Power Transformers Blog – Expert Safety and Usage Info

10.       Even if they don’t know the song, used transformers hum along as if they did.

9.         Used transformers require no burn in period. They are good to put in service right out of the crate. 

8.         Used transformers are very green. The carbon footprint you save may very well be your own.

7.         Buying used transformers helps create jobs.  With the money saved, your company will have more resources to put into that next great business expansion.

6.         Buying used transformers puts you in the drivers seat ─ of your golf cart that is. As your boss will no doubt give you the afternoon off after saving the company money.

5.         Our used transformers meet national testing standards.

4.         Our used transformers are readily available. Lead times for new transformers can run into weeks if not months. Your used transformer can be in your hands as soon as preparation time allows. 

3.         Our used transformers come in designer colors. Check out our beautiful array of designer gray colors.

2.         You may choose to rent one of our used transformers to serve as a temporary power solution.

1.         And the number one reason to buy used transformers is it saves money, up to 70% off the cost of new.

PCB (polychlorinated biphenyl), that little man made molecule that was so good it just would not go away, that is, without the help of man.  The problem with PCB is also its strength. Unlike many things on the planet, PCB is a highly inert molecule meaning it does not easily combine with other molecules in nature. Drop it off in a field somewhere, come back in 100 years and it will still be there waiting for you in pretty much the same shape you left it. How many things can you say that about? From approximately 1930 through 1979 PCB was used as a dielectric fluid and coolant in old electrical transformers and capacitors. Since 1979 Federal register regulation 40 CFR 761 has regulated the manufacturing, processing, distribution and use of PCB’s in Commerce.  Today the use of PCB in existing electrical devices has all but disappeared. Today MIDWEST is actually surprised when we find a PCB transformer. 

One popular misconception was that old transformers created PCB as a by product of the electro magnetic process. This myth grew from the fact that many mineral oil filled transformers were found to contain low levels of PCB in their oil. The truth of the matter is not that mystical. The oil in these transformers became cross contaminated with PCB from PCB contaminated pumping equipment used to recondition the oil in these units in the days before PCB was regulated.

A salvage company called MIDWEST and complained because they had an old transformer filled with silicone oil and they couldn’t get rid of it. It seemed to them that no one really wanted an old silicone oil transformer. At least no one would pay as much as they wanted for it.  They wanted to know why, because they knew oil filled transformers were used everywhere. Since MIDWEST Switchgear Division deals in used and new electrical power transformers, they came to us for some quick help. The simple answer is that silicone is not oil.  Transformer oil is mineral oil, much like you put into your car, but it is refined differently.  To use the term silicone oil doesn’t make sense.  You could say silicone dielectric fluid, but not oil.  Silicone filled transformers provide fire protection for indoor use. And since silicone is very expensive, it is not needed or used in outdoor fluid filled power transformers.  Regular oil filled transformers must be installed in a secure vault if installed indoors.  But they are used every where outdoors. Silicone is really never used outdoors. Therefore, for many installations, silicone has lost favor as a transformer fluid. It especially does not lend itself to informative routine dielectric testing or combustible gas-in-oil testing, which is commonly used to monitor the condition of old and new electrical power transformers used in industry.  It is a simple case of supply and demand. And there is not a great demand for old or refurbished or retrofilled, so called silicone oil filled transformers. We referred them to Dow Corning 561 Silicone Transformer Liquid if they wanted to know more about silicone. In addition, there are now substitutes for silicone dielectric fluid on the market.  

One common concern with pad mount transformers is in the area of oil sampling. Companies with large pad mount transformers may sample and test the oil in the transformers annually to determine the reliability of the transformer. The condition of the oil reflects the current state of the transformer. Now here’s where it gets tricky. Large pad mount transformers are designed with two cabinet doors. One door exposes the high voltage cables and bushings and the other door exposes the secondary, low voltage, side. The sample valve can be located in either compartment but most of the time the valve is located in the secondary cable side. Years ago it was not uncommon for an intrepid technician with nerves of steel to pull an oil sample from an energized pad mount transformer, the valve being located at the bottom of the transformer while hot cable lugs were located only a couple feet above the oil valve. With safety becoming a paramount concern in industry today, it is no longer prudent nor standard practice to pull an oil sample on an energized pad mount transformer.  The hot lugs being within short reach of the technician create a shock hazard.  And the secondary side of a transformer is one of the most dangerous arc flash hazards there is. Oil sampling is now performed only during scheduled shutdown of the transformer.

However, there still remains somewhat of a challenge when it comes to pulling an oil sample from a pad mount transformer.  The secondary compartment of pad mount transformers can be a pretty fully house. There may be as many as six cables attached to each secondary bushing, making it very difficult to access the sampling valve through that jungle of vines. One way around this, literally, and we’re finding it used more and more in industry, is extending the sample value system to a small secure box on the exterior of the transformer enclosure. The valve would then be enclosed in a newly created box with a locked access door mounted on the exterior wall of the cabinet. In this way the transformer can be sampled at any time, while energized, without exposing the technician to shock or arc blast hazards.

During a highly technical conversation about the life expectance of old and new electrical transformers, MIDWEST was asked by the Consulting Team what the most common failure mode for outdoor oil filled power transformers was. The discussion involved 1000 kva to 10 Mva power distribution transformers typically found in the outdoor substations of manufacturing plants.  We were discussing Failure Mode and Effects Analysis (FMEA) and its value for reliability optimization.  The consultant was using military data for failure mode and frequency of occurrence. There was poor connectivity between that data and our world of big old oil transformers used by industry. It was even less appropriate to use historical military data on the new oil transformers used today to replace those old tubs.  The whole thing was rather ridiculous as every one struggled to find legitimacy in the analysis. The solution came with a twist from a reliable and too often forgotten source.

MIDWEST’s senior field service technicians and service engineers were asked what the most common failure mode was, based on their experience, experience that exceeded 100 years. Their one word answer was, “Raccoons.”  After the technical minds recovered and realized the answer was more than just a little jab and a lot hilarious, they realized it was true. So now they asked what should be done to lower the probability of this critical failure mode.  The answer, “No raccoons.”  Problem solved.   

MIDWEST performed an Infrared Scan of the electrical system for a new customer.  They had two old outdoor oil filled transformers with load tap changers that had not been used in some time.  So when we scanned these old transformers, we made certain we scanned the load tap changer compartments.  Each tap changer was dangerously over heating. The electrician with us wondered why, since they hadn’t operated the tap changers in 20 years.  But tap changer contacts can cause coking, especially if they are not operated.  Later, during a scheduled maintenance outage, MIDWEST found both load tap changer compartments completely coked, full of black sludge.  The sludge had to be removed by hand, like scooping out sticky black mud.  Since they would never use the transformer tap changers again, MIDWEST removed the entire interior operating mechanisms and bussed the terminals. The old transformers were very lucky the tap changers didn’t fault. If they had, it would not have been cost effective to repair them.  It was just a matter of time before a catastrophic fault in a tap changer would have cost them a transformer.  We have seen this problem before in old transformers.  In this case, certain failure was avoided, and they reused the transformer after the repair. Infrared Scanning is very important, even on old, obsolete transformers and switchgear. 

MIDWEST sometimes finds strange things inside air cooled dry type used transformers we have purchased for reconditioning and resale.  But you can imagine the surprise of our switchgear shop when they removed the top from a “like new” looking transformer enclosure and found “nothing.”  They said it was the fastest used transformer reconditioning job they ever had. It took about three minutes.  Of course they had nothing to show for it but a metal box.  The old transformer core and coil had been removed, leaving only the metal enclosure.  This was a 225 kva transformer, so whoever removed the core and coil used more than the armstrong method.  If you are looking for a reconditioned used invisible dry type air cooled electrical power transformer, cheap freight, low maintenance, no electrical losses, no visible defects, we have a deal for you.  Of course the transformer does not work, but it’s free. The enclosure is extra.

MIDWEST was asked if we ever rejected a transformer even though it passed all our electrical tests.  The answer was “yes.”  We scrapped an old 1000 kva dry type transformer used in a fairly clean room.  We had purchased the old transformer after replacing it with a larger unit in a paper mill.  The transformer was trucked to MIDWEST.  But an outer high voltage winding had physical damage that was found during the “hard focus” visual inspection. The riggers had damaged the outside of one winding with the tie down chains.  All the standard test results were very good.  And we energized the transformer at full voltage.  Everything tested out great.  But our inspection told us the transformer could not be used.  It was junk. Not worth repairing. It had what we call an “Incipient Failure.”  It was damaged and was going to fail.  When, who knows.  A day, a week, two years?  We didn’t know.  But we did know it was not reliable.  The high voltage windings were going to fail, short out.  It was just a matter of time before the used transformer became scrap.  We just hurried it up and declared it junk.  Here is another great example of pure technical knowledge just not being enough.  Experience and Knowledge were needed. 

Three answers, NO and NO and NO.  This is a big deal for us. MIDWEST does not sell old, used, or obsolete circuit breakers, bus plugs, transformers or other electrical equipment to an end user, ie the consumer, unless it has been properly serviced, reconditioned, tested, and passed Quality Controls.  We strongly recommend no one buys old electrical equipment “as is.”  That could be very dangerous. There are many “listing” companies and auction type sites that sell “as is.”  For example, eBay does not warranty the used and old electrical equipment sold through their service.  They provide a great service, but they do not provide a warranty on the specific used electrical equipment sold on eBay.  The same may be true with services that just list equipment.  The only people MIDWEST will sell electrical equipment “as it,” are other qualified electrical dealers that have proper Quality Controls.  Old, used, or obsolete circuit breakers, bus plugs, transformers, and switchgear have too many dangerous failure modes to be sold without proper testing.  MIDWEST does not just process orders.  Anybody can do that.  And many do.  We actually have a name for that.  We call it TC, Trained Chimpanzee, work.  You could train a chimpanzee to put old circuit breakers into a box. 

We add value.  Our staff of engineers and technicians service, repair, recondition, and test electrical equipment for a living.  We’ve done it for over 30 years.  That is what we do day after day. And it is what we think others should do if they are going to sell something.  “As Is” is just scary.  When electrical equipment gets unhappy, it can fail with a boom and a flash.  And that can hurt.

MIDWEST bought a 500 kva general purpose dry transformer that was taken out of service as part of an expansion job.  The transformer was well secured to a large wood pallet.  It was wrapped in plastic and looked great when it came in our door.  It was a used transformer, but looked like a brand new transformer, except for two knockout holes and a strange bulge on one side. When our switchgear shop checked it out, they found the shipping bolts had not been replaced before shipping.  The transformer was now a boat anchor.  A very large boat anchor.  New dry type transformers are shipped from the manufacturer with bolts holding the core and coil assembly to the base frame. After installation, these shipping bolts are removed so the transformer sits on absorbent pads that minimize vibration transfer from the energized transformer windings to the transformer enclosure.  But, if you move the transformer without replacing these hold down bolts, the transformer core and coils are just setting on a frame and they will trip over, inside the enclosure, the first time the truck goes around a sharp corner or stops suddenly. As soon as the outer high voltage windings hit the inside of the enclosure, the transformer becomes expensive junk.