Transformer

4.5.6 The transformer - Use in High-Voltage Transmission

Transformers are crucial components in the electrical grid, particularly for the efficient transmission of electricity over long distances. This section will detail how transformers are used to step up voltage for transmission and step down voltage for safe use in homes and industries.

Why High-Voltage Transmission?

Transmitting electricity at high voltages offers significant advantages:

• Reduced Current: For a given amount of power (P = VI), increasing the voltage (V) while keeping the power constant requires a decrease in current (I).
• Reduced Power Loss: Power loss in transmission lines due to resistive heating (I²R) is proportional to the square of the current. Reducing the current significantly reduces these losses.
• More Efficient Use of Conductors: Using lower currents allows for the use of thinner and lighter conductors, reducing the overall cost of the transmission infrastructure.

Step-Up Transformers

At power stations, transformers are used to step up the voltage generated by the generators. This is done using a step-up transformer. Step-up transformers have more turns in the secondary coil than in the primary coil. The voltage in the secondary coil is higher than in the primary coil.

The relationship between the number of turns and the voltage is given by:

$$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $$

Where:

• $V_s$ is the voltage in the secondary coil.
• $V_p$ is the voltage in the primary coil.
• $N_s$ is the number of turns in the secondary coil.
• $N_p$ is the number of turns in the primary coil.

Step-Down Transformers

As electricity reaches homes and businesses, it needs to be reduced to a safe and usable voltage. This is achieved using step-down transformers. Step-down transformers have fewer turns in the secondary coil than in the primary coil. The voltage in the secondary coil is lower than in the primary coil.

Again, the relationship between the number of turns and the voltage applies:

$$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $$

Transformer Construction (Simplified)

A transformer typically consists of two coils of wire (primary and secondary) wound around a common iron core. The iron core concentrates the magnetic flux. An alternating current (AC) in the primary coil creates a changing magnetic field, which induces a voltage in the secondary coil. The ratio of the turns in the two coils determines the voltage transformation ratio.

Table Summary

Suggested diagram: A diagram showing a step-up transformer at a power station and a step-down transformer at a substation or near a house. The diagram should clearly label the primary and secondary coils, and indicate the direction of current flow and magnetic flux.