The Science Behind Power Transformers

The Science Behind Power Transformers

Emily Newton 26/03/2023
The Science Behind Power Transformers

You’ve probably seen a big metal box near a power line before, but you may not have known what it was or how it worked.

What is a power transformer? It’s an electrical energy transfer device that can change the voltage and current of a cable, allowing a dangerously high-powered cable to safely deliver electricity to buildings such as businesses and homes. Essentially, it connects power stations to buildings. Here’s the science behind it.

The Basics of Electricity

If you tried to plug your computer or coffee maker directly into an electricity pylon – which carries electricity away from a power station – you’d probably start a fire. At the very least, you’d destroy the appliance by burning out the cables. Why? To understand this, it’s important to know the science of circuits.

When electrons move randomly, they don’t generate electricity because random movement is not a current. A current is the flow of electrons in one direction at the same time, just like the current of a river.

You can place a component such as a light bulb in the electrons’ path so the particles have to pass through it. This creates resistance for the electrons, and that’s what turns on the light. The higher the resistance in a system, the lower the flow of electrons – or current – becomes. The whole system is called a circuit.

The circuit’s components can only handle a specific amount of electrons at once. A light bulb, for example, has a set number of electrons it can tolerate flowing through it. Like a river swelling with water, if too many electrons flow through at once, they’ll cause the components to burst and burn out.

An electric current is measured in amps. This measurement tells you how many electrons can pass through a component per second – and 1 amp equates to 6.28 x 1018. That’s such a huge number that it’s easier to abbreviate it as 1 amp. So, if a cable says “1A” on it, that means it’s rated for 1 amp of current, or 6.28 x 1018 electrons, to pass through it per second. Any more and it will burn out.

To make electrons flow, there must be a voltage difference between the two ends of the circuit. If not, the particles will move randomly. In higher-voltage circuits, electrons can flow better. It’s analogous to higher water pressure allowing water to flow more easily.

AC and DC Circuits

Before you can learn what a power transformer is, there’s another crucial piece of information to learn about: The two types of circuits.

Direct Current Circuits

Abbreviated as DC, in this circuit, electrons flow in a single direction. The electrons in a DC circuit are easier to control, allowing the circuit to be more compact. It’s often used for electronics like phones, laptops, and TVs.

Alternating Current Circuits

In AC circuits, the flow of electrons continually switches direction. Keep in mind that the electrons are still travelling as a group. Many appliances use a combination of AC and DC electricity, such as a washing machine with a DC controller and AC motor.

Transformers only use AC electricity.

What Is a Power Transformer Made Of?

When you use a generator to pass an AC current through a cable, it creates a magnetic field that grows and shrinks constantly. You can create an even stronger magnetic field if you coil the cable.

If you place this coiled cable next to a separate cable that’s not connected to anything, the magnetic field’s changing intensity and polarity – the direction it faces – will force the electrons in the second cable to move. This is called inducing an electromotive force (EMF).

In a power transformer, the generator is only connected to one coil, called the primary side. This side generates the pulsing magnetic field. The load, which is the thing you’re trying to power, is connected to the secondary side.

Transformers only use AC electricity because DC circuits provide a constant, steady magnetic field that doesn’t change in size or polarity. Remember: The magnetic field has to fluctuate to induce an electromotive force in the secondary cable.

Much of the magnetic field coming from the primary side of the AC circuit is wasted. Engineers solve this by placing a metal core in a loop between the two coils. The loop guides the magnetic field along a path through the secondary coil.

Thus, a transformer is made of two separate coils of wire wrapped around an iron core. One side is connected to the power generator and the other is connected to the load. Transformers use oil to both insulate and cool their wires. This can be made of naphthenic oil, ester-based oil, paraffinic oil, bio-based hydrocarbons, or biodegradable fluids.

Transformers are rated in kilovolt-amps, abbreviated kVA, which describes how much power the transformer can give you.

What Is a Power Transformer Used For?

A power station could be producing 11,000 volts of electricity, but if you live in the U.K., your home only needs 230 volts. Any more would fry the circuits. Since the power station is far away, the electrons encounter a lot of resistance in the cables along the way. So, if there weren’t transformers, electricity would be wasted.

What a power transformer does is first increase the voltage coming out of the power plant to as much as 400,000 volts. This gives the electrons the needed boost to travel a long distance along the transmission line to your house. The type of transformer that increases the voltage is called a step-up transformer.

Next, a step-down transformer farther down the line reduces the voltage back to 11,000 volts to supply your neighbourhood. Finally, another step-down transformer reduces the voltage to just 230 volts to power your home.

Transforming Society

What is a power transformer? Now you know: It’s a mediator between a high-voltage source and the appliances that will ultimately use that electricity. Step-up transformers increase the voltage along a transmission line so the electricity can travel farther without being wasted. Step-down transformers lower the electricity’s voltage as it arrives at your house. 

You probably don’t think about transformers much, but they play a huge role in your daily life. In a world without transformers, there would still be power, but you wouldn’t be able to use it.

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Emily Newton

Science & Tech Expert

Emily Newton is the Editor-in-Chief of Revolutionized. She is a science and technology journalist with over three years covering industry trends and research. 

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