Hydroelectric Power Plants Questions and Answers

Answer: A

The speed should be 375.0 rpm.

For the same turbine at the same efficiency, the velocity triangles must stay similar. Flow velocities scale as \(\sqrt{H}\), and so must the blade speed, so with the diameter fixed:

\[ \begin{aligned} \frac{N}{\sqrt{H}} &= \text{constant} \\ N_{2} &= 750\sqrt{\frac{5}{20}} = 750 \times 0.5 = 375\ \text{rpm} \end{aligned} \]

187.5 rpm scales the speed with H instead of its square root, and 750 rpm ignores the change of head. 524.5 rpm corresponds to neither relation.

Answer: C

It is called firm power.

Firm power is the power a hydroelectric plant can supply continuously at all times, even in the driest period when stream flow is at its minimum. Because it is always available, it is the part of the output a utility can commit to supply.

Secondary power is the surplus above firm power, available only when flows are higher, so it cannot be guaranteed. Base power describes the load a plant carries, not the guaranteed output under adverse flow. Some texts treat 'primary power' as another name for the same idea, but the standard term for this definition, and the one the key uses, is firm power.