## 2009-04-05

### Transmission of Electricity

Most power stations are located far away from populated areas. Electricity is transmitted from the power station to consumers through power lines.

Unfortunately, some electrical energy is always lost as heat when it travels through wires.

Since the heat dissipated depends on the magnitude of the current, it is more efficient to transmit electrical energy at very low currents.

To produce this low current, the voltage has to be increased. Step-up transformers are used for this purpose to increase the voltage at the power plant.

Step-down transformers are used to decrease the voltage before being delivered to the consumers.

In addition, the long thick cables used as transmission lines are made of copper or aluminium because they have low resistance and thus less energy will be lost when current flows through them.

Example 1:

A power station supplies a factory with 1.0 MW of electrical power at a potential difference of 2 kV. The resistance of the cable between the power station and the factory is 5 Ohm. Find the power loss in the cable.

Current to factory : from equation P = IV, I = P / V (P divided by V)

= 1 X 10^6 (ten to the power of six OR ten exponent six) / 2 X 10^3 = 500 A.

Power loss in the cable = I^2R ( I squared times R)

= (500)^2 X 5

=1.25 X 10^6 W (Watt)