Turbomachinery Package Specification

Taurus 60 Compressor Set and Mechanical Drive

 

 

7 Start System

7.1General 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.

7.2Direct-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.

7.2.1Functional 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.

7.2.2Starter 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.

7.2.3Variable 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.

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TPS60CSMD/309

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