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A groundbreaking pump - pioneering storage pump

Increases efficiency by more than 7% while simplifying maintenance and ensuring long-term reliability. 

Austrian utility Kelag decided to invest in the replacement of the Oschenik 1 storage pump, a key component of the Innerfragant pumped storage power plant. The Innerfragant pumped storage scheme represents one of the most important assets in Kelag’s hydropower portfolio. The Oschenik stage contributes 98 MW of the plant’s total installed pumping capacity of 230 MW and plays a vital role in energy storage and grid balancing.

ANDRITZ Oschenik 1 storage pump at the Innerfragant pumped storage power plant in Austria

Advanced design for higher efficiency and easier maintenance

Following a competitive evaluation process, ANDRITZ was awarded the contract to design, manufacture, and commission a completely new pump concept. The result was a technological milestone: a six-stage storage pump featuring an internal spiral casing and a horizontally split pump casing – a configuration that had never before been implemented in this power and pressure class. Today, the pump has proven its performance in daily operation, delivering an efficiency increase of more than 7% compared to the previous unit.

This innovative configuration offers several advantages:

•    Simplified assembly and disassembly of the rotor
•    Significantly reduced maintenance time
•    Improved accessibility for inspections and service activities
•    Enhanced operational availability through shorter outages

ANDRITZ storage pump multi-stage impeller at the workshop in Austria
ANDRITZ storage pump multi-stage impeller at the workshop in Austria

Oschenik 1 storage pump at the Innerfragant pumped storage power plant in Austria

Oschenik 1 storage pump at the Innerfragant pumped storage power plant in Austria

Engineered for extreme conditions

The Oschenik 1 pump operates under exceptional hydraulic conditions. During operation, pressure increases from approximately 262 meters water column at the first stage to around 1,220 meters water column in the spiral casing. To withstand these loads, ANDRITZ engineers developed a highly robust bolting system for the split casing. The design employs high-strength martensitic materials and a multiple-bolting concept using large-diameter M120 and M140 fasteners equipped with Superbolt tensioning technology. In total, 852 bolts secure the two casing halves.

Designed for a lifetime

Long-term reliability was a primary project objective. Based on expected operating conditions of approximately 3,200 operating hours per year and up to 10 start-stop cycles per day, the pump was designed for an estimated service life of 75 years. Material selection played a decisive role in achieving this target. Together with Kelag, ANDRITZ selected a corrosion-resistant martensitic chromium-nickel-molybdenum steel for both upper and lower casing sections. This material provides superior mechanical strength while eliminating the need for additional corrosion protection. Special attention was also given to rotor components, including the shaft and impellers. To prevent galling between mating surfaces, ANDRITZ implemented advanced surface treatment solutions that significantly improve wear resistance and operational reliability.

ANDRITZ storage pump casing at the workshop in Austria

Innovation milestone

The Oschenik 1 project represents a significant innovation milestone for ANDRITZ. Never before had a storage pump with an internal spiral casing and horizontally split housing been built in this power and pressure class. The successful implementation of this concept demonstrates the capability of ANDRITZ to deliver innovative solutions for challenging pumped storage applications. After years of successful operation, the pump continues to confirm the benefits of the design. The project serves as a proven reference for future pumped-storage installations where high efficiency, reliability, maintainability, and long service life are critical requirements. Through close cooperation with Kelag, ANDRITZ transformed an ambitious engineering concept into a highly successful operating reality.

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