Stranding

Twisting refers to the twisting and the helical winding of fibers or wires around one another . When twisting wires and in telecommunications technology , one also speaks of stranding . A typical application in electrical lines is the twisted pair cable , as it is used in the field of Ethernet .

In the case of a twisted line, the individual conductors of a circuit swap their place with one another either in their entire course (for cables) or at certain points (for overhead lines ). The twisting reduces the mutual influence of electrical conductors. Twisting is an effective measure to reduce inductively coupled differential mode interference .

8 wires twisted in pairs result in 4 pairs or 4 twin wires
(twisted pair cable)

Communication technology

Stranding in pairs

Quad distribution
(telephone cable JY (St) Y 2-pair)

In telecommunications technology, stranding is used to reduce crosstalk coupling . The essential dimension in stranding is the twist - also known as the twist length , twist pitch or lay length . The twist is the pitch or pitch of the helix that results from the stranding of the wires and has an influence on the cable coverings . The stranding makes the individual cores longer than the cable itself. The stranding factor indicates the ratio of individual core length to cable length; for telecommunication cables it is approximately 1.02 to 1.04.

Stranding types

In practice, the following types of stranding occur more often:

Stranding in pairs

Two single wires are stranded to form a wire pair ( twin wire ). Typical applications of twisted pairs are e.g. B.

• Network cable with 4 pairs.
• Telephone installation cable
  • JY (St) Y (from 3-pair, 2-pair is four-stranded)
  • G51 (from 1 pair, Switzerland )
  • F-YAY (from 1 pair, Austria )

Triple stranding

Three individual cores are stranded to form a group of three. Shift cables in triple stranding were z. B. formerly used in analog telephone exchanges .

Quad distribution

Typical applications can be found in the article Quadruple .

• Star
  stranding (star quad) Four single wires have the same position to each other at every point of the stranding, whereby the wires of a pair of wires ( double wire ) are diagonally opposite each other.
  Cables stranded in a star quad have the following advantages over cables stranded in pairs:
  Higher packing density and lower attenuation due to the lower operating capacity of the pairs.
• Dieselhorst-Martin stranding (DM)
  A special type of quad in telephone long-distance cables that has been out of date for decades (see article Quad stranding ).

Both in the star and in the DM quad, the additional transmission of a third speech circuit is possible using phantom switching. This technology is hardly of any importance today.

Interference suppression through twisting

The twist has the effect that an interference voltage induced by a magnetic field is reduced. As a result of the twisting, the partial areas spanned between the wires count alternately negative and positive. When integrating a magnetic flux density over all sub-areas , the effective magnetic flux , from which the induced voltage follows, is very low or ideally to zero, so that the induced interference voltage is greatly reduced. The following applies to the river: ${\displaystyle {\vec {B}}}$ ${\displaystyle {\vec {A}}}$ ${\displaystyle \Phi }$

${\displaystyle \Phi =\int \limits _{A}{\vec {B}}\cdot \mathrm {d} {\vec {A}}}$

The following applies to the induced voltage:

${\displaystyle U_{i}=-{\frac {\mathrm {d\Phi } }{\mathrm {d} t}}=-{\frac {\mathrm {d} }{\mathrm {d} t}}\cdot \left(\int \limits _{A}{\vec {B}}\cdot \mathrm {d} {\vec {A}}\right)}$

Energy Technology

Twisting mast for the north-south line

Also with electrical overhead lines which are conductors twisted to minimize transmission losses. Since it would be technically too complex to twist continuously as in the cable, special twisting masts are used instead , on which the outer conductors change their positions. The cable is untwisted between two twisting masts. Although it is also possible to twist the span between two masts, this has mechanical disadvantages (smaller distance between the conductors, greater susceptibility to wind).

The twisting reduces the unbalance of the line , which can lead to different capacitive coatings on earth in three-phase systems. This balancing of the earth capacitances is essential for the application of earth fault compensation .

In the case of longer overhead lines without branches, the twisting usually follows a fixed twisting scheme , the twisting masts are regularly distributed. But with closely meshed networks and parallel routing of different circuits - especially with several voltage levels on the same masts - the mutual influence can lead to the need to deviate significantly from the twisting schemes. In such systems, twisting points are often to be found on masts immediately before the introduction into the switchgear, so that the switchgear can work with cross-free external conductors (L1 / L2 / L3), although this arrangement on the line would be disadvantageous.

If the mutual influence of circuits changes due to a network modification, it is often necessary to adapt the position or number of twisting points to the changed conditions.

Technical mechanics

The twist, even relative twist called, are a on torsion claimed stick to how much its cross section twisted, based on the length:

${\displaystyle \varphi _{\text{rel}}={\frac {\varphi }{l}}}$

With

• the absolute angle of rotation ${\displaystyle \varphi }$
• the rod length ${\displaystyle l}$

literature

• Manfred Ellrich: Magnetic coupling in telephone cables with Dieselhorst-Martin stranding ; Bamberg, 1971

See also

• Anti-twist protection
• Bifilar

Web links

Commons : Twisted cables  - collection of images, videos and audio files