Operations & Maintenance – Balance of Plant – North Pole Expansion Plant

The relentless drive for performance enhancement

North Pole Expansion Plant
Golden Valley Electric Association Inc

 Challenge. Plant engineer Paul Park was developing operating procedures for training purposes when he discovered that a 250-hp backup boiler-feed pump was drawing one-third of its full-load amps while offline. I&E Supervisor Ian Strang and his team of electricians—including Steve Wengelewski, Nate Callis, and Jay Adams—verified that the 480-V, variable-frequency drive (VFD) was drawing 55 amps in motor-off/standby status. Further investigation found that the harmonic filter installed with the VFD was source of that load (Fig 14).

Solution. Plant I&E personnel were challenged to eliminate electrical consumption by the standby pump. Logic drawings provided by the VFD OEM for the drive, inverter, and harmonic-filter installation were studied. A normally open relay installed in the inverter contactor circuit was proposed as a means for de-energizing the harmonic filter in standby operation.

  The OEM approved the change and plant I&E personnel performed the relay installation and programming revisions in the plant control system (Fig 15). Now, when a pump start is commanded by the plant control system (PCS), the new relay is closed and powers up the inverter/harmonic filter, a 1-sec timer activates, and the VFD is started. A local bypass was installed around the new relay so the inverter/harmonic filter can be energized in manual if required (Fig 16).

Results. This simple retrofit saves more than 11 MWh/month in plant electrical use and represents an electrical energy saving for the facility of nearly 1%. Total cost of the project was approximately $3000 including parts.

   This remote combined cycle burns naphtha from a nearby refinery as its primary fuel, making wasted therms quite expensive. As employees and co-op members, we are proud of reducing plant energy use by 15 homes worth of power per month with this upgrade.