Why are Pelton or cross-flow turbines suitable for this site?

It is a medium-to-high head, low-flow site, and these are cheap and practical at small size

It is a low-head, high-flow site

Which statement about a Pelton turbine is correct?

It runs at atmospheric pressure with jets striking double-hemispherical buckets, regulated by a spear valve

It is a reaction turbine with a draft tube

It is best for very low heads and large flows

Its efficiency falls sharply at part load

2072 Kartik · 8 marks

Hydropower site power and turbine

Short answer

Use P = ηρgQH with η=0.5, Q=0.2 m³/s, H=100 m. Hydraulic power is 196.2 kW, so delivered power is 98.1 kW (about 0.1 MW). Pelton or cross-flow turbines suit this medium-to-high head, low-flow site; Pelton is impulse type with nozzle and buckets, efficient at high head.

A potential site has the net head of 100 m with 200 lit/sec of flow. What will be the power delivered from such site if the constructed power house overall efficiency is 50%? Which types of turbines would be suitable for such plants / site and also write its features.

Given

Net head H = 100 m, flow Q = 200 L/s = 0.2 m³/s, overall efficiency η = 50% = 0.5, ρ = 1000 kg/m³, g = 9.81 m/s².

Formula

Power delivered P = η ρ g Q H

Calculation

Hydraulic power (input) = 1000 x 9.81 x 0.2 x 100
                        = 196,200 W = 196.2 kW
Power delivered = 0.5 x 196.2
                = 98.1 kW

Answer: P ≈ 98 kW (about 0.1 MW) of electrical power is delivered.

Suitable turbines

Head 100 m with a small flow (0.2 m³/s) is a medium-to-high head, low-flow site. Suitable options:

Pelton turbine (impulse), commonly used for micro-hydro in the hills of Nepal.
Cross-flow (Banki) turbine (impulse): cheap, locally made, good for 5–200 m heads.
A Francis turbine is possible (head 60–250 m), but at this small size Pelton or cross-flow is more practical and cheaper.

Features of a Pelton turbine

Impulse type: high-velocity jets from nozzles strike double-hemispherical buckets on the runner periphery.
Works at atmospheric pressure; a casing only prevents splash.
Suited for heads above about 50 m (up to 1800 m) and small flow; low specific speed.
Flow is regulated by a spear (needle) valve; a deflector protects against overspeed.
Efficiency 85–90% (at full load), flat efficiency curve at part load; no draft tube; easy to maintain.
Not suitable for low heads or large flows, and is vulnerable to sand erosion.

Features of a cross-flow turbine

Drum-shaped runner with blades; water crosses the runner twice.
Simple, low cost, easily made in local workshops; efficiency about 65–80% but flat over a wide flow range.

✓ Answer checked by Claude Opus 5.5 (high effort)

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