Armature Winding in DC Machines
Elements of an armature windings
A turn – two conductors connected to an end by an end connector
Elements of an armature windings
A coil – several turns connected in series
Elements of an armature windings
A winding – several coils connected in series
Elements of an armature windings
The angle between centers of adjacent poles is 180o (electrical)
N
N
S S
360o electrical
= 180o mech
180o electrical
= 90o mech
Elements of an armature windings
The angle between centers of adjacent poles is 180o (electrical)
N
N
S S
If coil sides are placed 180o electrical apart, the coil is said to be full-pitch
a
b
180oelec
a b
Elements of an armature windings
The most common ways of connecting coils for armature windings:
Lap winding Wave winding
Ends of the coils are connected to the commutator bars
In DC machines most of the coils are full-pitch.
Elements of an armature windings
Commutator bar
Lap winding
• One coil between adjacent commutator bars
• 1/p of total coils are connected in series
• No. of poles ≡ no. of brushes ≡ no. of parallel paths
Elements of an armature windings
Advantages of Lap Winding
1. This winding is necessarily required for large current application because it has more parallel paths.
2. 2. It is suitable for low voltage and high current generators.
Disadvantages of Lap Winding
1. It gives less emf compared to wave winding. This winding is required more no. of conductors for giving the same emf, it results high winding cost.
2. 2. It has less efficient utilization of space in the armature slots.
Elements of an armature windings
Wave winding
• p/2 coils in series between adjacent commutator bars
• ½ of all coils between brushes
• Regardless of no. of poles, there are always 2 parallel path
• The distance between end coils (commutator pitch) is 2(C±1)/p where C is the no. of commutator bars
Elements of an armature windings
Single Layer and Double Layer Winding
• If the winding is so designed that one coil- side occupies the total slot area, then it is called a single layer winding.
• In case the slot contains even number (2, 4, 6 etc) of coil sides in two layer, the
winding is referred to as a two layer.
Top layer: odd numbers
Bottom layer: Even numbers
• Pole Pitch:
• Coil Pitch or Coil Span
• If Coil-pitch = Slot/Pole (180 electrical degrees), it results in Full Pitch Coil If less than 180, it is short pitched.
• Back Pitch: The distance between the top and the bottom coil sides of one coil,
measured at the back of the armature is called back pitch. Must be an odd number yb: back pitch
• Front Pitch: The distance between the two coil sides connected to the same
commutator segment, is front pitch. Must be an odd number
yf: front pitch
± 2
=
±
=
b fw
y y
y
• +2: Progressive Winding
• -2: Retrogressive Winding
• yb>yf : Progressive winding
• yb<yf : Retrogressive winding
• Commutator Pitch: The distance between two commutator segments, to which the two ends of one coil are joined (yc)
± 1
c
=
y
Simplex Lap Winding
• C: The number of armature coils
• P: The number of Poles
• The back pitch yb must be an odd number and equal to the pole pitch
• Back pitch = Pole Pitch (odd)
• If one coil side per slot, then number of slots = number of coil sides
• If one slot has two coil sides (double layer) then no. coil sides = 2* no. of slots
• Similarly: No. of Coils sides = n * no. of slots (n= number of coil sides per slot)
• Hence: Back pitch = n*coil span (odd)
P k y No
P k
Coils of
y no
P k S y n
P k y S
b b b b
±
=
±
=
±
=
±
=
Sides Coil
of .
.
* 2
*
Note:Number of commutator segments = no. of coils
Multiplex Lap Winding
Duplex m
Simplex m
m y c
; 2
; 1
=
=
±
=
Example 1
• For a commutator machine with 6 poles and 40 coils, determine for simplex lap winding:
• (a) number of commutator segments
• (b) back pitch and front pitch
• (c) Commutator pitch
solution
• C = 40
• yb = 2*C/P +-k = 2*40/6 = 13
• yb-yf = +-2
• yf = 11 for progressive winding
• = 15 for retrogressive winding
• Commutator pitch +- 1
Example 2
• For a commutator machine with 12 coils and 4 poles, design a progressive simplex lap winding with two coils sides per slot.
Draw the winding diagram.
Solution
• There are 12 coils, hence the number of coil sides are 24.
• Each slot has two coil sides hence the number of slots should 12.
• Number of commutator segments = 12
• yb =2*C/P = 24/4 = 6, hence the back pitch can be either 7 or 5.
• For progressive winding: yb-yf = +2
• Hence yf = 5 for yb = 7
• And yf = 3 for yb = 5
• Consider yb = 7 and yf = 5
• The connection scheme should be such that the back pitch is 7 and from pitch is 5
• 1—8—3—10—5—12—7—14—9—16—
11—18—13—20—15—22—17—24—
19—26 (2)—21 – 28 (4)– 23– 30 (6)—1
• It is closed winding
• What is equalizer rings?
Tutorial-1
• A progressive simplex lap winding is to be designed for a 4-pole, 14-slots, 2 coil sides per slot dc armature
• (a) winding table
• (b) Winding diagram
• (c) Position of brushes
Solution
• yb = 2*C/P = 2*14/4 = 7
• yf = yb – 2 = 7 – 2 = 5
• (1-8)-(3-10)-(5-12)-(7-14)-(9-16)-(11-18)- (13-20)-(15-22)-(17-24)-(19-26)-(21-28)- (23-30 (2))-(25-32 (4))-(27-34(6))-1
Class Work-Do yourself in a graph paper/Tutorial-2
• Design a suitable lap winding for a 6-pole dc armature with 18 slots and two coil
sides per slot. Draw the developed diagram and show the brushes.
Wave Winding
• In a 2-pole machine, the commutator pitch yc is 180 degree electrical.
• In a 4-pole machine, the commutator pitch yc is 360 degree electrical as shown in
Fig. of previous slide.
• Hence 4/2yc = C+-1 or
( )
ofcoils no
P C y C
C P y
c c
. 1 ;
2 2 1
± =
=
±
=
• The winding pitch in a wave winding is given as:
• This is also proved using the Fig. shown in next slide
c f
b
w
y y y
y = + = 2
c b
f
b f
c
y y
y
y y
y
2
1 2
1
= +
+
=
−
+
Algorithm for Wave Winding
• Compute the number of Coils (C)
• Then compute the commutator pitch yc
• Double of yc is winding pitch.
• Either consider yb = yf = yw/2 or take yb 2 more than the yf as in lap winding.
Features of Wave Winding
• The number of parallel path is 2 irrespective of number of Poles.
• No. of brushes = No. of Poles.
• Spacing between the brushes = C/P
• Brushes are alternatively Positive and negative
• All positive brushes are connected
together and all negative brushes are connected together.
Tutorial-3
• For a 6-pole dc armature with 16 slots having two coil sides per slot and single turn coils, calculate the relevant pitches for a wave winding and draw the
developed winding diagram.
Solution
( )
5 2
/ 10
10 5
* 2
6 5
1 16
2
=
=
=
=
=
± =
=
f b
w c
y y
y
y
Example
• Design and draw a wave winding with the following data: 4-pole, 11 slots, 2-coil
sides per slot, progressive winding
Solution
• C = 11 coils
• Position of Brushes?
6 2
/ 12
4 12 ) 1 11 (
* 2 2 2
=
=
=
+ =
=
=
f b
c w
y y
y y
• Thanks
