1) What
is a D.C generator ?
ANS:
A d.c generator is a
rotating machine which converts mechanical energy (or power) into electrical
energy (or power) delivering direct current .
2) On
what principle does the d.c generator work ?
ANS:
A d.c generator works
on the principle of faraday's laws of electromagnetic induction.
3) What
is the working principle of a d.c generator ?
ANS:
The working principle
is that when magnetic flux is cut by a conductor of a number of conductors,
e.m.f is induced in the conductor or conductors and the mechanical energy is
supplied by a prime-mover is converted into electrical energy.
4) What
is the nature of the induced e.m.f in a d.c generator ?
ANS:
The nature of the
induced e.m.f in the armature of a d.c generator is alternating because the nos.
of lines of force intersected by the armature conductors is always varying .
5) What
are the differences between a d.c generator and an alternator ?
ANS:
in a d.c generator
field is static and armature is rotating , but in an alternator either field or
armature can be made rotating .in d.c generator generated alternating e.m.f if
rectified to d.c by the arrangements of commutator but alternator requires no
such commutator .most d.c generators are self-excited but the field of an
alternator is excited from a separate exciter which is practically a self-excited
d.c generator mounted on the same shaft of the alternator .in d.c generator a
closed type of winding is arranged on the armature but in alternator coils are
not arranged in closed fashion.
6) Is
there any difference between d.c generator and motor by construction ?
ANS:
No.
7) In
what unit the capacity of a generator is rated ?
ANS:
Generators are rated
in kilowatt (kw)
8) What
are the essential features of a d.c generator ?
ANS:
Magnetic field,
conductor and motion of conductor in the field.
9) What
are the main parts of a d.c generator ?
ANS:
a) Stationary parts-
A. Yoke or body,
B.
Eye bolts
C.
Pole shoes
D.
Field winding
E.
Rocker ring
F. Carbon brushes
G.
Brush holder
H.
Side covers
b) Rotating parts
A. Shaft
B.
Armature core
C.
Armature windings
D.
Commutator
E.
Ventilating fan
F. Bearings
10) Mention
the parts which form electric circuit ?
ANS :
A. Armature winding
B.
Field winding
C.
Commutator winding
D.
Carbon brushes
11)
Mention the parts which form magnetic circuit
ANS:
A. Yoke
B.
Pole cores
C.
Armature core
D.
Air gaps (between the poles and
armature core)
12) What
material is used in yoke ?
ANS:
Cast steel
13) What
percentage of flux per pole the yoke carries ?
ANS:
The yoke carries
about 50% of total flux per pole
14)
What do you mean by magnetic leakage and leakage co-efficient of a d.c machine?
ANS:
In a dc machine a
portion of the total flux developed in the poles completes its path through the
air without entering the armature core. this is called magnetic leakage .the
radio of the total flux developed in the poles to the total useful flux
entering the armature core is known as the leakage co-efficient of a dc machine
the value of which lies between 1.1 to 1.2
15)
What is the function of yoke in dc generator ?
ANS:
Yoke provides a
mechanical protection to the internal system of the machine and magnetic path
of the pole flux
16) Is
the pole core made of solid homogeneous material ?
ANS:
No, it is made of
laminations of silicon steel .
17) How
are the field poles fitted with the body of a dc machine ?
ANS:
The field poles are
fitted with the body or yoke of a dc machine with the help of bolts & nuts
.
18) How
many types of pole shoes are used in dc generator ?
ANS:
There are two main
types -
A. Solid core made out of either cast iron or
cast steel
B. Laminated core built of thin laminations
of annealed steel riveted together under hydraulic pressure
19) Why
are the pole shoes curved ?
ANS:
The pole shoes are
curved to provide uniform air gap around the armature core
20) What
are the functions of pole shoes in a dc machine ?
ANS:
The functions of pole
shoes are as follows-
A. These support the field coils
B. These reduce the reluctance of the
magnetic path
C. These achieve uniform flux
distribution in the gap by spreading out the flux
21)
What type of conductor is used in field coils ?
ANS:
Copper or aluminium enameled
wire or strip
22) What
is the function of field coil in a dc generator ?
ANS:
Being
electromagnetised it produces necessary magnetic flux to be cut by the
revolving conductors
23) What
is leading pole tip ?
ANS:
The pole tip towards
which the armature conductor enters in the influence of pole is called leading
pole tip
24) What
is trailing pole tip ?
ANS:
The pole tip from
which the armature conductor leaves the influence of pole is called trailing
pole tip
25) What
will be the effect of increasing air gap ?
ANS:
The reactance will be
increased and as a result the machine will draw more current in case of motor
and the machine will give less output in case of generator .
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