1. 1
POWER ANGLE CHARACTERISTIC OF AN ALTERNATOR
By:-
ROHIT KUMAR

2. 2
Introduction of an ALTERNATOR
Classification of an ALTERNATOR
Power flow in an ALTERNATOR
Power relation of a salient pole ALTERNATOR
Power angle characteristic of a salient pole ALTERNATOR
Power relation of a cylindrical pole ALTERNATOR
Power angle characteristic of a cylindrical pole ALTERNATOR
conclusion

3. 3
 An alternator is also called as SYNCHRONOUS
GENERATOR.
 In Synchronous Generator, a DC current is
applied to rotor winding (produce rotor
magnetic field).
 The rotor is turned by primemover producing
a rotating magnetic field.
 The rotating magnetic field produce three
phase sets of voltages within the stator.

4. 4
ON THE BASIS OF TYPE OF ROTOR
SALIENT POLE ROTOR Alternator
CYLINDRICAL POLE ROTOR Alternator

5. 3 cos T L V I
5
 Not all the mechanical power going into a synchronous generator becomes
electrical power out of the machine. The difference between input power and
output power represents the losses of the machine. The input mechanical power
is the shaft power in the generator.
Rotational
losses (Pr)
Pconverted
(Pm)
Pout
Stray losses
(Pst)
conv ind m P  
Core losses
(Pc)
Copper losses
(Pcu)
A A I R 2 3
in s m P  
c r st P  P  P

6. 6
POWER RELATION OF A SALIENT POLE ALTERNATOR…
The TOTAL power relation of a salient pole
alternator is:-
P=3(EV Sin /Xd ) +{v^2(Xd – Xq) Sin2  /2 Xd Xq}
E=Generator internal emf.
V=Terminal voltage.
Xd= Direct axis synchronous reactance.
Xq=Quadrature axis synchronous reactance.
=power angle.
The first term in the above equation indicates EXCITATION POWER.
The second term in the above equation is due to power due to variable
reluctance Called as reluctance power OR power due to SALIENCY.

7. 7
OF A SALIENT POLE ALTERNATOR….

8. 8
CONTINUE…
The power angle characteristic of an alternator is the curve between total
power developed and the load angle.
For a given excitation, bus bar voltage is constant the power developed
Is significantly depending on load angle  .
Operating region of synchronous machine is 30-40 degree{  ).
As the generator is loaded, it supplies power proportionally with  upto 90
degree . If the load increases further, the machine goes out of
synchronisation with the bus bar.
 =90 is the steady state stability limit.

9. 9
The power converted from mechanical to electrical is given by;
3 cos A A  E I conv ind m P   
Where  is the angle between EA and IA:
If the armature resistance RA is ignored (XS >>
RA), Therefore:
S
A
E
A X
I


sin
cos 
Substituting this equation into Pout, gives;.
S
V E
A
X
P
  3 sin
 
Where  is the angle
between EA and VT.

10. 10
Power Angle Characteristics of
cylindrical pole alternator..
 The P(δ) curve shows that the
increase of power increases the angle
between the induced voltage and the
terminal voltage.
 The power is maximum when δ=90o
 The further increase of input power
forces the generator out of
synchronism. This generates large
current and mechanical forces.
 The maximum power is the static
stability limit of the system.
 Safe operation requires a 15-20%
power reverse.
V E
S
A
P  3
max  
X

11. 11
As the generator
is loaded, it
supplies power
proportionally
with  upto 90
degree . If the
load increases
further, the
machine goes
out of
synchronisation
with the bus
bar.
 =90 is
the
steady
state
stability
limit.

12. 12

13. 13