v curve of synchronous motor

1. V curve of synchronous Motors
Waleed
15103122-028

2. Synchronous Motor:
• Motor that run at constant speed at all load applied to it.
• Speed equal to rotating magnetic field produced due to 3-phase
armature winding.
• Where f is supply frequency and P is number of Poles in motor.
• Here armature is stator and rotor is field.
120
s
f
N
P


3. V curve tells us about….
• Relation between (Armature Current) and Field Current at different loads
where and
Field Current is used to fill the gap with magnetic flux. Which depends upon the
applied dc voltage to the field winding.
aI FI
dc
f
f
V
I
R
 b
a
V E
I
Z



4. Stages of Curve:
• There are 3 stages of curves depending upon field current.
I. Under excitation
II. Normal excitation
III. Over excitation

5. Under excitation:
• When the field current is sufficient to produce magnetic flux but no
enough to fill the air gap in motor then this condition is called under
excitation. In this condition motor draws magnetizing current from
armature winding and motor goes to lagging power factor.

6. Normal Excitation:
• If field current is increased and is sufficient to produce and fill the air
gap then no magnetizing current is required. This stage is called
normal excitation. At this stage power factor is unity.

7. Over excitation:
• If field current is further increased then flux passes through armature
winding and armature draws a demagnetizing current. This stage is
called over excitation and power factor is leading in this stage.
• In this stage motor us also called synchronous condenser and used to
improve power factor.

8. Sample curve: