It was undoubtedly a huge project for EW Mels, which has been supplying its customers in the Sarganserland district with hydroelectric power for many decades.

As part of a comprehensive renewal, renovation and expansion project in which the local community invested around 25.8 million CHF, on the one hand operational reliability was restored and on the other hand a considerable increase in production capacity of more than 7 GWh was achieved. As well as renovating the dam walls and renewing the traditional Chapfensee-Plons power plant, another three small-scale hydropower plants were constructed. After the bureaucratic process to secure a licence took more than 18 years and the subsequent process to obtain final building permission took another 3.5 years, the overall project was essentially completed in around two years. The new facilities have been operating since December 2018 and are proving their worth every single day.

The 8,600 residents of the municipality of Mels in the canton of St. Gallen have been relying on hydropower for decades. To the present day, it still remains the backbone of the community’s power supply, for which the community’s own company EW Mels is responsible. EWM supplies around 4,600 customers via a 65-kilometre medium-voltage grid and a 208-kilometre low-voltage grid. A key role has always been played here by the Chapfensee-Plons power plant, which began operating in 1948. The power plant utilises the 430,000 m3 storage capacity of Chapfensee reservoir and the natural drop of 550 m down to the powerhouse. When the licence ran out at the end of 1996, the people in charge at EW Mels decided to request an extension to the licence. “We never thought that it would take so long to achieve this. It took 21.5 years from the first letter requesting a renewal of the licence through to the final building permission being granted,” explains the director of EW Mels, Erich Riget.

ACTION NEEDED TO BE TAKEN
Fundamentally, there was definitely an urgent need for action. Chapfensee-Plons power plant was showing its age and was requiring maintenance and repair work increasingly frequently; there was also a need for urgent renovation of the penstock and the two dam walls at Chapfensee reservoir. “If we had no longer been able to guarantee the safety of the plant, the power plant would have had to be switched off – with clear economic consequences,” says Erich Riget. To avoid a patchwork of expensive individual measures and at the same time to utilise its own hydropower resources even more efficiently, EW Mels made the decision to combine all renewal, renovation and expansion measures in one overall project. In 2015, a loan of 25.8 million CHF was taken out to cover the planned renovation and expansion works. The funding from the KEV (feed-in compensation at cost) which was secured beforehand ensured that the costs resulting from the investment were covered.

SOURCES UTILISED FOR POWER GENERATION
The pre-project also involved drawing up various options for the upper stage in order to determine how the individual bodies of water could best be utilised, or which possible combinations would make sense in terms of generating energy efficiently. In the end, one option emerged and the overall design also included utilising the springs of Mädems. Previously the water in the Mädems area had been collected, but not utilised for hydroelectric purposes. The plan now envisaged creating the new Weissenstein power plant at an altitude of 1,065 m above sea level in which the water from the Mädems equalizing basin is channelled through the turbine. This involved creating the Mädems equalizing basin, a storage basin at an altitude of 1,655 m above sea level with a capacity of 500 m3 into which several sources flow. From the equalizing basin, a penstock was laid to the Weissenstein central facility to produce a maximum discharge of 130 l/s. The 2,750 m long pipe traverses a natural height difference of 583 m. In the central building at a height of 1,065 m above sea level, a 2-nozzle Pelton turbine with a horizontal shaft from the company Andritz was installed. With a nominal pressure of 59 bar, the machine achieves a power output of 650 kW. The turbine is coupled directly to the end of the shaft of the 3-phase synchronous generator from Hitzinger which is driven at the high rated speed of 1,500 rpm. In a normal year, since the machine unit at the new Weissenstein PP started operating, it has been delivering around 2.36 GWh of clean electricity to overall production. Today the drinking water which is fed from the high-level sources into the new Mädems equalizing basin can likewise be utilised – at least partially – for producing hydroelectric power. For this purpose, a drinking water turbine was also installed before the mouth feeding into the small basin. The turbine of the Mädems drinking water power plant is designed for 70 l/s with a drop of 46 m. The cross-flow turbine delivers 21.5 kW of power. At any rate, in a normal year the machine contributes 120,000 kWh to the overall power generation of EW Mels.

POWER FROM THE INVISIBLE POWER PLANT
Finally, a previously unused cascade was presented as another upper stage for the existing Chapfensee-Plons power plant. Here too a new, modern small-scale hydropower plant was to be integrated. What makes the concept of the Chapfensee power plant particularly elegant is the fact that all the components of the power plant were created under­ground – and even the underground powerhouse has only a very small amount protruding out of the landscape. At the heart of this “invisible” power plant is a powerful cross-flow turbine. For this purpose, the traditional all-round hydropower company Wasserkraft Volk AG (WKV for short) from Gutach in the Breisgau region supplied a 420 kW cross-flow turbine which was designed for an extraction water quantity of 1,780 l/s and a drop of 29 metres. The turbine with two guide vanes of different sizes drives a 3-phase synchronous generator from Hitzinger via a coupling. In total, the “power couple” will supply around 1.7 GWh to the grid in a normal year. The turbine for the Chapfensee power plant was likewise chosen with careful consideration. First of all, the operators were keen at this point to install a very low-maintenance machine which was also efficient and operationally reliable. In addition, the turbine also boasts another quality feature that is rarely found with comparable turbines: It remains connected to the grid for a very long time even when there is little water. Erich Riget says: “We wanted to know precisely and tested at what point the machine stops operating. We reduced the load down to 8 kW and it was only below this that it dropped off. This is less than 2 per cent of the nominal power output, I have not encountered such a low capacity with any other machine.” Given that in January and February very little water is available, this is an advantage that should not be underestimated.

MACHINE MEETS EXPECTATIONS
However, the biggest gain when it came to increasing production capacity was achieved with the expansion and renewal of the existing Chapfensee-Plons power plant. Contrary to the initial plans, the developers from Mels decided not to convert the old power plant building in Plons. “The original plan was to have a machinery ensemble, consisting of two different machine units. This would inevitably have involved converting the existing central building. But we changed the plans, and with the type of turbine that we chose we found a solution that we could fit into the existing cubic space in the building – even if this meant that the new machine is today oriented diagonally in the powerhouse,” says Erich Riget. The model chosen was thus a single turbine which should be ideally suited to the prevailing high-pressure conditions: a 2-nozzle Pelton turbine made by WKV which offers a persuasive choice not just thanks to its high levels of efficiency, but also thanks to its exceptionally smooth running. “The machine is so quiet that you can easily have a conversation while standing next to it,” enthuses Erich Riget. He refers to “real German craftsman­ship” which exceeded all expectations. The two control nozzles and the deflector are opened via hydraulic cylinders, and they are closed by spring force. The installation has a hydraulic speed regulator unit which is suit­able for island operation and is noted for very fast response times. “This turbine really does respond very quickly thanks to the special regulator unit and the Rittmeyer controller, which is a vital prerequisite for island operation. It is a real Ferrari,” says Joachim Kipp, Senior Commissioning Engineer at WKV, with great delight.

MACHINE TECHNOLOGY FROM ONE SOURCE
With a drop of 529 m and an extraction water quantity of 1.5 m3/s, the WKV turbine is designed for an installed capacity of 7.2 MW. The impeller drives the rotor of the directly coupled 3-phase synchronous generator which was likewise produced by WKV itself. The generator weighing 35 tonnes has water cooling with a closed heat cycle and is designed for 8,000 kVA. In addition, the powerful energy converter has an external oil lubrication system for lubricating the generator bearings. Moreover, with a view to stable island operation an extra flywheel mass is attached to the generator shaft. The ball valve, which is likewise supplied by WKV, is opened via a hydraulic cylinder and closed via a drop weight. In addition, a small bypass system with a shut-off valve and energy dissipation valve was installed for draining the complete penstock. The order package for WKV generally included all the installation work, including commissioning. There were very good reasons why a single equipment supplier was trusted to deliver the machine unit for the new Chapfensee-Plons power plant, as Erich Riget explains: “It just makes sense to have a single point of contact if there are any problems with the machine. We have been really impressed with the machines from WKV.” On behalf of KeK, the Swiss electrical engineering and automation specialist Rittmeyer AG from Baar drew up a ground-breaking control engineering concept which was designed to guarantee maximum communication and control possibilities. The control engineering was designed to reflect the latest criteria and the individual requirements of the operators.

STEP TOWARDS SELF-SUFFICIENCY
In December 2018, all the relevant works on the major project in Mels were completed and the power plants started trial operation. Erich Riget is evidently proud of successfully completing the huge project, which at its peak had up to 13 construction sites operating simultaneously. He is particularly pleased that it was implemented in a net construction time of around 14 months and he is keen to emphasise the excellent cooperation between the partners involved. “If you consider that the lead time through to obtaining final permission was 21.5 years, the delivery of the actual construction was a piece of cake in comparison,” says the director of the company.
He also mentions the significant boost to electricity production which is attributable to the renewal of the Chapfensee-Plons power plant and the delivery of the small-scale power plants upstream. In total, around 7 GWh more are delivered to the grid in an average year. “In our grid, we have so far sold 34 GWh of our own power. Thanks to our new facilities, today we feed on average 35.5 GWh of electricity into our distribution grid. This ­means that we have managed to make an important leap beyond ‘energy neutrality’ and in purely mathematical terms we are now self-sufficient,” says Erich Riget with delight.