An electrical transformer is a static and reversible electrical machine that allows the electrical voltage (potential difference or voltage) to be increased or decreased in an alternating current electrical circuit while maintaining electrical power. The input power to an ideal transformer (without losses) is the same that will be obtained at the output. To achieve this, it is based on the principle of electromagnetic induction. The transformer converts alternating electrical energy with one voltage level into alternating energy with another voltage level.
To transport electrical current from the point of origin where it is generated, it must be in high voltage. The difficulty is that, when you reach your destination, the homes, you have to reduce the electrical current to 230V (low voltage). To achieve this we use electrical transformers, which allow us to increase the voltage when the current leaves the power plant, to be able to transport it and then reduce it when it reaches homes, factories, industries, and so on.
Parts of an electrical transformer
In the example of an ideal single-phase transformer, the electrical transformer is mainly composed of two coils of conductors with wound turns (winding) and a closed soft-iron core, magnetic core.
The core of an electrical transformer is made of silicon steel sheets, insulated from one sheet to another. It is formed by the columns, which is the section where the windings are mounted and is formed by the cylinder heads, which is the section where the columns are joined. The function of the nucleus is to conduct the magnetic flux.
The winding is made up of two coils, the primary coil and the secondary coil. It is a copper wire wound through the core at one end and is covered by an insulating layer of varnish (usually). The primary winding is where we apply the input voltage and the secondary winding is where we get the output voltage. The turns ratio of the copper wire between the primary winding and the secondary winding indicates what the transformation ratio is.
How an electrical transformer works
Electrical transformers are based on the principle of electromagnetic induction. This phenomenon consists of generating an electric current (induced) by means of a magnetic field and/or vice versa.
The primary coil receives a certain voltage. Being in a closed electrical circuit made up of turns, an electric current will begin to flow through the turns of the primary winding. As this electric current circulates, a magnetic field, a magnetic flux, will be generated around it. This generated magnetic flux will advance through the core of the electrical transformer to the secondary winding, and it will be variable because the intensity that creates it is an alternating current.
When the magnetic flux reaches the coils of the secondary winding, as it is a variable magnetic flux, it will cut the turns of the secondary winding. This phenomenon will create tension in them. And when connecting a load, for example, a resistance, to one of the ends of the secondary winding, as we have generated a voltage at its ends, we will obtain an electric current that will circulate through the load that we have connected.
Why can’t it run on direct current?
If the current generated in the primary winding were direct current, the magnetic flux created would not be variable. If the flux created is not variable, it will not cut the turns of the secondary winding, because it would always be the same flux. And as a consequence, no voltage or current would be generated in the secondary winding.
By Lenz’s Law, the current must be alternating for this variation of magnetic flux to occur. The electrical transformer cannot be used with a direct current.
Types of electrical transformers
All electrical transformers are based on the same fundamental principles that we have described in their operation. But there are several types of transformers that are grouped into electrical power transformers and electrical measurement transformers.
Electric power transformers
Power transformers are used to vary the voltage values of an alternating current electrical circuit but maintain its power value.
- Elevating electrical transformers. Its main characteristic is to increase the output voltage with respect to the input voltage. To achieve this, the number of turns of its secondary winding is higher than the number of turns of its primary winding.
- Step-down electrical transformers. Its main characteristic is to reduce the output voltage if we compare it with the input voltage. In this case, to achieve this, the number of turns of the primary winding is greater than the number of turns of the secondary winding.
- When it is necessary to change the value of a voltage, but in a very small amount, the autotransformer is used. The coils are mounted in a summation way and the voltage, in these situations, is not introduced through the primary winding to exit through the secondary winding, it is introduced through an intermediate point of the only coil that constitutes the electrical transformer.
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