Cable overheating assessment method and device based on pyrolysis gas

Abstract

The invention provides a cable overheating assessment method and device based on pyrolysis gas. The cable overheating assessment method comprises the following steps: constructing a plurality of characteristic quantities; each characteristic quantity represents the sum of the generation quantity of one or more pyrolysis gases; calculating the correlation degree between each characteristic quantity and the pyrolysis temperature; selecting a target feature quantity based on the correlation degree; establishing a fitting curve between each target characteristic quantity and the pyrolysis temperature; based on a preset overheating temperature range and the fitting curve corresponding to each target characteristic quantity, obtaining an overheating threshold range corresponding to each target characteristic quantity; detecting to obtain an actual detection value of each target characteristic quantity; and if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, determining that the target cable is in an overheating state. According to the scheme, based on the relation between the outer sheath pyrolysis gas and the temperature, the overheating threshold value range is determined, the pyrolysis gas is detected, and overheating evaluation is carried out through the overheating threshold value range, so that the purpose of early-stage, accurate and dead-corner-free overheating evaluation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of cable equipment safety detection, and in particular to a cable overheating assessment method and device based on pyrolysis gas. Background Art

[0002] For high-voltage cable lines, the cable outer sheath provides electrical isolation between the metal sheath and the grounding electrode, while also physically protecting the cable's internal structure. Damage to the outer sheath can easily cause localized overheating. If these hot spots are not discovered in time, the cable can develop into a fire.

[0003] In the existing technology, it is impossible to perform early, accurate and comprehensive overheating assessment of high-voltage cables in cable tunnels. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a cable overheating assessment method and device based on pyrolysis gas, so as to achieve the purpose of early, accurate and comprehensive overheating assessment.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] A first aspect of an embodiment of the present invention discloses a cable overheat assessment method based on pyrolysis gas, the method comprising:

[0007] Acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of the target cable; the experimental data includes: the amount of multiple pyrolysis gases generated at different pyrolysis temperatures;

[0008] Based on the experimental data, a plurality of characteristic quantities are constructed; each characteristic quantity represents the sum of the generated amounts of one or more pyrolysis gases;

[0009] Calculate the correlation between each characteristic value and the pyrolysis temperature using a grey correlation algorithm;

[0010] Selecting a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities;

[0011] Establishing a fitting curve between each target characteristic value and pyrolysis temperature;

[0012] Based on the preset overheat temperature range and the fitting curve corresponding to each target characteristic value, an overheat threshold range corresponding to each target characteristic value is obtained;

[0013] In the environment where the target cable is located, detecting an actual detection value of each target characteristic quantity;

[0014] If the actual detection value of each of the target characteristic quantities is within the corresponding overheating threshold range, it is determined that the target cable is in an overheating state.

[0015] Preferably, the grey correlation algorithm is used to calculate the correlation between each characteristic value and the pyrolysis temperature, including:

[0016] Using a averaging method to perform dimensionless processing on each of the characteristic quantities;

[0017] Utilizing each of the dimensionless characteristic quantities and a grey correlation coefficient calculation formula, a correlation coefficient between each of the characteristic quantities and the pyrolysis temperature is calculated;

[0018] Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

[0019] Preferably, selecting a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities includes:

[0020] A preset number of the feature quantities are selected as target feature quantities in descending order of the association degrees corresponding to the feature quantities.

[0021] Preferably, the step of establishing a fitting curve between each target characteristic value and the pyrolysis temperature comprises:

[0022] A polynomial fitting algorithm is used to establish a fitting curve between each target characteristic quantity and the pyrolysis temperature.

[0023] Preferably, obtaining the overheat threshold range corresponding to each target characteristic value based on the preset overheat temperature range and the fitting curve corresponding to each target characteristic value includes:

[0024] Based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range, and the fitting curve corresponding to each target characteristic quantity, a general overheating threshold range, a warning overheating threshold range, and a severe overheating threshold range corresponding to each target characteristic quantity are respectively obtained; wherein the general overheating temperature range is smaller than the warning overheating temperature range, and the severe overheating temperature range is larger than the warning overheating temperature range;

[0025] Correspondingly, if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, determining that the target cable is in an overheating state includes:

[0026] If the actual detection value of each of the target characteristic quantities is within the corresponding general overheating threshold range, it is determined that the target cable is in a general overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding warning overheating threshold range, it is determined that the target cable is in a warning overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding severe overheating threshold range, it is determined that the target cable is in a severe overheating state.

[0027] A second aspect of an embodiment of the present invention discloses a cable overheat assessment device based on pyrolysis gas, the device comprising:

[0028] An acquisition unit is used to acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of a target cable; the experimental data includes: the amount of multiple pyrolysis gases generated at different pyrolysis temperatures;

[0029] A construction unit, configured to construct a plurality of characteristic quantities based on the experimental data; each characteristic quantity represents the sum of the generated amounts of one or more pyrolysis gases;

[0030] a calculation unit, configured to calculate the correlation between each characteristic value and the pyrolysis temperature using a grey correlation algorithm;

[0031] a screening unit, configured to select a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities;

[0032] An establishing unit, for establishing a fitting curve between each of the target characteristic quantities and the pyrolysis temperature;

[0033] a threshold determination unit, configured to obtain an overheat threshold range corresponding to each target characteristic value based on a preset overheat temperature range and the fitting curve corresponding to each target characteristic value;

[0034] a detection unit, configured to detect an actual detection value of each target characteristic quantity in an environment where the target cable is located;

[0035] An evaluation unit is configured to determine that the target cable is in an overheated state if an actual detection value of each of the target characteristic quantities is within the corresponding overheat threshold range.

[0036] Preferably, the computing unit is specifically configured to:

[0037] Using a averaging method to perform dimensionless processing on each of the characteristic quantities;

[0038] Utilizing each of the dimensionless characteristic quantities and a grey correlation coefficient calculation formula, a correlation coefficient between each of the characteristic quantities and the pyrolysis temperature is calculated;

[0039] Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

[0040] Preferably, the screening unit is specifically used for:

[0041] A preset number of the feature quantities are selected as target feature quantities in descending order of the association degrees corresponding to the feature quantities.

[0042] Preferably, the establishing unit is specifically configured to:

[0043] A polynomial fitting algorithm is used to establish a fitting curve between each target characteristic quantity and the pyrolysis temperature.

[0044] Preferably, the device further comprises:

[0045] Based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range, and the fitting curve corresponding to each target characteristic quantity, a general overheating threshold range, a warning overheating threshold range, and a severe overheating threshold range corresponding to each target characteristic quantity are respectively obtained; wherein the general overheating temperature range is smaller than the warning overheating temperature range, and the severe overheating temperature range is larger than the warning overheating temperature range;

[0046] Correspondingly, if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, determining that the target cable is in an overheating state includes:

[0047] If the actual detection value of each of the target characteristic quantities is within the corresponding general overheating threshold range, it is determined that the target cable is in a general overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding warning overheating threshold range, it is determined that the target cable is in a warning overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding severe overheating threshold range, it is determined that the target cable is in a severe overheating state.

[0048] Based on the above-mentioned embodiment of the present invention, a cable overheat assessment method based on pyrolysis gas is provided, and experimental data obtained by performing a pyrolysis experiment on the outer sheath of a target cable is obtained; the experimental data includes: the generation amount of multiple pyrolysis gases at different pyrolysis temperatures; based on the experimental data, multiple characteristic quantities are constructed; each characteristic quantity represents the sum of the generation amount of one or more pyrolysis gases; a grey correlation algorithm is used to calculate the correlation between each characteristic quantity and the pyrolysis temperature; according to the correlation corresponding to each characteristic quantity, a target characteristic quantity is selected from each characteristic quantity; a fitting curve between each target characteristic quantity and the pyrolysis temperature is established; based on a preset overheat temperature range and the fitting curve corresponding to each target characteristic quantity, an overheat threshold range corresponding to each target characteristic quantity is obtained; in the environment where the target cable is located, the actual detection value of each target characteristic quantity is detected; if the actual detection value of each target characteristic quantity is within the corresponding overheat threshold range, it is determined that the target cable is in an overheated state. In this scheme, characteristic gases are selected from the pyrolysis gas of the high-voltage cable outer sheath and characteristic quantities are constructed. A fitting curve between the characteristic quantities and the pyrolysis temperature is established, and the corresponding overheating threshold range is determined using the characteristics of the fitting curve. The early appearance and easy detection characteristics of the pyrolysis gas are utilized. When the actual detection value of the characteristic quantity reaches the corresponding overheating threshold range, the cable is determined to be overheated, thereby achieving the purpose of early, accurate and comprehensive overheating assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0050] Figure 1 This is a flow chart of a cable overheat assessment method based on pyrolysis gas disclosed in an embodiment of the present invention;

[0051] Figure 2 A schematic diagram of pyrolysis experimental data disclosed in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the relationship between a characteristic quantity and temperature disclosed in an embodiment of the present invention;

[0053] Figure 4 This is a structural diagram of a cable overheat assessment device based on pyrolysis gas disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0055] In this application, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0056] As can be seen from the background technology, in the prior art, it is impossible to perform early, accurate and comprehensive overheating assessment of high-voltage cables in cable tunnels.

[0057] Therefore, an embodiment of the present invention discloses a cable overheating assessment method and device based on pyrolysis gas. In this solution, characteristic gases are selected from the pyrolysis gas of the high-voltage cable outer sheath and characteristic quantities are constructed. A fitting curve between the characteristic quantities and the pyrolysis temperature is established, and the corresponding overheating threshold range is determined using the fitting curve characteristics. The early appearance and easy detection characteristics of pyrolysis gas are utilized. When the actual detection value of the characteristic quantity reaches the corresponding overheating threshold range, the cable is determined to be overheated, thereby achieving the purpose of early, accurate and comprehensive overheating assessment.

[0058] like Figure 1 FIG2 is a flow chart of a cable overheat assessment method based on pyrolysis gas disclosed in an embodiment of the present invention. The method detects and analyzes characteristic gases generated during the pyrolysis process and combines mathematical models to accurately assess and provide early warning of high-voltage cable overheating conditions. The method includes the following steps:

[0059] Step S101: Acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of a target cable.

[0060] Before a high-voltage cable fire breaks out, its PE outer sheath decomposes at elevated temperatures to produce a series of temperature-dependent, rarely found gases, such as CO and olefins. By studying the correlation between these characteristic gases produced by the pyrolysis of the PE outer sheath and temperature, we can directly identify overheating conditions in high-voltage cables and thus prevent cable fires.

[0061] It should be noted that the outer sheath of the cable is made of different materials. This application takes the PE outer sheath as an example for explanation, but the method disclosed in this application is applicable to outer sheaths made of various materials including the PE outer sheath.

[0062] The experimental data include: the generation amount of various pyrolysis gases at different pyrolysis temperatures.

[0063] The pyrolysis experiment on the outer sheath of the target cable is carried out in advance. The specific operation is as follows:

[0064] Place the treated PE outer jacket sample in a heating device, turn off the heating device, evacuate the device, and let it sit for 1 hour to allow any decomposition products adsorbed on the wall surface from the previous experiment to fully release and minimize their impact on the current experiment. Set the heating device temperature to 90°C and the pyrolysis time to 180 minutes. After the experiment, adjust the pyrolysis temperature to 100°C and continue with the next experiment until the pyrolysis temperature reaches 250°C, concluding the experiment. The collected gases were analyzed using a Fourier transform infrared spectrometer.

[0065] The pyrolysis gas detection process is as follows:

[0066] The collected pyrolysis gas samples are tested in turn by Fourier infrared spectrometer and gas chromatograph. During the Fourier infrared spectrometer detection process, the gas outlet of the gas sampling bag is connected to the gas inlet of the optical path cell of the infrared spectrometer, and the other interface of the optical path cell is connected to the flow meter and a small vacuum pump. The optical path cell is evacuated until it is in a vacuum state, the gas sampling bag is opened and the collected gas sample is introduced, and the detection is started to obtain the infrared spectrum of the pyrolysis gas. According to the position and intensity of the absorption peak in the spectrum, combined with the known functional group vibration frequency information, the gas components contained in the pyrolysis gas are determined. For example, in the spectrum, it is observed that the wave number at 2349cm -1 There is an obvious absorption peak around 3270 ~ 3300cm -1 The presence of an absorption peak nearby indicates the possible presence of alkyne gases. When using a gas chromatograph to quantitatively analyze pyrolysis gases, a gas sample is injected into the chromatograph and the amount of pyrolysis gas generated is calculated based on the area of ​​the chromatographic peak and the standard curve.

[0067] like Figure 2 , which is a schematic diagram of pyrolysis experimental data disclosed in an embodiment of the present invention.

[0068] Taking the PE outer sheath as an example, through the pyrolysis experiment of the high-voltage cable PE outer sheath, it was found that the gas generated in the temperature range of 90-250℃ has significant temperature dependence.

[0069] The high-voltage cable PE outer sheath begins to pyrolyze at a temperature of about 90°C, initially producing a small amount of CO2 and C2H2 gases; as the ambient temperature increases to about 120°C, the high-voltage cable PE outer sheath further pyrolyzes, and the high-voltage cable PE outer sheath pyrolyzes to produce a small amount of C2H4 gas, and the amount of the two gases initially produced also increases with the temperature; when the ambient temperature increases to about 230°C, the high-voltage cable PE outer sheath pyrolyzes to produce new gases, including CO and a trace amount of C3H6 gas, and in the process of temperature rising, the amount of CO2, C2H2 and C2H4 generated initially has been increasing with the temperature rising; when the ambient temperature is around 240°C, the high-voltage cable PE outer sheath pyrolyzes to produce a small amount of C2H6 and C3H8 gases; when the temperature increases to 250°C, all seven gases detected are generated and the amount generated is greater than the amount generated at the previous ambient temperature.

[0070] Step S102: constructing and obtaining a plurality of feature quantities based on experimental data.

[0071] The experimental data above show that the production of the seven gases (CO2, C2H2, C2H4, CO, C3H6, C2H6, and C3H8) is strongly positively correlated with temperature. As temperature increases, the types and concentrations of these gases change significantly, directly reflecting the degree of cable overheating. With the exception of CO2, these gases are rare in air and exhibit minimal background interference, meeting the sensitivity requirements for early warning. Therefore, these seven gases were extracted as pyrolysis gases to construct characteristic quantities of pyrolysis gases.

[0072] Each characteristic quantity represents the sum of the generated amount of one or more pyrolysis gases. The specific characteristic quantity construction process is as follows:

[0073] Taking the experimental data of PE outer sheath as an example, the seven pyrolysis gases (CO2, C2H2, C2H4, CO, C3H6, C2H6, C3H8) are divided into the following five types of characteristic quantities according to the experimental data:

[0074] The first type is that the initial generation temperatures of CO2, C2H2, and C2H4 are low and similar, the reaction energies are close, the generation amounts have similar trends with temperature changes, and they account for a large proportion of the pyrolysis gas. Their sum is defined as T1, T1=T(CO2)+T(C2H2)+T(C2H4), which reflects the early to middle stage of pyrolysis.

[0075] The second type, CO, C3H6, C2H6, C3H8 have high and similar initial formation temperatures, large reaction energy requirements, and similar production trends with temperature. Their sum is T2, T2=T(CO)+T(C3H6)+T(C2H6)+T(C3H8), reflecting the characteristics of the high-temperature stage of pyrolysis;

[0076] The third type is that carbon atoms react with O2 to generate CO2 during pyrolysis. At high temperatures, carbon atoms are incompletely burned to generate CO, and CO is converted into CO2. The sum of the two is T3, T3=T(CO)+T(CO2), which reflects the relationship between pyrolysis redox and temperature.

[0077] The fourth type, when the temperature rises, the long chain of the PE outer sheath macromolecule decomposes into C2H2, and C2H2 is hydrogenated to generate C2H4 and C2H6 in sequence. Because the hydrogenation reaction requires a large amount of energy and has a low conversion rate, the sum of the three generated is T4, T4=T(C2H2)+T(C2H4)+T(C2H6), reflecting the relationship between the generation of C2 hydrocarbon compounds and temperature;

[0078] The fifth category produces C3 hydrocarbon compounds at high temperatures. The generation pattern is similar to that of C2 hydrocarbons. The sum of the production of C3H6 and C3H8 is T5, T5=T(C3H6)+T(C3H8), which describes the relationship between the generation of C3 hydrocarbon compounds and temperature at high temperatures.

[0079] like Figure 3 FIG. 1 is a schematic diagram showing the relationship between a characteristic quantity and temperature disclosed in an embodiment of the present invention. Figure 3 The relationship between the pyrolysis gas characteristic quantities T1, T2, T3, T4 and T5 and different ambient temperatures is shown when the high-voltage cable PE outer sheath is overheated.

[0080] from Figure 3 It can be seen that all the pyrolysis gas characteristic quantities continue to increase with the increase of ambient temperature. Especially when the temperature is too high, the amount of pyrolysis characteristic gas generated increases sharply with the increase of ambient temperature. This shows that at high temperature, the PE outer sheath of the high-voltage cable is rapidly pyrolyzed into small molecular gases by the long chains of PE macromolecules. Therefore, the size of the pyrolysis gas characteristic quantities T1, T2, T3, T4 and T5 defined for this purpose can be used to determine the ambient temperature of the high-voltage cable outer sheath at this time.

[0081] Step S103: using the grey correlation algorithm, calculate the correlation between each characteristic value and the pyrolysis temperature.

[0082] In step S103, the grey correlation algorithm uses the pyrolysis temperature sequence as a reference benchmark, performs dimensionless averaging on the pyrolysis gas characteristic quantity data, eliminates dimension differences to ensure data comparability, and then calculates the correlation coefficient and correlation degree.

[0083] The specific implementation process of step S103 includes the following steps:

[0084] Step S201: Dimensionless processing is performed on each feature quantity using a averaging method.

[0085] Specifically, the pyrolysis temperature series is used as the reference series. When performing correlation analysis on series with different units or initial values, it is necessary to first perform dimensionless processing. The commonly used method is the mean value method. The calculation process is as follows:

[0086] (1)

[0087] where x i (k) are the characteristic quantities of pyrolysis gases at temperature k, i.e., T1 to T5, i represents the characteristic quantity of the i-th gas, k is the k-th temperature point, x mean is the average value of the i-th characteristic quantity at all temperatures.

[0088] Step S202: using each dimensionless feature quantity and the grey correlation coefficient calculation formula, calculate the correlation coefficient between each feature quantity and the pyrolysis temperature.

[0089] Specifically, the grey correlation coefficient calculation formula is:

[0090] (2)

[0091] in, is the correlation coefficient of the i-th characteristic quantity at the k-th temperature point; ρ is the resolution coefficient. Its range is (0~1), and its function is to control the discrimination degree. The smaller its value, the greater the discrimination degree, and the larger its value, the smaller the discrimination degree. 0.5 is usually taken as the resolution coefficient, and ρ is taken as 0.5. Among them, It is called the absolute difference of the two sequences at the k temperature point; It is called the minimum difference of level 2, which is the minimum difference of all gas characteristic quantities at all temperatures; It is called the maximum difference of level 2, which is the maximum difference of all gas characteristic quantities at all temperatures.

[0092] It should be noted that when calculating the Grey Correlation Coefficient, the discrimination coefficient ρ in the formula is set to 0.5, which has been verified through extensive experiments. This value effectively reflects the degree of correlation between data while ensuring discrimination. If the ρ value is too small, the discrimination may be too high, which may cause data fluctuations to have a significant impact on the results. If the ρ value is too large, the discrimination may be too low, making it difficult to accurately reflect the differences between data.

[0093] Step S203: Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

[0094] Specifically, the correlation equation is as follows:

[0095] (3)

[0096] Among them, r iis the grey correlation degree between the ith feature value and temperature, n is the number of temperature points, and n=17 in this application.

[0097] In the embodiment of the present invention, the degree of correlation between each pyrolysis gas characteristic quantity and temperature can be determined by calculating the correlation degree, which provides a basis for selecting the target characteristic quantity.

[0098] Taking the PE outer sheath as an example, the correlation between each characteristic quantity and the ambient temperature is evaluated by using the gray correlation algorithm mentioned above, and the dimensionless processing is used to eliminate the influence of the data dimension. The following correlation is calculated, as shown in Table 1:

[0099]

[0100] Step S104: selecting a target feature quantity from each feature quantity according to the correlation degree corresponding to each feature quantity.

[0101] In step S104, target feature quantities that are highly correlated with temperature changes are accurately screened out to lock key input parameters for subsequent modeling (i.e., establishing a fitting curve).

[0102] In the specific implementation process of step S104, a preset number of feature quantities are selected as target feature quantities in descending order of the correlation degrees corresponding to the feature quantities.

[0103] Taking the PE outer sheath as an example, the characteristic quantities of the pyrolysis gas of each high-voltage cable PE outer sheath are ranked according to the correlation between the pyrolysis temperature and the characteristic quantity: T1>T3>T4>T5>T2.

[0104] A higher correlation indicates a closer relationship between the pyrolysis gas characteristic and temperature, so the decision based on the characteristic with the highest correlation has the highest priority. Based on the correlation of the pyrolysis characteristic, the top three priority characteristics, T1, T3, and T4, are selected as the target characteristics for the high-voltage cable PE outer sheath.

[0105] Step S105: establishing a fitting curve between each target characteristic value and the pyrolysis temperature.

[0106] In step S105, the polynomial fitting algorithm constructs a high-precision mathematical model (i.e., fitting curve) of temperature and gas characteristic quantities based on the screened target characteristic quantities through nonlinear curve fitting. This model can accurately characterize the evolution law of characteristic quantities in different overheating stages and provide a direct quantitative basis for the evaluation of overheating status.

[0107] To determine the characteristic value threshold (i.e., overheating threshold range) corresponding to the warning temperature critical value (i.e., overheating temperature range), a polynomial fitting algorithm was used to establish a mathematical model (i.e., fitting curve) between each target characteristic value and the ambient temperature. Each target characteristic value corresponds to a mathematical model. By fitting the experimental data, the optimal fitting order was determined to be sixth order. The polynomial fitting algorithm expression is as follows:

[0108] (4)

[0109] is an n-order polynomial, where n represents the highest power of the polynomial, arrive is the fitting coefficient. is the pyrolysis temperature; x is the gas characteristic quantity; to is the regression coefficient, which reflects the sensitivity of gas generation to temperature changes; is the constant term, which is used to fit the theoretical temperature value of the polynomial when x=0; n is the order of the polynomial.

[0110] Step S106: Based on the preset overheating temperature range and the fitting curve corresponding to each target characteristic value, an overheating threshold range corresponding to each target characteristic value is obtained.

[0111] It should be noted that the maximum rated operating temperature of a high-voltage cable is 90°C, the maximum short-term overload temperature must not exceed 130°C, and the maximum short-circuit temperature must not exceed 250°C. However, research has found that new gas is generated at ambient temperatures of 90°C, 120°C, 230°C, and 240°C. The temperatures at which new gas is generated are close to the specified maximum rated operating temperature, maximum short-term overload temperature, and maximum short-circuit temperature of the high-voltage cable. Therefore, the present invention uses these three high-voltage cable temperature categories to assess the overheating status of the high-voltage cable PE outer sheath.

[0112] That is to say, the overheating temperature range can be greater than or equal to 90°C. By using the fitting curve corresponding to each target characteristic quantity, the overheating threshold range corresponding to each target characteristic quantity can be obtained when the overheating temperature range is 90°C. Subsequently, the overheating threshold range corresponding to each target characteristic quantity is used to evaluate the overheating state.

[0113] In one embodiment, the overheating temperature range greater than or equal to 90° C. can be further subdivided to obtain a corresponding threshold range, and then the overheating state of the outer sheath is subsequently divided into three states: general, warning, and severe.

[0114] Specifically, based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range and the fitting curve corresponding to each target characteristic quantity, the general overheating threshold range, the warning overheating threshold range and the severe overheating threshold range corresponding to each target characteristic quantity are obtained respectively.

[0115] Among them, the general overheating temperature range ([90℃, 130℃)) is smaller than the warning overheating temperature range ([130℃, 250℃)), and the severe overheating temperature range (≥250℃) is larger than the warning overheating temperature range.

[0116] Step S107: Detecting the actual detection value of each target characteristic quantity in the environment where the target cable is located.

[0117] It should be noted that the present invention does not limit the specific detection method.

[0118] Step S108: If the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, it is determined that the target cable is in an overheating state.

[0119] For example, when the overheat temperature range can be greater than or equal to 90°C, the overheat threshold range corresponding to each target characteristic quantity is greater than 0μL / L. That is to say, as long as the actual detection value of each target characteristic quantity is greater than 0μL / L, it is determined that the target cable is in an overheated state.

[0120] Corresponding to the above-mentioned situation of further subdividing the overheat temperature range greater than or equal to 90°C, if the actual detection value of each target characteristic quantity is within the corresponding general overheat threshold range, it is determined that the target cable is in a general overheat state; if the actual detection value of each target characteristic quantity is within the corresponding warning overheat threshold range, it is determined that the target cable is in a warning overheat state; if the actual detection value of each target characteristic quantity is within the corresponding severe overheat threshold range, it is determined that the target cable is in a severe overheat state.

[0121] Taking the PE outer sheath as an example, the classification of different overheating states and their corresponding temperatures and actual detection values ​​of characteristic quantities are shown in Table 2:

[0122]

[0123] In the general overheating state, the high-voltage cable temperature has exceeded the maximum rated operating temperature for normal operation. At this time, the pyrolysis gas characteristic quantity T1 will be monitored within the range of (0, 510μL / L]; T3 will be monitored within the range of (0, 195μL / L]; T4 will be monitored within the range of (0, 318μL / L]). The alarm area should be closely observed and maintenance should be arranged at the appropriate time.

[0124] In the overheat warning state, the high-voltage cable temperature has exceeded the maximum short-term overload temperature. At this time, the pyrolysis gas characteristic quantity T1 is monitored within the range of (510μL / L, 27857μL / L]; T3 is within the range of (195μL / L, 20068μL / L]; T4 is within the range of (318μL / L, 9604μL / L], etc., which requires immediate on-site inspection and timely repair of the high-voltage cable overheating.

[0125] In a severe overheating state, the temperature of the high-voltage cable has exceeded the maximum temperature specified for short circuit. At this time, the characteristic quantity of pyrolysis gas T1 greater than 27857μL / L; T3 greater than 20068μL / L; T4 greater than 9604μL / L will be detected. At this time, the power supply should be disconnected immediately and fire-fighting measures should be taken to deal with the fire.

[0126] Based on the above-mentioned embodiment of the present invention, a cable overheat assessment method based on pyrolysis gas is disclosed. In this scheme, by selecting characteristic gases from the pyrolysis gas of the high-voltage cable outer sheath and constructing characteristic quantities, a fitting curve between the characteristic quantities and the pyrolysis temperature is established, and the corresponding overheat threshold range is determined using the characteristics of the fitting curve. The early appearance and easy detection characteristics of the pyrolysis gas are utilized. When the actual detection value of the characteristic quantity reaches the corresponding overheat threshold range, the cable is determined to be overheated, thereby achieving the purpose of early, accurate and comprehensive overheat assessment. Furthermore, the present invention can accurately assess the overheating state of the high-voltage cable outer sheath before a fire occurs, timely warn of a fire, effectively prevent the occurrence of cable fires, improve the operation and maintenance efficiency and safety of the power system, and has strong applicability and is not affected by the cable laying environment.

[0127] Corresponding to the cable overheat assessment method based on pyrolysis gas disclosed in the above embodiment of the present invention, as Figure 4 As shown, this is a structural diagram of a cable overheat assessment device based on pyrolysis gas disclosed in an embodiment of the present invention, including: an acquisition unit 401, a construction unit 402, a calculation unit 403, a screening unit 404, an establishment unit 405, a threshold determination unit 406, a detection unit 407 and an evaluation unit 408.

[0128] The acquisition unit 401 is configured to acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of a target cable; the experimental data includes: the generation amounts of various pyrolysis gases at different pyrolysis temperatures.

[0129] The construction unit 402 is used to construct a plurality of characteristic quantities based on the experimental data; each characteristic quantity represents the sum of the generated amount of one or more pyrolysis gases.

[0130] The calculation unit 403 is used to calculate the correlation between each feature value and the pyrolysis temperature using a grey correlation algorithm.

[0131] In one embodiment, the calculation unit 403 is specifically configured to:

[0132] Each characteristic quantity is dimensionless processed using the averaging method;

[0133] Using each characteristic quantity after dimensionless processing and the grey correlation coefficient calculation formula, the correlation coefficient between each characteristic quantity and pyrolysis temperature was calculated;

[0134] Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

[0135] The screening unit 404 is configured to select a target feature quantity from each feature quantity according to the correlation degree corresponding to each feature quantity.

[0136] In one embodiment, the screening unit 404 is specifically configured to:

[0137] A preset number of feature quantities are selected as target feature quantities in descending order of the correlation degrees corresponding to the feature quantities.

[0138] The establishing unit 405 is used to establish a fitting curve between each target characteristic value and the pyrolysis temperature.

[0139] In one embodiment, the establishing unit 405 is specifically configured to:

[0140] A polynomial fitting algorithm is used to establish a fitting curve between each target characteristic quantity and the pyrolysis temperature.

[0141] The threshold determination unit 406 is configured to obtain an overheat threshold range corresponding to each target characteristic value based on a preset overheat temperature range and a fitting curve corresponding to each target characteristic value.

[0142] The detection unit 407 is used to detect the actual detection value of each target characteristic quantity in the environment where the target cable is located.

[0143] The evaluation unit 408 is configured to determine that the target cable is in an overheated state if the actual detection value of each target characteristic quantity is within the corresponding overheat threshold range.

[0144] In one embodiment, the evaluation unit 408 is specifically configured to:

[0145] Based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range, and the fitting curve corresponding to each target characteristic quantity, the general overheating threshold range, the warning overheating threshold range, and the severe overheating threshold range corresponding to each target characteristic quantity are respectively obtained; wherein the general overheating temperature range is smaller than the warning overheating temperature range, and the severe overheating temperature range is larger than the warning overheating temperature range;

[0146] Correspondingly, if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, it is determined that the target cable is in an overheating state, including:

[0147] If the actual detection value of each target characteristic quantity is within the corresponding general overheating threshold range, the target cable is determined to be in a general overheating state; if the actual detection value of each target characteristic quantity is within the corresponding warning overheating threshold range, the target cable is determined to be in a warning overheating state; if the actual detection value of each target characteristic quantity is within the corresponding severe overheating threshold range, the target cable is determined to be in a severe overheating state.

[0148] Based on the above-mentioned embodiment of the present invention, a cable overheat assessment device based on pyrolysis gas is disclosed. In this solution, by selecting characteristic gases from the pyrolysis gas of the high-voltage cable outer sheath and constructing characteristic quantities, a fitting curve between the characteristic quantities and the pyrolysis temperature is established, and the corresponding overheat threshold range is determined using the characteristics of the fitting curve. The early appearance and easy detection characteristics of the pyrolysis gas are utilized. When the actual detection value of the characteristic quantity reaches the corresponding overheat threshold range, the cable is determined to be overheated, thereby achieving the purpose of early, accurate and comprehensive overheat assessment. Furthermore, the present invention can accurately assess the overheating state of the high-voltage cable outer sheath before a fire occurs, timely warn of a fire, effectively prevent the occurrence of cable fires, improve the efficiency and safety of power system operation and maintenance, and has strong applicability and is not affected by the cable laying environment.

[0149] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple. For relevant parts, refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without expending creative work.

[0150] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0151] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cable overheat assessment method based on pyrolysis gas, characterized in that: The method comprises: Acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of the target cable; the experimental data includes: the amount of multiple pyrolysis gases generated at different pyrolysis temperatures; Based on the experimental data, a plurality of characteristic quantities are constructed; each characteristic quantity represents the sum of the generated amounts of one or more pyrolysis gases; Calculate the correlation between each characteristic value and the pyrolysis temperature using a grey correlation algorithm; Selecting a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities; Establishing a fitting curve between each target characteristic value and pyrolysis temperature; Based on the preset overheat temperature range and the fitting curve corresponding to each target characteristic value, an overheat threshold range corresponding to each target characteristic value is obtained; In the environment where the target cable is located, detecting an actual detection value of each target characteristic quantity; If the actual detection value of each of the target characteristic quantities is within the corresponding overheating threshold range, it is determined that the target cable is in an overheating state.

2. The method according to claim 1, characterized in that The grey correlation algorithm is used to calculate the correlation between each characteristic value and the pyrolysis temperature, including: Using a averaging method to perform dimensionless processing on each of the characteristic quantities; Utilizing each of the dimensionless characteristic quantities and a grey correlation coefficient calculation formula, a correlation coefficient between each of the characteristic quantities and the pyrolysis temperature is calculated; Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

3. The method according to claim 1, characterized in that Selecting a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities includes: A preset number of the feature quantities are selected as target feature quantities in descending order of the correlation degrees corresponding to the feature quantities.

4. The method according to claim 1, wherein The step of establishing a fitting curve between each target characteristic value and the pyrolysis temperature includes: A polynomial fitting algorithm is used to establish a fitting curve between each target characteristic quantity and the pyrolysis temperature.

5. The method according to any one of claims 1 to 4, characterized in that: The obtaining of the overheat threshold range corresponding to each target characteristic value based on the preset overheat temperature range and the fitting curve corresponding to each target characteristic value includes: Based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range, and the fitting curve corresponding to each target characteristic quantity, a general overheating threshold range, a warning overheating threshold range, and a severe overheating threshold range corresponding to each target characteristic quantity are respectively obtained; wherein the general overheating temperature range is smaller than the warning overheating temperature range, and the severe overheating temperature range is larger than the warning overheating temperature range; Correspondingly, if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, determining that the target cable is in an overheating state includes: If the actual detection value of each of the target characteristic quantities is within the corresponding general overheating threshold range, it is determined that the target cable is in a general overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding warning overheating threshold range, it is determined that the target cable is in a warning overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding severe overheating threshold range, it is determined that the target cable is in a severe overheating state.

6. A cable overheat assessment device based on pyrolysis gas, characterized in that: The device comprises: An acquisition unit is used to acquire experimental data obtained by performing a pyrolysis experiment on the outer sheath of a target cable; the experimental data includes: the amount of multiple pyrolysis gases generated at different pyrolysis temperatures; A construction unit, configured to construct a plurality of characteristic quantities based on the experimental data; each characteristic quantity represents the sum of the generated amounts of one or more pyrolysis gases; a calculation unit, configured to calculate the correlation between each characteristic value and the pyrolysis temperature using a grey correlation algorithm; a screening unit, configured to select a target feature quantity from each of the feature quantities according to the correlation degree corresponding to each of the feature quantities; An establishing unit, for establishing a fitting curve between each of the target characteristic quantities and the pyrolysis temperature; a threshold determination unit, configured to obtain an overheat threshold range corresponding to each target characteristic value based on a preset overheat temperature range and the fitting curve corresponding to each target characteristic value; a detection unit, configured to detect an actual detection value of each target characteristic quantity in an environment where the target cable is located; An evaluation unit is configured to determine that the target cable is in an overheated state if an actual detection value of each of the target characteristic quantities is within the corresponding overheat threshold range.

7. The device according to claim 6, characterized in that The computing unit is specifically configured to: Using a averaging method to perform dimensionless processing on each of the characteristic quantities; Utilizing each of the dimensionless characteristic quantities and a grey correlation coefficient calculation formula, a correlation coefficient between each of the characteristic quantities and the pyrolysis temperature is calculated; Based on the correlation equation and the correlation coefficient between each characteristic quantity and the pyrolysis temperature, the correlation between each characteristic quantity and the pyrolysis temperature is calculated.

8. The device according to claim 6, characterized in that The screening unit is specifically used for: A preset number of the feature quantities are selected as target feature quantities in descending order of the correlation degrees corresponding to the feature quantities.

9. The device according to claim 6, characterized in that The establishing unit is specifically configured to: A polynomial fitting algorithm is used to establish a fitting curve between each target characteristic quantity and the pyrolysis temperature.

10. The device according to any one of claims 6 to 9, characterized in that The device further comprises: Based on the preset general overheating temperature range, the preset warning overheating temperature range, the preset severe overheating temperature range, and the fitting curve corresponding to each target characteristic quantity, a general overheating threshold range, a warning overheating threshold range, and a severe overheating threshold range corresponding to each target characteristic quantity are respectively obtained; wherein the general overheating temperature range is smaller than the warning overheating temperature range, and the severe overheating temperature range is larger than the warning overheating temperature range; Correspondingly, if the actual detection value of each target characteristic quantity is within the corresponding overheating threshold range, determining that the target cable is in an overheating state includes: If the actual detection value of each of the target characteristic quantities is within the corresponding general overheating threshold range, it is determined that the target cable is in a general overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding warning overheating threshold range, it is determined that the target cable is in a warning overheating state; if the actual detection value of each of the target characteristic quantities is within the corresponding severe overheating threshold range, it is determined that the target cable is in a severe overheating state.

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