Transformer design

01 November 2011

Bruce Klimpke on the art of designing efficient transformers

Whether you know it or not, it is likely that in today’s connected, sophisticated electronic world you will never be more than few a metres away from a transformer. While the microchip gets all the attention from the press and public, the role of the transformer is crucial in all areas of life from power stations to mobile phones. Without these components vital procedures such as transferring power from source to home and the tasks which we take for granted, such as charging mobile phones and using a PC, would be impossible.

Because transformers play such a pivotal role in everything we do, the design and engineering behind them will have a clear impact on their efficiency. There are key areas in transformer design that affect efficiency and by using design simulation software, engineers can simulate the parameters at an early stage reducing development time and costs.
One of the biggest issues around low efficiency in transformers is that of heat loss. This problem is most common with the larger transformers such as those in power stations. The hysteresis and eddy current losses (often collectively known as iron losses) occur through a combination of ohmic and dielectric losses and magnetic field core changes. Simulation of an amalgamation of these losses is an area where significant improvements can be made.

While not all energy will be conserved, the amount lost through hysteresis and eddy currents can become minimal. The resulting reduction of these losses has a twofold benefit. Firstly, there is an improvement in efficiency because of the increase in energy conserved and, secondly, less energy, space, and time is required for creating and implementing a cooling system.

If a transformer is constantly overheating through large amounts of eddy current losses then a large cooling system is required to ensure the transformer continues to operate. If this cooling system is no longer required, or if it does not need to be quite so big and powerful, then the overall efficiency of the transformer will further improve as less power is then required to keep the cooling system running.

One of the key ways in which eddy current and hysteresis losses can be reduced is through changing the materials used. The retention of electrical energy and ability to remain at a stable temperature are features that can be attributed to a range of materials. Using simulation software can help the transformer designer at an early stage in the design and pre-production processes. Parametric solvers allow designers to automatically vary and experiment with both materials and sources. By changing the material and/or source parameters, Boundary Element Method (BEM), Finite Element Method (FEM) and Hybrid solvers are used to calculate which combinations provide the greatest efficiency.

Another major issue concerning transformer design is the trade-off between the size and weight of a transformer and its efficiency. On the whole, the greater the size of the transformer the more efficient it will be. This is because an increase in the cross section of the coil results in a reduction of its resistance. While this may seem like a simple solution, not all transformers have the capacity for a large coil. In the case of phone chargers and other small electronic products, size and weight are key issues.

Having the ability to simulate all the options at an early stage using an appropriate software platform allows the designer to choose materials that have the best size, weight, and conductivity for the particular transformer in question. It also enables companies to make an informed decision on trade off between the extra cost of high quality materials that are a perfect fit for that transformer against savings made in the long term through a more efficient transformer.

The skill of designing transformers is therefore one of trade-offs and fine lines. The use of design simulation software is vital for companies hoping to increase the efficiency of their products alongside keeping on top of the added costs that this may bring. In-depth, yet flexible design simulation at the starting point will lower costs, improve time to market and provide an end product that is both efficient and fit for purpose.

Bruce Klimpke is technical director, Integrated Engineering Software. The examples discussed in this article are simulations based on Integrated’s OERSTED application.