Question

In what sense eddy current considered undesirable in a transformer

Answer 1

Hello friend...

We can induce currents not only in conducting coils but also, in conducting sheets or blocks. In the case of conducting sheets or blocks also, whenever the magnetic flux linked to the conducting sheet or block changes, there is an induced emf in it. Due to this induced emf, there is a corresponding induced current in the conducting sheet or block. This is as per Faraday’s law.

Now,
As per Lenz’s law, when an emf is induced in the conducting sheet or block, the direction of the induced current will be such that the direction of the magnetic field produced by this electric field induced will oppose the cause that produced this change (of magnetic flux).

Thus, eddy currents are produced so that the magnetic field produced by the eddy current opposes the magnetic field of the cause that causes a change in the magnetic flux.
These currents are “localized” and also, look like eddies/whrlpools. Thus they are named as eddy currents. A scientist, named Focault first discovered it and thus they are also known as Focault currents.

Hope this helps you...

Answer 2

Answer:

The eddy currents are considered undesirable in a transformer as they cause heating of iron core of transformer. On one hand, it means loss of electrical energy i.e., decrease in efficiency of the transformer, on the other hand, due to excessive heating the insulation of transformer windings may be damaged.