Most modern gas turbines use a ______ shaft design.

• A. Two
• B. Three
• C. Locked
• D. Single

Answer: (D)

The main idea here is how the rotating parts are connected and driven: by using one shaft, the compressor, turbine, and generator all spin at the same speed on a single drive train. This keeps the drivetrain simple, compact, and cost-effective, which is why many modern stationary gas turbines use a single shaft. It provides straightforward startup, load response, and maintenance with fewer components than multiple-spool designs.

Two- or three-spool designs separate the compressor and turbine onto different shafts to let each operate at its own optimal speed, which can improve efficiency over a wide range of conditions, but that added complexity and cost make them less common in most modern gas turbines. The option described as locked isn’t a practical design for operation.