Question

Power transmission is carried out at ........................ and ..........................?

• A. high voltage, high current
• B. low voltage, high current
• C. high voltage, low current
• D. low voltage, low current

Answer 1

The correct option is C high voltage, low current

One of the key concerns in the transmission of electricity is the power loss in transmission lines, dissipated as heat due to the resistance of the conductors.
The power loss $P_{loss}=I^{2}R={\left(\frac{P}{V}\right)}^{2}R(\because p=VI)$
Since $P$and $R$ are fixed conditions, less power will be lost if high voltages V are used.
The transmission line then uses a transformer to step down the voltage.
For a given amount of power, a higher voltage reduces the current and thus the resistive losses occurs in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the$I^{2}R$ losses by a factor of 100, provided the same sized conductors are used in both cases.