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C192042 Pages:2

respectively. Find (i) load current (ii) armature current (iii) emf generated.
PART C
Answer any two full questions, each carries 10 marks.

Explain the characteristics curves of a ‏عل‎ series motor with the help of relevant
equations?
Why transformer rating is in kVA and not in KW?

A 250V 60 shunt motor takes SA on no-load. The armature and field resistances
are 1Q and 125Q respectively. Find its efficiency when it takes a line current of
25A.

The OC and SC test results of a 5k VA, 200/400V, 50117 single phase transformer
is as follow.

OC Test SC Test
0.7 60 22 10

220 120

Draw the equivalent circuit of transformer as referred to low voltage side.
PART D

Answer any twofull questions, each carries 10 marks.
Draw the circuit diagram of Sumpner’s test and derive the equation for efficiency
of each transformer?
Explain how the Scott connection can be used to obtain two phase supply from a
three phase supply?
The primary and secondary voltages of an autotransformer are 1200V and 600V
respectively. Calculate the economy of Cu when the secondary current is 120A.
Draw the circuit and show the current distribution in the winding.
Define all day efficiency of transformer. Why this efficiency is less than
commercial efficiency?
A 10 kVA, 200/400V, 50Hz single phase transformer gave the following result.

O.C test: 200۷, 1.36, 1209 ................ on L.V side
S.C test: 22%, 30A, 200W ................ on H.V side

Calculate (i) the magnetising current and the component corresponding to core
loss at normal frequency (ii) the magnetising branch impedances.

With the aid of three phase transformer connections and phasor diagram, explain
the vector group Dy11.

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