Question

To reduce the iron losses in a transformer, the core should be made of a material having:
A. low permeability and high resistivity
B. high permeability and high resistivity
C. low permeability and low resistivity
D. high permeability and low resistivity

Answer 1

Hint: The transformer core brings a magnetic path to channel flux. This is necessary to reduce the no-load losses of the transformer. The core is a source of heat in the transformer and as a core becomes larger in size, cooling ducts within the core may become necessary.

Complete step-by-step answer:
The core of a transformer is constructed of soft iron because it has high permeability so it gives complete linkage of magnetic flux of the primary coil to the secondary coil. And also the hysteresis loss of energy in soft iron is very less. The core is laminated to decrease these to a minimum as they will interfere with the efficient transfer of energy from the primary coil to the secondary one. The eddy currents result in energy to be lost from the transformer as they heat up the core which means that electrical energy is being wasted as unwanted heat energy by these currents. Therefore to reduce the iron losses in a transformer, the core should be made of a material having high permeability and high resistivity since high permeability helps in carrying high magnetic flux and high resistivity helps out by preventing eddy currents by providing low conductivity.
Hence option B is the correct answer.

Note:In all kinds of transformer construction, the central iron core is produced from a highly permeable material made from thin silicon steel laminations. These thin laminations are being assembled together to give the required magnetic path with the minimum of magnetic losses.