PHT Project

455 kW, MA

Year: 2016
Running Gear: 3 units: Vertical shaft synchronous generator driven by a Francis turbine.  Vertical shaft synchronous generator driven by a propeller turbine, and a vertical shaft induction generator driven through a flat belt by a Kaplan turbine.
Scope: Replacement control system, switchgear, excitation, wicket gate operators..

Located in Massachusetts, this hydroelectric plant traces its history back to the late 1800s. The original timber dam was built to supply turbines for shaft power for a number of factories along the river. In 1940, the dam was reconstructed after the catastrophic flood of 1938 damaged the prior dam. The dam in place in 2016 includes two bascule gates, which can be rotated down to pass flood flows.

The hydropower plant has been repaired and upgraded many times over the decades. Prior to the equipment supplied by PHT in 2016, the plant was controlled by a PLC-5 installed in the 1990s.

The North Powerhouse generating unit, “T1,” a 1940 Leffel Z turbine with 175 KW generator, was installed at the time of the dam reconstruction. The South Powerhouse contains 2 generating units; “T2”, a 1944 Leffel A turbine with 120 KW generator and “T3,” an HSI double-regulated Kaplan turbine with 160 KW generator. T2 was relocated from a mill building along another river located in Massachusetts to its current location in the South Powerhouse in 1995. T3 was purchased new and installed in 2010, replacing a 1944 turbine-generator that had the same capacity as T2 (120 KW).

PHT was hired to provide a new control system, switchgear, excitation equipment, and wicket gate operators. The new PHT control system integrates some of the existing equipment with a suite of new components. 

Equipment installed in 2016 by PHT includes new control cabinets with PLC and touch screens, Basler 11g generator protection relays, plus new instrumentation including sensors for water level, temperatures, vibration, oil level, and speed. In the North Powerhouse, the PHT system controls the existing Payne exciter and vacuum contactor. PHT also supplied a new AC powered HPU with accumulator to control existing wicket gate operator. In the South Powerhouse, PHT supplied a new Payne exciter for the Unit 2 generator, as well as new switchgear with vacuum contactors for each generator. Unit 3 required a switched capacitor bank to correct power factor. PHT also supplied a new AC powered HPU with accumulator, plus a Woodward governor conversion to a high pressure cylinder.

In addition to unit controls, the PHT provided the new dam bascule gate controller.  A separate PLC in the gate house measures water level and gate position, and automatically lowers dam gate in the event of a flood.  This subsystem is integrated with the main control system via Ethernet communication with the other PLCs and touch screens.

The two powerhouses on opposite sides of the river communicate via fiber optic Ethernet.  This allows coordination for optimal use of river flow, by dividing flow between units and dispatching the most efficient combination of turbines for the river flow.  Additionally, each powerhouse can run in a stand-alone mode in the event that communication is disrupted.
This is the third project completed by PHT for this customer; a private company that owns and operates a portfolio of hydroelectric sites in the north eastern US.



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