OSSBERGER GmbH + Co
The original OSSBERGGER® Turbine
Heads: H = 1…200 m
Water flow: Q = 0,025…13 m³/s
Power range: N = 1…2.000 kW
Principle and Flow Path in an OSSBERGER Turbine
An Ossberger turbine is a radial flow turbine. Because of its specific speed, it is considered a slow current turbine. It functions by water flowing from the outside of the turbine through a regulating unit that creates a rectangular-shaped stream of water and directs it across the curved blades of a cylindrical rotor. The water passes through the blades twice (providing additional efficiency) and then out to the opposite side.
One benefit of this crossflow pattern is that when leaves, grass and wet snow flow with water into the turbine, they are flushed out after approximately half a turn of the rotor, providing a self-cleaning effect. Where the water flow warrants it, the Ossberger can be built with multiple chambers; the most common grouping is 1:2. The smaller chamber is used for low water flow and the main chamber with medium flow; to handle maximum flow, both chambers would operate together. Because of this division, the turbine can work with maximum efficiency from full flow (1/1) down to 1/6, making the Ossberger turbine extremely effective in waters with varying flows.
The mean overall efficiency of the smallest Ossberger turbines is estimated at 80% over the working area. Higher efficiency rates of 86% are regularly measured in medium-sized and large turbines.
Figure 4 shows the efficiency curve of a two-chamber turbine measured in terms of the supplied water flow. The Ossberger turbine has a relatively flat efficiency curve in the range of 100% and as low as 17% of maximum water flow.
Unregulated rivers often have little water flow for long periods of the year. Their ability to produce electricity in these periods depends on the efficiency characteristics of the individual turbines. Because of this, the average annual production of power is greater in an Ossberger turbine than in a turbine that exhibits high efficiency at full load and poor efficiency at partial load.
Figure 4. Efficiency curve of an OSSBERGER Turbin with two chambers.
In an Ossberger turbine with two chambers, the flow of water is controlled by two vane-shaped regulating units (guide vanes). During operation, the guide vanes have a relatively limited impact because of the “force balance” design of the vanes and the turbine. The guide vanes divide and direct the flow of water, allowing it to flow freely onto the bladed rotor, regardless of the opening width. Both guide vanes are precisely matched to the turbine house and are able to keep leakage at such a low level they can be used as a shut-off valve. As a result, there is no need for extra valves between the delivery pipe and the turbine. Both guide vanes can be operated independently, either manually or by an automatic control system.
The turbine housing in an Ossberger turbin is made of steel. It is unrivaled in terms of durability, is lighter than cast iron and is shock- and frostproof.
The rotor is the turbine’s central component. It is equipped with blades made of cold drawn profile steel. A special procedure is used to weld the blades to two end plates.
Depending on the size of the turbine, the rotor can have up to 37 blades. The blades have a curved and linear shape that produces small axial forces on the rotor, thus eliminating the need for separate thrust bearings. In rotors with larger widths, the blades are also supported by interposed support plates. The rotors are balanced prior to installation in the turbine.
The main bearings of Ossberger turbines are fitted with standard spherical roller bearings. These bearings center the rotor in the turbine. The use of roller bearings in water turbines is beneficial provided the design of the bearing housing prevents leakage or other moisture penetrating or forming in the housing. This potential problem is solved by the patented design of the maintenance free seal elements of the bearing construction in Ossberger turbines. The bearings require only annual replacement of lubricant.
Draft Tube The Ossberger turbine is in principle a free-stream turbine. However, in systems with medium or small heads (vertical drop/fall of water), turbines should be equipped with a draft tube. This allows the turbine to operate safely in high water while efficiently utilizing full flow. In a free-stream turbine with a wide operating range, the draft tube must be controllable. This is achieved with an adjustable air valve that affects the pressure in the turbine house. As a result, the Ossberger turbine can exploit heads of as little as one meter. The draft tube reduces costs significantly in facilities that have small heads. In many cases, it can be that savings that determines if development is profitable.
Operating conditions There is a no cavitation in an Ossberger turbine due to its special design. Therefore it is not necessary to construct expensive facilities under water at the turbine site. Maximum speed of the turbine without load is approximately 1.8 times the nominal speed, allowing the use of serial generators.
”Keep it simple” was the motto as the Ossberger turbine was being developed. It is designed for continuous operation over many decades and can be run without any special maintenance equipment. It is frequently installed and run by non-experts, especially in third world countries.
Ossberger GmbH & Co.,
Low Cost Design Formula
Growing environmental awareness is raising the demand to harness natural forces to produce energy in an ecologically responsible way. Hydropower has a long and proud history in Norway but development of our larger hydro facilities has stalled due to a seeming lack of political backing. This means there is now a focus on building small and mini-micro power plants around the country.
Capital expenditures related to the design, planning and construction of machines and plants can be relatively high in this kind of hydropower development. Consulting engineers and turbine manufacturers are trying to reduce costs through standardization. Standardization has been possible in larger systems but has not been particularly effective in small and micro-facilities where the design must also take into account varying water levels throughout the year. However, because the Ossberger turbine consists largely of individual, standardized components, it is a modular concept that allows for a cost-effective production while ensuring a turbine solution tailored to a particular project.
The OSSBERGER Turbin is basically individually tailored to the operating conditions of its environment, i.e. the flow and power of the water. Over 9000 turbines have been delivered in over 100 countries on 5 continents.