POWER September 2023 - 18

TOP PLANT
Hydropower Horizons: Pioneering
a Pelton Turbine Breakthrough
Courtesy: VERBUND
Voith Hydro in 2022 replaced four vertical Pelton turbines at Verbund's 75-year-old
326-GWh Gerlos 1 pumped storage facility in Austria with a first-of-its-kind horizontal
six-nozzle Pelton turbine. Revolutionizing 140-year-old Pelton technology, the innovation
is poised to transform efficiency, reduce costs, and enhance flexibility-attributes
that could give the hydropower sector new leverage to modernize.
Sonal Patel
I
n the late 1870s, American inventor
Lester Allan Pelton devised the Pelton
wheel, an impulse-type hydraulic
turbine, to enhance energy generation
in Western mining operations, which
typically used lower-volume mountain
streams. The hydraulic turbine employs
a straightforward design, oriented horizontally
or vertically, comprising a large
circular wheel (the runner) with elliptical
cup-shaped blades (buckets) affixed to a
rotating shaft (the rotor). Upon propelling
a high-velocity water jet through a
nozzle (or injector) from the penstock-
which connects to the water reservoir-
the water strikes a bucket on the Pelton
wheel, generating a force that sets the
turbine in motion. The rotating shaft powers
a generator for electricity production.
While the first Pelton turbines were positioned
horizontally, they were limited to
one or two nozzles to control backsplash,
which could slow down the runner-and
ultimately reduce the turbine's efficiency.
To increase their output with more nozzles,
Pelton turbines installed from the
1950s have generally featured turbines
with vertical shafts, commonly equipped
with four to six nozzles, a configuration
that allows water discharged by the buckets
to be drained upwards and downwards
with relatively less effort.
For more than 10 years, researchers
at Voith Hydro, a long-time German
manufacturer, have been pondering how
to resolve the essential challenge of
outfitting Pelton turbines with three or
more nozzles horizontally without sacrificing
performance. The main driving
factor for the HP3+ initiative-Voith's
18
elusively financed strategic development
to advance the breakthrough-was
to " improve power density while making
maintenance easier, " Reiner Mack,
a Voith Hydro development engineer,
told POWER. " Increasing the number of
nozzles increases the power density and
thus also the rotational speed. As a result,
both the generator and turbine can
be built smaller, " he noted. At the same
time, " Servicing a horizontal machine is
much easier than a vertical shaft because
everything is one level in a horizontal arrangement. "
General maintenance of
vertical machines often requires tilting
the entire generator and then dismantling
the rotor horizontally. Construction
is also markedly more accessible given
that horizontal machines don't need multiple
levels and can be placed on top of
existing foundations, he said.
Digital Fine-Tuning Yields a
Revolutionary Solution
Putting the concept into practice, however,
required substantial creativity to
resolve the Pelton turbine's fundamental
water management. The solution required
effectively utilizing the available
space " by using a cone that acts both as
a baffle plate for the outflowing water,
and as a drain for the water that would
fall back onto the runner without the
cone, " essentially preventing the runner
from being slowed down by backsplash,
Mack said.
In the beginning, Voith's research
team created some " relatively simple "
simulators to confirm the conical shield
housing concept would work. The initial
computational effort proved to be a big
www.powermag.com
lift, Mack noted. " Housing flow is very
complex, and 14 years ago, computers
were not as capable as today. " However,
the rudimentary simulations showed
promise, so Voith pressed on with modeling
that ultimately helped the team
refine a housing concept.
" Computational fluid dynamics played
a big role, " Mack added. " Basically, the
whole thing is 95% filled with air, and only
5% of the space is filled with water, " he
said. Compounding the challenge is that,
owing to its very high heads, the interaction
between the water jet and the buckets
of the Pelton wheel is concise-often
just a few milliseconds. " Today, we have
a different technology where only the
water sheet development inside the air
is calculated. " That's important because
" the housing itself is relatively close to
the runner, and we needed to optimize
the situation so the water that comes out
of the runner doesn't fall over it and will
be redirected to the runner " without being
impeded by parts that are situated in
between the nozzle and runner, he said.
The final concept uses a circular or polygonal
cover sheet around the runner that
serves on one side as a guide vane for the
discharging water and on the other side
as a protection for the runner from back
splashing water. " The housing is more
complex and larger. However, it provides
a much higher power density than two-jet
[horizontal] machines, " Voith noted.
An Innovative Customer
According to Mack, a critical prong that
shepherded development of the concept
has been interaction with Voith's customers,
specifically customers confident
POWER | September 2023
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POWER September 2023

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