TURBINE RUNNER HEALTH AND THE EXIGENCIES OF … · International Journal of Electrical Engineering & Technology (IJEET) Volume 6, Issue 8, Sep-Oct, 2015, pp.26-36, Article ID: IJEET_06_08_003

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International Journal of Electrical Engineering & Technology (IJEET)

Volume 6, Issue 8, Sep-Oct, 2015, pp.26-36, Article ID: IJEET_06_08_003

Available online at

http://www.iaeme.com/IJEETissues.asp?JType=IJEET&VType=6&IType=8

ISSN Print: 0976-6545 and ISSN Online: 0976-6553

© IAEME Publication

___________________________________________________________________________

TURBINE RUNNER HEALTH AND THE

EXIGENCIES OF PRODUCTION UNDER

POWER MARKET REFORMS

Prof. Marialis ÇELO

Faculty of Electrical Engineering,

Polytechnic University of Tirana, Albania

ABSTRACT

The reforms undertaken on the Albanian Power Sector strated in 2004

with the unbundling process of Public Utility -KESH focused on functional

unbundling as per the three core activities: generation, transmission and

distribution & retail supply, accounting unbundling, i.e. identification of costs

for each service/function and Legal unbundling (corporatization). As a result

of this process the Transmission System Operator was registered firstly as

Joint Stock Company on 2004 and in 2005 the Transmission System Operator

was legally unbundled. In 2008 the Distribution System Operator (performing

the retail service as well) was legally unbundled. The privatization of the

Distribution System Operator (DSO) started in 2008 and was finalized in mid-

2009 but in 10/27/2014, the distribution company moved again from private to

government administration, known as "Distribution Network Operator"

(OSHEE).The liberalization of generation sector started in 2002 – the small

hydro power plants (up to 15 MW) were given by concession or privatized. It

is a fact that in now days, the hydro generation units are more and more

called for commercial operation due to the exigency of production, necessity

to supply ancillary services as spinning reserve etc.

In this paper we will treat technical problems faced with hydro mechanical

equipment, i.e. runner blade cracking of the units of one of the major HPP in

Albania as a consequence of operation conditions changed.

Key words: Hydroelectric Power Plant, Hydro Mechanical Equipment, Tail

Water, Vibration Measure, Runner Blade, Cavitation Damages, Market Power.

Cite this Article: Prof. Marialis ÇELOTurbine Runner Health and the

Exigencies of Production under Power Market Reforms. International Journal

of Electrical Engineering & Technology, 6(8), 2015, pp. 26-36.

http://www.iaeme.com/IJEET/issues.asp?JType=IJEET&VType=6&IType=8

Turbine Runner Health and The Exigencies of Production Under Power Market Reforms


1. INTRODUCTION

The total installed capacity of all power plants in Albania is around 1,878 MW. The

total installed capacity of private producers is around 347 MW. Installed generation

capacity that is owned by public company, KESH Generation (Drin Cascade),

represents 81.5% of total installed generation capacity in Albania and accounts for

1,450 MW (hydro generation capacity is 1,350 MW and 98 MW is by thermo power

plants-TPP). Production of electricity, in Albania in 2013, was realized 100% by

hydroelectric power plants (HPP).

The country’s power sector relies heavily on hydropower. Fierza Hydroelectric

Power Plant is the first in a cascade series of hydro plants on the Drin River in

Albania. The other stations in the cascade are, in downstream descending order,

Komani, Vau i Dejes and Ashta. While the first three HPP’s on the cascade are state

owned and managed by Albanian power Corporation (KESH), Ashta is a private

hydropower plans recently commissioned, owned and managed by Verbund

Company. Active storage capacity of the Fierza reservoir is 2,700 million m3. The

Fierza powerhouse containing four 127.6 MW Francis vertical generating units is

located at the toe of the earth filled dam. Rated head of the turbines is 118 m and

annual energy production is 1,328 GWh(Fig.1).

The generating units and the majority of the electrical equipment at Fierza HPP

originally were manufactured in China. The generating units were commissioned

between 1978 and 1982.

The hydropower plants of Fierza had been subject of an entire rehabilitation

Project, concerning replacement and or refurbishment of hydro mechanical

equipment, electrical equipment and installation of a new control monitoring system.

The implementation of the rehabilitation Project started in 2002 and was finalized in

2006. The major technical aspects of the intervention done are treated in different

articles published as listed in the references [1-7]. Since our focused in the paper are

the runner blade cracking identified on the rehabilitated runners four years after the

rehabilitation of the HPP, we will detail the work done during the rehabilitation on the

runner, as well as the operation condition after rehabilitation which have been subject

of changes, following the philosophy adopted during the establishment of the Market

Model in Albania.

2. SHORT DESCRIPTION OF REHABILITATION PROJECT

AND OUTCOMES FOR FIERZA HPP

As a result of rehabilitation Project, the power generation is increased by about 4%

per unit (8% for two units) mainly as a result of the two new turbines with a new

profile. The results of the intervention are proved by the index tests carried out after

the completion of the rehabilitation. The overall rehabilitation is very good and the

quality of the work on the mechanical, electrical equipment and CMS equipment is

excellent, Fig.2.



Figure 1 Fierza Hydropower Station (Power Generation Building and Dam)

Figure 2 Generator Units (Fierza Machine Hall after finalization of rehabilitation Project)

The plant is more reliable and there is an increase of energy production due to

reduction of the repair time and for non interruption of turbine running compared with

the period prior the rehabilitation as per table Nr.1.Unplanned outage hours totaled

about 1,456 hours before the commencement of rehabilitation (2001), whilst as shown

in Table 1, unplanned outage hours after the rehabilitation (2008–2009) were

dramatically reduced to around 52–44 hours. This is because the frequency of

failures/malfunctions was significantly reduced after rehabilitation of all generator

units as it was expected from the original objective of the Project.

Table Nr.1 Unplanned Outage Hours at Fierza Hydropower Plants (Unit: hours/year)

2001 2008 2009

Unplanned Outage Hours 1456 44 52

Outage Hours by Human Error 0 0 0

Outage Hours by Machine trouble 1456 44 52

3. OPERATING CONDITIONS – FIERZA HPP

Typically before year 2000, (before start of the implementation of rehabilitation

Project) two units only were operated for base load during the day, the other two units

being employed for short term peaking operation. The station having a big reservoir

with annual regulation is typically shut down or on very low output overnight. It was

planned to operate the units with the new runners replaces during rehabilitation at

point of best efficiency using the other two units for part load and peaking. Hence,

based upon previous operation both the units with the new runners it was supposed to

operate for about 7 hours per day as close as possible to load for best efficiency at the



prevailing head, being subject to approximately two start/stops per day. Table Nr.2

shows the operating heads and levels of the reservoir

Table Nr.2 Operating heads and levels of Fierza reservoir

Heads and levels Unit [m]

Flood level EL 297 m

Maximum Normal Reservoir level EL 296 m

Normal Minimum Reservoir level EL 240 m

Minimum Reservoir level EL 237 m

Design net head 99 m

Maximum net head 128 m

Minimum net head 70 m

Rated net head 118 m

Minimum tail water level for operation of a single unit and establishment of the

model test cavitations guarantees is EL 169m. Maximum tail water level with

spillway operation is EL 177m. This is established by Koman reservoir (which is the

second on the descending order on the cascade and was constructed after Fierza).

4. REHABILITATION OF RUNNERS AND WICKET GATES AT

FIERZA HPP (UNIT 1 AND UNIT 3)

The runner of unit 3 is one of the original runners as supplied by Dongfang of China.

These original runners have always had a cracking problem and, to a lesser extent, a

cavitation problem. Before the implementation of the rehabilitation Project they had

been extensively weld repaired by KESH and were further weld repaired by the

Contractor selected during the rehabilitation Project.

As part of the rehabilitation the original runners of Units 2 and 4 were replaced

with new ones manufactured by Vatech (now Andritz) Fig. 3. The design of the new

runners were model tested for improved performance compared to the original

runners and subjected to extensive Finite Element (FEM) stress analysis to guard

against any possibility of cracking in service. The new runners carried a stringent

cracking and cavitation guarantee.

Figure 3 New and old runner



Because of lack of funds when letting the rehabilitation Project and the mode of

operation of Fierza at that time replacement runners were proposed for only two of the

Fierza units. Accordingly the two original runners of Units 1 to 4 with the least

history of weld repair were weld repaired by the Contractor and used for Units 1 and

3.

The units have been dismantled and the existing runner were removed from the

unit and transported to the erection bay. There, all 4 runners have been non

destructively tested for cracks using ultrasonic, magna flux and dye penetrant

methods. Any cracks or defects in excess of those permitted by the standards

stipulated on the Contract have been weld repaired according the approved

Contractual procedure. The existing runners are a hybrid construction of carbon steel

crown and band and stainless steel blades. A lot of cracks have been identified. The

testing and repair activities, such as welding, gridding and testing again are shown in

the following photographs in Fig. 4 and Fig.5.

Figure 4 Testing, welding of the runner



Figure 5 Repair and NTD test Fierza runner Unit 3

The wicket gates have been also damaged and erosion can be seen in the

following photographs in Fig.6 (a,b,c).

Figure 6(a) Erosion, damages



Figure 6 (b) Welding, repair activities

Figure 6 (c) PT Test on wicket gates

5. VIBRATION TESTS ON THE FOUR UNITSOF FIERZA

Before rehabilitation of the Fierza units the Contractor conducted vibration tests on all

four units. The results of these tests are summarised in the curves of Figure 7.

Figure 7 Results of vibration tests

As is evident in this figure, draft tube vibrations become seriously high at low

loads. The Unit 3 & 4 tests were conducted at a maximum net head of 114 m but



other tests were conducted at lower net heads. The report concluded that part load

draft tube pressure fluctuations increased considerably with increase of net head.

As it was mentioned in the Introduction, the power production in Albania is 100

% based on hydrogeneration and consequently is heavily depended on the hydrologic

condition, rain fall and precipitation, as well as on the upstream leavel of Fierza

reservoir.

In the period between the commissioning of Unit 3 and May 2008 the net heads

were very low and ranged between about 80m and 105m, compare with maximum net

head of 128 m and rated net head of 118 m. Late 2009 up to and including 2010 the

head increased considerably and throughout most of 2010 has been at about 118m. In

the meantime is worth to mention that Transmission System Operator, which has in its

own organization also the Dispatching Center, responsible for the regime of the units,

was since 2005 an Independent Operator, legally unbundled from KESH – Generation

Company.

Besides the power market demands, system operator must satisfy the following

technical demands:

Regulate the frequency;

Ensure power balance (maintaining the appropriate spinning reserve and ready-

reserve);

Compensate power losses;

Ensure the generation for de-loading of overloaded lines;

Regulate the voltage, ensuring an adequate voltage profile;

Ensure power system restoration and the start up of the generation without a

external voltage, that is, ensure black start capabilities.

Ancillary services depend on the power reserve. Taking this into account, the

ancillary service in power market can be divided in two categories:

The active power ancillary service;

The reactive power ancillary service.

In the Albanian Market Model, it is Albanian Power Corporation responsible to

gurantee the ancilliary services for TSO. Scheduling of the units production, start/stop

sequences defined by Dispatching Center to gurantee also the stady state stability of

the system are an evidence that the philosophy of the operation of the units is

changed. The operation records and statistics has shown that now the number of

start/stop sequences of the units are much more higher than originally foreseen and it

is evident that the units subject of the investigation (Unit 1 and Unit 3) have been in

operation with low loads at high heads as well as some times with high loads at low

heads, accelerating in this way the deterioration process of the runner blades,

createing cracks and cavitations damages.

During the reforming process of the power sector, it is essential an harmonize

coordination between all market operators and especially between Transmission

System operator – TSO and KESH Gen in order to adress the following issues:

Organizative aspects of power system functioning;

Technical aspects of power system functioning;

Study aspects for an harmonize and efficient development of the system and

market power.



All the Fierza units are equipped with vibration measuring equipment. According

to statistics, about 80% of the hydropower units failt will be reflected in the vibrating

signal [8].

The curves of Fig.8 are plotted from operation records and clearly demonstrate

that at net heads above 115m part load vibrations become extremely high especially at

118m at which the units operated for most of 2010.

Figure 8 Head Cover Vibrations

The most pertinent vibration measure to the problem of runner blade cracking is

head cover vibration. Accordingly the Hydro-Mechanical Specialist considers that the

cracking currently seen in the original runners of Unit 3 are a result of operation at

part load at high heads. This borne out by the appearance of cavitation damage on the

crown between blades which is a typical location of the origin of the part load vortex

[2].

6. CRACKING OF THE RUNNER OF UNIT 3 FOUR YEARS

AFTER REHABILITATION PROJECT

As the runners of Units 1 and 3 are the original they are still prone to cracking. It was

envisaged by the expert of hydromechanical works at the time of the rehabilitation

Project that Units 2 and 4 with the new runners would be operated for the majority of

the time and Units 1 and 3 only occasionally. As a matter of fact the record of data

operation had shown that due to the exigencies of production and regime of operation

of the Drin River Cascade (Hydropower plants which are managed by Albanian

Power Corporation) defined from the Dispatching Center -TSO, such philosophy is

changed.

The first inspection after finalization of the rehabilitation Project was carried out

in May 2008. When inspected at that time the runner of Unit 3 was found to be crack

and cavitation damage free. Another inspection was carried out on August 2010 and

were identified that four blades exhibited cracks with Blade 4 having two cracks.

Most of the cracks were in the crown to blade weld however those of Blade 4 were in

the centre of the runner blade. The photographs of Fig.9 and 10 demonstrate the type

Unit 3 Head Cover Vibrations

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140

MW

mm

/s

Hg=118m Hg=115m Hg=104m Hg=80



and extent of the cracks which in most cases were up to approximately 500mm long.

There was also some evidence of cavitation damage on the crown between blades as

can be seen in the photograph of Fig.11. As guaranteed, the new runners of Units 2

and 4 have been crack free.

Figure 9 Cracks on blade Nr.4 Figure10 Craks on welding part og blade Nr.1

Figure 11 Cavitation damage on the crown between blades

Referring to the fact that two years after rehabilitation, at the end of guarantee

period, when inspected in May 2008, the runner of Unit 3 was crack free, the

operating conditions have been checked verified and evaluated, if they have changed

considerably post that date, when compared with those before. The yearly statistics of

2009 and 2010 of power values and the corresponding data of the net head and

vibration measurements obviously show that the unit was not operated in the best way

to minimize cavitations. Hydraulic turbine runners, which operate under a wide range

of heads and outputs, are subjected to considerable dynamic forces at off design

conditions.

It is crucial to follow the recommended operation condition for both Units 1 and 3

to be restricted between 95MW and 118MW at net heads above 105m, in order to

reduce the propensity for cracking, until a new runner is installed. Furthemore a better

coordination between Dispatching Center – Transmission System Operator and KESH

Generation Company should be established in respect of power set point and its

frequency of changes in order to mimize cavitations and erosions damages on runner

blade and wicket gates, but not limitted too.



7. CONCLUSIONS

1. Coordination between Generation Company and Transmission System Operation

is very important and crucial with the aim to satisfy the obligations borned from

the Market Model for all partecipants and to guarantee optimal operation

conditions for the units in order to avoid possible damages.

2. A new concept should be established for Maintenance and Operation philosophy

in order to guarantee the sustainability of the invetsment done. Special attention

should be given to the structural aspects of operation and maintenance moving

towards preventive maintenance and condition based preventive maintenance.

3. The Department of Operation in charge of operations related to the

starting/stopping of generator units, where the data of various instruments and

equipments including generator units and transformers are measured and relevant

operations are monitored should be trained and qualified.

4. Continous monitoring of head cover vibration measuring and interpretation of the

results should be done by the staff of HPP.

5. The other rehabilitated runner of Unit 1 should be be non destructively tested in

order to verify the situation.

6. Periodic maintenance on generators and auxiliaries facilities should be done in

time and with an allocated budget, in order to guarantee the expected life time of

the equipment.

REFERENCES

[1] J. H. Gummer, H. Obermoser and M. Çelo, Fierza Station hydro-mechanical

rehabilitation onthe Drin River in Albania, Porto Conference Hydro 2004,

Portugal, November 2004.

[2] J. H. Gummer, Stay vane vibrations in the Nkula Falls turbines, International

Journal for Hydropower and Dams, January 1994.

[3] J. H. Gummer, H. Obermoser, Vau i Dejes hydro-mechanical rehabilitation on the

Drin River inAlbania,Villach Conference Hydro 2005, Austria, October 2005.

[4] M. Çelo and H. Obermoser, Revitalization of the Generator at the Fierza HPP,

Albania, MedPower Conference 2004, Cyprus November 2004

[5] J.H. Gummer, D. M. Barr and G. P. Sims, Evaluation criteria for upgrading

hydro-powerplant, Water Power and Dam Construction, December 1993.

[6] M.Çelo, R.Bualoti , M. Kullolli, The Implementation of Rehabilitation Project of

Main Hydropower Plants in Albania, a way for Improvement of Operational

Reliability, Safety and Environmental Standard, MedPower΄08 – 6th

Mediterranean Conference and Exhibition on Power Generation, Transmission

and Distribution, Thessaloniki, Greece, November 2 – 5, 2008.

[7] M.ÇELO, Hydropower Infrastructure Rehabilitation, Energy, Development and

Climate Change, ENERGY WEEK 2009 THE WORLD BANK GROUP,

March 31- April 2, 2009 Washington, DC 20433

[8] Bide, Z.; Yuan, T.; Ping, Z.J. Vibration fault diagnosis of hydropower units based

on Choquet fuzzy integral. J. Vibr. Shock 2013, 32, 61-66.

[9] P Sridhar and K Bhanu Prasad, Fault Analysis in Hydro Power Plants Using

Matlab/Simulink. International Journal of Electrical Engineering & Technology,

5(5), 2015, pp. 89-99.

[10] Shambhu Ratan Awasthi, Vishnu Prasad and Saroj Rangnekar, Demand Based

Optimal Performance of A Hydroelectric Power Plant, International Journal of

Advanced Research in Engineering & Technology, 4(7), 2013, pp. 109-119.

TURBINE RUNNER HEALTH AND THE EXIGENCIES OF … · International Journal of Electrical Engineering & Technology (IJEET) Volume 6, Issue 8, Sep-Oct, 2015, pp.26-36, Article ID: IJEET_06_08_003

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