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A transformer transforms electric energy from one electrical circuit to another. More specifically, a step-up transformer increases the voltage while it is being transferred from a primary circuit to a secondary one. A step-down transformer, on the other hand, decreases the voltage while it is being transferred from a primary circuit to a secondary one. In order to understand how a transformer does this, you need to learn about the operation of a transformer.
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Team Operation of a Transformer Teachers
The transformation of energy is done by mutual induction between the windings. The simplest form of a transformer is shown in figure 1, which depicts a transformer that consists of two inductive coils, primary and secondary windings. The two coils are connected through a laminated steel core that allows the flow of magnetic flux through the laminated path.
Figure 1. Diagram of a transformer. Source: Georgia Panagi, Vaia.
When the primary winding is connected to an external source of alternating voltage, magnetic flux is induced in the wingdings according to Faraday’s Law.
Faraday’s law states that a varying magnetic field induces an electromotive force that opposes the changes in the magnetic field.
When an alternating current passes through the primary winding, the magnetic field changes, thus inducing an electromotive force. The resulting magnetic field cuts the winding of the secondary coil, which generates an alternating voltage in that winding through electromagnetic induction.
Transformers can only achieve their purpose while an AC current is being applied. This is because DC current doesn’t create any electromagnetic induction.
Most of the magnetic flux becomes linked with the secondary winding, which is called ‘main flux’, while the remaining flux does not get linked with secondary winding and is known as ‘leakage flux’.
Leakage flux is a small portion of flux that leaks beyond the magnetic flux path.
The induced EMF is known as mutually induced EMF, and its frequency is the same as the supplied electromotive force.
When the secondary winding is a closed circuit, the mutually induced current flows through the circuit, transferring electrical energy from the primary circuit to the secondary one.
The core of a transformer consists of laminated sheets of steel that are positioned in such a way that there is a minimum air gap between each sheet. This is done to provide a continuous path for the magnetic flux. The type of steel that is used provides high permeability and reduces eddy current losses and low hysteresis losses.
Hysteresis losses occur due to the magnetisation and de-magnetisation of the core when the current is supplied in both directions.
Steel has high permeability, which means that its ability to carry magnetic flux is much greater than in air, thus allowing the magnetic flux to occur.
Eddy currents circulate in conductors like swirling eddies in a stream induced by varying magnetic fields flowing in a closed loop.
There are various types of transformers with different geometrical variations.
In a core-type transformer, windings are in a cylindrical shape and positioned in the core, as shown in figure 2 below. The cylindrical coils have different layers, with each layer being insulated from the other. Core-type transformers exist in both small and large-size versions. The effective core area of the transformer can be reduced with the use of lamination and insulation.
In a shell-type transformer, the coils are mounted in layers and stacked with insulation between them. A shell-type transformer may have a simple rectangular form, as shown in figure 3 (left), or can have a distributed configuration (right).
Figure 3. Shell-type rectangular transformer (left) and shell-type distributed transformer (right). Source: CircuitsToday.
A zigzag transformer has a zigzag connection, in which the currents in the windings on the core department flow in opposite directions to avoid saturation.
Figure 4. Zigzag transformer configuration.
Transformers are classified based on their uses, purposes, and supply. There are two main purposes for which transformers are used:
The transformer ratio equation specifies the ratio between the secondary and primary voltages V1 and V2 measured in Volts, currents I1 and I2 measured in Amperes, and the number of turns in the coils n1 and n2. This ratio can be used to decrease or increase a quantity proportionally to the second or primary winding.
\[a = \frac{n_1}{n_2} = \frac{V_1}{V_2} = \frac{I_2}{I_1}\]
The ratio of voltages is equal to the ratio of the number of turns, as shown in the previous equations. In an ideal transformer without any electrical energy losses, which includes core losses, eddy current losses, or hysteresis losses, the input power is equal to the output power.
Therefore, the efficiency of the transformer is 100%, or the ratio of the output to input power is 1. This is also shown in the equation of the ideal transformer below, where I1 and V1 are the current and voltage of the primary winding, respectively, while I2 and V2 are the current and voltage of the secondary winding, respectively.
\[\text{Input Power = Output Power} \qquad V_1 \cdot I_1 = V_2 \cdot I_2\]
An input voltage of 5V is supplied to a primary coil of a transformer, while an output voltage of 15V is induced in the secondary coil. If we replace the primary input voltage with 25V, what is the new induced output voltage of the secondary coil?
We use the transformer equation to determine the ratio between the primary and secondary voltages. Then we use that ratio to determine the new induced voltage in the secondary coil based on the new primary input voltage.
\(a = \frac{V_1}{V_2} = \frac{5}{15} = 0.330 \qquad 0.33 = \frac{25V}{V_2'} \Rightarrow V_2' = \frac{25V}{0.33} = 75V\)
Transformers can also be classified in terms of their type of supply. There are two types of supply:
The current in a three-phase transformer has three peaks and troughs for each period. Hence, the maximum amplitude is reached many times, which helps provide power at a constant rate.
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Describe how electromagnetic induction explains the operation of a transformer.
When AC current flows through primary winding, the magnetic flux changes induce an electromotive force, which induces a voltage in the secondary coil. By doing so, voltage levels can be increased or decreased while being transferred to another circuit.
What is the main operation of a step-up transformer?
The operation of a step-up transformer is to increase the voltage in a secondary winding.
How does a transformer operate?
Transformers operate based on the electromagnetic induction principle, where the change in the magnetic field in the primary coil induces a potential difference in the secondary coil.
What are the 3 types of transformers?
The three types of transformers are zigzag, shell, and core-type transformers.
Does a transformer convert AC to DC?
No, a transformer doesn’t convert AC to DC by its own.
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