Water Power and Dam Construction

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IWP& DC

as well as doubling overall US hydro power

capacity by 2025. These goals would posi-

tion the industry to meet President Obama’s

call to double renewable energy generation,

as well as keeping the industry’s focus on

important policy areas.

“I’d argue that the industry enjoys more

opportunity now than we’ve had since the

time of the Great Depression,” Munro said,

referring to the growing interest in Congress

and the Obama administration in water

power issues. “I wa nt to leverage this

momentum to reach our goals.”

According to Church Ciocci, these goals

not only signal NHA’s course over the next

INSIGHT

WWW.WATERPOWERMAGAZINE.COM JULY 2009 11

and increme ntal hydro power projects, as

well as th e potential for powering non-

powered dams.”

PPORTUNITIES TO GROW

Other events throughout the week included

sessions on hydro-wind integration, devel-

opment issues, research priorities, new tech-

nologies, and legal and regulatory issues.

NHA a lso sponsored a post-co nference

forum on non-federal hydro development at

federal dams.

“All of these issues speak of the many

opportunities the indus try has to grow,”

Church Ciocci said. “Focusing on growth –

and moving beyond the issues that ha ve

slowed development in the past – is a refrain

we heard from legislators and industry lead-

ers. Mark Crisson - President and CEO of

the American Public Power Associati on;

Glenn English – CEO of the National Rural

Electric Cooperative Association; and Tom

Kuhn – president of the Edison Electr ic

Institute, reiterated this during our opening

plenary session too: Now is the time for us

to expand.”

NHA’s leadership also put a strong

emphasis on growth. The organi sation

applauded the achievements of Hydro Green

Energy, which secured the first commercial

hydrokinetic licence this year, with its pres-

tigious President’s Award, and announced

that longti me industry developer and

Brookfield Ren ewable Power executive

David Youlen will receive this year’s

Henwood Award.

Addressing the member ship in his new

role as NHA’s 2009-2010 president, Grant

County PUD’s Andrew Munro also focused

on growth and set out an aggressive course

for the industry.

“I believe we’re standing at a critical junc-

ture, where the hydro industry ’s benefits

align with o ur country’s most pressing

needs,” Munro said. “We must take bold

action…str ike now while our interests are

the public’s interest.”

Munro went on to challenge the industry

to double the total megawatts of new hydro

power projec ts before FERC and the

number of jobs in the US industry by 2012,

year, they also focus energy building within

he industry.

“I think Andrew Munro’s speech and the

challenges he set out are in tune with the

industry’s i nterests and directions today, ”

she said. “Throughout the conference, we

could feel a tremendous sense of energy and

momentum from both our attendees and

speakers.”

Church Ciocci pointed to the conference’s

strong attendance figures as a clear indica-

tor of the entire sec tor’s inter est in hydro

power. “Despite the travel restrictions many

companies a re facing, budget freezes, and

even the swine flu scare, we saw attendance

increase almost 50% over la st year,” she

said. “I think people were really looking to

NHA and the conference to see how we can

move forward as an industry.”

She believes that the conference helped

capture that for the atten dees. “There’s

a growing understanding that this is the

time for hydro po wer to shine,” she said.

“Hydro power offers the energy, environ-

mental, and economic benefits policymakers

around the world are seeking, so it’s

our duty as an industry to capitalise on

the opportunity.”

Left: NHA 2008-09 President, Richard Miller

presents Senator Maria Cantwell with the

Legislator of the Year Award

New leadership and board

Thee National Hydropower Association installed its new member president, officers, and board members

on the final day of the association’s annual conference in Washington, D.C. “We’re pleased to have such

a strong executive committee and board, which I think will carr y on in the productive, effective direction

the outgoing officers and board have established,” said NHA Executive Director Linda Church Ciocci. “Its

composition reflects the professional and regional diversity we find throughout the hydro power industr y,

and I am confident about the association’s direction under this new team.”

At its Januar y 2009 meeting, the NHA Board elected the following officers:

• President – Andrew Munro, Grant County Public Utility District

• Vice President – John Dulude, Normandeau Associates, Inc.

• Treasur er – Gregory Lewis, Duke Energy Corporation

• Secretary – David Moller, Pacific Gas and Electric Company

The officers will serve a term of one year, until the installation of new officers at NHA’s 2010 conference.

“I’m very proud to take the reins from the 2008-9 NHA President Rick Miller,” said Munro. “With hydro’s

recognition in the stimulus plan and increased funding for water power research in the federal

government, Rick and his team have made great strides in securing hydro power’s role in our energy,

environmental, and economic policies.”

NHA is also welcoming five new members to its Board of Directors. They are:

• John Claybrook, North American Phoenix-Energy Services

• Jim Crew, Alabama Power

• Tim Oakes, Kleinschmidt Associates

• John Ragonese, TransCanada

• Ed Schild, Puget Sound Energy

In addition, five new members will join the Advisor y Board:

• Dan Adamson, Davis Wright Tremain LLP

• Jessica Matlock, Snohomish County PUD

• Cherise Oram, Stoel Rives LLP

• Michael Perry, AMP-Ohio

• Rennie M. Singletary, Santee Cooper

“We have great leadership and a great board in place,” Church Ciocci said. “I’m looking forward to

working with them and continuing in our effor ts to support the growth and development of America’s

lar gest renewable energy resource.”

12 JULY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

OPERATION & MAINTENANCE

mated by adjusting the basic flow record on the basis of drainage area

(1530km

at the gauge and 1528.5km

at the intake), resulting in a

long-term Mean Annual Discharge (MAD) estimate of 31.85m

/sec.

Not all the water in the river is available for power generation; a

prescribed minimum must be left in the river at all times to protect

its health, primarily the fish. These so-called Minimum Instream Flow

Requirements (IFRs) vary from project to project and with time of

year. They have been set for Aberfeldie as 0.25m

/sec for December

to March, 0.5m

/sec for April, May, October and November and

/sec for June to September. Table 1 is a summary of project

details and Figure 1 a general arrangement plan of the project.

PTIMIZATION EXERCISE

Prior to engaging KPL, BC Hydro had performed its own studies to

determine the optimum capacity for the new development. KPL’s

first task was to confirm BC Hydro’s conclusions. The optimisation

exercise proceeded as follows:

• A decision was made to locate the new powerhouse adjacent to

and downstream of the existing one rather than at a new site some

250m upstream.

• It was determined that the possible incorporation of a rubber dam

on the existing Aberfeldie Dam spillway crest was not cost-effec-

tive (the extra head and energy did not justify the cost).

• For each of three chosen capacities (20, 25 and 30MW) the Low

Pressure Conduit (LPC or low pressure section of the waterway)

was first optimised to find the greatest benefit/cost of various pipe

sizes and types, comparing the capital cost of the installed pipe

(and bulk bench excavation where appropriate) with the value of

the average annual energy generated (the net head at the turbines

depends on the friction lost in the waterway).

• The High Pressure Penstock (HPP or high pressure section of the

waterway) was then sized one diameter smaller than the optimized

LPC, for each capacity.

HE Aberfeldie Hydroelectric Project on the Bull River in

Southeastern British Columbia, Canada, is owned by the

provincial power utility, BC Hydro. The original 5MW

facility was constructed in 1922, with water for power gen-

eration diverted from the river with a small timber crib dam and

transported via woodstave conduit and steel penstock to a power-

house where it was then returned to the river. The original dam was

replaced with a larger concrete gravity dam in 1953, constructed fur-

ther downstream, between the original intake and the powerhouse.

BC Hydro decided in the early 2000’s that the facility had reached

the end of its useful life (in particular the woodstave conduit and

much of the electro-mechanical equipment) and initiated the rede-

velopment project. This started with an exercise to determine the

economic optimum size for the facility, followed by geotechnical site

investigations and detail design and construction of a completely

new facility (with the single exception that the 1953 dam remains).

In a departure from tradition, consulting engineering was outsourced

by BC Hydro to a team headed by Knight Piésold Ltd (KPL) of

Vancouver, assisted by subconsultants Amnis Engineering, Gygax

Engineering Associates, Rutter-Hinz and JM Bean and Co. Ltd. One

of the aims of the outsourcing was to familiarize BC Hydro with the

work being done by private sector independent power producers in

BC. Construction was done through conventional design-bid-build

contracts: main (civil) works by contracto r Western Versatile

Construction Company and generating equipment by contractor VA

Tech Hydro (now Andritz) . Constr uction is presently essentially

complete, with all three horizontal Francis turbines now in service.

The official opening was held on Friday 12 June 2009.

Water Survey of Canada has maintained a flow measurement gauge

on the Bull River immediately downstream of the point of discharge

of the powerhouse tailrace, with a period of record in excess of 90

years. This provided a very good basis for reevaluating the hydro

power potential of the project. Flows at the intake location were esti-

Michael J Robertson of consulting engineers Knight Piésold discusses the technical aspects

of a project to redevelop BC Hydro’s Aberfeldie hydroelectric project, including the

optimization exercise, geotechnical investigations, hydraulic model studies of possible

sediment excluders, removal of the old components and replacement with new

Waterway headworks

Dam

Aberfeldie

Reservoir

Surge tank

11kV powerline

to intake

6.9kV powerline

Switchyard

Tailrace

Powerhouse

Public Road

Water conveyance

system

alignment

Road bridge

over penstock

Access road

5 4

4 2

Modified intake

structure

R edeveloping Aberfeldie

Below: Figure 1 – Project General Arrangement Plan

WWW.WATERPOWERMAGAZINE.COM JULY 2009 13

• This was followed by the optimisation o f the turbine-generator

machine arrangement for each capacity, using the relevant opti-

mised waterway. Combin ations considered were two equal

machines, three equal machines, four equal machines, two equal

machines and one smaller machine, and two unequal machines.

Horizontal axis Francis machines were assumed throughout.

Comparison was on the basis of a Modified Unit Energy Cost

(UEC), also incorporating estimates of the cost of the intake mod-

ifications, the powerhouse and other relevant data provided by BC

Hydro. The UEC was ‘modified’ to reflect the fact that the value

of energy generated differs from month to month.

• Modified UE Cs were compa red over the ran ge of capacity and

machine options, for a range of discount rates.

The study concluded that the Aberfeldie Project could be redevel-

oped with a capacity anywhere between 20 and 25MW, using three

equal sized horizontal axis Francis turbine-generators, without sac-

rificing any significant cost effectiveness. BC Hydro chose to rede-

velop on the basis of the 25MW option.

It was determined that with this optimised arrangement the pro-

ject will produce an average of 105GWh of energy per year, corre-

sponding to a plant capacity factor of approximately 48%.

EOTECHNICAL INVESTIGATIONS

Geotechnical i nvestigations were undertaken in 2005 to provide

foundation data for the design of the new facilities – modifications

to the existing intakes at the Aberfeldie Dam, and construction of a

new LPC, Surge Facility, HPP, Powerhouse and Switchyard. The site

had also been investigated by KPL in 1990; the 2005 investigations

incorporated those findings.

The 2005 investigations comprised:

• Three boreholes, four seismic cone penetration tests and one hand

excavated test pit at the location of the proposed powerhouse.

These holes were undertaken in order to establish ground and

groundwater conditions for the geotechnical design.

• Three machine excavated test pits and one hand excavated test pit

along t he pipel ine alignment in order to investigate further the

nature and extent of organic soils identified in the fill platform in

the 1990 investigation and to assess the downslope inclination of

the rockhead surface.

• Three machine excavated test pits at the location of the proposed

waterway headworks structures immediately downstream of the dam.

The investigations concluded that:

• At the site of the proposed powerhouse, the bedrock is overlain by

a succession of alluvial and glacial deposits, which become thick-

er towards the Bull River. Subsequent seismic and differential set-

tlement analyses of these superfic ial deposits confi rmed the

viability of a raft foundation solution for the proposed power-

house. There was particular concern about possible seismic lique-

faction of zones of cohesionless sand in the alluvium. Groundwater

control during construction was identified as another significant

issue, as was the possible impact of excavation works upon the

stability of the adjacent natural soil slope.

• The ground conditions along the LPC alignment generally provide

adequate founding material. However, there were sections identi-

fied where t he existing woodstave pipeline had settled differen-

tially due to uncompacted and/or saturated gro und. The

investigation also confirmed the presence of unsuitable founding

material in the form of topsoil that was covered by fill pla ced

during the original construction. All adverse foundation materials

were removed and replaced with suitable fill. Significant volumes

of rock were confirmed towards the end of the LPC, with some

unstable sections in existing cuts.

• The rock in the face behind the powerho use terrac e, extending

through the surge tank site at the top of the cliff and the end of the

LPC, comprises moderately strong to strong sandstone and weak

to moderately weak siltstone. The investigations revealed unsta-

ble sections of the natural rock slopes that would need to be (and

later were) stabilized.

ESIGN DETAILS

Intake

Water enters the waterway through intakes in the Aberfeldie Dam.

The old scheme was fed through one intake, with a design flow of

approximately 8m

/sec. Provision was also made during construc-

tion of the dam for a second intake, which was effectively left

blanked off. These two intakes were modified so that each can take

approximately 20m

/sec. Modifications included:

• a new trashrack on the face of the d am, together with an auto-

matic raking machine;

• retention of the existing single set of stoplogs, supply of a second

set and refurbishment of the slots into which they are designed to

be installed;

OPERATION & MAINTENANCE

Table 1: Summary of Project Details

ITEM DESCRIPTION

Project Owner / Client BC Hydro

Water Source Bull River

Catchment Area at 1528.5km

Intakes

Mean Annual Flow 31.85m

/sec (20.83 l/s/km

)

at Intakes

Maximum Design Flow 38.5m

/sec

Gross Head 83.9m

Project Operation Run-of-River

Maximum Power Capacity 25MW

Instream Flow 0.25m

/sec December to March

Requirements(IFR’s)

0.5m

/sec April, May, October and November

/sec June to September

Capacity Factor 48%

Average Annual Ener gy 105GWh

Intakes Existing intakes in Aberfeldie Dam, one originally in

service, one blanked off, modified to produce two

identical intakes of 19.25m3/sec capacity.

Water way Low Pressure Conduit (LPC) ~850 m buried 3.35m

(132”) dia. Weholite HDPE plus ~150m surface-

mounted 2.9m (114”) dia. steel pipes.

Steel surge tank 15m high 13m dia. at junction of

the LPC and HPP.

150m long 2.74m (108”) dia. steel High Pressure

Penstock (HPP) down cliff face immediately behind

powerhouse.

Turbines 3 x 8.33MW horizontal axis Francis

Generators 13.8kV direct-coupled synchronous

Powerhouse Concrete substructure, steel superstructure

Switchyard At powerhouse, step-up 13.8 to 66kV

Transmission Line None – direct connection to grid at switchyard

Design Earthquake BC Building Code - 1:2,500 event

14 JULY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

OPERATION & MAINTENANCE

• new head gates on both intakes, capable of remote and automat-

ic hydraulic operation;

• removal of the existing steel pipe and replacement with a larger

new one in the existing intake, and installation of an identical new

pipe in the originally blanked-off intake; and

• a vortex suppression device upstream of the intakes and/or in the

stoplog and gate slots, if this should prove desirable when tested

during operation.

The modified intakes were included in a physical hydraulic model,

as discussed in the following section.

Photos 1 and 2 above are general views of the dam and intake

before and after the redevelopment and Figure 2 below is a schemat-

ic cross section after redevelopment.

Sediment excluder

The Aberfeldie Reservoir is filled with sediment and can no longer trap

most of the sediment being transported by the Bull River. As the water

abstracted for power generation will therefore contain some entrained

sediment and this will subject the waterway and generating and other

equipment to abrasion, an attempt was made to design a sediment

removal facility at the head of the waterway. Knight Piésold has designed

a number of run-of-river intakes for hydroelectric projects based on the

opportunistic use of a lateral draw-off trough and submerged weir in the

intake structure to pass the necessary IFR flows. We have found that the

horizontal vortex induced by this design can result in 90% or more of

the entrained sediment being discharged with the IFR flows rather than

going on through the penstock, although it has to be said that the results

are largely qualitative and the whole sediment delivery and transport

process is difficult to predict and model with any quantitative accuracy.

It was originally anticipated that the Aberfeldie sediment exclusion

structure would be provided immediately downstream of the dam and

the modified intakes, on the bench of the existing pipeline. The struc-

ture was envisaged as a large open box, collecting the flow from the

two inlet pipes, and passing it through a horizontal vortex sediment

removal device and over a submerged weir before it enters the LPC.

The discard flow from the structure would have provided the IFRs.

A physical hydraulic mode l was const ructed to investigate this

structure. It consisted of the existing dam, the proposed modifica-

tions to the existing intakes and the proposed sediment exclusion

structure, to determine final hydraulic design details for these struc-

tures. The model showed that the sediment excluder was only par-

tially successful in removing the sedime nt and tha t a significant

proportion still went through to the turbines. BC Hydro therefore

decided that it was not cost-effective to incorporate the excluder.

The head of the waterway was therefore changed to a steel pipe wye,

with offtakes in the bottom of both legs to provide the IFR flow

return. The bottom offtakes will also trap and divert the larger sized

portions of any sediment that is drawn into the intakes.

Sediment entrainment and abrasive equipment wear will be min-

imised through good operation (including, for example, cl osing

down the turbines during large floods, when the flood waters are

carrying high sediment concentrations). It was also noted, however,

that the old turbine runners showed comparatively little abrasive

erosion for their age, probably because of the nature of the sediment

and the relatively low operating head on the turbines.

The site investigation included the excavation of a number of test

pits at the proposed site of the sediment exclusion structure. A ll

Trash rack

cleaning

machine

Weir

Normal

operating

water level

Control gate house

Vent shaft

Intake structure

Concrete support

structure

Steel wye pipe

Bedrock

Concrete transition

structure

low pressure

conduit

Interlocking concrete

block wall

Steel pipe

head gate

Trash rack

Figure 2 – Cross section of Aberfeldie Dam

and redeveloped intake

Photo 1: Dam and intake before redevelopment Photo 2: After redevelopment

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16 JULY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

revealed so lid rock wi thin approximately 1.5m of the exi sting

ground surface.

Waterway including surge facility

The waterway comprises the following main components:

• Headworks immediately below the dam where the two outlet pipes

join in a wye at the head of the waterway – as discussed earlier.

• A Low Pressure Conduit (LPC) consisting of approximately 850m

of buried 3.35m diameter Weholite HDPE pipe together with

approximately 150m of surface-mounted 2.9m diameter steel pipe,

the latter including two gulley crossings. Weholite is a structured-

wall lightweight pipe manufactured as a speciality product by KWH

ipe, Canada. Photos 3 and 4 compare the original woodstave pipe

with the new Weholite HDPE pipe. The old woodstave surge tank

can also be seen in the background of Photo 3, and the new steel sec-

tion of the LPC in Photo 6. Figure 3 shows a typical cross section of

the buried LPC.

• A steel surge tank 15m high and 13m diameter at the junction of

the LPC and HPP, to cater for transient pressures and surges during

operation. The new surge tank can be seen in Photo 6.

• A 2.74m diameter continu ously welded steel High Pressure

Penstock (HPP) approximately 150m long down the clif f face

immediately behind the powerhouse. The pipe is laid as straight

as possible, on support pedestals, with appropriate thrust blocks

and movement couplings. It terminates behind the powerhouse in

a generating unit and emergency bypass distribution manifold. The

old HPP can be seen in Photo 5 and the new one in Photo 6. Figure

4 shows a typical cross section of the HPP.

The new waterway follows as far as possible the alignment of the

original, with the LPC on the same bench cut into the hillside and

the HPP basical ly following the same pat h down the cliff.

Exceptions are that the LPC had to be cut lower, to ensure that it

remains safely under the hydraulic grade line, and all the bends but

one in the HPP were removed.

Powerhouse

The powerhouse has been designed to house three identical Francis

horizontal axis turbine-generators procured through a ‘Water-to-

Wire’ generating equipment co ntract, along with the associated

Turbine Inlet Valves (TIVs) and other m echanical, electri cal and

hydraulic equipment. It also houses all the mechanical and electri-

al ‘Balance of Plant’ equipment. The machines are arranged ‘en ech-

elon’ to optimize the use of space and the hydraulics of the penstock

manifold. The building was set, in the vertical plane, primarily by

the level of the tailrace weir (to exclude the annual flood in the Bull

River) and the amount of submergence required by the turbines.

The substructure of the building is reinforced concrete, sized to suit

the dimensions and forces supplied by the generating equipment con-

tractor and the steel building superstructure, and to protect against

flotation. It is founded on the insitu alluvial deposits that the site inves-

tigation showed to be more than adequate for the purpose. A move-

ment joint is incorporated at the end of the HPP to allow for any

differential settlement that might occur between the powerhouse and

the HPP, which is founded on solid rock. The superstructure is a ‘pre-

engineered’ insulated steel frame building complete with full service

65 tonne gantry crane supported by the main structural columns. The

building includes control and washrooms and a service bay.

Photos 5 and 6 are external views of the old and new powerhouses,

together with the HPPs. Photo 6 also shows the new surge tank and

the end of the new LPC (the steel surface mounted section). Photos 7

and 8 are internal views of the old and new powerhouses. Figures 5

and 6 show the basic powerhouse plan and section respectively.

Emergency bypass facility

In the event of an electrical load rejection or any other event lead-

ing to a rapid closure of the turbines, there will be a lag time between

the sub sequent spill of wat er at the intake/dam and its arri val

OPERATION & MAINTENANCE

Access road

Drain outlet

pipe

Drain

Pipe bedding

General fill

Conduit

Penstock

Stiffener (Typ.)

Anchor bolt (Typ.)

Rock dowel (Typ.)

Below, top: Photo 3 – Old Woodstave low pressure conduit and surge tank;

Bottom: Photo 4 – New Weholite HDPE low pressure conduit

Below top: Figure 3 – Typical cross section of buried low pressure conduit;

Bottom: Figure 4 – Typical cross Section of high pressure penstock

WWW.WATERPOWERMAGAZINE.COM JULY 2009 17

OPERATION & MAINTENANCE

through the natural watercourse at the powerhouse tailrace. This

could result in fish being stranded until the rejected flow arrives. A

bypass facility is required to mitigate this possibility. The facility will

open immediately when the turbines start to close and will then close

(ramp down) slowly over a sufficient time period to allow the fish

to escape into the main river channel. Ramping of the units will also

be required when generation starts (ramping up). Ramp rates are in

the order of two hours between full flow and zero.

The bypass has been designed to be a separate facility adjacent to

the powerhouse as opposed to being incorporated inside the building.

Bypass design capacity was established by BC Hydro, in consultation

with Federal, Provincial and Local Agencies and other interested par-

ties, as 50% of the maximum design flow, or approximately 20m

/sec.

After much investigation of appropriate valves a wafer multi-port

valve designed and manufactured by Stealth was selected, with

backup/isolating butterfly valve and submerged diffuser. Water is final-

ly discharged over a weir into the powerhouse tailrace.

‘Water-to-wire’ generating equipment

The initial optimization exercise indicated that the ‘Water-to-Wire’

(WTW) generating equipment should be three identical horizontal-

axis Francis turbines direct-coupled to three identical horizontal-

axis salient-pole synchronous generators, operating with a combined

maximum design flow of 38.5m

/sec (12.83m

/sec each), and a gross

head of approximately 84m. WTW tenderers were given a table of

flows and net heads immediately upstream of the turbine inlet valves

and asked to complete Performance Guarantees for their equipment

based on the inlet conditions (i.e. guaranteed output MW for each

flow). Since the project operates run-of-river, with no storage, there

is effectively very little variation in dam water levels and subsequent

heads across the turbines.

The WTW scope of supply is summarized as follows:

Penstock

manifold

Turbine

generator

Tailrace tunnel

Tailrace channel

Stoplog slot

Bull River

Tailrace walkway

Turbine

inlet valve

Control

room

Turbine

unit #3

Turbine

unit #2

Turbine

unit #1

High pressure penstock Penstock manifold

Tailrace

Overflow

weir

Environmental

bypass facility

Figure 5 – Plan of new powerhouse

Figure 6 – Cross section of

new powerhouse

Above from top: Photo 5 – Old powerhouse and high pressur e penstock;

Photo 6 – New power house, high pressure penstock, surge tank and end of

low pressure conduit; Photo 7 – Inside old powerhouse;

Above: Photo 8 – Inside new powerhouse

18 JULY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

OPERATION & MAINTENANCE

• Upstream pipe extension: a 2m long piece of steel pipe designed to

be f ield fitted to the penstock manifold after installation of a ll

WTW equipment.

• Turbine Inlet Valve (TIV): a flanged, open-lattice type, high per-

formance butterfly valve, selected to match turbine inlet piping

and minimise head loss. Capable of eme rgency shutoff against

rated turbine flow.

• Franc is turb ine: horiz ontal-axis, overshot, overhung on

generator shaft.

• Generator: horizontal-axis, salient pol e, synch ronous, closed

circuit water cooled.

• Hydraulic Power Unit (HPU): one per generating unit.

• Generator switchgear/breaker: 13.8kV.

• Station service power supplies includ ing transformer and auto-

transfer switch, batteries and chargers, MCCs for equipment in

supplier’s scope, etc.

• Control and protection panel, including PLC, I/O and I/O cabi-

nets for unit control logic and synchronization, instrumentation

monitoring and data logging, etc. Includes provision for commu-

nication with works at intake (water level sensor, isolating gate

control, etc).

• Human-Machine Interface (HMI), consisting of PC-based annun-

ciation and display screens for alarms, set points and control vari-

ables, data logging and trending.

• Installation, erection and commissioning of all equipment.

Electrical/mechanical balance of plant

The main civil contract included the supply and installation of all

necessary mechanical and electrical equipment not included in the

WTW Contract. So-called ‘Balance of Plant’ includes:

• Site services (s ervice and potable water, septic and sewer

system, compresse d air, cooling water, dewatering systems, etc.,

as requi red).

• Building grounding system (up to individual equipment pigtails).

• Powerhouse AC power distribution to auxiliaries.

• Power and control cable tray layouts (including tray installation

details).

• Interconnection wiring diagrams for items outside of the generat-

ing equipment contract.

• Building lighting layouts and details.

• Powerhouse crane.

• Heating, ventilation, and air conditioning as required.

• Powerhouse internal and external communications.

• Wiring/cabling to switchyard.

• Electrical and control services at the intake

Switchyard and interconnection

The scope for the switchyard design included all systems and equip-

ment from the limit of the WTW Contract (the generator MV unit

switchgear) through to the interconnecti on with the existing BC

Hydro transmission line at the site.

ONCLUSIONS

The project has successfully achieved its overall objectives of deliv-

ering mor e generating capacity and energy to BC Hydro and the

people of British Columbia and it has done so in a cost-effective and

environmentally responsible manner. The old 5MW generating facil-

ity that ha d reached the end of its useful life has been completely

replaced with a 25MW facility and the average annual energy pro-

duction has gone from 34 to 105GWh. The redeveloped project is

operating successfully.

Michael J Robertson, Knight Piésold Ltd.,

Vancouver, Canada

mrobertson@knightpiesold.com

IWP& DC

Views of the original facility

A selection of photographs showing construction of the original

facility are included here for interest. Courtesy of BC Hydro

The original construction crew Woodstave penstock and surge tank

Woodstave penstockTurbine scroll caseTop of surge tank

Second dam

Old dam

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20 JULY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

OPERATION & MAINTENANCE

A more frequent and even worse problem is the grass content of

the river. Although the bar-width of the trash racks is quite amply

dimensioned, some grass enlaces the rack-bars and reduces the flow

rate. Because the grass could not be removed by a crane, divers had

to clean the trash racks several times a year. This laborious proce-

dure was extremely expensive because not only did the divers have

to be paid but the generators also had to be switched off.

To improve matters the operator of Rock Isla nd hydro project

decided to install a specifically customised TRCS to help increase

efficiency of the plant and simultaneously reduce labour costs.

TRCS

REQUIREMENTS

The TRCS had to be capable of:

• Cleaning all intakes at Powerhouse II.

• Removing all debris and discharging this onto a truck or a con-

tainer to be placed on the dam.

• Travelling on the existing rail system that is also used by the local

gantry cranes.

• Offering enough height clearance to avoid passing traffic – between

the rails of the rail system there is a road which is used by vehicles,

including large trucks.

OCK Island project was the first dam to span the Columbia

river in the US. The project is located near the geographi-

cal centre of Washington State, about 19km downstream

from the city of Wenatchee. It consists of two units.

Powerhouse I was constructed in 1933 and includes 11 generators.

Since 1979 Powerhouse II has eight additional horizontal shaft gen-

erators with a common nameplate capacity of 410MW. Both pow-

erhouses achieve a total power plant capacity of 62MW. The 1022m

wide dam also contains 31 spillway gates and three fishways.

RASH RACK CLEANING SYSTEM

At Rock Island, the Columbia River mainly contains two types of

floating debris: coarse materials like wood, trees etc that float on the

water surface; and fine material (mainly grass) dispersed in the water.

Coarse materials accumulate in masses before the intakes, where

they have to be removed. Without a trashrack cleaning system (TRCS)

this had to be done by one or more truck-mounted cranes. The disad-

vantage of this method was that every time debris had to be removed,

the crane and a truck onto which the lifted debris was discharged had

to be prepared. Another problem was the quite limited operating range

of the crane. To clean all intakes it had to be displaced several times.

German company Muhr, in partnership with its US distributor Lakeside Equipment

Corporation, has developed and installed the world’s largest trash rack cleaning system at

Rock Island dam in the US. Florian Kufner gives more details

Cleaning up

Hydronic M-5000 with retracted telescope and

cleaning rake. All images by Erhard Muhr GmbH

Water Power and Dam Construction - Issue July 2009

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