Step Down Transformer:Construction, Working, Applications

Points of Discussion:


A transformer transfers electrical energy. Step down transformer is one kind of it. A step-down transformer decreases the voltage applied on primary windings and supplies reduced voltage on the secondary side. However, the power and frequency remain constant in the process.

A Single Phase Electrical Step Up Transformer, Image Credit – Mtodorov 69Transformer-hightolow smallerCC BY-SA 3.0

Construction of Step Down Transformer

The construction process of a step-down transformer lies in its core and windings, and it is very much similar to a step-up transformer.

Construction of Core of a Transformer:

Core of a transformer is made of soft iron-like metals. It allows the magnetic flux to pass through it. The coils of both the windings are wrapped around the core. The core can be of two types based on the wrapping up of the locks. If the coils are wrapped outside the body, then that is Closed Core Transformer. If the windings are inside the iron core, then that will be Shell Core Structure. A closed core type transformer suffers a problem of ‘Leakage Flux’ while a shell type does not. That’s why a shell core structure is more preferred rather than a closed core. 

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Transformer Windings:

Windings are the conductors of current inside the transformer. They are made of a coil of wires. The material of the wire is copper or aluminium. Windings are of two types – Primary windings and Secondary windings. Primary windings receive the applied voltage, and the secondary windings supply the induced voltage to load. Though electrical energy transfers from the primary side to secondary windings without metallic contacts—the main classification parameter to decide whether a transformer is a step up or step down lies here.

In case of a step-down transformer, the number of turns in primary windings is more than the number of turns in the secondary windings. However, the density of wire is thinner in primary windings than the thickness of the secondary windings.

660px Transformer Flux.svg
Construction of a Step Down Transformer, Image credit: Fred the OysterTransformer FluxCC BY-SA 4.0

Working of a Step Down Transformer

The working principle of a step-down transformer is the same as a typical transformer. A step-down transformer gives higher output voltages than a lower input voltage and works on Faraday’s law and Turn Ratio.

Due to the applied voltage in the primary windings, the current flows through the wires. The flow of alternating current generates magnetic flux around the windings. The core of the transformer allows this magnetic flux to flow through it.

Change in magnetic flux further induces a voltage in the secondary windings.

Now the turn ratio factor comes into action.

Turns ratio = Np/Ns =Vp/Vs ———————- (i)

Or, Vs = Vp *(Ns /Np) ——————— (ii)

Here, Np = number of turns in the primary windings.

Ns = number of turns in the secondary windings

Vp = voltage at the primary side

Vs = voltage at the secondary side.

Now in the equation (ii), we are calculating Vs – the secondary voltage. We can see Vp is constant as the applied voltage is constant. Now increasing or decreasing the (Ns/Np) ratio, we will able to get our desire voltage at the output side. While using a step-up transformer, our motive is to generate lesser voltage than the input. So, we have to keep the Ratio of (Ns/Np) less than 1.

That means the value of Np should be higher than the magnitude of Ns. As we know, Np is the number of turns in the primary windings, that’s why a step-down transformer is designed with higher no. of turns in the primary winding side. As mentioned earlier, the power of the electrical signal remains the same. The voltage gets reduced, and to keep the power constant, the current gets increased. The frequency of energy also remains unchanged.

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Applications of Step down transformer

Transformers have various applications. Step down transformer is designed to do some specific tasks and has a wide range of applications in both electrical and electronics circuitries.

255px Drehstromtransformater im Schnitt Hochspannung
Step Down Transformer in power stations, Image By: StahlkocherDrehstromtransformater im Schnitt HochspannungCC BY-SA 3.0
  • Power System: Step down transformers are used in power distribution systems. In a various phase of supplying power, step down transformers is used to reduce voltage whenever necessary.
  • Electronic devices: Step-up transformers are used in various electronics device where the device works on lower voltages than the supplied voltage. Tools like adapters of different electronic devices and low voltage applications use this type of transformers.
  • Transformers, which we found at streets near our home step down transformers.

Know about different types of transformers and their applications! Click to navigate!

Frequently asked questions on a step down transformer

1. Does a step down transformer decrease current?

No, a step down transformer does not decrease or reduce current. Instead, it reduces the voltage and increases current. The power of the signal remains constant, though.

2. Why do we need to step-up transformers?

The name of the transformer helps us to find out what it does. A step-down transformer delivers reduced supplied voltages to its load. So, when we need to step down or reduce the voltage provided for our workings, then we should use a step-down transformer. But that the current value gets increased. So if we need to minimise voltage source with the same current, then a step-down transformer would not serve our purposes.

3. A transformer has 2000 turns of copper wire wrapped in a side, and 1000 turns of copper wire surrounded at another side. If an AC voltage of 440 volts is applied at 2000 turn side, what will be the voltage at the 1000 turn side? Also what type of transformer is this?

Voltage is applied at the 2000 turn side. So, that is the primary winding and the number of turns of wire = 2000. Let’s say that is Np.

1000 turn side is the secondary side. So this is the secondary winding and the number of turns of wire = 1000. Let’s say that is ns.

440 volt is supplied at the primary side, so that is primary voltage and let’s say that = Vp

We have to calculate the voltage at the secondary side; let’s say that = Vs.

We know that turn ratio = Np/Ns

That is also= Vp/Vs

So, Np/Ns = Vp/Vs

Or, Vs = (Ns/Np) * Vp

Substituting the values, we get-

Vs = (1000/2000) * 440

Or, Vs = 220 volt

The voltage at the secondary side will be = 220 volt.

Now, as we can see, the voltage is lower than the supplied voltage, so this is a step-down transformer.

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4. Write some differences between step up and step down transformers

The fundamental difference of step up and step down transformers lies in their working. Step-up transformers increase the supplied voltage, whereas step down transformers reduces that. Here are some of the more differences. Click Here!

5. Practical Significance of Step-Down transformers

Step down transformers have impacts on our day to day life. The power which generates at a power station is of high voltages (Range of Megawatt to Gigawatt). If there are no step-down transformers, then there would not be electricity in households. When we need to transfer power from power stations to the home, then it is necessary to use a step-down transformer. Using a step-down transformer, we can reduce the high voltage and can be supplied to houses.

6. What is the turn ratio for a step-up transformer?

The turn’s ratio of a transformer is an essential parameter for the calculation of power. It is given by the balance of the number of turns of the wire in primary windings to the number of the arches of the wire in secondary windings. The equation gives the ratio –

Turns ratio = Np/Ns

Np is the number of turn in the primary windings, and Ns is the number of bend in the secondary windings.

Step down transformer has no ideal turn’s ratio. It varies as per the need. But to work as a step-down transformer, the turn ratio must be greater than unity.

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