CAT Titan 250 - Manual (Page 18)

Turbomachinery Package Specification Titan 250 Generator Set
6 Start System
6.1 General Description
The start system includes a direct-drive AC starter motor driven by a solid-state variable
frequency drive (VFD). The start system provides torque to initiate engine rotation and to
assist the engine in reaching a self-sustaining speed. The starter motor is mounted
directly on the gas turbine accessory drive gearbox. The VFD regulates voltage and
frequency to the starter motor for engine rotation as commanded by the Turbotronic 4
control system.
6.2 Functional Description
To begin gas turbine rotation, the VFD initially provides low-frequency AC power to the
starter motor. The VFD gradually increases the speed of the starter motor until the gas
turbine reaches purging speed. When purging is completed, the control system activates
the fuel system. The speed of the starter motor is gradually increased until the gas
turbine reaches starter dropout speed. The VFD then deenergizes the starter motor and
the motor clutch assembly is disengaged.
6.2.1 Starter Motor
The starter motor (Figure 7) provides high breakaway starting torque and acceleration
from standstill to starter dropout speed. The motor is standard frame size and is
constructed to be explosion proof and flameproof. The motor includes an integral
over-temperature protection thermostat connected to the Turbotronic 4 control system for
hazardous area motor certification and protection. Separate cable entry points are
provided for power connections, thermal protection wiring, and the space heater wiring.
Starting power is transferred to the gas turbine via the reduction-drive gearbox and over-
running clutch and shaft assembly. After a shutdown, the starter motor rotates the turbine
at low speed to prevent deformation of the rotor during cool down.
Figure 7. Direct-Drive AC Starter Motor and VFD Cabinet
© 2008 Solar Turbines Incorporated. All rights reserved. TPS250GS/908 - Preliminary
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