Power Transformers Blog – Expert Safety and Usage Info

MIDWEST replaced the old main electrical power transformers for a manufacturing facility.  When we were done, the outdoor substation looked barren. It looked like the power capacity went way down.  We removed one 1000 kva oil filled three phase Westinghouse transformer, one 1000 kva oil filled three phase GE General Electric Transformer, and three 167 kva single phase oil filled transformers. We replaced all these transformers with one new oil filled 3750 Kva transformer. We replaced the concrete pad, of one of the old 1000 kva transformers, with a larger pad. Installed a new grounding system and replaced the fencing. But the new installation made the substation look bare.  Where there were five old oil filled transformers, there was now one new oil filled power transformer. The new 3750 kva transformer wasn’t much larger than one of the old scrap 1000 kva transformers. But, when you looked at the substation, you saw four abandoned concrete pedestals for the removed transformers. And that made the place look like it was going out of business, rather than growing.

The size of many very old GE General Electric, Westinghouse, and especially Allis Chalmers oil filled electrical power transformers was a third to even 100% larger than a new same Kva power transformer. Pad mount transformers are especially smaller because of their low profile.  The low profile green box pad mount transformers got extensive early use in subdivision developments, where the new owners of dream homes didn’t want ugly electrical overhead lines and transformers outside their windows. The little green boxes were small and everywhere, but there were barely noticeable because of their size and color.

So, for electrical power transformers, new is less, less space that is.  

MIDWEST was asked what we did with perfectly good obsolete or old used transformers. Bit of an oxymoron since obsolete might be understood to mean no longer any good. But the intent of the question was obvious. Transformers that are too old to be sold in the used transformer market might be maintained in MIDWEST’s pool of rental, temporary, and emergency transformers or they are just scrapped. Typically a rental transformer is just for temporary use. But we have had many transformers on rental for over a year. Especially larger Mva transformers. We have a few we didn’t scrap out but kept around solely because of the special voltages or size or physical configuration, to be used in those rare occasions when a manufacturing company, for example, is in trouble with delivery of a special replacement transformer. This usually happens when they had a non typical transformer suddenly fail. The difference between these special temporary transformers, which we sometimes call cling-ons, and our rental transformers is that we’d really like to get rid of the cling-ons. But about every time we think we’ll scrap out an obsolete old unit, we get a desperate call and it is the only thing that will work and the only one the customer can find. So it is resuscitated again and lives on. We do have fewer of these than ten years ago. We just scrapped out a 2000 Kva oil filled power transformer, 13,200 volts to a variable secondary of 120 volts to 600 volts. Weighed 18,000 pounds. A big old power transformer, specially built for a transformer power lab about 60 years ago. We finally got rid of it because we never rented it in two decades; And we did not have a good biography on the unit, although all our test results were good. The install cost as a rental, emergency, or temporary transformer would have been potentially huge because of the oversize and weight due to the many voltage taps. A potential customer would only need one functional voltage and would be paying a premium for a monster oil filled power transformer when they probably could find a unit with their specific voltage. Plus MIDWEST can not rent a transformer we no longer have full confidence in, even during an emergency. In the last month we designated over ten transformers to the scrap heap. Mainly because of a lack of full confidence in their reliability, even though many of them had good test results. MIDWEST knows electrical tests, on used oil filled and dry type power transformers, are not a perfect indication of the condition of the transformers. So MIDWEST looks for reasons to get rid of the old and the cling-ons.

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. 

225 KVA Dry Type Transformer For Sale

Many facilities are declaring their maintenance budget to be revenue neutral. Our recommendations for maintenance of old transformers are both condition based and time based. For example, one may recommend annual infrared scanning and annual dielectric fluid analysis on fluid filled power transformers, especially old or obsolete transformers. Whereas, old indoor dry type transformer should be cleaned and maintained based on their condition, their environment. A foundry would be more condition based than a commercial facility. A problem occurs when the conditioned based maintenance costs are unusually high in a particular year, say this year. Some maintenance supervisors have been told if they add cost in one area, they must remove cost somewhere else. Revenue neutral decision making. This can be roulette in some facilities that have a lot of old or aging equipment that really needs attention.  Unfortunately what often happens is time scheduled maintenance is postponed in favor of condition based service. MIDWEST suggests a compromise. Review “Schedule Services” and perform those services on equipment that is most critical and has the poorest service condition. Likewise, service “Condition Based” equipment that is both the most critical and most in need of service.  These decisions are only good “if nothing goes wrong.” If something goes wrong, then, of course, it will be attributed to you choosing poorly. You can’t win.  You might escape the first year.  But as the financial stress on the maintenance dollar continues, what seemed to work last year, now appears more reasonable to “do the same” this year.  And next.  Until something goes wrong.  Then you lose. You chose poorly. We recommend reviewing the maintenance services on obsolete, old, and new equipment each year using the cumulative information of all the prior years. Do not go back just one year.  Also, good luck.

MIDWEST was challenged by a technical skeptic to give him just one example of a large old oil filled transformer that obviously outlasted its useful life expectancy.  Apparently he got into a heated argument with some old timer electricians who claimed they trusted the old transformers a lot more than new stuff they had seen.  It may not be wise to argue with experienced electricians.  They have ways to argue with enthusiasm and sometimes expressions that leave little doubt as to the strength of their convictions.  And they have real world experience, usually a good trump card. 

 MIDWEST gave him the example of two 2000 Kva old substation transformers built in the 1950s that have been running at 107% full load for the last 20 years.  These are not rebuilt or reconditioned transformers.  But they are pretty inefficient and about 3 times as large as a new oil transformer the same kva.  MIDWST is not suggesting old transformers are better than new.  But, be careful when buying new transformers.  Specify quality and reliability, or you may get cheap and disposable.