CN108801501B - Cable core thermometry based on temperature gradient and thermal power conduction model - Google Patents

Cable core thermometry based on temperature gradient and thermal power conduction model Download PDF

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CN108801501B
CN108801501B CN201810312754.9A CN201810312754A CN108801501B CN 108801501 B CN108801501 B CN 108801501B CN 201810312754 A CN201810312754 A CN 201810312754A CN 108801501 B CN108801501 B CN 108801501B
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temperature
layer
thermal
medium
temperature gradient
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CN108801501A (en
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杜林�
王有元
陈伟根
周湶
李剑
王飞鹏
严涵
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Chongqing University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01KMEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K13/00Thermometers specially adapted for specific purposes
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00Investigating or analyzing materials by the use of thermal means
    • G01N25/18Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00Investigating or analyzing materials by the use of thermal means
    • G01N25/20Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity

Abstract

The cable core thermometry based on temperature gradient and thermal power conduction model that the present invention relates to a kind of, comprises the following steps: S1: one layer of thermal insulation layer is arranged in the outer surface of cable, and temperature sensor Tr and Tw is arranged in thermal insulation layer;S2: the thermal power of the medium surfaces externally and internally with a thickness of dw of thermal insulation layer outer surface is denoted as P0 and P1;S3: the thermal power of the medium surfaces externally and internally with a thickness of dr of thermal insulation layer inner surface is denoted as P2 and P3;S4: according to step S2 and S3, the .Pn that the thermal power of the radial surfaces externally and internally of each layer dielectric layer of cable core is denoted as P4, P5 respectively ...;S5: the temperature gradient equivalent network inside cable is established in conjunction with thermal losses;S6: measuring the temperature of thermal insulation layer surfaces externally and internally by temperature sensor Tr and Tw, and the temperature of cable core is calculated according to temperature gradient equivalent network.The method of the present invention has many advantages, such as that measurement scheme structure is simple, while at low cost and measurement accuracy is high.

Description

Cable core thermometry based on temperature gradient and thermal power conduction model
Technical field
The invention belongs to temperature measurement of cable conductor technical fields, are related to a kind of based on temperature gradient and thermal power conduction The cable core thermometry of model.
Background technique
With the fast development of expansion and the economic construction of city size, the voltage class of cable is continuously improved, conveying Energy continues to increase.This causes the operational management of power cable, monitoring and maintenance work to become more and more important.Running temperature is electricity One important parameter of cable, when cable is run under rated load, conductor temperature reaches permissible value;Once overload, conductor Temperature will steeply rise, and accelerate insulation ag(e)ing, or even thermal breakdown occurs.Therefore, it is either run from power cable inherently safe Angle, or the angle needed from electric power system dispatching, require to measure the conductor temperature of power cable.
There are mainly two types of currently used temperature measurement of cable conductor methods, the first is the indirect method of measurement, that is, passes through temperature Sensor measurement cable surface temperature is spent, calculates core wire internal temperature further according to thermodynamics method.Its main method is to establish electricity A kind of thermodynamical model of power cable studies the profiling temperatures of each layer of high voltage power cable and calculates the thermal resistance of each layer Value, or by establishing Laplace thermal circuit model and BP neural network model, with solve temperature in thermodynamical model transmit it is dynamic State response problem;But this there are two, first cable system by establishing the anti-indirect method of measurement for pushing away temperature of model Thermal resistance and thermal capacitance value and environment it is closely related, directly survey skin temperature be affected by temperature greatly, it is difficult to obtain general numerical value Calculation method;The temperature-time constant of followed by cable is larger, generally more than a few houres, therefore can not quick obtaining conductor temperature Degree.
Another method of temperature measurement of cable conductor is the direct method of measurement, and studying at present more is dissipated based on Raman The distribution type fiber-optic method and fiber Bragg grating measuring method penetrated.It, can be straight since optical fiber has good insulating properties Contact cable conductor or conductor joint heating position.But temperature-measuring system of distributed fibers needs are previously implanted light inside cable Fibre requires harsh, higher cost to the production and transportation of cable.Meanwhile using optical fiber direct temperature measurement method to in-site installation mistake The technique of journey is more demanding, and especially connection type and optical fiber of the optical fiber in joint are led core from high potential and sensed to zero potential The lead-out mode of device equipment still has certain technology difficulty.Therefore the technology has obtained good achievement on Theoretical Design, But there are still obstacles for large-scale promotion application.
To sum up, how to realize that the accurate measurement of cable conductor temperature still has very big researching value.Directly measurement side Although method is accurate, due to device complexity, it is greatly difficult to realize that application on a large scale exists for higher cost, and surveys indirectly Amount can only establish thermodynamical model by measurement skin temperature and measure core temperature indirectly, and measured value is greatly influenced by temperature, No matter how model optimizes, this factor bring can not be avoided to influence.
Summary of the invention
In view of this, the purpose of the present invention is to provide a kind of cable based on temperature gradient and thermal power conduction model Core thermometry provides a kind of scheme that can accurately measure cable conductor steady temperature, and measuring device device is simple, surveys It is accurate to measure result.
In order to achieve the above objectives, the invention provides the following technical scheme:
Cable core thermometry based on temperature gradient and thermal power conduction model, comprises the following steps:
S1: one layer of thermal insulation layer is set in the outer surface of cable, and temperature sensing is respectively set in the surfaces externally and internally of thermal insulation layer Device Tr and Tw;
S2: the thermal power of the medium surfaces externally and internally with a thickness of dw (minimum) of thermal insulation layer outer surface is denoted as P0 and P1;
S3: the thermal power of the medium surfaces externally and internally with a thickness of dr (minimum) of thermal insulation layer inner surface is denoted as P2 and P3;
S4: according to step S2 and S3, respectively by the thermal power of the radial surfaces externally and internally of each layer dielectric layer of cable core be denoted as P4, P5 ... .Pn, wherein n is the surfaces externally and internally sum of dielectric layer;
S5: after reaching thermal balance stable state, the temperature gradient equivalent network inside cable is established in conjunction with thermal losses;
S6: the temperature of the thermal insulation layer surfaces externally and internally is measured by temperature sensor Tr and Tw, according to the temperature established The temperature of field gradient equivalent network calculating cable core.
Further, the step S5 specifically:
S51: after thermal balance stable state, being calculated by formula, and every layer of medium is in each layer medium when reaching hot homeostasis The thermal power of outer surface and the heat being stored in each layer medium meet:
P0=P1=P2=P3=...=Pn
Q=Q0=Q1=Q2=Q3=...=Qn
Wherein, Q is the thermal energy for each layer dielectric surface unit time issuing or absorbing, PnWhen for each layer dielectric surface unit Between issue or absorb thermal power;
S52: according to dielectric boundaries condition intended temperature gradient;
S53: intended temperature difference and temperature gradient, medium radius, the calculating formula of the coefficient of heat conduction;
S54: the relationship of temperature gradient Yu medium radius is fitted according to Temperature Field Simulation.
Further, each layer dielectric surface unit time issues in step S51 or the thermal energy of absorption is
Wherein, T0 is the temperature that thermal insulation layer and air contact outer surface, and T1 is thermal insulation layer inner surface and dielectric layer interface Temperature, λ1For the coefficient of heat conduction of thermal insulation layer, L is cable length, and R1, R2 are the interior outer radius of thermal insulation layer.
Further, temperature gradient described in step S52 are as follows:
In formula,For temperature gradient, i is medium number of plies i ∈ [0,1,2 ..., n/2], wherein representative and air when i=0 The surface of contact, i=n/2 are cable wicking surface, λiThe coefficient of heat conduction for radius in R (i+1) to the dielectric layer between Ri, r For medium radius, Ti is that radius is dielectric surface temperature at Ri.
Further, step S54 moderate difference and temperature gradient, medium radius, the calculating formula of the coefficient of heat conduction are as follows:
In formula, T is that medium radius is temperature at r.
The beneficial effects of the present invention are:
1, measurement scheme structure of the invention is simple, when detecting temperature, does not need by complicated equipment and high-new Expensive sensor.
2, measurement cost is reduced, may be implemented to apply on a large scale.Due to optimizing measurement method method, the device of use It is also relatively inexpensive with device, it is possible to realize large-scale application.
3, measurement accuracy is improved.Present invention employs a kind of completely new multilayer dielectricity sensor arrangements, using one The new method for calculating temperature based on temperature gradient and thermal power flow model of kind, improves the precision of measurement.
4, no longer by the way of measuring skin temperature, a kind of novel measurement method for increasing insulation medium layer is proposed. It is different from the mode for directly measuring cable skin temperature in the past, the interference of outside environmental elements is avoided, also improves measurement Accuracy.
5, without the differential equation of solution relational expression containing heat source.
6, it analyzes multi-medium-layer temperature distributing characteristic and proposes a kind of new sensor arrangement, before being different from Single-sensor measurement pattern.
Detailed description of the invention
In order to keep the purpose of the present invention, technical scheme and beneficial effects clearer, the present invention provides following attached drawing and carries out Illustrate:
Fig. 1 is the construction of cable of the present invention and temperature sensor arrangement schematic diagram;
Fig. 2 is cable core of embodiment of the present invention temperature computation schematic diagram;
Fig. 3 is in same mediumCurve;
Fig. 4 is the relation curve of temperature gradient and r;
Fig. 5 is temperature gradient equivalent network schematic diagram.
Specific embodiment
Below in conjunction with attached drawing, a preferred embodiment of the present invention will be described in detail.
As shown in Figure 1, the construction of cable includes internal cable core 4, middle dielectric layer 3, measurement method proposed by the present invention In cable outer layer, thermal insulation layer 5 and thermal insulation layer external temperature sensor 1 (Tw) and thermal insulation layer internal temperature sensor 2 are set (Tr)。
Temperature due to cable due to generally can only obtain epidermis, this method are used by wrapping up one in cable sheath Layer medium thermal insulation layer 5 obtains thermal insulation layer surfaces externally and internally two o'clock temperature and avoids the influence of environmental factor, simultaneously because heat transfer By multilayer dielectricity, the measurement process in short-term that is added of thermal insulation layer not will lead to the raising of core temperature.Since the present invention measures It is directed to steady temperature, reaches thermal balance in each dielectric layer surface at this time, the general power above each dielectric layer is equal to Heat source (cable core) transfers out the thermal power come.
Specific embodiment is as follows:
As shown in Fig. 2, the thermal power P of thermal insulation layer surfaces externally and internally is obtained by hot simulation model first0And P1, while also obtaining The P of thermal insulation layer inner surface is taken2And P3, and the thermal power P of the past each layer medium surfaces externally and internally in cable core direction3、P4、P5…….Pn。
When thermal balance stable state, each layer dielectric surface temperature reaches a thermal balance, and temperature also reaches a stabilization Temperature value has:
P0=P1=P2=P3=...=Pn
Q=Q0=Q1=Q2=Q3=...=Qn
Q is the thermal energy for issuing (or absorption) each layer dielectric surface unit time, PnWhen for each layer dielectric surface unit Between issue the thermal power of (or absorb).
As shown, R2 and R1 is outer radius in thermal insulation layer, cable core radius R5, λ 1 is the thermal insulation layer coefficient of heat conduction, and λ 2 is The coefficient of heat conduction of medium III, λ 3 are the coefficient of heat conduction of medium II, and λ 4 is the coefficient of heat conduction of medium I.
ρ1For thermal insulation layer outer surface unit area heat flow, ρ2For III outer surface unit area heat flow of medium, ρ3For medium II outer surface unit area heat flow, ρ4For I outer surface unit area heat flow of medium, h is thermal insulation layer and air change of current coefficient, S is cable surface area, and L is cable length.
For thermal insulation layer (R1 > r > R2), there are heat convection, thermal insulation layer outer surface and air to belong to third class with air Boundary condition, outer surface internal and external temperature are respectively Ta+ and Ta, and Tb is the temperature of thermal insulation layer inner surface and dielectric layer interface.
S=2 π rL
Tb=T |R=R2(boundary condition)
For medium III (R2 > r > R3)
For medium II (R3 > r > R4)
For medium I (R4 > r > R5)
The relational expression of temperature difference and temperature gradient, radius, the coefficient of heat conduction:
Thermal insulation layer (R1 > r > R2):
For medium III (R2 > r > R3):
For medium II (R3 > r > R4):
For medium I (R4 > r > R5):
It is all satisfied in same medium as shown from the above formulaFor definite value,Meet curve as shown in Figure 3 Relationship.
Each media inside surface temperature Tc, Td, Te (cable core temperature can be successively solved according to the temperature gradient curve of fitting Degree).
Thermal insulation layer surfaces externally and internally temperature Ta and Tb are obtained by temperature sensor, to obtain temperature difference and heat flow Q's Relationship, and according to Temperature Field Simulation fit comeThe relation curve of curve --- temperature gradient and r as shown in figure 4, The value of core temperature Te can be obtained in conjunction with above-mentioned formula principle.
The temperature gradient equivalent network of cable internal temperature is finally established as shown in figure 5, wherein DC indicates cable core heat Source, Ra, Rb, Rc, Rd respectively indicate the thermal resistance of each dielectric layer, and the measuring table for building experiment is completed to temperature experiment curv Verification and amendment.
Finally, it is stated that preferred embodiment above is only to illustrate the technical solution of invention rather than limits, although passing through Above preferred embodiment is described in detail the present invention, however, those skilled in the art should understand that, can be in shape Various changes are made in formula and to it in details, without departing from claims of the present invention limited range.

Claims (5)

1. the cable core thermometry based on temperature gradient and thermal power conduction model, it is characterised in that: comprising as follows Step:
S1: one layer of thermal insulation layer is set in the outer surface of cable, and temperature sensor Tr is respectively set in the surfaces externally and internally of thermal insulation layer And Tw;
S2: the thermal power of the medium surfaces externally and internally with a thickness of minimum dw of thermal insulation layer outer surface is denoted as P0And P1
S3: the thermal power of the medium surfaces externally and internally with a thickness of minimum dr of thermal insulation layer inner surface is denoted as P2And P3
S4: according to step S2 and S3, P will be denoted as toward the thermal power of each layer medium surfaces externally and internally in cable core direction respectively4、P5……Pn, Wherein n is the surfaces externally and internally sum of dielectric layer;
S5: after reaching thermal balance stable state, the temperature gradient equivalent network inside cable is established in conjunction with thermal losses;
S6: measuring the temperature of the thermal insulation layer surfaces externally and internally by temperature sensor Tr and Tw, according to the temperature field ladder established Spend the temperature that equivalent network calculates cable core.
2. the cable core thermometry according to claim 1 based on temperature gradient and thermal power conduction model, It is characterized by: the step S5 specifically:
S51: after thermal balance stable state, the thermal power of each layer medium surfaces externally and internally of the every layer of medium when reaching hot homeostasis and The heat being stored in each layer medium meets following relationship:
P0=P1=P2=P3=...=Pn
Q=Q0=Q1=Q2=Q3=...=Qn
Wherein, Q is the thermal energy for each layer dielectric surface unit time issuing or absorbing, PnFor hair of each layer dielectric surface unit time Out or absorb thermal power;
S52: according to dielectric boundaries condition intended temperature gradient;
S53: intended temperature difference and temperature gradient, medium radius, the calculating formula of the coefficient of heat conduction;
S54: the relationship of temperature gradient Yu medium radius is fitted according to Temperature Field Simulation.
3. the cable core thermometry according to claim 2 based on temperature gradient and thermal power conduction model, It is characterized by: the thermal energy that each layer dielectric surface unit time issues or absorbs in step S51 is
Wherein, T0 is the temperature that thermal insulation layer and air contact outer surface, and T1 is the temperature of thermal insulation layer inner surface and dielectric layer interface Degree, λ1For the coefficient of heat conduction of thermal insulation layer, L is cable length, and R1, R2 are the interior outer radius of thermal insulation layer.
4. the cable core thermometry according to claim 3 based on temperature gradient and thermal power conduction model, It is characterized by: temperature gradient described in step S52 are as follows:
In formula,For temperature gradient, i is medium number of plies i ∈ [0,1,2 ..., n/2], wherein represents when i=0 and contacts with air Surface, i=n/2 be cable wicking surface, λiIt is radius in the coefficient of heat conduction of R (i+1) to the dielectric layer between Ri, r is to be situated between Matter radius, Ti are that radius is dielectric surface temperature at Ri.
5. the cable core thermometry according to claim 4 based on temperature gradient and thermal power conduction model, It is characterized by: temperature difference and temperature gradient in step S53, medium radius, the calculating formula of the coefficient of heat conduction are as follows:
In formula, T is that medium radius is temperature at r.
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