Extending Static Excitation System Life

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Extending Static Excitation System Life

Built in 1929 and operating since 1931, this 85MW hydro plant in southern Quebec underwent it’s latest excitation system upgrade in 1994.  23 years later, the Owner determined that a failure in the excitation system could lead to a significant loss of revenue due as OEM technical support and spare parts were difficult to come by.  The existing excitation system was a UNITROL equipment with single channel controls and redundant thyristor bridges.

The existing power section was experiencing some occasional overheating issues, but was still in relatively good condition, so the owner decided to tender the replacement as an excitation front-end control upgrade and retaining the existing PPT, thyristor bridges, breaker, discharge circuit etc.  

REIVAX was awarded the upgrade project by offering a solution with the following benefits:

  • Increased system reliability
  • Better Mean Time To Repair (MTTR)
  • Extending the unit life expectancy
  • Improved NERC testing capabilities

After a few months of operation of the new system, the customer was asked to provide a performance feedback on the overall experience with REIVAX and the product performance and gave an overall Excellent rating with a recommendation to buy from REIVAX again should the need for another excitation system arise.

Reivax's solution

An increased system reliability was achieved by implementing redundant control channel in the same overall space as the existing controls.  In the event of a failure in one of the control channels, the stand-by controller automatically takes over without any interruption in operation.  See the below picture of the front-end control upgrade mounting plate installed in the existing cabinet.

The existing thyristor bridges were operated as a 1+1 system, where one active thyristor bridge assumed all the field current.  The excitation cabinets are located close to some hot air from the generator and would occasionally cause a unit trip due to over temperature.  REIVAX bridge interface allowed the bridges to operate in parallel, thus sharing the current and operating at a lower temperature, hence improving both reliability and extending the life expectancy of the power section.  To accomplish this, Hall Effect CTs were installed for current sharing purpose and PT100 sensors were added, so that temperatures could be monitored more accurately and to have the ability to pin point the exact failure location, see the below picture.

REIVAX intuitive 15” HMI interface provides an automatic tuning tool for both the AVR and PSS functions.  The built-in step response function allows the user to validate that the chosen tuning parameters provide the acceptable response.  The same function also allows the user to easily perform NERC testing.  The AVR transfer function, as per IEEE 421.5, is illustrated on the HMI screen with access to the various excitation limiter functions.  The built-in frequency response tool with the result in a Bode plot makes for a very powerful, yet simple way to tune the Power System Stabilizer (PSS), see the below picture.