1. SYNCHRONOUS MACHINES Basic principles
SEE 3433
MESIN ELEKTRIK
SYNCHRONOUS MACHINES Basic principles

2. General features Doubly excited machine
Rotor – field winding – DC current
Stator – Armature winding – AC supply
e.g. operated as a generator
Field circuit
Slip rings
3- Stator terminals
Prime mover

3. Construction Magnetic axis of rotor Salient pole A B’ If C’ Stator
Magnetic axis of phase a
Stator
- Armature -
Rotor - field
Low speed operation
Large number of poles
e.g. application in
hydroelectric

4. Construction Cylindrical A B’ C’ B C High speed operation A’
Magnetic axis of rotor
Magnetic axis of phase a
High speed operation
Small number of poles
e.g. application in
steam turbines

5. Salient rotor

6. Stator under construction

7. Synchronous generator – non-salient pole

8. Synchronous generators
Field current in rotor produce sinusoidal flux in airgap
Rotating filed produced when rotor rotates
Rotating field induced 3 voltage in 3 phase windings on stator
Similar to induction machine, the RMS of induced voltage per phase is
Ef = 4.44 f  N Kw
Frequency of induced voltage given by:
Ef known as excitation voltage

9. Synchronous generators
Open circuit characteristic (OCC)
Ef depends on:
speed
Flux per pole hance If
Exhibit saturation as flux in core saturated

10. Synchronous generators
Application in power system:

11. Synchronous motors
Stator terminals connected to 3 supply – producing rotating magnetic flux
However, rotor won’t be able to rotate or start:
Due to inertia, rotor cannot catch-up with the fast rotating field !

12. 1 Synchronous motors Solved by:
Frequency is slowly increased from 0 using power electronics converter

13. 2 Synchronous motors Solved by: (Damper winding)
Rotor has ‘squirrel cage’ construction
At synchronous speed no current induced in the winding