When current flows through a wire, the wire can become hot.
Think back to Ohm's law:
The current will then be:
Increasing the Voltage (U) will result in an equal increase in current (I) under the condition that the resistance (R) of the wire stays constant. Increasing the current, however will also increase the risk of electron particles colliding with each other. These collisions result in friction (increasing R of the wire) which causes heat, a form of energy loss.
The powerplant only produces a certain amount of energy (E) during the day (t). Preferably all of the produced energy is delivered to the factories and households without any losses occuring during transport.
You can calculate the supplied power using:
To calculate the consumed power at home:
Without any energy loss (efficiency = 100%), the consumed power will be the same as the supplied power. But normally the efficiency is not a 100% because of heat loss during transport. A big current will directly increase the amount of heat loss because of the friction of the electrical particles in the wire. Therefore you want to keep this current as small as possible. The way to do this is by increasing the Voltage using transformers
Rewriting the formula will make it clear why it is vital to lower the current by increasing the Voltage. First thing to do is to replace U with I.R
Doing this will result in:
As you can see the power lost is equal to the root of the current. Therefore lowering the current will have a big impact.