Transformers

Although the transformer changes the voltage, the frequency of the alternating current is not affected by the transformer.

The transformer equation states:

\dfrac{N_s}{N_p} = \dfrac{V_s}{V_p}

• N_s is the number of turns on the secondary coil.
• N_p is the number of turns on the primary coil.
• V_s is the voltage at the secondary coil in volts \left(\text{V}\right).
• V_p is the voltage at the primary coil in volts \left(\text{V}\right).

Example: A transformer changes a 230 \: \text{V} power supply to 100 \: \text{V} output. If the primary coil has 120 turns, how many turns are on the secondary coil?

[2 marks]

\dfrac{N_s}{N_p} = \dfrac{V_s}{V_p}

\dfrac{N_s}{120} = \dfrac{100}{230}

N_s = \dfrac{100}{230} \times 120

N_s = 52 \: \text{turns}

A transformer may either be a step-up or step-down transformer. A step-up transformer increases the voltage and a step-down transformer decreases the voltage supply.

The most common use of a step-up transformer is to increase the voltage (decrease the current) of a power supply for efficient transport in transmission cables. It always has more turns on the secondary coil than the first.

A step-down transformer reduces the voltage to a level that is safe enough to use in a device or certain area. They always have more turns on the primary coil than the secondary.

The Eddy currents can be reduced by laminating the iron core. This is where the iron core is sliced into smaller pieces with insulating materials wedged between the slices of iron. The higher the resistivity of metal also reduces eddy currents.