Reducing Power Losses by Transmitting Electricity at High Voltages
When a current
flowsalong a wire of resistance
thepower loss in the the resistor needed to drive the current throughthe resistor is equal to
Byreducing the current, we reduce the power loss. We can reduce thecurrent by increasing the voltage at the input to the wire.
Suppose the power supply has a power output of 200W. We can adjustthe voltage of the supply to 20 V then
The power burnt in the wire is
You may also have seen the expression for power,
Itis important to realise that
inthis expression is the voltage drop along the wire, not the supplyvoltage. The voltage drop along the wire is
Then
asbefore.
Suppose we adjust the voltage of the power supply so that it is 40V then
The power burnt in the wire is
The voltage drop along the wire is
Then
asbefore.
Doubling the supply voltage has halved the current and halved thevoltage across the resistor. Because the power burnt variesas
and
thepower wasted in the wire is reduced to
ofit's value.
