Applied research projects


  • TRAFOFLEX – Advanced concept of efficient use of transformers leveraging the DTR technology

OPERATO d.o.o. (2021-2023)

We estimate that in the Slovenian distribution approx. 100 transformer replacements per year occur, which are replaced before the end of their service life due to overloads. We have conservatively estimated that we can safely overload – according to the nominal value – transformers by 15%. With an average 2% increase in workload, this means that its replacement is delayed by 7 years. The average cost of replacing the transformer was taken in the amount of € 15,000. Based on this, we calculate the economics by calculating the investment lag (considering the 15-year period). In order to cover the whole of Slovenia with such systems, we estimate the investment at € 4.5 M (total cost of ownership – TCO for 15 years). With the assumptions used, the net benefits amount to approx. 4 M €, and the investment would be repaid in 4 years. The results of the first DTR tests for transformers show that it is possible to safely overload them in the coldest periods, when we usually have peak loads, even significantly more than 15%, so the savings can be even greater. We also do not mention here the benefits of asset management, which are still difficult to evaluate at the moment, as this task will develop the concept. The benefits of ELES have also not been evaluated, as they are difficult to extract from the comprehensive SUMO System which is already in use.

TR calculation concept for distribution transformers (left). Temperature measurements of pylon mounted Kolektor-Etra transformer (right).
TR calculation concept for distribution transformers (left). Temperature measurements of pylon mounted Kolektor-Etra transformer (right).

The project aims to increase the load capacity of transformers (TR) in a safe way, without adversely affecting the service life and thus gain, together with flexibility services, additional space for managing peak loads, especially on LV networks. So far, the calculation of DTR for TR has been performed only within the framework of ELES’ SUMO project for two cases of energy TR and for one case of distribution TR in TP of mast construction – in all cases TR was directly exposed to weather influences. In the framework of this project, we want to extend the applicability of the DTM model to the consideration of typical buildings in which TRs are located. The ultimate goal of the project is to develop and test the concepts of advanced use of transformers for the purposes of operation, flexibility market and asset management, and thus to prepare the ground for mass implementation of the technology.


  • Forecasting tap changer regulatory maintenance with advanced analytics

ELES d.o.o. (2021-2022)

The Diagnostics and Analytics Centre (DAC) of the Slovenian power transmission operator (ELES) is a meeting point for mass data, advanced analytics, technical expertise and good engineering practices, which data engineers and scientists transform into modern management of ELES’ assets. DAC is collaborating with JSI in an effort to bring modern data analytics in optimization of maintenance costs of several transformer units that utilize on load tap changers (OTLP). These units units require regular maintenance after they perform a certain number of switching operations. To plan future maintenance, a prediction of the number of switching operations is required per unit on a short- medium, and long-term time horizon. Switching operation is influenced indirectly by many variables, some of which are not predictable themselves. Therefore JSI will develop a prediction model fro the number of switching operations based on domain knowledge, statistics, and machine learning.

The Diagnostics and Analytics Centre control room (left). The phase-shifting transformer in Divača. (right).
The Diagnostics and Analytics Centre control room (left). The phase-shifting transformer in Divača. (right).

Besides developing a model, JSI will deploy software implementation of the model into operative use for DAC. The software will run in real time, poviding regular updates of its predictions based on current and predicted variables that govern the operation of the transformers in question.


  • Identifikacija topologij energetskih omrežij

GRID INSTRUMENTS d.o.o. (2020-2022)

Electrical Grid Topology Identification

The project addresses the problem of a network topology identification in the low-voltage power distribution grids. We are studying the shortcomings of the existing methods and developing new solutions. We have proposed a topology identification approach that avoids the assumption of a linearized power flow in order to reduce the sensitivity of the reconstruction process to the measurement errors.


ELES d.o.o. (2018-2022)

Dynamic Thermal Rating Natural Convection 

DiTeR is the name of the project as a whole and of the resulting software package. The core of the DiTeR is a physical model for the simulation of heat transfer within the transmission power line under realistic weather conditions, where ambient temperature, wind velocity, rain rate, humidity, pressure and solar irradiance are considered as major factors of influence. DiTeR comprises the heat transport through the power line, heat generation by Joule heating and heat exchange with surrounding via convection, solar heating, radiation, rain impinging and evaporation. The DiTeR problem can be stated as the problem of heat transport with non-linear boundary conditions describing different heat terms due to the weather conditions. The results obtained with DiTeR have been compared against available published data as well as measurements provided by in-house testing site.