Transformers


Transformers

A transformer is a device that changes ac electric power at one voltage level to ac electric power at another volt age level through the action of a magnetic field. It consists of two or more coils of wire wrapped around a common ferromagnetic core. These coils are (usually) not directly connected. The only connection between the coils is the common magnetic flux present within the core.

One of the transformer windings is connected to a source of ac electric power, and the second transformer winding supplies electric power to loads. 1st transformer winding connected to the power source is called the primary winding or input winding, and the winding connected to the loads is called the secondary winding or output winding.
If there is a third winding on the transformer, it is called the tertiary winding.

So transformer is a static machine which only transfer electric power from one electric circuit to another electric circuit. The frequency in a transformer remains constant.
The transformers does not have any moving part so its efficiency is very high. Usually the alternator steps up the output of alternator to reduce the transmission losses. This increases net output power.

The principal purpose of a transformer is to convert ac power at one voltage level to ac power of the same frequency at another voltage level. Transformers are also used for a variety of other purposes e.g., voltage sampling, current sampling, and impedance transformation.

There are two types of transformers core type and shell type.

Shell type


This consists of a laminated core with the windings wrapped around the centre leg. This type of construction is known as shell form. These transformers have three limbs viz. one is centrally placed and other two are on both sides. Both windings are placed on central limb and LV windings are place over core near to HV windings. In shell type transformer interleaved windings are used to reduce the magnetic leakage. In this winding LV windings are placed near the core and hv outside the LV winding for insulation purpose. This types of transformers are generally of high KVA. This type of transformers requires less copper than core type.
. 
These transformers have following characteristics.
1.    They require adequate cooling system.
2.    They are used in high power system
3.    They required less copper

Core type  


Here the two windings are placed on opposite limbs of transformers core. Hence steel core is surrounded by windings on both side. Concentric type windings used. This type of transformers are mechanically bad. It has small KVA rating and required more amount of copper.
.
 These transformers have following characteristics.
1.    They have adequate cooling
2.    They are used in Low power system
3.    They required more copper

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