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.

High Voltage Switch Interphase Barrier being destroyed by high voltage corona and tracking

If you’re a manufacturing plant and your main electrical power transformer is a 10 MVA, 10,000 kva, oil filled station type transformer, you’re probably not interested in failure modes and probability analysis from your service company. You just want to know everything is being done to make sure it doesn’t failure. In the world of sophisticated test procedures and test equipment and lengthy specifications for the application of the procedures to your 5 MVA, 10 MVA, or even 50 MVA high voltage power transformer, there is still need for old fashion maintenance and inspection services. Too often the main high voltage power transformer for a facility can never be turned off because of the interruption of production or data processing. We know that is the real world today and we have to deal with it in the best way possible to maintain reliability. Periodic combustible gas analyses and routine oil analysis are extremely useful.  But there is still room for some old fashion basic maintenance services. MIDWEST likes “Ultrasonic Scanning” of medium voltage and high voltage equipment for indications of destructive corona or tracking. We recommend this on high voltage equipment, especially metal enclosed. And if you have a 20 MVA oil filled power transformer, you have something in front of it to protect it. If that protection fails, your transformer becomes very unhappy. For example, it is not unusual for us to find destructive corona or tracking damage to the inter-phase barriers in the high voltage switch protecting a power transformer. A good example is a lightning arrester lead that rests against the inter-phase barrier and is slowing destroying the barrier. Eventually one of the barriers will fail, usually a phase to phase fault and frequently during a lightning storm when a voltage surge screams down the line into the high voltage switch. Ultrasonic Scanning of the high voltage transformer main switch would catch this before it fails. Not real sophisticated, but an extremely effective preventive procedure. Find it, Fix it before it fails.