Transformer Trivia

1. Core mission: to change the voltage of an alternating current

Core function: The primary function of a transformer is to raise or lower the voltage of an alternating current.

Why need to change the voltage?

Long-distance power transmission (voltage): power from the power plant (such as thermal power plants, hydroelectric power plants) to distant cities and factories, in order to reduce the energy loss on the wire (mainly converted into heat), the voltage needs to be increased to hundreds of thousands or even millions of volts. Power = Voltage × Current, in the case of delivering the same power, the higher the voltage, the smaller the current required, and the smaller the losses caused by the resistance of the wires.

Safe Electricity (Voltage Reduction): Hundreds of thousands of volts of high voltage electricity is too dangerous for our lives and factory equipment. Therefore, before entering the home and factory, the voltage needs to be gradually reduced to a safe level through a transformer (e.g. 220V/380V for home use, voltage required for factory equipment, etc.).

Equipment requirements: Various electronic devices (mobile phones, computers, routers, etc.) require different operating voltages (e.g. 3.3V, 5V, 12V, etc.) inside the device. The small transformer in the charger or power adapter (usually part of the switching power supply) converts the household 220V AC power into the low voltage AC or DC power required by the device. 2.

2. Core principle: Electromagnetic induction (Faraday's law)

Key figure: Michael Faraday.

Brief description of the principle: This is the cornerstone of the work of the transformer, the core is ‘electricity generates magnetism, magnetism generates electricity’.

Primary Coil Energised Magnetism: When alternating current passes through one of the coils of a transformer (called the primary/primary coil), it creates a constantly changing magnetic field around it.

The core conducts the magnetic field: This changing magnetic field is concentrated by the core in the centre of the transformer (made of silicon steel sheets, which have good magnetic conductivity) and conducted to the other coil (known as the secondary/casual side coil).

Secondary Coil Magneto-electricity: The changing magnetic field passing through the secondary coil induces an alternating current voltage in the secondary coil.

Simple analogy: Imagine two separate coils facing each other with a ‘magnetic highway’ (core) running between them. The current in one coil ‘vibrates’ (changes AC), and through this motorway sends ‘vibration waves’ (changing magnetic field) to the other side, forcing the coil on the other side to ‘vibrate’ (generate induced voltage) as well. "(induced voltage).

3. Important characteristic: only for alternating current

The principle of operation of a transformer depends on a changing magnetic field. Only alternating current (current that changes direction and magnitude) can produce a continuously changing magnetic field.

Direct current, which is constant in direction and magnitude, produces a constant magnetic field. A constant magnetic field cannot induce a constant voltage in the secondary coil (only a small induction may be possible at the moment of switching on or off). Therefore, a transformer cannot be used to directly change the voltage of a direct current.

4. Core structure: simple and efficient

Iron core: usually made of thin silicon steel sheets laminated together. Silicon steel sheet has high resistance and good magnetic conductivity, which can effectively conduct the magnetic field and reduce the eddy current loss (heat generation) inside the core due to changes in the magnetic field.

Coil (winding): Primary and secondary coils are wound on the core with insulated copper wire (sometimes aluminium wire). They are the conduits through which electrical energy is transferred.

Insulation and cooling: Small transformers: Air-cooled or potting insulation.

Medium/large transformers: immersed in insulating oil. The insulating oil not only provides insulation, but also carries away the heat generated during operation (heat dissipation). Oil-immersed transformers usually have heat sinks or heat pipes on the outside.

5. Ubiquitous applications

Power systems: step-up transformers in power plants → high-voltage transmission lines → step-down transformers in substations (multi-stage step-downs) → distribution transformers (‘square boxes’ on poles or in neighbourhood distribution rooms) → into homes and factories.

Electronic devices: Power adapters/chargers: step down 220V AC and convert it to the low voltage DC required by the device (usually contains a transformer and rectifier and filter circuits).

Household Appliances: Transformers for stereos, old TVs, etc. that may have different voltage requirements inside.

Industrial equipment: to provide the required operating voltage for various motors and control circuits.

Measurement and protection: Voltage transformers and current transformers are essentially specially designed transformers for scaling down high voltages and currents to a safe range for use in measuring instruments and protective devices.

6. Safety tips

Transformers (especially large transformers in power systems) operate with high voltages and currents inside and are very dangerous. Never approach or touch it, even if it looks like a quiet ‘iron box’ or equipment on the pole.

Non-professionals are strictly prohibited from dismantling or repairing the transformer.