Taurus Group 60 - Manual (Page 23)

Turbomachinery Package Specification Taurus 60 Compressor Set and Mechanical Drive
7 Start System
7.1 General Description
The start system provides torque to initiate engine rotation and to assist the engine to
reach a self-sustaining speed. The start system consists of either a direct-drive AC starter
motor driven by a solid-state variable frequency drive (VFD) or an optional pneumatic
start system.
7.2 Direct-Drive AC Start System
The direct-drive AC (DAC) start system consists of a squirrel cage, three-phase, ac-
induction motor with a solid-state variable frequency drive (VFD). 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.
7.2.1 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.
7.2.2 Starter Motor
The starter motor (Figure 9) 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/conduit 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.
7.2.3 Variable Frequency Drive
The VFD (Figure 9) is a motor speed controller that provides pulse-width modulated
power with variable frequency and voltage to the starter motor. Controlled by the
Turbotronic
4 control system, the VFD regulates voltage and frequency to the starter
motor to control engine speed from standstill to starter dropout speed. The system is
capable of performing up to six start attempts per hour, as well as extended purge cycles
for heat recovery unit applications and engine wash cycles. The VFD cabinet is designed
for installation in a non-hazardous location. Electrical disconnects and overcurrent
protection devices are not provided.
© 2009 Solar Turbines Incorporated. All rights reserved. TPS60CSMD/309
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