Question

Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:

Statement (I): The armature structures of all rotating machines are laminated in order to reduce the eddy-current losses.

Statement (II): The armature windings of both the D.C. and A.C. machines have to deal with alternating currents only.

1. Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I
2. Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I
3. Statement I is true but Statement II is false
4. Statement I is false but Statement II is true

Answer 1

Correct Answer - Option 1 : Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I

• The armature windings of both the D.C. and A.C. machines have to deal with alternating currents only.
• In DC machine also alternating current flow in armature which by mechanical rectifier (commutator) is converted into direct current with ripples.
• Eddy current losses are due to emf induced by a changing magnetic field. This emf causes the circulating current in the core which causes power loss.
• The process of lamination involves dividing the core into thin layers held together by insulating materials such as Varnish, Impregnated paper etc.
• Due to lamination effective cross-section area of each layer reduces and hence the effective resistance increases. As effective resistance increases, the eddy current losses will get decrease.

 

Therefore, both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I.