Power Transformers Blog – Expert Safety and Usage Info

Transformer Blocking Shows Its Age

MIDWEST’s Engineering Department has a shelf with miscellaneous parts that we use for training.  One of the items is a very simple 2” X 2” X 5” porcelain block. This is from a 1000 kva, 13,200 volt primary to 480/277 volt secondary, dry type power transformer.  The transformer was one of seven new transformers installed in the 1960s at a customer’s commercial facility.  MIDWEST’s service included cleaning and inspecting the transformers.  They ranged in size from 500 kva 120/208 to 2000 kva 480/277 volts.  The transformers were very clean from service by many companies over the years.  All the test results were good.  Previous maintenance notes classified all the transformers as “Excellent condition for continued service.”  This facility handled critical data processing and the “results of failure” would include lose of power to data processing equipment.  MIDWEST’s physical inspection revealed the winding blocking for one of the transformers was loose.  Much of the upper blocking was so loose it could be removed.  The porcelain block in our training room was taken from one of the 1000 kva dry transformers after it was replaced two years later.  But based solely on the test results and a cursory visual inspection, the transformers looked great.  The only problems were defective fans.  But a focused inspection, TBLR in our jargon, a “top to bottom, left to right” hard focused inspection revealed very brittle insulation and loose blocking that could not be secured.  The transformers ‘might’ have lasted another 20 years, but not reliably and this owner wanted reliability.  So based on the physical condition, not the test results, the customer initiated a 5 year plan to replace the transformers and some of the associated secondary switchgear.  This is another example of the value of experience when servicing power transformers, old, used, new, GE General Electric, Siemens, or Cutler Hammer, it doesn’t make a difference.

The internet might be a great tool to find a replacement reconditioned or used 20 MVA transformer, fast. But the internet information could be deceptive and expensive. Nothing wrong or illegal, but it just might not be as good a deal as you think. Consider this example of what has happened to MIDWEST. A customer calls for a 25 MVA Transformer. Say a 138 Kv to 34.5 Kv, oil filled power transformer. And say our sell price is $300,000.00, plus freight. This should be a straight forward transaction.  And often these transactions happen fast, especially when someone has had a transformer fail. But, in this example, the buyer is a transformer ‘lister’ who marks up our price a whopping 30%.  A ‘lister’ is an entity that just lists equipment on their web site. They have no inventory themselves. They have limited technical value. They basically just have the information. This is not an indictment of all listers. Some are very good. But, in this case the ‘lister’ has been contacted by an electrical equipment dealer who also does not stock large equipment, much less large transformers. The dealer marks up the lister’s price a whopping 30% also, because he thinks the buyer just has to have the transformer. The dealer has been contacted by an electrical contractor, who also thinks he can mark it up 30%, because his customer, the actual end purchaser and user of the transformer, just has to have it. The problem is, by the time the shark’s get done marking up the price, the cost has doubled to over $650,000.00 and the end user knows they can buy a brand new unit for much less than $400,000.00.  They feel taken, so they decide to cripple along until they get a brand new transformer. 

This same scenario can happen with high and low voltage switchgear, circuit breakers, and any number of other type electrical equipment.  So how can you tell if you are talking to an intermediary or directly to the source of the equipment? The best bet is to be talking to someone who knows the equipment. Is an expert on the equipment you want to purchase.  Can give you detailed additional information immediately rather than making you wait two hours for answers to each question. Deal with the experts.

What do you do if your manufacturing company suddenly loses its main 5000 kva, 34.5 kv to 480 volt transformer? You have orders pending. And if you can’t fill them, a key account may go elsewhere. You have employees suddenly out of work.  You need to heat the buildings.  And you are told it will take 10 weeks to get a new replacement transformer. This is one of a manufacturer’s worse nightmares. What to do? This happens more frequently than one may realize. MIDWEST actually recommends a “Disaster Action Plan,” on the shelf, ready to go, in case of such a nightmare.

MIDWEST receives these calls all too frequently. You might be fortunate and MIDWEST have a replacement reconditioned or used 5000 kva transformer that can be shipped immediately. No one has new transformers this size in stock. And many companies will not accept anything but a new replacement power transformer. In that case, the best solution is to rent a temporary transformer that will provide power until a new replacement transformer can be specified and manufactured. A new replacement transformer may take 10 weeks.

Renting transformers, and other electrical equipment, is a common solution to this critical problem. The first big question to ask when such an emergency occurs is, “Do you want power back on permanently as quickly as possible or do you just want power back on as quickly as possible?”  There is a huge difference in the time to perform either of these solutions. And way too often there is the presumption that one just must get power back on permanently. This presumption continues until the customer realizes how long it will actually take. Meanwhile many hours, even days, are wasted by chasing the wrong solution.

So the most critical event is to decide how fast one wants power restored.  MIDWEST has transformers, temporary high voltage cables and low voltage cables, and switches in stock.  But, more important, is the knowledge that temporary power installations can be a life saver for a facility that is suddenly down.

MIDWEST frequently replaces old oil filled transformers with more efficient new oil filled power transformers. Being a specialty engineering firm, we usually get involved when the project is messy. We had a recent project involving replacement of very old Allis Chalmers 600 kva and 1000 kva oil filled conservator tank transformers.  These were monster units compared to the size the replacement transformers, which were 1000 kva.  As a training exercise, MIDWEST had a shop crew tear one of the old transformers apart. They quickly found out that the bushings for the old transformers extended twice as far inside the tank as they did outside. These may have been obsolete transformers, but they were built like battleships and who knows how long they may have lasted. The crew got a good look at the workings of the conservator tank.  Then they removed the top. The old transformer had a bolted on top and the core and coil assembly was bolted to the top, such that the transformer core and coil came out of the tank when the top was lifted. The crew was surprised at how small the core and coil assembly was. They thought it probably took up only the bottom third of the tank. We know that new replacement transformers are much smaller and lighter than the old and obsolete transformers used for manufacturing plants across the country. When we do a power transformer replacement, we seldom have to worry about space when the transformer being replaced is 60 years old.  Actually we have to provide a raised concrete pedestal when installing a new oil filled power transformer in place of one of these old units. So, as strange as it may be in this case, for a replacement electrical power transformer, new is small and old is tall. And seeing is believing.   

We like it when we run into something unusual.  Recently we had a request for a replacement transformer.  That wasn’t unusual until they told us they wanted a pad mount dry type transformer. That was a surprise. He was surprised we had one.  The company may have been trying to go green and was under a mandate to no longer use fluid filled transformers. This is becoming more common.  We see quite a few companies that require all replacement transformers to be dry type because of their “Green” policy.  Fortunately most of these companies are commercial facilities and do not use higher voltages and do not have huge loads. In addition, the transformers for commercial facilities are often indoors where dry type transformers are appropriate. Therefore non fluid filled replacement transformers are available and “Going Green” is a good option.  But an outdoor dry type pad mount transformer is uncommon.  Most pad mount transformers are oil filled.  And most pad mount transformers are green, painted green.  Pad mount transformers were developed decades ago for use in subdivision developments.  They were replacements for overhead distribution transformers.  The under ground distribution systems and low profile green box shaped transformers were unobtrusive in the beautiful new subdivisions.  So suburbia went green decades before it became environmentally important, but they did it for cosmetic reasons.

But that is not true for industrial facilities that frequently have higher voltages and larger loads, for example over 25 kv and over 3750 kva.  MIDWEST did have one occasion where a manufacturing plant wanted to eliminate the fire hazard of fluid filled transformers. But it was only because their insurance carrier determined their transformers were so close to the outside building walls that they created a fire hazard.  They were not trying to go green, they were trying to avoid going black.  Dry type replacement transformers would not reasonably work because of the size of their transformers.