Transformers

Transformer is one of the most vital electrical machinery. The development of the present day power system is very much attributable to the large number and types of transformer that are in operation in the system, such as, generator transformers, step-up transformers, step-down transformers, interlinking transformers, power transformers & distribution transformers etc. It is important that utmost care is taken in the design, manufacture, testing, installation, and maintenance of transformers.


About Transformers
The transformer helps in converting low voltage into high voltage or visa-versa and accordingly the transformer is termed step - up or step-down. The transformer works on the principle of electro-magnetic induction. Such phenomena can take place in a static device, only, if the magnetic flux is continually varying. It is therefore clear that static transformers can only be used with alternating currents only. When an alternating EMF is applied to the primary winding of a transformer with the secondary winding open circuited, a small current flows in the primary winding which serves to magnetize the core and to feed the iron losses of the transformer.

As primary and secondary windings are wound on the same core, the magnetizing flux is the same for both the windings. The magnetizing flux corresponds to the magnetizing current in the primary and the number of turns of the primary winding. Primary and secondary windings are wound on the same core. Hence, the induced voltage per turn is the same for both primary and secondary winding. Also the absolute value of induced voltage in the primary and secondary windings is proportional to the number of turns in the respective windings.

Parts Of Transformers
Every transformer has a core, which is surrounded by windings. The core is made out of special cold rolled grain oriented silicon sheet steel laminations. The thickness of the laminations is usually around 0.27 to 0.35 mm. The transformer cores constructions are of two types- core type and shell type. In core type transformers, the windings are wound around the core, while in shell type transformers; the core is constructed around the windings. The shell type transformers provide a low reactance path for the magnetic flux, while the core type transformer has a high leakage flux and hence higher reactance.
The primary and secondary windings in a core type transformer are of the concentric type only, while in case of shell type transformer these could be of sand-witched type as well. The concentric windings are normally constructed in any of the following types depending on the size and application of the transformer

1. Cross over type
2. Helical type
3. Continuous disc type