HT transmission

QUESTION: What is high tension transmission? Why is it necessary to use high tension?

Answer:

High tension (or HT) transmission means the transmission of electricity at high voltage. In Britain this may be at 220 000 V or even 440 000 V for transmission over long distances.

The reason for transmitting at HT is as follows.

When a current flows down a wire the wire heats up due to the resistance of the wire to the electric current. There is a power loss in the wire per kilometre given by I²R – where I is the current in the wire and R is the resistance of the wire per kilometre.

Since for a given wire the resistance per kilometre is constant (at a constant temperature) the only way you can reduce this power loss is to reduce the current.

For a given power input (and output) the Power is given by the formula:

Power = Input voltage x Current in the wire

For a given power you can see that if you increase the voltage you decrease the current. Decreasing the current in the wire will also decrease the power loss per kilometre.