Method of characterizing a bundle of electric cables

Abstract

A method of characterizing a bundle (1) of electrical cables (2, 3, 4, . . . ), comprising taking into consideration for at least one surface temperature of the cables (T.sub.surface), firstly of at least one sum of heat fluxes (?.sub.1, ?.sub.2, . . . , ?.sub.n) calculated for each cable (2, 3, 4, . . . ) for the heating effect due to the electrical resistance of each cable passing a respective electric current (i.sub.1, i.sub.2, . . . , i.sub.n), and secondly of a heat flux (?.sub.s) calculated for the heat given off by the bundle (1) into its environment in order to make the dimensioning of the cables (2, 3, 4, . . . ) compatible with their use.

Claims

1. A method of characterizing a bundle of electrical cables, comprising: taking into consideration for at least one surface temperature of the cables: first at least one sum of incoming heat fluxes calculated for each cable for a heating effect due to an electrical resistance of each cable passing a respective electric current, and second an outgoing heat flux calculated for a heat given off by the bundle into its environment in order to make a dimensioning of the cables compatible with their use, wherein making the dimensioning of the cables compatible with their use includes confirming that a predetermined level of heating is not exceeded, comparing the at least one sum of incoming heat fluxes to the outgoing heat flux to determine whether the bundle satisfies a predetermined heat flux constraint; and evaluating, for at least one power cable of the bundle, a voltage drop calculated between two ends of the cable to determine whether the bundle satisfies a predetermined voltage drop constraint; wherein the bundle of electrical cables includes a plurality of cables arranged in parallel.

2. The method according to claim 1, wherein the consideration of said sum of incoming fluxes and said outgoing flux comprises calculating the sum of incoming fluxes and the outgoing flux for a given temperature constituting a maximum level of heating and comparing the numerical values of the incoming fluxes and the outgoing flux to confirm that the maximum level of heating is not exceeded.

3. The method according to claim 1, wherein the consideration of said sum of incoming fluxes and said outgoing flux comprises solving an equation to obtain temperatures that are actually reached in operation.

4. The method according to claim 1, wherein said sum of incoming fluxes and said outgoing flux are compared at a maximum temperature at which the cables can operate without degradation.

5. The method according to claim 1, wherein said sum of incoming fluxes and said outgoing flux are compared at a maximum operating temperature for human operators acting on the cables.

6. The method according to claim 1, wherein said sum of incoming fluxes and of said outgoing flux are compared at currents corresponding to a maximum authorized temperature rise in operation for limiting losses by a Joule effect in the cables.

7. The method according to claim 1, wherein said sum of incoming fluxes and said outgoing flux are compared at different temperatures in order to determine the temperatures actually reached.

8. The method according to claim 1, for performing preliminary design of the cable bundle by determining diameters of the cables or by recommending that one or more cables be excluded from the bundle.

9. The method according to claim 1, for modifying a bundle design by reducing a weight of the bundle.

10. The method according to claim 1, further including comparing the outgoing heat flux and a capacity of the environment for which the bundle is designed to dissipate heat.

11. The method according to claim 1, wherein a material and a load specific to each cable of the bundle are taken into account when calculating fluxes.

12. The method according to claim 1, wherein the bundle of cables includes at least one cable with a cross-section that varies along a length of the at least one cable.

13. The method according to claim 1, wherein the bundle is a bundle for aircraft, and wherein the method further includes calculating the temperature rise of the cables in the bundle during each stage of flight in order to take account of loading cycles of equipment, of temperature and pressure variations in zones of the aircraft, and of the characteristics of zones of the aircraft.

14. A bundle of cables fabricated by a method of fabrication including characterization in accordance with claim 1.

15. The method according to claim 1, wherein the heat flux constraint is satisfied when the sum of incoming heat flux is less than the outgoing heat flux, and not when the sum of incoming heat flux is greater than the outgoing flux.

16. The method according to claim 1, further including calculating a voltage drop for each cable of the bundle.

17. The method according to claim 1, wherein the sum of incoming heat flux is governed by the equation:
?.sub.cables (linear resistance*segment length*current.sup.2).

18. The method according to claim 1, wherein the outgoing heat flux is governed by the equations:
?.sub.outgoing=?r.sub.adiant+?.sub.convective;
?.sub.radiant=emissivity*form factor*?*area*(T.sub.surface.sup.4?T.sub.ambient.sup.4); and
?.sub.convective=h.sub.convective*area*(T.sub.surface?T.sub.ambient); where, ?is the Stefan Boltzmann constant, h.sub.convective is based on a pressure, temperature, and altitude of a stage of flight, the emissivity is based on a material of each of the cables and/or a material surrounding each of the cables, and the form factor is a form factor of the cables.

19. The method according to claim 15, further including calculating a voltage drop for each cable of the bundle, wherein: the sum of incoming heat flux is governed by the equation ?.sub.cables (linear resistance*segment length*current.sup.2); and the outgoing heat flux is governed by the equations:
?.sub.outgoing=?r.sub.adiant+?.sub.convective;
?.sub.radiant=emissivity*form factor*?*area*(T.sub.surface.sup.4?T.sub.ambient.sup.4); and
?.sub.convective=h.sub.convective*area*(T.sub.surface?T.sub.ambien); where, ?is the Stefan Boltzmann constant, h.sub.convective is based on a pressure, temperature, and altitude of a stage of flight, the emissivity is based on a material of each of the cables and/or a material surrounding each of the cables, and the form factor is a form factor of the cables.

20. The method according to claim 19, wherein the bundle is a bundle for aircraft, and wherein the method further includes calculating the temperature rise of the cables in the bundle during each stage of flight in order to take account of loading cycles of equipment, of temperature and pressure variations in zones of the aircraft, and of the characteristics of zones of the aircraft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and features of the invention will become apparent upon reading the following description referring to the appended drawings wherein:

(2) FIG. 1 shows a bundle of cables.

(3) FIG. 2 illustrates the principles of the invention.

(4) FIG. 3 shows an implementation of the invention.

DETAILED DESCRIPTION

(5) In the following detailed description, it is referred to the accompanying drawings showing examples of compaction assembly or examples of manufacturing process. It is intended that these examples be considered as illustrative only, the scope of the invention not being limited to these examples.

(6) FIG. 1 is a section view showing an example of a bundle 1 of cables to which the invention applies. It is made up of cables 2, 3, 4, . . . of different diameters, that are tied together by collars, e.g. arranged once every 5 cm (not shown). The cables, which are generally circular in section, are pressed against one another. Some of them are made of aluminum and others are made of copper, or indeed of other materials. Some of them are electrical power supply cables, e.g. cables for powering landing gear or electrical racks in an aircraft, and others are data communication cables for transmitting data from one node of a telecommunications network to another node of the network, e.g. a network on board an aircraft.

(7) FIG. 2 illustrate the principles of the invention. In accordance with the invention, provision is made both to calculate an overall outgoing heat energy flux ?.sub.s for a cable surface temperature T.sub.surface that is assumed to be constant, i.e. under steady conditions, and for currents i.sub.1, i.sub.2, . . . , i.sub.n flowing in the cables that correspond to the intended use of the cables, which flux is calculated for the bundle as a whole while taking account of the environment (temperature and pressure) in which said bundle is situated, and also to calculate the incoming energy fluxes ?.sub.1, ?.sub.2, . . . , ?.sub.n for the various cables. The sum of the incoming fluxes ?.sub.1, ?.sub.2, . . . , ?.sub.n is then compared with the outgoing flux ?.sub.s.

(8) In this calculation, transient stages are ignored. However this solution provides all of the functions made available by a multi-physical simulation, while minimizing computation.

(9) Instead of comparing the temperature reached with the authorized maximum temperature, as has been done in the past, the incoming and outgoing fluxes as simulated at a given surface temperature are compared. It is thus verified whether an authorized maximum level of heating is exceeded. This is the heating at the skin of the bundle or at the skin of the cables, so as to perform a calculation that is conservative. Thus, with cabling that has been dimensioned using this method, the real temperature reached for the currents i.sub.1, i.sub.2, . . . , i.sub.n flowing in the cables is necessarily less than the authorized maximum temperature.

(10) The method is shown in greater detail in FIG. 3. Account is taken of the configuration of the bundle 10, including in particular, but not necessarily only, the diameters of the cables and the form factors of the cables and of the bundle. Account is also taken of the environment of the cables 20, including in particular, but not necessarily only, the electrical loads applied to each of the cables, and ambient temperature and pressure.

(11) The method makes it possible to obtain results showing whether the bundle under study under the envisaged conditions complies with a constraint on heat fluxes 30 and a constraint on the voltage drop 40 observed on the modeled bundle segment.

(12) The sum of the incoming energy fluxes is calculated on the basis of the following formula:
?.sub.incoming=?.sub.cables (linear resistance*segment length*current.sup.2)

(13) The outgoing energy flux is calculated using the maximum authorized surface temperature as mentioned above and taking account of the characteristics of the environment. This flux is made up of a radiant flux and a convective flux and it is based on the following formulae:
?.sub.outgoing=?.sub.radiant+?.sub.convective
?.sub.radiant=emissivity*form factor*?*area*(T.sub.surface.sup.4?T.sub.ambient.sup.4)
?.sub.convective=h.sub.convective*area*(T.sub.surface?T.sub.ambient)

(14) where ? represents the Stefan Boltzmann constant and the constant h is set as a function of pressure and temperature, and thus in particular of altitude, and for further simplification on the stage of flight. It should be recalled that emissivity is related to the irradiating material, in this case each of the cables or possibly the protection applied to the cables (sheaths providing protection against fire, electromagnetic interference, mechanical attacks, . . . ).

(15) The incoming and outgoing fluxes are compared in order to determine whether the heat flux constraint 30 is satisfied, with this constraint not being satisfied if the incoming flux is greater than the outgoing flux.

(16) The expected voltage drops are also calculated for each of the cables, with the above-mentioned temperatures and currents. Voltage drop is calculated using Ohm's law U=RI, where R is preferably corrected with the maximum authorized temperature or the temperature determined for the bundle, and this calculation is automated. Optionally, the sum of the individual voltage drops calculated for each bundle segment is calculated. The voltage drop as calculated in this way is compared with the maximum drop authorized in the application, e.g. as a function of specifications set out in specifications, and while taking account of the environment of the bundle. This is how the voltage drop constraint 40 is verified.

(17) If the constraints 30 and 40 are satisfied, it is then possible to reiterate the process with bundles of smaller dimensions, so as to reduce the overall weight of the cabling, with this continuing until the constraints are no longer satisfied. The cabling is finally dimensioned as a function of these results.

(18) The mathematical method as described above can be applied during a predesign stage, thus making it possible to have a first estimate for the sections to be used for each bundle, even if the system is still incomplete. This can be helpful, in particular for estimating the diameter of a bundle and possibly for deciding against certain bundles during the design stage, if the estimated bundle diameter exceeds the maximum authorized diameter.

(19) This method of dimensioning can also be applied to verifying an existing configuration, thus making it possible to determine quickly whether electrothermal constraints are satisfied by an apparatus. If not, those constraints that are not satisfied are all identified and specified in order to change the bundles.

(20) This method of dimensioning can also be applied for correcting a configuration that does not satisfy one or more constraints. Thus, by using automation, it is possible to modify the sections of the bundles in order to correct the constraints that are not satisfied by a system.

(21) Finally, the method can be used for optimizing a configuration. Automation makes it possible to modify the sections of bundles in order to optimize them on the system weight criterion while complying with all of the thermal and electrical requirements.

(22) This solution improves the dimensioning of bundles since it enables a significant weight saving to be obtained on the cabling of an airplane, it provides better knowledge about the heat fluxes in various zones of the airplane, better knowledge of heat losses due to the cabling, and it enables satisfied constraints to be determined quickly, including for a system of large size, because the calculations can be automated and because of the automatic optimization of the dimensioning of the airplane cabling as a whole.

(23) In a particular implementation, after calculating the outgoing heat flux, attention is given to whether it is compatible with the environment in which the bundle is to be installed, e.g. following a path under a floor between the passenger floor of an airliner and the ceiling of a hold, or indeed following a path between passenger cabin trim and the skin of the airplane, both of which are confined spaces with relatively little ventilation. It is verified whether the surface temperature of the bundle remains similar to that previously determined and/or compatible with safety and operating specifications.

(24) Comprises/comprising when used in this specification is taken to specify the presence of stated features but does not preclude the presence or addition of one or more other features.

(25) The invention is not limited to the implementations described, but extends to any variant coming within the ambit of the scope of the claims.

(26) The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope of the invention. Further, the various features of the embodiments or examples disclosed herein can be used alone or in varying combinations with each other, and are not intended to be limited to the specific combinations disclosed herein.