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The original ABB UNITROL F excitation systems at US Army Corps of Engineer’s (USACE) Fort Gibson hydro plant were installed and commissioned in 2005. In 2023, the customer made a decision to perform a life extension (Front-End Control Upgrade) on the four (4) static excitation systems.

When consider upgrading a digital static excitation system, there are three (3) options to consider:

1. Complete replacement of the excitation system and the excitation transformer (PPT).
2. Replacing the excitation system, but maintaining the excitation transformer (PPT)
3. Replacing the excitation controls and SCR bridge interfaces (Firing Cards). The power section of the system is maintained.

Old ABB UNITROL F excitation control door.

Option 1 is obviously the most expensive option to procure as well as to install. This may be a preferred option if the excitation power section is either not reliable or if it was undersized when originally installed. New grid codes, requiring the system to operate at a higher ceiling voltage, or a generator upgrade, requiring more field current, may also be a reason to replace the complete system including the PPT.

Option 2 may be the best option if aging parts is an issue for both the controls and power components.

Option 3 often referred to as a front-end control upgrade, is an increasingly common retrofit approach. It is the least costly option to procure as well as to install. The primary reason for this type of refurbishment is that microprocessors in some control boards have reached end-of-life and are no longer manufactured or supported. The upgrade could also be driven by a need for better diagnostics offered in newer digital excitation systems, or easier interface to perform NERC model validation testing.

FRONT-END CONTROL UPGRADE

New REIVAX RTX Power excitation control door.

In the case of Fort Gibson, USACE selected option 3 and after a competitive RFQ/RFP process, the contract was awarded to Reivax North America inc. The scope included design, equipment supply, interface engineering, removal/install, commissioning and NERC model validation.

Aside from the excitation controls and SCR bridge interface boards, Reivax solution also included a 15″HMI screen for the new REIVAX RTX Power excitation controls. The pictures to the right shows the door mounted equipment of the original UNITROL F system vs the new REIVAX RTX Power door mounted equipment.

PROJECT COMPLETION AND SYSTEM DETAILS

The original system had a max continuous field current rating of 815 Adc, which was maintained with the new front-end control upgrade. The existing system had redundant excitation controllers and redundant SCR bridges. The same system topology was maintained with the new Reivax RTX Power system.

Original UNITROL F control mounting panel.

New Reivax RTX Power Control Mounting Panel.

In order to facilitate a fast installation of the new RTX Power excitation controls, Reivax delivered the redundant excitation controls on a mounting panel, which fit into the existing cabinet. All existing field wiring was left terminated on terminal blocks for external wiring, which were located on the left and right side of the cabinet. The new RTX Power excitation control panel included a wire harness, which was connected to the other side of the terminal blocks for external wiring.

The original SCR bridge interface boards were also replaced by REIVAX SCR interface boards.

EXCITATION LIFE EXTENSION

The REIVAX life extension retrofit of the UNITROL F static excitation system will provide US Army Corps of Engineers the following:

• Risk mitigation against aging control components
• Better diagnostics capabilities (SOE, datalogger, pinpointing fault location etc.)
• Easier NERC testing capability (built-in testing tools)
• Up-to-date cyber security protection
• Trained maintenance personnel
• Fresh set of spare parts for the excitation controls

If you are interested to know more about this project or if you have an upcoming excitation project that you would like to discuss, please feel free to contact:

Mike Wallin (514) 915-3103, mike.wallin@reivax.com
Derek Monk (514) 236-6588, derek.monk@reivax.com