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

This MIDWEST blog is about a low voltage, high current transformer used in a hardening process. The transformer was physically located deep in the process equipment. It was very difficult for the owner to access the transformer for maintenance. They just could not maintain it during normal production schedules. The process operators were having more and more trouble controlling the output voltage and current. It got to the point they just could no longer regulated the output current as necessary to perform the metal hardening process. MIDWEST was contracted to remove and replace the transformer or repair it. Whatever could be done. When the transformer was being removed, the problem was found immediately.  There were massive copper bus bars on the secondary side of the transformer to carry the high currents. One of the output bus bar bolted connections had failed. It was held by only four bolts and the bolted connection had become loose. The copper at the connection was discolored and distorted from overheating. The connection contact surfaces were all destroyed by being overheated.  The damaged copper and damaged connection contact surfaces for this damaged transformer could not be repaired. The copper was damaged all the way into the winding. All the other connections were intact. The repair bill was over $50,000.00. This four bolt connection cost over $12,000.00 per bolt to repair.  The transformer replacement was not caused by a transformer failure, but by a simple bolted connection failure. MIDWEST frequently finds dry type transformer failures or replacement transformer projects are caused by the most probable failure mode because the needed preventive maintenance was not performed, because it would have been relatively expensive compared to routine, specified, maintenance. Everyone understands the value of the maintenance dollar. But it does not make sense to continually spend hard to get maintenance dollars on preventing very low probability failure modes and totally ignore the most probably failure mode all together, when the most probable mode would be catastrophic and the low probability failure modes have little consequence.  This is a nightmare for maintenance supervisors. It can be tough to sell critical maintenance procedures that are not found in standard maintenance specifications.

MIDWEST works a lot with electricians, maintenance mechanics, and other assorted electrical folks that have the every day job of keeping production machines running. When they call for help, for example when they suddenly need a replacement transformer, they want the short answer to their question. Sometimes you can tell from the edge in their voice that they are overwhelmed, in a real jam, and, if we put more burden on them by asking twenty questions about their old transformers, they are just going to stop listening, say thank you, and hang up. They want an immediate short answer to their immediate question.  This isn’t always possible or safe, but, since we have so much field service experience, we usually can get to the point quickly.

Sometimes the simplicity of the request can be amazing. For example, we had an electrician call during his lunch break and ask how he could tell if one of their old dry type transformers, used for production machines, was overheating. They had added a ton of equipment to it over recent years and he was worried the transformer was overloaded and would fail. His boss knew nothing about old, new, replacement electrical transformers and really didn’t want to be bothered with a “maybe problem.” The electrician needed something to get his bosses attention. He couldn’t measure the load, but he just knew it was overloaded.

Our unscientific suggestion was to put his hand on the top of the old power transformer enclosure. If he couldn’t hold it there for a few seconds, the transformer is in danger of being overloaded. The load should be measured and compared to the nameplate rating. If they don’t, they run the risk of the transformer failing when they least expect it, say the day before a holiday. Getting and installing a replacement transformer under emergency conditions can be a lot more expensive than scheduled transformer replacement. You don’t want to get burned.

Safety note. Be sure the transformer is grounded before touching it.