Submersible pump-turbines and motor-generators enhance efficiency in pumped storage projects primarily through their reversible, integrated design and potential for variable speed operation.
How Submersible Pump-Turbines and Motor-Generators Improve Efficiency
1. Reversible Operation
These units combine pump and turbine functions in a single assembly, allowing the same machine to pump water to the upper reservoir during low demand and generate electricity when water flows back at high demand. This eliminates the need for separate pumps and turbines, reducing complexity and losses associated with multiple machines. The reversible pump-turbine/motor-generator assemblies can operate efficiently in both modes, typically achieving round-trip efficiencies greater than 80%.
2. High Efficiency Near Nominal Power
Synchronous motor-generators used in these systems operate efficiently, typically within 90-100% of nominal power. Double-fed induction machines (DIFM) can pump efficiently even between 65 and 100% of nominal power, offering operational flexibility that maintains high efficiency across a range of loads.
3. Variable-Speed Operation
Traditional pump-turbine units run at constant speeds, optimized for either pumping or generating mode, but not both simultaneously. Variable-speed pump-turbine and motor-generator units can adjust rotational speed to independently optimize pumping and generating efficiencies. This capability reduces hydraulic losses and improves the overall energy conversion efficiency of the pumped storage system, potentially surpassing 91% efficiency.
4. Reduced Mechanical Issues
Variable speed and optimized operation reduce turbulence, cavitation, vibration, and noise that often occur during off-design load conditions in constant-speed units. This reduces wear and maintenance costs while improving operational reliability.
5. Ancillary Grid Services
Motor-generators in pumped storage plants contribute to grid stability by providing reactive power support, voltage regulation, spinning reserve, and black start capabilities. The ability to operate in synchronous condenser mode or quickly switch between generating and pumping helps balance grid loads efficiently, indirectly improving the system’s overall functional efficiency.
Summary Table
| Feature | Efficiency and Performance Benefit |
|---|---|
| Reversible pump-turbine design | High round-trip efficiency by using one machine for both pumping and generating |
| Synchronous motor-generators | Efficient operation near nominal power (90-100%) |
| Variable-speed operation | Independent optimization of pump and turbine speeds, higher overall efficiency (~91%) |
| Reduced vibration & cavitation | Lower maintenance, better reliability |
| Grid ancillary services | Improves grid stability and system responsiveness |
In conclusion, submersible pump-turbines and motor-generators improve pumped storage project efficiency by integrating pumping and generating functions into a single reversible unit optimized for variable speed, which minimizes losses, reduces mechanical problems, and enhances grid support capabilities.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-do-submersible-pump-turbines-and-motor-generators-improve-efficiency-in-pumped-storage-projects/
