1. •A synchronous machine is a most important type of
electric machine.
•Synchronous Machine used at generating stations are
known as Synchronous Generators or Alternators
•Synchronous motors are widely used in Industries and
are well known for their const. speed operation
•Electromechanical energy conversion occurs whenever
a change in flux is associated with mechanical motion.
4. It is a stationary member
It is the cylindrical portion inside which the rotor
rotates
An air gap is provided between the stator and the rotor
Armature winding are 3 phased and are housed in the
slots cut in the stator
It consists of cast iron stator frame, a cylindrical
laminated , a cylindrical laminated and uniformly slotted
core.
5. Rotor is the rotating part of the machine
Can be classified as: (a) Cylindrical Rotor and (b) Salient
Pole rotor
Large salient-pole rotors are made of laminated poles
retaining the winding under the pole head.
6. Armature windings connected are 3-phase and are either
star or delta connected
The windings are 120 degrees apart and normally use
distributed windings
7. The 3-phase armature winding is distributed in the slots
along the armature air gap periphery
For example: Consider that we have 18 slots, 2-pole 3-
phase winding..
Hence we have 9 slots/per pole as shown figure..
8. The winding diagram of phase ‘a’ can be shown as:
Similarly, phase ‘b’ and phase ‘c’ are distributed in
same manner
9. This implies that per phase emf is getting divided in
each phase.
When all the 3-phase are connected then mmf-phase
graph for each phase is displaced by 120 degrees
The mmf-phase graph can be drawn as:
10. The field winding of a synchronous machine is always
energized with direct current
Under steady state condition, the field or exciting
current is given
Ir = Vf/Rf
Vf = Direct voltage applied to the field winding
Rf= Field winding Resistance
11. Mostly all the synchronous machines use Distributed
winding
Attempt is made to use all the slots available under a
pole for the winding which makes the nature of the
induced e.m.f. moe sinusoidal
Consider a sync. Machine with 3-phase winding,
Slots, s= 18 slots
Poles=2
slots per pole, g= s/p= 9
slots/pole/phase= g/3 = 3
12. • Let E = Induced e.m.f. per coil and there are 3 coils per phase
•In concentrated type all the coil sides will be placed in one slot
under a pole. So induced e.m.f. in all the coils will achieve maxima
and minima at the same time i.e. all of them will be in phase.
Hence resultant e.m.f. after connecting coils in series will be
algebraic sum of all the e.m.f.s. as all are in phase
13. As against this, in distributed type, coil sides will be
distributed, one each in the 3 slots per phase available
under a pole as shown in the Fig.
Slot pitch , Y= ԓP/s = 20 deg.
14. In general, let there be
Slots per pole = n
slots/pole/phase= m
Let turns/phase= Nph
Turns per slot, N1 = Nph/ q
Induce emf/turn =E1 = Ec / N
Induced emf/ slot= E = E1 * N1
= Ec * Nph
Nph q
= Ec
q
15. q – slots for each phase under one pole
Since all the coils are connected in series, hence the
resultant emf is phasor sum of all the emfs
