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Working Of A Transformer


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This video gives a detailed animated illustration on the working of Electrical Transformers. It explains the basic working principle and construction of the transformer, step-up transformer, step-down transformer, transformer winding and core construction.

Here is the transcription of the above video:

Transformers are capable of receiving AC power at one voltage and delivering at another voltage. In this way, they help us achieve better transmission efficiency while transferring power over longer distances.  In this video, will be going through the working and construction of a 3 Phase transformer by starting from its simplest form.

The basic working principle of a transformer is “Electromagnetic Induction”. According to this principle, a varying magnetic flux associated with a loop will induce an electromotive force across it. Such a fluctuating magnetic field can easily be produced by a coil and an alternating EMF system. A current carrying conductor produces a magnetic field around it. The magnetic field produced by a coil will be shown in the video. With the fluctuating nature of the alternating current, the magnetic field associated with the coil will also fluctuate. This magnetic flux can be effectively linked to a secondary winding with the help of a core made up of a ferromagnetic material. This fluctuating magnetic field will induce an EMF in the secondary coils due to Electromagnetic Induction.

Since the currents are arranged in a series, the net EMF induced across the winding will be the sum of the individual EMFs induced in each turn.

Es= es X Ns

N= Number of turns

e= EMF per turn

Since the same magnetic flux is passing through the primary and secondary coils, the EMF per turn for both the primary and secondary coils will be the same. The EMF per turn for the primary coil is related to the applied input voltage as shown in the video.



As the result, the induced EMF at the secondary coil is expressed as follows:


This means that the fewer turns in the secondary than in a primary, one can lower the voltage.

For the reverse case, one can increase the voltage. But since the energy is conserved, the primary and the secondary current have to obey the following relationship


Three phase transformer use three such single phase transformers but with slightly different coil configuration. Here primary and the secondary coils sit concentrically. Two more such windings are employed in a three phase transformer.

Transformers with high power ratings generally employs a special kind of winding known as the disc type winding, were separate disc type windings are connected in series through outer and inner crossovers.

The low voltage windings are connected in a Delta configuration and the high voltage windings are connected in a star configuration. Thus the line voltage further rises to √3  times at high voltage side. This also means that from a three phase step-up transformer we can draw four output wires, three phase power wires and a neutral.

High insulated bushings are required to bring out the electrical energy.

The core of a transformer is made of thin insulated steel laminations. Such steel laminations are stacked together to form a three phase limbs. The purpose of thin laminations is to reduce energy loss due to Eddy current formation. The low voltage windings sit near the core.

Various kinds of energy loss occur while transferring power from primary to secondary such as Eddy Current Loss, Hystrises Loss and I2R Loss. All these energy losses are dissipated as heat. So the transformers are emerged in a cooling oil to dissipate the heat. The oil dissipates the heat via natural convection. Oil in the tank expands as it absorbs the heat. A conservative tank helps to accommodate this volume change.

Courtesy: Learn Engineering


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