Variable frequency drives supplied for retrofit project

Siemens is supplying two Robicon Perfect Harmony VFDs to the Otter Tail Power Company for their plant in South Dakota as part of a $490 million environmental retrofit project that is scheduled for completion by 2015.


Siemens, in partnership with Fougner Engineered Sales, has been selected by Otter Tail Power Company to provide two Robicon Perfect Harmony variable frequency drives (VFD) for environmental upgrades at the Big Stone Plant, a coal-fired power plant that the company operates in Big Stone City, South Dakota.

In May, plant owners Otter Tail Power Company, Montana-Dakota Utilities Co., and NorthWestern Energy, approved a plan calling for $490 million in environmental retrofits, including a new air-quality control system to be commissioned within five years of the Environmental Protection Agency's approval of the South Dakota Regional Haze State Implementation Plan.

Two Siemens Robicon Perfect Harmony WCIII drives will support a new dry scrubber to reduce sulfur dioxide. Plans also call for a selective catalytic reduction (SCR) unit to reduce emissions of nitrogen oxide. 

Siemens Robicon Perfect Harmony Drives use a series of low-voltage cells linked together and scaled precisely for a wide range of voltage and output power. The cell bypass ensures automatic bypass of a failed power cell in less than 500 milliseconds and instead of shutting down the entire drive, a process-tolerant protection system (ProToPS) provides a hierarchical system of warnings. This control strategy allows time to evaluate the situation and respond appropriately. This concept also enables easy access to drive components for scheduled maintenance. Siemens VFDs also meet IEEE 519 standards for input power harmonic distortion.

Otter Tail Power Company estimates that retrofits to the 475-MW Big Stone Plant, in operation since 1975, will be completed by mid-2015.


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