Background

The Bull Shoals hydro plant is owner and operated by US Army Corps Of Engineers. In the 90’s the plant replaced the mechanical fly-ball regulators with digital controls. However, in the fall of 2024, the customer felt that the frequency control of the digital controllers needed to be more responsive. The digital controllers were Allen-Bradley MicroLogic 1200. In addition, the governors would also occasionally loose the position feedback of the distribution valve.

As such, USACE decided to tender an RFP for a turn-key replacement of the digital controllers as well as any mechanical equipment related to the Electrical-Hydralic-Interface and feedback sensors. All major governor companies were invited to submit proposals.

Important evaluation factors were Reliability, Experience and Ease of use.  After a thorough evaluation the customer determined that REIVAX’s proposal would offer the best technical solution and the highest chance of a successful project execution.

Old digital governor (Allen-Bradley MicroLogic 1200).

Project completion and System details

Before starting the design of the project, REIVAX performed a condition assessment of the existing hydraulic system.  This condition assessment was essential to establish if the conceptual design in the bid stage would solve the identified problems.

When REIVAX started the pre-design, it was noticed that the old digital governor system did not have a speed (rpm) input.  During the start of the governor, the wicket gate was opened and the digital controller only became aware of the unit speed once the PTs had sufficient voltage. At this time, the PTs would provide a frequency feedback to the digital controller.

In order to improve the speed sensing, REIVAX installed a tooth wheel and two (2) inductive sensors with supports. As such, the speed sensing is derived from the new inductive speed sensors during the turbine start.  Once the PTs have sufficient voltage, the speed sensing is automatically switched from the inductive sensors to the PTs for frequency control.

Another difference in interface was the lack of CT signal to the old digital governor.  The old governor received an active power signal from a 3rd party equipment, which was used in the digital governor.

Hence, in order to make the power measurement independent, REIVAX installed a new cable for the CT measurement, so that the active power calculation could be done within the new REIVAX’s RVX digital governor controller.

Conclusion

After a successful installation and subsequent start-up, the customer confirmed that the frequency control was much tighter and that the position feedback worked consistantly.

The REIVAX life extension retrofit of the Woodward digital governor system will provide US Army Corps Of Engineers the following:

• Risk mitigation against component obsolescence
• Better diagnostics capabilities
• Built-in testing tools
• Up-to-date cyber security protection
• Trained maintenance personnel
• Fresh set of spare parts

REIVAX specializes in governor retrofits of Woodward gate shaft and cabinet actuators, but also retrofits other OEM equipment. If you are interested to know more about this project or if you have an upcoming governor retrofit project that you would like to discuss, please feel free to contact:
Bruno Campos (514) 337-3737, bruno.campos@reivax.com
Mike Wallin (514) 915-3103, mike.wallin@reivax.com

New REIVAX RVX digital governor.

New REIVAX speed measuring system.