Until the late 1980s, the global trend in hydro power technology was to increase the size of a plant. But in recent years local small scale energy production has received growing attention as transmission costs have increased and environmental statutes have tightened. However, power production from conventional small hydro technology has not always been competitive when compared with larger units.

Waterpumps WP Oy, a Finnish engineering company which specialises in hydro technology, has responded to these challenges and developed compact and prefabricated turbine technology which aims to increase the competitiveness of small scale hydro power plants. Throughout the 1990s, the company has also been developing low head turbine technology.

Benefits from modularity and compactness

Waterpumps’ solutions for heads of up to 30m and outputs from 5-5000kW include tube turbine generators, compact turbine generators and multi-generators.

In the tube turbine, the rotor and generator are mounted on the same shaft so a gearbox is not needed. In the multi-generator, several gear-driven generators are arranged around the turbine. In both cases, the turbine is a propeller-type with no adjustment of the vanes or runner, and is integrated with the generator or generators into a watertight module for direct installation in the waterways. All the turbines are suitable for renovating old hydro power plants.

In a new hydro power plant, three or more compact turbines with different capacities are usually installed, which allows discharge through the power plant to be controlled by varying the number and combination of turbines in operation. This is more cost-effective than using a single turbine with adjustable blades. When no transmission is needed, the turbines allow the efficiency of hydro power plants as small as 300-500kW to be raised to levels typical of much larger units.

Automatic control is provided by a dedicated computer program. The level of upstream water is constantly monitored by a control panel which determines the best combination of turbines to give maximum output, depending on the water available for discharge.

In new projects, the entire machine module is placed completely under-ground, leaving the environment unaffected. Only a small building for the switchgear and automation is visible above ground and the turbine generator is almost silent.

These compact, modular turbine generators are easy to install into existing structures and so can be used to renovate old small hydro power plants, many of which are currently out of use. In Europe, for example, at least 2000 disused hydro power plants with power production capacities from 100- 500kW could be renovated using advanced turbine technology.

Cutting costs by one-third

Due to the modular and prefabricated, nature of the turbines, the cost and construction time are reduced both for new plants and for renovating old plants. In total the construction costs for a small hydro power plant are about one-third lower than they are using conventional techniques. Comprehensive automation also offers improved reliability and lower personnel costs.

The turbines are constructed from stainless steel which allows them to withstand harsh environments and reduces maintenance. There are no parts that require continuous service. The turbines are fitted with asynchronous alternators and the operating voltage and frequency are selected in accordance with the client’s specifications. The instrumentation and control for the turbines and dam sluices can be remotely operated via a modem which reduces labour costs. According to Waterpumps, the turbines provide the following benefits:

•Improved efficiency.

•Reduced investment costs (by more than 30%).

•Minimal environmental impact.

•Fully automated and remote-controlled turbines.

•Simple installation.

Waterpumps delivered two turbines to Switzerland in 1997, and in 2000 provided turbine technology for an ultra low head project at Kellankoski rapids in Finland.

Kellankoski rapids

Kellankoski Voima Oy’s former power house in Konnevesi in central Finland burned down in the summer of 1998 and Waterpumps was selected to design and rebuild the new power house, on a turnkey basis, in the same place as the former power plant.

The turbine installation comprised five compact turbine generators, each with a capacity of 33kW, and it was completed in spring 2000. The turbines will operate under a head of 2m. The turnkey delivery packages supplied by Waterpumps included design, delivery of equipment, installation, testing, commissioning and training.

The Kellankoski plant is said to be the first commercially profitable investment in low head renovation in Finland in the last ten years. Waterpumps identifies two reasons for the plant’s commercial success: the short time taken to erect the power plant and the use of stainless steel, which has reduced maintenance costs and doubled the life of the turbines.

Waterpumps is also involved with the renovation of another small hydro power project in Finland, on the Loimi river, about 150km from Helsinki.

The plant was built in 1926 with three 120kW Francis turbines and was acquired in 1992 by energy company, Jokioisten Voima Oy, which decided to renovate it. Waterpumps was chosen to undertake the renovation design.

As the old power house was a protected building, its original shape had to be maintained. The draft tubes for the three new turbines were drawn into the old waterways beneath the building. The 100m long wooden intake canal had concrete supports, and it was completely rebuilt with pine bars. The trash rack was renewed to bring it in line with modern requirements. The dam itself, with an available head of 9m and a discharge rate of 9m3/sec, did not require any refurbishment and only the dam sluices were changed.

Three compact turbine generators, each with a capacity of 215kW and with runner diameters of 800mm, were installed in the old turbine chambers.

The units operate at a synchronous speed of 600rpm and annual output is about 3.2GWh.

Waterpumps provided a compact solution for the hydro project which consists of a turbine, a generator and a sluice in a compact unit ready for installation, based on direct drive — the turbine and the generator are linked to the same axle. The plant’s automatic system selects the turbine or turbines to match the discharge. The sluice is a cylinder gate and, when opened, does not create a loss of flow.

Hydro power for Estonia

On the river Pöltsamaa in Kamari, Estonia, Waterpumps installed a submersible compact turbine generator with a capacity of 200kW, operating under a head of 5m. The company also supplied new automation, switchgear equipment and a transformer, as well as carrying out the design, installation commissioning and testing. The gateworks were also renovated at this plant which produces 1.7GWh/year and is owned by Kamari Hüdro.

The second hydro renovation in Estonia was at Tudulinna and involved two submersible units, (50kW and 100kW), which operate under a head of 6m. A new trash rack was also installed and one of the old draft tubes was replaced.

Innovative solutions

New possibilities for utilising hydro power are opening up in water treatment plants. Small hydro power units can be installed in the outlets of treatment plants and the electrical energy produced can be used to operate the plant itself.

An example of this kind of project is a new plant commissioned by Waterpumps for North West Water, part of United Utilities based in Oswestry, UK. Two tube turbine generators, each with a capacity of 180kW and a control system, were installed under a head of 25m in the water pipeline at Oswestry water treatment plant. This innovative solution has aroused a lot of interest in the UK, where its environmental features are attracting many customers.

In total, Waterpumps has now commissioned around 30 plants totalling up to 2000kW in Finland, UK, Sweden, Switzerland and Estonia. All of the plants have been built in close co-operation with environmentalists and local people, which has improved the public’s perception of hydro power.
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