Coal Age

JUN 2018

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38 www.coalage.com June 2018 operating ideas Short-Circuiting the High Cost of Transformer Upgrades Ameren's Rush Island generating station's use of retrofitted transformers offers insights for any plant that seeks to increase capacity on a budget Increase capacity. When the call comes from upper management to produce more energy, a plant manager faces the chal- lenge of upgrading the infrastructure, and upgraded power transformers often repre- sent the biggest ticket item. Adding to the expense is the fact that such change-outs usually require com- pletely reworking the connections to and from the transformer. When spatial con- straints that require rebuilding a new en- closure or pad mount are factored in, the prospect of increasing capacity can ex- plode into a budget-busting endeavor. In response, many plant managers are discovering the advantages of new retro- fit transformers. These fully customized power transformers provide the benefits of increased power capacity while dupli- cating the form and fit of the originals. The option of a perfectly matched, plug-and- play transformer holds the potential for capacity upgrades that meet regulations, timelines and budgets. The experience of one major power utility demonstrates that plant managers can successfully balance the demand for upgrades against the cost constraints set by the controller by retrofitting. Saving Money in the 'Show Me' State Since "first fire" more than 40 years ago, management at Ameren Missouri's Rush Island Energy Center in Festus, Missouri, has run a tight ship. The plant's two coal- fired generating units have often scored one and two in the nation for the lowest NOx produced by units without selective catalytic reduction, while producing 1,242 megawatts of electricity. Here, the impetus for transformer up- grade stemmed from a larger project that re- quired more power for added in-house load. "We were upgrading our bottom ash system, changing from a wet sluicing sys- tem with bottom-ash clinker grinders to a submerged flight conveyor, and the exist- ing auxiliary boiler stood in the way of the conveyor," said Herb Fischer, consulting engineer, Rush Island Technical Support. "So, we demolished the old aux's boiler and put in a new one." The jump from 75 horsepower (hp) to 250 hp needed for the forced draft fan on that boiler drove the need for the larg- er transformers. The load study called for upgrading the supply transformers from 1,000 kVA to 1,300 kVA. On the face of it, ordering bigger trans- formers with larger secondary windings would seem simple enough, except that Fischer and his team faced the difficulty of having to fit the new transformers into an existing cabinet with no leeway for extra girth. Rebuilding the enclosure and reworking the terminations would have pushed back the project deadline and led to a large cost overrun. "There were several components in- volved in making a decision for the replace- ments, and cost and fit were high on the list," continued Fischer. "For those reasons, we had to have a supplier that could handle this type of custom work, and having used ELSCO Transformers before we figured that was the route to go. They built a number of units for us that continue to operate in our boiler circulation pump application." Founded in 1912 by former Westing- house engineers, ELSCO specializes in providing new, repaired and rebuilt trans- formers with ratings ranging from 500 kVA through 3,750 kVA in 2.5, 5 and 15 kV pri- mary voltages, including both liquid-filled and dry-type models. The project took place at a dou- ble-ended unit substation within the ener- gy center and only four days were allotted for the complete removal of the old trans- formers and the installation of the two 6,900-V to 480-V replacements. "The enclosure was going to stay so the dimensions had to fit and the transform- ers had to match up with the high-voltage connection and the low voltage bus bar," explained Fischer. "Not having to perform any field modifications was critical, so only a duplicate retrofit would do." Customized transformers provide increased power capacity while duplicating the form and fit of the originals. For the retrofit manufacturing process, hand-wiring yields the highest quality.

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