Variable speed operation of hydraulic turbines has been researched for over two decades. It provides advantages such as improved performance at off-design heads and discharges. Variable speed allows turbines to operate at higher efficiencies over a wider range of flows and heads. This increases energy production and reduces operational issues like cavitation. Commercially available variable speed turbine systems include Turbinova, the DIVE turbine, VLH turbine, and systems from Kawasaki Plant Systems which use permanent magnet generators and water lubrication for high efficiency without oil requirements.

1. Variable Speed Operation of
Hydraulic Turbines

2. Variable Speed
Two Decades of
Research
Variable 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.

3. 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

4. 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 Operation
Perez, 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.

5. 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.

6. 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.

7. 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 to
mismatching Runner inlet flow

8. 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

9. 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

10. Commercial Available
VLH 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/

11. 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 Bearing
Radial Bearing
Thrust Bearing
Turbine Rotor
Lubricating Water
Removed the
trash by this
filter
Used for generator cooling