Journal of Energy - Energija

Testing of insulation systems in accelerated aging conditions

Slaven Nađ, Josip Treger, Stjepan Car — Sun, 15 Dec 2024 00:00:00 +0100

The paper describes the testing procedure of the insulation system of electrical rotating machines with form-wound windings in accordance with the standards IEC 60034-18-31 and IEC 60034-18-42. Testing is based on a comparison of reference insulation system which has given satisfactory service experience and candidate insulation system which is intended to be used instead of existing insulation system. To prove or disprove the reliability of candidate systems in reasonable time, the accelerated aging test is carried out, considering various factors that reduce the life of the insulation system in greater or lesser extent: heat, exposure to mechanical vibrations and moisture (according to IEC 60034-18-31) and voltage (according to IEC 60034-18-42). In order to save materials and easier handling of test samples, tests are carried out on reduced models of coils (so-called formette coils) that are placed in frames imitating the stator core. The purpose of the test is to verify the potential contributions of a new impregnating resin, as well as the addition of nanoparticles in a new impregnating resin in a condition of increased voltage stress due to machine connection to the grid via frequency converter. In addition to the test procedure, the paper presents the results obtained so far.

Development of Electrolyser Projects for Production of Renewable Hydrogen

Ivan Andročec, Martina Mikulić, Martina Rubil — Sun, 15 Dec 2024 00:00:00 +0100

Hydrogen is one of the important factors in reaching climate neutrality from the European Green Deal, particularly hydrogen made from renewable energy sources. The paper describes electrolysis plants in technical, environmental and regulatory aspects and presents obstacles that need to be overcome for the successful implementation of electrolyser projects, looking at the bigger picture of the energy sector. Part of the paper is dedicated to the research of existing projects and the plans for the development of electrolysers. Possible contribution of the development of electrolysis plants is in the application at the locations of existing thermal power plants that are no longer suitable for operation due to technological, economic or environmental reasons, which would take advantage of the existing location of the power plant for the installation of new technology that meets the concept of low-carbon development.

Evaluation and Modeling the Performance of Rice Husk Gasifier Cook Stove for Household Energy Use

Dessye B. Tikuneh, A. Fetene Mersha — Sun, 15 Dec 2024 00:00:00 +0100

This research paper aims to evaluate and model the performance of rice husk gasifier cook stoves for household energy use, a byproduct of rice milling. The study aims to address environmental issues and promote the use of rice husk as a renewable energy source and pest repellent in stoves. The study compared insulated and non-insulated gasifier stoves using rice husk gasification. The study compared the start-up time of insulated and non-insulated gasifier stoves, where the insulated stove showed a lower start-up time, but there was no significant difference at a 5% probability level. The temperature change was also not significant, as heat transfer and temperature change started when the husk was ignited. The burner stoves had different sizes and volumes. The maximum operated or flame temperature was 1,190.30 oC at room temperature or a minimum temperature of 27.33 ^oC, whereas the average temperature was 758.916 oC for the non-insulated type of gasifier stove. The insulated gasifier stove also observed maximum and average temperatures of 518.30 ^oC and 289.014 oC, respectively, at the same room temperature. The operating time of stoves directly influences the fuel consumption rate, specific gasification rate, and combustion zone rate of stoves. The fuel consumption rate has a significant effect on the type of gasifier stove, with the maximum rates being 3.820 and 2.099 kg/hr. The time to consume rice husks to gasify them depends on the density of the rice husk, reactor volume, and fuel consumption rate. The average specific gasification rate for insulated and non-insulated stoves is 106.45 and 120.63 kg/m²h, respectively. The fuel or rice husk holding capacity of each type of stove is significant at a 5% level, with the amount of rice husk and biochar produced being 1.18kg and 0.27kg for insulated stoves, and 2.511kg and 0.688kg for non-insulated stoves, respectively. The performance of gasifier stoves varies based on the biochar conversion rate, with non-insulated stoves producing a higher biochar mass per rice husk. Multiple regression analysis was used to model the relationship between time elapse and temperature and heat energy. The Squirrel-2020 data logger was used to measure the temperature produced by burning rice husks in the reactor of the stove as well as related heat generated and losses. A relationship between the heat energy produced and the operating time of gasifier stoves was conducted to estimate the model. The cubic polynomial model was found to be the best predictive model fit for all variables in this study.

Review of Supercapacitor Equivalent Circuit Models

Karlo Kobeščak, Tomislav Baškarad — Tue, 11 Feb 2025 00:00:00 +0100

Supercapacitors are a promising technology for addressing the challenges faced by power systems with an increasing share of inverter-based resources. Due to their unique characteristics, supercapacitors can provide ancillary services to the grid. Understanding the behavior of supercapacitors under various conditions is crucial. Therefore, modeling and analysis are of significant interest in the research of supercapacitors for a wide range of applications. This article provides a brief overview of supercapacitor technology and presents a systematic review of five equivalent circuit models of supercapacitors.

Impact Of Climate Changes on Transmission System Operator Assets: Experiences from Croatia and Need for Resilience Plan

Sun, 15 Dec 2024 00:00:00 +0100

The consequences of climate change are felt everywhere, especially on power systems assets, whereby overhead lines as one of its most exposed elements. It is expected that impact of climate changes, especially effects of evident global warming will be even more expressed in the coming decades, with increased frequency and severity of extreme weather events in the form of storms, winds, snow, ice, high temperatures, fires, etc. Therefore, it is essential to ensure the safe and stable operation of power networks. An experience with two strong storms which appeared within only two days in July, 2023 affecting larger part of Croatian transmission network are presented, in order to discuss whether it is necessary to change valid requirements for new overhead lines, and to consider establishment of internal resilience mechanisms for better withstand the impacts of climate change and global warming.