When it comes to big-ticket items, power transformers are near the top of the list. So, when they fail prematurely, it’s all the more painful: Damages can far exceed the cost of a replacement. The added expenses may include the loss of production time, damaged credibility, and regulatory fines and civil lawsuits.
Although many plants and facilities have had to live through this problem, others (hopefully) are learning from those mistakes, thanks to failure-analysis experts who investigate transformers that die an early death. As such, the job is a lot like that of a detective on a CSI crime show drama. They show up at the “scene of the crime” and try to determine what went wrong and who’s at fault.
“I’ve been involved in dissecting numerous transformer failures,” says Jeff Jones, one of those transformer “crime scene investigators” and founder of Electrical Certification Inc. in Cincinnati, a firm that specializes in testing, certification, and failure analysis. “After a transformer failure, the first thing out of the customer’s mouth is inevitably, ‘Hey, it’s just a year old! What happened?’”
But it’s no mystery, according to Jones. Ultimately, you get what you pay for.
Plant engineers, facilities managers, general contractors, and specifying electrical engineers can learn a lot from the “post-mortem” experiences of a CSI tech such as Jones. In most cases, the premature failures of transformers could have been avoided, and the culprit is often an inadequately designed or constructed unit.
As a master electrician, test technician, and member of the IBEW for 44 years, Jones possesses a wealth of knowledge and has spent endless hours combing through the evidence. For the first time he is opening his archives and revealing his list of “usual suspects” that cause premature transformer failure.
Transformers rarely fail and turn out like this, but when they do, costs can be immediate and devastating.
“You want equipment that is cost-effective, not cheap,” says Jones. “Cheaper transformers often cost you more in the long run, especially if [they are] critical to your business process or data center. Then the extra $10,000 or $20,000 for a better unit represents inexpensive insurance.”
Jones admits it is hard to convince someone of this because of upfront cost concerns, but the proof of his conviction lies in what he has observed in the failure of countless transformers.
“Probably the most influential factor in transformer longevity is the level of craftsmanship, the attention to detail in the manufacturing process, and the quality control,” says Jones. “This is often overlooked in today’s rush to automate every manufacturing process.”
According to Jones, transformers often fail because an assembly machine overlooked a point of weakness that an experienced craftsman would have spotted and corrected while winding the transformer by hand.
“Pride of work and experience went away when machines started building transformers,” Jones opines. “That is especially the case in manufacturing outside the U.S. where they lack experience and often rely on highly automated processes. A machine doesn’t have the feel to detect defects.”
In combing through his files, Jones came up with a classic example.
“In this case, the client had a large 10,000 kVA dry-type transformer that suffered a catastrophic failure within five years,” begins Jones. “Knowing a replacement core and coil would run $110,000, not counting the rigging and installation which would add another $40,000, the owner demanded the manufacturer let me witness the technicians dissect the transformer.”
As Jones watched, the manufacturer cut into the insulation and epoxy with a gasoline powered concrete saw and found the fault at the crossover where the opposite-polarity windings pass through a guide tube. There should have been at least 1.5 in. of separation; instead, the wires were almost touching one another.
“A clear example of someone failing to inspect and fix that area before resin was poured and baked in,” Jones says. “The manufacturer had to supply a new core and coil.”
However, the client was not completely off the hook for cash outlays.
“Look where they put transformers these days: in tight spaces when the buildings are first being erected or on the roof where you’ll need a crane to replace it,” says Alan Ober, VP of engineering for Electric Service Co. (ELSCO), a Cincinnati-based transformer manufacturer. He has been on site to witness many transformer installations.
“It will cost twice as much in the long run to swap it out when it is mounted on the roof or in a tight spot,” adds Ober. “When you factor in lost production while the equipment is out of service, nobody wins when a transformer dies an early death.”
The most influential factor in how long a transformer will last is the craftsmanship that went into building it. This level of attention to detail in manufacturing is often overlooked in the rush to automate everything.
After craftsmanship, material is the next most important factor in transformer construction. According to Jones, using the right wire and insulating materials makes a huge difference in longevity.
“A well-known university hired me to investigate a pair of 2,000 and 2,660 kVA dry-type transformers that failed within a month or two of installation,” recounts Jones. “I discovered the area of failure at the crossover where the winding material spools out at a 45-deg. angle across a flat area to start the next coil over. At that point, this manufacturer put a single wrap of Kevlar, whereas a high-quality transformer would have double or triple layering of insulating material because it’s a high-stress area.”
The manufacturer tried to avoid the rap by explaining that their transformers needed a snubber, a capacitor-filter-resistor network that connects in parallel with the primary winding to absorb high-voltage transients.
“But a snubber is a $25,000 add-on,” explains Jones. “If you have a cheaply manufactured transformer and need to buy this extra equipment, where are the savings in that? The university had 10 of these transformers, so they were facing a quarter-million-dollar jump in costs. Now who is going to pay for that? It becomes a big fight.”
Jones also discussed the importance of the iron core material. Pure original—as opposed to recycled—magnetic silicon steel is best. Also, the thinner the core steel pieces, the better.
Commonly used M6 steel has a thickness of 0.014 in. per piece, whereas the M3 steel is only 0.009 in. thick. To cover the same volume or area, you have more pieces with M3. The more pieces, the lower the no-load losses and the higher the efficiency.
“High heat contributes to transformer failures,” explains Ober. “A 150°C transformer wastes a lot of energy creating heat, which shortens the life of the insulation. However, a beefier 80°C rise dry-type transformer with better core steel will have less heat rise under the same conditions while putting out equal kVA.”
Aluminum might be adequate for transformers, but copper is by far the superior metal for the windings. Not coincidently, material quality is the second-most important factor in transformer longevity.
Whether wet- or dry-type, the way coils are wound around the transformer’s core greatly affects its durability. Because of increased axial forces acting at the corners of rectangular-wound transformers, energy gets wasted and noise is created. With round-wound designs, however, voltage stresses are lower, so they stay cooler, run quieter, and present less risk of short-circuit with the sheet wound secondary.
Beyond the improved reliability factor, the round-wound designs further increase efficiencies and save costs in real time as the plant consumes less electricity. Some well-designed transformers even exceed the proposed efficiency standards for Energy Star compliance, drastically lowering a plant’s utility costs.
“In the past, they made transformers that were somewhat overdesigned in terms of capacity and durability,” adds Ober. “Today, with tighter profit margins, if you want a 1,500 kVA transformer, that’s exactly what you will get. So, it is critical that you don’t skimp on materials and design.”
“Don’t be surprised if you end up doubling your upfront costs by specifying value engineered transformers,” Jones warns. “But at least you won’t be calling me to investigate what went wrong.”
If you have any questions regarding transformers or electrical equipment failures, please feel free to call an application engineer from Electric Service Co. (ELSCO) at (800) 232-9002 or click here.