TRANSMISSION LINES

Transmission line    

1.         A  conductor or conductors designed to carry electricity or an electrical signal over large distances with minimum losses and distortion
   
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         Transmission lines are used to carry electromagnetic energy from one point to another . It means it transfer from one point to another. Generally it consists of two conductors. It is used to connect a source to a load. The source may be a transmitter or an electric generator and the load may be an antenna. Transmission lines are used for operational frequencies equal to or less than about 3GHz. Above 3GHz they will be replaced by waveguides.

         Transmission lines are commonly used in power systems for power transmission. These lines can be used as circuit elements like capacitors, inductors at ultra high frequencies(300-3000MHz)

   

Performance of Transmission Line

 

The overhead transmission lines are categorized as three types:

  In transmission line determination of voltage drop, transmission efficiency, line loss etc. are important things to design. These values are affected by line parameter R, L and C of the transmission line. Length wise transmission lines are three type. 

Short transmission line:

      The line length is up to 60 km and the line voltage is comparatively low less than 20KV.

Medium transmission line:

    The line length is between 60 km to 160 km and the line voltage is between 20kV to 100kV.   

Long transmission line:

      The line length is more than 160 km and the line voltage is high greater than 100K

Types of Transmission Line:  

(a)    Two wire transmission line:- This transmission line consists of a pair of parallel conducting wires separated by a uniform distance .These are used in power systems or telephones line.

(b)   Coaxial transmission line:- This consists of an inner and a coaxial outer conducting sheath separated by a dielectric medium . They are used as TV cables, telephones cables and power cables.

(c)    Parallel plate transmission line or planar line:- It has two parallel conducting plates separated by a dielectric slab of uniform thickness.

(d)   Optical fibres transmission line:- It consists of core and cladding . Information passes through the core in the form of totally internal reflected TEM waves.