NPTEL
PRESENTATION
Three Phase Windings
Submitted to Prof. SHAILENDRA PRATAP SINGH
Submitted By
• Nisha Bhatele ( 0901EE161059 )
• Ayushi Gupta ( 0901EE161033 )
• Ankit Sahu ( 0901EE161017 )
Terminology• A turn consists of two conductors connected to one end
by an end connector.
• A coil is formed by connecting several turns in series.
• A winding is formed by connecting several coils in series.
• The pole pitch is defined as peripheral distance between center of
two adjacent poles in dc machine. This distance is measured in
term of armature slots or armature conductor come between two
adjacent pole centers. This is naturally equal to the total number
of armature slots divided by number of poles in the machine.
Example • If there are 96 slots on the armature periphery and 4 numbers of
poles in the machine, the numbers of armature slots come
between two adjacent poles centers would be 96/4 = 24.
• Hence, the pole pitch of that dc machine would be 24.
One pole pitch = 180oed = 360omd/P
• Regardless of the no. of poles in the machine, a pole-pitch is
always 180 electrical degree.
• Coil span is defined as peripheral distance between two sides of a
coil, measured in terms of number of armature slots between
them.
• That means, after placing one side of the coil in a particular slot,
after how many conjugative slots, the other side of the same coil is
placed on the armature. This number is known as coil span.
EMF induced in Armature• If the coil span is equal to the pole pitch, then the armature
winding is said to be full - pitched. At this situation, two opposite
sides of the coil lie under two opposite poles.Hence emf induced in
one side of the coil will be in 180° phase shift with emf induced in
the other side of the coil. Thus, total terminal voltage of the coil will
be nothing but the direct arithmetic sum of these two emfs.
• If the coil span is less than the pole pitch, then the winding is
referred as fractional pitched. In this coil, there will be a phase
difference between induced emfs in two sides, less than
180°.Hence resultant terminal voltage of the coil is vector sum of
these two emfs and it is less than that of full-pitched coil.
QUESTION A 4-pole AC machine has 48 slots. Find slots per pole.
QUESTION A six-pole AC machine has 60 slots. Find slots per pole-pair.
QUESTION • A 4-pole AC machine has 48 slots. How many slots
correspond to 180 electrical degrees?
QUESTION • A 6-pole AC machine has 48 slots. Find the slot-pitch or β
(i.e. the angle between two consecutive slots) in
electrical degrees?
QUESTION • An 8-pole AC machine has 72 slots. One side of a coil is in slot
number 1 and another side of the coil is in slot number 9. How
much is the coil span in electrical degrees?
QUESTION • A 6 pole AC machine has 54 slots. The coil span of a coil is 140
electrical degree. If one side of the coil is in slot number 1 then in
which slot the side should be. (If there are multiple answers then
enter the number which is greater than 1)
QUESTION• The span of a coil is 150 electrical degree. Assume the air-gap flux
density to be perfectly sinusoidal. If the voltage induced in one
side of the coil is expressed by 𝐸𝑚 sin(𝜔𝑡), then the voltage
induced in the other side of the coil can be written as
•
•
•
•
a. 𝐸𝑚 sin(𝜔𝑡)
b. −𝐸𝑚 sin(𝜔𝑡)
c. 𝐸𝑚 sin(𝜔𝑡 ± 150°) (+/- depending on the direction of rotation)
d. −𝐸𝑚 sin(𝜔𝑡 ± 120°) (+/- depending on the direction of rotation)
Ans- c
-The span of a coil is 150 electrical degree. Therefore,
the induced EMF in the other side of the coil will lead or
lag (depending on the direction of rotation) the EMF in
the first side by 150 electrical degree.
QUESTION • An 8 pole AC machine has 96 slots. The two sides of coil-1 are in
slot number 1 and 13. Similarly two sides of coil-2are in slot
number 2 and 14. How much phase difference will be there
between the EMF induced in coil-1 and the EMF induced in coil-2
(in degree)?
Pitch Factor Or Coil Span
Factor• The pitch factor is the measure of resultant emf of
a short-pitched coil in comparison with resultant
emf of a full pitched coil.
Distribution Factor• The Distribution Factor or the Breadth Factor is
defined as the ratio of the actual voltage obtained to
the possible voltage if all the coils of a polar group
were concentrated in a single slot.
QUESTION • An AC machine has 3 coils in a coil group. The three coils are placed
20 electrical degree apart from each other (i.e. slot pitch β = 20
degree). Find the distribution factor rounded to two decimal
places.
QUESTION • If a coil is short chorded by 40 electrical degrees, what
would be the pitch factor (for 1st harmonic or
fundamental component of EMF)?
Ans Pitch factor = Cos(40o/2)
= 0.94
QUESTION• An AC machine has coils short-chorded by 30 degree (electrical).
The slot pitch is 30 degree (electrical). There are two coils in each
coil group. Find the winding factor?
THANK YOU