CN116522715A - Function calculation method for temperature of cable loop conductor wrapped with fireproof blanket in tunnel - Google Patents
Function calculation method for temperature of cable loop conductor wrapped with fireproof blanket in tunnel Download PDFInfo
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Abstract
The invention discloses a function calculation method for the temperature of a cable loop conductor of a wrapping fireproof blanket in a tunnel, which comprises the following steps: s1, establishing a magnetic-thermal-flow coupling simulation model of a corresponding tunnel wrapping a fireproof blanket cable loop according to actual laying conditions; s2, simulating and calculating current to be loaded when the temperature of the conductor reaches 90 ℃ and a corresponding radial heat flow distribution coefficient of the outer sheath; s3, establishing a local thermal path model of a single-phase cable loop wrapping the fireproof blanket, and calculating heat source and thermal resistance parameters of each layer of the cable in the local thermal path model; s4, identifying residual thermal resistance parameters of the local thermal path model based on a thermal field simulation result; s5, establishing a functional relation with the surface temperature value of the fireproof blanket and the cable current as input and the conductor temperature of the cable loop as output according to the local thermal path model with all the parameters; s6, measuring the surface temperature of the fireproof blanket, and calculating the temperature of the cable loop conductor wrapping the fireproof blanket in the tunnel according to the functional relation.
Description
Technical Field
The invention relates to the technical field of cable temperature calculation, in particular to a function calculation method for the temperature of a cable loop conductor of a wrapping fireproof blanket in a tunnel.
Background
The cable is buried underground, and once a fire disaster occurs, the cable has concealment and flame retardation and can bring about huge loss and disaster. The cable body and the accessory wrapping flexible cable fireproof blanket can prevent the cable from burning, have the advantages of convenient construction, low cost, and the like, can be disassembled and used at once, and can be applied to a certain degree in a cable tunnel. The wrapping fire blanket inevitably affects the heat dissipation capacity of the cable, reduces the current carrying capacity of the cable, causes overheat of heavy-duty lines and even endangers operation safety. The steady-state temperature of the conductors of the high-voltage cable laid in the tunnel of the wrapping fireproof blanket is monitored, and the method has important significance for improving the operation safety of the power transmission line.
When the electric power department takes fireproof measures for important lines in the tunnel, an online temperature monitoring system is often additionally arranged at the same time. In practice, the temperature sensor such as a thermocouple or a temperature measuring optical fiber is difficult to be embedded into the cable, and the sensor is required to be arranged on the surface of the fireproof blanket to measure the surface temperature of the fireproof blanket, and then the conductor temperature of the cable is calculated. Because the tunnel is laid with high-voltage cables and is often arranged in a triangle, the fireproof blanket is arranged in a way of wrapping three-phase cables at the same time, radial thermal resistance around the cables is not uniform at the moment, and the traditional temperature monitoring algorithm based on the one-dimensional thermal path model is not applicable any more. Therefore, research and development of a function calculation method for the temperature of the cable loop conductor of the wrapping fireproof blanket in the tunnel are very necessary, the calculation precision of the temperature and the current-carrying capacity of the cable loop conductor of the wrapping fireproof blanket is improved, and the utilization rate of a cable line of the tunnel is improved.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provides a function calculation method for the temperature of a cable loop conductor of a wrapping fireproof blanket in a tunnel. The method is based on a magnetic heat flow multi-physical coupling field model and a thermal circuit model of a tunnel cable loop, and realizes accurate calculation of the steady-state temperature of a high-voltage cable conductor from the surface temperature of the fireproof blanket by a shape factor method and finite element parameter identification in consideration of non-uniformity of radial thermal resistance of the cable loop wrapping the fireproof blanket along the circumferential direction, thereby providing important technical support for tunnel cable temperature monitoring and current-carrying capacity calculation by the fireproof blanket.
The aim of the invention can be achieved by adopting the following technical scheme:
a method of calculating a function of the temperature of a cable loop conductor of a wrap-around fire blanket in a tunnel, the method comprising the steps of:
s1, establishing a magnetic-thermal-flow coupling simulation model of a corresponding tunnel wrapping a fireproof blanket cable loop according to actual laying conditions;
s2, simulating and calculating current to be loaded when the temperature of the conductor reaches 90 ℃ and a corresponding radial heat flow distribution coefficient of the outer sheath;
s3, establishing a local thermal path model of the single-phase cable loop wrapping the fireproof blanket, and calculating heat source and thermal resistance parameters of each layer of the cable in the local thermal path model;
s4, identifying residual thermal resistance parameters in the local thermal path model based on a thermal field simulation result;
s5, establishing a functional relation with the surface temperature value of the fireproof blanket and the cable load as input and the cable conductor temperature as output according to the cable loop local thermal path model with all the parameters;
s6, measuring the surface temperature of the fireproof blanket, and calculating the conductor temperature of a cable loop wrapping the fireproof blanket in the tunnel according to the functional relation.
Further, in the step S1, a magnetic-thermal-flow coupling simulation model for wrapping a fireproof blanket cable loop in a tunnel is established according to actual laying and running conditions; and adopting finite element simulation to solve a thermal field result of the tunnel cable loop under the condition of wrapping the fireproof blanket, and providing a data sample for subsequent finite element parameter identification.
Further, the inner structure of the fire blanket wrapped with the cable in step S1 is a sandwich structure, and is composed of the middle fire-resistant layer and the protective layer, and the protective layer is thinner and has similar heat conduction performance to the middle fire-resistant layer, so that the protective layer is reduced to the middle fire-resistant layer when the geometric model is built, and the fire blanket is simplified to a single-layer structure, thereby achieving the effect of reducing the calculation amount of finite element simulation.
Further, in the step S2, the current to be loaded when the conductor temperature reaches 90 ℃ and the corresponding radial heat flow distribution coefficient of the outer sheath are calculated in a simulation manner, and the current and the corresponding radial heat flow distribution coefficient of the outer sheath are used as samples for identifying residual heat resistance parameters in the local thermal path model in the step S4; when the temperature of the cable conductor reaches 90 ℃, the analysis method calculates that the error of the heat source value of each layer of the cable compared with the finite element simulation result is minimum, at the moment, the temperature field simulation result is selected as a sample for parameter identification, and the calculated error of the radial heat flow distribution coefficient of the outer sheath is minimum.
Further, in the step S2, based on the thermal field simulation result, the outer surface of the cable is divided into two approximately isothermal surfaces along the circumferential direction, so that the outer sheath layer of the cable is divided into two parts; according to the invention, the cable core temperature is calculated according to the cable current and the surface temperature of the fireproof blanket, only the cable loop local thermal path model of the tight contact part of the fireproof blanket and the cable is needed to be identified, and the shape factor method is only suitable for calculating the steady-state heat conduction problem between two isothermal surfaces.
Further, the purpose of the simulation calculation of the radial heat flow distribution coefficient of the outer sheath in the step S2 is to: when the fireproof blanket is coated, the heat flow of the cable loop is unevenly distributed along the circumference, but the geometric structure and the laying condition of the cable line are basically unchanged in actual operation, so that the radial thermal resistance distribution from the cable core to the surface layer of the fireproof blanket is basically unchanged, and the radial heat flow coefficient under the input of different heat sources can be regarded as a certain value; the radial heat flow under the input of different heat sources in the isothermal surface direction can be solved by calculating the radial heat flow distribution coefficient of the outer sheath, and the temperature result can be solved by combining the local heat path model of the single-phase cable loop wrapping the fireproof blanket.
Further, in the step S3, a local thermal path calculation model of the cable loop of the wrapped fireproof blanket is built in the tunnel, and parameters of the local thermal path model of the single-phase cable loop of the wrapped fireproof blanket are calculated, including thermal resistance and heat source of the cable core, the insulating layer, the buffer layer and the aluminum sheath; equivalent radial thermal resistance T of close contact part of cable outer sheath and fireproof blanket 3out And equivalent radial thermal resistance T of fire blanket F The remaining parameters in the local thermal path model may be calculated with reference to the relevant formulas in IEC-60287.
Further, in the step S4, based on the thermal field simulation result, equivalent radial thermal resistance T is set for the close contact portion of the cable sheath and the fireproof blanket of the local thermal path model 3out Equivalent radial thermal resistance T of fireproof blanket F Identifying; based on the simulation result of the thermal field in the step S2, calculating the radial heat flow q of the close contact part of the cable outer sheath and the fireproof blanket out Average temperature θ of the portion of the cable jacket in intimate contact with the fire blanket in1 Average temperature theta of cable aluminum sheath s Surface temperature θ of fire blanket F T of local thermal path model of wrapped fire blanket is identified through shape factor method 3out 、T F Thermal resistance parameters.
Further, in the step S5, according to the local thermal path model obtained with all parameters, a functional relation is established with the surface temperature value of the fire blanket and the cable load as input and the cable conductor temperature as output; model parameters calculated according to IEC-60287 and T identified in step S4 3out 、T F The model parameters are substituted into a local thermal circuit model of the single-phase cable loop, so that the surface temperature theta of the fireproof blanket can be obtained simply F Cable current I, cable core temperature θ c The mapping function between the two is used for realizing the monitoring of the surface temperature of the fireproof blanket to the temperature of the cable core.
Further, the step S6 is to measure the fire blanket tableAnd calculating the conductor temperature of a cable loop wrapping the fire blanket in the tunnel according to the function relation. The cable load current I can be obtained through monitoring data of a dispatching center, and a temperature sensor is used as a data acquisition device to obtain the surface temperature theta of the fireproof blanket F . The temperature sensors are respectively arranged on the outer surfaces of the fireproof blankets of the three phases of the triangular arrangement cables A, B, C, and the temperature value of each temperature measuring point corresponds to the surface temperature theta of the fireproof blanket of the local thermal circuit model of the phase cable loop F 。
Furthermore, in the step S6, the error of the calculated cable conductor temperature value through the functional relation is positively correlated with the cable load I, and the error is small under the condition that the more common load is not large or is low in the online monitoring of the cable temperature, so that the monitoring precision is high in practical application.
Compared with the prior art, the invention has the following advantages and effects:
(1) According to the function calculation method for the cable loop conductor temperature of the wrapping fireproof blanket in the tunnel, a practical thermal path model is provided for the high-voltage cable loop which is arranged in a triangular manner and wraps the fireproof blanket in the tunnel based on the principle of isothermal surface division, and the problem of how to calculate the cable conductor temperature according to the surface temperature of the fireproof blanket is solved; on the other hand, the method uses the temperature sensor as a data acquisition device, calculates based on the local cable thermal circuit model identified by the finite element parameters, is easy to realize in engineering, and is beneficial to realizing on-line monitoring of the high-voltage cable loop of the wrapping fireproof blanket in the tunnel.
(2) According to the function calculation method for the cable loop conductor temperature of the wrapping fireproof blanket in the tunnel, provided by the invention, the non-uniformity of the radial thermal resistance of the cable loop wrapping the fireproof blanket along the circumferential direction is considered, and the calculation precision of the cable loop conductor temperature is improved; because the error between the high-voltage cable conductor temperature calculated by the step S6 and the finite element simulation result is the largest under the condition of current-carrying capacity, the error is small under the condition that the more common load is not large or is low in the online monitoring of the cable temperature, and the beneficial effect of improving the monitoring precision is obtained.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:
FIG. 1 is a flow chart of a method for calculating the function of the temperature of a cable loop conductor of a wrap-in-tunnel fire blanket disclosed in the present invention;
FIG. 2 is a schematic diagram of the geometric parameters of a two-dimensional cross section of a tunnel and the cable routing arrangement in the present invention;
FIG. 3 is a two-dimensional magneto-thermo-flow coupled finite element simulation model of a tunnel cable loop incorporating a fire blanket constructed in accordance with the present invention;
FIG. 4 is a schematic view of the fire blanket of the present invention;
FIG. 5 is the result of the temperature field at 90℃for the conductor in step S2 of example 1 according to the invention;
FIG. 6 is a schematic diagram of isothermal surface division in the present invention;
FIG. 7 is a schematic diagram of a single-phase cable loop local thermal circuit model of the wrapped fire blanket of the present invention;
FIG. 8 is a schematic view of a fire blanket wrapping pattern and temperature sensing points in accordance with the present invention;
FIG. 9 is a graph showing the result of the temperature field at 90℃for the conductor in step S2 of example 2 according to the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The embodiment discloses a function calculation method for cable loop conductor temperature of a wrapping fireproof blanket in a tunnel, which can provide a feasible thermal path model for a high-voltage cable loop in triangular arrangement laid in the tunnel wrapping the fireproof blanket, solves the problem of how to calculate the cable conductor temperature according to the surface temperature of the fireproof blanket, and has the specific flow shown in fig. 1, and comprises the following steps:
s1, establishing a two-dimensional magnetic-thermal-flow coupling finite element simulation model of a cable loop of the fire blanket wrapped in a corresponding tunnel according to the actual laying condition of a high-voltage cable of the fire blanket wrapped in the tunnel;
in step S1, a two-dimensional magnetic-thermal-flow coupling finite element simulation model of a tunnel cable loop wrapping the fireproof blanket is established according to the actual condition of a cable tunnel in which a certain fan is stopped. The geometric parameters of the tunnel section and the cable line arrangement are shown in figure 2 (the bracket structure is omitted), the center of the tunnel is about 3m away from the ground, the inner diameter of the tunnel is 3.6m, the wall thickness is 0.25m, 10 loops of single-core cables comprising 6 loops of 110kV cables and 4 loops of 220kV cables are laid together, and the model numbers are YJLW03-64/110 multiplied by 1200mm respectively 2 And YJLW02-127/220 1X 2000mm 2 。
The two-dimensional magnetic-thermal-flow coupling finite element simulation model of the tunnel cable loop which is wrapped with the fire blanket is shown in fig. 3, three-phase cables of the 4-loop 220kV cable line are arranged in a triangular mode and are wrapped with the fire blanket, and 6-loop 110kV cable loops do not wrap the fire blanket. In the embodiment, the fans in the tunnel are stopped, no axial heat transfer exists, the axial air flow in the tunnel is ignored, and only the influence of the heating of the cable and the natural convection of the air under the action of gravity are considered, so that the three-dimensional field can be simplified into a two-dimensional model for simulation. Considering actual parameters of the cable tunnel, the length and the width of the geometric model are respectively 12m and 8m; the lower boundary of the model is set to be 20 ℃ of deep soil temperature, the left and right boundaries are set to be heat insulation, the upper boundary is set to be a natural convection boundary outside the ground, and the surface temperature is set to be 30 ℃.
The inner structure of the fire blanket of the wrapped cable is a sandwich structure, and consists of an intermediate fire-resistant layer and a protective layer, as shown in fig. 4. The thickness of the middle refractory layer and the protective layer in the embodiment are respectively 9mm and 1mm. Because the protective layer is thinner and has similar heat conduction performance with the middle fire-resistant layer, the protective layer is reduced to the middle fire-resistant layer when the geometric model is built, the fire-resistant blanket is simplified into a single-layer structure, and the equivalent thickness of the simplified fire-resistant blanket is 10mm.
The relevant material parameters of this example are shown in table 1:
TABLE 1 related Material parameters Table
S2, simulating and calculating current to be loaded when the temperature of the conductor reaches 90 ℃ and a corresponding radial heat flow distribution coefficient of the outer sheath;
setting 6 times of 110kV cable load as 0, setting 4 times of 220kV cable load current as same, continuously adjusting the loaded load current from 100A according to the difference between the simulation result of the conductor temperature and 90 ℃, and calculating the conductor temperature of the cable in a simulation way until the difference between the conductor temperature and 90 ℃ is less than +/-0.05 ℃. The current-carrying capacity of the 220kV four-circuit cable group operation is 1228.5A, the highest temperature of a conductor is 90.0146 ℃, the current temperature field result (shown in figure 5) is taken for further analysis, and the cables refer to A-phase cables of the highest temperature loop.
The solving steps of the radial heat flow distribution coefficient of the outer sheath are as follows, and the calculation results are shown in table 1:
(1) Based on the thermal field simulation result, dividing the outer surface of the cable into two approximate isothermal surfaces, and dividing the outer sheath layer of the cable into two parts according to the two approximate isothermal surfaces, as shown in fig. 6;
(2) Performing post-processing on the thermal field simulation data, and respectively calculating radial heat flows passing through two parts of the cable outer sheath;
(3) Calculating the radial heat flow distribution coefficient k of the outer sheath, wherein the calculation can be performed by the formula (1):
wherein q is out Radial heat flow through the tight contact portion of the cable jacket and the fire blanket, unit: w/m; q in Radial heat flow in units of the portion of the cable jacket that is close to the other two-phase cable: w/m; the solution results are shown in Table 2Shown.
TABLE 2 solution results of radial heat flow distribution coefficients of outer sheath
S3, establishing a local thermal path model of the single-phase cable loop wrapping the fireproof blanket, and calculating heat source and thermal resistance parameters of each layer of the cable in the local thermal path model;
in this step S3, a single-phase cable local thermal circuit model is created taking into account the fire blanket as shown in fig. 7. In this embodiment, the a-phase cable is taken as an example, and the parameters thereof include the following: θ c The temperature value of the cable conductor in the running state; θ F Is the surface temperature value of the fireproof blanket; θs is the temperature value of the metal sheath in the running state; θ in1 The temperature value of the tight contact part of the cable outer sheath and the fireproof blanket in the running state; θ in2 The temperature value of the part of the cable outer sheath, which is close to other two-phase cables, is the temperature value of the part of the cable outer sheath, which is close to other two-phase cables in the running state; w (W) c Joule heat loss for the cable conductor current; w (W) d Dielectric loss for the cable insulation layer; w (W) s Is a metal sheath loss; t (T) 1 、T 2 、T 3out 、T 3in 、T F The cable insulation layer, the buffer layer, the tight contact part of the outer sheath and the fireproof blanket, the part of the outer sheath close to other two-phase cables and the equivalent thermal resistance of the fireproof blanket are sequentially arranged; k is the radial heat flow distribution coefficient of the outer sheath.
W c For joule heat loss generated by the cable conductor current, the calculation of the heat source is performed by referring to the related formula in IEC-60287, using formula (2):
W c ＝I 2 R 0 ·(1+α 20 (θ-20))·(1+Y s +Y p ) (2)
wherein I represents the cable load in units of: a, A is as follows; r is R 0 The DC resistance of the conductor at 20 ℃ is expressed in units: omega/m; alpha 20 Representing the temperature coefficient of the cable conductor; θ represents the maximum operating temperature of the cable conductor, in units: the temperature is lower than the temperature; y is Y p Representing skin effect coefficients; y is Y s Representing the neighborhoodA near-effect coefficient;
W d for the loss of the insulating layer of the cable, the loss of the insulating layer of each phase of cable in unit length is calculated by adopting the formula (3):
where f represents frequency, unit: hz; u (U) 0 Rated voltage, unit, to which the cable insulation is subjected: a kV; tan delta represents the dielectric loss tangent; c represents the capacitance per unit length of cable, unit: f/m;
W s for metal sheath loss, the calculation is performed by adopting the formula (4):
W s ＝(α 1 +α 2 )·W c (4)
wherein alpha is 1 Representing the circulation loss coefficient; alpha 2 Representing the eddy current loss coefficient;
T 1 、T 2 the equivalent radial thermal resistance of the cable insulating layer and the buffer layer is calculated by adopting the formula (5):
wherein lambda is 1 The heat conductivity coefficient of the cable insulating layer material is as follows: W/(mK); lambda (lambda) 2 The thermal conductivity coefficient of the cable buffer layer material is as follows: W/(mK); r is (r) 1 The inner diameter of the cable insulating layer is as follows: m; r is (r) 2 The outer diameter of the cable insulation layer is as follows: m; r is (r) 3 The outer diameter of the cable buffer layer is as follows: m;
T 1 、T 2 and 1228.5a the corresponding heat source solution results are shown in table 3:
TABLE 3 thermal resistance and Heat Source solving results Table
S4, identifying residual thermal resistance parameters in a local thermal circuit model of the single-phase cable loop based on the calculated radial thermal flow distribution coefficient of the outer sheath;
in the step S4, based on the simulation result of the thermal field in the step S2, equivalent radial thermal resistance T is generated on the close contact part of the cable outer sheath and the fireproof blanket of the local thermal path model 3out Equivalent radial thermal resistance T of fireproof blanket F Identification can be performed by using the formula (6):
wherein lambda is 3 The heat conductivity coefficient of the cable outer sheath material is as follows: W/(mK); lambda (lambda) F The heat conductivity coefficient of the fireproof blanket material is as follows: W/(mK); s is S 3 、S F The first shape factor and the second shape factor are respectively;
calculating the shape factor S using equation (7) 3 、S F ：
Wherein q is out Radial heat flow through the tight contact portion of the cable jacket and the fire blanket, unit: w/m; θ in1 The average temperature of the tight contact part of the cable outer sheath and the fireproof blanket is as follows: the temperature is lower than the temperature; θ s The average temperature of the cable aluminum sheath is as follows: the temperature is lower than the temperature; θ F The surface temperature of the fireproof blanket is as follows: DEG C.
Reading the required parameter values from the thermal field simulation result in the step S2, and combining the data in the table 1, wherein the solving result is shown in the table 4:
watch 4.T 3out And T F Finite element identification result table
S5, establishing a functional relation with the surface temperature value of the fireproof blanket and the cable load as input and the cable conductor temperature as output according to the cable loop local thermal path model with all the parameters;
in the step S5, according to the local thermal path model for obtaining all parameters, a functional relation is established with the surface temperature value of the fire blanket and the cable load as input and the cable conductor temperature as output, and the specific steps are as follows:
s51, according to a single-phase cable local thermal path model considering the fireproof blanket, an equivalent thermal path equation is written, and calculation is carried out by adopting a formula (8):
in θ c The cable conductor temperature in units of: the temperature is lower than the temperature; θ F The surface temperature of the fireproof blanket is as follows: the temperature is lower than the temperature; t (T) 1 、T 2 、T 3out 、T F The equivalent radial thermal resistance of the cable insulating layer, the buffer layer, the tight contact part of the cable outer sheath and the fireproof blanket and the unit are respectively: k.m 2 /W；W c 、W d 、W s Joule heat loss, insulation layer loss and metal sheath loss generated by cable conductor current are respectively as follows: w/m; k is the radial heat flow distribution coefficient of the outer sheath;
s52, substituting the formulas (2), (3) and (4) into the formula (8), and simplifying the formula (9):
wherein I represents the cable load in units of: a, A is as follows; r is R 0 The DC resistance of the conductor at 20 ℃ is expressed in units: omega/m; alpha 20 Representing the temperature coefficient of the cable conductor; θ represents the maximum operating temperature of the cable conductor, in units: the temperature is lower than the temperature; y is Y p Representing skin effect coefficients; y is Y s Representing the proximity effect coefficient; f represents frequency, unit: hz; u (U) 0 Rated voltage, unit, to which the cable insulation is subjected: a kV; tan delta represents the dielectric loss tangentThe method comprises the steps of carrying out a first treatment on the surface of the c represents the capacitance per unit length of cable, unit: f/m; alpha 1 Representing the circulation loss coefficient; alpha 2 Representing the eddy current loss coefficient; except for cable load I and fire blanket surface temperature theta F In addition, the remaining parameters do not change with the change in cable load I.
Will T 1 、T 2 、T 3out 、T F W under 1228.5A c 、W d 、W s θ under thermal field simulation results F Substituting into (8), verifying the error between the local thermal path model and the finite element simulation result, wherein the calculation result is shown in table 5:
TABLE 5 error analysis Table for local thermal path model
Table 6.IEC-60287 correlation parameter values table
Referring to the relevant formulas and parameter values of IEC-60287, as shown in Table 6, a functional relation (10) is established:
θ c ＝θ F +1.43287×10 -5 ·I 2 +1.3733×10 -5 (10)
s6, measuring the surface temperature of the fireproof blanket, and calculating the conductor temperature of a cable loop wrapping the fireproof blanket in the tunnel according to the functional relation.
In this step S6, the substituted surface temperature θ of the fire blanket F The measured values obtained by the temperature sensors are respectively arranged in three phases of the triangular arrangement cable A, B, C, and correspond to the temperature measuring points 1, 2 and 3, as shown in fig. 8. The temperature value of each temperature measuring point corresponds to the surface temperature theta of the fireproof blanket of the local thermal circuit model of the phase cable loop F 。
In this embodiment, the thermal field result of finite element simulation is used as the measurement value of the temperature sensor, and the cable currents I are set to be respectively628.5A, 828.5A and 1228.5A, taking the temperature value of the 1 position of the temperature measuring point as the surface temperature theta of the fireproof blanket of the local thermal path model of the A-phase cable loop F Comparing the calculated result of the functional relation (10) with the cable conductor temperature theta c Error of the simulation values as shown in table 7:
TABLE 7 comparison of calculation results for different Cable loads I
The analysis shows that the error of the cable conductor temperature value calculated by the functional relation (10) is positively correlated with the cable load I, the error is small under the condition that the more common load is not large or is low in the online monitoring of the cable temperature, and the monitoring precision is high in practical application.
Example 2
The embodiment discloses a function calculation method of cable loop conductor temperature of a wrapping fireproof blanket in a tunnel, which can provide a feasible thermal path model for a high-voltage cable loop in triangular arrangement laid in the tunnel wrapping the fireproof blanket, solves the problem of how to calculate the cable conductor temperature according to the surface temperature of the fireproof blanket, and comprises the following steps:
s1, establishing a magnetic-thermal-flow coupling finite element simulation model of a corresponding tunnel wrapping a fireproof blanket cable loop according to actual laying conditions;
the geometric model used in this embodiment refers to step S1 in example 1 except for the thickness of the fire blanket.
The thickness of the intermediate refractory layer and the protective layer in this embodiment are 14mm and 1mm, respectively. Because the protective layer is thinner and has similar heat conduction performance with the middle fire-resistant layer, the protective layer is reduced to the middle fire-resistant layer when the geometric model is built, the fire-resistant blanket is simplified into a single-layer structure, and the equivalent thickness of the simplified fire-resistant blanket is 15mm.
S2, simulating and calculating current to be loaded when the temperature of the conductor reaches 90 ℃ and a corresponding radial heat flow distribution coefficient of the outer sheath;
setting 6 times of 110kV cable load as 0A, setting 4 times of 220kV cable load current as same, continuously adjusting the loaded load current from 100A according to the difference between the simulation result of the conductor temperature and 90 ℃, and calculating the conductor temperature of the cable in a simulation way until the difference between the conductor temperature and 90 ℃ is less than +/-0.05 ℃. The current-carrying capacity of the 220kV four-circuit cable group operation is 1197.5A, the conductor temperature is 90.0109 ℃, and the current temperature field result (shown in figure 9) is taken for the next analysis.
The step of solving the radial heat flux distribution coefficient of the outer sheath is referred to step S2 in example 1, and the calculation results are shown in table 8:
TABLE 8 solution results Table for radial Heat flow distribution coefficient of outer sheath
S3, establishing a single-phase cable loop local thermal path model wrapping the fireproof blanket, and calculating heat source and thermal resistance parameters of each layer of cable in the cable loop local thermal path model;
in this step S3, a single-phase cable loop local thermal path model is created taking into account the fire blanket as shown in fig. 7. The parameters and calculation formula are referred to in step S3 in example 1.
T 1 、T 2 The corresponding heat source solving results of 1197.5a are shown in table 9:
TABLE 9 thermal resistance and Heat Source solving results Table
S4, identifying residual thermal resistance parameters in the local thermal path model based on the calculated radial heat flow distribution coefficient of the outer sheath;
in the step S4, based on the simulation result of the thermal field in the step S2, equivalent radial thermal resistance T is generated on the close contact part of the cable outer sheath and the fireproof blanket of the local thermal path model 3out Equivalent radial thermal resistance T of fireproof blanket F For identification, the calculation formula refers to step S4 in embodiment 1.
Reading the required parameter values from the thermal field simulation result in the step S2, and combining the data in the table 1, wherein the solving result is shown in the table 10:
TABLE 10T 3out And T F Finite element identification result table
S5, establishing a functional relation with the surface temperature value of the fireproof blanket and the cable load as input and the cable conductor temperature as output according to the cable loop local thermal path model with all the parameters;
in the step S5, a functional relation with the fire blanket surface temperature value and the cable load as input and the cable conductor temperature as output is established according to the local thermal path model with all the parameters obtained, and the specific steps and calculation formulas refer to the step S5 in the embodiment 1.
Will T 1 、T 2 、T 3out 、T F W under 1197.5A c 、W d 、W s θ under thermal field simulation results F Substituting into equation (8) of step S5 in the embodiment, verifying the error between the local thermal path model and the finite element simulation result, and calculating the result as shown in table 11:
TABLE 11 error analysis Table for local thermal path model
Table 12 IEC-60287 correlation parameter value table
Referring to the relevant formulas and parameter values of IEC-60287, as shown in Table 12, a functional relation (1) is established:
θ c ＝θ F +1.6883358×10 -5 ·I 2 +1.327033479×10 -5 (1)
s6, measuring the surface temperature of the fireproof blanket, and calculating the conductor temperature of a cable loop wrapping the fireproof blanket in the tunnel according to the functional relation.
In this step S6, the substituted surface temperature θ of the fire blanket F The measured values obtained by the temperature sensors are respectively arranged in three phases of the triangular arrangement cable A, B, C, and correspond to the temperature measuring points 1, 2 and 3, as shown in fig. 8. The temperature value of each temperature measuring point corresponds to the surface temperature theta of the fireproof blanket of the local thermal circuit model of the phase cable loop F 。
In this embodiment, the thermal field result of finite element simulation is used as the measurement value of the temperature sensor, the cable current I is set to 597.5A, 797.5A and 1197.5A, and the temperature value at the 1-position of the temperature measuring point is used as the surface temperature θ of the fire blanket of the local thermal path model of the a-phase cable loop F Comparing the calculated result of the functional relation (1) with the A-phase cable conductor temperature theta c Error of the simulation values as shown in table 13:
further taking different cable loads I, comparing errors of the calculation result of the functional relation (1) and the finite element simulation result, as shown in a table 13:
TABLE 13 comparison of calculation results for different Cable loads I
The analysis shows that the error of the cable conductor temperature value calculated by the functional relation (1) is positively correlated with the cable load I, the error is small under the condition that the more common load is not large or is low in the online monitoring of the cable temperature, and the monitoring precision is high in practical application.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (9)
1. A method for calculating a function of the temperature of a cable loop conductor of a wrapped fire blanket in a tunnel, the method comprising the steps of:
s1, establishing a magnetic-thermal-flow coupling simulation model of a corresponding tunnel wrapping a fireproof blanket cable loop according to actual laying conditions;
s2, simulating and calculating current to be loaded when the temperature of the conductor reaches 90 ℃ and a corresponding radial heat flow distribution coefficient of the outer sheath;
s3, establishing a local thermal path model of the single-phase cable loop wrapping the fireproof blanket, and calculating heat source and thermal resistance parameters of each layer of the cable in the local thermal path model;
s4, identifying residual thermal resistance parameters in the local thermal path model based on a thermal field simulation result;
s5, establishing a functional relation with the surface temperature value of the fireproof blanket and the cable current as input and the cable conductor temperature as output according to the cable loop local thermal path model with all the parameters;
s6, measuring the surface temperature of the fireproof blanket, and calculating the conductor temperature of a cable loop wrapping the fireproof blanket in the tunnel according to the functional relation.
2. The method according to claim 1, wherein in step S1, a two-dimensional magneto-thermo-fluid coupled finite element simulation model of the cable loop of the wrapped fire blanket in the tunnel is created according to the cable geometry and position in the tunnel, the tunnel geometry, the ground surface temperature, the deep soil temperature, the fire blanket thickness and the related material parameters.
3. The method according to claim 1, wherein in the step S1, the fire blanket is wrapped in a three-phase cable which is simultaneously wrapped in a delta arrangement, and the protection layer of the fire blanket is reduced to an intermediate fire-resistant layer to simplify the fire blanket into a single-layer structure.
4. The method for calculating the function of the cable loop conductor temperature of the wrapping fireproof blanket in the tunnel according to claim 1, wherein in the step S2, frequency domain-steady simulation is performed on the finite element simulation model, the frequency is set to be 50Hz, the cable conductor temperature is calculated in a simulation manner, the loaded load current is continuously adjusted according to the difference between the conductor temperature simulation result and 90 ℃ until the difference between the conductor temperature and 90 ℃ is smaller than +/-0.05 ℃, the loaded load current on the current cable is the current carrying capacity, and the current temperature field simulation result is taken for the next analysis.
5. The method for calculating the function of the temperature of the cable loop conductor of the wrapping fire blanket in the tunnel according to claim 1, wherein in the step S2, the solving step of the radial heat flow distribution coefficient of the outer sheath is as follows:
s21, dividing the outer surface of the cable into two approximate isothermal surfaces along the circumferential direction based on a thermal field simulation result, and dividing the cable outer sheath layer into two parts according to the two approximate isothermal surfaces;
s22, performing post-processing on thermal field simulation data, and respectively calculating radial heat flows passing through two parts of the cable outer sheath;
s23, calculating radial heat flow distribution coefficient k of the outer sheath by adopting a formula (1):
wherein q is out Radial heat flow through the tight contact portion of the cable jacket and the fire blanket, unit: w/m; q in Radial heat flow in units of the portion of the cable jacket that is close to the other two-phase cable: w/m.
6. The method for calculating the function of the cable loop conductor temperature of the wrapped fire blanket in the tunnel according to claim 1, wherein in the step S3, a single-phase cable loop local thermal path model of the wrapped fire blanket is established, parameters of the single-phase cable loop local thermal path model of the wrapped fire blanket are calculated, including thermal resistance and heat source of each layer of the cable are calculated as follows:
W c for joule heat loss generated by the cable conductor current, the calculation of the heat source is performed by referring to the related formula in IEC-60287, using formula (2):
W c ＝I 2 R 0 ·(1+α 20 (θ-20))·(1+Y s +Y p ) (2)
wherein I represents the cable load in units of: a, A is as follows; r is R 0 The DC resistance of the conductor at 20 ℃ is expressed in units: omega/m; alpha 20 Representing the temperature coefficient of the cable conductor; θ represents the maximum operating temperature of the cable conductor, in units: the temperature is lower than the temperature; y is Y p Representing skin effect coefficients; y is Y s Representing the proximity effect coefficient;
W d for the loss of the insulating layer of the cable, the loss of the insulating layer of each phase of cable in unit length is calculated by adopting the formula (3):
where f represents frequency, unit: hz; u (U) 0 Rated voltage, unit, to which the cable insulation is subjected: a kV; tan delta represents the dielectric loss tangent; c represents the capacitance per unit length of cable, unit: f/m;
W s for metal sheath loss, the calculation is performed by adopting the formula (4):
W s ＝(α 1 +α 2 )·W c (4)
wherein alpha is 1 Representing the circulation loss coefficient; alpha 2 Representing the eddy current loss coefficient;
T 1 、T 2 the equivalent radial thermal resistance of the cable insulating layer and the buffer layer is calculated by adopting the formula (5):
wherein lambda is 1 Thermal conductivity coefficient of cable insulating layer materialUnits: W/(mK); lambda (lambda) 2 The thermal conductivity coefficient of the cable buffer layer material is as follows: W/(mK); r is (r) 1 The inner diameter of the cable insulating layer is as follows: m; r is (r) 2 The outer diameter of the cable insulation layer is as follows: m; r is (r) 3 The outer diameter of the cable buffer layer is as follows: m.
7. The method for calculating the function of the temperature of the cable loop conductor of the wrapped fire blanket in the tunnel according to claim 1, wherein in the step S4, based on the simulation result of the thermal field in the step S2, the equivalent radial thermal resistance T of the tight contact part of the cable sheath of the local thermal path model and the fire blanket 3out Equivalent radial thermal resistance T of fireproof blanket F Identifying, and calculating by using a formula (6):
wherein lambda is 3 The heat conductivity coefficient of the cable insulating layer material is as follows: W/(mK); lambda (lambda) F The thermal conductivity coefficient of the cable buffer layer material is as follows: W/(mK); s is S 3 、S F The first shape factor and the second shape factor are respectively;
calculating the shape factor S using equation (7) 3 、S F ：
Wherein q is out Radial heat flow through the tight contact portion of the cable jacket and the fire blanket, unit: w/m; θ in1 The average temperature of the tight contact part of the cable outer sheath and the fireproof blanket is as follows: the temperature is lower than the temperature; θ s The average temperature of the cable aluminum sheath is as follows: the temperature is lower than the temperature; θ F The surface temperature of the fireproof blanket is as follows: DEG C.
8. The method for calculating the function of the cable loop conductor temperature of the wrapped fire blanket in the tunnel according to claim 1, wherein in the step S5, according to the local thermal path model obtained with all parameters, a functional relation is established with the fire blanket surface temperature value and the cable load as input and the high voltage cable steady state conductor temperature as output, and the method is specifically as follows:
s51, according to a high-voltage cable local thermal circuit model considering the fireproof blanket, an equivalent thermal circuit equation is written, and calculation is carried out by adopting a formula (8):
in θ c The temperature value of the cable conductor in the running state is as follows: the temperature is lower than the temperature; θ F The surface temperature of the fireproof blanket is as follows: the temperature is lower than the temperature; t (T) 1 、T 2 、T 3out 、T F The equivalent radial thermal resistance of the cable insulating layer, the buffer layer, the tight contact part of the cable outer sheath and the fireproof blanket and the unit are respectively: k.m 2 /W；W c 、W d 、W s Joule heat loss, insulation layer loss and metal sheath loss generated by cable conductor current are respectively as follows: w/m; k is the radial heat flow distribution coefficient of the outer sheath;
s52, substituting the formulas (2), (3) and (4) into the formula (8), and simplifying the formula (9):
wherein I represents the cable load in units of: a, A is as follows; r is R 0 The DC resistance of the conductor at 20 ℃ is expressed in units: omega/m; alpha 20 Representing the temperature coefficient of the cable conductor; θ represents the maximum operating temperature of the cable conductor, in units: the temperature is lower than the temperature; y is Y p Representing skin effect coefficients; y is Y s Representing the proximity effect coefficient; f represents frequency, unit: hz; u (U) 0 Rated voltage, unit, to which the cable insulation is subjected: a kV; tan delta represents the dielectric loss tangent; c represents the capacitance per unit length of cable, unit: f/m; alpha 1 Representing the circulation loss coefficient; alpha 2 Indicating vortexA flow loss coefficient; except for cable load I and fire blanket surface temperature theta F In addition, the remaining parameters do not change with the change in cable load I.
9. The method for calculating the function of the temperature of the cable loop conductor of a wrapped fire blanket in a tunnel according to claim 1, wherein in the step S6, the substituted fire blanket surface temperature θ F The measured values obtained by using temperature sensors are respectively arranged in three phases of the triangular arrangement cable A, B, C and correspond to the temperature measuring points 1, 2 and 3.
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