Transformer Formula: Definition, Types & Working Principle

Transformer is an electrical device used to 'step up' or ‘step down' the voltage levels between circuits. A transformer is a passive electrical device that uses electromagnetic induction in order to transmit electrical energy from one circuit to another. The transformer raises or reduces AC voltage between circuits while keeping the current's frequency constant. Transformer formula is given by the equation,

\(\frac{V_p}{V_s} = \frac{N_p}{N_s}\)

Key Terms: Transformer, Transformer Formula, Step up, Step down, current, faraday’s law, circuit, EMF, Current Coil, Electromagnetic Induction.

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What is a Transformer?

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Transformers are electrical devices that employ a changing magnetic field to transmit electrical energy between two or more coils of wire.

• A transformer is a simple stationary electromagnetic device that uses Faraday's Law of Induction to convert electrical energy from one value to another.
• The transformer does this conversion by connecting multiple electrical circuits via a common oscillating magnetic circuit that is generated by the transformer.
• In the form of Mutual Induction, a transformer acts on the principles of "electromagnetic induction." 
• The transformer formula or transformer equation can be written as V_p × I_p = V_s × I_s.

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The video below explains this:

Transformer Detailed Video Explanation:

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Transformer Formula

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An electric circuit’s power can be calculated by multiplying the current intensity with the voltage. 

(Primary coil input voltage) + (Primary coil input current) = (Secondary coil output voltage).(Output current on the secondary coil)

\(\frac{\text{Input Voltage on Primary Coil}}{\text{Output Voltage on Secondary Coil}} = \frac{\text{No. of truns of wire on Primary Coil}}{\text{No. of turns of Wire on Secondary Coil}}\)

The formula for the transformer is as follows:

\(\frac{V_p}{V_s} = \frac{N_p}{N_s}\)

Where,

• Vp denotes main voltage
• Vs denotes secondary voltage.
• Np denotes the number of primary turns.
• Ns denotes the number of secondary turns.
• The ratio N_p/N_s is also called the turn ratio as it denotes the difference between the number of turns in a primary coil with that of the secondary coil.

Step Up Transformer Formula

On the primary side, a step-up transformer converts low voltage (LV) and high current to high voltage (HV) and low current on the secondary side. In a step-up transformer, which transforms a low primary voltage to a high secondary voltage, the primary coil turns are smaller than the secondary coil turns. The formula for a step-up transformer is as follows:

VS = NS/NP x VP  

Step Down Transformer Formula

A step-down transformer lowers the secondary voltage from a high primary voltage. In a Step Down Transformer, the primary winding of a coil has more turns than the secondary winding. The formula is as follows:

VS = NS/NP x VP

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Types of Transformers

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The two main types of transformers are:

1. Step-up Transformer: As the number of turns on the secondary is always more than the number of turns on the primary, the step-up transformer aids in the voltage rise on the output side. The secondary side of the transformer generates a high voltage. 
2. Step-down Transformer: The output voltage is reduced using a step-down voltage transformer. In other words, it transforms high voltage, low current electricity into low voltage, high current electricity. The power supply, for example, has a voltage of 230-110 V, while the doorbell only needs 16 V. As a result, a step-down transformer should be used to lower the voltage from 110 V or 220 V to 16 V.

Parts of Transformer

The different parts of a transformer are as follows.

• The magnetic core, primary winding, and secondary winding are the three main components of a transformer. 
• A live supply of AC power is connected to the primary winding. 
• An oscillating magnetic field surrounds the coil as a result of this. 
• The secondary winding experiences an EMF. 
• If the secondary winding circuit is closed, AC current will flow through it. 
• The magnetic core, which is commonly formed of laminated steel sheets and offers a low resistance route for the magnetic field, is shared by these windings. 
• The ratio of the number of turns between the two windings is the same as the ratio of output and input voltage. 
• The secondary winding in a step-down transformer has fewer turns than the primary, whereas the secondary winding in a step-up transformer has more.

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Working Principle of a Transformer

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Mutual inductance between two circuits connected by a shared magnetic flux is the primary basis of the functioning of a transformer. A basic transformer is made up of two inductive coils that are electrically distinct yet magnetically coupled by a reluctance channel. The transformer's operating principle may be seen in the diagram below.

Principle of Transformer

• The core laminations are linked in the shape of strips, and you can see some tiny gaps along the length of the cross-section of the core. The mutual inductance of both coils is quite high. 
• The alternating flux that is built up in the laminated core, due to the coil that is coupled to an alternating voltage source, induces a mutual electromotive force in the transformer. 
• The mutual induced electromotive force is created when the majority of the alternating flux produced by this coil is coupled with the other coil. 
• Faraday's equations of electromagnetic induction may be used to describe the electromotive force that has been created.
• A current flows through the second coil circuit while it is closed, and electrical energy is transmitted magnetically from the first to the second coil.
• The first coil receives an alternating current source and hence is referred to as the primary winding. 
• The energy is extracted from the second coil, which is referred to as the secondary winding.

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Things to Remember

• A transformer transfers AC current from one circuit to another while raising or reducing voltage via electromagnetic induction.
• The primary winding, secondary winding, and magnetic core are the three main components of a transformer.
• A transformer is an electrical device that allows us to sustain power while increasing or decreasing the voltage in an alternating current electrical circuit. 
• The formula for the transformer is as follows:

\(\frac{V_p}{V_s} = \frac{N_p}{N_s}\)

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