SEE 3433 MESIN ELEKTRIK SYNCHRONOUS MACHINES Basic principles.
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SEE 3433 MESIN ELEKTRIK SYNCHRONOUS MACHINES Basic principles
General features Doubly excited machine Rotor – field winding – DC current Stator – Armature winding – AC supply Prime mover e.g. operated as a generator Slip rings 3 - Stator terminals Field circuit
Magnetic axis of rotor Magnetic axis of phase a Salient pole Construction A A’ B B’ C C’ IfIf Rotor - field Stator - Armature - Low speed operation Large number of poles e.g. application in hydroelectric
Magnetic axis of rotor Magnetic axis of phase a Construction A A’ B B’ C C’ Cylindrical High speed operation Small number of poles e.g. application in steam turbines
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 E f = 4.44 f N K w E f known as excitation voltage Frequency of induced voltage given by:
Synchronous generators E f depends on: speed Flux per pole hance I f Open circuit characteristic (OCC) 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 !
1 Synchronous motors Solved by: Frequency is slowly increased from 0 using power electronics converter
Synchronous motors Solved by: 2 Rotor has ‘squirrel cage’ construction At synchronous speed no current induced in the winding (Damper winding)