CN104730388A - Method and device for evaluating influence of environment thermal resistance on three-core cable core temperature - Google Patents

Abstract

The invention relates to a method and a device for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable. The method comprises the steps of: obtaining the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying according to the thermal circuit model of the three-core cable; obtaining the wire core of the three-core cable according to the thermal circuit model of the three-core cable temperature; if the three-core cable is laid by air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the environmental thermal resistance under air laying; if the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the thermal resistance of the environment under soil laying. The invention can accurately analyze the influence degree of environmental thermal resistance on the core temperature of the three-core cable; according to the sensitivity of air laying or soil laying, when the three-core cable is loaded with a large current, especially when the three-core cable is laid by air radiation , Increase the monitoring of the ambient temperature, so as to ensure the safe and stable operation of the power cable.

Description

Method and device for evaluating the influence of environmental thermal resistance on the core temperature of three-core cables

technical field

The invention relates to the technical field of power cables, in particular to an evaluation method for the influence of environmental thermal resistance on the core temperature of a three-core cable and an evaluation device for the influence of environmental thermal resistance on the core temperature of a three-core cable.

Background technique

The temperature of the wire core during the operation of the power cable is the basis for determining whether the power cable has reached the current carrying capacity. The cable ampacity is an important dynamic operating parameter affected by environmental conditions and load factors during cable operation, and its importance affects the safety and reliability of transmission lines, economical and reasonable operation, and cable life. If the ampacity of the cable is too large, the working temperature of the cable core temperature will exceed the allowable value, which will affect the life of the insulation; if the ampacity of the cable is too small, the copper or aluminum of the cable core will not be fully protected. use, resulting in unnecessary waste.

At present, there are many methods for estimating the current carrying capacity of cables through the core temperature, such as the IEC (International Electrotechnical Commission) standard, thermal circuit method, simulated thermal charge method, finite element method and finite difference method. The IEC60287 standard is currently the most recognized and widely used analytical algorithm for calculating the ampacity of cables using the principle of heat transfer. The thermal circuit model proposed by many scholars is basically an improvement on the thermal circuit model proposed by the IEC standard. . However, since the current-carrying capacity of the cable line in actual operation is affected by many factors, such as the external environment (ambient temperature and environmental thermal resistance, etc.), the IEC60287 series standards ignore many external factors in the calculation of the current-carrying capacity, so it cannot be accurately calculated. Ampacity. In addition, the research on applying the sensitivity analysis of the core temperature to the external environment to the single-core cable at home and abroad has become mature. It is far more complex than single-core cables, so the sensitivity analysis of existing single-core cables cannot be applied to three-core cables. In order to study the influence of the external environment on the core temperature and ensure the safe operation of power cables, it is urgent to provide a sensitivity evaluation method for three-core cables.

Contents of the invention

Based on this, it is necessary to address the above problems and provide a method and device for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable, which can analyze the degree of influence of environmental thermal resistance on the core temperature of a three-core cable.

A method for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable, comprising steps:

According to the thermal circuit model of the three-core cable, the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying is obtained;

According to the thermal circuit model of the three-core cable, the core temperature of the three-core cable is obtained;

If the three-core cable is laid by air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying;

If the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the ambient thermal resistance under soil laying;

in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance.

An evaluation device for the influence of environmental thermal resistance on the core temperature of a three-core cable, comprising:

The environmental thermal resistance determination module is used to obtain the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying according to the thermal circuit model of the three-core cable;

The wire core temperature determination module is used to obtain the wire core temperature of the three-core cable according to the thermal circuit model of the three-core cable;

The first sensitivity determination module is used for when the three-core cable is laid in air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying;

The second sensitivity determination module is used for when the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the ambient thermal resistance under soil laying;

in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance.

The method and device for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable in the present invention analyze the influence degree of environmental thermal resistance on the temperature of the cable core through the concept of sensitivity in biology, that is, the effect of the temperature of the cable core on the environmental thermal resistance Sensitivity size. Experimental research shows that the invention can accurately analyze the degree of influence of environmental thermal resistance on the core temperature of a three-core cable. In addition, according to the sensitivity of air laying or soil laying according to the present invention, it is obtained that with the increase of the loading current, the sensitivity of the core temperature to the thermal resistance of the external environment is increasing, so when the loading current of the three-core cable is large, Especially when the laying of the three-core cable is air radiation, the monitoring of the ambient temperature should be strengthened to ensure the safe and stable operation of the power cable.

Description of drawings

Fig. 1 is the schematic flow sheet of the method embodiment of the present invention;

Fig. 2 is a schematic diagram of a three-core cable steady-state thermal circuit model of the present invention;

Fig. 3 is that the present invention's experimental measurement 10kV three-core cable reaches steady state when wire core and skin temperature experiment value;

Fig. 4 is a schematic structural diagram of an embodiment of the device of the present invention.

Detailed ways

The specific implementation of the method for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable according to the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, an evaluation method for the influence of environmental thermal resistance on the core temperature of a three-core cable includes steps:

S110, according to the thermal circuit model of the three-core cable, obtain the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying;

S120. Obtain the core temperature of the three-core cable according to the thermal circuit model of the three-core cable;

S130. If the three-core cable is laid by air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying;

S140. If the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the ambient thermal resistance under soil laying;

in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance.

The three-core cable of the present invention may be a 10kV (kilovolt) three-core cable or the like. As shown in Figure 2, it is a schematic diagram of the steady-state thermal circuit model of a three-core cable. In the thermal circuit model of a three-core cable, according to IEC60287, it can be known that:

When laying in air, the ambient thermal resistance _T4 is:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, π in formula (1) represents the circumference ratio; D _e represents the outer diameter of the three-core cable, and the unit can be m (meter); h represents the heat transfer coefficient; Δθ _s represents the temperature rise of the three-core cable skin, and the unit is K (Kelvin) .

When laying in soil, the ambient thermal resistance T ₄ is:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, π in formula (2) represents the circumference ratio; ρ _T represents the thermal resistivity of the soil, and the unit can be K m/W (Kelvin m/watt); L represents the distance from the axis of the three-core cable to the ground surface, and the unit can be mm (mm); D _e represents the outer diameter of the three-core cable, and the unit can be mm; ln represents a logarithmic function.

Compared with the node voltage method in the circuit, the temperature difference balance equation is listed according to Figure 2:

θ ₁ -θ ₂ =T ₁ /3×(3I ² R+3Q _d /2) (3)

θ ₂ -θ ₃ ＝T ₂ ×[3Q _d +3(1+λ ₁ )I ² R] (4)

θ ₃ -θ ₄ ＝T ₃ ×[3Q _d +3(1+λ ₁ +λ ₂ )I ² R] (5)

θ ₄ -θ ₀ ＝T ₄ ×[3Q _d +3(1+λ ₁ +λ ₂ )I ² R] (6)

Adding formula (3), formula (4), formula (5) and formula (6), the core temperature of the three-core cable is obtained as:

θ ₁ ＝θ ₀ +T ₁ (I ² R+Q _d /2)+3T ₂ [I ² R(1+λ ₁ )+Q _d ]+3(T ₃ +T ₄ )[I ² R(1 +λ ₁ +λ ₂ )+Q _d ] (7)

θ ₁ in formula (7) is the core temperature of the three-core cable; θ ₂ is the temperature of the outer surface of the insulation and the metal shielding layer; θ ₃ is the temperature of the armor layer; θ ₄ is the surface temperature of the cable outer sheath; θ ₀ is the ambient temperature; T ₁ is _the thermal resistance of ^the insulation layer of a single core; I is the current carrying capacity of the three-core cable; R is the AC resistance of the core; Q _d is the dielectric loss of a single core insulation and insulating shielding layer; T ₂ is the thermal resistance of the filling layer and the inner sheath, λ ₁ is the loss factor of a single core metal sheath and shielding, T ₃ is the outer sheath Thermal resistance, T ₄ is the thermal resistance of the environment, λ ₂ is the loss factor of a single core armor layer.

Indicates the sensitivity of core temperature θ ₁ to ambient thermal resistance T ₄ , T ₄ is the independent variable parameter, θ ₁ is the dependent variable parameter. According to the data obtained in step S110 and step S120, according to That is, the degree of influence of the ambient thermal resistance on the core temperature can be analyzed. Since the conditions of air laying and soil laying are different, the following two situations will be used to illustrate the influence of ambient thermal resistance on the core temperature.

(1) When laying by air:

Since the ambient thermal resistance T ₄ is related to the ambient temperature θ ₀ , it is inaccurate to only consider the influence of the ambient thermal resistance on the core temperature, so the influence of two factors should be considered. Therefore, the normalized sensitivity of the core temperature θ ₁ to the ambient thermal resistance T ₄ is obtained as:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}^{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}\mathrm{<span\; class="notranslate">\; h</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}^{\frac{\mathrm{<span\; class="notranslate">\; 5</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; I</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

(2) When laying for soil:

Due to the large environmental thermal resistance of the soil, the ambient temperature remains basically unchanged, so the slight change in the ambient temperature can be ignored, and only the influence of the environmental thermal resistance on the core temperature is considered. The normalized sensitivity of the wire core temperature to the ambient thermal resistance when the soil is laid is obtained as:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}^{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; I</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

According to the formula (8) and formula (9), the sensitivity of the wire core temperature to the ambient thermal resistance can be obtained under different laying conditions and when the loading current is different values. Some of the data are shown in Table 1 below.

Table 1 Sensitivity of wire core temperature to ambient thermal resistance under two different laying conditions

The parameter sensitivity classification is shown in Table 2 below:

Table 2 Parameter sensitivity classification

According to the above Table 1 and Table 2, in the case of air laying: when the loading current is 200A, It is moderately sensitive; when the loading current is 300A, 400A, 500A, The most sensitive, and the highest sensitivity at 500A. In the case of soil laying: when loaded with different currents as insensitive.

The experimental values of the core and skin temperature when the 10kV three-core cable reaches a steady state are shown in Figure 3. A in Figure 3 represents the core temperature difference between air laying and soil laying, and b in Figure 3 represents the skin temperature difference between air laying and soil laying. Combining the data in Table 1 and Figure 3, it can be seen that under the same laying condition, as the loading current increases, the sensitivity of the core temperature to the thermal resistance of the external environment becomes larger and larger. At the same time, it also proves that the invention is effective for determining the degree of influence of environmental thermal resistance on the core temperature of a three-core cable. In addition, according to the above analysis, when the loading current is large, especially in the case of air laying, it is necessary to increase the monitoring of the ambient temperature to prevent the core temperature from being too high and ensure the safe and stable operation of the power cable.

Based on the same inventive concept, the present invention also provides a device for evaluating the influence of environmental thermal resistance on the core temperature of a three-core cable. The specific implementation of the device of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figure 4, an evaluation device for the influence of environmental thermal resistance on the core temperature of a three-core cable includes:

The environmental thermal resistance determination module 410 is used to obtain the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying according to the thermal circuit model of the three-core cable;

The wire core temperature determination module 420 is used to obtain the wire core temperature of the three-core cable according to the thermal circuit model of the three-core cable;

The first sensitivity determination module 430 is used for when the three-core cable is laid in air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying;

The second sensitivity determination module 440 is used for when the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the ambient thermal resistance under soil laying;

in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance.

According to the schematic diagram of the steady-state thermal circuit model of the three-core cable shown in Figure 2, it can be known that the ambient thermal resistance under air laying Where D _e represents the outer diameter of the three-core cable, h represents the heat transfer coefficient, Δθ _s represents the temperature rise of the three-core cable skin; the environmental thermal resistance under the soil laying where _ρT is the soil thermal resistivity coefficient, L represents the distance from the axis of the three-core cable to the ground surface, and D _e represents the outer diameter of the three-core cable. Core temperature of three-core cable θ ₁ ＝θ ₀ +T ₁ (I ² R+Q _d /2)+3T ₂ [I ² R(1+λ ₁ )+Q _d ]+3(T ₃ +T ₄ )[I ² R(1+λ ₁ +λ ₂ )+Q _d ], where θ ₁ is the core temperature of the three-core cable, θ ₀ is the ambient temperature, T ₁ is the thermal resistance of the insulation layer of a single core, and I is The ampacity of the three-core cable, R is the AC resistance of the core, Q _d is the dielectric loss of the insulation and insulation shielding layer of a single core, T ₂ is the thermal resistance of the filling layer and the inner sheath, λ ₁ is the metal sheath of a single core and The loss factor of shielding, T ₃ is the thermal resistance of the outer sheath, T ₄ is the thermal resistance of the environment, and λ ₂ is the loss factor of a single core armor layer.

According to the data obtained by the ambient thermal resistance determination module 410 and the core temperature determination module 420, the first sensitivity determination module 430 or the second sensitivity determination module 440 can be based on Analyze the influence of ambient thermal resistance on the core temperature. When laying air: because the ambient thermal resistance _T4 is related to the ambient temperature _θ0 , the first sensitivity determination module 430 will consider the influence of two factors, so the normalization of the core temperature _θ1 to the ambient thermal resistance _T4 is obtained The sensitivity is: $S_{T_4}^{{\mathrm{\&theta;}}_1}=\{4\mathrm{\&pi;}{\mathrm{D.}}_{e}h{\left(\mathrm{\&Delta;}{\mathrm{\&theta;}}_S\right)}^{\frac{5}{4}}+3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d\left]\right\}\&CenterDot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$ When laying in soil: because the ambient thermal resistance of the soil is relatively large, the ambient temperature remains basically unchanged, so the second sensitivity determination module 440 can ignore the small changes in the ambient temperature, and only consider the influence of the ambient thermal resistance on the core temperature. The normalized sensitivity of core temperature to ambient thermal resistance when laying in soil is: $S_{T_4}^{{\mathrm{\&theta;}}_1}=3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d]\&Center\; Dot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$

According to the sensitivity formula obtained by the first sensitivity determination module 430 and the sensitivity formula obtained by the second sensitivity determination module 440, the degree of influence of the environmental thermal resistance on the wire core temperature during different laying under different loading currents can be obtained, that is, with the increase of the loading current The sensitivity of the core temperature to the thermal resistance of the external environment is increasing, so when the three-core cable is loaded with a large current, especially when the laying of the three-core cable is air radiation, the monitoring of the ambient temperature should be strengthened, so that Ensure the safe and stable operation of power cables.

Other technical features of the device of the present invention are the same as those of the method of the present invention, and will not be repeated here.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A method for assessing the impact of environmental thermal resistance on the core temperature of a three-core cable, characterized in that it comprises steps: According to the thermal circuit model of the three-core cable, the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying is obtained; According to the thermal circuit model of the three-core cable, the core temperature of the three-core cable is obtained; If the three-core cable is laid by air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying; If the three-core cable is laid in soil, according to Determine the sensitivity of wire core temperature to environmental thermal resistance under soil laying; in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance. 2. the environmental thermal resistance according to claim 1 influences the assessment method of three-core cable core temperature, it is characterized in that the environmental thermal resistance under air laying Where D _e represents the outer diameter of the three-core cable, h represents the heat transfer coefficient, Δθ _s represents the temperature rise of the three-core cable skin; the environmental thermal resistance under the soil laying where _ρT is the soil thermal resistivity coefficient, L represents the distance from the axis of the three-core cable to the ground surface, and D _e represents the outer diameter of the three-core cable. 3. The method for assessing the impact of environmental thermal resistance on the core temperature of a three-core cable according to claim 2, wherein the core temperature of the three-core cable θ ₁ =θ ₀ +T ₁ (I ² R+Q _d / 2)+3T ₂ [I ² R(1+λ ₁ )+Q _d ]+3(T ₃ +T ₄ )[I ² R(1+λ ₁ +λ ₂ )+Q _d ], where θ ₁ is The core temperature of the three-core cable, θ ₀ is the ambient temperature, T ₁ is the thermal resistance of the insulation layer of a single core, I is the current carrying capacity of the three-core cable, R is the AC resistance of the core, and Q _d is the insulation and insulation of a single core The dielectric loss of the shielding layer, T ₂ is the thermal resistance of the filling layer and the inner sheath, λ ₁ is the loss factor of a single core metal sheath and shielding, T ₃ is the thermal resistance of the outer sheath, T ₄ is the thermal resistance of the environment, λ ₂ is the loss factor of a single core armor layer. 4. the evaluation method that environmental thermal resistance affects three-core cable core temperature according to claim 3, is characterized in that, the sensitivity of core temperature to the environmental thermal resistance under air laying $S_{T_4}^{{\mathrm{\&theta;}}_1}=\{4\mathrm{\&pi;}{\mathrm{D.}}_{e}h{\left({\mathrm{\&Delta;\&theta;}}_S\right)}^{\frac{5}{4}}+3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d\left]\right\}\&Center\; Dot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$ 5. the evaluation method that environmental thermal resistance affects three-core cable core temperature according to claim 3, is characterized in that, the sensitivity of core temperature to the environmental thermal resistance under soil laying $S_{T_4}^{{\mathrm{\&theta;}}_1}=3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d]\&Center\; Dot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$ 6. An evaluation device for the influence of environmental thermal resistance on the core temperature of a three-core cable, characterized in that it comprises: The environmental thermal resistance determination module is used to obtain the environmental thermal resistance under air laying and/or the environmental thermal resistance under soil laying according to the thermal circuit model of the three-core cable; The wire core temperature determination module is used to obtain the wire core temperature of the three-core cable according to the thermal circuit model of the three-core cable; The first sensitivity determination module is used for when the three-core cable is laid in air, according to the relationship between the ambient thermal resistance and the ambient temperature under air laying and Determine the sensitivity of the wire core temperature to the ambient thermal resistance under air laying; The second sensitivity determination module is used for when the three-core cable is laid in soil, according to Determine the sensitivity of the wire core temperature to the ambient thermal resistance under soil laying; in Indicates the sensitivity of the core temperature to the environmental thermal resistance under air laying or the sensitivity of the core temperature to the environmental thermal resistance under soil laying, θ ₁ represents the core temperature, T ₄ represents the environmental thermal resistance under air laying or soil laying ambient thermal resistance. 7. the evaluation device that environmental thermal resistance affects three-core cable core temperature according to claim 6, is characterized in that the environmental thermal resistance under air laying Where D _e represents the outer diameter of the three-core cable, h represents the heat transfer coefficient, Δθ _s represents the temperature rise of the three-core cable skin; the environmental thermal resistance under the soil laying where _ρT is the soil thermal resistivity coefficient, L represents the distance from the axis of the three-core cable to the ground surface, and D _e represents the outer diameter of the three-core cable. 8. The evaluation device for the influence of environmental thermal resistance on the core temperature of a three-core cable according to claim 7, wherein the core temperature of the three-core cable is θ ₁ =θ ₀ +T ₁ (I ² R+Q _d / 2)+3T ₂ [I ² R(1+λ ₁ )+Q _d ]+3(T ₃ +T ₄ )[I ² R(1+λ ₁ +λ ₂ )+Q _d ], where θ ₁ is The core temperature of the three-core cable, θ ₀ is the ambient temperature, T ₁ is the thermal resistance of the insulation layer of a single core, I is the current carrying capacity of the three-core cable, R is the AC resistance of the core, and Q _d is the insulation and insulation of a single core The dielectric loss of the shielding layer, T ₂ is the thermal resistance of the filling layer and the inner sheath, λ ₁ is the loss factor of a single core metal sheath and shielding, T ₃ is the thermal resistance of the outer sheath, T ₄ is the thermal resistance of the environment, λ ₂ is the loss factor of a single core armor layer. 9. the evaluation device that environmental thermal resistance affects three-core cable core temperature according to claim 8, is characterized in that, the sensitivity of core temperature to the environmental thermal resistance under air laying $S_{T_4}^{{\mathrm{\&theta;}}_1}=\{4\mathrm{\&pi;}{\mathrm{D.}}_{e}h{\left({\mathrm{\&Delta;\&theta;}}_S\right)}^{\frac{5}{4}}+3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d\left]\right\}\&Center\; Dot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$ 10. The evaluation device that environmental thermal resistance affects the core temperature of a three-core cable according to claim 8, characterized in that the sensitivity of the core temperature to the environmental thermal resistance under soil laying $S_{T_4}^{{\mathrm{\&theta;}}_1}=3[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)I^{2}R+Q_d]\&CenterDot;\frac{T_4}{{\mathrm{\&theta;}}_1}.$