Water Power and Dam Construction - Issue December 2009
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WWW.WATERPOWERMAGAZINE.COM DECEMBER 2009 21
PUMPED STORAGE
The third concept consists in a set of retaining bolts (or
u-shaped rods) that fix the winding overhang to an auxiliary rim
mounted on the rotor rim. Figure 3 shows an extract of a patent
describing this kind of solution [8]. Cooling air can directly pass
through the winding overhang in radial direction. Furthermore it
is possible to dismantle individual bars if required. The main dis-
advantage of this solution consists in the large number of bolts
used in the machine.
The bolts need to be designed for frequent starts and stops and
a defined number of excursions of the machine to runaway speed.
Due to the high number of bolts, detailed statistical analyses based
on mechanical cycling tests need to be carried out for the validation
of the used materials. Furthermore a strict quality process defining
individual checking of each bolt is required.
Rotor rim
The third part worth mentioning is the rotor rim, also called rotor
yoke. Similar to the winding overhang retaining system, the rotor rim
is also exposed to mechanical cycling. Finite element, and analytical
calculations can be used to define the required mechanical properties.
Since the rotor rim consists of a highly inhomogeneous stack of var-
nished steel laminations, it is advisable to cross check the calculation
by practical tests.
In contrast to the rotor rim of a salient pole machine, the rim of
an induction machine is carrying an alternating magnetic field. To
reduce the iron losses created by eddy currents and hysteresis effect
materials with low loss coefficients can be used. See reference [9]
for more details on iron losses. Generally materials with high yield
strengths have relatively high magnetic loss coefficients. Especially
for machines with higher speed ranges, the corresponding losses can
become important and need to be computed carefully.
VARIABLE SPEED POW ER STATIONS IN EUROPE
I
Nant de Drance
ii
power station is being developed in the south west
of Switzerland, close to the French border, and is expected to be com-
missioned in 2015. Alstom will supply four 157MW vertical Francis
reversible turbines, four 170 MVA vertical asynchronous motor/
generator units and further key equipment to the new plant, as well
as handling complete site delivery, erection, supervision and commis-
sioning. Rotational speed is 428.6 rpm with a speed range of ± 7%,
with the rotor fed by a voltage source inverter. The project’s upper
reservoir holds a volume of 11.4Mm
3
, and the head varies between
250 and 390m.
Also planned for commissioning in 2015 is the Linthal 2015
iii
project in northeast Switzerland. Alstom will provide four 250MW
variable speed pump turbine and motor generator units. Scope
includes: design, engineering, manufacturing, installation, testing,
commissioning and training services. Rotational speed is 500rpm
with a speed range of ± 6%, and the rotor is again fed by a voltage
source inverter. The upper reservoir holds a volume of 25Mm
3
, and
the head varies between 560 and 724m.
Dr. Alexander Schwery holds a Phd degree in Electrical
Engineering from the Swiss Federal Institute of
Technology (EPFL 1999) in Lausanne. He joined Alstom
(Switzerland) Ltd. (former ABB Kraftwerke AG) in
1999 were his main field of application are the use and
development of different simulation and calculation tools
for salient pole generators. Currently he is the head of the
Electrical and Ventilation group and deputy to the head
of the Generator Technology Centre.
Thomas Kunz joined Alstom in 1991 as a electrical
designer for Hydro Generators. He held various positions
in the Hydro Generator Engineering department in
Switzerland. Since Thomas was appointed to R&D
/ Technology Director in 2002, he has the overall
responsibility for the Electrical R&D and leads product
development programs in Alstom Hydro.
This article is based on a paper originally presented at
the Waterpower XVI conference held in July 2009 in
Spokane, Washington. The conference technical papers
are available on CD from PennWell’s Hydro Group.
www.waterpowerconference.com
References and footnotes
1 Schwery, A., Fass, E., Henry, J-M., Bach, W., Mirzaian, A., „Pump storage
power plants Alstom’s long experience and technological innovation.”,
Hydro 2005, Villach, Austria
2 Schwery, A., “Drehzahlvariable Energieproduktion. Neue Perspektiven für
Wasserkraftwerke”, Bulletin SEV/VSE 9/04 S. 13 - 16, 2004
3 Schafer, D. and Simond, J.-J., “Ajustable speed Asynchronous Machine
in Hydro Power Plants and its Advantages for the Electric Grid Stability”,
Cigré Report, Paris 1998
4 Hodder, A. and Simond, J-J. and Schwery, A., “Double-Fed Asynchronous
Motor-Generator Equipped with a 3-Level VSI Cascade”, IEEE / IAS 39th
annual meeting, Seattle, 2004
5 de.wikipedia.org/wiki/Druckluftspeicherkraftwerk
6 Henry, J-M., Lee, S., „Yang Yang pumped storage power plants in Korea
under 817M net head: Selection of double-stage regulated pump turbines
technology.”, Hydro 2007, Granada, Spain
7 Pannatier, Y., Nicolet, C., Kawkabani, B., Deniau, J.-L., Schwery, A.,
Avellan, F., Simond, J.-J., „Transient Behavior of Variable Speed Pump-
Turbine Units ”, IHAR 24TH Symposium 2008, Foz Do Iguassu, Brazil
8 “Rotor einer elektrischen Maschine”, European Patent EP0736953 B1
9 Traxler-Samek, G., Ardley, G., “Iron Losses in Salient Pole Synchronous
Machines Considering Unidirectional and Elliptic Magnetization.”,
Electromotion 2009, Lille, France
i For Nant de Drance and Linthal 2015, Alstom carried out the model
tests of the pump turbine and is currently working on the basic design
of the motor-generator.
ii www.nant-de-drance.ch
iii www.axpo.ch/internet/nok/de/energieproduktion/hydraulik/
linthal_2015.html
IWP& DC
Below: Xxxxx
22 DECEMBER 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PUMPED STORAGE
T
HERE’S no doubt that 2009 was an interesting year
for pumped storage developments. A number of new
projects were announced, while other schemes were
given the go-ahead for redevelopment. As we come to
the end of the year, we take a look back and highlight some of
the most important developments to occur within the industry
over the last 11 months.
NORTH EDEN MOVING ON
At the start of the year, it was reported that US company Symbiotics
Energy had submitted further development plans for the 700MW
North Eden pumped storage project in Utah to the Federal Energy
Regulatory Commission (FERC). This was followed by an in-depth
report on the project in the April edition of IWP&DC.
Symbiotics received a preliminary permit for the project from
FERC in late December 2008. It is developing the project through
North Eden Hydro LLC, which has submitted a notification of intent
(NoI) and pre-application document (PAD).
The preliminary permit covers studies for a potential pumped stor-
age project in North Eden Canyon off Bear Lake in Rich County,
Utah, close to the border with Idaho. Work on the PAD began in the
third quarter of 2007.
It is envisaged that the project will have two dams and reservoirs
plus a surface powerhouse fitted with seven 100MW pump turbines,
a surface penstock and tailrace tunnel. The developer aims to produce
approximately 2027GWh annually from the plant.
Company spokesman Justin Barker told IWP&DC that a conserva-
tive development budget of approximately US$700M has been set for
the project, which it is hoped will become operational around 2011-
12. He said the timing was related to the construction of the Gateway
West transmission link to which the project would connect.
Symbiotics’ earlier attempt to develop a hydropower project at
Bear Lake – in Hook Canyon – was a 1120MW scheme covering ter-
ritory over Utah and Idaho but was dropped due to opposition.
US GOVERN MENT SUPP ORT
In March, we included news that the National Hydropower
Association (NHA) had welcomed US Government’s recognition of
the importance of pumped storage to the wider development of grid-
connected renewable energy resources.
NHA said that expanding pumped storage capacity beyond
the country’s existing resources for storing energy, dominated by
20.3GW of pumped storage, was a high priority. The resource offers
major benefits in fast-response stabilization to the electricity trans-
mission grids to help balance the fluctuating inputs of resources like
wind power.
It called for the Government to build on recognition of the impor-
tance of pumped storage, as voiced by Energy Secretary Steven Chu,
by establishing policies that encourage aggressive investment in
projects using the proven, established technology.
The Association also announced it had established a pumped
storage council to help develop strategies to speed development of
projects. In a statement it said: “We are reaching out to all sectors
of the energy industry, to the Administration, and to Congress to
expand understanding of this technology and create sound policies
that will serve all Americans.”
NHA added that a key goal is to help establish incentives, such as
tax credits, that will attract investors and encourage rapid develop-
ment of more pumped storage projects.
Vital statistics –
pumped storage in 2009
IWP&DC provides a roundup of
developments in the pumped storage
industry over the last year
Voith Hydro delivered pumps, converters, spherical
valves and butterfly valves for Kops II in Austria.
Turbines were supplied by Andritz Hydro
WWW.WATERPOWERMAGAZINE.COM DECEMBER 2009 23
PUMPED STORAGE
NEW PROJECTS IN THE UK?
New pumped storage developments in the UK looks likely following
the announcement by Scottish and Southern Energy (SSE) in May
that it would submit an application to Scottish Ministers to develop
a 60MW pumped storage scheme alongside its 152MW Sloy hydro-
electric power station, near Loch Lomond.
In an average year, Sloy produces around 120GWh of electricity
and, according to SSE, converting it to a pumped storage facility
will allow it to produce an additional 100GWh to help meet peak
demand. The project is expected to require an investment of over
£30m (US$48M).
SSE said at the time that it was also exploring whether other
potential sites could be suitable for the development of pumped
storage schemes: “Hydroelectric schemes which use stored water
to generate electricity have an important part to play in meet-
ing peak demand and also in complementing the growing, but
variable, amount of output from wind farms,” said Ian Marchant,
Chief Executive of SSE. “This means that developments like Sloy
that increase storage and generation capability will play a bigger
part in meeting energy needs as the development of renewable
energy gathers pace.”
A few months after the initial announcement, SSE then officially
announced plans two new pumped storage schemes in Scotland, with
planning applications likely to be submitted in 2011.
The plants, to be located in the Great Glen, are expected to have
installed capacities between 300-600MW. Although both schemes
would require construction of a dam, the majority of the infrastruc-
ture is likely to be built underground, avoiding any impact in the
Great Glen itself.
The company is planning to seek the Scottish Government’s formal
opinion on the scope of the environmental impact statement for the
projects, If the projects are given the go-ahead, they would be the first
pumped storage schemes to be developed in the UK since work began
on the Dinorwig scheme in Wales in 1974.
KOPS II INAUGURATED
Also in May we reported that the Kops II pumped storage plant in Austria
has been inaugurated by the developer Vorarlberger Illwerke AG.
The 450MW (3 x 150MW) underground plant is located near
the Ill river in Montafon Valley in west Austria, in the province of
Vorarlberg.
The facility is operating with separate pumps and Pelton turbines
instead of reversible pump turbines. The design enables both turbines and
pumps to be operated at the same time in “short hydraulic circuits”.
There is a head difference of just over 800m between the Kops upper
reservoir and the Rifa lower, balancing reservoir. The pressure tunnel to
the plant is 5.5km long and is of 4.9m diameter, there is a two-chamber
surge tank and an almost 1.2km long, 3.8m wide steel penstock.
Voith Hydro and Andritz Hydro supplied the pumps and turbines,
respectively, plus other equipment.
Construction of the plant started in late 2004 and underground
excavation was undertaken for the powerhouse and transformer cav-
erns and associated tunnels to late 2005. The powerhouse cavern is
88m long, 30.5m wide and 60.5m high.
It was originally planned to have all units commissioned by the
first half of 2008.
RELICENSING SMITH MOUNTAIN
The US Federal Energy Regulatory Commission (FERC) issued sup-
port in August for the 636MW Smith Mountain Pumped Storage
scheme to be relicensed with only some modifications to owner
Appalachian Power Co’s submitted plans.
Following the Final Environmental Impact Assessment, and
Statement (FEIS), the Commission’s staff reviewed the feedback
on the draft EIS and made the recommendation mostly based on
Appalachian Power’s resource management plans for the scheme.
The owner plans no new capacity build at the facility .
The scheme comprises two dams (Smith Mountain, Leesville) and
586MW installed capacity at the main powerhouse plus 50MW at
a second facility. The upper lake is 64km long and has a shoreline
length of 800km.
Appalachian Power’s initial public work on the relicensing proposal
began just over four years ago. The FERC licence expires next year.
The resource management plans include erosion and sedimenta-
tion, water management and quality, habitat and aquatic vegetation,
recreation, navigation, and cultural and historical resources.
Appalachian Power Co is owned by American Electric Power.
ENGINEERING NANT DE DRANCE
In September, AF Group’s Swiss subsidiary, AF Colenco, was award-
ed a EUR 27M (US$39M) contract for engineering services at the
Nant de Drance pumped storage project, near Finhaut in the south-
western Canton Valais of Switzerland.
Awarded by NdD SA – a joint venture of Swiss energy provider
Alpiq, Forces Motrices Valaisannes (FMV) and Swiss federal railways
SBB – the contract will include general project management, detailed
engineering and site supervision services.
The 628MW pumped storage project is due to be commissioned
in 2015. Earlier this year Alstom Hydro was awarded the contract
to supply the plant with four 157MW vertical Francis reversible tur-
bines, four 170 MVA vertical asynchronous motor/generator units
and further key equipment.
IWP&DC will bring you all the key developments in
pumped storage in 2010. To make sure you’re kept up-to-
date, sign up for our twice weekly email newsletter at
www.waterpowermagazine.com
Kops reservoir in Vorarlberg, Austria
IWP& DC
24 DECEMBER 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PUMPED STORAGE
P
UMPED storage will play an important supporting role in the
US federal push to see more renewable energy projects devel-
oped. While economic bulk energy storage is the foundation of
the pumped storage system, albeit at a net load cost to trans-
mission grids, increasingly its features of rapid response and flexibility
are finding fresh opportunity. The Electric Power Research Institute
(EPRI) has noted that the surge in interest in pumped storage is due,
not least, to benefits it can provide to networks and facilitate stable
operations when integrating other renewable resources, particularly
fluctuating wind power. Other studies have also pointed to the poten-
tial gain from a combination of research on technological smaller scale
plants and market needs to help support, for instance, local grids with
significant wind power or even down to wind farms themselves.
There are financial opportunities to meet demand bursts as well
as provide those stabilisation and support services, but the gain for a
potential developer is dependent on particular market arrangements
and conditions, especially for the longer term. Economics will always
be a challenge, even in changing and liberalised energy markets. A
recent benchmarking analysis, by EDF’s David Surla, says that the
percentage of pumped storage plants in liberalised markets is gener-
ally less than the economic optimal in most countries.
Distinct new ventures are however underway to build pumped
storage schemes, such as the plans being developed by Riverbank
Power Corporation in North America.
RIVERBANK POWER
Riverbank Power is an independent power producer (IPP) with a
concept – Aquabank –which it plans to use to build 1GW pumped
storage plants across North America.
Each of the facilities calls for excavation of a half dozen caverns to
form an underground reservoir and for the upper reservoir it can adopt
various surface waters – flooded quarry, river, lake or coastal – depend-
ing on location. The Toronto-based company terms recirculation of
water between tunnels and a flooded quarry ‘a closed loop’ arrange-
ment, and all others are its diversion systems. Riverbank says there
should be minimal effect on water and fisheries caused by operation of
Aquabank facilities, although further studies will be conducted.
Typically, the powerhouse and underground reservoir will be exca-
vated at a depth of a little over 600m, and will cover 10-12 times that
of the surface structures. The power plant will house four, 250MW
single-stage reversible Francis pump-turbines, and Riverbank is inves-
tigating the potential of variable speed drives for various possible
benefits, such as increasing overall plant efficiency, load following
during pumping, and smoother operations.
Beyond site-specific design for each project location, no addi-
tional R&D is required as all components have been proven, it says.
However, it does note that model tests will be conducted for the first
pump-turbine to confirm the basic design for use in Aquabank. Once
comfortable with the basic design, only refinement for application in
separate projects would then be required, it adds.
The optimum size of the Aquabank system, at 1GW to provide six
hours of generation, has been reached from examining a range of vari-
ables, including construction costs and financial return. The finance
model also takes account of possible ancillary services and capacity
payments, though each project’s potential offering to customers would
depend on where it is located and where it connects in to the grid.
Each project has an estimated cost of US$2B and the construc-
tion phase is envisaged to last four years. The company will seek
both equity and debt funding to finance the projects, and its primary
investor is BlackRock. It will, though, look at possibilities for federal
funding support in light of the US Government’s aims to push renew-
able energy development.
Riverbank says it has agreements with various firms in environmen-
power cables
lower reservoir
access ramp
10-acre
surface development
Back River
powerhouse
Investigating Aquabank
A new venture is pursuing a fresh approach to closed, standardised pumped storage systems
in North America – and possibly beyond. Report by Patrick Reynolds
Cross section schematic of
the Wiscasset project
WWW.WATERPOWERMAGAZINE.COM DECEMBER 2009 25
PUMPED STORAGE
tal, hydro power, civil, excavation and turbines manufacture. Details
were not disclosed but on its website, for the planning work and
studies, it has mentioned geological consultant Continental Placer,
environmental consultants Stantec and Malcolm Pirnie, and other
consultants covering hydrology, mining design and project manag-
ers – Groupe RSW and SNC-Lavalin. Support on price forecasting
and market intelligence is provided by Energy Security Analysis and
London Economics International.
DIFFERENCES
The concept of water recirculation with an underground reservoir is
not totally new (see box: Some earlier Closed Loop PS proposals).
In the 1990s, there were private sector plans for a one-off project of
2GW capacity at Mt Hope, New Jersey. While it has not yet been
built the most recent plans had seen a re-think with the concept
altered to a 1GW, multi-stage underground scheme.
Riverbank notes the superficial similarities to Mt Hope of water
circulation to an underground reservoir and powerhouse, and the con-
vergence in scale, but says the prime differences relate to environmental
aspects, the energy market, community support and grid access – and
emphasises that location is a vital factor in selecting sites. Should one
of its projects be built in the next few years then it says it would be the
first to combine pumped storage with deep excavation.
However, beyond any aspects of similarity to a previous concept,
Riverbank’s proposals are different to what has been conceived before
by a major order: it aims to rollout a portfolio of Aquabank plants in
North America, and possibly beyond. But it will be no little challenge
as the first candidate site, at Sparta in New Jersey, was eventually
determined to have unsuitable geology. Presently, the main focus on
project development is at a potential site in Wiscasset, Maine.
WISCASSET
The project site at Wiscasset was announced by Riverbank in late
2008 and the current plan is to have the facility online in 2015, a year
later than initially stated.
Riverbank is developing the project through a subsidiary, Riverbank
Wiscasset Energy Center, LLC. It says the pumped storage scheme
would help the state to meet its goals of improving the reliability of
the grid and integrating up to 3GW of wind generation by 2020.
Located on land bought five years ago by Connecticut-based prop-
erty firm National Resources from Maine Yankee Atomic Power Co,
the scheme is to be a diversion system, the upper reservoir being the
tidal Black river. The company contends that there should be minimum
effects on the quality and temperature of water temporarily diverted
underground during generation and returned in pumping operations.
It is estimated from the outline design that approx. 215m
3
/sec would
be diverted to the pump-turbines, each of which will have a rated capac-
ity of 254MW at 514 rev/min. The nominal net head is approximately
550m. The capacity of each motor-generator is 278MVA.
The lower reservoir would consist of six caverns, each approxi-
mately 27m wide by 47m high, and excavated to free-stand in unlined
rock. Site investigation began a year ago and test drilling was under-
taken by Boart Longyear.
Geology in the area is dominated by the Cape Elizabeth Formation,
which is schist. At the range of depths for the powerhouse and cav-
erns, the rock was found to be predominantly granitic gneiss with
good to excellent rock mass rating based on core sampling. Packer
tests in boreholes showed little water absorption. Further site investi-
gation has been underway.
SPARTA
Poor rock quality terminated Riverbank’s hopes for a pumped stor-
age plant at Sparta, which was one of the top candidate sites. It would
have been a closed loop system.
The proposed site for the scheme was Limecrest Quarry, which it
was agreed with the owner would have formed the upper reservoir
with water being circulated with the lower reservoir, excavated in the
bedrock approximately 610m below.
The company was cleared at the beginning of the year to begin
site investigation and environmental assessment studies. Riverbank’s
store
Traditional
- flooding
- large surface footprint
-
impacts on upstream and
downstream reservoirs
Riverbank Power
- 5-10 acre surface footprint
- no upstream impoundment
-
flexible intake velocity
flow
flow generate
return
generate store
high impact
low impact
Comparing traditional
pumped storage projects with
Riverbank Power’s concept
The Wiscasset project would be developed on the site of the
decommissioned Maine Yankee nuclear power station
26 DECEMBER 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PUMPED STORAGE
programme called for the plant to be operational by 2015. However,
within months of the studies getting underway, the data from the
initial drill tests showed the strata to be unsuitable to host the pow-
erhouse and six large storage galleries.
Riverbank announced the project was cancelled in August –
only two months after the Federal Energy Regulatory Commission
(FERC) had issued a preliminary permit and cleared the way for
a priority application.
PORTFOLIO PLANS
With progress ongoing at Wiscasset, and despite the Sparta set-
back, Riverbank Power Corp is pushing ahead with its plans to
develop a range of sites in North America that will result in a
portfolio of 1GW facilities.
The company has looked at more than 50 possible sites in North
America and continues with the work. So far, Riverbank has found
15 sites that meet its initial selection criteria, and disclosure of can-
didate sites will only be announced when sufficient progress is made,
including planning support. Its main areas of focus are the northeast
US and Canada.
There are four main criteria Riverbank uses for an early judgment on
the development potential – geology, hydrology, distance to transmis-
sion grid and community support. Passing these criteria enables disclo-
sure of a candidate project site, and then in-depth studies commence
with drilling and testing into the bedrock, environmental assessment
and evaluating the energy market and transmission capacity.
Riverbank aims to develop five of the pumped storage plants over
the next few years. While originating in, and focused on, North
America, Riverbank would also consider developing project in other
countries, said Kuo-Bao Tong, project manager of the Wiscasset site
and who also helped oversee early development progress on the other
candidate sites.
References
New Opportunities for Pumped Storage – Amler, P.; Hydro 2009
Assessment of Waterpower Potential and Development Needs – Electric
Power Research Institute (EPRI), 2007
Preliminary Assessment of US Water Power Potential and Development
Needs – Dixon, D.A., Bahleda, M., and Adonizo, M.A. Hydro 2009
Influence of the Market Structure on the Installed Capacity of Pumped
Storage Plants – Surla, D. Hydro 2009
IWP& DC
One of the earlier proposals to excavate an underground reservoir for a grid-scale
pumped storage project in the US was to have been at Mt Hope, in New Jersey. The
plant was initially conceived as a 2GW facility. A more minor endeavour, in size if not
ambition for its replicability, was the concept for distributed, or modular, pumped
storaget (DPS) systems, such as that envisioned for the 200MW Brink project, in Utah.
The Mt Hope scheme would have called for one of the largest underground excavations
in the US and was to operate with closed loop water circulation between the grid of
tunnel galleries and the upper reservoir, which would fluctuate 33.5m in level.
A key strength of the Mt Hope project, on a mining property owned by Halecrest,
was its proximity to a power pool serving Pennsylvania, New Jersey and Maryland.
It was to be a 2GW facility, employ pump-turbine/generator-motor technology that
was faster than then used in the US, handle more load demands (up to 20 mode
changes daily) and provide faster response to dispatch calls.
The broad idea for such a scheme was conceived in the 1970s. Halecrest
submitted a licence application to the Federal Energy Regulatory Commission
(FERC) in 1985. Three years later it formed a subsidiary to take forward the
plans, and then set up a partnership, Mt Hope Waterpower Project (MHWP), with
Scandinavian companies in 1990. The general partner was My Hope Hydro, Inc,
and it was also project manager.
The project was aimed to bring more of the advanced pumped storage systems to
the country, it was said, by drawing upon the concept of the Dinorwig power plant,
in Wales, although lessons from Northfield Mountain in the US were also to be
employed. A key difference, though, was that Mt Hope did not have to optimise
location and topography to obtain the highest head possible.
The upper reservoir was to be a bunded structure. The lower reservoir was to
be excavated about approximately 760m below the ground surface, and the
powerhouse and associated caverns were to be deeper still. The arrangement
would provide for 732m minimum net head in generation mode and 810m
maximum head in pumping mode, respectively. The power output of each of the six
pump-turbines was to be 339MW and input for pumping was 368MW, respectively.
A four-year development licence was obtained in 1992, and concurrent with the
award Kvaerner bought Mt Hope Hydro, Inc. The firm would supply pump-turbines
and other firms involved were ABB to provide generator-motors and contractors
included Stone & Webster and Atkinson Construction. The plant was to be brought
online by 2002.
However, the planned start on construction in 1994 was repeatedly rescheduled
by FERC to 1996 and 1999 – when Australia-based Pacific Energy with Macquarie
Bank received Kvaerner’s interest as part of a larger package of assets to
be handled by their new associate firm Atlantic Pacific Infrastructure Ltd. But
legislation was needed to extend the deadline to 2002, and when construction
hadn’t begun by 2005 the licence was terminated by FERC.
A fresh application was made in 2006, seeking a three-year preliminary permit.
The project by then was described with the lower reservoir at approximately 880m
depth and to be associated with the inactive Mt Hope Mine. The powerhouse level
would be slightly deeper still, and five pump-turbines were planned for the facility,
still listed as 2GW. But soon after, still in 2006, the application was dismissed by
FERC, which wanted a ‘cooling off’ period after the hydro power site had been tied
up with one entity for years without work starting.
The project plan was re-thought and FERC received a new application, in 2007, for
a smaller, 1GW facility that was to be developed in four stages and have, in effect,
four pumped storage plants. Pacific Energy, with a 74% holding in the venture, said
it would seek a joint venture industry partner to advance the project.
The new concept envisaged having underground reservoirs within mine-linked
caverns at three levels – depths of 300m below the ground surface, 520m and
760m, respectively. There was to be operational overlap between these staged
upper and lower reservoirs. The scheme also proposed separate powerhouses,
each with a 250MW unit, again at three different levels – depths of 400m,
610m and 850m.
FERC denied the permit application, citing problems with unpaid fees due over the
years when considering regulatory compliance matters.
The Mt Hope land is now host to a 33MW biomass project being developed by
Pacific Energy.
While the last pumped storage scheme for Mt Hope conceived of a cluster of
smaller projects, in effect, the plan drawn up by US renewables venture firm Energy
Unlimited for the Brink pumped storage facility was always for relatively small-
scale, in comparison. The project and the more general, modular-style DPS system
were concepts envisioned in the mid-1990s by the enterprise, although some
other firms were exploring the field.
Energy Unlimited pursued the project with rights having been brought over from
LB Industries, which in late 1995, as permittee of Brink, notified FERC it had
surrendered its preliminary permit for the scheme. The development plan was
to have DPS at the Brink project, including constructing a lower, underground
reservoir that a powerhouse sat alongside in a 76m deep concrete caisson.
The shaft was to house two single-stage reversible Francis units, and it would
operate about 10 pumping-generating cycles per day under net head of 262m.
Water was to be circulated in the closed system, and Brink was planned to be
operational by 2000.
However, market economics put a halt to the scheme: prices were too weak;
the well established gas-fired generation sector enjoyed too much of market
dominance despite DPS costs coming to within its range; and, utilities were wary
of commitments in light of uncertainties in how deregulation would play out.
Closed Loop pumped storage proposals
WWW.WATERPOWERMAGAZINE.COM DECEMBER 2009 27
INSPECTION
T
HE inspection of the underwater structural components
of dams, locks, flood-gates and other water control
structures is crucial if such components are to main-
tain dependable performance and reach the maximum
number of years expected for operation. Until recently the technol-
ogy to perform such inspections was limited to the use of divers
and robotic vehicles that perform largely visual and tactile surveys.
This is problematic under inclement environmental conditions
such as high current flow, extensive structural surfaces, hazardous
high flow dynamics through small aperture openings on dams, and
low to no visibility.
Due to the significant impact of these conditions on results and
findings, these surveys tend to be extremely subjective and provide
only very generalised comparison information. These typical cursory
surveys cannot be used to establish a baseline of structure condition
due to the limited information provided.
With the development of underwater acoustic, steered beam sonar
and profiling, remote sensing systems which have the ability to pro-
duce very high definition sonar imagery, as well as precise acous-
tic profile measurement, there is now a cost effective alternative to
conventional methods of underwater substructure inspections. These
can provide a baseline reference for future surveys as well as a non-
subjective data set that can be used for comparison with previously
recorded structure conditions. This methodology can be used to pro-
vide a comprehensive spatial element map of underwater structure
surfaces and their interface with the water bottom.
SYSTEM DETAILS
Underwater acoustic imaging and measurement systems contain an
emitter and a receiver, and rely on the emission of a sound wave and
measurements of the time required for a reflection of the emitted sound
pulse to return to the receiver, as well as measurement of the intensity
or amplitude of the reflected sound pulse. In many systems the emitter
and receiver are the same physical sensor or transducer. The physical
characteristics of the acoustic pulse wave are critical to the resolution of
the sonar imagery and precision of the acoustic measurement.
The main critical physical characteristics are the frequency of the
acoustic wave form, pulse length of the acoustic transmission and the
beam width of the acoustic wave form. Generally speaking, the higher
the frequency the greater the resolution – but there is a tradeoff in effec-
tive range. A narrower beam width also produces higher definition but
reaches a tradeoff limit with scan coverage requirements increasing the
time required to complete a scan. The best compromise to optimize the
physical beam forming characteristics are a fairly high frequency in
the range between 500kHz and 900kHz, a horizontal beam width of
less than 1°, and the shortest pulse length that can effectively produce
the desired detection range. For acoustic profiling measurement the
smallest practical acoustic footprint for the beam produces the greatest
range of measurement accuracy, and reduces the noise from multi-path
reflections due to nearby structural components.
The configuration of the instrumentation that Fenstermaker has
utilised in multiple dam evaluation surveys is a dual element, fan
beam/conical beam, 360° mechanically scanned imaging and profil-
ing sonar. The system operates at a frequency above 500 kHz and is
configured for a horizontal beam width of less than 1° and a conical
beam of less than 2°. The system is also configured for beam steera-
bility in both the horizontal and vertical planes with redundant steer-
ability in one of the axes, the redundancy axis being defined by the
operator. The system is largely based on a variation of the Kongsberg
Mesotech MS1000 digital, high resolution, mechanically scanned
sonar. The system scan patterns are reflected in Figures 1 and 2.
DEPLOYMENT METHODOLO GY
The inspection of underwater structural components with high defini-
tion acoustic imaging techniques requires significant considerations
in the deployment methodology. The sensor must be maintained in
a stable position during the scan segment and the sensor orientation
must be such that the grazing angle of the acoustic beam across the
structure surface provides for visualisation of surface undulations,
projections and abnormalities in the plane of observation. Because of
this aspect of the methodology, most scenarios will require the ability
to vary the sensor orientation in order to remain normal to a specific
observational plane that corresponds to a structure surface.
The deployment methodology can be problematic in environments
where high water currents or close proximity heavy shipping traffic
exists. Fenstermaker has overcome these problems by designing and
constructing several self-contained deployment mechanisms, which
Kenneth J LaBry explains how Fenstermaker has applied underwater acoustic remote
sensing to underwater substructure inspection and spatial element mapping
Making sense of
underwater acoustics
Figure 1: Underwater acoustic imaging
directionally steered beam characteristic
Figure 2 Underwater acoustic profiling beam charateristic
28 DECEMBER 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
INSPECTION
are portable and can be quickly deployed.
The quantitative measurement of profiles of structural abnormali-
ties and the interface between the substructure and the water bottom
requires the use of steered beam profiling. By utilising dual axis steer-
ability we can gather quantitative measurement data over areas where
abnormalities were observed utilising underwater acoustic imaging.
The steered beam profiling with a narrow conical beam provides for
acoustic measurement accuracies of 0.1” at ranges of 75’ on abso-
lute acoustic boundaries and provides the capability to collect profile
measurements between narrowly spaced structural members.
The steered beam profiling methodology is also utilised to generate
water bottom elevation models to evaluate scour and deposition. It
maps scour depressions, sediment accretion, and erosion patterns and
correlates these to the corresponding hydrodynamic flow characteris-
tics that would produce these water bottom characteristics.
The profiling methodology involves the incorporation of a com-
pendium of remote sensing instruments to resolve angular motion,
providing heading reference, positional reference and acoustic meas-
urement of submerged features.
The example shown in the figures above is a result of data ren-
dering from a survey performed for a Louisiana Department of
Transportation and Development project at D’Arbonne dam in Union
Parish Louisiana. In this case terrestrial lidar (HDS) laser scanning
was utilised to scan the superstructure of the dam and surrounding
environment and Fenstermaker’s underwater acoustic system was use
to scan the submerged structural components of the dam as well as
the water bottom upstream and downstream of the concrete spillway
structure. The data sets were then integrated to construct a compre-
hensive ‘as-found’ 3D model of the dam system from which geo-
graphic position and metrology can be extracted. This provided a
comprehensive baseline, assisted in identifying areas of concern that
were in need of repair or remediation and provided volumetric and
measurement data for determining extents of repair and material
needs (see Figure 4 and Figure 5).
The resulting model identified the complex erosion pattern and
scour characteristics downstream as well as providing data to qualify
any differential movement in the spillway apron slabs and concrete
dam structure. The survey also defined possible problematic charac-
teristics at the toe of the concrete structure on the reservoir side of the
dam that potentially indicated a piping condition. This prompted a
recommendation for more intensive diver aided investigation.
When this investigation occurred approximately 60 days later, a
dynamic situation was observed whereby the depressions in the silt
at the toe of the structure were considerably larger and had grown
together. The acoustic imaging system was utilized to guide a pipe
probe into the depression and inject dye to define any significant flow
prior to sending a diver into the environment. Flow was not observed,
however the dye did not pool either. Upon close inspection by divers
the hole in the sediment was caused by a compromised joint and seal
at the base of the structure allowing water and sediment to be trans-
ported through the structure and into the drainage system.
This case study shows the multi-faceted role of the acoustic remote
sensing system to map and identify problems, then assist in defining a
safe working environment and finally assist in directing diving efforts
expediently to problem sites in conditions of low to no visibility.
A MATTER OF COS T
Incorporating both underwater acoustic imaging and underwater
acoustic profiling allows for the qualification and quantification of
structural and water bottom abnormalities in a cost effective manner
and adds an element of safety by providing a visual rendering of the
working environment for dive team direction. The production rate
of area covered relative to other methods provides for a significant
cost savings. It provides a much more extensive and non-subjective
data set to be used for subsequent comparative analysis with future
surveys that are performed in the same manner. The geo-referencing
of all acoustic data provides for real world displacement measure-
ment along the water bottom and structural surfaces.
Subsequent to the D’ Arbonne dam evaluation the Louisiana
Department of Transportation and Development, Public Works and
Water Resources Division selected Fenstermaker for the inspection of
19 other dams maintained by the State of Louisiana.
Kenneth LaBry is a physicist with over 20 years of
experience in underwater acoustics remote sensing.
www.fenstermaker.com
IWP& DC
Above, top, left to right – Figure 3: Underwater acoustic scan showing complex erosion and submerged spillway apron; Figure 4: Lake D’Arbonne Dam HDS scan
of damage spall areas and leaking buttress. Bottom – Figure 5: Further scan of Lake D’Arbonne dam; Photo of the underwater acoustic team scanning the dam
WWW.WATERPOWERMAGAZINE.COM DECEMBER 2009 29
PLANNING & PROJECTS
A
S public and political concerns about the environment
grow, the construction of new dams is facing increasing
difficulties. A good alternative that has little environ-
mental impact is to increase the storage capacity of an
existing dam without raising the maximum water level.
A successful example of this solution is the recent augmentation of
the Urra Dam in the Columbian state of Cordoba. The project – to
raise the full supply level of the dam – required the removal of a 5.2m
high section of the existing concrete spillway and structural modifica-
tions to the remaining crest to accommodate Fusegates.
Urra 1 is an 85MW hydro power scheme located on the River
Sinu in Cordoba, Colombia and is owned and operated by Empressa
URRA ESP SA. It compromises a 73m high rockfill embankment
impounding 1.740Mm
3
of water and a 182m long free overflow spill-
way. This is spanned over its entire length by a bridge with piers at
14m intervals.
It was decided to raise the reservoir by 2m in order to increase
storage capacity and improve flood mitigation. The project was sub-
ject to the prior approval of the Colombian authorities through a
comprehensive environmental impact study, which concluded that
the reservoir raising had negligible impacts on the area surrounding
the reservoir.
ACCOMMODATING FUSEGATES
After an evaluation of a number of technical options, Empressa Urra
ESP SA decided to meet the project requirements by installing 22
double Hydroplus Fusegates on 11 of the 13 bays of the spillway. The
remaining two spillway bays were to be fitted with flap gates – each
5.5m high and 12m wide.
The 11 bays required some structural modification in order to
be equipped with Fusegates and a search was conducted to find a
company with the skills to lower the overspill crest by 5.3m without
causing any structural damage to the remaining concrete. There was
particular concern that the bridge piers might be damaged during the
concrete removal process.
DecoTEC Pty Ltd, an Australian based structural modification
company, was chosen from the shortlist of contractors due to their
experience in dam modification and references provided in respect to
DecoTEC’s ongoing work modifying the Hinze water supply dam on
the Gold Coast, Australia.
Prior to bidding for the project, DecoTEC’s Managing Director
and Technical Director, Allan Moss, went to Colombia to ensure that
there was a sufficient level of security for the company’s personnel.
While these security concerns proved to be unfounded, the logistical
difficulties in working in a remote area of Colombia proved to be a
real issue.
“The bigger challenges were logistical, due to the extreme isolation
of the dam, the language barrier and the custom clearance arrange-
ments for importing plant and equipment to Colombia,” said Moss.
“Mostly these challenges were overcome by over estimating the con-
sumables required to complete the job, and by bringing at least one
back up machine for each of the operations.
“This required significant co-operation between DecoTEC’s
Australian and New Zealand-based technicians, the Columbian
employees and the Urra Dam’s project manager.”
DecoTEC scoping of the project involved four possible methods:
U Traditional breaking using either hydraulic or pneumatic equip-
ment. This methodology was quickly rejected because of the risk
of micro-cracking to the remaining structure, the proximity of the
bridge piers to the excavated edge of the concrete, noise and envi-
ronmental impacts.
U Cutting the outline with wire saws and then using a hydraulic
breaker to remove the concrete. There were, however, still micro-
cracking issues using this methodology. In addition, it required the
building of platforms for the excavator to work from until such
time as there was a sufficient base on the structure itself. The con-
crete rubble would also have to be contained.
U Hydro-demolition. This methodology was given serious considera-
tion but rejected primarily on economic and environmental grounds
– principally the need to control large amount of contaminated
water from the hydro-demolition operations.
U Cutting and bursting into large blocks. This was the method ulti-
mately chosen. It involved cutting the outline of the excavation
using wire saws, and then cutting and bursting the concrete into
pieces that could be craned from the spillway and deposited into
the upstream side of the crest.
“We were able to show the dam’s owners that this was also the most
time-efficient and cost-effective method, as well as meeting their envi-
ronmental goals,” added Moss.
Empressa Urra also had stringent Environmental and Health &
Safety requirements. DecoTEC initially thought that its approach
to meeting these standards would make its quote uncompetitive.
Scoping of the project, however, revealed that Urra’s and DecoTEC’s
standards were at a similar level and this proved to be one of the key
elements in DecoTEC being awarded the project.
ON A TIGHT SCHE DULE
Having been appointed, DecoTEC had just four weeks to organize the
necessary equipment and ship it to Colombia, organize its Australian
and New Zealand crew with the correct work visas and inoculations
DecoTEC gets to
work on Urra Dam
Australian company DecoTEC has
overcome a range of logistical and
engineering challenges to successfully
complete the structural modification of a
remote hydroelectric dam in Colombia
Taking on the challenges
30 DECEMBER 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING & PROJECTS
and then transport them to the remote site.
At the same time, contracts for the design and building of the work-
ing platforms and access ways had to be let and the work started
without delay. Colombian law required DecoTEC to employ three
locals for every foreign worker. It awarded the contract to Prospera
ILB EU, a local company who were able to complete the work within
the extremely tight time frames.
WIRE SAWI NG
Once onsite, DecoTEC’s plan was to wire saw an outline, wire saw an
additional horizontal line at about the half way point, 2.9m above the
bottom cut, and then wire saw one internal cut so that the first block
could be removed easily to create space for the remaining blocks to
be burst into.
In any wire sawing operation, the critical part is accurately drilling
the wire holes. The holes were drilled from the upstream side with the
two outside holes being crucial in that they had to be accurate both
in the horizontal and vertical planes. The plan called for the bottom
surface of the cut to be on a slope of 2% upstream/downstream as
well as perpendicular to the axis of the dam, which was significantly
different to the face of the concrete at that point.
“The cross-section of the dam wall was 12m deep and the design
called for a fall in the cut profile of 2%, so accurately drilling the hole
for the wire was vital,” said Moss.
Having surveyed the hole for accuracy on the downstream
side, wire sawing could commence. This was also done from the
downstream side so that the wire hole drilling and wire sawing
operations could be done at the same time, with appropriate
safety precautions.
The as-built drawings indicated that, apart from reinforcing steel
150-200mm below the surface of the concrete on the downstream
side, there was no other reinforcing steel within the monolith.
Once drilling began, however, it quickly became apparent that
there was significantly more reinforcing steel within the concrete
than indicated by the drawings. DecoTEC decided to wire saw the
upstream/downstream sections rather than burst them.
The drilling and wire sawing were originally planned to take 53
days. With the addition, however, of a further 240m
2
of wire sawing,
the drilling/wire sawing actually took 58 days.
BURSTING OUT
DecoTEC decided the transverse sections could still be burst, but
this required the hiring of a burster with twice the power than the
one they had originally specified. The burster was one machine that
DecoTEC was unable to provide a backup for and, proving Murphy’s
Law, it was also the one machine that had a major break down.
However, the Swiss manufacturers were able to fly in a technician
complete with spare parts within a few days of the problem being
diagnosed, so little time was lost.
The unexpected reinforcement meant bursting the blocks apart
was more time consuming than expected. The burster had sufficient
power to break the reinforcing steel if there was only one or two
pieces within the concrete. Some blocks, however, had up to 20 pieces
of reinforcing steel joining them to the next block, with the average
being about eight. As there was no discernable pattern to the reinforc-
ing steel, each block had to be burst sufficiently far apart so that the
steel was exposed and could then be cut using oxy-acetylene cutting
equipment or other methods as appropriate.