Jumat, 31 Desember 2010
Turbines can be divided into two categories based on their principle of operation:
Impulse turbine- Operates in air, driven by jet(s) of water that remain at atmospheric pressure before and after making contact with the runner blades.
Reaction turbine- Rotor is fully immersed in water and enclosed in a pressure casing. Runner blades are profiled so that pressure differences across them impose lift forces, which cause the runner to rotate.
| Turbine Type
|| Head Classification:
|Impulse|| High (>50m)
| Medium (10-50m)
| Low (<10m)
|Reaction||Francis (spiral case)|| Francis (open-flume)
Impulse turbines tend to be better for microhydro projects (especially in developing countries) for several reasons:
- More tolerant of sand and other particles in the water.
- Better access to working parts.
- No pressure seals or glands around the shaft.
- Easier to fabricate and maintain.
- Better part-flow efficiency.
- Unsuitable for low-head sites.
A Pelton turbine is jet-fed water from a nozzle attached to the penstock. The water flows from the nozzle tangential to the path of the runner. Pelton turbines are the most efficient impulse turbines and can be designed with a single jet or multiple jets.
(European Communities, Layman's Guidebook on how to develop a small hydro site)