exposed power supply cable with water;

[0010] A short-circuit stability verification test is performed on the short-circuit detection point of the power supply cable, and whether the dynamic thermal stability of the power supply cable is qualified is determined based on whether line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test.

[0011] Furthermore, the short-circuit detection points for determining the dynamic thermal stability of the power supply cable include:

[0012] If the power supply cable is in the state of being laid and used, the point with the maximum loss of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable;

[0013] If the power supply cable is in an unlaid and waiting-for-use state, the point with the maximum short-circuit current of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable.

[0014] Further, the determining of the maximum loss point of the buried power supply cable includes:

[0015] The point where the average soil thermal conductivity of the power supply cable buried underground within a preset time is the smallest, and the point where the rate of change of the buried depth of the power supply cable within the preset time is the largest, are used as loss detection points;

[0016] Install optical fiber temperature sensors on the surface of the power supply cables at the loss detection points to record the temperature changes of the power supply cables in real time during operation;

[0017] Calculate the real-time loss at the loss detection point based on the recorded temperature data and combined with the resistance temperature coefficient of the power supply cable and the load current;

[0018] The loss detection point with the largest real-time loss is taken as the maximum loss point.

[0019] Further, the determining of the maximum loss point of the exposed power supply cable includes:

[0020] The point where dust accumulation is the thickest on the exposed power supply cable and the point where the number of cracks is the largest on the completely exposed power supply cable are used as loss detection points;

[0021] Install optical fiber temperature sensors on the surface of the power supply cables at the loss detection points to record the temperature changes of the power supply cables in real time during operation;

[0022] Calculate the real-time loss at the loss detection point based on the recorded temperature data and combined with the resistance temperature coefficient of the power supply cable and the load current;

[0023] The loss detection point with the largest real-time loss is taken as the maximum loss point.

[0024] Further, determining the dust accumulation thickness of the exposed power supply cable includes:

[0025] If the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is less than a preset rainfall frequency, determining the dust accumulation thickness after flushing the exposed power supply cable with water;

[0026] If the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is greater than or equal to a preset rainfall frequency, the dust accumulation thickness of the exposed power supply cable is directly determined.

[0027] Furthermore, the maximum short-circuit current point of the power supply cable includes the point where the maximum short-circuit current of the cable loop occurs, that is, for a single cable that does not exceed the manufacturing length, the maximum short-circuit current point is determined at the end of the cable; for cables with intermediate joints, the maximum short-circuit current point is determined at the beginning of each line segment that reduces the cable cross-section; when the cable segments have equal cross-sections, the maximum short-circuit current point is determined at the beginning of the next cable segment, that is, the first intermediate joint; for parallel-connected cables without intermediate joints, the maximum short-circuit current point is determined after the parallel point.

[0028] Further, determining whether the dynamic thermal stability of the power supply cable is qualified includes:

[0029] If the short-circuit detection point of the power supply cable is damaged or deformed after the test, it is determined that the dynamic thermal stability of the power supply cable is unqualified;

[0030] If no line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test, it is determined that the dynamic thermal stability of the power supply cable is qualified.

[0031] Furthermore, it is determined that after the test, line damage or deformation occurs at the short-circuit detection point of the power supply cable, including insulation damage, insulation burnt, insulation peeled off, conductor shape change, conductor melting, and conductor breakage.

[0032] Furthermore, the short-circuit stability verification test performed on the short-circuit detection point of the power supply cable includes the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the laid and used state is the historical maximum short-circuit current of the power supply cable, or the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the unlaid and waiting to be used state is the rated peak withstand current of the power supply cable connection device.

[0033] On the other hand, the present invention further provides an evaluation system applied to the evaluation method of the dynamic thermal stability of the power supply cable, comprising:

[0034] A data acquisition module is used to obtain the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environmental data;

[0035] a short-circuit detection point determination module, which is connected to the data acquisition module, and includes a short-circuit detection point type determination unit for determining a short-circuit detection point of the dynamic thermal stability of the power supply cable according to the state of the power supply cable, and a maximum loss point determination unit for determining the maximum loss point of the power supply cable according to the laying mode of the power supply cable and the soil thermal conductivity of the power supply cable within a preset time, the rate of change of the buried depth of the power supply cable within a preset time, the dust accumulation thickness of the power supply cable, and whether there are cracks in the completely exposed power supply cable;

[0036] A test module, which is connected to the short-circuit detection point determination module and is used to perform a short-circuit stability verification test on the short-circuit detection point of the power supply cable;

[0037] A determination module is connected to the test module and is used to determine whether the dynamic thermal stability of the power supply cable is qualified according to whether line damage or deformation occurs at a short-circuit detection point of the power supply cable after the test.

[0038] Compared with the prior art, the beneficial effect of the present invention is that, for the power supply cable in the laying and use state, the present invention uses the point with the maximum loss as the short-circuit detection point. Because in the actual operation process, the loss of the cable is one of the key factors affecting its dynamic thermal stability. By focusing on the maximum loss point, the position where the cable is most likely to have thermal stability problems under normal working conditions can be accurately found. When the cable is in an unlaid and waiting to be used state, the point with the maximum short-circuit current is determined as the short-circuit detection point. When the cable has not yet been put into use, the main potential risk faced by the cable is short-circuit failure. By predetermining the maximum short-circuit current point, the dynamic thermal stability of the cable under the most unfavorable short-circuit condition can be evaluated in advance. Considering the two different states of the power supply cable, and determining the short-circuit detection point according to their respective characteristics, the accuracy of the analysis of the short-circuit detection point is improved, energy waste is reduced, and energy utilization efficiency is improved.

[0039] In particular, the present invention determines the point where the average soil thermal conductivity is minimum and the point where the burial depth change rate is maximum within a preset time as the loss detection point, so that it can accurately focus on the position where large losses are most likely to occur in buried cables. For example, in areas with complex soil composition and underground construction, changes in soil thermal conductivity and burial depth will have a significant impact on the heat dissipation and operating status of the cable. This targeted determination of the detection point avoids indiscriminate inspection of the entire cable, making subsequent monitoring, evaluation and other work more focused. The above method is used to improve the accuracy of short-circuit detection point analysis to reduce energy waste and thus improve energy utilization efficiency.

[0040] In particular, the present invention uses the places where the dust accumulation thickness of the exposed power supply cable is the largest and the places where the number of cracks is the largest as loss detection points, which can accurately locate the key parts of the cable that are most likely to have large losses during operation. In actual open-air environments, dust accumulation and cracks on the cable surface are important factors that affect the heat dissipation, insulation and other properties of the cable and thus lead to increased losses. In this way, it is possible to avoid comprehensive and complicated inspections of the entire section of exposed cables. The dust accumulation thickness is determined based on the comparison results of the rainfall frequency of the cable environment within a preset period and the preset rainfall frequency, which fully considers the impact of environmental factors on the dust accumulation on the cable surface. Different rainfall frequencies will cause the dust on the cable surface to be washed to different degrees. This method of flexibly determining the dust accumulation thickness according to the actual environmental conditions makes the evaluation of the impact of dust on cable losses more in line with actual working conditions. The above method improves the accuracy of the short-circuit detection point analysis to reduce energy waste and thus improve energy efficiency.

[0041] In particular, the present invention provides an intuitive and easy-to-understand judgment criterion by clearly determining whether the dynamic thermal stability is qualified by determining whether there is line damage or deformation at the short-circuit detection point of the power supply cable after the test. Both the operation and maintenance personnel of the power system and the relevant detection technicians can make a quick and accurate judgment on the dynamic thermal stability of the power supply cable based on this clear standard. The above method improves the accuracy of the short-circuit detection point analysis to reduce energy waste and thus improve energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flowchart of a method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention;

[0043] Figure 2 This is a flowchart of determining the maximum loss point of an underground power supply cable in the method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention;

[0044] Figure 3 A flowchart of determining whether the dynamic thermal stability of a power supply cable is qualified in the method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention;

[0045] Figure 4 The present invention is a schematic diagram of the structure of an evaluation system for a method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0048] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0049] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] See also Figure 1-Figure 3 As shown, Figure 1 This is a flowchart of a method for evaluating the dynamic thermal stability of a power cable according to an embodiment of the present invention; Figure 2 A flowchart of determining the maximum loss point of an underground power supply cable in the method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention; Figure 3 This is a flowchart of determining whether the dynamic thermal stability of a power supply cable is qualified in the method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention.

[0051] Step S1, obtaining the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environment data;

[0052] Step S2, based on the state of the power supply cable being in a laid and used state, or being unlaid and ready for use, determining a point with a maximum short-circuit current of the power supply cable, or a point with a maximum loss of the power supply cable, as a short-circuit detection point for dynamic thermal stability of the power supply cable;

[0053] Step S3, based on the soil thermal conductivity of the buried power cable within a preset time, and the rate of change of the buried depth of the power cable within the preset time, determine the maximum loss point of the buried power cable, and based on the dust accumulation thickness of the exposed power cable, and whether there are cracks in the completely exposed power cable, determine the maximum loss point of the exposed power cable;

[0054] Step S4, when determining the dust accumulation thickness of the exposed power supply cable, directly determine the dust accumulation thickness of the exposed power supply cable based on the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period, or determine the dust accumulation thickness after flushing the exposed power supply cable with water;

[0055] Step S5, performing a short-circuit stability verification test on the short-circuit detection point of the power supply cable, and determining whether the dynamic thermal stability of the power supply cable is qualified based on whether line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test.

[0056] The physical parameter data of the power supply cable in the embodiment of the present invention includes but is not limited to "power supply cable length, power supply cable outer diameter and power supply cable material resistivity", the fault-related electrical parameter data includes but is not limited to "short-circuit current magnitude and duration data, voltage level and phase number data of the line before the fault and fault point location data", and the environmental data of the power supply cable includes but is not limited to "temperature data, humidity data and chemical substance data".

[0057] Specifically, in step S2, when determining the short-circuit detection point of the dynamic thermal stability of the power supply cable, the short-circuit detection point of the dynamic thermal stability of the power supply cable is determined according to the state of the power supply cable;

[0058] When the power supply cable is in the state of being laid and used, the point with the maximum loss of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable;

[0059] When the power supply cable is in an unlaid waiting-for-use state, the maximum short-circuit current point of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable.

[0060] The present invention uses the point with the maximum loss as the short-circuit detection point for the power supply cable in the laying and use state. Because in the actual operation process, the loss of the cable is one of the key factors affecting its dynamic thermal stability. By focusing on the point with the maximum loss, the position where the cable is most likely to have thermal stability problems under normal working conditions can be accurately found. When the cable is in the state of not being laid and waiting to be used, the point with the maximum short-circuit current is determined as the short-circuit detection point. When the cable has not yet been put into use, the main potential risk faced by the cable is short-circuit failure. By predetermining the point with the maximum short-circuit current, the dynamic thermal stability of the cable under the most unfavorable short-circuit condition can be evaluated in advance. Considering the two different states of the power supply cable, and determining the short-circuit detection point according to their respective characteristics, the accuracy of the analysis of the short-circuit detection point is improved, energy waste is reduced, and energy utilization efficiency is improved.

[0061] Specifically, in step S3, the step of determining the maximum loss point of the buried power supply cable includes:

[0062] Step S3301, taking the point where the average soil thermal conductivity of the power supply cable buried underground within a preset time period is the smallest, and the point where the rate of change of the buried depth of the power supply cable within the preset time period is the largest, as loss detection points;

[0063] Step S3302, installing an optical fiber temperature sensor on the surface of the power supply cable at the loss detection point to record the temperature change of the power supply cable during operation in real time;

[0064] Step S3303, calculating the real-time loss at the loss detection point according to the recorded temperature data and in combination with the resistance temperature coefficient and the load current of the power supply cable;

[0065] Step S3304, taking the loss detection point with the maximum real-time loss as the maximum loss point.

[0066] The preset time length described in the embodiment of the present invention is set to 25 days, but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs. For example, in the past 25 days, the soil around the power supply cable was regularly tested by professional soil thermal conductivity measuring equipment. Since the soil composition in this area is relatively complex and some areas are undergoing construction such as underground pipeline laying, there are large differences in soil thermal conductivity. After measurement and analysis, it was found that the average soil thermal conductivity of an area with a length of about 50 meters was the smallest, which was 0.8W / (m·K). At the same time, a high-precision measuring instrument was used to monitor the burial depth of the power supply cable during this period. Due to the influence of construction activities, the burial depth of some areas has changed. After measurement, it was found that the burial depth change rate at one place was the largest, from the original 1.5 meters to 1.2 meters within 25 days. These two locations were determined as loss detection points, and optical fiber temperature sensors were installed on the surface of the power supply cable at the two determined loss detection points. These sensors can record the temperature changes of power cables in real time and accurately during operation, and have the advantages of anti-electromagnetic interference and corrosion resistance, which are suitable for use in complex underground environments. First, obtain the resistance temperature coefficient of the power cable. Assume that the resistance temperature coefficient of the cable is 0.004 / ℃, and then obtain the load current of the power cable in real time through the power monitoring equipment. Assume that at a certain moment, the load current is 200A. According to the temperature data recorded by the optical fiber temperature sensor, it is assumed that the temperature at the loss detection point is 40℃ at this time. In the initial state (assuming the ambient temperature is 20℃), the resistance change of the cable is calculated according to the resistance temperature coefficient, and the real-time loss of the two loss detection points at different times is continuously recorded and calculated. After a period of monitoring and comparison, it is found that the real-time loss of one of the loss detection points is the largest at a certain moment. Assuming that on the 15th day of monitoring, the real-time loss of one of the loss detection points reaches the maximum value, which is 500W, then this point is determined as the maximum loss point of this buried power cable.

[0067] The present invention determines the point where the average soil thermal conductivity is minimum and the point where the burial depth change rate is maximum within a preset time as the loss detection point, and can accurately focus on the position where large losses are most likely to occur in buried cables. For example, in areas with complex soil composition and underground construction, changes in soil thermal conductivity and burial depth will have a significant impact on the heat dissipation and operating status of the cable. In this way, the detection point is determined in a targeted manner, avoiding indiscriminate inspection of the entire cable, making subsequent monitoring, evaluation and other work more focused. The above method is used to improve the accuracy of short-circuit detection point analysis to reduce energy waste and thus improve energy utilization efficiency.

[0068] Specifically, in step S3, the step of determining the maximum loss point of the exposed power supply cable includes:

[0069] The point where dust accumulation is the thickest on the exposed power supply cable and the point where the number of cracks is the largest on the completely exposed power supply cable are used as loss detection points;

[0070] Install optical fiber temperature sensors on the surface of the power supply cables at the loss detection points to record the temperature changes of the power supply cables in real time during operation;

[0071] Calculate the real-time loss at the loss detection point based on the recorded temperature data and combined with the resistance temperature coefficient of the power supply cable and the load current;

[0072] The loss detection point with the largest real-time loss is taken as the maximum loss point.

[0073] Specifically, in step S3, when determining the dust accumulation thickness of the exposed power supply cable, the dust accumulation thickness is determined according to a comparison result of the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period and a preset rainfall frequency;

[0074] When the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is less than a preset rainfall frequency, determining the dust accumulation thickness after flushing the exposed power supply cable with water;

[0075] When the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is greater than or equal to a preset rainfall frequency, the dust accumulation thickness of the exposed power supply cable is directly determined.

[0076] In the embodiment of the present invention, the preset period is set to 30 days, the range of the preset rainfall frequency is set to 0.2-0.5, and the value of the preset rainfall frequency is preferably 0.3, but the above value is not limited thereto, and the technicians in this field can also adjust the value according to actual needs. For example, in 30 days, the staff inspects the power cable every 5 days, and determines the dust accumulation thickness and crack conditions at different positions of the cable through professional dust detection equipment and manual observation. After multiple tests, it is found that the dust accumulation thickness at 200 meters away from the starting point of the cable is the largest, reaching 3 mm. At the same time, on a 10-meter-long cable at 400 meters away from the starting point, the number of cracks is the largest, with a total of 5 cracks. Therefore, these two positions are determined as loss detection points, and optical fiber temperature sensors are installed on the surface of the power cable at the two determined loss detection points to ensure that the sensor is firmly installed and can accurately record the temperature changes of the cable. The staff query the data of the local meteorological department and count the rainfall in the area within 30 days. It is found that there are a total of 6 days of rain in these 30 days, with an average of rain every 5 days. The rainfall frequency in this area during these 30 days is 0.2, the preset rainfall frequency range is 0.2-0.5, and the preferred value is 0.3. Since the actual rainfall frequency of 0.2 is less than the preset rainfall frequency, it is determined that the dust accumulation thickness is determined after flushing the exposed power supply cable with water. Under the condition of ensuring safety, the staff uses professional flushing equipment to flush this section of the power supply cable. After flushing, the dust thickness at the point where the dust accumulation thickness is the largest (200 meters from the starting point) is measured again. After measurement, it is determined that the dust accumulation thickness after flushing is 1 mm. It is known that the resistance temperature coefficient of the power supply cable is 0.004 / ℃. By connecting to the power monitoring system, the load current of the power supply cable is obtained in real time. Assuming that at a certain moment, the load current is 180A, the resistance change and loss are calculated based on the temperature data, and the temperature of the two loss detection points is continuously monitored and the real-time loss is calculated. After a period of comparison, it is assumed that the loss detection point at the point where the dust accumulation thickness is the largest has a large real-time loss in multiple calculations, and one of them reaches the maximum value of 400W. The maximum real-time loss of the loss detection point at the location with the largest number of cracks in the same time period is 350W. Therefore, the loss detection point at the location with the largest dust accumulation thickness is determined as the maximum loss point of this section of exposed power supply cable.

[0077] The present invention uses the places where the dust accumulation thickness of the exposed power supply cable is the largest and the places where the number of cracks is the largest as loss detection points, which can accurately locate the key parts of the cable that are most likely to have large losses during operation. In actual open-air environments, dust accumulation and cracks on the cable surface are important factors that affect the heat dissipation, insulation and other properties of the cable and thus lead to increased losses. In this way, it is possible to avoid comprehensive and complicated inspections of the entire section of exposed cables. The dust accumulation thickness is determined based on the comparison results of the rainfall frequency of the environment in which the cable is located within a preset period and the preset rainfall frequency, which fully considers the impact of environmental factors on the accumulation of dust on the cable surface. Different rainfall frequencies will cause different degrees of dust scouring on the cable surface. This method of flexibly determining the dust accumulation thickness according to actual environmental conditions makes the evaluation of the impact of dust on cable losses more in line with actual working conditions. The above method improves the accuracy of short-circuit detection point analysis to reduce energy waste and thus improve energy efficiency.

[0078] Specifically, in step S2, the maximum short-circuit current point of the power supply cable is determined, including the point where the maximum short-circuit current of the cable loop occurs, that is, for a single cable that does not exceed the manufacturing length, the maximum short-circuit current point is determined at the end of the cable; for cables with intermediate joints, the maximum short-circuit current point is determined at the beginning of each line segment that reduces the cable cross-section; when the cable segments have equal cross-sections, the maximum short-circuit current point is determined at the beginning of the next cable segment, that is, the first intermediate joint; for parallel-connected cables without intermediate joints, the maximum short-circuit current point is determined after the parallel point.

[0079] In the embodiment of the present invention, it is assumed that there is a power supply cable with a length of 500 meters, which is used to supply power to a small factory workshop. The cable is led out from the distribution room of the factory without an intermediate joint, and its length is within the manufacturing length range. According to the above rules, the maximum point of the short-circuit current is determined at the end of the cable. This is because in this case, the line impedance from the distribution room to the end of the cable gradually increases. When a short circuit occurs, according to Ohm's law, when a short circuit occurs at the end of the cable, the equivalent impedance is the largest, so the short-circuit current is the largest.

[0080] Specifically, in step S5, when determining whether the dynamic thermal stability of the power supply cable is qualified, whether the dynamic thermal stability of the power supply cable is qualified is determined according to whether line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test;

[0081] When the short-circuit detection point of the power supply cable is damaged or deformed after the test, it is determined that the dynamic thermal stability of the power supply cable is unqualified;

[0082] When no line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test, it is determined that the dynamic thermal stability of the power supply cable is qualified.

[0083] In the embodiment of the present invention, after the test, it is determined that the line damage or deformation phenomenon at the short-circuit detection point of the power supply cable includes insulation damage, insulation burnt, insulation peeled off, conductor shape change, conductor melting and conductor broken strands.

[0084] Specifically, in step S5, the short-circuit stability verification test performed on the short-circuit detection point of the power supply cable includes the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the laid and used state is the historical maximum short-circuit current of the power supply cable, or the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the unlaid and ready-to-use state is the rated peak withstand current of the power supply cable connection device.

[0085] In the embodiment of the present invention, it is assumed that through query, it is found that the maximum short-circuit current that the power supply cable has ever experienced is 5000A during the past operation process. This historical maximum short-circuit current of 5000A is used as the short-circuit current for the short-circuit stability verification test of the power supply cable in the laid and used state. The test equipment is connected at the short-circuit detection point of the power supply cable to simulate the short-circuit current of 5000A passing through the cable. The situation at the short-circuit detection point of the power supply cable during the test is observed and recorded, including whether the line is damaged, deformed, overheated, etc. For example, during the test, a professional temperature sensor is used to monitor the temperature changes at the short-circuit detection point, and a high-definition camera is used to record the changes in the appearance of the cable. For the power supply cable that has not been laid and is ready for use, the rated peak withstand current of the equipment connected to it is determined. Assuming that the rated peak withstand current of the equipment to be connected by the power supply cable is 4000A, this 4000A is used as the short-circuit current for the short-circuit stability verification test of the power supply cable that has not been laid and is waiting to be used. Similarly, the test equipment is connected to the short-circuit detection point of the power supply cable to simulate the short-circuit current of 4000A passing through the cable. Carefully observe and record various conditions at the short-circuit detection point of the power supply cable during the test. Similar to the test of the laying and use status, monitor temperature changes, appearance changes, etc. For the power supply cable in the laying and use status, if there is no line damage or deformation at the short-circuit detection point after the test, it means that the dynamic thermal stability of the power supply cable is qualified. On the contrary, if there is line damage, deformation, etc., the dynamic thermal stability is unqualified and needs to be repaired or replaced. For the power supply cable that has not been laid and is waiting to be used, whether its dynamic thermal stability is qualified is also determined based on whether there is line damage or deformation at the short-circuit detection point after the test. If qualified, it can be laid and installed; if unqualified, the cable needs to be inspected or replaced to ensure the safe and stable operation of the power system after installation.

[0086] The present invention provides an intuitive and easy-to-understand judgment criterion by clearly determining whether the dynamic thermal stability is qualified by determining whether there is line damage or deformation at the short-circuit detection point of the power supply cable after the test. Both the operation and maintenance personnel of the power system and the relevant detection technicians can make a quick and accurate judgment on the dynamic thermal stability of the power supply cable based on this clear standard. The above method improves the accuracy of the short-circuit detection point analysis to reduce energy waste and thus improve energy utilization efficiency.

[0087] See also Figure 4 As shown, Figure 4 The present invention is a schematic diagram of the structure of an evaluation system for a method for evaluating the dynamic thermal stability of a power supply cable according to an embodiment of the present invention.

[0088] Specifically, an evaluation system applied to the evaluation method of the dynamic thermal stability of the power supply cable comprises:

[0089] A data acquisition module is used to obtain the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environmental data;

[0090] a short-circuit detection point determination module, which is connected to the data acquisition module, and includes a short-circuit detection point type determination unit for determining a short-circuit detection point of the dynamic thermal stability of the power supply cable according to the state of the power supply cable, and a maximum loss point determination unit for determining the maximum loss point of the power supply cable according to the laying mode of the power supply cable and the soil thermal conductivity of the power supply cable within a preset time, the rate of change of the buried depth of the power supply cable within a preset time, the dust accumulation thickness of the power supply cable, and whether there are cracks in the completely exposed power supply cable;

[0091] A test module, which is connected to the short-circuit detection point determination module and is used to perform a short-circuit stability verification test on the short-circuit detection point of the power supply cable;

[0092] A determination module is connected to the test module and is used to determine whether the dynamic thermal stability of the power supply cable is qualified according to whether line damage or deformation occurs at a short-circuit detection point of the power supply cable after the test.

[0093] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the dynamic thermal stability of a power supply cable, characterized in that: include: Obtain the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environment data; Based on the state of the power supply cable being in a laid and used state, or being unlaid and waiting to be used state, determining a point with a maximum short-circuit current of the power supply cable, or a point with a maximum loss of the power supply cable, as a short-circuit detection point for dynamic thermal stability of the power supply cable; Based on the soil thermal conductivity of the power cable buried underground within a preset time and the rate of change of the buried depth of the power cable within the preset time, the maximum loss point of the buried power cable is determined, and based on the dust accumulation thickness of the exposed power cable and whether there are cracks in the completely exposed power cable, the maximum loss point of the exposed power cable is determined; When determining the dust accumulation thickness of the exposed power supply cable, the dust accumulation thickness of the exposed power supply cable is directly determined based on the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period, or the dust accumulation thickness is determined after flushing the exposed power supply cable with water; A short-circuit stability verification test is performed on the short-circuit detection point of the power supply cable, and whether the dynamic thermal stability of the power supply cable is qualified is determined based on whether line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test.

2. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 1, characterized in that: The short-circuit detection points for determining the dynamic thermal stability of the power supply cable include: If the power supply cable is in the state of being laid and used, the point with the maximum loss of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable; If the power supply cable is in an unlaid and waiting-for-use state, the point with the maximum short-circuit current of the power supply cable is determined as the short-circuit detection point of the dynamic thermal stability of the power supply cable.

3. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 2, characterized in that: Determining the maximum loss point of the buried power supply cable includes: The point where the average soil thermal conductivity of the power supply cable buried underground within a preset time is the smallest, and the point where the rate of change of the buried depth of the power supply cable within the preset time is the largest, are used as loss detection points; Install optical fiber temperature sensors on the surface of the power supply cables at the loss detection points to record the temperature changes of the power supply cables in real time during operation; Calculate the real-time loss at the loss detection point based on the recorded temperature data and combined with the resistance temperature coefficient of the power supply cable and the load current; The loss detection point with the largest real-time loss is taken as the maximum loss point.

4. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 3, characterized in that: Determining the maximum loss point of the exposed power supply cable includes: The point where dust accumulation is the thickest on the exposed power supply cable and the point where the number of cracks is the largest on the completely exposed power supply cable are used as loss detection points; Install optical fiber temperature sensors on the surface of the power supply cables at the loss detection points to record the temperature changes of the power supply cables in real time during operation; Calculate the real-time loss at the loss detection point based on the recorded temperature data and combined with the resistance temperature coefficient of the power supply cable and the load current; The loss detection point with the largest real-time loss is taken as the maximum loss point.

5. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 4, characterized in that: Determining the dust accumulation thickness of the exposed power supply cable comprises: If the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is less than a preset rainfall frequency, determining the dust accumulation thickness after flushing the exposed power supply cable with water; If the rainfall frequency of the environment in which the exposed power supply cable is located within a preset period is greater than or equal to a preset rainfall frequency, the dust accumulation thickness of the exposed power supply cable is directly determined.

6. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 1, characterized in that: Determine the maximum point of short-circuit current of the power supply cable, including the point where the maximum short-circuit current of the cable loop occurs, that is, for a single cable that does not exceed the manufacturing length, the maximum point of short-circuit current is determined at the end of the cable; for cables with intermediate joints, the maximum point of short-circuit current is determined at the beginning of each line segment that reduces the cable cross-section; when the cable segments have equal cross-sections, the maximum point of short-circuit current is determined at the beginning of the next cable segment, that is, the first intermediate joint; for parallel-connected cables without intermediate joints, the maximum point of short-circuit current is determined after the parallel point.

7. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 1, characterized in that: Determining whether the dynamic thermal stability of the power supply cable is qualified includes: If the short-circuit detection point of the power supply cable is damaged or deformed after the test, it is determined that the dynamic thermal stability of the power supply cable is unqualified; If no line damage or deformation occurs at the short-circuit detection point of the power supply cable after the test, it is determined that the dynamic thermal stability of the power supply cable is qualified.

8. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 7, characterized in that: After the test, it is determined that there are line damage or deformation phenomena at the short-circuit detection point of the power supply cable, including insulation damage, insulation burnt, insulation peeled off, conductor shape change, conductor melting and conductor broken strands.

9. The method for evaluating the dynamic thermal stability of a power supply cable according to claim 1, characterized in that: The short-circuit stability verification test performed on the short-circuit detection point of the power supply cable includes the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the laid and used state is the historical maximum short-circuit current of the power supply cable, or the short-circuit current when the short-circuit stability verification test is performed on the power supply cable in the unlaid and waiting to be used state is the rated peak withstand current of the power supply cable connection device.

10. An evaluation system applied to the evaluation method for dynamic thermal stability of a power supply cable according to any one of claims 1 to 9, characterized in that: include: A data acquisition module is used to obtain the power supply cable's own physical parameter data, fault-related electrical parameter data, and the power supply cable's environmental data; a short-circuit detection point determination module, which is connected to the data acquisition module, and includes a short-circuit detection point type determination unit for determining a short-circuit detection point of the dynamic thermal stability of the power supply cable according to the state of the power supply cable, and a maximum loss point determination unit for determining the maximum loss point of the power supply cable according to the laying mode of the power supply cable and the soil thermal conductivity of the power supply cable within a preset time, the rate of change of the buried depth of the power supply cable within a preset time, the dust accumulation thickness of the power supply cable, and whether there are cracks in the completely exposed power supply cable; A test module, which is connected to the short-circuit detection point determination module and is used to perform a short-circuit stability verification test on the short-circuit detection point of the power supply cable; A determination module is connected to the test module and is used to determine whether the dynamic thermal stability of the power supply cable is qualified according to whether line damage or deformation occurs at a short-circuit detection point of the power supply cable after the test.

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