[Q:-01]
What is called armature winding ?
Ans :
When a collection of coils
of insulated conductors are placed in armature slots and wound around the
armature core in such a way that electric currents are induced in the coils
while the armature is rotated in the magnetic field, then the net formation of conductors
is called armature winding.
[Q:-02]
What are the types of armature slots ?
Ans :
The main types of slots are—
(i) Open type ,
(ii) Semi-closed type, and
(iii) Closed type.
[Q:-03]
What are the applications of different types of slots ?
Ans :
(i) Open type slots are used in medium and high voltage low speed large
machines.
(ii) Semi-closed type slots are used in low and medium voltage high
speed machines.
(iii) Closed type slots are used mainly in a.c. rotors as because these
provide very low reactance.
[Q:-04]
What materials are used in armature winding ?
Ans :
Conducting materials in the
form of wires and insulating materials in the form of sleeves, tape, varnish
etc. are used in armature winding.
[Q:-05]
How many types of wires are used in armature winding and which of them is
common ?
Ans :
The following types of wires
are generally used :—
(i) Super enamelled copper or aluminium wire,
(ii) Enamelled copper or aluminium wire,
(iii) Double silk covered wire,
(iv) Single silk covered wire,
(v) Double cotton covered wire &
(vi) Single cotton covered wire. Out of them super enamelled copper
wire is commonly used.
[Q:-06]
What sizes of enamelled wires are generally used ?
Ans :
12 SWG to 48 SWG enamelled wires are generally used.
[Q:-07]
Classify the insulating materials according to their functions ?
Ans :
The insulating materials
perform mainly two functions, namely, to provide mechanical protection and to
serve as electrical insulation.
Classification—
(i) For mechanical protection and electrical insulations—Press board,
Presspahn paper, Vulcanized fibre, Hard fibre, Fish paper, Rope paper, Japanese
and Manila paper, Bamboo chips,
(ii) For electrical insulation only--Cotton tape, Oiled or treated
cloth which includes cotton or linen muslin, Varnished cambric, Varnished
muslin and empire cloth, Black adhesive tape, Empire tape, Empire sleeve, P.V.C
tape, P.V.C sleeve, Black & Yellow varnish, Silk tape, Leathered paper,
Cotton sleeve.
(iii) For high temperature and electrical insulation—Mica, Micanite,
Mica paper and Mica cloth.
[Q:-08]
What should be the properties of insulating materials used in armature winding
?
Ans :
A good insulating material
should have the following properties.
(i) A good stability to withstand vibration.
(ii) Ability to withstand allowable temperature.
(iii) Non-hygroscopic.
[Q:-09]
What do you mean by impregnation of insulating materials ? Why it is done ?
Ans :
The process by which the
pores of insulating materials like woods, clothes, papers etc. are filled by
the varnish paraffin or solidifying liquid, Is called as impregnation.
Impregnation is done to
improve the electrical and mechanical properties as air weakens the dielectric
strength & mechanical strength.
[Q:-10]
What is called armature conductor ?
Ans :
That part of a wire, which
lies in an armature slot and cuts the magnetic lines of force or field flux as
the armature rotates, is called an armature conductor or an inductor.
[Q:-11]
What is called turn ?
Ans :
When two conductors are
connected in series by end connection, it is called a turn.
[Q:-12]
What do you mean by a coil ?
Ans :
When a winding element
consists of more than one turn of wire or two conductors it is usually known as
a coil.
[Q:-13]
What do you mean by active sides and inactive sides of a coil ?
Ans :
The sides of a coil which
lies within the slots are known as active sides of a coil and the parts of a
coil which does not lie in the slots are known as inactive sides of a coil.
[Q:-14]
What do you mean by leads of a coil ?
Ans :
The two ends (top and
bottom) coming out from a coil are called leads of a coil.
[Q:-15]
What do you mean by armature end connection ?
Ans :
The portion of the armature
conductors which project beyond the end of the armature core and which are used
for making connections between the various conductors, is called armature end
connection or overhang.
[Q:-16]
What is coil span ?
Ans :
Coil span or coil pitch or
winding pitch is the distance measured in terms of armature slots or armature
conductors between the centre of the two sides of a coil.
[Q:-17]
What is pole pitch ?
Ans :
Pole pitch is the distance
in slots between the centres of the two adjacent poles which may also be
defined as the periphery of the armature divided by the number of poles i.e.
the number of conductors per pole.
[Q:-18]
What is called back pitch ?
Ans :
In d.c. armature winding the
distance measured in terms of the armature conductors, which a coil advances on
the back side of the commutator is called back pitch and is denoted by YB.
[Q:-19]
What is called front pitch ?
Ans :
In d.c. armature winding the
distance measured in terms of the armature conductors spanned by a coil on the
front or commutator end, is called the front pitch and is denoted by YF.
[Q:-20]
What is called resultant pitch ?
Ans :
In d.c. winding resultant
pitch is the distance between the beginning of one coil and the beginning of
the next coil to which it is connected. It is denoted by YB.
[Q:-21]
What is commutator pitch ?
Ans :
In d.c. winding commutator
pitch is the distance between the commutator segments to which the two ends of
a coil are connected. It is denoted by YC.
[Q:-22]
What is pitch factor ?
pins :
Pitch factor is the ratio of
the winding pitch to the pole pitch.
[Q:-23]
What do you mean by full pitch winding ?
Ans :
When the pitch factor is
unity the winding is said to be full pitch winding.
[Q:-24]
What is fractional pitch winding ?
Ans :
When the pitch factor is
either greater or lesser than unity the winding is said to be fractional pitch
winding.
[Q:-25]
What is long chord winding ?
Ans :
When the pitch factor is
greater than unity the winding is said to be long chord winding.
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