Water Power and Dam Construction. Issue August 2010
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RISKS AND OPPORTUNITIES
The following risks and opportunities were identied as those which
are critical and will be addressed through implementation of the
refurbishment project:
Risk mitigation:
r Mitigate the risk of catastrophic equipment failure which has the
potential to cause substantial secondary damage to associated plant
and pose a risk to operations and maintenance staff.
r Avoid plant becoming unavailable for long periods while parts are
being procured or where obsolete repairs are affected.
r Ensure that the plant remains compliant with legislative and regula-
tory requirements.
r Avoid stranding the assets and constraining generation due to a failure
of either pole 1 or the interconnecting or converter transformers.
r Avoid constraining the HVDC as a result of multiple unit outages
due to plant and local service failures.
Asset management:
r Implement changes that ensure plant performance targets can be
maintained or enhanced through the replacement of ageing assets
and/or reconguration to provide segregation and diversication
of critical systems.
r Implement changes that will ensure future compatibility with
Transpower’s proposed HVDC upgrades.
r Support the operational life of Benmore for a further 40 years.
r Ensure that life cycle costs are minimised through avoiding escalat-
ing maintenance requirements and costs and minimising the revenue
earning impact due to the reduced reliability of ageing assets.
The scope of works for this ve-year refurbishment project is exten-
sive and began in January 2006. The following are the main aspects
of the project.
TURBINE RUNNERS
The turbine runners in each of Benmore’s six turbines are the origi-
nal runners designed and manufactured by Dominion Engineering
(now part of General Electric), Ontario, Canada. To the original
designer’s credit, the turbines have remained in service continuously
from commissioning in 1965-6, except for planned maintenance
activities.
Of the six Benmore machines, three have never been completely
dismantled whilst three have undergone refurbishment in the mid
1990s. However, the runners on all six machines have required cavi-
tation damage repair every three years, which has resulted in distor-
tion of the runner blades.
Efciency testing in 2002 compared the existing runner efciency
to that of the as- commissioned turbines in 1965. From the results it
was evident there had been a signicant loss in turbine efciency due,
predominantly, to the distortion of the runner blades. An opportu-
nity also existed to further improve station efciency over and above
the original design. This gain was proven following CFD analysis
and model testing. The replacement of the runners will eliminate the
maintenance burden associated with cavitation repairs through using
available advanced design techniques.
The plots in figure 2 show the reduction in turbine efficiency
between 1965 and 2002 together with a shift in the peak efciency
point to higher turbine loads. The shift in peak efciency load has the
effect of decreasing the time when the turbine is operating around its
best efciency. The above comparison was the basis for implementing
a runner and associated turbine components replacement programme
at Benmore.
Subsequent tendering for replacement turbine runners returned a
large range of turbine enhancement options ranging from replacing
the turbine runners only, through to replacing the runners and wicket
gates together with modifying the stay vane proles and turbine ow
passage shape. All of the above options had an increased cost together
with an increase in turbine efciency, but following extensive evalua-
tion of the bid options from various turbine manufacturers, a replace-
ment runner and wicket gate option supplied by Toshiba was deemed
to give the best return to Meridian.
16 KV GENERATOR CI RCUIT BREAKER S
The 16kV circuit breakers provide a critical protection function, but
are nearing the end of their life (normal life expectance of a circuit
breaker is 35 years according to international statistics). Forced out-
ages are becoming more frequent and severe and present a signicant
risk to plant, personnel and the station availability.
WWW.WATERPOWERMAGAZINE.COM AUGUST 2010 21
AUSTRALASIA
VG4
G6
90MW
G5
90MW
G4
90MW
G3
90MW
G2
90MW
G1
90MW
16kV
Bus B
16kV
Bus A
VG3
T5
232MVA
T2
232MVA
VG2 VG1
T6 T4
987
T3 T1
220kV
Pole 2
500MW
Top: Figure 1 – Existing grid injection configuration at Benmore power station;
Middle: Figure 2 – Existing runner efficiency curves;
Bottom: Figure 3 – Proposed configuration for Benmore
Generation durations
1966 base efficiency curve
2002 base efficiency curve
100
90
80
70
60
50
40
30
20
10
0
Efficiency (%)
40 50 60 70
Runner output (MW)
80 90 100
Position of
maximum efficiencies
New
overhead
220kV
circuit
461 (relocated)
465
462 482
483
521
523
Bus A
Transpower 220kV AC switchyard
220kV
220kV
220kV
220kV overhead
circuits
225 MVA 3
winding trfs
16kV new
compact IPB
16kV GCB’s
16kV existing IPB
Generators
Bus B
Bus C
485
522
T46 T44T5
CB6 CB5 43 21
T42T2
G3G4G5G6 G2 G1
BENRP:
Completed
BENFCP (Final configuration project):
Stage 1
Stage 2 Stage 3
22 AUGUST 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
AUSTRALASIA
The 16kV circuit breakers, designated CB1 to CB6, connecting the
generators to the main bus are Brown Boveri model DB 20RC 1500/1
single phase air breaker type. They have a 5000A load rating with
a fault rating of 2500MVA. They are originally-installed equipment
and although routine maintenance is conducted they have not been
refurbished or upgraded since commissioning.
Based on analysis of historical forced outage data and discussion
with maintenance staff it was estimated that the circuit breakers
would reach the end of their operational life by 2009. The acqui-
sition of spare parts is difcult and lengthy – a breaker failure in
February 2003 caused a six-week forced outage which resulted in a
six-fold increase in annual forced outage factors and 5% reduction
in annual availability for that year. The types of faults occurring are
increasingly due to age deterioration of components. Spare parts are
very expensive to obtain and it is difcult to determine what parts to
hold as the age-related failures are hard to predict.
Efforts have been made to limit the number of circuit breaker
operations in recent years in an attempt to reduce degradation by
encouraging operators to run the units on tail water depressed
mode when not required, rather than stop the units. This is not
an adequate long-term solution as running the units in this mode
is not an efcient way to use water. To maintain adequate service
in the short term, it is critical to address the issue of spare parts
availability as soon as possible.
The circuit breakers will be replaced with ABB HEC-80S SF6 cir-
cuit breakers, 8500A rated continuous current, 80 kA rated short
circuit breaking current.
EXCITATION AND AUTOMATIC VOLTAGE REGULATION
The excitation system suffers from age related faults and requires
an increasing maintenance effort. The equipment is based on 1950s
technology that is no longer supported and future failures will
result in protracted unit outages due to the reduced availability of
spare parts and maintenance expertise. The market driven increas-
ing number of stop/starts will also further escalate the rate of
deterioration.
Maintaining power quality and compliance with Electricity
Governance Rules have become increasingly difcult and opportu-
nities exist for improving voltage support performance and reduc-
ing synchronising time with modern equipment. The excitation
upgrade will increase the asset life and maintain operational efcien-
cy and availability by reducing the risk of failure of obsolete ageing
equipment.
This project will replace the electromechanical AVR with digital
controlled types and replace the existing motor driven Amplidynes
with controlled bridge rectiers. The exciter eld supply will be from
new unit excitation transformers. The existing generator slip rings
and brush gear will be retained and DC interrupting devices will be
installed. Grid power system stabilisers will also be installed.
The excitation project will:
r Extend the life of the excitation and AVR by 25 years.
r Reduce the risk of failure of the aging excitation and AVR system.
r Improve spares availability.
r Reduce the maintenance requirement on the system by 50%.
r Not impact the current generator capability with respect to achiev-
ing 100 MW output, or the ability to interface to existing voltage
control signals.
The excitation components are supplied by Basler Electric from
France and installed by Transeld Services New Zealand. The new
excitation systems are commissioned concurrently with the commis-
sioning of the new turbine runners.
MECHANICAL REFURBISHMENT
In the late 1990s units 2, 3 and 6 underwent a mechanical refurbish-
ment to address the deteriorated state of critical items of plant. The
remaining three units now require refurbishment to maintain target
levels of station availability and minimise lifecycle O&M costs.
This work includes all systems associated with each hydro unit (eg
governors, stator coolers, bearings, brakes, rotors, etc), but excludes the
stators. The stators will have at least ten years remaining life left and
where appropriate will undo selected re-wedgings of the windings.
3.3KV AND 415V LOCAL SERVICE SUPPLIES
The lack of diversity and segregation of the essential supplies
presents a signicant risk of multiple unit or even whole station
forced outages, particularly as the component parts are reaching
the end of their operational life. There was also a requirement to
maintain the equipment in a live state, which does not align with
safe working practice and presented a health and safety risk that
could result in a fatality.
The existing conguration relies on the interconnecting trans-
formers (T2 and T5) and the HVDC Pole 1 to be available to avoid
constraining the Benmore power station. The existing Pole 1 will be
decommissioned by 2012 and replaced with a static converter pole
supplied from the 220 kV grid. This has forced Meridian to recong-
ure the grid injection point.
The existing interconnecting transformers and their associated
16 kV circuit breakers are at the end of their life and have a high
likelihood of failure. So as part of the reconguration, Meridian is
replacing the interconnecting transformers and adding extra trans-
former capacity.
This project will install three new 225MVA winding transformers
through which the generators G1 to G6 will connect directly to the
220kV grid by means of a strung bus. The proposed conguration
is shown in Figure 3. The two low voltage windings in each trans-
former are loosely coupled to reduce fault levels. This allows for
more economical generator circuit breakers to be used.
All 16 kV connections are made by isolated phase bus duct. This pro-
vides a fully phase segregated conguration, a high reliability and low
maintenance. The bus duct will be supplied by Alfa Standard in Italy.
PROJECT PROGRESS
The project is well underway with four of the six units refurbished.
The excitation and local services upgrade have been completed, one
new 225 MVA transformer installed and supply contracts for isolated
phase bus duct and circuit breakers awarded.
Once complete, Benmore will provide a reliable generation capacity
of 540MW at an increased efciency. It will continue supporting the
HVDC link to New Zealand’s North Island.
The author is Johan Hendriks, Strategic Electrical
Engineer with Meridian Energy Ltd. New Zealand.
Email: Johan.hendriks@meridian.co.nz
This article is based on two papers originally presented
at the EEA conference in New Zealand. The conference
technical papers are available from Electricity Engineers’
Association, New Zealand www.eea.co.nz
IWP& DC
The Waitaki system
Name Commissioned Generation
(GWh/yr)
Output
(MW)
Net head
(m)
Tekapo A 1951 160 25.5 30.5
Tekapo B 1977 833 160 145.7
Ohau A 1979 1140 264 59
Ohau B&C 1984/5 958 212 47.5
Benmore 1965 2215 540 92
Avlemore 1968 942 220 37
Waitaki 1935-54 496 105 21.5
* Facts are the same for each station Ohau B&C
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EXPPERTS
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AUGUST 2010
Serving the hydro industry for over 60 years
Earthquakes and dam safety
The rise in multi-purpose projects
Restoration scheme
Replacing post-tensioned anchors at Catagunya Dam
INTERNATIONAL
& DAM CONSTRUCTION
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24 AUGUST 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
AUSTRALASIA
C
ATAGUNYA Dam is located on the Derwent River in the
southeast of Tasmania, Australia. It is the third in a cascade
of six dams forming the lower Derwent power develop-
ment. Designed in the late 1950s and completed in 1962,
Catagunya is a 49m high concrete gravity dam which relies on a large
number of 200 ton capacity post-tensioned steel cables to provide the
necessary structural stability against the stored water load. Its design
was considered leading edge, being the highest post-tensioned dam in
the world at the time of its construction, and the designers adopted
a 50-year design life for the anchors. It was estimated that the use of
post tensioning provided a saving in the order of 20% compared with
a conventional gravity dam.
During construction of the dam in the early 1960s, 412 post-tensioned
anchors were installed but the integrity of the original anchors can no
longer be assured. The stability of the dam has been restored over the
past two years using 92 modern, large diameter and corrosion protected,
post-tensioned anchors that can be monitored for deterioration. These
are the most highly stressed anchors applied to a dam at this time.
CONSTRUCTION CHALLENGES AND SOLUTIONS
A number of challenges were addressed during implementation,
including:
r Installing more than half the anchors within an operating spillway,
utilising a limited construction window over the summer months.
r Providing access for drilling equipment and installation of the
anchors well below the spillway crest on a 54˚ degree slope, 25m
above the riverbed, and demobilising these platforms sufciently to
allow oods to pass during the winter months.
r Replacing severed surface reinforcement with 9m long carbon
bre rods.
In order to gain access to the spillway of Catagunya dam for instal-
lation of the temporary access platform brackets on the spillway and
the carbon bre tensile reinforcing on the spillway face, a purpose
designed and built travelling gantry was suspended from the spillway
crest. This gantry had ve working deck levels, with four of these
providing access to the full length of the 9m long carbon bre rods
which were to be installed.
Two 200m long temporary platforms were constructed to access
the spillway. The upper platform was designed to provide access for
the drilling, installation, and stressing equipment, as well as to pro-
vide safe and efcient egress in times of ood. The lower platform
was used to give direct access to the anchor hole locations for instal-
lation of anchorage assemblies.
With the unique cross-section of Catagunya dam, tensile steel rein-
forcing is required on the top surface of the downstream face of the
spillway to support the large cantilevers overhanging the spillway. This
steel was to be severed as the large diameter holes for the spillway head-
blocks were cored, so a replacement was required prior to the coring.
Ageing post-tensioned anchors have
been replaced at Hydro Tasmania’s
Catagunya Dam in Australia.
Catagunya Dam restoration
WWW.WATERPOWERMAGAZINE.COM AUGUST 2010 25
AUSTRALASIA
A major innovation of the project was the design and installation
of carbon bre reinforcing into the spillway face to provide tensile
reinforcing for the cantilever section of the dam. Used widely in
the bridge industry as a method to upgrade and restore structures,
epoxy bonded carbon bre strips are a very cost effective and simple
solution. However, to date, these have not been used for a similar
application in the dams industry.
The 9m long carbon bre rods were installed in the face of the spill-
way by wall sawing a 9m long, 15mm wide, and 90mm deep slot in
the concrete. Each of the six 8mm diameter rods were installed indi-
vidually, guided into place on a bed of epoxy adhesive injected into
the slot and bonded to the concrete. The overall solution took around
four months to complete, installing over 10km of carbon bre rod.
A requirement of the design of Catagunya dam was to maintain the
hydraulic performance of the ogee crest spillway. This meant anchors
installed within the spillway were required to be constructed within
the current prole. Coring of 1.2m diameter holes into the slope, 3m
into the dam was undertaken to install the precast reinforced concrete
headblocks to distribute loads into the structure. Abutment anchors
were installed onto a specially designed concrete beam, located above
the level of the parapet walls.
The drilling was undertaken using a 350mm downhole hammer
(DHH) from a Rotomech drilling rig. The longest drill hole was circa
78m through the concrete and into the dam foundation, and in total
6.2km was drilled throughout the project.
The modern post-tensioned anchors were all fabricated on site using
specialist equipment to open and grease the cable, and then install into
a 20mm HDPE sleeve over the free length. The bond length is cleaned
back and left bare, with all 91 lengths of cable twisted into an hour
glass shape to increase the bond with the dolerite rock in the area.
The complete anchor is installed into a part corrugated, part smooth
polyethylene sheath within the anchor hole, and grouted into the hole
using Class G Oilwell and GP cement. Once the grout reaches its
strength, a purpose built 2200 tonne capacity hydraulic jack is used to
load the anchor to over 70% of its minimum breaking load, making
these anchors the highest stressed ground anchors in the world.
LONG TERM MAINTENANCE
The newly installed post tensioned anchors will be monitored ve-
yearly by Hydro Tasmania, with the rst of these checks to be under-
taken between November 2010 and March 2011. To undertake these
tests, the travelling gantry has been modied to carry all load moni-
toring equipment.
The tests for the rst four anchors installed on the spillway have
already been completed and found the anchors in excellent condi-
tion. The lift off tests performed on these anchors has found only
a very small loss in load over the past year, well within a tolerable
margin and below what has been observed in other anchoring
jobs of this size.
Gantry on the dam face
Catagunya Dam on spill at 370m
3
/sec on 27 Jul 2010
Installing cables on block P, right abutment
IWP& DC
26 AUGUST 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
MULTIPUPOSE PROJECTS
A
MULTIPLICITY of water needs can be served by hydro
and multipurpose projects, and in the near- to medium-
term there is going to be relatively greater demand to
employ them as an adaptation strategy to the anticipated
increase in weather instability, as projected from the effects of cli-
mate change, notes The World Bank Group in its Directions in
Hydropower report, which was published last year.
The World Bank says it ‘is keenly aware of this timely and impor-
tant period for hydropower’ though adds that this particular use of
water resources will be only part of the picture in future. It says that
given the increasing importance of climate change, water security,
and regional cooperation, the bank has consequentially a wider view
that ‘encompasses water infrastructure that serves multiple objectives,
among which energy may be a subsidiary goal’.
The Directions report adds, ‘As part of a exible, well-planned
water resources infrastructure, hydropower can help countries
manage oods and droughts and improve water resources alloca-
tions across a complex set of users’.
It goes on, ‘Multipurpose hydropower can also support adaptation
to increasingly difcult hydrology by strengthening a country’s ability
to regulate and store water and so resist ood and drought shocks.’
But before facing any climate change impact on hydrology, some
countries are already experiencing great water-stress, prime among them
being Ethiopia, Haiti and Niger, the World Bank said in March, when
releasing an internal review of support given to water-related activities
over 1997-2007. Almost a third of all projects worldwide approved by
the World Bank for funding since 1997 have been water-related.
In every country, from the most water-stressed to those far less
strained – possibly even with an abundance of hydrological resources,
there is far more attention demanded, and being given now, to a
wider range of planning factors, including strategies being developed
around river basins, large and small. One such major planning initia-
tive is underway for the river Nile – the world’s longest – and its many
regional, national and local sub-catchments.
THE NILE & ETHIOPIA
Africa holds immense untapped water resource and hydropower
potential, and yet in the north it also has some of the most water-
stressed regions anywhere. Also in the north is the Nile, one of the
world’s longest rivers, and in the Horn of Africa is Ethiopia which,
despite facing signicant water-stress, ranks as one of the countries
on the continent with most hydropower potential, notes its Ministry
of Water Resources (MoWR).
The Nile Basin Initiative (NBI) was established just over a decade
ago and is one of the largest river basin strategies in the world. The
Hydro and multipurpose projects are being sought more due to climate concerns and are
vital in regions of high water stress, such as Ethiopia. Report by Patrick Reynolds
Multiple benefits
The EPB-DSU TBM used on the
Beles II Headrace tunnel
WWW.WATERPOWERMAGAZINE.COM AUGUST 2010 27
MUTIPURPOSE PROJECTS
Nile’s extensive catchment area extends over parts of many countries
in northeast Africa. Draining through Egypt to the Mediterranean
Sea, south of Sudan the river is fed by two branches – the White Nile,
which arises in east central Africa, and the Blue Nile, which rises near
Lake Tana in the highlands of Ethiopia.
With so many competing visions and needs for the water resources,
and the cross-border nature of the ows, it is vital to have co-opera-
tion. Like so many river basins elsewhere, the need for effective part-
nerships and co-operation will become increasingly important when
countries and people become presented with weather instability and
other foreseen impacts from predicted climate change.
NBI provides a mechanism for the shared visions, and needs, to
have the Nile basin developed to deliver multiple and widespread
benets. Having formally launched the Initiative in 1999, the partici-
pating countries held their 18th Council of Ministers meeting in late
June this year, in Addis Ababa, Ethiopia. The Council leads the NBI
to help deliver the socio-economic benets that are commonly, and
separately, sought while helping to promote peace and security in the
region where water is relatively scarce.
The development efforts on the White Nile and Blue Nile are
handled under two units within NBI – the Nile Equatorial Lakes
Subsidiary Action Programme (SAP) and the Eastern Nile Subsidiary
Action Programme (ENSAP), respectively.
Ethiopia has 12 basins – eight river basins, one lakes basin and
three that are, in effect, dry as they have insignicant ows, if any,
says MoWR. Under NBI, developments in water-stressed Ethiopia fall
within the function and partnership discussions enabled by ENSAP.
There have been a range of water projects developed over many
years, both prior to and since NBI was established. A number of
countries and foreign rms have worked on plans and schemes,
and over the last couple of years the Norwegian Water Resources
and Energy Directorate (NVE) has been measuring sediments and
hydrology to support reservoir development on the Blue Nile, which
is known as Abay in Ethiopia.
Presently, there are a series of hydro, multipurpose and various
other water schemes either in studies, construction or operations, and
these include the multipurpose Mandaya and Beko Abo projects, the
Genale-Dawa basin development, the Gilgel Gibe III addition to the
Gibe cascade scheme, and the Beles Multipurpose (Beles II) project.
MANDAYA & BEKO ABO
The Mandaya and Beko Abo projects are being studied as potential
major developments, some 300km apart, on the Blue Nile in west/
central Ethiopia. While they are being examined together and would
be neighbours in the river basin, and operationally they would inu-
ence each other, the projects would be developed separately.
The study into the projects is being undertaken by a consortium of
companies comprising consultants Norplan/Multiconsult, Norconsult
and Scott Wilson with energy utility Electricte de France (EdF). They
are being supported by local rms Shebelle Consult and Tropics. The
work is to be completed by mid-2012.
In the study, a full technical and economic assessment of the 2GW
Mandaya project is being undertaken. The surface plant is envisaged
to generate 12.100GWh per year. Planning for the 2.1GW Beko
Abo scheme is proceeding with, rst, a techno-economic pre-feasi-
bility study. The Beko Abo underground plant would generate about
12,600GWh annually.
Both projects are anticipated to have large RCC dams, and at the
Mandaya site the structure would impound a reservoir extending
300km upstream to the location of Beko Abo. The reservoir behind
the Beko Abo dam would be about half the length, at approximately
150km long.
Mandaya was examined at the pre-feasibility stage by a joint ven-
ture of Scott Wilson and EdF, and they completed the work almost
three years ago. Around the same time a separate JV of Norplan/
Multiconsult, Norconsult and Lahmeyer nished reconnaissance-
level studies for Beko Abo.
The RCC dams to be built at Mandaya and Beko Abo have been
estimated will be 200m and 285m high, respectively. At Mandaya,
the structure will have a crest length of approximately 1400m and
a volume of 13Mm
3
, and at Beko Abo the comparable gures are
880m and 10.5Mm
3
.
Bids are being sought by 31 August to undertake the geotechnical
site investigation works for the studies underway for each project.
The Beko-Abo and Mandaya plans are complementary to the
NVE’s technical support to MoWR for the Blue Nile measure-
ment studies, which are part of the Joint Multipurpose Programme
Identication Phase 1 (JMP1 ID) that is to develop an optimum cas-
cade scenario.
GENALE-DAWA
Planning for development of the water resource of the Genale-Dawa
river basin comprises studies for six potential projects ranging from
irrigation (Lower Genale, Welmel), water supply (Negele Yabelo) and
multipurpose hydropower (GD-3) to an integrated watershed man-
agement project (Bonora).
The studies are being advanced by MoWR, and planning has been
underway over much of the last decade. The bulk of funding for the
early studies was provided by the African Development Bank (AfDB),
and the work was mostly carried out by consultant Lahmeyer with
local rm Yeshi-Ber Consult. A separate task, to accelerate planning
for the 357MW GD-3 project, was performed by consultant Ardico-
Rodio through government resources.
In addition, Norwegian consultants Norplan and Norconsult
undertook a feasibility study for the GD-6 multipurpose hydropower
project, which is estimated to have an installed capacity of approxi-
mately 257MW in a surface powerhouse, an 18km long headrace
tunnel and require a 39m high RCC dam. It is expected to generate
1230GWh of electricity annually.
AfDB notes that there have been expressions of interest from poten-
tial investors from Turkey, Japan and China for both the GD-3 and
GD-6 projects and that they are ready for investment. It further notes
that the Ethiopian government, in addition to fast-tracking the hydro
projects, is pushing for rapid development of the Welmel irrigation
and Negele water supply schemes, although it is the Lower Genale
project that is furthest in the requirement for immediate investment.
The Genale-Dawa basin is estimated to have economically exploita-
ble hydropower energy potential of 15.7TWh annually, says MoWR.
GIBE CASCADE, BELES
The largest hydropower project under construction in Ethiopia is
Gilgel Gibe III, the latest – though it won’t be the biggest – addition
to the cascade development on the Omo-Gibe basin, which is one of
the signicant water resources in the country. There are four Gibe
projects in the cascade and they constitute one of the country’s most
attractive hydro developments, says EEPCo.
Gilgel Gibe III will have a surface plant with an installed capacity
of 1870MW and housing 10 Francis turbines, which are to generate
about 6400GWh of electricity annually from the reservoir that is be
impounded by a RCC dam (231m high, 580m long). The average net
head is 186m, the design ow is 950m
3
/sec and the plant load factor
is 0.46. Extensive studies were undertaken to examine the environ-
mental impact of the scheme and potential mitigation measures.
The dam and powerhouse are being built approximately 155km
downstream of the Gilgel Gibe II plant, which has an installed capac-
ity of 420MW and recently became operational, although there’s a
short-term outage to clear and repair a rockfall blockage in the head-
race tunnel. It is to generate 1635GWh per year.
Gilgel Gibe I was smaller again, but still a large development, at
184MW and generating 722GWh per year.
Planning is continuing for the Gilgel Gibe IV project, which will be
the farthest downstream in the cascade. It is estimated the plant will
have an installed capacity of 2GW and generate 8000GWh annually.
Also under recent development is Beles, which involved signicant
tunnelling works, like Gilgel Gibe II. The plant capacity is 460MW
and it will tap the waters of Lake Tana, and so be one of the furthest
upstream of hydro plants along the Nile.
IWP& DC
28 AUGUST 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
GATES
T
HIS project details the design and development of a port-
able milling machine and the innovative process that
will be used by the Army Corps of Engineers (USACE)
to machine, drill and tap the four quoin blocks that are
positioned between the Markland lock walls and doors. By using
the portable milling to machine the quoins in situ, USACE will
signicantly shorten the machining time and reduce the overall
costs of future repairs, making it possible to replace lock quoins
more efciently. This method of machining represents a paradigm
shift in the way quoins are repaired or replaced, but promises to
be a best practice for changing worn and corroded parts on other
locks on waterways.
PROJECT BACKGROUND
The Markland locks and dam are vital to the Ohio River navigation
system in the US. Over the past ve years, it passed an average of 55M
tons of commodities annually. The project is located 5.6km down-
stream of Warsaw, Kentucky. USACE operates and maintains the locks
on this inland waterway out of its Louisville, Kentucky District ofce.
Lawrence E Rentz and Karl Williams from Climax Portable Machine Tools report on the design
of the portable milling machine that will be used at the Markland locks and dam in the US
On-site machining at Markland
Climax tests the linear mill on a mock-up of the lock gate
WWW.WATERPOWERMAGAZINE.COM AUGUST 2010 29
GATES
The main lock chamber has clear dimensions of 33.53m x 365.76m
and the auxiliary lock 33.53m x 182.88m. Each lock has two doors –
an upstream and downstream pair – which are 19.81m x 2.13m, each
with two quoin blocks. In both cases the doors close against a slightly
concave surface and seal up to prevent excess water from entering the
locks. The pivot point in the door is slightly back and has support arms
on the top and a pintle hemisphere at the bottom.
The Markland locks are more than 50 years old and because its
doors’ quoin blocks are made of carbon steel material, they experi-
ence corrosion. This corrosion causes the door seals to close improp-
erly resulting in a substantial amount of water leakage. As a stop-gap,
USACE has traditionally repaired corroded quoin blocks by putting
epoxy materials on the face of the blocks to build them back up so
they meet the door again. Alternatively if these blocks were to be
replaced, the Army Corps would cut out a very large piece of the
concrete and remove that material, weld in new quoin blocks and
then re-cast around the blocks with concrete, similar to original
construction.
Because the old process could take months, USACE sought a better
way to repair and replace the quoins and issued a request for pro-
posals. Its rst criteria was for the best technical and more efcient
method for machining the carbon steel quoin blocks so that they
could easily be unbolted and replaced with stainless steel ones that
resist corrosion and last longer. Secondly, any new machining method
had to enable USACE machinists to do the work in the shortest
amount of time, eliminating the need for a long term shutdown.
A PARA DIGM SHIFT
Out of all the responses, USACE found in Climax’s proposal a para-
digm shift to the current method used to repair quoins. Climax pro-
posed to design and manufacture a portable, custom-made vertical
milling machine that would enable USACE’s machinist’s to machine
the quoins in situ. The machine would be delivered and set up at
the Markland locks, then be attached to the lock wall. It would be
capable of travelling up to 21.34m in height in a single pass, removing
up to 63.5mm of metal material over multiple passes. The machine
would also drill and tap the quoin blocks. Using this method, the
entire job could be completed within a 17-day period.
In situ machining has been used successfully throughout the power
industry and for infrastructure maintenance and repair when critical
pieces of heavy equipment are too large or impractical to disassemble
and ship offsite to a machine shop. Climax engineers were condent
they could build a custom milling machine precise and powerful enough
to do the work in the time allotted. They provided proof of similar suc-
cessful in-situ machining projects such as line-boring the bushings on
the wicket gates at the Hoover dam, then demonstrated how a similar
machine operated, and was ultimately awarded the job.
At the Markland locks there are two different styles of quoin blocks
– an extended design and an embedded design. The extended blocks
are 203.2mm wide and protrude 76.2mm from the lock wall. The
milling machine will remove metal 63.5mm x 203.2mm. It will also
drill and tap holes as specied by USACE so the machinist can bolt
the replacement pieces on.
The second style is a 254mm wide embedded block design that
protrudes about 12.7mm from the wall. The milling machine will put
a pocket into this area – cutting a 203.2mm x 63.5mm deep slot in
the existing quoin block. Drilling and tapping will also be done so the
replacement quoin blocks can be bolted into the lock walls.
The portable linear mill was specically designed to work on both
embedded and extended quoin blocks.
DESIGNING THE PORTABLE LINEAR MILL
Climax collaborated with USACE throughout the linear mill’s design
process, conducting both a 30% design review and then another when
the machine’s design plans were completed. In addition, alternative
control and alignment systems were discussed and selected. There were
some technical risks associated with being able to move the machine
at across sections of beds that had interlocking devices. These too
were discussed to ensure that the nal product t the project’s needs.
The portable milling machine developed for USACE was modular
for easy transportation and assembly at the job site. It consisted of
six 4m long sections that connect end-to-end. The milling machine
consisted of two separate sleds – a utility sled that houses the electrical
and power components, and a machining sled. These sleds would be
attached to each other. Dual rack and pinion drives using the NEXEN
roller-pinion system were proposed to drive the machine vertically up
and down the entire length of the lock doors. Servo-mechanisms were
used for position control and to eliminate machining errors.
Its heavy duty beds are extremely rigid to provide precision mill-
ing within a +/- 7.6mm tolerance. A robust spindle design provides
the power to utilize 203.2mm diameter cutter heads. Its user-friendly
wireless controls included a wireless antenna that communicates to
the device and a touch screen interface that is used to manage the
entire machine’s programmed functions. The system operates for up
to six hours, and a battery charger was also provided.
TESTING AND TRAINING
Before the portable milling machine could be delivered USACE
required a factory acceptance test during which Climax had to dem-
onstrate all the capabilities of the portable milling machine and its
ability to meet all the functional requirements of the job. An extensive
functional test requirement procedure was conducted by Climax at
its facility. This procedure included a mock-up of the lock wall, test
blocks and surrogate quoins that were machined to demonstrate how
the portable mill would operate in the eld.
During this time, USACE requested some changes to the machine such
as revising the drilling and tapping head from a horizontal to a vertical
orientation for better reach. These changes were easily made and the
milling machine was retested and passed the stringent acceptance test.
At the same time, seven members of USACE’s team were also
trained by Climax on how to set-up and safely operate the machine
since they would be doing the actual work.
COMPLETING THE REPAIR
All the components of the portable milling machine were delivered in
June 2010. The machining is scheduled to take place in 2011.
USACE’s machinists will take about 7-8 days to set-up the machine,
three days to do the actual machining, and 4-5 days to dismantle the
equipment. To install the machine, USACE machinists will set down
the rst bed section on the concrete oor of the lock then drill and
mount it to a concrete wall adjacent to the quoin blocks.
A laser system supplied with the machine will be used to indicate
if and where the machine is out of alignment, and then a series of
individual jacking screws will be used to adjust the mill to within a
tolerance of 0.5mm to ensure that the beds are straight and at. Once
the rst section of the mill is levelled up, other sections will be added
and aligned until the machine is ready to operate. The operator will
use the wireless controls to drive the milling machine vertically up and
down, enabling them to hold a very tight +/-7.6mm overall machining
tolerance over the entire 619.81m length of the door.
EFFICIENT A ND COST-EFFECTIVE
The expected outcome of the repair is that USACE will have the ability
to repair or replace the quoin blocks more efciently and cost-effectively
by just unbolting and replacing the blocks whenever wear and corrosion
necessitate a change-out. In addition, replacing the carbon steel blocks
with stainless steel ones that are more corrosion resistant will greatly
extend the mean time between repairs and replacement.
The authors are Lawrence E Rentz, Vice President of
Engineering/Quality and Karl Williams, Senior Design
Engineer at Climax Portable Machine Tools.
More information can be found at www.cpmt.com
or via email at info@cpmt.com
IWP& DC
30 AUGUST 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW HYDRO DEVELOPMENTS
S
UDAN is blessed with the largest supply of fresh water in
the eastern Africa region. However, with an annual growth
rate of 2.8%, it is also considered to be one of the least
developed countries. At the backbone of the Sudanese econ-
omy is its agricultural sector which determines to a great extent
economic performance.
Seventy percent of the country’s 40M population live in rural areas
with electricity only providing a small percentage of energy needs.
The main energy sources are wood fuel and petroleum. Hydropower
supplies about 50% of electricity.
Like many tropical countries, Sudan has ample water resources
that can be efciently exploited in a manner that is both protable
and sustainable. Small hydropower offers cost-effective and environ-
mentally friendly energy solutions for Sudan, with the added benet
of providing sustainable livelihoods in rural areas. The use of hydro
energy resources could play an important role in this context. It rep-
resents an excellent opportunity to offer a higher standard of living to
the local people and will save local and regional resources.
WATER AND POWER RESOURCES
Annual average rainfall in Sudan ranges from about 1mm in the
northern desert to about 1600mm in the equatorial region. The
total annual rainfall is estimated at 1093.2 x 10
9
m
3
. The Ministry
of Irrigation and Water Resources (MIWR) is in charge of water
resources and total water storage available at all dams is 18km
3
.
Sudan’s installed capacity on the grid is 640MW, of which about
520MW is available. The country has a generation and transmis-
sion programme, according to which total capacity will increase to
3383MW in 2016.
Some of the major hydro plants in operation are: Roseires (280MW)
and Sennar (15MW), both on the Blue Nile, Rumela (20MW) and
Khashm El Girba (13MW), on the Atbara River. However, in May
2010, Sudanese President, Omer Al-Bashir, inaugurated a fth project.
The Merowe hydropower station had swung into operation earlier in
the year after completion of the tenth Francis unit, and the addition of
1250MW of capacity to the national electricity network.
The scheme has been described by Sudanese ofcials as a great
accomplishment and good evidence of genuine development in the
country. The generation of 600GWh of electricity annually will boost
different agricultural, industrial and services sectors in the country.
It will also help to enhance living conditions and bolster the develop-
ment process in Sudan, especially in the northern states.
Up to 2000MW of hydropower capacity could also be developed in
The development of hydropower resources in Sudan
will help meet increasing energy demands. New hydro
plants, both large and small, will play their role along
with untapped power potential at existing structures
Sudanese
development
Hydropower for existing dams
Raising Roseires Dam
The Roseires Dam is located on the Blue Nile about 500km southeast of the
Sudanese capital of Khartoum. The 280MW hydroelectric plant supplies nearly half
of Sudan’s power output, and also provides irrigation water for the Gezira Plain.
The Nile rises dramatically in the ood season between July and September when
the dam’s ve massive sluice gates are opened, allowing silt to ow down the
Nile and to avoid siltation of the reservoir. Since the dam’s completion in the mid-
1960s the steel lining of the gates has become corroded. To date repair work has
been undertaken at the three of the dam’s ve gates.
As of June 2010 work was progressing rapidly on a project to raise the height
of Roseires dam. The project has been undertaken to increase the dam height
by 10m and storage capacity from 3Bm
3
to 7.3Bm
3
. This is set to double
power capacity at the project. In addition it will also double generation at the
15MW Sennar dam on the Blue Nile, as well as increase the power potential at
the 1250MW Merowe hydro station.
Concrete works at the project for Roseires Dam are reported to be 34% complete
and the daily landll rate has increased to more than 40,000m
3
. Good project
progress is important as a number of engineering works have to be implemented
before the rainy season starts; as the accompanying increase in humidity will
subsequently stop the work. The project is set for completion by mid 2013.
Hydromatrix solutions
Jebel Aulia dam is southwest of Khartoum. Built in 1937 its original purpose
was for irrigation. However the dam has since been equipped with Hydromatrix
turbines to utilise power potential at the existing structure.
VA Tech Hydro (now Andritz Hydro) was awarded a contract in December
2000 to equip the dam with 40 Hydromatrix modules. Each of these has
two turbine generating units which were installed in front of the existing
discharge openings on the dam. The project was divided into lots. The rst was
commissioned in 2002 with the project becoming fully operational in 2005.
The Jebel Aulia is now a 30.4MW hydropower project which generates 116GWh
annually, producing US$80M of income a year for the Sudanese economy.
Jebel Aulia dam area
Site of Merowe dam
Merowe community