Nam Theun 2 Power Company Limited operates a large-scale hydropower plant in Laos, where four turbines collectively generate approximately 1000 MW of electrical power. Each turbine is a critical component in the energy production process and must be protected against unsafe operating conditions such as overspeed.
An overspeed detection system functions as a dedicated safety layer within rotating equipment. It continuously monitors rotational speed and initiates a shutdown when predefined limits are exceeded, preventing mechanical damage and unsafe situations.
Challenge: Replacing the Jaquet T401 Overspeed Detection System
The existing overspeed detection system at the plant was based on the Jaquet T401 platform. Over time, the system had become obsolete, making maintenance and troubleshooting increasingly difficult. Spare parts availability and system flexibility were limited, which reduced the ability to adapt the system to current operational requirements.
The complexity of the project increased due to the plant configuration. Each of the four turbines required its own independent overspeed protection system with a 2oo3 voting structure. This type of configuration relies on three independent measurement channels to ensure reliable detection and safe shutdown behaviour.
In addition to the technical challenges, the replacement had to be carried out without interrupting ongoing plant operations. The new system needed to integrate with existing SCADA and EWS environments while maintaining full visibility of alarms, trip signals, and system status.
Solution: Using SpeedSys® 200 for Turbine Overspeed Protection
TriSystems engineered and delivered a new Overspeed Detection System panel to replace the existing installation. The solution was based on the SpeedSys® 200 Overspeed Detection System, with Istec providing the hardware and technical support during the project.
For each turbine, a dedicated 2oo3 voting structure was implemented using three independent SpeedSys® 200 modules. In total, twelve modules were installed across the four turbines. This configuration ensures that an overspeed trip is only initiated when at least two out of three channels detect an overspeed event, providing a robust and fault-tolerant protection mechanism.
The modular design of SpeedSys® allows for scalable system architectures and enables low-impact retrofit installations. This makes it possible to integrate the system into existing infrastructure without major modifications, while maintaining compatibility with different sensor types and control systems.
Execution of the Multi-Turbine ODS Retrofit Project
The project was executed by TriSystems, who were responsible for engineering, installation, configuration, and commissioning of the new ODS panels. Istec supported the project through the supply of SpeedSys® 200 modules and technical guidance during system design and validation.
During installation, each turbine system was configured individually, including its voting logic, signal processing, and trip outputs. The systems were integrated into the existing SCADA and EWS environment to ensure full operational visibility and control.
System validation was carried out through a structured Site Acceptance Testing process. Overspeed conditions were simulated to verify the behaviour of the detection logic and the correct activation of turbine trip signals. Such simulation-based testing is essential, as it allows full system verification without exposing the turbine to actual overspeed conditions.
Key Deliverables
- Engineering and delivery of new ODS panels for four turbines
- Supply of twelve SpeedSys® 200 modules
- Implementation of four independent 2oo3 voting structures
- Integration with existing SCADA and EWS systems
- Configuration, testing, and commissioning of the full system
Results of the Overspeed Detection System Upgrade
Following commissioning, the new overspeed detection system is fully operational across all four turbines. Each turbine now operates with an independent and consistent protection system based on a standardised architecture.
The Site Acceptance Testing was completed successfully, confirming accurate speed detection and reliable activation of turbine trip mechanisms under simulated conditions. The system was accepted by the client without critical outstanding issues, demonstrating that the implementation met all functional and safety requirements.
The transition to a modular system improves maintainability and allows for easier future modifications. The standardisation across all turbines simplifies system management and reduces complexity within the plant’s protection infrastructure.
Conclusion
This project demonstrates the replacement of an obsolete overspeed detection system across multiple turbines using a structured and scalable approach. By combining the engineering and execution capabilities of TriSystems with the SpeedSys® 200 platform and technical support from Istec, a consistent and reliable protection system was implemented.
The result is a maintainable and clearly structured overspeed protection solution that integrates with the existing plant infrastructure and supports safe long-term operation.
