KWO Enhances Hydroelectric Efficiency with Eaton’s Advanced Automatic Basket Strainer

This Swiss case study showcases the effectiveness of the Eaton Model 2596 automatic self-cleaning strainer’s effectiveness and how it was used at the Kraftwerke Oberhasli AG hydroelectric power plant (KWO) in Innertkirchen, Switzerland. Here, the challenge was to shield a vital control valve from the damaging effects of glacial runoff and suspended particles in the valves and pipes. Despite exploring various solutions, none sufficiently resolved KWO’s issues. Persistent downtime and surging maintenance expenses, primarily due to the deterioration of sliding valves, continued to plague the plant.

KWO’s Vital Role and Challenges

The Kraftwerke Oberhasli AG power plant (KWO) is crucial in producing electricity and maintaining grid stability in Switzerland, representing about 7% of the country’s total hydroelectric energy production. Energy is produced on-demand at the Grimselsee Dam, which is located at an elevation of 1909 meters above sea level. Hydroelectric dams function like natural batteries, utilising their reservoirs to store energy for generation when needed.

The Catalyst 

KWO began encountering problems due to natural glacial runoff and rainwater, which brought suspended particles. As the glacial runoff flows down the mountains, it erodes and picks up small stone particles. Arriving at the reservoir, it mixes with particles arriving through rainwater. These particles, ranging in size from 25 to 200 microns, present a significant challenge to the power plant’s large turbines, eroding the slide valves.

The slide valves are crucial in the plant’s operations, acting as pressure regulators for the ball valves that lead into the generator turbines. The piping systems are subject to high pressures, resulting from water dropping over 670 meters in height.

Limitations of Existing Solutions

An earlier solution was devised in the form of sediment-settling tanks to stop the particles from reaching the control valves. Franz Christen of BT-Hydraulik AG explained that the valves required an overhaul every three to four months. KWO also resorted to replacing these valves outright every few months; that solution became untenable as these valves ceased production. There was a dire need for a cost-effective and practical solution. Limited space, high hydraulic pressures, and environmental concerns meant they could not install larger settling tanks or switch to oil-based hydraulic systems. 

The Collaborative Solution 

With the help of BT-Hydraulik, KWO devised a way to install filtration systems right before the control valves. The experts at this Bern-based company advised KWO to use an automatic basket strainer. Conventional filtration systems become clogged and need to be serviced and replaced regularly. So, the suggested economical solution was automatically self-cleaning strainers. 

Why? 

Self-cleaning filtration systems offer the advantage of needing less maintenance, thereby minimising downtime and reducing costs. However, standard backwash filters cannot withstand the high pressures of 1,450 psi required in hydroelectric power plants. To overcome this, BT-Hydraulik collaborated with Eaton to enhance the Eaton Model 2596 automatic self-cleaning strainer, enabling it to operate effectively under these high-pressure conditions.

Customising The Strainer

Eaton’s Model 2596 strainer continuously cleans itself to remove contaminants from pipelines. But it was only designed to handle pressures up to 232 psi. So, Eaton partnered with the fluid power expert, BT-Hydraulik, to modify the strainer to meet KWO’s specifications. They reinforced the housing and thickened the cover to withstand high pressure. They also sealed the drive shaft with a four-part mechanical seal for smooth operation. They optimised the backwash sequence to prevent deformation of the strainer basket.

The Eaton Model 2596 Strainer is designed to continuously self-clean, removing contaminants from pipelines and intended initially to handle maximum pressures up to 232 psi. Modifying the strainer included strengthening the housing and making the cover thicker to endure high pressures. Additionally, they equipped the drive shaft with a four-part mechanical seal. The backwash sequence was also optimised to prevent any deformation of the strainer basket.

Filter Element Optimisation

The efficiency of the strainer’s filtration hinged on choosing the appropriate filter element. Eaton’s DuraWedge® wire, capable of filtering particles as small as 25 microns, required enhancement to resist high pressure. The V-shaped stainless steel wire filters were fortified to endure backwashing at pressures exceeding 1,160 psi. This fine filtration level successfully eliminated more than 90% of abrasive particles, safeguarding the downstream valves from potential damage.

Optimised strainer integration

They installed four customised strainers – two 2-inch ones and two 3-inch ones – for flows of 53-106 gallons per minute. The automated backwash cycle is activated when the differential pressure reaches 11.6 psi, keeping the filters from getting clogged.

That is how Eaton’s collaboration with BT-Hydraulik brought up a high-pressure filtering solution when the conventional methods failed.

Tangible results with maximised protection and minimised maintenance

KWO is currently testing its new filter system, which is expected to continue for several years. Impressively, there have been no outages, and the system is effectively meeting their requirements for maintaining and cleaning the baskets. Notably, the new system has drastically decreased wear and tear, particularly in turbine lines where the sliding gate valves are yet to be upgraded. Resulting in reduced maintenance costs and fewer interruptions, leading to significant cost savings. 

Conclusion

The combination of Eaton’s expertise in filtration and BT-Hydraulik’s knowledge of fluid power created a new solution for KWO’s specific needs. They successfully customised self-cleaning strainers to work under high pressure to reduce the abrasive wear on critical valves. This operation saved maintenance costs and made the equipment last longer.

The Eaton Model 2596 Automatic Backwash Strainer is designed to remove solids from liquids in pipeline systems without interruptions. These strainers are available in various sizes from DN50 to DN900 (with standard pressure ratings of PN10/PN16), equipped with automatic backwash and a wide selection of screen options. Contact fltr.com.au for more information on solving your fluid filtration needs.