Power Transformers Blog – Expert Safety and Usage Info

How does an air cooled or ventilated electrical power transformer located outside in the rain survive?  Why doesn’t the rain cause an electrical short? These are the occasional questions of someone who wants to replace an existing dry type or air cooled transformer with a larger power transformer, when the existing power transformer is located outside, exposed to the rain, wind and sometimes snow.  It does look a little strange sometimes, but the general purpose air cooled dry type electrical power transformers are fitted with weather shields. They should be. If they are not, you will find out very quickly the first time it rains. The weather shields are metal shrouds, hoods, fastened over the upper vent openings. They prevent rain and snow from entering the top open vents of the transformer. This is true as long as the rain is falling vertical or possibly at a 45 degree angle. The rain or snow hits the weather shield and drips off rather than landing inside the metal enclosure of the air cooled power transformer.  We do see these 50 kva, 75 kva, or even 150 kva air cooled transformers fail. This really does not happen very often. And when it does, it’s usually because of a very unusual storm. Possibly where the wind is so strong, the rain is being driven almost sideways. More often we see failures due to snow filling the inside of the metal enclosure due to swirling and drifting of snow about and eventually inside the enclosure. We have seen this happen with 5 kv and even 15 kv class transformers. We are not fans of medium voltage outdoor air cooled transformers. As long as the enclosure remains intact, there should be no problem. And as long as there isn’t some unusual weather condition, they should be okay. In our business the term “should be” makes us cringe. When folks use the term “should be,” we think “sooner or later.”  It’s healthy to be paranoid around electrical power.  

MIDWEST Uncategorized 15 Kv Transformers, 150 Air Cooled Transformer, 5 Kv Class Transformers, 50 Kva Transformer, 75 Kva Transformer, air cooled transformer, Electrical Power, electrical power transformer, electrical transformers, Large Power Transformer, Medium Voltage Outdoor Air Cooled Transformers, Metal Enclosure, Metal Shrouds, Replacement Dry Type Transformer, Weather Shields

This MIDWEST blog is about a low voltage, high current transformer used in a hardening process. The transformer was physically located deep in the process equipment. It was very difficult for the owner to access the transformer for maintenance. They just could not maintain it during normal production schedules. The process operators were having more and more trouble controlling the output voltage and current. It got to the point they just could no longer regulated the output current as necessary to perform the metal hardening process. MIDWEST was contracted to remove and replace the transformer or repair it. Whatever could be done. When the transformer was being removed, the problem was found immediately.  There were massive copper bus bars on the secondary side of the transformer to carry the high currents. One of the output bus bar bolted connections had failed. It was held by only four bolts and the bolted connection had become loose. The copper at the connection was discolored and distorted from overheating. The connection contact surfaces were all destroyed by being overheated.  The damaged copper and damaged connection contact surfaces for this damaged transformer could not be repaired. The copper was damaged all the way into the winding. All the other connections were intact. The repair bill was over $50,000.00. This four bolt connection cost over $12,000.00 per bolt to repair.  The transformer replacement was not caused by a transformer failure, but by a simple bolted connection failure. MIDWEST frequently finds dry type transformer failures or replacement transformer projects are caused by the most probable failure mode because the needed preventive maintenance was not performed, because it would have been relatively expensive compared to routine, specified, maintenance. Everyone understands the value of the maintenance dollar. But it does not make sense to continually spend hard to get maintenance dollars on preventing very low probability failure modes and totally ignore the most probably failure mode all together, when the most probable mode would be catastrophic and the low probability failure modes have little consequence.  This is a nightmare for maintenance supervisors. It can be tough to sell critical maintenance procedures that are not found in standard maintenance specifications.

MIDWEST Uncategorized Copper Bus Bars, Damaged Transformer, dry type transformer, High Current Transformer, Low Voltage Transformer, Preventive Electrical Maintenance, Replace Transformer, replacement transformer, Transformer Replacement

MIDWEST had a curious question from an engineering student about large oil filled electrical power transformers. He couldn’t understand why a 20 Mva power transformer filled with oil didn’t burn when it had electricity actually flowing through it. It was his gut instinct that electricity and any flammable liquid didn’t mix and would result in an immediate explosion or fire. Just made sense to him. He associated electricity with sparks and arcs.  In our world, his question seemed ridiculous because we work around 2000 kva, 10,000 kva and 30 Mva oil filled power transformers all the time and it never occurs to us that electricity and oil don’t mix. Actually a quick load check on oil filled transformers is to put your hand on the side of the tank and see how hot it is. Yup, first we check to be sure the transformer is grounded. But we don’t worry about an explosion or fire if the tank is so hot you can’t keep your hand on it. We do worry about other things when a transformer is that hot, but not fire and explosion. Oil has been used for decades in oil switches and oil circuit breakers along with large oil filled power transformers. It’s the coolant and was used to quench the arc when the oil circuit breaker opened to interrupt the circuit.  This student saw a video on the internet of a large high voltage oil filled transformer exploding and couldn’t believe there was actually oil in it. We explained oil flash point and fire point. Discussed the need for a source of ignition and that, under normal conditions, there would be no arcing in a transformer. Talked about oil not getting anywhere near hot enough to vaporize into an ignitable mixture with air, oxygen. But he had fixed in his mind that electricity and oil do not mix. We guessed he needed an opportunity to work on an old outdoor 10,000 Kva oil filled power transformer in the middle of Winter. That would probably cure his misconception.

MIDWEST Uncategorized 10000 KVA Transformers, 20 MVA Power Transformer, 2000 KVA Oil Transformers, 30 MVA Oil Filled Transformers, High Voltage Oil Transformer, Oil Filled Electrical Power Transformers, Oil Switches, Oil Transformers

MIDWEST received an emergency call from a customer who had lost a 30 Mva 138 Kv to 13.8 Kv oil filled power transformer.  There was no storm or other unusual occurrence and they said it failed “last night.”  We are skeptical of transformers that appear to fail in the middle of the night when the sky is clear and nothing else unusual happened. We prepared to get a replacement reconditioned 30 Mva oil filled power transformer, and to arrange the resources to replace the transformer if necessary. Meanwhile MIDWEST Field Services went to check out the transformer. Differential relay protection took the transformer off line.  But we found the problem immediately in the form of a toasted raccoon and slightly blasted secondary bushing. We cleaned the secondary bushing such that it could be energized, tested the transformer, and figured someone at the Utility would want to use the fried raccoon as a wall ornament. But there were no takers. The transformer was okay. There was what we considered an unusual discussion as to why the raccoon was on the transformer. The consensus of management was that it did not make sense. Something more dramatic had to be in play, because one lousy raccoon could not be the cause of so much trouble and expense. The inquisition focused on the need for a good reason a raccoon would climb on top of the transformer. We explained that this was not an unusual occurrence. It was rather common. We explained that raccoons like the warm transformers and tend to climb over everything near their food supply. There were woods next to the substation. We recommended they put screen mesh along the bottom of the substation fencing and at the gate, to keep raccoons out.  And we suggested they move the park bench, used by employees as an outdoor lunch table, to an area away from the substation.

MIDWEST Uncategorized 13.8 kva, 138 kv, 30 MVA Substation Transformer, Field Services, Oil Filled Power Transformer, oil filled transformers, Reconditioned Oil Filled Transformer, Replace Transformer, Replacement 30 MVA, Secondary Bushing, Transformer Failed

We received feedback from a new Technician who was scrapping out an old 5000 kva oil filled power transformer. It was over 40 years old and hadn’t been in service for 20 years. The primary voltage was 13,800 and the secondary ranged from 120 volts to 600 volts. These voltages made it an unusual transformer, but it was worth more for scrap copper and steel than for reliable reuse. In addition we had limited knowledge of the history of this 5 Mva transformer.  The test results were barely acceptable, not good.

The young technician had never seen the inside of an old oil filled power transformer, especially such an unusual power transformer out of a foundry. The things he found interesting, a veteran oil transformer repair technician would take for granted. He was surprised how tightly the core and coils fit inside the tank and how the high and low voltage bushings connected to the transformer. He was amazed by the over 3” diameter round solid copper secondary bushings. He saw how the liquid level gauge and temperature gauge for a 5 Mva oil filled transformer worked. The level gauge inside the power transformer had a simple small rod with a cork at the end. The temperature gauge was just a well extending through the wall of the 5 Mva transformer with a temperature gauge installed in the well. The transformer had a basic tubing and pressure gauge system to add nitrogen or dry air.  All very basic stuff, but once he saw all this stuff and the interior of the transformer, these basic things made a lot more sense. Good experience. If a picture is worth a 1000 words, then this simple experience was worth 10,000. Whether a 5000 Kva transformer, 10 Mva, 20 Mva or 50 Mva oil transformer, some of these transformer basics are the same.  

MIDWEST Uncategorized 10 MVA Transformer, 20 MVA Transformers, 5 MVA Transformers, 50 MVA, 5000 Kva Oil Transformer, oil filled power transformers, Oil Transformers, power transformers

This is a horror story from an electrical contractor about an event that took place around 1970. But the event reinforces the requirement to follow protocol to the letter when working on a large, say 50 Mva oil filled power transformer.  This was a 30 MVA, 40 MVA, 50 MVA 138000 volts to 13800 volt oil filled power transformer. This is the story of a 10 cent washer making a 50 mva transformer useless.

It was not a MIDWEST project. And MIDWEST’s protocol is that everything is removed from the top of a transformer before the manhole covers are removed. Everyone has removed everything from their person and clothes and they must be wearing special coveralls and other secure clothing and all tools are secured. 

In this case, all the bolts and washers for the manhole covers were left on top of the transformer and placed six feet away from the three manholes. The work on the 50 mva transformer was complete and the crew was lowering a manhole cover in place and “kind of dropped it” the last ½ inch. That caused one of the flat washers to bounce up, roll about 6 feet and plunk into one of the other open manholes on the top of the 138 Kv 50 Mva transformer. The chance of this happening was zero. Well almost zero. The transformer had to be hauled back to the manufacture for detanking to find the washer. A very sad day for that crew and a very expensive washer.

We don’t follow protocol just for what we know can happen. We also follow it for things we can’t image would happen.

MIDWEST Uncategorized 50 MVA Oil Filled Transformer, 50000 KVA Oil Transformer, electrical safety, Oil Filled Power Transformer, oil filled transformers, Transformers For Sale

The internet might be a great tool to find a replacement reconditioned or used 20 MVA transformer, fast. But the internet information could be deceptive and expensive. Nothing wrong or illegal, but it just might not be as good a deal as you think. Consider this example of what has happened to MIDWEST. A customer calls for a 25 MVA Transformer. Say a 138 Kv to 34.5 Kv, oil filled power transformer. And say our sell price is $300,000.00, plus freight. This should be a straight forward transaction.  And often these transactions happen fast, especially when someone has had a transformer fail. But, in this example, the buyer is a transformer ‘lister’ who marks up our price a whopping 30%.  A ‘lister’ is an entity that just lists equipment on their web site. They have no inventory themselves. They have limited technical value. They basically just have the information. This is not an indictment of all listers. Some are very good. But, in this case the ‘lister’ has been contacted by an electrical equipment dealer who also does not stock large equipment, much less large transformers. The dealer marks up the lister’s price a whopping 30% also, because he thinks the buyer just has to have the transformer. The dealer has been contacted by an electrical contractor, who also thinks he can mark it up 30%, because his customer, the actual end purchaser and user of the transformer, just has to have it. The problem is, by the time the shark’s get done marking up the price, the cost has doubled to over $650,000.00 and the end user knows they can buy a brand new unit for much less than $400,000.00.  They feel taken, so they decide to cripple along until they get a brand new transformer. 

This same scenario can happen with high and low voltage switchgear, circuit breakers, and any number of other type electrical equipment.  So how can you tell if you are talking to an intermediary or directly to the source of the equipment? The best bet is to be talking to someone who knows the equipment. Is an expert on the equipment you want to purchase.  Can give you detailed additional information immediately rather than making you wait two hours for answers to each question. Deal with the experts.

MIDWEST Uncategorized 20 MVA Transformer, 25 MVA Transformer, Electrical Equipment Dealer, Electrical Equipment Experts, Experts on Transformers, Large Transformers, Oil Filled Power Transformer, Power Transformer Experts, Reconditioned Transformers, replacement transformers, Used Transformers

What do you do if your manufacturing company suddenly loses its main 5000 kva, 34.5 kv to 480 volt transformer? You have orders pending. And if you can’t fill them, a key account may go elsewhere. You have employees suddenly out of work.  You need to heat the buildings.  And you are told it will take 10 weeks to get a new replacement transformer. This is one of a manufacturer’s worse nightmares. What to do? This happens more frequently than one may realize. MIDWEST actually recommends a “Disaster Action Plan,” on the shelf, ready to go, in case of such a nightmare.

MIDWEST receives these calls all too frequently. You might be fortunate and MIDWEST have a replacement reconditioned or used 5000 kva transformer that can be shipped immediately. No one has new transformers this size in stock. And many companies will not accept anything but a new replacement power transformer. In that case, the best solution is to rent a temporary transformer that will provide power until a new replacement transformer can be specified and manufactured. A new replacement transformer may take 10 weeks.

Renting transformers, and other electrical equipment, is a common solution to this critical problem. The first big question to ask when such an emergency occurs is, “Do you want power back on permanently as quickly as possible or do you just want power back on as quickly as possible?”  There is a huge difference in the time to perform either of these solutions. And way too often there is the presumption that one just must get power back on permanently. This presumption continues until the customer realizes how long it will actually take. Meanwhile many hours, even days, are wasted by chasing the wrong solution.

So the most critical event is to decide how fast one wants power restored.  MIDWEST has transformers, temporary high voltage cables and low voltage cables, and switches in stock.  But, more important, is the knowledge that temporary power installations can be a life saver for a facility that is suddenly down.

MIDWEST Uncategorized 5000 KVA Transformer, Disaster Action Plan, Emergency Transformers, Failed Transformer, new transformers, Reconditioned Transformers, rental transformers, Renting Transformers, replacement transformers, temporary high voltage cables, temporary low voltage cables, temporary transformer, Used Transformers

This blog concerns a very simple maintenance procedure MIDWEST performs on electrical arc furnace transformers. It has saved our customers tons of money over the years. First a little information on arc furnaces and arc furnace transformers. 

Electrical arc furnaces are basically monstrous arc welders. Instead of the electrodes being pencil thin, they might be 14 inches or more in diameter. And there are three electrodes. The arcing is extremely loud and creates a lot of dust. The dust collectors take care of most of the dust, but there always seems to be dust that gets on to the secondary bus bar of the arc furnace electrical transformers. Whether McGraw Edison, Pennsylvania Transformer, or many of the other arc furnace transformer manufacturers, dust can be a real enemy of the secondary bus bar.

On some arc furnace transformers, both ends of an individual winding come out of the transformer in such a configuration that there may be only a quarter of an inch between the end winding bus bar. In other words, two massive copper buses, separated by only a ¼”, may have 280 volts potential between them during operation of the electrical furnace transformer.  And the secondary windings are huge masses of bus bar. If these bus bars become coated with foundry dust and the dust is conductive enough, a massive arcing fault may occur at the secondary of the transformer. Unfortunately MIDWEST has responded to such emergencies, and they are a mess. Very expensive repairs.  And so easily preventable.

The unsophisticated solution is to clean the dust and any other contaminates from between the bus bars before they become a threat. One has to do this carefully so as not to damage the seal where the bus comes through the top of the transformer, for example. It may look simple, but only experienced and qualified electrical personnel, who know what they are doing, should do this. In the wrong hands, this maintenance procedure could easily be the cause of a major blowout rather than the prevention.

MIDWEST Uncategorized Arc Furnace Transformer, bus bar, Bus Cleaning, Electric Arc Furnace Transformer, electric transformer, electrical furnace transformer, massive arcing fault, power electrical transformers, Prevent Secondary Fault, qualified electrical personnel, secondary bus bar, secondary windings

MIDWEST works a lot with electricians, maintenance mechanics, and other assorted electrical folks that have the every day job of keeping production machines running. When they call for help, for example when they suddenly need a replacement transformer, they want the short answer to their question. Sometimes you can tell from the edge in their voice that they are overwhelmed, in a real jam, and, if we put more burden on them by asking twenty questions about their old transformers, they are just going to stop listening, say thank you, and hang up. They want an immediate short answer to their immediate question.  This isn’t always possible or safe, but, since we have so much field service experience, we usually can get to the point quickly.

Sometimes the simplicity of the request can be amazing. For example, we had an electrician call during his lunch break and ask how he could tell if one of their old dry type transformers, used for production machines, was overheating. They had added a ton of equipment to it over recent years and he was worried the transformer was overloaded and would fail. His boss knew nothing about old, new, replacement electrical transformers and really didn’t want to be bothered with a “maybe problem.” The electrician needed something to get his bosses attention. He couldn’t measure the load, but he just knew it was overloaded.

Our unscientific suggestion was to put his hand on the top of the old power transformer enclosure. If he couldn’t hold it there for a few seconds, the transformer is in danger of being overloaded. The load should be measured and compared to the nameplate rating. If they don’t, they run the risk of the transformer failing when they least expect it, say the day before a holiday. Getting and installing a replacement transformer under emergency conditions can be a lot more expensive than scheduled transformer replacement. You don’t want to get burned.

Safety note. Be sure the transformer is grounded before touching it.

MIDWEST Uncategorized electrical transformer, Old Dry Transformers, Overloaded Transformer, Power Transformer Enclosure, replacement transformer, Transformer Replacement