Since 1954 the Belgian utility company “EDF Luminus” has operated six hydroelectric power plants on the River Meuse. One of them is located at a lock in the Belgian town of Andenne.

Andenne Power Station has been in operation since 1980 and back at this time it was equipped with three horizontal Straflo turbines. In order to improve the efficiency and flexibility of the power plant, last year it underwent a comprehensive upgrade. Part of this involved replacing two of the three Straflo units with two modern Kaplan bulb turbines from ANDRITZ HYDRO. In addition, the technical control and regulation systems were brought right up to the latest standard. EDF Luminus invested a total of €9 million in modernising the 33 GWh plant. At the beginning of 2016, the power plant successfully started operating again following an intensive test phase.

The Belgian utility company EDF Luminus accounts for around 14% of the total electrical capacity in Belgium. With an installed generation capacity of 2,137 MW, it is one of the largest power companies in Belgium and employs around 1,000 workers. EDF Luminus operates a large number of power plants with different energy sources – including six hydroelectric power plants on the River Meuse and one on the River Sambre. One of these seven power plants is located at the level of the lock on the River Meuse in the town of Andenne in Belgium’s Wallonia region.

RARE STRAFLO TURBINE
The Andenne run-of-river power plant has been in operation since its licence to operate was granted back in 1980, and it has always been a reliable source of power. Up until August 2014, the plant was still equipped with three horizontal Straflo turbines with an installed output of 3.05 MW each, with a drop height of 5.35 m and a flow rate of 75 m³/s. Their name “Straflo” comes from the term “straight flow”, which describes the flow characteristics of the turbine. With this type of turbine, the rotor of the turbine and the rotor of the generator form one unit and share the same axis. This means that the Straflo turbine does not have a shaft of its own. Instead the turbine blades have a circumferential ring in which the excitation winding is integrated. By contrast, the stator winding is located around the housing of the turbine. A system of seals is installed to isolate the rotor winding from the water. The turbine shaft is mounted on one side in a sealed housing. The Straflo turbine usually has a single regulated design. At the Andenne Power Plant, two of the three units are single regulated Straflo turbines. The third unit, on the other hand, was a double-regulated version, which it is extremely rare to find installed in Europe. Straflo turbines in general were regarded at the time they were commissioned as having a high-end technical status, but they are only occasionally encountered nowadays. The reason for this is the poor operating range of the single regulated Strafloturbine, whose efficiency drops off dramatically with an admission flow of less than 70 per cent. The start-up with the double-regulated version failed in turn due to turbulent operation and problems with cavitation. In addition to its poor control characteristics, this type of turbine is very high-maintenance and therefore costly in the area of the seals.

NEW EQUIPMENT
After more than 30 years of operation, in 2013 the operator of the Andenne Power Plant decided that it needed an upgrade. The plan was that state-of-the-art power plant technology would make the plant more flexible and more efficient. The decision was taken to replace two of the three machine units. In addition, all of the electrical equipment and control technology in the plant was to be modernised. As well as achieving more flexible performance, another important aim in the upgrade of the Andenne Power Plant was to reduce the cost of maintenance. This is because the complex system of seals means that Straflo turbines have to be maintained at more regular intervals – this will now be a thing of the past with the new Kaplan turbines.

DEMOLITION WORKS DURING OPERATION
In August 2014, work to dismantle the two machine units began. The first step in this process was to install a new indoor crane with a load-bearing capacity of up to 40 tons in the machine hall. The intention was that it should support and facilitate the construction work in the powerhouse. “When we converted our power plant in Lixhe, we also installed a new indoor crane and at the time this proved to be extremely helpful,” says Anne-France Fontaine, senior project manager from EDL Luminus. The work to dismantle the two Straflo turbines, including the double-regulated one, took around two months. Reinforcement works were then carried out to prepare the building for the forthcoming demolition works. Further preparation was needed to completely isolate the remaining Straflo turbine from the construction site because the plan was that it should keep operating throughout all of the conversion work. As it is cooled by air, no dust was allowed to get into the turbine’s ventilation system. It was therefore completely separated off from the construction site by means of wooden cladding and supplied with clean air through a ventilation hose. Apart from one minor interruption, the demolition works proceeded without any problems and were completed in February 2015. “We only had to stop the demolition works for a short period of time as the construction company re-moved too much material at one point and we had to do some more reinforcement works”, reports project manager Fontaine.

LOST FORMWORK
Following the demolition works, it was possible to start rebuilding the structure. In order to save time, the works on both turbine shafts took place in parallel. For the concrete works on the exhaust pipe, the decision was taken to opt for “lost formwork”. „We decided to opt for this technology while for Lixhe we used traditional wooden formworks. The handling of the parts had to be carefully designed, but once the formworks in place, this technology brought other advantages and facilitated the rest of the concreting operations”, reports Mrs Fontaine. This process involves leaving the welded metal formwork in the structure after the concreting process. This saves the need for costly and complicated cleaning and dismantling – and therefore also saves real cash. Another advantage is the very good surface finish, which ensures a high level of efficiency thanks to low friction losses.

NEW KAPLAN TURBINES
After this phase of construction lasting around five months, the two new machine units were delivered and installed from the ANDRITZ HYDRO plant in Ravensburg in July 2015. The operator replaced the two old units with two modern Kaplan bulb turbines. They each have a power output of 2.0 MW with a maximum flow rate of 48 m³/s and a drop height of 4.94 m. This means that although they each deliver just over 1 MW less power than their predecessors, they offer a more flexible response and can still be operated efficiently even when there is a low admission flow. The installation of the machines was completed after around five weeks of work.

CONNECTION TO THE CONTROL CENTRE
At the same time, the power plant was also equipped with new control technology. A PLC system now regulates the old relay system. This makes Andenne Power Plant more reliable as old relays were starting to fail and no more spare parts were available and also facilitates some maintenance processes. The special feature here is the fact that the power plant is connected to the EDF Luminus control centre in Seraing. This connection was provided via the “Profinet” Ethernet protocol.

SAME OUTPUT
On 10 December 2015, the first kilowatt hour was produced using the new machine units in Andenne. Up until the beginning of 2016, the power plant underwent trials and was adjusted to the optimum settings by the control experts from ANDRITZ HYDRO. Although the overall power output of the power plant was reduced by around 2.1 MW as a result of two smaller machines being installed, the annual production will remain roughly the same at around 33 GWh. EDF Luminus has invested a total of 9 million euros in upgrading Andenne Power Plant, which is now perfectly equipped to operate for decades to come. EDF Luminus was established in 1978 as a public utility company called SPE (Société productrice d‘électricité). After a number of structural and shareholding changes, this Belgian company, now called EDF Luminus, has become a significant renewable electricity producer and energy services supplier. EDF Luminus supplies electricity and gas to 1.8 million Belgian customers, which equates to a market share of 20%.