Compactness is the key to the distribution transformer of tomorrow

The various changes driven by the energy transition and pressure on electricity prices result in a growing list of constraints on distribution transformers. A series of technological and operational solutions are at hand to solve the often-challenging trade-offs, with compactness as a common denominator. Regulators could stimulate the deployment of such solutions by tackling the remaining regulatory barriers.?

In recent years, distribution transformers are requested to do more at several levels: more numbers must be manufactured, their capacity must grow as well as their peak capacity, they must do better regarding energy efficiency and material efficiency, come at a reasonable cost to avoid rising distribution tariffs and fit into existing substations to avoid high installation costs. Combining all these constraints will only be possible through conceptual changes that allow distribution grid operators to do more with less.?

Compactness as a key characteristic

Two types of compactness can be highly favourable. The first one concerns transformers that provide a better energy performance without increasing the unit size. Normally, improving the energy efficiency of a unit will directly lead to an increase in weight and volume. In compact solutions, on the contrary, the energy losses will go down for the same capacity, weight and volume.?

The second type of compactness increases the capacity and peak capacity of the unit without increasing its weight and volume and without degrading its energy performance.??

Both types of compactness lead to better material efficiency of the unit, with a positive impact on its environmental performance. Additionally, both make it possible to upgrade the transformer without the need to enlarge the substation, leading to cost savings at system level.??

Solutions to achieve compactness are at hand?

Innovative solutions are at hand to achieve such forms of compactness. One type of solution is related to the choice of the active metals in the transformer. New types of electrical steel reduce the core losses without impacting the size of the unit, and a switch from aluminium to high-conductivity copper reduces the losses in the windings without increasing size, or even reducing it.?

A second type of solution concerns new insulation materials, such as thermally upgraded paper and natural esters, which allow the unit to handle a higher temperature rise, and consequently higher peak demand, without compromising unit reliability or lifetime.??

A final category is not related to technology as such, but to the way the transformer is designed and operated. By optimizing the balance between load and no-load losses using the Peak Efficiency Index (PEI), and by allowing higher peak loads thanks to the Sustainable Peak Load (SPL) concept, a transformer of the same size can be installed where conventionally an exchange for a larger unit would have been required. The use of SPL transformers can prepare distribution grids for the expected increase in peak loads caused by the electrification of transport and heating, without the need to increase the transformer size. Its use is favourable in a grid with a low average load, which is usually the case in distribution grids, but requires a different approach to load loss definitions.?

Regulatory barriers for achieving compactness?

Given the important advantages that compactness can bring in facing the challenges of the distribution grid, it is interesting to assess which regulatory barriers are still hampering its deployment, and how these barriers could be removed.??

In EU regulation, the PEI is currently only adopted for large power transformers. Developing a similar regulatory approach for distribution transformers would pave the way for an optimal balance between load and no-load losses for each individual case, ultimately resulting in compacter solutions.?

Fully adopting the SPL concept in Europe would also require some changes in regulation and standardization. Different options to do so can be found in the literature, but whatever the preferred solution, care should be taken to restrict the use of the SPL concept to cases where the cumulative annual energy losses are not affected negatively.??

Finally, national regulations imposed on distribution grid operators should stimulate them to take decisions based on life-cycle principles and for the entire system in which the transformer is operated, including the substation and cabling. Today, incentives to minimize upfront costs for the transformer unit as such, without looking at the broader picture, are still common. As a consequence of such policies, opportunities for applying more compact transformer designs are being missed.??