CN102323496A - System for monitoring current-carrying capacity of cable conductor and method - Google Patents

Abstract

The invention provides a method for monitoring the current-carrying capacity of a cable conductor, which comprises the following steps of: firstly, monitoring the temperature of an outer sheath layer of the cable conductor and current of a cable core of the cable conductor; deducting the cable conductor into a conductor layer, a conductor shielding layer, an insulating layer, an insulated shielding layer, a cushion layer, an air gap layer, an aluminum sheath shielding layer and an outer sheath layer in advance according to the heat transfer characteristic of the cable conductor; acquiring the heat resistance of each layer for the cable conductor and the loss generated by each layer for the cable conductor according to the heat conducting performance of each layer of material of the cable; acquiring the temperature of the cable conductor by using a node method according to the heat resistance, the loss, the outer sheath layer temperature of the cable conductor and the current of the cable cote of the cable conductor, wherein the temperature of the cable conductor comprises the steady temperature and the transient temperature of the cable conductor; and monitoring the current-carrying capacity of the cable conductor according to the temperature of the conductor cable. The invention further provides a device for monitoring the current-carrying capacity of the cable conductor. According to the method and the device, disclosed by the invention, the temperature of the cable conductor can be monitored in a real time.

Description

The monitoring system of cable conductor current-carrying capacity and monitoring method

Technical field

The present invention relates to the temperature measurement technology of cable conductor, be specifically related to measure the system and method for cable conductor temperature.

Background technology

The most directly characteristic quantity of power cable conductor current-carrying capacity magnitude is that conductor temperature changes; In case confirmed cable conductor transient state and steady temperature; Just be easy to confirm power cable line transient state and stable state current-carrying capacity, remain at technical difficulty but directly measure the cable conductor temperature.

Confirm that at present current-carrying capacity of cable is by means of thermoelectricity continuous coverage power cable line hull-skin temperature occasionally; The method of passing through cable hull-skin temperature acquisition conductor temperature that is provided according to the IEC standard is then confirmed conductor temperature; And then definite current-carrying capacity of cable; This standard is under the stable state prerequisite to definite mode of conductor steady temperature, is used for the difference that AC system still is straight-flow system and system of laying according to cable, in conjunction with the cable laying environment; And the hypothesis cable conductor reaches the working temperature of the highest permission, and the utilization heat transfer principle obtains the conductor temperature of cable.

For conductor transient state temperature, the IEC standard is divided into two types on the above cable of 35kv and following cable and 35kv with cable, and they are adopted different account forms.For 35kv and following cable, standard has provided passes through cable hull-skin temperature calculating conductor method of temperature when loading cycle property load and fringe load, and this type cable can be ignored the thermal capacitance influence.For the cable more than the 35kv, under load cycling, the cable thermal capacitance can not ignore, and the cable conductor variation of temperature is divided into stable state temperature rise and the two-part summation of transient state temperature rise.The computing method of conductor temperature are similar with above-mentioned stable state prerequisite lower conductor temperature calculation method during the stable state temperature rise.The computing method of conductor temperature are to adopt to concentrate hot road thought during the transient state temperature rise, and cable is represented with the hot road of lumped parameter, obtain according to heat transfer principle.

But the definite cable conductor transient state that present IEC standard is provided and the method for steady temperature have following defective: because this standard is based on following hypothesis: 1. big ground surface is an isothermal surface; 2. cable surface is an isothermal surface; 3. superposition principle is suitable for.But in fact the cable surrounding medium is very complicated: soil is inhomogeneous, water cut is inequality; The cable line of power supply system, daily load electric current alter a great deal etc.Above factor can't satisfy the rules hypothesis, and then causes error bigger.In addition, this method hypothesis cable is 100% load and is in the worst environmental baseline, so often there is excessive nargin in result of calculation.For example crosslinked polyethylene is at current-carrying capacity 6.5% o'clock bigger than normal, allows that the working temperature value surpasses 8%, and this moment, cable life reduced half the.If is example with the 6kv crosslinked polyethylene, if current-carrying capacity is on the low side 12.6%, then the cable investment increases by 17.2%.Further, the IEC standard provides the method for 100% stable state current-carrying capacity that ambient condition is made simply, supposes uniformly, and its transient state method is also made the consistance hypothesis to daily load curve, and therefore, the result of its current-carrying capacity is relevant with many uncertain factors all the time.From these worries, the actual load of power department control at present is no more than usually and calculates 70% of ratings; And on the other hand, when summer, peak of power consumption loaded big electric current, owing to the uncertainty of various parameters is difficult to make decision.

Summary of the invention

The present invention provides a kind of monitoring system and monitoring method of cable conductor temperature, can improve the accuracy of measuring the cable conductor temperature, and then can improve current-carrying capacity.

The monitoring method of cable conductor current-carrying capacity provided by the invention comprises step:

The oversheath skin temperature of monitoring cable conductor and the core electric current of cable conductor;

According to the heat transfer characteristic of cable conductor in advance to said cable conductor being deducted marks into conductor layer, conductor shield, insulation course, insulation screen, bed course, air gap layer, aluminium sheath screen layer, external sheath layer;

Heat conductivility according to the cable layers of material obtains the thermal resistance of said each layer of cable conductor and the loss of said each layer of cable conductor generation;

Utilize nodal method to obtain the temperature of cable conductor according to the oversheath skin temperature of said thermal resistance, said loss, said cable conductor and the core electric current of cable conductor, the temperature of said cable conductor comprises the transient state temperature of the steady temperature and the said cable conductor of cable conductor;

Current-carrying capacity according to the said cable conductor of temperature monitoring of said cable conductor.

The present invention also provides the system of the core temperature of monitoring cable conductor, comprising:

The surface temperature detection module is used for detection streamer oversheath surface temperature;

Current detection module is used for the core electric current of detection streamer conductor;

The conductor temperature acquisition module is used for obtaining the thermal resistance of said each layer of cable conductor and the loss of said each layer of cable conductor generation according to the heat conductivility of cable layers of material; Said cable conductor is deducted marks into conductor layer, conductor shield, insulation course, insulation screen, bed course, air gap layer, aluminium sheath screen layer, external sheath layer;

Utilize nodal method to obtain the temperature of cable conductor according to the oversheath skin temperature of said thermal resistance, said loss, said cable conductor and the core electric current of cable conductor, the temperature of said cable conductor comprises the transient state temperature of the steady temperature and the said cable conductor of cable conductor;

The current-carrying capacity monitoring modular is used for according to cable conductor transient state temperature and steady temperature monitoring current current-carrying capacity being monitored.

The present invention obtains the cable conductor real time temperature through measuring conductive surface temperature and running current, thereby realizes the real-time monitoring of current-carrying capacity of cable.Simultaneously, can and improve cable short time current-carrying capacity nargin space according to cable conductor temperature prediction ampacity.Can accurately assess the current-carrying capacity of high-tension cable, reliable basis is provided for whether changing the heavy load cable line.Monitoring system provided by the invention can be carried out monitoring and evaluation to the current capacity of operation cable simultaneously, for the in time reliable scheduling of dispatching system provides foundation and urgent early warning.The present invention has very high economic benefit: Voltage Cable Lines Construction is adopted the increase-volume strategy of changing circuit, and the replacing of 1 110kv circuit is promptly up to up to ten million units.Achievement in research of the present invention can accurately be assessed the actual current-carrying capacity of Voltage Cable Lines Construction based on the actual load characteristic.

Description of drawings

Fig. 1 is the sectional view of the single core cable of 110kv;

Fig. 2 is the monitoring method process flow diagram of cable conductor current-carrying capacity of the present invention;

Fig. 3 is the single core cable equivalent circuit diagram under the stable state among the embodiment;

T among the figure ₁It is the cable conductor skin temperature; T ₂～T _N-3It is each stratification temperature of cable insulation; T _N-2It is the bed course temperature; T _N-1It is the air gap layer temperature; T _nIt is cable metal screen layer temperature; T ₀It is the cable jacket surface temperature; T _O1-T _OmIt is cable external heat source temperature; R ₁～R _N-3Be each layering of cable insulation and screen layer thermal resistance; R _N-1It is the air gap thermal resistance; R _nIt is the cable jacket thermal resistance; R _O1-R _OmIt is cable external heat source to cable surface medium thermal resistance; Q ₁' be the loss that cable conductor produces; Q ₂～Q _N-3Be that each layering Jie of cable decreases; Q _nIt is the cable metal shadow loss.

Fig. 4 is the monitoring method process flow diagram of cable conductor current-carrying capacity among the embodiment;

T among the figure ₁It is the cable conductor surface temperature; T ₂～T _N-3It is each stratification temperature of cable major insulation; T _N-2It is the bed course temperature; T _N-1It is air gap temperature; T _nIt is cable metal screen layer temperature; T _oIt is the cable surface temperature; T _O1～T _OmIt is cable external heat source temperature; C ₁' be the cable conductor thermal capacitance; C ₁", C ₂～C _N-3It is each layering thermal capacitance of cable major insulation; C _N-2It is the bed course thermal capacitance; C _N-1It is the air gap thermal capacitance; C _n' be cable metal screen layer thermal capacitance; C _n" be the protective coverings of cable thermal capacitance; C _oIt is cable external agency equivalence thermal capacitance; R ₁～R _N-3It is each layering thermal resistance of cable major insulation; R _N-2It is the bed course thermal resistance; R _N-1It is the air gap thermal resistance;

Fig. 5 is the monitoring system structure principle chart of cable conductor current-carrying capacity.

Embodiment

Current-carrying capacity of cable should satisfy that the cable core working temperature is no more than allowable temperature value of heat-resisting life-span of cable insulation under the function of current, and meets the conductor reliability requirement.If current-carrying capacity is bigger than normal, cause the cable core working temperature to surpass allowable value, shorten than expectation value the serviceable life of cable.If current-carrying capacity is less than normal, then core or aluminium just make full use of for obtaining, and cause the wasting of resources.The present invention proposes to utilize cable jacket skin temperature and environment temperature to obtain the cable conductor temperature, and then regulates the size of current-carrying capacity of cable through the cable conductor temperature.

Single core cable with 110kv is an example; Fig. 1 is the sectional view of the single core cable of 110kv; As shown in the figure, outwards can cable be divided into conductor, conductor shield, insulation course, insulation screen, bed course (being twining package tape among Fig. 1), air gap layer, aluminium sheath screen layer (corrugated aluminium sheath among Fig. 1), external sheath layer in having according to the heat transfer characteristic of cable material.The present invention is according to the correlativity of calorifics and circuit; Utilize Re Lufa that cable is become circuit according to above-mentioned each layer equivalence; The temperature that Re Lufa obtains cable conductor is divided into steady temperature and transient state temperature, and cable steady-state operation heating temperature rise does not change in time, and temperature rise then receives time effects during the operation of cable transient state; In the transient state temperature analysis, use many times periodic line structures; According to the steady-state analysis on cable heat generation characteristic and equivalent hot road, can obtain conductor temperature through surface temperature, environment temperature and the current value of cable, transient state is better analyzed actual motion.

In order to obtain the cable conductor temperature under the stable state, as a preferred embodiment, in order to simplify computation process, as one deck, insulation course and insulation screen are as one deck with conductor and conductor shield, and therefore, cable conductor is reduced to 6 layers altogether.The cable conductor temperature T ₁, cable insulation (containing inside and outside insulation screen) T ₂, bed course (containing zone of swelling, twining package tape etc.) temperature T ₃, the air gap layer temperature T ₄, cable metal screen layer (the for example aluminium sheath screen layer among Fig. 1) temperature T ₅, cable jacket surface temperature T ₆, as shown in Figure 2:

Step 1: detection streamer oversheath surface temperature T ₆

Step 2: (as an embodiment, the thermal resistivity of air gap layer is 41Km/W, and the thermal resistivity of aluminium sheath is 1/237Km/W according to every layer material thermal resistivity.), the thermal resistance through the every layer material of following formula acquisition single core cable comprises cable insulation (containing inside and outside screen layer) thermal resistance R ₂, bed course thermal resistance R ₃, air gap thermal resistance R ₄, cable jacket (containing anticorrosive coat) thermal resistance R ₆:

(1) obtains insulation course thermal resistance R ₂:

$R_2=\frac{{\mathrm{\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}}{2\mathrm{\&pi;}}\mathrm{Ln}(1+\frac{2t_1}{d_c})$ (formula 1)

In the formula 1: ρ _TBe insulating material thermal resistivity, unit K gm/W.d _cBe conductor diameter; t ₁Be the insulation thickness between conductor and the metallic sheath;

What deserves to be mentioned is, as an embodiment, for the t of corrugated metallic sheath ₁Press the mean value calculation of metallic sheath interior diameter: ${\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">t</figure-callout>}}_1=\frac{D_1-{\mathrm{<figure-callout\; id="2"\; label="d\; c"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">d</figure-callout>}}_c}{2}$

${\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=\frac{D_{\mathrm{It}}+D_{\mathrm{Oc}}}{2}-t_s$ (formula 2)

In the formula 2: D _ItFor with the diameter of the tangent imaginary concentric cylinder of wrinkle metallic sheath trough inside surface, D _OcBe the diameter with the tangent imaginary concentric cylinder of wrinkle metallic sheath crest, t _sBe metallic sheath thickness;

(2) the thermal resistance R of bed course ₃:

${\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_3=\frac{{\mathrm{\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}}{2\mathrm{\&pi;}}\mathrm{Ln}[1+\frac{2t_2}{D_s}]$ (formula 3)

In the formula 3: t ₂Be inner liner thickness; D _sIt is the metallic sheath external diameter.

(3) air gap layer thermal resistance R4: $R_4=\frac{{\mathrm{\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}}{2\mathrm{\&pi;}}\mathrm{Ln}[1+\frac{2t_4}{D_s}]$ (formula 4)

In the formula 4: t ₄It is internal diameter; D _sIt is external diameter.

(4) outer jacket thermal resistance R ₆:

$R_6=\frac{{\mathrm{\&rho;}}_{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}}{2\mathrm{\&pi;}}\mathrm{Ln}\left[\frac{D_{\mathrm{Oc}}+2t_6}{(D_{\mathrm{Oc}}+D_{\mathrm{It}})/2+t_s}\right]$ (formula 5)

D in the formula 5 _ItFor with the diameter of the tangent imaginary concentric cylinder of wrinkle metallic sheath trough inside surface, D _OcBe the diameter with the tangent imaginary concentric cylinder of wrinkle metallic sheath crest, t _sBe metallic sheath thickness; ρ _TBe the insulating material thermal resistivity.

As an embodiment, because conductor thermal resistance R ₁Metal screen layer thermal resistance R ₅All be metallic conductor, can ignore as 0 and handle.

Step 3: because the present invention need obtain the cable real time temperature; The cable layers of material can show under the condition that cable core temperature and external condition change than thermal characteristics; Therefore the present invention also provides the approach that obtains cable layers of material thermal capacitance value; Be equivalent to the electric capacity in Fig. 3 circuit, the electric capacity that needs to obtain is shown in hereinafter:

(1) obtains conductor thermal capacitance C ₁:

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_1={\mathrm{\&sigma;}}_c\frac{\mathrm{\&pi;}}{4}{d}_c(D_i-d_c)$ (formula 6)

In the formula 6: D _iBe the insulation external diameter; δ _cCable conductor volumetric specific heat capacity, unit are J/m ³K; d _cBe conductor diameter.

(2) insulation course thermal capacitance C ₂:

${\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_2={\mathrm{\&delta;}}_{\mathrm{XLPE}}\frac{\mathrm{\&pi;}}{4}{D}_i(D_i-d_c)$ (formula 7)

δ in the formula 7 _XLPEExpression: the volumetric specific heat capacity of insulation course, unit are J/m ³K;

(3) bed course (twining package tape) thermal capacitance C3

C ₃=δ _rρ _rS _r(formula 8)

δ in the formula 8 _rThe specific heat capacity of twining package tape, ρ _rBe the specific heat capacity of twining package tape, s _rSectional area for twining package tape;

(4) air gap layer thermal capacitance C ₄=C ₄=δ _qρ _qS _q(formula 9)

δ in the formula 9 _qBe the specific heat capacity of air, ρ _qBe the specific heat capacity of air, s _qSectional area for air;

(3) metal level thermal capacitance C ₅:

$C_5={\mathrm{\&delta;}}_{\mathrm{Al}}\frac{\mathrm{\&pi;}}{4}{D}_2(D_2-D_i)$ (formula 10)

δ in the formula 10 _AlExpression: the volumetric specific heat capacity of metallic aluminium sheath, unit are J/m ³K;

(4) outer jacket thermal capacitance C ₆:

$C_6={\mathrm{\&delta;}}_{\mathrm{XLPE}}\frac{\mathrm{\&pi;}}{4}{D}_3(D_3-D_2)$ (formula 11)

D in the formula 11 ₃Be the outside diameter of cable.

Step 4: the thermal resistance of acquisition layers of material and thermal capacitance and then layers of material loss are equivalent to the current source in the electrical circuit, so find the solution the corresponding waste of different layers different materials, the loss Q that cable conductor produces according to materialogy in this step ₁, each layering of cable is situated between and decreases Q ₂-Q _N-3, protective coverings of cable loss Q _n(each layering of cable insulation is situated between and decreases Q ₂-Q _N-3Total loss sum is W _d)

The loss Q that the unit length cable conductor produces ₁, Q ₁=I ₂GR ^S

Protective coverings of cable loss Q _nSolution formula such as insulation course loss W _dIn like manner:

The insulation loss W of unit length single core cable _dComputing formula be:

$W_d=\mathrm{\&omega;}\&CenterDot;c\&CenterDot;U_0^2\&CenterDot;\mathrm{tg\&delta;}(W/m)$

Wherein, ω=2 π f; U ₀It is voltage-to-ground; Tg δ is the insulation loss factor under power-supply system and working temperature; C is the unit length electric cable capacitance.

Obtain by following formula for round conductor electric capacity:

$c=\frac{\mathrm{\&epsiv;}}{18\ln \left(\frac{D_i}{d_c}\right)}\&times;{10}^{-9}(F/m)$

Wherein ε is the relative dielectric coefficient of insulating material, the acquisition of can tabling look-up; D _iBe insulation course diameter (except the screen layer); d _cBe conductor diameter, (then comprising screen layer) if any screen layer.

The protective metal shell loss is λ with the ratio of core loss ₁, the ratio λ of protective metal shell loss and core loss ₁Comprise circulation loss λ ' ₁With eddy current loss λ " ₁Therefore total losses are:

λ ₁＝λ′ ₁+λ″ ₁

It is worthy of note,, only need to consider circulation loss the situation of metallic sheath two ends interconnection ground connection.

${\mathrm{\&lambda;}}_1^{\&prime;}=\frac{{\mathrm{<figure-callout\; id="1"\; label="R\; S\; R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_S}{R}\frac{1}{1+{\left(\frac{R_S}{X}\right)}^2}$

Wherein, R _SResistivity for the cable unit length metallic sheath under the working temperature;

$R_S=\frac{{\mathrm{\&rho;}}_s}{A_s}[1+{\mathrm{\&alpha;}}_{20}(\mathrm{\&theta;}\&CenterDot;\mathrm{\&eta;}-20)](\mathrm{\&Omega;}/m)$

Wherein, ρ _sIt is the conductance of metallic sheath material; A _sIt is the sectional area of metallic sheath; α ₂₀The temperature coefficient of material when being 20 ℃ can check in through GB/T 3956-1997; θ is the conductor working temperature; η is the temperature and the conductor temperature ratio of metallic sheath, generally gets (0.7-0.8); X is the reactance of unit length metallic sheath or shielding.

$X=2\mathrm{\&omega;}{10}^{-7}\ln \left(\frac{2s}{d}\right)$

ω＝2π×f(1/s)

Wherein, f is a frequency; S is the conductor axial line distance; D is the metallic sheath mean diameter.

Step 5: according to the approximation of Re Lu and circuit, because cable jacket surface temperature T ₆Be monitor value, cable jacket surface temperature T ₆Each parameter value of acquisition obtains cable conductor temperature T in step 1 to the step 3 with utilizing according to the nodal method of analysis ₁The present invention utilizes Re Lufa that the equivalence of the single core cable under the stable state is become as shown in Figure 3.Modal equation such as formula 12 according to Fig. 3 acquisition:

$\frac{1}{R_1}{T}_1-\frac{1}{R_1}{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}_2={\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1$

$-\frac{1}{R_1}{T}_2(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{1}{R_2})T_2-\frac{1}{R_2}{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">T</figure-callout>}}_2=Q_2$ (formula 12)

$-\frac{1}{R_2}{T}_2(\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}+\frac{1}{R_3})T_3-\frac{1}{R_3}{T}_4={\mathrm{<figure-callout\; id="3"\; label="Q"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">Q</figure-callout>}}_3$

L L L L L L L

$-\frac{1}{R_{n-2}}{T}_{n-2}(\frac{1}{R_{n-2}}+\frac{1}{R_{n-1}})T_{n-1}-\frac{1}{R_{n-1}}{T}_n=0$

$-\frac{1}{R_{n-1}}{T}_{n-1}(\frac{1}{R_{n-1}}+\frac{1}{R_n})T_n=Q_n+\frac{1}{R_n}{T}_o$

Following formula transformed can draw following formula:

AT＝Q T＝A ^-1Q

Wherein:

$A=\left[\begin{array}{ccccc}\frac{1}{R_1}& -\frac{1}{R_1}& & K& \\ -\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}& \frac{1}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}+\frac{1}{R_1}& -\frac{1}{R_2}& & \\ & -\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}& \frac{1}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}+\frac{1}{R_3}& -\frac{1}{R_3}& \\ & & & K& \\ & & & -\frac{1}{R_{n-1}}& \frac{1}{R_{n-1}}+\frac{1}{R_n}\end{array}\right]$

T＝[T ₁ T ₂ T ₃ K T _n]

Q＝[Q ₁ Q ₂ Q ₃ K Q _n+T ₀/R ₀]

A ^-1Be the inverse matrix of A, T ₁Be the cable conductor temperature A that is asked and confirm T by the structure and material parameter of cable ₂～T _N-3Be the temperature of insulation course and screen layer, T _N-2Be bed course temperature, T _N-1Be air gap layer temperature, T _nBe the metal screen layer temperature.Q is confirmed by cable conductor loss, Jie's damage and metallic sheath and screen layer loss.External heat source T does not appear in the following formula _O1～T _Om, the cable conductor temperature can be through measuring oversheath surface temperature T ₆Measure, therefore the influence that need not to consider external thermal resistance, thermal source can consider cable external heat source temperature T because the Ben Relu model is based on the skin temperature calculating cable conductor temperature of cable _O1-T _OmWith cable external heat source to cable surface medium thermal resistance R _O1-R _OmFor accurately, can insulation screen be divided into the n-3 layer, simultaneously in order to simplify calculating, can think R ₁～R _N-3Be the thermal resistance of insulation course and screen layer, R _N-2Be bed course thermal resistance, R _N-1Be air gap layer thermal resistance, R _nBe the external sheath layer thermal resistance.

More than be to obtain cable conductor method of temperature under the steady temperature, the present invention provides also that cable conductor method of temperature: Fig. 4 is the transient state equivalent circuit diagram of single core cable under the acquisition transient state temperature.

The electric current of actual motion cable and external environment are always Protean; Because the change of cable running current and then will influence the loss of each layer of cable and the cable rate of heat dispation; And destroyed the balance of heat production and heat radiation in the steady-state operation cable, further caused the conductor temperature of cable to raise or descend.At cable fluctuation of service state; Cable layers of material heat accumulation characteristic just can display; In order to obtain cable core temperature and each layer of cable temperature in real time, therefore not only will obtain the thermal resistance of cable layers of material, but also the specific heat capacity of with good grounds layers of material is calculated corresponding thermal capacitance value.Obtain relevant parameter value according to above-mentioned steps 1 to step 4, obtain the conductor temperature T of cable then according to following modal equation ₁(t), i.e. t cable conductor temperature constantly:

T _n+1＝ξ+h[AT _n+EBQ] (1)

$h=\frac{t}{n}$

Wherein, T=[T ₁T ₂T ₃... T _n] ^T

If T (0)=ξ is arranged during t=0

$A=\left[\begin{array}{cccccc}-\frac{1}{C_1{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}& \frac{1}{C_1{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}& & & ...& \\ \frac{1}{C_2{R}_1}& -\frac{1}{C_2}(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{1}{R_2})& \frac{1}{C_2{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}& & & \\ & \frac{1}{C_3{R}_2}& -\frac{1}{C_3{R}_3}(\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}+\frac{1}{R_3})& \frac{1}{C_3{\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">R</figure-callout>}}_3}& & \\ & ...& & & ...& \\ & & & & \frac{1}{C_n{R}_{n-1}}& -\frac{1}{C_n}(\frac{1}{R_{n-1}}+\frac{1}{R_n})\end{array}\right]$

E---unit matrix

$B={\left[\begin{array}{ccccc}\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}& \frac{1}{{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}& \frac{1}{{\mathrm{<figure-callout\; id="3"\; label="C"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_3}& ......& \frac{1}{C_n}\end{array}\right]}^T$

$Q={\left[\begin{array}{ccccc}{Q}_1& Q_2& {\mathrm{<figure-callout\; id="3"\; label="Q"\; filenames="HDA0000065104480000031.png"\; state="\{\{state\}\}">Q</figure-callout>}}_3& ......& Q_n+\frac{1}{R_n}{T}_o\end{array}\right]}^T$

What deserves to be mentioned is: h should be tending towards 0 in theory, and in fact the more little computational accuracy of h is high more.

The method for determination of amount that respectively becomes in the following formula can repeat no more with reference to formula 12.Obtain the transient state temperature or steady temperature of cable conductor according to above-mentioned steps after, confirm the current-carrying capacity of cable according to the conductor temperature of cable.

The skin temperature that the present invention is based on cable is calculated the core temperature of cable; Can accurately assess the current-carrying capacity of high-tension cable; On IEC criterion calculation value, get a promotion; For whether changing the heavy load cable line reliable basis is provided, can accurately assesses the actual current-carrying capacity of Voltage Cable Lines Construction according to the actual load characteristic.Because Voltage Cable Lines Construction is adopted the increase-volume strategy of changing circuit, and the replacing of 1 110kv circuit is promptly up to up to ten million units, so the present invention can produce huge economic benefit.

In addition, handle, can insulation course and insulation screen be classified as the identical one deck of thermal resistivity as a simplification to technique scheme; Equally, conductor shield also can be classified as the identical one deck of thermal resistivity with conductor layer, simplifies computation process.

The present invention also provides a kind of monitoring system of cable conductor current-carrying capacity, and is as shown in Figure 5.The surface temperature detection module is used for detection streamer oversheath surface temperature; Current detection module is used for the core electric current of detection streamer conductor; The conductor temperature acquisition module is used for obtaining the thermal resistance of said each layer of cable conductor and the loss of said each layer of cable conductor generation according to the heat conductivility of cable layers of material; Said cable conductor is deducted marks into conductor layer, conductor shield, insulation course, insulation screen, bed course, air gap layer, aluminium sheath screen layer, external sheath layer; Utilize nodal method to obtain the temperature of cable conductor according to the oversheath skin temperature of said thermal resistance, said loss, said cable conductor and the core electric current of cable conductor, the temperature of said cable conductor comprises the transient state temperature of the steady temperature and the said cable conductor of cable conductor; The current-carrying capacity monitoring modular is used for according to cable conductor transient state temperature and steady temperature monitoring current current-carrying capacity being monitored.

It is worthy of note; The monitoring method and the monitoring system of the cable conductor current-carrying capacity that the present invention is above all are to be example with the single core cable; Processing changed and simplified to the cable of other types can, re-uses above-mentioned monitoring method and monitoring system after changing into single core cable.

Above-described embodiment of the present invention does not constitute the qualification to protection domain of the present invention.Any modification of within spirit of the present invention and principle, being done, be equal to replacement and improvement etc., all should be included within the claim protection domain of the present invention.

Claims (9)

1. the monitoring method of a cable conductor current-carrying capacity is characterized in that, comprises step:

The oversheath skin temperature of monitoring cable conductor and the core electric current of cable conductor;

According to the heat transfer characteristic of cable conductor in advance to said cable conductor being deducted marks into conductor layer, conductor shield, insulation course, insulation screen, bed course, air gap layer, aluminium sheath screen layer, external sheath layer;

Heat conductivility according to the cable layers of material obtains the thermal resistance of said each layer of cable conductor and the loss of said each layer of cable conductor generation;

Utilize nodal method to obtain the temperature of cable conductor according to the oversheath skin temperature of said thermal resistance, said loss, said cable conductor and the core electric current of cable conductor, the temperature of said cable conductor comprises the transient state temperature of the steady temperature and the said cable conductor of cable conductor;

Current-carrying capacity according to the said cable conductor of temperature monitoring of said cable conductor.

2. the monitoring method of cable conductor current-carrying capacity according to claim 1 is characterized in that: said conductor layer is identical with the thermal resistivity of said conductor shield.

3. the monitoring method of cable conductor current-carrying capacity according to claim 1 is characterized in that: said insulation course is identical with the thermal resistivity of said insulation screen.

4. according to the monitoring method of any described cable conductor current-carrying capacity in the claim 1 to 3, it is characterized in that:

The thermal resistivity of said conductor shield and said conductor layer is identical.

5. a system that monitors the core temperature of cable conductor is characterized in that, comprising:

The surface temperature detection module is used for detection streamer oversheath surface temperature;

Current detection module is used for the core electric current of detection streamer conductor;

The conductor temperature acquisition module is used for obtaining the thermal resistance of said each layer of cable conductor and the loss of said each layer of cable conductor generation according to the heat conductivility of cable layers of material; Said cable conductor is deducted marks into conductor layer, conductor shield, insulation course, insulation screen, bed course, air gap layer, aluminium sheath screen layer, external sheath layer;

Utilize nodal method to obtain the temperature of cable conductor according to the oversheath skin temperature of said thermal resistance, said loss, said cable conductor and the core electric current of cable conductor, the temperature of said cable conductor comprises the transient state temperature of the steady temperature and the said cable conductor of cable conductor;

The current-carrying capacity monitoring modular is used for according to cable conductor transient state temperature and steady temperature monitoring current current-carrying capacity being monitored.

6. the monitoring system of cable conductor current-carrying capacity according to claim 5 is characterized in that: said conductor layer is identical with the thermal resistivity of said conductor shield.

7. the monitoring system of cable conductor current-carrying capacity according to claim 5 is characterized in that: said insulation course is identical with the thermal resistivity of said insulation screen.

8. according to the monitoring system of any described cable conductor current-carrying capacity in the claim 5 to 7, it is characterized in that:

The thermal resistivity of said conductor shield and said conductor layer is identical.

9. the monitoring system of cable conductor current-carrying capacity according to claim 8 is characterized in that:

Said cable is a single core cable.

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