EE6401 Question Bank Electrical Machines 1
EE6401 Question Bank Electrical Machines 1 Regulation 2013 Anna University
Sample EE6401 Question Bank:
1. Mention the difference between core and shell type transformers.
In core type , the windings surround the core considerably and in shell type the core surround the winding.
2. What is the purpose of laminating the core in a transformers ? (April –98) To reduce eddy current loss.
3. Give the emf equation of a transformer and define each term (April –99)
Emf induced in primary coil E1 = 4.44 fΦ mN1 volt
Emf induced in secondary coil E2 = 4.44fΦ mN2 volt
Where f is the frequency of AC input
Φ m is the maximum value of flux in the core
N1, N2 are the number of primary and secondary turns.
4. Does the transformer draw any current when secondary is open ? Why ?
Yes,it (primary) will draw the current from the main supply in order to magnetise the core and to supply iron and copper losses on no load . There will not be any current in the secondary since secondary is open.
5. Define voltage regulation of a transformer (April –98)
When a transformer is loaded with a constant primary voltage , the secondary voltage decreases for lagging power factor load, and increases for leading pf load because of its internal resistance and leakage reactance . The change in secondary terminal voltage from
no load to full load expressed as a percentage of no load or full load voltage is termed as regulation.
% regulation down = (0V2-V2) x 100/0V2
% regulation up = (0V2-V2) x 100/V2
6. Full load copper loss in a transformer is 1600 watts. What will be the loss at half load ?
If x is the ratio of actual load to full load then copper loss = x2(full load copper loss).Here Wc = (0.5)2 x 1600 = 400 watts
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