The need for peak power has prompted Bulgaria to re-assess the condition of its hydro power facilities. Peter Jedelhauser spoke to Suzanne Moxon about Electrowatt Engineering’s role in Bulgaria’s ambitious refurbishment programme

The inauguration of the refurbished 125MW Peshtera hydro power plant in May 1998 was a satisfying occasion for Bulgarian utility Natsionalna Elektricheska Kompania (NEK), its Swiss suppliers (ABB, electrowatt Engineering, Marty Corrosion Protection and Sulzer Hydro) and the financing agency, which was the Swiss government. The commissioning of the plant was not only the culmination of two years of hard work for the Swiss/Bulgarian team, but the beginning of a new challenge.

A renewed focus on the effectiveness of Bulgaria’s power generating capacity has brought some of its hydroelectric plants into discussion, and refurbishment is the word on everybody’s lips. Bulgaria has 87 hydro power plants which contribute approximately 20% of the country’s total power generating capacity. However 13 of these plants, which are located on four river cascades, supply more than 80% of the country’s total hydroelectric energy. These stations have become the focal point of a detailed study and subsequent refurbishment programme.

Hydro power plays an important role in Bulgaria’s electricity industry. The country has a great need for peak power and, besides imported power, hydro is its main resource capable of fulfiling such requirements. By 1993 NEK had already carried out a rehabilitation study of its thermal power plants and transmission grids but the utility soon realised it did not have adequate information about its hydro stations. Peter Jedelhauser from Electrowatt Engineering (EWE) takes up the story.

‘As hydro power plays a key role in peak power generation,’ he said, ‘a study scrutinising Bulgaria’s hydro power facilities and defining priorities was mandatory if NEK wanted to fund any required refurbishment work through bilateral financing or loans from international financing agencies.’ EWE successfully bid to win the task of implementing the Bulgaria Hydropower Study. Carried out in 1994-5 the study had to give an overview of the Bulgarian power system and define the role that hydro power played in it. In addition the following had to be accomplished: •Prepare a ranked list of economically attractive rehabilitation measures on existing hydro power generation facilities along the four major river cascades (Belmeken-Sestrimo, Batak, Dospat-Vatcha and Arda).

•Assess the present water resources patterns including the hydrology of the various cascades and the water balances for the major reservoirs; appraise present water management along the four cascades; and make recommendations for possible improvements.

•Examine the current operating and maintenance organisation of NEK’s hydro power facilities and, if required, prepare recommendations for improvements.

•Determine the safety of the dams associated with the hydro power plants or complexes for which refurbishment appears to be an attractive option.

•Prepare a ranking study of four potential new hydro projects: Rila; Sreden Iskar; Gorna Arda; and Sredna Vatcha.

A prestigious task

‘EWE viewed the contract award for the Bulgarian hydro study as being a highly prestigious task,’ Jedelhauser said. ‘Mainly because it created a unique opportunity to assess a country’s existing and potential hydro generating facilities.’ The study also helped to enhance relationships between Bulgaria and Switzerland — the Swiss Government funded the study through its trust fund for the World Bank. Within the framework of its financial aid programme to Bulgaria, the Swiss Government was interested in creating a basis for sustainable co-operation between the two countries and decided to offer financial assistance. Bearing in mind NEK’s need for reliable peak power generation, Bulgaria’s lack of spare parts for the hydro power plants, and the capabilities of the Swiss hydro power industry, such a study was found to be attractive.

Co-operation with the World Bank for hydro power rehabilitation seemed very feasible. The Bank was interested in such hydro power projects in Bulgaria and they therefore agreed to act as the Executing Agency for the Swiss-financed study.

Jedelhauser outlines the methodology used to implement the study: ‘We had (and still have) a co-operation agreement with Energoprojekt, the former designer of all the plants included in the study,’ he said. ‘So we had access to vital documentation from the plants’ design and construction phases. We also worked closely with NEK staff at all levels, particularly with personnel from the plants themselves.

‘To obtain relevant information on the O&M procedures we developed questionnaires which were written in Bulgarian. These were handed over to the plant operation staff who filled them in, with assistance from EWE and/or Energoprojekt staff if required.’ Co-operation has featured heavily in EWE’s work. Contractually the World Bank was the Executing Agency for the study but NEK still had to approve any work carried out by EWE. ‘In practice we worked well with all NEK departments and this was the key to our success,’ Jedelhauser says.

Data collections and site investigations necessary for the study were carried out by a joint team of EWE, Energoprojekt and NEK personnel. ‘The crucial part about such investigations into plant equipment is of course the scheduling,’ Jedelhauser acknowledges. ‘We were lucky in that during the execution of this study a substantial number of units were being overhauled and so could be inspected very carefully. More importantly, efficiency measures ordered by NEK directly were carried out by the Technical University of Sofia, and we had access to all that data.’ The safety of the dams was evaluated with NEK’s dam monitoring department, who were able to provide detailed information about the long-term behaviour of the structures. Together with this information the overall safety of the dams was assessed by a thorough visual inspection; a review of the design criteria applied; a new seismic risk assessment and static/dynamic recalculation; a new flood hydrology; and (where required) particular technical investigations including material testing. Safety recommendations were made where necessary but, Jedelhauser stressed, all dams were found to be in a satisfactory condition.

After assessing the results of the hydro power study all parties involved had to decide if, and how, to implement it. As is well known, the economic attractiveness of hydro power refurbish-ment is dependent on the power market, the investment cost and the available alternatives. In this case, as Jedelhauser explains, if rehabilitation is not implemented, despite the enormous efforts of NEK to keep the plants running, there is a high risk that the technical condition of these Bulgarian plants will worsen. The possibility of a sudden breakdown, with subsequent increased operating costs and a less than desirable use of the plant, must not be ignored.

‘To determine the exact date when a plant cannot be used any more is difficult,’ Jedelhauser says. ‘The most likely time span determined from this study was between zero and a maximum of ten years. Although shorter time spans will apply to cases where any urgent measures on important components are overdue.’ In the case of the Bulgarian hydro power plants, the EWE study found that little financial investment would be required in civil structures to keep the plants running reliably. The main rehabilitation costs would be related to the generating and hydromechanical equipment, including the steel lining of the penstocks. If these rehabilitation measures were to be undertaken, EWE was confident the plants would once again be safe and reliable in operation.

Economic analysis of the proposed rehabilitation programme proved it to be more favourable than the construction of new plants. The resulting overall energy production cost for the rehabilitation of the four river cascades varies from1.6US cent/kWh (Batak cascade) to 2.5US cent/kWh for the Arda cascade.

‘These figures are much lower than for any of the four potential new hydro power developments in Bulgaria, which were also examined throughout the study,’ Jedelhauser says.

‘Taking into consideration the importance of the existing Bulgarian hydro power plants, and their intangible benefits in irrigation and raw water supply, rehabilitation is extremely attractive,’ he added.


From the 13 plants under examination, Peshtera was selected as being the most critical in terms of safety and reliability. Since commissioning in 1959, four of the five generating units at the plant have operated for more than 150,000hr (unit five was installed at a later date). Despite NEK’s concerted efforts it was becoming an increasingly difficult task to keep the plant in good condition. ‘Already in two separate incidents, buckets from one of the horizontal axis Pelton runners have broken during operation,’ Jedelhauser said. ‘They were thrown off through the turbine casing into the power cavern. The accidents caused severe damage to the generating equipment and of course the working conditions for the operating staff were anything but safe’.

Peshtera was considered to be extremely important to NEK, for the energy it provides, and for Bulgaria as a whole for its water supply and irrigation functions. These would be put at risk if the plant is disabled as it has no bypass facility.

The most urgent areas of work uncovered by EWE’s study, and which needed to be addressed at the plant, were rehabilitation of the four units (which are equipped with two Voith runners each) and rust protection works along more than 4km of a steel-lined section of the underground penstock.

As various components of the Peshtera plant were described as being in a critical condition, one option would have been to only replace these critical components. EWE, however, is not in favour of changing single components: ‘Financially, changing the runners alone may have been attractive in the short term due to increased efficiency and less maintenance. But,’ Jedelhauser added, ‘this might reduce the economic attractiveness of future rehabilitation works and thus the chance that the plant will be rehabilitated entirely. Indeed, carrying out rehab-ilitation in stages (ie the runners first followed some years later by other parts of the electrical systems) leads to a tech-nical patchwork, complicating main-tenance. In addition, a unit has to be shut down several times instead of just once.’ Following the willingness of the Swiss Government and NEK to provide sufficient foreign and local funds for the rehabilitation work, an ordinary rehabilitation approach was implemented. The aim of this is to secure reliable energy production over a period of 20 to 25 years. To achieve this it was necessary to:

•Keep all the components in place which are still in a good working condition.

•Combine ‘new’ with ‘old’ technology — using up-to-date Western electronic equipment with former East European-standard technology.

•Make use of NEK’s own resources to the utmost possible extent.

•Maximise the contribution of Bulgarian suppliers and manufacturers.

•Foster co-operation between Western and Bulgarian firms in all stages of the project. (See table on p16 for a summary of the rehabilitation work carried out).

A test case

Peshtera was a test case for NEK, and equally for its Swiss and Bulgarian suppliers. ‘In order to minimise the foreign cost component, EWE proposed in the hydro power study to carry out a test project based on the philosophy outlined above (ie a “designed to budget” rehabilitation project),’ Jedelhauser added. ‘At that time (in 1994) there was little knowledge of whether such combinations of old East European and new Western equipment was feasible. More importantly, we didn’t know what surprises were in store for us when doing the work. We didn’t know if the costs could be adhered to and whether the technical expertise and capabilities of the Bulgarian suppliers and NEK would be adequate within the stipulated time frames.’ There were plenty of day-to-day issues which occurred when work started at Peshtera in October 1996 — which could have easily led to more major problems. ‘But thanks to the excellent working relationship between all parties,’ Jedelhauser said, ‘and the willingness of all individuals involved to work together, such problems were prevented.’ Both NEK and the Swiss Government were described as being highly flexible toward the project. In one example EWE was able to change the entire methodology for the rust protection works in the penstock. This was necessary to comply with Bulgarian labour and safety at work regulations and, as water had to be available for the irrigation schemes at Peshtera by May 1997, the penstock could only be empty for five months. ‘Despite the technical challenges, the Bulgarian rust protection contractor, with the assistance of a specialist Swiss firm, managed to complete the work to a high specification on budget and to schedule. This was only possible,’ Jedelhauser commented, ‘as NEK helped with the logistics, equipment, manpower and site management.’ In another example NEK staff were very much involved in the erection and testing activities of the upgraded/new equipment. They also received training on how to operate the equipment, with special efforts being made to translate the standard operating manuals into Bulgarian. ‘We realised the importance of transferring such knowledge so that day-to-day operation and maintenance is possible,’ Jedelhauser said.

When completed in May 1998, the Peshtera plant was on time and below budget. Jedelhauser explains why. ‘From the very beginning our aim was to limit the risk of being above budget. This was achieved by ensuring that electrical and mechanical supply options were included in the tender documents which enabled us to reduce the scope of supply or increase it in case the prices obtained from the suppliers were above or below budget.

‘Our cost estimates were also based on the clear understanding between NEK and EWE about the various objectives to be achieved with the rehabilitation,’ Jedelhauser said. ‘This was an interactive process and various options were discussed and cost benefit analyses were made.’ Regular meetings were also held throughout the project and budget and schedules were discussed. The pressure to provide sufficient water for irrigation purposes from May 1997 drove everyone involved in the project to early completion. ‘This boundary condition was just accepted by everybody,’ Jedelhauser added.

EWE believes that its good working relationship with NEK and the other parties is the key to the success of the project. From Jedelhauser’s own experience, he says ‘I strongly believe that for hydro power rehabilitation projects like Peshtera, where so many boundary conditions have to be considered and where the budget is insufficient for the “complete replacement” approach, a trust-based working relationship between the owner and the engineer and also between the owner/engineer and suppliers, is mandatory.’

The future

EWE has now won a contract from the Swiss government to appraise rehabilitation at other Bulgarian plants. In the next phases, design work on Batak (a 40MW plant located upstream of Peshtera) and Aleko (a 66MW plant downstream of Peshtera) is expected to start at the end of 1998.

Refurbishment work is expected to start at Batak during the winter of 1999-2000. The nature of the work to be undertaken will probably be very similar to that carried out at Peshtera, with the exception of the rust protection works. This has already been carried out at Batak by NEK, utilising the equipment and technology provided by the Peshtera project.

Final approval from the Bulgarian side is still awaited, but Jedelhauser is hopeful that EWE’s experience will mean that the company has something to offer. Nevertheless he is not content to offer a carbon copy of the Peshtera project: ‘If we are involved we will certainly try to elaborate on that project’, he says, ‘There is always room for improvement.’