Electrical Machine - IES Academy
Electrical Machine - IES Academy
Electrical Machine - IES Academy
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India’s No. 1<br />
<strong>IES</strong> <strong>Academy</strong><br />
Transformer<br />
Chapter-1<br />
(a) Insulation and cooling<br />
(c) Protection against short circuit<br />
(b) Protection against lightning<br />
(d) Lubrication<br />
<strong>IES</strong>-45.<br />
<strong>IES</strong>-46.<br />
<strong>IES</strong>-47.<br />
Which among the following magnetic materials has the highest energyproduct<br />
to make it a permanent magnet<br />
[<strong>IES</strong>-2006]<br />
(a) Alnico<br />
(b) Ferrite<br />
(c) Samariurm Cobalt<br />
(d) Cobalt-Iron alloy<br />
Assertion (A): For obtaining improved magnetic properties, the transformer<br />
magnetic core is assembled using cold-rolled silicon-steel sheets. [<strong>IES</strong>-2005]<br />
Reason (R): The laminations for the core could be cut out of the cold-rolled silicon<br />
steel sheets, cutting either in the direction of rolling or transverse thereof, without<br />
affecting the magnetic properties in any way.<br />
Cores of large power transformers are made from which one of the<br />
following<br />
[<strong>IES</strong>-2008]<br />
(a) Hot-rolled steel<br />
(b) Cold-rolled non-grain oriented steel<br />
(c) Cold-rolled grain oriented steel (d) Ferrite<br />
Principle of Transformer Action<br />
<strong>IES</strong>-48. Assertion (A): Transformer is not used in a D.C. line. [<strong>IES</strong>-2004]<br />
Reason (R): Losses in the D.C. circuit are not negligible.<br />
<strong>IES</strong>-49.<br />
Match List-I (Type of coil) with List-II (Use of coil) and select the correct<br />
answer using the codes given below the lists:<br />
[<strong>IES</strong>-2005]<br />
List-I<br />
List-II<br />
A. Sandwitch coils 1. Lw voltage coils for currents above<br />
100A<br />
B. Disc coils 2. High voltage windings of small<br />
transformers<br />
C. Cross-over coils 3. Cooling oil is in contact with each<br />
turn of the winding<br />
D. Spiral type 4. Shell-type transformer core<br />
Codes: A B C D A B C D<br />
(a) 2 3 4 1 (b) 4 1 2 3<br />
(c) 2 1 4 3 (d) 4 3 2 1<br />
Voltage Regulation<br />
<strong>IES</strong>-50. Percentage resistance and percentage reactance of a transformer are 1%<br />
and 4%, respectively. What is voltage regulation at power factor 0.8<br />
lagging and 0.8 leading<br />
[<strong>IES</strong>-2006]<br />
(a) 2.4% and –0.8%, respectively (b) 3.2% and –1.6%, respectively<br />
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