Cable with adapted stranding

Abstract

The present disclosure relates to a cable. An exemplary embodiment of the cable (2) comprises a plurality of conductors, wherein the conductors form several conductor groups (4, 6a-6d), in which respectively two or more of the plurality of conductors are stranded with one another. The several conductor groups (4, 6a-6d) are stranded overall around a common stranding center (1) and the conductors of at least two of the several conductor groups (4, 6a-6d; 4a-4d, 6a-6k) are stranded with one another with a different lay length.

Claims

1. Cable including at least a first group of conductors and a second group of conductors, each group of conductors including a plurality of litz wires, wherein the litz wires form several litz wire pairs in which, respectively, two of the plurality of litz wires are stranded with one another and said litz wire pairs are stranded overall around a common stranding center, and said litz wires of said first group and said litz wires of said second group have the same mechanical length; said litz wire pairs of said first group located at a first radial distance with respect to said common stranding center and said litz wire pairs of said second group located at a second radial position with respect to said common stranding center, said second radial distance being greater than said first radial distance; said litz wire pairs of said first conductor group being stranded with one another at a first lay length and said second group of litz wire pairs being stranded at a different lay length, whereby currents conducted in the first group of conductors and currents conducted in said second group of conductors reach the end of the cable substantially simultaneously.

2. Cable according to claim 1 wherein said lay length of said first group of conductors is shorter than the lay length of the second group of conductors.

3. Cable according to claim 1, wherein the at least two of the several litz wire pairs are formed so that they have a same stranding factor.

4. Cable according to claim 1, wherein all of the several litz wire pairs are formed so that they have a same stranding factor.

5. Cable according to claim 1, wherein the at least two of the several litz wire pairs respectively include one litz wire as a forward conductor and one litz wire as a return conductor.

6. Cable according to claim 1, wherein the cable is formed as a power cable.

7. Cable according to claim 1, wherein the cable is formed for conducting currents of at least 10A at an alternating current frequency between 8kHz and 200kHz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure is to be explained further below with reference to figures. These figures show schematically:

(2) FIG. 1 a cross-sectional view of a possible configuration of a cable according to a first exemplary embodiment;

(3) FIG. 2 a cross-sectional view of a possible configuration of a cable according to a second exemplary embodiment;

(4) FIG. 3a a side view of a cable to explain the lay length; and

(5) FIG. 3b a side view of details of the cable according to the second exemplary embodiment from FIG. 2.

DETAILED DESCRIPTION

(6) In the following, without being restricted hereto, specific details are presented to supply a complete understanding of the present disclosure. However, it is clear to a person skilled in the art that the present disclosure can be used in other exemplary embodiments, which may deviate from the details set out below. For example, specific configurations and arrangements of a cable are described below that should not be regarded as restrictive. For example, the arrangement according to FIGS. 2 and 3b is described in relation to a plurality of litz wires as an example of a plurality of conductors. The arrangement from FIGS. 2 and 3b is not limited to this specific arrangement, however, but rather solid conductors or other conductors can also be used as conductors instead of or in addition to litz wires.

(7) The cable described below can be formed as a power cable. For example, the cable can be formed to conduct currents of over 10 A, for example between 40 A and 100 A, e.g. 70 A, at an alternating current frequency between 8 kHz and 200 kHz, for example 85 kHz.

(8) The cable can be used for various applications. This means that various application areas of the cable are conceivable. These application areas can be all application ranges in which high currents and/or great frequencies (e.g. high-frequency range) are used. It is conceivable, without being restricted hereto, for the cable to be used in connection with a device for the inductive charging of vehicles, e.g. pure electric vehicles. One possibility for the inductive charging of vehicles provides that the charging station, e.g. a wall charging station, is connected to a charging arrangement, such as e.g. a charging plate, via a cable/charging cable. The charging arrangement, e.g. the charging plate, can be arranged on the ground and comprise one or more coils. The wall charging station is thus not connected directly to the vehicle for the charging process, but to the charging arrangement. The vehicle can then be charged inductively in a known manner by placing/moving it onto the charging arrangement.

(9) The cable described here can be, without being restricted hereto, said cable/charging cable for connection of a wall charging station to the charging arrangement, for example. The charging cable can have a length of 1 m or more, e.g. of several meters.

(10) Another application area of the cable that can be cited purely as an example is that the cable can be a cable for supplying a sputtering unit with alternating current at high frequencies.

(11) FIG. 1 shows a cross-sectional view of a cable 2 with seven segments 4, 6a to 6f, which are insulated from one another and described generally as elements below. The seven elements 4, 6a to 6f insulated from one another are stranded overall around a common stranding centre 1. This stranding centre 1 is the central axis/longitudinal axis of the cable 2, as shown by way of example in FIG. 1. The inner element 4 (inner in the sense of the position in a radial direction of the cable 2) lies symmetrically around the longitudinal axis of the cable 2 and thus around the stranding centre 1. Furthermore, the outer elements 6a to 6f (outside in the sense of the position in a radial direction of the cable 2) are stranded around the stranding centre 1 and thus around inner element 4. Since the outer elements 6a to 6f (outer-lying elements 6a to 6f) describe a helix/spiral shape, they cover a greater path in the longitudinal direction of the cable 2, i.e. their mechanical length is greater than that of the inner element 4 (element 4 lying inside). An alternating signal, such as e.g. an alternating current/alternating current signal, therefore reaches the end of the cable 2 faster via the inner element 4 than via the outer elements 6a to 6f. This results in a part of the cable 2, namely the inner element 4, having a different potential for a period of time than other parts of the cable 2, namely the outer-lying elements 6a to 6f. In this period of time a short circuit can occur inside the cable 2, which short circuit consumes energy on the one hand and on the other leads to increased self-heating of the cable 2. Furthermore, the short current pulse of the short circuit can have high harmonics on account of the high frequency. This can increase the EMC radiation.

(12) Let it be assumed purely by way of example that the propagation velocity of an alternating signal amounts to 60% of the speed of light, for example. Over a 10 m path length the signal thus arrives at the end of the inner element 4 after 55.55 nsec. With a stranding input of 2% assumed, however, the signal at the end of an outer-lying element 6a to 6f from FIG. 1 is available only after 56.7 nsec. A potential difference, which converts energy in the cable, thus exists between elements of the same cable 2 in the 1.2 nsec.

(13) A reduction in this effect, if not even an avoidance of it, is achieved in that the mechanical length of the outer-lying elements 6a to 6f is artificially shortened and/or that the mechanical length of the inner-lying element 4 is artificially lengthened. Here the actual length of the corresponding elements in their own longitudinal direction is understood as the mechanical length. The length of the corresponding elements in an unstranded/unwound state can therefore be understood by mechanical length. The mechanical length of the inner-lying element 4 should correspond due to the artificial adaptation at least virtually, ideally exactly, to the mechanical length of the outer-lying elements 6a to 6f. On account of the at least virtually identical mechanical length, an alternating signal reaches the end of the cable at the same time. Differences in running time are compensated/prevented. Short circuits are therefore reduced or avoided altogether. The elements named in relation to FIG. 1 can be litz wires/litz wire conductors and/or solid conductors as conductors.

(14) An option for artificial adaptation, e.g. artificial lengthening and/or artificial shortening, is now explained in relation to the FIGS. 2 to 3b.

(15) FIG. 2 also shows a cross-sectional view of a cable 2 according to an exemplary embodiment. The principles and details explained in relation to FIG. 1 apply correspondingly to the exemplary embodiment from FIG. 2 also. In the example in FIG. 2, the inner-lying element 4 comprises inner cores 4a to 4d. The outer-lying elements are formed as an example by eleven outer-lying cores 6a to 6k. In addition, purely by way of example, each inner-lying core 4a to 4d is formed as a litz wire pair (as an example of a conductor pair) and is accordingly designated below as inner litz wire pair 4a to 4d. As an alternative example, each inner-lying core 4a to 4d can be formed as a solid conductor pair. Likewise, each outer-lying core 6a to 6k is formed by way of example as a litz wire pair (as an example of a conductor to pair) and is accordingly designated below as outer litz wire pair 6a to 6k. As an alternative example, each outer-lying core 6a to 6k can be formed as a solid conductor pair. Each litz wire pair 4a to 4d and 6a to 6k shown in FIG. 2 comprises, for example, two litz wires 8a, 8b, as illustrated with reference to the litz wire pair 6k in FIG. 2. The litz wires 8a, 8b can be a forward conductor and a return conductor, for example.

(16) As explained in relation to FIG. 1, due to the overall stranding around the central axis/longitudinal axis of the cable 2 as common stranding centre 1, each outer litz wire pair 6a to 6k (and thus each outer litz wire) covers a longer path distance than each of the inner litz wire pairs 4a to 4d (and thus each inner litz wire). Expressed another way, the mechanical length of each litz wire pair 6a to 6k is greater than the mechanical length of each inner litz wire pair 4a to 4d. In the exemplary embodiment from FIG. 2 the inner litz wire pairs 4a to 4d lie at the same level in a radial direction of the cable 2. The mechanical length of each inner litz wire pair 4a to 4d (and thus of each inner litz wire) and consequently (in the case of the same material) their electrical resistance are identical. The same applies to the outer litz wire pairs 6a to 6k. This means that in the exemplary embodiment from FIG. 2, the outer litz wire pairs 6a to 6k lie at the same level in a radial direction of the cable 2. The mechanical length of each outer litz wire pair 6a to 6k (and thus of each outer litz wire) and consequently (in the case of the same material) their electrical resistance are identical.

(17) This means that the mechanical length of each litz wire pair 4a to 4d, 6a to 6k is a function of its position in a radial direction of the cable 2. The mechanical length of the inner litz wire pairs 4a to 4d and thus of the inner litz wires is shorter than the mechanical length of the outer litz wire pairs 6a to 6k and thus of the outer litz wires. Alternating signals accordingly reach the end of the cable 2 faster via the inner litz wire pairs 4a to 4d than via the outer litz wire pairs 6a to 6k. As explained, short circuits and thus increased energy consumption, increased self-heating and/or increased EMC radiation can be caused by this.

(18) To remedy this problem, the litz wires for forming the outer litz wire pairs 6a to 6k are stranded with a different lay length than the litz wires for forming the inner litz wire pairs 4a to 4d. For further explanation reference is made first to FIG. 3a, which illustrates the lay length l of a cable in general. As shown in FIG. 3a, the lay length l is the lead of the wires laid spirally around the stranding axis. This means that the lay length l of a conductor, e.g. a litz wire or a solid conductor, is the lead measured parallel to the conductor longitudinal axis, e.g. litz wire longitudinal axis and/or solid conductor longitudinal axis, of an outer wire in a complete winding around the axis of the conductor, e.g. of the litz wire or of the solid conductor. The term lay length thus describes the length of the path required by a single wire in the conductor, e.g. in the litz wire or the solid conductor, for a 360 revolution. As explained, in the stranding of (symmetrical) cables, individual wires or wire pairs are twisted/stranded against one another. They are wound spirally, so to speak, around the stranding axis/the stranding centre. Thus a lay length of 70, for example, signifies that the wires have made a spiral stranding of 360 degrees around the stranding axis after 70 cm.

(19) FIG. 3b now shows very schematically one of the outer litz wire pairs 6a to 6k, which is described as the first litz wire pair 6a below, and one of the inner litz wire pairs 4a to 4d, which is described below as the second litz wire pair 4a.

(20) As can be recognised in FIG. 3b, the litz wires for forming the first (outer) litz wire pair 6a are stranded with a lay length l_long, which is greater than the lay length l_short of the stranding of the litz wires for forming the second (inner) litz wire pair 4a. This applies likewise to all outer litz wire pairs 6a to 6k and inner litz wire pairs 4a to 4d. The mechanical length of the inner litz wire pairs 4a to 4d and thus of the inner litz wires is lengthened compared with the mechanical length of the outer litz wire pairs 6a to 6k and thus of the outer litz wires. The lay lengths l_long, l_short can be chosen in this case in particular so that the mechanical length of the inner litz wire pairs 4a to 4d corresponds at least virtually to the mechanical length of the outer litz wire pairs 6a to 6k. Expressed another way, the lay lengths can be selected so that the actual lengths of the litz wires of the cable 2 and thus their stranding factors at least virtually correspond to one another in spite of overall stranding around the stranding centre 1 and a different position in a radial direction of the cable 2.

(21) Due to the adaptation described of the stranding or bundling, an approximation of the actual lengths of the conductors, e.g. litz wires or solid conductors, of the cable 2 is achieved. This leads to a marked reduction in the running time difference of alternating signals described above, if not even to complete avoidance. Inner layers of a cable 2 are formed e.g. by a pair-stranded layer, the stranding factor of which is of the same magnitude as the stranding factor of the outer layer. Differences in the running time are avoided by this. The same applies also to divided forward and return conductors as outlined in relation to FIG. 3b, which were stranded into a litz wire pair, a core or a cable. Here, too, compensation of the running time differences can be achieved.

(22) Although the invention has been described with a certain degree of particularity, those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.