Transmission Lines Case Study

Question - Present a case study on different transmission lines origin and their usage.

Ans -

What are Transmission lines?

Transmission lines are cables or other structure which are specialized and designed for conducting AC (alternating current) of very high frequencies. For such currents with high frequency, the wave nature has to be taken into account. Ordinary electrical cables are enough to carry audio signals and AC of low frequencies, like mains power in which the direction is reversed 100 to 120 times in a second but they cannot be used to carry currents of very high frequencies, above thirty kilohertz. The reason for this being that the energy is radiated from the cable in the form of radio waves and this causes loss of power. Another reason is that currents of radio frequency are reflected from the discontinuities present in the cable joints and connectors which leads to the current travelling backward down the cable and directed towards the source. Thus this does not let the power of signal to reach the destination. To solve these problems, transmission lines come into picture. These have specialized construction and matching impedance in order to carry EM signals such that there are minimal reflections and loss of power.

Brief history of Transmission Lines

The work of of James Clerk maxwell, Oliver Heaviside and Lord Kelvin let to the growth of mathematically analysing electrical transmission lines. In the year 1855, diffusion model of submarine cable current was formulated. This model had predicted c in 1858 correctly the bad performance of the trans-Atlantic submarine telegraph cable. Later papers were also published describing analysis of propagation using cables.

Types of Transmission