WO2019144657A1

WO2019144657A1 - Method for dynamically determining optimal number of insulating layers in transient thermal path of high-voltage cable

Info

Publication number: WO2019144657A1
Application number: PCT/CN2018/111212
Authority: WO
Inventors: 刘刚; 韩卓展
Original assignee: 华南理工大学
Priority date: 2018-01-29
Filing date: 2018-10-22
Publication date: 2019-08-01
Also published as: ZA202005139B; CN108388700A

Abstract

A method for dynamically determining an optimal number of insulating layers in a transient thermal path of a high-voltage cable, comprising the following steps: S1, choosing a high-voltage cable needed; S2, building a transient thermal path model and corresponding mathematical model of the cable body; S3, determining each parameter in the models; S4, editing a calculation program in the mathematical model in S1; S5, importing each model parameter, calculating a temperature value of a conductor in different numbers of layers at the same moment, and solving a change rate of the conductor temperature along with the number of layers, wherein when the change rate reaches a lower limit of a set change rate, the number of layers at this time is the optimal number of layers; S6, determining the optimal number of insulating layers at the next moment based on a calculation result in S5; and S7, repeating S5 and S6 to obtain a real-time optimal number of of insulating layers in a transient thermal path of the high-voltage cable. By means of the method, a better transient thermal path model can be obtained, and the model has a real-time correction property, laying an important foundation for accurate calculation of the carrying capacity of a cable.

Description

Method for dynamically determining optimal insulation layer number in transient thermal path of high voltage cable

Technical field

The invention relates to the technical field of current carrying capacity calculation of high voltage cables, in particular to a method for dynamically determining the optimal number of insulation layers in a transient thermal path of a high voltage cable.

Background technique

With the large increase in electricity consumption in cities, and in order to improve the utilization of urban space, urban transmission networks use large-capacity cable lines to transmit electricity. In recent years, some cable lines in the central city have gradually approached or even exceeded their designed current carrying capacity, seriously threatening the safe operation of the power system. The expansion of cable lines is costly, long-term, and subject to land acquisition and other issues, and the line overload problem cannot be solved in a short period of time. Therefore, the expansion of cable lines is imperative, and the basis for capacity expansion is to accurately calculate the current carrying capacity of cable lines.

At present, the calculation of cable current carrying capacity mainly includes numerical solution and analytical method. The former includes finite element method and boundary element method, and the latter includes IEC 60287, IEC 60853, and heat path. In the calculation of the transient process, the thermal path method needs to construct the transient thermal path model according to the cable structure size and physical property parameters and determine the parameters, and the treatment of the insulation layer is an extremely important part.

Zhou Fan et al. used four different layering methods for the insulation layer in the transient thermal path model processing to explore the influence of layering type and layer number on the current carrying capacity calculation. It was found that the insulation layering can improve the calculation accuracy of the cable current carrying capacity. . However, the study only stayed at the qualitative level, and did not quantitatively give the optimal number of layers of insulation. Moreover, it did not analyze the influence of the change of the number of layers at different times on the current carrying capacity during the whole temperature rise process.

Summary of the invention

The object of the present invention is to overcome the shortcomings and deficiencies of the prior art, and to provide a method for dynamically determining the optimal number of insulation layers in a transient thermal path of a high voltage cable, and not only a method for quantitatively determining the optimal number of layers of insulation, Moreover, the variation of the optimal number of layers in different temperature rise times is considered, and the purpose of dynamically and real-time determining the optimal number of layers in the transient thermal path of the high-voltage cable is realized.

The object of the present invention is achieved by the following technical solution: a method for dynamically determining the optimal number of insulation layers in a transient thermal path of a high voltage cable, comprising the following steps:

S1, selecting a required high-voltage cable, determining its size and physical property parameters of each layer;

S2, constructing a cable body transient thermal path model and a corresponding mathematical model, the steps are specifically:

S201, constructing a transient thermal path model of the cable body;

S202. Construct a mathematical model corresponding to the heat path model;

S3. Determine each parameter in the transient thermal path model, and the step is specifically:

S301, determining the time-invariant parameter;

S302, determining a time-varying parameter;

S4, according to the mathematical model in step S2, using MATLAB to edit the calculation program;

S5, importing each model parameter, using a loop statement, calculating the temperature value of the conductor under different layer numbers at a certain time, and solving the rate of change of the conductor temperature with the number of layers, when the rate of change reaches the lower limit of the set rate of change, at this time, layering The number is the optimal number of layers;

S6, based on the calculation result in S5, and repeating the steps in S5 to determine the optimal number of layers of the insulation layer at the next moment;

S7, repeat S5, S6, the real-time optimal stratification number of the insulation layer in the transient hot path of the high-voltage cable can be obtained.

Preferably, in step S1: according to the calculation requirement, the high-voltage cable of the target model is selected as a calculation prototype, and parameters for determining the structure of each layer of the relevant cable include: size data, material properties, thermal conductivity, specific heat capacity, and resistivity.

Preferably, the step S201 is specifically:

According to the characteristics of the cable line and the material of each layer, the transient thermal path model is based on the following assumptions: 1) the cable length is infinite relative to the cable radius, and the axial heat transfer is ignored for the long straight cable section; 2) in general laying Conditions, especially under experimental conditions, the external environment of the cable is uniform, the material of each layer of the cable is isotropic, and the center is symmetrical; 3) the heat capacity of each layer of material does not change with time space; 4) the inner and outer shielding layers are thin and thermal parameters Similar to the insulating layer, so the three are combined with the same layer of processing, 5) the dielectric loss is negligible in terms of relative conductor loss, and the sheath loss is ignored in the case of single-ended grounding;

Based on the above assumptions, the cable body thermal path is simplified into a one-dimensional heat path model along the radial direction, while the insulation layer is treated by equal thickness stratification, the cable thermal path model is a distributed parameter transient thermal path model; and the setting: P represents the cable conductor Loss; n-3 indicates the number of layers of the insulation layer; T ₁ indicates the cable conductor temperature; T ₂ -T _n-3 indicates the cable insulation layer, including the inner and outer shield delamination temperatures; T _n-2 indicates the winding temperature T _n-1 denotes the temperature of the air gap layer; T _n denotes the temperature of the aluminum sheath; T _o denotes the temperature of the cable skin; C ₁ ' denotes the heat capacity of the cable conductor; C ₁ ', C ₂ - C _n-3 denote the insulation of the cable , containing the heat capacity of each layer of the inner and outer shield layers; C _n-2 represents the heat capacity around the cladding; C _n-1 represents the heat capacity of the air gap layer; C _n ' represents the heat capacity of the aluminum sheath; C _n ′′ indicates the outside Sheath heat capacity; R ₁ —R _n-3 denotes the cable insulation layer, including the inner and outer shields of each layer of thermal resistance; R _n-2 denotes the thermal resistance of the cladding layer; R _n-1 denotes the thermal resistance of the air gap layer; R _n represents the thermal resistance of the outer sheath.

Further, the step S202 is specifically:

Write a node equation for each node in the heat path and convert it into a matrix representation:

Where C ₁ =C ₁ '+C ₁ ′′, C _n =C _n '+C _n ′′, and the matrices are as follows:

T=[T ₁ T ₂ T ₃ L T _n ] ^T

Preferably, the step S301 is specifically:

In the transient thermal path model, based on the assumption, the time-invariant parameters include the heat capacity and thermal resistance of each layer of material, and the heat capacity of each layer is calculated according to the IEC 60287 standard;

The formula for calculating the heat capacity per unit length is as follows:

Where: d ₂ is the calculated layer outer diameter; d ₁ is the calculated layer inner diameter; δ is the calculated volumetric heat capacity of the layer material;

The formula for calculating the thermal resistance per unit length is as follows:

Where: d ₁ represents the inner diameter of the calculation layer; d ₂ represents the outer diameter of the calculation layer.

Preferably, the step S302 is specifically:

In the transient thermal path model, the time-varying parameters include conductor loss and cable surface temperature, wherein the cable surface temperature is measured by the thermocouple in real time, and the conductor loss changes with the change of the conductor resistance;

The conductor loss per unit length is calculated as follows:

P=I ² r

Where: P is the heating power of the conductor; I is the load current; r is the AC resistance per unit length of the conductor;

Calculation formula of AC resistance per unit length at conductor operating temperature:

r=r'(1+Y _s +Y _p )

Where: r is the alternating current resistance of the conductor of unit length; r' is the direct current resistance of the conductor of unit length; Y _s is the skin effect factor; Y _p is the adjacent effect factor;

The formula for calculating the DC resistance of a conductor per unit length:

r'=r ₀ ×[1+α(θ-20)]

Where: r ₀ is the DC resistance of the cable conductor per unit length at 20 ° C; α is the temperature coefficient of resistance of the conductor; θ is the operating temperature;

Skin effect factor Y _s calculation formula:

Where: k _s is the empirical value; f is the current frequency.

Preferably, the step S4 is specifically: according to the equations listed in the series of nodes and the calculation method of each parameter thereof, the calculation program of the matrix A, B, and P and the solution program of the differential equations are edited by using MATLAB software.

Preferably, the step S5 is specifically:

Step 1: Select a certain moment as the starting point of calculation, import the calculation parameters at the moment, and proceed to the next step;

Step 2: Set the number of layers to 1 layer, calculate the conductor temperature value T ₁₁ at this time, and proceed to the next step;

Step 3: Set the number of layers to 2 layers, calculate the conductor temperature value T ₁₂ at this time, calculate the rate of change of temperature with the number of layers compared with the previous layer, and take the absolute value |T ₁₁ -T ₁₂ |, if | T ₁₁ -T ₁₂ | is less than the set value, then the optimal number of layers of the insulating layer is 2, ending, otherwise it proceeds to the next step;

Step 4: Take the layer number variable i=3 and proceed to the next step;

Step 5: Set the number of layers to i, calculate the conductor temperature value T _1i at this time, calculate the rate of change of temperature with the number of layers compared with the previous layer, and take the absolute value |T _1(i-1) -T _1i |, if |T _1(i-1) -T _1i | is less than the set value, the optimal number of layers of the insulating layer is i, end, otherwise proceed to the next step;

Step 6: i=i+1, return to step 5.

Preferably, the step S6 is specifically: step S5 determines the conductor temperature calculation result under the optimal layer number as the conductor temperature import value calculated at the next time, and then imports the skin temperature value at the next moment, and the other imported parameters remain. Without changing, the steps in step S5 are repeated to obtain the optimum number of layers of the insulating layer at the next moment.

Preferably, the step S7 is specifically: the calculation of the conductor temperature at each next time is based on the calculation result of the previous time, and the steps in the step S5 and the step S6 are continuously repeated to obtain the insulation at different times during the whole temperature rise process. The optimal number of layers in the layer, that is, the optimal number of layers of the insulating layer in the transient hot path of the high-voltage cable is determined in real time.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The invention optimizes the treatment of the insulation layer in the transient hot road model of the high-voltage cable, and can obtain a more optimized transient thermal path model. Considering the time-varying factor, the method for determining the optimal stratification of the insulation layer is given and the model is real-time. The correction feature lays an important foundation for accurate calculation of cable current carrying capacity.

DRAWINGS

Figure 1 is a schematic cross-sectional view of a high voltage cable of an embodiment;

2 is a schematic diagram of a distributed parameter transient thermal path model of an embodiment.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

Example 1

A method for dynamically determining the optimal number of layers of insulation in a transient thermal path of a high voltage cable includes the following steps:

S1, select the required high-voltage cable, determine its size and material properties of each layer.

According to the calculation needs, select a certain type of high-voltage cable as the calculation prototype. The general structure diagram of the high-voltage cable is shown in Figure 1. The data is determined to determine the dimensional data, material properties, thermal conductivity, specific heat capacity and resistivity of the relevant layers of the relevant cable. and many more.

S2. Construct a transient thermal path model of the cable body and a corresponding mathematical model.

S201, constructing a transient thermal path model of the cable body;

According to the characteristics of the cable line and the material of each layer, the transient thermal path model is based on the following assumptions: 1) the cable length is infinite relative to the cable radius, and the axial heat transfer is ignored for the long straight cable section; 2) in general laying Conditions, especially under experimental conditions, the external environment of the cable is uniform, the material of each layer of the cable is isotropic, and the center is symmetrical; 3) the heat capacity of each layer of material does not change with time space; 4) the inner and outer shielding layers are thin and thermal parameters Similar to the insulating layer, so the three are combined with the same layer of processing, 5) relative to the loss of the conductor, the dielectric loss is negligible, and the sheath loss is ignored in the case of single-ended grounding. Based on the above assumptions, the cable body thermal path is simplified into a one-dimensional heat path model along the radial direction, while the insulating layer is processed by equal thickness stratification, and the distributed parameter transient thermal path model is shown in FIG. 2 .

Where: P represents the cable conductor loss, W; n-3 represents the number of layers of the insulation layer; T ₁ represents the cable conductor temperature, ° C; T _{2 -} T _n-3 represents the cable insulation layer (including the inner and outer shield) layers Temperature, °C; T _n-2 represents the wrapping temperature, ° C; T _n-1 represents the air gap temperature, ° C; T _n represents the aluminum sheath temperature, ° C; T _o represents the cable skin temperature, ° C; C ₁ ' Indicates the heat capacity of the cable conductor, J/K; C ₁ ′′, C ₂ — C _n-3 represents the heat capacity of each layer of the cable insulation layer (including the inner and outer shield layers), J/K; C _n-2 represents the package layer heat _{capacity, J / K; C n-} 1 represents the heat capacity of air gap, J / K; C _n 'represents aluminum sheath heat capacity, J / K; C _n "represents the outer jacket heat capacity, J / K ; R ₁ —R _n-3 denotes the thermal resistance of each layer of the cable insulation layer (including inner and outer shields), K·m/W; R _n-2 denotes the thermal resistance of the cladding, K·m/W; R _{n -1} represents the thermal resistance of the air gap layer, K·m/W; R _n represents the thermal resistance of the outer sheath, K·m/W.

S202. Construct a mathematical model corresponding to the heat path model;

The thermal path has an analysis method similar to that of the circuit. The node equations are written for each node in the thermal path and converted into a matrix representation:

T=[T ₁ T ₂ T ₃ L T _n ] ^T

S3. Determine parameters in the transient thermal path model.

S301, determination of time-invariant parameters

In the transient thermal path model, based on the assumption, the time-invariant parameters include the heat capacity and thermal resistance of each layer of material, and the heat capacity of each layer is calculated according to the IEC 60287 standard.

The formula for calculating the heat capacity per unit length is as follows:

Where: d ₂ is the calculated layer outer diameter, mm; d ₁ is the calculated layer inner diameter, mm; δ is the calculated volumetric heat capacity of the layer material, J / K · m ³ .

Where: d ₁ represents the inner diameter of the calculated layer, mm; d ₂ represents the outer diameter of the calculated layer, mm.

S302, determination of time-varying parameters

In the transient thermal path model, time-varying parameters include conductor loss and cable surface temperature, where the cable surface temperature is measured in real time by a thermocouple, and the conductor loss changes as the conductor resistance changes.

The conductor loss per unit length is calculated as follows:

P=I ² r

Where: P is the heating power of the conductor, W; I is the load current, A; r is the AC resistance per unit length of conductor, Ω.

r=r'(1+Y _s +Y _p )

Where: r is the AC resistance of the conductor per unit length, Ω; r' is the DC resistance of the conductor per unit length, Ω; Y _s is the skin effect factor; Y _p is the adjacent effect factor.

The formula for calculating the DC resistance of a conductor per unit length:

r'=r ₀ ×[1+α(θ-20)]

Where: r ₀ is the DC resistance of the cable conductor per unit length at 20 ° C, Ω; α is the temperature coefficient of resistance of the conductor, 1 / K; standard soft copper: α = 0.00393, depending on the type of insulation material used; θ is the operating temperature, K.

Skin effect factor Y _s calculation formula:

Where: k _s is the empirical value, which can be taken as 1 for a dry copper round wire; f is the current frequency, Hz.

S4, according to the mathematical model in S1, using MATLAB to edit the calculation program;

According to the equations listed in the series of nodes and the calculation methods of each parameter, the calculation program of matrix A, B, P and the solution program of differential equations are edited by MATLAB software.

S5, importing each model parameter, using a loop statement, calculating the temperature value of the conductor under different layer numbers at a certain time, and solving the rate of change of the conductor temperature with the number of layers, when the rate of change reaches the lower limit of the set rate of change, at this time, layering The number is the optimal number of layers.

specific:

Step 1: Select a certain moment as the starting point of calculation, and introduce the calculation parameters of the conductor temperature, the skin temperature, the thermal resistivity of each layer of material and the specific heat capacity at the moment, and proceed to the next step;

Step 4: Take the layer number variable i=3 and proceed to the next step;

Step 6: i=i+1, return to step 5.

S6. Based on the calculation result in S5, repeat the steps in S5 to determine the optimal number of layers of the insulation layer at the next moment.

In step S5, the conductor temperature calculation result under the optimal layer number is determined as the conductor temperature introduction value calculated at the next time, and then the skin temperature value at the next moment is imported, and the other imported parameters remain unchanged, and step S5 is repeated to obtain the next step. The optimal number of layers of insulation at a time.

The calculation of the conductor temperature at each next moment is based on the calculation result at the previous moment. Repeating steps S5 and S6 are repeated to obtain the optimal number of layers of the insulation layer at different times during the entire temperature rise process, that is, real-time and dynamic. Determine the optimal number of layers of insulation in the transient thermal path of the high voltage cable.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and combinations thereof may be made without departing from the spirit and scope of the invention. Simplifications should all be equivalent replacements and are included in the scope of the present invention.

Claims

A method for dynamically determining the optimal number of layers of insulation in a transient thermal path of a high voltage cable, characterized in that it comprises the following steps:

S1, selecting a required high-voltage cable, determining its size and physical property parameters of each layer;

S2, constructing a cable body transient thermal path model and a corresponding mathematical model, the steps are specifically:

S201, constructing a transient thermal path model of the cable body;

S202. Construct a mathematical model corresponding to the heat path model;

S3. Determine each parameter in the transient thermal path model, and the step is specifically:

S301, determining the time-invariant parameter;

S302, determining a time-varying parameter;

S4, according to the mathematical model in step S2, using MATLAB to edit the calculation program;

S5, importing each model parameter, using a loop statement, calculating the temperature value of the conductor under different layer numbers at a certain time, and solving the rate of change of the conductor temperature with the number of layers, when the rate of change reaches the lower limit of the set rate of change, at this time, layering The number is the optimal number of layers;

S6, based on the calculation result in S5, and repeating the steps in S5 to determine the optimal number of layers of the insulation layer at the next moment;

S7, repeat S5, S6, the real-time optimal stratification number of the insulation layer in the transient hot path of the high-voltage cable can be obtained.
The method for dynamically determining the optimal number of insulation layers in a transient thermal path of a high voltage cable according to claim 1, wherein in step S1: selecting a high voltage cable of the target model as a calculation prototype according to calculation requirements, and determining the relevant cable. The parameters of each layer structure include: size data, material properties, thermal conductivity, specific heat capacity, and electrical resistivity.
The method for dynamically determining the optimal number of layers in the transient thermal path of the high-voltage cable according to claim 1, wherein the step S201 is specifically:

According to the characteristics of the cable line and the material of each layer, the transient thermal path model is based on the following assumptions: 1) the cable length is infinite relative to the cable radius, and the axial heat transfer is ignored for the long straight cable section; 2) in general laying Conditions, especially under experimental conditions, the external environment of the cable is uniform, the material of each layer of the cable is isotropic, and the center is symmetrical; 3) the heat capacity of each layer of material does not change with time space; 4) the inner and outer shielding layers are thin and thermal parameters Similar to the insulating layer, so the three are combined with the same layer of processing, 5) the dielectric loss is negligible in terms of relative conductor loss, and the sheath loss is ignored in the case of single-ended grounding;

Based on the above assumptions, the cable body thermal path is simplified into a one-dimensional heat path model along the radial direction, while the insulation layer is treated by equal thickness stratification, the cable thermal path model is a distributed parameter transient thermal path model; and the setting: P represents the cable conductor Loss; n-3 indicates the number of layers of the insulation layer; T 1 indicates the cable conductor temperature; T 2 -T n-3 indicates the cable insulation layer, including the inner and outer shield delamination temperatures; T n-2 indicates the winding temperature T n-1 represents the air gap layer temperature; T n represents the aluminum sheath temperature; T o represents the cable skin temperature; C 1 ' represents the cable conductor heat capacity; C 1 ”, C 2 — C n-3 represents the cable insulation layer Containing the heat capacity of each layer of the inner and outer shield layers; C n-2 means the heat capacity around the cladding; C n-1 means the heat capacity of the air gap layer; C n ' indicates the heat capacity of the aluminum sheath; C n ” means outside Sheath heat capacity; R 1 —R n-3 denotes the cable insulation layer, including the inner and outer shields of each layer of thermal resistance; R n-2 denotes the thermal resistance of the cladding layer; R n-1 denotes the thermal resistance of the air gap layer; R n represents the thermal resistance of the outer sheath.
The method for dynamically determining the optimal number of layers in the transient thermal path of the high-voltage cable according to claim 3, wherein the step S202 is specifically:

Write a node equation for each node in the heat path and convert it into a matrix representation:

Where C 1 =C 1 '+C 1 ”, C n =C n '+C n ”, and the matrices are as follows:

T=[T 1 T 2 T 3 L T n ] T
The method for dynamically determining the optimal number of layers in the transient thermal path of the high-voltage cable according to claim 1, wherein the step S301 is specifically:

In the transient thermal path model, based on the assumption, the time-invariant parameters include the heat capacity and thermal resistance of each layer of material, and the heat capacity of each layer is calculated according to the IEC 60287 standard;

The formula for calculating the heat capacity per unit length is as follows:

Where: d 2 is the calculated layer outer diameter; d 1 is the calculated layer inner diameter; δ is the calculated volumetric heat capacity of the layer material;

The formula for calculating the thermal resistance per unit length is as follows:

Where: d 1 represents the inner diameter of the calculation layer; d 2 represents the outer diameter of the calculation layer.
The method for dynamically determining the optimal number of layers in the transient hot path of the high-voltage cable according to claim 1, wherein the step S302 is specifically:

In the transient thermal path model, the time-varying parameters include conductor loss and cable surface temperature, wherein the cable surface temperature is measured by the thermocouple in real time, and the conductor loss changes with the change of the conductor resistance;

The conductor loss per unit length is calculated as follows:

P=I 2 r

Where: P is the heating power of the conductor; I is the load current; r is the AC resistance per unit length of the conductor;

Calculation formula of AC resistance per unit length at conductor operating temperature:

r=r'(1+Y s +Y p )

Where: r is the alternating current resistance of the conductor of unit length; r' is the direct current resistance of the conductor of unit length; Y s is the skin effect factor; Y p is the adjacent effect factor;

The formula for calculating the DC resistance of a conductor per unit length:

r'=r 0 ×[1+α(θ-20)]

Where: r 0 is the DC resistance of the cable conductor per unit length at 20 ° C; α is the temperature coefficient of resistance of the conductor; θ is the operating temperature;

Skin effect factor Y s calculation formula:

Where: k s is the empirical value; f is the current frequency.
The method for dynamically determining the optimal number of layers in the transient hot path of the high-voltage cable according to claim 4, wherein the step S4 is specifically:

According to the equations listed in the series of nodes and the calculation methods of each parameter, the calculation program of matrix A, B, P and the solution program of differential equations are edited by MATLAB software.
The method for dynamically determining the optimal number of layers of insulation in the transient thermal path of the high-voltage cable according to claim 1, wherein the step S5 is specifically:

Step 1: Select a certain moment as the starting point of calculation, import the calculation parameters at the moment, and proceed to the next step;

Step 2: Set the number of layers to 1 layer, calculate the conductor temperature value T 11 at this time, and proceed to the next step;

Step 3: Set the number of layers to 2 layers, calculate the conductor temperature value T 12 at this time, calculate the rate of change of temperature with the number of layers compared with the previous layer, and take the absolute value |T 11 -T 12 |, if | T 11 -T 12 | is less than the set value, then the optimal number of layers of the insulating layer is 2, ending, otherwise it proceeds to the next step;

Step 4: Take the layer number variable i=3 and proceed to the next step;

Step 5: Set the number of layers to i, calculate the conductor temperature value T 1i at this time, calculate the rate of change of temperature with the number of layers compared with the previous layer, and take the absolute value |T 1(i-1) -T 1i |, if |T 1(i-1) -T 1i | is less than the set value, the optimal number of layers of the insulating layer is i, end, otherwise proceed to the next step;

Step 6: i=i+1, return to step 5.
The method for dynamically determining the optimal number of layers in the transient thermal path of the high-voltage cable according to claim 8, wherein the step S6 is specifically:

Determine the conductor temperature calculation result under the optimal layer number according to claim 8 as the conductor temperature introduction value calculated at the next time, and then import the skin temperature value at the next moment, and the other imported parameters remain unchanged, repeating the claim 8 In each step, the optimal number of layers of the insulating layer at the next moment is obtained.
The method for dynamically determining the optimal number of layers in the transient thermal path of the high-voltage cable according to claim 9, wherein the step S7 is specifically:

The calculation of the conductor temperature at each next moment is based on the calculation result at the previous moment, and the steps in claims 8 and 9 are continuously repeated to obtain the optimum number of layers of the insulating layer at different times during the entire temperature rise process, that is, The optimal number of layers of the insulation layer in the transient thermal path of the high voltage cable is determined in real time.