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B3D047 Total Pages:2

A short shunt compound generator has armature, series field & shunt field resistances
of 0.0642, 0.03Q and 110Q respectively. It supplies 100 lamps rated at 25017, 40W.

Find the generated e.mf. Assume that contact drop per brush = 1 ५.

PART ^
(Answer any 2 questions, each question carries 10 marks)

Why is a starter necessary for a motor? Give the diagram and explain the working of a
three- point starter for a shunt motor including the features of no volt release’ and
‘overload release’.

A 200V series motor has a total resistance of 0.5Q. It runs at 800 rpm taking an input
current of 10A. Find the series resistance required to reduce the speed to 600 rpm, the
input current being kept constant.

A transformer on no load has a core loss of 50W, draws a current of 2A (rms) and has
an induced emf of 230V (rms). Determine the no load power factor, core loss current
and magnetizing current. Also calculate the no load circuit parameters of the

transformer. Neglect winding resistances & leakage flux.

PART D

(Answer any 2 questions, each question carries 10 marks)

Explain sumpner’s method of testing transformers. What are its advantages over OC
and SC tests?

Explain the operation of an autotransformer. How saving of copper is achieved in an
autotransformer as compared to an ordinary two winding transformer. What are the

advantages of autotransformer over conventional two winding transformer?

. The efficiency of 10079 ‏ہش‎ 110۷/220۷, 50112 single phase transformer is 98.5% at half

full load and 0.8 pf lead and 98.8% at full load upf, find (a) Iron loss (b) Full load copper

loss (c) maximum efficiency at upf.

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