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2-cell Crossflow Turbine

Our Crossflow turbines are designed correspondent to the Ossberger type. They are made of standardized components configured according to customer requirements – i.e. the quantity of water and the head of the particular location. Such a modular system enables short delivery times and good prices at the same time.

Crossflow turbines have a long service life and they are almost maintenancefree. During operation, they do not require any costly or complex spare parts; repairing them is feasible on site. A specific advantage of Crossflow turbines is the possibility of using them in drinking water systems, even in very long conduits, not causing undesirable water hammer effects and thus not affecting the quality of drinking water during operation. This has been successfully tested by our company several times in numerous countries around the world.

Operating turbine range

  • Head height: H = 3… 200 m
  • Flow: Q = 0,03… 16 m³/s
  • Capacity: N = 10… 7 000 kW

Principle of a 2-cell Crossflow Turbine

Crossflow turbines are radial, slightly overpressure turbines with tangential injection of the runner blades and with a horizontal shaft. They rank among low-speed turbines. The water flow comes through an inlet pipe, then, it is regulated by guide vanes and finally enters the runner of the turbine. After passing through, the water leaves on the opposite side of the runner, providing so additional efficiency. Finally, it flows from the casing either freely or through a draft tube to a stilling basin under the turbine.

fig.1: Horizontal inlet
fig.2: Vertical inlet

If the water flow is variable, then the Crossflow turbine is designed with two cells. The standard division of the inlet cells is 1:2. The narrower cell processes small water flow and the wider cell processes medium flow. Both cells together process full flow. As a result, the water flow is used from 100 to 12 % with maximum efficiency, and the turbine is able to start operation even with only 6% of the design flow.

In practice, the water flow in the runner provides a self-cleaning effect. Any impurities that are pushed between the blades when water enters the runner are also pulled out by centrifugal force.After a half revolution of the runner, the water takes the impurities out of the runner and flushes them away to the stilling basin.

Level of turbine efficiency

fig.3: Crossflow turbine curve of efficiency, if the flow is regulated by guide vanes in the proportion of 1:2, compared to a Francis turbine.

The total efficiency of small Crossflow turbines with a small head is between 80-84% throughout the flow. The maximum efficiency of medium and big turbines with a higher head is 87%.

The advantages of a partially loaded Crossflow turbine are illustrated by the efficiency curve shown in fig.3. The actual river flows are very small for several months of the year, if compared to the design flow of the turbine. During those months, the energy production depends solely on the ability of the turbine to utilize these partial flows efficiently. As a result, our two-cell Crossflow turbines with their flat curve of efficiency achieve higher annual energy output, than turbines reaching high efficiency with full flow, but rather low efficiency with partial flow.

Turbine casing

The casing of a Crossflow turbine is made of structural steel; it is robust, resistant to impacts and frost. If there is high contents of abrasive material in the water (e.g. sand, silt) or if the the actual composition of the water is considered aggressive (e.g. sea water, acidy water), all parts of the turbine in contact with water are made of stainless steel.

Guide vanes

In a split Crossflow turbine, the working water is directed by two force-balanced profile guide vanes. The vanes split the water beam, balance it and let it enter the runner smoothly – independently of the width of the cells. Both rotary guide

vanes are set precisely in the turbine casing and they can serve as the closing device of the turbine if there is a lower head. Then it is not necessary to use a shutoff valve between the pressure piping and the turbine. Both guide vanes are fitted independently with extended arms, to which automatic or manual control is connected. Guide vanes are placed in highly resistant slide bearings, which do not require any maintenance. The turbine will be able to close by gravitation in the event of its shutdown, by added weights to the arms ends.

fig.4: Design of a two-cell Crossflow turbine

Runner

The runner is the most important part of the turbine. It is equipped with blades which are made of polished drawn profile steel by a well-proven method. Depending on the actual hydraulic data, either structural steel or stainless steel is used for their construction. Both ends of the blades are fitted in runner discs and welded with intermediate discs of the runner following a specific procedure. Depending on the size, the runner has up to 37 blades. The linearly slanted blades create only slight axial force and therefore reinforced axial bearings with complex fitting and lubrication are not required. Blades of wider runners are supported by multiple discs. Runners are carefully balanced before final installation of the turbine and are subject to crack detection control.

Bearings

Crossflow turbines are equipped with self-aligning roller bearings having several advantages, such as low rolling resistance and simple maintenance. The design of the bearing housing prevents water leakage into bearings and contact of lubricants with working water. This is an important quality of the patent design of our Crossflow turbine bearing housing. Furthermore, the runner is centred in the turbine casing by means of the bearings. Such an inventive technical solution is completed with maintenance-free sealing elements. Apart from grease change every year, the bearings do not require any maintenance. Moreover, the used technical solution enables simple replacement of the runner without taking the entire turbine out of its position.

Draft Tube

The Crossflow turbine is a free stream turbine, just like a Pelton turbine. However, in case of medium or low head, it is possible to apply a draft tube in order to utilize the entire head. The water column in the draft tube must be controllable, though. This is ensured by a regulation air valve, affecting the suction pressure in the turbine casing. In such a manner, turbines with a suction head from 1 to 3 m can be optimally used without any danger of cavitation.

Application

  • 10 kW-7.000 kW/unit
  • Head range: 5-200 m
  • Run of river SHPP
  • Dam SHPP
  • SHPP in drinking water systems
  • SHPP in wastewater treatment plants
  • SHPP for electrification of remote areas

Advantages

  •  Increased annual production because of high efficiency
  •  from 12% to 100% of flow
  • Starts operation with only 6% of flow
  • Tailor-made for every installation
  • Non-clogging runner
  • Highly tolerant against varying head
  • Simple installation and minimal civil works
  • Almost maintainance-free
  • Highly tolerant against foreign substances
  • Proven quality from almost 10.000 installations