Krarup cable

Submarine cable cores wrapped with iron or mu-metal to increase the inductance coating

As Krarupkabel a special, historical construction for coil-loaded trunk lines of communication engineering called from the period from 1900's. It is named after the Danish civil engineer Carl Emil Krarup .

history

In 1893 the Englishman Oliver Heaviside discovered the possibility of reducing the attenuation by artificially increasing the inductance of the telephone cables. The Frenchman Aimé Vaschy had independently come to the same results. Around the same time as Mihajlo Pupin's attempts in America to implement these ideas by inserting inductances ( coils ) into the long-distance cables ( coiled cables ), these ideas were also taken up in Germany. The reason was the intention to link Sweden and Norway with the German telephone network. Karl Strecker suggested tests that were carried out in the Rheydt cable works . The copper wires were wrapped with iron tape. The attempts were successful, so the plan was made to build the new Scandinavian cable according to this principle. The Danish postal administration took part in further experiments carried out at the University of Würzburg . It was there that Carl Emil Krarup developed the final form of construction in which the cable cores were wrapped with thin iron wire. In 1903 the cable named after Krarup was laid between Fehmarn and Laaland , and it met all expectations. In the same year telephone traffic with Sweden and Norway was started.

Krarup cables were also used later, on March 4, 1927, such a cable was put into operation as a transatlantic telephone cable between Emden and New York (via Horta / Azores ). However, this and other cables used the mu-metal , invented in 1914, instead of iron , which served the purpose even better due to its much higher permeability .

Advantages and disadvantages of the Krarup cable

Advantages :

• In the Krarup cable, the increase in the line inductance had a completely uniform effect over the line length.
• In contrast to the Pupin cable, the Krarup cable had no pronounced cut-off frequency.
• A later extension or relocation was not a big problem in contrast to the pupin cable.
• The cable had a homogeneous mechanical structure (in contrast to the pupin cable with its coil boxes). This was particularly advantageous when it was laid as a submarine cable .

Cons :

• The additional inductance was specified when the cable was manufactured and could not be changed afterwards.
• It was not possible to achieve inductance values ​​as high as with the pupin cable.

Technical background

When transmitting signals over long lines, the impedance is matched to the line impedance , which is calculated using the following formula:

Equivalent circuit diagram of a line

${\displaystyle Z_{\mathrm {Ltg} }={\sqrt {\frac {R'+j\omega L'}{G'+j\omega C'}}}}$

• ${\displaystyle Z_{\mathrm {Ltg} }:}$ Line impedance
• ${\displaystyle R':}$ Resistance coating , resistance per length
• ${\displaystyle C':}$ Capacity coverage
• ${\displaystyle L':}$ Inductance coating

• ${\displaystyle G':}$ Dissipation coating
• ${\displaystyle \omega :}$ Angular frequency 2 · π · f

In the case of low frequency, low inductance and negligible discharge, the following applies:

${\displaystyle Z_{\mathrm {Ltg} }\approx {\sqrt {\frac {R'}{j\omega C'}}}}$

A large part of the signal energy to be transmitted is therefore lost due to ohmic losses in the resistance layer. The magnetic material in the cable jacket increases the inductivity of the cable and the energy stored in the magnetic field is carried on instead of converted into heat. This results in the equation:

${\displaystyle Z_{\mathrm {Ltg} }\approx {\sqrt {\frac {L'}{C'}}}}$

Put simply, the line impedance increases. More voltage but less current is required for the same output, which reduces the power loss.

${\displaystyle P'_{V}=I^{2}\cdot R'}$

literature

• M. Klein: Cable technology. The theory - calculation and manufacture of the electrical cable, Julius Springer, Berlin 1929.
• F. Moeller: Electrical engineering internship. Springer Verlag, Berlin / Heidelberg 1949.
• Julius Wallot: Introduction to the theory of weak current technology. Springer Verlag, Berlin / Heidelberg 1932.
• Jan-Peter Domschke: Streams connect the world. Telegraphy - Telefonie - Telekommunikation, BG Teubner Verlag, Leipzig 1997, ISBN 978-3-8154-2507-7 .
• Andres Keller: "Data transmission in the cable network". Technical principles and standards, 2nd edition, Springer Verlag, Berlin / Heidelberg 2005, ISBN 3-540-22501-3 .

See also

• Heaviside condition
• Line theory

Web links

• Via underwater telephone cables
• Picture of a Krarup telecommunication cable from 1938
• The SBB telecommunications systems (accessed on August 14, 2017)

Individual evidence

1. ↑ http://www.zeno.org/Lueger-1904/A/Telephonie?hl=krarup
2. ↑ Archived copy ( Memento of the original from April 18, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.