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ii) The voltage lost due to armature reaction when 100A are passing in
the armature at terminal voltage of 175V.

111) The percentage reduction in speed for the machine to fail to excite
on open circuit.

PART C
Answer any two full questions, each carries 10 marks.

A 460V 60 series motor runs at 500 rpm taking a current of 40A. Calculate the
speed and percentage change in torque if the load is reduced so that the motor is
taking 30A. The total resistance of the armature and field circuits is 0.8Q.
Assume that flux is proportional to the field current.
Explain different methods of speed control of 0൦ shunt motor.
Distinguish between core and shell type transformer?
Draw the phasor diagram of an ideal transformer on no load. Also, draw a
phasor diagram of a practical transformer supplying lagging power factor load.
Why transformers are rated in KVA?
PART 0

Answer any two full questions, each carries 10 marks.

The test results of 2.51. ४.4, 230/115V single-phase transformer are as follows:

OC Test : LISV, 1.2A, ۷
SC Test : 12V, 10.86A. 120W
Find i. efficiency at 50% full load, 0.8 pf

ii. regulation at 30% full load, 0.8 pf lag and lead
Derive an expression for the saving of copper in an autotransformer as
compared to an equivalent two winding transformer.
Explain the working of off-load tap changing transformer with help of neat
diagram.
Draw the connection diagram for T-T connection of transformers and explain
the formation of three-phase four wire system with two single phase

transformers. Point out its advantages and disadvantages.

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