A transformer is a machine that changes AC voltage so electrical energy can travel efficiently from renewable energy sources to homes, schools, and businesses. Wind turbines, solar farms with inverters, hydroelectric generators, and other renewable systems often produce electricity at voltages that are not ideal for long-distance transmission. By stepping voltage up for transmission and stepping it down for use, transformers help reduce wasted energy in power lines.
This makes them a key link between clean energy generation and the electrical grid.
A transformer works by electromagnetic induction between two coils of wire wrapped around a shared iron core. Alternating current in the primary coil creates a changing magnetic flux in the core, which induces an alternating voltage in the secondary coil. The voltage change depends on the ratio of turns in the two coils, so more turns on the secondary coil means higher output voltage, while fewer turns means lower output voltage.
Because transformers require changing magnetic flux, they work with AC and with inverter-produced AC, not with steady DC.
Key Facts
- Transformer voltage ratio: Vs / Vp = Ns / Np
- Ideal transformer power relation: Pp = Ps, so VpIp = VsIs
- Step-up transformer: Ns > Np, so Vs > Vp and Is < Ip
- Step-down transformer: Ns < Np, so Vs < Vp and Is > Ip
- Transmission line loss: Ploss = I^2R, so raising voltage lowers current and reduces heat loss
- Faraday's law: induced voltage depends on changing magnetic flux, so transformers need AC or changing current
Vocabulary
- Transformer
- A device that changes AC voltage using two coils connected by a changing magnetic field in a core.
- Primary coil
- The coil connected to the input electrical source of a transformer.
- Secondary coil
- The coil connected to the output side where the induced voltage appears.
- Magnetic flux
- A measure of the magnetic field passing through a surface or core.
- Laminated iron core
- A stack of thin iron sheets that guides magnetic flux while reducing energy loss from eddy currents.
Common Mistakes to Avoid
- Using a transformer with DC, because a steady direct current does not create the changing magnetic flux needed to induce voltage in the secondary coil.
- Thinking a transformer creates extra energy, because an ideal transformer conserves power and real transformers lose some energy as heat.
- Forgetting that current changes opposite to voltage, because stepping voltage up lowers current when power is approximately conserved.
- Mixing up turns ratio and voltage ratio, because the output voltage depends on Vs / Vp = Ns / Np and not on the thickness of the wire or the size of the core alone.
Practice Questions
- 1 A wind turbine system sends 600 V AC into a transformer with 200 turns on the primary coil and 4000 turns on the secondary coil. What is the secondary voltage?
- 2 An ideal transformer steps 240 V up to 4800 V and sends 10 A through the secondary side. What current flows in the primary side?
- 3 Explain why a solar farm usually needs an inverter before a transformer can send its energy to the grid.