Transformers are devices used to lower or increase the voltage and the electric current. Transformers consist of two windings of wires, primary and secondary, involved in a metal core. The passage of an alternating electrical current in the primary winding induce to the formation of an alternating electrical current in the secondary winding. THE proportion between the primary and secondary currents depends on the relationship between the number of turns in each of the windings.
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how they work
Transformers are used to lower or increase electrical voltages and currents in consumer circuits or electric power transmission. If a transformer lowers an electrical voltage, it automatically increases the intensity of the output electrical current and vice versa, always keeping the potency transmitted, given by product gives chain for the voltage.
P - electric power
U - Electric tension
i - electric current
For reasons of efficiency, the transmission of electrical energy over large distances always takes place in
high voltage and with low electric current, in response to energy losses caused by the joule effect, since the energy dissipated in the wires is proportional to the electric current.For energy consumption circuits, such as residential ones, low voltage values are used, for safety reasons — very high electrical potentials can produce electrical discharges. It is for this reason that we find large transformers on poles, whose function is to lower the electrical potential of the current that is carried by the wires, carrying it to homes with voltages in 110V or 220V.
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Common transformers are constructed with two windings of copper wire, called the primary and secondary. These windings always have different numbers of turns and are then twisted around an iron core, with no contact between them. Look at the figure below:
Transformer with primary and secondary windings.
the winding primary is turned on directly to one electromotive force generator alternating (transformers do not work with direct current), that is, an electric current is formed in it. intensity and variable sense, leading to the generation of a magnetic field with same features.
This magnetic field is then focused and amplified through the iron core towards the secondary winding. The changing magnetic field induces the appearance of an electric current in the secondary. The relationship between the electrical potentials between the primary and secondary windings is given by the following formula:
VP — voltage in the primary winding
Vs — voltage in the secondary winding
NP — number of turns in the primary winding
Ns — number of turns in the secondary winding
As we know, electrical voltage and current are inversely proportional, therefore, the ratio for the electrical currents of the primary and secondary windings is inverted:
IP — electric current in the primary winding
Is — electric current in the secondary winding
NP — number of turns in the primary winding
Ns — number of turns in the secondary winding
The physical phenomenon behind the operation of transformers is called electromagnetic induction and is described by the Faraday-Lenz law. This law informs us that when we produce a variation of the magnetic flux through some region of space, a magnetic field must arise in order to oppose this variation. Want to know more about the subject? Access our text: Faraday's Law.
See too: What is alternating current?
Types of Transformers
Despite having similar functions, there are different types of transformers that meet different needs. Check out some of the most common types:
Current transformer: Its main purpose is to lower the intensity of the electrical current, in order to transmit it to transmission networks or devices that do not support high electrical currents.
Potential transformer: is the most common type of transformer, it can lower or increase electrical potential according to demand and the number of windings in the primary and secondary coil.
Distribution Transformer: present in the distribution centers of power plants, it is responsible for distributing electric current to different types of consumers through the transmission lines.
Power transformer: operates with very high levels of electrical potential and electrical current, is used in power generation electrical, but also in applications that require a lot of electrical power, such as industrial ovens and induction.
Exercises
1) A transformer receives an electrical voltage of 4400 V in its primary winding. Determine the number of turns in the primary winding so that the output voltage across the secondary winding, 10 turns, is 110 V.
Resolution:
To solve the exercise, just use the formula that lists the tensions and the number of turns in each turn:
2) A transformer receives 20 V of voltage in its main winding, which contains N turns. If the secondary winding of this transformer is formed by 3N turns, what will be the electrical output voltage?
Resolution:
Using the formula for the input and output voltages in the transformer, we will do the following calculation:
3) Regarding the operation of transformers, identify the statements below as true or false:
I - Transformers are capable of operating both with direct electrical current and with alternating electrical current.
II - If the number of turns of the secondary winding of a transformer is greater than the number of turns of the primary winding, then the output voltage of this transformer will be necessarily greater than the voltage of Entrance.
III - Despite the transformations suffered by electrical voltage and current, electrical power remains constant in ideal transformers.
IV - Transformers operate according to a phenomenon called electrostatic induction, discovered by Faraday.
They are true:
a) F, F, V, F
b) V, V, V, F
c) F, V, V, F
d) F, V, F, F
e) F, V, V, V
Template:
Reply: Letter C
I - Transformers only work with alternating currents, as it is necessary for them to appear magnetic field flux variations to induce electrical currents in the winding secondary.
II - The formula that relates the output voltages and the number of windings confirms this statement.
III - For ideal transformers, that is, that do not dissipate electrical energy, this statement is true.
IV - The phenomenon that explains the operation of transformers is the principle of electromagnetic induction.
By Me. Rafael Helerbrock
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/fisica/o-que-e-um-transformador.htm