Question

(a) What are eddy currents? How are these currents reduced in the metallic cores of transformers? 

(b) A step down transformer operates on a 2.5KV line. It supplies a load with 20A. The ratio of the primary winding to the secondary is 10: 1. If the transformer is 90% efficient, calculate: 

(i) the power output, 

(ii) the voltage, and 

(iii) the current in the secondary.

Answer 1

(a) Eddy Currents: When a conductor is placed in a varying magnetic field the magnetic flux linked with the conductor changes, so induced currents are induced in the body of conductor, which causes heating of conductor. The currents induced in the conductor are called the eddy currents. In varying magnetic field, the free electrons of conductor experience Lorentz force and traverse closed paths; which are equivalent to small current loops. These currents are the eddy currents; they cause heating effect and sometimes the conductor becomes red-hot. Eddy current losses may be reduced by using laminated soft iron cores in galvanometers, transformers, etc. and making holes in conductor