The Shaft Extension Tubular Turbine, often referred to as the “S-type” tubular turbine, is a critical technology in the field of low-head hydropower generation. Unlike bulb turbines where the generator is housed within a submerged “bulb” in the water passage, the shaft extension design features a turbine shaft that extends through a curved water conduit to an external generator. This configuration offers distinct advantages in terms of maintenance accessibility and cost-effectiveness for specific hydraulic conditions.
Technical Application Scope
The application scope of shaft extension tubular turbines is primarily defined by hydraulic head and flow rate. They are engineered to operate where traditional vertical axial-flow or Francis turbines would be inefficient or overly expensive.
Hydraulic Head Range: Typically optimized for low-head environments ranging from 2 meters to 25 meters. Some specialized designs can extend slightly beyond this range, but the peak efficiency is usually found between 3m and 15m.
Flow Capacity: These turbines are designed to handle large discharge volumes relative to their size. The straight-through flow path minimizes hydraulic losses, making them ideal for high-flow, low-head sites.
Unit Capacity: Generally used for small to medium-scale hydropower projects, with unit capacities typically ranging from 50 kW to 15 MW.
Application Scenarios
A. Run-of-River Power Stations
The most common scenario for shaft extension units is in run-of-river projects on plain rivers or downstream sections of large basins. Because these rivers have minimal vertical drop but consistent, large volumes of water, the horizontal arrangement of the S-type turbine allows for a compact powerhouse design and reduced excavation costs.
B. Irrigation Canals and Water Conservancy Projects
Many large-scale irrigation systems feature significant drops (falls) between different elevations of the canal. Shaft extension tubular turbines are frequently installed in these “drops” to recover energy that would otherwise be dissipated. Their simple structure allows them to be integrated into existing canal infrastructure with minimal disruption to water management operations.
C. Retrofitting and Upgrading of Old Stations
Older hydropower plants that originally used vertical axial-flow units or aging Francis turbines often face declining efficiency. The shaft extension turbine is an excellent candidate for “rehabilitation” projects. Due to its flexible layout, it can often be fitted into the existing civil works of an old station, significantly increasing power output and simplifying future maintenance of the external generator.
D. Tidal Power Generation
In coastal areas with significant tidal ranges, shaft extension turbines can be utilized in tidal barrages. Their ability to handle large flows and the protection of the generator (which is kept outside the saltwater passage) makes them a durable choice for marine environments compared to fully submerged bulb units.
3. Advantages in Implementation
The selection of a shaft extension turbine in the above scenarios is driven by several practical benefits:
Ease of Maintenance: Since the generator, gearbox (if applicable), and excitation system are located outside the water passage in a dry environment, routine inspections and repairs are significantly easier and safer.
Reduced Civil Engineering Costs: The horizontal layout requires less deep excavation compared to vertical units, which is particularly beneficial in areas with high groundwater levels or hard rock.
High Hydraulic Efficiency: The simplified water passage (with only a slight curve for the shaft extension) results in high hydraulic efficiency and excellent cavitation performance.
The Shaft Extension Tubular Turbine occupies a vital niche in the renewable energy landscape. By focusing on the 2–25 meter head range, it provides an economically viable solution for harvesting energy from low-head rivers, irrigation systems, and modernization projects. As the global focus shifts toward decentralized and small-scale renewable energy, the application of S-type units is expected to grow, offering a reliable and maintainable alternative to more complex turbine configurations.
Post time: Apr-30-2026
