The presentation contains Vector diagram and phasor diagram of synchronous motor

1. Vector diagram and Phasor diagram of Synchronous Motor
Contents:
 Vector diagram
 Phasor diagram
 Synchronous condenser
 Applications of Synchronous motor
 References
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

2. Vector Diagram and Phasor diagram of
Synchronous Motor
• The equivalent circuit of a synchronous motor is exactly same as the equivalent
circuit of a synchronous generator, except that the reference direction of IA is
reversed.
• The basic difference between motor and generator operation in synchronous
machines can be seen either in the magnetic field diagram or in the phasor diagram.
• In a generator, EA lies ahead of Vf, and BR lies ahead of Bnet. In a motor, EA lies
behind Vf, and BR lies behind Bnet.
• In a motor the induced torque is in the direction of motion, and in a generator the
induced torque is a countertorque opposing the direction of motion.
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

3. Vector Diagram
d
IA
Vf
EA
jIA Xs
d
IA
Vf
EA
jIA Xs
d
Bs
Bnet
BR
wsync
Fig. The phasor diagram (leading PF: overexcited and |Vt|<|EA|) and
the corresponding magnetic field diagram of a synchronous motor.
Fig. The phasor diagram of an underexcited synchronous
motor (lagging PF and |Vt|>|EA|).
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

4. Phasor Diagram
• (a) Unity power factor
• In this unity power factor, the excitation of the synchronous
motor is 100% or in normal excitation.
• (b) Lagging power factor
• In this unity power factor, the excitation of the synchronous
motor is less than 100%.
• (c) Leading power factor
• In this unity power factor, the excitation of the synchronous
motor is greater than 100%.
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

5. Phasor Diagram
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

6. Synchronous motor can be used as synchronous
condenser
• An over excited synchronous motor running on no load is known as
synchronous capacitor or synchronous condenser.
• A synchronous motor takes a leading current when over excited and
therefore, behaves as a capacitor.
• As compared with a synchronous motor with equal armature voltage
and current rating a synchronous capacitor requires more copper in the
field winding to carry large field current.
• The synchronous capacitor does not require so large shaft and bearings
as the synchronous motor because no shaft torque is required.
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

7. Applications of Synchronous Motor
Synchronous motors are usually used in large sizes because in small sizes
they are costlier as compared with induction machines. The principal
advantages of using synchronous machine are as follows:
– Power factor of synchronous machine can be controlled very easily
by controlling the field current.
– It has very high operating efficiency and constant speed.
– For operating speed less than about 500 rpm and for high-power
requirements (above 600KW) synchronous motor is cheaper than
induction motor.
In view of these advantages, synchronous motors are preferred for driving
the loads requiring high power at low speed; e.g; reciprocating pumps and
compressor, crushers, rolling mills, pulp grinders etc.
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram

8. References :
Kongunadu College of Engineering & Technology Synchronous Motor vector and phasor diagram
S.No Book s / Web Sources
1
A.E. Fitzgerald, Charles Kingsley, Stephen. D. Umans, ‘Electric Machinery’, Tata Mc Graw Hill publishing
Company Ltd, 2003.
2 D.P. Kothari and I.J. Nagrath, ‘Electric Machines’, Tata McGraw Hill Publishing Company Ltd, 2002.
3 P.S. Bhimbhra, ‘Electrical Machinery’, Khanna Publishers, 2003.
4 M.N.Bandyopadhyay, Electrical Machines Theory and Practice, PHI Learning PVT LTD., New Delhi, 2009.
5 K. Murugesh Kumar, ‘Electric Machines’, Vikas Publishing House Pvt. Ltd, 2002.
6
Syed A. Nasar, Electric Machines and Power Systems: Volume I, Mcgraw -Hill College; International ed Edition,
January 1995.
7 J. Ganavadivel, ‘Electrical Machines II’, Anuradha publications, Fourth edition, 2015.
8 U.A.Bakshi &M.V.Bakshi, ”Electrical Machines II,” Technical Publications, Second revised edition, 2016.
9 Google and Wikipedia