Power Transformers Blog – Expert Safety and Usage Info

At MIDWESTwe often get calls or receive inquiries from individuals or company employees seeking an exact transformer replacement for a particular unit.  The reasons are numerous.  Their existing transformer failed suddenly or they have a transformer that is in the process of failing.  Maybe they are trying to expand their facility with limited funds and do not want to pay for the services of an engineering consultant.  They look around and decide to copy what they already have and reason if they just had another one just like it and moved the walls out a bit, their newly purchased used machine ( another blog at another time) which hopefully will mean more income.  Possibly the building has a new owner and they are looking for a spare transformer (a gold star to them for being pro-active).  ‘Finding another one just like it’ is easy if you are shopping for a jar of Jiff ® or Skippy®.  But looking for running shoes just like the kind you purchased last year can be difficult.  Now you can imagine just how difficult it is to locate an identical twin to transformer in a building over thirty years old, assuming the transformer nameplate exists, is still legible and not covered with paint.  If you are fortunate to have the model or type number, a Google search may yield a possible match. Hopefully it is an available unit for sale and not a line item on a specification for a future construction project.

A GOOGLE search with only the transformer brand will help you find a soulmate who is usually looking for product data or a wiring diagram for that brand of transformer. 

Sadly, some transformer companies are no longer in business, their assets were sold to another company, the factory shuttered and you trail runs cold.

Assuming the transformer was not built for an Arc furnace and is a one-of-a kind relic (see future blog) you can usually replace a transformer that was made by company X with a transformer that was manufactured by Company Y.  To do so requires a complete list of specifications with all available information on the transformer whether you think it is relevant or not.  There are a lot of parameters that need to be known: KVA, footprint, height and weight, impedance and most importantly the primary and secondary voltage and also if this is a single phase or three phase transformer.  You also need to know where the transformer will be used (outdoors, indoors).  If it is a fluid filled unit, what type of fluid?  If it is a dry transformer (conventional dry type or encapsulated).  You have to know if this transformer needs to have high side voltage taps and if the primary and secondary are Delta or Wye.  If it is a large power transformer, where are the bushings and how are they arranged. Doing your homework first before you have the transformer shipped to you from another state will help you avoid the embarrassment, grief and additional charges that will rack up if the replacement transformer arrives and it will not fit or is suitable for the application or you discover your cable stretcher is undersized.

by Vince

How does an air cooled or ventilated electrical power transformer located outside in the rain survive?  Why doesn’t the rain cause an electrical short? These are the occasional questions of someone who wants to replace an existing dry type or air cooled transformer with a larger power transformer, when the existing power transformer is located outside, exposed to the rain, wind and sometimes snow.  It does look a little strange sometimes, but the general purpose air cooled dry type electrical power transformers are fitted with weather shields. They should be. If they are not, you will find out very quickly the first time it rains. The weather shields are metal shrouds, hoods, fastened over the upper vent openings. They prevent rain and snow from entering the top open vents of the transformer. This is true as long as the rain is falling vertical or possibly at a 45 degree angle. The rain or snow hits the weather shield and drips off rather than landing inside the metal enclosure of the air cooled power transformer.  We do see these 50 kva, 75 kva, or even 150 kva air cooled transformers fail. This really does not happen very often. And when it does, it’s usually because of a very unusual storm. Possibly where the wind is so strong, the rain is being driven almost sideways. More often we see failures due to snow filling the inside of the metal enclosure due to swirling and drifting of snow about and eventually inside the enclosure. We have seen this happen with 5 kv and even 15 kv class transformers. We are not fans of medium voltage outdoor air cooled transformers. As long as the enclosure remains intact, there should be no problem. And as long as there isn’t some unusual weather condition, they should be okay. In our business the term “should be” makes us cringe. When folks use the term “should be,” we think “sooner or later.”  It’s healthy to be paranoid around electrical power.