ASSIGNMENT-4
Unit-4(TRANSFORMERS).
1.
(A) Explain the working
principle of 1-Ø (Single phase) Transformer and what happens If DC supply is
given to transformer?
(B) Derive the induced
emf equation of transformer
( C) A 220/110V,50Hz,1.5KVA transformer has primary and
secondary winding resistance of 1ohm and 2 ohm respectively and reactance of
3ohm and 5ohm respectively. Find the total resistance, equilibrium reactance
and impedance referred to primary and secondary
2. (A)Explain the losses that occur in Transformers
(B) (A) Derive the maximum efficiency condition and expression for load
KVA corresponding to Maximum efficiency
( c)
B).The required no load voltage ratio in a 150 KVA, 50Hz single phase
transformer is 5000/250V.find the efficiency at half rated KVA. Unity power
factor and also efficiency at full load 0.8 PF lagging if the full load copper
losses are 1800watt, core losses are 100W.
3.
(A) Draw the phasor diagram of Transformer under no load.(IDEAL T/F
AND PRACTICAL T/F)
(B) Draw the phasor diagram
of transformer on load (consider resistance and leakage reactance)
4.
(A)Define efficiency and
regulation of a Transformer. Explain how will you pre - determine the
efficiency and regulation with neat circuit diagrams.
(OR)
Explain OC and SC tests on single phase
transformer to determine regulation and efficiency
(B) Explain why the
transformer is rated in KVA instead of KW.
( c) A100KVA lighting transformer has full load
loss of 3 KW; the loss is being equally divided between iron and copper. During
a day the transformer operates on full load for 3 hours, on half load for 4
hours, the output being negligible for the remaining day.Caluculate the all day
efficiency
5. (a)A single
phase transformer working at unity power factor has an efficiency of 90 % at both
one half load and at the full load of 500 W. Determine the efficiency at 75 %
of full load.
(b) A 100 kVA, 1000/10000 V, 50 Hz,
Single phase transformer has an iron loss of 1100 W. The copper loss with 5 A
in the high voltage winding is 400 W. Calculate the efficiency at 25 %, 0.8
Power factor. The output terminal voltage being maintained at 10000 V.
( c)a 200/400V, 50 Hz1-phase transformer on test gave the following
readings,
OC Test
(LV):200V, 0.7A, 70w,
SC Test
(Hv); 15V, 10A, 80W.
Find
the voltage regulation at 0.8 pf lagging at full load.