SINGLE PHASE TRANSFORMER CONSTRUCTION & OPERATION

 The transformer is a static device which converts the magnetic energy into electrical energy. It consists of two or more than two stationary circuits interlinked by a common magnetic circuit; the energy transfer takes place through this circuit without having any change in frequency from one circuit to another.

The transformer consists of two windings. The winding which is connected with the supply a.c. voltage is called the primary winding, and the winding which is connected to load and delivers the energy to load is called secondary winding.

Construction of Single - Phase Transformers

In the core type transformer, the magnetic circuit consists of two vertical legs or limbs with two horizontal sections, called yokes. To minimize the leakage flux, half of each winding is placed on each leg of the core. The low voltage winding is placed next to the core, and the high voltage winding is placed around the low voltage winding to reduce the insulating material required. Thus, the two winding are arranged as concentric coils. Such type of winding is called as concentric winding or cylindrical winding.

Shell type Construction

In the shell type transformer, both the primary and secondary winding are wounded on the central limb, and the low reluctance path is completed by the outer limbs. Each winding is subdivided into sections. Low voltage (lv) and High voltage (hv) subsections are alternatively placed in the form of sandwich that is why this winding is also called sandwich or disc winding.

Transformer Working Principle

The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance. The working principle of the transformer can be understood from the figure below

As shown above the electrical transformer has primary and secondary windings. The core laminations are joined in the form of strips in between the strips you can see that there are some narrow gaps right through the cross-section of the core. These staggered joints are said to be imbricated’. Both the coils have high mutual inductance. A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage. Most of the alternating flux developed by this coil is linked with the other coil and thus produces the mutual induced electro-motive force. The so produced electro-motive force can be explained with the help of Faraday’s laws of Electromagnetic Induction as

e=M*dI/dt

If the second coil circuit is closed, a current flows in it and thus electrical energy is transferred magnetically from the first to the second coil.

The alternating current supply is given to the first coil and hence it can be called as the primary winding. The energy is drawn out from the second coil and thus can be called as the secondary winding.

In short, a transformer carries the operations shown below:

Transfer of electric power from one circuit to another.

 Transfer of electric power without any change in frequency.

Transfer with the principle of electromagnetic induction.

The two electrical circuits are linked by mutual induction.

Application of Transformer.

 The transformer is the electrical device that is used to provide the required voltage level

 The output voltage & output current are the important parameters that are required for designing the transformer. Power rating (KVA / MVA) can also be specified instead of output current rating.

Transformers have variety of application, right from stepping down hundred’s of Kilovolts from power generation., to bringing it down to usable 110V or 230V level, which is supposedly safe operating level.

Transformers can be both, 1-phase typeOr3-phase type.

Transformers are further classified in accordance to their application areas., For eg, Control Transformers, Potential Transformers, Current Transformers, Isolation Transformers, Rectifier Transformers, etc.