Pelton turbine
An impulse hydro turbine in which high-velocity water jets strike double-cupped buckets on a wheel; the standard choice for high heads above roughly 250 m.
Patented by Lester Pelton in 1880, the Pelton wheel converts the pressure of a high-head water column into the kinetic energy of one or more free jets via nozzles. The jets hit split buckets, each with a central ridge that divides the flow and turns it back by about 165–170°, transferring almost all its momentum. Unlike reaction turbines, the runner operates in air at atmospheric pressure.
The jet velocity follows from head, and maximum efficiency occurs when bucket speed is about half the jet speed:
At 1,000 m head the jet travels about 135–140 m/s.
- Head range: roughly 50 m for micro-hydro up to about 1,900 m (Bieudron, Switzerland, 3 × 423 MW at about 1,880 m)
- Peak efficiency: 90–93% for large units
- Part-load behaviour: very flat efficiency curve, since nozzles can be shut individually and spear valves throttle each jet; a six-jet vertical unit stays efficient down to about 10–20% of rated flow
Deflectors can divert the jet in a fraction of a second while the spear closes slowly, avoiding water hammer in long penstocks. Peltons are common in Alpine, Norwegian, Andean and Himalayan schemes and in off-grid micro-hydro, where a small wheel on a steep stream can supply a village. Sediment abrasion of buckets and needles is the main wear issue in glacial rivers.
Related terms
All terms →- Hydraulic head
The vertical height difference between the water surface at a hydropower intake and the turbine outlet or tailwater, which together with flow determines available power.
- Francis turbine
A reaction-type hydro turbine with fixed blades in which water enters radially and leaves axially; the most widely installed design, used for medium heads of about 30 to 700 m.
- Kaplan turbine
A propeller-type reaction hydro turbine with adjustable runner blades and wicket gates, suited to low heads of about 2 to 40 m and large flows.
- Run-of-river hydro
Hydropower that diverts or uses the natural flow of a river with little or no reservoir storage, so output follows river flow rather than demand.
- Pumped hydro storage
Energy storage that pumps water to an upper reservoir when electricity is cheap or abundant and releases it through turbines when power is needed; the largest form of grid storage worldwide.