CN101697291B - Method for calculating OPGW optical cable short circuit current heat effect by using improved synthetic method - Google Patents

Abstract

The invention relates to a method for calculating the OPGW optical cable short circuit current heat effect by using an improved synthetic method, which comprises the following steps: giving a line structure and a geometric dimension relation, giving a current intensity value or effective value, giving (or selecting) the structure and the relevant dimension of an optical cable, giving the duration of short circuit current and respectively carrying out section processing on the time and the dimension of the optical cable; starting to solve the parameter in the next time interval by the initial condition; solving the distribution of current on all media according to the skin effect; solving heat by the current in the time interval and the area according to the current heat effect principle and further solving the temperature of the area; solving heat exchange by the temperature and the resistance in the area and further solving the current distribution; solving the heat and the temperature by the current distribution; and repeating till the calculation in the given time is finished. The invention can be used for solving the highest temperature of the optical cable and the distribution of the temperature along with time and space by giving the process of the short circuit current and solving the maximal allowable short circuit current of the given optical cable by giving limiting temperature and can also give the temperature distribution.

Description

Improved integration algorithm is utilized to calculate the method for OPGW optical cable Short circuit current heating effect

Technical field

The present invention relates to field of power, particularly relate to a kind of method utilizing improved integration algorithm to calculate OPGW optical cable Short circuit current heating effect.

Background technology

At present, Optical Fiber composite overhead Ground Wire (OPGW) is used on a large scale, and its Short circuit current heating effect is one of current study hotspot.OPGW optical is a kind of composite overhead ground wire integrating communication function and transmission line lightning function, therefore in the design and selection of OPGW, the performance requirement of optical fiber communication should be considered, consider the requirement such as electric property and mechanical strength of overhead ground wire again, thermal effect requirement to be considered especially, namely, when circuit is short-circuited fault, the electric current flowing through OPGW does not cause the temperature rise of its internal optical fiber to be above standard and makes optical fiber too fast aging or cause the direct damage of optical fiber.

There is conductor to exist, during by electric current, will joule's heat energy be produced.Electric current I that OPGW passes through square and the product of function of current time T are proportional to the temperature rise of OPGW.The savings of heat makes conductor temperature raise.The temperature rise of the ectonexine conductor of OPGW generally can be divided into two kinds of situations: a kind of is long-term fever effect influenced by ambient temperature, in this case, by modes such as the convection current of conduction, radiation and air, conductor constantly by heat to external diffusion, and reach poised state; Another kind is the heating functioin of short circuit, and in this case, can not considering to outdiffusion of heat, heat will be stored in body completely, and the moment showing as temperature sharply raises.By short circuit test standard-required, short circuit current snap is generally no more than 0.5 second, considers relatively actual conditions by this situation.In temperature rise calculates, can consider that the action of relaying protection is very fast, the short circuit current duration is very short, and the heat in OPGW has little time outwardly to spread, and OPGW can be considered as and the electric heating transfer problem in the closed area of external world's thermal insulation.Different with structure by the type of OPGW, instantaneous maximum permissible temperature is also different, and temperature maximum often occurs between optical fiber time outer field adjacent two AA lines.To fill the stainless loose casing fiber optic of oil plant, the temperature of optical fiber should higher than 180 DEG C.

The maximum current I flowing through OPGW during correct computational scheme generation single-phase short circuit is very important.If the I value provided in the design is bigger than normal, calculates too conservative, then can cause waste economically; If but the I value provided is less than normal, then may damage optical fiber when line failure.Generally, when fault point is positioned at line shelves (i.e. the first base shaft tower) of transformer station, the current component flowing through ground wire is maximum.Therefore, in order to check the thermal effect of OPGW, generally only need calculating to flow through the electric current of OPGW and the temperature rise of generation thereof when the first base shaft tower generation shorted to earth.

The method of current calculating optical cable thermal effect has same warm therapy, different warm therapy, synthesis, theoretical approximation method etc.

(1) same to warm therapy

The derivation of this theoretical formula is that when considering inner transient heat transfer, various metal reaches same temperature simultaneously, therefore also can be called same warm therapy.The method is overall as one using optical cable, does not consider the distribution of electric current.Because computational methods are simple, be therefore once widely adopted.

(2) different warm therapy

In OPGW, heat transfer ratio heating is much slow, so within the short circuit current duration, the maximum temperature that various metal reaches is different.Experiment shows that the temperature difference between different metal can reach more than 100 DEG C.Basic different warm therapy does not consider heat transfer, each metal the heat sent out absorb temperature rise by oneself.The variations in temperature of each metal of adstante febre is different, and resistance ratio, in change, is obtained by resistance inverse proportion the electric current that each metallic member distributes, the current sharing ratio between each metal is constantly being changed.These computational methods are more conservative, but than accurate with warm therapy.

It is first suppose that a short circuit current is to calculate the maximum temperature of each metal that the permissible short circuit current of different warm therapy calculates.Temperature as certain part exceedes its permissible value, then can suitably reduce electric current and calculate; Otherwise raising electric current.Iteration like this is until maximum temperature equals permissible value.

(3) synthesis

Synthesis is based on different warm therapy, supplements heat transfer and skin effect.Because heat radiation is than slow several thousand times of heating, therefore can ignore.And in OPGW, ground wire is generally made up of several layers of plain conductor, be Multi-contact between each layer conductor, and surface have oxide layer dirty with collection.Capacity of heat transmission between them is poor, and the short circuit current duration is very short, and the heat that electric current produces on the wire of each top layer is difficult to exchange, and also has little time outwardly to spread in air.So this can regard an adiabatic process approx as.

(4) theoretical approximation method

In actual applications, short-circuit current density and optical cable short circuit current bearing capacity also can be adopted to reflect the thermal effect of optical cable.

The method adopts theory calculate substantially, with the process comparing class of same warm therapy seemingly, only introduce current density parameter herein, the current density that recycling calculates distributes electric current in a certain way between each unit medium, namely with same warm therapy ratio, in distribution electric current, process has been done.Therefore, the method precision should with the magnitudes such as same warm therapy process.By said method, given limit temperature can solve current limit, and given short circuit current can solve maximum temperature.

To sum up, " same to warm therapy " considers the identical Traditional calculating methods of temperature of the various metal of OPGW; " different warm therapy " does not then consider heat transfer, and various metal temperature is different; " synthesis " suitably considers heat transfer, and consider skin effect, thus this method more simultaneously, but do not consider the heat trnasfer between each layer metal and heat radiation.

Summary of the invention

The object of the invention is: the size of the short circuit current that can bear during the OPGW optical cable short circuit of accurate analog different structure, can be used for the structure and the type selecting that instruct OPGW optical cable.

Therefore, the invention provides a kind of method utilizing improved integration algorithm to calculate OPGW optical cable Short circuit current heating effect, it is characterized in that given line construction and physical dimension relation, given current strength or effective value, the structure of given or selected optical cable and relative dimensions, the given short circuit current duration, time and cable size are carried out segment processing respectively, utilize initial condition, start the parameter solving subsequent period, the distribution of electric current on each medium is solved according to skin effect, according to heating effect of current principle, heat is solved by the electric current in this this region of period, and then solve this regional temperature, heat exchange is solved by this temperature, and ask this zone resistance, and and then ask CURRENT DISTRIBUTION again, heat and temperature is asked again by CURRENT DISTRIBUTION, so repeatedly, until complete the calculating of preset time.

Method as above, is further characterized in that:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature;

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise: density, conductivity and temperature coefficient etc., length l, the geometry space D between itself and power line and the current peak I in power line and phase place;

Output rusults: the stable temperature of OPGW optical;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

$M_{21}=\frac{\mathrm{\μ}}{2\mathrm{\π}}(l*\ln \frac{l+\sqrt{D^2+l^2}}{D}-\sqrt{D^2+l^2}+D);$

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20)),

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer, if OPGW optical has n layer;

First calculate coefficient correlation, wherein monofilament conductivity is γ, and temperature coefficient is α,

$\mathrm{\γ}\left(t\right)=\frac{1}{{\mathrm{\ρ}}_{20}[1+\mathrm{\α}*(T\left(t\right)-20)]},$

Current spread coefficient $\mathrm{\Γ}=\sqrt{2\mathrm{\π\μ\γ}}$

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

$\left\{\begin{array}{c}{A}_1=\frac{2\mathrm{\&pi;}{e}^{-{\mathrm{\&Gamma;}}_1{R}_1}}{{{\mathrm{\&Gamma;}}_1}^2}(e^{{\mathrm{\&Gamma;}}_1{R}_1}(-1+R_1{\mathrm{\&Gamma;}}_1)+e^{{\mathrm{\&Gamma;}}_1{R}_2}(1-R_2{\mathrm{\&Gamma;}}_1))\\ A_i=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{i}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-{\mathrm{\&Gamma;}}_{i-1}(R_{i-1}-R_i)-{\mathrm{\&Gamma;}}_i{R}_i}}{{{\mathrm{\&Gamma;}}_2}^2}(e^{{\mathrm{\&Gamma;}}_i{R}_i}(-1+R_i{\mathrm{\&Gamma;}}_i)+e^{{\mathrm{\&Gamma;}}_i{R}_{i+1}}(1-R_{i+1}{\mathrm{\&Gamma;}}_i))1<i<n\\ A_n=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{n}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-((\underset{k=1}{\overset{n-1}{\mathrm{\&Sigma;}}}{\mathrm{\&Gamma;}}_k(R_k-R_{k+1})+{\mathrm{\&Gamma;}}_n{R}_n)}}{{{\mathrm{\&Gamma;}}_n}^2}(1+e^{{\mathrm{\&Gamma;}}_n{R}_n}(-1+{\mathrm{\&Gamma;}}_n{R}_n))\end{array}\right.$

Obtain surface current density again in outermost value $J_1=\frac{I}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{A}_i}$

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature that each layer conductor is carved at this moment, getting the time interval is Δ t;

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits $\mathrm{exchange}\_\mathrm{heat}=\frac{2\mathrm{\&pi;\&lambda;}*\mathrm{length}}{\ln (\mathrm{outdiameter}/\mathrm{indiametere})}*(T1\left(t\right)-T2\left(t\right))$

(one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of)

Outermost layer is to the heat of atmospheric dispersion

Loss_heat=α * (T _{outer wall}(t)-T _air(t)) * Δ t

(α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air) total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality);

5th step: the time becomes t=t+ Δ t, then counts from second step, until complete the calculating of preset time.

For given short circuit current process ask the maximum temperature of optical cable and temperature in time with the distribution in space, its step is as follows:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature;

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise density, conductivity and temperature coefficient etc., length l, the geometry space D between itself and power line and the current peak I in power line and phase place,

Output rusults: maximum temperature and temperature in time with the distribution in space;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

$M_{21}=\frac{\mathrm{\&mu;}}{2\mathrm{\&pi;}}(l*\ln \frac{l+\sqrt{D^2+l^2}}{D}-\sqrt{D^2+l^2}+D)$

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20))

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer,

First calculate coefficient correlation (monofilament conductivity gamma, temperature coefficient α)

$\mathrm{\&gamma;}\left(t\right)=\frac{1}{{\mathrm{\&rho;}}_{20}[1+\mathrm{\&alpha;}*(T\left(t\right)-20)]},$

Current spread coefficient $\mathrm{\&Gamma;}=\sqrt{2\mathrm{\&pi;\&mu;\&gamma;}}$

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

$\left\{\begin{array}{c}{A}_1=\frac{2\mathrm{\&pi;}{e}^{-{\mathrm{\&Gamma;}}_1{R}_1}}{{{\mathrm{\&Gamma;}}_1}^2}(e^{{\mathrm{\&Gamma;}}_1{R}_1}(-1+R_1{\mathrm{\&Gamma;}}_1)+e^{{\mathrm{\&Gamma;}}_1{R}_2}(1-R_2{\mathrm{\&Gamma;}}_1))\\ A_i=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{i}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-{\mathrm{\&Gamma;}}_{i-1}(R_{i-1}-R_i)-{\mathrm{\&Gamma;}}_i{R}_i}}{{{\mathrm{\&Gamma;}}_2}^2}(e^{{\mathrm{\&Gamma;}}_i{R}_i}(-1+R_i{\mathrm{\&Gamma;}}_i)+e^{{\mathrm{\&Gamma;}}_i{R}_{i+1}}(1-R_{i+1}{\mathrm{\&Gamma;}}_i))1<i<n\\ A_n=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{n}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-((\underset{k=1}{\overset{n-1}{\mathrm{\&Sigma;}}}{\mathrm{\&Gamma;}}_k(R_k-R_{k+1})+{\mathrm{\&Gamma;}}_n{R}_n)}}{{{\mathrm{\&Gamma;}}_n}^2}(1+e^{{\mathrm{\&Gamma;}}_n{R}_n}(-1+{\mathrm{\&Gamma;}}_n{R}_n))\end{array}\right.$

Obtain surface current density again in outermost value $J_1=\frac{I}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{A}_i}$

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature that each layer conductor is carved at this moment, getting the time interval is Δ t

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits $\mathrm{exchange}\_\mathrm{heat}=\frac{2\mathrm{\&pi;\&lambda;}*\mathrm{length}}{\ln (\mathrm{outdiameter}/\mathrm{indiametere})}*(T1\left(t\right)-T2\left(t\right))$

(one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of)

Outermost layer is to the heat loss_heat=α * (T of atmospheric dispersion _{outer wall}(t)-T _air(t)) * Δ t

(α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air) total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality)

Writing time t and temperature T (t) now

C.T T (t+ Δ t) and T (t), gets higher value T _max=max (T (t), T (t+ Δ t))

5th step: the time becomes t=t+ Δ t, then counts from second step, until complete preset time, draws T (t) over time, and maximum temperature T _max.

For given limit temperature, ask the maximum permissible short circuit current of given optical cable, equally also can provide Temperature Distribution, its step is as follows:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature.；

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise density, conductivity and temperature coefficient etc., length l, the geometry space D between itself and power line and the current peak I in power line and phase place, setting short-circuit current value;

Output rusults: maximum permissible short circuit current and Temperature Distribution;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

$M_{21}=\frac{\mathrm{\&mu;}}{2\mathrm{\&pi;}}(l*\ln \frac{l+\sqrt{D^2+l^2}}{D}-\sqrt{D^2+l^2}+D)$

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20))

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer;

First calculate coefficient correlation (monofilament conductivity gamma, temperature coefficient α)

$\mathrm{\&gamma;}\left(t\right)=\frac{1}{{\mathrm{\&rho;}}_{20}[1+\mathrm{\&alpha;}*(T\left(t\right)-20)]},$

Current spread coefficient $\mathrm{\&Gamma;}=\sqrt{2\mathrm{\&pi;\&mu;\&gamma;}}$

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

$\left\{\begin{array}{c}{A}_1=\frac{2\mathrm{\&pi;}{e}^{-{\mathrm{\&Gamma;}}_1{R}_1}}{{{\mathrm{\&Gamma;}}_1}^2}(e^{{\mathrm{\&Gamma;}}_1{R}_1}(-1+R_1{\mathrm{\&Gamma;}}_1)+e^{{\mathrm{\&Gamma;}}_1{R}_2}(1-R_2{\mathrm{\&Gamma;}}_1))\\ A_i=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{i}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-{\mathrm{\&Gamma;}}_{i-1}(R_{i-1}-R_i)-{\mathrm{\&Gamma;}}_i{R}_i}}{{{\mathrm{\&Gamma;}}_2}^2}(e^{{\mathrm{\&Gamma;}}_i{R}_i}(-1+R_i{\mathrm{\&Gamma;}}_i)+e^{{\mathrm{\&Gamma;}}_i{R}_{i+1}}(1-R_{i+1}{\mathrm{\&Gamma;}}_i))1<i<n\\ A_n=\frac{2\mathrm{\&pi;}\left(\underset{k=2}{\overset{n}{\mathrm{\&Pi;}}}{B}_{k-1,k}\right)e^{-((\underset{k=1}{\overset{n-1}{\mathrm{\&Sigma;}}}{\mathrm{\&Gamma;}}_k(R_k-R_{k+1})+{\mathrm{\&Gamma;}}_n{R}_n)}}{{{\mathrm{\&Gamma;}}_n}^2}(1+e^{{\mathrm{\&Gamma;}}_n{R}_n}(-1+{\mathrm{\&Gamma;}}_n{R}_n))\end{array}\right.$

Obtain surface current density again in outermost value $J_1=\frac{I}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{A}_i}$

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature (getting the time interval is Δ t) that each layer conductor is carved at this moment

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits $\mathrm{exchange}\_\mathrm{heat}=\frac{2\mathrm{\&pi;\&lambda;}*\mathrm{length}}{\ln (\mathrm{outdiameter}/\mathrm{indiametere})}*(T1\left(t\right)-T2\left(t\right))$

(one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of)

Outermost layer is to the heat loss_heat=α * (T of atmospheric dispersion _{outer wall}(t)-T _air(t)) * Δ t

(α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air) total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality),

Writing time t and temperature T (t) now,

C.T T (t+ Δ t) and T (t), gets higher value T _max=max (T (t), T (t+ Δ t));

5th step: the time becomes t=t+ Δ t, then counts from second step, until temperature stabilization.Relatively T _maxwith the difference of giving fixed temperature, change short circuit current and recalculate, until temperature T _maxstop time equal with given temperature value calculating, record temperature in time and spatial variations.

The invention has the beneficial effects as follows: the method that the improved integration algorithm that in the present invention, optical cable thermal effect calculates calculates OPGW optical cable Short circuit current heating effect improves on the basis of the synthesis of prior art, its compared with the synthesis of prior art advantage applies in environmental impact, the distribution of electric current skin effect in optical cable, heat exchange etc.:

1, investigate initial condition, calculate the induced current thermal effect under OPGW circuit normal running (operation) conditions, whole process considers heat transfer, radiation processes, and draws the influence degree of transmission system to initial condition accordingly.

2, all consider in the whole process of short circuit the radiation processes that conducts heat, heat transfer adopts cylindrical process but not original linear pattern process, and carry out the method for layered method, make the more realistic process of result of calculation, embody the feature of overall emulation instead of only calculate certain several parameter.

3, propose neodoxy, the new algorithm that utilization index class curve simulation field is measured and electric current distributes in OPGW, by third-party the results show the method, there is higher precision, and more practical.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the present invention is further described.

Fig. 1 is according to the calculation process schematic diagram calculating the initial temperature of the method for OPGW optical cable Short circuit current heating effect of the present invention.Due to faradic existence, the temperature in OPGW will raise gradually, but outermost layer will dispel the heat to air simultaneously, and heat exchange also will be carried out in inside, and this tends towards stability with regard to making the temperature of OPGW, instead of rising of having no limits.

Fig. 2 is according to the calculation process schematic diagram calculating the temperature of the short circuit current of the initial temperature of the method for OPGW optical cable Short circuit current heating effect of the present invention.

Embodiment

(1) environmental influence research

Environment is comparatively large on the impact of OPGW optical cable, and indication environment of the present invention is mainly reflected in the impact of transmission line system on optical cable, shows as the change of initial condition.

Generally the initial temperature of optical cable is equal to ambient temperature, in fact when optical cable is in the electromagnetic environment of transmission line, induced current can be formed in optical cable inside, although this induced current is little, but still impact can be had on optical cable temperature, this section by the computational methods of this induced current thermal effect under this environment of proposition, and is applied in the exploitation of program.

Induced current in optical cable derives from the mutual inductance effect of the electric current transmitted in neighbouring power circuit, can be derived the electric current in optical cable by electromagnetic induction principle.

Induced electromotive force is relevant with coefficient of mutual inductance and curent change.

The heat of each several part can be calculated according to induced current, and then calculate the resistance variations of each several part, heat exchange and radiating effect, variations in temperature, and the variation tendency of each physical quantity along with time variations.

(2) the skin effect research of optical cable electric current

According to electromagnetic theory, in electromagnetic environment, the phenomenon that field amount trends towards being distributed in conductive surface is called skin effect, and the field amount that is actually of its reflection is entering the attenuation process of conductor.In recent years, along with deepening continuously of studying OPGW, the skin effect phenomenon in optical cable also more and more causes the attention of people, because this is related to the accuracy calculated with analyzing.Usually, when not considering skin effect, process problem is very simple, and electric current distributes by resistance inverse ratio mode in each conducting medium part, but this differs far away with actual conditions again.Therefore, people start to introduce this effect in the calculation gradually, but due to the more complicated of problem own, therefore, normal employing introducing one parameter is similar to and replaces this effect, specifically, and general introducing parameter F, and optical cable conductive compositions is divided into inside and outside two parts, during calculating, reduce inner electric current artificially, reduction ratio is F, the electric current reduced is added on outer contact again, and F is determined by experiment.This process visible does not consider the rule of skin effect itself, just embodies this effect by the plus-minus of electric current, and process is too simple, easily disconnects with actual, and needs experiment to determine due to F, makes the method be difficult to be applied in reality.

1. index process

Known to skin effect research, if consider the conductive plane infinitely stretched along certain direction, then electromagnetic field amount is approximately exponential distribution along depth direction distribution.

Optical cable surface is not plane herein, and therefore for this cylindrical structure of optical cable, simple exponential distribution formula is not strictly set up.But when frequency is higher or electric conductivity is fine, skin depth is little, and cylindrical radius is relatively large, then can be similar to and regard dull and stereotyped as, fields inside amount exponentially decays with distance.Although the frequency under this condition is not very high, electric conductivity impact is also comparatively large, therefore, can consider using this model as a kind of Changing Pattern, and carry out trial research, its result is differentiated by experimental data and analyzes.

Constraints is: optical cable short circuit current effective value I.

OPGW optical cable is multilayer dielectricity, after given physical dimension and total current, according to the skin formula that becomes, and utilizes each dielectric interface place tangential field continuous print feature can obtain the concrete CURRENT DISTRIBUTION of each layer.

2. strictly process

The Maxwell equation group must separated under this condition is strictly solved for skin effect.Simple for considering a problem, be reduced to 2 layers of medium, solving result is the combining form of Bessel function.

For the OPGW optical cable model being simplified to 3 layers or 4 layers, said method is still effective, and result is still Bessel distribution.

Concrete distribution can be obtained in conjunction with boundary condition, thus release current density and each layer current value.

Solving of above-mentioned equation is very complicated, can adopt approximation method (the possibility of result is special function combination) on the one hand, and numerical computations (still complicated) can be adopted on the other hand to solve.

(3) heat exchange performance research

The research of heat exchange problem and the Changing Pattern solved for understanding optical cable each several part temperature significant.Heat exchange comprises in two at this: heat radiation and heat transfer.

1. dispel the heat

The outer media of OPGW optical cable, after energising temperature raises, can dispel the heat towards periphery in the air.Heat dissipation law can be described according to calorifics theory

2. heat transfer

Steady heat conduction between the adjacent layer of multi-layer cylinder wall with cylindrical wall length, each layer radius, certain moment each layer temperature, each layer conductive coefficient, that each layer contacts precision is relevant.

Heat exchange runs through the overall process that whole short circuit occurs, originally simple and convenient in order to what process, does not consider heat transfer, contemplated by the invention the heat transfer in this process, conform to actual during often supposing the function of current.Experiment is considered under proving condition of the same race and is not considered that the series result of heat exchange compares, and has significant difference.

According to specific exemplary embodiment, invention has been described herein.It will be apparent under not departing from the scope of the present invention, carrying out suitable replacement to one skilled in the art or revise.Exemplary embodiment is only illustrative, instead of the restriction to scope of the present invention, and scope of the present invention is defined by appended claim.

Claims (2)

1. the method utilizing improved integration algorithm to calculate OPGW optical cable Short circuit current heating effect, given line construction and physical dimension relation, given current strength or effective value, the structure of given or selected optical cable and relative dimensions, the given short circuit current duration, time and cable size are carried out segment processing respectively, utilize initial condition, start the parameter solving subsequent period, the distribution of electric current on each medium is solved according to skin effect, according to heating effect of current principle, heat is solved by the electric current in this this region of period, and then solve this regional temperature, heat exchange is solved by this temperature, and ask this zone resistance, and and then ask CURRENT DISTRIBUTION again, heat and temperature is asked again by CURRENT DISTRIBUTION, so repeatedly, until complete the calculating of preset time, it is characterized in that specifically comprising the following steps:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature;

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise: density, conductivity and temperature coefficient, length l, the geometry space D between itself and power line and the current peak I in power line and phase place;

Output rusults: the stable temperature of OPGW optical;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20)),

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer, if OPGW optical has n layer;

First calculate coefficient correlation, wherein monofilament conductivity is γ, and temperature coefficient is α,

Current spread coefficient

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

Obtain surface current density again in outermost value

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature that each layer conductor is carved at this moment, getting the time interval is Δ t;

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits

Wherein, one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of,

Outermost layer is to the heat of atmospheric dispersion

Loss_heat=α * (T _{outer wall}(t)-T _air(t)) * Δ t

α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air,

Total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality);

5th step: the time becomes t=t+ Δ t, then counts from second step, until complete the calculating of preset time;

Described given short circuit current process asks the maximum temperature of optical cable and temperature as follows with the step of the distribution in space in time:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature;

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise density, conductivity and temperature coefficient, length l, the geometry space D between itself and power line and the current peak I in power line and phase place,

Output rusults: maximum temperature and temperature in time with the distribution in space;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20))

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer,

First calculate coefficient correlation, wherein, monofilament conductivity is γ, and temperature coefficient is α,

Current spread coefficient

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

Obtain surface current density again in outermost value

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature that each layer conductor is carved at this moment, getting the time interval is Δ t

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits

Wherein, one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of,

Outermost layer is to the heat of atmospheric dispersion

Loss_heat=α * (T _{outer wall}(t)-T _air(t)) * Δ t

α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air,

Total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality)

Writing time t and temperature T (t) now

C.T T (t+ Δ t) and T (t), gets higher value T _max=max (T (t), T (t+ Δ t))

5th step: the time becomes t=t+ Δ t, then counts from second step, until complete preset time, draws T (t) over time, and maximum temperature T _max.

2. the method for claim 1, is characterized in that given limit temperature, and ask the maximum permissible short circuit current of given optical cable, equally also can provide Temperature Distribution, its step is as follows:

First suppose: in OPGW optical, the temperature of each monofilament is identical with air in the t=0 moment, i.e. T (0)=ambient temperature;

Input parameter is: in OPGW optical, the radius r of each monofilament, material and characterisitic parameter thereof comprise density, conductivity and temperature coefficient, length l, the geometry space D between itself and power line and the current peak I in power line and phase place, setting short-circuit current value;

Output rusults: maximum permissible short circuit current and Temperature Distribution;

Concrete steps are:

The first step: ask for coefficient of mutual inductance

Second step: calculate induced current

In t, mutual inductance magnetic linkage

The change of mutual inductance magnetic linkage produces induced electromotive force

The resistance value of t is R (t)=ρ ₂₀(1+ α * (T (t)-20))

The electric current that induced electromotive force produces is

3rd step: the distribution rule that exponentially distributed by induced current is distributed in each layer;

First calculate coefficient correlation, wherein, monofilament conductivity is γ, and temperature coefficient is α,

Current spread coefficient

B ₁₂＝γ ₂/γ ₁，B ₂₃＝γ ₃/γ ₂

Obtain surface current density again in outermost value

Finally obtain the value I being distributed in each layer electric current _i=A _ij ₁

4th step: calculate the temperature (getting the time interval is Δ t) that each layer conductor is carved at this moment

The heat current_heat=I that induced current produces _k* I _k* R (t) * Δ t

The energy that adjacent layer transmits

Wherein, one deck that temperature is high gets negative value, one deck that temperature is low get on the occasion of,

Outermost layer is to the heat of atmospheric dispersion

Loss_heat=α * (T _{outer wall}(t)-T _air(t)) * Δ t

α is coefficient of heat transfer, T _{outer wall}t () is the surface temperature of solid wall, T _airt temperature that () is air,

Total heat is heat=current_heat+exchange_heat (-convec_heat)

Temperature becomes T (t+ Δ t)=T (t)+heat/ (specific heat * quality),

Writing time t and temperature T (t) now,

C.T T (t+ Δ t) and T (t), gets higher value T _max=max (T (t), T (t+ Δ t));

5th step: the time becomes t=t+ Δ t, then counts from second step, until temperature stabilization, compares T _maxwith the difference of giving fixed temperature, change short circuit current and recalculate, until temperature T _maxstop time equal with given temperature value calculating, record temperature in time and spatial variations.