Transcript SYNCHRONOUS GENERATOR CONSTRUCTION

Synchronous generator
Basic Construction
SYNCHRONOUS GENERATOR
CONSTRUCTION
SYN. GEN. USED to CONVERT MECHANICAL ENERGY TO AC
ELECTRIC ENERGY: GENERATORS IN POWER PLANTS
 GENERATOR CONSTRUCTION
- in synchronous generator, rotor winding energized by dc source to
develop rotor magnetic field
- rotor is turned by a prime mover, producing a rotating magnetic field
which induce 3 phase voltages in stator windings
In general rotor carry the “field windings” , while “armature
windings” (or “stator windings”) carry the main voltages of machine
 therefore:
- rotor windings ≡ field windings
- stator windings ≡ armature windings
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SYNCHRONOUS GENERATOR
CONSTRUCTION
Rotor of synchronous machine can be
Nonsalient: 2 pole rotor Salient: six-pole rotor
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SYNCHRONOUS GENERATOR
CONSTRUCTION
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Photograph of a salient 8-pole synchronous
machine rotor
SYNCHRONOUS GENERATOR
CONSTRUCTION
Rotor experience varying magnetic fields, therefore
is constructed of thin laminations to reduce eddy
current losses
 SLIP RINGS: are metal rings encircling shaft and
are insulated from it
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Basic Operation
Basic operation
 The operation of a synchronous
motor is simple to imagine.
 From an external source, the field
winding is supplied with a DC current
-> excitation.
 Rotor (field) winding is mechanically
turned (rotated) at synchronous
speed.
The field winding, which acts as a
permanent magnet, simply locks in with
the rotating magnetic field and rotates
along with it.
 During operation, as the field locks in
with the rotating magnetic field, the
motor is said to be in synchronization.
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Once the motor is in operation, the
speed of the motor is dependent only on
the supply frequency.
 The motor immediately stalls after it falls
out of synchronization.
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ADVANTAGES OF
SYNCHRONOUS GENERATORS
Synchronous Generators are the primary source of all
electrical energy and commonly used to convert the
mechanical power output of steam turbines, gas turbines,
reciprocating engines, hydro turbines and wind turbines into
electrical power for the grid. They are known as synchronous
generators because they operate at synchronous speed. The
speed of the rotor always matches supply frequency.
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They are more stable and secure during normal
operation and they do not require an additional
D.C supply for the excitation circuit.
The permanent magnet synchronous generators
avoid the use of slip rings, hence it is simpler and
maintenance free.
Higher power coefficient and efficiency.
Synchronous generators are suitable for high
capacities
Voltage regulation is possible in synchronous
generators
Synchronous generators can more easily
accommodate load power factor variations.
Disadvantages
 These
motors cannot be used for
variable speed jobs as there is no
possibility of speed adjustment
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It cannot be started under load,
the starting torque being zero
It has a tendency to hunt.
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It may fall out of synchronism and stop
when over-loaded.
Collector rings and brushes are required.
For some applications these motors are not
desirable as for driving shafts in small workshops having no power available for starting
and in cases where frequent starting or
strong starting torque is required.