High Voltage Dry Type Transformers Over 600 Volts

A dry type transformer is a voltage changing (Step-up or Step-down) or isolation device that is air cooled rather than liquid cooled. The transformer case is ventilated to allow air to flow and cool the coil (coils).

MIDWEST sells and rents new and reconditioned used transformers. We can often find repaired, overhauled, or obsolete transformers and offer substantial savings over new units. We can recondition and repair a transformer so that is looks and performs like new.

Dry type transformers are a cost effective way to get a desired voltage not currently available. Sand cast coils are available for applications requiring low noise levels. Medium voltage dry type transformers are often used in unit substations in large commercial and industrial applications.

Transformers of this size are usually used for distribution or general purpose applications. These power transformers have electrical properties that allow them to be used in wide and varied applications.

Yes but obtaining a larger transformer would be a better long-term solution. Transformers that are truly in parallel have their primary windings connected together and their secondary windings connected together. If you used a matched pair from a given manufacturer, ABC Serial number #128 and #129 and set them on the same high side tap and hooked the units in parallel, they would act like a transformer twice as big as seen from the load. Both transformers would share the load equally assuming all wire distances were equal, etc. The result of the transformers in parallel would provide a higher level of available fault current than what a transformer, alone, could deliver. If this is done with dissimilar transformers (different voltages, different tap ranges, different impedance, different sizes) you can get circulating currents between the two transformers in addition to the current flowing to the load. The circulating currents can be destructive and can lead to premature failure of one or both of the transformers. If either of the transformers fails while carrying the load, the remaining transformer will see the entire load. This we already know was too large for the first transformer and the reason the question was asked about connecting two transformers in parallel. The arrangement of parallel transformers to serve a much larger load is poor because neither transformer can be taken out of service with the load energized. Such an arrangement can lead to an extended period when routine maintenance is missed or skipped and minor issues are left unresolved which can progress further and lead to eventual transformer failure of one or both transformers. Generally, if a transformer is too small to serve a load it should be replaced by a unit that is large enough to serve the load without any additional help.

This Question comes up frequently with new customers. The answer may be obvious and may not be so obvious. The cost of a used transformer is approximately one-half that of a new transformer. Lead times for used transformers are about 2-3 days on average. Lead times on new transformers are considerably longer: they vary from 2-3 weeks for smaller sizes (<150 kva) to 3-4 weeks for larger sizes. The lead times may be even longer if uncommon voltages are involved, (480/380, 600/480).