- Bulb Hydro Turbines



Alstom Bulb units provide the most efficient solution when faced with heads up to 30m. Bulb units have almost replaced Kaplan turbines for new low head power plants.With more 309 Bulbs installed worldwide, Alstom has outstanding knowledge and experience in design, manufacturing, installation, commissioning and management of complex Bulb projects, whatever the environmental conditions.

  • Most efficient solution for low heads up to 30 meters
  • Negligible need for flooding of landscape due to run-off-river type of the operation
  • Reduced size, cost and civil works requirements of up to 25% thanks to the straight water passage in the draft tube that improves the hydraulic behaviour of the bulb unit and also results in a lower need for excavation
  • Meet the needs of any particular application - our Bulb turbines also operate as pumps in both flow directions for tidal plant applications
  • Sluice operation may also impact favourably both the hydro mechanics and the navigability close to the dam

The name 'Bulb' comes from the shape of the upstream watertight casing which contains a generator located on a horizontal axis.

Runners up to 8m diameter
Runner design is one of the most important tasks that Alstom carries out when optimising a unit for each project. Blades can be oriented by a moving servomotor cylinder located inside the runner hub. Runner hubs are filled with oil or water as a lubricant.

Shaft line and bearings
Two radial bearings ensure the dynamic stability of the horizontal shaft line during operation.

Advance generator design
Alstom design concepts ensure reliability in all operating circumstances taking account of the Bulb unit’s sensitivity to instability and vibrations due to the horizontal position of the generator. They have been developed to handle conditions such as roundness and air gap concentricity, and have been successfully applied in bulb units up to 60 MVA.

Downstream gate
A draft tube gate provides a reliable protective system for bulb units.
Downstream gate functions are:

  • Protection against runaway conditions
  • Downstream isolation during unit dewatering
  • Sluice operation

Erection time optimisation
The following operations are carried out simultaneously:

  • Erection of rotor, stator and bulb nose in the upstream pit.
  • Erection of the runner hub, blades, turbine cone and runner discharge in the downstream pit.
  • Erection of accessories.

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