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.
Transformers come in many different flavors of course. One popular type found in and out of industry is the pad mount transformer. Most people have seen these without knowing what they were seeing. If you look outside an apartment complex, grocery store, or small industrial facility you might see a green colored rectangular shaped enclosure sitting on a concrete pad at ground level. That more than likely would be a pad mount transformer. What makes these unique in the family of transformers is their placement outside of a secure restricted access area such as that of a typical electrical substation. These units are designed to be placed in public access areas eliminating the need for a fenced secure area. These units are fully enclosed and have locking cabinet doors preventing public access to high voltage cable connections.
Although these transformers are fully enclosed and locked, it would be misleading to say they were safe since they are still energized. Concrete posts or steel guard rails are often placed around pad mount transforms to protect them from vehicle traffic. Pad mount transformers are reliable and aesthetically pleasing units with typically underground cable feeds. Although they can be fed from the side or from overhead. These transformers are for outdoor use and as such are usually mineral oil filled.
If you have questions about old pad mount transformers, call MIDWEST. They sell, rent, repair and buy them. They would be more than happy to speak to you.
Anyone in our business has seen transformers with concrete pads no longer level. MIDWEST frequently sees padmount transformers off kilter because the concrete pad has shifted, usually because the soil in one area has washed out. It occurs far less frequently, but sometimes we see the concrete pad for a large outdoor power transformer has settled on one side, causing the transformer to no longer be level. Slight settling might not pose a problem. But we frequently, using Infrared Scanning, find old oil filled outdoor power transformers that are not cooling properly. This occurs when an old electrical power transformer has long cooling tubes. On some transformers, the oil level may only fill 2/3 of the upper heads for the cooling tubes. If the transformer is slightly out of level, some of the outer cooling tubes on the transformer may tilt high enough that the oil will no longer reach the head and will not circulate. These cooling tubes will actually look cold when viewed with Infrared Thermography.
If you find your transformer is not level or is actually not circulating properly, do not attempt to correct this while the transformer is energized. This is a very bad idea. You are too close if anything goes wrong. And there are things that can go wrong with oil filled transformers that you can’t even imagine. Transformers are very heavy, especially old obsolete transformers. They can get very unhappy and the equipment they are connected to, can get very unhappy and make a big mess, if you try to level them energized. It’s tempting, because it looks so easy. But, if something goes wrong, it’s hard to get out of the way.
MIDWEST was called on an emergency after a contractor tried to level a 3750 kva, 25 kv to 480 volt transformer, that was connect to service bus. The secondary bus faulted at the transformer throat connection and pretty much destroyed everything, transformer and bus. What seemed like a good idea one moment, turned into a catastrophe the next. Again, MIDWEST recommends thinking “consequences, not probability.”
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.