Water Power and Dam Construction. Issue September 2010

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32 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

REHABILITATE-operate-transfer (ROT) project cover-

ing seven hydropower plants was awarded to Hydropol

Project & Management AS through its Macedonian sub-

sidiary MacHydro Project Co AD in 2002. The project

includes construction of one new power plant, complete rehabilita-

tion of six power plants, and 11 years of operation of the project

with total installed power exceeding 38MW. The project includes

the following small hydropower plants of medium and high head

located across Macedonia: Dosnica, Kalimanci, Matka (new power

plant), Pena, Pesocani, Sapuncica, and Zrnovci. The core works

(construction works) on this project were completed this year.

BEFORE REFURBISHMENT

Most of the power plants in the ROT scheme were built in the rst

half of the 20th century. The only exception is the HPP Kalimanci

which was commissioned in 1970 together with the Kalimanci earth-

ll dam. The majority of the plants were operated without any major

modernisation or general refurbishment since commissioning.

Major repairs were performed only at Pena hydro plant (built in

1926) due to severe ooding in 1984. This repair included tunnel-

ling of a new derivation channel, outer penstock replacement, and

replacement of a major part of the electromechanical equipment.

After years of operation without major repairs, most of the electro-

mechanical equipment was far behind its exploitation period. State of

repair included heavily damaged turbine parts due to erosion, cavita-

tion and fatigue, heavy leaking of valves, signicant oil leaks through-

out the equipment, low generator winding insulation resistance etc.

Hydropol has been working on a

rehabilitate-operate-transfer (ROT) project

which covers seven hydropower plants in

Macedonia. Tomáš Cerný gives an insight

into the work which has been undertaken

ROT work in Macedonia

Below, left: Pesocani hydropower plant – Scope of civil works connected with

turbine exchange; Below, right: Zrnovci – Improvised support of penstock

valve counterweight

Description of sites

HPP Dosnica is located on the Dosnica River near to the town of Demir Kapija.

The water supply scheme consists of a weir with an alpine type intake and

sedimentation tank, a 10km long system of buried channels, tunnels, and

steel siphons overcoming one of the valleys. From the water chamber, a

600m long steel penstock leads to the powerhouse, where 3x2.2MVA, 6.3kV

generators are driven by Pelton single jet horizontal shaft turbines. The tailrace

channel supplies fresh water to a nearby sh farm.

HPP Kalimanci is located on the Bregalnica River near to the town of Delcevo.

It is part of the Bregalnica hydro system where Kalimanci earthll dam is

the main facility. This irrigation system provides water for 28,000ha in the

Kocansko and Ovce Pole regions, so operation of the dam and power plant

complies mainly with irrigation needs. HPP Kalimanci is thus the only power

plant not operated mainly in run-of-river mode. The plant has 2x6.8MW vertical

Francis turbines and is the largest power plant of the ROT project.

HPP Matka is located on the River Treska 14km away from the Macedonian capital,

Skopje. It was constructed in 1938 and has been in regular operation since then.

The dam is a reinforced concrete arch type 38m in height. There are three units in

the powerhouse of Old Matka (the original power plant) with Francis turbines with

a total discharge 19.5m

/sec. In 2005 HPP Kozjak was commissioned on the

upstream dam. With its large storage capacity and maximum discharge of 80m

sec, it is used as a peak load power plant. Such peaks could not be utilised by the

Old HPP Matka and thus large discharge uprating of the site was necessary.

HPP Pena is located on the River Pena near to the town of Tetovo. The plant is a

derivation type plant with a weir side intake facility, a 1km derivation tunnel, water

chamber, and a 120m long steel penstock. There are two unevenly sized (1.3 and

2.0MW) horizontal units with Francis turbines installed in the powerhouse.

HPP Pesocani is located on the River Pesocani near the town of Ohrid. A 4.9km

long derivation channel collects water from the main intake and two smaller side

intakes to an open water reservoir. Then, a 950m long steel penstock leads to the

powerhouse, where two synchronous 2.2MVA generators are driven by four single

Pelton jet turbines (two turbines per generator on each side).

HPP Sapuncica is located on the River Sapuncica near to the town of Bitola. It

is a derivation type plant with a small dam and side intake facility, a few smaller

side intakes, a 4.9km long buried derivation channel, water chamber, and a

1.85km long steel penstock. There are 2x1.6MW horizontal units installed in the

powerhouse with Pelton single jet turbines. The tailrace channel supplies water

directly to the main municipality drinking water treatment reservoir of Bitola.

HPP Zrnovci is located on the Zrnovka River near to the town of Kocani. It is a

derivation type plant with a weir and side intake facility. There are 2x0.85MW units

with single Pelton jet turbines installed in the powerhouse. A 3.4km long water

supply tunnel is used in the summer months as a water storage reservoir. This

enables operation of the turbine in optimal ow range in the morning and evening

hours, when the tailrace channel feeds water to the local irrigation system.

WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 33

UPRATING & REFURBISHMENT

The state of the power plants before the refurbishment can be illus-

trated by a few examples. Some of the equipment was not capable of

proper operation and of performing their safety functions – none of the

overow detectors were functioning, most of the penstock valves were

not capable of automatic or remote closing. Even simple automation

was not installed on most of the power plants, eg the level control of

the units was based on a water chamber level reading and communica-

tion over the radio between personnel. Before Hydropol oversaw the

rehabilitation of the plants, Zrnovci‘s average production of 5.2MkWh

barely covered operational costs involving 20 employees.

SCOPE OF THE WORKS

Generally, before refurbishment the power plants suffered from low

efciency, large maintenance requirements and an enormous number

of employees were involved in the operation. Therefore, general refur-

bishment and modernisation of the power plants became inevitable.

The key goals of the ROT project were as follows:

rIncrease the turbine efciency to state-of-the-art parameters.

r Uprate the utilisable discharge.

r Full automation of the operation.

rRemote control and monitoring of the operation.

The scope of works for the seven power plants was very wide. It started

with construction of the new HPP Matka (next to the original HPP

Matka) using the existing dam and modied water inlet tunnel; through

to rehabilitation of Pena and Pesocani accompanied with medium scale

civil works connected with the complete replacement of the units or tur-

bines; ending with the reconstruction of Kalimanci, Sapuncica, Dosnica

and Zrnovci, representing a typical technological refurbishment with a

small amount of civil works of auxiliary character.

Although the scale of works was different at each site, the scope

of rehabilitation of the electro-mechanical equipment was in general

the same for all power plants involved in the project. The list below

contains the typical scope of rehabilitation:

rNew or general overhaul of the turbine, including new runner,

guide vanes/nozzles, repair of bearings, new hydraulic actuation,

new or repaired shafts, new instrumentation.

rNew or general overhaul of the generator, including new magnetic

circuit and electric circuit of the stator, rewinding of the rotor,

repair of mechanical parts, and new instrumentation, including unit

speed metering sensors.

rNew hydraulically actuated penstock, turbine, and bypass valves

(buttery, ball, needle valves).

rNew high pressure hydraulic aggregate of the speed governor,

common also for turbine inlet valve and its bypass.

rNew lubrication and oil cooling system with focus on the minimisa-

tion of water pollution risk by oil.

rPiping works – new assembly joints and adjustment of the pipeline

and penstock parts for the new equipment, installation of valves.

rNew overhead travelling cranes in machine halls – electrically controlled.

rNew automatic intake technology, including new steel gates and

trashrack, new hydraulic controlled trashrack cleaning machine,

sedimentation tank level control and ushing.

Above, left: Kalimanci – Modern design GE Energy X-blade runner installation;

Above, right: Matka – Installed spiral cases and turbine valves; Left: Pesocani –

Turbine runner buckets

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WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 35

UPRATING & REFURBISHMENT

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Table 1: Comparison of parameters of the hydropower plants before

and after rehabilitation

Before rehabilitation

SHPP Dosnica Kalimanci Matka Pena Pesocani Sapuncica Zrnovci

Commissioning Year 1952 1970 1938 1926/84 1951 1952 1950

Installed Capacity [MW] 4.62 12.00 4.21 2.50 2.74 2.91 1.40

No. of Units 3 2 3 2 2 2 2

Turbine type

Pelton

horizontal

Francis

vertical

Francis

vertical

Francis

horizontal

Pelton

horizontal

Pelton

horizontal

Pelton

horizontal

Discharge [m3/sec] 2.1 18.0 19.5 4.0 1.2 0.8 0.8

Head [m] 232.7 80.0 24.5 72.0 291.1 412.0 215.0

After rehabilitation

Commissioning Year 2008 2006 2008 2007 2008 2007/2008 2009

Installed Capacity [MW] 5.28 12.48 9.60 3.30 3.52 3.20 1.76

No. of Units 3 2 2 2 2 2 2

Turbine type

Pelton

horizontal

Francis

vertical

Kaplan

vertical

Francis

horizontal

Pelton

horizontal

Pelton

horizontal

Pelton

horizontal

Discharge [m3/sec] 2.4 18.0 42.0 5.0 1.4 0.9 0.9

Head [m] 232.7 80.0 24.5 72.0 291.1 412.0 215.0

Unit peak efciency increase [%] 10.1 N/A* N/A** 10.7 9.3 12.9 10.6

*The measurement before rehabilitation was not performed. The peak measured value of turbine efciency form the site efciency test is 92.4%

** Completely new power plant was constructed. The peak measured value of turbine efciency form the site efciency test is 93.8%

Above, left: Pena – Spiral cases ready for installation;

Above, right: Sapuncica – Penstock incrustation

36 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

nal scheduling. As most parts were replaced completely or new main

turbine parts (runners, shafts, guide vanes/nozzles) were installed,

the only really lengthy repair was the overhaul of the generators.

Therefore, the schedule was modied to this situation and two gener-

ators were disassembled in the fall of 2007, rehabilitated, and assem-

bled back with the present turbines to catch the 2008 spring water.

When the water ow dropped in the beginning of summer, the third

generator and turbine were disassembled and sent for overhauling.

This schedule adjustment helped the economy of this particular reha-

bilitation as production losses were minimised.

For the shutdown during rehabilitation, the needs of the connect-

ed water consumer had to be considered. At Dosnica, the supply of

fresh cold water to the nearby sh farm through the buried diversion

channel could not be interrupted, even for one single day in the hot

Balkan summer. Therefore, overnight disassembly of the turbine inlet

pipeline had to be performed. A diversion pipeline from the penstock

directly to the tailrace was installed.

Local irrigation in Zrnovci village had to be maintained during

the shut-down. Based on an agreement with local farmers, a mobile

pump was installed into the river bed and water was pumped back

to the tailrace channel.

PERFORMANCE EVALUATION

In the preparatory phase of the rehabilitation, detailed performance

measurements were performed in order to assess the technical con-

dition of the equipment and establish real design parameters for the

refurbishment. From these measurements, unit efciency measurements

prior to refurbishment can be pointed out. This measurement not only

gives efciency data for future comparison, but also important infor-

mation about the whole pressure water system and gives the necessary

background data for design parameters of the new equipment.

HPP Sapuncica is a good example of such measurements. Its opera-

tional performance indicated signicant pressure losses in the pen-

stock. Among production losses due to lower head, decrease of the

turbine hydraulic efciency could be expected as the turbines worked

out of the design head range. After thorough investigation, enormous

incrustation inside the steel penstock was discovered.

This goethite blister-like incrustation of peak ca 20mm in height

was caused by the reaction of the steel pipe with highly oxygen-sat-

urated water. The incrustation was removed by a loosely inserted

abrasive cleaning tool being pushed down the penstock by water.

After the cleaning, a 2% increase in turbine efciency was measured

as well as a penstock loss decrease of about 33%.

A full scale site acceptance test was performed after the commis-

sioning of the refurbished power plants. The measurements included

turbine efciency (either with ow measurement by pressure-time

method and generator efciency conrmed by calorimetric methods,

or direct thermodynamic method measurement of turbine efciency),

governor and automatic processes, unit noise level, unit vibrations,

generator electrical test, and island operation tests.

SUCCESSFUL COMPLETION

As described above, the so-called core works on the project have been

nished successfully and all the power plants are operating smoothly

in fully automatic mode as expected.

Throughout the remaining period of the ROT project, auxilia-

ry works must be completed. These include the bottom outlet gate

exchange at the Matka dam which will allow automatic releasing of the

biological minimum during emergency shutdown of the units. The cor-

rosion protection of steel penstocks will also be completely renewed or

repaired on all power plants, all intakes will be automated, and small

civil repairs of the structures will be nished.

Tomáš Cerný, Project Manager, Hydropol Project &

Management AS.

Email: cerny@hydropol.cz

IWP& DC

Table 2: Timeline of the

reconstruction works at the HPPs

HPP 2005 2006 2007 2008 2009

Kalimanci

Matka

Pena

Sapuncica

Pesocani

Dosnica

Zrnovci

Construction

Production cut-off

Above, left: Matka – Construction site in 2004;

Above, right: Pesocani – Machine hall after refurbishment

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38 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

HE primary water source for the canal network in the

English West Midlands is under threat. The 200-year-

old reservoir, known as Chasewater, a key piece of the

region’s infrastructure, is leaking and in need of signi-

cant and extensive improvements.

The large raised, category A reservoir, which covers an area of

around 1.06km

, and holds approximately 4.5Mm

of water, is

retained by two dams. The western embankments are 4m high and

1200m long, and the eastern dam rises to a height of 12m and stretch-

es for over 560m long.

The challenge to bring it up to contemporary safety standards, for

the benet of the region, is being faced by Licheld District Council

– a small council in Staffordshire, with no in-house engineering staff

or expertise, limited funds, and no ability to exploit the value of the

water in the reservoir to recoup the costs of the work.

A BRIEF HISTORY

In the late 1700s, the area of Birmingham and the Black Country was

the cradle of the industrial revolution. To support the rapid expan-

sion of industrial activity, an extensive canal network was built to

provide fast and effective transport between its growing towns and

cities and the markets for their products.

Initially the canal network relied on water from streams and rivers.

But in 1797 work started on the construction of a reservoir in the

Crane Brook valley, between Walsall and Licheld. Although the

original dam was washed away in a summer storm of 1798, the dam

was immediately rebuilt and is still standing today.

In 1957, with the canal network seemingly in terminal decline, the

British Transport Commission sold Chasewater and its land to the

local council. Fifty years later, ownership now rests with Licheld

District Council – a small second tier local government authority.

PRESENT DA Y

Today the canal network carries leisure boaters and holiday makers,

rather than freight, and together the canals and Chasewater sup-

port an increasingly valuable part of the region’s economic and

social landscape.

But the reservoir’s main eastern dam is leaking, and it requires extensive

improvements to ensure that it can withstand the next two centuries.

In his 2007 report, the council’s inspecting engineer, Rod Bridle of

Dam Safety Ltd, concluded that in the ‘interests of safety’, the council

needed to implement the following actions:

Addressing the twin threats of internal erosion and overtopping at Chasewater dam in the

UK has presented Licheld District Council with a multitude of challenges. The search for an

improvement scheme which not only addresses safety issues but is practicable and affordable

has been a big ask for a small council with limited funds and no in-house engineering

expertise. Neil Turner and Lizzie Thatcher report

Challenges at Chasewater

WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 39

UPRATING & REFURBISHMENT

r Investigate the effects of water seeping through the eastern dam and

quantify the dam’s resistance to internal erosion. The fear is that the

velocity and volume of water owing through the dam could lead

to internal erosion, causing pipes to form which could threaten the

dam’s structural integrity.

r Ensure there is sufcient overow capacity, so that the reservoir

can withstand levels of water expected during a period of very

heavy rainfall.

A DAM WITHOUT RECORDS

The age of the reservoir, and the many changes of ownership over the

years, has meant any records or drawings that were prepared in the

dam’s early years have long since been lost. Not knowing its exact

composition has meant that assessment of the dam’s robustness has

been extremely challenging. It may have stood strong for 200 years, but

there is no guarantee that it could stand for another two centuries.

Because of this lack of knowledge about the dam, a quantitative

risk assessment was completed. It suggested that the probability of the

dam failing in any one given year was 1 in 1700 – which is an intoler-

able and unacceptable level of risk. It was forecast that a sudden and

catastrophic failure could release a wave of up to 5m in height, which

would ow rapidly downstream towards the town of Tamworth.

Without adequate notice this wave of water could lead to the loss

of 80 lives, threaten the homes of around 2000 residents and cause

considerable damage to major pieces of infrastructure including the

M6 Toll motorway, the trunk roads of the A5 and the A38 and the

Birmingham Cross City railway line.

This worrying scenario has focused the minds of the engineers and

the council. Over the last three years, Chasewater has been studied

from all angles, rstly to assess the problem and secondly to ensure

that improvement works can be specied. Investigations have con-

cluded the dam is best dened as an old, unzoned heterogeneous dam,

with no clay core or lters. The following investigations have been

carried out:

r Hydrological ows have been calculated and assessed.

r Boreholes have been drilled and trial pits dug to plot the composi-

tion of the dam and its foundations. Investigations were started

with high hopes that we would encounter a clay core, or other

forms of protection against erosion. No clay core, or other defence

mechanism, was found.

r Groundwater surveys have been completed.

r The mining history of the area has been collated and plotted against

the dam’s foundations.

r The chemistry and temperature of the water in the lake, the dam

and downstream has been sampled and compared.

r Silt samples and water quality tests have been undertaken.

r Core samples of the dam have been tested as to their resistance to

internal erosion.

But it’s not that straightforward. If the engineering problems were

not challenging enough, project managers and engineers are further

hampered by a series of other complications and factors.

Complex land ownership arrangements, the presence of European

protected species, high public interest, and the availability of funding

to a small district council, have all bought additional complexity to

the project.

Parts of the eastern dam are in the control of two other public

bodies – British Waterways and Staffordshire County Council. This

in itself ought not to be too troublesome because all parties are part

of the public sector and are committed to ensuring public safety, but

what is difcult is that a large sector of the downstream face is occu-

Above left: Chasewater reservoir area. Photograph copyright Tim Marshall Above right: Winding wheels at the Chasewater Country Park

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