CN102539964A - Method for judging insulation characteristics of cross linked polyethylene (XLPE) power cables on line - Google Patents

Abstract

The invention relates to a method for judging insulation characteristics of cross linked polyethylene (XLPE) power cables on line, which obtains the temperature and dielectric loss of an insulating layer and relation of insulating thermal resistance by establishing a thermal circuit model of the power cables, further establishes mathematic relation of temperature parameters and dielectric constant of the insulating layer, and judges the insulation damages of current power cables through the dielectric constant of a current insulating layer. According to the dielectric constant of the insulating layer, the method for judging the insulation characteristics of the XLPE power cables on line judges the insulation characteristics of the power cables and learns the insulation damages of power cables, thereby facilitating adoption of corresponding measures and achieving in-advance detection and prevention of accidents.

Description

The online insulation characterisitic determination methods of XLPE power cable

Technical field

The present invention relates to a kind of determination methods, relate in particular to the online insulation characterisitic determination methods of a kind of XLPE power cable.

Background technology

At present, China's big and medium-sized cities transmission and distribution network progressively uses high voltage power cable to replace traditional overhead power transmission network, and this also is that intelligent grid progressively advances the prerequisite that realizes in order with the wisdom city.How to make the transmission electric energy of safety and stability on the power cable, just become the tenure of use that prolongs cable of crucial importance.

Mainly be meant the serviceable life of power cable insulation the tenure of use of power cable.Along with the development of electronics, computing machine, photoelectricity, signal Processing and various sensing technologies, can make at any time the reliability of insulation and judge and the residual life of insulation is made prediction, thereby can in time find incipient fault.

Many in recent years researchers have proposed the method for some new online charged detection power cable insulation characteristics, and these methods exist insulation defect and aging conditions that effect is arranged very much to early detection power cable, particularly cross-inked polyethylene power cable.These methods comprise:

(1) dc superposition method: the neutral point place at the voltage transformer (VT) of ground connection adds low-voltage dc power supply; Make the alternating voltage stack of this DC voltage and power cable in service; Detect atomic weak DC current through cable insulation; Can record the insulation resistance of whole piece cable, thereby judge the quality of cable.The characteristics of dc superposition method are that antijamming capability is stronger, but the correlativity of insulation resistance and cable insulation residual life and bad is dispersed big.

(2) DC component method: through atomic weak flip-flop in detection streamer heart yearn and the screen layer electric current, in the cable certain a bit or a certain local branchization (water tree, the electric branch) insulation defect that exists carry out the deterioration diagnosis.A little less than the electric current that the DC component method records was atomic, also not quite stable sometimes, small interference current will cause very mistake.

(3) dielectric dissipation factor method: the voltage that will be added on the cable takes out with voltage transformer (VT) or voltage divider; The power current Current Transformer that will flow through in the insulation is taken out; In the self-poise loop, detect the phase differential of above-mentioned signal then, can measure the dielectric dissipation factor of cable insulation.This dielectric dissipation factor method troublesome poeration, the difficult realization.

(4) shelf depreciation method: the shelf depreciation method is to utilize signals such as electromagnetic wave, ultrasound wave to detect the shelf depreciation that fault location takes place, and can onlinely detect in theory, but receives background interference easily, and the on-line monitoring difficulty is bigger.

(5) ground wire current method: this method reaches the monitoring purpose through at the increment that detects through the capacitance current of ground wire.Method is simple for this, and cover can be realized with current sensor on the ground wire of being everlasting, but the ground wire at other end cable end place will break off when measuring temporarily.

(6) low frequency overlay method: the low method of superposition of low frequency mainly is the voltage signal of stack certain frequency on the screen layer of cable, amplifies tested deterioration signal, judges the degree of cable deterioration according to the power that detects deterioration signal.This method is simple, and available a set of equipment detects many cables, can produce influence to a certain degree to original system but shortcoming is the stack electric signal.

Therefore, we press for a kind of simple to operate, the online insulation characterisitic determination methods of XLPE power cable that can accurately judge the power cable insulation characteristic.

Summary of the invention

Technical matters to be solved by this invention provide a kind of simple to operate, can accurately the online insulation characterisitic determination methods of XLPE power cable.

The technical scheme that the present invention adopted is:

The online insulation characterisitic determination methods of a kind of XLPE power cable; It is through setting up the hot road model of power cable; Try to achieve insulation course temperature and dielectric loss; And the relation of insulation thermal resistance, thereby set up the mathematical relation of temperature parameter and insulation course specific inductive capacity, through judge the damaged condition of current power cable insulation when the specific inductive capacity of front insulation layer.

The online insulation characterisitic determination methods of XLPE power cable specifically comprises the steps:

The first step is obtained the skin temperature at power cable point place and the environment temperature of this region;

In second step,, calculate current conductor thread core temperature according to the electric current and the environment temperature that flow through in the known current conductor

θ _c＝θ ₀+[T ₁+(1+λ ₁)*T ₂+(1+λ ₁+λ ₂)*(T ₃+T ₄)]*W _c+(0.5*T ₁+T ₂+T ₃+T ₄)*W _d

In the formula:

θ ₀The expression environment temperature,

θ _cExpression conductor thread core temperature,

λ ₁Expression metallic shield loss factor,

λ ₂Expression armouring/reinforcing band loss factor,

T ₃Represent equivalent outer jacket thermal resistance,

W _cRepresentation unit length of conductor power attenuation,

T ₂Represent equivalent inner liner thermal resistance,

W _dThe dielectric loss of representation unit length,

T ₁Represent equivalent insulation course thermal resistance,

T ₄Represent equivalent external environment condition thermal resistance;

In the 3rd step, obtain conductor thread core and insulation course temperature difference θ according to the hot road of power cable Model Calculation _Cm:

${\mathrm{\&theta;}}_{\mathrm{cm}}=(W_c+\frac{1}{2}*W_d)*{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1$

In the formula:

W _c＝I ²*R

$W_d=\mathrm{\&omega;}*c*U_0^2*\mathrm{tg\&delta;}$

ω＝2*π*f

Wherein:

W _cRepresentation unit length of conductor power attenuation,

T ₁Represent equivalent insulation course thermal resistance,

W _dExpression insulation loss, every meter of unit watt (W/m),

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

ω representes the angular frequency of voltage,

C representation unit length cables electric capacity,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor;

The 4th step, the situation of change of the DIELECTRIC CONSTANTS through calculating this point, computing formula is:

$\mathrm{\&epsiv;}=\frac{18*({\mathrm{\&theta;}}_{\mathrm{cm}}-I^2*R*T_1)}{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1*\mathrm{\&pi;}*f*U_0^2*\mathrm{tg\&delta;}}*\ln \left(\frac{D_i}{d_c}\right)*{10}^9$

In the formula:

θ _CmExpression conductor thread core and insulation course temperature difference,

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

T ₁Represent equivalent insulation course thermal resistance,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

D _iExpression insulation course diameter,

d _cThe expression conductor diameter;

The 5th step, DIELECTRIC CONSTANTS and specific inductive capacity reference table that the 4th step was calculated compare, and draw judged result:

5.1 when the DIELECTRIC CONSTANTS that calculates be reduced to the specific inductive capacity reference table numeral 50% the time, show to have insulation defect, must overhaul power cable;

5.2 when the DIELECTRIC CONSTANTS that calculates greater than the numeral of specific inductive capacity reference table 50% the time, show that state of insulation is normal.

Such scheme, the skin temperature at the power cable point place in the first step adopts the point measurement of optical fiber grating temperature monitoring system to obtain with the environment temperature of this region.

The present invention obtains the skin temperature at power cable point place and the environment temperature of this region through the optical fiber grating temperature monitoring system, through setting up the hot road model of power cable, tries to achieve the relation of insulation course temperature and dielectric loss and insulation thermal resistance then.Thereby set up the mathematical relation of temperature parameter and insulation course specific inductive capacity; Just can obtain specific inductive capacity through online detection streamer temperature when front insulation layer; And then reflect the damaged condition of current cable insulation, and be convenient to take appropriate measures, accomplish to find in advance, shift to an earlier date trouble-saving generation.

Description of drawings

Fig. 1 is the structural representation of power cable with cross-linked polyethylene insulation.

Fig. 2 is a power cable Transient Thermal Circuit model.

Fig. 3 is a power cable steady state thermal road model.

Fig. 4 is an optical fiber grating temperature monitoring system synoptic diagram.

Among the figure: 1, conductor; 2, conductor shielding; 3, insulation course; 4, insulation shielding; 5, metallic shield; 6, inner liner; 7, armor; 8, outer jacket; 9, temperature-sensing probe, 10, connect optical cable, 11, optical connector, 12, transmission cable.

Embodiment

Further specify embodiments of the invention below in conjunction with accompanying drawing.

The online insulation characterisitic determination methods of a kind of XLPE power cable, its analysis foundation are the hot road models of power cable.XLPE power cable (cross-linked polyethylene insulated cable cable) structure is as shown in Figure 1; This power cable comprises conductor 1 and outer jacket 8; Between conductor 1 and outer jacket 8, be provided with conductor shielding 2, insulation course 3, insulation shielding 4, metallic shield 5, inner liner 6, armor 7 from inside to outside successively.Main heater is a conductor in the power cable, and in addition, the various losses of cable itself finally also distribute with the form of heat; Like dielectric loss; The metallic shield loss, the armouring loss is so the thermal source in the hot road model of power cable should comprise the conductor power attenuation; Dielectric loss, metallic shield loss and armouring loss.The conductor power attenuation is the loss that conductor produces, and dielectric loss is the loss that insulation course produces, and the metallic shield loss is that the loss that armor produces is represented in loss, the armouring loss that metal screen layer produces), the loss that other each layers produced can be ignored.

The heat that conductor 1 sends will pass through all structures except that conductor 1 to external diffusion; The heat that dielectric loss produces then will pass through metal screen layer, armor, several parts such as outer jacket; The heat that the metallic shield loss produces will pass through armor and outer jacket; The heat that the armouring loss is produced is then only through outer jacket.

Consider that conductor thread core is to adopt the good conductor of heat such as copper or aluminium to process, so the thermal resistance of conductor thread core is ignored, only considers the thermal capacitance of conductor thread core; The propagation that 3 pairs of insulation courses can hinder heat also can storing heat, so should consider the thermal resistance and the thermal capacitance of insulation course 3; The thermal resistance of metal screen layer 5 and inner liner 6 also can be ignored and only considers its thermal capacitance; Also should consider its thermal resistance and thermal capacitance for outer jacket 8.

Consider the character of thermal source in the power cable, can thermal source in the model of hot road be divided into two types.Ambient temperature is thought invariable generally speaking, is equivalent to a constant temperature source, so external environment condition is equivalent to a constant pressure source in the model of hot road; And the conductor thread core loss, the insulation loss, the metallic shield loss, what the armouring loss was produced is heat, is not temperature (according to thermal conduction study knowledge: to heat=temperature difference/thermal conduction resistance), so these several kinds of thermals source can be regarded as constant current source.Adopt lumped parameter method (in the thermal conduction study below; When thermal conduction resistance on solid interior unit's heat-conducting area and the heat exchange thermal resistance on the per surface area smaller; Can be regarded as the quality of continuous distribution in the object and thermal capacity to converge; The temperature of this point is the lump temperature) it is carried out modeling, its hot road model is as shown in Figure 2.Wherein, T ₁, T ₂, T ₃, T ₄Represent equivalent insulation course thermal resistance respectively, equivalent inner liner thermal resistance, equivalent outer jacket thermal resistance, equivalent external environment condition thermal resistance; θ _cExpression conductor thread core temperature, θ _mExpression insulation course temperature, θ _sExpression inner liner temperature, θ _eThe expression skin temperature, θ ₀The expression environment temperature; W _cRepresentation unit length of conductor power attenuation, W _dThe dielectric loss of representation unit length, λ ₁Expression metallic shield loss factor, λ ₂Expression armouring/reinforcing band loss factor; λ ₁W _cRepresentation unit length metallic shield power attenuation; λ ₂W _cRepresentation unit length armouring power attenuation; Q _c, Q _i, Q _s, Q _Cp, Q _tRepresent the conductor thermal capacitance Deng respectively, insulation course thermal capacitance, inner liner thermal capacitance, armouring thermal capacitance, outer jacket thermal capacitance; P and p ' represent insulation course thermal capacitance allocation proportion factor and outer jacket allocation proportion factor respectively; D _iExpression insulation course diameter, d _cThe expression conductor diameter, D _eThe expression outside diameter of cable, D _sExpression outer jacket internal diameter, Q ₁Be the equivalent thermal capacitance between conductor thread core and the insulation course, Q ₂Equivalent thermal capacitance between insulation course and the inner liner, Q ₃Equivalent thermal capacitance between inner liner and the outer jacket, Q ₄Outer jacket equivalence thermal capacitance, their expression formula is shown below:

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1={\mathrm{<figure-callout\; id="9"\; label="Q\; c\; +"\; filenames="HDA0000123146820000021.png"\; state="\{\{state\}\}">Q</figure-callout>}}_c+9*{\mathrm{<figure-callout\; id="2"\; label="Q\; i\; Q"\; filenames="HDA0000123146820000012.png,HDA0000123146820000013.png"\; state="\{\{state\}\}">Q</figure-callout>}}_i& \\ Q_{}{}_2=(1-p)*Q_i+p^{\&prime;}*Q_s+{\mathrm{<figure-callout\; id="3"\; label="Q\; cp\; Q"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_{\mathrm{cp}}& \\ Q_{}{}_3=(1-p^{\&prime;})*Q_s\\ {\mathrm{<figure-callout\; id="4"\; label="Q"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">Q</figure-callout>}}_4=Q_t\\ p=\frac{1}{2*\ln \left(\frac{D_i}{d_c}\right)}-\frac{1}{{\left(\frac{D_i}{d_c}\right)}^2-1}\\ p^{\&prime;}=\frac{1}{2*\ln \left(\frac{D_e}{D_s}\right)}-\frac{1}{{\left(\frac{D_e}{D_s}\right)}^2-1}\end{array}\right.---\left(1\right)$

Consider the effect of the existing thermal source of insulation course, again can storing heat, and hinder the characteristic of the propagation diffusion of heat, the dielectric loss W of unit length _dSeparated into two parts, that is: insulation course can only hinder the wherein propagation diffusion of a part of dielectric loss, and its size is W _d/ 2; Half the in addition dielectric loss only influences each layer beyond the insulation course through insulation course.Can know that from the model analysis of hot road the heat that conductor produces forms hot-fluid to the skin transmission, as unit length conductor power attenuation W _cThe rising of each layer temperature such as conductor thread core 1, insulation course 3, inner liner 6, outer jacket 8 can be caused during increase,, also environment temperature θ maybe be caused if the heat radiation of cable surrounding environment is obstructed or is drawn badly ₀Rising.When hot-fluid increased, because the existence of each layer thermal capacitance Q, the temperature of each layer raise gradually, that is to say that the temperature of each layer can not be suddenlyd change.When hot-fluid does not change, when cable was in stable state, the temperature computation of each layer can be ignored thermal capacitance, because thermal capacitance heat absorption this moment and heat radiation are in equilibrium state.Hot road model during the power cable stable state is as shown in Figure 3.

The corresponding relation of physical quantity from hot road model and electromagnetics (is seen thermal conduction study: " formula

Do can find out after the contrast with the Ohm law expression formula I=Δ U/R in the DC circuit, temperature difference t and the corresponding temperature and pressure that can be described as of voltage Δ U, hot-fluid Q is corresponding with electric current I, so R _KAJust corresponding with resistance R, be called the thermal conduction resistance that A is amassed in the hot cross-section "), can get the temperature that stable state is a power cable in conjunction with Fig. 3, the relational expression between hot-fluid and the thermal resistance:

θ _c＝θ ₀+[T ₁+(1+λ ₁)*T ₂+(1+λ ₁+λ ₂)*(T ₃+T ₄)]*W _c+(0.5*T ₁+T ₂+T ₃+T ₄)*W _d (2)

Can also obtain simultaneously the temperature expression formula of other each layers of power cable:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_e={\mathrm{\&theta;}}_0+[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)*W_c+W_d]*{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_4\\ {\mathrm{\&theta;}}_s={\mathrm{\&theta;}}_e+[(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)*W_c+W_d]*{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_3\\ {\mathrm{\&theta;}}_m={\mathrm{\&theta;}}_s+[(1+{\mathrm{\&lambda;}}_1)*W_c+W_d]*T_2\end{array}\right.---\left(3\right)$

According to the size of insulation loss and the electric pressure of cable, the classification of the insulating material of employing, the size of capacitance of conductor, the structure of cable is following about drawing round conductor CALCULATION OF CAPACITANCE formula:

$c=\frac{\mathrm{\&epsiv;}}{18*\ln \left(\frac{D_i}{d_c}\right)}*{10}^{-9}---\left(4\right)$

ε representes the specific inductive capacity of insulating material in the formula (4); Di representes not comprise the insulation course diameter of screen layer, unit millimeter (mm); d _cThe expression conductor diameter is if having screen layer then comprise screen layer, unit millimeter (mm); Every meter of the per unit system (F/m) of current potential length cables electric capacity c.Every insulation loss of middle unit length mutually has following formula to draw:

$\left\{\begin{array}{c}{W}_d=\mathrm{\&omega;}*c*U_0^2*\mathrm{tg\&delta;}\\ \mathrm{\&omega;}=2*\mathrm{\&pi;}*f\end{array}\right.---\left(5\right)$

W in the formula (5) _dBe insulation loss, every meter of unit watt (W/m), U ₀Be voltage-to-ground (phase voltage), unit volt (V), tg δ is the insulation loss factor, and ω representes the angular frequency of voltage, and C representes current potential length cables electric capacity.

Can obtain conductor thread core and insulation course temperature difference θ according to hot road model _CmDo not receive the influence of environment temperature, only receive the actual current-carrying capacity of power cable and the influence of dielectric loss, when for a certain fixedly current-carrying capacity, conductor thread core and insulation course temperature difference θ _CmOnly relevant with dielectric loss.Because the working voltage of power cable and physical dimension can not change, so conductor thread core and insulation course temperature difference θ _CmVariation finally can react the variation of the specific inductive capacity of insulation course, i.e. the loss situation of insulation.

Can be according to hot road model in the hope of conductor thread core and insulation course temperature difference θ _CmMathematic(al) representation:

${\mathrm{\&theta;}}_{\mathrm{cm}}=(W_c+\frac{1}{2}*W_d)*T_1---\left(6\right)$

Again because of unit length conductor power attenuation W _cComputing formula as shown in the formula:

W _c＝I ²*R (7)

Simultaneous formula (5), formula (6), formula (7) can get conductor thread core and insulation course temperature difference θ _CmWith the mathematical relation of insulation course DIELECTRIC CONSTANTS, shown in (8):

$\mathrm{\&epsiv;}=\frac{18*({\mathrm{\&theta;}}_{\mathrm{cm}}-I^2*R*T_1)}{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1*\mathrm{\&pi;}*f*U_0^2*\mathrm{tg\&delta;}}*\ln \left(\frac{D_i}{d_c}\right)*{10}^9---\left(8\right)$

In the formula (8),

θ _CmExpression conductor thread core and insulation course temperature difference,

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

T ₁Represent equivalent insulation course thermal resistance,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

D _iExpression insulation course diameter,

d _cThe expression conductor diameter.

Through type (8) can get conductor thread core and insulation course temperature difference θ _CmWith the insulation course DIELECTRIC CONSTANTS be relation in direct ratio, consider that in actual motion the change of insulation course DIELECTRIC CONSTANTS can cause equivalent insulation course thermal resistance T simultaneously ₁Change with insulation loss factor tg δ makes conductor thread core and insulation course temperature difference θ _CmThrough type (8) can not be correct the variation of reaction ε.But when the electric current I that flows through in the electric power body is got fixed value, conductor thread core and insulation course temperature difference θ _Cm, equivalent insulation course thermal resistance T ₁With the variation of insulation loss factor tg δ all be because the variation of insulation course DIELECTRIC CONSTANTS causes.We suppose when the insulation course DIELECTRIC CONSTANTS changes, equivalent insulation course thermal resistance T ₁Still get the definite value before the insulation course DIELECTRIC CONSTANTS changes, θ like this with insulation loss factor tg δ _CmVariation just all be attributed to the variation of the DIELECTRIC CONSTANTS of insulation course.And through type this moment (8) can be similar to the insulation course DIELECTRIC CONSTANTS that obtains, though this value can not be counted as the specific inductive capacity when front insulation layer, it can reflect necessarily whether work as front insulation layer damages.

When the DIELECTRIC CONSTANTS that calculates be reduced to the specific inductive capacity reference table numeral 50% the time, show to have insulation defect, must overhaul power cable; When the DIELECTRIC CONSTANTS that calculates greater than the numeral of specific inductive capacity reference table 50% the time, show that state of insulation is normal.

In view of above reason; The present invention provides a kind of XLPE power cable online insulation characterisitic determination methods; It tries to achieve insulation course temperature and dielectric loss through setting up the hot road model of power cable, and the relation of insulation thermal resistance; Thereby set up the mathematical relation of temperature parameter and insulation course specific inductive capacity, through judge the damaged condition of current power cable insulation when the specific inductive capacity of front insulation layer.

The online insulation characterisitic determination methods of this XLPE power cable specifically comprises the steps:

The first step is utilized optical fiber grating temperature monitoring system (see figure 4), is installed in the skin temperature θ that the surperficial temperature-sensing probe of power cable obtains power cable point place by distribution _eEnvironment temperature θ with this region ₀

In second step,, calculate current conductor thread core temperature according to known current power current-carrying capacity of cable and environment temperature

θ _c＝θ ₀+[T ₁+(1+λ ₁)*T ₂+(1+λ ₁+λ ₂)*(T ₃+T ₄)]*W _c+(0.5*T ₁+T ₂+T ₃+T ₄)*W _d

In the formula:

θ ₀The expression environment temperature,

θ _cExpression conductor thread core temperature,

λ ₁Expression metallic shield loss factor,

λ ₂Expression armouring/reinforcing band loss factor,

T ₃Represent equivalent outer jacket thermal resistance,

W _cRepresentation unit length of conductor power attenuation,

T ₂Represent equivalent inner liner thermal resistance,

W _dThe dielectric loss of representation unit length,

T ₁Represent equivalent insulation course thermal resistance,

T ₄Represent equivalent external environment condition thermal resistance;

In the 3rd step, obtain conductor thread core and insulation course temperature difference θ according to the hot road of power cable Model Calculation _Cm

${\mathrm{\&theta;}}_{\mathrm{cm}}=(W_c+\frac{1}{2}*W_d)*{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1$

In the formula:

W _c＝I ²*R

$W_d=\mathrm{\&omega;}*c*U_0^2*\mathrm{tg\&delta;}$

ω＝2*π*f

Wherein:

W _cRepresentation unit length of conductor power attenuation,

T ₁Represent equivalent insulation course thermal resistance,

W _dExpression insulation loss, every meter of unit watt (W/m),

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

ω representes the voltage angle frequency,

C representation unit length cables electric capacity,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor;

The 4th step, the situation of change of the DIELECTRIC CONSTANTS through calculating this point, computing formula is:

$\mathrm{\&epsiv;}=\frac{18*({\mathrm{\&theta;}}_{\mathrm{cm}}-I^2*R*T_1)}{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1*\mathrm{\&pi;}*f*U_0^2*\mathrm{tg\&delta;}}*\ln \left(\frac{D_i}{d_c}\right)*{10}^9$

In the formula:

θ _CmExpression conductor thread core and insulation course temperature difference,

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

T ₁Represent equivalent insulation course thermal resistance,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

D _iExpression insulation course diameter,

d _cThe expression conductor diameter;

The 5th step, DIELECTRIC CONSTANTS and specific inductive capacity reference table that the 4th step was calculated compare, and draw judged result:

5.1 when the DIELECTRIC CONSTANTS that calculates be reduced to the specific inductive capacity reference table numeral 50% the time, must overhaul power cable;

5.2 when the DIELECTRIC CONSTANTS that calculates greater than the numeral of specific inductive capacity reference table 50% the time, show that state of insulation is normal.

Fig. 4 representes optical fiber grating temperature monitoring system synoptic diagram, and this optical fiber grating temperature monitoring system is the TGW fire probe system with optical fiber and grating sensing temperature product that Wuhan incorporated company of science and engineering light section produces.

The present invention is divided into the monitoring that segment carries out the insulation course insulation characterisitic to whole power cable according to the numbering and the position of each fiber-optical grating temperature sensor.

$\mathrm{\&epsiv;}\left(n\right)=\frac{18*({\mathrm{\&theta;}}_{\mathrm{cm}}\left(n\right)-I^2*R*T_1)}{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000123146820000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1*\mathrm{\&pi;}*f*U_0^2*\mathrm{tg\&delta;}}*\ln \left(\frac{D_i}{d_c}\right)*{10}^9---\left(10\right)$

In the formula

N representes the numbering of fiber-optical grating temperature sensor,

ε (n) expression is numbered the insulation course specific inductive capacity of the fiber-optical grating temperature sensor position of n,

θ _Cm(n) expression is numbered the core and the insulation course temperature difference of the fiber-optical grating temperature sensor position of n,

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

T ₁Represent equivalent insulation course thermal resistance,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

D _iExpression insulation course diameter,

d _cThe expression conductor diameter.

The present invention obtains the skin temperature at power cable point place and the environment temperature of this region through the optical fiber grating temperature monitoring system, through setting up the hot road model of power cable, tries to achieve the relation of insulation course temperature and dielectric loss and insulation thermal resistance then.Thereby, can set up the mathematical relation of temperature parameter and insulation course specific inductive capacity, just can obtain specific inductive capacity through online detection streamer temperature, and then reflect the damaged condition of current insulation when front insulation layer.

In the literary composition, environment temperature θ ₀, skin temperature θ _eObtain by the optical fiber grating temperature monitoring system; The electric current I that flows through in the conductor, voltage-to-ground (phase voltage) U ₀, electric voltage frequency f, the angular frequency of voltage, pi be known; Metallic shield loss factor λ ₁, armouring/reinforcing band loss factor λ ₂, equivalent insulation course thermal resistance T ₁, equivalent inner liner thermal resistance T ₂, equivalent outer jacket thermal resistance T ₃, equivalent external environment condition thermal resistance T ₄, conductor thermal capacitance Q _c, insulation course thermal capacitance Q _i, inner liner thermal capacitance Q _s, armouring thermal capacitance Q _Cp, outer jacket thermal capacitance Q _t, the AC resistance R of cable conductor, insulation loss factor tg δ obtain by existing IEC60287 criterion calculation.

Claims (3)

1. online insulation characterisitic determination methods of XLPE power cable; It is characterized in that: this determination methods is through setting up the hot road model of power cable; Try to achieve insulation course temperature and dielectric loss; And the relation of insulation thermal resistance, thereby set up the mathematical relation of temperature parameter and insulation course specific inductive capacity, through judge the damaged condition of current power cable insulation when the specific inductive capacity of front insulation layer.

2. the online insulation characterisitic determination methods of XLPE power cable according to claim 1 is characterized in that comprising the steps:

The first step is obtained the skin temperature at power cable point place and the environment temperature of this region;

Second step according to the electric current and the environment temperature that flow through in the known current conductor, calculated current conductor thread core temperature,

θ _c＝θ ₀+[T ₁+(1+λ ₁)*T ₂+(1+λ ₁+λ ₃)*(T ₃+T ₄)]*W _c+(0.5*T ₁+T ₂+T ₃+T ₄)*W _d

In the formula:

θ ₀The expression environment temperature,

θ _cExpression conductor thread core temperature,

λ ₁Expression metallic shield loss factor,

λ ₂Expression armouring/reinforcing band loss factor,

T ₃Represent equivalent outer jacket thermal resistance,

W _cRepresentation unit length of conductor power attenuation,

T ₂Represent equivalent inner liner thermal resistance,

W _dThe dielectric loss of representation unit length;

T ₁Represent equivalent insulation course thermal resistance,

T ₄Represent equivalent external environment condition thermal resistance;

In the 3rd step, obtain conductor thread core and insulation course temperature difference θ according to the hot road of power cable Model Calculation _Cm,

${\mathrm{\&theta;}}_{\mathrm{cm}}=(W_c+\frac{1}{2}*W_d)*T_1$

In the formula:

W _c＝I ²*R

$W_d=\mathrm{\&omega;}*c*U_0^2*\mathrm{tg\&delta;}$

ω＝2*π*f

Wherein:

W _cRepresentation unit length of conductor power attenuation,

T ₁Represent equivalent insulation course thermal resistance,

W _dExpression insulation loss, every meter of unit watt (W/m),

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

ω representes the angular frequency of voltage,

C representation unit length cables electric capacity,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

The 4th step, the situation of change of the DIELECTRIC CONSTANTS through calculating this point, computing formula is:

$\mathrm{\&epsiv;}=\frac{18*({\mathrm{\&theta;}}_{\mathrm{cm}}-I^2*R*T_1)}{T_1*\mathrm{\&pi;}*f*U_0^2*\mathrm{tg\&delta;}}*\ln \left(\frac{D_i}{d_c}\right)*{10}^9$

In the formula:

θ _CmExpression conductor thread core and insulation course temperature difference,

I representes the electric current that flows through in the conductor,

R representes the AC resistance of cable conductor,

T ₁Represent equivalent insulation course thermal resistance,

π representes circular constant,

F representes electric voltage frequency,

U ₀Be voltage-to-ground (phase voltage), unit volt (V),

Tg δ is the insulation loss factor,

D _iExpression insulation course diameter,

d _cThe expression conductor diameter;

The 5th step, DIELECTRIC CONSTANTS and specific inductive capacity reference table that the 4th step was calculated compare, and draw judged result:

5.1 when the DIELECTRIC CONSTANTS that calculates be reduced to the specific inductive capacity reference table numeral 50% the time, must overhaul power cable;

5.2 when the DIELECTRIC CONSTANTS that calculates greater than the numeral of specific inductive capacity reference table 50% the time, show that state of insulation is normal.

3. the online insulation characterisitic determination methods of XLPE power cable according to claim 2 is characterized in that: the skin temperature at the power cable point place in the first step adopts the point measurement of optical fiber grating temperature monitoring system to obtain with the environment temperature of this region.

Images