Transcript Synchronous1.ppt

SEE 3433
MESIN ELEKTRIK
SYNCHRONOUS MACHINES
Basic principles
General features
Doubly excited machine
Rotor – field winding – DC current
Stator – Armature winding – AC supply
Field circuit
e.g. operated as a generator
3- Stator terminals
Slip rings
Prime mover
Construction
Magnetic axis
of rotor
Salient pole
A
B’
If
C’
Magnetic axis
of phase a
Stator
- Armature B
C
A’
Rotor - field
• Low speed operation
• Large number of poles
• e.g. application in
hydroelectric
Construction
Cylindrical
A
Magnetic axis
of rotor
B’
C’
Magnetic axis
of phase a
B
C
• High speed operation
A’
• Small number of poles
• e.g. application in
steam turbines
Salient rotor
Stator under construction
Synchronous generator – non-salient pole
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
Ef known as excitation voltage
Frequency of induced voltage given by:
Synchronous generators
Open circuit characteristic (OCC)
Ef depends on:
• speed
• Flux per pole hance If
• Exhibit saturation as flux in
core saturated
Synchronous generators
Application in power system:
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 !
Synchronous motors
Solved by:
1
Frequency is slowly increased from 0 using power
electronics converter
Synchronous motors
Solved by:
(Damper winding)
2
Rotor has ‘squirrel cage’ construction
At synchronous speed no current induced in the winding