State the advantages of high-voltage transmission

4.5.6 The Transformer

Objective

State the advantages of high‑voltage transmission.

Why Transmit Electricity at High \cdot oltage?

Electrical power transmitted through a line is given by

\$P = VI\$

where P is power, V is voltage and I is current. For a given power, increasing the voltage allows the current to be reduced:

\$I = \frac{P}{V}\$

Since the resistive loss in a conductor is

\$\text{Loss} = I^{2}R\$

lower current means much lower losses. This is the fundamental reason for using high‑voltage transmission.

Key Advantages of High‑Voltage Transmission

• Reduced I²R losses – lower current reduces heating and energy wasted as heat.
• Smaller conductor size – less material is needed for the same power rating, reducing cost and weight.
• Higher transmission capacity – more power can be sent over a single line without exceeding thermal limits.
• Longer transmission distances – losses remain acceptable over hundreds of kilometres.
• Improved voltage regulation – voltage drop along the line is smaller because ΔV = IR is reduced.

Comparison of Low‑Voltage vs. High‑Voltage Transmission

Role of the Transformer

Transformers step the voltage up for transmission and step it down for distribution:

1. Power is generated at a relatively low voltage (e.g., 400 V).
2. A step‑up transformer increases the voltage to several hundred kilovolts.
3. Transmission lines carry the high‑voltage, low‑current power over long distances.
4. Near the consumption point, a step‑down transformer reduces the voltage to safe, usable levels (e.g., 230 V).

Summary

High‑voltage transmission is essential for efficient, economical, and reliable delivery of electrical energy over long distances. By reducing current, it minimises resistive losses, allows the use of lighter conductors, and enables the power grid to serve large, dispersed populations.