Proceedings, Electrical engineering institute "Nikola Tesla"

Electricity Consumption Forecasting using ARIMA and LSTM

Živko Sokolović, Sasa Milic — Thu, 26 Jun 2025 00:00:00 +0200

Accurate load forecasting is essential for the reliable and efficient operation of modern power systems. This study presents a comparative analysis of two prominent forecasting models—Autoregressive Integrated Moving Average (ARIMA) and Long Short-Term Memory (LSTM)—to assess their effectiveness in predicting electricity consumption. Both models were developed and fine-tuned through hyperparameter optimization to ensure fair and optimal performance. The evaluation considered predictive accuracy, computational efficiency, and resource usage. While ARIMA demonstrated advantages in inference speed and model simplicity, the LSTM model consistently outperformed it in terms of forecasting accuracy and its ability to capture complex temporal dependencies. These findings underscore the importance of selecting appropriate models and tuning strategies for specific forecasting scenarios. The study highlights LSTM as a more suitable approach for applications that demand high accuracy and adaptability, and it provides a foundation for future research involving advanced or hybrid methods.

Estimation of the moment of inertia of a unit in a thermal power plant

Mon, 29 Dec 2025 19:52:57 +0100

Increasing integration of renewable energy sources and the withdrawal of fossil-fuel generators reduce overall power-system inertia, making the grid more vulnerable to disturbances and threatening transient and frequency stability. Low inertia can lead to large frequency deviations, equipment damage, and financial losses, which highlights the need for accurate assessment of inertia contributions from remaining generation units and determination of the minimum inertia required for stable operation. While synchronous generator inertia constants are usually provided by manufacturers, corresponding data for steam turbines are often unavailable. Since post-fault transient stability depends on the true inertia of the combined generator–turbine assembly, this gap complicates stability studies. This paper proposes a method for estimating the inertia of turbogenerators using coast-down measurements from thermal unit B1 of the "Nikola Tesla B" power plant. The method is based on Newton’s rotational motion equation and enables more accurate evaluation of inertia in large thermal units.

Remote Control Implementation of the Hydraulic Turbine Governor on the Test Field

Jovan Stevanović, Goran Kvaščev, Miroslav Dragićević, Jelena Pavlović — Mon, 29 Dec 2025 19:54:47 +0100

This paper presents the enhancement of the turbine governor test field of a hydraulic turbine through the implementation of a modern SCADA system based on an integrated PLC web server and OPC UA communication with a Simulink environment simulator and turbine governor. The system enables realistic simulation of turbine governor operation under laboratory conditions, with the capability of remote monitoring and parameter adjustment via a standard web browser. Within the research, a web server SCADA system was developed on the Siemens S7-1500 PLC, connecting the physical controller and the simulation model into a unified hardware-in-the-loop (HIL) environment. The obtained results demonstrate a significant improvement in the flexibility, transparency, and efficiency of the turbine governor testing process.

Methodology for Assessing Voltage–Reactive Power Capability of Synchronous Units under Modified Transformer Impedance

Anita Mijajlovic, Jasna Dragosavac, Žarko Janda, Ilija Klasnić — Mon, 29 Dec 2025 19:56:37 +0100

This paper presents a methodology for evaluating the voltage–reactive power capability of synchronous generators following changes in transformer impedance. The framework integrates per-unit calculations, an equivalent generator–transformer model, and numerical simulations across multiple grid-voltage scenarios. The SIM-Operating Map application provides analytical and graphical verification of reactive margins, limiting factors, and grid-code compliance, supporting operational decision-making and enhancing system security after transformer replacement.

Conceptual solution for enhancing the electrolyser power supply system and hydrogen production

Nikola Kovačević, Kristina Lazović, Milorad Igić, Sava Dobričić — Mon, 29 Dec 2025 20:01:12 +0100

The paper presents a realized solution for powering an alkaline electrolyser for hydrogen production and offers a proposal for its improvement. By connecting photovoltaic panels, via a DC-DC converter, directly to the DC side of the existing twelve-pulse rectifier, it is possible to achieve savings in electrical energy necessary for hydrogen production through the alkaline electrolysis process. Measurements of electrical quantities for the existing power supply system are provided, along with a simulation of the improved system's operation and a proposal for its more efficient control. Hydrogen obtained using energy from renewable sources in the electrolysis process is green hydrogen, which will be a significant energy carrier in the future and the backbone of the energy transition.

Determination of the Efficiency of the Turbogenerator B3 Rated 412 MVA at Thermal Power Plant “Kostolac B”

Mon, 29 Dec 2025 00:00:00 +0100

In modern power systems, which are rapidly transforming toward a sustainable future, the role of conventional generation units — synchronous generators — remains of fundamental importance. During the ongoing energy transition, the increasing share of renewable energy sources connected to the grid through power electronic converters poses a challenge, as their generation does not inherently contribute to the system’s inertial stability. For this reason, the construction of the new unit B3 at thermal power plant Kostolac B, equipped with a synchronous turbogenerator, has particular significance for the Serbian power system. It ensures the preservation of system reliability and operational security while enabling further integration of renewable energy sources.

This paper presents the results of the performance tests of the B3 turbogenerator, rated 412 MVA (350 MW), at thermal power plant Kostolac B, with a focus on determining the generator efficiency — one of the guaranteed parameters defined in the contract between the supplier and the customer. In the context of achieving green agenda objectives, where maximum reliability and optimal utilization of existing resources are required, precise determination of generator efficiency is of great importance. The tests were carried out on-site, following a methodology agreed upon between the supplier and the customer, and in accordance with the IEC 60034 standard for rotating electrical machines. The generator efficiency was determined using the calorimetric method, selected as the reference approach due to its highest accuracy and minimal measurement uncertainty. The obtained results confirm that the achieved efficiency of the B3 turbogenerator exceeds the guaranteed value, thereby validating the high quality of the delivered equipment.

Srpski

Mon, 29 Dec 2025 19:49:36 +0100

Uninterruptible Power Supply (UPS) systems are of vital importance for many consumers in complex facilities such as a thermal power plant. This paper presents a solution for the parallel operation of two inverters with nominal powers of 60 kVA, based on controlling the nature of the inverters. All challenges and technical details of parallelizing the two inverters are presented, from uniform load sharing and communication to establishing a "master-slave" relationship, and even the transient phenomena during the failure of one of the inverters. Detailed simulations of all relevant events and phenomena are simulated using the Plecs software tool. In accordance with the calculations, the inverters were developed, and experimental results of the operation of these inverters under simulated operational conditions are also included.

Kinetics of the reaction between elemental sulfur and silver in synthetic esters and comparison with mineral oils

Milica Djukic, Jelena Lukic, Jelena Jankovic, Dejan Kolarski — Mon, 29 Dec 2025 00:00:00 +0100

For decades, the problem of corrosive sulfur was considered to be exclusively associated with mineral oils. However, recent cases from industry have disproved this assumption. The presence of elemental sulfur in insulating oil causes corrosion of silver contacts and consequently leads to power transformer failures. The aim of this study is to determine the kinetics of the reaction between elemental sulfur and silver in synthetic ester within the temperature range of 120–180 °C. The elemental sulfur content in the oil during the reaction is determined using gas chromatography with an electron capture detector (GC-ECD). The results show that the reaction between silver and elemental sulfur follows the first-order law. A comparative analysis of the examined reaction in synthetic ester and mineral oil shows that the reaction proceeds faster in synthetic ester.

Technical specifications for the procurement of power transformers

Tue, 30 Dec 2025 12:03:41 +0100

The paper presents a comprehensive and complex project of the Internal Standard, IS2 Technical specifications for the procurement of power transformers, for the needs of Elektroprivreda Srbije ad (EPS ad), according to contract no. 2.5.0.012.01 - 39646/4-2022 and 02/04/5076-22 dated 29.12.2022. The project deals with 21 chapters, according to the program task and includes 209 pages. Considering the complexity of the project, it also contains 6 shemas and 25 table views. The project was adopted by the Expert Council of EPS ad.

Measurements of power transformers winding frequency response using the SFRA (Sweep Frequency Response Analysis) method - examples after failures in power transformers and factors that have influence on the recorded frequency responses

Momčilo Milić, Djordje Jovanovic, Marko Dimitrijevic — Mon, 29 Dec 2025 19:58:29 +0100

Sweep Frequency Response Analysis (SFRA) represents an unconventional method used in case of recording the frequency response of transformer windings. The method has found application in the analysis of geometry of power transformer windings in order to determine integrity of the core and winding geometry. Recently, this method has become an almost indispensable part of factory acceptance tests of transformers. Frequency responses recorded in factory or first time in transformer life are used as „fingerprint“ for all future comparisons. The method is applied in on-site tests when mechanical failures are suspected due to the action of dynamic forces during operation, as well as during the transport of transformers. In addition, it can also indicate certain electrical failures. The paper will present examples of recorded frequency responses on transformers that had some failures during their operation. Also it will be shown some examples of various influences on the frequency responses which can be misinterpreted and lead to an error in the assessment of the state of the winding geometry.