Which two types of impulse turbines are used exclusively for auxiliary operations?

The correct answer is the Curtis-Rateau or straight Rateau turbines. These types of impulse turbines are specifically designed for auxiliary operations within various systems. Their design allows them to operate efficiently under varying load conditions, which is essential for auxiliary machinery that requires flexibility and reliability.

Impulse turbines work by converting kinetic energy from a fast-moving fluid jet into mechanical energy. The Curtis-Rateau design is notable because it incorporates multiple stages of impulse blades, which permits greater efficiency and smaller size compared to other turbine types. This makes them particularly suited for auxiliary applications, where space and operational demands can vary widely.

Other turbine types mentioned are typically used in primary power generation or large-scale applications. For example, Francis and Kaplan turbines are commonly utilized for large hydroelectric power production, and the Pelton and Turgo turbines are mainly adapted for high-head applications rather than auxiliary operations. Thus, the characteristics of the Curtis-Rateau turbine align more closely with the requirements for auxiliary functions, making it the correct choice.