Synchronous Generator Flashcards
Stator
Outer part of machine that is stationary
Rotor
Inner shaft of machine that is free to rotate
Field Winding
Produces main magnetic field (rotor for AC)
Armature Winding
Where main voltage is induced (stator for AC)
Synchronous machine
Magnetic field current supplied by separate DC source
Induction machine
Field current supplied by magnetic induction into field winding
What produces rotating magnetic field
Rotor is supplied with DC current for rotor magnetic field and moved by prime mover like turbine
Salient pole
Protruding from surface (4+ poles)
Nonsalient pole
Flush with surface (2-4 poles)
Why is rotor constructed of thin laminations
To reduce eddy current losses from changing magnetic field
Slip rings
Metal rings commonly encircling shaft of machine, but insulated from it
Brush
Block of graphite like carbon compound that conducts electricity freely but has very low friction
Smaller machines are supplied by
Slip rings and brushes
Larger machines are supplied by
Brushless exciters
Brushless exciters has field cirucit on ______ and armature circuit on _____
Stator
Rotor
Why is it called synchronous generator
Electrical frequency produced is locked in with mechanical rate of rotation
Internal generated voltage Ea is directly proportional to
Speed and flux
Flux depends on
Field current in rotor circuit
The graph of Ea over If is called
Magnetization curve or Open Circuit Characteristics
VT = Ea if
Generator is at no load
What effects Vt under load conditions
Armature reaction
Self inductance of armature
Resistance of armature
Effect of salient pole rotor shape
What is Armature reaction
Distortion of air gap magnetic field by current flowing in stator
Estat ____ the plane of maximum current
Lags by 90 degrees
For given phase voltage and armature current we need ______ Ea for lagging loads
Larger
For given field current and load current Vt is ______ for lagging loads
Lower
What is the power flow for synchronous generator
Input mechanical power first loses stray losses then it goes into the rotor where friction and windage losses occur, then the core is magnetized causing core losses after which power is converted to electrical. Here we have copper losses, then finally output power
What is torque angle
Angle between Vphi and Ea (power depends on this)
What is static stability limit
Maximum power of generator
Why is the short circuit characteristics linear
In short circuit, rotor and stator magnetic fields almost cancel each other and net magnetic field is very small so the machine is unsaturated
Why is value of Xs calculated only an approximate
Ea taken from OCC is different from Ea at same If for short circuit
Short circuit ratio
Ratio of If for rated voltage at open circuit to If for rated Ia for short circuit
Adding lagging load ______ Vt
Decreases
