PHT Project
3.3 MW, MA
Year: 2022
Running Gear: 3 Vertical shaft Francis turbines with synchronous generators
Scope: Replacement of control system, exciters, HPUs
This is the third controls upgrade project completed for this customer, who operates a portfolio of hydroelectric plants in central MA.
Originally constructed in 1928, this hydroelectric power plant was owned and operated for many years by the local utility, until it was purchased by the current owner in 2017, as part of a sale that included a handful of other plants in the area. The project today consists of a masonry overflow dam and canal gate intake structure, a 1300 foot long canal, forebay, trash racks for each of the generating units, and a powerhouse with three vertical shaft generating units, for a total capacity of 3.3 MW.
Prior to the extensive upgrades in 2021 and 2022, the existing equipment was a mix of hardware vintages dating back to original construction, and redone as recently as 2005. The controls and switchgear were mostly from the 1980s and 1990s, and had become unreliable, unsupportable, and difficult to diagnose and operate. Operations required extensive on-site labor time, plant trips were frequent and difficult to troubleshoot, and the control system lacked features to enable effective operation.
PHT was hired to provide a new PLC based control system, excitation, and new hydraulic power units for wicket gate control, while another party was hired to provide all new switchgear and station electrical service. All of the old control and switchgear equipment was demolished and removed from the powerhouse and replaced with new, modern equipment in late 2021, and the plant was re-commissioned for operation in February 2022.
The PHT provided automation system for the plant includes new Power-Tronics static exciters, and additional instrumentation and machine condition monitoring. As is typical of most retrofits of older generating units, in addition to integrating some of the existing equipment, PHT provided a suite of new sensing and machine protection, including; new water level sensors, RTD temperature sensors on the stator, bearings and oil loops, added RPM and vibration sensors, oil level sensors, and more. PHT standard hydraulic power units (HPUs) replaced the original Woodward governors for wicket gate control.
As is often the case, plants that have been modified over many years are poorly documented, and often the customer themselves are not aware of how many subsystems work, or are intended to work. Part of the value PHT provides is to evaluate existing equipment and make recommendations for re-use, modification, or replacement to ensure reliable operation for many years into the future. For example, at this plant, re-using the existing bearing lubrication system for two of the units was the clear cost-trade-off solution, but required reverse engineering and some modification to address existing problems and provide for reliable integration into the new automation system. Such system integration and improvement for unit and auxiliary equipment is common for PHT control system upgrades.
The new PHT controls include automatic pond level control, including response to peaking inflows from another plant upstream, automatic starting and unit dispatch, user friendly alarming and notifications, and remote access. User controls, data, trending, and operational reports are accessed through the easy-to-use touch screen user interface. Per usual, PHT designed and assembled the hardware and control cabinets for this project at our shop in NC, and then traveled to MA for installation and commissioning.
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