Power Transformers Blog – Expert Safety and Usage Info

MIDWEST sells new oil filled large Kva and very large Mva power transformers. But because MIDWEST buys electrical equipment to remanufacture and resell, we get calls from demolition companies and electrical contractors asking what they should do with old oil filled power transformers. They are concerned with the PCB rules regulating oil filled transformers. As an example, MIDWEST had a project to remove the electrical switchgear from a large industrial facility. The demolition company wanted to sell the oil filled transformers in the main outdoor substation right by the building to be torn down. But no legitimate company would take them without the PCB classification certification. The demo company figured the oil recyclers would be happy to buy the old oil and the metal scrap companies would be happy to buy the empty transformers. But they all wanted certification of the PCB classification. The demo contractor asked MIDWEST for some advice, because they were ready to start tearing down the building the next day. Our strong advice was simple. Do not touch the transformers. Do not risk damage to the transformers. Don’t take any chances. And do not trust a “Non PCB” label unless there is documentation of the Non PCB classification and have certification the transformers have not been serviced since that analysis was performed. MIDWEST strongly recommends sampling the transformers by qualified personnel and testing the transformers for PCB and PCB Classification regardless of existing labeling. For decades, oil filled transformers have been labeled Non PCB by manufacturers. Most old transformers have been tested and labeled. The owner should have the documentation or the label should identify the lab that did the analysis. A call to the lab with the location, owner, and serial number may be all that is needed for the lab to ID their analysis. A quick email from the lab should confirm the Non PCB classification and the owner must certify no service has been performed on the oil since the respective analysis. It is very important the demolition company keep a copy of that analysis and certification as Non PCB. If the classification can not be documented, we strongly recommend “do not touch the transformers” until they can be sampled and the Non PCB classification confirmed. Do not move them. Do nothing that has any chance of damaging the transformers and causing a spill. It is not worth it. The seriousness of this is deceiving because the rules for using the transformers are very simple, but the risk is incredible. If anything happens and you spill PCB contaminated oil, the consequences could be disastrous. You may have just gone out of business. Also, oil leakage or weepage from old oil filled power transformers must be properly cleaned up per EPA requirements.

Here is an example of the success of an Unlimited RCM (Reliability Centered Maintenance) program for large kva and Mva oil filled power transformers. Our Engineering Technicians and Engineers know what the most common problems are for oil filled electrical power transformers, whether 1000 Kva, 5000 kva or 25 Mva. We do the more glamorous transformer tests, but most of these require an outage, which has become unheard of for many large manufacturing facilities and some small municipal utilities. Fluid samples for routines and GCs on dielectric fluid still can be taken safely in some cases. But a hard focused inspection by an experienced, trained, and knowledgeable expert will find many of the probable, but unapparent, deficiencies in oil filled power transformers. Someone following a simple TC Checklist is nearly useless. By TC Checklist, MIDWEST means a “Training Chimpanzee” Checklist. The person performing the service has to think. They have to focus or they will miss subtle things that individually may mean nothing, but collectively may reveal a serious problem or danger. We find things others have looked right at and missed. Some of the things we look for are hard to explain. Others, that seem obvious to the pros, may be invisible to the inexperienced. MIDWEST’s Unlimited RCM Services have saved customers more money than all the transformer testing put together. Here is a simple example of a fluid filled transformer oil leak discovered only by the not so sophisticated “look and feel” test. It wasn’t the ordinary transformer oil weepage or leakage that allowed plenty of time to correct. It was invisible because the transformer was a large pad mount unit and it was leaking into the cable entrance pit under the cable connection compartment. The tank was fire hot, but the cooling tubes and top headers were not unreasonable hot. We could tell the oil level was so low that we were worried the high voltage cables inside the transformer or the core or even the coils might be exposed. Usually a fatal problem. A quick outage was arranged, despite production’s pleas to wait. We found the lowest high voltage bushing was actually cracked and fluid was coming out in a steady little stream. Not just weeping or slowing dripping. A quick temporary repair was made in order to get production back up until a replacement bushing could be purchased. We’ve seen this crisis before. Emergency outage, drop the oil, remove the bushing, make a crazy careful temporary epoxy repair, refill, test, and energize. The only other safe choice was to leave power off until a replacement bushing could be delivered. Terror for production. Later the new bushing was delivered and installed during a scheduled outage. A gas sample was taken and all was well. The transformer was days, if not hours, from failing. If we were not performing Unlimited RCM inspections, they would have had a failure, at great cost to critical production. One additional note. We have a customer who, against our advice, operated a transformer for over 20 years with the temporary repair. Our technical term for that is ‘luck.’ The Unlimited Services by experts works. If you don’t have an electrical power transformer expert, consider starting by using a qualified electrician. A safety note, before you touch an energized transformer, make sure it is properly grounded.

Buy 45 KVA Jefferson Electric Dry Type Transformer

The small dry-type transformer – what can one say about these marvels?  They come close to achieving the perfect combination of form and function.  Designed to be cooled by movement of air, not moving water, the dry type transformer is perfect for indoor use or anywhere that it can be sheltered from the elements: porches, below lean-tos or beneath small structures.  There are some with optional rain ‘gutters’ intended to direct water away from the transformer coils.  Wherever they are found, the dry type transformer, one of the most common type of transformers seen today.  It is the ubiquitous work horse of the industry.  The three phase 480 Volt Delta to 240 Volt Delta, from between 50 to 150 KVA, are among the most popular.  As many utilities have moved to away from offering 240 Volt services, they are commonly used to transform the incoming 480 Volts to power 240 Volt equipment.  Most are designed so you can usually run them backwards to produce 480 volts from 240 volts. What happens when this very reliable workhorse fails?  No spare readily available, you obtain a replacement.  Right?

But why wait till then?  It would be good practice if they were looked at occasionally, once installed, but small transformers of this type are typically not tested during routine plant shutdowns.  So they are frequently used as tables, workbenches, shelves, ladders or stationary hotplates to keep lunches and bakery warm.  There are usually indicators well in advance of a transformer’s doom.  Little warning signs that if left uncorrected will lead to failure; excessive noise, excessive vibration, the usually warm transformer gradually becomes hot to the touch transformer.  If you look underneath one and see only dusty clogged vents, chances are it is running at a higher temperature than recommended. 

At MIDWEST we perform an insulation resistance test and load test on all of our reconditioned transformers before they leave our door.

Meanwhile take care of the dry type transformers you are presently using.  Be smart and keep them free and clear from clutter, dirt and moisture…

The good news is if the need for replacement arises, you can usually find something to take the place of the one you just lost.  You can buy a new one from us because the manufacturers still make them or you can ask us for a quote on a reconditioned transformer.