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.
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.”
The best test to predict the reliable operating condition of an oil filled transformer is the combustible gas-in-oil analysis. Using a syringe, 40 cc of oil is taken from the transformer and analyzed. When threshold levels of specific gases in the oil are reached, protocol demands appropriate action be taken. This is an extreme oversimplification of a combustible gas-in-oil analysis.
One such case involved a 3000 kva, 25 kv primary, 600 volt secondary, foundry furnace transformer. The oil test results indicated the transformer began generating high levels of acetylene. Additional tests were performed and the transformer was shut down and taken out of service. A temporary transformer was put in its place to continue plant production. The defective transformer was sent out to be rebuilt.
Furnace transformers are special breeds of cats, designed to withstand the stresses of heavy shifting loads. Often times these transformers are pushed to the max in terms of load limits. Based on secondary ampere readings, this transformer was pushed to over 100% of rated load capacity, creating high thresholds of heat in the windings. Transformers don’t much like that too well. Heat puts all kinds of funny stresses on the internals of transformers.
In two months time the rebuilt transformer was put back in service and life continued on.
Two quick qualifiers: One, switchgear manufacturers get it right most of the time. And two, it often takes a pair of fresh eyes to spot the obvious. Now that some perspective has been established we can continue with impunity.
An educational facility had a 13.8 kv primary dry type transformer located in a basement substation. The transformer panels (the skin) had just been pulled per a routine scheduled shutdown testing and maintenance procedure. What our techs found staggers the imagination, the scene echoing with “what were they thinking?” terminology. No, it was not Al Capone’s hidden treasure or Indiana Jones’s arc of the covenant. But the word arc is getting close.
Lying on the concrete floor, like an extension cord, were the standard 15 kv non-shielded switchgear cables. The cables ran from the primary switch compartment to the transformer compartment and had a white chalk like substance running the length of the cable where it made contact with the floor. The chalk like substance was the result of corona (ionization of nitrogen in the air) induced by the intense electrical field between the cables and ground, the concrete floor.
A chemical cocktail soon forms as the corona goes about its business and over time arcing takes place causing carbon tracking (dark carbon deposits) and eventual destruction of the cable or an electrical fault. The cables were replaced and were properly supported in open air with proper clearances. A certain disaster was avoided.