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Operation of a Transformer

Operation of a Transformer

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A transformer is a device transfers electric energy from one circuit to another. There are two types of transformers: step-up and step-down. A step-up transformer increases the voltage as it moves from the primary circuit to the secondary circuit. A step-down transformer, on the other hand, decreases the voltage as it moves from the primary circuit to the secondary circuit. To understand how a transformer works, it is important to know about its operation.

Operation of a transformer: Principle

Transforming energy is made possible through mutual induction of windings. Figure 1 shows the most basic form of a transformer, which includes two inductive coils: the primary and secondary windings. These coils are connected through a laminated steel core that allows the magnetic flux to flow through the laminated path.

Diagram of a transformer
Diagram of a transformer

create a magnetic field, the primary winding is connected to an external source of alternating voltage following Faraday's Law. This law states that a varying magnetic field creates an electromotive force that opposes the changes in the magnetic field. When the primary winding carries an AC current, it creates a changing magnetic field. This field cuts across the winding of the secondary coil, inducing an electromotive force. This results in an alternating voltage in the secondary winding through electromagnetic induction. It's important to note that transformers only work with AC current, as DC current does not create electromagnetic induction.

Most of the magnetic flux links with the secondary winding, resulting in "main flux," while the remaining flux, known as "leakage flux," doesn't link with the secondary winding. Leakage flux is a small portion of flux that leaks beyond the magnetic flux path. The induced EMF is called the 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 circuit.

The core of a transformer

To create a continuous path for magnetic flux, the core of a transformer is made up of laminated sheets of steel. These sheets are carefully positioned to minimize the air gap between them. The type of steel used ensures high permeability, which reduces eddy current and hysteresis losses.

Hysteresis losses occur due to the magnetization and demagnetization of the core when the current is supplied in both directions. Steel has high permeability, which means it can carry magnetic flux much more effectively than air, allowing for the creation of magnetic flux.

Eddy currents are currents that circulate in conductors, similar to swirling eddies in a stream. These currents are induced by varying magnetic fields flowing in a closed loop. Eddy current losses occur in the transformer core when the magnetic fields cause current to flow in the laminations, resulting in heat generation and energy loss. To minimize these losses, the laminations are made thin and insulated from each other.

Types of transformers

There are various types of transformers with different geometrical variations.

Core-type transformer

In a core-type transformer, the windings are arranged in a cylindrical shape and positioned within the core, as can be seen in figure 2. The cylindrical coils consist of multiple layers, with each layer being insulated from the others. Core-type transformers are available in both small and large sizes. Lamination and insulation can be used to reduce the effective core area of the transformer.

The primary and secondary coils are wound around the core in such a way that they're both in close proximity to the core, but not touching it. This arrangement ensures that the magnetic field generated by the primary winding efficiently induces a current in the secondary winding.

Core-type transformers are efficient and commonly used in power transmission and distribution systems. They can handle large amounts of power and are available in a wide range of voltages and currents. However, they can be heavy and bulky due to the size of the core and windings.

 

Core-type transformer
Core-type transformer

Shell-type transformer

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).

Shell-type rectangular transformer (left) and shell-type distributed transformer (right)
Shell-type rectangular transformer (left) and shell-type distributed transformer (right)

Zigzag or interconnecting star type transformer

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.

The uses and purposes of a transformer

Transformers are classified based on their purpose, use, and power supply. There are two main purposes for which transformers are used: step-up and step-down.

Step-up transformers increase the voltage at the secondary winding. is achieved by having more turns on the secondary coil than on the. These transformers are used in power transmission systems to increase the voltage to reduce energy losses during transmission.

Step-down transformers decrease the voltage at the secondary winding. This is achieved by having fewer turns on the secondary coil than on the primary one. These transformers are used in electronic devices to decrease the voltage to a level that is suitable for use by the device.

The transformer ratio equation specifies the ratio between the secondary and primary voltages, currents, and the number of turns in the coils. This ratio can be used to decrease or increase a quantity proportionally to the second or primary winding. The transformer ratio equation is given as V1/V2 = n1/n2 = I2/I1, where V1 and V2 are the primary and secondary voltages, n1 and n2 are the number of turns in the primary and secondary coils, and I1 and I2 are the primary and secondary currents. This equation is important in designing and selecting transformers for specific applications. 

The ideal transformer equation

The ratio of voltages is equal to the ratio of the number of turns, as shown in the equation below:

V2/V1 = N2/N1

Where V2 is the secondary voltage, V1 is the primary voltage, N2 is the number of turns in the secondary coil, and N1 is the number of turns in the primary coil.

In an ideal transformer without any electrical energy losses, the input power is equal to the output power, and the efficiency of the transformer is 100%. This is also shown in the equation of the ideal transformer below:

I1V1 = I2V2

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.

Given that an input voltage of 5V is supplied to a primary coil of a transformer, and an output voltage of 15V is induced in the secondary coil, the ratio of the primary and secondary voltages is 3:1 (15V/5V = 3).

If we replace the primary input voltage with 25V, the new induced output voltage of the secondary coil is 75V (25V x 3 = 75V).

Single and three-phase transformers

Transformers can also be classified in terms of their type of supply. There are two types of supply: single-phase and three-phase.

Single-phase transformers contain one conductor and one neutral wire. They work using a voltage cycle that operates in a time phase and are used widely in today's technology to convert AC values to the desired ones. These transformers are used for low-power applications, such as in homes and small businesses.

Three-phase transformers are widely used for electrical distribution and network applications. They work with the same principle as single-phase transformers. However, there are three conductors, each of which contains a set of primary and secondary winding and one neutral wire. 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. These transformers are used for high-power applications, such as in commercial and industrial settings.

The operation of a transformer is based on Faraday's law of induction, which states that a changing magnetic field induces an electromotive force (EMF) in a conductor. When an alternating current is passed through the primary coil of a transformer, it creates a changing magnetic field that induces an EMF in the secondary coil. The ratio of the number of turns in the primary coil to the number of turns ratio

Operation of a Transformer

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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