CAT Titan 250 - Manual (Page 16)

Turbomachinery Package Specification Titan 250 Generator Set
Any variations in bus potential will also be sensed and corrected by this circuit. After
voltage builds, the generator accelerates to 100% speed and excitation and voltage
control is assumed by the CGCM. A crosscurrent-compensating transformer provides the
signal to the CGCM for reactive loadsharing between multiple paralleled units.
It should be noted that the generator rotor windings rotate and the generator armature is
stationary. The exciter field coils are also stationary and the exciter armature rotates with
the main generator rotor shaft. As a result, a single rotating assembly consisting of the
exciter armature, exciter rectifier, and the generator rotor windings is formed. This single
rotating assembly greatly simplifies all electrical connections within the generator.
5.2.1 Standard Features
Generators include the following standard features:
• Sleeve bearings with pressure fed sumps
• Terminal box
• Form wound stator windings
• Amortisseur windings
• Rotor balance to 125% rated speed
• Anti-condensation space heaters
• Permanent magnet generator (PMG)
• Rotating armature-type VAC exciter
• Full-wave rectifier assembly
Special order generators are available to meet unique customer requirements including
non-U.S. specifications.
5.2.2 Rotor
The salient, four-pole, forged rotor is dynamically balanced to minimize vibration. Motor
fans move cooling air through the generator and around the rotor. The rotors have
layer-wound field windings cemented with a high-strength resin and are baked to cure the
resin. The rotor is in electrical and mechanical balance at all speeds up to 125% of rated
speed.
5.2.3 Stator
The stator is built with high-grade silicon steel laminations that are precision-punched and
individually insulated. Windings are typically form-wound and treated with thermosetting
synthetic varnish or vacuum pressure impregnated (VPI) epoxy for maximum moisture
resistance, high dielectric strength, and high bonding qualities. The windings are braced
to withstand shock loads such as motor starting and short circuits. Space heaters can be
supplied to minimize condensation during shutdowns.
5.2.4 Shaft
The shaft diameter provides the necessary stiffness to avoid torsional vibration. The
turbine-driven generator set is given a complete torsional analysis.
5.2.5 Frame
The frame is heavy-duty steel and is fabricated with deep welds and internal reinforcing
for extra rigidity and strength. The frame also includes lifting lugs.
5.2.6 Exciter
Excitation current for the generator field coils is provided by a brushless rotating exciter
with a PMG pilot exciter. The exciter is mounted directly on the generator rotor shaft. The
exciter consists of two basic parts, a small three-phase, AC generator with rotating
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