Variable Speed Operation of Hydraulic

Turbines

Variable SpeedTwo Decades of

ResearchVariable speed operation of hydraulic turbines are by no means a new topic, already in 1983 a series of investigations into this topic was published in the USA of which Cesar Farell (1983) gives a good overview of the findings.

The potential advantages of the variable-speed turbine are:

a) Improved performance at off-design heads and improved range of operating head,

b) Improved performance at off-design discharge

Cesar Farell, J.A., Nicholas Cruz, and.John S. Gulliver, HYDROMECHANICS OF VARIABLE SPEED TURBINES. 1983, UNIVERSITY OF MINNESOTA, ST. ANTHONY FALLS HYDRAULIC LABORATORY: Minneapolis, Minnesota.

Status report on variable speed

operation in small hydro power plants

The application of variable-speed generation schemes to hydroelectric power plants offers a series of advantages, based essentially on the greater flexibility of the turbine operation in situations where the flow or the head deviate substantially from their nominal values. Specifically, the following aspects may be emphasized:

• In general, for variations in head and flow, the variable speed option would be more advantageous.

• Running the turbine at a variable speed avoids cavitation and draft tube oscillations.

• In hydro plants with reservoir, the operating range of head variations can be increased, thus reducing the need for flooded areas.

• In the run-of-the-river hydro plants, the continuity of operation will be increased because of the higher range of allowable flows in the turbine.

• Tests performed on a run-of-the-river small hydro plant confirms that significant gains in generated energy may be obtained.

KWI ARCHITECTS ENGINEERS CONSULTANTS., statusreport on variable speed operation in small hydro power plants. 2000, ENERGIE

Variable Speed Operation

Firstly, in hydro plants with certain regulating capacity, that is, associated to a reservoir, ASO allows the plant to operate over a wider range of reservoir volumes. Secondly, ASO also enlarges the range of operating flows, especially in the case of high specific speed turbines such as axial flow propeller turbines, which may result in significant improvements in the case of run of river hydropower plants. In summary, it can be stated that ASO allows better use of the available energy resources and greater flexibility for energy dispatch. Thirdly, ASO allows the turbine to operate at higher efficiencies, thus increasing the amount of energy generated and avoiding the appearance of operational problems such as cavitation, draft tube pressure oscillations and shaft torque fluctuations. As a consequence, equipment life can be extended and, in turn, long term maintenance requirements can be significantly reduced.

(ASO) Adjustable Speed OperationPerez, J.I., J.R. Wilhelmi, and L. Maroto, Adjustable speed operation of a hydropower plant associated to an irrigation reservoir, in 3rd International Conference on Thermal Engineering: Theory and Applications. 2008.

Variable-speed Turbine Generator

The high efficiency power generation system, which can operate under variable heads and flows, is developed by applying variable speed control technologies, used for rotating equipment, on Francis turbine generating system. The annual output can be increased at the variable head site, compared with the constant speed Francis turbine generating system, since the efficiencies under partial load and variable head operations are improved by applying this technology.

Efficiency Hill Diagram

Understanding the Efficiency Hill Diagram is vital to understand the variable speed operation of Hydraulic Turbines

At constant wicket gate (Guide Vane) opening and varying flow, measure the speed, Net Head, flow and torque. Calculate the efficiency as the ratio between supplied energy and delivered energy to the turbine shaft.

Repeat the measurements for a number of different wicket gate (Guide Vane) openings.

Kjølle, A., Hydrauliske målinger. 1971, Trondheim: NTH Vannkraftlaboratoriet.

The main reason variable speed give a

better part load efficiency

Due to the variable speed the flow entering the Runner will coincidence better with the Runner inlet angle. Consequently lower inlet losses and higher efficiency

Relative loss in wicket gate

Relative loss in Runner

Relative loss in Draft Tube

Relative loss due tomismatching Runner inlet flow

Commercial Available

Turbinova

• Variable rotational speed – energy production benefits

• Permanent magnet technology – high efficiency

• No need of installation of transmission gear and blade rotational mechanism – reliability

• Application of integrated PMG leads to a significant simplification of mechanical systems but this in turn requires an application of a power electronic unit (PEU) in the energy conversion system.

0 150 300 450

0

10

20

30

40

50

60

70

80

90

100

P[kW]

n [rpm]

αmax

α3

α2

α1P1max

P2max

P3max

Pmax

Commercial Available

The Dive Turbine

The DIVE-Turbine is an innovative turbine concept for small hydropower plants. The concept fulfils all requirements for a modern hydropower plant with low head and an installed capacity of up to 2 MW per unit.

The DIVE-Turbine is an efficient, reliable and cost-effective turbine solution. Based on the permanent magnet synchronous generator from OSWALD Elektromotoren GmbH an all-round conclusive concept was developed.

A customized turbine design, in combination with the latest generation of power electronics guarantees high efficiency of the complete Turbine-Generator-Inverter-Unit, from water to wire.

http://www.dive-turbine.de

Commercial AvailableVLH Turbine

The VLH concept only addresses a relatively narrow range of heads and flow rates, it is perfectly well adapted to being totally standardized.

• Range of products. A range of machines provided in 5 diameters (3,150-3,550- 4,000- 4,500- 5,000 mm) has thus been designed.

• Net head range. The net head range addressed by the VLH concept extends from 1.5 to 3.4 m. (up to 4,5 m in customised reinforced version).

• The reinforcing of the supporting structure has enabled to bring the acceptable net head up to more than 4.5 m for the three smallest models in the range.

• Flow range. The range of flow rates of the equipment extends from 10 to 27 m3/s, and the addition of several units on a same site enables considering very high total equipment flow rates.

• Power range. This results in a range of power per unit from 100 to 500 kW (at the network level). It is estimated that below 100 kW, the expected profitability will not be achieved, and the studies performed up to now demonstrate that above 500 kW, it is more profitable to install several smaller machines rather than a single large one.

http://www.vlh-turbine.com/

Commercial Available

Kawasaki Plant Systems, Ltd.

High efficiency system by high turbine efficiency and permanent magnet generator- Oil-free system by applying water-lubricated bearings- Applicable for high head sites by installing two or more units in series"

The compact system can be easily installed in small spaces, such as areas between existing pipelines that are too small for conventional hydropower systems.- No daily maintenance, such as oiling and replacing belts, is required."

Fitted with water-lubricated bearings that use only water pressure to support the rotation of the hydroturbine, the system does not require the use of oil and has no adverse effect on water quality.

発電機冷却に使用

Ceramic Bearing

Radial BearingRadial Bearing

Thrust Bearing

Turbine Rotor

Lubricating Water

Removed the trash by this

filter

Used for generator cooling