1
GATE EE 2001
Subjective
+5
-0
An ideal transformer has a linear $$B-H$$ characteristic with a finite slope and a turns ratio of $$1:1.$$ The primary of the transformer is energized with an ideal current source, producing the signal i as shown in figure. Sketch the shape (neglecting the scale factor) of the following signals, labeling the time axis clearly

$$(a)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{oc}}$$ with the secondary of the transformer open
$$(b)$$ $$\,\,\,\,\,$$ the open-circuited secondary terminal voltage $${V_2}\left( t \right).$$
$$(c)$$ $$\,\,\,\,\,$$ the short-circuited secondary current $${i_2}\left( t \right)$$
$$(d)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{sc}},$$ with the secondary of the transformer short-circuited.

2
GATE EE 1999
Subjective
+5
-0
Two single phase transformers $$A$$ and $$B$$ have the following parameters.
Transformer $$A$$: $$400V/200V,$$ $$10$$ $$kVA,$$ percentage resistance and percentage reactance are $$3\%$$ and $$4\%$$ respectively.
Transformer B: $$5$$ $$kVA,$$ $$400V/200V,$$ percentage resistance and percentage reactance are $$4\%$$ and $$3\%$$ respectively.
These two transformers are connected in parallel and they share a common load of $$12$$ $$kW$$ at a power factor of $$0.8$$ lag. Determine the active and reactive power delivered by transformer $$A.$$
3
GATE EE 1998
Subjective
+5
-0
In a $$50$$ $$KVA,$$ $$11$$ $$KV/400$$ $$V$$ transformers, the iron and copper losses are $$500$$ $$W$$ and $$600$$ $$W$$ respectively under rated conditions. Calculate the efficiency on unity power factor at full load. Find the load for maximum efficiency and the iron and copper losses corresponding to this load.
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