Monday, January 5, 2009


> A transformer may be defined as a piece of apparatus
> without a continuously moving part which employs the
> principles of electromagnetic induction to transform
> alternating or intermittent voltage or current in one
> winding into alternating voltage or current in one or more
> windings, usually of different value of voltage or current.
> A transformer used to increase voltage of an a.c is called
> step up transformer while the one used to decrease voltage
> of an a.c is called step down transformer.
> Moreover, transformer can also be used to isolate one
> circuit from another, which ensures safety and guide against
> electric shock when working on the low side of an a.c.
> A transformer consists of laminated sheets made of silicon
> steel insulated from one another. This reduces eddy current
> loss. The vertical positions of the core are referred to as
> limb and the top and bottom positions are the yoke. Both the
> primary and secondary coils are wound on the limbs. The
> primary coil is connected to the a.c supply while the
> secondary is usually connected to the load.
> There are different types of transformers:
> 1. Single phase transformers
> 2. Three phase transformers
> 3. Auto-transformers
> 4. Current transformers
> 5. Voltage (or potential) transformers
> 6. Power transformers.
> Power transformers have a high utilization factor, that is,
> they are designed to run with almost constant load, which is
> equal to their rating or capacity.
> The maximum efficiency is designed to be at full load, this
> means that the full load winding losses must be equal to
> core losses.
> When transformer is supplying power to a load, heat is
> generated in the winding and core due to losses. The heat
> dissipated due to losses should be transferred away from the
> winding and core of the transformer to avoid damage.
> The cooling methods used are:
> 1. Air cooled system: - The transformer casing is
> perforated on both sides. Air circulates through the unit by
> convention. This is usually confined to small transformer of
> the range 1KVA – 5KVA.
> 2. Oil –filled cooling system
> 3. Water cooled system
> 4. Air blast (force air) cooling system.

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