A two-shaft gas turbine arrangement typically involves

• A. Three separate shafts
• B. Two shafts that are geared together to allow different speeds for compressor and power turbine
• C. A single shaft for all components
• D. No shafts are involved

Answer: (B)

A two-shaft gas turbine uses two separate rotating assemblies (spools) so each can run at its own optimum speed. One spool handles the compressor and its turbine, while the other spool drives the power turbine that delivers the useful output. The shafts are geared together to establish a fixed relationship to the connected load, which lets the compressor operate efficiently at its required speed while the power turbine delivers the needed power at a different speed. This arrangement improves overall efficiency, startup, and response compared with forcing every component to run on a single shared speed.