Step Up Transformer

Step Up Transformer: Definition, Construction, Working & Applications

Step Up Transformer

Step Up Transformer

Step Up Transformer Definition

A Step up transformer is a form of electrical instrument that transforms the low voltage (LV) and high current input from the primary section of the device to the high voltage (HV) and low current output on the secondary section of the instrument.

What is Step Up Transformer?

If there are fewer turns in the primary winding than in the secondary winding, the secondary voltage will be higher than the secondary circuit. This type of transformer is called a step-up transformer. That’s because it steps up, or increases, the voltage. In other words, a step up transformer is a transformer that increases the voltage from the primary coil to the secondary coil while managing the same power at the rated frequency in both coils.

Diagram of Step Up Transformer

What is Transformer?

A transformer is a static device that transfers AC electrical power from one circuit to the other at the same frequency but the voltage level is usually changed. In simple words Transformer step up or step down the voltage.

Step Up Transformer

What is the main difference between a step up and step down transformer?

Step up and step down transformer:

In a step up transformer the voltage is raised on the output side (V2 > V1), whereas, in a step down transformer the voltages is lowered on the output side (V2 < V1).

Why do we need step up transformers?

Necessity of Transformer:

  • In our country, usually electric power is generated at 11 kV. The voltage level is raised to 220 kV, 400 kV or 750 kV by employing step up transformers for transmitting the power to long distances.
  • Then to feed different areas, as per their need, the voltage level is lowered down to 66 kV, 33 kV or 11 kV by employing step-down transformers. Ultimately for utilisation of electrical power, the voltage is stepped down to 400/230 V for safety reasons.
  • Thus, transformer plays an important role in the power system.

Construction of Transformer:

Step Up Transformer Construction

The following are the major elements of a transformer:

  • Magnetic circuit mainly comprises of transformer core having limbs and yokes.
  • Electric circuits mainly comprise of windings, insulation and bushings.
  • Tank mainly comprises of cooling devices, conservator and ancillary apparatus.

How Transformer Work?

Working Principle of a Transformer:

The principle of working of transformer is electromagnetic induction.

  • A single-phase transformer consists of two windings placed over a laminated silicon steel core. The winding having less number of turns is called low-voltage winding and the winding having more number of turns is called high voltage winding.
Working Principle of a Transformer


  • Also, the winding to which AC supply is connected is called a primary winding and the other one is called a secondary winding to which load is connected.
  • Once AC supply of voltage V1 is given to primary winding, an alternating flux is set-up in the magnetic core which links with the primary and secondary winding.
  • Consequently, self-induced emf E1 and mutually-induced emf E2 are induced in primary and secondary, respectively.
  • These induced emf’s are developed in phase opposition to V1 as per Lenz’s law. The self-induced emf in the primary is also called back emf since it acts in opposite direction to the applied voltage. Although, there is no electrical connection between primary and also secondary winding, still electric power is transferred from one circuit (primary side) to the other circuit (secondary side). It is all because of magnetic coupling, i.e., the alternating flux which is set-up in the core linking with both the windings.  

Induced EMF:

The magnitude of induced emf in a coil depends upon rate of change of flux linkages i.e., e v N. since, the rate of change of flux for both the winding is the same, the magnitude of induced emf in primary and secondary will depend upon their number of turns, i.e., primary induced emf E1 v N1 and secondary induced emf E2 v N2. When N2 > N1, the transformer is called a step up transformer, on the other hand, when N2< N1 the transformer is called step-down transformer.

Turn ratio:

  • The ratio of primary to secondary turns is called turn ratio, i.e., turn ratio = N1/ N2.
  • Transformation ratio: The ratio of secondary voltage to primary voltage is called voltage transformation ratio of the transformer. It is represented by K. K = E2/E1=N2/N1

Applications of Transformer in electrical:

Main applications of the transformers in electrical are given below:

  • To change the level of voltage and also current in electric power systems.
  • As impedance-matching device for maximum power transfer in low-power electronic and control circuits.
  • As a coupling device is electronic circuits
  • To isolate one circuit from another, since primary and secondary are not electrically connected.
  • To measure voltage and currents; these are known as instrument transformers.

Transformers are extensively used in AC power systems because of the following reasons:

  • Electric energy can be generated at the most economic level (11–33 kV)
  • Stepping up the generated voltage to high voltage, extra high voltage EHV (voltage above 230 kV), or to even ultra high voltage UHV (750 kV and above) to suit the power transmission requirement to minimize losses and also increase transmission capacity of lines.
  • The transmission voltage is stepped down in many stages for distribution and utilization for domestic, commercial and also industrial consumers


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