Power Transformers Blog – Expert Safety and Usage Info

Buy 45 KVA Jefferson Electric Dry Type Transformer

The small dry-type transformer – what can one say about these marvels?  They come close to achieving the perfect combination of form and function.  Designed to be cooled by movement of air, not moving water, the dry type transformer is perfect for indoor use or anywhere that it can be sheltered from the elements: porches, below lean-tos or beneath small structures.  There are some with optional rain ‘gutters’ intended to direct water away from the transformer coils.  Wherever they are found, the dry type transformer, one of the most common type of transformers seen today.  It is the ubiquitous work horse of the industry.  The three phase 480 Volt Delta to 240 Volt Delta, from between 50 to 150 KVA, are among the most popular.  As many utilities have moved to away from offering 240 Volt services, they are commonly used to transform the incoming 480 Volts to power 240 Volt equipment.  Most are designed so you can usually run them backwards to produce 480 volts from 240 volts. What happens when this very reliable workhorse fails?  No spare readily available, you obtain a replacement.  Right?

But why wait till then?  It would be good practice if they were looked at occasionally, once installed, but small transformers of this type are typically not tested during routine plant shutdowns.  So they are frequently used as tables, workbenches, shelves, ladders or stationary hotplates to keep lunches and bakery warm.  There are usually indicators well in advance of a transformer’s doom.  Little warning signs that if left uncorrected will lead to failure; excessive noise, excessive vibration, the usually warm transformer gradually becomes hot to the touch transformer.  If you look underneath one and see only dusty clogged vents, chances are it is running at a higher temperature than recommended. 

At MIDWEST we perform an insulation resistance test and load test on all of our reconditioned transformers before they leave our door.

Meanwhile take care of the dry type transformers you are presently using.  Be smart and keep them free and clear from clutter, dirt and moisture…

The good news is if the need for replacement arises, you can usually find something to take the place of the one you just lost.  You can buy a new one from us because the manufacturers still make them or you can ask us for a quote on a reconditioned transformer.   

Transformers are placed in parallel by electric utilities when they want to provide a ‘stronger’ voltage source and will result in higher available fault current that can be delivered downstream.  Usually the utility transformer can serve its own load but two are put together to achieve with a ties primary and secondary bus to ‘stiffen’ the voltage to ride through system load changes.

Yes the utilities have to worry about automatic load tap changers that could hunt forever.

Some industrial customers try this method to serve a load that is too large for a single transformer.  This arrangement has to be done carefully or you can damage one or both of the transformers.  You need an exactly matched pair of transformers or transformers of different manufacturers with identical characteristics or circulating currents can build up in the parallel connection that consumes energy and does not pass to the load.  Routine maintenance of the parallel connected transformers in the non-utility world is nixed because neither transformer is big enough to serve the load on its own.  This would mean extended outages to the load during maintenance of either transformer.  Parallel connections of transformers in the industrial world are usually not attempted because the lack of maintenance makes for a less reliable installation.  Transformers come in various sizes and the best or optimum transformer size is one that can adequately handle its load all by itself.

Customers can be skeptical of purchasing a transformer used compared to buying a new one.  It is understandable since a transformer is an electrical device, there is always the possibility that the unit is on its last legs and could fail and then the buyer is faced with the costly disposal of a cumbersome item that has little or no value.  But look at the cost savings if you can find a quality unit on the secondary market that will do the job compared to a new one priced at full retail or wholesale from a supply house.  There are many ways to obtain a transformer that is not ‘new’.  The secondary market can include demolition companies, scrap yards, friends, closeouts, new surplus, scratched and dented etc.  You can also find reconditioned units that have been tested and carry a warranty that is usually as long as the one offered when the unit was new.  Shopping for a transformer requires some homework to know every last detail of the transformer you want so when you stumble on a ‘non-new’ transformer, the lead time is immediate and you can snatch it up before somebody else does.  In the event you can’t find a bargain, you can always hope someone has a new one in stock.