D R3947 Pages: 2

Reg No.: Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2018

Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS

Max. Marks: 100 Duration: 3 Hours
PARTA
Answer all questions, each carries 5 marks. Marks
1 The armature of a 250 ۷, 1009, 4 pole lap connected generator was
reconnected in wave. Find the new voltage, current and power ratings. (5)
Derive the E M F equation of a DC generator. (5)
3 Why a starter is required to start a DC motor? What is the essential element of a
starter? (5)
4 Draw the phasor diagram of a transformer on no load. Show the two
components of the no load current and write their names. (5)
5 What is meant by negative voltage regulation? For what type of load you may
get negative voltage regulation? (5)
6 A 1000/800V, 8kVA autotransformer supplies rated current to a load on low

voltage side. Draw a schematic diagram and mark input current, output current
and current in the section of the winding common to high voltage and low

voltage sides. (5)
7 Find the rated line currents on high voltage and low voltage sides of a SOOkKVA
11kV/400V delta-star transformer. (5)
8 What is meant by vector group? What is ۷۹1 vector group? (5)
PART ‏تا‎
‎Answer any two full questions, each carries 10 marks.
9 Draw the developed view of a double layer lap winding of a 4 pole 12 slot
armature. Commutator and brushes need not be drawn. (10)
10 Draw the developed view of mmf and flux distribution of a loaded 2 pole
machine. (10)
11 The table shows OCC of a ‏عل‎ shunt generator at a speed 1000 rpm. What is the

residual voltage? Find the critical resistance. Also find the maximum voltage
build up at 1000 rpm and critical speed for a field resistance of 300 Q. (You
can find the answers by carefully observing the table. If necessary you may
draw a rough sketch. Graph sheet is not required)

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

12 A 250 V shunt motor has resistances 0.2 Q and 250 Q. The motor is driving (10)

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