August 2023 – Upgrading of distribution grid transformers leads to higher efficiency in Slovakia

Východoslovenská energetika Holding a.s. (VSE Holding), an electric utility company based in Košice, Slovakia, is primarily engaged in supplying electricity and natural gas. It is the third largest electricity distributor in Slovakia, which serves the Košice Region and Prešov Region, where it delivers and distributes electricity to circa 500,000 customers – businesses and households.

To cover the supply area with an area of almost 16,000 km2 and a consumption of roughly 4,000 GWh, an extensive electricity grid with transformers is needed. Transformers are a component in electrical engineering that is used to convert alternating voltages. With the help of the transformer, high voltages are transformed to low voltages or vice versa. Distribution transformers are installed in various substations within VSE, each located in a different area and delivering electricity to different levels and types of consumers.

VSE’s Energy Scouts Lukáš Pinka and Lukáš Mokriš decided to calculate the savings in electricity and CO2 for the case of replacing old transformers with new, more efficient types. When estimating the losses of a specific transformer, its load, and basic parameters significantly impact the amount of efficiency. When older transformers with a greater maximum load are in use, but the electricity demand “behind the transformer” has reduced significantly over the years, the energy loss during transformation tends to be higher. For this reason, checking the idle losses as well average and maximum load is crucial, when replacing a transformer. In a typical power distribution grid, electric transformer power loss typically contributes to about 40-50% of the total transmission and distribution loss.

Two standard solutions were calculated in the Energy Scout project. First, replacing a typical “old” transformer with a more efficient one that has significantly lower energy losses during operation (Measure A). In some cases, it is also possible to reduce and adapt the nominal power of the transformer during replacement (Measure B). Comparing the two approaches, the reductions in energy and CO2-Emissions of measure A are significant, but the higher investment costs nearly balance its advantage. The payback period of 3.75 years for measure A and 3.49 years for measure B are almost the same.

Interestingly transformers have a lifetime of 30 to 50 years. Therefore, it is crucial to plan ahead and estimate the growth or decline in electricity demand among the connected consumers.


  • Industry sector: electricity and natural gas supplier & distribution system operator
  • Energy source: electrical energy
  • Energy saving potential: Measure A: 8.83 MWh/year, Measure B: 5.19 MWh/year
  • Savings potential CO2: Measure A: 1.7 tons CO2/year, Measure B: 1.0 tons CO2/year
  • Potential cost reduction:Measure A: 3,533 €/year, Measure B: 2,075 €/year
  • Investment costs: A: 13,250 €, B: 7,250 €
  • Payback period: A: 3.75 years, B. 3.49 years
  • Company:
    Východoslovenská energetika Holding, a.s.
    Mlynská 31
    042 91 Košice
A power transformer on two pillars
An existing transformer in Soľ at the end of its lifespan, ready to get replaced with a more efficient type (©Východoslovenská energetic a Holding, a.s.)
A power transformer on two pillars and power poles
When replacing this transformer in Klenov, a lower nominal power would be recommended. (©Východoslovenská energetika Holding, a.s.)
Detailed photo of a transformer
The average load of transformers in distribution networks is typically only around 20% of the maximum load, as the power drawn by consumers varies greatly and the capacity of the transformers must be sufficient in any case. (©Východoslovenská energetika Holding, a.s.)
Two men dressed casual business, one talking into a microphone, behind them, two "Young Energy Europe" Roll-ups
Lukáš Pinka and Lukáš Mokriš shared their project approach in Berlin with Energy Scouts from eight countries. (©YEE/Enters)