David N. Ratliff
Marelco Power Systems Inc.
Custom-designed transformers got a bad reputation a decade or two ago. One of the knocks against them was a lack of repeatability. It could be tough to get replacements that worked like the originals after production ceased. So mass-produced components usually were the preferred choice. This despite the fact that custom magnetic components could weigh less, be cooler, and more compact. However, modern manufacturing methods have solved the repeatability problem, And ever more stringent installation constraints now make custom components viable candidates for numerous uses.
Engineers designing custom transformers have the advantage of knowing where and how the transformer will operate. They may be able to put this information to use in the design. For example, one custom-designed transformer benefited from a water-cooling system already present in a piece of equipment on which it would reside. The new 100-kVA unit weighed 230 lb less than the off-the-shelf transformer it replaced. Much of the original unit's extra weight came from the mass it needed for air cooling.
Use of water cooling isn't the only way to save weight. Transformers built using new impregnation technologies along with the latest magnetic steels and high-grade insulation weigh up to 30% less than earlier models.
Sometimes off-the-shelf transformers won't fit in the space available. For example, one system needed a 63-kVA transformer, but no distributor could supply one that fit. The solution was a custom-designed 63-kVA transformer that fit the available space with enough room for air to circulate.
Many times machinery contains electrical equipment that requires power supplied at more than one voltage or power rating. This poses a problem for off-the-shelf units that typically supply only a single voltage. So it's quite possible a piece of equipment may have five or more transformers. Frequently a better approach is to custom-design one multitapped combination transformer replacing all of the individual transformers. The combination transformer generally takes up less space, weighs less, and needs less cooling.
Engineers often ask about the repeatability of custom-magnetic components. The worry is whether a replacement unit will have the same magnetic qualities as the original custom unit. One way to solve this problem is to assign a part number for every particular design. Any change in design parameters triggers the creation of a new number. This eliminates worries about revision numbers. Every number carries with it process specifications and drawings to ensure replacements are identical to the original design even if the original is 20 years old.
Of course, modern versions of old designs can incorporate improved technology such as new insulating materials and better impregnation processes while maintaining original design integrity. But the new item will have form, fit, and function identical to that of the original first device.
Marelco Power Systems Inc.