Download em 1 cat 2 set 1

LOYOLA – ICAM
COLLEGE OF ENGINEERING AND TECHNOLOGY (LICET)
Loyola College Campus, Nungambakkam , Chennai – 34
Branch: EEE
Date:
Semester: IV
Time:
CAT II
EE6401 ELECTRICAL MACHINES I
Part A (Answer all questions)
1.
2.
3.
4.
5.
6.
(6 X 2 =12)
Give the relation between energy and co-energy for linear system.
Why the energy storage in a magnetic material does occurs mainly in the air gap?
What is the energy conversion medium in a singly-excited magnetic field system?
Write down the emf equation for d.c.generator.
Why commutator is employed in d.c.machines?
Distinguish between shunt and series field coil construction
PART B (Answer all the questions)
(3 X 16 = 48)
7. a.(i) Describe with sketches the construction of a DC machine.
(8)
(ii) Derive the EMF equation of DC generator.
(8)
(or)
b. (i) A 4-pole, 50 kW, 250 V, wave wound shunt generator has 400 armature
conductors. Brushes are given a lead of 4 Commutator segments. Calculate the
demagnetization ampere-turns per pole if shunt field resistance is 50 ohm. Also
calculate extra shunt field turns per pole to neutralize the demagnetization.
(10)
(ii) Explain the process of commutation in a DC machine.
(6)
8. a. Consider an attracted armature relay is excited by an electric source. Explain about
the mechanical force developed and the mechanical energy output with necessary
equations. For linear and non-linear cases.
(16)
(or)
b. (i) Discuss about the ‘field energy’ and ‘coenergy’ in magnetic system.
(4)
(ii) The magnetic flux density on the surface of an iron face is 1.6 Twhich is a typical
saturation level value for ferromagnetic material.Find the force density on the iron
face.
(4)
(iii)A 3-phase ,400 kVA ,50 Hz star connected alternator (synchronous
generator)running at 300 rpm is designed to develop 3300 V between terminals .the
armatureconsists of 180 slots ,each slot having one coil side with 8 conductors .
Determinethe peak value of the fundamental mmf in AT/pole when the machine is
deliveringfull load current.
(8)
9. a. Find an expression for magnetic force developed in a multiply excited magnetic
systems.
(16)
(or)
b. (i) Explain the different methods of excitation of DC generators with suitable
diagrams.
(8)
(ii)A 4-pole, lap-wound dc machine has 728 armature conductors. Its field winding is
excited from a dc source to create an air-gap flux of 32 m Wb/pole. The machine
(generator) is run from a prime mover (diesel engine) at 1600 rpm. It supplies a
current of 100 A to an electric load.
(1) Calculate the electromagnetic power developed.
(4)
(2) What is the mechanical power that is fed from the prime mover to the
generator?
(2)
(3) What is the torque provided by the prime mover?
(2)