Meeting Tier 2 MEPS & Designing the Transformers of the Future

June 14, 2017 by Jeff Shepard

Transformer design today is affected by a number of changing conditions in our electricity distribution network. Energy generation, for example, is increasingly being generated through renewable sources like wind and solar power, replacing more traditional forms of energy generated through power plants. Applications such as electric mobility are gaining popularity, meaning increased pressure on the distribution network. There's also the digital influence, as seen in smart grids and the impact of complex monitoring and automated processes enabled by the internet of things, and last but not least, the importance of global energy efficiency regulations.

Since 2010, energy performance legislation for distribution transformers has been gradually introduced globally. In July 2015, CENELEC’s (the European Committee for Electrotechnical Standardization) Minimum Energy Performance Standard (MEPS) specified maximum losses for both the core and the winding for distribution transformers and minimum peak efficiency for power transformers.

The tier 2 MEPS – due to be implemented in 2021 – will require higher quality grades of steel, as well as changes to the design, windings and manufacturing methods to reduce coil losses.

“You can reduce losses by using advanced core materials like higher quality electric steel, implementing flat core design, implementing high precise stacking (robo-stacking) or implementing step-lap cutting. To achieve this, changes to the design of a transformer include implementing oval design, using foil technology in low-voltage coils or implementing right tensioning in low-voltage and high-voltage coils,” explains Ales Bertuzzi, leader of European transformer manufacturer alliance Trafogrid and managing director at L.A.E.

Packing in the windings tighter can improve transformer performance. Today, 90% of the total direct cost of manufacturing transformers is spent on material, so not only is it important to have a machine that creates a transformer in the most compact possible way to meet current energy regulations, it also saves material and therefore a large proportion of the total manufacturing cost.

“Some of the latest coil winding machines for low voltage winding now feature the same electronic system used in hybrid car technology for braking and accelerating,” says Bertuzzi. “They have very accurate tension control, and allow much better tolerances in the tension of the foil meaning more compact coil winding, resulting in the reduction of material and overall a better quality transformer.”

Another way to improve transformer performance is by using higher quality electric steel in the core. Kevin Wilson, technical manager at Wilson Power Solutions is currently considering the future implications of tier 2 MEPS. His company is already producing super low-loss amorphous metal core transformers, but is also exploring the possibility of high probability core steel.

“I think if you want to increase your transformer efficiency level, the easiest way to achieve this is through better quality material in the core. There are certain manufacturers across the globe who are developing this steel but there are still questions about how much it will cost and how much of it is going to be available, if interest in the market increases. It’s an area we are monitoring closely.”

Other areas of interest focus on temperature and the drying process. “There is debate in the industry about whether we can consider more realistic temperatures on fixed temperature transformers. Something more like 65 degrees instead of 75,” says Wilson. “If we have a constant temperature, fans can be turned on sooner, which would keep the core of the transformer cooler and thereby, increase efficiency.”

According to Bertuzzi, updating the process of drying the transformer can also increase efficiency. “By using the traditional oven and vacuum method, and mixing it with a low frequency heating system, this solution removes the humidity from the transformer in nearly half the time compared to previous models, which helps reduce the time of manufacturing, reducing costs and making the overall process more efficient.”

The industry is entering a new era of transformer design which needs to be adapted to meet the needs of a changing world. In situations like this, it can be easy to accept an update or solution at face value, but with little or no experience of new adaptations and their performance yet, it’s worth approaching each new situation carefully. Wilson advises caution when considering new transformer design, because changing conditions can lead to problems where both manufacturers and their customers are not completely clear about what is required.

“For example, when considering transformer design for a renewable energy source like a solar farm and seeing that its harmonics are really large, a manufacturer may think it has to make its transformer huge, but on closer inspection, this may not be the case. The harmonics might only be large for a short amount of time, so in fact, there is no need to overcompensate.”

Essentially, collaboration with customers is key to efficient transformer design. “When you are dealing with flexible ac transmission systems (FACTS) or anything to do with reactive power, it’s important to speak to your customer about the upper and lower impedance limits. They need to be guaranteed right from the beginning. Consider your tolerances as well. Are they enough for the rest of your system? Because tolerances on a transformer don't just affect a transformer, they affect the cable and the filter system, so it’s important to know the wider picture. Finally, do you need to consider harmonics? These are the questions you need to ask from the start.”

Ales Bertuzzi and Kevin Wilson will discuss these topics and more in further detail at two separate tutorials held during the forthcoming CWIEME Berlin exhibition for coil winding, insulation and electrical manufacturing.

Wilson’s tutorial will highlight challenges in transformer design and identify major pitfalls, providing practical suggestions and best practice drawing from real life experiences. Entitled “Beyond historical boundaries – transformer application design and anticipating customer needs for non-standard applications” it will take place at 14.15-15.45 on Tuesday 20th June.

Bertuzzi will address key challenges and explore solutions across the entire distribution transformer design and production process at a tutorial entitled “Adapting your distribution transformers to meet the SMART changes”. This will take place 14:15-15:45 on Wednesday 21st June.