CN107563018B - Method and device for determining optimal number of insulating layers in cable thermal circuit model - Google Patents
Method and device for determining optimal number of insulating layers in cable thermal circuit model Download PDFInfo
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Abstract
The invention relates to a method and a device for determining the optimal number of insulating layers in a cable hot circuit model. The method comprises the following steps: determining insulation model layering, and establishing a cable hot circuit model according to the insulation model layering; determining a state equation corresponding to the cable thermal circuit model, and solving the temperature of each node in the cable thermal circuit model and the temperature difference of each two adjacent insulation model layers; detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, updating the layer number of the insulation model layers, re-determining the state equation and continuing the subsequent steps; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model. The device is a device corresponding to the method. The method can quickly calculate and determine the optimal number of the insulating layers, and the calculated calculation precision of the conductor temperature of the thermal circuit model meets the engineering requirement.
Description
Technical Field
The invention relates to the technical field of electronic circuits, in particular to a method and a device for determining the optimal number of insulating layers in a cable thermal circuit model.
Background
In the operation management of urban transmission and distribution networks, it is necessary to fully master the real-time operation condition of the distribution network, perform online monitoring and calculation on the temperature distribution of the cable, accurately acquire the real-time temperature of the cable, thereby accurately calculating the current-carrying capacity of the cable and better inhibiting the long-term overload condition of the cable temperature. When the cable temperature is monitored on line, the real-time temperature of a cable conductor is usually obtained by a method for establishing a cable thermal circuit model, a cable insulating layer is divided into a plurality of insulating units when the cable thermal circuit model is established, and the conductor temperature calculated by the cable thermal circuit model is closer to a real value along with the increase of the layering number of the insulating layer. However, when the number of insulating layers reaches a certain value, the number of insulating layers continuously increased will exceed the precision value of the temperature measurement instrument, and the difficulty of solving the hot-circuit model is increased continuously, which may affect the efficiency and difficulty of temperature calculation. Therefore, it is necessary to find a solution that can rapidly solve the optimal number of insulating layers in the cable thermal path model.
Disclosure of Invention
Based on the method and the device, the optimal number of the insulating layers in the cable thermal circuit model can be quickly solved.
The scheme of the invention comprises the following steps:
a method for determining the optimal number of insulating layers in a cable hot-circuit model comprises the following steps:
s1, determining at least two insulation model layers by the insulation layer of the cable, and establishing a cable hot circuit model according to the at least two insulation model layers; s2, determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model, and solving the state equation to obtain the temperature of each node in the cable thermal circuit model; s3, calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node; s4, detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, and returning to the step S2; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model.
An apparatus for determining an optimal number of layers of insulation in a cable thermal path model, comprising:
the hot circuit model building module is used for determining at least two insulation model layers by an insulation layer of the cable and building a cable hot circuit model according to the at least two insulation model layers; the temperature calculation module is used for determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model and solving the state equation to obtain the temperature of each node in the cable thermal circuit model; the temperature difference calculation module is used for calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node; the iterative optimization module is used for detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, the number of layers of the current insulation model layer is added with a set number of layers, the number of layers of the insulation model layer is updated, and the temperature calculation module is returned; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model.
A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method as described above.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the method described above when executing the program.
According to the technical scheme, a cable thermal circuit model is established by layering insulation models, a state equation corresponding to the cable thermal circuit model under the layered layer number of the current insulation model is determined, and the state equation is solved to obtain the temperature of each node in the cable thermal circuit model; calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node; detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, re-determining the insulation model layer, and returning to solve the state equation and the node temperature corresponding to the cable thermal circuit model; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model. The optimal number of layers of the insulating layers in the cable thermal circuit model is rapidly determined by adopting an iteration method, and the calculation precision of the conductor temperature of the thermal circuit model can be ensured to meet engineering requirements through the cable thermal circuit model determined by the optimal number of layers of the insulating layers.
Drawings
FIG. 1 is a schematic flow chart diagram of a method for determining an optimal number of layers of insulation in a cable thermal path model according to one embodiment;
FIG. 2 is a schematic block diagram of a modeled layer of insulation for a cable according to one embodiment;
FIG. 3 is a schematic block diagram of an equivalent thermal circuit model of a cable insulation of an embodiment;
FIG. 4 is a schematic block diagram of a cable hot-circuit model of an embodiment;
FIG. 5 is a schematic view of an iterative optimization process in the method for determining the optimal number of insulating layers in the cable thermal path model according to an embodiment;
FIG. 6 is a schematic structural diagram of an apparatus for determining an optimal number of layers of insulation in a cable thermal path model according to an embodiment;
fig. 7 is a schematic structural diagram of an iterative optimization module in the apparatus for determining the optimal number of insulating layers in the cable thermal path model according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Although the steps in the present invention are arranged by using reference numbers, the order of the steps is not limited, and the relative order of the steps can be adjusted unless the order of the steps is explicitly stated or other steps are required for the execution of a certain step.
The embodiment of the invention provides a method for determining the optimal number of insulating layers in a cable thermal circuit model, which comprises the following steps: determining at least two insulation model layers by an insulation layer of the cable, and establishing a cable thermal circuit model according to the at least two insulation model layers; determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model, and solving the state equation to obtain the temperature of each node in the cable thermal circuit model; calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node; detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, re-determining a state equation corresponding to the cable hot circuit model under the layer number of the current insulation model layer, and continuing to complete the subsequent steps; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model. The embodiment of the invention also provides a corresponding device for determining the optimal number of the insulating layers in the cable thermal circuit model. The following are detailed below.
Fig. 1 is a schematic flow chart of a method for determining an optimal number of insulating layers in a cable thermal path model according to an embodiment. Referring to fig. 1, the method for determining the optimal number of insulating layers in the cable thermal circuit model according to the embodiment mainly includes steps S1 to S4, which are described in detail as follows:
s1, determining at least two insulation model layers by the insulation layer of the cable, and establishing a cable thermal circuit model according to the at least two insulation model layers.
In the embodiment, the insulating layer material of the cable can be polyvinyl chloride, natural rubber, ethylene-propylene rubber, silicon rubber, cross-linked polyethylene and the like, and the specific insulating layer material is not limited by the invention and only needs to be the cable insulating material. Preferably, the insulating layer of the cable comprises a separate insulating layer and an inner shielding layer and an outer shielding layer, which are considered as insulating layers.
In an alternative embodiment, the layering method for determining at least two insulation model layers from an insulation layer of a cable comprises: the insulation layer of the cable is divided into at least two insulation model layers in a manner of equal thickness, equal thermal capacitance or thickness ratio. In one embodiment, said delamination of at least two insulation model layers determined by the insulation layer of the cable is performed in a manner of equal thickness. Referring to fig. 2, fig. 2 is a schematic layered structure diagram of a cable insulation layer layered in an equal thickness manner, and fig. 2 is a schematic layered structure diagram of a cable insulation layer layered in an equal thickness manner, wherein the cable insulation layer is divided into k layers in an equal thickness manner, and the loop widths of the insulation model layers are the same.
For at least two insulation model layers determined by the insulation layers of the cable, the number of the insulation model layers can be selected from 2, 3, 4 or other values, and only an integer greater than or equal to 2 is required. In one embodiment, the insulation model is layered into two layers, that is, the insulation model layer is calculated from 2 layers, and the subsequent calculation is iterated step by step until the optimal number of insulation layers is found.
The model layering of the cable is determined by adopting a thermal conductivity principle, and besides the insulation model layering, each model layering is determined through points on each isotherm on the axial section of the cable, please refer to fig. 4, and fig. 4 is a schematic structural diagram of a cable thermal circuit model according to an embodiment of the invention. In the embodiment of the present invention, the model layer includes a conductor layer 401, an insulating layer 402, a wrapping layer 403, an air gap layer 404, a metal sheath layer 405, an outer sheath layer 406, and an outer skin layer 407, which are sequentially distributed from inside to outside, where a is a conductor temperature, and B is an environmental boundary temperature.
The model layering of the cable thermal circuit model comprises a model layering of an insulating layer, and the model layering of the insulating layer is arranged on one part of the model layering of the cable thermal circuit model. Referring to fig. 3, fig. 3 is a schematic structural diagram of a cable thermal circuit model of a cable insulation layer according to an embodiment, and in fig. 3, P is1′、P2～PkRepresenting the dielectric loss of each insulation model after layering; r1′、R2～RkRepresenting the thermal resistance of each insulation model after layering; c1′、C2～CkThe heat capacity of each insulation model after delamination is shown. As shown in fig. 4, the cable hot-circuit model includes a cable hot-circuit model of the insulating layer.
S2, determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model, and solving the state equation to obtain the temperature of each node in the cable thermal circuit model.
In one embodiment, each model layer can be equivalent to a cylindrical wall structure, and the thermal resistance R and the thermal capacity C of each model layer of the cable per unit length are calculated by combining the heat transfer theory:
wherein, lambda is the heat conductivity coefficient of the material corresponding to the model layering, c is the volume specific heat capacity of the material corresponding to the model layering, and r1Is the inner radius of the cable structure, r2The outer radius of the cable structure.
The internal heat sources of the cable can be divided into three categories: joule loss P of conductor1The dielectric loss of each insulation model layer is P1′、P2～Pn-4(ii) a The circulating current loss of the metal sheath (aluminum sheath) is Pn-1. Known from IEC 60287.
The calculation method of the Joule loss of the conductor comprises the following steps:
P1＝I2Rz；
the calculation mode of the dielectric loss of each insulation model layer is as follows:
the calculation formula of the circulation loss of the metal sheath is as follows:
Pn-1＝λ1P1
wherein I represents the current loaded by the cable conductor; rzAc resistance per unit length of conductor; omega is the frequency of the cable loading load; qiA capacitance layered for the ith insulation model; u shapeiVoltage layered for the ith insulation model; tg δ is a dielectric loss tangent value of the insulating material; lambda [ alpha ]1The ratio of the metal sheath loss and the conductor loss can be obtained by an empirical formula, and is generally 0.03.
And calculating the thermal resistance R and the thermal capacity C of each model layer of the cable in unit length according to the formula by combining the equivalent cylindrical wall structure of the model layer and the heat transfer theory. A thermal circuit model of the cable is analyzed by utilizing a thermoelectric analogy theory, and a thermal balance equation is listed for each node in the thermal circuit, so that the cable thermal circuit model can be converted into a state equation.
In an optional embodiment, the determining a state equation corresponding to the cable thermal circuit model at the number of layers of the current insulation model hierarchy includes:
determining a first heat transfer matrix A and a second heat transfer matrix B of the cable thermal circuit model under the layered number of the current insulation model as follows:
constructing a state equation of the cable thermal circuit model according to the heat transfer matrix A and the heat transfer matrix B:
P＝[P1 P′1 P2 … Pn-5 Pn-4 0 0 Pn-1 0 tn+1/Re]T；
wherein e represents the total number of model layers contained in the cable hot-circuit model; n represents the total number of insulation model layers; t is t0Indicating the temperature of the conductor layer; t is t1～tn-4Representing the temperature of each insulation model layer; t is tn-3Indicating the temperature of the wrapping; t is tn-2Represents the temperature of the air gap layer; t is tn-1Represents the temperature of the metal sheath layer; t is tnRepresents the temperature of the outer jacket layer; t is tn+1Indicating the temperature of the outer skin layer; c1Representing the heat capacity of the conductor layer; c1′、C2～Cn-4Representing the heat capacity of each insulation model layer; cn-3Representing the heat capacity of the wrapping layer; cn-2Represents the thermal capacity of the air gap layer; cn-1The thermal capacity of the metal sheath layer; cnRepresents the thermal capacity of the outer sheath; ceRepresents the heat capacity of the outer epidermal layer; r1Represents the thermal resistance of the conductor layer; r1’、R2～Rn-4Representing the thermal resistance of each insulation model layer; rn-3Representing the thermal resistance of the wrapping layer; rn-2Represents the thermal resistance of the air gap layer; rn-1Represents the thermal resistance of the metal sheath layer; rnRepresenting the thermal resistance of the outer jacket; reRepresents the thermal resistance of the outer skin layer; p1Representing loss of the conductor layer; p1′、P2～Pn-4Representing the dielectric loss of each insulation model layer; pn-1Indicating the loss of the metal sheath layer.
And after determining a state equation corresponding to the cable thermal circuit model under the layered layer number of the current insulation model, solving the state equation to obtain the temperature of each node in the cable thermal circuit model.
Optionally, the method for solving the state equation to obtain the temperature of each node in the cable thermal circuit model may be calculated by programming in Java, C + +, MATLAB, or other languages, or may be calculated by selecting other non-programming methods. In one embodiment, the state equation is programmed using MATLAB to derive the temperature of each node in the cable thermal circuit model.
And S3, calculating the temperature difference of every two adjacent insulation model layers according to the temperature of each node.
S4, detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, and returning to the step S2; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model.
The temperature measuring instrument can be selected from a thermocouple thermometer, a resistance thermometer, a radiation thermometer or other temperature measuring instruments, and the temperature measuring instrument is not limited by the invention as long as the temperature of the cable can be measured. In one embodiment, the temperature measuring instrument is a thermocouple thermometer which is high in accuracy and wide in measuring range and is a thermometer commonly used for measuring the temperature of the cable, and the temperature difference in the cable thermal circuit model can be compared with the accuracy of the thermocouple thermometer, so that whether the number of layered layers of the current insulation model meets the accuracy requirement or not can be judged well.
The precision of the temperature measuring instrument can be selected to be 0.1, 0.5, 1 ℃ or other precisions, and the precision of the temperature measuring instrument is not limited by the invention. In one embodiment, the precision of the temperature measuring instrument is 0.1 ℃, and when the temperature difference between two adjacent insulation model layers is smaller than the precision of the temperature measuring instrument, the measuring instrument cannot be used for accurately distinguishing the size relation of the two node temperatures. When the temperature difference of two adjacent insulation model layers is less than 0.1 ℃ of the measurement accuracy of the thermocouple thermometer, it has no obvious significance to further increase the number of the insulation model layers.
The set number of layers can be selected to be 1, 2, 3, 4 or other values, and the set number of layers is not limited by the invention and only needs to be an integer. In one embodiment, the set number of layers is 1, that is: and if the temperature difference of two adjacent insulation model layers is not smaller than the precision value of the temperature measuring instrument, adding 1 to the number of the current insulation model layers, updating the number of the insulation model layers, and returning to the step S2.
The process from step S2 to step S4 is an iterative optimization process in the method for determining the optimal number of insulating layers in the cable thermal circuit model, please refer to fig. 5, and fig. 5 is a schematic diagram of the iterative optimization process in the method for determining the optimal number of insulating layers in the cable thermal circuit model according to an embodiment. And determining the optimal number of layers of the insulating layer by iterating the number of layers of the insulating model layers and calculating the temperature difference of every two adjacent insulating model layers.
Step S1 of the above embodiment may be: and dividing the cable insulation layer into k insulation model layers according to a mode of equal thickness, wherein the ring width of each insulation unit is the same after division, and the k value is undetermined. And layering the divided insulation models, and establishing a thermal circuit model of the cable insulation layer according to the heat transfer theory.
Step S2 of the above embodiment may be: according to the theory of heat transfer, a cable thermal circuit model with a plurality of layers of the current insulation model is established. Let k be n-4, the corresponding cable thermal circuit model is shown in fig. 4. Based on the theory of thermoelectric analogy, a state equation is written for a cable thermal circuit model.
Step S2 specifically includes:
s21, according to the manufacturing process of the cable, each layer structure of the cable can be equivalent to a cylindrical wall structure. And (3) calculating the thermal resistance R and the thermal capacity C of each model layer of the cable in unit length by combining the heat transfer theory:
wherein, lambda is the heat conductivity coefficient of the material corresponding to the model layering, c is the volume specific heat capacity of the material corresponding to the model layering, and r1Is the inner radius of the cable structure, r2The outer radius of the cable structure.
S22, analyzing the cable thermal circuit model by using the thermoelectric analogy theory, and arranging a thermal balance equation for each node in the thermal circuit, so that the cable thermal circuit model can be converted into a state equation.
Determining a first heat transfer matrix A and a second heat transfer matrix B of the cable thermal circuit model under the layered number of the current insulation model as follows:
constructing a state equation of the cable thermal circuit model according to the heat transfer matrix A and the heat transfer matrix B:
P＝[P1 P′1 P2 … Pn-5 Pn-4 0 0 Pn-1 0 tn+1/Re]T；
wherein e represents the total number of model layers contained in the cable hot-circuit model; n represents the total number of insulation model layers; t is t0Indicating the temperature of the conductor layer; t is t1～tn-4Representing the temperature of each insulation model layer; t is tn-3Indicating the temperature of the wrapping; t is tn-2Represents the temperature of the air gap layer; t is tn-1Represents the temperature of the metal sheath layer; t is tnRepresents the temperature of the outer jacket layer; t is tn+1Indicating the temperature of the outer skin layer; c1Representing the heat capacity of the conductor layer; c1′、C2～Cn-4Representing the heat capacity of each insulation model layer; cn-3Representing the heat capacity of the wrapping layer; cn-2Represents the thermal capacity of the air gap layer; cn-1The thermal capacity of the metal sheath layer; cnRepresents the thermal capacity of the outer sheath; ceRepresents the heat capacity of the outer epidermal layer; r1Represents the thermal resistance of the conductor layer; r1’、R2～Rn-4Representing the thermal resistance of each insulation model layer; rn-3Representing the thermal resistance of the wrapping layer; rn-2Represents the thermal resistance of the air gap layer; rn-1Represents the thermal resistance of the metal sheath layer; rnRepresenting the thermal resistance of the outer jacket; reRepresents the thermal resistance of the outer skin layer; p1Representing loss of the conductor layer; p1′、P2～Pn-4Representing the dielectric loss of each insulation model layer; pn-1Indicating the loss of the metal sheath layer.
Alternatively, the initial insulation model number of layers k is set to 2. And solving a state equation of the cable thermal circuit model under the current insulation model hierarchical number k value, and solving the state equation by using MATLAB programming to obtain the temperature of each node of the equivalent thermal circuit model.
Step S4 of the above embodiment may include: and recording the temperature difference of every two adjacent layers of insulating units, and if the temperature difference is less than 0.1 ℃ of the measurement precision of the thermocouple thermometer, deriving the current stratification number k value. The k value is the optimal number of insulating layers which not only meets the calculation precision requirement, but also can realize quick calculation; if not, the value of k is set to 1, and the process proceeds to S2.
It should be noted that, for the sake of simplicity, the foregoing method embodiments are described as a series of acts or combinations, but those skilled in the art should understand that the present invention is not limited by the described order of acts, as some steps may be performed in other orders or simultaneously according to the present invention.
Based on the same idea as the method for determining the optimal number of insulating layers in the cable thermal circuit model in the embodiment, the invention further provides a device for determining the optimal number of insulating layers in the cable thermal circuit model, and the device can be used for executing the method for determining the optimal number of insulating layers in the cable thermal circuit model. For convenience of illustration, the schematic structural diagram of the embodiment of the apparatus for determining the optimal number of insulating layers in the cable thermal path model only shows the part related to the embodiment of the present invention, and those skilled in the art will understand that the illustrated structure does not constitute a limitation to the apparatus, and may include more or less components than those illustrated, or combine some components, or arrange different components.
As shown in fig. 6, the apparatus for determining the optimal number of insulating layers in the cable thermal circuit model includes a thermal circuit model building module 601, a temperature calculating module 602, a temperature difference calculating module 603, and an iterative optimization module 604.
The hot circuit model building module 601 is configured to determine at least two insulation model hierarchies according to an insulation layer of a cable, and build a cable hot circuit model according to the at least two insulation model hierarchies.
In one embodiment, referring to fig. 7, the hot-circuit model building module 601 includes: the insulation layering submodule 701 is used for dividing an insulation layer of the cable into at least two insulation model layers according to the mode of equal thickness, equal heat capacity or thickness ratio; the model building submodule 702 is configured to determine a model hierarchy of the cable by using a thermal theory, and build a cable thermal circuit model according to the model hierarchy. Optionally, the model layer includes a conductor layer, an insulating layer, a wrapping layer, an air gap layer, a metal sheath layer, an outer sheath layer, and an outer skin layer, which are sequentially distributed from inside to outside.
The temperature calculation module 602 is configured to determine a state equation corresponding to the cable thermal circuit model in the number of layered layers of the current insulation model, and solve the state equation to obtain the temperature of each node in the cable thermal circuit model.
The temperature difference calculating module 603 is configured to calculate a temperature difference between each two adjacent insulation model layers according to the temperature of each node.
The iterative optimization module 604 is configured to detect whether a temperature difference between two adjacent insulation model layers is smaller than a precision value of the temperature measurement instrument, if not, add a set number of layers to the number of layers of the current insulation model layer, update the number of layers of the insulation model layer, and return to the temperature calculation module 602; and if so, acquiring the number of the layered layers of the current insulation model as the optimal number of the insulating layers in the cable hot circuit model.
In one embodiment, the iterative optimization module 604 may be implemented according to the process shown in fig. 5.
In an alternative embodiment, the temperature calculation module 602 includes:
the heat transfer matrix determining submodule is used for determining that a first heat transfer matrix A and a second heat transfer matrix B of the cable thermal circuit model under the layered number of the current insulation model are as follows:
the state equation determination submodule is used for constructing a state equation of the cable thermal circuit model according to the first thermal matrix A and the second heat transfer matrix B:
P＝[P1 P′1 P2 … Pn-5 Pn-4 0 0 Pn-1 0 tn+1/Re]T；
wherein e represents the total number of model layers contained in the cable hot-circuit model; n represents the total number of insulation model layers; t is t0Indicating the temperature of the conductor layer; t is t1～tn-4Representing the temperature of each insulation model layer; t is tn-3Indicating the temperature of the wrapping; t is tn-2Represents the temperature of the air gap layer; t is tn-1Represents the temperature of the metal sheath layer; t is tnRepresents the temperature of the outer jacket layer; t is tn+1Indicating the temperature of the outer skin layer; c1Representing the heat capacity of the conductor layer; c1′、C2～Cn-4Representing the heat capacity of each insulation model layer; cn-3Representing the heat capacity of the wrapping layer; cn-2Represents the thermal capacity of the air gap layer; cn-1The thermal capacity of the metal sheath layer; cnRepresents the thermal capacity of the outer sheath; ceRepresents the heat capacity of the outer epidermal layer; r1Represents the thermal resistance of the conductor layer; r1’、R2～Rn-4Representing the thermal resistance of each insulation model layer; rn-3Representing the thermal resistance of the wrapping layer; rn-2Represents the thermal resistance of the air gap layer; rn-1Represents the thermal resistance of the metal sheath layer; rnRepresenting the thermal resistance of the outer jacket; reRepresents the thermal resistance of the outer skin layer; p1Representing loss of the conductor layer; p1′、P2～Pn-4Representing the dielectric loss of each insulation model layer; pn-1Indicating the loss of the metal sheath layer.
In one embodiment, the temperature calculation module 602 further includes:
and the resistance-capacitance calculation submodule is used for equivalent each model layer into a cylindrical wall structure, and calculating the thermal resistance R and the thermal capacity C of each model layer of the cable with unit length:
wherein, lambda is the heat conductivity coefficient of the material corresponding to the model layering, c is the volume specific heat capacity of the material corresponding to the model layering, and r1Is the inner radius of the cable structure, r2The outer radius of the cable structure.
And the dielectric loss calculation submodule is used for calculating the dielectric loss of the conductor as follows:
P1＝I2Rz；
calculating the dielectric loss of each insulation model layer:
and calculating the circulation loss of the metal sheath:
Pn-1＝λ1P1
wherein I represents the current loaded by the cable conductor; rzAc resistance per unit length of conductor; omega is the frequency of the cable loading load; qiA capacitance layered for the ith insulation model; u shapeiVoltage layered for the ith insulation model; tg δ is a dielectric loss tangent value of the insulating material; lambda [ alpha ]1The ratio of the metal sheath loss and the conductor loss can be obtained by an empirical formula, and is generally 0.03.
It should be noted that, in the above-mentioned embodiment of the apparatus for determining the optimal number of insulating layers in the cable thermal circuit model, contents such as a state equation of the equivalent thermal circuit model and calculation of the node temperature are listed, and since the same concept is based on the foregoing method embodiment of the present invention, technical effects brought by the method embodiment of the present invention are the same as those of the foregoing method embodiment of the present invention, and specific contents may be referred to the description in the method embodiment of the present invention, and are not described again here.
In addition, in the above-mentioned exemplary embodiment of the apparatus for determining the optimal number of insulating layers in the cable thermal circuit model, the logical division of each program module is only an example, and in practical applications, the above-mentioned function allocation may be performed by different program modules according to needs, for example, due to the configuration requirements of corresponding hardware or the convenience of implementation of software, that is, the internal structure of the apparatus for determining the optimal number of insulating layers in the cable thermal circuit model is divided into different program modules to perform all or part of the above-described functions.
It will be understood by those skilled in the art that all or part of the processes of the methods of the above embodiments may be implemented by a computer program, which is stored in a computer readable storage medium and sold or used as a stand-alone product. The program, when executed, may perform all or a portion of the steps of the embodiments of the methods described above. In addition, the storage medium may be provided in a computer device, and the computer device further includes a processor, and when the processor executes the program in the storage medium, all or part of the steps of the embodiments of the methods described above can be implemented. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments. It will be understood that the terms "first," "second," and the like as used herein are used herein to distinguish one object from another, but the objects are not limited by these terms.
The above-described examples merely represent several embodiments of the present invention and should not be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A method for determining the optimal number of insulating layers in a cable hot-circuit model is characterized by comprising the following steps:
s1, determining at least two insulation model layers by the insulation layer of the cable, and establishing a cable hot circuit model according to the at least two insulation model layers;
s2, determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model, and solving the state equation to obtain the temperature of each node in the cable thermal circuit model;
s3, calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node;
s4, detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, and returning to the step S2; if so, acquiring the number of layered layers of the current insulation model as the optimal number of insulating layers in the cable hot circuit model; wherein the temperature measuring instrument is selected from a thermocouple thermometer, a resistance thermometer and a radiation thermometer.
2. The method for determining the optimal number of layers of insulation in a cable thermal path model according to claim 1, wherein determining at least two insulation model layers from the insulation layers of the cable comprises:
the insulation layer of the cable is divided into at least two insulation model layers in a manner of equal thickness, equal thermal capacitance or thickness ratio.
3. The method for determining the optimal number of layers of insulation layers in a cable thermal circuit model according to claim 1, wherein the step of establishing the cable thermal circuit model in layers according to the at least two insulation models comprises:
determining a model layer of the cable by adopting a heat transfer principle, wherein the model layer comprises a conductor layer, an insulating layer, a wrapping layer, an air gap layer, a metal sheath layer, an outer sheath layer and an outer surface layer which are sequentially distributed from inside to outside;
and establishing a cable hot circuit model according to the model layers.
4. The method of claim 3, wherein determining the model hierarchy for the cable using thermal principles comprises:
in addition to the insulation model layering, each model layering is determined by points on each isotherm on the axial cross-section of the cable.
5. The method for determining the optimal number of insulating layers in the cable thermal circuit model according to claim 3 or 4, wherein the determining the state equation corresponding to the cable thermal circuit model at the number of insulating layers layered in the current insulating model comprises:
determining a first heat transfer matrix A and a second heat transfer matrix B of the cable thermal circuit model under the layered number of the current insulation model as follows:
constructing a state equation of the cable thermal circuit model according to the first thermal matrix A and the second thermal matrix B:
P＝[P1 P′1 P2 … Pn-5 Pn-4 0 0 Pn-1 0 tn+1/Re]T；
wherein, t0Indicating the temperature of the conductor layer; t is t1～tn-4Representing the temperature of each insulation model layer; t is tn-3Indicating the temperature of the wrapping; t is tn-2Represents the temperature of the air gap layer; t is tn-1Represents the temperature of the metal sheath layer; t is tnRepresents the temperature of the outer jacket layer; t is tn+1Indicating the temperature of the outer skin layer; c1Representing the heat capacity of the conductor layer; c1′、C2～Cn-4Representing the heat capacity of each insulation model layer; cn-3Representing the heat capacity of the wrapping layer; cn-2Represents the thermal capacity of the air gap layer; cn-1The thermal capacity of the metal sheath layer; cnRepresents the thermal capacity of the outer sheath; ceRepresents the heat capacity of the outer epidermal layer; r1Represents the thermal resistance of the conductor layer; r1’、R2～Rn-4Representing the thermal resistance of each insulation model layer; rn-3Representing the thermal resistance of the wrapping layer; rn-2Represents the thermal resistance of the air gap layer; rn-1Represents the thermal resistance of the metal sheath layer; rnRepresenting the thermal resistance of the outer jacket; reRepresents the thermal resistance of the outer skin layer; p1Representing loss of the conductor layer; p1′、P2～Pn-4Representing the dielectric loss of each insulation model layer; pn-1Indicating the loss of the metal sheath layer.
6. The method of determining the optimal number of layers of insulation in a cable thermal circuit model according to claim 5, wherein prior to determining the first heat transfer matrix A and the second heat transfer matrix B of the cable thermal circuit model at the number of layers of the current insulation model layer, further comprising:
and (3) equating each model layer to a cylindrical wall structure, and calculating the thermal resistance R and the thermal capacity C of each model layer of the cable with unit length:
wherein, lambda is the heat conductivity coefficient of the material corresponding to the model layering, c is the volume specific heat capacity of the material corresponding to the model layering, and r1Is the inner radius of the cable structure, r2Is the outer radius of the cable structure;
calculating the dielectric loss of the conductor:
P1＝I2Rz；
calculating the dielectric loss of each insulation model layer:
and calculating the circulation loss of the metal sheath layer:
Pn-1＝λ1P1
wherein I represents the current loaded by the cable conductor; rzAc resistance per unit length of conductor; omega is the frequency of the cable loading load; qiA capacitance layered for the ith insulation model; u shapeiVoltage layered for the ith insulation model; tg δ is a dielectric loss tangent value of the insulating material; lambda [ alpha ]1Is the ratio of the dielectric loss of the metal sheath layer to the dielectric loss of the conductor.
7. An apparatus for determining an optimal number of layers of insulation in a cable thermal path model, comprising:
the hot circuit model building module is used for determining at least two insulation model layers by an insulation layer of the cable and building a cable hot circuit model according to the at least two insulation model layers;
the temperature calculation module is used for determining a state equation corresponding to the cable thermal circuit model under the layered layers of the current insulation model and solving the state equation to obtain the temperature of each node in the cable thermal circuit model;
the temperature difference calculation module is used for calculating the temperature difference of each two adjacent insulation model layers according to the temperature of each node; and the number of the first and second groups,
the iterative optimization module is used for detecting whether the temperature difference of two adjacent insulation model layers is smaller than the precision value of the temperature measuring instrument, if not, adding the set layer number to the layer number of the current insulation model layer, updating the layer number of the insulation model layer, and returning to the temperature calculation module; if so, acquiring the number of layered layers of the current insulation model as the optimal number of insulating layers in the cable hot circuit model; wherein the temperature measuring instrument is selected from a thermocouple thermometer, a resistance thermometer and a radiation thermometer.
8. The apparatus of claim 7, wherein the thermal circuit modeling module comprises:
the insulation layering submodule is used for dividing the insulation layer of the cable into at least two insulation model layers according to the mode of equal thickness, equal heat capacity or thickness ratio;
the model building submodule is used for determining a model layer of the cable by adopting a heat transfer principle, and the model layer comprises a conductor layer, an insulating layer, a wrapping layer, an air gap layer, a metal sheath layer, an outer sheath layer and an outer surface layer which are sequentially distributed from inside to outside; and establishing a cable hot circuit model according to the model layers.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.
10. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the steps of the method of any of claims 1 to 6 are performed when the program is executed by the processor.
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