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Accessories 87<br />

Figure 6-1. Courtesy of United Technologies Corporation, Pratt &<br />

Whitney Aircraft. A typical starting cycle for a gas turbine. Note that<br />

the time from starter ‘on’ to engine ‘idle’ is measured in seconds. This<br />

could be as little as 10 seconds for an aero-derivative gas turbine to<br />

30 seconds for a heavy frame industrial gas turbine.<br />

Electric Motors<br />

Alternating Current<br />

Where alternating current (AC) power is available, three-phase<br />

induction type motors are the preferred choice for starter drivers. In<br />

general, the induction motor is directly connected to the compressor<br />

shaft or the starter pad of the accessory gearbox. On some engine<br />

models the starter pad mount is a tight fit due to the size of an electric<br />

motor and the configuration of the accessory gearbox. Also, as

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