MIDWEST is frequently asked about some of our unusual experiences over the years. Things that happened that had no text book solution. Here is one of those experiences, having to do with an old outdoor askarel (PCB) filled transformer. The transformer was a transplant from indoor to outdoor. A little crazy, even in those days. This happened decades ago. Back when old askarel transformers were still sampled. The fluid dielectric strength test results were horrible, 14 Kv. During their next plant shutdown, we inspected the transformer and found about 4” of water layered and floating on top of the askarel fluid. Askarel fluid weighed about 12.7 lbs. per gallon, so the lighter water, about 8 lbs per gallon, just mostly floated on the top of the dielectric fluid, askarel. The exposed glass rupture disk on top of the old power transformer had cracked when rained turned to ice during the winter. The internal high voltage (13,800 volts) leads, from the high voltage bushings to the transformer windings, actually passed through the layer of water. These leads were insulated, but not insulated against water. The secondary bushing leads were below the free water level. The plant would be in crisis without this transformer. They had no spare replacement transformer. It would take too long to get a reconditioned, rebuilt or new transformer. So the plant engineer said, “It was working when we turned it off, so, when you’re done, we’re turning it back on.” We removed the layer of free water; Added R-Temp Transformer Fluid to the proper level; Turned the transformer back on; and no noise, good. All the PCB contaminated fluid and debris was properly disposed at an EPA authorized facility.
MIDWEST told the customer the transformer needed to be replaced as soon as possible. There was an incipient, even imminent, failure. The next time we heard from the customer was seven months later when the 1000 kva transformer failed. Our advice was ignored. But we were amazed the transformer lasted that long.
MIDWEST Uncategorized 1000 KVA Transformer, askarel filled transformers, dielectric fluid, PCB contaminated fluid, power transformer, R-Temp Transformer Fluid, replacement transformer, transformers
A MIDWEST Thermographer found an interesting problem with a 208 volt, 3 phase, 75 kva dry type general purpose transformer. The Infrared Scan showed the enclosure of a Square D transformer was much warmer on one side compared to the middle and other side. It was an older transformer and had been in service for many years. An enclosure must re-emit enough heat from the air cooled transformer and the difference in heat from one area of the transformer to another must be substantial enough for the Thermographer to see the difference in heat pattern. But when you’ve scanned 1000s of these dry type transformers over 15 years, you have a pretty good idea of what’s normal or not. A load check revealed one phase was at 220 amps, another at about 115 amps, and the third phase 90 amps. They definitely had a large load imbalance on their old transformer. The maintenance man said they had been having nuisance tripping on the output breaker, but when he checked the load, there was less than 100 amps, 50% load. Unfortunately he only checked the load on one phase and got unlucky enough to pick the lightest loaded phase. But it was also very easy for our Thermographer to see the load imbalance on the circuit breakers on the load and line side of the transformer. It is amazing how tough these old air cooled transformers are. 10 kva to 500 kva, general purpose dry type transformers are found everywhere. Some are real dinosaurs, beyond old, but not obsolete because they are still running. Some over 70 years. A couple other things about these really old dry type transformers. They were so overbuilt that they can be very forgiving of overloading and they can be really loud.
MIDWEST Uncategorized air cooled transformer, dry type transformer, generual purpose transformer, Infrared Scanning, load imbalance, square d transformer
Here is another MIDWEST transformer horror story. This involves a 1000 kva indoor dry type power transformer, 13.2 Kv to 120/208 volts. The first time we saw this transformer, we thought it was just a spare new transformer core and coil being stored in one of the customer’s equipment rooms. It looked just like a replacement transformer because the core and coil were not in a metal enclosure. It was out in the wide open area of the room with no protective enclosure or barriers, nothing to protect it. To our great surprise, we soon realized that this old transformer was energized. The hmmm and the exposed wires connected to it were a big tip. One had to walk around the transformer to get to one corner of the room. Beside electrical conduits, there were other overhead pipes in the room, plus communication cables. There were electrical panels and non electrical equipment in the room. The electrician said he was told it was okay because it was a locked door and nobody was suppose to go in there. He told his boss that he thought it was very dangerous, but he was told it met code. He thought the whole thing was nuts. We asked where the key was secured so that unqualified personnel could not enter the room, which they called a vault. The key was hung on a nail over a nearby doorway going into a mechanical equipment room. This was considered secure because nobody knew what the key was for, except the ‘right’ people. We explained the extreme shock hazard and arc flash hazard to anyone, even qualified personnel, entering the room and the fact that unqualified personnel may acquire access to the room because of the key location. In plain English, this set up was crazy. To this day, nothing may have changed, because someone decreed “it met code.”
MIDWEST Uncategorized dry type transformer, electrical panels, old transformer, replacement transformer
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.
MIDWEST Uncategorized Allis Chalmers Transformers, conservator tank transformers, oil filled transformers, power transformers, replacement transformers
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 Uncategorized infrared scan, Infrared Scanning, oil filled transformers, old transformers, tap changer, transformers
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.
MIDWEST Uncategorized pad mount transformer, pad mount transformers, transformers
What do you do if you have a 750 Kva oil filled transformer that has no valves, no gauges, is leaking oil and the owner tells you they can’t possibly do anything for weeks. But they want to know if there is enough oil left in the transformer to make it 45 days, because they can’t stop production. Production verses maintenance, it’s a familiar battle. The reality today is that production wins. One has to find “best fit” solutions. In this case, the transformer was only about 30 years old, so it wasn’t a total dinosaur. Why anyone would buy a naked transformer is the subject of another blog. Both the production manager and maintenance manager were actually worried about their jobs if they lost this transformer, so they were looking for some serious guidance from MIDWEST. They wanted to know if they should get a replacement oil filled transformer. We used a highly technical protocol to determine if the oil level was too low. We first made sure the old power transformer was properly grounded. Then we felt the case of the transformer and then the cooling tubes. Yes, the sophisticate instrument of choice was the human hand. All the cooling tubes were warm and the tank was slightly warmer than the cooling tubes. The heat distribution was as we would expect for a properly cooling old or new oil filled power transformer. We knew from the type of bushings that they extended below the oil level. The oil stain from the leak was fairly large, but it was caused by chronic weepage and not an aggressive leak. So MIDWEST’s opinion was the old obsolete naked power transformer would last until they could schedule repair. Ironically enough, the oil weepage was from the plug that was installed in place of a top valve. So they scheduled the repair and updating service per their production schedule. They didn’t need to replace this old oil filled power transformer after all. We repaired the leak, added valves and gauges, sampled the oil, added some new oil, and ran some transformer tests and all was well.
A very important note, MIDWEST made sure the transformer was grounded before toughing it. This is an important safety tip. You do not want to become the transformer case ground. Electricity through your body will make you very unhappy.
MIDWEST General Transformer Information 750 KVA Oil Filled Transformer, Naked Transformer, Oil Filled Power Transformer, power transformer, Replacement Oil Filled Transformer, Transformer Leak
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.
MIDWEST General Transformer Information dry type pad mount transformers, fluid filled transformers, go green, going green, pad mount transformers, replacement transformers
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 General Transformer Information dry type transformers, fluid filled power transformers, obsolete transformers, old transformers
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 Uncategorized large outdoor power transformer, leveling transformers, oil filled power transformers, padmount transformers