Basics of transformer physics

Transformers have been around for decades. No, not the robots from the science fiction film franchise, although that would be amazing. Rather, the huge, technologically complex metal box-like things that play a key role in the electrical grid. You have likely seen transformers hidden behind extensive fencing, cabling, and ‘Danger! High Voltage!’ warning signs. These areas are not exactly accessible to tourists.

Transformers play a crucial part in providing power to everything from your electric toothbrush to heating for your house to giant factories and just about anything in between. So it may come as a surprise that since their invention in the late 1800s, very little about them has changed. There are a number of different types of transformers that vary depending on voltage level, end user, location, etc. However, this article will only cover conventional transformers or, more specifically, the basic physics concepts behind how a typical transformer works. 

For those without a physical or electrical background, transformers can seem impossible to understand, but there are only two physics laws you need to understand: Ampere’s Law and Faraday’s Law. 

Ampere’s Law

When charged particles like electrons flow in a particular direction, such as through a wire, this is an electric current. The moving charged particles affect the energy surrounding the wire, and we call this changing energy a magnetic field. Ampere’s Law mathematically describes the relationship between the flowing electrical current and the resultant magnetic field. The more intense the electrical current is, the stronger the magnetic field.

Faraday’s Law

Faraday’s Law allows us to predict how the magnetic field and the electrical current will interact. This interaction produces an electromotive force, which essentially means that as a magnetic field changes over time, it produces a force that creates or induces an electrical current.

Basic physics of the transformer core

Conventional transformers harness both Ampere’s Law and Faraday’s law in its core. The core is made of sheets of silicon steel, also known as electrical steel, that are very carefully stacked together. They are manufactured to form a square-like closed loop. A wire is wound on one side of the square loop, which carries the input current from the power source. On the opposite side of the square loop, a second wire is wound, which carries the output current leading farther downstream into the electrical grid. This may be to a ‘load’ or endpoint for the current, i.e. a house, warehouse, etc. 

Wire 1, carrying the input current, is not physically connected to Wire 2, the output current. These are two completely different wires. Ampere’s Law + Faraday’s Law is used to create, or induce, the output current in Wire 2. 

Recall that a moving electrical current creates a magnetic field. This is what occurs on the side of the core with Wire 1. The input current flows along Wire 1 as it coils around that side of the core, and a strong magnetic field is produced. 

For all intents and purposes, we can say that Wire 2 is ‘empty’, meaning that there is no input current here - it is not connected to a power source. However, as the current in Wire 1 produces a magnetic field, this field affects the energy around Wire 2 and induces a current in Wire 2, which then flows out of the transformer farther into the electrical grid. 

While there are different types of transformers with varying core configurations as well as additional complex physics to consider during manufacturing, it is too extensive to consider in this article. However, the processes described here form the basis of conventional transformer physics.

Written by Amber Elinsky

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