PHT Project
3.4 MW, NC
Year: 2022
Running Gear: 2 vertical shaft Francis turbines with synchronous generators
Scope: Replacement of control system, excitation, and governors
Set in a resort town in the mountains of North Carolina, this hydroelectric project was originally constructed in 1925-1926 by a private developer. Its primary purpose was to create a beautiful lake as the centerpiece of a huge resort/real estate development. The dam's power plant began operations in 1928 with the sale of electricity under a 10-year contract to a local predecessor of Duke Energy. The dam, power company, and real estate were acquired by the Town in 1965, and has since operated as a municipally owned project.
The concrete arch-buttress dam is 120 feet high and impounds approximately 800 acres. Buttress walls separate its 10 interior bays, and a gravity section on the left abutment contains three radial Tainter spillway gates and one radial trash gate. In 2022, the original 1920s generators and turbines had been maintained and re-built, and are capable of running for many more years. The balance of plant equipment, however, including the control system, was a mix of hardware vintages dating back to the 1980s and earlier.
By 2022, the control system was obsolete, unable to be supported, and lacked modern features to enable effective operation. The previous controls used a dead-field start, rather than properly synchronizing the generators before bringing them online. In a dead-field start, the synchronous generator is sped up to near its operating speed, without the rotor field energized. The excitation is not brought up until after the breaker is closed. While this technique had worked for over 30 years, it also caused a noticeable voltage sag in the town at every startup. Other issues included the Tainter spill gate controls, which were manual-only. This required an operator to be on top of the dam to open the gates, often in terrible weather.
PHT was hired to provide an upgraded control system, including new Power-Tronics static exciters to replace the original rotary exciters, and new hydraulic power units for wicket gate control. The new controls provide automatic start and synchronization, which is much smoother than the dead-field start, and eliminates the power quality problem during startup. The Tainter spill gates were fitted with position sensors, and a PLC and touch screen, to allow control from the powerhouse and operations center. Other features include:
Automatic pond level control
Generator and electrical protection
Machine condition monitoring
Effective alarming and push notifications
The new PHT controls also use fiber optic communication and coordination between the powerhouse, dam, and operations center.
User controls, operational data, trending, and operational reports are accessed through the easy-to-use touch screen interface. PHT assembled the hardware for this project at our shop in NC, and then traveled to the power plant site for installation and commissioning.
