Pelton wheel performance — typical overall efficiency range Select the most appropriate overall efficiency (ratio of shaft power to water power at runner inlet) usually achieved by well-designed Pelton turbines.

Introduction:
Overall efficiency incorporates hydraulic, mechanical, and volumetric effects. Pelton turbines, used at high heads and modest flows, are renowned for high efficiencies due to clean jet formation and limited cavitation risk when designed correctly.

Given Data / Assumptions:

• Well-designed runner and nozzles with proper jet deflection.
• Good bearings and seals; minimal leakage.
• Operation near best-efficiency point.

Concept / Approach:
Overall efficiency η_o = P_shaft / (ρgQ*H_net). Empirical data and manufacturer curves commonly show Pelton turbines achieving mid-to-high 80% efficiency in practical installations. Achieving above ~90% consistently is rare and typically reflects idealized or test conditions.

Step-by-Step Solution:

Verification / Alternative check:
Comparative data: Francis ~0.90 at mid-heads, Kaplan ~0.90 at low heads under ideal settings; Pelton generally 0.85–0.90 depending on specific speed and jet quality.

Why Other Options Are Wrong:

• 0.50–0.75: Undervalues modern machines.
• 0.75–0.85: Possible but below the usual best range.
• 0.90–0.96: Overly optimistic for routine operation.

Common Pitfalls:
Confusing hydraulic efficiency with overall; ignoring part-load operation and nozzle throttling effects which reduce efficiency.

Final Answer: