Final answer:
Electricity is generated at power stations at voltages greater than 10 kV and transmitted at 120 kV to 700 kV to limit energy losses. It's then stepped down to levels safe for local distribution and end-user utilization. The high voltages reduce line currents, which decreases energy losses and improves overall system efficiency.
Step-by-step explanation:
Electric power stations typically generate electricity at voltages greater than 10 kV. To transmit this power over long distances efficiently, they use high voltages ranging from 120 kV to 700 kV. At the power station exit, the voltage is stepped up using a step-up transformer. This high-voltage transmission is due to the need to limit energy losses, which are inversely proportional to the square of the voltage when transmitting electrical energy through power lines.
Once the electricity arrives at a population center or industry, the voltage is stepped down at substations to between 5 kV and 30 kV for local distribution. Then, before it enters individual homes or businesses, it's further reduced to safer, usable levels such as 120 V, 240 V, or 480 V.
High-voltage transmission reduces the current for the same power. Since the power loss in the lines is proportional to the square of the current (P = I2R), lower current results in significantly lower energy losses. Hence, despite transformers causing some energy loss as heat, the overall system efficiency is improved with high-voltage, long-distance transmission.