Alstom Power has developed a new solution for the small hydro market that incorporates a turbine, generator and control system in one compact package

The small hydro market for applications from 0.5-15MW is a global market representing more than US$341.8M per year. Its rapid growth is fuelled by the development of distributed power and by the political will in many countries to increase significantly the share of renewable energy produced. alstom Power Hydro has worked for the past 18 months to develop a new solution which it claims will help customers in this market to increase their revenues and reduce their investment cost. This new solution, called Mini-Aqua, is an integrated package including a turbine, a generator and control system to be used on a turnkey basis.

Mini-Aqua has been designed to cover all small hydro applications including: heads from 2-1000m; flows from 0.2-200m3/sec; outputs from 300kW-15MW; and voltages from 3-15kV.

A specific range of standardised small generators has been developed by the Alstom Power Generator Technology Centre, in Birr, Switzerland, to complement Mini Aqua, together with a specialised control system – the Aqua. According to Alstom, the Aqua provides all the necessary control, monitoring, voltage, regulation, speed governing, synchronising, coupling and electrical protection, for a variety of applications.

For high head applications, Mini-Aqua incorporates Pelton type turbines, and high speed generators directly coupled to them. Two configurations are available – horizontal shaft, with one or more injectors, and vertical shaft, which incorporates four or more injectors.

Low head applications

The horizontal solution is generally used for low outputs under higher heads. These machines have been designed to give good performances on a large range of flows, provided the head does not significantly fluctuate. Alstom has selected a modular standardisation approach, which allows the company to size the machines precisely to site requirements, and keep the advantages of the standardisation.

For medium head applications, Mini-Aqua incorporates Francis turbines and more often, the generators are directly coupled to them. Three configurations are available: Francis horizontal shaft, single runner (FHS); Francis horizontal shaft, double runner (FHD); and Francis vertical shaft (FV).

FHS is the most common type for small hydro as it is designed to be easy to install resulting in economical civil works, says the company. The design is standardised and the turbine size is adjusted to the hydraulic characteristics of the site. FHD is similar to FHS type, but dedicated to higher discharges as its shaft crosses the water passages. FV is preferable for higher outputs as its interface with civil works is usually more important.

For low head applications, Mini-Aqua incorporates Kaplan turbines of the S-type family, with generators directly coupled to it, or indirectly through a gearbox for larger outputs under a lower head. Alstom has selected Sam, the upstream elbow type, as this turbine can be installed in different positions to optimise the civil works. These positions are:

• The elbow in a vertical plan, allowing the turbine to remain horizontal to limit the building width.

• The elbow in a horizontal plan, allowing easy accessibility to the generator as well as limiting the building height.

• The elbow in an inclined axis, to compromise between accessibility and building width.

• An inclined draft tube and generator axis, to reduce excavations.

These machines are tolerant of all hydraulic conditions and offer good performances over a range of flows and heads, claims Alstom. A fully standardised range with predetermined dimensions has been designed to cover needs from 15-500MW.

For very low head applications, Mini-Aqua incorporates Kaplan turbines, usually with high speed generators coupled indirectly through a gearbox. Two configurations are available – Pit and Kaf. Pit has been specifically designed for applications with high flows of water. It incorporates a Kaplan type runner, in a straight and horizontal hydraulic duct. As standard, the gearbox is parallel. The generator and gearbox are installed in an accessible open pit, where the pit walls can be made of concrete or steel for higher heads, to reduce building width.

Kaf is a fronto-spiral Kaplan, simplified for small hydro applications. The spiral case is larger than a classical Kaplan, it has a rectangular section and is made of concrete. The distributor is usually fixed for simplification, or optionally adjustable when operation on a wider range of discharges and heads is required.

First customer reactions are positive, says Alstom, with recent orders for 15 machines in Brazil, including four units ordered by Brazil-based Guaranta for its 7500kW Paso Do Meio plant, and two machines in Morocco.