Transmission system

 Introduction, necessity of TS

The electricity is generated in bulk in the generating stations and then transmitted over long distances to the load points. The transmission system interconnects all the generating stations and major load centers in the system. It forms the back bone of the power system. Since the power loss in a transmission line is proportional to the square of line current, the transmission lines operate at the highest voltage levels, usually 220 KV and upwards. The transmission lines mainly perform the two functions

•  It transports the energy from generating stations to bulk receiving stations.
•  It interconnects the two or more generating stations. The neighboring substations are also interconnected through the transmission lines.

The component of an electrical power system connecting all the consumers in an area to the bulk power sources is called a

distribution system. The bulk power stations are connected to the generating substations by transmission lines. They feed some substations which are usually situated at convenient points near the load centers. The substations distribute the power to the domestic, commercial and relatively small consumers. The consumers require large blocks of power which are usually supplied at sub-transmission or even transmission system.

Transmission Layout, voltage level, insulation, right of way

Transmission-level voltages are usually considered to be 110 kV and above such as 132 kV or 220 kV or 400 kV or 765 kV depending upon how long the transmission lines are. Lower voltages, such as 66 kV and 33 kV, are usually considered sub transmission voltages, but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution.

AC. and DC applications: introduction and comparison

AC is much easier (consider cheaper) to step up and down in voltage than DC, and can be done more efficiently (typically, currently) than the much more expensive and complex DC step-up/step-down systems. That is why AC is used for mains power transmission at a national level.

AC is, in fact, not inherently better for long-distance power transmission than DC. And this is why HVDC (high voltage DC) is actually used

AC has one limitation compared with DC: inductive and capacitive losses. The larger the inductance and capacitance of a piece of wire is, the more difficult it is to keep trying to change the direction of flow of electrons, which is what AC is doing at 50 times a second. DC on the other hand, has the current flowing in one direction all the time, and so is not impeded by this inductance, and has negligible capacitive losses.

Straight wires in air have very little inductance and capacitive losses. Over the distances that mains power is transmitted, there are some losses when using AC, but the losses are small. A DC system would have better transmission efficiencies as it has lower losses, but would be more expensive and less efficient at the step-up/step-down stages.