Question

State the material used for core and describe its structure.

Answer 1

A transformer consists of three basic parts, as shown in figure. These are an iron core which provides a circuit of low reluctance for magnetic lines of force, a primary winding which receives the electrical energy from the source of applied voltage, and a secondary winding which receives electrical energy by induction from the primary coil. The primary and secondary of this closed core transformer are wound on a closed core to obtain maximum inductive effect between the two coils.
Transformer core construction:
In all types of transformer construction, the central iron core is constructed from of a highly permeable material made from thin silicon steel laminations assembled together to provide the required magnetic path with the minimum of losses. The resistivity of the steel sheet itself is high reducing the eddy current losses by making the laminations very thin. These steel transformer laminations vary in thickness from between 0.25mm to 0.5mm and as steel is a conductor, the laminations are electrically insulated from each other by a very thin coating of insulating varnish or by the use of an oxide layer on the surface.
On a step-down transformer there are more turns on the primary coil than the secondary coil. The induced voltage across the primary coil is greater than the applied voltage across the secondary coil or in other words the voltage has been stepped-down".
In the figure given, the input voltage is 220V and the output voltage is 44V. The voltage across the primary coil is greater than the secondary coil. Hence, it is a step-down transformer.